| The crystallographic features of sigma phase precipitation in superaustenitic Fe-22Cr-21Ni-6Mo-(0.3N) stainless steels during isothermal aging were investigated utilizing transmission electron microscopy. The sigma phase precipitated along the austenite grain boundaries even after solution treatment due to higher Mo contents and remained stable throughout aging at 900℃ up to 168 hours. The sigma phase observed in thin study was found to be ternary Fe-Cr-Mo sigma phase and had tetragonal structure with lattice parameters of a=9.17Å and c=4.74Å. The orientation relationships between the sigma phases and austenite were determined from the analyses of selected area diffraction patterns taken by various zone axes and stereographic analyses. The orientation relationships between sigma and austenite phases obtained in this study were as follows; 1) (110)_γ ∥ (110)_σ, [1￣11]_γ, ∥[001￣]_σ and (11￣2)_γ ∥(1￣10)_σ, [1￣11]_γ ∥[001￣]_σ and 2) (1￣10)_γ∥(1￣10)_σ, [11￣2]_γ∥[113]_σ and (1￣11)_γ∥(332￣)_σ, [1￣12]_γ∥[113]_σ. However, the former orientation relationship was predominant throughout aging and the latter orientation relationship was scarcely observed in very limited aging condition. |
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