Title of Invention	"A METHOD FOR PRODUCING A GRAIN-ORIENTED ELECTRICAL STEEL SHEET"
Abstract	A method for producing a grain-oriented electrical steel sheet having a B8 value satisfying the relation 1.80 < B8 (T) < 1.88, by as a starting material, a coil obtained by heating a slab formed from molten steel and hot rolling the slab or obtained by direct casting from the molten steel, the molten steel having a composition comprising, in terms of percent by weight, 0.02 to 0.15%; of C, 2.5 to 4.0% of Si, 0.02 to 0.20% of Mn, 0.015 to 0.065% of Sol, Al, 0.0030 to 0.0150% of N, 0.005 to 0.040% as the sum of at least one of S and Se and the balance consisting of Fe, comprising the steps of annealing the coil, and then carrying out cold rolling at a reduction ratio of 65 to 95%, serially decarburization annealing, final finish annealing and final coating, characterized in that annealing of said coil is carried out at 900 to 1, 100°C so that a grain-oriented electrical steel sheet has a thickness of 0.20 to 0.55 mm and said cold, an average grain diameter of 1.5 to 5.5 mm and a W17/50 value expressed by the formula given below: 0.5884e1.9154t < W17/50(W/kg) < 0.7558e1.7378t wherein t is sheet thickness (mm).

Title of Invention

"A METHOD FOR PRODUCING A GRAIN-ORIENTED ELECTRICAL STEEL SHEET"

Abstract

A method for producing a grain-oriented electrical steel sheet having a B8 value satisfying the relation 1.80 < B8 (T) < 1.88, by as a starting material, a coil obtained by heating a slab formed from molten steel and hot rolling the slab or obtained by direct casting from the molten steel, the molten steel having a composition comprising, in terms of percent by weight, 0.02 to 0.15%; of C, 2.5 to 4.0% of Si, 0.02 to 0.20% of Mn, 0.015 to 0.065% of Sol, Al, 0.0030 to 0.0150% of N, 0.005 to 0.040% as the sum of at least one of S and Se and the balance consisting of Fe, comprising the steps of annealing the coil, and then carrying out cold rolling at a reduction ratio of 65 to 95%, serially decarburization annealing, final finish annealing and final coating, characterized in that annealing of said coil is carried out at 900 to 1, 100°C so that a grain-oriented electrical steel sheet has a thickness of 0.20 to 0.55 mm and said cold, an average grain diameter of 1.5 to 5.5 mm and a W17/50 value expressed by the formula given below: 0.5884e1.9154t < W17/50(W/kg) < 0.7558e1.7378t wherein t is sheet thickness (mm).

Full Text	Technical Field: This invention relates to a grain-oriented electrical steel sheet having an improved orientation of the {11Q} texture for use as an iron core of a transformer, etc, and a method of producing such a steel sheet. Background Art: A grain-oriented electrical steel sheet has been mainly used as a core material of electric appliances such as transformers, and must have excellent magnetic properties such as excitation characteristics, iron loss characteristics, and so forth. A magnetic flux density B in a magnetic field of BOO A/m (hereinafter called "B8" in the present invention) is ordinarily used as the numerical value representing the excitation characteristics, while W17/50 is used as a typical numerical value representing the iron loss characteristics. The magnetic flux density is one of the very important factors that govern the iron loss characteristics. Generally speaking, the higher the magnetic flux density, th€> better the iron loss. When the magnetic flux density becomes excessively high, however, secondary recrystallization grains become coarse, so that an abnormal eddy current loss becomes increase and the core loss may deteriorate. In other words, the secondary recrystallization grains must be appropriately controlled. Thee iron loss comprises a hysteresis loss and an eddy current loss. The former is associated with purity, internal strain, etc, besides the crystal orientation of a steel sheet and the latter is associated with an electric resistance, a sheet thickness, etc, of the steel sheet. The iron loss can be reduced by improving the purity and removing the internal strain as much as possible, as is well known in the art. The iron loss can be reduced also by improving the electric resistance and reducing the sheet thickness. One of the methods of improving the electric resistance increases the Si content, for example, but this method has a limit because the production process or the workability of the product deteriorate when the Si content is increased. Similarly, because a reduction in the sheet thickness results in the drop of productivity, an. increase in the production cost will occur. Therefore, there is also a limit to the reduction of the sheet thickness. A grain-oriented electrical steel sheet can be obtained by causing secondary recrystallization in finish annealing so as to develop a so-called "Goss texture" having {110} in the direction of the sheet plane and in a rolling direction. Typical production process of the grain-oriented electrical steel sheet are described in U.S.P. No. 1,965,559 owned by N.P, Goss, U.S.P. No. 2,533,351 owned by v.W. carpenter and U.S.P. NO. 2,595,340 owned by M.F. Littmann et al, These production processes features that MnS is used as a principal inhibitor so as to cause the secondary recrystallisation of the Goss texture at a high temperature during finish annealing, a slab is heated at a high temperature of not lower than 1,800°F so as to cause solid solution of MnS and cold rolling and annealing inclusive of intermediate annealing are carried out a plurality of times after hot rolling and before high temperature finish annealing. From the aspect of the magnetic properties, this grain-oriented electrical steel sheet satisfies the relationships of 1310 = 1.80T and W10/60 = 0.45W/lb (2.37 w/kg in terms of W17/50). As described above, the iron loss characteristics of the grain-oriented electrical steel sheet results from various factors. The method of producing the grain-oriented electrical steel sheet requires a longer production process and is more complicated than production methods of other steel products. Therefore, in order to obtain stable qualit, a greater number of control items exist and this problem is a great burden to operating engineers. Needless to say, this problem greatly affects the production yield. On the other hand, grain-oriented electrical steel sheets includes two types of the steel sheets, i.e. a high flux density grain-oriented electrical steel sheet having B8(T) of at least 1.88 (JIS standard) and a CGO. (Commercial Grain Oriented Silicon Steel) having a flux density of not higher than 1.88. The former mainly uses A1N, (Al.Si)N, Sb, MnSe, MnS, etc, as the inhibitor whereas the latter mainly uses MnS as the inhibitor. The producing methods vary also depending on the types of the products described above. Namely, the former includes a single (or one stage) cold rolling method and a double cold rolling method while the latter includes a second stage cold rolling method. In other words, there is hardly the case where the grain-oriented electrical steel sheet of the CGO grade is produced by the single cold rolling method, and the development of the grain-oriented electrical steel sheet of the CGO grade which can be produced by a shorter process and at a lower cost of production has been earnestly desired. Summary of the Invention: To solve these problems of the grain-oriented electrical steel sheet, the present invention provides a grain-oriented electrical steel sheet exhibiting an excellent iron loss characteristic curve by fundamentally investigating the components such as the Si content, the sheet thickness, the average grain diameter of the product and the combination of textures, etc, and simplifying the producing process to an extent that has not been achieved so far. The first feature of the present invention relates to a greiin-oriented electrical steel sheet which contains;, in terms of percent by weight, 2.5 to 4.0% of Si, 0.02 to 0.20% of Mn and 0.005 to 0.050% of acid-insoluble Al, and has an average grain diameter of 1.5 to 5.5 ram, a Wl7/50 of iron loss value expressed by the formula given below and a B8(T) value satisfying the relation 1.80 (Formula Removed) [t: sheet thickness (mm)] The second feature of the present invention relates to a grain-oriented electrical steel sheet which contains, in terms of percent by weight, 1.5 to less than 2.5% of Si, 0.02 to 0.20% of Mn and 0.005 to 0.050% of acid-insoluble Al, and has a mean crystal grain size of 1.5 to 5.5 mm, a W17/50 of iron loss value expressed by the formula given below and a B8(T) value satisfying the relation 1.88 sheet thickness of 0.20 to 0.55 mm: (Formula Removed) [t: sheet thickness (mm)] The third feature of the present invention according to the first or second features relates to a grain-oriented electrical steel sheet which further contains 0.003 to 0.3%, in terms of each element amount, of at least one element selected from the group consisting of Sb, Sn, Cu, Mo and B. In a method for producing a grain-oriented electrical steel sheet by using, as a starting material, a hot rolled coil obtained, by heating a slab and hot rolling, or a coil directly cast from a molten steel having & composition comprising, in terms of percent by weight, 0.02 to 0.15% of C, 2.5 to 4.0% of Si, 0.02 to 0.20% of Mn, 0.015 to 0.065% of Sol, Al, 0.0030 to 0.0150% of N, 0.005 to 0.040% as the sum of at least one of S and Se, and the balance consisting substantially of Fe, by slab heating, hot rolling, hot rolled coil annealing, and then serially cold rolling, decarburization annealing, final finish annealing and final coating, the fourth feature of the present invention relates to a method for producing a grain-oriented electrical steel sheet characterized in that hot rolled coil annealing is carried out at 900 to 1,, 100°C so that a steel sheet has a sheet thickness of 0.20 to 0.55 mm, an average grain diameter of 1.5 to 5.5 mm, a W17/5o iron loss value expressed by the formula given below and a B8(T) value satisfying the relation 1.80 s B8(T) s 1.88: (Formula Removed) [t: sheet thickness (mm)) In a method for producing a grain-oriented electrical steel sheet by using a coil, as a starting material, obtained by hot rolling a slab having a composition comprising, in terms of percent by weight, 0.02 to 0.15% of C, 1.5 to less than 2.5% of Si, 0.02 to 0.20% of Mn, 0.015 to 0.065% of Sol. Al, 0.0030 to 0.0150% of N, 0.005 to 0.040% as the sum of at least one of S and Se and the balance substantially consisting of Fe, by slab heating and hot rolling the slab, or a coil directly cast from a molten steel, hot rolling the slab, annealing the hot rolled coil and then carrying out serially cold rolling, decarburization annealing, final finish annealing and final coating, the fifth fea.ture of the present invention relates to a method for producing a grain-oriented electrical steel sheet characterized in that hot rolled coil annealing is carried out at 900 to 1,100°C so that the grain-oriented electrical steel sheet has a sheet thickness of 0.20 to 0.55 mm, an average grain diameter of 1.5 to 5.5m, a W17/50 of iron loss value expressed by the formula given below and a B8(T) value satisfying the relation 1.88 [t: sheet thickness (mm)] The sixth feature of the present invention according to tne fourth or fifth reatures relates to a method for producing a grain-oriented electrical steel sheet which contains 0.003 to 0.3%, in terms of weight% of each element, of at least one element selected from the group consisting of Sb, Sn, Cu, Mo and B. The seventh feature of the present invention according to the sixth feature relates to a method for producing a grain-oriented electrical steel sheet, wherein cold rolling is carried out at a reduction ratio of 65 to 95%. The eighth characterizing feature of the pressent invention according to the sixth feature relates to a method for producing a grain-oriented electrical steel sheet, wherein cold rolling is carried out at a reduction ratio of 80 to 86%. The ninth feature of the present invention according to the seventh or eighth features resides in a method for producing a grain-oriented electrical steel sheet, wherein cold rolling is carried out by a tandem mill or zendimier mill having a plurality of stands,. The tenth feature of the present invention according to any of features of fourth to ninth features resides in a method for producing a grain-oriented electrical steel sheet, wherein heating the slab in a high temperature zone of not lower than 1,200°C is carried out at a heating rate of at least 5°C/min and the slab is heated to 1,320 to 1,490°C. The eleventh feature of the present invention according to the tenth feature relates to a method for producing a grain-oriented electrical steel sheet, wherein the slab to be heated to a temperature within the range of 1,320 to 1,490°C is a slab to which hot deformation is applied at a reduction ratio of not higher than 50%. Therefore, the present invention relates to a method for producing a grain-oriented electrical steel sheet having a Be value satisfying the relation 1.80 <: b8 by using as a starting material coil obtained heating slab formed from molten steel and hot rolling the or direct casting having composition comprising in terms of percent weight to c si mn sol al n sum at least one s se balance substantially consisting fe steps annealing then carrying out cold serially decarburization final finish coating characterized that said is carried so grain-oriented electrical sheet has thickness mm an average grain diameter w17 value expressed formula given below:> (Formula Removed) wherein t is sheet thickness (mm). Brief Description of Accompanying Drawings: Fig. 1 is a graph showing the relationship between the sheet thickness of a product containing Si: 3.00%, Mn: 0.08%, acid-insoluble Al: 0.02% having B8 = 1.87T and W17/50. Fig. 2 is a graph showing the relationship between the sheet thickness of a product containing Si: 2.00%, Mn: 0.08%, acid-insoluble Al: 0.022% having B8 = 1.94T and W17/50. Fig. 3 is a graph showing the relationship between a slab heating rate and an iron loss in the case of Si: 3.00%. Fig. 4 is a graph showing the relationship between a slab heating rate and an iron loss in the case of Si: 2.00%. Fig. 5 is a graph showing the relationship between a cold rolling reduction ratio and an iron loss in the case of Si: 3.00%. Fig. 6 is a graph showing the relationship between a cold rolling reduction ratio and an iron loss in the case of Si: 2.00%. The Most Preferred Embodiments: Hereinafter, the present invention will be explained in further detail. The inventors of the present invention have conducted various studies on the conditions providing the iron loss characteristics and the production process of such a grain-oriented electrical steel sheet, and have succeeded in providing a grain-oriented electrical steel sheet of the grade generally called "CGO" having excellent iron loss characteristics by one stage cold rolling method by fundamentally investigating the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the crystal orientations, and simplifying the production process to such an extent that has never been achieved so far. The reasons for limitation of the component composition of the product will be explained. The C content of less than 0.02% is not desirable because grains grow abnormally at the time of slab heating before hot rolling, and a secondary recrystallization defect called "streaks" occurs in the product. When the C content exceeds 0.15%, on the other hand, a longer decarburization time is necessary in decarburization annealing after cold rolling, This is not only uneconomical but is also likely to invite an incomplete decarburization defect, so that a. magnetic defect called "magnetic aging" occurs in the product. If the Si content is less than 1.5%, an eddy current loss increases in the product. If it exceeds 4.0%, on the other hand, cold rolling at normal temperature becomes undesirably difficult. Mn is a principal inhibitor element that governs the secondary recrystallization for obtaining the magnetic properties as the grain-oriented electrical steel sheet. If the Mn content is less than 0.02%, the absolute amount of MnS for causing the secondary recrystallization becomes insufficient and if it exceeds 0.20%, on the other hand, a dissolution of MnS at the time of slab heating becomes more difficult. Moreover, the precipitation size becomes coarser during hot rolling and the appropriate size distribution as an inhibitor is lost. Mn has the effects of increasing the electric resistance and reducing the eddy current loss. If the Mn content is less than 0.02%, the eddy current loss increases and if it exceeds 0.20%, the effect of Mn is saturated. Acid-soluble Al is also a principal inhibitor element for a grain-oriented electrical steel sheet. If such an Al content is less; than 0.015%, the amount is not sufficient and the inhibitor strength drops undesirably. If it exceeds 0.065%, on the other hand, AlN to be precipitated as the inhibitor becomes coarser and eventually, the inhibitor strength drops undesirably. Acid-insoluble Al is contained as acid-soluble Al at the molten metal stage. It is used as the principal inhibitor for the secondary recrystallization in the same way as Mn and at the same time, it reacts with the oxide applied as the annealing separator and constitutes a part of the insulating film formed on the surface of the steel sheet. When this Al content is outside the range of 0.005 to 0.050%, the appropriate state of the inhibitor is collapsed and the glass film formation state j.s adversely affected, as well. In consequence, the iron loss reducing effect by the glass film tension is undesirably eliminated, S and Se are the important elements for forming MnS and MnSe with Mn, respectively. The inhibitor effect cannot be obtained sufficiently if their contents are outside the respective ranges described above, and the sum of one or both of them must be limited to the range of 0.005 to 0.040%. N is the important element that forms AlN with acid-soluble Al described above. When the N content is out of the range described above, the inhibitor effect cannot be obtained sufficiently. Therefore, the N content must be limited to the range of 0.0030 to 0.0150%. Furthermore, Sn is effective as the element for obtaining the stable secondary recrystallization of thin gauge products and has also the function of refining the secondary recrystallization grain diameter. To obtain such an effect, Sn must be added in the amount of at least 0.003%. When the Sn content exceeds 0.30%, the effect gets into saturation. From the aspect of the increase of the production cost, therefore, the upper limit is set to up to 0.30%. Cu ie effective as an element that improves the glass film of the Sn containing steel and is also effective for obtaining stable secondary recrystallization. If the Cu content is less than 0.003%, the effect is not sufficient and if it exceeds 0.30%, the magnetic flux density of the product drops undesirably. Sb, Mo and/or B are effective elements for obtaining the stable secondary recrystallization. To obtain this effect, at least 0.0030% of Sb, Mo and/or B must be added and if the amount exceeds 0.30%, the effect is saturated. From the aspect of the increase of the production cost, the upper limit is set to not greater than 0.30%. If the product sheet thickness is less than 0.20 mm, the hysteresis loss increases or productivity drops undesirably. If it exceeds 0.55 mm, on the other hand, the eddy current loss increases and the decarburization time becomes longer, so that productivity drops. If the average grain diameter of the product is smaller than 1.5 mm, the hysteresis loss increases desirably. When it exceeds 5.5 mm, the eddy current loss increases undesirably. For reference, U.S.P. No. 2,533,351 and U..S.P. No. 2,599,340 stipulate the average grain diameter of the product to 1.0 to 1.4 mm. Next, the method for producing the grain-oriented electrical steel sheet according to the present invention will be explained. The raw material of the grain-oriented electrical steel sheet, the components of which are regulated as described above, is cast as a slab or is directly cast as a steel strip. When the material is cast as the slab, it is processed into a coil by an ordinary hot rolling method. It is the feature of the present invention that the hot rolled coil is subsequently subjected to hot rolled coil annealing, and after it is reduced to a final sheet thickness by one stage cold rolling, the process steps after decarburization annealing is carried out. This hot rolled coil annealing is characterized in that annealing is carried out at a temperature between 900"C and 1,100°C. Annealing is carried out for 30 seconds to 30 minutes for a precipitation control of A1N. If annealing is conducted at a temperature higher than 1/100°C, the secondary recrystallization defect is wore likely to occur due to coarsening of the inhibitor. A heavy reduction ratio of 65 to 95% is preferred ae the cold rolling ratio. The decarburization annealing condition is not particularly limited, but this annealing is preferably carried out at a temperature within the range of 700 to 900"C for 30 seconds to 30 minutes, in a wet hydrogen atmosphere or in a mixed atmosphere of hydrogen and nitrogen. To prevent seizure in the secondary recrystallization and to form an insulating film, an annealing separator is applied by an ordinary method to the surface of the steel sheet after decarburization annealing. Secondary recrystallization annealing is carried out at a temperature not lower than. 1,000°C for at least 5 hours in a hydrogen or nitrogen atmosphere or in a mixed atmosphere. After the excessive annealing separator is removed, continuous annealing is thereafter carried out to correct the coil set and at the same time, the insulating and tensionirig film is applied and baked. Fig. 1 shows the relationship between the sheet thickness; and W17/50 of the product containing Si: 3.00%, Mn: 0.08%, acid-insoluble Al: 0,02% and B8 = 1.87T obtained by the steps of hot rolling a slab containing C: 0.065%, Si: 3.00%, Mn: 0.08%, S: 0-026%, acid-soluble Al: 0.030% ahd Ns 0.0089%, annealing the hot coil at 1,100°C after hot rolling, conducting final cold rolling to a thickness of 0.20 to 0.55 mm by one stage cold rolling, and thereafter conducting decarburization annealing and secondary recrystallization annealing. The grain-oriented electrical steel sheet exhibiting an excellent iron loss characteristic curve as expressed by the formula (1) given below can be obtained by fundamentally research into the components ssuch as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures and simplifying the production steps to such an extent that has not been achieved in the past: (Formula Removed) [t: sheet thickness (ram)] Fig. 2 shows the relationship between the sheet thickness and W17/50 of the product containing Si: 2.00%, Mn: 0.08%, acid-insoluble Al: 0.022% and B8 = 1.94T and obtained by the steps of hot rolling a slab containing C: 0.039%, Si: 2.00%, Mn: 0,08%, S: 0.026%, acid-soluble Al: 0.030% and N: 0.0078%, hot coil annealing the slab at l,090eC after hot rolling, conducting final cold rolling of the hot coil to a thickness of 0.20 to 0.55 mm by one stage cold rolling, and thereafter conducting decarburization annealing and secondary recrystallization annealing. The grain-oriented electrical steel sheet paving the excellent iron loss .characteristic curve expressed by the formula (1) described above can be obtained by fundamentally research into the components such as the Si content, the sheet thickness, the product average grain diameter and further, the combination of the textures, and simplifying the production process to such 4n extent that has not been achieved in the conventional CGO production process. Next, the producing method of the present invention will be explained in detail. The molten steel the components of which are regulated as described above is cast to a slab,or is directly cast to a steel strip. When the molten steel is cast to the slab, it is processed to a hot coil by an ordinary hot rolling process through slab heating steps. When the slab is heated, heating in a high temperature range exceeding 1,200°C is prof«rably carried out at a heating rate of at least 5°C/min. Fig. 3 shows the result of the experiments carried out by the inventors of the present invention. Slabs containing C: 0.056%, Si: 3,00%, Mn: 0.03%, S: 0,026%, Sol. Al: 0.030% and N: 0.0089% were continuously cast. After the slabs were heated to 1,350°C at various heating rates in an induction heating furnace, hot rolled coils having a thickness of 2.30 mm were produced. The hot rolled coils were annealed at 1,080°C, and cold rolled to a thickness of 0.300 mm and thereafter subjected to decarburization annealing, finish annealing, and flattening, and insulating and tensioning film baking annealing. Fig. 3 shows the relationship between W17/50 of the products thus obtained and the heating rates. Fig. 4 shows the result of the experiments, wherein slabs containing C: 0.037%, Si: 2.00%, Mn: 0.08%, S: 0.028%, Sol. Al: 0.032% and N: 0.0077% were continuously cast and were heated at various heating rates in the induction heating furnace to 1,350°C to obtain hot rolled coils having a sheet thickness of 2.30 mm. The hot rolled coils were annealed at 1,080°C, and cold rolled to a thickness of 0.300m and were subjected serially to decarburization annealing, finish annealing, and flattening, insulating and tensioning film baking annealing. Pig. 4 shows the relationship between W17/50 of the products thus obtained and the heating rate. In the experiments shown in Figs, 3 and 4, the secondary recrystailization defect partly occurred when slab heating at a temperature of not lower than 1,200°C was carried out at a heating rate less than 5°C/min. When the heating rate was higher than 5°C/min, the average grain diameter was 2.2 to 2.6 mm. When slab heating at a temperature higher than 1,200°C was carried out at a heating rate less than 5°C/min/ variation in the iron loss was great and the iron loss was inferior in some cases. The intended iron loss (0.5884e1'9154t The causes are assumed as tollows. When the slab is heated at a high temperature, the grains abnormally grow in the slab, so that the structure of the hot rolled coil becomes heterogeneous and is likely to occur variation of the magnetic properties. When the slab heating in a high temperature range of not lower than 1,200°C is carried out at a heating rate of at least 5°C/min, the abnormal grain growth can be restricted at the time of slab heating, the structure of the hot rolled coil becomes uniform, and consequently, variation in the magnetic properties can be restricted. The slab heating temperature is set to 1,320 to 1,490°C, If this heating temperature is less the.n 1,320°C, the inhibitors such as AlN, MnS and MnSe cannot be converted sufficiently to the dissolution, the secondary recrystailization is not stabilized, and the desired iron loss cannot be obtained. If the slab heating temperature exceeds 1,490°C, the slab is melted. When hot deformation is applied to the slab to be heated to a temperature within the range of 1,320 to 1,490°C at a reduction ratio of not higher than 50%, the columnar structure of the slab is destroyed, and this is effective for making the structure of the hot rolled coil uniform, and the magnetic properties can be further stabilized. The upper limit is set to 50% because the effect gets into saturation when the reduction ratio is increased beyond this limit. Slab heating may be conducted in an ordinary gas heating furnace but may also be carried out in an induction heating furnace or a electric resistance heating furnace. A combination system comprising the gas heating furnace for the low temperature zone and the induction heating furnace or the electric resistance heating furnace for the high temperature zone may be used, as well. In other words, slab heating may be carried out by the following combinations: 1) gas heating furnace (low temperature zone)-hot deformation (0 to 50%)-gas heating furnace (high temperature zone) 2) gas heating furnace (low temperature zone)-hot deformation (0 to 50%)-induction heating furnace or electric resistance heating furnace (high temperature zone) 3) induction heating furnace or electric resistance heating furnace (low temperature zone)-hot deformation (0 to 50%)-gas heating furnace (high temperature zone) 4) induction heating furnace or electric resistance heating furnace (low temperature zone)-hot deformation (0 to 50%)-gas heating furnace (high temperature zone) Here, the term "hot deformation 0%" means that heating is done in the low temperature zone by the gas heating furnace and heating is subsequently done by the induction heating furnace or electric resistance heating furnace without subsequent hot deformation in the case of 2), for example. When heating of the slab in a high temperature zone of not lower than 1,.200°C, which is carried out at a heating rate of at least 5°C/min, is carried out by the induction heating furnace or the electric resistance heating furnace, the slag (molten ferrosilieon oxides) do not form because slab heating can be carried out in a non-oxidizing atmosphere (nitrogen, for example) in the induction heating furnace or electric resistance heating furnace. Consequently, the surface defects of the steel sheet can be decreased, and the removing of the slag deposited on the floor of the heating furnace car. be eliminated. When heating of the slab before the application of hot deformation is carried out by the gas heating furnace, slab heating can be done at a lower cost and with higher productivity than by using the induction heating furnace or the electric resistance heating furnace. The hot rolled coil thus obtained is subsequently annealed so as to control the precipitation of the inhibitor. More particularly, the present invention carries out this hot rolled coil annealing at 900 to 1,000°C for 30 seconds to 30 minutes. If the annealing temperature is less than 900°C, the precipitation of the inhibitor is not sufficient and the secondary recrystallization does not get stable, and if it exceeds l,100°C, the secondary recrystallization defect is more likely to occur due to coarsening of the inhibitor. A lower temperature than the hot rolled sheet annealing temperature of 1,150°C of the conventional grain-oriented electrical steel sheets using A1N as the inhibitor, that is, a temperature of the equal level to the intermediate annealing temperature of products of the conventional CGO grade, can be employed for this hot rolled coil annealing. Next, the coil subjected to the hot rolled coil annealing described above is cold rolled so as to obtain the final sheet thickness. Generally, cold, rolling of the grain-oriented electrical steel sheet is conducted at least twice inclusive of intermediate annealing but the present invention is characterized in that the steel sheet is manufactured by one stage cold rolling. Though this cold rolling has been conventionally carried out by a zendimier mill or a tandem mill, the present invention conducts this cold rolling by using a tandem mill having a plurality of stands in order to reduce the cost of production and to improve productivity. In the present invention, the cold rolling is preferably carried out applying a heavy reduction ratio of 65 to 95% and more preferably, 75 to 90%. The most preferable reduction ratio is 80 - 86%. Fig. 5 shows the relationship between the reduction ratio and W17/50 of the product which is obtained by the steps of hot rolling a slab containing C: 0.066%, Si: 3.00%, Mn: 0.08%, S: 0.025%, Sol. All O.C'31% and N: 0.0090%, conducting hot rolled coil annealing at 1,080°C, conducting cold rolling at various reduction ratios to a final sheet thickness of 0.300 nm and, serially conducting decarburization annealing, finish annealing, and flattening, insulating and tensioning film baking annealing. Fig. 6 shows similarly the relationship between the reduction ratio and W17/50 of the product obtained by the steps of hot rolling a slab containing C: 0.038%, Si: 2.00%, Mn: 0.08%, S: 0-027%, Sol. Al: 0.031% and N: 0.0078%, conducting hot rolled coil annealing at 1,080°C, conducting cold rolling at various reduction ratios to a final sheet thickness of 0.300 mm, and conducting serially decarburization annealing, finish annealing, and flattening, insulating and tensioning film baking annealing. In the experiment conducted in Fig. 5 and Fig. 6, the partial secondary recrystallization defects tends to occur in case of the reduction ratio less than 80% and more than 86%. In addition, the average grain diameter of 2.2 to 2.6 mm is stably obtained when the above reduction ratio' is applied. It can be appreciated from Figs. 5 and 6 that when the reduction ratio of cold rolling is less than 80% or exceeds 86%, variation in the iron loss becomes increase, and a worse iron loss obtains in some cases. The desired iron loss (0.5884e1.9154t A slab containing C: 0.052%, Si: 3.05%, Mn: 0.08%, S: 0.024%, acid-soluble Al: 0.0261 and Ns 0.0080% was heated at 1,360°C and, immediately after heating, the slab was hot rolled into a hot rolled coil having a thickness of 2-3 mm. The hot rolled coil was annealed at 1,050°C and was then reduced to a thickness of 0.300 and 0.268 mm by one stage cold rolling. Then, decarburization annealing and the coating of an annealing separator were carried out at 860°C, and secondary recrystallization annealing was carried out at 1,200°C. Subsequently, a secondary film was applied to obtain the final product. Table 1 shows the characteristics of each product. Incidentally, conventional products were produced in the following way. A slab containing C: 0.. 044%, Si: 3.12%, Mn: 0.06%, S: 0.024% and N: 0.0040% was heated at 1,360°C and was immediately hot rolled to obtain a hot rolled coil having a thickness of 2.3 mm. The coil was reduced to a thickness of 0.300 and 0.269 mm by second stage cold rolling method inclusive of intermediate annealing at 840°C. Decarburization annealing and the coating of an annealing separator were then carried out at 860°C, and secondary recrystallization annealing was conducted at; 1,200C. An insulating and tensioning film was applied to obtain the final product. Table 1 (Table Removed) Grain-oriented electrical steel sheets exhibiting an excellent iron loss characteristic curve expressed by the formula (2) given below could be obtained by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and. the combination of the textures, and simplifying the manufacturing process to such an extent that, had not been achieved so far: (Formula Removed) [t: sheet thickness (min) ] [Example 2] A slab containing C: 0.032%, Si: 2.05%, Mn: 0.03%, S: 0.024%, acid-soluble Al: 0.026% and N: 0.0082% was heated at 1,360°C and was immediately hot rolled to obtain a hot rolled coil having a thickness of 2.. 3 mm . The hot rolled coil was annealed at 1,050°C and was cold rolled by one stage cold rolling to a thickness of 0.550 and 0.270 mm. Decarburization annealing and the coating of an annealing separator were carried out at 860°C, and then secondary recrystallization annealing was carried out at l,200°C. Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 2 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by the steps of Example 1. (Table Removed) The grain-oriented electrical steel sheets exhibiting the excellent iron loss characteristics expressed by the formula (2) described above could be obtained, by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been achieved so far. [Example 3] A slab containing C: 0,063%, Si: 2.85%, Mn: 0.08%, Ss 0.025%, acid-soluble Al: 0.028%, N: 0.0079% and Sn: 0.08% was heated at 1,350°C and was immediately hot rolled to a hot rolled coil having a thickness of 2.0 mm. The hot. rolled coil was annealed at 1,020°C and was cold rolled by one stage cold rolling to a thickness of 0.30 and 0.20 mm. Decarburization annealing and the coating of an annealing separator were carried out at 850°C, and secondary recrystallization annealing was carried out at 1,200°C. Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 3 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by the steps of Example 1. Table 3 (Table Removed) The grain-oriented electrical steel sheets exhibiting the excellent iron loss characteristic curve expressed by the formula (2) could be obtained by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been achieved so far. [Example 4] A slab containing C: 0.028%, Sis 2.44%, Mn: 0,08%, S: 0.025%, acid-soluble Al: 0.030%, N: 0.0078% and Sn: 0.05% was heated at 1,350°C and was immediately hot rolled to a hot rolled coil having a thickness of 2.5 mm. The hot rolled coil was annealed at 1,000°C and was cold rolled to a thickness of 0.35 and 0.30 mm by one stage cold rolling. Decarburization annealing and the coating of an annealing separator were carried out at 850°C and secondary recrystallization annealing was carried out at 1,200°C. Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 4 tabulates the characteristics of the products. Incidentally, the conventional product was produced by the manufacturing process of Example 1. Table 4 (Table Removed) The grain-oriented electrical steel sheets having the excellent iron loss characteristic curve expressed by the formula (2) could be obtained by adjsuting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been achieved so far. [Example 5] A molten steel containing C: 0.07%, Si: 3.15%, Mm 0,08%, 5: 0.026%, acid-soluble Al: 0.030%, N; 0.0078%, Sn: 0.05% and Cus 0.05% was directly cast to a coil having a thickness of 2.5 mm. The hot rolled coil was annealed at 950°C, and was cold rolled to a thickness of 0.280 mm by one stage cold rolling. Decarburization annealing and the coating of an annealing separating agent, were carried out at 850°C, and secondary recrystallization annealing was carried out at 1,200°C. Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 5 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by the manufacturing process of Example 1. Table 5 (Table Removed) The grain-oriented electrical steel sheets exhibiting the excellent iron loss characteristic; curve expressed by the formula (2) could be obtained by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been aghieved so far. [Example 6] A slab containing C: 0.02%, Si: 1.85%, Mn: 0,08%, S: 0.026%, acid-soluble Al: 0.030%, N: 0.0078%, Sn: 0.05% and Cu: 0.05% was heated at 1,360°C and was then hot rolled to a hot rolled coil having a thickness of 2.3 mm. The hot rolled coil was annealed at 950°C and was then cold rolled to a thickness of 0.255 mm by one stage cold rolling. Decarburization annealing and the coating of an annealing separator were carried out at 850°C and secondary recrystallization annealing was carried out at 1,200°C, Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 6 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by th€! manufacturing processs of Example 1. Table 6 (Table Removed) Th« grain-oriented electrical steel sheet exhibiting the excellent iron loss characteristic curve expressed by the formula (2) could be obtained by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been achieved so far, [Example 7] A slab containing C: 0,07%, Sis 3.50%, Mn: 0.08%, Se: 0.026%, acid-soluble Al: 0.030%, N: 0.0078%, Sb: 0.02% and Mo: 0.02% was heated at 1,360°C and was then hot rolled to a hot rolled coil having a thickness of 2.4 nun. The hot rolled coil was annealed at 1,025°C and was cold rolled to a thickness of 0.290 mm by one stage cold rolling, Decarburization annealing and the coating of an annealing separator were carried out at 850°C and secondary recrystallization annealing was carried out at 1,200°C. Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 7 tabulates the characteristics of the products- Incidentally, the conventional product was manufactured by the manufacturing process of Example 1. Table 7 (Table Removed) The grain-oriented electrical steel shoet exhibiting the excellent iron loss characteristic curve c6uld be obtained, by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures and simplifying the manufacturing process to such an extent that had. not been achieved so far. [Example 8], A slab containing C: 0.035%, Si: 2.20%, Mn: 0.08%, Se: 0.026%, acid-soluble Al: O.O1O%, N: 0.0078%, Sb: 0.02% and Mo: 0.02% was headed at 1,360°C and was hot rolled to a hot rolled coil having a thickness of 2.4 nun. The hot rolled coil was annealed at 1,050°Cand was cold rolled to a thickness of 0.290 mm by one stage cold rolling. Decarburization annealing and the coating of an annealing separator were carried out at 850°C and secondary recrystallization annealing was carried out at 1,200°C. Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 8 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by the manufacturing process of Example 1. Table 8 (Table Removed) [Example 9] A slab containing C: 0.053%, Si: 3.0,5%, Mn: 0,08%, S: 0.024%, acid-soluble Al: 0.026% and N: 0.0080% was heated at 1,360°C and was immediately hot rolled to obtain a hot rolled coil having a thickness of 2 .3 mm. The hot rolled coil was annealed at l,050°C and was cold rolled to a thickness of 0.300 mm. Decarburization annealing and an coating of the annealing separator were carried out at 830 to 860° and secondary recrystallization annealing was carried out at 1,200°C. Subsequently, an insulating and tensioning film was applied to obtain the final products, Table 9 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by the manufacturing process of Example 1. Table 9 (Table Removed) The grain-oriented electrical steel sheets sxhibiting the excellent iron loss characteristic curve expressed by the formula. (2) could be obtained by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been achieved so far. [Example 10] A slab having a component system A comprising [C]: 0.050%, [Si]: 2.92%, [Mn]: 0.08%, [S]: 0.022%, [Sol. Al]: 0.023% and [H]: 0.0088% was heated at various heating rates in the temperature zone of not lower than 1,200°C in an induction heating furnace, and the slab was heated to 1,350°C. Thereafter, the slab was hot rolled to a thickness of 2-0 mm, was hot rolled and hot rolled coil annealing at 1,060C, and cold rolled to a thickness of 0.300 mm by one stage cold rolling. Thereafter, decarburization annealing, finish annealing and flattening/insulating and tensioning film baking annealing were carried out to obtain the final products. On the other hand, a slab having a component system B comprising C: 0.038%, [Si]: 3.05%, [Mn]: 0.06%, [S]: 0-026%, 50l, Al]: 0.001% and [NJ: 0.0037% was heated to 1,350'f at a heating rate of 10°C/min in the temperature zone of not lower than 1,200°C in an induction heat ing furnace, and was hot rolled to obtain a hot coil having a thickness of 2.0 mm. The hot rolled coil was hen cold rolled to a thickness of 0.300 mm by second sage cold rolling inclusive of intermediate annealing at 840°C. Thereafter, decarburization annealin finish annealing, and flattening, insulating and tensioning film baking annealing were carried out to obtain to final products. As fmlated in Table 10, it can be appreciated that the pro rolling method. Table 10 (Table Removed) [Example 11] Slabs each containing [C]: 0.050%, [Si]: 2.921, [Mn]: 0,08%, [S]: 0.022%, [Sol. A1]: 0.023% and ]N]: 0.0088% were heated to 1,150*0 in a gas heating furnace. Thereafter, some of the slabs were subjected to hot deformation at various reduction ratios, were th)en heated at various heating rates in the temperature zone of not lower than 1,200°C in the gas heating furnace an\|d an induction heating furnace (nitrogen atmosphere) and was heated to 1,375'C. Thereafter, the slabs were hot rolled to a thickness of 2.0 mm, were annealed at 1,040°C and were cold rolled by one stage cold rolling to a thickness of 0.300 mm. Decarburisation annealing, finish annealing, and flattening and insulating and tensioning film baking annealing were carried out to obtain the products. As tabulated in Table 11, it can be appreciated that the products of the present invention could obtain the excellent magnetic properties by the one stage cold rolling method. Table 11 (Table Removed) [Example 12] A slab having a component system A comprising [C]: 0.052%, [Si]: 2.95%, [Mn] : 0.07%, [S]: 0.020%,, [Sol. Al]: 0.023% and [N]: 0.0089% was heated and Was then hot rolled to obtain hot coils having various sheet thickness. The hot rolled coils were annealed at l,050°c and were cold rolled to a thickness of 0.300 mm at various reduction ratios by one stage cold rolling. Thereafter,decarburization diniealliiy , finish annealing, and flattening, and insulating and tensioning film baking annealing were carried out to obtain the products. On the, other hand, a slab having a component system B of the; conventional method comprising [C): 0.0391, (Si]: 3.08%, [Mn]: 0.06%, [S]: 0.023%, [Sol. Al]; 0.001% and [N]: 0,0038 was heated and was hot rolled to obtain a thickness of 2.3 mm. The hot rolled coil was cold rolled to a thickness of 0.300 mm by second stage cold rolling inclusive of intermediate annealing at 840°C. Thereafter, decarburization annealing, finish annealing, and flattening, and insulating and tensioning film baking annealing were carried out to obtain the products. It can be appreciated from Table 12 that the products, according to the example of the present invention could provide the excellent magnetic properties with high productivity of cold rolling by the one stage cold rolling method. Table 12 (Table Removed) Note 1): first rolling reduction ratio: 67% second cold rolling reduction ratio: 60% [Example 13] A slab having a component system A comprising [C]: 0.030%, [Si]: 2.08%f [Mn]: 0.08%, [$]: 0.027%, [Sol. Al]: 0.025% and [N]\ 0.0090% was heated and was then hot rolled to obtain hot coils having various thickness. The hot coils were annealed at 1,060°C and were cold rolled to a thickness of 0,350 mm at various reduction ratios by one stage cold rolling. Thereafter, decarburization annealing, finish annealing, and flattening, and insulating and teiisiunlug film caxing annealing were carried out to obtain the final products. On the other hand, a slab having a component system B of the conventional method comprising [C]: 0.040%, [Si]: 3.09%, [Mn]: 0.06%, [S]: 0.024%, (Sol. Al]: 0.001% and [N]: 0.0039% was heated and was then hot rolled to obtain hot coils having a thickness of 2.3 ram. The hot coil were cold rolled to a thickness of 0.350 mm by second stage cold rolling inclusive of intermediate annealing at 840°C. Thereafter, decarburization annealing, finish annealing, and flattening, and insulating and tensioning film baking annealing were carried out. It can be appreciated from Table 13 that the products according to the example of the present invention could provide the excellent magnetic properties by the one stage cold rolling method. Table 13. (Table Removed) Note 1): first cold rolling reduction ratio: 62% second cold rolling reduction ratio: 60% [Example 14] A slab having a component system A comprising [C]: 0.051%, [Si]: 2.99%, [Mn]: 0.08%, [S]i 0.027%,, [Sol. Al]: 0.022% and [N]: 0.00905 was heated and was then hot rolled to obtain a hot coil having a thickness of 2.3 mm. The hot coil was annealed at l,050aC and was cold rolled to a thickness of 0.300 mm by one stage cold rolling by a tandem mill or zendiraier mill having a plurality of'stands. Thereafter, decarburization annealing, finish annealing, and flattening, and insulating and tensioning film baking annealing were carried out to obtain the products. On the other hand, a slab B of the conventional method having a component system B comprising [C]: 0,040%, [SiJ: 3.09%, [Mn]: 0.06%, [S]: 0.024%,, [Sol. Al]: 0.001% and [N]: 0.0039% was heated and was then hot rolled to a hot coil having a thickness of 2,3 mm. The hot coil was then cold rolled to a thickness of 0.300 mm by second stage cold rolling inclusive of intermediate annealing at 840°C by a tandem mill or zendimier mill having a plurality of stands. Thereafter, decarburization annealing, finish annealing, and flattening, and insulating and tensioning film baking annealing were carried out to obtain the final products. It can be appreciated from Table 14 that tne products according to the example of the present invention could obtain the excellent magnetic properties with high productivity of cold rolling by the one stage cold rolling method. Table 14 (Table Removed) Note 1): ZM: zendimier mill, TCM: tandem mill 2): Cold rolling productivity of second stage cold rolling nwat.hnd was the Suiti of first and second cold rolling. INDUSTRIAL APPLICABILITY A grain-oriented electrical steel sheet exhibiting an excellent iron loss curve can be obtained by adjusting components such as a Si content, a sheet thickness, a product average grain diameter size and the combination of textures, and simplifying the manufacturing steps to such an extent that has not been achieved in the conventional method. WE CLAIM: 1. A method for producing a grain-oriented electrical steel sheet having a B8 value satisfying the relation 1.80 (Formula Removed) wherein t is sheet thickness (mm). 2. A method for producing a grain-oriented electrical steel sheet as claimed in claim 1 the molten steel having a composition comprising, in terms of percent by weight, 0.02 to 0.15% of C, 1.5 to less than 2.5% of Si, 0.02 to 0.20% of Mn, 0.015 to 0.65% of Sol. Al, 0.0030 to 0.0150% of N, 0.005 to 0.040% as the sum of at least one of S and Se and the balance consisting of Fe. 3. A method for producing a grain-oriented electrical steel sheet as claimed in claim 1, wherein in terms of each element amount, 0.003 to 0.3% of at least one element selected from the group consisting of Sb, Sn, Cu, Mo and B. 4 A method for producing a grain-oriented electrical steel sheet as claimed in claim 1, wherein said cold rolling is carried out at a reduction ratio of 80 to 86%. 5. A method for producing a grain-oriented electrical steel sheet as claimed in claim 1, wherein said cold rolling is carried out by a tandem mill having a plurality of stands of zendimier mill. 6 A method for producing a grain oriented electrical steel sheet as claimed in claim 4, wherein heating of slab in a high temperature zone of not lower than 1,200°C is carried out to 1,320 to 1,490°C at a heating rate of at least 5°C/min. 7. A method for producing a grain-oriented electrical steel sheet as claimed in claim 7, wherein said slab to be heated to a temperature within the range of 1,320 to 1,490°C is a slab to which hot deformation is applied at a reduction ratio of not higher than 50%. 8. A method for producing a grain-oriented electrical steel sheet substantially as herein described with reference to the accompanying drawings.

Full Text

Technical Field:
This invention relates to a grain-oriented electrical steel sheet having an improved orientation of the {11Q} texture for use as an iron core of a transformer, etc, and a method of producing such a steel sheet. Background Art:
A grain-oriented electrical steel sheet has been mainly used as a core material of electric appliances such as transformers, and must have excellent magnetic properties such as excitation characteristics, iron loss characteristics, and so forth. A magnetic flux density B in a magnetic field of BOO A/m (hereinafter called "B8" in the present invention) is ordinarily used as the numerical value representing the excitation characteristics, while W17/50 is used as a typical numerical value representing the iron loss characteristics.
The magnetic flux density is one of the very important factors that govern the iron loss characteristics. Generally speaking, the higher the magnetic flux density, th€> better the iron loss. When the magnetic flux density becomes excessively high, however, secondary recrystallization grains become coarse, so that an abnormal eddy current loss becomes increase and the core loss may deteriorate. In other words, the secondary recrystallization grains must be appropriately controlled.
Thee iron loss comprises a hysteresis loss and an eddy current loss. The former is associated with purity, internal strain, etc, besides the crystal orientation of a steel sheet and the latter is associated with an

electric resistance, a sheet thickness, etc, of the steel sheet.
The iron loss can be reduced by improving the purity and removing the internal strain as much as possible, as is well known in the art.
The iron loss can be reduced also by improving the electric resistance and reducing the sheet thickness. One of the methods of improving the electric resistance increases the Si content, for example, but this method has a limit because the production process or the workability of the product deteriorate when the Si content is increased.
Similarly, because a reduction in the sheet thickness results in the drop of productivity, an. increase in the production cost will occur. Therefore, there is also a limit to the reduction of the sheet thickness.
A grain-oriented electrical steel sheet can be obtained by causing secondary recrystallization in finish annealing so as to develop a so-called "Goss texture" having {110} in the direction of the sheet plane and in a rolling direction.
Typical production process of the grain-oriented electrical steel sheet are described in U.S.P. No. 1,965,559 owned by N.P, Goss, U.S.P. No. 2,533,351 owned by v.W. carpenter and U.S.P. NO. 2,595,340 owned by M.F. Littmann et al,
These production processes features that MnS is used as a principal inhibitor so as to cause the secondary recrystallisation of the Goss texture at a high temperature during finish annealing, a slab is heated at a high temperature of not lower than 1,800°F so as to cause solid solution of MnS and cold rolling and annealing inclusive of intermediate annealing are carried out a plurality of times after hot rolling and before high temperature finish annealing. From the aspect of the magnetic properties, this grain-oriented electrical

steel sheet satisfies the relationships of 1310 = 1.80T and W10/60 = 0.45W/lb (2.37 w/kg in terms of W17/50).
As described above, the iron loss characteristics of the grain-oriented electrical steel sheet results from various factors. The method of producing the grain-oriented electrical steel sheet requires a longer production process and is more complicated than production methods of other steel products. Therefore, in order to obtain stable qualit, a greater number of control items exist and this problem is a great burden to operating engineers. Needless to say, this problem greatly affects the production yield.
On the other hand, grain-oriented electrical steel
sheets includes two types of the steel sheets, i.e. a high flux density grain-oriented electrical steel sheet having B8(T) of at least 1.88 (JIS standard) and a CGO. (Commercial Grain Oriented Silicon Steel) having a flux density of not higher than 1.88. The former mainly uses A1N, (Al.Si)N, Sb, MnSe, MnS, etc, as the inhibitor whereas the latter mainly uses MnS as the inhibitor. The producing methods vary also depending on the types of the products described above. Namely, the former includes a single (or one stage) cold rolling method and a double cold rolling method while the latter includes a second stage cold rolling method. In other words, there is hardly the case where the grain-oriented electrical steel sheet of the CGO grade is produced by the single cold rolling method, and the development of the grain-oriented electrical steel sheet of the CGO grade which can be produced by a shorter process and at a lower cost of production has been earnestly desired. Summary of the Invention:
To solve these problems of the grain-oriented electrical steel sheet, the present invention provides a grain-oriented electrical steel sheet exhibiting an excellent iron loss characteristic curve by fundamentally

investigating the components such as the Si content, the sheet thickness, the average grain diameter of the product and the combination of textures, etc, and simplifying the producing process to an extent that has not been achieved so far.
The first feature of the present invention relates to a greiin-oriented electrical steel sheet which contains;, in terms of percent by weight, 2.5 to 4.0% of Si, 0.02 to 0.20% of Mn and 0.005 to 0.050% of acid-insoluble Al, and has an average grain diameter of 1.5 to 5.5 ram, a Wl7/50 of iron loss value expressed by the formula given below and a B8(T) value satisfying the relation 1.80 (Formula Removed)
[t: sheet thickness (mm)]
The second feature of the present invention relates to a grain-oriented electrical steel sheet which contains, in terms of percent by weight, 1.5 to less than 2.5% of Si, 0.02 to 0.20% of Mn and 0.005 to 0.050% of acid-insoluble Al, and has a mean crystal grain size of 1.5 to 5.5 mm, a W17/50 of iron loss value expressed by the formula given below and a B8(T) value satisfying the relation 1.88 sheet thickness of 0.20 to 0.55 mm:
(Formula Removed)
[t: sheet thickness (mm)]
The third feature of the present invention according to the first or second features relates to a grain-oriented electrical steel sheet which further contains 0.003 to 0.3%, in terms of each element amount, of at least one element selected from the group consisting of Sb, Sn, Cu, Mo and B.
In a method for producing a grain-oriented electrical steel sheet by using, as a starting material, a hot rolled coil obtained, by heating a slab and hot

rolling, or a coil directly cast from a molten steel having & composition comprising, in terms of percent by weight, 0.02 to 0.15% of C, 2.5 to 4.0% of Si, 0.02 to 0.20% of Mn, 0.015 to 0.065% of Sol, Al, 0.0030 to 0.0150% of N, 0.005 to 0.040% as the sum of at least one of S and Se, and the balance consisting substantially of Fe, by slab heating, hot rolling, hot rolled coil annealing, and then serially cold rolling,
decarburization annealing, final finish annealing and final coating, the fourth feature of the present invention relates to a method for producing a grain-oriented electrical steel sheet characterized in that hot rolled coil annealing is carried out at 900 to 1,, 100°C so that a steel sheet has a sheet thickness of 0.20 to 0.55 mm, an average grain diameter of 1.5 to 5.5 mm, a
W17/5o iron loss value expressed by the formula given below
and a B8(T) value satisfying the relation 1.80 s B8(T) s 1.88:
(Formula Removed)
[t: sheet thickness (mm))
In a method for producing a grain-oriented electrical steel sheet by using a coil, as a starting material, obtained by hot rolling a slab having a composition comprising, in terms of percent by weight, 0.02 to 0.15% of C, 1.5 to less than 2.5% of Si, 0.02 to 0.20% of Mn, 0.015 to 0.065% of Sol. Al, 0.0030 to 0.0150% of N, 0.005 to 0.040% as the sum of at least one of S and Se and the balance substantially consisting of Fe, by slab heating and hot rolling the slab, or a coil directly cast from a molten steel, hot rolling the slab, annealing the hot rolled coil and then carrying out serially cold rolling, decarburization annealing, final finish annealing and final coating, the fifth fea.ture of the present invention relates to a method for producing a grain-oriented electrical steel sheet characterized in that hot rolled coil annealing is carried out at 900 to

1,100°C so that the grain-oriented electrical steel sheet has a sheet thickness of 0.20 to 0.55 mm, an average grain diameter of 1.5 to 5.5m, a W17/50 of iron loss value expressed by the formula given below and a B8(T) value satisfying the relation 1.88 [t: sheet thickness (mm)]
The sixth feature of the present invention according to tne fourth or fifth reatures relates to a method for
producing a grain-oriented electrical steel sheet which contains 0.003 to 0.3%, in terms of weight% of each element, of at least one element selected from the group consisting of Sb, Sn, Cu, Mo and B.
The seventh feature of the present invention according to the sixth feature relates to a method for producing a grain-oriented electrical steel sheet, wherein cold rolling is carried out at a reduction ratio of 65 to 95%.
The eighth characterizing feature of the pressent invention according to the sixth feature relates to a method for producing a grain-oriented electrical steel sheet, wherein cold rolling is carried out at a reduction ratio of 80 to 86%.
The ninth feature of the present invention according to the seventh or eighth features resides in a method for producing a grain-oriented electrical steel sheet, wherein cold rolling is carried out by a tandem mill or zendimier mill having a plurality of stands,.
The tenth feature of the present invention according to any of features of fourth to ninth features resides in a method for producing a grain-oriented electrical steel sheet, wherein heating the slab in a high temperature zone of not lower than 1,200°C is carried out at a heating rate of at least 5°C/min and the slab is heated to 1,320 to 1,490°C.
The eleventh feature of the present invention

according to the tenth feature relates to a method for producing a grain-oriented electrical steel sheet, wherein the slab to be heated to a temperature within the range of 1,320 to 1,490°C is a slab to which hot deformation is applied at a reduction ratio of not higher than 50%.
Therefore, the present invention relates to a method for producing a grain-oriented electrical steel sheet having a Be value satisfying the relation 1.80 <: b8 by using as a starting material coil obtained heating slab formed from molten steel and hot rolling the or direct casting having composition comprising in terms of percent weight to c si mn sol al n sum at least one s se balance substantially consisting fe steps annealing then carrying out cold serially decarburization final finish coating characterized that said is carried so grain-oriented electrical sheet has thickness mm an average grain diameter w17 value expressed formula given below:> (Formula Removed)
wherein t is sheet thickness (mm).

Brief Description of Accompanying Drawings:
Fig. 1 is a graph showing the relationship between the sheet thickness of a product containing Si: 3.00%, Mn: 0.08%, acid-insoluble Al: 0.02% having B8 = 1.87T and W17/50.
Fig. 2 is a graph showing the relationship between the sheet thickness of a product containing Si: 2.00%, Mn: 0.08%, acid-insoluble Al: 0.022% having B8 = 1.94T and W17/50.
Fig. 3 is a graph showing the relationship between a slab heating rate and an iron loss in the case of Si: 3.00%.
Fig. 4 is a graph showing the relationship between a slab heating rate and an iron loss in the case of Si: 2.00%.
Fig. 5 is a graph showing the relationship between a cold rolling reduction ratio and an iron loss in the case of Si: 3.00%.
Fig. 6 is a graph showing the relationship between a cold rolling reduction ratio and an iron loss in the case of Si: 2.00%. The Most Preferred Embodiments:
Hereinafter, the present invention will be explained in further detail.
The inventors of the present invention have conducted various studies on the conditions providing the iron loss characteristics and the production process of such a grain-oriented electrical steel sheet, and have succeeded in providing a grain-oriented electrical steel sheet of the grade generally called "CGO" having

excellent iron loss characteristics by one stage cold rolling method by fundamentally investigating the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the crystal orientations, and simplifying the production process to such an extent that has never been achieved so far.
The reasons for limitation of the component composition of the product will be explained.
The C content of less than 0.02% is not desirable because grains grow abnormally at the time of slab heating before hot rolling, and a secondary recrystallization defect called "streaks" occurs in the product. When the C content exceeds 0.15%, on the other hand, a longer decarburization time is necessary in decarburization annealing after cold rolling, This is not only uneconomical but is also likely to invite an incomplete decarburization defect, so that a. magnetic defect called "magnetic aging" occurs in the product.
If the Si content is less than 1.5%, an eddy current loss increases in the product. If it exceeds 4.0%, on the other hand, cold rolling at normal temperature becomes undesirably difficult.
Mn is a principal inhibitor element that governs the secondary recrystallization for obtaining the magnetic properties as the grain-oriented electrical steel sheet. If the Mn content is less than 0.02%, the absolute amount of MnS for causing the secondary recrystallization becomes insufficient and if it exceeds 0.20%, on the other hand, a dissolution of MnS at the time of slab heating becomes more difficult. Moreover, the precipitation size becomes coarser during hot rolling and the appropriate size distribution as an inhibitor is lost. Mn has the effects of increasing the electric resistance and reducing the eddy current loss. If the Mn content is less than 0.02%, the eddy current loss increases and if it exceeds 0.20%, the effect of Mn is

saturated.
Acid-soluble Al is also a principal inhibitor element for a grain-oriented electrical steel sheet. If such an Al content is less; than 0.015%, the amount is not sufficient and the inhibitor strength drops undesirably. If it exceeds 0.065%, on the other hand, AlN to be precipitated as the inhibitor becomes coarser and eventually, the inhibitor strength drops undesirably.
Acid-insoluble Al is contained as acid-soluble Al at the molten metal stage. It is used as the principal inhibitor for the secondary recrystallization in the same way as Mn and at the same time, it reacts with the oxide applied as the annealing separator and constitutes a part of the insulating film formed on the surface of the steel sheet. When this Al content is outside the range of 0.005 to 0.050%, the appropriate state of the inhibitor is collapsed and the glass film formation state j.s adversely affected, as well. In consequence, the iron loss reducing effect by the glass film tension is undesirably eliminated,
S and Se are the important elements for forming MnS and MnSe with Mn, respectively. The inhibitor effect cannot be obtained sufficiently if their contents are outside the respective ranges described above, and the sum of one or both of them must be limited to the range
of 0.005 to 0.040%.
N is the important element that forms AlN with acid-soluble Al described above. When the N content is out of the range described above, the inhibitor effect cannot be obtained sufficiently. Therefore, the N content must be limited to the range of 0.0030 to 0.0150%.
Furthermore, Sn is effective as the element for obtaining the stable secondary recrystallization of thin gauge products and has also the function of refining the secondary recrystallization grain diameter. To obtain such an effect, Sn must be added in the amount of at least 0.003%. When the Sn content exceeds 0.30%, the

effect gets into saturation. From the aspect of the increase of the production cost, therefore, the upper limit is set to up to 0.30%.
Cu ie effective as an element that improves the glass film of the Sn containing steel and is also effective for obtaining stable secondary recrystallization. If the Cu content is less than 0.003%, the effect is not sufficient and if it exceeds 0.30%, the magnetic flux density of the product drops undesirably.
Sb, Mo and/or B are effective elements for obtaining the stable secondary recrystallization. To obtain this effect, at least 0.0030% of Sb, Mo and/or B must be added and if the amount exceeds 0.30%, the effect is saturated. From the aspect of the increase of the production cost, the upper limit is set to not greater than 0.30%.
If the product sheet thickness is less than 0.20 mm, the hysteresis loss increases or productivity drops undesirably. If it exceeds 0.55 mm, on the other hand, the eddy current loss increases and the decarburization time becomes longer, so that productivity drops.
If the average grain diameter of the product is smaller than 1.5 mm, the hysteresis loss increases desirably. When it exceeds 5.5 mm, the eddy current loss increases undesirably. For reference, U.S.P. No. 2,533,351 and U..S.P. No. 2,599,340 stipulate the average grain diameter of the product to 1.0 to 1.4 mm.
Next, the method for producing the grain-oriented electrical steel sheet according to the present invention will be explained.
The raw material of the grain-oriented electrical steel sheet, the components of which are regulated as described above, is cast as a slab or is directly cast as a steel strip. When the material is cast as the slab, it is processed into a coil by an ordinary hot rolling method.
It is the feature of the present invention that the

hot rolled coil is subsequently subjected to hot rolled coil annealing, and after it is reduced to a final sheet thickness by one stage cold rolling, the process steps after decarburization annealing is carried out.
This hot rolled coil annealing is characterized in that annealing is carried out at a temperature between 900"C and 1,100°C. Annealing is carried out for 30 seconds to 30 minutes for a precipitation control of A1N. If annealing is conducted at a temperature higher than 1/100°C, the secondary recrystallization defect is wore likely to occur due to coarsening of the inhibitor.
A heavy reduction ratio of 65 to 95% is preferred ae the cold rolling ratio.
The decarburization annealing condition is not particularly limited, but this annealing is preferably carried out at a temperature within the range of 700 to 900"C for 30 seconds to 30 minutes, in a wet hydrogen atmosphere or in a mixed atmosphere of hydrogen and nitrogen.
To prevent seizure in the secondary recrystallization and to form an insulating film, an annealing separator is applied by an ordinary method to the surface of the steel sheet after decarburization annealing.
Secondary recrystallization annealing is carried out at a temperature not lower than. 1,000°C for at least 5 hours in a hydrogen or nitrogen atmosphere or in a mixed atmosphere.
After the excessive annealing separator is removed, continuous annealing is thereafter carried out to correct the coil set and at the same time, the insulating and tensionirig film is applied and baked.
Fig. 1 shows the relationship between the sheet thickness; and W17/50 of the product containing Si: 3.00%,
Mn: 0.08%, acid-insoluble Al: 0,02% and B8 = 1.87T
obtained by the steps of hot rolling a slab containing

C: 0.065%, Si: 3.00%, Mn: 0.08%, S: 0-026%, acid-soluble Al: 0.030% ahd Ns 0.0089%, annealing the hot coil at 1,100°C after hot rolling, conducting final cold rolling to a thickness of 0.20 to 0.55 mm by one stage cold rolling, and thereafter conducting decarburization annealing and secondary recrystallization annealing.
The grain-oriented electrical steel sheet exhibiting an excellent iron loss characteristic curve as expressed by the formula (1) given below can be obtained by fundamentally research into the components ssuch as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures and simplifying the production steps to such an extent that has not been achieved in the past:
(Formula Removed)
[t: sheet thickness (ram)]
Fig. 2 shows the relationship between the sheet thickness and W17/50 of the product containing Si: 2.00%, Mn: 0.08%, acid-insoluble Al: 0.022% and B8 = 1.94T and obtained by the steps of hot rolling a slab containing C: 0.039%, Si: 2.00%, Mn: 0,08%, S: 0.026%, acid-soluble Al: 0.030% and N: 0.0078%, hot coil annealing the slab at l,090eC after hot rolling, conducting final cold rolling of the hot coil to a thickness of 0.20 to 0.55 mm by one stage cold rolling, and thereafter conducting decarburization annealing and secondary recrystallization annealing.
The grain-oriented electrical steel sheet paving the excellent iron loss .characteristic curve expressed by the formula (1) described above can be obtained by fundamentally research into the components such as the Si content, the sheet thickness, the product average grain diameter and further, the combination of the textures, and simplifying the production process to such 4n extent that has not been achieved in the conventional CGO production process.

Next, the producing method of the present invention will be explained in detail.
The molten steel the components of which are regulated as described above is cast to a slab,or is directly cast to a steel strip. When the molten steel is cast to the slab, it is processed to a hot coil by an ordinary hot rolling process through slab heating steps.
When the slab is heated, heating in a high
temperature range exceeding 1,200°C is prof«rably carried out at a heating rate of at least 5°C/min.
Fig. 3 shows the result of the experiments carried out by the inventors of the present invention. Slabs containing C: 0.056%, Si: 3,00%, Mn: 0.03%, S: 0,026%, Sol. Al: 0.030% and N: 0.0089% were continuously cast. After the slabs were heated to 1,350°C at various heating rates in an induction heating furnace, hot rolled coils having a thickness of 2.30 mm were produced. The hot rolled coils were annealed at
1,080°C, and cold rolled to a thickness of 0.300 mm and thereafter subjected to decarburization annealing, finish annealing, and flattening, and insulating and tensioning
film baking annealing. Fig. 3 shows the relationship between W17/50 of the products thus obtained and the heating rates. Fig. 4 shows the result of the experiments, wherein slabs containing C: 0.037%, Si: 2.00%, Mn: 0.08%, S: 0.028%, Sol. Al: 0.032% and N: 0.0077% were continuously cast and were heated at various heating rates in the induction heating furnace to 1,350°C to obtain hot rolled coils having a sheet thickness of 2.30 mm. The hot rolled coils were annealed at 1,080°C, and cold rolled to a thickness of 0.300m and were subjected serially to decarburization annealing, finish annealing, and flattening, insulating and tensioning film baking annealing. Pig. 4 shows the relationship between W17/50 of the products thus obtained
and the heating rate.

In the experiments shown in Figs, 3 and 4, the secondary recrystailization defect partly occurred when slab heating at a temperature of not lower than 1,200°C was carried out at a heating rate less than 5°C/min. When the heating rate was higher than 5°C/min, the average grain diameter was 2.2 to 2.6 mm. When slab heating at a temperature higher than 1,200°C was carried out at a heating rate less than 5°C/min/ variation in the iron loss was great and the iron loss was inferior in some cases. The intended iron loss (0.5884e1'9154t The causes are assumed as tollows. When the slab is heated at a high temperature, the grains abnormally grow in the slab, so that the structure of the hot rolled coil becomes heterogeneous and is likely to occur variation of the magnetic properties. When the slab heating in a high temperature range of not lower than 1,200°C is carried out at a heating rate of at least 5°C/min, the abnormal grain growth can be restricted at the time of slab heating, the structure of the hot rolled coil becomes uniform, and consequently, variation in the magnetic properties can be restricted.
The slab heating temperature is set to 1,320 to 1,490°C, If this heating temperature is less the.n 1,320°C, the inhibitors such as AlN, MnS and MnSe cannot be converted sufficiently to the dissolution, the secondary recrystailization is not stabilized, and the desired iron loss cannot be obtained. If the slab heating temperature exceeds 1,490°C, the slab is melted.
When hot deformation is applied to the slab to be
heated to a temperature within the range of 1,320 to 1,490°C at a reduction ratio of not higher than 50%, the columnar structure of the slab is destroyed, and this is effective for making the structure of the hot rolled coil

uniform, and the magnetic properties can be further stabilized. The upper limit is set to 50% because the effect gets into saturation when the reduction ratio is increased beyond this limit.
Slab heating may be conducted in an ordinary gas heating furnace but may also be carried out in an induction heating furnace or a electric resistance heating furnace. A combination system comprising the gas heating furnace for the low temperature zone and the induction heating furnace or the electric resistance heating furnace for the high temperature zone may be used, as well.
In other words, slab heating may be carried out by the following combinations:
1) gas heating furnace (low temperature zone)-hot
deformation (0 to 50%)-gas heating furnace
(high temperature zone)
2) gas heating furnace (low temperature zone)-hot
deformation (0 to 50%)-induction heating
furnace or electric resistance heating furnace
(high temperature zone)
3) induction heating furnace or electric
resistance heating furnace (low temperature
zone)-hot deformation (0 to 50%)-gas heating furnace (high temperature zone)
4) induction heating furnace or electric
resistance heating furnace (low temperature
zone)-hot deformation (0 to 50%)-gas heating
furnace (high temperature zone)
Here, the term "hot deformation 0%" means that heating is done in the low temperature zone by the gas heating furnace and heating is subsequently done by the induction heating furnace or electric resistance heating furnace without subsequent hot deformation in the case of 2), for example.
When heating of the slab in a high temperature zone of not lower than 1,.200°C, which is carried out at a

heating rate of at least 5°C/min, is carried out by the induction heating furnace or the electric resistance heating furnace, the slag (molten ferrosilieon oxides) do not form because slab heating can be carried out in a non-oxidizing atmosphere (nitrogen, for example) in the induction heating furnace or electric resistance heating furnace. Consequently, the surface defects of the steel sheet can be decreased, and the removing of the slag
deposited on the floor of the heating furnace car. be eliminated.
When heating of the slab before the application of hot deformation is carried out by the gas heating furnace, slab heating can be done at a lower cost and with higher productivity than by using the induction heating furnace or the electric resistance heating furnace.
The hot rolled coil thus obtained is subsequently annealed so as to control the precipitation of the inhibitor. More particularly, the present invention carries out this hot rolled coil annealing at 900 to 1,000°C for 30 seconds to 30 minutes. If the annealing temperature is less than 900°C, the precipitation of the inhibitor is not sufficient and the secondary recrystallization does not get stable, and if it exceeds l,100°C, the secondary recrystallization defect is more likely to occur due to coarsening of the inhibitor. A lower temperature than the hot rolled sheet annealing temperature of 1,150°C of the conventional grain-oriented electrical steel sheets using A1N as the inhibitor, that is, a temperature of the equal level to the intermediate annealing temperature of products of the conventional CGO grade, can be employed for this hot rolled coil annealing.
Next, the coil subjected to the hot rolled coil annealing described above is cold rolled so as to obtain the final sheet thickness.
Generally, cold, rolling of the grain-oriented

electrical steel sheet is conducted at least twice inclusive of intermediate annealing but the present invention is characterized in that the steel sheet is manufactured by one stage cold rolling. Though this cold rolling has been conventionally carried out by a zendimier mill or a tandem mill, the present invention conducts this cold rolling by using a tandem mill having a plurality of stands in order to reduce the cost of production and to improve productivity. In the present invention, the cold rolling is preferably carried out applying a heavy reduction ratio of 65 to 95% and more preferably, 75 to 90%. The most preferable reduction ratio is 80 - 86%.
Fig. 5 shows the relationship between the reduction ratio and W17/50 of the product which is obtained by the steps of hot rolling a slab containing C: 0.066%, Si: 3.00%, Mn: 0.08%, S: 0.025%, Sol. All O.C'31% and N: 0.0090%, conducting hot rolled coil annealing at 1,080°C, conducting cold rolling at various reduction ratios to a final sheet thickness of 0.300 nm and, serially conducting decarburization annealing, finish annealing, and flattening, insulating and tensioning film baking annealing. Fig. 6 shows similarly the relationship between the reduction ratio and W17/50 of the product obtained by the steps of hot rolling a slab containing C: 0.038%, Si: 2.00%, Mn: 0.08%, S: 0-027%, Sol. Al: 0.031% and N: 0.0078%, conducting hot rolled coil annealing at 1,080°C, conducting cold rolling at various reduction ratios to a final sheet thickness of 0.300 mm, and conducting serially decarburization annealing, finish annealing, and flattening, insulating and tensioning film baking annealing. In the experiment conducted in Fig. 5 and Fig. 6, the partial secondary recrystallization defects tends to occur in case of the reduction ratio less than 80% and more than 86%. In addition, the average grain

diameter of 2.2 to 2.6 mm is stably obtained when the above reduction ratio' is applied. It can be appreciated from Figs. 5 and 6 that when the reduction ratio of cold rolling is less than 80% or exceeds 86%, variation in the iron loss becomes increase, and a worse iron loss obtains in some cases. The desired iron loss (0.5884e1.9154t A slab containing C: 0.052%, Si: 3.05%, Mn: 0.08%, S: 0.024%, acid-soluble Al: 0.0261 and Ns 0.0080% was heated at 1,360°C and, immediately after heating, the slab was hot rolled into a hot rolled coil having a thickness of 2-3 mm.
The hot rolled coil was annealed at 1,050°C and was then reduced to a thickness of 0.300 and 0.268 mm by one
stage cold rolling. Then, decarburization annealing and the coating of an annealing separator were carried out at 860°C, and secondary recrystallization annealing was carried out at 1,200°C.
Subsequently, a secondary film was applied to obtain the final product. Table 1 shows the characteristics of each product.
Incidentally, conventional products were produced in the following way. A slab containing C: 0.. 044%, Si: 3.12%, Mn: 0.06%, S: 0.024% and N: 0.0040% was heated at 1,360°C and was immediately hot rolled to obtain a hot rolled coil having a thickness of 2.3 mm. The coil was reduced to a thickness of 0.300 and 0.269 mm by second stage cold rolling method inclusive of intermediate annealing at 840°C. Decarburization annealing and the coating of an annealing separator were then carried out at 860°C, and secondary recrystallization annealing was conducted at; 1,200*C. An

insulating and tensioning film was applied to obtain the final product.
Table 1
(Table Removed)
Grain-oriented electrical steel sheets exhibiting an excellent iron loss characteristic curve expressed by the formula (2) given below could be obtained by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and. the combination of the textures, and simplifying the manufacturing process to such an extent that, had not been achieved so far:
(Formula Removed)
[t: sheet thickness (min) ] [Example 2]
A slab containing C: 0.032%, Si: 2.05%, Mn: 0.03%, S: 0.024%, acid-soluble Al: 0.026% and N: 0.0082% was heated at 1,360°C and was immediately hot rolled to obtain a hot rolled coil having a thickness of 2.. 3 mm .
The hot rolled coil was annealed at 1,050°C and was cold rolled by one stage cold rolling to a thickness of

0.550 and 0.270 mm. Decarburization annealing and the coating of an annealing separator were carried out at 860°C, and then secondary recrystallization annealing was carried out at l,200°C.
Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 2 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by the steps of Example 1.

(Table Removed)
The grain-oriented electrical steel sheets exhibiting the excellent iron loss characteristics expressed by the formula (2) described above could be obtained, by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been achieved so far. [Example 3]
A slab containing C: 0,063%, Si: 2.85%, Mn: 0.08%, Ss 0.025%, acid-soluble Al: 0.028%, N: 0.0079% and Sn: 0.08% was heated at 1,350°C and was immediately hot rolled to a hot rolled coil having a thickness of 2.0 mm.

The hot. rolled coil was annealed at 1,020°C and was cold rolled by one stage cold rolling to a thickness of 0.30 and 0.20 mm. Decarburization annealing and the coating of an annealing separator were carried out at 850°C, and secondary recrystallization annealing was carried out at 1,200°C.
Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 3 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by the steps of Example 1.

Table 3

(Table Removed)
The grain-oriented electrical steel sheets exhibiting the excellent iron loss characteristic curve expressed by the formula (2) could be obtained by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been achieved so far.
[Example 4]
A slab containing C: 0.028%, Sis 2.44%, Mn: 0,08%, S: 0.025%, acid-soluble Al: 0.030%, N: 0.0078% and Sn: 0.05% was heated at 1,350°C and was immediately hot rolled to a hot rolled coil having a thickness of 2.5 mm.
The hot rolled coil was annealed at 1,000°C and was cold rolled to a thickness of 0.35 and 0.30 mm by one stage cold rolling. Decarburization annealing and the coating of an annealing separator were carried out at 850°C and secondary recrystallization annealing was carried out at 1,200°C.
Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 4 tabulates the characteristics of the products. Incidentally, the conventional product was produced by the manufacturing process of Example 1.

Table 4

(Table Removed)
The grain-oriented electrical steel sheets having the excellent iron loss characteristic curve expressed by the formula (2) could be obtained by adjsuting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been achieved so far. [Example 5]
A molten steel containing C: 0.07%, Si: 3.15%, Mm 0,08%, 5: 0.026%, acid-soluble Al: 0.030%, N; 0.0078%, Sn: 0.05% and Cus 0.05% was directly cast to a coil having a thickness of 2.5 mm.
The hot rolled coil was annealed at 950°C, and was cold rolled to a thickness of 0.280 mm by one stage cold rolling. Decarburization annealing and the coating of an annealing separating agent, were carried out at 850°C, and secondary recrystallization annealing was carried out at
1,200°C.
Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 5 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by the manufacturing process of Example 1.

Table 5

(Table Removed)
The grain-oriented electrical steel sheets exhibiting the excellent iron loss characteristic; curve
expressed by the formula (2) could be obtained by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been aghieved so far. [Example 6]
A slab containing C: 0.02%, Si: 1.85%, Mn: 0,08%, S: 0.026%, acid-soluble Al: 0.030%, N: 0.0078%, Sn: 0.05% and Cu: 0.05% was heated at 1,360°C and was then hot rolled to a hot rolled coil having a thickness of 2.3 mm.
The hot rolled coil was annealed at 950°C and was then cold rolled to a thickness of 0.255 mm by one stage cold rolling. Decarburization annealing and the coating of an annealing separator were carried out at 850°C and secondary recrystallization annealing was carried out at 1,200°C,
Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 6 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by th€! manufacturing processs of Example 1.

Table 6

(Table Removed)
Th« grain-oriented electrical steel sheet exhibiting the excellent iron loss characteristic curve expressed by the formula (2) could be obtained by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been achieved so far, [Example 7]
A slab containing C: 0,07%, Sis 3.50%, Mn: 0.08%, Se: 0.026%, acid-soluble Al: 0.030%, N: 0.0078%, Sb: 0.02% and Mo: 0.02% was heated at 1,360°C and was then hot rolled to a hot rolled coil having a thickness of 2.4 nun.
The hot rolled coil was annealed at 1,025°C and was cold rolled to a thickness of 0.290 mm by one stage cold rolling, Decarburization annealing and the coating of an annealing separator were carried out at 850°C and secondary recrystallization annealing was carried out at 1,200°C.
Subsequently, an insulating and tensioning film was applied to obtain the final products. Table 7 tabulates the characteristics of the products- Incidentally, the conventional product was manufactured by the manufacturing process of Example 1.

Table 7

(Table Removed)
The grain-oriented electrical steel shoet exhibiting the excellent iron loss characteristic curve c6uld be obtained, by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures and simplifying the manufacturing process to such an extent that had. not been achieved so far. [Example 8],
A slab containing C: 0.035%, Si: 2.20%, Mn: 0.08%, Se: 0.026%, acid-soluble Al: O.O1O%, N: 0.0078%, Sb: 0.02% and Mo: 0.02% was headed at 1,360°C and was hot rolled to a hot rolled coil having a thickness of 2.4 nun.
The hot rolled coil was annealed at 1,050°Cand was cold rolled to a thickness of 0.290 mm by one stage cold rolling. Decarburization annealing and the coating of an annealing separator were carried out at 850°C and secondary recrystallization annealing was carried out at 1,200°C.
Subsequently, an insulating and tensioning film was
applied to obtain the final products. Table 8 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by the manufacturing process of Example 1.
Table 8

(Table Removed)
[Example 9]
A slab containing C: 0.053%, Si: 3.0,5%, Mn: 0,08%, S: 0.024%, acid-soluble Al: 0.026% and N: 0.0080% was heated at 1,360°C and was immediately hot rolled to obtain a hot rolled coil having a thickness of 2 .3 mm.
The hot rolled coil was annealed at l,050°C and was cold rolled to a thickness of 0.300 mm. Decarburization annealing and an coating of the annealing separator were carried out at 830 to 860° and secondary recrystallization annealing was carried out at 1,200°C.
Subsequently, an insulating and tensioning film was applied to obtain the final products, Table 9 tabulates the characteristics of the products. Incidentally, the conventional product was manufactured by the manufacturing process of Example 1.

Table 9
(Table Removed)

The grain-oriented electrical steel sheets sxhibiting the excellent iron loss characteristic curve expressed by the formula. (2) could be obtained by adjusting the components such as the Si content, the sheet thickness, the product average grain diameter and the combination of the textures, and simplifying the manufacturing process to such an extent that had not been achieved so far. [Example 10]
A slab having a component system A comprising [C]: 0.050%, [Si]: 2.92%, [Mn]: 0.08%, [S]: 0.022%, [Sol. Al]: 0.023% and [H]: 0.0088% was heated at various heating rates in the temperature zone of not lower than 1,200°C in an induction heating furnace, and the slab was heated to 1,350°C. Thereafter, the slab was hot rolled to a thickness of 2-0 mm, was hot rolled and hot rolled coil annealing at 1,060*C, and cold rolled to a thickness of 0.300 mm by one stage cold rolling. Thereafter, decarburization annealing, finish annealing and flattening/insulating and tensioning film baking annealing were carried out to obtain the final products. On the other hand, a slab having a component system B comprising C: 0.038%, [Si]: 3.05%, [Mn]: 0.06%, [S]: 0-026%, 50l, Al]: 0.001% and [NJ: 0.0037% was heated to 1,350'f at a heating rate of 10°C/min in the temperature zone of not lower than 1,200°C in an induction heat ing furnace, and was hot rolled to obtain a hot coil having a thickness of 2.0 mm. The hot rolled coil was hen cold rolled to a thickness of 0.300 mm by second sage cold rolling inclusive of intermediate annealing at 840°C. Thereafter, decarburization annealin finish annealing, and flattening, insulating and tensioning film baking annealing were carried out to obtain to final products.
As fmlated in Table 10, it can be appreciated that the pro
rolling method.
Table 10

(Table Removed)
[Example 11]
Slabs each containing [C]: 0.050%, [Si]: 2.921, [Mn]: 0,08%, [S]: 0.022%, [Sol. A1]: 0.023% and ]N]: 0.0088% were heated to 1,150*0 in a gas heating furnace. Thereafter, some of the slabs were subjected to hot deformation at various reduction ratios, were th)en heated at various heating rates in the temperature zone of not lower than 1,200°C in the gas heating furnace an|d an induction heating furnace (nitrogen atmosphere) and was heated to 1,375'C. Thereafter, the slabs were hot rolled to a thickness of 2.0 mm, were annealed at 1,040°C and were cold rolled by one stage cold rolling to a thickness

of 0.300 mm. Decarburisation annealing, finish annealing, and flattening and insulating and tensioning film baking annealing were carried out to obtain the products.
As tabulated in Table 11, it can be appreciated that the products of the present invention could obtain the excellent magnetic properties by the one stage cold rolling method.
Table 11

(Table Removed)
[Example 12]
A slab having a component system A comprising [C]: 0.052%, [Si]: 2.95%, [Mn] : 0.07%, [S]: 0.020%,, [Sol.
Al]: 0.023% and [N]: 0.0089% was heated and Was then

hot rolled to obtain hot coils having various sheet thickness. The hot rolled coils were annealed at l,050°c and were cold rolled to a thickness of 0.300 mm at various reduction ratios by one stage cold rolling. Thereafter,decarburization diniealliiy , finish annealing,
and flattening, and insulating and tensioning film baking annealing were carried out to obtain the products.
On the, other hand, a slab having a component system B of the; conventional method comprising [C): 0.0391, (Si]: 3.08%, [Mn]: 0.06%, [S]: 0.023%, [Sol. Al]; 0.001% and [N]: 0,0038 was heated and was hot rolled to obtain a thickness of 2.3 mm. The hot rolled coil was cold rolled to a thickness of 0.300 mm by second stage cold rolling inclusive of intermediate annealing at 840°C. Thereafter, decarburization annealing, finish annealing, and flattening, and insulating and tensioning film baking annealing were carried out to obtain the products. It can be appreciated from Table 12 that the products, according to the example of the present invention could provide the excellent magnetic properties with high productivity of cold rolling by the one stage cold rolling method.

Table 12

(Table Removed)
Note 1): first rolling reduction ratio: 67%
second cold rolling reduction ratio: 60% [Example 13]
A slab having a component system A comprising [C]: 0.030%, [Si]: 2.08%f [Mn]: 0.08%, [$]: 0.027%, [Sol. Al]: 0.025% and [N]\ 0.0090% was heated and was then hot rolled to obtain hot coils having various thickness. The hot coils were annealed at 1,060°C and were cold rolled to a thickness of 0,350 mm at various reduction

ratios by one stage cold rolling. Thereafter, decarburization annealing, finish annealing, and flattening, and insulating and teiisiunlug film caxing annealing were carried out to obtain the final products.
On the other hand, a slab having a component system B of the conventional method comprising [C]: 0.040%, [Si]: 3.09%, [Mn]: 0.06%, [S]: 0.024%, (Sol. Al]: 0.001% and [N]: 0.0039% was heated and was then hot rolled to obtain hot coils having a thickness of 2.3 ram. The hot coil were cold rolled to a thickness of 0.350 mm by second stage cold rolling inclusive of intermediate annealing at 840°C. Thereafter, decarburization annealing, finish annealing, and flattening, and insulating and tensioning film baking annealing were carried out. It can be appreciated from Table 13 that
the products according to the example of the present
invention could provide the excellent magnetic properties by the one stage cold rolling method.

Table 13.

(Table Removed)
Note 1): first cold rolling reduction ratio: 62% second cold rolling reduction ratio: 60%
[Example 14]
A slab having a component system A comprising [C]: 0.051%, [Si]: 2.99%, [Mn]: 0.08%, [S]i 0.027%,, [Sol. Al]: 0.022% and [N]: 0.00905 was heated and was then hot rolled to obtain a hot coil having a thickness of 2.3 mm. The hot coil was annealed at l,050aC and was cold rolled to a thickness of 0.300 mm by one stage cold
rolling by a tandem mill or zendiraier mill having a plurality of'stands. Thereafter, decarburization annealing, finish annealing, and flattening, and insulating and tensioning film baking annealing were carried out to obtain the products.
On the other hand, a slab B of the conventional method having a component system B comprising [C]: 0,040%, [SiJ: 3.09%, [Mn]: 0.06%, [S]: 0.024%,, [Sol. Al]: 0.001% and [N]: 0.0039% was heated and was then hot rolled to a hot coil having a thickness of 2,3 mm. The hot coil was then cold rolled to a thickness of 0.300 mm by second stage cold rolling inclusive of intermediate annealing at 840°C by a tandem mill or
zendimier mill having a plurality of stands. Thereafter, decarburization annealing, finish annealing, and flattening, and insulating and tensioning film baking annealing were carried out to obtain the final products. It can be appreciated from Table 14 that tne products according to the example of the present invention could obtain the excellent magnetic properties with high productivity of cold rolling by the one stage cold rolling method.

Table 14

(Table Removed)
Note 1): ZM: zendimier mill, TCM: tandem mill
2): Cold rolling productivity of second stage cold rolling nwat.hnd was the Suiti of first
and second cold rolling.
INDUSTRIAL APPLICABILITY
A grain-oriented electrical steel sheet exhibiting an excellent iron loss curve can be obtained by adjusting components such as a Si content, a sheet thickness, a product average grain diameter size and the combination of textures, and simplifying the manufacturing steps to such an extent that has not been achieved in the conventional method.

WE CLAIM:
1. A method for producing a grain-oriented electrical steel sheet having a B8 value satisfying the relation 1.80 (Formula Removed)
wherein t is sheet thickness (mm).
2. A method for producing a grain-oriented electrical steel sheet as claimed in claim 1 the molten steel having a composition comprising, in terms of percent by weight, 0.02 to 0.15% of C, 1.5 to less than 2.5% of Si, 0.02 to 0.20% of Mn, 0.015 to 0.65% of Sol. Al, 0.0030 to 0.0150% of N, 0.005 to 0.040% as the sum of at least one of S and Se

and the balance consisting of Fe.
3. A method for producing a grain-oriented electrical steel sheet as claimed in claim 1, wherein in terms of each element amount, 0.003 to 0.3% of at least one element selected from the group consisting of Sb, Sn, Cu, Mo and B.
4 A method for producing a grain-oriented electrical steel sheet as claimed in claim 1, wherein said cold rolling is carried out at a reduction ratio of 80 to 86%.
5. A method for producing a grain-oriented electrical steel sheet as claimed in claim 1, wherein said cold rolling is carried out by a tandem mill having a plurality of stands of zendimier mill.
6 A method for producing a grain oriented electrical steel sheet as claimed in claim 4, wherein heating of slab in a high temperature zone of not lower than 1,200°C is carried out to 1,320 to 1,490°C at a heating rate of at least 5°C/min.
7. A method for producing a grain-oriented electrical steel sheet as
claimed in claim 7, wherein said slab to be heated to a temperature
within the range of 1,320 to 1,490°C is a slab to which hot
deformation is applied at a reduction ratio of not higher than 50%.

8. A method for producing a grain-oriented electrical steel sheet substantially as herein described with reference to the accompanying drawings.

Documents:

972-del-1998-abstract.pdf

972-del-1998-claims.pdf

972-del-1998-correspondence-others.pdf

972-del-1998-correspondence-po.pdf

972-del-1998-description (complete).pdf

972-del-1998-drawings.pdf

972-del-1998-form-1.pdf

972-del-1998-form-13.pdf

972-del-1998-form-19.pdf

972-del-1998-form-2.pdf

972-del-1998-form-3.pdf

972-del-1998-form-4.pdf

972-del-1998-form-6.pdf

972-del-1998-gpa.pdf

972-del-1998-petition-138.pdf

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Patent Number

215346

Indian Patent Application Number

972/DEL/1998

PG Journal Number

11/2008

Publication Date

14-Mar-2008

Grant Date

26-Feb-2008

Date of Filing

15-Apr-1998

Name of Patentee

NIPPON STEEL CORPORATION

Applicant Address

6-3, OTEMACHI 2-CHOME, CHIYODA-KU, TOKYO 100 8071, JAPAN

Inventors:

#	Inventor's Name	Inventor's Address
1	YOUSUKE KUROSAKI	C/O NIPPON STEEL CORPORATION HIROHATA WORKS, 1, FUJICHO, HIROHATA-KU, HIMEJI CITY, HYOGO, JAPAN
2	NORITO ABE	C/O NIPPON STEEL CORPORATION HIROHATA WORKS, 1, FUJICHO, HIROHATA-KU, HIMEJI CITY, HYOGO, JAPAN
3	NOBUO TACHIBANA	C/O NIPPON STEEL CORPORATION HIROHATA WORKS, 1, FUJICHO, HIROHATA-KU, HIMEJI CITY, HYOGO, JAPAN
4	KENTARO CHIKUMA	C/O NIPPON STEEL CORPORATION HIROHATA WORKS, 1, FUJICHO, HIROHATA-KU, HIMEJI CITY, HYOGO, JAPAN
5	KIYOKAZU ICHIMURA	C/O NIPPON STEEL CORPORATION HIROHATA WORKS, 1, FUJICHO, HIROHATA-KU, HIMEJI CITY, HYODO, JAPAN
6	SADANOBU HIROKAMI	C/O NIPPON STEEL CORPORATION HIROHATA WORKS, 1, FUJICHO, HIROHATA-KU, HIMEJI CITY, HYOGO, JAPAN
7	MASAYUKI YAMASHITA	C/O NIPPON STEEL CORPORATION HIROHATA WORKS, 1, FUJICHO, HIROHATA-KU, HIMEJI CITY, HYOGO, JAPAN

PCT International Classification Number

C12D 8/12

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	10-60216	1998-03-11	Japan
2	10-60215	1998-03-11	Japan