NITROGEN UPTAKE IN BRIGHT-ANNEALED AISI-304 TYPE STAINLESS-STEEL THINSHEET FROM A RUNNING PRODUCTION LINE STUDIED WITH AUGER-ELECTRON SPECTROSCOPY

The nitrogen content in the surface of bright annealed steel sheet is of vital importance for the corrosion resistance and the mechanical pr operties of the surface. Too much nitrogen in the surface region embri ttles the surface and supports the formation of different chromium nit rides, in turn increasing the susceptibility to pitting. Surfaces of s heets, taken from a running production line, have been investigated by Auger electron spectroscopy (AES) and electron probe X-ray microanaly sis (EPXMA). Both techniques show that it is possible to reduce the ni trogen absorption in the steel by raising the dew point of the reducin g atmosphere in the annealing furnace from -45-degrees-C to -35-degree s-C. It is suggested that the lowered nitrogen absorption is partly ca used by interstitial, or grain boundary, oxygen acting as a diffusion rate limiter in a surface zone of about 50 nm thickness, thus being a complement to the more generally accepted mechanism of reduced nitroge n adsorption due to surface adsorption of oxygen.