Effects of temperature and strain rate on the mechanical properties of T91 material tested in liquid lead bismuth eutectic

Abstract

The effects of temperature and strain rate on the susceptibility of one of the most promising candidate materials for cladding and high temperature components for ADS, Ferritic/Martensitic steel (T91), to liquid metal embrittlement have been investigated in the temperature interval 150-450°C, at strain rates between 1 · 10 À3 s À1 and 1 · 10 À6 s À1 . The effect of the liquid lead bismuth eutectic has been evaluated by comparison between tests in the liquid metal and in Ar with 5% H 2 . Although the untreated T91 material did not undergo liquid metal embrittlement and there was no apparent change in trends of the tensile properties as function of temperature or strain rate due to the liquid metal, the pre-exposed T91, which was exposed to oxygen poor LBE at 450°C for 4000 h and tested at 450°C did show a decrease in total elongation. The total elongation of the untreated T91 specimens in liquid lead bismuth and in H 2 /Ar-gas mixture followed the same dependence on the temperature up to 245°C. At temperatures above 375°C no results are available from testing in controlled gas environment however reference data measured on the same batch of steel in air are used for comparison. Varying the strain rate did not cause any deterioration in the tensile properties of the material in liquid metal compared to those in gas atmosphere. The results are discussed in terms of self-healing mechanism and crack initiation processes.

Liquid metal embrittlement susceptibility of ferritic–martensitic steel in liquid lead alloys

“…The full and dashed lines in Fig. 2 were obtained by, respectively, fitting tensile data of the same batch of T91 tested in air or inert gas by several labs in Europe [16] and by fitting tensile data of EUROFER97 tested in air from the Fusion database [31]. Fig.…”

“…This is explained by the absence of intimate contact or wetting of the solid metal by the liquid metal and/or by the absence of initiated cracks in the outer surface of the solid. Surface cracks created by EDM cutting [23], liquid metal corrosion or plastic deformation at a machined notch [16] have shown to strongly increase the possible risk for LME. Apart from wetting and surface cracks it has also been shown from tests on heat treated material that an increase in hardness by thermal treatment also increases the risk for LME [32].…”

“…Although some experiments have shown that liquid lead alloys may reduce the performance of T91 in terms of total elongation [19][20][21][22], T91 does not show liquid metal embrittlement by LBE under all conditions [16,23].…”

“…The tests on non-irradiated T91 were performed using Liquid Metal Embrittlement Testing Station 1 (LIMETS 1) which allows controlled and clean LBE chemistry conditions [16], whereas the T91 irradiated in water was tested in a crucible filled with LBE placed inside one of the autoclaves otherwise used for testing active materials under PWR conditions [29]. The latter allowed less stringent control of the oxygen concentration due to the absence of an oxygen probe.…”

“…Moreover the concept of specificity of the solid metal-liquid metal couple has been questioned by several authors [5,12,13] and various parameters such as metallurgical state, surface state, composition, solubility, temperature, strain rate, stress concentrators, etc. are known to influence the risk of LME [14][15][16].…”