Direct quenching of low manganese steels microalloyed with vanadium or titanium

Direct quenching from the finish rolling temperature and tempering (Q-T) was investigated on four V-microalloyed and four Ti-microalloyed steels. The effects of reheating temperature in the range of 1,000 to 1,250°C and finish-rolling temperature (quenching temperature) in the range of 800 to 1,000°C were also studied. Strengthening was accomplished by martensite formation during quenching and secondary hardening during temperature at 600°C. Ti-microalloyed steels were more sensitive to reheating and finish rolling temperatures than V-microalloyed steels due to the lower solubility of titanium carbide in comparison with vanadium carbide or vanadium nitride. At higher reheating and finish rolling temperatures (1,250 and 1,000°C, respectively), Q-T-titanium steel showed higher yield and ultimate tensile strength than that of Q-T-vanadium steel containing the same carbon content. The direct quenching-tempering technique more effectively produced high strength than conventional quenching and tempering heat treatment. By applying this technique, high strength levels of more than 1,100 N/mm2 and elongation of about 18 percent were attained.