Effects of Several Alloy Elements on the Microstructure and Properties of Gray Cast Iron
Gray cast iron is a type of cast iron with a high carbon content and silica content. It has good comprehensive performance, such as a small shrinkage rate and a large inverted pyramidal structure. Because of its high strength and low cost, it has been extensively used for automobiles, machine tools and other industrial applications. When producing gray cast iron, several alloy elements needs to be added for the purpose of obtaining excellent properties such as improved strength, ductility and toughness. This article will introduce several important alloy elements and its effects on microstructure and properties of gray cast iron.
Chromium
Chromium is a non-ferrous element and is one of the most important alloy elements in gray cast iron. Chromium can form carbide and nitride in ferrite, which not only increases the hardness of the matrix, that is, the average carbide index C, but also improves the thermal fatigue resistance of cast iron. At the same time, chromium can also play an appropriate role in improving the overall wear resistance of the matrix by promoting the graphitization of cast iron, which can improve the casting process and reduce defects such as cracks and cold shuts.
Nickel
Nickel is also an important alloy element in gray cast iron. Nickel can form austenite and carbide in gray cast iron, which can refine graphite and increase density, thus improving the ability of gray cast iron to resist thermal fatigue, abrasion and erosion. In addition, nickel can also reduce the temper brittleness of gray cast iron, increase its impact toughness and greatly improve the chilling tendency of gray cast iron, so that the as-cast structure of gray cast iron can be obtained.
Molybdenum
Molybdenum is a strong carbide stabilizer, which can form a range of microalloy precipitation phases in cast iron, such as molybdenum-bearing hard carbide, which has a certain feature of strengthening matrix. Molybdenum can significantly increase the plasticity of cast iron, reduce the shrinkage allowance and even improve the wear resistance and corrosion resistance of the matrix.
Aluminum
Aluminum is a reducing element that can form AlN in the ferrite matrix, which can significantly improve the hardenability and thermal fatigue resistance of the matrix. In addition, aluminum can also form aluminum oxide and improve the thermal shock strength of the matrix, which can significantly reduce the production hot tearing defects. Moreover, aluminum can also promote the graphitization of cast iron, improve its machinability and affect its secondary crystallization behavior, which can refine the as-cast structure of cast iron.
Vanadium
Vanadium can also form nitride and carbide in ferrite, improve the hardenability, improve the chilling sensitivity of cast iron and improve the strength and wear resistance of the matrix. In addition, vanadium can also form vanadium carbide, which can significantly improve the resistance of cast iron against thermal fatigue, corrosion and erosion.
Conclusion
Therefore, chromium, nickel, molybdenum, aluminum and vanadium are important alloy elements in gray cast iron. These five elements can form various carbide and nitride in gray cast iron matrix, which can improve the hardenability, strength, toughness and wear resistance of gray cast iron. In addition, these alloy elements also have certain effects on graphitization, temperature shock resistance and machinability, which greatly affect the microstructure and performance of gray cast iron.
