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Abstract
A sample of AISI type 316 stainless steel from a power station steam header, showing reheat cracking, was removed from service and has been examined by a combination of microscale X-ray computed tomography (CT), nanoscale serial section focused ion beam–scanning electron microscopy (FIB-SEM), energy dispersive X-ray (EDX) spectrum imaging and transmission electron microscopy (TEM). Multiscale three-dimensional analysis using correlative tomography allowed key regions to be found and analysed with high resolution techniques. The grain boundary analysed was decorated with micrometre sized, facetted cavities, M23C6 carbides, ferrite and G phase but no σ phase. Smaller intragranular M23C6 particles were also observed, close to the grain boundaries. This intimate coexistence suggests that the secondary phases will control the nucleation and growth of the cavities. Current models of cavitation, based on isolated idealised grain boundary cavities, are oversimplified.
Acknowledgements
We acknowledge FEI funding of TLB. Useful comments and help from T. Slater and M. G. Burke, BP ICAM funding of PJW and SAM, EDF Energy for the supply of the test component and funding for HJ. R. Mokso at the TOMCAT beamline at the Swiss Light Source. We are grateful to the EPSRC whose grant funding (grant nos. EP/I02249X, EP/F007906 and EP/F028431) enabled the purchase and support of the imaging equipment in the Henry Moseley X-ray Imaging Facility. The FEI Titan G2 is funded by HM Government (UK) and is associated with research capability of the Nuclear Advanced Manufacturing Research Centre.
