Structure of the Ion-Nitrided Layer of 18–8 Stainless Steel*
Kazuo Ichii, Kimio Fujimura, Takao Takase
Abstract
Structure of the ion-nitrided layer of the surface of 18–8 stainless steel in the atmosphere of N2–H2 gas mixtures, was investigated by means of X-ray diffraction, microscopy, hardness testing, and electron probe microanalysis. The nitrided layer at 673 K had 3–7 µm in thickness, ferromagnetism, and about HMV 1000 in hardness. This layer was composed of a compound of the form, M4N [M = (Fe, Cr, Ni, …)] which had the same crystalline structure as Fe4N. At 773 and 873 K, CrN, α, and γ′ phase were detected and the compound layer of the surface had several µm in thickness and about 9 wt% nitrogen. The highest value in hardness of the surface of nitrided layer could be obtained at 773 K in the three experimental temperatures and its value was HMV 1250.