(1. The State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110004, Liaoning, China 2. Technical Center, Laiwu Steel Group, Laiwu 271104, Shandong, China 3. School of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200240, China)
Abstract: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.