High carbon steel is a carbon material with carbon content of 0.6-1.7%, density of 7.81g/cm3 and hardness of HRC60-65. It is usually called tool steel and is usually quenched and tempered. Dual liquid quenching is often used because of its high carbon content and easy to crack due to water quenching, and the parts are usually oil quenched. The weldability of high carbon steel is poor. In addition to high carbon structural steels, there are also high carbon steel castings and carbon tool steels. These steelworks are used as parts and tools for high hardness or worn parts, mainly for repair and surface treatment. High carbon steel is more likely to produce hot cracks than medium carbon steel. High carbon steel is more sensitive to quenching. The HAZ and hardened martensite structure are easy to occur during welding, so the tendency of hardening and cold cracking is great. High carbon steel has poor thermal conductivity at the bottom of carbon steel. At high temperature, the grain grows faster, and the carbides tend to accumulate and grow at the grain boundary, which increases the brittleness of the weld and reduces the bonding strength and joint. The internal stress of the middle lead is also very large, and it is easier to cause cracks.


Because of the poor weldability of high carbon steel, it is mainly used for high hardness or wear parts, parts and tools, so arc welding of high carbon steel is common. Welding materials are usually selected according to the carbon content of the port, the design of the workpiece, the conditions of use, etc., and it is difficult to weld to the same performance as the base metal. The tensile strength of this steel is mostly higher than 675 MPa. Welding materials are determined by product design requirements. When high strength is required, J7O7 or J607 are usually used; when low strength is required, J507 or J506 are used; or low alloy steel electrodes and metals equivalent to the above strength levels can be selected. All welding materials should be of low hydrogen type. If necessary, chromium-nickel austenitic stainless steel electrode can also be used for welding. The grade of welding rod is the same as that of medium carbon steel, such as A102, A107, A302, A307, etc. It can be preheated, but when the stiffness of the weldment is large, the prewelding is the appropriate heat.


During welding operation, the welding is annealed before welding to reduce the tendency of fracture. When welding with structural steel, it is necessary to preheat before welding, and the preheating temperature should be controlled above 250-350 C. Before welding, pay attention to drying the electrodes according to the regulations, and put them into the incubator or heat preservation tube to prevent dampness. Before welding, the workpiece must be cleaned, and the same welding process as medium carbon steel should be adopted, such as reducing fusion ratio, low current, low welding speed, continuous welding, etc. Measures should be taken to reduce internal stress.