When welding important structural steels or high-strength steels, preheat the components before welding, and heat the components to a certain temperature before welding. Preheating can reduce the temperature difference between the metal in the weld zone and the surrounding metal. After welding, it can be cooled relatively uniformly at the same time, thereby reducing the internal stress of welding. When welding steel with better plasticity, you can use a hand hammer to hammer the weld. The hammering should be carried out in a certain direction in the hot state after welding to extend the plasticity of the weld metal and reduce internal stress. When welding steel with better plasticity, you can use a hand hammer to hammer the weld. The hammering should be carried out in a certain direction in the hot state after welding to extend the plasticity of the weld metal and reduce internal stress.

　　Heat treatment technology of Head

　　Recent years, in the manufacture of welded structures such as heads, the application of low-alloy high-strength steel materials has been increasing, but while increasing the strength of steel materials, the crack sensitivity of welding has also increased. Therefore, weld preheating and post-weld heat treatment and other technical measures are very important, they are the key link to ensure the quality of welded structural parts such as head.

　　Preheating before welding

　　It is carried out before welding, and its purpose is to reduce the cooling rate of the weld deposited metal and the base material, so as to prevent the cracking caused by the joint effect of the hardened structure sensitive to cracks and hydrogen. In the manufacturing process of large pressure vessels, especially pressure vessels made of Cr-Mo steel, in order to prevent the generation of hydrogen-induced cracks in the weld, it is often necessary to enter the furnace multiple times for intermediate stress relief annealing (ISR).

　　The post-weld heat treatment of welded structures such as heads is to improve fracture toughness and reduce the level of residual stress to enhance the ability to resist cracking, soften the material structure and eliminate the possibility of stress corrosion cracking. According to the construction method, post-weld heat treatment can be divided into heat treatment inside the furnace and heat treatment outside the furnace. Studies have shown that after stress-relieving heat treatment, the stress of the workpiece can generally be removed by more than 60% to 80%.