Ultrahigh Strength Ductility Research Articles

Tailoring Hetero-Grained Austenite Via a Cyclic Thermomechanical Process for Achieving Ultrahigh Strength-Ductility in Medium-Mn Steel

Tailoring Hetero-Grained Austenite Via a Cyclic Thermomechanical Process for Achieving Ultrahigh Strength-Ductility in Medium-Mn Steel

High carbon microalloyed martensitic steel with ultrahigh strength-ductility

Based on the idea of rising the mechanical stability of retained austenite by the addition of Si in Fe-Mn based steels, an Fe-0.63C-1.52Mn-1.49Si-0.62Cr-0.036Nb was designed, then its hot rolled plate was successively tread by normalization process as pretreatment of novel quenching-partitioning-tempering (Q-P-T) process. Product of tensile and elongation (PSE) of 53.94GPa% were obtained for this high carbon Q-P-T martensitic steel, and the PSE (40.18GPa%) obtained by the conversion of tensile sample size using Oliver formula still is more excellent PSE than those of other microalloyed advanced high strength steels reported. The microstructural characterization reveals origin of ultrahigh PSE resulting from both the increase of considerable and dispersed carbon enriched retained austenite with relative high mechanical stability in volume fraction and the decrease of brittle twin-type martensite with the sensitivity of notch.

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

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.