Formation of residual ferrite in 9Cr-ODS ferritic steels

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Vol. 527; no. 16; pp. 4418 - 4423
• Main Authors: Yamamoto, M., Ukai, S., Hayashi, S., Kaito, T., Ohtsuka, S.
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier B.V 25.06.2010; Elsevier
• Subjects: Applied sciences; Constant-composition solid-solid phase transformations: polymorphic, massive, and order-disorder; Cross-disciplinary physics: materials science; rheology; Dispersion hardening metals; Exact sciences and technology; Ferrite; Martensite; Materials science; Mechanical alloying; Metals. Metallurgy; ODS; Phase diagrams and microstructures developed by solidification and solid-solid phase transformations; Physics; Pinning; Powder metallurgy. Composite materials; Production techniques; Thermal expansion; X-ray diffraction; Y 2O 3; α to γ reverse transformation; Thermal expansion; Ferrite; α to γ reverse transformation; Pinning; X-ray diffraction; Martensite; Y 2O 3; Mechanical alloying; ODS; Ferritic steels; Scanning electron microscopy; Phase transformations; XRD; High temperature; Dispersion strengthened metal; O; Hot pressing; Y; Thermodynamic analysis; Yttrium oxide; Microstructure
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2010.03.079

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 Y 2O 3, 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% Y 2O 3; however, it is not formed for steels without and with 0.1 mass% Y 2O 3 normalized for 1 h at 1050 °C. 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 °C, and this ferrite phase cannot be δ-ferrite that is in equilibrium with the γ-phase.