Carbon steels are steel grades with a carbon content of up to 2.1% by weight. Carbon steel does not contain any minimum amount of other alloying elements, such as chromium, cobalt, molybdenum or tungsten. Nonetheless, it often contains manganese. However, the maximum amount of manganese in the metal should not exceed 1.65% by weight. Further, the amount of silicon and copper should be less than 0.6% by weight.
With the rise of the carbon amount in the steel, the hardness of the workpiece increases. However, the weldability and ductility reduces with higher carbon content.
Types of carbon steel
Carbon steel grades are classified by their content of carbon into the three types low-carbon steel, medium-carbon steel and high-carbon steel. The different grades can be distinguished by their carbon content, the microstructure and the properties:
Carbon content by weight in %
|< 0.25||Ferrite, pearlite||Low hardness, cost. High ductility, toughness, machinability, weldability.|
0.25 – 0.60
Low hardenability. Medium strength, ductility, toughness.
(AISI 440C, EN 10088-3)
|0.60 – 1.25||Pearlite||
High hardness, strength. Low ductility.
Carbon steel grades which contain more than 1.25% of carbon by weight are called ultra-high-carbon steels. These steel grades are used for mostly non-industrial purposes, such as knives, axles or punches. These steel grades can be tempered to great hardness.
Due to the fact that low-carbon steels cannot be hardened by heat, the metal is usually treated by cold work. Furthermore, the material shows low strength and hardness, though the properties can be improved through carburizing. On the other hand, low-carbon steels show high ductility, toughness, are cheap and easy to form. They are characterized by a carbon content of less than 0.25% by weight. Low-carbon steel is the most widely used carbon steel grade. In Addition, it is also known as mild steel.
Low-carbon steels are widely used in the automobile industry. Further applications are:
- Structural shapes
- Bridge components
Medium-carbon steel is characterized by a martensitic microstructure which is achieved through heat treatment followed by quenching and tempering. The amount of carbon ranges between 0.25 – 0.65% by weight. Further, the manganese content lies between 0.60 – 1.65% by weight.
Unlike low-carbon steels, medium-carbon steel grades can be heat treated, however only thin sections. The addition of alloying elements such as chromium, nickel or molybdenum can improve the ability of such steel grades to be heat treated.
In Comparison to low-carbon steel, medium-steel grades show greater strength. However, low-carbon steel excels in ductility and toughness.
Due to the combination of high strength, wear resistance and toughness, medium-carbon steels are used for railway tracks. Further applications are:
- Train wheels
- Machinery parts
The amount of carbon in high-carbon steels ranges from 0.60 – 1.25% by weight. These steel grades show the highest hardness and toughness of all steel grades. Furthermore, they have the lowest ductility. In most cases, high-carbon steels are hardened and tempered. As a result, they are very wear resistant. This makes high-carbon steel perfect for the production of cutting tools.
Advantages and disadvantages carbon steel
In comparison to other materials, carbon steel show many benefits:
- Carbon steel is extremely durable. The shock resistance makes such steel grades very popular for the construction industry.
- The resistance to fires, earthquakes and hurricanes makes carbon steels a great material for building homes and houses.
- The fact that carbon steel is very easy to recycle makes it environmentally friendly.
- Compared to other materials, carbon steel can be made very thin. As a consequence, it is very cost effective.
On the other hand however, there are some disadvantages. Due to the low weldability, carbon steels can be difficult to work with. Furthermore, other steel grades often show better corrosion resistance.
Differences between stainless and carbon steel
Both steel grades contain iron. However, the amount of carbon differs which results in different melting points, durability and weldability. In addition, stainless steel has a high chromium content which prevents corrosion. Due to the shiny look, stainless steel is often used decoratively in construction, while carbon steel is mostly hidden.