Effect Of Welding Process On The Structure And Properties Of XDS-2 High Silicon Austenitic Stainless Steel

High silicon austenitic stainless steel has excellent corrosion resistance in high temperature and strong oxidation medium,and it has been widely used in sulfuric acid preparation and conveying equipment.However,there was still a lack of systematic research on the welding of high silicon austenitic stainless steel.This paper focused on the butt welding of XDS-2 high silicon stainless steel plates.TIG welding,MIG welding,laser welding,and laser+MIG composite welding methods was employed to join the XDS-2 high silicon stainless steel plates.The forming quality,microstructure,mechanical properties and corrosion resistance of XSD-2 welded joints were studied systematically.It provided theoretical support and technical support for the safe application of high silicon austenitic stainless steel in sulfuric acid chemical industry.The main works and conclusions are as follows:（1）The weldability of XDS-2 high silicon stainless steel was analyzed by chemical composition.XDS-2 austenitic stainless steel has high sensitivity to solidification heat crack.During welding,Si and O elements segregate seriously at grain boundary.（2）The welded joint of XDS-2 high silicon stainless steel is welded by four welding processes,and the welded joint has good macro-morphology.The microstructure of welded joint was columnar austenite and a small amount of delta ferrite.EDS scanning of the grain boundary showed that brittle precipitates of Cr,Ni,Si intermetallic compounds and BCC-rich Si,Ni,Mo structures are formed.The results of EBSD analysis showed that the grain size of the sample was obviously increased,and the columnar crystal was larger in laser+MIG hybrid welding with higher heat input.Through the analysis of the KAM diagram,the stress concentration in the weld area was obvious.Because of the heat input concentration,high temperature gradient and fast cooling speed,the laser weld joint had large direction difference in the weld center.When laser+MIG composite welding was used,the heat input was larger and the arc affects.It made the residual stress in the welded joint higher.（3）The mechanical properties of welded joint of XDS-2 high silicon steel decreased remarkably,the tensile strength of the tensile specimen was above90%of the strength of the base metal,and the elongation was in the range of10%～15%.After welding,the plasticity of the specimen decreased remarkably.Remarkable tear ridges and cleavage steps could be observed on the tensile fracture surface,which were characterized by brittle fracture.The impact toughness of welded specimens in different welding processes was in the same range,the highest was 15%of the base metal,and the fracture was characterized by brittle fracture.The hardness of the weld increased remarkably due to solution strengthening.From the weld center to the base metal region,the hardness value increased first and then decreased.The hardness of laser weld zone is the highest,due to the high energy density of laser zone makes the HAZ very small and avoids hardened zone.（4）Study the effect of different processes on the corrosion resistance of weldments.The self-corrosive potential of laser welding and laser+MIG hybrid welding were lower than that of base metal,and higher in TIG welding and MIG welding.The pitting potential of different welding specimens was in the same level range.Comparing the intergranular corrosion sensitivity of XDS-2 steel welded joints with different welding processes,it was found that the intergranular corrosion sensitivity of MIG welding and TIG welding was low.Laser welding and laser+MIG welding have high heat input,so that M₂₃C₆ and sigma phases precipitate at the grain boundary of XDS-2 high silicon steel weld,and chromium poor zone was formed.In addition,the larger residual stress in the weld zone destroyed the passivation film.Therefore,laser welding and laser+MIG welding had higher susceptibility to pitting and intergranular corrosion.Compared with the characteristic EBSD orientation diagrams of the base metal and different welded joints,the proportion of low?CSL grain boundaries with intergranular corrosion resistance in the welded specimens decreased greatly.In MIG welding and laser+MIG composite welding,the proportion of grain boundaries of?3 is relatively high,which may be due to its high and concentrated heat input.But in fact,laser+MIG is not sensitive to intergranular corrosion,and the evaluation of actual corrosion boundary was inconsistent with that of EBSD.