2011 Volume 51 Issue 10 Pages 1688-1695
Designed Fe-0.25C-1.5Mn-1.2Si-1.5Ni-0.05Nb (mass%) hot-rolled plates with different thicknesses are subjected to a novel quenching-partitioning-tempering (Q-P-T) process suitable for engineering with water quenching followed by salt bath tempering or water quenching followed by air cooling. A passing underwater quenching equipment (PUQE) is specially designed for realization of the Q-P-T process suitable for engineering. The tensile results show that the Q-P-T samples exhibit both high yield strength of over 900 MPa and elongation of over 15%. Microstructural characterization indicates that the high strength is attributed to the dislocation-type lath martensite or bainite and the dispersively distributed NbC-carbides in the martensite matrix, and the adequate elongation results from the flake-like retained austenite between martensite laths. In addition, effects of the retained austenite in Q-P-T steels on mechanical properties and the feasibility of Q-P-T processes for engineering industry applications are discussed.