Argon-rich gas shielded welding of 42CrMo sprocket
The sprocket is one of the important parts of the coal machine equipment of our factory. The sprocket and the drum are integrated by welding. The sprocket must bear enough torque during the rotation process. The weld requirements must have high strength and toughness. High quality requirements. If gas shielded welding is used instead of manual arc welding, the production efficiency can be greatly improved, the labor intensity can be reduced, the mass production problem can be solved, and mechanized production can be easily realized. 2 Selection of welding materials 3 Process plan 3.2 Preheating before welding 3.3 Interlayer temperature 3.4 Welding process parameters 3.5 Post-weld heat treatment. 4 welded joints comprehensive mechanical properties 5 use effect Gearbox Transmission,Car Gearbox Assembly,Transmission Gearbox,Auto Transmission Gearbox ShaoXing Change Auto Synchronizer Ring Co.,Ltd , https://www.sxcjautoparts.com
1 Weldability analysis
The sprocket is made of 42CrMo medium carbon quenched and tempered steel. The carbon equivalent of steel is high (Ceq = 0.8%). It is a high-hardening tendency alloy structural steel, and its cold cracking tendency is relatively serious. In addition, since the sprocket needs to be welded in the quenched and tempered state, it is used in the as-welded state, thereby causing a decrease in the comprehensive mechanical properties of the joint. Therefore, how to correctly select the welding material and welding process to prevent the occurrence of welding cold cracks, and ensure that the welded joint has excellent comprehensive mechanical properties is the main technical key of the steel welding.
According to the comparative test, the 42CrMo steel sprocket was welded by Φ1.6 mm HS-70 welding wire produced by Harbin Welding Research Institute. The welding wire has excellent welding performance, and the deposited metal has excellent comprehensive mechanical properties. Using 20% ​​Ar+80% CO2 gas shielded welding, the chemical composition and mechanical properties of the deposited metal are shown in Table 1. 
3.1 Groove processing and cleaning
The X-shaped groove is used, the groove angle is 60 degrees, and the blunt edge is 2 mm. The groove is machined. Before welding, clean it on the surface of the groove and 5 mm on both sides, and there shall be no impurities such as scale, oil and rust.
Spot welding is carried out with Φ3.2 mm J506 electrode. The electrode should be baked at 300 °C for 2 h before use. According to the results of the weldability test, in order to prevent the occurrence of cold cracks in the weld, the preheating temperature should not be lower than 250 °C. The preheating measures the overall preheating and measures the temperature with a surface thermometer.
The proper layer temperature is one of the necessary conditions to prevent welding cold cracks and obtain excellent welded joints, combined with actual production conditions. The interlayer s temperature is selected to be 200-250 °C.
Multi-layer welding is used for welding, and it is necessary to ensure that the crater is filled during the welding process. The welding process parameters used are shown in Table 2. 
After welding, the workpiece needs to be tempered in time, the tempering temperature is 470-500 ° C, the temperature is 2.5-3.0 h, and the furnace is naturally cooled to room temperature in the air.
The 42CrMo steel sprocket is welded according to the above process by HS-70 welding wire. The comprehensive mechanical properties of the welded joint are shown in Table 3. The mechanical properties of the welded joint meet the technical requirements of sprocket welding. 
The use of HS-70 welding wire argon-rich gas shielded welding 42CrMo sprocket has the following advantages:
(1) The welding process is stable, the welding spatter is small, the smoke is less, and the weld bead is beautifully formed;
(2) The welded joint has excellent comprehensive mechanical properties, sufficient strength and good impact toughness;
(3) Compared with manual arc welding, the efficiency is improved by nearly 5 times, and the welder's working conditions are significantly improved.