Research on Rolling Contact Fatigue Strength of Two Phases A11oy Steel Containing Martensite+Ferrite or Pearlite+Ferrite

In order to elucidate the influence of the variation of the ferrite content of matrix on the rolling contact fatigue strength of SCM 21, the ferrite content of which is changed with heat treatment, the author conducted experiment using a Nishihar type wear testing machine under lubricated state with sliding The results obtained are summarized as follows : 1)The rolling contact fatigue endurance limits of two phases alloy steel,the ferrite content of which is changed with heat treatment, are lower compared with one phase alloy steel, The tendency is stronger with increasing amount of ferrite and matrix hardness. 2)Since ferrite is considered as a sort of internal defect,the reduction factor for two phases alloy steel was large compared with one phase alloy steel,regardless the amount of ferrite and matrix hardness. 3)The crack propagation along boundary of ferrite and matrix, and after that it penetrates into the the vicinity of the region where the stress value calculated according to the maximum shearing stress theory reached the maximum and the crack propagation gone in the parallel direction with the contact surface.