Cast iron is an iron-based metal that is an alloy of iron with 2 to 4% carbon and other elements. It also have traces of impurities such as sulfur and phosphorus. It’s made by reducing ore in a blast furnace. Because of its name, some people believe that cast iron is 100% iron. To determine a cast iron, an iron alloy must contain at least 2% carbon. The addition of manganese and silicon is common in cast irons. These extra alloying elements are being used to alter the characteristics of cast iron and create specific cast iron alloys.
Making Cast Iron
Making Cast Iron starts with heating an in a furnace to make molten iron. The molten metal is then cast ( poured out and allowed to harden, in the form of an ingot). After this, the cast iron ingots are being re-melted into a final mold. During this second re-melting, the cast iron may be then subjected to a variety of metallurgical changes. This happens via the addition of alloying materials or heat-treating techniques.
Different Types Of Cast Iron
- Gray Iron
The flake shape of the graphite molecules in the metal distinguishes gray iron. When the metal fractures, the fracture runs along the graphite flakes. It gives it a gray hue on the surface of the fractured metal. This feature handles the name “gray iron.” Gray iron is a strong, lightweight and durable material. It has 20–25 times the damping capacity of steel and outperforms all other cast irons.
Compared to other cast iron, gray iron is easier to the machine. It wear resistance makes it one of the highest volume cast iron products.
- White Iron
After shearing the white iron, the fractured face appears white since there is no graphite present. The cementite microcrystalline structure is tough and brittle. It has a high compressive strength and good wear resistance.
Using a good heat conductor can create part of the mold, allowing faster cooling. The molten metal will be then drawn out of that region. While the rest of the casting cools at a slower pace.
- Malleable Iron
The end result of heating and tempering is malleable iron. Using a heat treatment process transforms it into soft iron. The breakdown of the iron carbide molecules causes the release of free graphite particles into the iron. A malleable iron with a microcrystalline structure results from the addition of alloys and varied cooling rates.
- Ductile Iron (Nodular iron)
Ductile iron obtains its special properties through the addition of magnesium into the alloy. The magnesium present in the graphite causes it to take on a spheroid form rather than the flakes of gray iron.
During the manufacturing process, the control of composition is very important. Magnesium reacts with impurities such as sulfur and oxygen. This affects the shape of the graphite molecules.
Both steel types are composed of iron. Yet, the addition of magnesium to the alloy gives nodular iron its distinctive characteristics.
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