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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.…”

“…[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. Recently we discussed the rapid nitriding analogously with simple lasering model 11 based on a cyclic mechanism of formation and reversion of a Cr･N type G.P.…”

“…zone in a meta-stable N supersaturated solid solution (expressed as meta-γSN phase) formed just under the nitrided surface of austenitic Fe-Cr-Ni alloys. 9 Concentration of N in the γSN phase formed in austenitic stainless steels at/near 673 K has been reported as high as 38-45 mol%N. 12,13 This N concentration is too high according to the conventional idea of the austenitic stainless steels.…”

The nitrogen-absorption isotherm for Fe–21.5 at. % Cr alloy: dependence of excess nitrogen uptake on precipitation morphology

“…Chromium is often used as alloying element in ferritic nitriding steels because of its affinity for nitrogen, leading to the precipitation of CrN in the nitrided zone. Nitriding of iron-based alloys containing Cr has been the subject of several investigations [5][6][7][8][9][10][11][12][13][14][15][16][17][18].…”