Electron backscattered diffraction study of ε/α′ martensitic variants induced by plastic deformation in 304 stainless steel

The electron backscattered diffraction (EBSD) technique has been used to assess crystallographic features of the residual gamma phase and the strain-induced epsilon/alpha' martensites in a 304 stainless steel, tensile tested to 10 pct strain at T = -60 degrees C. The martensitic transformation rate varies according to the, gamma-grain orientation against the applied stress and the gamma-grain size. The alpha'-transformation textures as well as the gamma-misorientation spreads observed in specific gamma-grain orientations have been analyzed. Large misorientation spreads are observed in the less-transformed gamma grains. This reveals an important crystallographic slip activity, even if less strain-induced martensite has been formed. A strong gamma -> alpha' variant selection was detected in the cube- and Goss-oriented gamma grains for which the transformation is less developed. For the {101}< 1-11 > and copper-oriented gamma grains, the amount of alpha' martensite is significantly higher and the gamma -> alpha' variant selection is less pronounced. Tais variant selection is then analyzed on at a local scale and is related to the presence of {111)(gamma) localized deformation bands on which further epsilon/alpha' martensites have nucleated.