Weldability in High Pressure Nitrogen Atmosphere and Mechanical Property of Weld Metal of Austenitic Stainless Steel

Austenitic stainless steel was welded by GTA and GMA methods in high pressure up to 6.1MPa nitrogen pressure. Welding condition, nitrogen absorption and microstructure of solidified metals have been investigated. Nitrogen content (N) of GMA solidified metal increased from 0.2 to 0.65 mass% with increasing in pressure from 0.1 to 6.1 MPa. The fracture toughness of the weld metals was measured by means of the Charpy impact test at test temperature range from 77K to 290K. The Vickers's hardness number increased from 225HV to 350HV with N. The toughness increased with N up to 0.4%. However, N exceeded about 0.5% the intergranular fracture was easily caused by Cr2N and solidification micro cracks. Cr2N at the grain boundary can be absorbed in γ matrix and micro cracks were prevented by several % of Mn additions, then the fracture toughness at low temperature can be improved.