Title of Invention

"AN ALUMINUM TYPE PLATED STEEL SHEET HAVING HEATING DISCOLORING RESISTANCE AND WELDABILITY"

Abstract An aluminum type plated steel sheet having heating-discoloring resistance and weldability, including: not more than 0.2 mass% of C; not more than 0.007 mass % of N; not less than 0.1 mass% and not more than 0.5 mass% of Si; not more than 0.1 mass% of P; not more than 0.02 mass% of S; not less than 1.05 mass% and not more than 2.0 mass% of Mn; not more than 1.0 mass% of soluble Al; and a residual amount of Fe and inevitable impurities, and optionally including traces of Niobium (Nb) as herein described, wherein the melting aluminum and silicon type plated steel sheet comprises an aluminum and silicon plated layer mainly consisting of Al and Si being deposited thereon, the aluminum and silicon plated layer having more than 6 mass% Si and less than 12 mass% Si.
Full Text The present invention relates to an aluminum type plated steel sheet having heating-discoloring resistance and weldability.
TECHNICAL FIELD
[0001]
The present invention relates to an aluminum type plated steel sheet having excellent heating-discoloring resistance and weldability, and a heat shrink band using the same.
Priority is claimed on Japanese Patent Application No. 2005-34357, filed February 10, 2005, the content of which is incorporated herein by reference.
BACKGROUND ART
[0002]
In general, a CRT (cathode-ray tube) is reinforced with a heat shrink band, in order to prevent an implosion thereof. This heat shrink band is made of a belt-shaped steel sheet by bending it to the shape of a side face of the CRT, and then welding both . ends with each other to form a frame. Moreover, a metal bracket is attached to each of the four comers of the heat shrink band by welding. When fixing the heat shrink band to the circumference of the CRT, .the heat shrink band is thermally expanded by heating it at approximately 500 to 600oC, and then the heat shrink band is set to the circumference of CRT and simultaneously cooled quickly. As a result, the heat shrink band shrinks due to this quick cooling, so that deformation caused by air pressure is corrected by the tension of the heat shrink band generated at that time.
' [0003]
Furthermore, there is a problem in that the weight of a heat shrink band is likely to increase in order to provide sufficient tension to rectify the deformation of the CRT caused by air pressure.
For example, a heat shrink band for use in a CRT of 21 inches in diagonal length weighs 700g or more. Moreover, some heat shrink bands are subjected to 0-T bending processing, depending on the shape of the heat shrink band, and hence such a heat shrink band necessitates a steel sheet which satisfies both strength and processability. Further, there is also a problem in that this heat shrink band develops rust due to a change of temperature and humidity in a room, after the heat shrink band is fixed to a CRT. There is a possibility that this rust may have a negative influence on the electronic beam of the CRT in addition to a problem of external appearance. However, it is not possible to apply oil onto the surface of the steel sheet for use in a heat shrink band, in view of its use. So, in the heat shrink band, an electric galvanized steel sheet, a melting galvanized steel sheet, a melting zinc-aluminum plated steel sheet, a melting aluminum plated steel sheet, etc. are used in order to prevent the generation of such rust. [0004]
Among them, a zinc type plated steel sheet has a problem in that alloying of zinc occurs causing discoloration, in the step of heating and expanding the heat shrink band at a temperature of 500 to 600°C. This discoloration, although only a problem of appearance, will decrease its commercial value significantly. On the other hand, as for an aluminum type plated steel sheet, although it does not discolor at all upon being heated at a high temperature for a short time such as a high-frequency induction heating, if it is heated by gas at a high temperature such as 550°C for a relatively long time, for example at 650°C for approximately 15 seconds or more, then it may become
discolored. [0005]
It should be noted that references relevant to the present invention include the following patent documents 1 to 4.
Namely, Patent document 1 discloses a production method of a heat-resistant aluminium-surface-treated steel sheet which includes generating a fine A1N layer which prevents counter diffusion of Fe and Al during heating after metal plating, thereby suppressing alloying.
Patent document 2 discloses a melted aluminum-plated steel sheet which has a component system, as a steel component, consisting of a predetermined amount of O and each of of Ti, Nb, V, B, etc., in a restricted amount so as to maintain sol-N stably, and which is subjected to melted aluminum plating, thereby preventing discoloration due to alloying.
Patent document 3 discloses an aluminum-plated steel sheet suitable for processing at high temperature which achieves high strength after being processed at high temperature, as a result of adding Ti, P, Ni, and Cu thereto.
Patent document 4 discloses a production method of a molten Al-plated steel sheet which excels in gloss retention of the plated layer at high temperature, i.e. a steel sheet having a plated layer which does not discolor even if the steel sheet is used at a high temperature of approximately 550°C, because a barrier layer made of A1N is formed at the boundary between the plated layer and steel sheet upon being heated, by leaving free nitrogen after plating. However, since the Si content and Mn content are small, if the Al content is 0.02 or less, then deoxidization may become insufficient at the time of exchanging of a ladle during a continuous casting, etc. [Patent document 1] Japanese Patent Publication No.2-61544 official report.
[Patent document 2] Japanese Unexamined Patent Application, First Publication
No.H9-195021 official report.
[Patent document 3] Japanese Unexamined Patent Application, First Publication
2003-34844 official report
[Patent document 4] Patent Publication 5-26864 official report
[0006]
Thus, the present invention is proposed in view of such conventional circumstances, and it is an object of the invention to provide an aluminum type plated steel sheet which excels in discoloration resistance, and weldability, which does not decorate after re-heating and which can prevent increasing strength, and a heat shrink band using the same.
DISCLOSURE OF INVENTION
[0007]
In order to attain this object, a first aspect of the present invention provides a[n] melting aluminum type plated steel sheet including a steel sheet being composed of not more than 0.005 mass% of C; not more than 0.005 mass % of N; not less than 0.1 mass% and not more than 0.5 mass% of Si; not more than 0.1 mass% of P; not more than 0.02 mass% of S; not less than 1.05 mass% and not more than l.3 mass% of Mn; not more than 1.0 mass% of sol Al; a residual amount of Fe and inevitable impurities, and an aluminum type plated layer mainly consisting of Al being deposited thereon, whereby discoloration can be prevented upon being re-heated at a temperature of not less than 500°C to not more than 700°C.
Moreover, a second aspect of the present invention provides the melting aluminum type plated steel sheet as set forth in the first aspect of the present invention,
in which when the C is not more than 0.003 mass%, the N is not more than 0.004 mass%, the P is not less than 0.05 mass% and not more than 0.08 mass%, and the Mn is not less than 1.05 mass% and not more than 1.3 mass%, 0.2 mass% proof stress PS is not less than 300MPa and a tensile strength TS is not less than 400 MPa. [0008]
Moreover, a third aspect of the present invention provides a[n] melting aluminum type plated steel sheet including a steel sheet being composed of not more than 0.2 mass% of C; not more than 0.007 mass % of N; not less than 0.1 mass% and not more than 0.5 mass% of Si; not more than 0.1 mass% of P; not more than 0.02 mass% of S; not less than 1.05 mass% and not more than 2.0 mass% of Mn; not less than 0.01 and not more than 0.08 mass% of Nb; not more than 1.0 mass% of sol Al; a residual amount of Fe and inevitable impurities, and an aluminum type plated layer mainly consisting of Al being deposited thereon, whereby discoloration can be prevented upon being re-heated at a temperature of not less than 500°C to not more than 700°C. [0009]
Moreover, a fourth aspect of the present invention provides the melting aluminum type plated steel sheet as set forth in the third aspect of the present invention, in which when the C is not less than 0.05 mass% and more than 0.2 mass%, the Si is not less than 0.1 mass% and not more than 0.3 mass%, the Mn is not less than 1.05 mass% and not more than 1.5 mass%, and the Nb is not less than 0.03 mass% and not more than 0.05 mass%, a yield point YP is not less than 400MPa and a tensile strength TS is not less than 550 MPa.
Moreover, a fifth aspect of the present invention provides a[n] melting aluminum type plated steel sheet including a steel sheet being composed of not more
than 0.005 mass% of C; not more than 0.005 mass % of N; not less than 0.1 mass% and not more than 0.5 mass% of Si; not more than 0.1 mass% of P; not more than 0.02 mass% of S; not less than 1.05 mass% and not more than [2.0] 1.3 mass% of Mn; not more than 1.0 mass% of sol Al; a residual amount of Fe and inevitable impurities, and an aluminum type plated layer mainly consisting of Al being deposited thereon, whereby the reduction in strength upon being heated at a temperature of not less than 500°C to not more than 700°C after being plated is not more than 10 [ma39]%-compared to that before being heated (re-heated). [0010]
Moreover, a sixth aspect of the present invention provides the melting aluminum type plated steel sheet as set forth in the fifth aspect of the present invention, in which when the C is not more than 0.003 mass%, the N is not more than 0.004 mass%, the P is not less than 0.05 mass% and not more than 0.08 mass%, and the Mn is not less than 1.05 mass% and not more than 1.3 mass%, 0.2 mass% proof stress PS is not less than 300MPa and a tensile strength TS is not less than 400 MPa.
Moreover, a seventh aspect of the present invention provides a[n] melting aluminum type plated steel sheet including a steel sheet being composed of not more than 0.2 mass% of C; not more than 0.007 mass % of N; not less than 0.1 mass% and not more than 0.5 mass% of Si; not more than 0.1 mass% of P; not more than 0.02 mass% of S; not less than 1.05 mass% and not more than 2.0 mass% of Mn; not less than 0.01 mass% and not more than 0.08 mass% of Nb, not more than 1.0 mass% of sol Al; a residual amount of Fe and inevitable impurities, and an aluminum type plated layer mainly consisting of Al being deposited thereon, whereby the reduction in strength upon being heated at a temperature of not less than 500°C to not more than 700°C after being plated is not more than 10 [maaa]% compared to that before being
heated (re-heated). [0011]
Moreover, an eighth aspect of the present invention provides the melting aluminum type plated steel sheet as set forth in the seventh aspect of the present invention, in which when the C is not less than 0.05 mass% and not more than 0.2 mass%, the Si is not less than 0.1 mass% and not more than 0.3 mass%, the Mn is not less than 1.05 mass% and not more than 1.5 mass%, and the Nb is not less than 0.03 mass% and not more than 0.05 mass%, a yield point YP is not less than 400 MPa and a tensile strength TS is not less than 550 MPa.
Moreover, a ninth aspect of the present invention provides a heat shrink band using a[n] melting aluminum type plated steel sheet comprising a steel sheet being composed of not more than 0.005 mass% of C; not more than 0.005 mass % of N; not less than 0.1 mass% and not more than 0.5 mass% of Si; not more than 0.1 mass% of P; not more than 0.02 mass% of S; not less than 1.05 mass% and not more than [2.0]-1.3 mass% of Mn; not more than 1.0 mass% of sol Al; a residual amount of Fe and inevitable impurities, and an aluminum type plated layer mainly consisting of Al being deposited thereon. [0012]
Moreover, a tenth aspect of the present invention provides the heat shrink band as set forth in the ninth aspect of the present invention, in which the melting aluminum type plated steel sheet is one in which when the C is not more than 0.003 mass%, the N is not more than 0.004 mass%, the P is not less than 0.05 mass% and not more than 0.08 mass%, and the Mn is not less than 1.05 mass% and not more than 1.3 mass%, 0.2 mass% proof stress PS is not less than 300MPa and a tensile strength TS is not less than 400 MPa.
Moreover, an eleventh aspect of the present invention provides a heat shrink band using a[n] melting aluminum type plated steel sheet including a steel sheet being composed of not more than 0.2 mass% of C; not more than 0.007 mass % of N; not less than 0.1 mass% and not more than 0.5 mass% of Si; not more than 0.1 mass% of P; not more than 0.02 mass% of S; not less than 1.05 mass% and not more than 2.0 mass% of Mn; not less than 0.01 and not more than 0.08 mass% of Nb; not more than 1.0 mass% of sol Al; a residual amount of Fe and inevitable impurities, and an aluminum type plated layer mainly consisting of Al being deposited thereon. [0013]
Moreover, a twelfth aspect of the present invention provides the heat shrink band as set forth in the eleventh aspect of the present invention, in which the melting aluminum type plated steel sheet is one in which when the C is not less than 0.05 mass% and more than 0.2 mass%, the Si is not less than 0.1 mass% and not more than 0.3 mass%, the Mn is not less than 1.05 mass% and not more than 1.5 mass%, and the Nb is not less than 0.03 mass% and not more than 0.05 mass%, a yield point YP is not less than 400MPa and a tensile strength TS is not less than 550 MPa. [0014]
As mentioned above, in accordance with the present invention, it is possible to provide an aluminum type plated steel sheet having excellent discoloration resistance and weldability suitable for forming a heat shrink band, which does not discolor even after being re-heated, and which can prevent deterioration of strength.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015]
FIG. 1 is a perspective view showing an embodiment of a heat shrink band to which
the heat shrink band shown in FIG. 1.
BEST MODE FOR CARRYING OUT THE INVENTION
[0017]
A detailed explanation will be given about an aluminum type plated steel sheet to which the present invention has been applied and a heat shrink band using the aluminum type plated steel sheet below, with reference to the drawings. It should be noted, % indicates mass%, unless otherwise noted. [0018]
First, an explanation will be given about the first aluminum type plated steel sheet to which the present invention has been applied.
The first aluminum type plated steel sheet is characterized in that it includes a steel sheet being composed of not more than 0.005 mass% of C; not more than 0.005 mass % of N; not less than 0.1 mass% and not more than 0.5 mass% of Si; not more than 0.1 mass% of P; not more than 0.02 mass% of S; not less than 1.05 mass% and not more than 2.0 mass% of Mn; not more than 1.0 mass% of sol Al; a residual amount of Fe and inevitable impurities, and an aluminum type plated layer mainly consisting of Al being deposited thereon. [0019]
Specifically, among each compositional element that constitutes this first aluminum type plated steel sheet, C contained in a steel component is fixed by Ti, Nb, etc., in order to obtain an extreme-low carbon steel (IF: Interstitial Free), however if the C content increases, then adding a large amount of Ti and Nb, which are also necessary for fixing C, becomes necessary, thereby increasing cost. Moreover, the upper limit thereof is determined as 0.005 % (which includes a range of tolerance)
10
because C has a negative influence on the magnetic property, such as magnetic permeability. On the other hand, in view of ease in production, the C content is preferably not more than 0.003 %. [0020]
Similarly to C, N contained in a steel component is fixed by Ti, Nb, etc., in order to obtain an extreme-low carbon steel, however if the N content increases, then addition of a large amount of Ti and Nb, which are also necessary for fixing C, becomes necessary, thereby increasing cost. Moreover, the upper limit thereof is determined as 0.005 % (which includes a range of tolerance) because N has a negative influence on the magnetic property, such as magnetic permeability. On the other hand, in view of ease of production, the N content is preferably not more than 0.003 %.
Mn in a steel component is an effective element for providing the discoloration resistance upon being re-heated, and strength at an ordinary temperature and upon being re-heated, and hence at least 1.05 % (which includes a range of tolerance) of Mn is added in order to secure strength. If the Mn content is not less than 1.05 %, then it is possible to prevent discoloration upon being re-heated and deterioration in strength of not less than 10% upon being re-heated. On the other hand, if the Mn content exceeds 2.0%, then variation in weldability and the mechanical property of welded portion will become large and workability will deteriorate, and hence the upper limit thereof is determined as 2.0% (which includes a range of tolerance). It should be noted that the Mn content is preferably not more than 1.3%, in view of ease in production. [0021]
Although Si contained in a steel component is an effective element for
securing discoloration resistance upon being re-heated, if the Si content increases, then wettability of plating will deteriorate to cause non-plating, and hence the upper limit thereof is determined as 0.5% (which includes a range of tolerance). That is, as for Mn and Si contained in a steel component, if the content of each increases, then the same effect as in A1N (aluminum nitride) which suppresses Al-Si alloying will be exhibited. On the other hand, the lower limit of the Si content is determined as 0.1%. Because, if the Si content is less than this value, then discoloration resistance cannot be obtained. In addition, if the Si content is not less than 0.1%, then deterioration in strength of not less than 10% upon being re-heated can be suppressed. Each of Mn and Si exists near the surface of a steel sheet in an intercrystallized form in iron and in the form of oxide in a concentrated state during heating before plating or during plating.
Each of Mn and Si exists in a crystal grain and at crystal grain boundary. [0022]
It is known that if a large amount of Si or Mn, which is likely to generate an oxide is contained in the case of performing zinc plating, then an oxide film will be formed on the surface the steel plate before plating, thereby deteriorating the plating performance. This is because neither oxide of Mn or of Si which has been already generated can be easily reduced, since the affinity between Mn or Si and oxygen is larger than the affinity between Zn and oxygen.
However, in the case of performing aluminum plating, since the affinity of aluminum with oxygen is stronger than that of Si or Mn with oxygen, the oxide of Si or Mn can be reduced. Therefore, even if a large amount of Mn or Si is contained, the oxide which is generated during heating before plating will be reduced without deteriorating plating performance, in addition, it will be present in the form of a
concentrated solid solution of Mn or Si at the interface after plating. However, since the oxidative performance of Si is stronger than that of Mn, if oxide is generated excessively, then oxide in an amount which deteriorates the plating performance will be generated at the interface, and hence the upper limit thereof is determined as mentioned above. [0023]
Each of these concentrated Mn and Si which exists at the interface prevents Fe from diffusing from a steel sheet into plating during re-heating after plating. Thereby it prevents discoloration during re-heating within the range of temperature and time demonstrated in the present invention. However, if Mn or Si which exists at the interface moves from the interface during this re-heating, then the effect of preventing diffusion of Fe will decrease, and as a result, discoloration will be generated even within the range of time and temperature of the present invention. In order to prevent each of Si and Mn from moving freely, it is necessary that a sufficient amount of Mn or Si already exist in the grain boundary before re-heating, so that each of Si and Mn which is soluted within a crystal grain may not move to the grain boundary. [0024]
Moreover, the inventors of the present invention have found that if a large amount of Mn or Si, which is a solution hardening type element, is contained in a steel sheet, then it is possible to suppress deterioration of strength to be not more than 10% when re-heating at high temperature. It is thought that if Mn or Si moves freely in steel during re-heating, then the strength will deteriorate. In order to prevent each of Si and Mn from moving freely, it is necessary that a sufficient amount of Mn or Si already exist in the grain boundary, so that each of Si and Mn which is soluted within
a crystal grain may not move to the grain boundary. For this reason, it is better that the concentration of Mn and Si becomes higher, and hence the lower limit thereof exists.
Therefore, it is thought that in order to prevent both discoloration and deterioration in strength during re-heating, it is necessary that a sufficient amount of Mn or Si already exist in the grain boundary, so that each of Si and Mn which is soluted within a crystal grain may not move to the grain boundary. The inventors of the present invention have found that for this reason, each of the lower limit of the Mn content and the lower limit of the Si content, which are required to prevent both discoloration and deterioration in strength during re-heating, is approximately the same quantity. [0025]
As for this lower limit, the Si content is not less than 0.1%, and the Mn content is not less than 1.05%, which are sufficient amounts for not affecting diffusion at the interface and deterioration of strength, even if solid soluted elements existing at the interface or the inside of steel move during re-heating.
Although P in the steel component is an effective element in securing hardness, if the P content increases, then toughness as well as weldability of the steel sheet will deteriorate, and hence the upper limit thereof is determined as 0.1% (including the range of tolerance).
On the other hand, the lower limit of the P content is preferably 0.01%. Because, if the P content is less than this value, then sufficient strength cannot be obtained. [0026]
S contained in the steel component is an element which is contained
inevitably as an impurity, and which causes cracking or scratches during hot-rolling. Moreover, since S deteriorates weldability or magnetic property, it is necessary to be reduced as much as possible, however, such a problem can be suppressed by making the upper limit thereof to be 0.02% (including the range of tolerance).
A sol. (acid soluble) Al in the steel component is added as a deoxidizer of molten steel, the upper limit of which is determined as 1.0% (including the range of tolerance). On the other hand, the lower limit of the sol.Al content is preferably 0.005%. Because, if the sol.Al content is less than this value, then a sufficient deoxidation effect cannot be obtained.
It should be noted that the upper limit or the lower limit referred to here is defined with an average value derived from measured values, and the phrase "including the range of tolerance" means that in the case in which analyzed values include accidental errors, a common difference is added to or subtracted from the upper limit or the lower limit defined with the above average value, respectively, and the resultant value is determined as the new upper limit or new lower limit. [0027]
In the case of an aluminum type metal plating, an Al-Fe alloy layer is liable to grow to be thick at the plating interface, such that the grown alloy layer causes delamination during processing. For this reason, by adding Si in an amount of approximately not less than 6% and not more than 12% by weight ratio into a hot dip aluminum coating bath which contains mainly Al, it is possible to provide discoloration resistance, while suppressing growth of the alloy layer, similarly to Si contained in the above steel component. [0028]
The first aluminum type plated steel sheet having the above component will
not cause discoloration even if it is re-heated, for example, at a temperature of not less than 500°C and not more than 700°C for 250 to 450 seconds, in addition, it is possible to suppress deterioration in strength to be not more than 10% upon being re-heated at a temperature of not less than 500°C and not more than 700°C. Moreover, in the case of heating it for a period shorter than that in the above at a temperature of not less than 500°C and not more than 700°C, discoloration will not occur. However, if it is heated for not less than 900 seconds, then discoloration may occur. Moreover, in the first aluminum type plated sheet, it is possible to make the 0.2% proof stress PS be not less than 300 MPa and tension strength TS be not less than 400 MPa, by making the component in the steel component contain not more than 0.03% of C, not more than 0.004% of N, not less than 0.05% and not more than 0.08% of P, and not less than 1.05% and not more than 1.3% of Mn. [0029]
Next, an explanation will be given about the second aluminum type plated steel sheet to which the present invention is applied.
The second aluminum type plated sheet is characterized by performing thereon an aluminum type plating which mainly consists of Al on a steel sheet having a composition consisting of not more than 0.2% of C, not more than 0.07% of N, not less than 0.1% and not more than 0.5% of Si, not more than 0.1% of P, not more than 0.02% of S, not less than 1.05% and not more than 2.0 of Mn, not less than 0.01% and not more than 0.08% of Nb, not more than 1.0% of sol.Al, remnant of Fe and inevitable impurities. [0030]
Specifically, in each element which constitutes the second aluminum type steel sheet, C contained in the steel component is an element effective to ensure
strength, however, if the C content is high, then processability and weldability will deteriorate, and hence the upper limit thereof is determined as 0.2% (including the range of tolerance).
N contained in the steel component is an element which is inevitably contained, and if the N content becomes high, then a large amount of Ti and Nb should be added, thereby increasing cost. Moreover, N has a negative influence on the magnetic performance such as magnetic permeability, and hence the upper limit thereof is determined as 0.007% (including the range of tolerance). [0031]
Mn in a steel component is an effective element for providing discoloration resistance upon being re-heated and strength at an ordinary temperature and after being re-heated, and at least 1.05% (including the range of tolerance) or more of Mn is added for securing strength. On the other hand, if Mn in excess of 2.0% is added, then dispersion of weldability or mechanical performance of a welded portion increases to deteriorate processability, and hence the upper limit thereof is determined as 2.0% (including the range of tolerance).
Si contained in the steel component is an element effective for providing discoloration resistance upon being re-heated, however, if the Si content increases, then wettability of plating deteriorates to cause non-plating, and hence the upper limit thereof is determined as 0.5% (including the range of tolerance). That is, if the Mn content or Si content of the steel component increases, then the same effect as in A1N (aluminum nitride) suppressing Al-Si alloying can be obtained. On the other hand, the lower limit of Si is determined as 0.1%. If the Si content is less than this value, then alloying will progress upon being re-heated to cause discoloration. [0032]
Although P in the steel component is an effective element for providing hardness, if the Al content increases, then toughness and weldability of the steel will deteriorate, and hence the upper limit thereof is determined as 0.1% (including the range of tolerance). On the other hand, the lower limit of P is preferably 0.01%. Because, if the P content is less than this value, then sufficient strength cannot be obtained.
S in the steel component is an element inevitably contained as an impurity, which causes cracks or scratches upon being hot-rolled. Moreover, S deteriorates weldability or magnetic performance, and hence it is necessary to decrease S as much as possible, however, such a problem can be suppressed by making the upper limit to be 0.02% (including the range of tolerance).
Nb contained in the steel component is an element which forms a carbo-nitride and contributes to improving hardness, and at least 0.01% (including the range of tolerance) or more of Nb is added in order to improve the strength. On the other hand, since the effect of improvement in hardness will be saturated even if more than 0.08% of Nb is added, the upper limit thereof is determined as 0.08% (including the range of tolerance).
Sol.Al contained in the steel component is added as a deoxidizer of molten steel, and upper limit thereof is determined as 1.0% (including the range of tolerance). On the other hand, the lower limit of sol (solid solution) aluminum is preferably 0.005%. If the sol (solid solution) aluminum content is less than this value, then a sufficient deoxidation effect cannot be obtained.
It should be noted that the upper limit or the lower limit referred to here is defined with an average value derived from measured values, and the phrase "including the range of tolerance" means that in the case in which analyzed values
include accidental errors, a common difference is added to or subtracted from the upper limit or the lower limit defined with the above average value, respectively, and the resultant value is determined as the new upper limit or new lower limit.
[0033]
In the case of an aluminum type metal plating, an Al-Fe alloy layer is liable to grow to be thick at the plating interface, such that the grown alloy layer causes delamination during processing. For this reason, by adding Si in an amount of approximately not less than 6% and not more than 12% by weight ratio into a hot dip aluminum coating bath which contains mainly Al, it is possible to provide discoloration resistance, while suppressing growth of the alloy layer, similarly to Si contained in the above steel component.
[0034]
The second aluminum type plated steel sheet having the above component will not cause discoloration even if it is re-heated, for example, at a temperature of not less than 500°C and not more than 700°C for 250 to 450 seconds, in addition, it is possible to suppress deterioration in strength to be not more than 10% upon being re-heated at a temperature of not less than 500°C and not more than 700°C for 10 to 30 seconds. However, if it is heated for not less than 900 seconds, then discoloration may occur. Moreover, in the second aluminum type plated sheet, it is possible to make the yield point YP be not less than 400 MPa and tension strength TS be not less than 550 MPa, by making the component in the steel component contain not less than 0.05% and not more than 0.2% of C, not less than 0.1% and not more than 0.3% of Si, not less than 1.05% and not more than 1.5% of Mn, and not less than 0.03% and not more than 0.05% of Nb. [0035]
The first and the second aluminum type plated sheets in the above are optimum for a heat shrink band 1 of a CRT (Cathode-Ray Tube) 10 as shown, for example in FIG, 1. Specifically, the heat shrink band 1 is equipped with a band main body la which is engaged to the periphery of the CRT 10, and a bracket 2 which is disposed to the band main body 1 a.
Among these, the band main body la is shaped into a frame shape as a whole by bending that which is cut from the above-mentioned aluminum type plated steel sheet into a belt-like shape with a predetermined length and processing, corresponding to the panel side shape of the CRT 10, and welding both ends in the longitudinal direction at a welded part 3. On the other hand, the bracket 2 is, for example, a metallic member which is bent into an approximately "L" shape, in order to attach the CRT 10 to the cabinet of a television receiver, and the bracket 2 is attached to each of the welded parts 3 at the diagonal position of the four corners of the band main body la with spot welding. [0036]
The spot welding is performed as shown in FIGS. 1 and 2, when processing the steel sheet into the shape of a heat shrink band. At this time, the steel sheet is merely plated, and hence no change in the surface of plating such as discoloration has occurred yet. Moreover, the thickness of the alloy layer which exists in a plating bath and is likely to be related to weldability is influenced greatly by the Si concentration during the plating process, regardless of components of the steel, as mentioned in the above, and the growth of the alloy layer can be suppressed in the case in which the Si content in the plating bath is within the range of not less than 6% and not more than 12%, and hence the influence of the plating layer on weldability is very small, as long as the Si content is within this range. The inventors of the present
.nvention have found that an element contained in the steel sheet such as C, S, and P would rather influence, in the case of a plated steel sheet which mainly consists of Al. These elements may accumulate at the melting interface or deteriorate the strength of the melting interface, when the surface of the steel sheet melts together with the plate layer at the time of performing spot welding. The inventors of the present invention have ascertained that if C≤ 0.2% or P ≤ 0.1 and S ≤ 0.02% in the case of the plated steel sheet which consists mainly of Al, then there is no problem in weldability. [0037]
As for the heat shrink band 1 having the structure described in the above, the band main body 1 a, which is heated for example at a temperature of approximately not lower than 500°C and not higher than 600°C for 10 to 30 seconds so as to be expanded, is rapidly cooled at the same time it is engaged with the circumference of the CRT 10. Then, this band main body la shrinks to be thermally fitted to the circumference of the CRT 10. And the deformation due to air pressure of the CRT 10 is rectified by the tension of the band main body la which is generated at this time. [0038]
As described in the above, this heat shrink band 1 is constituted from the above aluminum type plated steel sheet which is capable of preventing deterioration in strength of the welded part 3 without causing discoloration of the band main body la even after being re-heated and which excels in discoloration resistance and weldability. Therefore, the heat shrink band 1 which is made of the above aluminum type plated steel sheet maintains gloss even after being re-heated and excels in corrosion prevention. Furthermore, this heat shrink band 1 has a lighter weight than the conventional one, excellent processability and sufficient strength, and hence it can stably attach the CRT 10 to the cabinet of television receiver.[Example] [0039]
Hereafter, although the effect of the present invention will be clarified with examples, the following examples do not restrict the technical scope of the present invention. First, as Examples and Comparative Examples of the first aluminum type plated steel sheet, each steel sheet of which the steel components differ from each other as shown in Table 1 was cast, re-heated, and thereafter hot-rolled, pickled, cold-rolled, and annealed to obtain each steel plate. And each steel sheet was subjected to a hot-dip plating using a hot-dip plating line of a Non Oxygen Furnace (NOF)-Reduction Furnace (RF) type (NOF sheet temperature ≥600°C, RF sheet temperature ≥ 800°C), while changing the kind of aluminum plating bath (Si concentration ranges from 9% to 11%, plating bath temperature ranges from 640 °C to 670 °C). The dew point in the reduction furnace was adjusted to be within the range of 0 °C to -40 °C. And a skin pass rolling was performed to produce each of samples 1 to 17 having a thickness of 1.7 mm finally. It should be noted that, in Table 1, CR in sample No.3 indicates a cold-rolled sheet, GI in sample No.4 indicates a hot dip galvanizing, and GL in sample No.5 indicates Galbarium (aluminum 55%-Zn). [0040] [Table 1]
Table. 1
(Table Removed)
Evaluation as to mechanical characteristics at ordinary temperature, mechanical characteristics after being heated, corrosion resistance, discoloration resistance, weldability, and processability of each sample shown in Table 1 produced in the above was performed. The evaluation results are shown in Table 2. It should be noted that, in Tables 2 and 4, the unit of PS and TS is MPa and the unit of El is %. [0042] [Table 2]
(Table Removed)Table. 2

[0043]
It should be noted that as to mechanical characteristics, both a tension test at ordinary temperature and a tension test in the case of heating samples (excepting sample Nos. 2 to 6, 10, and 17) at 550°C for 30 seconds were performed on each samples, and 0.2% proof stress PS (MPa), tension strength TS (MPa), and elongation (%) were measured. It should be noted that according to the metal material tension test of JISZ2241, test pieces according to JIS No.5 were prepared for each sample, and the tension test was performed making the direction of drawing as the width direction (C). Moreover, as to corrosion resistance, a salt spray test (SST) was performed on each sample (except sample Nos. 10 and 17), and the resultant red rust incidence rate and white rust incidence rate after 72 hours were measured. As to discoloration resistance, each sample (excepting sample Nos. 3, 10 and 17) was heated in a lab heating furnace (furnace temperature of 700°C), and was evaluated from the appearance thereof when the temperature of the sheet (heating time) reached 500°C (250 sec.), 550°C(280 sec.), 600°C (360 sec.), and 650°C(450 sec.). It should be noted that, among the evaluation of discoloration resistance in Table 2, "O" indicates no discoloration, "A" indicates that 10% or less of the surface area generated gray discoloration, "□" indicates that 50% or less of the surface area generated grayish black discoloration, and "x" indicates that over 50% of the surface area generated black discoloration. Moreover, as to weldability, a peeling test was performed on each sample (excepting sample Nos. 10 and 17). It should be noted that in the peeling test, a pair of test pieces with a size of 30 mmx 150 mm were prepared for each sample, and after these test pieces were subjected to a spot welding (nugget diameter of 5 mm), each test piece was peeled with a vise and pliers and the fracture situation in the nugget portion was observed by viewing. It should be noted that among the
peeling test evaluation in Table 2, "O" indicates fracture outside the nugget, and "x" indicates indicates fracture inside the nugget. Moreover, as to processability, a OT bending test (i.e. a test of bending a board-like test piece until the bending angle thereof becomes 180°) was performed on each sample (except sample Nos. 10 and 17). It should be noted that, in this bending test, a test piece having a size of 30 mmx 150 mm was prepared for each sample, and the resultant test piece was bent without inserting another test piece therebetween by a bending tester, and thereafter the presence or absence of cracking at the bent portion thereof was observed by viewing. It should be noted that among the OT bending test evaluation, "O" indicates no cracks or minute cracks (1/9 or less of the length of the test piece), "A" indicates small cracks (1/2 or less of the length of the test piece), and "x" indicates large cracks, breaking, or nearly breaking. [0044]
As is clear from Table 2, sample Nos. 3 to 6 which had a C content exceeding 0.005% were liable to show aging, and cracks were observed in the OT bending test. Moreover, in sample Nos. 2 to 5 and 7, of which the Mn content was less than 1.05%, TS thereof became not less than 400MPa (TS ≥ 400MPa) and hardness thereof was insufficient. Moreover, in sample No.7, of which the Mn content exceed 2.0%, TS thereof became not less than 600MPa (TS ≥ 600MPa), and hardness thereof was too high, thereby deteriorating processability. Furthermore, alloying cost also becomes high. Moreover, in sample No. 10, of which the Si content exceeded 0.5%, wettability thereof deteriorated to cause no plating. Moreover, in sample No. 14, of which S content exceeded 0.02%, fracture inside the peeling was generated in the peeling test, and the strength reduction of a welded portion was observed. Moreover, in sample No. 16, of which the P content exceeds 0.1%, fracture inside the peeling was
generated in the peeling test, and the strength reduction of a welded portion was observed. It should be noted that in sample No. 17, of which the N content exceeded 0.005%, was not prepared because the production cost thereof is high. Accordingly, values of components such as C, Si, Mn, etc. are not described. [0045]
From the results in the above, it was revealed that the first aluminum type plated steel sheet of the present invention excels in discoloration resistance, weldability, and processability, because the first aluminum type plated steel sheet of the present invention is capable of preventing deterioration in strength of the welded part, without causing discoloration even after being re-heated. [0046]
Next, as Examples and Comparative Examples of the second aluminum type plated steel sheet, each steel sheet of which the steel component differ from each other as shown in Table 3 was cast, re-heated, and thereafter hot-rolled, pickled, cold-rolled, and annealed to obtain each steel plate. And each steel sheet was subjected to a hot-dip plating using a hot-dip plating line of a Non Oxygen Furnace (NOF)-Reduction Furnace (RF) type (NOF sheet temperature ≥ 600°C, RF sheet temperature ≥ 800°C), while changing the kind of aluminum plating bath (Si concentration ranges from 9% to 11%, plating bath temperature ranges from 640 °C to 670 °C). The dew point in the reduction furnace was adjusted to be within the range of 0 °C to -40 °C. And skin pass rolling was performed to produce each of samples 1 to 18 having a thickness of 1.7 mm finally. It should be noted that, in Table 3, CR in sample No.3 indicates a cold-rolled material, GI in sample No.4 indicates a hot dip galvanizing, and GL in sample No.5 indicates Galbarium (aluminum 55%-Zn). [0047]

(Table Removed)Table. 3[0048]
Evaluation as to mechanical characteristics at ordinary temperature, mechanical characteristics after being heated, corrosion resistance, discoloration resistance, weldability, and processability of each sample shown in Table 3 produced in the above was performed. The evaluation results are shown in Table 4. It should be noted that the units in Table 4 are the same as in that in Table 2. [0049] [Table 4]
(Table Removed)
Table. 4[0050]
It should be noted that as to mechanical characteristics, both a tension test at ordinary temperature and a tension test in the case of heating samples (except sample Nos. 2 to 7, 9, and 10) at 550°C for 30 seconds were performed on each sample, and yield point thereof YP (MPa), tension strength TS (MPa), and elongation (%) were measured. It should be noted that according to the metal material tension test of JISZ2241, test pieces according to JIS No.5 were prepared for each sample, and the tension test was performed making the direction of drawing as width direction (C). Moreover, as to corrosion resistance, a salt spray test (SST) was performed on each sample (excepting sample Nos. 9 and 17), and the resultant red rust incidence rate and white rust incidence rate after 72 hours were measured. As to discoloration resistance, each sample (excepting sample Nos. 3, 9 and 17) was heated in a lab heating furnace (furnace temperature of 700°C), and was evaluated from the appearance thereof when the temperature of the sheet (heating time) reached 500°C (250 sec.), 550°C(280 sec.), 600°C (360 sec.), and 650°C(450 sec.). It should be noted that, among the evaluation of discoloration resistance in Table 4, "O" indicates no discoloration, "Δ" indicates that 10% or less of the surface area generated gray discoloration, "□" indicates that 50% or less of the surface area generated grayish black discoloration, and "X" indicates that over 50% of the surface area generated black discoloration. Moreover, as to weldability, a peeling test was performed on each sample (except sample Nos. 9, 16 and 17). It should be noted that in the peeling test, a pair of test pieces with a size of 30 mmx 150 mm were prepared for each sample, and after these test pieces were subjected to a spot welding (nugget diameter of 5 mm), each test piece was peeled with a vise and pliers and the fracture situation in the nugget portion was observed by viewing. It should be noted that among the peeling
test evaluation in Table 4, "O" indicates fracture outside the nugget, and "X" indicates
indicates fracture inside the nugget.
[0051]
As is clear from Table 4, in sample No. 19, which has a C content exceeding 0.2%, it was difficult to determine the condition desirable for welding, fracture inside the nugget was generated, and deterioration in strength of the welded portion was observed. Moreover, in sample Nos. 2 to 5 and 7, each of which the Mn content is less than 1.05%, TS thereof became not less than 550MPa (TS > 550MPa) and hardness thereof was insufficient. Moreover, sample No.6, of which the Mn content exceeded 2.0%, was not prepared because production cost thereof is high. Moreover, in sample No. 9, of which the Si content exceeded 0.5%, wettability thereof deteriorated to cause no plating. Moreover, in sample No. 13, of which the S content exceeded 0.02%, the fracture inside the peeling was generated in the peeling test, and the strength reduction of a welded portion was observed. Moreover, in sample No. 15, of which the P content exceeded 0.1%, the fracture inside the peeling was generated in the peeling test, and the strength reduction of a welded portion was observed. Moreover, sample No. 16, of which the N content exceeds 0.007%, was not prepared because production cost thereof is high. Moreover, in sample No. 17, of which the Nb content is less than 0.01%, it was insufficient in effect for reinforcing the deposition of NbC and had insufficient strength. [0052]
From the results in the above, it was revealed that the second aluminum type plated steel sheet of the present invention excels in discoloration resistance, weldability, and processability, because the first aluminum type plated steel sheet of the present invention is capable of preventing deterioration in strength of the welded
part, without causing discoloration even after being re-heated.
[Industrial availability]
[0053]
It should be noted that the aluminum type plated steel sheet to which the present invention is applied is not necessarily limited to application to the heat shrink band mentioned above, but can also be applied to those which require heat-resistance and corrosion resistance such as an exhaust pipe of an automobile, a home heating instrument, a fuel cell panel, etc.







We Claim:
1. An aluminum type plated steel sheet having heating-discoloring resistance and
weldability, including:
not more than 0.2 mass% of C;
not more than 0.007 mass % of N;
not less than 0.1 mass% and not more than 0.5 mass% of Si;
not more than 0.1 mass% of P;
not more than 0.02 mass% of S;
not less than 1.05 mass% and not more than 2.0 mass% of Mn;
not more than 1.0 mass% of soluble Al;
a residual amount of Fe and inevitable impurities, and
optionally including traces of Niobium (Nb) as herein described,
wherein the melting aluminum and silicon type plated steel sheet comprises an
aluminum and silicon plated layer mainly consisting of Al and Si being deposited
thereon, the aluminum and silicon plated layer having more than 6 mass% Si and
less than 12 mass% Si.
2. The melting aluminum type plated steel sheet as claimed in claim 1, wherein
said C is not more than 0.005 mass%,
said N is not more than 0.005 mass%, and
said Mn is not less than 1.05 mass% and not more than 1.3 mass%.
3. The melting aluminum type plated steel sheet as claimed in claim 2 , wherein
said C is not more than 0.003 mass%,
said N is not more than 0.004 mass%, and
said P is not less than 0.05 mass% and not more than 0.08 mass%,
whereby 0.2% proof stress PS is not less than 300MPa and a tensile strength TS is not less than 400 MPa.
4. The melting aluminum type plated steel sheet as claimed in claim 1, including not less than 0.01 and not more than 0.08 mass% of Nb.
5. The melting aluminum type plated steel sheet as claimed in claim 2 or 4, wherein a reduction in strength upon being heated at a temperature of not less than 500°C to not more than 700°C after being plated is not more than 10% compared to that before being heated or reheated.
6. The melting aluminum type plated steel sheet as claimed in claim 4 or 5, wherein said C is not less than 0.05 mass% and not more than 0.2 mass%,
said Si is not less than 0.1 mass% and not more than 0.3 mass%,
said Mn is not less than 1.05 mass% ahd not more than 1.5 mass%, and
said Nb is not less than 0.03 mass% and not more than 0.05 mass%,
whereby a yield point YP is not less than 400 MPa and a tensile strength TS is not
less than 550 MPa.
7. A heat shrink band as and when prepared with aluminum type plated steel sheet as claimed in one of claims 1-6.

Documents:


Patent Number 251888
Indian Patent Application Number 6100/DELNP/2007
PG Journal Number 16/2012
Publication Date 20-Apr-2012
Grant Date 13-Apr-2012
Date of Filing 06-Aug-2007
Name of Patentee NIPPON STEEL CORPORATION
Applicant Address 6-3, OTEMACHI 2-CHOME CHIYODA-KU, TOKYO, JAPAN.
Inventors:
# Inventor's Name Inventor's Address
1 KUNIO NISHIMURA C/O NIPPON STEEL CORPORATION, YAWATA WORKS, 1-1, TOBIHATA-CHO, TOBATA-KU, KITAKYUSHU-SHI, FUKUOKA-KEN,JAPAN.
2 MASAYUKI ABE C/O NIPPON STEEL CORPORATION, YAWATA WORKS, 1-1, TOBIHATA-CHO, TOBATA-KU, KITAKYUSHU-SHI, FUKUOKA-KEN,JAPAN
3 HARUHIKO EGUCHI C/O NIPPON STEEL CORPORATION, YAWATA WORKS, 1-1, TOBIHATA-CHO, TOBATA-KU, KITAKYUSHU-SHI, FUKUOKA-KEN,JAPAN
4 YOSHIHISA TAKADA C/O NIPPON STEEL CORPORATION, YAWATA WORKS, 1-1, TOBIHATA-CHO, TOBATA-KU, KITAKYUSHU-SHI, FUKUOKA-KEN,JAPAN
PCT International Classification Number C22C 38/00
PCT International Application Number PCT/JP2006/302270
PCT International Filing date 2006-02-09
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 2005-034357 2005-02-10 Japan