The paper deals with the mechanical strength in air and in liquid lead bismuth at 300°C and 380°C of a T91/316L weld joint assembled by electron beam process. Prior to this, the individual response of each base material has been investigated using the small punch test. The T91 is tested according to several tempering conditions. 316L and T91 tempered at 750°C did not exhibit any sign of liquid metal embrittlement. However, for the T91 steel tempered at 600°C or 500°C, a ductile to brittle transition is induced by liquid lead bismuth. After tempering at 650°C and 700°C, liquid lead bismuth promotes a decrease in mechanical properties and a reduction of the ductility of materials. The load-displacement curves in air of the weld joint are similar to that of the T91 base material. The plastic deformation is mainly concentrated in the T91 part of the weld joint which promotes cracking in this material. Testing in liquid lead bismuth bath results in a reduction in ductility and the formation of brittle cracks. The T91/weld interface is found to be rather resistant as it cracks late in the test and after a large crack propagated in the T91 steel.

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