Determination of simulated SHCCT curves and welding procedure qualification of 960 MPa grade high strength steel

The continuous cooling transition curve of 960 MPa grade high strength steel was measured by Gleeble-3800 thermal simulation test machine combined with the structural transformation characteristics and microhardness changes. And Y-groove welding cold crack sensitivity test and welding procedure qualification of the steel were carried out by the argon-rich gas shielded welding procedure. The results show that microstructure transformation of the steel in heat affected zone is as follows,martensite transformation of t_8/5＜ 30 s,mixed transformation of martensite and bainite of 60 s ＜ t_8/5＜ 100 s,bainite transformation of 150 s ＜ t_8/5＜ 600 s,pre-eutectoid ferrite,pearlite and bainite mixed transformation of t_8/5＞ 1 000 s. In the welding process,there is no softening phenomenon in the welded joint of 960 MPa grade high strength steel. As the heat input decreases,t_8/5 decreases,the tensile strength decreases,and the HAZ toughness increases. At the same t_8/5 level,the plate thickness has little effect on tensile strength and HAZ impact energy. For the 960 MPa grade high-strength steel plate with 8 ～ 15 mm thickness,preheating temperature is not lower than 80 ℃ when using 70 kg grade welding wire CHW-70 C,OK13. 29,and preheating temperature is not lower than 100 ℃ when using 90 kg grade welding wire GM120,no cold crack is generated under the above conditions.