抄録
An investigation was carried out on the reheated zone toughness of a 80kg/mm2 class high strength, multi-pass weld metal.
The reheated zone toughness deteriorated at the reheating temperature range of 750°C-950°C in both single thermal cycle and double thermal cycle conditions. This result was discussed in relation to both fractographic and metallurgical aspects.
The cause of embrittlement seems as follows.
When reheated to 750°C, the absorbed energy at the ductile fracture region (vEshelf) decreased. This is due to the strengthening of matrix caused by the precipitation of fine carbide and/or nitride by the tempering of ferrite matrix or martensite island.
When reheated to the temperature range of 850°C-950°C, the absorbed energy at low temperatures (for example vE-20) decreased. This is due to (1) the reversed austenization mainly along pre-austenite grain boundaries, (2) the transformation to martensite island of reversed austenite and the precipitation of cementite from reversed austenite during the subsequent cooling treatment, and (3) as a result, the increase in micro-crack initiation site and the decrease in resistance for cleavage fracture.
