Research On Welding Microstructure And Properties Of 07MnNiVDR High Strength Steel For Pressure Vessels

The quenched and tempered high strength low alloy steel?HSLA?for pressure vessel has been widely used in the domestic construction of reserve tank for petrole?m and chemical industry.Selecting suitable welding materials and welding technology for assembly welding process be able to achieve the goal of lightweight.Furthermore,it can prolong service cycle under extreme environmental conditions.In this paper,the joint microstructure and properties of 07MnNiVDR test steel and two flux-cored welding wires were studied under CO₂ gas protection.?1?Through OM,SEM,TEM analysis and hardness test,and welding with different welding parameters,the microstructure and mechanical properties of weld seam and heat-affected zone of imported DWS-60G and domestic YJL-60G flux-cored wire joints were studied,which can provide reference data for improving the weldability of HSLA steel and optimizing welding process.?2?The effects of welding matching and welding parameters on the microstructure of the weld were studied.The results show that the distribution of acicular ferrite?AF?in the weld of YJL-60G joint is relatively high,and the impact toughness at low temperature is excellent.The slab bainite bundle in the heat affected zone is the main factor to reduce the impact toughness at low temperature.?3?The effect of inclusions in weld structure on nucleation of acicular ferrite?AF?was analyzed.It was found that the inclusion content of YJL-60G joint was higher than that of DWS-60G joint,and Al-Si-Mn-Ti-O-S complex inclusion was the main type of inclusion promoting AF nucleation in the two kinds of joint welds.?4?The DWS-60G filler wire was used to study the influence of different welding heat input values on the microstructure and mechanical properties of the joint.The results show that as the heat input increases,the n?mber of inclusions increases and becomes uniform,and the AF distribution density in the weld increases large;joint weld tensile strength is slightly reduced,but still has good plasticity.At the same time,the hardness is lowered and the impact toughness of the weld is improved.When heat input is 222kJ/cm,Increasing the area fraction of precipitated phase hinders the growth of AF in the direction of ductile width,and produces a slender single ferrite,which is easy to become the path of crack growth and reduces the low temperature impact toughness of heat affected zone.