S-phase

The S-phase, also called expanded austenite, is a structure that can be obtained on austenitic or duplex stainless steel by interstitial super saturation of the metal lattice with carbon or nitrogen. The solution of massive amounts of carbon/nitrogen leads to compressive stresses that can be measured as increased hardness on the surface. The typical layer thickness, depending on material and the hardening process, ranges from 5 to 40 microns. Resulting benefits include an increase in abrasion resistance, improved fatigue life and the prevention of galling for austenitic material pairings.

See also Kolsterising.