Influence of accelerated cooling on microstructure and mechanical properties of C-Mn steels

Two commercial steels, based on 0.13C-0.85Mn and 0.12C-1.34Mn, were quenched from 900degreesC to temperatures between 288 and 484degreesC in a resistance annealing simulator. Different cooling rates ranging from 70 to 480 K s(-1) were generated. The microstructures and mechanical properties of these two steels heat treated under different conditions were investigated. The maximum volume fractions of bainite in the 0.13C-0.85Mn and 0.12C-1.34Mn steels were about 25 and 60%, respectively. Further increase in the cooling rate failed to increase the bainite volume fraction, because some of ferrite was replaced by acicular ferrite with increase in cooling rate. It was also found that up to about 10% acicular ferrite was obtained in the 0.13C-1.34Mn steel at a cooling rate higher than 340 K s(-1). The maximum yield strengths in the 0.13C-0.85Mn and 0.12C-1.34Mn steels were 480 and 520 MPa, respectively. The influence of manganese on the microstructures of these two steels was also investigated.