Carbon steels are the most common steels used in manufacturing, accounting for more than 75% of all steel produced. Their composition is relatively simple: iron combined with varying amounts of carbon, plus small traces of other elements such as manganese, phosphorus, sulfur, and silicon. What sets different carbon steels apart is mainly the percentage of carbon present in the alloy.
The Three Main Types of Carbon Steel
- Low-Carbon Steel: Less than 0.3% carbon
- Medium-Carbon Steel: Between 0.3% and 0.5% carbon
- High-Carbon Steel: More than 0.5% carbon
Each of these groups offers different mechanical properties and applications depending on the balance between strength, hardness, and formability.
Low-Carbon Steel
This type is softer and easier to shape compared to the other groups. It is commonly used for construction materials, automobile body panels, and general-purpose sheet metal. Its weldability and malleability make it one of the most widely used types.
Medium-Carbon Steel
Containing a higher percentage of carbon, this type is harder and stronger than low-carbon steel but still allows for some machining and shaping. It is often chosen for applications such as gears, axles, and railway tracks where durability is required.
High-Carbon Steel
High-carbon steel is the hardest and most wear-resistant of the three. It has less flexibility but excels in producing cutting tools, springs, and high-strength wires. Its resistance to abrasion makes it useful in demanding applications.
Comparing Properties of Carbon Steels
| Type | Carbon Content | Properties | Common Uses |
|---|---|---|---|
| Low-Carbon Steel | < 0.3% | Soft, ductile, easy to weld | Construction, auto body, sheet metal |
| Medium-Carbon Steel | 0.3% – 0.5% | Stronger, less ductile, wear-resistant | Gears, axles, machinery parts |
| High-Carbon Steel | > 0.5% | Very hard, brittle, wear-resistant | Cutting tools, springs, wires |
Crystal Structures in Steel
Steel’s properties also depend on its phases at different temperatures. At room temperature, it is in the ferrite phase with a body-centered cubic structure. When heated to about 1,340°F, it transitions into austenite, which has a face-centered cubic structure and can hold much more carbon. These shifts affect hardness and strength.
Designations for Carbon Steels
- 10XX steels: Plain carbon steels
- 11XX steels: Extra sulfur for improved machinability
- 12XX steels: Extra sulfur and phosphorus
- 15XX steels: Higher manganese content (1.00–1.65%)
These codes help identify both the carbon content and any additional elements.
Example: Understanding the Numbers
Steel labeled 1023 contains 0.23% carbon, while 1029 contains 0.29% carbon. Both fall into the low-carbon category, but that small difference changes hardness and strength.
Test Your Knowledge
Think you’ve got a solid grasp on carbon steels? Head over to SawbladeUniversity.com and take the Carbon Steel Classification quiz. It’s a quick way to check what you’ve learned and see how well you can identify the differences between low, medium, and high-carbon steels.
Applications by Category
- Low-Carbon: Structural beams, pipelines, sheet metal
- Medium-Carbon: Automotive components, machinery parts
- High-Carbon: Knives, hand tools, springs
Interested in Other Metals?
If you’d like to expand your knowledge beyond carbon steels, take a look at our detailed guide: Aluminum Alloys Explained: 1xxx to 7xxx Series Overview. It breaks down the different series of aluminum alloys, their unique characteristics, and how they are used across industries.
Why Carbon Content Matters
The percentage of carbon has a direct impact on strength, hardness, and wear resistance. Even small variations, sometimes as little as 0.01%, can significantly alter how the steel performs.
Carbon steels remain the backbone of many industries because of their adaptability and cost-effectiveness. By choosing the right type, low, medium, or high, manufacturers can match the steel’s properties to the demands of each application.
