Microstructure and Mechanical Properties of 304 Stainless Steel Thin Wall Pipe Longitudinal Seam under Different Welding Processes

The longitudinal seam welding of 304 stainless steel thin wall pipe was carried out by using tungsten argon arc welding（TIG） and laser beam welding（LBW）, respectively. The microstructure and mechanical properties of the welded joints were observed and tested by optical microscope, scanning electron microscope and microhardness tester. The results show that the microstructure of the TIG weld center is austenite equiaxed crystal and worm ferrite, and the microstructure of the laser weld center is composed of columnar crystals growing perpendicular to the fusion line. The grain size of the TIG welded joint is obviously larger than that of laser welded joint, and the heat affected zone is obviously wider than that of laser welded joint, the width of heat affected zone of the laser welded joint is only about 20μm. The average microhardness values of weld zone of the TIG and laser welded joints are about 150 HV and 190 HV,respectively. The microhardness distribution law of the two welded joints is heat affected zone ＞ base metal ＞ weld zone.