Effect of Heating Temperature on Precipitation and Property of Ti-Nb Composite Microalloyed High-strength Steel

A low-carbon high-strength microalloyed steel was smelted in laboratory.Rolling,redissolving and tensile tests were performed.In addition,microstructure of the rolled steels was observed and the morphology,type and size of precipitates at different reheating temperature were analyzed.The results show that property of the sample heated at the temperature of 1 280 ℃ is superior to that of sample heated at 1 180 ℃;the microstructures of these steels under the two temperature schemes consist of ferrite and pearlite with basically the same grain size;and the（Ti,Nb）（C,N） composite precipitates,but the precipitates of the sample heated at 1 280 ℃ are smaller and more in quantity.The calculation based on precipitation hardening theory indicates that the precipitation hardening of the sample heated at high temperature is 131 MPa higher than that of low temperature-heated specimen.Furthermore,redissolving experiment shows that the precipitates virtually dissolve in steel as the sample is heated to 1 280 ℃ and kept at the temperature for 1.5 hours,while the precipitates cannot fully dissolve in steel as the sample is heated to 1 280 ℃ and kept at the temperature for 1.5 hours,which proves that heating temperature has a strong influence on the precipitation hardening of Ti-Nb composite microalloyed steel.