Formation of residual ferrite in 9Cr-ODS ferritic steels

概要

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It is recognized that the high-temperature strength of 9Cr-ODS ferritic steels is maintained by the presence of a ferrite phase. In order to clarify the formation process of the ferrite phase, 9Cr-ODS ferritic steels containing various contents of Y2O3, i.e., 0 mass%, 0.1 mass%, 0.35 mass%, and 0.7 mass%, are prepared by means of mechanical alloying and hot pressing. The ferrite phase is formed by the addition of 0.35 mass% and 0.7 mass% Y2O3; however, it is not formed for steels without and with 0.1 mass% Y2O3 normalized for 1 h at 1050℃. It is considered from the thermodynamic analyses that the pinning of the α-γ interface motion by the dispersed Y-Ti complex oxide particles can be attributed to the retention of the ferrite phase normalized at 1050℃, and this ferrite phase cannot be δ-ferrite that is in equilibrium with the γ-phase.
2010-06-25