The thermo-simulation tests showed that, for the microalloyed low carbon steel, after the steel was hot deformed in the non-recrystallization temperature, the relaxation of the austenite effected the refinement of intermediate transformation phase. The dilatometer results of the samples which deformed and relaxed for various time revealed that the phase transformation start temperatures raise with the relaxation time increasing. By applying the relaxation-precipitation-phase transformation control (RPC) technology, the ultra-fine low carbon bainitic steel has been developed. The microstructure is composed of ultra-fine bainitic packet and acicular like ferrite. The strength of such low carbon bainitic steel is increased about 30% comparing with the same composition steel that processed by conventional reheated and quenching process. The high performance ultra-fine low carbon 600MPa-800MPa grade bainitic steels have been produced nearly a hundred thousand tons in the steel companies.
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