Abstract
The microstructural state of two grades of the creep-resistant austenitic stainless steels NF709, a Fe–20Cr–25Ni (wt%) based steel, has been studied, in the as-received state, after an additional solution-treatment and after static ageing at 1023 and 1073 K. Although the two variants are chemically similar, they exhibit different microstructures following identical heat treatment. In particular, Z-phase and σ are found in largely different quantities. The study suggests that a seldom observed variant of the η structure, Cr3Ni2SiX, is stabilised by nitrogen. Both steels exhibit a yet undocumented precipitation sequence when compared to more conventional austenitic steels (for which the precipitation sequences have been reviewed).
Metallurgical and Materials Transactions A, Vol. 36A, 2005, pp. 23–34.
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