Changyi City, Shandong Province, the Yangtze River Foundry (www.changjiangzhuzao.com) located in Changyi City, Shandong Weifang City, Shandong Province, Lu Dong casting, Contact: Zhang microstructure due spheroidal graphite ductile iron, weakening vibration capability, excellent ductile milling in cast iron manhole covers, and therefore more conducive to reducing stress. One important reason is that the choice of ductile iron cast ductile lower than the cost. Ductile material cost makes this even more popular, more efficient production and milling cast iron manhole covers, but also less ductile iron machining costs. The strength and intensity of ductile iron cast are comparable. Ductile iron has a higher yield strength, yield strength minimum of 40k milling of cast iron manhole cover price, and the yield strength of steel is only 36k. In most municipal applications, such as: water, salt water, steam, etc., ductile iron corrosion and oxidation resistance are more than steel. Ductile iron manhole covers reuse the old value is not high gray cast iron manhole cover with high re-melted components using high value often become thieves frequented covers a complete object was labeled fragments sold to private yards of new government suffered huge losses ductile iron burglar covers of several synthetic materials containing impurities recovery process reuse value is not high which is the fundamental way to prevent theft thief.