Fracture behaviors of modified 9Cr-1Mo steels in liquid lead–bismuth eutectic immersion environment using in-situ testing technique

Abstract

The 9Cr-1Mo ferrite/martensite steel stands as a crucial candidate material for structural use in lead-cooled fast reactors. However, its susceptibility to embrittlement in liquid lead–bismuth eutectic (LBE) alloy represents a significant hurdle that hinders its widespread application. In this paper, two modified 9Cr-1Mo steels, designated as A-type steel and B-type steel, were proposed by adding aluminum and silicon elements, respectively. To examine the embrittlement caused by liquid LBE the uniaxial tensile tests were conducted on the original T91 steel, A-type steel, and B-type steel in liquid LBE at temperatures of 180 °C, 350 °C and 450 °C. Then, based on the proposed in-situ testing method and compliance method, the fracture properties (J-R curves and the crack initiation fracture toughness) of the above 9Cr-1Mo steels were analyzed at different temperatures. Results showed that the yield stress, tensile strength, and elongation of the modified 9Cr-1Mo steels are higher than those of the original T91 steel, but the A-type steel and B-type steel exhibit different mechanical responses with temperature changes. Moreover, with the increase of temperature, the fracture toughness of T91 steel and B-type steel significantly decreases, but the A-type steel decreases first and then increases. There is no doubt that the crack initiation fracture toughness of the modified 9Cr-1Mo steels is higher than that of the original T91 steel in all tested temperature ranges. Finally, combined with fractographic analysis, the effects of liquid LBE at various temperatures on the embrittlement mechanism of 9Cr-1Mo steels were discussed.