Enhanced Impact Toughness of Previously Cold Rolled High-Carbon Chromium Bearing Steel with Rare Earth Addition

Impact toughness is affected by chemical composition, defects, microstructure and ambient temperature. Higher impact toughness can prevent premature failure of the bearings. In present work, the microstructure evolution and impact toughness of high-carbon chromium bearing steels with and without rare earth (RE) addition have been investigated after cold rolling, quenching and tempering (QT) treatment. The results show that the addition of RE elements converts irregular MnS, TiN and Al₂O₃ inclusions with an average size of 9.02 μm into RE inclusions with an average size of 3.76 μm. As a consequence, the impact toughness of specimens with RE is 2.2 times that of without RE. When the cold rolling is applied, since the prior cold rolling can refine the prior austenite grain and increase the residual austenite after QT treatment, the impact toughness also exhibits a significant enhancement from 6.4 to 15.9 J. In addition, for the RE-GCr15 subjected to cold rolling process, the impact toughness can be further increased. This should be attributed to that the refined RE inclusions with good roundness reduce the crack initiation caused by cold rolling, so as to maximize the advantages of cold rolling. The results obtained in this work suggest a good prospect to combine cold rolling process with bearing steel with RE addition.