1.Purification degree of molten iron
Some high melting point and high hardness particles remain in the molten iron and become hard spots in the casting, which aggravates the wear of tools in the cutting process. Therefore, an effective means to improve the machinability of gray cast iron is to improve the purification degree of molten iron. The purification degree of molten iron can be improved by using high-quality raw materials and increasing melting temperature. In practical production, the method of filtering molten iron can greatly avoid slag inclusion defects in castings, so as to improve the mechanical properties and processability of gray iron castings. This method of using filter screen is easier to popularize.
The graphite morphology and matrix structure are greatly affected by the cooling rate of castings, and the machinability of gray iron castings is deeply affected. Setting other conditions, pouring temperature and unpacking temperature affect the cooling rate of castings. The higher the pouring temperature and the lower the unpacking temperature, the slower the cooling speed of the casting. The slower the cooling rate, the less carbides in the casting structure, and the better the machinability of gray iron castings. After pearlite is formed, reducing the unpacking temperature can make the graphite distribution of gray iron castings uniform, which is conducive to the improvement of cutting performance of gray iron castings.
3.Composition of raw materials
The machinability of gray cast iron is greatly affected by the quality of raw materials. This may be an important reason why the machinability of foreign castings is better than that of domestic gray iron castings. The type and content of trace elements in raw materials determine the quality of raw materials. For example, titanium compound particles formed by titanium have high hardness, which is not conducive to machining; Lead seriously deteriorates the morphology of graphite; Vanadium promotes the formation of a large amount of sorbite, which deteriorates the cutting performance of gray castings. These trace elements come from iron and scrap steel. Therefore, in order to obtain good machinability of castings, technical means must be used to improve the quality of cheap local pig iron.
Considering the machining process, in order to improve the cutting performance, the selection of tool materials is matched with gray cast iron, and the selection of tool geometric parameters and cutting parameters is reasonable. Among the above factors affecting the machinability of gray cast iron, the easiest way to improve the machinability of gray cast iron in production is to change the alloy composition and inoculant. This paper focuses on these two aspects to explore and study how to improve the machinability of gray cast iron.