Crystallographic characteristics of the process of σ-phase precipitation in chromium–nickel austenitic steels

Transmission electron microscopy has been used to determine the crystallographic characteristics of the σ-phase precipitation process in austenitic steels. The σ-phase precipitating inside the austenite grains was found to exhibit a close similarity to the austenite described by Nenno, Tagaya & Nishijama [Trans. Jpn. Inst. Met. (1962), 3, 82–91]. Transition matrices of the austenite planes and direction indices to the a phase have been determined. The σ-phase lamellae were found to lie on the {111} austenite plane which is their habit plane and grow most rapidly in the 〈112〉_γ direction. The habit of these lamellae are bound by four {110}_σ and two {001}_σ σ-phase planes.