Microstructural Investigation of LME Crack Initiated in Ferritic/Martensitic Steel T91 Loaded in Liquid Lead-Bismuth Eutectic at 300 °C.

Patricie Halodová,Anna Hojná,Jan Lorinčík

doi:10.3390/ma12010038

Abstract

Liquid lead-bismuth eutectic (LBE) is one of the candidate materials for advanced nuclear systems. The structural materials used in contact with LBE are selected according to the resistance to liquid metal corrosion, irradiation embrittlement, and compatibility with the coolant. However, simultaneous presence of mechanical strain and LBE environment can induce liquid metal embrittlement (LME) in these materials. In this study, a specimen from candidate ferritic-martensitic steel T91 was tested by Constant Extension Rate Tensile (CERT) test exposed to PbBi environment with oxygen concentration 6 × 10−6 wt % at 300 °C up to rupture. Post-test examination using scanning electron microscopy (SEM) showed a deep crack indicating features of LME in the plastic strained region of the tested specimen. Further investigations focused on characterization of the fracture path and microstructure determination using focused ion beam (FIB) and energy dispersive X-ray spectrometry/electron backscatter diffraction (EDX/EBSD). This observation revealed that the dominant LME failure mode of the observed crack is translath or transgranular and the crack stopped at the high-angle grain boundary. The role of oxides in the crack initiation is discussed.

Highlights

Ferritic martensitic steel T91 is one of the potential structural materials for liquid lead or advanced lead–bismuth alloy cooled nuclear reactors (Gen IV reactors) and one of the candidate targets and coolant materials for experimental accelerator driven systems (ADS)
This phenomenon, resulting in crack initiation and sub-critical crack growth leading to premature failure of metals, was observed in T91 steel when tested in lead-bismuth eutectic (LBE) over a wide range of applied experimental conditions [2,3,4,5,6,7,8]
In this paper we report on the study of T91-T1 specimen microstructure along the crack induced by liquid metal embrittlement (LME) by means of scanning electron microscopy (SEM) and Electron Back Scattered Diffraction (EBSD) technique

Summary

Introduction

Ferritic martensitic steel T91 is one of the potential structural materials for liquid lead or advanced lead–bismuth alloy cooled nuclear reactors (Gen IV reactors) and one of the candidate targets and coolant materials for experimental accelerator driven systems (ADS). If a mechanical strain/stress in contact with LBE is applied, it can induce a phenomenon called Liquid. This phenomenon, resulting in crack initiation and sub-critical crack growth leading to premature failure of metals, was observed in T91 steel when tested in LBE over a wide range of applied experimental conditions [2,3,4,5,6,7,8]. The main prerequisites for the occurrence of LME are wetting by the liquid metal together with sufficient level of applied stress, which probably results in localized plastic deformation [2,6,9]

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Conclusion