As a substitute for steel in 1949, the human development of ductile cast iron. Less than 0.3% carbon steel, while the cast iron and ductile iron with carbon content the amount of at least 3%. Low carbon steel makes as free graphite carbon sheet structure will not form. The natural form of carbon in cast iron is the free graphite flake form. In ductile iron, the graphite flakes change through special processing methods into a tiny ball. The improved ball made of cast iron makes has physical properties greater than cast iron and steel. It is this nodular microstructure of carbon, the nodular cast iron has better extension and impact resistance, while the flake form of cast iron results no ductility. To obtain the best ductility, the ferrite matrix therefore, ductile iron pressure containing parts are treated with a ferritizing annealing cycle, ductile iron spheroidal nodules also eliminate the crack phenomenon of flake graphite cast iron internal prone. In microscopic photos of ductile iron, can see the cracks in the procession to the ball after the termination of graphite. In the ductile iron industry, the graphite ball called “ crack terminator ”, because of their ability to prevent breakage.
Compared with cast iron, ductile iron has the absolute advantage in strength. Tensile strength of cast iron is 60K, while the tensile strength of cast iron is only 31k. The yield strength of ductile iron is 40K, and the iron did not show the yield strength, and ultimate fracture. Ductile iron strength-to-cost ratio is much better than that of cast iron.
The strength of ductile iron and steel strength is comparable. Ductile iron has a higher yield strength, yield strength minimum of 40K, while the yield strength of steel is only 36k. In most municipal applications, such as: water, salt water, steam, ductile iron corrosion and oxidation resistance than cast steel. As the spherical graphite cast iron microstructure, the decrease vibration capability, ductile iron better than steel, therefore more conducive to reducing stress. Choose one of the important reasons of ductile cast iron is ductile iron casting low cost ratio. The low cost of nodular cast iron makes the material more popular, casting more efficient, less the cost of machining ductile cast iron.
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