SUS 430 Stainless Steel TIG Welding Process Optimization And Subsequent Heat Treatment On The Structure And Performance Of Weldments

The chromium content of ferritic stainless steel with body-centered cubic crystal structure is generally between 11-30%.In addition to good strength,magnetic and wear resistance,the ferritic stainless steel also has moderate corrosion resistance,especially chloride resistance stress corrosion and pitting corrosion are excellent.It is commonly used in these industries,such as ships,vehicles,household appliances,kitchen equipment,and building decoration.Austenitic stainless steel is often replaced by ferritic stainless steel in the occasions where performance requirement is not high.However,ferritic stainless steel has problems such as intergranular corrosion and welded joint embrittlement during welding,which limits its development.Therefore,430 ferritic stainless steel was welded by TIG welding method,and the effect of process parameters and post-weld heat treatment process on the microstructure and performance of welded joint was studied.Good welding process and post-weld heat treatment process were obtained,which provided theoretical support for production practice.The main research contents are as follows:1. When the welding current was between 160 A and 190 A,a welded joint with a good surface morphology was obtained.The chromium equivalent(Cr_eq)in the weld metal decreased and the nickel equivalent(Ni_eq)increased with increasing welding current.The heat-affected zone?HZA?of the welded joint was mainly equiaxed grains.The columnar grains were mainly near the center of the weld and the equiaxed grains near the edge of the weld.The weld is composed of ferrite and martensite.When the welding current is 170 A,the most content of martensite was obtained.The hardness was significantly increased from the base metal and the HAZ to the center of the weld.The hardness of the base metal was about 180 HV,and the hardness of the center of the weld was about 1.5 times the hardness of the base metal.The tensile strength of welded joints reached the maximum value of 456.24 MPa at 170 A,and the elongation was 15.84%.2. When the heat treatment time reached 2 h,the band shape in base metal disappeared,the grain boundaries were clear,and the grain size was uniform.At this time most of the grains of base metal were recrystallized equiaxed grains.Continue to increase the heat treatment time,the grains grew abnormally.The content of martensite in the weld joint and HZA of the welded joint was significantly reduced after heat treatment,some ferrite grains in the weld have recrystallized at 2 h.At 2 h and 20 h,the precipitation in the HZA increased,and most of them were located at the grain boundaries of ferrite grains.3. The tensile strength of welded joints increased firstly and then decreased with increasing post-weld heat treatment time.The tensile strength and elongation of welded joints reached the maximum value of 483.48 MPa at 2 h,and the elongation was 21.43%.After the post-weld heat treatment,the hardness of the base metal,the weld and the HAZ all had a significant downward trend compared with that in the welded state.From the results of the electrochemical curve,corrosion morphologies and corrosion rate,the corrosion resistance of the base metal and the weld were significantly improved after the post-weld heat treatment,and the improvement is most obvious when the time was 10 min.After annealing at 930?for 2 h,the weldment showed the best combination of tensile strength and elongation;after annealing at 930?for 10 min,the weldment showed the best corrosion resistance.Therefore,the SUS 430 ferritic stainless steel TIG welded joints with good comprehensive performance can be obtained after the post-weld heat treatment of 10 min-2 h.By selecting appropriate welding process parameters and post-weld heat treatment process,the brittleness of welded joints was reduced,and the corrosion resistance of welded joints was improved.The recrystallization kinetics of ferrite grains at the heat treatment temperature of 930? was obtained.