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 degrees C, while substantial decomposition into ferrite + cementite occurs above 500 degrees 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 degrees C. In comparison, the highest austenite carbon content is obtained at 466 degrees 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.