Cast irons and its properties

Cast irons

Cast iron is a mixture of various elements, with its welding complexities, it is a multi-use metal used both in general and commercial purposes.

The elements may include in cost iron are as follows:

• Carbon 1.7 to 4.5%  
• Silicon 0.5 to 3%
• Phosphorus 0.8% 
• Sulfur 0.2% 
• Manganese 0.2 to 1.3%

Apart from this, some other elements can also be included such as Molybdenum Nickel Chromium andCopper.

Classification of cast iron

Cast iron may be classified in various types upon its chemical composition like :

•  Gray Cast Iron 
•  Malleable Cast Iron 
• Nodular Cast Iron.
• White Cast Iron 

Gray Cast Iron

Gray cast iron has a brownish surface and contains 25 to 38 percent carbon content, in addition to other elements such as silicon 1.1 to 2.8 percent, manganese 0.4-1.0%, phosphorus 0.15%, sulfur 0.10%, and remaining iron.

Although cast iron is brittle in nature and gray cast iron has the lowest melting points of iron ore (around 1178 ° C), and is easy to machine. But economically probably the hardest of all metals to weld. is.

Welding of Gray Cast Iron

 To be welded, a molten pool of gray cast iron is formed while welding, forming a weld when solidified. If the percentage of silicon in gray cast iron is appropriate, the amount of carbon remaining in the composite state (as cement, etc.) or free form (as ash) depends on the cooling rate of the weld metal. If the cooling rate of the metal is slightly faster, most of the carbon will move to the joint state ”and will result in very hard, brittle cast iron. Cracks can also form with this condition. To avoid this situation, the cooling rate of the weld metal needs to be balanced, for that the joint area is heated to about 600 to 700 degrees through preheating before welding. The cooling rate is balanced through post-heat after welding.

Welding Process May applied in Gray Cast Iron

For welding, gray cast iron, the following welding methods are used:

Thermit welding, Braze Welding, Oxyacetylene welding, Metal-Arc welding

Materials for Cast Iron Welding electrode

Following types of materials may be used for cast iron welding electrodes:

• Copper-steel
• Cast iron itself with high silicon and low sulfur content
• Mild steel or soft iron
• Phosphor bronze
• Monel metal and other nickel alloys

Malleable Cast Iron

-While white cast iron is heated to 760 ° C for 24mm to 25mm thickness and then cooled slowly_ This heat treatment converts graphite to a semi-spheroidal shape from the crust. Malleable iron is obtained. The content of malleable cast iron is as follow:

• Carbon      2-3%
• Silicon      0.6-1.3%
• Manganese  0.2-0.6% 
• Phosphorus  0.15%
• Sulfur 0.10%  

Nodular Cast Iron

While in gray cast iron, a layer of graphite appears, it contains nodular cast iron.

Spheroidal graphite, which is a cast-iron resulting from a small addition of magnesium, cerium, or cadmium, provides better digestibility and hardness.

Contains nodular, ductile or spherical cast iron

• Carbon 32-42%
•  Silicon 1.1-3.5%
•  Manganese 0.3.80.8%
•  Phosphorus 0.08% 
• Sulfur 0.02%

White Cast Iron

White cast iron is more brittle and unimaginable and rarely welding or brazing due to its brittleness hardness.

Conclusion

Although cast iron can be mechanized and welded by both the gas welding process and the arc welding process, the essential thing is heat maintenance before welding and during welding. Post heat is required for cooling down the temperature slowly to avoid cracks.