Very high cycle fatigue behavior of bearing steel with rare earth addition

This study aims to clarify the effect of rare earth (RE) addition on the very high cycle fatigue (VHCF) behavior of high-carbon chromium bearing steel. For this purpose, ultrasonic tension-compression fatigue tests were carried out on specimens extracted from bearing steels with and without RE addition. As a result, RE addition can prolong the fatigue life of bearing steel over 10 times and improve the fatigue limit at 10(9) cycles by 9.4% from 720 MPa to 788 MPa, which mainly result from the modification of RE elements to common CaO-Al2O3-MgOSiO2-CaS inclusions, forming complex RE inclusions and leading to the decrease of inclusion size and the volume fraction of inclusions in bearing steel with RE addition. On the VHCF fracture of bearing steels with and without RE addition, both internal cracking mode and interface cracking mode exist at inclusions. Compared with bearing steel with RE addition, bearing steel without RE addition exhibits a longer crack initiation life due to stronger internal binding force of complex inclusions and interfacial binding force between complex inclusions and the matrix. However, smaller complex RE inclusions make crack propagation life of the former significantly longer than that of the latter. In addition, fine granular area (FGA) can be used to estimate the fatigue limit of different fatigue life in the VHCF regime and the fatigue limit at 10(9) cycles evaluated based on FGA indicates an error of around 2% with respect to the fatigue limit measured by staircase method.