1, preheating is beneficial to reduce the maximum hardness of heat affected zone of medium carbon steel and prevent cold cracking, which is the main technological measure in welding. Preheating can also improve the plasticity of the joint and reduce the residual stress after welding. Usually, the preheating temperature of 35 and 45 steels is 150-250℃. If the weldment is too large and the overall preheating is difficult, local preheating can be carried out, and the heating range of local preheating is welding.

2. covered electrode conditions, it is best to use alkaline covered electrode when allowed;

3. In the form of groove, the weldment shall be welded in the U-shaped groove as far as possible. If the casting is defective, the shape of the groove dug by shovel should be smooth, in order to reduce the proportion of the base metal melting into the weld metal, thus reducing the carbon content of the weld and preventing cracks;

4. Welding process parameters Because the proportion of base metal melting into the first layer of weld metal is as high as about 30%, when welding the first layer of weld, low current and slow welding speed should be used as much as possible to reduce the penetration of base metal;

5. Heat treatment after welding. It is best to carry out stress-relieving heat treatment on weldments immediately after welding, especially weldments with large thickness, high structural rigidity and harsh working conditions. The tempering temperature for stress relief is 600-650℃.