Difference Between Cast Iron and Carbon Steel

Main Difference – Cast Iron vs Carbon Steel

Iron is an important metallic element. It is used in the production of many different useful metal alloys such as steel. There are different types of iron alloys including steel, wrought iron, cast iron, anthracite iron, etc. Cast iron is composed of a high amount of carbon and tends to be brittle. Carbon steel is a form of steel that is composed of iron and carbon along with trace amounts of some elements. The main difference between cast iron and carbon steel is that cast iron contains 2-4% of carbon whereas carbon steel contains up to 1% of carbon.

Key Areas Covered

1. What is Cast Iron
      – Definition, Properties and Different Forms
2. What is Carbon Steel
      – Definition, Properties and Different Forms
3. What is the Difference Between Cast Iron and Carbon Steel
      – Comparison of Key Differences

Key Terms: Alloy, Carbon Steel, Cast Iron, High Carbon Steel, Iron, Low Carbon Steel, Mild Steel, Steel

What is Cast Iron

Cast iron is a hard, relatively brittle alloy of iron and carbon which can be readily cast in a mould. It contains a higher proportion of carbon than steel. Cast iron is a metal alloy. Carbon content of this alloy is 2-4%. Cast iron has a relatively low melting temperature than other iron alloys.

Along with carbon and iron, cast iron is composed of silicon, manganese and trace amounts of sulfur and phosphorous as well. Its carbon content is high. Cast iron solidifies as a heterogeneous alloy. Cast iron also has about 1-3% of silicon. Therefore, cast iron is actually a metal alloy of iron-carbon-silicon. Molten cast iron is less reactive with molding material. However, cast iron is not that much ductile. Therefore, it is not suitable for rolling.

Figure 1: Cast Iron Pans

There are few types of cast iron based on the microstructure of the alloy. They are,

• Gray Cast Iron
• Ductile Cast Iron
• Malleable Cast Iron
• White Cast Iron

Cast iron is more brittle due to the high carbon content. Carbon tends to clump into carbides or form graphite sheets, making the cast iron more irregular and brittle. Therefore, cast iron is less ductile. It has a lower strength. Cast iron also has a high weight due to high iron-to-carbon ratio.

What is Carbon Steel

Carbon steel is composed of iron and carbon. Alloy elements are present in trace amounts. Some of these elements are silicon, manganese, sulfur and phosphorous. Carbon steel is also divided into three groups as below.

• Mild carbon steel – carbon content up to 0.3%
• High carbon steel – carbon content up to 0.3-0.6%
• Low carbon steel – carbon content up to 1%

Figure 2: Carbon Steel is used as Building Material

Mild steel has more iron than carbon. Therefore, it is highly corrosive in moist environments. High carbon steel is very strong and is used as construction materials. Due to the high amount of carbon present in carbon steel, it shows properties such as hardness, less ductility, reduced weldability, and low melting point. Low carbon steel contain about 0.04-0.30%carbon content. Depending on the desired properties, other elements are added to improve the quality of the steel. This form is stronger than mild carbon steel and is less strong than high carbon steel. 

In general, carbon steel is highly ductile. Due to the presence of a less amount of carbon when compared to the amount of iron present in the alloy, carbon steel is less brittle and has a high strength.

Difference Between Cast Iron and Carbon Steel

Definition

Cast Iron: Cast iron is a hard, relatively brittle alloy of iron and carbon which can be readily cast in a mould and contains a higher proportion of carbon than steel.

Carbon Steel: Carbon steel is a type of steel having a high amount of carbon and low amounts of other elements.

Carbon Content

Cast Iron: Cast iron contains up to 2-4% carbon.

Carbon Steel: Carbon steel contains up to 1% carbon.

Strength

Cast Iron: Cast iron is more brittle due to the presence of a high amount of carbon.

Carbon Steel: Carbon steel is stronger than cast iron.

Ductility

Cast Iron: Cast iron is less ductile.

Carbon Steel: Carbon steel is more ductile.

Melting Point

Cast Iron: Cast iron has relatively a low melting point.

Carbon Steel: Carbon steel has relatively a high melting point.

Other Elements

Cast Iron: Cast iron is composed of iron along with carbon, silicon manganese and trace amounts of sulfur and phosphorous as well.

Carbon Steel: Carbon steel contains mainly iron and carbon. Other elements can be present in trace amounts.

Conclusion

Cast iron and carbon steel are iron alloys that are composed of iron and carbon. They differ from each other depending on the amount of carbon present and the other elements added to the alloy. The main difference between cast iron and carbon steel is their carbon content.

References:

1. “Cast iron.” Wikipedia, Wikimedia Foundation, 25 Nov. 2017, Available here.
2. Media, Site by Reshift. “The Four Types of Steel | Metal Supermarkets.” Metal Supermarkets – Steel, Aluminum, Stainless, Hot-Rolled, Cold-Rolled, Alloy, Carbon, Galvanized, Brass, Bronze, Copper, 15 Sept. 2016, Available here.
3. “Carbon Steel versus Cast Iron.” Cook’s Illustrated, Available here.

Image Courtesy:

1. “Castiron-skillets” By FiveRings at English Wikipedia – Transferred from en.wikipedia to Commons by pd_THOR., (Public Domain) via Commons Wikimedia
2. “53176” (CC0) via PEXELS