Quenching-Partitioning-Tempering Process and Its Engineering Feasibility of 900MPa Grade Hot-Rolled Plate

Two kinds of experimental low alloy steels were prepared based on composition design. Following Quenching-Partitioning-Tempering (Q-P-T) process with the combination of water quenching plus tempering in salt bath, both the steels exhibited high yield strength of over 900MPa combined with good elongation of above 15%, which would be the basis of self-designed the single-cycle passing underwater quenching equipment applied in Q-P-T process of hot-rolled plate for engineering feasibility. Microstructure characterization indicates that for Q-P-T steels, high strength is attributed to dislocation-type lath martensite matrix and dispersive distributed alloying-carbides in martensite matrix, while relatively high elongation results from flake-like retained austenite between martensite laths, comparing with the steels treated by conditional Quenching & Tempering (Q&T) process. In addition, the role of retained austenite in Q-P-T steels and the feasibility of online Q-P-T process treated by multi-cycle passing underwater quenching equipment for different hot-rolled plates in thickness were discussed.