Abstract: Microstructure and mechanical properties of 0.2C-5.0Mn-0.5Si-1.0Al TRIP steel with different original microstructure after intercritical annealing were studied by Factsage software, SEM, XRD, etc. The results show that the microstructure of the steel treated by different pretreatment processes are as follows: ferrite+blocky type retained austenite (pretreatment at 700 ℃ for 10 min), ferrite+martensite+small amount of retained austenite (pretreatment at 800 ℃ for 5 min), and martensite+small amount of carbides (pretreatment at 900 ℃ for 5 min). The residual austenite with different morphologies can be obtained by different pretreatment processes. By pretreatment at 700 ℃ and intercritical annealing, blocky-type retained austenite is obtained, and the film-type one can be obtained by the other processes. The specimen pretreated at 800 ℃+intercritical annealing has the best mechanical properties with the yield strength of 840 MPa, the tensile strength of 1121.5 MPa, the elongation of 33.25 %, and the product of strength and plasticity of 37.29 GPa·%. The morphology of retained austenite has a significant impact on the work hardening performance. The blocky-type retained austenite pretreated at 700 ℃ and intercritical annealing has poor stability, showing high work hardening rate, but the continuous interval is short. However, the stability of film retained austenite pretreated at 800 ℃ and intercritical annealing is better, showing higher work hardening rate and longer duration.

Key words: medium manganese TRIP steel containing Al, original microstructure, mechanical properties, retained austenite