Ductile iron manhole covers are a type of ductile iron product. Through spheroidization and inoculation treatment, ductile iron achieves spherical graphite, significantly enhancing its mechanical properties. This improvement in plasticity and toughness results in a strength that exceeds that of carbon steel. Ductile iron, a type of cast iron developed in the 1950s, boasts comprehensive properties nearly equivalent to steel. It is precisely due to the superior properties of ductile iron that it has successfully been used in casting parts with complex stress conditions, requiring high strength, toughness, and wear resistance. Ductile iron has rapidly become the second most widely used cast iron material, after gray cast iron. The phrase "using iron instead of steel" primarily refers to ductile iron.