Main Difference – Iron vs Cast iron
Iron is an important metallic element. It is used in the production of many different useful metal alloys such as steel. The major problem with iron is the rusting of the surface. In order to prevent rusting, different prevention methods such as galvanizing, painting, etc. are used. Metal alloys such as stainless steel are also produced to prevent zero rusting. Cast iron is a form of iron which has a high amount of carbon than other alloy forms of iron. The main difference between iron and cast iron is that iron is a pure metal whereas cast iron is a metal alloy.
Key Areas Covered
1. What is Iron
– Definition, Chemical Properties, Extraction
2. What is Cast Iron
– Definition, Properties, Different Types
3. What is the Difference Between Iron and Cast Iron
– Comparison of Key Differences
Key Terms: Cast Iron, Ductile Iron, Gray Cast Iron, Iron, Metal, Malleable Iron, Metal Alloy, Rusting, Steel, White Cast Iron, Wrought Iron
What is Iron
Iron is a metallic element with the symbol “Fe”. The atomic number is 26, and the molar mass is about 56 g/mol. This chemical element belongs to the d block of the periodic table. It is considered as a transition element as it has partially filled d orbitals according to its electron configuration ([Ar] 3d6 4s2).
Figure 1: Atomic Structure of Iron
Iron is a solid at room temperature. The melting point is 1538 °C, and the boiling point is about 2862 °C. It is very important as a metal and is also used in the production of various metal alloys. Iron, when exposed to air and moisture, can undergo deterioration. This is called rust formation. It is a chemical reaction which involves oxidation of the iron surface. Iron alloys are made with reduced or zero rusting by adding enough amount of chromium with iron; stainless steel is the best example for this.
There are different types of iron alloys including, steel, wrought iron, cast iron, anthracite iron, etc. Steel is one of the most used metal alloys around the world due to its various desirable properties such as strength, ductility, etc. Wrought iron is metal alloy with a low carbon content. It is tough and malleable. Cast iron is composed of a high amount of carbon. It tends to brittle.
Iron can be extracted from iron ores using a blast furnace. Generally, an iron ore is composed of iron in two forms as ferrous and ferric oxides. These forms can be reduced to iron in a blast furnace by heating raw material with coke. Molten iron can be obtained from the bottom of the furnace. This molten iron can be used to make cast iron, steel and other forms of alloys.
What is Cast Iron
Cast iron is a hard, relatively brittle alloy of iron and carbon which can be readily cast in a mould. This contains a higher proportion of carbon than steel. Cast iron is a metal alloy. The carbon content of this alloy is 2-4%. Cast iron has a relatively low melting temperature than other iron alloys.
In addition to carbon and iron, cast iron also contains silicon, manganese and trace amounts of sulfur and phosphorous as well. Since the carbon content is high, cast iron solidifies as a heterogeneous alloy. Cast iron has about 1-3% of silicon. Therefore, it is actually a metal alloy of iron-carbon-silicon. Molten cast iron is less reactive with molding material. However, cast iron is not very ductile and is not suitable for rolling.
Cast iron is a good engineering material due to its low melting point, good fluidity, good machinability, etc. There are several types of cast iron as given below. This classification is based on the microstructure of the alloy.
- Gray Cast Iron
- Ductile Cast Iron
- Malleable Cast Iron
- White Cast Iron
Figure 2: A Pan Made of Cast Iron
These cast iron forms differ from each other according to the form and shape of carbon present in the iron. In the production of gray cast iron, inoculants are used to control the graphite type and size of the alloy. In the production of malleable iron, trace amounts of bismuth are used to improve the malleability. Ductile iron is produced by adding a trace amount of magnesium, which causes the formation of spheroidal graphite in the alloy. White cast iron has white colored cracks when broken. That is due to the presence of iron carbide impurities. Likewise, the presence of some other compounds can provide desired properties to the cast iron.
Difference Between Iron and Cast Iron
Definition
Iron: Iron is a metallic element with the symbol “Fe.”
Cast Iron: Cast iron is a hard, relatively brittle alloy of iron and carbon which can be readily cast in a mold.
Nature
Iron: Iron is a pure metal.
Cast Iron: Cast iron is a metal alloy.
Carbon Content
Iron: Pure iron is not composed of carbon, but iron alloys can have different percentages of carbon.
Cast Iron: Cast iron is composed of 2-4% of carbon.
Melting Point
Iron: Iron has a higher melting point of 1538 °C.
Cast Iron: Cast iron has relatively a low melting point.
Rust Formation
Iron: Rust formation occurs on the surface of iron and iron alloys except stainless steel.
Cast Iron: Cast iron undergo rust formation.
Malleability
Iron: Iron and most iron alloys are malleable.
Cast Iron: Cast iron is less malleable and is brittle (except malleable cast iron).
Conclusion
Iron is a metal. It is used in the production of different types of metal alloys which are used for different purposes depending on their favorable properties. Cast iron is one such form of iron. The main difference between iron and cast iron is that iron is a pure metal whereas cast iron is a metal alloy.
References:
1. “Understanding Cast Irons.” Atlas Foundry Company, Available here.
2. “Cast iron.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 4 Aug. 2016, Available here.
3. “The Extraction of Iron.” Chemistry LibreTexts, Libretexts, 29 Nov. 2015, Available here.
Image Courtesy:
1.”Electron shell 026 Iron – no label” By commons:User:Pumbaa (original work by commons:User:Greg Robson) – http://commons.wikimedia.org/wiki/Category:Electron_shell_diagrams (corresponding labeled version) (CC BY-SA 2.0 uk) via Commons Wikimedia
2. “Cast-Iron-Pan” By Evan-Amos – Own work (Public Domain) via Commons Wikimedia
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