Austempering of hot rolled transformation-induced plasticity steels

Zhuang Li1,2) and Di Wu2) 1) Department of Materials Engineering, Institute of Shenyang Aeronautical Engineering, Shenyang 110034, China 2) State Key Lab of Rolling and Automation, Northeastern University, Shenyang 110004, China

摘 要：Thermomechanical controlled processing （TMCP） was conducted by using a laboratory hot rolling mill. Austempering in the salt bath after hot rolling was investigated. The effect of isothermal holding time on mechanical properties was studied through examining of the microstructure and mechanical properties of the specimens. The mechanism of transformation-induced plasticity （TRIP） was discussed. The results show that the microstructure of these steels consists of polygonal ferrite, granular bainite, and a significant amount of stable retained austenite. Strain-induced transformation to martensite of retained austenite and TRIP occur in the hot rolled Si-Mn TRIP steels. Excellent mechanical properties were obtained for various durations at 400°C. Prolonged holding led to cementite precipitation, which destabilized the austenite. The mechanical properties were optimal when the specimen was held for 25 min, and the tensile strength, total elongation, and strength ductility balance reached the maximum values of 776 MPa, 33%, and 25608 MPa?%, respectively.

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