Effect of preheating on welding cold crack sensitivity of China low activation martensitic steel

Highlights: • The calculation results of welding cold crack sensitivity index indicated that the CLAM steel tends to cracking during the welding. • Both the results of HAZ maximum hardness and y-groove test showed the 250 °C was the suitable preheating temperature for reducing the hardness and the cracking rate of the joints. • The main defects in the weld joints were cracks and the small inclusions, impurity or contaminants might be the cause of the cracks. - Abstract: The China low activation martensitic (CLAM) steel has been chosen as the primary structure material in Chinese series PbLi blankets for fusion reactors. The assembly preparation of the blanket would be seriously influenced by the weld performance of the CLAM steel. In this study, the welding cold crack sensitivity index of the CLAM steel was analyzed, then the maximum hardness in weld heat-affected zone (HAZ) and y-groove tests were performed. Based on the analysis to the maximum hardness in weld HAZ and the cracking rate of y-groove test at different preheating conditions, the results indicated that the HAZ maximum hardness of CLAM increased at firstly and then decreased with the increase of the preheating temperature (PT). The cracking rate of y-groove test reduced with the increase of the PT, and the crack rate maintained at a relative stable stage when the PT exceeded 250 °C. It revealed high welding crack tendency of the CLAM steel. Thus, the preheating before welding should be applied, and a PT at about 250 °C was proposed in order to prevent welding cracking.