Effect of Tempering on Microstructure and Properties of Direct Quenching Steel

Compared to a kind of steel tried on direct quenching at two kinds of different cooling rates,the effect of tempering on properties of direct quenching steel was studied.A series of tempering experiments were carried out on four different tempering temperature(500,550,600 and 650℃).The results show that secondary hardening appears in the condition of relatively slower cooling rate,and the higher tempering temperature,the better toughness.However,at the relatively faster cooling rate,when the tempering temperature is elevated,the strength and toughness both decrease.