JP5896713B2 - Manufacturing method of machine parts with excellent rolling fatigue life - Google Patents

Description

  The present invention relates to the manufacture of mechanical parts made of steel, such as bearings, gears, hub units, continuously variable transmissions, constant velocity joints, piston pins, etc., and has an annular shape that requires good rolling fatigue life as its characteristics. The present invention relates to the production of machine parts.

  In recent years, with the improvement in performance of various machinery and equipment, the use environment for machine parts and devices that require a rolling fatigue life has become extremely severe, and the improvement in the life and reliability of these machine components and devices has been strongly enhanced. It has been demanded. In response to such demands, as countermeasures from the aspect of steel materials, optimization of steel components and reduction of impurity elements contained together with steel components are performed.

Among the impurity elements contained together with the steel components forming these machine parts and devices, Al ₂ O ₃ , MnS, TiN and other non-metallic inclusions composed of these impurity elements are damaged steel parts in machine parts and devices. Is the starting point. For this reason, these non-metallic inclusions are known to be particularly harmful. Furthermore, it is known that the rolling fatigue life of steel parts becomes shorter as the diameter of these non-metallic inclusions is larger. Therefore, there are various high cleanliness steels with a small amount of non-metallic inclusions, that is, with a high degree of cleanliness of the steel and with a large amount of non-metallic inclusions having a diameter of 20 μm or more and extremely small number of non-metallic inclusions. It has been proposed (see, for example, Patent Document 1 and Patent Document 2).

  By the way, even when such steel materials made of high cleanliness steel are used for machine parts and devices, it is still not possible to sufficiently prevent these machine parts and devices from being damaged in a short life. For this purpose, development has been actively conducted to reduce the non-metallic inclusions in the steel material and to further reduce the diameter of the non-metallic inclusions.

  On the other hand, technology development that provides machine parts with excellent rolling fatigue life is being actively promoted without reducing non-metallic inclusions in steel and reducing the diameter thereof. For example, (1) Technology for obtaining an excellent rolling fatigue life by controlling the fiber flow (forged streamline) on the rolling part at the time of manufacturing by rolling parts (see, for example, Patent Document 3), ( 2) A technique for obtaining an excellent rolling fatigue life by applying a compressive stress to the rolling portion in advance (for example, see Patent Document 4) has been proposed. In addition, (3) a technique for obtaining an excellent rolling fatigue life has been filed by the applicant by using a steel material with an improved interface state between the nonmetallic inclusions contained in the steel material and the parent phase steel, These are published in Non-Patent Document 1 and Non-Patent Document 2.

  These Non-Patent Document 1 and Non-Patent Document 2 describe the process leading to breakage in rolling fatigue, that is, peeling. In other words, in the process of crack initiation from non-metallic inclusions and progressing to delamination, the initial crack in which the crack is displaced by the stress concentration effect around the non-metallic inclusions (hereinafter referred to as “open-type initial crack”) It goes through the process. After that, it is known that the crack is propagated through the propagation of the crack due to the shear stress. This means that if the initial crack of the opening type does not occur, subsequent crack propagation and damage do not occur. 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 has also been verified that no cracks occur.

On the other hand, after cutting out from a hot rolled steel material and performing ion milling, an image obtained by observing the presence or absence of cavities around non-metallic inclusions with a scanning electron microscope (FE-SEM) is shown in the conceptual diagram of FIG. In FIG. 5, reference numeral 5 is a non-metallic inclusion of Al ₂ O ₃ , and reference numeral 4 is a cavity or void. 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 5 produced at that time are likely to generate voids 4 particularly at the interface with the parent phase due to the difference in deformability and shape from the parent material. Therefore, in order to improve the rolling fatigue life of the mechanical component 7, it is effective to close the gap 4 existing at the interface between the nonmetallic inclusion 5 and the parent phase or to reduce the volume of the gap 4.

JP 2006-63402 A Japanese Patent Laid-Open No. 06-192790 JP-A-4-357324 JP 2006-77854 A

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 a technique related to (3) described in paragraph 0005 above, in which a nonmetallic inclusion contained in a steel material that is a ring-shaped material and a steel material that is a parent phase. By improving the interface state by plastic working, the inner diameter of the ring-shaped material is superior to conventional steel manufacturing methods that reduce non-metallic inclusions and reduce the diameter of non-metallic inclusions during steel manufacturing. Another object of the present invention is to provide a method of manufacturing a machine part which is a rolling part having a rolling part having a rolling fatigue life.

According to a first aspect of the present invention for solving the above-mentioned problems, in the invention of claim 1, in the manufacture of a mechanical part having a rolling part in which the rolling part rolls on the inner diameter of the ring-shaped material, an attempt is made to form the rolling part. Forging in which the hydrostatic pressure of 1.5 times the yield stress of the material is applied to the inner diameter surface of the ring-shaped material to be compressed, and the plastic strain in the rolling direction of the rolling component is 0.10 or more. A method of manufacturing a ring-shaped machine part having a rolling part with excellent rolling fatigue life, characterized in that a rolling part on which the rolling part rolls is formed on the inner diameter surface of the ring-shaped material by machining. . The forging process may be hot or cold.
That is, at the time of forging , the inner diameter surface of the ring-shaped material to be formed with the rolling part is applied with a hydrostatic pressure of at least 1.5 times the yield stress of the material in the rolling direction of the rolling component. By forming a compression rolling surface in which the plastic strain due to compression of the steel becomes 0.10 or more, the voids present at the interface between the nonmetallic inclusions in the steel and the parent steel are directed to close. Thus, it is possible to manufacture a mechanical component having an excellent rolling fatigue life.

The manufacturing method of the present invention applies a compressive hydrostatic stress to the inner diameter surface of the ring-shaped material during the forging process of the ring-shaped material of the above-described means, so that the static static pressure is at least 1.5 times the yield stress of the material. By applying a hydraulic stress and forming a rolling surface where the plastic strain due to compression in the rolling direction of the rolling parts is 0.10 or more , non-metallic inclusions are reduced and small diameter is produced during steel production Even if it is not intended to be made, the voids generated at the interface between the nonmetallic inclusions and the parent phase steel can be closed or reduced, and as a result, peeling due to rolling fatigue starting from the nonmetallic inclusions as the fracture origin Therefore, it is possible to manufacture a machine part having an excellent rolling part with a significantly improved rolling fatigue life.

It is the schematic explaining the forge process of the ring base material of this invention. It is a longitudinal cross-sectional view of the rolling bearing manufactured by the method of this invention. It is a figure which shows the analysis by CAE of the rolling bearing manufactured by the method of this invention. It is a conceptual diagram which shows the nonmetallic inclusion before and behind forging, and the space | gap of the circumference | surroundings. It is a conceptual diagram which shows the nonmetallic inclusion of the conventional hot rolled steel materials, and the space | gap of the circumference | surroundings.

  EMBODIMENT OF THE INVENTION The form for implementing this invention is demonstrated below with reference to a table | surface and drawing. First, steel materials required for the manufacture of machine parts that are rolling parts of the present invention include steel for machine structure and bearing steel.

  These steel materials are: 1) oxidation refining of molten steel by an arc melting furnace or converter, 2) reductive refining by a ladle refining furnace (LF), 3) recirculation vacuum degassing treatment by a recirculation type vacuum degassing apparatus (RH) ( RH treatment) 4) Casting of steel ingot by continuous casting or general ingot and 5) Hot rolling or hot forging and cold rolling of steel ingot, or plastic working process by cold rolling and cold forging It is manufactured to steel materials through.

  Through the series of steps 1) to 5), a steel material specified in JIS such as the above-mentioned steel for machine structure and bearing steel is manufactured, and this steel material is processed by an Assel mill, extruded, or heat such as hot forging. After processing into a steel pipe by the inter-process, this steel pipe was cut into a predetermined length. Furthermore, the ring base material 2 of the present invention was obtained by cutting the outer diameter and the inner diameter of the cut steel pipe into a steel pipe having a predetermined size by a cutting process.

The construction method of the present invention will be described with reference to FIG. The ring base material 2 having a predetermined shape or a mold for processing is subjected to appropriate lubrication treatment, and the ring base material 2 having a temperature near room temperature or a temperature suitable for hot working is constrained in an annular shape of the press device. Set in the frame 1 as shown in FIG. In the restraint frame 1, molds 3 are respectively arranged up and down, and these molds 3 are respectively fixed to operating parts (not shown) above and below the press device. As the press apparatus starts the processing operation, the upper punch 3a of the fixed mold 3 and the annular upper punch 3b arranged around the upper punch 3b start a downward movement in the arrow direction. In the ring base material 2 set at a predetermined position in the mold 3, the inner diameter 2a and the upper end surface 2b of the ring base material 2 are subjected to plastic working by the upper punch 3a and the annular upper punch 3b that have been lowered. Further, as the upper punch 3a and the annular upper punch 3b are lowered, the ring base material 2 is pushed downward, and at the same time from the lower punch 3c and the annular lower punch 3d to the inner diameter 2a and the lower end surface 2c of the ring base material 2. Receives plastic working. That is, the upper end surface 2b of the ring base material 2 is pushed downward as the upper punch 3a and the annular upper punch 3b are lowered. As a result, the lower end surface 2c of the ring base material 2 is lowered to the lower punch 3c and the annular lower punch 3d. Is pushed up relatively. At the end of processing, the ring base material 2 is subjected to compression processing by forging from both the upper punch 3a and the annular upper punch 3b, and the lower punch 3c and the annular lower punch 3d, and the ring base material which is to form the rolling part 6 2 is applied with a hydrostatic pressure stress that is 1.5 times the yield stress of the material, and the compressive plastic strain in the rolling direction in the vicinity of the rolling part 6 is 0.10 or more. By performing the forging process, the gap 4 existing between the steel parent phase of the ring base material 2 and the non-metallic inclusion 5 is closed.

  By applying the above-described compression processing to the ring base material 2, as shown in FIG. 1B, the ring base material is placed in the vicinity of the rolling part 6 of the rolling part, which is the machine part 7 to be manufactured. The effect of closing the void 4 existing between the parent phase of steel No. 2 and its nonmetallic inclusions 5 is imparted. In FIG. 4 (FIG. 4), which exists between the nonmetallic inclusion 5 and the steel of the ring base material 2 which is the parent phase, by compressing the action of the hydrostatic stress of compression and the plastic strain in the rolling direction. It changes to the direction which the space | gap 4 shown to a) closes, or the direction where the volume of the space | gap 4 decreases. By this change, peeling due to rolling fatigue starting from the nonmetallic inclusion 5 is avoided. As a result, the machine part 7 having the rolling part 6 having an excellent rolling fatigue life is obtained.

  As an example of the present invention, conditions for implementation and results obtained will be described. First, Table 1 shows the component composition of the test material used as the steel type of the steel material of the ring base material 2.

  In this example, the test materials of the steel types shown in Table 1 were used. First, the molten steel is oxidatively refined in an arc melting furnace, this is reduced and refined in a ladle smelting furnace (LF), and further the oxygen component in the molten steel is reduced by degassing in a reflux type vacuum degasser (RH). The molten steel was manufactured into a steel ingot by continuous casting. The steel ingot was made into a steel material by hot rolling as usual, and then made into a steel pipe by an Assel mill, and these were prepared into a steel pipe subjected to a conventional spheroidizing heat treatment. It is also conceivable that the steel material is made into a ring-shaped material by conventional hot forging.

After the steel pipe made of the specimen shown in Table 1 having an outer diameter of 90.0 mm and a wall thickness of 9.75 mm obtained above is cut into a width of 30.0 mm, which is the longitudinal direction of the steel pipe, the outer diameter and inner diameter are cut. Was made into a ring-shaped material having an outer diameter of 89.5 mm and a wall thickness of 9.0 mm. Next, the ring-shaped material was subjected to a conventional lubrication treatment to obtain a ring base material 2 for forging. It is also conceivable that the steel material is made into a ring-shaped material by conventional hot forging and cut into the ring base material 2. As shown in FIG. 2, the ring base material 2 has a width of 29.0 mm, an outer diameter of φ90.0 mm, a central portion of the inner diameter of 10.0 mm in width and a protruding portion 2d having an inner diameter of φ65.0 mm, a rolling portion. 6 of the outer consisting inner diameter 2a 75.0 mm of the forged product is obtained so designed mold 3, that the upper punch 3a shown in FIG. 1, the annular punch 3b, following forging with a lower punch 3c and the annular punch 3d Processing was performed. Forging was performed for both cold forging and hot forging. In the case of cold forging, both the ring base material 2 and the mold 3 are at a temperature around room temperature, and the processing method using the mold 3 shown in FIG. 1 above is a load of 4000 to 4200 kN at the time of molding, and the processing surface pressure at the time of molding. Cold forging was performed at 1800 to 1900 MPa. In the case of hot forging, the ring base material 2 is heated to a temperature of 900 ° C. and 1100 ° C., and the processing method using the mold 3 shown in FIG. Hot forging was performed to a pressure of 700 to 1000 MPa. The yield stress of the material is about 500 MPa around room temperature, about 120 MPa around 900 ° C., and about 50 MPa around 1100 ° C.

  With this forging, as can be seen in the CAE analysis drawing shown in FIG. 3, at least 1.5 times the hydrostatic stress of the material yield stress acts in the vicinity of the rolling part 6. In the vicinity of the rolling part 6, it is considered that a compressive plastic strain is generated in the rolling direction.

  Moreover, the schematic diagram of the mode of the change of the space | gap 4 which exists between the nonmetallic inclusion 5 and the steel which is the ring base material 2 before and after this forging process is shown in FIG. FIG. 4A shows the shape of the non-metallic inclusion 5 of the ring base material 2 before forging, and a gap 4 is formed adjacent to the non-metallic inclusion 5. However, as shown in FIG. 4B, after the forging process, only the non-metallic inclusions 5 exist, and therefore the voids 4 existing between the non-metallic inclusions 5 and the steel that is the ring base material 2. Was confirmed to be closed.

  Furthermore, in order to examine the evaluation of the rolling fatigue life of the rolling part which is the mechanical part 7 which is the effect of the present invention, Table 2 shows processing conditions A to R and steel type conditions 1 to 4 of SUJ2, SUJ3, S45C. , S53C steel type. From these, test pieces of processing conditions A to R were collected. In Table 2, processing conditions A, B, C, D, E, and F are cold forging with a processing start temperature of 20 ° C., and processing conditions G, H, I, J, K, and L are processing start temperatures. Is hot forging at 900 ° C., and processing conditions M, N, O, P, Q, and R are hot forging at a processing start temperature of 1100 ° C. The maximum hydrostatic pressure stress of each material is 1 to 6 times the yield stress of the material, as shown in Table 2. The generated plastic strain in the rolling direction is as shown in Table 2 in terms of compressive strain or tensile strain. The life evaluation, which is an evaluation of the fatigue life of rolling parts, is excellent, ◯ is good, △ is acceptable, and those whose life evaluation is ◎, ○, △ are generated plasticity All strains are compressive strains. On the other hand, those having a life evaluation of x indicate impossibility, and the plastic strains are all tensile strains.

  These collected test pieces are turned into a washer disk shape that is a member of a thrust type rolling bearing and subjected to quenching and tempering, so that SUJ2 and SUJ3 are 58 HRC or higher, S45C is HRB94 or higher, and S53C is HRC20. The above hardnesses were obtained. Furthermore, these were polished to finish thrust type rolling bearings, and a comprehensive evaluation of rolling fatigue life was performed. A commercially available thrust-type ball for a rolling bearing was used as the rolling element.

  Table 3 shows the results of the comprehensive evaluation of the rolling fatigue life. This is a comprehensive evaluation based on combinations of the processing conditions A to R and the steel type conditions 1 to 4 in Table 2. The rolling fatigue life was evaluated by comparison between the same steel types. First, when the maximum hydrostatic stress during cold forging at a processing start temperature of 20 ° C. is 1.5 times the yield stress of the material and a compressive plastic strain occurs, as shown in Table 3, It was confirmed that the dynamic fatigue life was improved as indicated by ○ or ◎. When the generated plastic strain in the rolling direction is tensile, the evaluation of the rolling fatigue life is x, and the rolling fatigue life is not improved. On the other hand, when the maximum hydrostatic pressure stress during hot forging at a processing start temperature of 900 ° C. or 1100 ° C. is 1.5 times the yield stress of the material, and a compressive plastic strain occurs, the rolling fatigue life is The improvement was confirmed as indicated by ○ or ◎. When the generated plastic strain in the rolling direction is tensile, the evaluation of the rolling fatigue life is x, and the rolling fatigue life is not improved.

  From the results of the evaluation shown in Table 3 of the rolling fatigue life test using the test piece under the 18 processing conditions under the above four steel grade conditions, at least in the vicinity of the rolling surface, whether cold forging or hot forging. Steel which is a non-metallic inclusion 5 and a ring base material 2 by applying a hydrostatic stress of compression 1.5 times or more of the yield stress of the steel and processing the plastic strain in the rolling direction to be compressed. It was found that the gap 4 between the two was closed or reduced, and the role of improving the rolling fatigue life was played. Needless to say, in the ring material for the outer ring of the double row raceway, the rolling fatigue life is improved as described above.

DESCRIPTION OF SYMBOLS 1 Restraint frame 2 Ring base material 2a Inner diameter 2b Upper end surface 2c Lower end surface 2d Protrusion part 3 Die 3a Upper punch 3b Annular upper punch 3c Lower punch 3d Annular lower punch 4 Air gap 5 Non-metallic inclusion 6 Rolling part 7 Machine part

Claims (1)

In the manufacture of a machine part having a rolling part in which the rolling part rolls on the inner diameter of the ring-shaped material, the inner surface of the ring-shaped material to be formed with the rolling part has a yield stress of 1.5 times or more of the material. Rolling in which the rolling part rolls on the inner diameter surface of the ring-shaped material by forging that gives compressive hydrostatic stress and the plastic strain in the rolling direction of the rolling part becomes 0.10 or more. A method for manufacturing a ring-shaped mechanical component having a rolling part with excellent rolling fatigue life, wherein the part is formed.

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