Weldability of high nitrogen austenitic stainless steel. Reports 2: Nitrogen absorption of 316L weld metal and its fine particles in extreme environments

Abstract

The suitability of the high nitrogen pressure Metal Inert Gas (MIG) ARC welding process (constant arc length condition) for high nitrogen containing stainless steel was investigated. The formation of fine stainless steel particles by the high nitrogen pressure MIG arc welding process was examined. The welding atmosphere consisted of pressurized N2 gas. Nitrogen absorption of 316L stainless steel weld metal in the high nitrogen pressure MIG process was studied. The effect of nitrogen in remelted weld metal and changes in the microstructure of the weld metal were observed. The nitrogen content of weld metal and the number of fine particles increased with increasing pressure of N2. Approximately 0.64 and 2.4 mass percent nitrogen was absorbed in the weld metal and fine particles at pressure of N2 6 Mpa and 3 Ma nitrogen respectively. Nitrogen content of the weld metal was lower than that representing equilibrium solubility of 316L stainless steel at close to the melting point. Nitride in the fine particles could not be found by X-ray analysis.

高窒素含有ステンレス鋼への、高窒素圧金属不活性ガス(MIG)アーク溶接(一定アーク長条件)の適合性を検討した。高窒素圧MIGアーク溶接プロセスでのステンレス鋼微粒子の形成を検討した。溶接雰囲気は加圧N2ガスで構成した。高窒素圧MIG溶接での316L鋼溶接金属の窒素吸収を研究した。再融解溶接金属中の窒素の効果と、溶接金属の微細構造の変化が認められた。溶接金属の窒素含有量と微粒子数は、N2圧力の増大につれて増加した。N2圧力6Mpaと3Mpaとでは、溶接金属と微粒子中に吸収された窒素量は、それぞれ約0.64%と2.4%であった。溶接金属中の窒素含有量は、316Lステンレス鋼の融点近くでの平衡溶解度に相当する量よりも低かった。X線分析では、微粒子中に窒化物は認められなかった。