AbstractType 304 stainless steel was welded using argon, nitrogen, and ammonia as shielding gas in gas metal arc welding. Nitrogen diffusion into the base metal was measured using Auger electron spectroscopy, which also permitted the carbides and nitrides formed during the welding and heating processes to be identified. Weldments of higher nitrogen contamination have greater resistance to sensitisation. The best results for arc initiation and stability and for nitrogen diffusion into the base metal were obtained using a shielding gas containing (vol.-%) about 10% nitrogen and 0·5% ammonia.MST/820