Study On Microstructure And Mechanical Properties Of High Heat Resisting Austenitic Stainless Steel 310S MIG Welding Joint

310S heat resistant stainless steel is a kind of advanced material in stainless steel products,not easy to be oxidized under high temperature,and often can be used to replace some expensive nickel-based alloy,serviced in the high temperature working condition.From this,it can reduce a large number of production costs,so has been widely used in many industries.Compared with conventional stainless steel,310 S heat resistant stainless steel has higher contents of alloy elements Cr and Ni.This leads to this kind of heat resistant material easy to appear materials organization coarsening,mechanical properties of welding joints got worse and many other problems in welding,and these problems will affect 310 S heat resistant stainless steel performance,results in the decrease of 310 S heat resistant stainless steel usage.At present,many scholars have focused their attention on the research of 310 S heat treatment,and high temperature performance,but little research has been done on MIG welding of 310 S.Therefore,in this paper,studying the simulation of 310 S heat resistant stainless steel heat-affected zone.According to the thermal simulation experiment,determine reasonable welding process parameter range and carry out 310 S heat resistant stainless steel MIG welding experiment under this process.After that,the experiment of tensile test at high temperature on MIG welding joint under different welding heat input was carried out.It is hoped that we can get a better welding process parameters through a series of research,so that it can better serve the practical application of 310 S.First,the Gleeble-3800 thermal simulation machine was used to simulate the heat-affected area of 310 S heat resistant stainless steel.The influence of different heat input and welding path times on the microstructure and microhardness of the simulated heat-affected area was analyzed by metallographic microscope and micro-hardness tester.We can find that the simulated grain size increases gradually with the increase of heat input and the number of welding passes,while the micro-hardness increases first and then decreases.Then,the thermal crack sensitivity of 310 S heat resistant austenitic stainless steel MIG welding joints experiment was carried out.The result show that the thermal crack presented initiation,propagation and maintenance three stages with the increase of the strain variable.In addition,under the condition of increasing the heat input used in welding,the joints need larger strain variables to produce cracks,which indicates that the joints have stronger resistance to heat cracks.At two heat inputs of 198J/mm and 243J/mm,the welding joints with uniform structure,good mechanical properties and good crack resistance can be obtained.Then,according to the variation rule obtained from the thermal simulation experiment,four kinds of smaller heat input were selected for MIG welding test of 310 S heat resistant stainless steel.The results show that as the heat input increases,the grain size of the heat-affected zone kept growing,the joints and the heat-affected zone were widened laterally.The unmixed zone(UMZ)formed by the melting and solidification of the base metal was formed near the welding seam fusion line.Finally,according to the structure change rule of MIG welding joints and heat-affected zone of 310 S heat-resistant stainless steel,the tensile test at 800? of welding joints was studied.We found that after stretching at 800 ?,the tensile parts broke in the weld area,and under the condition of high temperature,the yield and tensile strength of the welding joint can meet the requirements of the parent material.At the same time,with the welding heat input increased,the yield and tensile strength of the joint are decreasing and the elongation is increasing.Through the scanning observation,it was found that the welding joints had a ductile fracture at the welding heat input of 162J/mm,198J/mm,and 243J/mm.When the heat input increased to 308J/mm,the fracture morphology showed the dimples become shallower,and its number decreases,the bending and discontinuous pattern appears,the welding joints had a quasi-cleavage fracture.