Features of deformation localization in stable austenitic steel under thermomechanical treatment

Abstract

Features of structural states of Fe-18Cr-14Ni-Mo austenitic steel after thermomechanical treatment, including low-temperature and warm rolling deformation, were investigated by means of transmission electron microscopy. It is shown that mechanical twinning in multiple systems and strain localization bands contribute to grain fragmentation with the formation of the submicrocrystalline austenitic structure. These bands lie in the miсrotwin structure, have high-angle (≈60°–90°, 〈110〉) misorientations of the crystal lattice relative to the matrix and localize significant (up to ≈1) shear strain. In areas of the bands, structural states with high (tens of deg/μm) curvature of the crystal lattice and high local internal stresses are observed. The internal structure of the bands is presented by nanoscale fragments of austenite and α′-martensite. The presence of specific misorientations and fragments of martensite means that the formation mechanism of localized deformation bands are direct plus reverse (γ → α′ → γ) martensitic transformations with the reverse transformation follows by an alternative path. These structural states provide high strength properties of steel: the yield strength is up to 1150 MPa.