Study On Microstructure And Properties Of 443 Ferritic Stainless Steel Laser Welding Joint

443 ferritic stainless steel is an ultra-pure high-chromium ferritic stainless steel widely used in recent years.Compared with austenitic stainless steel,it has the advantage of low price and has excellent performance.It can replace 304 austenitic stainless steel in many aspects.In order to achieve the purpose of saving resources.However,it is highly prone to grain coarsening in the heat-affected zone during the welding process,affecting the microstructure and mechanical properties of the welded joint,hindering its popularization and use,and is currently an extremely problem to be solved.Heat input is the key factor affecting the thermal cycle of welding.This paper simulates the heat affected zone microstructure of 443 ferritic stainless steel by Gleeble-3800 thermodynamic simulation test machine,analyzes the thermal simulation sample,and selects the appropriate welding heat input.Laser welding tests were carried out and the welded joints were tested for mechanical and mechanical properties.The research results are expected to provide a theoretical basis for optimizing the actual welding process parameters.Firstly,the aging treatment of 443 ferritic stainless steel was carried out,and the microstructure after aging treatment was analyzed to find the sensitive temperature range of grain coarsening.The results show that when the aging temperature is increased to 900?,the grains begin to grow,and as the aging temperature increases,the grains grow continuously.It is known that the sensitive temperature of grain coarsening is above 900?,and the temperature interval is long.Time retention will result in coarsening of the grains.Then,Gleeble-3800 was used to simulate the microstructure of the 443heat-affected zone.The effects of heat input on the microstructure and microhardness of the heat-affected zone were studied by optical microscopy and hardness tester to find a suitable welding heat input value.The experimental results show that as the heat input increases,the cooling rate decreases.The residence time of the 443 ferritic stainless steel structure in the sensitive temperature range of grain coarsening is prolonged,and the grain size isgradually increased.In the thermal simulation test,when the heat input is0.1KJ/mm,the grain size of the heat-affected zone is still significantly larger than that of the parent material.Therefore,it is recommended to select a smaller welding heat input during actual welding.Finally,according to the influence of the heat input on the change law of the microstructure obtained by the thermal simulation test,the actual laser welding test is performed on the heat input 443 with the heat input value below100J/mm.The effects of heat input on the microstructure and mechanical properties of 443 welded joints were studied by means of optical microscopy,scanning electron microscopy,microhardness tester and tensile test.The results show that the grain size is equivalent to that of the parent metal when the heat input is 19.2 J/mm.As the heat input increases,the grain size of the welded joints grows.When the heat input is increased to 96J/mm,the microhardness increases obviously,and the tensile strength drops sharply.The tensile fracture of the welded joint is scanned.It is found that the 96J/mm fracture is a river-like cleavage fracture,which is brittle.When the fracture is broken,the welded joint under the rest of the heat input is a dimple-shaped fracture,which is a ductile fracture.No precipitation phase affecting the performance of the joint was observed for the welded joint.Considering the influence of heat input on the microstructure and mechanical properties of 443 ferritic stainless steel welded joints,the recommended heat input range for actual laser welding production is19.2J/mm?48J/mm.