What Is Carbon Tool Steel?
Carbon tool steel is a type of steel containing carbon and a small amount of alloying elements with properties such as high hardness, high strength, high wear resistance, and good machinability.
Compared to low-alloy tool steels and high-speed steels, carbon tool steels are easier to harden by machining and heat treatment, and are therefore used in the manufacture of cutlery, dies, tools, etc. Compared to alloy tool steels, carbon tool steels are relatively low cost and suitable for many applications.
Uses of Carbon Tool Steel
1. Blade Manufacturing
Due to its high sharpness and durability, it is used in the manufacture of knives, scissors, and other cutting tools.
2. Metalworking
Due to its high hardness, carbon tool steel is used in metal processing such as cutting, drilling, and press working.
3. Drill Bits
Sometimes used for drill bit tips. A drill bit is a tool used to drill holes in materials such as metal, wood, and plastic.
4. Tool Parts
Sometimes used to make tool parts, such as screwdrivers, wrenches, hammers, etc.
5. Cold Forging
Used in the manufacture of parts such as nails and bolts.
6. Metal Processing
Used in metal working, such as cutting, drilling, and stamping.
Properties of Carbon Tool Steel
1. Chemical Composition
- Carbon (C)
- Silicon (S): 0.10% to 0.35
- Manganese (Mn): 0.10% to 0.50
- Phosphorus (P): 0.030% or less
- Sulfur (S): 0.030% or less
2. Carbon Content
Carbon tool steel contains carbon as a major alloying element. Carbon content is 0.55% or higher, which is almost the same as that of high carbon steel (carbon content of 0.6% or higher). The higher carbon content results in higher hardness and wear resistance, but may reduce machinability.
3. Machinability
Carbon tool steels have low impurity content and high purity. As a result, it has excellent cutting and machinability, and is suitable for manufacturing precision parts such as knives and tools.
4. Wear and Corrosion Resistance
Because of its high hardness, carbon tool steel can be hardened by quench hardening to improve wear and corrosion resistance. Quenching is the process of heating at high temperature followed by rapid cooling. It is widely used in the manufacture of parts that require high cutting and wear resistance, such as blades, tools, and molds.
5. Brittle and Impact Resistant
The reason why carbon tool steel is brittle and impact-sensitive is its crystalline structure. Since hardness is obtained by quench hardening, the post-quenching microstructure is very hard and brittle. In addition, since the microstructure produced by quenching is aligned in one direction, strong bonding forces act in the direction of alignment and the material tends to be brittle in all directions except for the direction of alignment.
Furthermore, carbon tool steel contains a high amount of carbon among its alloying elements, and numerous carbon compounds are formed in the metallurgical structure. These carbon compounds strengthen the bonding force within the crystal structure, which weakens the bonding force between crystals, resulting in brittleness.
6. Unsuitable for Use in High Temperature Environments
Carbon tool steel is not suitable for use in high-temperature environments because of two main factors.
One is that carbon tool steel is susceptible to oxidation at high temperatures, which may degrade its mechanical properties due to surface degradation.
The high content of carbon among the alloying elements in carbon tool steel makes it susceptible to oxidation at high temperatures. Therefore, oxides and scales may be formed on the surface of carbon tool steel, and the surface texture and roughness may change. The formation of oxides and scale may also degrade the surface and reduce mechanical properties.
Scale is a film of oxides that forms on the metal surface or a film of impurities that adhere to the metal surface.
One is that “carbon tool steel” may experience progressive grain growth at high temperatures, resulting in reduced strength and hardness.
Carbon tool steel becomes hard by quench hardening, but its strength and hardness may decrease as a result of the growth of crystal grains due to use at high temperatures.
Grain growth at high temperatures weakens the strong bonds within the metallurgical structure, causing grain boundary bending and cavities at grain boundaries, which in turn leads to reduced strength and hardness. Decreased strength and hardness can result in reduced mechanical properties and fracture of metal parts when used at elevated temperatures.