Effect of nitrogen contamination on intergranular corrosion of stabilized ferritic stainless steels

Abstract

Three different alloys of AISI Type 444 (18Cr–2Mo) ferritic stainless steel, stabilized to different levels with titanium and/or niobium, were melted as welds or weld simulations with deliberate additions of nitrogen to the argon shielding gas in order to simulate the effects of accidental contamination by nitrogen during production welding. The oxalic acid etch test (ASTM A262–A) was used to assess the susceptibility of the melts prepared in this way to intergranular attack, and the extent of attack was quantified. It is shown that a clear correlation exists between the extent of intergranular corrosion and the amount of nitrogen taken up by the steel on melting. The implications of sensitization by nitrogen contamination both for steel design and integrity of production welds are discussed.

MST/415