Method for manufacturing a machine part

Abstract

Provided is a high strength steel machine part. A method for manufacturing a machine part comprises the steps of: preparing a workpiece of steel to be a machine part; and subjecting the workpiece to a quenching process by heating a surface portion of the workpiece, with shear strain applied to the surface portion, to a heating temperature of an A3 transformation point temperature or higher, and subsequently cooling the surface portion. The workpiece has a carbon content of 0.2 mass % or more. In the step of subjecting the workpiece to a quenching process, the heating temperature is 800° C. or higher, and in the quenching process the workpiece has the surface portion cooled at a rate of 35° C./second or faster for a temperature range of 850° C. to 300° C.

1 . A method for manufacturing a machine part, comprising the steps of:
 preparing a workpiece of steel to be a machine part; and   subjecting the workpiece to a quenching process by heating a surface portion of the workpiece, with shear strain applied to the surface portion, to a heating temperature of an A3 transformation point temperature or higher, and subsequently cooling the surface portion,   the workpiece having a carbon content of 0.2 mass % or more,   in the step of subjecting the workpiece to a quenching process, the heating temperature being 800° C. or higher, and in the quenching process, the workpiece having the surface portion cooled at a rate of 35° C./second or faster for a temperature range of 850° C. to 300° C.   
     
     
         2 . The method for manufacturing a machine part according to  claim 1 , wherein the workpiece has two portions held by first and second holding units, respectively, and the first holding unit is rotated relative to the second holding unit about a rotation axis extending from the first holding unit toward the second holding unit to apply shear strain to the surface portion of the workpiece. 
     
     
         3 . The method for manufacturing a machine part according to  claim 2 , wherein the first holding unit is rotated relative to the second holding unit at a rate of 0.05 (revolution/second) or faster. 
     
     
         4 . The method for manufacturing a machine part according to  claim 1 , wherein
 in the step of subjecting the workpiece to a quenching process the surface portion has a portion heated and the portion of the surface portion that is heated is also shifted, and   the heated portion is shifted at a rate of 0.5 mm/second or faster.   
     
     
         5 . The method for manufacturing a machine part according to  claim 1 , wherein in the step of subjecting the workpiece to a quenching process the shear strain is applied in an amount of 7.1 or more.