Analysis of layer structure of boronized steel surface by conversion electron Mössbauer spectrometry (CEMS)

Abstract

The surfaces of Cr-Mo-Ni and Cr-Mo steels were boronized by the solid phase reaction with B₄C powders at 900° C for 5 h, and the surfaces of a Cr-Mo steel and a pure iron were boronized by the gas phase reaction in BCI₃ at 800° C for 2 h and reheated at 800° C under vacuum. The layer structures of 4 different samples were studied by applying CEMS to them. The analyses of CEM spectra of exposed surfaces by grinding to the desired depth revealed that the boronized surfaces prepared by the thermal diffusion of boron atoms in the iron lattice at 900° C were, in principle, composed of distinct multilayers of four iron—boron compounds; FeB_1+x (x > 0), FeB, Fe₂B and distorted α-Fe. Only the Fe₂B was deposited on the steel surface boronized at 800° C by the gas phase reaction. No intermediate layer between any two compounds was recognized, showing the contrast with the nitrided steel surfaces.