JP5403945B2 - Manufacturing method of machine parts with excellent rolling fatigue life - Google Patents

Description

  The present invention requires a rolling fatigue life in which non-metallic inclusions such as bearings, gears, hub units, continuously variable transmissions, constant velocity joints, piston pins and the like are the starting points of damage, and has a surface hardness of 58 HRC or higher. The present invention relates to a machine part made of steel used.

  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, as countermeasures from the aspect of steel materials, optimization of steel components and reduction of impurity elements are performed.

Among the impurity elements of the steel component, Al ₂ O ₃ , MnS, TiN and other non-metallic inclusions made of these are known to be particularly harmful because they are the starting points for damage to steel parts. Furthermore, it is known that the rolling fatigue life of steel parts becomes shorter as the diameter of these non-metallic inclusions is larger. For this reason, various types of high cleanliness steels with a small amount of nonmetallic inclusions, that is, high cleanliness of steel and extremely small large oxide nonmetallic inclusions with an inclusion diameter of 20 μm or more have been proposed (for example, patents). (See Literature 1 and Patent Literature 2.)

  Even when such a steel material made of high cleanliness steel is used, it is not sufficiently possible to suppress damage with a short life. For this reason, development has been actively conducted to reduce non-metallic inclusions in steel materials and to further reduce the diameter of the non-metallic inclusions.

JP 2006-63402 A Japanese Patent Laid-Open No. 06-192790 Iron and Steel, 94 (2008), p. 13 2008 Hyogo Prefectural University Dissertation, Kazuhiko Hiraoka (January 2008)

  The problem to be solved by the present invention is that the state of the interface between the nonmetallic inclusions contained in the steel and the parent phase steel can be achieved without reducing the nonmetallic inclusions and reducing their diameters during the production of the steel. By providing an improved steel material, it is to provide a machine part that is stable and excellent in rolling fatigue life as compared with a steel material in which nonmetallic inclusions are reduced and the diameter thereof is reduced at the time of manufacturing the steel.

  In order to improve the rolling fatigue life of bearings and other machine parts, it is important to reduce non-metallic inclusions from these steels for machine parts. Furthermore, if there are large non-metallic inclusions under the rolling surface of bearings and other machine parts, they will cause separation and damage to the machine parts. It is known that reducing non-metallic inclusions appearing at the site is particularly important for improving the life of bearings and other machine parts. Thus, many measures for reducing the diameter of non-metallic inclusions have been invented in mass production processes, but it has been difficult to stably reduce the diameter of non-metallic inclusions.

  The present inventors diligently examined the process leading to breakage in rolling fatigue, that is, peeling, by using an artificial defect material and observing cracks. In the process of crack initiation from non-metallic inclusions and progressing to separation, the initial crack in which the crack is displaced by the effect of stress concentration around the non-metallic inclusions (hereinafter referred to as “open-type initial crack”). ) I found out through the process. After that, it is the conventional knowledge that cracks are propagated through the propagation of cracks due to shear stress. This means that subsequent crack propagation and damage do not occur unless the opening-type initial crack found by the present inventors occurs. In addition, the opening-type initial crack occurs on the premise that a physical gap, that is, a cavity, is generated at the interface between the nonmetallic inclusion and the parent phase. It is also verified by stress calculation that no crack occurs (see Non-Patent Document 1 and Non-Patent Document 2).

Furthermore, the physical gap is any plastic processing that is always performed in the manufacturing process of steel materials and in the process of forming into members, that is, hot rolling, cold rolling, hot forging, warm forging, cold forging, rolling. It has also been found that it is caused by forging, cold rolling, cold header processing and drawing. FIG. 1 is a conceptual diagram showing an image obtained by observing the presence or absence of cavities around non-metallic inclusions with a scanning electron microscope (FE-SEM) after cutting out from hot-rolled steel and performing ion milling. In FIG. 1, reference numeral 2 is Al ₂ O ₃ and reference numeral 3 is a cavity. In particular, in machine structural steel, deoxidation with Al is usually performed. It has been confirmed that the Al ₂ O ₃ -based non-metallic inclusions generated at that time tend to generate cavities, particularly at the interface with the parent phase, due to the difference in deformability and shape from the parent material. The present invention has been made based on the above newly obtained knowledge.

That is, the means of the present invention for solving the above-mentioned problems is as follows. In the invention according to claim 1, in the method of manufacturing a machine part, a part or the whole of the steel for machine structure obtains 58HRC or more by a quenching and tempering method. After the mechanical structural steel is subjected to plastic working in the step for obtaining the steel material shape or the subsequent step for obtaining the machine part shape, it is heated to 800 to 1100 ° C. and subjected to 100 MPa or more before quenching and tempering. A process for producing a machine part having excellent rolling fatigue life, characterized by applying a hydrostatic pressure to perform a process of closely contacting an interface between a non-metallic inclusion contained in the steel and a steel as a parent phase. is there.

  In the invention of claim 2, the plastic working received in the step for obtaining the steel material shape or the subsequent step for obtaining the machine part shape is composed of a plurality of times, and the last plastic working in the plurality of times is hot plastic working. The method according to claim 1, wherein the mechanical part is excellent in rolling fatigue life.

  In the invention of claim 3, the plastic working received in the step for obtaining the steel material shape or the subsequent step for obtaining the machine part shape is composed of a plurality of times, and the last plastic working in the plurality of times is warm plastic working. The method according to claim 1, wherein the mechanical part is excellent in rolling fatigue life.

  In the invention of claim 4, the plastic working received in the step for obtaining the steel material shape or the subsequent step for obtaining the machine part shape is composed of a plurality of times, and the last plastic working in the plurality of times is cold plastic working. The method according to claim 1, wherein the mechanical part is excellent in rolling fatigue life.

  By adopting the above-described means, the steel material of the present invention can be made of the non-metallic inclusions and the parent phase contained in the steel by some plastic working without reducing non-metallic inclusions and reducing the diameter during the production of the steel materials. If the physical gaps or cavities generated at the interface with a certain steel can be eliminated and the interface consisting of these can be adhered, separation due to rolling fatigue starting from nonmetallic inclusions can be avoided, and as a result, This is an extremely excellent method of manufacturing a machine part that is expected to greatly improve the service life.

  By using the above-described means of the present invention, the nonmetallic inclusions in the steel and the parent phase steel can be reduced without reducing nonmetallic inclusions and reducing the diameter of the nonmetallic inclusions during the production of the steel. By using a steel material with no gaps, a machine part having a surface hardness of 58 HRC or more and excellent in rolling fatigue life that does not peel off can be obtained.

  For steels required for mechanical parts such as bearings, gears, hub units, continuously variable transmissions, constant velocity joints, piston pins, etc., high carbon chromium bearing steel materials generally defined in JIS G 4805, JIS G 4051 Carbon steels for machine structures specified in JIS, structural steels (H steel) with guaranteed hardenability specified in JIS G 4052, alloy steels for machine structures specified in JIS G 4053, JIS Alloy steel pipe for machine structure specified in 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, carbon steel for cold heading specified in JIS G 3507-2-Part 2: Wire, alloy steel for cold heading specified in JIS G 3509-1-No. 2 Part: Wire, Alloy steel for cold heading specified in JIS G 3509-2-Part 2: Wire, each related foreign standard steel, and each component similar steel and component modified steel are used . The steel for machine structure in the present invention refers to a steel material that satisfies the chemical components described above.

  This steel is generally 1) Oxidative refining of molten steel by arc melting furnace or converter, 2) Reductive refining by ladle refining furnace (LF), 3) Recirculation vacuum degassing by recirculation type vacuum degassing apparatus (RH) Treatment (RH treatment) 4) Casting of steel ingot by continuous casting or general ingot and 5) Plastic working process by hot rolling or hot forging of steel ingot and cold rolling or cold forging After that, steel material is manufactured. The process for obtaining the steel material shape in the present invention refers to the process described above, and the steel material shape refers to a shape steel, a steel 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, plasticity of the above combination The material is formed into a member by performing heat treatment or turning for the purpose of softening and structural adjustment as needed. The process for obtaining the machine part shape in the present invention refers to the process described above.

  In the present invention, the hot of the hot plastic working refers to a temperature higher than the recrystallization temperature of the steel, the warm of the hot plastic working refers to a temperature higher than the room temperature and lower than the recrystallization temperature, the cold of the cold plastic working. Refers to room temperature and its vicinity.

  Next, in order to obtain a surface hardness of 58 HRC or more, quenching and tempering processes such as total quenching (sub-quenching), carburizing quenching, carburizing and nitriding quenching, nitriding quenching, carburizing and nitriding quenching, and induction quenching are performed according to steel materials and applications Thus, a machine part targeted by the present invention is manufactured through a finishing process such as polishing or grinding. 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, mechanical parts are quenched and tempered, and are forcibly present at the interface between the oxide-based nonmetallic inclusion and the parent phase before obtaining a surface hardness of 58 HRC or more. It is necessary to go through a process for eliminating the cavity. As the means, a method that can apply a hydrostatic pressure of 100 MPa or more after heating to 800 to 1100 ° C. is preferable. For example, a hot isostatic pressing method, that is, a HIP method, a hot pressing method, or a hot forging method by complete closure or complete sealing is preferable.

  In hot forging, sub-hot forging, warm forging, cold forging, rolling forging, cold rolling, cold header processing, and drawing processing that are not completely sealed in the mold, all steel parts are subjected to hydrostatic pressure. Can not be imparted, or the material is continuously stretched in a certain direction, so the effects of the present invention cannot be obtained.

Next, the reason for limitation when applying hydrostatic pressure 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 material, the lower the hydrostatic pressure required to eliminate gaps or cavities existing at the interface between the oxide-based nonmetallic inclusions and the parent phase. As a result of intensive studies by the present inventors, the effect of the present invention can be obtained if heated to 800 to 1100 ° C. and a hydrostatic pressure of 100 MPa or more can be imparted, so that it is heated to 800 to 1100 ° C. and 100 MPa or more. And

  The implementation conditions and the obtained effects of the embodiment of the present invention will be specifically described. First, Table 1 shows the component composition of one sample material according to the embodiment of the present invention. In this sample material, it implemented about SUJ2 steel which is steel which satisfy | fills the component of JISG4805. Oxidation refining of molten steel in an arc melting furnace, reduction refining in a ladle refining furnace (LF), recirculation vacuum degassing treatment (RH treatment) in a recirculation type vacuum degassing device (RH), and continuous casting A steel ingot was cast, and the steel ingot was hot-rolled to produce a steel material. Next, spheroidizing annealing was performed at 800 ° C.

Further, the above spheroidally annealed steel material was cut into a washer shape which is a member of a thrust type rolling bearing in process condition 1. Process condition 2 was that the temperature was higher than room temperature and lower than the recrystallization temperature, heated to 600 ° C., and then set up, and then cut into the shape of a washer which was a member of a thrust type rolling bearing. In process condition 3, after cold upsetting, cutting was performed into the shape of a washer which is a member of a thrust type rolling bearing. The obtained washer-shaped products were each subjected to hot isostatic pressing (HIP) treatment. Table 2 shows the processing conditions. The pressing condition A and the pressing condition B satisfy the conditions of heating to 800 to 1100 ° C. and 100 MPa or more. The pressing condition C and the pressing condition D are pressing conditions, and the pressing condition E does not perform the HIP treatment, and these are not satisfied with the conditions of heating to 800 to 1100 ° C. and 100 MPa or more according to the present invention. These press condition A and press condition B washer-shaped products were held at 835 ° C. for 20 minutes, then quenched by oil cooling, and then subjected to tempering at 170 ° C. for 90 minutes to obtain a desired hardness of 58 HRC or higher. It was. Furthermore, it was ground and finished into a thrust type rolling bearing, and the rolling fatigue life was evaluated. The rolling element used was a commercially available thrust type rolling bearing ball.

The thrust type rolling fatigue test was performed at a maximum hertz stress Pmax of 5292 MPa, and was performed 10 times for each of the above pressing conditions. From the result, based on the Weibull distribution function, the total number of rotations until the 10% specimen was peeled from the short life side was obtained, and this was defined as the L ₁₀ life. Table 3 shows the L ₁₀ life evaluated from the surface hardness after quenching and tempering and the life of 10 test pieces under each condition in which the thrust type rolling fatigue test was conducted. In addition, the test piece of each condition was stopped when it reached 1 × 10 ⁸ cycle for convenience of the test even if it did not come off.

Incidentally, → is in L ₁₀ in Table 3 at 1 × 10 ⁸ cycle, means not peel. In Table 3, the surface hardness of the pressing condition A and the pressing condition B consisting of the conditions satisfying the configuration of heating to 800 to 1100 ° C. and 100 MPa or more of the present invention is 58 HRC or more. Also, heating to 800 to 1100 ° C. of the present invention, press forming from the condition which does not satisfy the structure of the above 100MPa conditions C~E the surface hardness is not less than 58 HRC. However, the invention example of the press condition A and the press condition B of the present invention has rolling fatigue compared to the comparative examples of the press conditions C to E regardless of whether the final is hot plastic working, warm plastic working, or cold plastic working. Life is much better.

After cutting out a sample from the hot-rolled steel material and performing ion milling, the image which observed the presence or absence of the cavity around a nonmetallic inclusion with a scanning electron microscope (FE-SEM) is shown with a conceptual diagram.

Explanation of symbols

1 Conceptual diagram 2 Al ₂ O ₃
3 cavity

Claims (4)

In a manufacturing method of a machine part that obtains 58 HRC or more by quenching and tempering a part or the whole of a machine structural steel, a process for obtaining the steel material shape of the machine structural steel or a subsequent machine part shape After being subjected to plastic working in the process and before quenching and tempering, it is heated to 800 to 1100 ° C. and applied with a hydrostatic pressure of 100 MPa or more, and the steel that is the parent phase of nonmetallic inclusions contained in the steel A process for producing a machine part having an excellent rolling fatigue life, characterized in that a treatment for closely adhering to the interface is performed.   The plastic processing received in the process for obtaining the steel material shape or the subsequent process for obtaining the machine part shape is composed of a plurality of times, and the last plastic processing in the plurality of times is a hot plastic working. The manufacturing method of the machine component excellent in the rolling fatigue life of Claim 1.   The plastic processing received in the process for obtaining the steel material shape or the subsequent process for obtaining the machine part shape is composed of a plurality of times, and the last plastic processing in the plurality of times is a warm plastic working. The manufacturing method of the machine component excellent in the rolling fatigue life of Claim 1.   The plastic working received in the process for obtaining the steel material shape or the subsequent process for obtaining the machine part shape is composed of a plurality of times, and the last plastic working in the plurality of times is a cold plastic working. The manufacturing method of the machine component excellent in the rolling fatigue life of Claim 1.

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