Yoshimitsu Okazaki1, Kazuya Miyahara2, Yuzo Hosoi2, Mitsuru Tanino3 and Hazime Komatsu3
1Graduate Student, Nagoya University, Nagoya
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.
iron-chromium-manganese alloy, σ phase formation, optical and electron microstructures, X-ray diffraction, chi phase formation, average electron concentration, Vickers hardness
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