Effect of low carbon equivalent on Microstructure and properties of gray cast iron

Gray cast iron has become the preferred material for automotive parts such as engine and cylinder block because of its good casting, wear reduction, shock absorption and other properties. In recent years, with the development of automobile towards high power, the performance requirements of cast iron castings are becoming higher and higher. In order to solve this problem, there are two ways: one is to cast high-strength gray cast iron; Second, casting vermicular cast iron. Because the casting process of vermicular graphite cast iron is difficult, the cylinder body material of vermicular graphite cast iron is difficult to control the quality and high cost. Compared with vermicular cast iron and nodular cast iron, grey cast iron has excellent thermal conductivity because flake graphite is distributed between eutectic clusters and connected to form a high thermal conductivity channel. Therefore, it is of great significance to study high strength gray cast iron.

(1) The matrix of gray cast iron is graphite and pearlite. When the carbon equivalent (CE) decreases from 3.8% to 3.2%, the length of matrix graphite decreases and the graphite morphology becomes fine and curved; The pearlite lamellar spacing decreased from 1175 nm to 397 nm and became dense and uniform.

(2) When the carbon equivalent decreases from 3.8% to 3.2%, the tensile strength increases from 303.9mpa to 385.9mpa, with an increase of 27.0%.

(3) When the carbon equivalent increases from 3.2% to 3.8%, the thermal diffusivity of gray cast iron with different carbon equivalent decreases gradually with the increase of temperature, and the dependence on temperature also increases gradually.

The microstructure of high-strength gray cast iron is mainly composed of pearlite and flake graphite. It is often used to control the graphite morphology of gray cast iron so that it has no directionality and reduce the ferrite content in the material to improve the properties of gray cast iron. Tianmiao et al. Have shown that in cast iron materials, C and Si elements play a major role in material properties. C and Si will strongly promote graphitization and affect ferrite content. The influence of these two elements on the matrix structure of cast iron can be described by carbon equivalent (CE). Linyanru et al. Studied high carbon equivalent gray cast iron (CE ≥ 3.9%) and concluded that when the carbon equivalent is increased, the thermal conductivity of the material can be improved. This is because the increase of carbon equivalent makes the graphite content in the gray cast iron become more and coarser, which leads to the improvement of the thermal conductivity of the material, but at the same time leads to the reduction of the mechanical properties of the material, which is difficult to meet the practical application [8]. Therefore, this paper mainly studies the properties of low carbon equivalent gray cast iron to solve this problem.

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