Method for shot peening

Abstract

The present invention is to provide a method for shot peening for producing a compressive residual stress that exceeds 60% of the yield strength at 0.2% offset without using stress shot peening. Shot media are peened onto a processed steel that has an amount of retained austenite in a range between 5 to 30%, and any change in the amount of retained austenite is controlled to be in a range of 2 to 30% before and after shot peening to produce the compressive residual stress in the processed steel.

1 . A method for shot peening, 
       wherein shot media are peened onto a processed steel that has an amount of retained austenite in a range between 5 to 30%, and wherein a change in the amount of retained austenite is controlled to be in a range of 2 to 30% before and after shot peening to produce a compressive residual stress in the processed steel. 
     
     
         2 . The method for shot peening of  claim 1 , wherein a change in the amount of retained austenite at the depth where the maximum compressive residual stress is generated is controlled to be in a range of 2 to 30% before and after shot peening to produce a compressive residual stress in the processed steel. 
     
     
         3 . The method for shot peening of  claim 1  or  2 , wherein the processed steel is a gas carburized steel.