For special purposes, some clients may require the higher hardness to the gray iron castings.
Improving the hardness of gray iron castings can be achieved by many methods, including adjusting the charge ratio, controlling the chemical composition, overheating the molten iron, and using inoculants.
1. Charge ratio and chemical composition adjustment
By using pig iron, scrap steel, return charge and carburizing agent, to change the shape and length of graphite, can effectively improve the hardness of gray cast iron.
In addition, the hardness of the gray iron castings can be optimized by appropriate silicon-carbon ratio and manganese-sulfur ratio.
2. Overheating treatment of molten iron
Increasing the temperature of molten iron within a certain range can refine graphite and make the matrix structure dense, thereby improving the tensile strength and Brinell hardness of cast iron.
3. Use inoculant
Slowly adding inoculant (such as 75Si-Fe) to the molten iron after it comes out of the furnace can make the hardness of gray cast iron more uniform, improve the machinability, and increase the strength. This helps to improve the overall performance of gray cast iron.
4. Heat treatment methods
Surface quenching technology can also be used to improve the surface hardness and wear resistance of gray cast iron. This is a local heat treatment method suitable for applications that require increased local hardness.
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