The Difference Between Gray Iron and Ductile Iron
The graphite of gray iron is flat, and the graphite of ductile iron is spherical.
When tapping on the ductile iron, if the sound is similar to that of carbon steel, indicating the grade of ductile iron is good. The gray iron tapping sound is very stuffy.
As for the spheroidization rate, the differnent spheroidization rate will cause huge differences on price and quality for those same material of ductile iron products.The general factory has regarded a spheroidization rate of 85% as a qualified product. The reason cause the spheroidization rate under 85% is that when the pouring is performed, and the spheroidization is not going pretty well which leads to the low temperature of molten iron, so comes to the bad bearing pressure of manufactured products.
From the appearance of the fracture (not the machined surface), the ductile iron and the gray iron can be easily distinguished, and the grain of the gray iron fracture is relatively coarse, grayish white, and the crystal surface has a metallic luster. The fracture grain of ductile iron is very small and dark gray. If the spheroidization is good, there is almost no metallic luster. If there is whitish luster, white mouth tissue is generally present.
From the mechanical properties, the mechanical properties of gray cast iron are lower than that of ductile iron. The mechanical properties of gray cast iron are 100-350 MPa, while the mechanical properties of ductile iron are 350-700 MPa. In addition, the ductile iron has elongation requirements, while gray cast iron has few requirements in this regard.
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