Nodular cast iron has high strength and good toughness, so nodular cast manhole covers are about 30% lighter than gray cast iron manhole covers of the same type. The grade of nodular cast iron is QT500-7, the molten iron temperature is not lower than 1456℃, and the rare earth ferrosilicon-magnesium alloy and coke with low sulfur content are added during the spheroidizing treatment, and the spheroidizing level is above grade 3. The mechanical properties of the nodular cast iron specimens are as follows:

Nowadays, the demand for spheroidal ink manhole covers is very large. There is a need for manhole covers in municipal administration, real estate, and villas. Therefore, the number of people purchasing manhole covers is increasing. Many purchases are not necessarily good for manhole covers because they usually need to purchase a lot of things. How can ordinary purchasers purchase good ductile manhole covers?