What is flakes in cast iron?

The graphite in gray cast iron has a flake-like structure which is largely responsible for the high machinability of this metal. The flake-like graphite structure gives rise to discontinuities in the metal matrix and subsequent reduced cutting forces.

What is nodular in nodular cast iron?

Nodular Cast Iron, also referred to as ductile iron or spheroidal graphite iron, is a group of irons in which the graphite forms as nodules (spherical) instead of flakes as in normal cast iron. Nodulizing elements, typically magnesium, are used to allow the solidification of the graphite into nodules.

What is the composition of nodular cast iron?

The range of the chemical composition for the nodular cast iron with carbides and a mixture of upper and lower bainite was as follows (wt \%): C=3.57–3.83 \%, Si = 2.36–2.87 \%, Mn 0.05–0.09 \%, Cr=0.00–0.34 \%, Mo = 1.91–2.05 \%, and Ni=1.33–1.62 \%.

Is nodular iron the same as cast iron?

The difference between traditional cast iron and modern-day ductile iron is the shape of the graphite. While cast iron has small flakes of graphite, ductile iron contains spherical graphite nodules. Because of the spherical shape of the graphite, ductile iron is often called spheroidal iron or nodular cast iron.

Why is GREY cast iron highly machinable?

The presence of graphite flakes makes the grey iron easily machinable as they tend to crack easily across the graphite flakes. Grey iron also has very good damping capacity and hence it is often used as the base for machine tool mountings.

How is nodular iron made?

Nodular cast iron is made by inoculating the molten metal, just before casting, with a small amount of magnesium or cerium. This causes the free carbon in the finished casting to appear as rounded nodules of graphite, rather than as flakes.

What does nodule mean?

A nodule is a growth of abnormal tissue. Nodules can develop just below the skin. They can also develop in deeper skin tissues or internal organs. Dermatologists use nodules as a general term to describe any lump underneath the skin that’s at least 1 centimeter in size. It’s not a specific diagnosis.

How is malleable cast iron produced?

Malleable Cast Iron: Malleable cast iron is produced from white cast iron by annealing. It is heat-treated iron-carbon alloy, which solidifies in the as-cast condition with a graphite-free structure, i.e., the total carbon content is presence in the cementite form (Fe 3C).

Why is white cast iron called white?

The presence of different carbides, depending on the alloy content, makes white cast irons extremely hard and abrasion resistant but very brittle. White cast iron is named after its white surface when fractured, which is caused by its carbide impurities, allowing cracks to pass straight through.

How is cementite formed?

Cementite forms directly from the melt in the case of white cast iron. In carbon steel, cementite precipitates from austenite as austenite transforms to ferrite on slow cooling, or from martensite during tempering.

What is the difference between nodular and cast iron?

Nodular iron is also called ductile iron. The graphite is present as tiny balls or spheroids. Because the spheroids interrupt the matrix much less than graphite flakes, nodular cast iron has higher strength and toughness than gray cast iron.

What is the formation of nodules or spheroids?

The formation of nodules or spheroids occurs when eutectic graphite separates from the molten iron during solidification. The separation of graphite in nodular form is similar to separation of graphite in gray cast iron except that the additives facilitate the graphite to take nodular shape.

How is graphite formed in spheroidal cast iron?

Spheroidal cast iron can be developed with addition of as low as 0.05\% magnesium which will act as nucleating site for graphite. These nucleating sites provide the surface for graphite nucleation. This means, there will be magnesium or cerium particle at center of each nodule around which graphite solidifies.

What are the different types of defects in nodular iron?

Nodular iron is however a material that contains different kinds of defects, such as inclusions, dross, surface defects, slag stringers and micro shrinkage pores. Nodular iron is also called ductile iron. The graphite is present as tiny balls or spheroids.