Ferromagnetism in interstitially hardened austenitic stainless steel induced by low-temperature gas-phase nitriding

Interstitial hardening via low-temperature gas-phase nitriding of 316L austenitic stainless steel can induce ferromagnetism in the outer regions of the hardened “cases”. Magnetic force microscopy, scanning electron microscopy, electron backscatter diffraction, X-ray diffractometry and Auger electron spectroscopy revealed that the transition from paramagnetic to ferromagnetic behavior requires a critical nitrogen concentration of about 14 at.% in interstitial solid solution, which expands the lattice parameter of the austenite by about 5%.