Abstract
The effect of heat treatment on the mechanical properties of Fe-25Cr-6Ni alloy has been investigated, and the results are summarized as follows.
(1) In case of aging at 475-525°C, the tensile strength and 0.2% proof srtess increase continuously with aging time owing to the precipitation of Cr-rich phase in ferrite matrix. In spite of the decrease in elongation, the reduction of area shows an approximately constant value of 60-70%.
(2) Heating at 650-800°C produces the α-γ transformation and proof stress decreases with the increase of γ content. The tensile strength that is affected by work hardening of γ phase during the deformation does not vary in parallel with the proof stress.
(3) Charpy impact value decreases with aging time at 475-525°C. The testing temperature dependence of the Charpy impact valus is based on the raise in the transition temperature due to the 475°C embrittlement.
(4) The prior α-γ transformation that produces an increase in γ content and an increase of Cr concentration in α phase leads to the reduction of susceptibility for 475°C embrittlement.
(5) It is observed that σ phase in two-phase stainless steel is formed by decomposition of high Cr ferrite phase into σ+γ, independently of Cr carbide.
