In order to avoid cold cracking in steel welds, a proper selection of welding conditions of heat input, preheat and interpass temperature is required corresponding with the interested plate, joint geometry and consumable.
Although cooling rate at 300°C or time to cool 100°C etc. have been considered as the parameters which may be used to estimate the avoidance of cracking, the thermal factor calculated by means of welding thermal cycle and diffusivity coefficient for hydrogen should be more directly concerned as a parameter.
From this point of view this paper firstly describes the estimation of the correlation between welding thermal cycles and welding conditions, and then, the effect of welding conditions on the thermal factors both for single root-pass weld by the y-slit test specimen and for the final pass of welds by large size multipass butt joint test specimen.
It is found from the investigation that the estimated welding thermal cycles show a coincidence with directly obtained ones and the value of heat transfer coefficient (α) of 7×10-4 cal/cm2⋅ sec⋅ °C is applicable to the temperature range of 300°C through 90°C for single root pass welding.
It is also found that the thermal factor is significantly influenced by heat transfer coefficient, and that the thermal factor in multipass butt welding shows the minimum value at the plate thickness of about 100 mm.
