Microstructure and mechanical properties of a Ti-microalloyed low-carbon stainless steel treated by quenching-partitioning-tempering process

Quenching-partitioning-tempering (Q-P-T) process was used to treat a Ti-microalloyed low-carbon stainless steel after cold rolling. In addition to martensite, ferrite and retained austenite, TiN, coarse TiC, fine TiC, (Fe,Cr)3C and ultra-fine TiC precipitates were formed after the Q-P-T treatment. Based on field emission-scanning electron microscope (FESEM) and transmission electron microscope (TEM) observations, thermodynamic, crystallographic and statistical analyses were used to reveal the precipitation behaviors of these particles. The effects of partitioning-tempering (P-T) temperature and time on the microstructure and mechanical properties of Q-P-T treated specimens were specially studied. The coarsening and spheroidization of (Fe,Cr)3C particles during P-T stage were obviously retarded by large Cr addition. The retained austenite was obtained significantly with appropriate P-T parameters. The precipitation of ultra-fine TiC particles in the martensite during the P-T stage at 500°C induced a secondary hardening.