Abstract
Some basic problems in the application of supplementary heat to a weld joint before or after welding have been investigated using a mild steel, medium carbon steels, 50 to 100 kg/mm2 high tensile steels and low alloy steels.
The results indicate that (1) cold cracking can not occur at temperatures above the critical point, which is 80°C in the case of HT-80 steel joint, (2) the activation energy determined by the incubation time is 11000 cal/mol at temperatures over-30°C and 2300 cal/mol below -30°C, (3) the activation energy determined by the effect of post-heating on cracking is 13000 cal/mol independently of steel grade, and (4) the preheat temperature may be reduced by using post-heating, but thermal stress cracking may occur under certain conditions under which blue brittleness or precipitation brittleness takes place.
