Recent Developments on the Weldability of a New High Nitrogen Stainless Steel

There is no other class of metallic materials offering a similar combination of strength, toughness. corrosion resistance and non magnetic properties as nitrogen alloyed austenitic stainless steels. However, welding characteristics of these materials still have to be quantified. In the present paper recent developments on the weldability of a new high nitrogen austenitic stainless steel are presented. Due to an approximate nitrogen content of 0.6% by weight, careful welding procedures are required to retain as much nitrogen as possible in the weld. Different are welding techniques such as shielded metal are welding (SMAW), gas metal are welding (GMAW) and gas tungsten are welding (GTAW) were used. To investigate the influence on the microstructure and the resulting mechanical properties different filler materials and gas compositions were used. The welding performance tests were carried out according to EN 288-3. All weld tests were successful. For the SMAW process the microstructure showed fusion zones without pores or any other defects. In the GMA and GTA welds the addition of nitrogen to the shielding gas promotes the formation of pores. It has been shown that a content of 8 vol.-% of nitrogen in the shielding gas is too high. An optimum can be expected around 4 vol.-% of nitrogen. Hardness tests exhibited lower values in the fusion zone. Lower values could also be observed in the ultimate tensile strength with a loss in the range of 15%. These results are due to a lower nitrogen content in the weld metal. The Charpy V values in the fusion zone are high. A weighting factor of 18 for nitrogen was used in the Schaeffler diagram and showed a good correlation.