Researching On Welding Process Of High Nitrogen Austenitic Stainless Steel With N-Ar Mixed Protecting Gas

High nitrogen steel (HNS), a kind of single-phase austenitic stainless steel in which nitrogen element instead of nickel, it has such characteristics as high strength, high toughness, high corrosion resistance. It has been applied gradually in the military industry, marine engineering, grid and so on. However, in the application of the welding of HNS, the losses of nitrogen, nitrogen porosity and the decrease of weldability have been become bottlenecks.HNS wire and 307Mo wire are used in the nitrogen-argon-oxygen and nitrogen-argon-carbon dioxide ternary melting polar gas shielded welding process test for 16 mm high nitrogen austenitic stainless steel plate in this paper.With different tests of two wires, in condition of nitrogen ratio adjustment and oxidizing gas category, the results showed:It turns out that with the increasing of nitrogen ratio, the content of nitrogen first rise, later down in welded joints. In the same proportion, the effect of 2.5% O2 to nitrogen fixation in welded joints is better than that of 2.5% CO2.When protecting gas changes to N2-Ar-O2, it turns out that the content of welded joints which are used with a HNS wire is higher than that of weld joints which with a 307Mo wire.When the nitrogen ratio of the N2-Ar-O2 protecting gas and N2-Ar-CO2 gas is 20%, the content of nitrogen is the highest. The nitrogen content of welded joints with a HNS wire can reach to 0.95%, those with a 307Mo wire is 0.57. With the increasing of the nitrogen content in welded joints, nitrogen porosities increase, and there exist not only macro nitrogen porosities and microscopic nitrogen porosities in the weld metal, measured by X-ray.With the protective atmosphere of nitrogen was added, Percentage weld ferrite content is reduced, when the protecting gas is 100%(97.5%Ar+2.5%02), the weld which used HNS wire, Ferrite percentage in the weld is 0.3%, the weld which used 307Mo wire, Ferrite percentage in the weld is 4.7%, when the protecting gas is 90%(97.5%Ar+2.5%O2)+10%N2, the weld which used HNS wire, Ferrite percentage in the weld is 0.27%, the weld which used 307Mo wire, Ferrite percentage in the weld is 0.23%.When the weld nitrogen content increase, the weld micro-hardness increase, Weld tensile strength from 850 MPa to 930 MPa. When the nitrogen content of the weld joint at the maximum 0.95%, weld tensile strength reached 930 MPa, it is 88.57% of the HNS’s level. Weld impact absorbed energy is low. Tensile and impact fracture dimples are isometric presence. This shows that the connector is ductile fracture.