Influence of original microstructure on the transformation behavior and mechanical properties of ultra-high-strength TRIP-aided steel

Hong-xiang Yin^1,2，Ai-min Zhao^1,2，Zheng-zhi Zhao^1,2，Xiao Li^1,2，Shuang-jiao Li^1,2，Han-jiang Hu^1,2，Wei-guang Xia³

1. Metallurgical Engineering Research Institute, University of Science and Technology Beijing2. Beijing Laboratory of Metallic Materials and Processing for Modern Transportation3. Key Laboratory for Mechanics in Fluid Solid Coupling Systems, Institute of Mechanics, Chinese Academy of Sciences

摘 要：The transformation behavior and tensile properties of an ultra-high-strength transformation-induced plasticity（TRIP） steel（0.2C–2.0Si–1.8Mn） were investigated by different heat treatments for automobile applications. The results show that F-TRIP steel, a traditional TRIP steel containing as-cold-rolled ferrite and pearlite as the original microstructure, consists of equiaxed grains of intercritical ferrite surrounded by discrete particles of M/RA and B. In contrast, M-TRIP steel, a modified TRIP-aided steel with martensite as the original microstructure, containing full martensite as the original microstructure is comprised of lath-shaped grains of ferrite separated by lath-shaped martensite/retained austenite and bainite. Most of the austenite in F-TRIP steel is granular, while the austenite in M-TRIP steel is lath-shaped. The volume fraction of the retained austenite as well as its carbon content is lower in F-TRIP steel than in M-TRIP steel, and austenite grains in M-TRIP steel are much finer than those in F-TRIP steel. Therefore, M-TRIP steel was concluded to have a higher austenite stability, resulting in a lower transformation rate and consequently contributing to a higher elongation compared to F-TRIP steel. Work hardening behavior is also discussed for both types of steel.

关键词：