Necessity of preheating submerged arc welding wire before welding
In submerged arc welding, some low-alloy steel structures with higher grade or thicker thickness must be preheated before welding. The preheating temperature is related to the steel's hardenability, plate thickness, restraint, hydrogen content and other factors. In the project, it can only be determined after testing in combination with specific conditions. Some recommended preheating temperatures can only be used as reference.
Preheating the workpiece before submerged arc welding mainly plays an important role in preventing cracks, reducing the cooling rate of weld and heat affected zone, and reducing welding stress. However, preheating worsens the working conditions and makes the production process more complex. Whether preheating is required for low alloy steel structure before welding shall be determined according to production time and weldability test results.
Generally speaking, preheating shall be considered when the carbon content of base metal is not less than 0.35%, and preheating shall be considered when the carbon content is not less than 0.45%. From the aspect of plate thickness, for low alloy steel with tensile strength of 500-550MPa, when the plate thickness exceeds 25mm, preheating before welding at above 100 ℃ shall be considered. Considering the ambient temperature during welding, when the plate temperature is lower than 0 ℃, it shall be preheated before welding. At this time, the range of 80mm around the welding point can be heated to about 150 ℃.
In a word, in some welding processes, preheating before welding is very necessary. For the above knowledge of preheating before welding, friends who need to know better.
It is believed that many people who have been exposed to submerged arc welding will know that there are two major links in the process of submerged arc welding: post heating and post welding heat treatment.