4 Types of Carbon Steel

What are the types of carbon steel?

  1. Low carbon steel
  2. Medium carbon steel
  3. High carbon steel
  4. Ultra-high carbon steel


Two of the most abundant elements found in steel are iron and carbon. While many have the misconception that all types of carbon steel have the same chemical and physical properties, this isn’t always the case. Nevertheless, they improve upon the durability and strength of steel, especially since pure iron alone is not enough. The addition of carbon assists in improving the performance of steel products by increasing yield strength, tensile strength, weldability, wear resistance, machinability, and the like.

Knowing these, before buying carbon steel parts for your automotive assembly or building wall framing, it’s crucial that you understand the differences among each carbon steel type. In this guide, you’ll learn more about the specific properties of low carbon, medium carbon, high carbon, or ultra-high carbon steel. Read on to learn more.


Low Carbon Steel

The most widely-used form of carbon steel is known as low carbon or mild carbon steel. Its carbon content is relatively minimal, with just less than 0.25%.

Compared to other types of steel, mild steel has a low hardness rating, meaning that it can’t easily resist against impacts. It does, however, have excellent ductility, machinability, toughness, and weldability. This makes mild steel useful in a number of applications, such as construction, sign making, car manufacturing, wire drawing, furniture making, and many more.

Due to the low carbon content, mild steel cannot undergo heat treatment methods like quenching — this is why carbon steel products are typically cold-drawn in room-temperature environments.


Medium Carbon Steel

Medium Carbon Steel

Medium carbon steel is a significant improvement from the low carbon variety. This type of steel has a carbon content that ranges from 0.25% to 1.65%, meaning it can be heat treated in order to improve upon the metallurgical properties.

Popular heat treatment methods for medium-carbon steel grades include austenitizing, quenching, and tempering. All of these transform the medium carbon steel into a martensitic metal alloy with a refined chemical structure and improved strength.

Compared to low carbon steel, medium carbon is much stronger but less ductile. Medium carbon steel products are often found as manufactured automotive parts like axles, crankshafts, couplings, forgings, and chassis. They provide stability to vehicle engines, as well as, improve upon safety and performance.


High Carbon Steel

Commonly referred to as tool steel, high carbon steel is extremely difficult to cut, bend, weld, shear, and punch. Once it has already been heat-treated, a high carbon steel prefinished material becomes much tougher — with an approximate 0.61% up to 1.50% carbon content.

Due to the strength of high carbon steels, they’re mainly used to fashion cutters, bits, reamers, and other machining tools. All of these are ingot-cast wrought products that can withstand extreme conditions and heavy loads. They are also heavily alloyed with other elements, like molybdenum, vanadium, chromium, and other performance-enhancing elements.


Ultra-High Carbon Steel

Ultra-High Carbon Steel

Finally, ultra-high carbon steel (UHCS) has the highest carbon content out of all kinds, with 1 to 2.1%, providing this metal with exceptional structural properties. These steels can undergo tempering — a process of heating below the melting point then rapid cooling in order to relieve internal stresses. This results in a tough material that can be manufactured into cutting tools or bladed objects.

Early records of UHCS use dates back to feudal Japan where swordsmiths design katanas and other sharp weapons. While modern techniques in tempering UHCS steel have emerged, this process still retains traditional concepts.

Ultra-high carbon steels can be made into various cutting tools useful for fabrication and machining. They may also be found in the construction industry as concrete reinforcement or heavy-duty structural springs.


Key Takeaway

Steel can be classified into different types of carbon steel that have varying properties depending on the carbon content. As discussed in this guide the different grades of carbon steel can be categorized into four, namely: low carbon, medium carbon, high carbon, and ultra-carbon steel.

Each of these types is ideal for specific uses. Where low carbon steel may be used structurally, they don’t have the sharpness and strength of ultra-high carbon to be used as bladed materials. In much the same way, medium carbon steel is much tougher than low carbon steel, but may not be used as tool steel like high carbon steel.

Before purchasing carbon steel products, make sure you’re aware of their specific grades. This helps you find the most practical option for any of your applications, allowing you to take advantage of the carbon steel material for long durations.