The fine structure of nitrided steels

Abstract

1. The structures formed in the process of nitriding are similar to those observed in aging alloys (Cu−Be and Ni−Be alloys, for example) during decomposition of supersaturated solid solutions. 2. It was found that the nitride phase precipitated in binary Fe−Al, Fe−Cr, and Fe−Mo alloys and steels 40Kh and 38KhMYuA have a B1 structure (NaCl type). 3. The high strength of the nitrided case on steel 38KhMYuA is due to a considerable extent to distortion of the matrix (α phase) resulting from the formation of finely dispersed nitrides completely or partially coherent with the matrix. The maximum hardness is reached in the initial stage of nitride formation when then thin (single layer of nitrogen atoms) lamellar nuclei are completely coherent with the matrix. 4. The high hardness of the nitride case is due mainly to aluminum. The addition of chromium and molybdenum to steel 38KhMYuA makes it possible to obtain (at a sufficiently high nitriding temperature) nitrides with a structure corresponding to the early stages of their formation, which favors a fairly large case depth and high hardness.