What is the effect of different forms of graphite on the properties of cast iron?

1. Gray cast iron.

Medium graphite is flaked, the strength, plasticity, toughness of flake graphite is almost zero, the more the number of graphite sheets, the coarser the size, the more uneven the distribution, the tensile strength of cast iron.

and the lower the plasticity. Due to the compressive strength of gray cast iron.

Hardness and wear resistance mainly depend on the matrix, and the presence of graphite has little effect on it.

2. Ductile iron.

The graphite is spherical, so the fragmentation effect on the metal matrix is small, which makes the matrix relatively continuous and causes stress concentration during tension.

The phenomenon decreases significantly, so that the strength utilization rate of the matrix is improved, and the tensile strength, plasticity and toughness, and fatigue strength of ductile iron are improved.

Higher than other cast irons.

3. The graphite in malleable cast iron is flocculent, which has less cracking effect on the metal matrix than gray cast iron, and malleable cast iron has high mechanical properties.

In particular, the plasticity and toughness have been significantly improved.

Graphite in gray cast iron is flaked, the strength, plasticity and toughness of flake graphite are almost zero, and the existence of graphite is equivalent to the existence of holes and microcracks, which not only destroys the continuity of the matrix, reduces the effective area of the matrix, but also forms a concentration at the tip of the graphite sheet, so that the material forms a brittle fracture. The higher the number of graphite sheets, the coarser the size, and the more unevenly distributed, the lower the tensile strength and plasticity of cast iron. Since the compressive strength, hardness and wear resistance of gray cast iron mainly depend on the matrix, the presence of graphite has little effect on it.

Therefore, the compressive strength of gray cast iron is generally 3-4 times of the tensile strength.

The graphite in ductile iron is spherical, so the fragmentation effect on the metal matrix is small, so that the matrix is relatively continuous, and the phenomenon of stress concentration caused by tensile is significantly reduced, so that the strength utilization rate of the matrix is increased from 30% 50% to 70% 90% of gray cast iron, which makes the tensile strength, plasticity and toughness, and fatigue strength of ductile iron not only higher than that of other cast iron, but also can be compared with the cast steel of the corresponding structure.

Graphite in malleable cast iron is in the form of a flocculent. Compared with gray cast iron, the splitting effect on the metal matrix is smaller, and the malleable cast iron has higher mechanical properties, especially the plasticity and toughness are significantly improved.

The graphite form of ductile iron, the graphite form of gray iron, and the graphite form of vermicular graphite cast iron are also different. The number and roundness of graphite required for ductile iron, the thickness of the branches of gray iron and the shape of the head are all different

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First of all, cast iron is an iron-carbon alloy with a carbon content. The most used is ductile iron, which has replaced steel in many places. In machinery manufacturing, cast iron accounts for 50-70%.

In industrial iron, carbon generally exists in a graphite state, and in iron-carbon alloy clocks, graphite has a simple hexagonal crystal structure.

If the graphite in the cast iron presents irregular flakes, splitting the body and reducing the mechanical properties of the cast iron, this kind of cast iron is called gray cast iron. Among them, the more uniform and finer the graphite of gray cast iron, the better.

If the graphite in the tissue is flocculent, the fragmentation effect on the matrix is much smaller than that of gray cast iron, and the toughness and strength are higher than that of gray cast iron, such cast iron is called malleable cast iron.

If the graphite in the tissue is spherical, the concentration of stress can be reduced, and its strength and toughness are higher, which is called ductile iron.

The morphology of graphite is related to the chemical composition and the rate of cooling.

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Gray cast iron and white cast iron are only formed by the different configurations of graphite in cast iron.

The construction of spherical graphite is able to make cast iron tough, such as ductile iron.

Graphite particles will be loose and the strength index will increase, and the structure of cast iron depends on the degree of graphitization, and in order to obtain the required structure, the key is to control the degree of graphitization.

Practice has proved that many factors such as the chemical composition of cast iron, the cooling rate of cast iron crystallization, the overheating and static setting of molten iron all affect graphitization and the microstructure of cast iron.

In fact, the influence of each element on the graphitization ability of cast iron is extremely complex, and its influence is related to the content of each element itself and whether it interacts with other elements, such as TI, ZR, B, CE, MG, etc., all hinder graphitization, but if its content is very low (such as B, CE< TI", they also show the effect of promoting graphitization.

Answer] The toughness and plasticity of :d cast iron are mainly determined by the quantity, shape, size and binning of graphite, among which the shape of graphite has the greatest influence on the line code. Brigade Finger.

Cast iron is a type of iron-carbon alloy, and compared with steel, its composition is characterized by high carbon and silicon content, and higher impurity content. However, the role of impurities in steel and cast iron is completely different, such as phosphorus is the main alloying element to improve its wear resistance in wear-resistant phosphorus cast iron, manganese and silicon are important elements in cast iron, and the only harmful element is sulfur. The structure of celery stamped cast iron is characterized by the presence of graphite.

The toughness and plasticity of cast iron are mainly determined by the quantity, shape, size and distribution of graphite, among which the shape of graphite has the greatest influence. Other properties of cast iron are also closely related to graphite, and the matrix structure is the main factor affecting the hardness, compressive strength and wear resistance of cast iron. According to the shape characteristics of graphite, cast iron can be divided into three categories: gray cast iron (graphite into flakes), ductile iron (graphite into spheroids) and malleable cast iron (graphite flocculent).