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High-carbon steel refers to carbon steel with a W(C) content higher than 0.6%. It has a greater tendency to harden compared to medium-carbon steel, forms high-carbon martensite, and is more susceptible to the formation of cold cracks. At the same time, the martensite structure that forms in the heat-affected zone of welding is hard and brittle in nature, which leads to a **decrease in the plasticity and toughness of the joint. As a result, high-carbon steel has very poor weldability, and special welding techniques must be employed to ensure the performance of the joint. Therefore, it is generally rarely used in welded structures. High-carbon steel is mainly used for machine components that require high hardness and wear resistance, such as shafts, large gears, and couplings. To save steel and simplify the manufacturing process, these machine components are also often assembled using welded structures. In heavy machinery manufacturing, welding issues with high-carbon steel components also arise. When formulating the welding process for high-carbon steel weldments, it is necessary to comprehensively analyze various potential welding defects and take corresponding welding process measures. 1 Weldability of high-carbon steel 1.1 Welding methods High-carbon steel is primarily used in structures that require high hardness and wear resistance; therefore, the main welding methods are shielded metal arc welding, brazing, and submerged arc welding. 1.2 Welding materials: For welding high-carbon steel, it is generally not required that the joint have the same strength as the base metal. In shielded metal arc welding, low-hydrogen electrodes are generally chosen, as they have strong desulfurization capabilities, a low content of diffused hydrogen in the deposited metal, and good toughness. When equal strength between the weld metal and the base material is required, low-hydrogen electrodes of the appropriate grade should be used; when equal strength is not required, low-hydrogen electrodes with a strength grade lower than that of the base material should be chosen. It is important to remember that electrodes with a strength grade higher than that of the base material must not be used. If preheating of the base material is not allowed during welding, in order to prevent cold cracks in the heat-affected zone, austenitic stainless steel electrodes can be used to obtain an austenitic structure with good plasticity and strong crack resistance. 1.3 Groove preparation: To limit the mass fraction of carbon in the weld metal, it is necessary to reduce the fusion ratio; therefore, U-shaped or V-shaped grooves are generally used during welding. It is also important to ensure that any oil, rust, or similar contaminants within 20 mm of the groove and its surrounding areas are removed. 1.4 Preheating: When welding with structural steel electrodes, preheating is necessary before welding, with the preheating temperature controlled between 250°C and 350°C. 1.5 Interlayer treatment: During multi-layer, multi-pass welding, the first pass is carried out using a weld rod with a small diameter and at a low current. Generally, the workpiece is placed in a semi-upward welding position or the welding rod is moved horizontally, so that the entire heat-affected zone of the base material is heated within a short time, thereby achieving preheating and heat retention effects. 1.6 Post-weld heat treatment: Immediately after welding, the workpiece is placed in a heating furnace and held at 650°C to carry out stress-relief annealing. 2 Welding defects in high-carbon steel and preventive measures: Due to its high tendency to harden, high-carbon steel is prone to hot cracks and cold cracks during welding. 2.1 Measures to prevent thermal cracks 1) Control the chemical composition of the weld, strictly regulate the levels of sulfur and phosphorus, and appropriately increase the manganese content in order to improve the weld structure and reduce segregation. 2) Control the shape of the weld cross-section; the width-to-depth ratio should be slightly larger to avoid segregation at the center of the weld. 3) For weldments with high rigidity, appropriate welding parameters, as well as the right welding sequence and direction, should be selected. 4) Preheating and slow cooling measures should be taken when necessary to prevent the formation of thermal cracks. 5) Increase the alkalinity of the electrode or flux in order to reduce the impurity content in the weld and improve the degree of segregation. 2.2 Measures to prevent cold cracks 1) Preheating before welding and slow cooling after welding can not only reduce the hardness and brittleness of the heat-affected zone, but also accelerate the outward diffusion of hydrogen in the weld. 2) Select appropriate welding measures. 3) Adopt an appropriate assembly and welding sequence to reduce the restraint stress in the welded joints and improve the stress state of the welded parts. 4) Select appropriate welding materials; dry the electrodes and flux before welding, and ensure they are used immediately after being taken out. 5) Before welding, water, rust, and other contaminants on the surface of the base metal surrounding the groove should be carefully removed in order to reduce the amount of diffused hydrogen in the weld. 6) Hydrogen removal treatment should be carried out immediately before welding to allow hydrogen to fully escape from the weld joint. 7) Stress-relief annealing should be carried out immediately after welding to facilitate the outward diffusion of hydrogen in the weld. 3 Conclusion: Due to its high carbon content, high-carbon steel has good hardenability but poor weldability. During welding, it tends to form high-carbon martensite structures, which can lead to welding cracks. Therefore, when welding high-carbon steel, it is necessary to select an appropriate welding process and take timely measures to reduce the occurrence of welding cracks and improve the performance of the welded joints.