The previously described flux cored wire has highlighted the advantages of many welding methods, such as the flux part played with the coated electrode to improve the chemical composition and mechanical properties of the molten metal. The production efficiency is also characterized by gas shielded metal arc welding and submerged arc welding. Flux cored wire can be used for welding carbon steel, low alloy high tensile steel, high strength quenched tempered steel, stainless steel and hard faced wear-resistant steel. Flux cored wire is a promising welding material. In recent years, the flux and flux of flux cored wire have been increasing day by day. Compared with solid wire, flux cored wire has the following advantages and disadvantages. (1) advantages: 1) for all kinds of steel welding, the adaptability emphasizes the composition and proportion of the whole flux is very convenient and easy, and can provide the required weld chemical composition. 2) good process performance, beautiful seam formation and joint protection with gas slag. The arc stabilizer is added to stabilize the arc and the droplet transfer is uniform. 3) the current density of the flux cored wire with the same welding current is fast, the melting rate is fast, the melting rate is about 85%-90%, and the productivity is about 3-5 times higher than that of the electrode arc welding. 4) all position welding can be carried out with larger welding current. (2) shortcomings 1) the process of welding wire is complicated 2) when welding, wire feeding is more difficult than solid wire 3) the appearance of the wire is easy to rust, and the powder is easy to absorb moisture. Therefore, the requirement for the management of flux cored wire is more stringent. 3.1, the function of the flux of flux: The manufacturer of flux cored wire is the unique ingredient of the flux, which is the same as the coated electrode. The composition of flux is different with the different function of the welding material. The basic functions of the flux composition are described as follows: (1) deoxidizer and denitrification agent As nitrogen and oxygen can cause porosity or embrittlement of weld metal, manganese and silicon deoxidizer must be added in the flux. As for self protective flux cored wire, AL is added as nitrogen removal agent in the flux. The above addition of deoxidizer and nitrogen removal agent is aimed at purifying molten metal. (2) slag forming agent Calcium, potassium, sodium or silicon are all welding slag forming agents. Adding in the flux can effectively protect the molten pool from air pollution. The slag can make the weld better appearance and can support the weld pool in full posture welding after fast cooling. The coverage of welding slag can ease the cooling rate of filler metal, which is especially important for welding of low alloy steel. (3) arc stabilizer Sodium and potassium can make the arc soft and smooth and reduce splash. (4) alloy elements The addition of alloying elements such as molybdenum, chromium, carbon, manganese, nickel and vanadium can improve the strength, ductility, hardness and toughness of the filler metal. (5) gas forming agent Fluorite and limestone need to be added to self shielded flux cored wire to protect the gas from combustion. 3.2 type of slag welding The composition of the flux determines the welding activity of the welding material and the mechanical properties of the molten metal. The flux in the flux is mainly acidic, and the acid welding slag is generated after welding. The same alkaline (limestone) flux is the main cause for producing alkaline welding slag. The welding property of the soldering material of the acid system is very good, the arc is smooth and stable in the welding process, the shape is similar to the jet arc, and the spatter is few. The welding personnel are widely used in the operation, and the mechanical properties of the molten metal can reach the requirements of the AWS specification. Flux is the welding material of the alkaline system, which can make the filler metal obtain excellent ductility and toughness, but the workability is far worse than that of the acid system. The droplet transfer is mainly caused by droplet transfer and more spatter. In recent years, the development of flux system for low alloy steel welding consumables the workability of acid system and the excellent mechanical properties of alkaline system. The electrode coating refers to the coating layer applied on the surface of the welding core. During the welding process, the skin is decomposed and melted to form gas and slag. It plays the role of mechanical protection, metallurgical treatment and improvement of process performance. The composition of drug skin: mineral (such as marble, fluorite, etc.), iron alloy and metal powder (such as ferromanganese, ferro titanium, etc.), organic compounds (such as wood flour, starch, etc.), chemical products (such as titanium dioxide, water glass, etc.). The commonly used electrode coating is titanium calcium type (J422 electrode, acid slag) and low hydrogen type (J507 electrode, alkaline slag).