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Carbon content in steel has a significant impact on its properties, features and applications. Hence, while selecting steel for any project, it is important to understand the expectations. Accordingly, you can select the right type of steel for your project. This article elaborates on the classification of steel as per carbon content, effects of carbon content and techniques to measure carbon content.

What is carbon content?

Carbon content in steel is the amount of carbon present in steel. Although carbon is a key element used to make steel alloy, the percentage of carbon in steel determines its features. So, what is the average percentage of carbon in steel? The percentage depends on the type of steel and its application. Depending on the carbon percentage, there are four types of steel.

Types of steel as per carbon percentage

Here are key types of steel according to the percentage of carbon content.

Type of steel Carbon percentage Features Applications
Low carbon steel The percentage of carbon in low carbon steel is 0.04–0.30%
  • Ductility
  • Ease of forming
  • Weldability
  • Automotive parts
  • Sheet metal
  • Other areas where high-strength is not a requirement
Medium carbon steel The carbon percentage in medium carbon steel is 0.30% and 0.60%.
  • Medium steel features moderate strength and toughness.
  • It is more difficult to machine/weld compared to low carbon steel
  • Axles
  • Gears
  • Railway tracks
  • Railway wheels
  • Machinery parts, etc.
High carbon steel The percentage of carbon in high carbon steel is 0.60% and 1.0%.
  • Hardness
  • Strength
  • Wear resistance


  • Cutting tools
  • Knives
  • Springs
  • Washers
  • Fasteners
Ultra-high carbon steel It contains a carbon percentage of more than 1%.
  • Exceptionally hard
  • Brittle


  • Bladers
  • Cutting tools
  • Hot water radiators
  • Industrial castings, etc.


Carbon content in other types of steel alloys

Here is a list of types of steel and their respective percentage of carbon content.

Type of steel Percentage of carbon content
Mild steel The percentage of carbon in mild steel is between 0.04–0.30%
Stainless steel The percentage of carbon in stainless steel is 0.10% to 1.20%
Cast iron
  • Cast iron contains a higher amount of carbon and falls under the classification of ultra high carbon steel.
  • The percentage of carbon in cast iron is around 1.7% to 3%.
Structural steel The percentage of carbon in structural steel is 0.15 to 0.30%


Selecting steel with the right carbon content

  • Firstly, determine the expectations from steel. For example, steel to be used in cutting tools needs to be wear-resistant. Hence, higher carbon content is suitable for the application.
  • Take other aspects into consideration, for example, the shape or design of the structure, weather conditions and so on. For example, higher carbon content increases the corrosion rate.
  • Select steel with a suitable carbon content.


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Measuring carbon content in steel

Carbon content in steel can be measured in various ways. Some of the popular methods to measure carbon content in steel are as follows:

Spark Optical Emission Spectroscopy (OES)

This is one of the most trusted ways to measure carbon content in steel. The technique uses sparks generated by an electrical discharge to analyse the composition of the steel.

X-ray fluorescence (XRF analysis)

This is a non-invasive method of detecting the percentage of carbon content in steel. It can determine carbon content by measuring the energy and intensity of emitted X-rays.

Laser Induced Breakdown Spectroscopy (LIBS)

LIBS is a relatively new technique for measuring carbon in steel. It uses a laser to determine chemical composition and measure carbon content.

Effect of carbon percentage in steel

With the percentage increase of carbon, steel gains strength. However, it also has a few disadvantages. Here are some of the effects of carbon percentage on steel’s key features.

  • Strength: It is one of the most critical features. As the carbon content increases, it features the added strength.
  • Ductility: With increasing carbon content, the ductility of steel decreases. This means, steel with more carbon content does not bend easily. Therefore, it may be difficult to give steel the desired shape.
  • Machinability: Due to high ductility, low carbon steel can be machined easily as compared to high carbon steel.
  • Weldability: Higher carbon content also reduces the weldability of steel. Hard steel can crack during welding. Therefore, connecting and joining steel parts can become difficult. Hence, high carbon steel is not used in industries where welding holds importance.
  • Wear resistance: Steel with a higher percentage of steel is more wear-resistant as compared to low carbon steel. Hence, it is suitable for applications where friction and abrasion are regular. Therefore, it is used in applications such as cutting tools.

Carbon content in steel..

Increases Decreases
Strength Ductility
Hardness Machinability
Wear resistance Weldability
Corrosion rate


Final thoughts

Understanding the carbon content in steel is important it can affect your project in multiple ways. For example, lower weldability can extend timelines. Therefore, understand the requirements and learn about the effects before finalising raw material for your project.