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⑴Preheating helps to reduce the maximum hardness in the heat-affected zone of medium-carbon steel, thereby preventing the formation of cold cracks. It is a key process measure when welding medium-carbon steel; preheating also improves the ductility of the joint and reduces residual stresses after welding. Generally, the preheating temperature for 35 and 45 steel is 150–250°C. If the carbon content is higher, or if the thickness and stiffness are great resulting in a higher tendency to cracking, the preheating temperature can be increased to 250–400°C. If the welded piece is too large and overall preheating is difficult, local preheating can be employed; the heating area for local preheating should cover 150–200 mm on each side of the weld joint. ⑵Welding electrodes: Alkaline welding electrodes should be preferred whenever conditions permit. ⑶Groove shape: The welded parts should be prepared with a U-shaped groove as much as possible for welding. In the case of casting defects, the shape of the groove created by chiseling should be smooth; this is done to reduce the proportion of base metal that merges into the weld metal, thereby lowering the carbon content in the weld and preventing cracks from forming. ⑷Welding process parameters: Since the proportion of base material that melts into the first layer of weld metal can be as high as around 30%, it is necessary to use a low current and a slow welding speed when welding the first layer of weld, in order to reduce the depth of melting of the base material. ⑸Post-weld heat treatment: It is advisable to carry out stress-relief heat treatment on the welded parts immediately after welding, especially for thick-walled components, highly rigid structural elements, and those that operate under severe conditions (such as dynamic or impact loads). The tempering temperature for stress relief is 600–650°C. If stress-relief heat treatment cannot be carried out after welding, post-weld heat treatment should be performed immediately. This post was last edited by The wise are not confused on 2008-5-24 14:43.]