Development And Performance Study Of Cr-Ni Series High Strength And Toughness MIG Welding Wire

With the extensive development of onshore oil,natural gas,coal mines,and other resources,the global energy crisis has begun to emerge,and countries have turned their eyes to the ocean with rich oil resources.As an important type of steel used for offshore engineering welding structures,10 Cr Ni3Mo V steel had the problems such as high labor intensity,low welding efficiency,and low automation in engineering applications.In order to address the above issues,this thesis conducts research from the perspectives of welding wire design,the influence of shielding gas,and the microstructure and mechanical properties of welded joints.The main research contents and conclusions are as follows:(1)A quantitative model between the chemical composition and mechanical properties of welding wire was established using neural networks,and various elements’ influence on the welding wire’s performance was predicted.The composition range of welding wire was designed.The results indicate that the two types of welding wires designed in this thesis have good performance within their scope,with only a difference of about50 MPa between the experimental and predicted values.(2)The effects of two different shielding gases,Ar+He+N2 and Ar+CO2,on the microstructure,mechanical properties,weld cleanliness,and grain boundary wetting of austenitic stainless steel weld metal were studied.The results show that the ternary shielding gas containing nitrogen reduced the chromium-nickel equivalent ratio of the weld metal,causing the solidification mode of the weld metal to change from F-A to A-F,the grain boundary to change from incomplete wetting to partial complete wetting,the ferrite content to decrease from 7.6% to 4.3%,the tensile strength to increase by 10 MPa,and the impact energy to increase by 40 J at-20℃.(3)The microstructure,mechanical properties,precipitates,and white bright bands of the deposited metal and welded joints of two new types of welding wires with different element contents(N,Ni,Mn)and Mn7 Mo welding wires were studied.The results show that ASH-1 and ASH-2welding wires with higher alloy elements such as Ni,Mn,and N have tensile strength Rm ≥ 670 MPa,and KV2 ≥ 162 J at-20 ℃,which improves the performance of Mn7 Mo welding wires by about 5%.The solid solution strengthening of alloy elements,fine grain strengthening of nitrogen elements,and the reduction of C/N mass ratio are harmful σ Phase reduction is the main factor for improving the performance of weld metal;There is a bright,bright and smooth white band formed by element diffusion near the fusion line of the joint.The microstructure is austenite + martensite,and the microhardness can reach 400,but it has little effect on the joint performance.(4)A comprehensive evaluation of the welding process,vertical welding overhead welding performance,and crack resistance of ASH-2welding wire with better performance was conducted.The results show that ASH-2 welding wire has a small spatter,stable arc,and beautiful weld bead formation.The joint strength at both vertical and overhead welding positions is also as high as 698 MPa,and no cracks appear in the oblique Y crack resistance experiment.It is suitable for gas-shielded welding of10 Cr Ni3Mo V steel,achieving automatic welding of welding structures.