Decomposition characteristic of austenite retained in GCr15 bearing steel modified by addition of 1.3 wt.% silicon during tempering

Zhihui Chen, Jianfeng Gu, Lizhan Han

Keywords: Bainite, Carbon partitioning, Cementite precipitation, Retained austenite (RA), Tempering

Abstract: The decomposition characteristic of austenite retained in a GCr15 bearing steel modified by the addition of 1.3 wt.% silicon during tempering was investigated by microstructural observation, X-ray determination, and dilatometric experiment. The addition of 1.3 wt.% silicon in the modified GCr15 bearing steel significantly increases the amount of remaining austenite. After tempering at 300 °C for 96 h, 18 vol.% of austenite with 1.6 wt.% carbon remained. Austenite decomposition during the tempering is a bainitic transformation, and occurs via the displacive mechanism, following by carbon partitioning into the remaining austenite. The bainite transformation becomes slower as the carbon enrichment in austenite improves. In contrast, carbide precipitation accelerates the bainite transformation kinetics. However, the carbon enrichment in austenite associated with carbon partitioning and the precipitation of carbides are competitive processes, with their relative rates depending on temperature. Consequently, the improvement in the thermal stability of austenite is ascribed to the combined effects of the partitioning of carbon into austenite and the suppression of carbide precipitation.