Crystallographic Features of Shear Transformation in Martensitic and Martensitic-Ferritic Stainless Steels

The microstructure of stainless steels belonging to the martensitic and martensitic-ferritic classes was examined by orientation microscopy (EBSD) after quenching. The steels comprised 15 wt % Cr, Ni, and Nb, and were distinguished by the addition of Cu or Mo as alloying elements. Using the spectra of deviation of interfacial alpha/gamma-boundaries from orientation relationships (OR), as well as the initial austenitic grain recovery procedure according to OR, it was found that the martensitic transformation occurring in both steels is realized according to the closest to Kurdyumov-Sachs OR, or (112)gamma || (113)alpha; [11 (1) over bar]gamma || [1 (1) over bar0]a OR. It is demonstrated that the d-ferrite grains present in the martensitic-ferritic grade steel prior to and after quenching are in the same OR with austenite. This appears to be a consequence of the nucleation of martensitic crystals at the delta-ferrite/austenite phase interface. It is demonstrated also that the application of orientation microscopy enables the ascertainment of the grain austenitic structure of stainless steels at elevated temperatures with an acceptable degree of precision. This is realized by analyzing the structure resulting from shear transformation.