Microstructure and fatigue strength of the roller-bearing steel 100Cr6 (SAE 52100) after two-step bainitisation and combined bainitic–martensitic heat treatment

Abstract

Abstract Possible processes for shortening the heat treatment of roller-bearing steels in the lower bainitic range were investigated by computer assisted dilatometric experiments and by practical heat treatment process simulations. Several processes were evaluated and used on the steel 100Cr6 (SAE 52100). The microstructures achieved have been investigated by metallography, X-ray analysis and electron microscopy. Influences on hardness, as well as on the fatigue strength were examined. No loss in hardness was achieved and the fatigue strength, determined by rotating bar fatigue tests, was enhanced significantly by the shortened treatments, particularly by the use of the two-step bainitic treatment. The results indicated that small amounts of retained austenite, homogeneously dispersed on a sub-microscopic scale, as obtained during various treatment cycles, have influenced the fatigue strength. By means of the processes evaluated the heat treatment time can be shortened to about 10–25% of the duration of complete bainitisation in the lower range.