The role of preheating before welding of Guangxi steel structure

The role of preheating before welding of Guangxi steel structure

Preheating before welding is very important to ensure welding quality. The welding of important components, the welding of alloy steel, and the welding of thick parts all require preheating before welding. The main functions of preheating before welding are as follows:

1) Preheating can slow down the cooling rate after welding, facilitate the escape of hydrogen diffused into the weld metal, and avoid hydrogen-induced cracks. At the same time, the hardening degree of the weld and the heat-affected zone is reduced, and the crack resistance of the welded joint is improved.

2) Preheating can reduce welding stress. Even partial preheating or overall preheating can reduce the temperature difference (also called temperature gradient) between the welded workpieces in the welding area. In this way, on the one hand, the welding stress is reduced, and on the other hand, the welding strain rate is reduced, which is beneficial to avoid the occurrence of welding cracks.

3) Preheating can reduce the degree of restraint of the welded structure, especially the degree of restraint of the corner joints. As the preheating temperature increases, the incidence of cracks decreases.

The choice of preheating temperature and interlayer temperature is not only related to the chemical composition of the steel and welding rod, but also related to the rigidity of the welded structure, the welding method and the ambient temperature, which should be determined after comprehensive consideration of these factors. In addition, the uniformity of the preheating temperature in the thickness direction of the steel plate and the uniformity of the weld area play an important role in reducing the welding stress. The width of the local preheating should be determined according to the constraints of the workpiece to be welded. Generally, it should be three times the wall thickness around the weld, and should not be less than 150-200mm. If the preheating is not uniform, not only will it not reduce the welding stress, but will increase the welding stress.

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