A new fcc-bcc orientation relationship observed in the strain-induced martensitic transformation of an austenitic stainless steel

Orientation relationship (OR) of the face-centered cubic austenite (gamma-fcc) and body-centered cubic structured martensite (alpha '-bcc) is a critical parameter affecting the microstructure-properties of metallic materials. So far, the ORs of Kurdjumov-Sachs (K-S), Pitsch and Nishiyama-Wassermann (N-W) are the most reported relationships involved in the martensitic transformation, where the K-S and Pitsch are preferred as the alpha '-bcc formed via the intermediated phase of hexagonal closed packed (hcp) z-plates, while the N-W only appeares as the alpha '-bcc direct nucleated from the gamma-fcc. Here, we observed a alpha '-bcc, formed at the intersection of parallel z1- and parallel z2plates with a new OR in an austenitic steel SS304 after shot peening. The new OR is distinctive among all of the known relationships in fcc-bcc systems, which was formed by the relative rotation of - 12.8 degrees from the Pitsch one, and expressed as the (002)fcc 12.8 degrees deviated from (101)bcc, [110]fcc//[111]bcc.

Automated summary

The orientation relationship between γ-fcc and α'-bcc is crucial for metallic materials, with K-S and Pitsch being preferred relationships for martensitic transformation. The newly discovered OR in an austenitic steel SS304 after shot peening is unique among all known relationships in fcc-bcc systems, showing a distinctive rotation of -12.8 degrees compared to the Pitsch relationship.