Volume and Grain-Boundary Self-Diffusion in a High-Purity Fe-50 mass% Cr Alloy

Abstract

Volume and grain-boundary self-diffusion coefficients of 51 Cr and 59 Fe in a high-purity Fe-49.7 mass% Cr alloy containing 13 mass ppm carbon and 6 mass ppm nitrogen have been determined in the temperature range between 923 and 1453 K by use of the sputter-microsectioning technique. Linear Arrhenius lines for volume self-diffusion coefficients of both tracers have been observed across the a-s phase-transformation temperature 1103 K, which is consistent with the suppression of the formation of the s-phase by purification. The Arrhenius equations can be expressed by D Fe ¼ 1:2  10 À4 expðÀ256 kJ mol À1 =RTÞ m 2 s À1 and D Cr ¼ 1:3  10 À4 exp ðÀ259 kJ mol À1 =RTÞ m 2 s À1 . Downward curved Arrhenius lines for the grain boundary diffusivity adD gb (s segregation factor, d width of grain boundary, and D gb grain boundary diffusion coefficient) of both tracers have been observed. This is attributed to the formation of very thin layer of the (Cr, Fe) 23 C 6 phase at the grain boundary near the surface of the specimens.

Metallurgical Characterization and Kinetics of Borided 34CrNiMo6 Steel

“…The diffraction patterns also show peaks belonging to chromium iron carbide (Cr,Fe)23C6 (Cr15.58Fe7.42C6). This phase was also identified by Yamazagi et al [28] and Ohta et al [29]. When the boriding temperature is increased to 1223 K, Fe3O4 (magnetite) is detected in addition to the FeB and Fe2B phases.…”

Diffusion of Cr and Fe in a High-Purity Fe-50 mass%Cr-8 mass%W Alloy

“…5) Then, we have presented the volume and grain boundary diffusion of 51 Cr and 59 Fe in a high purity Fe-50 mass%Cr alloy in the temperature range between 923 and 1453 K. 6,7) Linear Arrhenius relations for the volume diffusion of both components in the alloy have been observed across the transformation temperature of the σ phase, suggesting that the σ phase was barely formed in the alloy and that it gives negligible influence on the volume diffusion. However, Arrhenius * Graduate Student, Tohoku University.…”

“…The chemical composition of the alloy is shown in Table 1 in comparison with that of the high purity Fe-50Cr alloy used in a previous work. 6,7) The ingot was hot-forged and hot-rolled at 1373 K in an argon atmosphere to a rod 14 mm in diameter. Specimens of 12 mm in diameter and 1.5 mm in thickness were machined from the rod.…”

“…parison with those in the Fe-50Cr alloy. 6,7) The diffusion coefficients of both components in the Fe-50Cr-8W alloy take nearly equal values in the temperature range examined. However, both the values in the alloy are smaller than those in the high purity Fe-50Cr alloy.…”

“…Although the data are limited only at two temperatures, the activation energies for grain boundary diffusion of Cr and Fe are tentatively estimated to be 240 kJmol −1 and 200 kJmol −1 , respectively. The activation energies in the Fe-50Cr alloy in the corresponding temperature region 7) are about 270 kJmol −1 . Further discussion on the grain boundary diffusivities should await more extensive experimental data.…”