(1) Mechanical properties
The structure of gray cast iron is equivalent to taking steel as the matrix and adding flake graphite. The matrix contains more elements such as silicon and manganese than steel. These elements can dissolve into ferrite to strengthen the matrix, so the strength and hardness of the matrix are not lower than the corresponding steel. The strength, plasticity and toughness of flake graphite are almost zero, and it can be regarded as some micro-cracks. It not only cuts the continuity of the matrix structure, but also reduces the effective cross-section of the matrix under load, and it is easy to be at the tip of the graphite. Stress concentration occurs, and brittle fracture is easy to occur when the cast iron is subjected to tensile force or impact force. Therefore, the tensile strength, fatigue strength, plasticity and toughness of gray cast iron are much lower than those of steel with the same matrix. The greater the number of graphite flakes in cast iron, the coarser the graphite flakes, the more uneven the distribution, the more severe the splitting effect and stress concentration on the matrix, the lower the tensile strength, fatigue strength, plasticity and toughness.
The performance of gray cast iron mainly depends on the structure of the matrix and the quantity, shape, size and distribution of graphite. 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 and hardness of gray cast iron are similar to those of steel with the same matrix. The compressive strength of gray cast iron is generally 3 to 4 times its tensile strength.
(2) Other properties
Although graphite reduces the tensile strength, plasticity and toughness of gray cast iron, it is precisely because of the existence of graphite that cast iron has a series of other excellent properties.
1) Excellent casting properties. Gray cast iron has a low melting point, good fluidity and low shrinkage during casting, and is not prone to shrinkage cavities and shrinkage porosity during casting. Therefore, gray cast iron can be cast into thin-walled parts with complex shapes.
2) Good vibration damping performance. The graphite in gray cast iron can buffer vibration, prevent vibration transmission, and convert vibration energy into heat energy, so cast iron has good vibration damping (the vibration damping capacity of cast iron is about 10 times greater than that of steel), and is often used to withstand Parts such as machine bases, frames, fuselage and housing that are subject to pressure and vibration.
3) Good anti-friction performance. Graphite itself is a good lubricant, and the pores left after graphite peeling have the function of adsorbing and storing part of the lubricating oil during use, so that the oil film on the friction surface is easy to maintain and has good friction reduction. Therefore, parts such as machine tool guide rails and cylinder blocks that are subject to friction can be made of gray cast iron.