High carbon steel welding
Keywords:high carbon steel,welding
High carbon steel is a carbonaceous material with a carbon content of 0.6 to 1.7%, a density of 7.81 g/cm3, and a hardness of HRC 60 to 65. It is often called a tool steel and is usually quenched and tempered. Since the carbon content is high and water quenching is prone to cracking, double-liquid quenching is often used, and small parts are often oil quenched. High carbon steel has poor weldability. In addition to high carbon structural steel, there are also high carbon steel castings and carbon tool steels. These steel mills are used as parts and tools for high hardness or wear parts, mostly for repair and surfacing. High carbon steel is more likely to produce hot cracks than medium carbon steel. High carbon steel is more sensitive to quenching. The heat affected zone during welding and the hardened martensite structure are prone to occur, so the tendency of hardening and cold cracking are great. High carbon steel has poor thermal conductivity at the bottom of the carbon steel. The grain grows faster at the high temperature of welding, and the carbide tends to accumulate and grow at the grain boundary, which makes the brittleness of the weld increase, thereby reducing the joint strength and at the joint. The internal stress in the middle lead is also large, and it is easier to cause the crack to occur.
Due to the poor weldability of high carbon steel, it is mostly used in high hardness or wear parts, parts and tools, so welding 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 very difficult to weld the weld to the same performance as the base metal. The tensile strength of such steel is mostly above 675 MPa. The soldering material is determined by the product design requirements. When high strength is required, J7O7 or J607 is generally used; when the strength is not high, electrodes such as J507 or J506 may be used; or low alloy steel electrodes and metals equivalent to the above strength grades may be selected. All solder materials should be of low hydrogen type. If necessary, it can also be welded with chrome-nickel austenitic stainless steel welding rod. The welding rod grade is the same as the medium carbon steel welding rod, such as: A102; A107; A302; A307, etc., can be preheated, but when the weldment stiffness is large, pre-weld is appropriate heat.
During the welding operation, the weldment is annealed prior to welding to reduce the tendency to crack. When welding with structural steel, it must be preheated before welding, and the preheating temperature is controlled above 250-350 °C. Before welding, pay attention to drying the electrode according to the regulations and put it in the incubator or the insulation tube to prevent moisture. The workpiece must be cleaned before welding, and the same welding process measures as medium carbon steel, such as: reducing the fusion ratio, low current, low welding speed, continuous welding, etc., and taking measures to reduce internal stress.