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The strain rate: a key factor in liquid metal embrittlement sensitivity of steels by lead-bismuth eutectic


The use of liquid lead bismuth-eutectic (LBE) as spallation target and coolant in Accelerating Driven Systems or coolant in the future Lead-cooled Fast Reactor rises the question of the reliability of structural materials, in terms of liquid metal assisted damage (LMAD) and corrosion. Different studies have focused on the mechanical behavior of the T91 martensitic steel (in its standard heat treatment) in contact with LBE (oxygen saturated LBE and low oxygen LBE).The mechanical behavior of the T91 steel and of some austenitic steels were investigated in a temperature range from 200°C to 500°C by performing monotonic tests (Small Punch Tests and tensile tests) and Low Cycle Fatigue (LCF) tests in air and in liquid LBE. After tests, cracking and fracture surfaces were analyzed by scanning electron microscopy, energy dispersive X-ray, electron back scatter diffraction or time of flight secondary ion mass spectroscopy to characterize and understand the effects of the liquid metal.Under monotonic loading, T91 steel appeared in general as a ductile material, and became brittle only if the test was performed in oxygen saturated LBE and at low loading rate. In addition, a low oxygen content in LBE accelerated this brittle damage. Decreasing the oxygen content acted as a catalytic effect. Thus, in low oxygen LBE, the LBE embrittlement occurred for a loading rate 10 times higher in comparison with tests in oxygen saturated LBE.Furthermore, in presence of oxygen saturated LBE, under cyclic loading, the resistance to fatigue crack initiation and propagation was decreased. LCF lifetime was reduced in presence of LBE in comparison with tests in air, especially at high strain range. The presence of LBE promoted a reduction of the density of short cracks and modified the fatigue propagation mode of long crack. In air, the fracture surface was covered with ductile fatigue striations while it was brittle in LBE. Furthermore, decreasing oxygen content in LBE either did not play any effect or resulted in a harmful effect. Moreover, a low strain rate appeared to be a critical factor. Indeed, reducing the strain rate lead to a reduction in LCF lifetime in the oxygen saturated LBE, especially at high strain range.Considering the obtained results, the strain rate could be considered as a key parameter concerning the mechanical behavior of this steel in contact with LBE. Whatever the environment, the mechanical properties depend on the strain rate. In the case of a liquid metal, the strain rate modifies other parameters especially the time immersion of the steel in the liquid metal, the nature of the interface liquid metal/steel, the possibility of chemical reactions between the elements of the liquid metal and the steel. Taking into account all these parameters, all the results and some results concerning others steels loaded in contact with LBE, the aim of the present communication is to explain the effect of the strain rate on the LMAD of steels by LBE.
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Dates et versions

hal-03400786 , version 1 (25-10-2021)


  • HAL Id : hal-03400786 , version 1


Ingrid Proriol Serre, Jean-Bernard Vogt. The strain rate: a key factor in liquid metal embrittlement sensitivity of steels by lead-bismuth eutectic. Eurocorr 2021, Sep 2021, Budapest, Hungary. ⟨hal-03400786⟩
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