Gray cast iron is widely used in various mechanical parts, such as automobile ventilation plate, gear box, bed and so on. So far, gray cast iron is still the largest casting alloy. However, due to the low strength and poor toughness of gray cast iron, brittle fracture is easy to occur under the condition of heavy load wear, which seriously restricts the development of gray cast iron parts. How to give full play to the advantages of gray cast iron, improve its disadvantages of low strength and poor toughness, optimize the production process and expand its application scope has attracted more and more attention of scientific researchers and manufacturers.
Gray cast iron is a multicomponent alloy with iron (FE), carbon (c) and silicon (SI) as the main elements. Compared with steel, the carbon content in gray cast iron is relatively high, ranging from 2.11% to 4.3%. Most of the carbon in cast iron exists in the form of graphite (G) or carbide (fexcy). Because the graphite crystal is a simple hexagonal lattice structure, its strength and toughness are almost zero. Therefore, the existence of graphite phase in gray cast iron seriously restricts the mechanical properties of gray cast iron.
The graphite in gray cast iron has four basic shapes: flake, spherical, flocculent and intermediate shape. Among them, the graphite in nodular cast iron is fine, the end is passivated and the mechanical properties are the best, while the flake graphite in gray cast iron is coarse, flat and straight, the end is sharp, which is easy to split the continuity of the matrix, and it is easy to produce stress concentration at the sharp corner of flake graphite, resulting in cracks, Therefore, its mechanical properties are the worst. Due to the weak adhesion between graphite and matrix, when plastic deformation occurs on the surface of cast iron, it is easy to cause the interface separation between graphite and matrix, resulting in the cracking and spalling of gray cast iron matrix. Therefore, changing the morphology of flake graphite in gray cast iron is of great significance to reduce its cracking failure.