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Shenyang jingui casting factory
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Spheroidal graphite casting has absolute advantage in strength. Ductile iron has a tensile strength of 60k, while cast iron has a tensile strength of only 31k. Ductile iron has a yield strength of 40k, while cast iron does not show a yield strength and eventually breaks. Ductile iron is far superior to cast iron in strength - cost ratio.
The strength of ductile iron is comparable to that of cast steel. Ductile iron has higher yield strength, and its yield strength is at least 40k, while cast steel's yield strength is only 36k. In most municipal applications, such as water, salt water and steam, ductile iron is more resistant to corrosion and oxidation than cast steel. Because of the spheroidal graphite microstructure of ductile iron, ductile iron is superior to cast steel in reducing vibration, so it is more beneficial to reduce stress. An important reason to choose ductile iron is that ductile iron is cheaper than cast steel. The low cost of ductile iron makes it more popular, more efficient and less expensive to process.
As an alternative to steel, ductile iron was developed in 1949. Cast steel contains less than 0.3% carbon, while cast iron and ductile iron contain at least 3%. The low carbon content in cast steel prevents the carbon present as free graphite from forming structural sheets. The natural form of carbon in cast iron is free graphite sheet form. In ductile iron, the graphite sheet is changed into tiny spheres by special treatment. The improved sphere gives ductile iron better physical properties than cast iron or steel. It is the spheroidal microstructure of carbon that makes ductile iron have better ductility and impact resistance, while the inner flake form of cast iron causes no ductility of cast iron. The best ductility can be obtained by ferrite matrix.
Therefore, ductile iron pressure containing parts are treated with annealing cycle through ferrite, the inside of the nodular cast iron spheres can also eliminate iron internal flake graphite is easy to produce fracture phenomenon. In microscopic photos of ductile iron, cracks can be seen marching to the graphite ball and ending. In ductile iron, these graphite balls are known as "crack terminator" because of their ability to prevent fractures.