Effect of nitrogen addition on microstructure and fusion zone cracking in type 316L stainless steel weld metals

Nitrogen is known to have a significant effect on cracking behaviour of austenitic stainless steel during welding, although reports on its effects have often been controversial. A study was therefore undertaken to examine the effect of nitrogen on the weldability of two type 316L weld metals. Weldability was assessed using the longitudinal moving torch Varestraint test. The brittleness temperature range during solidification was calculated from crack length data. Nitrogen was added through the shielding gas to 316L (base N-0.036%) and 316LN (base N-0.073%) to produce weld metal nitrogen contents in the range 0.04–0.19%. In the primary austenitic solidification mode, nitrogen addition had little effect when the P+S levels were relatively low (316LN with 0.031%P, 0.001%S) while cracking increased for higher impurity levels (316L with 0.035%P, 0.012%S). Nitrogen additions also produced significant coarsening of the primary solidification structure. The study indicates that weldability effects of nitrogen may be influenced by the impurity levels, particularly S. The cracking data showed good correlation with the WRC Creq/Nieq ratio.