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06
2022
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The role of five elements in cast iron parts
Cast iron is a cast iron-based alloy with a carbon content of more than 2%, and also contains silicon and small amounts of elements such as manganese, phosphorus, and sulfur. White cast iron, gray cast iron, and ductile iron are common. The conventional elements of cast iron are carbon, silicon, manganese, sulfur, and phosphorus, which are our five major conventional elements and are important factors that directly affect the mechanical properties of castings.
Cast iron is a cast iron-based alloy with a carbon content of 2% or more, and also contains silicon and small amounts of elements such as manganese, phosphorus, and sulfur. White cast iron, gray cast iron, and ductile iron are common. The conventional elements of cast iron are carbon, silicon, manganese, sulfur, and phosphorus, which are our five conventional elements and are important factors that directly affect the mechanical properties of castings. The main functions are as follows:
1. Element silicon is a beneficial element in cast iron. Like carbon, it can promote graphitization. The effect of adding silicon as an inoculant is more obvious. For as-cast ductile iron castings, increasing the silicon content has a dual effect. On the one hand, it increases ferrite, reduces pearlite, cementite, and ternary phosphorus eutectic, thereby improving the plasticity of the casting and reducing its strength and hardness; on the other hand, the silicon solution strengthens the ferrite and increases the yield point and hardness; it increases the volume expansion during solidification and improves the casting fluidity of silicon; silicon can improve heat resistance and corrosion resistance.
2. Element carbon is the basic component of cast iron. It is the main basis for distinguishing steel and iron. Iron has a carbon content greater than 1.7%, and steel has a carbon content less than 1.7%. Moreover, in the production process, carbon will affect the mechanical properties of the casting. In casting, carbon can promote graphitization, reduce the tendency of white spots, that is, reduce cementite, pearlite, and ternary phosphorus eutectic, and increase ferrite, thereby reducing hardness and improving processing performance.
3. Element manganese is one of the important elements in cast iron. An appropriate amount of manganese can help form texture and increase firmness, strength, and wear resistance. Manganese, like sulfur, is an element that hinders graphitization, but it is also a stable compound. When coexisting with sulfur, manganese has a strong affinity with sulfur and will combine into compounds such as MnS. At an appropriate temperature, it can neutralize sulfur, play a role in desulfurization, and hinder graphitization. When manganese reaches a certain amount, the casting will have the advantages of high hardness, high strength, high density, and wear resistance, and the silicon content will also increase accordingly.
4. Element sulfur is also an impurity and harmful element. In the casting process, sulfur has a strong affinity with other elements such as manganese and magnesium. It produces stable carbides, hinders graphitization, consumes spheroidizing elements in molten iron, and forms residues such as MgS and MnS. If the effective residual spheroidizing element content is too low due to sulfur consumption, the spheroidization effect will be reduced, and problems such as slag inclusion and subcutaneous porosity will also be promoted. As sulfur reduces the spheroidization rate, accelerates spheroidization decay, and forms slag, mechanical properties decrease or become unstable. Sulfur should be removed and its content should be low. In ordinary gray cast iron, the sulfur content is generally 0.02% ~ 0.15%, and in ductile iron, S0.02%, sometimes depending on the situation.
5. Element phosphorus is a harmful element and is regarded as an impurity. Phosphorus often affects the mechanical properties of cast iron, especially reducing toughness and density, and is the main cause of cracking of castings, because the solubility of phosphorus in castings is very low.
Therefore, cast iron is actually a very complex chemical process based on elements such as carbon, silicon, manganese, sulfur, and phosphorus. Among them, carbon and silicon are the basic components, and the effect is generally small when the manganese content is low. Sulfur and phosphorus are often regarded as impurities, so their use is often restricted. Each element has a certain influence and effect on the quality, solidification crystallization, structure, and properties of cast iron, which requires the foundry to reasonably配比 the five elements in the casting process, which is a way to improve the quality of cast iron.
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