Effects of Quenching Process on Microstructure and Mechanical Properties of Low Carbon Nb-Ti Microalloyed Steel

The low carbon Nb-Ti microalloyed tested steel was prepared by the process of vacuum induction furnace smelting,forging and hot rolling.The new steel aims to meet the demand of high strength,high toughness and high plasticity for building facilities.The effects of quenching process on microstructure and mechanical properties of tested steel were investigated.The results showed that prior austenite grain size,phase type and precipitation behavior of（Nb,Ti）(C,N)play important roles in mechanical properties of the steel.Through modified appropriately,the model of austenite grain growth during heating and holding is d;=5.6478;+7.04×10;t;exp(-427.15×10;/（RT）).The grain growth activation energy is Q;=427.15 kJ.During quenching,the microscopic structures are mainly martensite and lath bainite which contains lots of lath substructure and dislocations.The content of phases,fine and coarsening（Nb,Ti）(C,N)precipitated changes during different quenching temperatures and holding time.Finally compared with the hardness value,the best quenching process can be obtained that heating temperature and holding time are900℃and 50 mins,respectively.