Preheating issue for Q345R material thickness
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Why is preheating required at ≥80°C for welds with a thickness of 25 mm in Q345R material, while only 15°C preheating is needed for welds 24 mm thick?
Preheating can slow down the cooling rate after welding, reduce welding stress, and prevent cracks from forming. The preheating temperature is related not only to the chemical composition of the steel and welding electrodes, but also to the rigidity of the welded structure, the welding method, and the ambient temperature. NB/T47015-2011 4.4 Preheating: Table 4 specifies requirements for Fe-I category; for those with a minimum tensile strength of 490 MPa or higher and a joint thickness of 25 mm or more, the minimum preheating temperature is 80°C℃ ； For all other materials, the minimum preheating temperature is 15°C. I’m not sure if this will be helpful to you.