Title of Invention	A PROCESS FOR PRODUCING THE HIGH-CONCENTRATION CARBURIZED/LOW STRAIN QUENCHED MEMBER
Abstract	The present invention can provide a super carburized, low-distortion quenched member with both higher performance and minimized heat-treatment distortion attained in the field of super carburized quenching which features high strength, high contact pressure and the like. A process for the production of the super carburized low-distortion quenched member includes a primary treatment and a secondary treatment. The primary treatment comprises heating a steel member for a machine structure to a temperature within an austenite region by vacuum carburizing (low-pressure carburizing) to have carbon dissolved at least at a eutectoid carbon concentration of a surface layer portion of the member and then quenching the member at a cooling rate of from 3 to 15°C/sec from the temperature within the austenite region to a temperature not higher than an A1 transformation point to have at least one of ultrafine carbide and nuclei of the carbide formed in the surface layer portion of the member. The secondary treatment comprises subsequently heating and soaking the member to a temperature within the austenite region and then conducting rapid quenching to have ultrafine carbide precipitated in a range of from 10 to 30% in terms of effective case depth percentage in an outermost surface layer portion.

Title of Invention

A PROCESS FOR PRODUCING THE HIGH-CONCENTRATION CARBURIZED/LOW STRAIN QUENCHED MEMBER

Abstract

The present invention can provide a super carburized, low-distortion quenched member with both higher performance and minimized heat-treatment distortion attained in the field of super carburized quenching which features high strength, high contact pressure and the like. A process for the production of the super carburized low-distortion quenched member includes a primary treatment and a secondary treatment. The primary treatment comprises heating a steel member for a machine structure to a temperature within an austenite region by vacuum carburizing (low-pressure carburizing) to have carbon dissolved at least at a eutectoid carbon concentration of a surface layer portion of the member and then quenching the member at a cooling rate of from 3 to 15°C/sec from the temperature within the austenite region to a temperature not higher than an A1 transformation point to have at least one of ultrafine carbide and nuclei of the carbide formed in the surface layer portion of the member. The secondary treatment comprises subsequently heating and soaking the member to a temperature within the austenite region and then conducting rapid quenching to have ultrafine carbide precipitated in a range of from 10 to 30% in terms of effective case depth percentage in an outermost surface layer portion.

Full Text	1 DESCRIPTION HIGH-CONCENTRATION CARBURIZED/LOW-STRAIN QUENCHED MEMBER AND PROCESS FOR PRODUCING THE SAME Technical Field [0001] This invention relates to carburizing and quenching treatment widely used as a reinforcement method for machine structural members, more specif ically to a super carburized, quenched member featuring temper softening resistance, high strength, high contact pressure and the like, especially to a super carburized, low-distortion quenched member (which may hereinafter be referred to simply as "member") with mutually conflicting properties, that is, higher performance and heat-treatment distortion attained together and also to its production process. Prior Art [0002] Owing to excellent properties such as high fatigue strength and wear resistance, carburized and quenched members (hereafter referred to as "case hardened members") are widely used as various members in transport equipment, industrial machines and the like. From the viewpoint of dimensional reductions, weight reductions and/or the like through further improvements in the performance of such members, numerous developments have been made on case 2 hardened members. Recently, the vacuum carburizing (low-pressure carburizing) process has been developed. Compared with the conventional gas carburizing process, the vacuum carburizing process has excellent characteristic features such as environmental friendliness, the prevention of intergranular oxidation, the feasibility of high-temperature carburizing treatment, and easy control of carburizing and carbon diffusion, and therefore, is expected to find still broader utility from the standpoints of further improvements in the performance and quality of members and further improvements in their productivity. [0003] As a method for providing a machine structural member such as a gear or axle member with improved pitting resistance by applying carburizing and quenching to the member, there is carbonitriding treatment. According to this treatment, carbon and nitrogen are caused to concurrently diffuse into the matrix of a member such that the member can be provided with improved temper softening resistance. In addition, there has also been developed super carburizing treatment to have carbide precipitated in a surface layer portion of a member such that the member can be provided with improved temper softening resistance. Keeping in step with evolutions in low-pressure carburizing facilities, a great deal of research has been conducted in recent years. [0004] As a representative example of the super carburizing treatment, Patent Document 1 discloses a carburizing 3 treatment process for a member. According to Patent Document 1, it is proposed to form quasispheroidal or spheroidal carbide at a volume percentage of 30% or higher within a range up to a depth of 0.4 mm by conducting precarburizing to such a carbon content that spheroidal carbide is caused to precipitate in a surface layer portion of a steel member and the carbon concentration in the surface layer portion becomes not higher than Acm but not lower than a eutectoid concentration between steel and carbon, slowly cooling or quenching the thus-treated member to convert the surface layer portion into a bainite, pearlite ormartensite structure, and then heating the member at a ramp rate of not greater than 20°C/min from the Ac1 point to a temperature in a range of from 750 to 950°C to effect carburizing and quenching. [0005] According to the above-described process, the member can be improved in properties such as pitting properties owing to the precipitation of the carbide in the surface layer portion of the member. Nonetheless, the resulting member involves problems such as a deformation and distort ion by heat treatment, because the process is super carburizing that causes the precipitation of the carbide as much as 30% in the surface layer portion. [0006] As a method for causing carbide to precipitate in an ultrafine form in a surface layer portion of a member by super carburizing, many heating and cooling methods have 4 been investigated. In Patent Document 1, it is described to be desirable that subsequent to the precurburizing, air cooling (which forms a bainite or pearlite structure) or quenching (which forms amartensite structure) is conducted, and that in the carbide-forming treatment as the next step, the member is heated at a slow ramp rate of not greater than 20°C/min from the Ac1 transformation temperature to a temperature within the range of from 750 to 950°C, and after direct quenching or air cooling, the member is again heated and quenched. [0007] Further, Patent Document 2 and Patent Document 3 propose, as an optimal method, to conduct slow cooling (or 30°C/hr or less) after precurburizing or primary carburizing. [0008] When the quenching after the precarburizing or primary carburizing is conducted by air cooling or slow cooling in the method disclosed in Patent Document 1, 2 or 3, however, a network of carbide tends to precipitate along grain boundaries in a surface layer portion of a member. The next step, that is, the carbide-forming treatment can hardly break up the network of carbide in a short time to have the carbide distributed and precipitated within the surface layer portion. To overcome this shortcoming, heating and subsequent cooling may be conducted a plurality of times in some instances. [0009] On the other hand, Patent Document 1 also discloses 5 quenching with an aim directed toward forming a martensite structure by increasing the cooling rate of a member subsequent to its precarburizing. This technique, however, involves a potential problem that carbide nuclei in a surface layer portion may dissolve out. It is also concerned that the quenching may take place with supersaturated carbon, and due to high-carbon martensitic transformation, the member may develop a greater deformation or distortion through an expansion, shrinkage or the like. [0010] Patent Document 4 discloses a production process of a case hardened member by low-pressure carburizing. There is a reference to the conversion of carbide into an ultraf ine form such as the control of the carbon concentration at 0.5 to 0.7 wt. % in primary carburizing and at 0.7 to 1 wt. % in secondary carburizing and the control of primary cooling at a very slow rate of from 1 to 10°C/min. Concerning deformation strain, however, this production process is not expected to be preferred like the above-mentioned Patent Documents 1, 2 and 3. [0011] Just for readers' information, a description is now made of some advantages of low-pressure carburizing, which is finding wide-spread commercial utility in recent years, over conventional gas carburizing. a) A change from a carburizing step to a diffusion step can be readily and promptly modified. b) High-temperature treatment is feasible so that prompt 6 carburizing can be conducted. c) No intergranular oxidation takes place in a surface layer portion of a member, and in the member under treatment, it is hence possible to inhibit the occurrence of cracks which would otherwise begin to take place from such a defect. d) No sooting takes place, thereby causing no uneven carburizing which would otherwise take place as a result of sooting. Patent Document 1: JP-B-62-24499 Patent Document 2: JP-B-2787455 Patent Document 3: JP-B-2808 621 Patent Document 4: JP-A-2002-348615 Disclosure of the Invention Problem to be Solved by the Invention [0012] Even in super carburizing by the conventional low-pressure carburizing, however, no optimal balance can be achieved between the progress of formation of carbide within a surface layer portion of a member under treatment and the microstructure of the surface layer portion. The problem of a deformation or strain of the treated member, therefore, still remains unresolved. As a consequence, grinding, strain-correcting finishing or the like is essential for the member after the carburizing step. Such additional work has led to a reduction in the inherent ability 7 of super carburizing that permits use under higher contact pressure, a reduction in productivity and an increase in manufacturing cost, thereby preventing the popularization of super carburizing treatment. Means for Resolving the Problem [0013] The present invention has resolved the above-described problem by developing an optimal process, which makes it possible to use a member under a higher contact pressure and also to provide the member with a lower strain whilemaking use of low-pressure carburizing facilities that permit a variety of control promptly with higher accuracy as to the concentration of carbon in the member, the repetition of carburizing treatment/diffusion treatment, and diverse temperature conditions, heating conditions and cooling rate (quenching) conditions for heating, soaking, carburizing, quenching and the like of the member. [0014] The above-described problem can be resolved by the present invention as defined below: 1. A process for producing a super carburized, low-distortion quenched member, which comprises a primary treatment of heating a steel member for a machine structure to a temperature within an austenite region by vacuum carburizing (low-pressure carburizing) to have carbon dissolved at least at a eutectoid carbon concentration of a surface layer portion of the member and then quenching the member at a cooling rate of from 3 to 15°C/sec from the 8 temperature within the austenite region to a temperature not higher than an A1 transformation point to have at least one of ultrafine carbide and nuclei of the carbide formed in the surface layer portion of the member; and a secondary treatment of subsequently heating and soaking the member to a temperature within the austenite region and then conducting rapid quenching to have ultrafine carbide precipitated in a range of from 10 to 30% in terms of effective hardened depth percentage in an outermost surface layer portion. [0015] 2. A production process as described above, wherein in the secondary treatment, additional carburizing treatment is applied to the surface layer portion of the member. 3. A production process as described above, wherein in the secondary treatment, the ultrafine carbide is caused to precipitate in the surface layer portion of the member to form a structure composed primarily of martensite and containing a mixed structure of troostite and retained austenite or the like in parts thereof such that the outermost layer portion (a portion A) of the layer, a layer portion (a portion B) inner than the portion A and a layer portion (a portion C) inner than the portion B are in an order of A≥O≥B in terms of the fineness of austenite grain size. [0016] A super carburized, low-distortion quenched member comprising a surface layer portion of a structure composed primarily of martensite and containing a mixed structure 1 9 of troostite and retained austenite or the like in parts thereof, wherein in the surface layer, an outermost surface layer (a portion A), a layer (a portion B) inner than the portion A and a layer (a portion C) inner than the portion B are in an order of A≥C≥B in terms of the fineness of austenite grain size. Advantageous Effects of the Present Invention [0017] The process according to the present invention performs the treatment of a member in low-pressure carburizing facilities while making the combined use of the primary treatment of conducting adequate super carburizing and quenching at an optimal cooling rate and the secondary treatment of subsequently causing a fine carbide to simply and efficiently precipitate; and can minimize the deformation and strain of the member treated through the heat treatment. Owing to the adoption of this process, the greatest concern about the conventional super carburizing, for example, the cumbersome grinding, strain correction and the like of the member after the treatment, such as the bending of an axle or the deformation strain of a tooth profile, can be substantially relieved, thereby bringing about advantageous effects that significant improvements can be made in the productivity, quality and cost of the case hardened member. [0018] According to the process of the present invention, additional carburizing treatment may be applied to the 10 surface layer portion of the member in the secondary treatment. This additional carburizing treatment makes it possible to achieve a high hardness of matrix and also to reduce the crystal grain size of an outermost surface layer portion of the member to an ultrafine grain size and, therefore, is also extremely effective for providing the member with higher strength and higher toughness. By the process of the present invention, it is possible to readily achieve higher strength, higher toughness, higher contact pressure and the like for members such as axles and gears to which super carburizing has heretofore been hardly applicable. Therefore, the process according to the present invention can be widely applied to fields where there is a high need for such properties, and has an advantageous effect that it can make significant contributions to improvements in the performance of a member and also to reductions in the size and weight of the member. Best Modes for Carrying out the Invention [0019] Based on best modes for carrying out the invention, the present invention will next be described in further detail. The followings are the course of technical endeavors and the findings, which have led to the present invention. With a view to developing a super carburizing process for causing ultrafine carbide to precipitate in a surface 11 layer portion of a member by using low-pressure carburizing facilities, the present inventors carried out a thorough investigation on possible relations between the concentration of carbon in the surface layer portion and various heating and cooling conditions and the precipitation form of the ultrafine carbide in the surface layer portion and the microstructure of the matrix. Concerning improvements or the like in strain by heat treatment while assuming members such as gears and axles, research and development was also conducted from many directions. An aim was then set at the establishment of a novel process for super carburizing and low-strain quenching, which can achieve both of mutually-conflicting properties of providing a member with higher performance by super carburizing and minimizing a deformation, distortion or the like of the member while balancing them at high levels. [0020] Upon applying super carburizing to a surface layer portion of steel (member), the most important point is to have ultrafine carbide precipitated as much as possible in a surface layer portion of the member through the optimal combination of the primary treatment and the secondary treatment. In the control of the formation of the ultrafine carbide, carburizing and quenching facilities also play an important role. In the present invention, a variety of developments were conducted while using low-pressure carburizing facilities that compared with conventional 12 carburizing facilities, permit a variety of control promptly with higher accuracy as to the concentration of carbon in the member, the repetition of carburizing treatment/diffusion treatment, and diverse temperature conditions, heating conditions and cooling rate (quenching) conditions for heating, soaking, carburizing, quenching and the like of the member. [0021] Described specifically, a variety of investigations were conducted on the heating, soaking, super carburizing, diffusion and cooling (quenching) conditions of a member during the primary treatment to firstly reduce the deformation or strain of the member at the stage of the primary treatment. In the secondary treatment as the next step, carburizing and quenching (cooling) conditions are important to permit adjustments or the like in the precipitation of ultrafine carbide and the grain size of austenite in the carburized layer. Specifically, it has been found that in the secondary treatment, the deformation or strain of a member by the heat treatment can be minimized by controlling a range, in which the ultrafine carbide precipitate in a surface layer portion of the member, to 10 to 30% in terms of effective case depth percentage and further by converting an outermost surface layer portion into an ultrafine crystalline structure. [0022] The term "effective case depth percentage" as used herein means a ratio (t/T) of a precipitated depth (t) of 13 ultrafine carbide existing in an outermost surface "layer portion of a member to an effective case depth (T) of the member after completion of the secondary treatment (including the tempering treatment at 180°C) . It is to be noted that the term "effective case depth" means a distance froma surf ace of a hardened layer, whichis still inaquenched state or has been tempered at a temperature not exceeding 200°C, to the position of a critical depth of a Vickers hardness (HV) of 550 as measured by the Method of Measuring Case Depth Hardened by Carburizing Treatment for Steel (JIS G0557) . Next, the term "precipitated depth of ultrafine carbide" means the maximum depth, where the ultrafine carbide exists, from the outermost surface layer portion of the member as determined by an analysis under an optical microscope or an electron microscope. To facilitate the discrimination of the ultrafine carbide, the member is analyzed in a state of being etched with an etching solution such as 5% nital etching reagent. [0023] The vacuum carburizing (low-pressure carburizing) facilities for use in the present invention are equipped with a carburizing and heating chamber including a treatment furnace which is sectionally controllable at different pressures of from 200 to 2,000 Pa, and are available on the market. Conventionally-available vacuum carburizing facilities are all usable in the present invention. As the 14 primary treatment in the present invention, the member is heated and soaked to a predetermined temperature in the furnace of the facilities, and to raise the concentration of carbon in the surface layer portion of the member to or higher than the eutectoid carbon concentration, the member is then quenched at an appropriate cooling rate. In the subsequent secondary treatment, the carbide is caused to precipitate in an ultraf ine form in the surface layer portion of the member, optionally followed by additional carburizing treatment as needed. [0024] According to the primary treatment in the process of the present invention, steel to be treated (member) is heated and soaked to an austenite region of from 900 to l,100°C, carburizing is conducted such that the carbon concentration of a surface layer portion becomes preferably 0.8 wt.% or higher, and from the thus-carburized state, quenching is then conducted at an optimal cooling rate. Optimal cooling conditions are to evenly cool the member at a cooling rate of from 3 to 15°C/sec over a temperature range of from the carburizing temperature (the temperature in the austenite region) to the A1 transformation temperature or lower, preferably to 400°C or lower. By this cooling, ultrafine carbide is caused to precipitate in the surface layer portion of the member so that a structure composed primarily of martensite is formed in the surface layer portion. The term "ultrafine carbide" means an M23C6 type carbide formed as 15 a result of bonding of carbide-forming elements such as Cr and Mo in Fe3C (cementite) or steel with carbon dissolved in supersaturation. [0025] In the secondary treatment, the non-carburized portion (interior) of the member is heated and soaked to a range of from an austenizing temperature to the austenizing temperature + 80°C, preferably to a range of from 10 to 70°C above the austenizing temperature, and is then rapidly quenched to effect precipitation of ultrafine carbide such that the carbon concentration of the surface layer portion becomes preferably 0.8 wt.% or higher, more preferably 1.0 to 2.0 wt.%. It is preferred to apply, in parallel with the precipitation of the ultrafine carbide in the surface layer portion, additional carburizing treatment to the surface layer portion to promote the precipitation of the ultrafine carbide in the surface layer portion, and from the state that the carbon concentration of the matrix has been adequately adjusted, to further conduct rapid quenching. [0026] The temperature of the final quenching after the secondary treatment varies depending on the pretreatment conditions, that is, whether the final quenching is after the heating and soaking or after the heating, soaking and additional carburizing. The rapid quenching can be conducted at the temperature after the pretreatment or at a temperature raised or lowered relative to the temperature 16 of the pretreatment. In other words, the temperature of the final quenching after the secondary treatment can be set at a level commensurate with the quality of heat treatment such as the hardness and microstructure required for the member. [0027] With a view to establishing optimal conditions for super carburizing, the present inventors conducted a detailed investigation on the carbon concentrations upon heating, soaking and carburizing and diffusion and various cooling (quenching) conditions with respect to the primary treatment in which super carburizing is applied to a surface layer portion of a member in low-pressure carburizing facilities and the secondary treatment in which ultrafine grains of carbide are caused to precipitated in the surface layer portion. As a result, it was succeeded in obtaining a super carburized, quenched member having a carbon concentration of preferably 0.8 wt.% or higher, more preferably from 1.0 to 2.0 wt.% in a range of from 10 to 30% in terms of the percentage of an effective case depth (t/T) in an outermost surface layer portion and having a three-layer structure consisting of a superultrafine grain layer of No. 10 or greater austenite grain size, a fine grain layer and an ultrafine grain layer in this order from the outermost surface layer. It has been found that the super carburized, quenched member is minimized in deformation or distortion after the treatment and that the correction of 17 a strain, which has been unavoidable in the conventional super carburizing, can be obviated or can be readily conducted compared with the conventional process. Examples [0028] Based on certain Examples, the present invention will next be described in further detail. Machine structural steels (materials) shown in Table 1 were provided. Those materials were subjected beforehand to normalizing treatment at 900°C and were then machined to prepare stepped round-bar test pieces of 30/25/20 X L300mm, respectively. As carburizing and quenching of each test piece, the primary treatment of the super carburizing step in the present invention was conducted using facilities which permitted heating and carburizing at a low pressure and also permitted oil hardening and high pressure gas cooling. [0029] It is to be noted that steel grades 1 and 2 are carburizing, quenching steels as specified under the JIS, steel grade 1 is SCM420, chromium-molybdenum steel, and steel grade 2 is SCr415, chromium steel. MAC14 as steel grade 3 is a grade for a commercial product developed by a steel maker, and is steel developed by increasing the Cr content in comparison with the above-described two steel grades and further adding Mo element with a view to causing M23C6 type ultraf ine carbide to precipitate upon super carburizing (the 18 primary and secondary treatments). [0030] Table 1: Used Steels and Their Chemical Components (wt.%) Steelgrade C Si Mn P S Cr Mo 1 SCM420 0.20 0.30 0.75 0.019 0.025 1.10 0.20 2 SCr415 0.16 0.35 0.78 0.021 0.019 1.05 0.02 3 MAC14 0.15 0.27 0.53 0.020 0.022 2.50 0.38 [0031] Table 2 summarizes the results obtained by experimenting in various ways effects of the cooling rate on the states of carbide to be precipitated in surface layer portions of test pieces and the deformations of the test pieces by heat treatment through the primary treatment in the present invention. As conditions for the primary treatment, super carburizing of each test piece was conducted by the heat cycle shown in FIG. 1 such that subsequent to heating and soaking, an effective case depth of 0. 5 mm would be achieved. Described specifically, supercarburizingand diffusion treatment of each test piece were alternately conducted at 950°C for about 70 minutes, respectively, such that the carbon concentration of the surface layer portion of the test piece in its final state would be controlled at about 1. 5 wt. % . Froma state that the carbon concentration of the surface layer portion of each test piece was in 19 supersaturation, quenching of the test piece was conducted under the corresponding cooling rate condition shown in Table 2 to investigate the shape and size of the carbide in the surface layer portion of the test piece and the microstructure of the surface layer portion of the test piece. [0032] To determine the deformations and strains of the above-described steel grades by the primary treatment, stepped round-bar test pieces 30/25/20 X L300 mm) of the respective steel grades were provided as test pieces. In a state of being supported at opposite ends, each test piece was analyzed for a runout at its axial central part to investigate a relationship between the cooling rate and the axial of the test piece. 21 [0034] The signs shown in the table and analysis methods of the properties shown there will now be described below. 1) The cooling rate indicates an average cooling rate at the axial central part of each test piece from the quenching temperature of 950°C after the completion of the carburizing and diffusion for the test piece to 400°C. 2) The shape and size of carbide was observed under a scanning electron microscope. 3) Abbreviations for microstructures F: ferrite, P: pearlite, B: bainite, T: troostite, M: martensite, y: retained austenite. 4) The radial runout indicates a runout of a test piece, which was mounted on a both-end supporting, runout measuring instrument, as measured at a central part of the test piece by a dial gauge. [0035] In each of the comparative examples shown as Test Piece Nos .1,4 and 6 in Table 2, the cooling rate during the cooling was as low as l°C/sec so that the carbide precipitated in the surface layer portion consisted primarily of a network of carbide formed of carbide flakes bonded together and the matrix was in the form of an slack quenching structure of ferrite, pearlite and bainite. As a consequence, those comparative examples were all large in radial runout and deformation. The comparative example shown as Test Piece No. 3, on the other hand, was subjected to rapid cooling equivalent to conventional oil quenching (20°C/sec). Its 22 surface layer portion contained a very small amount of precipitated carbide, and had a structure quenched from a high carbon state that carbon was in supersaturation. That comparative example was large in radial runout and deformation. [0036] When the cooling rate was 4 to 12°C/sec as in each of the examples as Test Piece Nos. 2, 5 and 7 (the present invention) , ultraf ine carbide precipitated in a large amount, and moreover, microstructures appeared as nuclei for the ultrafine carbide, leading to improvements in the deformation and distortion (runout) of the test piece as the outstanding serious problems of super carburizing. Described specifically, compared with slow cooling that cooling is slow or rapid quenching that cooling is fast in contrast, the radial runout of each of the test pieces according to the present invention was of approximately a half level of the radial runouts in the rest of the examples, thereby realizing a substantial reduction in radial runout. From these results, the cooling rate during the quenching in the primary treatment is optimally 3 to 15°C/sec. [0037] Table 3 shows the results obtained by using representative ones of the test pieces subjected to the primary treatment shown in Table 2, applying the secondary treatment in various ways to the representative test pieces to cause ultrafine carbide to finally precipitate in their surface layer portions, and investigating the carbon 23 concentrations, states of precipitated carbide, microstructures, crystal grain sizes, etc. in their surface layer portions and the radial runouts of the test pieces. As conditions for the secondary treatment, the heat cycle shown in FIG. 2 was followed, the soaking temperature was selectively set at three levels of 800°C, 850°C and 900°C, all above the A1 transformation temperature, and subsequent to the heating and soaking, additional carburizing was also conducted at the same time to achieve a carbon concentration higher than the eutectoid carbon concentration as a technique for further raising the carbon concentrations in the surface layer portions and also increasing the amounts of precipitated ultrafine carbide through the secondary treatment. The subscript "n" in (carburizing/diffusion)n or (additional carburizing/diffusion)n in FIGS. 1 through 3 means the number of repetitions of carburizing or diffusion in the corresponding step, and is set in commensurate with the quality required for each member. In the case of Test Piece No. 2 shown as an example in Table 2, for example, n was set at 8 (n = 8), and in the case of Test Piece No. 2-2 shown as an example in Table 3, on the other hand, n was set at 5 (n = 5). 26 [0039] [Analysis method of carbon concentration surface layer portion] Using each of the test pieces (30/25/20 X L300mm), chips were collected by lathe turning from the surface layer portion to the 0.05 mm depth of its 25 mm portion, and the carbon concentration of the surface layer portion was determined by a chemical analysis. [0040] From Table 3, the Test Piece No. 2 series indicate effects on the precipitation form of carbide and others when the secondary treatment temperature was varied, and the Test Pieces No. 5 and No. 7 series indicate effects on the precipitation of ultrafine carbide and the final carbon concentrations in the surface layer portions depending on whether or not the additional carburizing was applied in the secondary treatment. [0041] Concerning the secondary treatment temperature (which may hereinafter be called "the additional carburizing temperature"), the temperature of 900°C employed for Test Piece No. 2-1 involves a problem in that the carbide in a surface layer portion dissolves to lead to a reduction in the overall precipitation of carbide grains and also to an increase in the radial runout of the test piece. With the secondary treatment temperature of 800°C employed for Test PieceNo. 2-3, carbide flakes precipitate at grainboundaries in the surface layer portion, and the core portion of the member is quenched incomplete. Test pieces, therefore, 27 develop variations in radial runout. From these results, the optimal temperature for the treatment that causes ultrafine carbide to precipitate in a surface layer portion by the secondary treatment can preferably be a temperature equivalent to the A3 transformation temperature + 10-70°C, which is determined by the composition of the member (before the carburizing treatment). [0042] As to whether or not the additional carburizing treatment is applied in the secondary treatment, the application of the additional carburizing treatment has been recognized, as evident from the results of Test Piece Nos. 5-1 and 7-1, to bring about the advantageous effect that carbide precipitates in an ultrafine form, to say nothing of an improvement in the concentration of carbon in the surface layer portion. As a reason for the advantageous effect, it may be contemplated that, as the carbon in the surface layer portion precipitate as carbide and the concentration of carbon in the matrix becomes lean, the replenishment of carbon to the surface layer portion by the additional carburizing could promote the new formation of ultraf ine carbide, such as Fe3C and M23C6, and nuclei thereof. [0043] As shown in FIG. 4, it has also been found that in themember subjected to the additional carburizing treatment, the austenite grain size of the outermost surface layer portion is reduced to an ultrafine grain size. The term "ultrafine grain size" corresponds to an austenite grain 28 size of No. 10 or greater as measured by the carburized grain-size testing method in JIS-G0551, "Method of Testing Austenite Grain Size for Steel". A significant characteristic feature has also been discovered in that a three-layer structure formed of fine grains and ultrafine grains is formed extending toward the inside. Paying attention to a relationship between the austenite grain size and the carburized layer, the grain sizes of the outermost surface layer portion greatest in the amount of precipitated ultrafine carbide, the carburized layer portion (fine grain portion) located inside the outermost surface layer portion and the ultrafine grain portion located still inside the fine grain portion are in a relationship of A>C>B, in which "A", "C" and"B" stand for the outermost surface layer portion, the ultrafine grain portion and the fine grain portion, respectively. Incidentally, the austenite grain size of a surface layer portion in conventional carburizing is generally equivalent to No. 7 or 8 . In the present invention, the surface layer portion has a grain structure of the characteristic three-layer structure which does not appear in the conventional carburizing treatment. [0044] As an advantageous effect of such an ultrafine grain layer, it has a significant characteristic feature in that the toughness of a hardened surface layer, said toughness having been a concern about conventional carburized members, can be improved and high toughness can also be imparted to 29 the carburized layer itself in addition to the feasibility of higher contact pressure as a characteristic feature of the present invention, and therefore, is extremely effective for providing carburized members with still higher strength from now on. [0045] Table 4 shows effects of the percentage of an effective case depth of a carbide layer precipitated in super carburizing according to the present invention on various properties. Various test pieces were prepared by providing SCM420, JIS steel for machine structure, as a material, subjecting the material to normalizing treatment at 900°C beforehand, and then machining the resultant material. The super carburizing of each test piece was conducted by the heat cycle of primary treatment and secondary treatment shown in FIG. 3. Each treated test piece was analyzed and investigated for pitting life, impact strength, distortion by heat treatment, etc. Concerning effects of the carbon concentration of the outermost surface layer portion of each test piece shown in Table 5, the test piece was treated by the heat cycle shown in FIG. 3 in a similar manner as the various test pieces in Table 4, and the carbon concentration and the like of the treated test piece were investigated. [0046] The adjustment of the precipitation depth of carbide in Table 4 was effected primarily by the control or the like of the carburizing time and carbon concentration, and the adjustment of the carbon concentration of the outermost 30 surface layer portion in Table 5 was effected by controlling the process gas flow, treatment time and the like upon repeating carburizing and diffusion in the primary treatment and secondary treatment in accordance With a program calculated beforehand. Process gases for low-pressure carburizing include propane, acetylene, ethylene and the like. Among these, most popular and economical propane was used. As an inert gas upon diffusion, on the other hand, nitrogen gas was used. Further, the rapid quenching in the secondary treatment was conducted by oil. As an alternative, the rapid quenching can also be conducted by high pressure gas which makes sole or mixed use of gases such as N2, He and H2. 33 [0049] 1) The percentage of effective case depth indicates the ratio (t/T) of the depth (t) of an ultrafine carbide layer to a case depth (T) of 550 HMV or greater in terms of micro-Vickers hardness. 2) The rolling fatigue life indicates the number of repetitions of rotation until occurrence of pitting under the below-described conditions. Contact pressure: 3 GPa, rotation speed: 1,500 rpm, slipping ratio: -40%, oil temperature: 80°C. 3) The impact strength indicates destructive energy as measured using a Charpy test piece. 4) The roundness indicates the amount of a deformation of the inner diameter of a ring in the X-Y direction as measured by a profile measuring instrument while using as the ring a test piece in a ring form of 100 (80) X15t. [0050] A description will now be made about effects of the percentage of effective case depth on the rolling fatigue life. When an ultrafine carbide layer was as shallow as 5% in terms of the percentage of effective case depth as in the comparative example represented by the sign A, it is considered that the amount of precipitated ultrafine carbide itself was small and therefore, that the treated test piece did not have temper softening resistance, which is characteristic to super carburizing, and was low in pitting toughness. In the case of the comparative example 34 represented by the sign E in which the percentage of effective case depth was 40%, the high hardness range was broadened, resulting in a problem that the impact strength was reduced, and with respect to a deformation by heat treatment as determined in terms of roundness, there was also a tendency toward increased distortion. From these results, the percentage of effective hardened depth in a precipitated carbide layer is optimally in a range of from 10 to 30%. [0051] A description will next be made about effects of the carbon concentration of the outermost surface layer portion shown in Table 5 on the pitting life. It is considered that the signs H, J and K, in each of which the carbon concentration of the outermost surface layer portion was high, were superior in pitting life and that in the cases of the signs G and I in each of which the carbon concentration was 1%, that is, lower compared with the former signs, they were somewhat inferior in pitting life. When the carbon concentration of the outermost surface layer portion is lower than 0. 8 wt. % as in the sign F shown as a referential example, the test piece was significantly inferior in pitting toughness. Namely, the greater the amount of ultrafine carbide precipitated in the outermost surface layer portion and the higher the carbon concentration of the outermost surface layer portion, the better the pitting life. Accordingly, the carbon concentration of super carburizing can be set preferably at 0.8 wt. % or higher in the present 35 invention. [0052] Regarding the upper limit to the carbon concentration through carburizing, no particular problem arose up to 2.0 wt. % . An increase in carbon concentration to a still higher level in excess of 2.0 wt.% involves a potential concern that precipitation of carbide flakes may be facilitated and the impact strength and deformation by heat treatment of the test piece may tend to become disadvantageous. It is, therefore, necessary to set the carbon concentration of the outermost surface layer portion at a level commensurate with properties required for the member (test piece). [0053] A description will next be made about effects of the additional carburizing treatment in the secondary treatment in the signs I, J and K on the pitching life, impact strength and deformation (strain) by heat treatment. Compared with the signs G and H in each of which the carbon concentrations was similar but the additional carburizing was not applied, the signs I, J and K varied less in all the properties and were better. As a reason for this advantage, it can be contemplated that the additional carburizing treatment may stabilize the carbon concentration of the matrix and may also promote the formation of ultrafine carbide in the outermost surface layer portion, the carburized layer itself may be converted into a dense and well-balanced structure, and the quality available through the heat treatment may be thoroughly stabilized. 36 [0054] From the above-described various analysis results, it is desired, as optimal treatment conditions in the process of the present invention, to employ machine structural steel as a member, to conduct super carburizing as a combination of the primary treatment and the secondary treatment in low-pressure carburizing facilities to treat the member under optimal heating and cooling conditions, and then to control the final step such that the depth of precipitated carbide falls within the range of from 10 to 30% in terms of the percentage of effective case depth and the carbon concentration of the surface layer becomes 0.8 wt.% or higher. Industrial Applicability [0055] As appreciated from the above-described series of results, the present invention can provide an absolutely novel, super carburized, low-distortion quenched member and its production process. According to the present invention, machine structural members such as gears and axle members can be provided with higher strength and can be used under higher contact pressure, thereby making it possible to materialize with low distortion the needs for various members of higher strength, higher performance, lighter weight and smaller size, such as members required to have low distortion, rotary sliding or reciprocal sliding members equipped with bearing structures, and 37 members required to have high contact fatigue resistance and high abrasion resistance under high contact pressure. Brief Description of the Drawings [0056] [FIG. 1] Heat cycle of the primary treatment. [FIG. 2] Heat cycle of the secondary treatment. [FIG. 3] Heat cycle of the examples. [FIG. 4] Optical micrograph (magnification: X100) of Test Piece No. 2-2 in Table 3. 38 CLAIMS [1] A process for producing a super carburized, low-distortion quenched member, which comprises a primary treatment of heating a steel member for a machine structure to a temperature within an austenite region by vacuum carburizing (low-pressure carburizing) to have carbon dissolved at least at a eutectoid carbon concentration of a surface layer portion of said member and then quenching said member at a cooling rate of from 3 to 15°C/sec from said temperature within said austenite region to a temperature not higher than an A1 transformation point to have at least one of ultrafine carbide and nuclei of said carbide formed in said surface layer portion of the said member; and a secondary treatment of subsequently heating and soaking said member to a temperature within said austenite region and then conducting rapid quenching to have ultrafine carbide precipitated in a range of from 10 to 30% in terms of effective case depth percentage in an outermost surface layer portion. [2] A process according to claim 1, wherein in said secondary treatment, additional carburizing treatment is applied to said surface layer portion of said member. [3] A process according to claim 2, wherein in said secondary treatment, said ultrafine carbide is caused to precipitate in said surface layer portion of said member to form a structure composed primarily of martensite and 39 containing a mixed structure of troostite, retained austenite and the like in parts thereof such that said outermost layer portion (a portion A) of said layer, a layer portion (a portion B) inner than said portion A and a layer portion (a portion C) inner than said portion B are in an order of A≥C≥B in terms of the fineness of austenite grain size. [4] A super carburized, low-distortion quenched member comprising a surface layer portion of a structure composed primarily of martensite and containing a mixed structure of troostite and retained austenite or the like in parts thereof, wherein in said surface layer, an outermost surface layer (a portion A) , a layer (a portion B) inner than said portion A and a layer (a portion C) inner than said portion Bare in an order of A≥C≥B in terms of the fineness of austenite grain size. The present invention can provide a super carburized, low-distortion quenched member with both higher performance and minimized heat-treatment distortion attained in the field of super carburized quenching which features high strength, high contact pressure and the like. A process for the production of the super carburized low-distortion quenched member includes a primary treatment and a secondary treatment. The primary treatment comprises heating a steel member for a machine structure to a temperature within an austenite region by vacuum carburizing (low-pressure carburizing) to have carbon dissolved at least at a eutectoid carbon concentration of a surface layer portion of the member and then quenching the member at a cooling rate of from 3 to 15°C/sec from the temperature within the austenite region to a temperature not higher than an A1 transformation point to have at least one of ultrafine carbide and nuclei of the carbide formed in the surface layer portion of the member. The secondary treatment comprises subsequently heating and soaking the member to a temperature within the austenite region and then conducting rapid quenching to have ultrafine carbide precipitated in a range of from 10 to 30% in terms of effective case depth percentage in an outermost surface layer portion.

Full Text

1
DESCRIPTION
HIGH-CONCENTRATION CARBURIZED/LOW-STRAIN QUENCHED
MEMBER AND PROCESS FOR PRODUCING THE SAME
Technical Field
[0001] This invention relates to carburizing and quenching
treatment widely used as a reinforcement method for machine
structural members, more specif ically to a super carburized,
quenched member featuring temper softening resistance, high
strength, high contact pressure and the like, especially
to a super carburized, low-distortion quenched member (which
may hereinafter be referred to simply as "member") with
mutually conflicting properties, that is, higher
performance and heat-treatment distortion attained
together and also to its production process.
Prior Art
[0002] Owing to excellent properties such as high fatigue
strength and wear resistance, carburized and quenched
members (hereafter referred to as "case hardened members")
are widely used as various members in transport equipment,
industrial machines and the like. From the viewpoint of
dimensional reductions, weight reductions and/or the like
through further improvements in the performance of such
members, numerous developments have been made on case

2
hardened members. Recently, the vacuum carburizing
(low-pressure carburizing) process has been developed.
Compared with the conventional gas carburizing process, the
vacuum carburizing process has excellent characteristic
features such as environmental friendliness, the prevention
of intergranular oxidation, the feasibility of
high-temperature carburizing treatment, and easy control
of carburizing and carbon diffusion, and therefore, is
expected to find still broader utility from the standpoints
of further improvements in the performance and quality of
members and further improvements in their productivity.
[0003] As a method for providing a machine structural member
such as a gear or axle member with improved pitting resistance
by applying carburizing and quenching to the member, there
is carbonitriding treatment. According to this treatment,
carbon and nitrogen are caused to concurrently diffuse into
the matrix of a member such that the member can be provided
with improved temper softening resistance. In addition,
there has also been developed super carburizing treatment
to have carbide precipitated in a surface layer portion of
a member such that the member can be provided with improved
temper softening resistance. Keeping in step with
evolutions in low-pressure carburizing facilities, a great
deal of research has been conducted in recent years.
[0004] As a representative example of the super carburizing
treatment, Patent Document 1 discloses a carburizing

3
treatment process for a member. According to Patent
Document 1, it is proposed to form quasispheroidal or
spheroidal carbide at a volume percentage of 30% or higher
within a range up to a depth of 0.4 mm by conducting
precarburizing to such a carbon content that spheroidal
carbide is caused to precipitate in a surface layer portion
of a steel member and the carbon concentration in the surface
layer portion becomes not higher than Acm but not lower than
a eutectoid concentration between steel and carbon, slowly
cooling or quenching the thus-treated member to convert the
surface layer portion into a bainite, pearlite ormartensite
structure, and then heating the member at a ramp rate of
not greater than 20°C/min from the Ac1 point to a temperature
in a range of from 750 to 950°C to effect carburizing and
quenching.
[0005] According to the above-described process, the member
can be improved in properties such as pitting properties
owing to the precipitation of the carbide in the surface
layer portion of the member. Nonetheless, the resulting
member involves problems such as a deformation and distort ion
by heat treatment, because the process is super carburizing
that causes the precipitation of the carbide as much as 30%
in the surface layer portion.
[0006] As a method for causing carbide to precipitate in an
ultrafine form in a surface layer portion of a member by
super carburizing, many heating and cooling methods have

4
been investigated. In Patent Document 1, it is described
to be desirable that subsequent to the precurburizing, air
cooling (which forms a bainite or pearlite structure) or
quenching (which forms amartensite structure) is conducted,
and that in the carbide-forming treatment as the next step,
the member is heated at a slow ramp rate of not greater than
20°C/min from the Ac1 transformation temperature to a
temperature within the range of from 750 to 950°C, and after
direct quenching or air cooling, the member is again heated
and quenched.
[0007] Further, Patent Document 2 and Patent Document 3
propose, as an optimal method, to conduct slow cooling (or
30°C/hr or less) after precurburizing or primary
carburizing.
[0008] When the quenching after the precarburizing or primary
carburizing is conducted by air cooling or slow cooling in
the method disclosed in Patent Document 1, 2 or 3, however,
a network of carbide tends to precipitate along grain
boundaries in a surface layer portion of a member. The next
step, that is, the carbide-forming treatment can hardly break
up the network of carbide in a short time to have the carbide
distributed and precipitated within the surface layer
portion. To overcome this shortcoming, heating and
subsequent cooling may be conducted a plurality of times
in some instances.
[0009] On the other hand, Patent Document 1 also discloses

5
quenching with an aim directed toward forming a martensite
structure by increasing the cooling rate of a member
subsequent to its precarburizing. This technique, however,
involves a potential problem that carbide nuclei in a surface
layer portion may dissolve out. It is also concerned that
the quenching may take place with supersaturated carbon,
and due to high-carbon martensitic transformation, the
member may develop a greater deformation or distortion
through an expansion, shrinkage or the like.
[0010] Patent Document 4 discloses a production process of
a case hardened member by low-pressure carburizing. There
is a reference to the conversion of carbide into an ultraf ine
form such as the control of the carbon concentration at 0.5
to 0.7 wt. % in primary carburizing and at 0.7 to 1 wt. % in
secondary carburizing and the control of primary cooling
at a very slow rate of from 1 to 10°C/min. Concerning
deformation strain, however, this production process is not
expected to be preferred like the above-mentioned Patent
Documents 1, 2 and 3.
[0011] Just for readers' information, a description is now
made of some advantages of low-pressure carburizing, which
is finding wide-spread commercial utility in recent years,
over conventional gas carburizing.
a) A change from a carburizing step to a diffusion step can
be readily and promptly modified.
b) High-temperature treatment is feasible so that prompt

6
carburizing can be conducted.
c) No intergranular oxidation takes place in a surface layer
portion of a member, and in the member under treatment,
it is hence possible to inhibit the occurrence of cracks
which would otherwise begin to take place from such a
defect.
d) No sooting takes place, thereby causing no uneven
carburizing which would otherwise take place as a result
of sooting.
Patent Document 1: JP-B-62-24499
Patent Document 2: JP-B-2787455
Patent Document 3: JP-B-2808 621
Patent Document 4: JP-A-2002-348615
Disclosure of the Invention
Problem to be Solved by the Invention
[0012] Even in super carburizing by the conventional
low-pressure carburizing, however, no optimal balance can
be achieved between the progress of formation of carbide
within a surface layer portion of a member under treatment
and the microstructure of the surface layer portion. The
problem of a deformation or strain of the treated member,
therefore, still remains unresolved. As a consequence,
grinding, strain-correcting finishing or the like is
essential for the member after the carburizing step. Such
additional work has led to a reduction in the inherent ability

7
of super carburizing that permits use under higher contact
pressure, a reduction in productivity and an increase in
manufacturing cost, thereby preventing the popularization
of super carburizing treatment.
Means for Resolving the Problem
[0013] The present invention has resolved the
above-described problem by developing an optimal process,
which makes it possible to use a member under a higher contact
pressure and also to provide the member with a lower strain
whilemaking use of low-pressure carburizing facilities that
permit a variety of control promptly with higher accuracy
as to the concentration of carbon in the member, the
repetition of carburizing treatment/diffusion treatment,
and diverse temperature conditions, heating conditions and
cooling rate (quenching) conditions for heating, soaking,
carburizing, quenching and the like of the member.
[0014] The above-described problem can be resolved by the
present invention as defined below:
1. A process for producing a super carburized,
low-distortion quenched member, which comprises a primary
treatment of heating a steel member for a machine structure
to a temperature within an austenite region by vacuum
carburizing (low-pressure carburizing) to have carbon
dissolved at least at a eutectoid carbon concentration of
a surface layer portion of the member and then quenching
the member at a cooling rate of from 3 to 15°C/sec from the

8
temperature within the austenite region to a temperature
not higher than an A1 transformation point to have at least
one of ultrafine carbide and nuclei of the carbide formed
in the surface layer portion of the member; and a secondary
treatment of subsequently heating and soaking the member
to a temperature within the austenite region and then
conducting rapid quenching to have ultrafine carbide
precipitated in a range of from 10 to 30% in terms of effective
hardened depth percentage in an outermost surface layer
portion.
[0015] 2. A production process as described above, wherein in the
secondary treatment, additional carburizing treatment is
applied to the surface layer portion of the member.
3. A production process as described above, wherein in the
secondary treatment, the ultrafine carbide is caused to
precipitate in the surface layer portion of the member to
form a structure composed primarily of martensite and
containing a mixed structure of troostite and retained
austenite or the like in parts thereof such that the outermost
layer portion (a portion A) of the layer, a layer portion
(a portion B) inner than the portion A and a layer portion
(a portion C) inner than the portion B are in an order of
A≥O≥B in terms of the fineness of austenite grain size.
[0016] A super carburized, low-distortion quenched member
comprising a surface layer portion of a structure composed
primarily of martensite and containing a mixed structure

1
9
of troostite and retained austenite or the like in parts
thereof, wherein in the surface layer, an outermost surface
layer (a portion A), a layer (a portion B) inner than the
portion A and a layer (a portion C) inner than the portion
B are in an order of A≥C≥B in terms of the fineness of austenite
grain size.
Advantageous Effects of the Present Invention
[0017] The process according to the present invention
performs the treatment of a member in low-pressure
carburizing facilities while making the combined use of the
primary treatment of conducting adequate super carburizing
and quenching at an optimal cooling rate and the secondary
treatment of subsequently causing a fine carbide to simply
and efficiently precipitate; and can minimize the
deformation and strain of the member treated through the
heat treatment. Owing to the adoption of this process, the
greatest concern about the conventional super carburizing,
for example, the cumbersome grinding, strain correction and
the like of the member after the treatment, such as the bending
of an axle or the deformation strain of a tooth profile,
can be substantially relieved, thereby bringing about
advantageous effects that significant improvements can be
made in the productivity, quality and cost of the case
hardened member.
[0018] According to the process of the present invention,
additional carburizing treatment may be applied to the

10
surface layer portion of the member in the secondary
treatment. This additional carburizing treatment makes it
possible to achieve a high hardness of matrix and also to
reduce the crystal grain size of an outermost surface layer
portion of the member to an ultrafine grain size and,
therefore, is also extremely effective for providing the
member with higher strength and higher toughness. By the
process of the present invention, it is possible to readily
achieve higher strength, higher toughness, higher contact
pressure and the like for members such as axles and gears
to which super carburizing has heretofore been hardly
applicable. Therefore, the process according to the
present invention can be widely applied to fields where there
is a high need for such properties, and has an advantageous
effect that it can make significant contributions to
improvements in the performance of a member and also to
reductions in the size and weight of the member.
Best Modes for Carrying out the Invention
[0019] Based on best modes for carrying out the invention,
the present invention will next be described in further
detail. The followings are the course of technical
endeavors and the findings, which have led to the present
invention.
With a view to developing a super carburizing process
for causing ultrafine carbide to precipitate in a surface

11
layer portion of a member by using low-pressure carburizing
facilities, the present inventors carried out a thorough
investigation on possible relations between the
concentration of carbon in the surface layer portion and
various heating and cooling conditions and the precipitation
form of the ultrafine carbide in the surface layer portion
and the microstructure of the matrix. Concerning
improvements or the like in strain by heat treatment while
assuming members such as gears and axles, research and
development was also conducted from many directions. An
aim was then set at the establishment of a novel process
for super carburizing and low-strain quenching, which can
achieve both of mutually-conflicting properties of
providing a member with higher performance by super
carburizing and minimizing a deformation, distortion or the
like of the member while balancing them at high levels.
[0020] Upon applying super carburizing to a surface layer
portion of steel (member), the most important point is to
have ultrafine carbide precipitated as much as possible in
a surface layer portion of the member through the optimal
combination of the primary treatment and the secondary
treatment. In the control of the formation of the ultrafine
carbide, carburizing and quenching facilities also play an
important role. In the present invention, a variety of
developments were conducted while using low-pressure
carburizing facilities that compared with conventional

12
carburizing facilities, permit a variety of control promptly
with higher accuracy as to the concentration of carbon in
the member, the repetition of carburizing
treatment/diffusion treatment, and diverse temperature
conditions, heating conditions and cooling rate (quenching)
conditions for heating, soaking, carburizing, quenching and
the like of the member.
[0021] Described specifically, a variety of investigations
were conducted on the heating, soaking, super carburizing,
diffusion and cooling (quenching) conditions of a member
during the primary treatment to firstly reduce the
deformation or strain of the member at the stage of the primary
treatment. In the secondary treatment as the next step,
carburizing and quenching (cooling) conditions are
important to permit adjustments or the like in the
precipitation of ultrafine carbide and the grain size of
austenite in the carburized layer. Specifically, it has
been found that in the secondary treatment, the deformation
or strain of a member by the heat treatment can be minimized
by controlling a range, in which the ultrafine carbide
precipitate in a surface layer portion of the member, to
10 to 30% in terms of effective case depth percentage and
further by converting an outermost surface layer portion
into an ultrafine crystalline structure.
[0022] The term "effective case depth percentage" as used
herein means a ratio (t/T) of a precipitated depth (t) of

13
ultrafine carbide existing in an outermost surface "layer
portion of a member to an effective case depth (T) of the
member after completion of the secondary treatment
(including the tempering treatment at 180°C) . It is to be
noted that the term "effective case depth" means a distance
froma surf ace of a hardened layer, whichis still inaquenched
state or has been tempered at a temperature not exceeding
200°C, to the position of a critical depth of a Vickers
hardness (HV) of 550 as measured by the Method of Measuring
Case Depth Hardened by Carburizing Treatment for Steel (JIS
G0557) .
Next, the term "precipitated depth of ultrafine
carbide" means the maximum depth, where the ultrafine carbide
exists, from the outermost surface layer portion of the
member as determined by an analysis under an optical
microscope or an electron microscope. To facilitate the
discrimination of the ultrafine carbide, the member is
analyzed in a state of being etched with an etching solution
such as 5% nital etching reagent.
[0023] The vacuum carburizing (low-pressure carburizing)
facilities for use in the present invention are equipped
with a carburizing and heating chamber including a treatment
furnace which is sectionally controllable at different
pressures of from 200 to 2,000 Pa, and are available on the
market. Conventionally-available vacuum carburizing
facilities are all usable in the present invention. As the

14
primary treatment in the present invention, the member is
heated and soaked to a predetermined temperature in the
furnace of the facilities, and to raise the concentration
of carbon in the surface layer portion of the member to or
higher than the eutectoid carbon concentration, the member
is then quenched at an appropriate cooling rate. In the
subsequent secondary treatment, the carbide is caused to
precipitate in an ultraf ine form in the surface layer portion
of the member, optionally followed by additional carburizing
treatment as needed.
[0024] According to the primary treatment in the process of
the present invention, steel to be treated (member) is heated
and soaked to an austenite region of from 900 to l,100°C,
carburizing is conducted such that the carbon concentration
of a surface layer portion becomes preferably 0.8 wt.% or
higher, and from the thus-carburized state, quenching is
then conducted at an optimal cooling rate. Optimal cooling
conditions are to evenly cool the member at a cooling rate
of from 3 to 15°C/sec over a temperature range of from the
carburizing temperature (the temperature in the austenite
region) to the A1 transformation temperature or lower,
preferably to 400°C or lower. By this cooling, ultrafine
carbide is caused to precipitate in the surface layer portion
of the member so that a structure composed primarily of
martensite is formed in the surface layer portion. The term
"ultrafine carbide" means an M23C6 type carbide formed as

15
a result of bonding of carbide-forming elements such as Cr
and Mo in Fe3C (cementite) or steel with carbon dissolved
in supersaturation.
[0025] In the secondary treatment, the non-carburized
portion (interior) of the member is heated and soaked to
a range of from an austenizing temperature to the austenizing
temperature + 80°C, preferably to a range of from 10 to 70°C
above the austenizing temperature, and is then rapidly
quenched to effect precipitation of ultrafine carbide such
that the carbon concentration of the surface layer portion
becomes preferably 0.8 wt.% or higher, more preferably 1.0
to 2.0 wt.%. It is preferred to apply, in parallel with
the precipitation of the ultrafine carbide in the surface
layer portion, additional carburizing treatment to the
surface layer portion to promote the precipitation of the
ultrafine carbide in the surface layer portion, and from
the state that the carbon concentration of the matrix has
been adequately adjusted, to further conduct rapid
quenching.
[0026] The temperature of the final quenching after the
secondary treatment varies depending on the pretreatment
conditions, that is, whether the final quenching is after
the heating and soaking or after the heating, soaking and
additional carburizing. The rapid quenching can be
conducted at the temperature after the pretreatment or at
a temperature raised or lowered relative to the temperature

16
of the pretreatment. In other words, the temperature of
the final quenching after the secondary treatment can be
set at a level commensurate with the quality of heat treatment
such as the hardness and microstructure required for the
member.
[0027] With a view to establishing optimal conditions for
super carburizing, the present inventors conducted a
detailed investigation on the carbon concentrations upon
heating, soaking and carburizing and diffusion and various
cooling (quenching) conditions with respect to the primary
treatment in which super carburizing is applied to a surface
layer portion of a member in low-pressure carburizing
facilities and the secondary treatment in which ultrafine
grains of carbide are caused to precipitated in the surface
layer portion. As a result, it was succeeded in obtaining
a super carburized, quenched member having a carbon
concentration of preferably 0.8 wt.% or higher, more
preferably from 1.0 to 2.0 wt.% in a range of from 10 to
30% in terms of the percentage of an effective case depth
(t/T) in an outermost surface layer portion and having a
three-layer structure consisting of a superultrafine grain
layer of No. 10 or greater austenite grain size, a fine grain
layer and an ultrafine grain layer in this order from the
outermost surface layer. It has been found that the super
carburized, quenched member is minimized in deformation or
distortion after the treatment and that the correction of

17
a strain, which has been unavoidable in the conventional
super carburizing, can be obviated or can be readily
conducted compared with the conventional process.
Examples
[0028] Based on certain Examples, the present invention will
next be described in further detail.
Machine structural steels (materials) shown in Table
1 were provided. Those materials were subjected beforehand
to normalizing treatment at 900°C and were then machined
to prepare stepped round-bar test pieces of 30/25/20 X
L300mm, respectively. As carburizing and quenching of each
test piece, the primary treatment of the super carburizing
step in the present invention was conducted using facilities
which permitted heating and carburizing at a low pressure
and also permitted oil hardening and high pressure gas
cooling.
[0029] It is to be noted that steel grades 1 and 2 are
carburizing, quenching steels as specified under the JIS,
steel grade 1 is SCM420, chromium-molybdenum steel, and steel
grade 2 is SCr415, chromium steel. MAC14 as steel grade
3 is a grade for a commercial product developed by a steel
maker, and is steel developed by increasing the Cr content
in comparison with the above-described two steel grades and
further adding Mo element with a view to causing M23C6 type
ultraf ine carbide to precipitate upon super carburizing (the

18
primary and secondary treatments).
[0030]
Table 1: Used Steels and Their Chemical Components
(wt.%)

Steelgrade C Si Mn P S Cr Mo
1 SCM420 0.20 0.30 0.75 0.019 0.025 1.10 0.20
2 SCr415 0.16 0.35 0.78 0.021 0.019 1.05 0.02
3 MAC14 0.15 0.27 0.53 0.020 0.022 2.50 0.38
[0031] Table 2 summarizes the results obtained by
experimenting in various ways effects of the cooling rate
on the states of carbide to be precipitated in surface layer
portions of test pieces and the deformations of the test
pieces by heat treatment through the primary treatment in
the present invention. As conditions for the primary
treatment, super carburizing of each test piece was conducted
by the heat cycle shown in FIG. 1 such that subsequent to
heating and soaking, an effective case depth of 0. 5 mm would
be achieved. Described specifically, supercarburizingand
diffusion treatment of each test piece were alternately
conducted at 950°C for about 70 minutes, respectively, such
that the carbon concentration of the surface layer portion
of the test piece in its final state would be controlled
at about 1. 5 wt. % . Froma state that the carbon concentration
of the surface layer portion of each test piece was in

19
supersaturation, quenching of the test piece was conducted
under the corresponding cooling rate condition shown in Table
2 to investigate the shape and size of the carbide in the
surface layer portion of the test piece and the
microstructure of the surface layer portion of the test
piece.
[0032] To determine the deformations and strains of the
above-described steel grades by the primary treatment,
stepped round-bar test pieces 30/25/20 X L300 mm) of
the respective steel grades were provided as test pieces.
In a state of being supported at opposite ends, each test
piece was analyzed for a runout at its axial central part
to investigate a relationship between the cooling rate and
the axial of the test piece.

21
[0034] The signs shown in the table and analysis methods of
the properties shown there will now be described below.
1) The cooling rate indicates an average cooling rate at
the axial central part of each test piece from the
quenching temperature of 950°C after the completion of
the carburizing and diffusion for the test piece to 400°C.
2) The shape and size of carbide was observed under a scanning
electron microscope.
3) Abbreviations for microstructures
F: ferrite, P: pearlite, B: bainite, T: troostite, M:
martensite, y: retained austenite.
4) The radial runout indicates a runout of a test piece,
which was mounted on a both-end supporting, runout
measuring instrument, as measured at a central part of
the test piece by a dial gauge.
[0035] In each of the comparative examples shown as Test Piece
Nos .1,4 and 6 in Table 2, the cooling rate during the cooling
was as low as l°C/sec so that the carbide precipitated in
the surface layer portion consisted primarily of a network
of carbide formed of carbide flakes bonded together and the
matrix was in the form of an slack quenching structure of
ferrite, pearlite and bainite. As a consequence, those
comparative examples were all large in radial runout and
deformation. The comparative example shown as Test Piece
No. 3, on the other hand, was subjected to rapid cooling
equivalent to conventional oil quenching (20°C/sec). Its

22
surface layer portion contained a very small amount of
precipitated carbide, and had a structure quenched from a
high carbon state that carbon was in supersaturation. That
comparative example was large in radial runout and
deformation.
[0036] When the cooling rate was 4 to 12°C/sec as in each
of the examples as Test Piece Nos. 2, 5 and 7 (the present
invention) , ultraf ine carbide precipitated in a large amount,
and moreover, microstructures appeared as nuclei for the
ultrafine carbide, leading to improvements in the
deformation and distortion (runout) of the test piece as
the outstanding serious problems of super carburizing.
Described specifically, compared with slow cooling that
cooling is slow or rapid quenching that cooling is fast in
contrast, the radial runout of each of the test pieces
according to the present invention was of approximately a
half level of the radial runouts in the rest of the examples,
thereby realizing a substantial reduction in radial runout.
From these results, the cooling rate during the quenching
in the primary treatment is optimally 3 to 15°C/sec.
[0037] Table 3 shows the results obtained by using
representative ones of the test pieces subjected to the
primary treatment shown in Table 2, applying the secondary
treatment in various ways to the representative test pieces
to cause ultrafine carbide to finally precipitate in their
surface layer portions, and investigating the carbon

23
concentrations, states of precipitated carbide,
microstructures, crystal grain sizes, etc. in their surface
layer portions and the radial runouts of the test pieces.
As conditions for the secondary treatment, the heat cycle
shown in FIG. 2 was followed, the soaking temperature was
selectively set at three levels of 800°C, 850°C and 900°C,
all above the A1 transformation temperature, and subsequent
to the heating and soaking, additional carburizing was also
conducted at the same time to achieve a carbon concentration
higher than the eutectoid carbon concentration as a technique
for further raising the carbon concentrations in the surface
layer portions and also increasing the amounts of
precipitated ultrafine carbide through the secondary
treatment.
The subscript "n" in (carburizing/diffusion)n or
(additional carburizing/diffusion)n in FIGS. 1 through 3
means the number of repetitions of carburizing or diffusion
in the corresponding step, and is set in commensurate with
the quality required for each member. In the case of Test
Piece No. 2 shown as an example in Table 2, for example,
n was set at 8 (n = 8), and in the case of Test Piece No.
2-2 shown as an example in Table 3, on the other hand, n
was set at 5 (n = 5).

26
[0039] [Analysis method of carbon concentration surface layer
portion]
Using each of the test pieces (30/25/20 X L300mm),
chips were collected by lathe turning from the surface layer
portion to the 0.05 mm depth of its 25 mm portion, and the
carbon concentration of the surface layer portion was
determined by a chemical analysis.
[0040] From Table 3, the Test Piece No. 2 series indicate
effects on the precipitation form of carbide and others when
the secondary treatment temperature was varied, and the Test
Pieces No. 5 and No. 7 series indicate effects on the
precipitation of ultrafine carbide and the final carbon
concentrations in the surface layer portions depending on
whether or not the additional carburizing was applied in
the secondary treatment.
[0041] Concerning the secondary treatment temperature
(which may hereinafter be called "the additional carburizing
temperature"), the temperature of 900°C employed for Test
Piece No. 2-1 involves a problem in that the carbide in a
surface layer portion dissolves to lead to a reduction in
the overall precipitation of carbide grains and also to an
increase in the radial runout of the test piece. With the
secondary treatment temperature of 800°C employed for Test
PieceNo. 2-3, carbide flakes precipitate at grainboundaries
in the surface layer portion, and the core portion of the
member is quenched incomplete. Test pieces, therefore,

27
develop variations in radial runout. From these results,
the optimal temperature for the treatment that causes
ultrafine carbide to precipitate in a surface layer portion
by the secondary treatment can preferably be a temperature
equivalent to the A3 transformation temperature + 10-70°C,
which is determined by the composition of the member (before
the carburizing treatment).
[0042] As to whether or not the additional carburizing
treatment is applied in the secondary treatment, the
application of the additional carburizing treatment has been
recognized, as evident from the results of Test Piece Nos.
5-1 and 7-1, to bring about the advantageous effect that
carbide precipitates in an ultrafine form, to say nothing
of an improvement in the concentration of carbon in the
surface layer portion. As a reason for the advantageous
effect, it may be contemplated that, as the carbon in the
surface layer portion precipitate as carbide and the
concentration of carbon in the matrix becomes lean, the
replenishment of carbon to the surface layer portion by the
additional carburizing could promote the new formation of
ultraf ine carbide, such as Fe3C and M23C6, and nuclei thereof.
[0043] As shown in FIG. 4, it has also been found that in
themember subjected to the additional carburizing treatment,
the austenite grain size of the outermost surface layer
portion is reduced to an ultrafine grain size. The term
"ultrafine grain size" corresponds to an austenite grain

28
size of No. 10 or greater as measured by the carburized
grain-size testing method in JIS-G0551, "Method of Testing
Austenite Grain Size for Steel". A significant
characteristic feature has also been discovered in that a
three-layer structure formed of fine grains and ultrafine
grains is formed extending toward the inside. Paying
attention to a relationship between the austenite grain size
and the carburized layer, the grain sizes of the outermost
surface layer portion greatest in the amount of precipitated
ultrafine carbide, the carburized layer portion (fine grain
portion) located inside the outermost surface layer portion
and the ultrafine grain portion located still inside the
fine grain portion are in a relationship of A>C>B, in which
"A", "C" and"B" stand for the outermost surface layer portion,
the ultrafine grain portion and the fine grain portion,
respectively. Incidentally, the austenite grain size of
a surface layer portion in conventional carburizing is
generally equivalent to No. 7 or 8 . In the present invention,
the surface layer portion has a grain structure of the
characteristic three-layer structure which does not appear
in the conventional carburizing treatment.
[0044] As an advantageous effect of such an ultrafine grain
layer, it has a significant characteristic feature in that
the toughness of a hardened surface layer, said toughness
having been a concern about conventional carburized members,
can be improved and high toughness can also be imparted to

29
the carburized layer itself in addition to the feasibility
of higher contact pressure as a characteristic feature of
the present invention, and therefore, is extremely effective
for providing carburized members with still higher strength
from now on.
[0045] Table 4 shows effects of the percentage of an effective
case depth of a carbide layer precipitated in super
carburizing according to the present invention on various
properties. Various test pieces were prepared by providing
SCM420, JIS steel for machine structure, as a material,
subjecting the material to normalizing treatment at 900°C
beforehand, and then machining the resultant material. The
super carburizing of each test piece was conducted by the
heat cycle of primary treatment and secondary treatment shown
in FIG. 3. Each treated test piece was analyzed and
investigated for pitting life, impact strength, distortion
by heat treatment, etc. Concerning effects of the carbon
concentration of the outermost surface layer portion of each
test piece shown in Table 5, the test piece was treated by
the heat cycle shown in FIG. 3 in a similar manner as the
various test pieces in Table 4, and the carbon concentration
and the like of the treated test piece were investigated.
[0046] The adjustment of the precipitation depth of carbide
in Table 4 was effected primarily by the control or the like
of the carburizing time and carbon concentration, and the
adjustment of the carbon concentration of the outermost

30
surface layer portion in Table 5 was effected by controlling
the process gas flow, treatment time and the like upon
repeating carburizing and diffusion in the primary treatment
and secondary treatment in accordance With a program
calculated beforehand. Process gases for low-pressure
carburizing include propane, acetylene, ethylene and the
like. Among these, most popular and economical propane was
used. As an inert gas upon diffusion, on the other hand,
nitrogen gas was used. Further, the rapid quenching in the
secondary treatment was conducted by oil. As an alternative,
the rapid quenching can also be conducted by high pressure
gas which makes sole or mixed use of gases such as N2, He
and H2.

33
[0049] 1) The percentage of effective case depth indicates the ratio
(t/T) of the depth (t) of an ultrafine carbide layer to
a case depth (T) of 550 HMV or greater in terms of
micro-Vickers hardness.
2) The rolling fatigue life indicates the number of
repetitions of rotation until occurrence of pitting under
the below-described conditions.
Contact pressure: 3 GPa, rotation speed: 1,500 rpm,
slipping ratio: -40%, oil temperature: 80°C.
3) The impact strength indicates destructive energy as
measured using a Charpy test piece.
4) The roundness indicates the amount of a deformation of
the inner diameter of a ring in the X-Y direction as
measured by a profile measuring instrument while using
as the ring a test piece in a ring form of 100 (80)
X15t.
[0050] A description will now be made about effects of the
percentage of effective case depth on the rolling fatigue
life. When an ultrafine carbide layer was as shallow as
5% in terms of the percentage of effective case depth as
in the comparative example represented by the sign A, it
is considered that the amount of precipitated ultrafine
carbide itself was small and therefore, that the treated
test piece did not have temper softening resistance, which
is characteristic to super carburizing, and was low in
pitting toughness. In the case of the comparative example

34
represented by the sign E in which the percentage of effective
case depth was 40%, the high hardness range was broadened,
resulting in a problem that the impact strength was reduced,
and with respect to a deformation by heat treatment as
determined in terms of roundness, there was also a tendency
toward increased distortion. From these results, the
percentage of effective hardened depth in a precipitated
carbide layer is optimally in a range of from 10 to 30%.
[0051] A description will next be made about effects of the
carbon concentration of the outermost surface layer portion
shown in Table 5 on the pitting life. It is considered that
the signs H, J and K, in each of which the carbon concentration
of the outermost surface layer portion was high, were
superior in pitting life and that in the cases of the signs
G and I in each of which the carbon concentration was 1%,
that is, lower compared with the former signs, they were
somewhat inferior in pitting life. When the carbon
concentration of the outermost surface layer portion is lower
than 0. 8 wt. % as in the sign F shown as a referential example,
the test piece was significantly inferior in pitting
toughness. Namely, the greater the amount of ultrafine
carbide precipitated in the outermost surface layer portion
and the higher the carbon concentration of the outermost
surface layer portion, the better the pitting life.
Accordingly, the carbon concentration of super carburizing
can be set preferably at 0.8 wt. % or higher in the present

35
invention.
[0052] Regarding the upper limit to the carbon concentration
through carburizing, no particular problem arose up to 2.0
wt. % . An increase in carbon concentration to a still higher
level in excess of 2.0 wt.% involves a potential concern
that precipitation of carbide flakes may be facilitated and
the impact strength and deformation by heat treatment of
the test piece may tend to become disadvantageous. It is,
therefore, necessary to set the carbon concentration of the
outermost surface layer portion at a level commensurate with
properties required for the member (test piece).
[0053] A description will next be made about effects of the
additional carburizing treatment in the secondary treatment
in the signs I, J and K on the pitching life, impact strength
and deformation (strain) by heat treatment. Compared with
the signs G and H in each of which the carbon concentrations
was similar but the additional carburizing was not applied,
the signs I, J and K varied less in all the properties and
were better. As a reason for this advantage, it can be
contemplated that the additional carburizing treatment may
stabilize the carbon concentration of the matrix and may
also promote the formation of ultrafine carbide in the
outermost surface layer portion, the carburized layer itself
may be converted into a dense and well-balanced structure,
and the quality available through the heat treatment may
be thoroughly stabilized.

36
[0054] From the above-described various analysis results,
it is desired, as optimal treatment conditions in the process
of the present invention, to employ machine structural steel
as a member, to conduct super carburizing as a combination
of the primary treatment and the secondary treatment in
low-pressure carburizing facilities to treat the member
under optimal heating and cooling conditions, and then to
control the final step such that the depth of precipitated
carbide falls within the range of from 10 to 30% in terms
of the percentage of effective case depth and the carbon
concentration of the surface layer becomes 0.8 wt.% or
higher.
Industrial Applicability
[0055] As appreciated from the above-described series of
results, the present invention can provide an absolutely
novel, super carburized, low-distortion quenched member
and its production process. According to the present
invention, machine structural members such as gears and
axle members can be provided with higher strength and
can be used under higher contact pressure, thereby making
it possible to materialize with low distortion the needs
for various members of higher strength, higher performance,
lighter weight and smaller size, such as members required
to have low distortion, rotary sliding or reciprocal
sliding members equipped with bearing structures, and

37
members required to have high contact fatigue resistance
and high abrasion resistance under high contact pressure.
Brief Description of the Drawings
[0056] [FIG. 1] Heat cycle of the primary treatment.
[FIG. 2] Heat cycle of the secondary treatment.
[FIG. 3] Heat cycle of the examples.
[FIG. 4] Optical micrograph (magnification: X100) of Test
Piece No. 2-2 in Table 3.

38
CLAIMS
[1] A process for producing a super carburized,
low-distortion quenched member, which comprises a primary
treatment of heating a steel member for a machine structure
to a temperature within an austenite region by vacuum
carburizing (low-pressure carburizing) to have carbon
dissolved at least at a eutectoid carbon concentration of
a surface layer portion of said member and then quenching
said member at a cooling rate of from 3 to 15°C/sec from
said temperature within said austenite region to a
temperature not higher than an A1 transformation point to
have at least one of ultrafine carbide and nuclei of said
carbide formed in said surface layer portion of the said
member; and a secondary treatment of subsequently heating
and soaking said member to a temperature within said
austenite region and then conducting rapid quenching to have
ultrafine carbide precipitated in a range of from 10 to 30%
in terms of effective case depth percentage in an outermost
surface layer portion.
[2] A process according to claim 1, wherein in said
secondary treatment, additional carburizing treatment is
applied to said surface layer portion of said member.
[3] A process according to claim 2, wherein in said
secondary treatment, said ultrafine carbide is caused to
precipitate in said surface layer portion of said member
to form a structure composed primarily of martensite and

39
containing a mixed structure of troostite, retained
austenite and the like in parts thereof such that said
outermost layer portion (a portion A) of said layer, a layer
portion (a portion B) inner than said portion A and a layer
portion (a portion C) inner than said portion B are in an
order of A≥C≥B in terms of the fineness of austenite grain
size.
[4] A super carburized, low-distortion quenched member
comprising a surface layer portion of a structure composed
primarily of martensite and containing a mixed structure
of troostite and retained austenite or the like in parts
thereof, wherein in said surface layer, an outermost surface
layer (a portion A) , a layer (a portion B) inner than said
portion A and a layer (a portion C) inner than said portion
Bare in an order of A≥C≥B in terms of the fineness of austenite
grain size.

The present invention can provide a super carburized,
low-distortion quenched member with both higher performance and
minimized heat-treatment distortion attained in the field of super
carburized quenching which features high strength, high contact
pressure and the like. A process for the production of the super
carburized low-distortion quenched member includes a primary
treatment and a secondary treatment. The primary treatment
comprises heating a steel member for a machine structure to a
temperature within an austenite region by vacuum carburizing
(low-pressure carburizing) to have carbon dissolved at least at
a eutectoid carbon concentration of a surface layer portion of
the member and then quenching the member at a cooling rate of from
3 to 15°C/sec from the temperature within the austenite region
to a temperature not higher than an A1 transformation point to
have at least one of ultrafine carbide and nuclei of the carbide
formed in the surface layer portion of the member. The secondary
treatment comprises subsequently heating and soaking the member
to a temperature within the austenite region and then conducting
rapid quenching to have ultrafine carbide precipitated in a range
of from 10 to 30% in terms of effective case depth percentage in
an outermost surface layer portion.

Documents:

02642-kolnp-2007-abstract.pdf

02642-kolnp-2007-claims.pdf

02642-kolnp-2007-correspondence others 1.1.pdf

02642-kolnp-2007-correspondence others 1.2.pdf

02642-kolnp-2007-correspondence others 1.3.pdf

02642-kolnp-2007-correspondence others 1.4.pdf

02642-kolnp-2007-correspondence others.pdf

02642-kolnp-2007-description complete.pdf

02642-kolnp-2007-drawings.pdf

02642-kolnp-2007-form 1.pdf

02642-kolnp-2007-form 18.pdf

02642-kolnp-2007-form 2.pdf

02642-kolnp-2007-form 3.pdf

02642-kolnp-2007-form 5.pdf

02642-kolnp-2007-gpa.pdf

02642-kolnp-2007-international exm report.pdf

02642-kolnp-2007-international publication.pdf

02642-kolnp-2007-international search report.pdf

02642-kolnp-2007-pct request form.pdf

02642-kolnp-2007-priority document.pdf

02642-kolnp-2007-translated copy of priority document.pdf

2642-KOLNP-2007-ABSTRACT 1.1.pdf

2642-KOLNP-2007-ABSTRACT.pdf

2642-KOLNP-2007-AMANDED PAGES OF SPECIFICATION.pdf

2642-KOLNP-2007-CLAIMS.pdf

2642-KOLNP-2007-DESCRIPTION (COMPLETE) 1.1.pdf

2642-KOLNP-2007-DRAWINGS 1.1.pdf

2642-KOLNP-2007-EXAMINATION REPORT REPLY RECIEVED.pdf

2642-KOLNP-2007-FORM 1 1.1.pdf

2642-KOLNP-2007-FORM 2 1.1.pdf

2642-KOLNP-2007-FORM 3 1.1.pdf

2642-KOLNP-2007-OTHERS 1.1.pdf

2642-KOLNP-2007-PETITION UNDER RULE 137.pdf

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Patent Number

255185

Indian Patent Application Number

2642/KOLNP/2007

PG Journal Number

05/2013

Publication Date

01-Feb-2013

Grant Date

31-Jan-2013

Date of Filing

16-Jul-2007

Name of Patentee

PARKER NETSUSHORI KOGYO K.K.

Applicant Address

16-8, NIHONBASHI 2-CHOME, CHUO-KU, TOKYO

Inventors:

#	Inventor's Name	Inventor's Address
1	MACHIDA ISAO	C/O. PARKER NETSUSHORI KOGYO K.K. 16-8, NIHONBASHI 2-CHOME, CHUO-KU, TOKYO 103-0027
2	FUKUSHIMA TOSHIO	C/O. PARKER NETSUSHORI KOGYO K.K. 16-8, NIHONBASHI 2-CHOME, CHUO-KU, TOKYO 103-0027
3	HORIKIRI KOJI	C/O. PARKER NETSUSHORI KOGYO K.K. 16-8, NIHONBASHI 2-CHOME, CHUO-KU, TOKYO 103-0027
4	ABE HISASHI	C/O. PARKER NETSUSHORI KOGYO K.K. 16-8, NIHONBASHI 2-CHOME, CHUO-KU, TOKYO 103-0027

PCT International Classification Number

C23C 8/22, C21D 9/00

PCT International Application Number

PCT/JP06/302161

PCT International Filing date

2006-02-08

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1	JP2005-032302	2005-02-08	Japan