The Microstructural Design and Control of Ultrahigh Strength-Ductility Martensitic Steels Based on a Novel Quenching-Partitioning-Tempering Process

Abstract

Since Hsu in our group proposed a novel quenching-partitioning-tempering (Q-P-T) process in 2007, Q-P-T steels with ultrahigh strength and ultrahigh strength-ductility are greatly developed. In this paper a novel Q–P–T process based on design of microstructure is first introduced, including the comparison of Q-P-T process with a novel quenching-partitioning (Q&P) and traditional quenching and tempering (Q&T) process. The mechanical properties of Q-P-T steels at room temperature and elevated temperatures are then exhibited, including nanolath martensitic steel with the tensile strength of over 2000MPa and ultrahigh strength-ductility steel with the product of strength and elongation of over 30000MPa%. The mechanisms of ductility enhancement by retained austenite are finally summarized, including a new effect proposed by us, named DARA (dislocation absorption by retained austenite) effect after TRIP (transformation induced plasticity) effect and BMP (blocking microcrack propagation) effect proposed by other investigators 50 years ago.