JP6621315B2 - Manufacturing method of steel for machine parts with excellent rolling fatigue life - Google Patents

Description

  The present invention requires excellent rolling fatigue life of bearings, gears, hub units, continuously variable transmissions, constant velocity joints, piston pins, etc. in which non-metallic inclusions are the starting point of damage, and has a surface hardness of 58 HRC. The present invention relates to a method for producing steel for machine parts used after being cured.

  In recent years, with the improvement in performance of various mechanical devices, the use environment of mechanical parts and devices that require a rolling fatigue life has become extremely severe, and there is a strong demand for improved life and improved reliability. In response to such demands, efforts are being made to optimize steel components and reduce impurity elements. However, even when such a high clean steel material is used, it is not possible to sufficiently suppress short-life damage. Therefore, attempts have been made to reduce the nonmetallic inclusions in the steel material to increase the cleanliness and to further reduce the diameter of the nonmetallic inclusions.

By the way, the idea that non-metallic inclusions in steel such as well-known Al ₂ O ₃ , MnS, and TiN are harmful as a starting point of internal separation in rolling fatigue of steel parts is deeply rooted. This idea seems to be generally correct because the rolling fatigue life of steel parts decreases as the diameter of these non-metallic inclusions increases. Accordingly, various types of high cleanliness steels with a small amount of nonmetallic inclusions, that is, with a high cleanliness of steel and a large number of oxide-based nonmetallic inclusions having an inclusion diameter of 20 μm or more and extremely small ( For example, refer to Patent Document 1 and Patent Document 2.) However, it is not always easy to reduce the diameter of the nonmetallic inclusion stably.

  On the other hand, the present inventors examined in detail the process leading to breakage in rolling fatigue, that is, the process of separation by observing the cracking process of the artificial defect material, and the existence of gaps around cavities and nonmetallic inclusions It has been shown that there is a high possibility that it will play a dominant role (see Non-Patent Document 1, for example). Based on these findings, the present inventors have made it possible for a machine structural steel to obtain a steel material shape in a method for producing a machine part in which a part or the whole of a machine structural steel is obtained by a quenching and tempering method to obtain 58 HRC or more. After being subjected to plastic working in the process or subsequent process for obtaining the machine part shape, and before quenching and tempering, the steel is heated to 800 to 1100 ° C. and applied with a hydrostatic compression stress of 100 MPa or more. Proposes a method of manufacturing a machine part with excellent rolling fatigue life, characterized by performing a process of closely adhering the interface between the nonmetallic inclusions contained in the steel and the parent phase steel (for example, Patent Documents) 3). By this method, the interface between the mother phase and the steel is brought into close contact with each other, thereby achieving a significant improvement in life that has not been achieved in the past. Such a physical gap is a plastic process that is always performed in the process of manufacturing a steel material or forming a member, that is, hot rolling, cold rolling, hot forging, warm forging, cold It has been pointed out that it may be caused by forging, rolling forging, cold rolling, cold header processing and drawing.

The present inventors also provide a steel member used for a machine part having a surface hardness of 58 HRC or more, wherein the oxygen content in the steel is 8 ppm or less, the sulfur content is 0.008 mass% or less, and the rolling element When a specimen with a test area of 40 mm ² or more and 400 mm ² or less is collected from the rolling surface that rotates under load, the effective harmful length is 10 μm or more. All the inclusions having a width of 2 μm or more were observed, the gap ratio defined below was calculated for each inclusion, and the average of the observed gap ratios of all the inclusions was 8% or less and was observed. Of the total inclusions, when the ratio of the inclusions with a gap ratio of less than 1.0% to the total inclusions observed is defined as the zero gap number ratio, the zero gap ratio is 30% or more. Has proposed a steel member with excellent rolling fatigue life ( In example, see Patent Document 4.). In the present invention, the clearance ratio is defined as follows.
Gap ratio = gap area / (gap area + inclusion area)

  In addition, as described in Patent Document 4, the effective harmful length described above is a length including a gap around the inclusions in addition to the actual inclusions, and the effective harmful width is the actual inclusions. In addition, the width includes the gap around the inclusion. Both of these inventions by these inventors focus on the control of the interface between inclusions and the parent phase.

  In both of these inventions, sufficient attention is paid to the adhesion between the nonmetallic inclusions and the parent phase. However, Patent Document 4 does not mention any damage inherent in non-metallic inclusions, and has not been considered. Further, in Patent Document 3, the temperature for applying the hydrostatic pressure stress and the hydrostatic pressure compressive stress are not sufficiently high, so that there is an obvious effect on the adhesion between the inclusion and the steel that is the parent phase. The effect of repairing internal damage such as cracks introduced into the inclusion itself with plastic working was small. The inventors have found that there is room for further improvement in life by focusing on the internal damage of the nonmetallic inclusions. In other words, sharp edges of the inclusions are easily generated due to such internal damage, which promotes stress concentration and adversely affects the rolling fatigue life. The focus is on.

JP 2006-63402 A Japanese Patent Laid-Open No. 06-192790 Japanese Patent No. 5403945 Japanese Patent Application Laid-Open No. 2014-55346

Iron and steel, Vol. 94 (2008) No. 1 1, p. 13-20

  Problems to be solved by the present invention include chemical component limitation, inclusion composition limitation, improvement of interface state between nonmetallic inclusions contained in steel and steel as a parent phase, and further in nonmetallic inclusions By using a steel material that repairs damage inherent in steel, the steel for machine parts that exhibits a superior rolling fatigue life even when compared with steel that has improved the interface state between non-metallic inclusions and the parent phase. It is to provide a manufacturing method.

The inventor filled a metal container with a mixture of metal powder made from high carbon chromium bearing steel SUJ2 and a small amount of Al ₂ O ₃ powder, sealed it, and then extruded it hot. It was. Next, after normalizing at 870 ° C. and spheroidizing annealing at a maximum temperature of 800 ° C., the microstructure of the cross section was observed. Further, after the extruded steel is heated to 1150 ° C., which is higher than the temperature range proposed in Patent Document 3, after applying a hydrostatic compression stress of 140 MPa, the same normalizing and spheroidizing annealing is performed. The microstructure of the cross section after annealing was observed. As a result, as shown in FIG. 2, by applying hydrostatic compression stress under appropriate conditions, not only adhesion of the interface between the inclusion and the steel as the parent phase is achieved, but also cracks in the inclusion are repaired. I found out. Based on this knowledge, etc., means for solving the following problems were obtained.

Means for solving the problem is that in the first means, by mass ratio, O: ≦ 8 ppm, S: ≦ 0.008%, Al: 0.005 to 0.030%, and this steel The surface of the steel for machine parts in which the number ratio of MgO—Al ₂ O ₃ oxide in the total oxide inclusions in the steel is 70% or more is finally quenched and tempered as the steel parts. Prior to the step of imparting a hardness of 58 HRC or more , heating to 1105 to 1220 ° C., and imparting a hydrostatic compressive stress of 120 MPa or more, provides an interface between the nonmetallic inclusions in the steel and the steel that is the parent phase. Is a method for producing steel for machine parts having an excellent rolling fatigue life, characterized by repairing internal damage in non-metallic inclusions.

  As described above, in the method for producing steel for machine parts of the first means, the interface between the nonmetallic inclusions contained in the steel and the steel that is the parent phase is brought into close contact with the steel. For machine parts with excellent rolling fatigue life, with internal damage repaired and ultimately subjected to cutting as a steel part followed by partial or full quenching and tempering. It can be a steel product.

The heating temperature for applying the hydrostatic pressure of the above means is 1105 to 1220 ° C, preferably 1120 ° C to 1220 ° C. More desirably, the temperature is 1120 ° C to 1200 ° C. Note that the MgO-Al ₂ O ₃ based nonmetallic inclusions mentioned above, in addition to MgO-Al ₂ O ₃ as a stoichiometric ratio, in mass%, CaO: ≦ 15%, and / or SiO ₂ : It may have ≦ 15%.

  About the steel for machine parts used by said 1st means, the reason which shall be O: 8 <= ppm and S <= 0.008% by mass ratio is steel which is a nonmetallic inclusion and a parent phase in steel. Even if it is in a close contact state, when steel is formed into a part and then exposed to the surface of the part, oxide inclusions that have a detrimental effect on the life, and This is to reduce the size and frequency of sulfide inclusions.

The steel for machine parts used in the first means is preferably O: ≦ 6 ppm and S: ≦ 0.003%. Furthermore, in order to prevent the formation of soft inclusions compared to the MgO-Al ₂ O ₃ system, it is also possible to produce pure alumina (Al ₂ O ₃ ) that is hard and tends to agglomerate and form clusters in steel. In order to avoid this, Al: 0.005 to 0.030%, preferably 0.008 to 0.030%, more preferably 0.011 to 0.030% by mass.

Furthermore, in the steel for machine parts used for the first means, MgO—Al ₂ occupies the total composition of oxide inclusions under the regulation of the average composition of oxide inclusions. In the case where the number ratio of the O ₃ -based oxide is regulated to 70% or more, preferably 80% or more, these are oxide compositions having a high melting point. Since the oxide of this crystallized in a nearly spherical shape, even if the oxide crystallizes in such a nearly spherical shape, pure alumina (Al ₂ O, which tends to agglomerate and form clusters in the molten steel afterwards. ₃ ) Since the crystallization is suppressed, the oxide inclusions are dispersed in a small diameter and nearly spherical shape in the ingot after the molten steel solidifies, and therefore the final product is a rolling wheel. Non-metallic inclusions on the raceway surface as parts Even when exposed, effects are obtained stress concentration is reduced.

  By the way, by the plastic working given to the steel for machine parts in the process for obtaining the steel material shape or the subsequent process for obtaining the machine part shape, a gap is generated between the non-metallic inclusion and the parent phase, Furthermore, damage such as cracks may occur in the inclusions. As a countermeasure against this, as a manufacturing method of steel for machine parts, the steel is finally heated to 1105 to 1220 ° C. prior to the step of imparting a surface hardness of 58 HRC or more by cutting as the steel part and subsequent quenching and tempering. By applying a hydrostatic compressive stress of 120 MPa or more, the interface between the nonmetallic inclusions contained in the steel and the parent steel is brought into a close contact state, and internal damage in the nonmetallic inclusions is repaired. By using these steels, when used as final steel parts made by cutting and quenching and tempering these steels, it is possible to make steel products for machine parts that have an unprecedented rolling fatigue life. it can.

  According to a second means, a method for producing steel for machine parts includes a high carbon chrome bearing steel material defined in JIS G 4805, a carbon steel material for machine structure defined in JIS G 4051, and a JIS G 4805 steel composition. Structural steel (H steel) that guarantees the hardenability specified in G 4052, Alloy steel for machine structure specified in JIS G 4053, Alloy steel pipe for machine structure specified in JIS G 3441 , Carbon steel pipe for machine structure specified in JIS G 3445, Carbon steel for cold heading specified in JIS G 3507-1-Part 1: Wire material, Cold specified in JIS G 3507-2 Carbon steel for cold heading-Part 2: Wire, Alloy steel for cold heading specified in JIS G 3509-1-Part 1 Wire, Cold pressure specified in JIS G 3509-2 Use Alloy Steel - Part 2: A method of producing mechanical parts for steel which is excellent in rolling fatigue life of the first means, characterized in that any of the steel in the wire.

  In the third means, the method of manufacturing the steel for machine parts includes a plurality of plastic workings received in a process for obtaining a steel part shape made of this steel or a process for obtaining a machine part shape following the process. A method for producing steel for machine parts having excellent rolling fatigue life by a first means, characterized in that the last plastic processing excluding cutting of the plurality of processes is hot plastic processing.

  In the fourth means, the method of manufacturing steel for machine parts includes a plurality of times of plastic working received in a process for obtaining a steel material shape made of this steel or a process for obtaining a machine part shape following the process. The last plastic processing excluding cutting processing in a plurality of processes is warm plastic processing, which is a method for producing steel for machine parts having excellent rolling fatigue life by the first means.

  In the fifth means, the method of manufacturing the steel for machine parts used in the first means includes a plurality of times received in a process for obtaining a steel material shape made of the steel or a process for obtaining a machine part shape following the process. The last plastic working excluding the cutting work in these multiple processes is a cold plastic working, and the steel for machine parts having excellent rolling fatigue life by the first means It is a manufacturing method.

  By using the above-mentioned means of the present invention, the steel which is a parent phase with the nonmetallic inclusions contained in the steel material with respect to the steel for machine parts having a limited chemical composition and a limited nonmetallic inclusion composition As a result, it is possible to produce a steel material in which the damage inherent in the non-metallic inclusions is repaired. Therefore, compared to a steel whose interface state between the non-metallic inclusions and the parent phase is simply improved, A steel material for machine parts that exhibits a better rolling fatigue life can be obtained. By rolling and tempering a part made of the steel, the surface hardness is 58 HRC or more and the rolling fatigue is extremely low. It is possible to obtain a machine part having a long life.

Optical micrograph near the Al ₂ O ₃ non-metallic inclusions in SUJ2 steel of high carbon chromium bearing steel by hot extrusion, normalizing and spheroidizing annealing on SUJ2 steel prototyped by hot extrusion ₂ shows a cross-sectional microstructure in the vicinity of Al ₂ O ₃ -based non-metallic inclusions after applying. In an optical micrograph of the vicinity of Al ₂ O ₃ -based non-metallic inclusions in SUJ2 steel of high carbon chromium bearing steel by hot extrusion processing, after heating SUJ2 steel prototyped by hot extrusion to 1150 ° C, 140 MPa ₂ shows a cross-sectional microstructure in the vicinity of an Al ₂ O ₃ -based non-metallic inclusion after applying hydrostatic compression stress and further normalizing and spheroidizing annealing.

  The steel in the present invention required for machine parts such as bearings, gears, hub units, continuously variable transmissions, constant velocity joints, piston pins, etc., is generally a high carbon chromium bearing steel material defined in JIS G 4805, Carbon steel for machine structure specified in JIS G 4051, Structural steel (H steel) assured hardenability specified in JIS G 4052, Alloy steel for machine structure specified in JIS G 4053 Steel, Alloy steel pipe for machine structure specified in JIS G 3441, Carbon steel pipe for machine structure specified in JIS G 3445, Carbon steel for cold heading specified in JIS G 3507-1 Part 1: Wire rod, carbon steel for cold heading specified in JIS G3507-2-Part 2: Wire head, cold heading specified in JIS G 3509-1 Alloy steel-Part 1: Wire, Alloy steel for cold heading specified in JIS G 3509-2-Part 2: Wire, and related foreign standard steels are used. By the way, since the effects obtained by implementing the steel as the present invention described above are the same, the embodiment of the high carbon chromium bearing steel defined in the above JIS G 4805 will be described here. It shall be. However, the range of the chemical composition of the high carbon chromium bearing steel does not limit the chemical composition of all the steels targeted in the present invention.

  The steel of the above-mentioned JIS standard, which is the subject of the present invention, is generally 1) oxidation refining of molten steel using an arc melting furnace or converter, 2) reduction refining using a ladle refining furnace (LF), and 3) refluxing vacuum. Reflux vacuum degassing treatment (RH treatment) by degassing apparatus (RH), 4) casting of steel ingot by continuous casting method or ingot forming method, and 5) by hot rolling of steel ingot or hot forging. Or it manufactures through a plastic working process by cold rolling or cold forging. The process for obtaining the steel material shape in the present invention refers to each of the processes 1) to 5) described above, and the steel material shape refers to the shape of the shape steel, bar steel, pipe material, wire material, steel plate, and steel strip.

  Next, hot forging, sub-hot forging, warm forging, cold forging, rolling forging, cold rolling, cold header processing and drawing, and in some cases, drawing and cold header processing, and above A plastic working consisting of a combination of the respective processes and a heat treatment for softening and structure adjustment as necessary are performed, and further a cutting process is performed to form a member having a machine part shape. The process for obtaining the machine part shape in the present invention refers to each process described above.

  The hot in the hot plastic working such as hot forging in the present invention refers to a temperature range equal to or higher than the recrystallization temperature of the steel being processed, and the warm in the warm plastic working such as warm forging. Refers to a temperature range above room temperature and below the recrystallization temperature, and cold in cold plastic working such as cold forging refers to room temperature and the temperature range in the vicinity thereof.

  Subsequent to molding into the above-mentioned member having a machine part shape, in order to obtain a surface hardness of 58 HRC or more, total quenching (carbure quenching), carburizing quenching, carbonitriding quenching, nitriding quenching, carburizing and nitrogen quenching, or induction quenching, etc. Then, a quenching and tempering process, such as tempering after that, is performed according to the steel material and application, and a finishing process such as polishing and grinding is performed to produce the machine part targeted by the present invention. The quenching and tempering treatment method in the present invention refers to the treatment described above.

  In order to obtain the effect of the present invention, the steel is finally heated to 1105 to 1220 ° C. prior to the step of imparting a surface hardness of 58 HRC or higher by cutting as the steel part and subsequent quenching and tempering. In addition, by applying a hydrostatic compression stress of 120 MPa or more, the interface between the nonmetallic inclusions contained in the steel and the parent steel is closely adhered, and internal damage in the nonmetallic inclusions is As seen in the photomicrograph of FIG. 2, it needs to be in a repaired state. As the means, a method capable of applying a hydrostatic compression stress of 120 MPa or more after heating to 1105 to 1220 ° C. is suitable. For example, a hot isostatic pressing method, that is, a HIP method, a hot pressing method, or a hot forging method with complete closure or complete sealing is recommended as the construction method.

  In addition, hot forging, sub-hot forging, warm forging, cold forging, rolling forging that performs diameter expansion processing, cold header processing, or drawing processing without completely sealing with a mold In some cases, the hydrostatic compression stress cannot be applied equally to the steel material, or a gap is formed at the interface between the non-metallic inclusion and the parent phase steel due to the application of tensile stress in a specific direction, or non-metallic inclusion. The effect of the present invention cannot be obtained because cracks may occur inside the object, and particularly in the cold method or the warm method, the heating temperature is insufficient when applying the hydrostatic compression stress.

Next, the reason for limitation when applying hydrostatic compression stress will be described.
The higher the heating temperature of the steel material, the easier it is for the steel material to deform. Therefore, the higher the heating temperature of the steel, the more gaps or cavities that exist at the interface between the oxide-based nonmetallic inclusions and the parent phase disappear, and further, damage such as cracks in the nonmetallic inclusions is repaired. Therefore, the hydrostatic compression stress necessary for this is relatively low. As a result of earnest study, the inventor of the present application has found that the effect of the present invention is obtained if the steel material can be heated to 1105 to 1220 ° C. and a hydrostatic compression stress of 120 MPa or more can be applied to the steel material. Therefore, this invention shall heat a steel material to 1105-1220 degreeC, and shall provide the hydrostatic pressure compressive stress of 120 Mpa or more.

  The implementation conditions and the obtained effects of the embodiment of the present invention will be specifically described below. First, in Table 1 below, No. as a test material of the embodiment of the present invention is shown. The chemical composition of the steels 1-4 of 1-4 is shown by mass%. In addition, although these chemical composition remainders in Table 1 are Fe and unavoidable impurities of each steel, they are not shown in Table 1. No. 1 in Table 1 Steel No. 1 is SUJ2 steel in high carbon chromium bearing steel which is a steel satisfying the components of JIS G 4805. No. Steel No. 1 satisfies the regulations of steels subject to the production method of the present invention in the amounts of O, S and Al of the chemical components shown in Table 1. However, no. Steels 2 to 3 of 2 to 4 are those in which one or two of the O content, the S content, and the Al content of the chemical components do not satisfy the regulation of the steel targeted by the production method of the present invention.

  These are shown in No. 1 shown in Table 1. No. 1 Steel 1 and No. 1 Steels 2 to 4 are melted in an arc melting furnace to form molten steel, and after these molten steels are oxidatively refined, they are reduced and refined in a ladle refining furnace (LF), and further, a reflux-type vacuum degassing apparatus ( RH) was refluxed vacuum degassed (RH treated). Furthermore, these RH-treated molten steel was made into steel ingots by continuous casting, and these steel ingots were further made into steel materials having a diameter of 65 mm by hot rolling. Next, spheroidizing annealing was performed on these hot-rolled steel materials at 800 ° C.

Furthermore, the above-mentioned No. For each of the steel materials 1 to 4, the number ratio (%) of MgO—Al ₂ O ₃ -based oxide in the total oxide was evaluated and shown in Table 2 below. In order to accurately evaluate the number ratio of these MgO—Al ₂ O ₃ -based oxides, an oxide having an inclusion diameter of 1 μm or more in a test area in at least 40 mm ² selected from an arbitrary position of the steel cross section. for inclusions, by energy dispersive X-ray analysis and to perform the counting of the oxide number and component analysis of the oxide composition was performed on the test area 100 mm ² here. Based on the analysis result of the obtained oxide composition and the oxide count number, as shown in Table 2 below, the number ratio of the MgO—Al ₂ O ₃ -based oxide in the total oxide was calculated. In this calculation, oxides combined with sulfides and nitrides were counted as oxides.

  Further, in process condition 1 shown in Table 4, a steel plate having an outer diameter of 60 mm and a thickness of 5.8 mm is formed from the above-mentioned spheroidized and annealed steel material for a thrust type rolling fatigue test. Were cut into a disk shape having a hole with an inner diameter of 20 mm. In the process condition 2, the above-mentioned spheroidized and annealed steel was heated to a temperature of 650 ° C. above the room temperature and below the recrystallization temperature, and then placed into a disk shape similar to the above. processed. In the process condition 3, the spheroidized and annealed steel material was cold upset and cut into a disk shape similar to the above. These upsetting processes all simulate forging.

  The disk-shaped products obtained above were each subjected to hot isostatic pressing (HIP) treatment. The processing conditions are shown in Table 3 below. In Table 3, the press conditions of Condition A and Condition B satisfy the heating temperature of 1105 to 1220 ° C. and the press pressure of 120 MPa or more according to the present invention. As described in the remarks of Table 3, the invention It is an example. On the other hand, the press conditions of conditions C and D do not satisfy the heating temperature of 1105 to 1220 ° C. and the press pressure of 120 MPa or more according to the present invention, and are described in the remarks in Table 3. This is a comparative example.

  For the disk-shaped products of conditions A to D shown in Table 3, after performing normalization and spheroidizing annealing to adjust to the appropriate microstructure before quenching and tempering in the case of normal SUJ2 steel, A quenching and tempering treatment was applied. The normalization at this time is carried out under the condition of air cooling after holding at 865 ° C. for 1 hour, and the spheroidizing annealing is carried out under the condition of 800 ° C. In order to adjust the microstructure before proper quenching and tempering The heat treatment conditions are selected according to the steel type, and may be omitted if unnecessary. Next, after holding at 835 ° C. for 20 minutes with respect to the disk-shaped products of conditions A to D, quenching was performed by oil cooling, and then tempering treatment was performed at 170 ° C. for 90 minutes to obtain a desired hardness of 58 HRC or higher. . Further, cutting and polishing were performed to finish a disk specimen for performing a thrust type rolling fatigue test, and the rolling fatigue life was evaluated. In addition, the rolling element used the steel ball for commercially available thrust type rolling bearings.

The thrust type rolling fatigue test was performed under the condition that the maximum Hertz stress Pmax was 5292 MPa, and was performed 20 times for each of the conditions A to D of the press conditions shown in Table 3 above. The results, based on the Weibull distribution function, determine the total number of revolutions to flaking from the short life side test piece 5% proportion of the total specimen number occurs, which was used as L ₅ life. Table 4 below shows the surface hardness after quenching and tempering and the L ₅ life for each condition in which the thrust type rolling fatigue test was conducted. In addition, when the test piece of each condition reached 1 × 10 ⁸ cycle, a practically sufficient life was obtained, so the test was stopped even if it did not come off.

Symbols in the column of L ₅ lifetime of Table 4 "→" is either 1 × 10 ⁸ cycle of 20 test pieces, means not peel.

In Table 4, steel 1 satisfies the regulation of chemical components of the steel for machine parts and the regulation of the number ratio of MgO—Al ₂ O ₃ in the manufacturing method of the claims of the present invention. On the other hand, the steels 2 to 4 do not satisfy the regulation of steel for machine parts targeted by the manufacturing method of the claims of the present invention for any one or a plurality of chemical components and the number ratio of MgO—Al ₂ O _3. . Moreover, in Table 4, press conditions A and press conditions B consist of the conditions which satisfy | fill the structure of this invention which heats to 1105-1220 degreeC of this invention, and gives the hydrostatic compression stress of 120 Mpa or more. On the other hand, the press condition C and the press condition D consist of manufacturing conditions that do not satisfy the configuration of the present invention that is heated to 1105 to 1220 ° C. and imparts a hydrostatic compression stress of 120 MPa or more.

  According to the manufacturing conditions satisfying the regulations of chemical components and inclusions of steel for machine parts, which is the object of the manufacturing method of the present invention, and the heating temperature and hydrostatic pressure compressive stress satisfy the scope of the present invention Examples of the press condition A and the press condition B are steels for machine parts to be used in the manufacturing method according to the claims of the present invention regardless of whether the final process is hot plastic working, warm plastic working, or cold plastic working. In comparison with the comparative example of the pressing condition C and the pressing condition D according to the manufacturing conditions in which the heating temperature and the hydrostatic pressure compressive stress do not satisfy the claims of the present invention, while satisfying the regulation of chemical components and inclusions, rolling fatigue Life is much better. Furthermore, the chemical composition of steel for machine parts and the regulation of inclusions are satisfied by the manufacturing method of the claims of the present invention, and the heating temperature and the hydrostatic pressure compressive stress satisfy the scope of the claims of the present invention. The invention examples of the press condition A and the press condition B depending on the manufacturing conditions are covered by the manufacturing method of the claims of the present invention regardless of whether the final process is hot plastic working, warm plastic working, or cold plastic working. If the regulation of inclusions in steel for machine parts is satisfied, but the regulation of chemical components is not satisfied, or the regulation of chemical components and inclusions in the steel for machine parts used in the manufacturing method of the claims of the present invention is both If not satisfied, the heating temperature and the hydrostatic pressure compressive stress are compared with the comparative example of the pressing condition A and the pressing condition B according to the manufacturing conditions satisfying the claims of the present invention, or by the manufacturing method of the claims of the present invention. If the regulation of inclusions in steel for machine parts is satisfied, but the regulation of chemical components is not satisfied, or the chemical composition and inclusions in steel for machine parts targeted by the manufacturing method of the claims of the present invention are regulated In comparison with the comparative example of the press condition C and the press condition D according to the production conditions in which the heating temperature and the hydrostatic pressure compressive stress do not satisfy the claims of the present invention, the rolling fatigue life is clearly markedly higher. Is excellent.

Claims (5)

MgO—Al ₂ O ₃ -based oxidation that occupies O: ≦ 8 ppm, S: ≦ 0.008%, Al: 0.005-0.030%, and occupies all oxide-based inclusions in steel. Prior to the step of imparting a surface hardness of 58 HRC or higher by quenching and tempering as a steel part for the manufacturing method of steel for machine parts comprising 70% or more of the number ratio of objects, 1105 to 1220 ° C. To the interface between the non-metallic inclusions in the steel and the parent phase steel, and to repair internal damage in the non-metallic inclusions. A method for producing steel for machine parts having an excellent rolling fatigue life.   The manufacturing method of steel for machine parts is specified in JIS G 4052, a high carbon chromium bearing steel material whose steel composition is specified in JIS G 4805, a carbon steel material for machine structure specified in JIS G 4051. Structural steel with guaranteed hardenability (H steel), alloy steel for machine structure specified in JIS G 4053, alloy steel pipe for machine structure specified in JIS G 3441, specified in JIS G 3445 Carbon steel pipe for machine structural use, carbon steel for cold heading specified in JIS G 3507-1-Part 1: Wire rod, carbon steel for cold heading specified in JIS G 3507-2 Part 2: Wire, alloy steel for cold forging specified in JIS G 3509-1-Part 1 Wire material, Alloy steel for cold forging specified in JIS G 3509-2-Part 2 Method for manufacturing a machine component for steel excellent in rolling fatigue life of claim 1, characterized in that any of the steel composition in line.   The manufacturing method of the steel for machine parts is a cutting process of these multiple times in the multiple times of plastic working received in the process for obtaining the steel material shape or the process for obtaining the machine part shape following the process. The method for producing steel for machine parts having an excellent rolling fatigue life according to claim 1, wherein the last plastic working excluding the step is hot plastic working.   The manufacturing method of the steel for machine parts is a cutting process of these multiple times in the multiple times of plastic working received in the process for obtaining the steel material shape or the process for obtaining the machine part shape following the process. The method for producing steel for machine parts having an excellent rolling fatigue life according to claim 1, wherein the last plastic working excluding the step is warm plastic working.   The manufacturing method of the steel for machine parts is a cutting process of these multiple times in the multiple times of plastic working received in the process for obtaining the steel material shape or the process for obtaining the machine part shape following the process. The method for producing steel for machine parts having an excellent rolling fatigue life according to claim 1, wherein the last plastic working excluding the step is cold plastic working.