Method for Manufacturing Mechanical Part Excellent in Rolling Fatigue Life

Abstract

Disclosed is a method for producing a mechanical part superior in rolling fatigue life. The mechanical part includes a rolling portion for a rolling element to roll along an inner diameter surface of an annular workpiece material subjected to cold forging. The method includes performing cold forging by applying a hydrostatic stress to the inner diameter surface of the annular workpiece material on which the rolling portion is to be formed, thereby forming the rolling portion on the inner diameter surface of the annular workpiece material for the rolling element to roll therealong and increasing an inner diameter of the annular workpiece material other than the rolling portion, so as to provide an annular mechanical part including the rolling portion superior in rolling fatigue life.

Description

CROSS-REFERENCE TO RELATED APPLICATION[0001]This application claims priority to Japanese Patent Application No. 2009-194962 filed on Aug. 26, 2009 and Japanese Patent Application No. 2010-185927 filed on Aug. 23, 2010, the entire disclosures of which are incorporated herein by reference.TECHNICAL FIELD[0002]The present invention relates to production of a mechanical part made of a steel material, such as a bearing, a gear, a hub unit, a variable speed transmission, a constant velocity joint or a piston pin, particularly to production of a mechanical part comprising an annular body for which a good rolling fatigue life is required.BACKGROUND ART[0003]In recent years, with increasingly high performance in various mechanical apparatuses, usage environments of mechanical parts or apparatuses for which a rolling fatigue life is required become very severe, causing a strong demand for improvements in operating life and reliability of these mechanical parts or apparatuses. In response to s...

AI Technical Summary

Benefits of technology

The present invention provides a method for producing a mechanical part with a rolling portion that has superior rolling fatigue life on the inner diameter surface of an annular workpiece material. The method involves conducting plastic processing to improve the state of the interface between non-metallic inclusions and the matrix steel material contained in the steel material constituting the annular workpiece material. By applying a hydrostatic stress to the inner diameter surface of the annular workpiece material, the method forms the rolling portion for a rolling element to roll along the inner diameter surface of the annular workpiece material. The method also increases the inner diameter of the annular workpiece material other than the rolling portion, resulting in an annular mechanical part with the rolling portion having superior rolling fatigue life. The hydrostatic stress applied during cold forging is preferably at least 1000 MPa to close the cavities existing in the interface between non-metallic inclusions and the steel matrix and avoid flaking due to rolling contact fatigue originated from non-metallic inclusions.

Problems solved by technology

Among the impurity elements contained along with the steel ingredients constituting these mechanical parts or apparatuses, Al2O3, MnS, TiN and other non-metallic inclusions consisting of these impurity elements may originate a failure in steel parts of the mechanical parts or apparatuses.

For this reason, it is known that these non-metallic inclusions are particularly detrimental.

It is further known that a larger diameter of the non-metallic inclusion leads to a shorter rolling fatigue life of steel parts.

In the meantime, even if a steel material made of such high cleanliness steel is used for a mechanical part or apparatus, it has not yet been sufficiently achieved to prevent the mechanical part or apparatus from leading to failure in a short life span.

It is known that this then leads to failure through propagation of the crack by shear stress.

In addition, the Mode I-type initial crack occurs on the premise that there is generated a physical cavity, in an interface between the non-metallic inclusion and the matrix.

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