Research on direct quenching and tempering process of low alloy Q&T steel

The effect of the tempering process on microstructure and properties of low alloy QT steel under direct quenching condition was investigated.Results showed that,with the tempering temperature increasing,the strength of the controlled rolled and direct quenched steel decreased and the impact toughness increased.The high strength retained after tempering above 600 ℃.Precipitation of microalloy nano-carbide delayed the tempering softening effect.During the first 20 min of 600 ℃ tempering,the strength decreased apparently,and the impact toughness significantly improved.Subsequently the strength appeared a rising trend because the precipitation of microalloy nano-carbide compensated the matrix softening.Online direct quenching and tempering process could improve the comprehensive mechanical performance of offline Q T steel,reduce energy consumption and raise productivity.