Microstructure and residual stresses of stainless steels case hardened with nitrogen

In the presence of 13–16 wt-%Cr, nitrogen enhances interstitial solubility during austenitising. Therefore, five different martensitic or ferritic–martensitic stainless steels were case hardened by solution nitriding instead of carburising. The highest compressive residualstress at the surface was obtained by a high content of δ-ferrite in the core and a low content of retained austenite in the martensitic case. The limits of alloying, the resulting microstructure and the implications for production and service are discussed.