On the Evolution of Austenite During Tempering in High-Carbon High-Silicon Bearing Steel by High Energy X-Ray Diffraction

The evolution of retained austenite in a high-carbon high-silicon bearing steel is explored by high energy X-ray diffraction during continuous heating, giving insights on the control of austenite stability or decomposition during fast tempering. Retained austenite suffers two stages of slight decomposition into bainite below 400 °C, while substantial decomposition into ferrite + cementite occurs above 500 °C. Stress relief decreases retained austenite lattice anisotropy, previously introduced by the stresses caused by martensite formation during quenching. The highest rate of austenite carbon enrichment occurs at 370 °C. In comparison, the highest austenite carbon content is obtained at 466 °C, clarifying a process window for quick retained austenite stabilization with minimal phase decomposition. Austenite achieves intrinsic stacking fault energy values as high as 30 mJ m−2, avoiding the undesired transformation-induced plasticity effect for bearing application.