What are the properties of ductile iron manhole covers?

Ductile iron manhole covers are used in almost all major industrial sectors that require high strength, ductility, toughness, wear resistance, resistance to severe thermal and mechanical shocks, high or low temperature resistance, corrosion resistance and dimensional stability, etc. In order to meet these changes in service conditions, many grades of ductile iron are available, providing a wide range of mechanical and physical properties.

Most of the ductile iron castings, as specified by the International Organization for Standardization ISO1083, are mainly produced in an unalloyed state. Obviously, this range includes high strength grades with a tensile strength greater than 800 N/mm and an elongation of 2%. At the other extreme are high plastic grades with elongation greater than 17% and correspondingly lower strength (as low as 370 N/mm). Strength and elongation are not the only factors by which a designer chooses a material, but other decisively important properties include yield strength, modulus of elasticity, wear and fatigue strength, hardness, and impact properties. Additionally, corrosion and oxidation resistance as well as electromagnetic properties may be critical to the designer. In order to meet these special uses, a group of austenitic nodular iron, usually called Ao Ni-Resis nodular iron, has been developed. These austenitic ductile irons are mainly alloyed with zinc, chromium and manganese and are included in international standards.