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The Significance of Thermo-Mechanical Fabrication on Long Term Creep Life of Type 316H Austenitic Stainless Steel Components

Research output: Chapter in Book/Report/Conference proceedingConference contribution

Original languageEnglish
Title of host publicationInnovation in Testing and Evaluation of Structural Integrity
Subtitle of host publicationChapter 2: Analysis and Tests of the Structural Integrity of Machine Parts, Machines and Structures
EditorsXu Chen, Shan-Tung Tu
Publisher or commissioning bodyTrans Tech Publications Inc
Pages384-388
Number of pages4
DOIs
DateAccepted/In press - 4 May 2016
DateE-pub ahead of print - 10 Sep 2016
DatePublished (current) - Sep 2016

Publication series

NameApplied Mechanics and Materials
PublisherTrans Tech
Volume853
ISSN (Print)1662-7482

Abstract

The UK’s Advanced Gas Cooled Reactor (AGR) nuclear power generating plant operates at temperatures up to 550 oC, where creep life is important. We consider Type 316H austenitic stainless steel headers and tubes with thermo-mechanical fabrication histories that result in significantly different initial microstructures. The heat affected zone of weldments, in these thick section headers and thin walled boiler tubes, have been found to be susceptible to creep damage leading to cracking during service. In this work we explore these differences in the long term service aged microstructure and the link to overall creep life of these components. To achieve this, samples containing weldments have been removed from plant after extended periods of service. Specifically parent and HAZ regions have been examined to determine the types of precipitates arising from the long term ageing. In particular, thin foils have been examined in a JEOL ARM transmission electron microscope operating at 200KeV fitted with an Oxford Instruments energy dispersive spectrometer to allow comparison between high resolution images and chemical composition. The thin foils were removed from predetermined locations using gallium ion milling and finally thinned using a low ion current to minimise ion damage. Differences between the distributions and types of precipitates are considered in the context of the initial microstructure arising from the thermo-mechanical history on the loss of creep strength and initiation of creep cavities at grain boundaries. The impact on overall service life is addressed.

    Research areas

  • Creep, Austenitic stainless steel, phosphorus segregation, Chi phase, M23C6 carbide

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