The measurement of SH-CCT curve and analysis on microstructure and performance of heat-affected zone of Q690 high-strength bridge steel

Abstract

The heat-affected zone continuous cooling transition curve (SH-CCT) of the experimental steel is drawn by using the Gleeble-3500 thermal simulation testing machine. The influences of different cooling rates and peak temperatures on the microstructure and mechanical properties of HAZ were studied. The results show as the cooling rate increases, the experimental steel undergoes LB + GB and LM + LB + GB phase transformations successively, and the micro-hardness gradually increases. When the heat input is 20kJ/cm, the microstructure of inter-critical heat-affected zone (ICHAZ) is F + B, the microstructure of fine grain heat-affected zone (FGHAZ) and the coarse grain heat-affected zone (CGHAZ) is LM + LB + GB. As the peak temperature increases, the micro-hardness first increases and then decreases, the -40°C impact absorbing energy gradually decreases. This conclusion can provide a reference for further study on the microstructure and mechanical properties of HAZ of Q690 bridge steel.