Study On The Corrosion Resistance Improvement Of A-TIG Welded Joints

SUS444 stainless steel presents several obvious advantages,such as high thermal conductivity,small linear expansion coefficient and so on.In addition,it is very suitable for the field of heat exchange and heat cycling,and is widely used in the production of stainless steel water heater.However,from the use of products,the lap joint has serious corrosion problems.The reason is mainly due to the incomplete penetration in the lap joints.Moreover,the narrow gap formed between the two sheets is also favorable for crevice corrosion.Activating flux TIG?A-TIG?welding is a highly efficient TIG welding method.The process will be performed after coating the surface of the base metal with a layer of active fluxes.It can effectively increase the weld penetration and can greatly reduce the heat input.The current related researches of A-TIG welding mainly focus on the influence of active fluxes on the increase of weld penetration and mechanical properties.However,there have been not many reports about the corrosion resistance of A-TIG welding stainless steel joint.In this study,the SUS-444 ferrite stainless steel was welded by A-TIG welding method.Moreover,the effects of the single component active flux on the microstructure,mechanical properties and corrosion resistance of SUS-444 stainless steel welds were studied.Meanwhile,the effect of active flux on corrosion resistance of stainless steel angle joint was also studied.In this study four different kinds of oxides?Cr₂O₃,B₂O₃,TiO₂ and SiO₂?are used as the active fluxes.The joints are well formed and have no macro-defect.The experimental results show that the welding current used in A-TIG welding is lower,and the current used for A-TIG welded joints coated with SiO₂ is the smallest.The the X-ray diffraction diagrams of the welded joints show that the addition of the active flux does not change the phase of the weld zone,but the proportion of grain size,shape and the proportion of the phase change.The mechanical test results show that A-TIG welded joint hardness and tensile strength were improved,but the elongation decreased slightly.The results of immersion corrosion and electrochemical corrosion test showed that active flux had a significant effect on the corrosion resistance of A-TIG welded joint for SUS444ferritic stainless steel.The joint coated with SiO₂ showed excellent property of corrosion resistance while the active flux Cr₂O₃,B₂O₃ and TiO₂ had reduced corrosion resistance of welded joint.Moreover,SUS-444 stainless steel sheets were welded by different lapping angles.The joints are well formed and have no macroscopic irregularity.The electrochemical corrosion test results show that the lapping angles have a significant effect on the corrosion resistance of joints.In 3.5%NaCl solution,the corrosion resistance of joints with lapping angle of 12°is poor.The joint with lapping angle of 22°has the best corrosion resistance.SiO₂ was selected as the active flux for the A-TIG welding lap joint experiment.The results show that the joints are well formed and the corrosion resistance is further improved.