Behavior of the Steel T91 under Multi Axial Loading in Contact with Liquid and Solid Pb

Abstract

Abstract:In this work, the conditions for the occurrence of Liquid Metal Embrittlement (LME) in the ferritic-martensitic steel T91 in contact with lead, Pb, were examined. Slow tensile tests with notched specimens revealed that in a temperature range close to the melting point of Pb, the steel is sensitive to LME (350-400 • C) and to Solid Metal Induced Embrittlement (SMIE) (300 • C). The cracking was stimulated by wetting (using a chemical flux) and the notch effect. It was found that the multi axial stresses state and the high level of plastic strain in front of the notch were the key factors triggering crack initiation.

Characterisation of Oxides by Advanced Techniques

“…No cracks were found in studied specimens. The absence of cracking in these conditions is possibly due to lack of wetting [12][13][14] and the fact that the level of applied load was not sufficient to damage neither the surface of the steel nor the oxide formed during exposure. Oxides prevent corrosion/dissolution of steels in the liquid metal and serve as a barrier that prevents wetting, which is being considered as one of the assumptions for the LME initiation.…”

“…The primary factor limiting the technological viability of the Pb and Pb-Bi eutectic is their corrosive nature towards structural steels. Such coolant has tendency to corrode/dissolute alloying elements from the fuel cladding and structural materials [1,[5][6][7][8][9] within the reactor and causes liquid metal embrittlement (LME) [1,[10][11][12][13][14]. Oxide scales are known to be able to protect the structural alloys against the liquid metal corrosion [1,7].…”

Environmentally assisted cracking of T91 ferritic-martensitic steel in heavy liquid metals

“…All the specimen types are listed in Table 1. Besides the two types of specimens, which were used in previous test campaigns (Di Gabriele et al, 2008;Hojná et al, 2015;Di Gabriele et al, 2017), i.e. the smooth and notched tensile bars of 4-mm diameter and 20-mm gauge length, the other two new types used were (1) Flat coupons of 1-mm thickness, 5-mm width, and 22-mm length, manufactured by electrical discharged machining (EDM); the large flat surface was ground up to 500-grid finish, while the sides and edges stayed untreated; (2) flat tapered specimens of 3-mm thickness, 4-to 6.41-mm width and 26-mm gauge length, fabricated by wire cutting using EDM with the longitudinal axis oriented in the rolling direction.…”

“…The paper deals with the 9% Cr F/M steel T91, which used to be one of the best candidates for LFR internal structures, owing to its very good strength, toughness, resistance to the radiation, and oxidation/dissolution in HLM. However, suitability of the T91 was questioned due to its indicated sensitivity to cracking in HLM, namely, LBE and Pb, based on data from laboratory testing (Nicaise et al, 2001;Auger et al, 2004;Van den Bosch et al, 2006;Di Gabriele et al, 2008;Long & Dai, 2008;Vogt et al, 2008;Coen et al, 2010;Auger et al, 2011;Gorse et al, 2011;Hojná & Di Gabriele, 2011;Gong et al, 2015;Hojná et al, 2015;Stergar et al, 2016;Di Gabriele et al, 2017). (Martín et al, 2004;Heinzel et al, 2014;Schroer et al, 2014b), 304L (Martín et al, 2004), 1.4970 (Heinzel et al, 2014)], F/M (T91, E911 (Aiello et al, 2004a;Schroer et al, 2014a;Tsisar et al, 2017;Yurechko et al, 2018)], and martensitic steels (F82H (Martín et al, 2004), 56T5 (Deloffre et al, 2002)) exposed to LBE as a function of temperature (A) and time (B).…”

“…The testing of materials should preferably address the synergistic effects of the HLM environment with specific oxygen content, flow rate, temperature, and stress up to the levels allowed in operational design. However, in most of the previous studies, performance of the T91 under stress in HLM, namely, in LBE (Auger et al, 2004;Van den Bosch et al, 2006;Di Gabriele et al, 2008;Long & Dai, 2008;Vogt et al, 2008;Coen et al, 2010;Auger et al, 2011;Gorse et al, 2011;Hojná & Di Gabriele, 2011;Gong et al, 2015;Stergar et al, 2016), and also in Pb (Nicaise et al, 2001;Hojná et al, 2015;Di Gabriele et al, 2017) was studied under the out-ofdesign conditions, i.e. in static HLM containing too low or too high oxygen, and with high stresses and plastic strains applied, and mechanical testing after long-term exposure in dynamic LBE with oxygen content below the design level was also performed (Aiello et al, 2004b).…”