KR20120090942A - Method for manufacturing mechanical part excellent in rolling fatigue life - Google Patents

Abstract

Disclosed is a method for producing a mechanical component (7) having an excellent rolling fatigue life as a mechanical component (7) comprising a transmission (6) for rolling a rolling component. According to the method of the present invention, a hydrostatic pressure stress is applied to the inner diameter surface 2a of the ring base material 2 to form the transmission part 6 and cold forged, thereby driving the electric parts on the inner diameter surface 2a of the ring base material 2. The transmission part 6 for this transmission is formed, and the inner diameter of the ring base material 2 other than the transmission part 6 is enlarged. As a result, the interface state between the non-metallic inclusions contained in the steel which is the material of the ring base material 2 and the parent steel material is improved, and the ring-shaped machine part 7 having the transmission part 6 having an excellent rolling fatigue life in the inner diameter is improved. Are manufactured.

Description

METHOD FOR MANUFACTURING MECHANICAL PART EXCELLENT IN ROLLING FATIGUE LIFE}

Cross Reference of Related Application

This application claims the priority pursuant to Japanese Patent Application No. 2009-194962 filed on August 26, 2009 and Japanese Patent Application No. 2010-185927 filed on August 23, 2010, and their entire disclosures. It is hereby incorporated by reference.

Technical Field

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the manufacture of mechanical parts composed of steel materials such as bearings, gears, hub units, continuously variable transmissions, constant velocity joints, piston pins, and the like, and particularly mechanical parts of annular bodies requiring good electric fatigue life. It relates to the manufacture of.

In recent years, with the increase in the performance of various mechanical devices, the use environment in mechanical parts and devices requiring electric fatigue life has become very strict, and the life and improvement of the reliability of these mechanical parts and devices have been strongly demanded. In response to such a demand, as a countermeasure from the surface of steel materials, the optimization of a steel component and the reduction of the impurity element contained with a steel component are performed.

Among the impurity elements contained together with the steel components forming these mechanical parts and devices, Al ₂ O _{3 ,} MnS, TiN, and other non-metallic inclusions composed of these impurity elements are steel parts in mechanical parts and devices. Is the starting point of breakage. For this reason, it is known that these nonmetallic inclusions are especially harmful. Moreover, it is known that the larger the diameter of these nonmetallic inclusions, the shorter the rolling fatigue life of the steel part. For this reason, various kinds of high-cleanness steels having a small amount of nonmetallic inclusions, that is, high cleanliness of the steel, and extremely small oxide-based nonmetallic inclusions having a diameter of 20μm or more of extremely small metal inclusions have been proposed (for example, Patent Document 1). And Patent Document 2).

By the way, even if the steel material which consists of such high cleanliness steel is used for a mechanical component or an apparatus, suppressing the damage of these mechanical components or an apparatus with a short lifetime is not fully achieved yet. Therefore, the development which reduces the nonmetallic interference | inclusion in steel materials and is trying to small harden the nonmetallic interference | inclusion is actively performed.

On the other hand, even without reducing the non-metallic inclusions in steel materials and reducing their hardening, technology development to provide mechanical parts with excellent rolling fatigue life has been actively progressed. For example, (1) the technique of controlling the fiber flow on a transmission part at the time of manufacture by rolling of a part, and obtaining the outstanding rolling fatigue life (for example, refer patent document 3), Furthermore, (2 The technique (for example, refer patent document 4) which acquires the outstanding rolling fatigue life by applying compressive stress to a rolling part beforehand is proposed. Moreover, (3) the technique which obtains the outstanding rolling fatigue life is proposed by the applicant by making steel materials which improved the interface state of the nonmetallic inclusion contained in steel materials, and a steel phase which is a parent phase, and these are nonpatent literatures. 1 and Non-Patent Document 2.

In these non-patent literatures 1 and 2, the process leading to breakage, ie peeling, in electric fatigue is explained as follows. That is, in the process of generating and advancing the crack from the non-metallic inclusion and leading to peeling, an initial crack (hereinafter referred to as an "opening initial crack") process in which the crack is displaced by the stress concentration effect around the nonmetallic inclusion is referred to. Rough Thereafter, it is known to reach breakage through propagation of cracks due to shear stress. This means that subsequent crack propagation and breakage do not occur unless an opening type initial crack occurs. The initial crack of the opening type is assuming that a physical gap, or void, is generated at the interface between the nonmetallic inclusion and the mother phase. If the physical gap is not generated, the opening crack does not occur. None has been proven.

On the other hand, after cutting out from a hot rolled steel 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 in the conceptual diagram of FIG. 5, reference numeral 5 is non-metallic inclusions of Al ₂ O _3, reference numeral 4 is a cavity, that cavity. In particular, in mechanical steel, deoxidation with Al is usually performed. In the non-metallic inclusions 5 of the Al ₂ O ₃ system generated at that time, it is confirmed that the voids 4 are likely to be formed at the interface with the mother phase, in particular, from the difference in shape and deformation of the base metal. Therefore, in order to improve the rolling fatigue life of the mechanical component 7, it is effective to close the space | gap 4 which exists in the interface of the nonmetallic inclusion 5 and a mother phase, or to reduce the volume of the space | gap 4.

Patent Document 1: Japanese Patent Application Laid-Open No. 2006-63402 Patent Document 2: Japanese Patent Application Laid-Open No. 06-192790 Patent Document 3: Japanese Patent Application Laid-Open No. 4-357324 Patent Document 4: Japanese Patent Application Laid-Open No. 2006-77854

Non Patent Literature 1: Iron and Steel, 94 (2008), p.13 Non-Patent Document 2: Hyogo Prefectural University Degree Thesis, Hiraoka Kazuhiko (January 2008)

The present invention relates to the above (3), and the conventional steel by improving the interface state between the non-metallic inclusions contained in the steel, which is the material of the ring-shaped base material to be used for cold forging by the plastic working To provide a method for manufacturing a mechanical part having a rolling portion having a superior rolling fatigue life on the inner diameter surface of a ring-shaped base metal as compared to a method for manufacturing a steel material for reducing non-metallic inclusions and miniaturizing non-metallic inclusions during production. It is for the purpose.

According to the present invention, there is provided a method for producing a mechanical component having excellent rolling fatigue life, wherein the mechanical component is provided with a rolling section for rolling the rolling component on an inner diameter surface of a ring-shaped workpiece base material provided for cold forging. Cold forging is made by applying hydrostatic pressure stress on the inner diameter surface of the ring-shaped base material to be formed with the rolling part, thereby forming a rolling part for rolling the electric parts on the inner diameter surface of the ring-shaped workpiece base material, and ring-shaped base material other than the rolling part. There is provided a method comprising a process of providing a ring-shaped mechanical component having an electric rolling section having an excellent rolling fatigue life by enlarging the inner diameter thereof. By the action of the hydrostatic pressure, the pores existing at the interface between the non-metallic inclusions in the steel and the parent steel are closed in the direction of closing, whereby a mechanical part having excellent rolling fatigue life can be manufactured. On the other hand, the ring-shaped processing base material provided for cold forging is preferably a steel pipe or a hot forging ring.

According to a preferred aspect of the present invention, there is provided the above method, wherein the hydrostatic stress is at least 1000 MPa. By forming a rolling surface by applying a hydrostatic stress of at least 1000 MPa at the time of cold forging, it is possible to manufacture a mechanical component having excellent rolling fatigue life by closing the voids present at the interface between the nonmetallic inclusions contained in the steel and the parent steel.

According to the production method of the present invention, hydrostatic stress (preferably at least 1000 MPa) is applied during cold forging of a ring-shaped workpiece, so that nonmetallic inclusions and non-metallic inclusions are not reduced during the production of steel. It is possible to close or reduce the voids formed at the interface with the parent steel, and as a result, to avoid peeling due to electric fatigue, which is the starting point of non-metallic inclusions, to produce a mechanical part having an excellent electric part which greatly improves the electric fatigue life. Can be.

It is a schematic diagram explaining the cold forging process (before compression process) of the ring base material which concerns on this invention.
1B is a schematic diagram illustrating a cold forging process (after compression processing) of a ring base material according to the present invention.
2 is a longitudinal sectional view of a rolling bearing produced by the method of the present invention.
3 is a diagram showing an analysis by CAE of a rolling bearing manufactured by the method of the present invention.
4A is a conceptual diagram showing a nonmetallic inclusion before the cold forging and voids around it.
4B is a conceptual diagram showing the nonmetallic inclusions after the cold forging and the voids around them.
FIG. 5 is a conceptual diagram showing nonmetallic inclusions and voids around the hot rolled steel. FIG.

Examples of the steel required for the production method of the present invention include machine structural steel, bearing steel, and the like.

These steels include: 1) oxidation refining of molten steel by an arc melting furnace or converter, 2) reduction and refining of a blast furnace refining furnace (LF), and 3) reflux. Reflux vacuum degassing treatment (RH treatment) of the vacuum degassing apparatus (RH) 4) Casting of steel ingots by continuous casting or general ingot and 5) Hot rolling or hot rolling of steel ingots It is made of steel through a process of plastic working by forging and cold rolling or cold rolling and cold forging.

The ring base material 2 used for the manufacturing method of this invention can be manufactured as follows. First, the steel materials manufactured as mentioned above (for example, steel materials prescribed | regulated to JIS G 4805 (2008), JIS G 4051 (2005), JIS G 4104, JIS G 4105), and go through the process of the above plastic working Manufacture steels. This steel is processed into an exchange or hot forging ring by hot working such as an assel mill, extrusion or hot forging, and then the steel pipe or hot forging ring is cut into a predetermined length. Further, by cutting the outer diameter and inner diameter surfaces of the cut steel pipe or hot forging ring, a steel pipe or hot forging ring having a predetermined dimension is obtained as the ring base material 2.

The construction method of this invention is demonstrated based on FIG. The ring base material 2 of a predetermined shape is subjected to appropriate lubrication treatment to be at a temperature near room temperature. This ring base material 2 is set in the annular restraint frame 1 of a press apparatus as shown to FIG. 1A. In the restraint frame 1, the metal mold | die 3 is arrange | positioned up and down, respectively, and this metal mold | die 3 is being fixed to the movable part which is not shown in the upper and lower sides of a press apparatus. As the press device starts the machining motion, the upper hatch 3a of the fixed mold 3 and the annular upper hatch 3b disposed around it start the downward movement in the direction of the arrow. do. The ring base material 2 provided at a predetermined position in the mold 3 is formed by the lowered top hatch 3a and the annular top hatch 3b, and the inner diameter 2a of the ring base material 2 and its upper end face. (2b) is subjected to plastic working. In addition, with the lowering of the upper hatch 3a and the annular upper hatch 3b, the ring base material 2 is pressed downward, and simultaneously from the lower hatch 3c and the annular lower hatch 3d. The inner diameter 2a and the lower end surface 2c of the ring base material 2 are subjected to plastic working. In other words, the upper end face 2b of the ring base material 2 is pressed downward in accordance with the lowering of the upper hatch 3a and the annular upper hatch 3b, and as a result, the lower end face of the ring base material 2 ( 2c) is pushed up relatively by the lower hatch 3c and the annular lower hatch 3d. At the end of the processing, the ring base material 2 is subjected to compression processing by cold forging from both the upper hatch 3a and the annular upper hatch 3b, and the lower hatch 3c and the annular lower hatch 3d. In response, hydrostatic stress acts and the void 4 existing between the mother phase of the steel of the ring base material 2 and the nonmetallic inclusion 5 is closed.

By performing said compression process on the ring base material 2, as shown to FIG. 1B, in the vicinity of the transmission part 6 of the mechanical component 7 to be manufactured, the base image of the steel of the ring base material 2, and its nonmetallic interference | inclusions A hydrostatic stress acting which brings about the effect of closing the space | gap 4 which exists between (5) acts. In this case, in order to fully acquire the effect of closing the space | gap 4, it is preferable to apply hydrostatic pressure stress of at least 1000 Mpa to the vicinity of the transmission part 6 at the time of cold forging. By applying such hydrostatic stress, the void 4 existing between the nonmetallic inclusion 5 and the steel of the parent-shaped ring base material 2 changes in the direction of closing or in the direction of decreasing the volume of the void 4. By this change, peeling by the rolling fatigue which makes the base metal inclusion 5 the breakdown point is avoided. As a result, the mechanical part 7 which has the transmission part 6 of the outstanding rolling fatigue life can be obtained.

Example  One

As an Example of this invention, the conditions of implementation and the obtained result are demonstrated. First, Table 1 shows the component composition of the test material (供 試 材) provided as the steel type of the steel of the ring base material 2.

In this example, the test materials of the steel type shown in Table 1 were carried out. First, oxidizing and refining molten steel in an arc melting furnace, reducing and refining this in a scouring and refining furnace LF, and reducing oxygen components in the molten steel by degassing in a reflux vacuum degassing apparatus RH. Through molten steel, it was manufactured into steel ingots by continuous casting. The steel ingots were made of steel by hot rolling as usual, then steel tubes were used with an Asselmill, and then they were prepared as steel pipes subjected to conventional spheroidizing heat treatment.

After sawing the steel pipe which consists of the test materials shown in Table 1 of the outer diameter phi 80mm and thickness 8.7mm obtained above to 27.2mm in the width direction of the steel pipe length, the outer diameter and the inner diameter are cut and processed, and the outer diameter φ78.5mm, thickness 7.0 It was made of steel pipe of mm. Subsequently, the said steel pipe was lubricated conventionally and it was set as the ring base material 2 for cold forging. As shown in Fig. 2, the ring base material 2 has a width of 28.1 mm, an outer diameter of 77.9 mm, and a central portion of the inner diameter of the protrusion 2d and the transmission part 6 having a width of 7.5 mm and an inner diameter of 61.8 mm. The following cold forging was performed using the metal mold | die 3 which designed the outer diameter 2a of the outer side to obtain the cold forging of 68.2 mm. In the cold forging, the ring base metal 2 and the metal mold 3 are processed at a temperature of about 40 ° C. by the metal mold 3 shown in FIG. Cold forging was performed at a surface pressure of 1800 to 1900 MPa.

By this cold forging, as can be expected from the drawing by CAE analysis shown in FIG. 3, it is thought that the hydrostatic stress of about 1500 MPa is acting at the maximum in the vicinity of the transmission part 6 at most.

Moreover, the schematic diagram of the change of the space | gap 4 which exists between the base metal inclusion 5 and the steel which is the ring base material 2 before and after this cold forging is shown to FIG. 4A and FIG. 4B. FIG. 4A shows the shape of the nonmetallic inclusion 5 of the ring base material 2 before cold forging, and the void 4 is formed adjacent to the nonmetallic inclusion 5. However, as shown in FIG. 4B, after the cold forging, it was confirmed that the voids 4 existing between the non-metallic inclusion 5 and the steel of the ring base material 2 were closed.

Furthermore, in order to carry out the evaluation of the rolling fatigue life of the mechanical part 7 which is the effect of the present invention, the molding load and the molding method during cold forging are controlled, and as shown in Table 2, four types of steel conditions and Various test pieces were taken at five processing conditions.

These sample specimens are then turned into orbital plate shapes, which are members of thrust-shaped rolling bearings, and subjected to quenching and tampering, whereby S45C is HRB94 or more, S53C is HRC20 or more, SUJ2 and SUJ3. Obtained a hardness of 58HRC or more. The polishing was further performed to finish the thrust rolling bearing, and to evaluate the electric fatigue life. On the other hand, a commercial thrust-type rolling bearing ball was used as the rolling element.

The evaluation result of the above-mentioned electric rolling fatigue life was performed in three steps of (circle): very good, (circle): good, and x: backward. The results are shown in Table 3. Evaluation shows the steel conditions of Table 2 before the hyphen "-" among the conditions of Table 3, and the processing conditions of Table 2 after the hyphen "-". Since hardness is different for every steel type, the same evaluation cannot be made. Therefore, evaluation of the rolling fatigue life was performed by the comparison between the same steel types. As the maximum compressive stress during cold forging increased to 1500 MPa, it was confirmed that the rolling fatigue life improved as indicated by ◎. On the other hand, when tensile stress acts in the vicinity of the transmission part 6 by cold forging, "1-D" of the conditions of Table 3 processed by the processing condition D of Table 2, "2-D", "3 -D "and" 4-D ", evaluation is x, and the rolling fatigue life does not improve. On the other hand, although not shown in the table, even if manufactured by hot forging, the effect which improves a rolling fatigue life is also confirmed. However, the cold forging of the present invention is superior in that the steel temperature is not increased.

From the result of evaluation of the rolling fatigue life test by the test piece according to the above four steel type conditions and five processing conditions, by applying a predetermined compressive stress (preferably at least 1000 MPa) near the rolling surface during cold forging, It has been found that the gap 4 between the non-metallic inclusion 5 and the steel which is the ring base material 2 is closed or reduced, and a role in which the rolling fatigue life is improved is achieved. In addition, it goes without saying that the improvement of the rolling fatigue life is achieved as mentioned above also in the ring material for outer ring of a double row track ring.

Example  2

A test piece was produced in the same manner as in Example 1 except that a hot forged ring was manufactured instead of a steel pipe. The manufacturing method of hot forging ring is as follows. First, the molten steel is oxidized and refined in the arc melting furnace, which is reduced and refined in the scouring and refining furnace LF, and further, the oxygen component in the molten steel is reduced by degassing in the reflux vacuum degassing apparatus RH, and then passed through the molten steel. Manufactured from steel ingots by continuous casting. The ingot is made of steel by hot rolling as usual, and then the billet cut by shading (a washer that does not loosen the bolt even if the nut is loosened with a washer sandwiched between the bolt and the nut) is cut by hot forging with an outer diameter of φ80 mm and thickness of 8.7. mm and a width 27.2 mm hot forging ring, and these were prepared as a hot forging ring subjected to conventional spheroidizing heat treatment. The hot forging ring made of the test materials shown in Table 1 obtained above is cut into an outer diameter and an inner diameter to obtain a hot forging ring having an outer diameter of 78.5 mm and a thickness of 7.0 mm. Subsequently, the hot forging ring is subjected to a conventional lubrication treatment to obtain a ring base material 2 for cold forging. Cold forging using the ring base material 2 and subsequent steps are the same as in Example 1. Also in this case, the same result as in Example 1 is obtained.

Claims (4)

A method of manufacturing a mechanical component with excellent rolling fatigue life, comprising a rolling section for rolling the rolling component on an inner diameter surface of a ring-shaped base metal that the mechanical component provides for cold forging.
By cold forging by applying hydrostatic pressure stress to the inner diameter surface of the ring-shaped workpiece base to be formed in the rolling portion, a rolling portion for rolling the electric component is formed on the inner diameter surface of the ring-shaped workpiece base material, and a ring shape other than the rolling portion. And a step of expanding the inner diameter of the workpiece base material to provide a ring-shaped mechanical part having a rolling part having excellent rolling fatigue life.
The method according to claim 1, wherein the ring-formed base material provided for the cold forging is a steel pipe.
The method according to claim 1, wherein the ring-shaped workpiece base material provided for the cold forging is a hot forging ring.
The method according to any one of claims 1 to 3, wherein the hydrostatic stress is at least 1000 MPa.

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