High Strength Stainless Austenitic CrMnCN Steels ‐ Part II: Structural Changes by Repeated Impacts

Phase transformations and changes in the structure caused by impact loading of steel Cr18Mn18CN alloyed with carbon+nitrogen are studied in comparison with Hadfield steel using X‐ray diffraction, Mössbauer spectroscopy and TEM. It is shown that the surface layer of all the studied steels impacted by mineral particles of greywacke remains austenitic, although their magnetic structure within a depth of about 10 μm is similar to that of martensite. TEM studies reveal a mixture of amorphous, nanocrystalline and thin‐twinned fcc crystal structures. The suggestion is made that the atomic configuration at the twin boundaries is similar to that in the bcc lattice and induces the high‐spin state of the iron atoms in the thin twins. At the same time, the amorphous structure of the surface layer can be also a source of ferromagnetism like this occurs in rapidly quenched FeSiB ribbons. The extremely high wear resistance of the newly developed CrMnCN steels and of Hadfield steel seems to be related to the impact‐induced surface structure in its amorphous + nanocrystalline + thin‐twinned austenitic states.