Enhancement of Nitriding Rate in SUS304 Austenitic Stainless Steel under Gas Nitriding

An investigation on the microstructure, tribological and corrosion performance of AISI 321 stainless steel carbonitrided by RF plasma process

“…The variation in the corrosion performance as a function of treatment temperature is mainly attributed to the variation of the microstructure of the carbonitrided layer besides N and C contents [66,67]. It is addressed that the modified surface layers containing "expanded austenite" not adversely affect the good corrosion properties of austenitic stainless steel [68][69][70]. The superficial amorphous carbide or carbonitride/crystalline layer can play a significant role in protecting materials against corrosion.…”

Transition of rate mechanism from internal nitriding to rapid nitriding mechanism at 12.5 mol%Cr in austenitic Fe-Cr-Ni alloy system

“…zone in meta-γSN phase formed under the surface of austenitic stainless steels under giant N fugacity (fN) of NH3. 9 The fN of 90%NH3 -10%H2 mixture is calculated as approximate 10 6 [atm] at 723 K 21 ; subscripted [atm] is dimension of the fugacity related to equilibrium constant. Each reaction steps described above are summarized as follows in brief.…”

“…Anomalous nitriding behaviour of austenitic stainless steels (for example marked rapid nitriding above approximate 700 K and a sudden decrease of the nitriding rate around 873 K) have been reported by many investigators. [1][2][3][4][5][6][7][8][9][10] Cause of these anomalies, however, has not been revealed. Authors explained the decrease of the rate from the viewpoint of a termination of the rapid nitriding above the temperature of 873 K. 8,9 Therefore next issue was to reveal the cause of the rapid nitriding.…”

Importance of surface activation for nitrided layer formation on austenitic stainless steel

“…Only a few studies present results of gas nitriding. [6][7][8][9] In order to nitride an austenitic steel, an activation of the surface is needed to remove passive chromium oxide layer. During plasma nitriding, this layer is removed by means of ion sputtering, which is applied either as a treatment preceding nitriding or which takes place during nitriding due to the physical and chemical influence of the ions on the surface.…”

“…NH 4 Cl, 7 covering the surface with an active layer, e.g. phosphating, nickel plating, 14 preoxidation) (ii) mechanical (grinding or polishing) 15 (iii) physical (ion sputtering).…”