Influence of the Amount of Austenite on the Toughness of Two Phase Stainless Steels

Abstract

The variation in toughness of Fe-Cr-Ni alloys having variable amount of austenite (γ) have been investigated in order to estimate the influence of γ on the susceptibility to 475°C embrittlement and σ phase embrittlement of two phase stainless steels, and the principal results are summarized as follows.
(I) In case of heating at 700°C, the ferritic alloy was embrittled immediately by carbide precipitation. In the alloys containing more than 20%γ, there observed no embrittlement by carbide precipitation. However, marked embrittlement is observed after prolonged heating by formation of σ phase. The embrittlement by σ phase produced by decomposition of ferrite could not be reduced by coexisting γ.
(2) On aging at 500°C of water-quenched specimens, the maximum increases in hardness and Charpy impact transition temperature appeared at 20% γ, where the maximum residual stress of ferrite was observed by means of X-ray measurement. It was supposed that this promoting action for 475°C embrittlement resulted partially from the residual stress in ferrite produced by rapid quenching of two phase alloys.