RETAINED AUSTENITE IN 0.4-PERCENT C-SI-1.2-PERCENT MN STEEL SHEET ANNEALED IN INTERCRITICAL RANGE AND AUSTEMPERED

To clarify the formation process of the retained austenite in 0.4%C-Si-1.2%Mn steel intercritically aenealed followed by austempering, changes in fraction of reained austenite (V-gamma), solute carbon content in retained austenite (C-gamma) and microstructure with isothermal holding time at 350 approximately 450-degrees-C were examined by X-ray diffraction measurement and electron microscopic observation. It was concluded that blocky retained austenite grains with less than 2 approximately 3-mu-m dia. found in the above steel and the interlath retained austenite films having been reported by others in the higher carbon (greater-than-or-equal-to 0.6C)-Si-Mn steel annealed at single austenite range and austempered, were the same in chemical stability of austenite by carbon enrichment, in spite of differences in site and morphology. Formation of blocky retained austenite may be attributed to the smaller austenite grain size obtained by cold rolling and intercritical annealing. Addition of Si may cause decreasing of carbide precipitation and increasing V-gamma at the holding time the maximum of C-gamma-(C-gamma-max) is reached, with C-gamma-max unchanged.