JP2017106076A - Manufacturing method of steel for machine component excellent in rolling motion fatigue life - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing method of a steel for machine component exhibiting more excellent rolling motion fatigue life than a steel with improved boundary state between a non-metallic inclusion and a base phase.SOLUTION: There is provided a manufacturing method of a steel for machine component targeting the steel which is a machine component having surface hardness of 58 HRC or more by a cutting processing and hardening and tempering treatment, wherein the steel has O:≤8 ppm and S:≤0.008% by mass percentage, an oxide-based non-metallic inclusion generated by deoxidation with adding an oxidant containing Si in addition to Al or without adding an Al deoxidant is softened compared to a MgO-AlO-based oxide-based non-metallic inclusion, capable of providing the steel for machine component with a boundary between the non-metallic inclusion and the base phase steel in an adhesion state and internal breakage in the inclusion repaired shown in the Figure 2 by adding isostatic compression stress of 100 MPa or more at 1105 to 1220°C on the steel for machine structure small in difference of deformation performance from the steel of the base phase, having a machine component shape by a plurality of plastic processes and excellent in rolling motion fatigue life.SELECTED DRAWING: Figure 2

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 become 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 with the use of a steel material having a high cleanliness, it is not possible to sufficiently suppress short-life damage. Therefore, attempts have been made to reduce non-metallic inclusions in steel (high cleanliness) and further reduce the diameter of the non-metallic inclusions. The well-known 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. Since the rolling fatigue life of steel parts decreases as the diameter of these non-metallic inclusions increases, the above concept is considered to be generally correct. Accordingly, various high cleanliness steels have been proposed in which the amount of nonmetallic inclusions is reduced, that is, the cleanliness of the steel is increased, and the large oxide nonmetallic inclusions having an inclusion diameter of 20 μm or more are extremely reduced. (For example, refer to Patent Document 1 and Patent Document 2.) However, even in these cases, it is not always easy to reduce the diameter of the nonmetallic inclusion stably.

On the other hand, in Si deoxidized steel containing Al: 0.003% or less, Ti: 0.003% or less, Zr: 0.0010% or less, and Si: 0.05 to 4.0% in mass%. In addition, inclusions in this Si deoxidized steel are in mass% SiO ₂ : 45% or more, oxide (R ₂ O) of alkali metal R (R = Na, K, Li): 0.5 to 10 An invention relating to a Si-deoxidized steel excellent in fatigue strength and a method for producing the same is proposed (see, for example, Patent Document 3). However, the present invention has less harmful large inclusions compared to conventional steel, and the remaining inclusions are ductile inclusions, and the inclusions are finely dispersed, Si deoxidized steel with excellent fatigue strength and its manufacturing method have been proposed, and its effect has been confirmed by the rotating bending fatigue test, but it is effective against sulfide inclusions harmful to rolling fatigue life. Therefore, no regulation is made and the rolling fatigue life is not necessarily excellent.

  On the other hand, the present inventors have examined in detail the process leading to breakage, that is, separation in rolling fatigue by observing the cracking process of the artificial defect material, and the existence of gaps around cavities and nonmetallic inclusions. It was shown that there is a high possibility of playing a dominant role in crack initiation (for example, see Non-Patent Document 1). Based on these findings, the present inventors obtain a steel material shape in a machine part manufacturing method in which 58 HRC or more is obtained by a method of quenching and tempering a part or the whole of a machine structural steel. After being subjected to plastic working in the process for obtaining the shape of the machine part or the subsequent process for forming the machine part, it is heated to 800 to 1100 ° C. and subjected to hydrostatic compression stress of 100 MPa or more before quenching and tempering. Proposes a manufacturing method of machine parts with excellent rolling fatigue life, characterized by performing a process of closely adhering the interface between non-metallic inclusions contained in steel and steel as a parent phase (for example, Patent Documents) 4)).

Furthermore, the present inventors have added a oxidizer containing Si in addition to normal Al in a method of manufacturing a machine part that obtains 58 HRC or more by quenching and tempering a part or the whole of steel for machine structure. Alternatively, the oxide-based nonmetallic inclusions that are generated by deoxidation without adding a deoxidizing agent composed of Al are compared with the oxide-based nonmetallic inclusions of Al ₂ O ₃ .MgO-based, After this machine structural steel, which has been softened to reduce the difference in deformability from the parent phase, has undergone plastic working in the process for obtaining the steel material shape or the subsequent process for obtaining the machine part shape Before quenching and tempering, the steel for mechanical structure is heated to 780 to 1100 ° C. and a hydrostatic pressure of 80 MPa or more is applied, and the non-metallic inclusions contained in the steel and the steel that is the parent phase The process of adhering the interface We propose a method for manufacturing a machine component having excellent rolling fatigue life characterized (e.g., Patent Document 5).

By bringing the interface between the matrix and the steel into close contact by these methods, a significant improvement in the life that has not been achieved in the past has been achieved. This physical gap such as the interface between the parent phase and steel is a plastic process that is always performed in the manufacturing process of steel materials and the process of forming into members, that is, hot rolling, cold rolling, hot forging, It has been pointed out that it may be caused by warm forging, cold forging, rolling forging, cold rolling, cold header processing and drawing. Further, the present inventors are steel members used for machine parts having a surface hardness of 58 HRC or more, wherein the amount of O in the steel is 8 ppm or less, the amount of S is 0.008 mass% or less, and the rolling elements are loaded. When taking and observing a test piece having a test area of 40 mm ² or more and 400 mm ² or less in parallel with the rolling surface from the rolling surface that receives and rotates, the effective harmful length is 10 μm or more. Observe all inclusions with a harmful width of 2 μm or more, calculate the gap ratio defined below for each inclusion, and the average of the observed gap ratios of all the inclusions is 8% or less and is observed. Of all the inclusions, when the ratio of 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 (for example, , See Patent Document 6.). In the present invention, the clearance ratio is defined as follows.
Gap ratio = gap area / (gap area + inclusion area)

  The effective harmful length here is the length including the gap around the inclusion in addition to the actual inclusion, and the effective harmful width includes the gap around the inclusion in addition to the actual inclusion. (For example, refer to Patent Document 4). All of the inventions by these inventors focus on the control of the interface between inclusions and the parent phase.

  In the three inventions of these Patent Documents 4 to 6, sufficient attention is paid to the adhesion between the nonmetallic inclusions and the matrix. However, Patent Document 6 does not mention any damage inherent in non-metallic inclusions and has not been considered. Further, in Patent Document 4 and Patent Document 5, the temperature at which the hydrostatic pressure stress is applied and the hydrostatic pressure compressive stress are not sufficiently high, so the adhesion between the interface between the inclusion and the steel as the parent phase is obvious. Although effective, it was less effective for repairing internal damage such as cracks introduced into the inclusions themselves with plastic working. The inventors have found that there is room for further improvement in life by focusing on the internal damage of the 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 JP 2005-264335 A Japanese Patent No. 5403945 Japanese Patent No. 5473249 Japanese Patent Application Laid-Open No. 2014-55346

Iron and Steel, 94 (2008), 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 heating the extruded steel to 1150 ° C., which is higher than the temperature range proposed in Patent Document 4 and Patent Document 5, after applying a hydrostatic compression stress of 140 MPa, the same normalization, And the microstructure of the cross section after spheroidizing 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, the means for solving the following problems were obtained.

In the first means, a steel having an O content of 8 ppm or less and an S content of 0.008% or less by mass ratio is obtained by adding a deoxidizer containing Si in addition to normal Al or by removing Al. By performing deoxidation without adding an acid agent, the generated oxide-based non-metallic inclusions are softened compared to the MgO-Al ₂ O _3- based oxide-based non-metallic inclusions. In the process of giving a surface hardness of 58 HRC or higher to the steel for machine structural use in which the difference in deformability from the parent phase is reduced, by finally cutting the steel part and subsequent quenching and tempering. Prior to heating to 1105 ° C. to 1220 ° C. and further applying a hydrostatic compression stress of 100 MPa or more, the interface between the nonmetallic inclusions contained in the steel and the steel that is the parent phase is brought into a close contact state, and Repair internal damage in non-metallic inclusions It is an excellent method for producing mechanical parts for steel rolling fatigue life characterized.

  The heating temperature for applying the hydrostatic compression stress prior to the cutting and subsequent quenching and tempering steps as the steel part manufacturing method in the above means is preferably 1120 ° C to 1220 ° C, and more preferably Is 1120 ° C. to 1200 ° C.

By the way, in the steel for machine parts used in the first means, the reason for setting the O amount to 8 ppm or less and the S amount to 0.008% or less in the mass ratio is that it is in close contact with the steel that is the parent phase in the steel. Even if it exists, when steel is formed into a part and then appears on the surface of the part, oxide inclusions and sulfide inclusions that have a detrimental effect on the service life This is to reduce the size and frequency of objects. In these, more preferably, the O amount is 6 ppm or less and the S amount is 0.003% or less in terms of mass ratio. Furthermore, in order to make steel containing oxides softened compared to MgO-Al ₂ O ₃ oxide-based nonmetallic inclusions, the steel for machine parts used in the present invention is made of ordinary Al. In addition, deoxidation is performed without adding a deoxidizer containing Si or adding a deoxidizer composed of Al.

Usually, general mechanical structural steel is deoxidized with Al. For this reason, the oxide-based non-metallic inclusions produced increase in number of MgO—Al ₂ O ₃ and Al ₂ O ₃ systems. All of these are hard inclusions, and have a problem that they tend to aggregate after refining and take a shape classified into group B defined in JIS G 0555. Because of this problem, when hydrostatic pressure is applied, cavities existing at the interface between the oxide-based nonmetallic inclusions and the parent phase are completely eliminated, and internal damage in the nonmetallic inclusions is repaired. Therefore, the condition range when applying an appropriate hydrostatic compression stress is limited. Therefore, assuming that the deformability of the oxide-based nonmetallic inclusions contained in the steel is close to that of the parent phase, when the hydrostatic compression stress is applied, the oxide-based nonmetallic inclusions and the parent phase are mainly used. The effect of completely eliminating the cavities existing at the interface is enhanced. Furthermore, if the oxide inclusion is softer than the MgO—Al ₂ O ₃ system, the effect of repairing the internal damage of the inclusion accompanying the plastic processing of steel is enhanced. That is, as a means for this, non-oxide-based non-oxides produced by adding a deoxidizing material containing Si in addition to normal Al, or without adding a deoxidizing agent made of Al. It is to soften the metal inclusions and reduce the difference in deformability from the parent phase.

  By the way, 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 inclusion and the parent phase due to the plastic working applied to the steel, and further in the inclusion. Damage such as cracks may occur. Therefore, as a countermeasure against the occurrence of these gaps and damage, the steel is first 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. By heating and applying a hydrostatic compression stress of 100 MPa or more, the interface between the nonmetallic inclusions contained in the steel and the parent phase steel is brought into close contact, and internal damage in the inclusions is repaired. By using this steel, it is possible to obtain steel for machine parts that has an unprecedented rolling fatigue life.

  Further, in the second means, the method of manufacturing the steel for machine parts includes a high carbon chrome bearing steel material whose steel composition is specified in JIS G 4805, and a carbon steel material for machine structure specified in JIS G 4051. , Structural steel (H steel) with guaranteed hardenability specified in JIS G 4052, alloy steel for machine structure specified in JIS G 4053, alloy for mechanical structure specified in JIS G 3441 Steel pipes, carbon steel pipes for machine structures specified in JIS G 3445, carbon steel for cold heading specified in JIS G 3507-1-Part 1: Wire, 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, specified in JIS G 3509-2 Alloy steel for cold heading-Part 2: A method for producing steel for machine parts excellent in rolling fatigue life by the first means characterized in that it has any composition of wire.

  Further, in the third means, the method of manufacturing the steel for machine parts includes a plurality of processes in which the plastic processing received in the process for obtaining the steel material shape or the subsequent process for obtaining the machine part shape is performed. 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 during the round process is hot plastic processing.

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

  Further, according to a fifth means, the method of manufacturing steel for machine parts includes a plurality of processes in which plastic processing received in a process for obtaining the steel material shape or a subsequent process for obtaining a machine part shape is performed. The last plastic processing excluding cutting in a round is cold plastic processing, which is a method for producing steel for machine parts having excellent rolling fatigue life by the first means.

  By using the above-mentioned means of the present invention, improvement in the interface state between the non-metallic inclusions contained in the steel material and the steel as the parent phase with respect to the steel in which the chemical components are limited and the inclusions are regulated. In addition, it is possible to produce a steel material in which the damage inherent in the nonmetallic inclusions is repaired, so that superior rolling compared to steel with improved interface state between the nonmetallic inclusions and the parent phase. It is possible to produce steel for machine parts that exhibits fatigue life, has a surface hardness of 58 HRC or more, and has an extremely low possibility of peeling, and excellent in rolling fatigue life.

A micrograph of the microstructure of the cross section of Al ₂ O ₃ -based non-metallic inclusions (corrosion is caused by Picral) after normalizing and spheroidizing annealing of the SUJ2 steel prototype manufactured by hot extrusion is there. Of SUJ2 steel prototype in hot extrusion, after heating 1150 ° C., Grant isostatic compressive stress of 140 MPa, further subjected to a normalizing and spheroidizing annealing, Al ₂ O ₃ based nonmetallic inclusions A micrograph of the microstructure of the cross section in the vicinity of the object (corrosion is caused by Picral) shows that the internal damage has been repaired with the interface between the nonmetallic inclusions in the steel and the parent phase steel in close contact.

  The steel for machine parts in the present invention required for machine parts such as bearings, gears, hub units, continuously variable transmissions, constant velocity joints, piston pins and the like is generally a high carbon chromium bearing defined in JIS G 4805. Steel materials, carbon steel materials for machine structures specified in JIS G 4051, structural steel materials (H steel) that ensure hardenability specified in JIS G 4052, machine structures specified in JIS G 4053 Alloy steel for machinery, Alloy steel pipe for machine structure specified in JIS G 3441, Carbon steel pipe for machine structure specified in JIS G 3445, Carbon for cold heading specified in JIS G 3507-1 Steel-Part 1: Wire rod, carbon steel for cold heading specified in JIS G3507-2-Part 2: Wire, wire JIS G 3509-1 Alloy steel for cold heading-Part 1: Wire material, Alloy steel for cold heading specified in JIS G 3509-2-Part 2: Wire, and their respective foreign standard steels are used. By the way, since all the effects obtained by the implementation of the steel for machine parts as the present invention described above are the same, the embodiment in the high carbon chrome bearing steel material defined in JIS G 4805 is here described. Shall be explained. However, the range of the chemical composition of the steel carbon chromium bearing steel does not limit the chemical composition of all the above-mentioned steel for machine parts used 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 device (RH), 4) casting of ingot by continuous casting method or ingot-making method, and 5) by hot rolling or hot forging of ingot. 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 a shape steel, a bar, a pipe, a wire, a steel plate, and a 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 thereafter, is performed according to the steel material and application, and a finishing process such as polishing and grinding is performed to produce a 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. By applying an isostatic pressure stress of 100 MPa or more, the interface between the nonmetallic inclusions contained in this steel and the parent phase steel is brought into close contact, and internal damage in the nonmetallic inclusions is As seen in the photomicrograph 2 of FIG. As the means, a means capable of applying a hydrostatic compression stress of 100 MPa or more after heating to 1105 to 1220 ° C. is suitable. For example, as the means, hot isostatic pressing, that is, HIP, hot pressing, hot forging by complete closure or complete sealing is recommended.

  In addition, in hot forging, sub-hot forging, warm forging, cold forging, rolling forging that performs diameter expansion processing, cold header processing and drawing processing performed without completely sealing with a mold, Since the hydrostatic compression stress cannot be applied equally to steel materials, or tensile stress is applied in a specific direction, a gap is formed at the interface between the nonmetallic inclusions and the parent steel, or inside the nonmetallic inclusions. In some cases, cracking may occur, and particularly in the cold construction method and the warm construction method, the effect of the present invention cannot be obtained due to insufficient heating temperature when applying hydrostatic compression stress.

  Next, the reasons for limiting the temperature and pressure when applying hydrostatic compression stress will be described. A steel material is easily deformed as its heating temperature increases. Therefore, the higher the heating temperature of the steel, the more necessary to eliminate gaps or cavities existing at the interface between the oxide-based nonmetallic inclusions and the parent phase, and to repair damage such as cracks in the nonmetallic inclusions. The hydrostatic compression stress can be relatively low. As a result of intensive studies by the inventor, the effect of the present invention can be obtained by heating to 1105 to 1220 ° C. and applying a hydrostatic compression stress of 100 MPa or more. It is heated to 0 ° C. and applied with a hydrostatic compression stress of 100 MPa or more.

  The implementation conditions and the obtained effects of the embodiment of the present invention will be specifically described. For this reason, No. 1 as the test material of the embodiment is shown in Table 1. The chemical composition of the steels 1-4 of 1-4 is shown by the mass%. Table 1 shows SUJ2 steel in high carbon chromium bearing steel, which is a steel satisfying the components of JIS G 4805. Further, the O amount and S amount of chemical components are as defined in the claims of the present invention. A total of three types were prepared: Steel 1 and Steel 3 that satisfy the regulations of steels targeted by the manufacturing method, and Steel 2 that does not satisfy the regulations. These steels are subjected to oxidation refining of the molten steel in an arc melting furnace, reductive refining in a ladle refining furnace (LF), and reflux vacuum degassing treatment (RH treatment) in a reflux type vacuum degassing apparatus (RH). Then, steel ingots were formed by casting in continuous casting, and these steel ingots were made into steel materials by hot rolling. Next, this steel was subjected to spheroidizing annealing at 800 ° C.

  The implementation conditions and the obtained effects of the embodiment of the present invention will be described more specifically. First, Table 1 shows the component compositions of Steel 1 to Steel 3, which are test materials according to the embodiment of the present invention. Steels 1 to 3 which are the test materials are all SUJ2 steels, but the steels 2 are out of the regulation of chemical components in the steel for machine parts targeted by the manufacturing method of the claims of the present invention. is there. As described above, all types of steel types are oxidative refining of molten steel in an arc melting furnace, reductive refining in a ladle refining furnace (LF), and recirculation vacuum degassing treatment in a recirculation vacuum degassing apparatus (RH) ( RH treatment), a steel material having a diameter of 65 mm was produced by hot rolling of the steel ingot following the casting of the steel ingot by continuous casting. Steels 1 and 2 as test materials were deoxidized with Si and Mn without adding Al during deoxidation, and 0.003% and 0.002% of Al shown in Table 1 are It is contained as an inevitable impurity. Steel 3 has been deoxidized by Al, which is generally performed. These were subsequently subjected to spheroidizing annealing at 800 ° C. on the hot-rolled steel.

  With respect to the above-mentioned spheroidized steel, in process condition 1 shown in Table 3, a hole having an inner diameter of 20 mm is formed in the center of a steel plate having an outer diameter of 60 mm and a thickness of 5.8 mm for a thrust type rolling fatigue test. Cut into a hollow disk shape. In process condition 2, after heating up to a temperature of 620 ° C. which is not less than room temperature and not more than the recrystallization temperature, it was cut into a disk shape for a thrust type rolling fatigue test. In process condition 3, after cold upsetting, it was cut into a disk shape similar to the above. All these upsetting processes simulate forging.

  The obtained disk-shaped products were each subjected to hot isostatic pressing (HIP) treatment. Table 2 shows the processing conditions. Conditions A and B of the pressing conditions in Table 2 satisfy the conditions of heating at 1105 to 1220 ° C. and pressing pressure of 100 MPa or more according to the present invention. In the conditions C, D and E of the pressing conditions, either the heating at 1105 to 1220 ° C. of the present invention or the pressing pressure condition of 100 MPa or more is not satisfied. After subjecting the disk-shaped products of these pressing conditions A to E to 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, the disc-shaped products of conditions A to E were held at 835 ° C. for 20 minutes, then quenched by oil cooling, and then tempered 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 test, and a rolling fatigue life evaluation was performed. In addition, the rolling element used the steel ball for commercially available thrust type rolling bearings.

The thrust type rolling fatigue test was performed 20 times for each of the press conditions A to E under the condition that the maximum Hertz stress Pmax was 5292 MPa. The results, based on the Weibull distribution function, the 5% ratio of the test piece of the total specimen number from the short life side, determine the total number of rotations until flaking occurs, and it was used as a L ₅ life. Table 3 below shows the surface hardness after quenching and tempering and the L ₅ life for each condition in which a 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.

In addition, the symbol “→” in the column of L ₅ life of steel 1 in Table 3 means that none of the 20 test pieces was 1 × 10 ⁸ cycle and was not peeled off. The steel 1 in Table 3 satisfies the structure of the steel targeted in the manufacturing conditions of the claims of the present invention, while the steel 2 is a steel of which the S content and the O content are the target of the manufacturing conditions in the claims. The steel 3 exceeds the upper limit of regulation, and although the amount of S and O satisfy the claims, Steel 3 deviates from the target steel under the production conditions of the claims of the present invention from the point of melting by Al deoxidation. is there. In Table 3, press conditions A and B are heated from 1105 to 1220 ° C. according to the present invention, and from the manufacturing conditions satisfying the constitution of the claims of the present invention to apply hydrostatic compression stress of 100 MPa or more. Become. On the other hand, the pressing conditions C to E are the 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 100 MPa or more. The press according to the manufacturing conditions satisfying the regulation of the chemical composition of the steel for machine parts and the deoxidation method, and the heating temperature and the hydrostatic pressure stress satisfying the claims of the present invention. The invention examples of the condition A and the press condition B are covered by the manufacturing conditions in the claims of the present invention regardless of whether the final process is hot plastic working, warm plastic working, or cold plastic working. Rolling compared to comparative examples of press conditions C to E, which satisfy the chemical component of machine part steel and the regulation of deoxidation method, but the heating temperature and hydrostatic pressure compression stress do not satisfy the production conditions of the claims of the present invention The fatigue life is remarkably excellent. Furthermore, the heating temperature and the hydrostatic pressure compressive stress satisfy the claims of the present invention, although the chemical component of the steel for machine parts or the deoxidation method is not satisfied under the manufacturing conditions of the claims of the present invention. Compared with the comparative example of the pressing condition A and the pressing condition B depending on the manufacturing conditions, or does not meet the regulation of either the chemical component of the steel for machine parts or the deoxidation method which is the subject of the manufacturing conditions of the claims of the present invention. In addition, the rolling fatigue life is clearly superior to the comparative examples of the press conditions C to E in which the heating temperature and the hydrostatic pressure compressive stress do not satisfy the production conditions of the claims of the present invention. Furthermore, when the production conditions of the present invention are applied to steel 1 deoxidized with Si and Mn, compared to steel 3 melted by ordinary Al deoxidation, the optimum hydrostatic compression stress is applied. This is also excellent in that the condition range is expanded to a lower compressive stress.

Claims (5)

In a mass ratio, O: ≦ 8 ppm, S: ≦ 0.008%, deoxidation in which an oxidizing agent containing Si in addition to Al is added, or deoxidation in which no Al deoxidizing agent is added, The generated oxide-based non-metallic inclusions are softened compared to MgO-Al ₂ O _3- based oxide-based non-metallic inclusions, and the difference due to the deformability of the parent phase steel is reduced. Prior to the step of imparting a surface hardness of 58 HRC or higher to the steel for machine parts, by finally cutting the steel part and subsequent quenching and tempering, the hydrostatic compression stress of 1105 to 1220 ° C. and 100 MPa or higher. Is excellent in rolling fatigue life, characterized in that the interface between the nonmetallic inclusions in the steel and the parent phase steel is brought into close contact, and internal damage in the nonmetallic inclusions is repaired. Manufacturing method for steel for machine parts.   The manufacturing method of steel for machine parts is as follows: high carbon chrome bearing steel with JIS G 4805, carbon steel for mechanical structure with JIS G 4051, structural steel with guaranteed hardenability with JIS G 4052 ( Steel H), alloy steel for machine structure of JIS G 4053, alloy steel pipe for machine structure of JIS G 3441, carbon steel pipe for machine structure of JIS G 3445, carbon steel for cold heading of JIS G 3507-1 Part 1: Wire, JIS G 3507-2 cold head carbon steel-Part 2: Wire, JIS G 3509-1 cold head steel-Part 1: Wire, or JIS G 3509-2 The method for producing steel for machine parts having excellent rolling fatigue life according to claim 1, wherein the steel composition is any one of the following steel alloys for cold heading: Part 2: Wire.   The manufacturing method of steel for machine parts consists of a plurality of plastic workings received in the process for obtaining the steel material shape or the process for obtaining the machine part shape following the process, and cutting of these multiple processes. 2. The method for producing steel for machine parts having an excellent rolling fatigue life according to claim 1, wherein the last plastic processing excluding the processing is hot plastic processing.   The manufacturing method of steel for machine parts consists of a plurality of plastic workings received in the process for obtaining the steel material shape or the process for obtaining the machine part shape following the process, and cutting of these multiple processes. 2. The method for producing steel for machine parts having an excellent rolling fatigue life according to claim 1, wherein the last plastic processing excluding the processing is warm plastic processing.   The manufacturing method of steel for machine parts consists of a plurality of plastic workings received in the process for obtaining the steel material shape or the process for obtaining the machine part shape following the process, and cutting of these multiple processes. The method for producing steel for machine parts excellent in rolling fatigue life according to claim 1, wherein the last plastic processing excluding the processing is cold plastic processing.