Research On The Joint Design And Technology Of Improving The Corrosion Resistance Of 444 Stainless Steel Welded Joint

Due to the lack of nickel metal resources in China and the international price of nickel metal fluctuations,which lead to high cost of nickel-containing stainless steel.With the development of smelting technology,low nickel does not even contain nickel ferrite stainless steel has been rapid development,because of its low price,with good corrosion resistance,especially resistance to chloride ion corrosion,low coefficient of thermal expansion,heat transfer Performance and other characteristics,has been successfully used for heat transfer equipment,household appliances,ships,automobiles and other industries.However,ferritic stainless steel after welding process prone to many problems,such as joint tissue coarse,corrosion resistance and other issues.In this paper,444 ferritic stainless steel as the base material,the welding joint performance of different welding processes was studied,the research results to promote the application of ferritic stainless steel has important practical significance444 ferrite stainless steel sheet with 1.5mm thickness was used.The TIG welding experiment was carried out without using the filling material,the filler material as the base metal and the filling material for the ER316 L austenitic wirel respectively.Metallographic XRD test,microhardness hardness test,tensile test,fracture scanning experiment(SEM),electrochemical experiment,soaking experiment.Through the above experiments,the effect of different filler materials on the performance of welded joints was compared.experiment for the joint sample.Through the metallographic experiment of welded joints,welded joints include heat affected zone,fusion zone,weld zone three parts.No filler material,filler material for the base metal metal seam area does not occur changes in the organization,all a single ferrite,and ferrite showed columnar crystal distribution;the organization of filling material for the ER316 L wire weld area is Austrian Body and acicular ferrite.The microhardness test shows that the hardness of the weld joint with ER316 L stainless steel wire as the filler is the highest,220 HV,is 220 HV.The hardness of the weld zone without the filling material is 172.5HV.The hardness of the weld zone with base metal as the filler is 179 HV.The tensile test and fracture scanning experiments show that the fracture of three welded joints are ductile fracture,the tensile strength of the welded joints was 430.54 MPa,447.82 MPa and 476.87 MPa respectively.The elongation rates of the welded joints were 17.12%,22.38%,26.93%,respectively,The fracture position of the joint is the weld zone,the heat affected zone and the base material area respectively.The electrochemical test results show that the corrosion resistance of welded joints with ER316 L wire is the best,followed by the welded joints with base metal as the filler material,and finally welded joints without the filling materiale in 3.5% sodium chloride solution.In the soaking test of three sets of welded joints in 6% FeCl3,the three groups of welded joints were soaked for 8 hours and the corrosion rates were 3.152 g·m-2·h-1 、1.243g·m-2·h-1、0.125g·m-2·h-1,through the observation of corrosion samples,the three groups of soaking the sample pitting pit size in turn: do not use filler material welding samples,the use of metal materials as the filler material welding samples,the use of ER316 L as the filler material welding samples.In the 444 stainless steel horn welding test,the use of ER316 L stainless steel wire for the filling material for corner welding test,The angle was 10°,16°,20°,28°,40°and 50 respectively.Through the observation of the macroscopic structure of the welded joint,The angle of 10°,16°,20° of the joint shape is good,the angle of 28°,40°,50° of the joint shape is poor,joints appear lack of penetration,welding oxide serious and other defects.The microstructure of the joint consists of austenite and acicular ferrite.The electrochemical test in 3.5% NaCl solution showed that the corrosion resistance of the joints was from 20°,16°,10°,28°,40°and 50°,respectively.In order to improve the welding process,the welding process is improved by the protection of the gas,and the corrosion resistance of the corner joint is improved.