On the Crystallographic Features of Cr_2N Precipitates in High-Nitrogen Austenitic Stainless Steel (I) I. Precipitation Behavior of the Second Phases during Isothermal Aging at 900°C

摘要

In these sequential papers, the crystallographic features of Cr_2N precipitates in high-nitrogen austenitic stainless steel (HNS) were investigated with particular emphasis on the crystal structure of Cr_2N. In the first part of this study, the precipitation behavior of the second phases were examined utilizing electron microscopy and thermodynamic calculation. The precipitation sequence of the Cr_2N was found to be intergranular, cellular, and intragranular precipitation with aging time Based on the analyses of SAD patterns, the orientation relationship between gamma and Cr_2N was found to be [011]_gamma [1100]_(CR_2N) and (111)_gamma (0001) _(CR_2N)- On prolonged aging, the coarse a-phase with bet structure precipitated along grain and cell boundaries. The precipitation of a-phase could be explained by the mechanism that formation of nitrogen-depleted zone near Cr_2N induced nucleation of the o-phase, which was supported by thermodynamic calculation and electron microscopy.