Main Difference – Steel vs Graphite Irons

Iron is a metallic element that is a solid at room temperature. It is used in the production of many different useful metal alloys such as steel. These alloys are different from each other based on the carbon content and the elements added to the alloy during its production. Steel is an alloy of iron and carbon with some other elements added. Carbon is included in iron alloys in the form of graphite. The most common graphite included iron alloys include ductile iron, gray iron, and compacted graphite iron. The main difference between steel and graphite irons is that steel is a metal alloy containing a low amount of carbon whereas graphite irons are iron alloys containing a high amount of carbon.

Key Areas Covered

1. What is Steel
      – Definition, Different Types and Composition
2. What are Graphite Irons
      – Definition, Different Types and Composition
3. What is the Difference Between Steel and Graphite Irons
      – Comparison of Key Differences

Key Terms: Alloy, Carbon, Compacted Graphite Iron, Ductile Iron, Graphite, Graphite Iron, Gray Iron, Iron, Steel

What is Steel

Steel is a metal alloy containing iron, carbon and some other elements. There are many different forms of steel categorized based on the carbon content, elements added while smelting, etc.

According to the amount of carbon present, steel can be divided into few groups such as,

• Mild steel
• High carbon steel
• Low carbon steel

Types of steel according to the different elements present are;

• Carbon steel – major components are iron and carbon
• Alloy steel – major components are iron, carbon, and manganese
• Stainless steel – iron and chromium with little amount of carbon
• Tool steel – tungsten, molybdenum like metals are present with iron

Figure 1: A Cold-Rolled Sheet of Carbon Steel

Steel is hard, very strong and ductile. But it is not resistant to corrosion (Except stainless steel, which is made by mixing chromium with iron, which gives the property of corrosion resistance). Steel easily corrodes when exposed to a moist environment.

What are Graphite Irons

Graphite irons are types of iron alloys composed of graphite along with iron. These metal alloys contain carbon in different percentages. Therefore, the chemical and physical properties are different from each other. The major types of graphite irons are as follows.

• Gray iron
• Ductile iron
• Compacted graphite iron

Figure 2: Microstructure of Different Graphite Irons

Gray iron has a gray color appearance on its surface. In gray iron, graphite is flaked. These flakes cause the formation of stress concentration points. It has a good machinability and a good wear resistance.

Ductile iron is composed of graphite in the form of nodules. This type of iron is also called spheroidal graphite iron. Ductile iron has more impact resistance and fatigue resistance. It has ductility and toughness higher than all other cast iron types.

Compacted graphite iron contains shorter and thicker graphite particles which appear as individual worm-shaped particles. These particles are randomly arranged in the alloy. Compacted graphite iron has properties in between ductile iron and gray iron.

Difference Between Steel and Graphite Irons

Definition

Steel: Steel is a metal alloy containing iron, carbon and some other elements.

Graphite Irons: Graphite irons are types of iron alloys composed of graphite along with iron.

Different Types

Steel: Steel can be found in different forms as tool steel, carbon steel, stainless steel and alloy steel.

Graphite Irons: There are few types of graphite irons as ductile iron, compacted graphite iron, and gray iron.

Carbon Content

Steel: Steel is composed of up to 2% of carbon.

Graphite Irons: Graphite irons are composed of up to 4% of carbon.

Corrosion

Steel: Steel forms undergo corrosion with the exception of stainless steel.

Graphite Irons: Graphite irons are highly subjected to corrosion.

Cost

Steel: Steel is considerably less expensive than graphite iron forms.

Graphite Irons: Graphite irons are highly expensive.

Conclusion

Steel and graphite irons are alloys of iron with carbon and some other elements. Steel has a wide range of applications due to its low cost and durability. Graphite irons are much more expensive because of the advanced processes used for the production. The main difference between steel and graphite irons is that steel is a metal alloy containing a low amount of carbon whereas graphite irons are iron alloys containing a high amount of carbon.

References:

1. “Gray Iron Castings, Grey Iron Castings, Casting Solutions, Graphite Iron Castings, Compacted Graphite Iron.” Compacted Graphite Iron Vs Cast Iron, Graphite Iron Castings – Waupaca Foundry, Available here.
2. “Steel.” Wikipedia, Wikimedia Foundation, 24 Nov. 2017, Available here.

Image Courtesy:

1. “Carbon Steel Cold Rolled Sheet Coil” By Jatinsanghvi – Own work (CC BY-SA 3.0) via Commons Wikimedia
2. “GJV 100e 01 ies” By Frank Vincentz – Own work (CC BY-SA 3.0) via Commons Wikimedia, “Ductile Iron” By Michelshock – McGill University (Public Domain) Commons Wikimedia and “Gusseisen mit Lamellengraphit” By Hb tuw – Own work (CC BY-SA 4.0) via Commons Wikimedia [Combined]

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