Enhancement of Balance in Strength, Ductility, and Stretch Flangeability by Two-Step Austempering in a 1000 MPa Grade Cold Rolled Bainitic Steel

The microstructural evolution and properties for varied austempering routes are investigated in a cold-rolled bainitic steel. Special attention is given to the effect of retained austenite (RA) terms its fraction, carbon concentration, morphology resulting from different on mechanical stretch flangeability. Bimodal sized laths provided, concentration RA maintains highest value through two-step austempering. Total elongation (TEL) remarkably enhanced austempering, deviating exponential relationship between tensile strength (TS) TEL as maintained by one-step Considering two plateaus strain-hardening exponent, it considered that hierarchical stability provided leading postponed necking point so improve uniform elongation. Two-step could provide more complete transformation well stable film-like RA, supplying promising way combination strength, ductility,