1989 Volume 53 Issue 5 Pages 512-521
Allays of Fe-(8∼12%)Cr-(5∼30%)Mn were solution-treated at 1373 K for 3.6 ks, followed by cold-working of 50% reduction. Both solution-treated and 50% cold-worked materials were aged in the temperature range from 773 to 973 K for 3.6×103 ks.
The identification of σ phase formation was made by using X-ray diffraction from the electrolytically extracted residues of the aged specimens. The region of σ phase formation determined by the present work is wider than that on the phase diagram already reported. It is to be noted that Mn promotes markedly the σ phase formation, and that three different types of σ phase formation are observed depending on Mn content: α→γ+α→γ+α+σ in 10%Mn, α→γ+σ a in 15 to 20%Mn alloys, α→χ(Chi)→χ+σ+γ in 25 to 30%Mn alloys. An average electron concentration (e⁄a) in the σ phase was estimated by quantitative analysis of alloying elements using EPMA.
The e⁄a value in the σ phase formed in Fe-(12∼16%)Cr-Mn alloys aged at 873 K for 3.6×103 ks is about 7.3, which is independent of Mn content. In order to prevent σ phase formation in Fe-12%Cr-15%Mn alloy, the value of Ni*eq of 11 (Ni*eq=Ni+30(C)+25(N)) is required.
