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Precipitation within localised chromium-enriched regions in a Type 316H austenitic stainless steel

Research output: Contribution to journalArticle

Original languageEnglish
Pages (from-to)6183-6197
Number of pages15
JournalJournal of Materials Science
Volume53
Issue number8
Early online date9 Jan 2018
DOIs
DateAccepted/In press - 21 Oct 2017
DateE-pub ahead of print - 9 Jan 2018
DatePublished (current) - 1 Apr 2018

Abstract

A Type 316H austenitic stainless steel component containing Cr and impurity element-rich localised regions arising from component fabrication was aged for a prolonged period during service at a temperature of approximately 550 °C. These regions make up approximately 5% of the total volume of the microstructure. Previous work has shown that these regions contain ferrite and carbide precipitates and a finer austenite grain size than the adjacent matrix. The present study has used high-resolution transmission electron microscopy combined with compositional microanalysis to show that these regions have a highly complex microstructure containing G phase, chi phase and intragranular γ′ precipitates within the austenite grains. There is phosphorus migration to the chi austenite phase boundary, and the basis for this equilibrium impurity segregation is discussed. A Cr-depleted region was observed surrounding the chi phase precipitates, and the impact of this on the other precipitates is considered. The diversity of precipitates in these Cr-rich regions means that they behave significantly differently to the bulk material under long-term creep conditions leading to preferred nucleation and growth of creep cavities and the formation of localised creep cracks during service.

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