Study On Structure And Mechanical Properties Of Q235/304 Dissimilar Steel Welded Joints

Because of the dissimilar steel weldment of Q235 carbon steel and 304 stainless steel is often applied in structural design and manufacture.And the fusion welding method is the most widely applied in the actual industrial production,Based on this,this paper mainly in the welding of inert gas welding process and its joints to study the organization and performance.Q235 and 304 stainless steel are welded together by reasonable welding parameters and the microstructures,mechanical properties(tensile,impact,hardness,bending,torsion,fatigue)and corrosion resistance of the welded joints were analyzed.According to the analysis results,evaluating whether the welded joint structure and performance meet the engineering requirements.Q235 carbon steel and 304 stainless steel welded joint microstructure observation results show that:At the Q235/weld joint,a decarburization layer is formed on the base material side of the fusion line Q235,While the layer near the weld to form a layer of carbon.Through the interface element line scan and surface scan shows:C,Cr,Ni,Mn and other elements in the region showed different concentrations of gradient distribution and alloy elements did not appear segregation phenomenon.The welded joint structure is skeletal or vermicular ferrite distributed on the austenite matrix and weld two-phase structure is more reasonable.In the fusion zone at the 304/weld joint,304 stainless steel heat affected zone near the austenite grain boundaries and grain boundaries near the formation of a number of fine strip precipitates.Through the EDS spectrum analysis,Where the C,O,Cr elements are significantly increased,while the Ni element decreased significantly,so the precipitates may be carbide or oxide.The results of the mechanical properties of welded joints shows;the tensile fracture position of the joint specimen is on the side of Q235 base metal,The tensile strength of welded joint is 505.23MPa,498.69MPa and 508.65MPa respectively and is not lower than Q235 base metal itself tensile strength.120°three-point bending test was performed and the joints did not produce any cracks.At room temperature impact test,the impact energy of Q235 heat affected zone is the smallest,while the impact energy of weld is slightly higher than that of Q235 base metal.The average Vickers hardness of welded joint welds is higher than the base metal and heat affected zone on both sides and Q235 in the vicinity of the weld line produced a large hardness changes.And this is mainly due to close to the Q235 side of the fusion line to form a layer of decarburization occurs softening,resulting in lower hardness,and close to the weld side to produce a layer of high hardness of the carbon layer,resulting in the hardness of the site increased significantly.The torsion angle of the joint weld reached 850°,and The welded joints were fractured on the side of the Q235 base metal,exhibiting a good torsional properties.High cycle fatigue test results show:Its fatigue limit is about 70.27%of the base material yield strength,Showing a good fatigue performance.