The mechanical properties of gray iron casting during operation are related to the microstructure of the matrix and the morphology of the graphite. The flake graphite in gray iron casting is severely cracked on the substrate, and it tends to cause stress concentration at the sharp corners of the graphite. The tensile strength, plasticity and toughness of the gray iron casting are much lower than that of the steel, but the compressive strength is equivalent to that of the steel. The worst mechanical iron casting in the piece. At the same time, the matrix structure has a certain influence on the mechanical properties of gray iron casting. The graphite sheet of ferrite matrix gray iron casting is coarse, with the lowest strength and hardness, so it is less applied.
Gray iron casting pearlite base gray iron casting graphite sheet is small, has high strength and hardness, is mainly used to manufacture more important castings. The graphite sheet of ferrite-pearlite matrix gray iron casting is slightly thicker than pearlitic gray iron casting, and its performance is not as good. Pearlitic gray iron casting. Therefore, the gray iron casting of the pearlite matrix is used more in the industry.
Gray iron casting has good casting properties, good vibration damping, good wear resistance, good cutting performance and low notch sensitivity.
Factors affecting the performance of gray iron casting
1 The influence of chemical composition. The production is mainly to control the mass fraction of carbon and silicon. The carbon and silicon mass fraction is too low, the iron casting is prone to white mouth structure, and the mechanical properties and casting properties are very low. When the carbon and silicon mass fraction is too high, the graphite flakes are too large and coarse, and even the graphite floats on the surface of the molten iron. Reduce the performance and quality of castings. Therefore, the carbon and silicon contents in the gray iron casting are generally controlled at 2% to 4% C; 1.0% to 2.0% Si; 0.5% to 1.4% Mn.
2 The effect of cooling rate: Under certain casting process conditions, the cooling rate of castings has a great influence on the degree of graphitization. As the wall thickness of the casting increases, the cooling rate slows down, and the carbon atoms have sufficient diffusion time, which is beneficial to the graphitization process. The room temperature structure is easy to form gray iron structure, but the thin-walled parts are cold during the cooling process. The speed is too fast, and it is easy to form white iron tissue.