Carbon Steels are iron carbon alloys that contain trace amounts of elements like manganese, silicon, sulphur and phosphorus in their structure due to steel production methods. Since they are widely used in construction and manufacturing industries, they are also known as tool steels.
All characteristics of carbon steels is directly related to the structures they have depending on the carbon amount they contain. With increasing carbon amount, the hardness, yield and tensile strength of the steel increases while ductility (% elongation and % cross section reduction) and impact resistance characteristics decrease. The increase in carbon amount (depending on these characteristics) plays a decreasing role in the plastic forming of steels. On the other hand, as a very important and effective element in martensitic transformation, it enables steels to be hardened by the mechanism referred to as steeping. The increase in carbon amount has an adverse effect on steeping capability and weldability of steel. Low carbon steels can be separated into three groups according to their carbon content.
Low Carbon Steels: Steels that contain up to 0.20% carbon are considered to be in this group. Considering their mechanical characteristics, they are also named soft steels. Low carbon steels cover the majority of the world steel production. The low-carbon range includes especially flat products and steel rods and shapes that are used in the construction industry and basic structures. Low carbon steels cannot be adequately hardened as a mass through heat treatment process due to their low carbon content. But their surfaces can be hardened by surface hardening process such as case-hardening, nitration, etc.
Intended Use and Specifications: They can be used in the manufacturing of bolts, nuts, tempered machine components as well as in construction and building industry. They can be hardened with surface hardening process.
Medium Carbon Steels: The steels in this group are those with a carbon content of 0.20-0.60%. This type of steels has medium range mechanical properties depending on their carbon content. The most important feature of these steels is that they can be adequately hardened through heat treatment. Thus, the fields of use for medium carbon steels are specific. They are preferred especially by machine manufacturing industry. Their machinability and malleability capability is lower compared to low carbon steels. The welding capability of the steels in this group is also lower compared to low carbon steels. That’s because the uncontrolled heat effects occurring during welding cause the structural change of steel to be uncontrolled as well. This may cause faults in materials. For this reason, particular care must be exercised during the welding process of medium carbon steels, especially those that contain alloys.
Intended Use and Specifications: They are used for manufacturing of several types of items such as machinery, bolts, nuts, shafts, spindles, propeller shafts, tail shafts, sprockets, transmission shafts, spline shafts, load hooks, lever arms, rails, pickaxes, shovels, etc. These steels are suitable for hardening with heat treatment.
High Carbon Steels: Steels that contain more than 0.60% carbon. They are normally high strength and low ductile steels. They gain high hardness thanks to being hardened through heat treatment. Thus, they are resistant to wear and have cutting capability. Their machinability and malleability is lower compared to low and medium carbon steels. Since their weldability is low, they can be welded with special techniques. The steels in this group are used especially for manufacturing of tools. Even though the limit of the carbon content found in high carbon steels can be increased up to 2% as per the iron-carbon balance diagram, this value is actually limited to 1,2-1,4%. Especially high carbon steels can be steeped easier when compared to low and middle carbon steels, and the hardness of the martensitic structure is higher.
Intended Use and Specifications: They are used for manufacturing of spindles, shafts, bolts, nuts, spiral and laminated springs, scissors, simple cutting tools, staples, bucket tooth, grader blades, high strength machine components and parts, files, adzes, wood saws, and similar tools. These steels are suitable for hardening with heat treatment.