Main properties of gray cast iron

mechanical property 

The mechanical properties of gray cast iron are related to the microstructure of the matrix and the morphology of graphite. The flake graphite in gray cast iron severely cuts the matrix, causing stress concentration at the graphite tips, resulting in much lower tensile strength, plasticity, and toughness of gray cast iron than steel. However, its compressive strength is comparable to steel and it is also the cast iron with the worst mechanical properties among commonly used cast iron parts. At the same time, the matrix structure also has a certain influence on the mechanical properties of gray cast iron. The ferrite matrix gray cast iron has coarse graphite flakes, the lowest strength and hardness, so it is less commonly used; The graphite flakes of pearlite matrix gray cast iron are small, with high strength and hardness, mainly used to manufacture important castings; The graphite flakes of ferrite pearlite matrix gray cast iron are slightly coarser than those of pearlite gray cast iron, and their performance is not as good as that of pearlite gray cast iron. Therefore, gray cast iron with pearlite matrix is commonly used in industry. 

Other performance

Gray cast iron has good casting performance, good vibration damping, good wear resistance, good cutting performance, and low notch sensitivity. 

Factors affecting the properties of gray cast iron

① The influence of chemical composition. The main focus in production is to control the quality fractions of carbon and silicon. Low carbon and silicon mass fractions make cast iron prone to white cast structure, resulting in low mechanical and casting properties; When the mass fraction of carbon and silicon is too high, there are too many and coarse graphite sheets, and even graphite floating on the surface of the molten iron, which reduces the performance and quality of the castings. Therefore, the carbon and silicon content in gray cast iron is generally controlled between 2% and 4% C; 1.0%～2.0%Si;  0.5% to 1.4% Mn.

② The influence of cooling rate: Under certain casting process conditions, the cooling rate of castings has a significant impact on the degree of graphitization. As the wall thickness of the casting increases, the cooling rate slows down and carbon atoms have sufficient diffusion time, which is conducive to the complete graphitization process. At room temperature, the structure is prone to form gray iron structure; However, if the cooling rate of thin-walled parts is too fast during the cooling process, it is easy to form white cast iron structure.