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Nodular cast iron identification
Posted on:Saturday, September 24, 2016

Nodular cast iron:

Nodular cast iron can be identified on the basis of its structure that differentiates it from the other types of cast iron. Ductile iron or nodular cast iron can be identified into different grades depending upon the microstructure, chemical composition, mechanical properties and physical properties. This type of ductile iron is mainly used for the manufacture of pipes used for water supply lines. Ductile iron is also used in manufacturing various automotive components. Other uses include agricultural vehicles, trucks, tractors, oil pumps and sewage lines. They are also used in the production of durable propeller shafts.

The ductile iron and malleable iron have high strength, ductility, heat-resistance and toughness, so a wider application, in some cases can replace the carbon steel. However, its production technology is high, production process is more complex, and production cost is higher than normal grey cast iron and cast steel, therefore, there are more casting defects for ductile iron. There are many fields that ductile iron are using for, such as Pressure pipes and fittings, Automotive applications, Agriculture, road and construction applications, General engineering applications.

1. Structure:
Nodular cast iron otherwise popularly known as ductile cast iron varies from the rest of the cast iron varieties with its nodular graphite spherical structures. These graphite spheres differ in their size, quantity and the arrangement pattern. The main difference is the spherical shape of these graphite molecules unlike the graphite flakes found in grey iron. Ductile iron or nodular cast iron differs in its chemical composition due to the presence of these graphite inclusions formed by the influence of magnesium, cerium and other particles. Therefore nodular cast iron or ductile iron has more tensile strength, high elasticity and toughness than any other cast iron types. Since it has a high stiffness equal to that of a cast steel, it serves as a suitable choice for the manufacturing of parts like propeller shafts.

Nodular cast iron is produced by melting the metal initially. This molten metal is then inoculated with smaller quantities of magnesium and cerium. The free carbons present in the final product form a surface of the round graphite nodules or spheres which are surrounded by ferrite. This adds to the elasticity of the metal.

2. Mechanical properties:
The mechanical properties of nodular cast iron are greatly influenced by the arrangement patterns of the graphite nodules. This determines the various grades of ductile iron offering a wide range of choice for various purposes. The various mechanical properties of nodular cast iron include toughness, tensile strength, elasticity, ductility, hardness and fatigue strength.

3. Physical properties:
The various physical properties of a nodular cast iron include density, thermal expansion, conductivity, magnetic properties, electrical properties and heat capacity. In comparison to grey iron, nodular cast iron has a very high tensile strength up to 90k psi. It is also very strong than grey iron and has good fracture resistance. It has good resistance to any pressure than grey iron.

4. Chemical composition:Nodular cast iron has a chemical composition of several elements including Carbon, Silicon, Manganese, Phosphorous, Sulfur and Magnesium. Carbon is present up to 3.8%, Silicon is up to 3.2, Magnesium up to 0.06. Manganese less than 0.5, Phosphorous less than 0.08, Sulfur less than 0.08 and copper less than 0.40%.

All the mechanical properties, physical properties and the chemical composition along with the arrangement of the graphite nodules influence the capacity of nodular cast iron. Depending upon these combinations, nodular cast iron is classified into different grades used for various needs.

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