Structure of the Surface Layers of Metastable Austenitic Stainless Steel Nitrided in Electron Beam Plasma

Abstract

The effect of the nitriding temperature in electron beam plasma on the structural and phase composition of the surface layers of metastable austenitic stainless steels is studied. Conversion electron Mössbauer spectroscopy shows that nitriding at 350°C results in the transition of the austenite into the α (bcc) phase by the shear mechanism in the surface layers of a plate (tenths of a micron). A nitrogen supersaturated austenite and a mixture of nitrides with a predominant configuration of three nitrogen atoms in the environment of iron are formed in layers 1–5 μm thick. Nitriding at a temperature of 500°C and above leads to nitrogen supersaturated austenite decomposition, the escape of chromium and nitrogen from the matrix into nitrides CrN, Fe₄N, and Fe_xN, and the subsequent γ → α phase transformation.