1. How does carbon affect the fluidity of gray cast iron?
Within the carbon content range of commonly used gray cast iron, the higher the carbon content, the lower the grade, and the better the fluidity. However, the higher the carbon, the worse the mechanical properties of gray cast iron.
The control standard for the carbon content of gray cast iron is based on comprehensive factors such as casting grade, casting weight, and casting wall thickness.
Generally speaking, the smaller the weight of the casting and the thinner the wall thickness, the higher the carbon content of the casting.
2. What effect does carbon have on the fluidity of ductile iron?
The higher the carbon content of ductile iron, the better the fluidity. However, if the carbon content is high, graphite will easily float, and if the carbon content is low, the spheroidization will decline.
The carbon content control principle of ductile iron is the same as that of gray cast iron. It is also controlled based on factors such as the wall thickness of the casting, the weight of the casting, and the casting process.
However, the difference in carbon control between ductile iron and gray cast iron is that since ductile iron is mostly composed of eutectic or hypereutectic components, magnesium, and rare earth elements are added during the spheronization treatment, which increases the shrinkage rate of the casting. To increase the shrinkage cavities that appear, ductile iron needs to increase carbon and silicon, and the amount of graphite to avoid shrinkage cavities. Therefore, the carbon content of ductile iron is generally higher.
Because after graphite is spheroidized, the splitting effect on cast iron is reduced. Ductile cast iron has a high carbon content and a large amount of graphite will not have a major impact on the mechanical properties of the casting. Therefore, the carbon-silicon control principle of ductile iron is high carbon and high silicon.
Of course, some ductile iron requires high carbon and low silicon, or making high-silicon ductile iron is an exception. Also, I don’t know whether the looseness you are talking about refers to molten iron or castings. Ductile iron will be loose. Design the gating system according to the shape of your product, hot nodes, etc. Shrinkage is a characteristic of ductile iron. During the solidification process, graphite is first released. It expands and then shrinks again to a certain extent.
3. The role of carbon in steel
Carbon is the main alloying element of steel materials, so steel materials can also be called iron-carbon alloys. The main functions of carbon in steel are:
1) Form a solid solution structure to improve the strength of steel, such as ferrite and austenite structures, both of which contain dissolved carbon elements;
2) The carbide structure formation can improve steel’s hardness and wear resistance. For example, cementite, namely Fe3C, is a carbide structure.
Therefore, the higher the carbon content in steel, the higher the strength and hardness of the steel, but the plasticity and toughness will also decrease; conversely, the lower the carbon content, the higher the plasticity and toughness of the steel, and its strength. , the hardness will also decrease accordingly.
Therefore, the carbon content determines the use of steel:
Low carbon steel (carbon content <0.25%), generally used as profiles and stamping materials;
Medium carbon steel (carbon content <0.6%), generally used as mechanical parts;
High carbon steel (carbon content >0.7%) is generally used as tools, cutters, molds, etc.
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