Characterization of surface treated layers on Austenitic Stainless Steel and 9.3%Cr Ferritic steel resulting from High Temperature Nitriding

The paper presents the results of investigation into corrosion resistance behaviour of
gas nitrided 316L austenitic stainless steel and 9.3%Cr ferritic steel. Gas nitriding is
a heat treatment technique that improved fatigue life, strength and wears and
localized corrosion resistance. However, at certain temperature the steel becomes
sensitized to possible intergranular corrosion. The heat treatment permits the
formation to small precipitate particles of chromium carbide, Cr23C6 by reaction
between the chromium and carbon in the material. During the heat treatment process,
the samples are heated at two different temperatures for two samples which are at
600°C and 900°C in a tube furnace through which nitrogen gas is allowed to pass.
The nitrogen reacts with the steel penetrating the surface to form nitrides. In order to
investigate the presence of chromium carbine in grain boundary, further studies were
conducted to analyse the microstructure, physical and mechanical properties by
comparing the specimens before and after the nitriding process.