1. Chemical composition of the base material: 45# steel is a medium carbon steel. The welding performance of carbon steel will change significantly with the increase of carbon content. The thicker the pipe wall, the higher the carbon content. Under the action of welding thermal cycle, Hardened tissue is produced in the near suture area. This brittle state coupled with large shrinkage stress will lead to cold cracks in the near-seam area.
2. Reduce the diffusible hydrogen content of the weld metal: During welding, the weld area absorbs hydrogen. Hydrogen is the moisture contained in the welding fluid and the oil, rust, etc. on the base material. It decomposes into hydrogen atoms under the high temperature of the arc and dissolves into the welding pool. As the temperature drops, the solubility of hydrogen decreases sharply. Since the joint cools very quickly, the weld area can also be saturated with dissolved argon. Hydrogen escapes and collects at some defects, and the hydrogen in the steel will also cause the performance to embrittle.
3. Preparation before welding: Be sure to use low-hydrogen welding rods for grooves and bevels before welding. Dry before welding at a drying temperature of 350 degrees and keep warm for 2 hours. When used, it is packed in a welding rod barrel and heated at any time to reduce the hydrogen content in the welding rod. Before welding, preheat the two nets at the weld groove. The preheating temperature is 250 degrees.
If cracks appear during the welding process, re-weld. Each interface requires continuous welding at one time.
