In-pile irradiation effected changes in high chromium steel weld joints

Weld joints in 11-14% Cr steels were studied after their exposure in a fast reactor at 70-550 C at damaging doses up to 40 dpa. Independent of the phase and chemical compositions weld joints as in-pile irradiated at temperatures below 400 C are subject to irradiation-heat brittleness (IHB) that shows up as a shift of the temperature threshold of the brittle-ductile transition Tc to reach 200 C and higher and as a reduction in the breaking strain at temperatures above Tc. Weld joints are more prone to IHB than the base metal. When tested under temperature conditions of IHB occurrence notched samples ruptured in the elastic range at low fracture resistance. At the irradiation temperature in excess of 400-420 C the IHB effect was reduced, the weld joints were quite adequately operationally in a wide temperature range. For high Cr steel weld joints the operation conditions at 400-600 C are most favourable. In this case there is essentially no difference in the behaviour of weld joints and a base metal, namely, ferritic-martensitic steels. Steel of the low carbon martensite structure and weld joints thereof are less subject to IHB. (orig.)