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Differences between Gray Iron Casting and Ductile Iron Casting
2019-01-19
1. In gray cast iron, the graphite is flaky and flat; in ductile cast iron, the graphite is spheroidal. When ductile cast iron is struck, if the sound is similar to that of carbon steel, it indicates good spheroidization. By contrast, gray cast iron produces a dull, muffled sound when struck.
2. Regarding spheroidization rate, it can be said that for ductile iron products of the same type, differing spheroidization rates result in varying quality and significant price differences. Typically, factories consider a spheroidization rate of 85% or higher to meet quality standards. A spheroidization rate below 85% usually indicates inadequate spheroidization during casting, often due to insufficient molten iron temperature, which leads to products that fail to meet the required load-bearing specifications.
3. The appearance of the fracture surface (not a machined surface) provides a simple way to distinguish ductile iron from gray iron. Under visual inspection, the fracture of gray iron exhibits relatively coarse grains and a grayish-white color, with metallic luster on the fracture faces. In contrast, the fracture of ductile iron shows very fine grains and a dark gray color; when spheroidization is well achieved, there is almost no metallic luster, though a faint whitish sheen may be present.
4. From the perspective of the smelting process, ductile iron is produced by adding inoculants and spheroidizing agents to gray iron during smelting, which transforms the graphite from a dispersed flocculent morphology into a spherical form. This reduces the degree of graphitic segregation in the ferrite matrix, increases strength, and enhances overall performance.
5. In terms of mechanical properties, gray cast iron exhibits lower performance than ductile cast iron: the tensile strength of gray cast iron ranges from 100 to 350 MPa, whereas that of ductile cast iron ranges from 350 to 700 MPa. Furthermore, ductile cast iron is subject to specific requirements for elongation, while such requirements are rarely imposed on gray cast iron.
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