Glow discharge nitriding in AISI 304 at different nitrogen–hydrogen atmospheres: Structural, mechanical and tribological properties

Structural, mechanical and tribological properties of AISI 304 steel submitted to nitrogen glow discharge at different atmospheres (N2:H2, 60:40) and (N2:H2, 20:80) and substrate temperatures are reported. Expanded austenite γN and Fe–Cr nitrides were identified as a function of the working conditions. Rietveld refinements indicate that ɛ-Fe2+xN is the predominant phase for the poorest nitrogen atmosphere while γ′-Fe4N phase is major for the richest one. The nitriding produces a surface hardening that can reach hardness values up to 14 GPa. Thicker nitrided regions are obtained in high nitriding temperatures. Reciprocating sliding tests in samples with rich or poor nitrogen atmosphere indicated long running-in regimes for high nitriding temperature. Both nitrogen atmospheres reduced the wear up to a factor of six even at the lowest temperature process. The nanoscratch tests do not show difference in the surface elastic recovering in all used nitriding conditions.