Effect of surface rolling process on rolling contact fatigue behavior and failure mechanism of powder metallurgy steel

Abstract

The effect of surface rolling process on the surface microstructure and rolling contact fatigue of the Fe-2Cu-0.6 C powder metallurgy steel was investigated in the present investigation. Results indicated that a densified and hardened layer with a densification depth of 330 μm and a surface hardness of 330 HV0.1 was generated in the surface layer after rolling process. Ferrite grain and pearlite lamellae became typical fibrous structures on the top surface. The microstructure of pearlite was presented by two typical features. One was that the discrete cementite plates were severely curled and wavy. The other one was that the cementite plates remained parallel to each other, but were a reticular structure at a macroscopic level. The rolling contact fatigue (RCF) test showed that the RCF life of the rolled sample was superior. The L10, L50, L63.2 life increased by 182%, 105%, 92%, respectively. Surface initiated spalling was the main fatigue failure mode. Subsurface equivalent contact stress and local equivalent stress were calculated. The results showed that surface cracks were due to the repetitive tensile stress, which caused pits. Subsurface cracks nucleated and propagated in the region where the local equivalent stress was higher than the matrix yield strength, which caused spalling as connecting with surface cracks. The surface densified layer plays an important role in improving the rolling fatigue resistance of the material.