Microstructural Refinement of Bainite and Martensite for Enhanced Strength and Toughness in High-Carbon Low-Alloy Steel

This study attempts to determine the scope and extent of microstructural refinement through complete/partial recrystallization of prior cold deformed ferrite during austenitizing (1223 K (950 °C), 15 minutes) and/or austempering (543 K (270 °C), 30 minutes) followed by water quenching to obtain ultrafine bainitic sheaves along with thin martensitic plates in SAE 52100 steel. The volume fraction and sheaf/plate dimension (thickness/length) of bainitic ferrite and martensite were determined by optical and scanning/transmission electron microscopy studies coupled with compositional microanalysis. Marginal improvement in the tensile strength and significant improvement in the impact properties is obtained at an optimum level of prior cold deformation by tension in comparison to that recorded in austempered condition without prior deformation.