An evaluation of weld metal nitrogen retention and properties in 316LN austenitic stainless steel

A series of tests were conducted using varying levels of nitrogen and helium in a conventional argon shielding gas when welding 316LN austenitic stainless steel. The outcome was that a 15 per cent nitrogen addition to the argon shielding gas had the most significant effect on increasing the weld metal nitrogen. Subsequent additions of helium to the argon 15 per cent nitrogen shielding gas had very little overall benefit. Increasing the nitrogen content of the weld metal had the consequential effects of decreasing the ferrite content and the hardness. As a result of solid solution strengthening, the yield strength increased with increase in nitrogen content. There was an increase in impact toughness as the nitrogen content increased. This was related to the decreased ferrite content associated with the strong austenetizing potential of nitrogen. It was also shown that an almost fully austenitic weld metal could still have very good toughness. In combination with these effects there was no loss in corrosion resistance. The addition of nitrogen to a conventional argon shielding gas presents attractive cost and quality benefits over the established requirement to over alloy the weld filler material with expensive alloys such as nickel.