At higher carbon equivalents (depending on production conditions), increasing Si / C decreases the tensile strength. At this time, increasing the silicon-to-carbon ratio still has the advantage of reducing the tendency of white mouth, and is suitable for the casting of thin-walled castings with low performance requirements. (2) Manganese and sulfur Manganese and sulfur are both elements that stabilize carbides and hinder graphitization. However, when the two coexist, they will combine to form MnS and (Fe, Mn) S compounds, which are distributed in the matrix in the brass gear Suppliers form of particles. The melting point of these compounds is above 1600 ° CIn ordinary gray cast iron, the sulfur content is generally 0.02% ~ 0.15%, and the manganese content is 0.4% ~ 1.2%. Therefore, manganese or sulfur that is too high after neutralization can work alone. Practice has shown that as long as the iron liquid is prevented from oxidizing and the ability to properly use the whitening prevention mouth, the increase in manganese content can not only increase and refine pearlite, but also relax the control of sulfur content properly. Many European manufacturers often use S0.12% to 0.15% molten iron to cast parts with grades above HT250 on cars and tractors. When the manganese is more than 1.5% or even exceeds the amount of silicon, gray cast iron is already alloyed cast iron. At this time, it has the advantages of high strength, high hardness, high density, high density, and wear resistance. It has been applied to machine tool castings. However, the amount of Si also needs to be increased accordingly. In order to ensure the inoculation effect of commonly used inoculants, the sulfur content in gray iron molten iron is generally not less than 0.05% ~ 0.06%. (3) Phosphorus Phosphorus moves the eutectic point of cast iron to the left, and the degree of action is similar to silicon, so when calculating the carbon equivalent, the phosphorus content should be included. Phosphorus exists in the grain boundary in the cast iron as a low melting point binary or ternary phosphorus eutectic, and its hardness is between 750 ~ 800HV and 900 ~ 950HV, so phosphorus can improve the wear resistance of gray cast iron, which is used in machine tools and cylinder liners. And brake shoes. However, it is necessary to avoid the appearance of ternary phosphorus eutectic; at the same time, as the amount of phosphorus increases, the mechanical properties, especially toughness and compactness decrease. High phosphorus content is often the cause of cold cracking of castings.
The phosphorus content of gray iron castings is generally less than 0.20%. For wear resistance and high fluidity requirements, it can be 0.3% to 1.5%. For compactness requirements, the phosphorus content should be less than 0.06%. 2. The charge of gray cast iron by changing the charge composition is generally composed of fresh iron, scrap steel, recycled charge and ferroalloy. Adding scrap steel to reduce the carbon content of molten iron can improve the mechanical properties of gray cast iron. When producing different types of gray cast iron, different proportions of scrap steel will be added as a control index to ensure the material performance. In recent years, due to the abundant supply of scrap steel in industrially developed countries, and the price is much cheaper than virgin iron, so synthetic cast iron and smelting methods that use no virgin iron but only scrap steel and recycled materials, and use carbon addition methods to adjust the carbon content have been developed. Synthetic cast iron can not only reduce the cost, but also get better mechanical properties under the same chemical composition. The production of synthetic cast iron requires smelting equipment that can overheat the molten iron temperature above 1500 ° C. In order to save energy and improve the structure and performance of gray cast iron, synthetic pig iron can also be used in the ingredients instead of cast pig iron. This is because the production of cast iron from blast furnaces requires more coke consumption than steel-making iron and reduces productivity. To this end, high-carbon low-silicon blast furnace liquid iron can be poured into liquid ferrosilicon to produce synthetic pig iron. Gray cast iron produced with synthetic pig iron has improved metallurgical structure and mechanical properties. 3. The temperature, chemical composition, and purity of the molten iron superheat treatment are the three main metallurgical indicators of molten iron, and the temperature of the molten iron directly affects the composition and purity. The increase of the temperature of the molten iron is conducive to improving the fluidity, obtaining sound castings, reducing the scrap rate, and improving the mechanical properties within a certain range. Increasing the temperature of the molten iron within a certain range can refine graphite, refine the matrix structure, increase the tensile strength, decrease the hardness, improve the maturity, relative hardness and quality factor, improve the elastic modulus slightly, and decrease the Poisson’s ratio first. Then it improved.
Excessive overheating not only wastes energy, but also has no beneficial or even harmful mechanical properties. This critical temperature is related to factors such as charge composition, melting equipment, chemical composition, etc. Different researchers draw different conclusions, but the effect and conclusion before overheating to 1500 ° C are consistent. The smelting iron temperature of industrial developed countries is maintained at 1520 ~ 1550 ℃, and the temperature of molten iron holding furnace is 1480 ~ 1500 ℃. With the increase of overheating temperature, the nitrogen content and hydrogen content in the molten iron increased slightly, but the oxygen content after 1450 ° C decreased greatly, and the purity of the molten iron increased. In addition to easily causing pinhole defects, higher nitrogen improves the tensile strength and hardness of cast iron. According to the reaction calculation of Si + O2 = SiO2, the balance of dissolved oxygen in cast iron increases with the increase of temperature. But the presence of carbon in the cast iron, after a certain equilibrium temperature, occurred: SiO2 + 2C → Si + 2CO ↑ reaction, so that the amount of dissolved oxygen in the cast iron began to decline. This equilibrium temperature TG can be calculated according to the content of carbon and silicon in the molten iron: lg [Si% / (C%) 2] = 27486 / TG + 15.47 For cast iron with carbon content 3.2% and silicon 1.6%, its TG is 1415 ℃ . When the temperature of the molten iron is lower than TG, oxygen remains in the molten iron, and compounds such as silicon and other elements can be used as part of the crystallization core. When the temperature is higher than TG, the oxygen in the molten iron escapes in the form of CO, reducing the oxidation of the molten iron. The equilibrium temperature TG is only a theoretical value, the actual reaction temperature is higher than this value. Due to the release of CO, the molten iron begins to boil, so the actual reaction temperature is called the boiling temperature TH, which can be calculated from the following formula: TH (℃) = 0.7866xTG (℃) +362 For C3.2%, Si1.6% For molten iron, its TH = 1475 ° C.
Tags: brass gear Suppliers
meiguo