Oxidation and nitridation of alloy 800 H at a growing creep crack and for unstressed samples

Time–Temperature–Precipitation Relations for Nitrides and Evaluation of Internal Oxidation Theory for Nitridation of Austenitic Stainless Steel

“…x CrN ≈ 60 µm. This is consistent with measurements by Welker et al [16], where CrN penetration in Alloy 800H was less than 100 µm for times 650 h and 1000 h at 1000°C.…”

“…CrN was also identified closest to the free surface (Figure 2). This is consistent with Welker et al's work on Alloy 800H [16], where CrN was only identified after nitriding at times exceeding 600 h at 1000°C. Ti(C,N) precipitates were present throughout all nitrided samples, but no precipitation front was observed.…”

“…Chromium nitrides are known to form in Alloy 800H upon nitridation [16]. Hence a purely theoretical approach to determining nitridation kinetics is unlikely to prove accurate in the present study.…”

“…Formation of nitrides of the minor alloying elements often present in commercial alloys has not been examined. Aluminium nitride is also known to form in 800H [2,16], but the current lack of solubility and diffusivity data for Fe-Ni-Cr-Al alloys means the applicability of Wagner's analysis has not yet been evaluated for this case. Determination of nitridation kinetics in the present study will therefore be reliant on experimental nitride penetration data.…”

“…Experimentally derived models [15][16][17] and some individual data points [18] for nitridation of 800H are available, but are limited to 1000°C. Parabolic behavior was assumed a priori, which is common in studies of nitridation kinetics in Fe-Ni-Cr alloys (see e.g.…”