Effect of Cr content on the microstructure evolution in weld metal for 1000 MPa grade high strength steel

Five kinds of submerged arc welding materials of 1000 MPa grade high strength steel with different Cr content were designed and deposited metals with Cr content of 0% ~ 0.9% were prepared by wire submerged arc welding. OM, SEM, TEM and CLSM were used to study the effect of Cr content on the microstructure evolution of 1000 MPa grade high strength steel, and the mechanical properties were evaluated by tensile and impact tests. The results show that, With the increase of Cr content, the initial temperature of ferrite transition increases from 723.3 ℃ to 740.2 ℃, and the initial temperature of bainite transition decreases from 470.2 ℃ to 458.5 ℃. The range of ferrite transition temperature expands, and the bainite transition rate is faster in high Cr deposited metal. The acicular ferrite and bainite ferrite in deposited metal increased, the M-A component gradually showed chain segregation from dispersion, and the preeutectoid ferrite and residual austenite decreased. The impact fracture of deposited metal changes from ductile fracture with low Cr to quasi-cleavage fracture with high Cr. Compared with 0%Cr, the tensile strength and yield strength of 0.9%Cr were increased by 12.4% and 17.0%, respectively. The impact toughness of deposited metal increases first and then decreases. At −40 ℃, the low temperature toughness of deposited metal with Cr content of 0.6% is the highest, which is 84 J. When Cr content of deposited metal is 0.6%, the matching effect of strength and toughness is the best.