An excellent combination of elongation over 26% and high strength about 1000 MPa is achieved in processing of 0.35%-2.0%C-2.0%Si-1. 6%Mn steel in 1150 ℃ solution treatment, hot rolling with a reduction of 53% by finishing at 740-780 ℃ cooling into bainite transformation temperature (350-400℃) at a cooling rate of 30-40 ℃/s, and coiling ferrite, bainite and 10-20% retained austenite. Bainite is the main strengthen phase, and high elongation is caused by transformation induced plasticity of retained austenite. Sufficient amount of stable retained austenite is requisite for the good ductility and high σ_b * δ. An combination of elongation over 20% and high strength about 1200 MPa is achieved by intercritical annealing, rapid cooling into bainite transformation temperature to soak several minutes. Furthermore, three types of retained austenite are observed in the steel. The first is in membrane shape, the second is in block shape, and there usually exist in ferrite matrix. The other is in strip shape and usually exist adjacent to bainite. Martensite which induced during deformation is measured by X-ray diffraction, and observed by transmission electron microscope in this paper.
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