Weldability of Q960 steel plate for hydraulic support

Objective The purpose of this study was to comprehensively analyze weldability of Q960 steel plate used for hydraulic support through theoretical and experimental means to determine preheating temperature that met service conditions. Methods Welding thermal simulation test of Q960 steel was carried out by Gleeble 3800-GTC thermal simulation tester, microstructure transformation of welding heat affected zone was analyzed under different cooling rates, and welding SH-CCT curve of Q960 steel was drawn. Through theoretical calculation, maximum hardness test of heat affected zone and Tekken test, weldability of Q960 steel was systematically studied. Results Equilibrium critical temperature A_c1 of Q960 steel plate was 702 ℃, and A_c3 temperature was 895 ℃. In the range of 8～80 ℃/s, cooling rate had no significant effect on hardness. Microstructure of welding heat affected zone was mainly martensite, and hardness was stable between 400～410 HV. Carbon equivalent C_E of Q960 steel was 0.621%, C_EV was 0.584%, and P_cm was 0.305%. When welding heat input was 10.7 kJ/cm, preheating temperature below 150 ℃ had no significant effect on maximum hardness of heat affected zone. When preheating temperature was above 80 ℃, no crack was produced in Tekken test. Conclusion Q960 high strength steel had obvious tendency of cold cracking sensitivity. When it was preheated to more than 80 ℃ before welding, cold cracking could be effectively avoided.