Microstructure evolution and synergistic improvement of strength-ductility through partitioned pearlite-based quenching and tempering process

This study investigates the microstructure evolution and mechanical properties implication of the amount of ghost pearlite (GP) in partitioned pearlite-based quenching and tempering steel. The GP microstructure consists of alternative Mn-enriched film retained austenite (RA) and Mn-depleted lath martensite, inherited from pearlite after fast austenitization. The change in the microstructure from heterogeneous lamellar to a homogeneous matrix accompanied by the decreasing GP amount was examined through systematically prolonging the fast austenitization time at 760 °C. After tempering, the steel containing highest amount of GP (53 ± 5 %) exhibit a higher UTS (∼1817 MPa) whereas the absence of GP results in a lower UTS (∼1674 MPa). This is due to the Mn-enriched film-like RA morphology in GP, which plays a critical role in enhancing mechanical stability, strain delocalization and fracture resistance. These findings highlight the pivotal role of lamellar film-like RA in achieving strength-ductility synergy and provide new insights for designing high-performance AHSSs through controlling thermal processing.