NSUF 19-2858: Advanced microstructural characterization of irradiation-induced phase transformation in 304 steel

The γ-austenite (FCC) to α-ferrite (BCC) phase transformation has been observed in 300 series austenitic steels in the past decades. The mechanism for this transformation has been largely attributed to Ni segregation and precipitation of Ni enriched phases, however, strain induced diffusionless phase transformation from γ-austenite to α’-martensite has also been observed during irradiation of high Ni austenitic steels. We hypothesize that both strain induced diffusionless γ-austenite to α’-martensite transformation as well as instability of the γ phase from precipitation and segregation of Ni contribute to the γ to α phase transformation. In this study we propose to use precession electron diffraction combined with super-X energy dispersive X-ray spectroscopy (EDS) to study two samples of 304 steel neutron irradiated at different temperatures. This advanced technique will allow us to study to what extent each mechanism plays a role in the phase transformation, and how temperature affects the phase transformation. The results of this study will help to develop austenitic steels that are resistant to phase transformation during irradiation. Because the ferritic phase has significantly different mechanical properties as well as poor corrosion resistance, prevention of this phase transformation will have a significant impact on extending the lifetime of these materials.

Допълнителна информация

Поле	Стойност
Abstract	The γ-austenite (FCC) to α-ferrite (BCC) phase transformation has been observed in 300 series austenitic steels in the past decades. The mechanism for this transformation has been largely attributed to Ni segregation and precipitation of Ni enriched phases, however, strain induced diffusionless phase transformation from γ-austenite to α’-martensite has also been observed during irradiation of high Ni austenitic steels. We hypothesize that both strain induced diffusionless γ-austenite to α’-martensite transformation as well as instability of the γ phase from precipitation and segregation of Ni contribute to the γ to α phase transformation. In this study we propose to use precession electron diffraction combined with super-X energy dispersive X-ray spectroscopy (EDS) to study two samples of 304 steel neutron irradiated at different temperatures. This advanced technique will allow us to study to what extent each mechanism plays a role in the phase transformation, and how temperature affects the phase transformation. The results of this study will help to develop austenitic steels that are resistant to phase transformation during irradiation. Because the ferritic phase has significantly different mechanical properties as well as poor corrosion resistance, prevention of this phase transformation will have a significant impact on extending the lifetime of these materials.
Award Announced Date	2019-09-17T14:35:41.3
Awarded Institution	None
Facility	None
Facility Tech Lead	Alina Zackrone
Irradiation Facility	None
PI	Andrew Hoffman
PI Email	[email protected]
Project Type	RTE
RTE Number	2858