Effect of Cold Rolling Reduction Ratio and Annealing Process on Microstructure and Mechanical Properties of St37-2G Structural Cold-Rolled Steel Sheet

The effect of cold rolling reduction ratio and annealing process on the microstructure and mechanical properties of St37-2G structural cold rolled steel sheet was studied and the production process was optimized. The results show that the microstructure of the tested steel sheet was composed of ferrite, a small number of cementite and marginala pearlite, and the characteristic of cenmentite distributing along rolling direction in the fibroid form was remained after the tested steel sheet was cold-rolled with different cold rolling reduction ratios and annealed at 670 ℃ for 5 h. The hardness of the tested steel sheet increased and then decreased with the increase of cold rolling reduction ratio, and the hardness showed maximum when the cold rolling reduction ratio was 60%. The yield strength, tensile strength and plastic strain ratio decreased obviously with the increase of heating rate during annealing, but the elongation and working hardening index changed a little. The optimal cold rolling and annealing process was as follows: the cold rolling reduction ratio of 40%-50%, annealing temperature of 670 ℃ and heating rate of 20 ℃·h-1.