Effect of post welding heat treatment of the HCPB TBM on Eurofer and lithium orthosilicate pebbles

In the breeder units (BUs) of the HCPB TBM, the lithium orthosilicate (OSi) pebbles are contained by cooling plates which are made of Eurofer. The assembly of the TBM box and BUs is based on welding processes which require post welding heat treatment (PWHT). According to the proposed TBM manufacture strategy, the BUs will be packed with the OSi pebbles during the TBM assembly; consequently the pebbles and the Eurofer plates will undergo the PWHT. Therefore the objective of this study is to investigate the effect of the PWHT on both Eurofer and OSi and their interaction. The test unit is a Eurofer box packed with OSi pebbles and Eurofer specimens. This test unit and all Eurofer specimens were heat treated inside a furnace which is capable of providing the required heating and cooling rates under a controlled atmosphere of vacuum or argon. Charpy impact and tensile tests of the Eurofer specimens and crush load tests of the OSi pebbles were performed after the heat treatment to investigate any changes in their mechanical properties. The results of these mechanical tests revealed that both materials did not suffer any significant degradation in their mechanical properties or chemical compatibility problems. The metallurgical analyses of both materials showed minimum chemical interaction.