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zh What is gray cast iron？
2025-01-13 16:27:56 hits：0
Gray cast iron is a major type of cast iron and is extremely widely used in the industrial field. Many castings belong to gray cast gray iron castings.
I. Gray Cast Iron Composition
Gray cast iron is mainly composed of elements such as iron (Fe), carbon (C), silicon (Si), manganese (Mn), sulfur (S), and phosphorus (P). The carbon content is generally between 2.5% - 4.0%, and the silicon content is around 1.0% - 3.0%. Its name originates from the dark gray color of its fracture surface. This is because most of the carbon exists in the form of flake graphite in gray cast iron. When the cast iron fractures, these graphite flakes are exposed, making the fracture surface appear gray.
II. Gray Cast Iron microstructurMicrostructure
At the micro level, gray cast iron consists of a metal matrix and flake graphite. The metal matrix can be pearlite, ferrite, or a mixed structure of both. Pearlite is a structure with alternating layers of ferrite and cementite, while ferrite is an interstitial solid solution of carbon dissolved in α - Fe. The graphite flakes are distributed in a flake shape within the matrix, which has a crucial impact on the properties of gray cast iron. For example, the graphite flakes are like tiny cracks, which will weaken the continuity of the matrix. When the material is subjected to external forces, stress concentration occurs at the tips of the graphite flakes, resulting in relatively low tensile strength of gray cast iron. However, the graphite flakes also have the effects of oil storage and shock absorption, endowing gray cast iron with good wear resistance and shock absorption.
III. Gray Cast Iron Properties
Mechanical Properties
Tensile Strength: The tensile strength of gray cast iron is generally low, usually between 100 - 300 MPa. For example, a certain type of ordinary gray cast iron used to manufacture a bracket that bears a small tensile force has a measured tensile strength of 180 MPa. This is because the splitting effect of the graphite flakes on the matrix makes it easy for cracks to occur and expand at the tips of the graphite flakes during stretching.
Compressive Strength: The compressive strength is relatively high, generally 600 - 1500 MPa. In the construction field, the basic support parts made of gray cast iron can withstand huge pressures, and the measured compressive strength can reach 1200 MPa. In the compression state, the harmful effects of the graphite flakes are relatively small, and the matrix can withstand greater pressures.
Hardness: The hardness is moderate, generally between HB130 - 270. This makes it suitable for occasions where a certain degree of wear resistance is required. For example, in the material selection of wear - resistant linings for mining machinery, gray cast iron effectively extends the service life of the linings due to its hardness advantage.
Process Performance
Casting Performance: Gray cast iron has good casting performance. It has good fluidity, which means that during the casting process, the liquid metal can easily fill the mold cavity, enabling the casting of parts with complex shapes. For example, an automobile cylinder head-casting car parts is cast with gray cast iron. Due to its good fluidity, a cylinder block with a complex internal structure has been successfully cast, and the qualified rate is as high as 95%. Moreover, the shrinkage rate of gray cast iron is relatively small, which helps to reduce casting defects such as shrinkage cavities and porosity.
Machinability: Due to the presence of graphite flakes, when gray cast iron is subjected to cutting processing, the chips are easy to break, and the tool wear is relatively small. Therefore, it has good machinability. According to processing data statistics, under the same processing conditions, when using the same tool to process gray cast iron compared with other materials, the tool life can be extended by about 30%.
IV. Application Of Gray Cast Iron
Gray cast iron is widely used in industry. In the field of machinery manufacturing, it is often used to manufacture machine tool beds, worktables, bases, etc. These parts of machine tools mainly bear pressure and do not require high tensile strength. Moreover, the good shock absorption of gray cast iron can reduce the vibration of the machine tool during operation and improve the machining accuracy. For example, a high - precision machining center produced by a well - known machine tool factory has its bed made of gray cast iron. Through vibration monitoring during the operation of the machine tool, it is found that compared with machine tools with beds made of other materials, the vibration amplitude is reduced by 40%, effectively improving the machining accuracy. In the automotive manufacturing industry, gray cast iron is used to manufacture engine cylinder blocks, cylinder heads, and other components. Its good casting performance can create complex internal structures, and at the same time, its wear resistance can meet the requirements of engine operation. According to feedback from automotive engine manufacturers, engine cylinder blocks made of gray cast iron can have a service life of more than 200,000 kilometers under normal use conditions, effectively reducing the maintenance rate and replacement cost of the engine.
Tiegu is a casting supplier that provides rich gray cast iron with guaranteed quality to global users. If you have any related needs, please feel free to contact us at any time.
