Austenite Stability and Cryogenic Impact Toughness of a Lamellar Fe-Mn-Al-C Lightweight Structural Steel Subjected to Quenching and Tempering Process

• Published in: Journal of materials engineering and performance 2022-07, Vol.31 (7), p.5259-5268
• Main Authors: Zhang, Xiao-feng, Li, Jia-xing, Yang, Yong, Zhang, Ke, Wu, Xue-jun, Huang, Zhen-yi
• Format: Article
• Language: English
• Subjects: Characterization and Evaluation of Materials; Chemistry and Materials Science; Corrosion and Coatings; Engineering Design; Materials Science; Quality Control; Reliability; Safety and Risk; Technical Article; Tribology
• ISSN: 1059-9495; 1544-1024
• DOI: 10.1007/s11665-022-06649-z

Based on the Q–T process and characterized by SEM, XRD, and TEM, the microstructure evolution and impact properties of medium-manganese aluminized steel under quenching at 650, 700, 750, and 800 °C and tempering at 200 °C were studied. The results showed that the microstructure of the steel was mainly composed of ferrite, martensite, and retained austenite. The volume fraction of retained austenite in steel decreased with the increase in quenching temperature, which was 79.1, 78.3, 48.6, and 33.4%, respectively. When quenching at 800 °C and tempering at 200 °C, the room-temperature tensile strength and yield strength of the steel were 1244 and 451 MPa, respectively, and the elongation after fracture was higher than 27.6%. When quenching at 700 °C and tempering at 200 °C, the impact energy reached 25.3 J at −80 °C. The elongation of the steel at different quenching temperatures mainly depended on the volume fraction of retained austenite. The main reason for the improvement of ductility and toughness was the martensitic transformation of retained austenite during deformation, which relieves the local stress concentration and enhances the plastic deformation ability during deformation, thus delaying the propagation of microcracks.