Analysis of valve body and welding material of imported all-welded ball valve
The body material of a fully welded ball valve is usually carbon steel or low alloy steel such as ASTM A105, A694, A350, A516, etc. Its chemical composition has an important influence on the formation of crystal cracks during welding. During welding, impurities such as S and P in the weld form a low-melting eutectic during the crystallization process. Among them, sulfur has a great influence on the formation of crystal cracks, but its influence is related to the content of other elements in steel, such as Mn and S, which combine to form MnS to remove sulfur, thereby suppressing the harmful effects of S. . Mn can also improve the properties, morphology and distribution of sulfides. Therefore, to prevent crystal cracks, there are certain requirements for the Mn/S value in the weld metal. The Mn/sS value is useful for preventing crystallization cracks and is also related to the carbon content. The higher the C content, the higher the required Mn/S value. Excessive presence of Si, Ni and impurities also increase the harmful effect of S. Strict control of the chemical composition of valve body materials and the development of appropriate material procurement standards is one of the effective ways to effectively prevent crystallization cracks when welding imported all-welded ball valves.
Choice of wire and flux
(1) Welding wire material selection Welding wire is mainly used as a filler metal, adding alloying elements to the weld and directly participating in the metallurgical reaction in the welding process. Its chemical composition and physical properties not only affect the stability in the welding process, productivity and weld quality, but also affect welding performance. The choice of wire material mainly depends on the material of the valve body. For common valve body materials, the commonly used welding wire materials are carbon steel welding wire such as H08MnA and low alloy steel welding wire such as H10Mn2. At the same time, the choice of the diameter of the welding wire also has a great influence on the shape of the weld. With constant welding current, arc voltage and welding speed, the penetration depth is inversely proportional to the size of the weld. diameter of the wire, and the welding width is proportional to the diameter of the welding wire. For automatic submerged arc welding, which is often used in all-welded ball valves, the welding wire diameter is usually 2.5-6mm.
(2) Choice of Flux Material The flux acts as an air seal, protecting the weld metal from air immersion and participating in the metallurgical reaction of the molten pool during the welding process. When determining the welding wire, the reference flux becomes the main material, which directly affects the mechanical properties (especially ductility and low-temperature toughness), crack resistance, the appearance of welding defects and the welding performance of the weld metal. This requires the flux to have good metallurgical properties and processing properties; the particle size meets the requirements (the particle size of ordinary flux is 0.45~2.50mm, fine particles less than 0.45mm should not exceed 5%, and large particles above 2.50mm should not exceed 2%. The particle size of fine-grained flux is 0.28~1.425mm, fine particles less than 0.28mm should not exceed 5%, and large particles over 1.425mm should not exceed 2%); water content w(H2O) ≤ 0.10%, content of mechanical impurities not more than 0.30% (mass fraction), sulfur and phosphorus content w (S) ≤ 0.060%, w (P) ≤ 0.080%. Depending on the selected welding wire material and the chemical composition of the valve body material, the flux is mainly made of high silicon melting flux or high alkalinity sintering flux