Fig. 4

Gas nitriding of S19 sample, at 900 °C for 5 min in electric furnace. (a) sample S19 after nitriding, (b) OM of cross-section microstructure on top part of the sample, (c) SEM image on the top part of S19 cross-section, (d,e) line scan SEM–EDS analysis on the top of S19 cross-section.