Preheat help reduce the carbon steel heat-affected zone of the highest hardness and prevent cold cracking, which is a major carbon steel welding process measures, preheating can improve joint plastic, reducing the welding residual stresses. Typically, high-pressure and high pressure boiler seamless pipe preheating temperature of 150 ~ 250 ℃ then high carbon content or because a large thickness and stiff ness, cracking tendency is large, the preheating temperature can be increased to 250 ~ 400 ℃. If too much solder pieces, the overall preheating of difficulty, can be partially preheated heating locally preheated weld both sides of the range of 150 ~ 200mm.
Welding conditions permit preferred alkaline electrode. Groove forms the weldment try to open a U -shaped groove type welding. If the casting defects, dig out the shape of the groove should be smooth, and its aim is to reduce the molten parent metal into the weld metal in proportion to the reduction in the carbon content of the weld to prevent the cracks.
Welding parameters due to the first layer of molten parent metal weld metal in the proportion of up to 30 %, so the first layer of weld, you should try using a small current, slow welding speed, to reduce the depth of penetration of the base material. Post weld heat treatment after welding, preferably carried out immediately weldment stress relief heat treatment, especially for large thickness of the welded parts, high-rigidity structure part and harsh conditions ( dynamic load or impact load ) working weldment even more so. Stress relief tempering temperature is 600 ~ 650 ℃. If after welding ( ie, when the temperature ≮ 200 ℃ ) can not be stress relief heat treatment, heat treatment should begin immediately ( ie, elimination of hydrogen processing, general heating temperature is about 150 ℃ for 2h slow cooling ).
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