Gray cast iron is a cast iron in which the fracture is gray and the carbon in the structure appears in the form of a sheet. Gray cast iron is widely used in various fields due to its high mechanical properties, superior casting properties and good cutting performance. However, when using gray cast iron, it is not only necessary to consider the strength, but to effectively utilize the various characteristics of gray cast iron to obtain suitable and good performance gray cast iron castings.
Let's talk about some of the main properties of gray cast iron.
First, the mechanical properties of gray cast iron
1, tensile strength
Gray cast iron has a high tensile strength. The tensile strength is mainly determined by the matrix structure of the gray cast iron. The tensile strength of the pearlite matrix gray cast iron is greater than that of the ferrite body. The strength can be ensured by adjusting the carbon, silicon, manganese and alloying elements such as nickel, copper and chromium in the gray cast iron.
2, elongation after break
The post-break elongation of gray cast iron is extremely low and increases slightly with the increase of tensile strength. The post-break elongation of gray cast iron is 0.2-0.8%.
3, compressive strength
Gray cast iron has a high compressive strength and is generally 3-4 times the tensile strength. Therefore, gray cast iron is often used for supporting members such as a base of a machine tool or the like.
The hardness of gray cast iron depends on the morphology, distribution and quantity of graphite. The hardness decreases with the decrease of the total carbon amount or the graphite changes from the A type to the D type. Increasing the hardness is beneficial to improve the wear resistance of gray cast iron.
5, impact performance
Gray cast iron is a brittle material with a certain impact resistance, but not suitable for high impact applications. The higher the strength of the gray cast iron, the lower the hardness and the better the impact performance.
Second, physical properties
The density of gray cast iron is particularly affected by the graphite content. The higher the graphite content, the lower the density. The density of different grades of gray cast iron is between 6.95 and 7.35 g/cm3.
Third, the use of performance
1, wear resistance
Gray cast iron has good wear resistance. Under sliding friction conditions, flake graphite gradually transitions to A-type graphite, and the adhesive wear decreases; D-type graphite and its accompanying ferrite increase wear; the more the matrix pearlite, the harder it is, the better the wear resistance.
2, vibration damping
The cast iron of flake graphite is prone to microscopic plastic deformation and dislocation under the action of cyclic stress, so that the vibration energy is irreversibly lossed and accelerates the vibration attenuation. Therefore, the gray cast iron has good vibration damping. In gray cast iron, the finer the flake graphite, the smaller the amount of graphite, and the worse the vibration damping property. The higher the gray cast iron grade, the worse the vibration damping.
Fourth, process performance
1, casting performance
Compared with other cast alloys, due to the narrow solidification range of gray cast iron and lower melting temperature, gray cast iron has good casting properties and good fluidity. At the same time, solidification shrinkage of gray cast iron is smaller than that of ductile iron and malleable cast iron. Larger secondary expansion can achieve no riser feeding and casting, and improve the casting process yield.
2, cutting performance
Due to the presence of graphite in gray cast iron, flake graphite acts as a lubricant chip breaker for the tool, so the gray cast iron has good machinability compared to other cast alloys.
Due to the presence of graphite in grey cast iron and the duality in the welding process, the weldability of grey cast iron is worse than that of steel.
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