The welding of GB/T 1591 Q345D steel plate needs preheating first under some conditions, because the carbon content of Q345D steel is high.
The purpose of Q345D steel plates preheating is to prevent cold cracks. The cold crack is directly related to the carbon equivalent. The carbon equivalent of Q345D low alloy high strength steel plates is less than 0.3%, so the weldability of GB/T 1591 Q345D steel is Ok. Generally speaking, the cold crack sensitivity is increased when the carbon equivalent exceeds 0.4%. So Q345D is usually not preheated.
But when the GB/T 1591 Q345D steel plates are very thick, they should be preheated because the cooling is very fast. If the thickness of Q345D structure steel plate is above 70mm, the risk of non preheating is very large.
The impurity S and P content of GB/T 1591 Q345D steel plates are low, so the low temperature impact performance of Q345D steel is good. From the welding point of view, less impurity elements of the parent material is beneficial to control the welding hot crack.
Of course, since the parent material chooses Q345D material, which is more expensive than Q345B. The application purpose of GB/T 1591 Q345D steel plates is special, so welding materials will be selected with attention. If the instructions of the electrodes require preheating for the base metal, they should be preheated. Because if the welding material is not used according to the manufacturer's instructions, the welding performance will be greatly reduced.
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