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The Main Role of Preheating before welding
Date:2017-01-11      View(s):1466      Tag:galvanized steel pipe,prime steel ,welded joints

Preheating is required before welding important components, alloy steels parts and thick parts. The main role of preheating before welding is as follows:

(1) Preheating can slow down the cooling rate after welding. It is conductive to the diffusion of hydrogen in the weld emtal escape. Besides, it can avoid to hydrogen-induce cracking, reduce the weld and heat affected zone hardened to improve the crack resistance of welded joints.

(2) preheating can reduce the welding stress. Uniform local preheating or integral preheating, the temperature difference (also called temperature gradient) between the workpiece to be welded in the weld zone can be reduced. In this way, on the one hand to reduce the welding stress, on the other hand, reduce the welding strain rate, help to avoid welding cracks.

(3) preheating can reduce the binding degree of welded structure, to reduce the degree of constraint is particularly obvious, with the preheating temperature increases, the incidence of crack down.

The choice of preheating temperature and interlayer temperature is not only related to the chemical composition of steel and welding rod, but also to the rigidity of welding structure, welding method, ambient temperature and so on, and these factors should be considered together. In addition, the preheating temperature uniformity in the direction of the thickness of the steel plate and the uniformity in the weld area, to reduce the welding stress has an important impact. Partial preheat width, should be based on the degree of restraint of the workpiece is welded, generally around the weld zone wall thickness of three times, and not less than 150-200 mm. If the preheating is not uniform, not only does not reduce the welding stress, but will increase the welding stress situation.

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