The Influence of Heat Treatment Process and Alloy on Microstructure and Rolling Contact Fatigue Life of High Carbon Chromium Bearing Steels

Microstructures and rolling contact fatigue properties of high carbon chromium bearing steels were investigated by means of electron microscopy, hardness and rolling contact fatigue tests. In order to examine the influence of heat treatment process and alloy composition on microstructure and rolling contact fatigue, two kinds of heat treatment processes, i.e., quenching/tempering (QT) and nitrocarburizing were performed on conventional AISI52100 and ASTM A485 Grade-1. Rolling contact fatigue life of the nitrocarburized alloys was longer than that of QT treated alloys by 3.7 times under a clean lubrication condition and was longer by 1.5 times under a contaminated lubrication condition. The amount of retained austenite in the nitrocarburized samples was found to be larger than that in the QT treated samples. As for alloy effects, rolling contact fatigue life of nitrocarburized ASTM A485 Grade-1 steel was superior to that of nitrocarburized AISI52100 steel. With increasing tempering temperature from 150°C to 300°C but tempering time held constant at 1 hr, the decreases in hardness for the nitrocarburized AISI52100 and ASTM A485 Grade-1 alloys were smaller compared to the QT treated AISI52100 alloy. This means that the nitrocarburized high carbon chromium steels are suitable for bearing materials for high temperature at 300°C. Very fine Fe₄(Fe(CN)₆)₃ carbonitride less than 100nm in diameter were found in both alloys. An improvement in rolling contact fatigue life in nitrocarburized ASTM A485 Grade-1 steel was attributed to the combination of formation of very fine Fe₄(Fe(CN)₆)₃ and retained austenite.