A Moessbauer study on the deformed surface of high-manganese steels

Conversion Electron Moessbauer Spectroscopy (CEMS) is a useful technique to study structures and properties near the surface of materials. In this study, CEMS was applied to investigate around the surface of a high-manganese steel, which is called Hadfield steel which is known for its remarkable work hardening. X-ray backscattering Moessbauer spectroscopy was also performed in order to compare the state of the Fe atom near surface to that of bulk and the cause of work hardening of Hadfield steel was discussed. Observed Moessbauer spectra were analyzed into two components, one was a singlet peak corresponding to Fe atoms without C atoms at the first or the second nearest neighboring interstitial site, the other a doublet peak corresponding to Fe atoms with C atoms at those sites. A widely split six line peak of α' martensites was not observed in any Moessbauer spectra so that α' martensites has no relation to work hardening of Hadfield steel. The comparison of CEMS spectra to X-ray backscattering Moessbauer spectra made it clear that the decarburization around the surface occurred even in the samples before working. The value of quadrupole splitting in CEMS spectra decreased by working and this could be explained by the introduction of stacking faults in samples. The decarburization around the surface and the decrease of quadrupole splitting by working lead to the conclusion that work hardening of Hadfield steel results from the introduction of stacking faults and the formation of thin ε martensites. (author)