Abstract
The effect of thermo-mechanical processing routes on the microstructure and mechanical properties of st37 low carbon steel was studied. Several dual phase (DP) ferritic-martensitic steels were produced by intercritical annealing of the martensitic, cold-rolled martensitic, and bimodal-sized ferritic microstructures. The latter microstructure was produced by subcritical tempering of cold-rolled DP steel to develop an aggregate of ultrafine and large ferrite grains. The DP steel obtained by intercritical annealing of cold-rolled martensite was shown to exhibit better strength-ductility balance compared with that obtained by intercritical annealing of the as-quenched martensite due to much finer microstructure and enhancement of work-hardening behavior in the former. The bimodal-sized ferritic structure showed high yield stress, yield-point elongation, and less pronounced work-hardening regime. The DP steel obtained by intercritical annealing of bimodal-sized ferritic structure exhibited inferior strength-ductility tradeoff compared with that obtained by intercritical annealing of cold-rolled martensite due to the coarser microstructure in the former. Conclusively, it is possible to enhance the mechanical properties of st37 low carbon steel by simple processing routes.

Key words
dual phase steels, microstructure, mechanical properties, strain hardening rate

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