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News
The electric welding crack of Q345D seamless steel pipe is a serious production and processing defect, which will reduce the total area of the welding cross-section and cause the bearing stress. Welding cracks are generally divided into vertical and horizontal. Vertical cracks are the most common in the notch of the molten pool. Because the notch of the molten pool is not fully covered, it is very easy to deposit harmful residues, which reduces part of the plasticity. And the notch is welded to the final condensation place during cooling, and the stress of cooling is also concentrated here. Transverse cracks are generally more common in carbon steel welding. Low-carbon environmental protection programs are also likely to cause lateral cracks when the cooling is too fast or the cooling is uneven.
The factors that produce the welding cracks of Q345D seamless steel pipe are as follows:
(1) The high cooling rate during electric welding is very prone to cracks. Therefore, it is necessary to bypass the air outlet and prevent it from being wetted by precipitation when welding. In electric welding, medium carbon steel or carbon steel, according to the chemical composition or characteristics of the raw material, some of them can be welded only after heating and heat insulation measures are adopted.
(2) The unreasonable welding sequence is also very prone to cracks. When the sequence is not allocated, there will be a deadlock of the welding force receiving force, which prevents the welding from being folded at will, and even causes a large folded ground stress and causes welding cracks.
(3) It is related to the composition of the seamless square tube, the crystal structure, and the method of the smelter. For example, the higher the carbon content of the steel or the higher the amount of aluminum alloy, the higher the strength of the stainless steel sheet, and the easier it is to crack during electric welding.
(4) When the ambient temperature is low during electric welding, or the heat removal standard at the air outlet is too good, the heat removal is too fast, which will also cause cracks.
(5) Causes of electric welding cracks in Q345D seamless steel pipes by electric welding The commonly used welding wires with high sulfur content, phosphorus and carbon are very prone to cracks. Sulfur and phosphorus are harmful elements, high sulfur content welding has hot ductility, high phosphorus content welding has cold ductility, and the sulfur content and phosphorus content of the welding wire needs to be below 0.0035.