They are iron-carbon alloys that contain a small amount of elements from steel production methods such as manganese, silicon, sulfur and phosphorus. They are also known as manufacturing steels because their usage areas are the building and manufacturing sector.
All properties of carbon steels are directly related to the structures they have, depending on the amount of carbon they contain. While increasing hardness, yield and tensile strength in steels with increasing carbon amount, ductility (elongation and% shrinkage) and impact resistance properties decrease. The increase in the amount of carbon (depending on these properties) plays a lowering role in the plastic forming ability of steels. However, as a very important and effective element in martensitic transformation, it makes it possible for steels to harden with the mechanism we call quenching. The increase in the amount of carbon adversely affects the ability of the steel to absorb water and its welding. Low carbon steels can be subdivided into three groups according to their carbon content.
Low Carbon Steels: Steels containing up to 0.20% carbon can be included in this group. They are also known as mild steels, considering their mechanical properties. Low carbon steels cover the largest amount of world steel production. Especially flat products and steel bars and profiles used in the construction sector and basic structures are in the class of low carbon steels. Low-carbon steels cannot be hardened sufficiently massively by heat treatment due to their low carbon content. However, cementation, nitration, etc. surface hardening processes can be hardened surfaces.
Medium Carbon Steels : Steels in this group are steels containing carbon between 0.20-0.60%. They have moderate mechanical properties depending on the amount of carbon. The biggest feature of steels in this group is that they can be hardened sufficiently by heat treatment. In this regard, the usage areas of medium carbon steels are characteristic. In particular, they are steels preferred by the machinery manufacturing industry. Their ability to process and take shape is lower compared to low carbon steels. The welding ability of steels in this group is also lower compared to low carbon steels. Because the uncontrolled thermal effects that occur during welding cause the structural change of the steel to be uncontrolled. As a result, it can cause errors in materials. For this reason, special care must be taken in welding processes of medium carbon steels, especially those containing alloy elements.
High Carbon Steels : They are steels containing more than 0.60% carbon. They are normally steels with high strength and low ductility. Thanks to their hardening with heat treatments, they gain high hardness. In this regard, they are wear-resistant and have cutting properties. Their processing and shaping capabilities are lower than those of low and medium carbon steels. Welding capabilities are also low and can be welded with more special techniques. Steels in this group are mostly used in tool production. Although the limit of the amount of carbon in the composition of high-carbon steels can be up to 2% in accordance with the iron-carbon balance diagram, this value is limited to 1.2-1.4% in practice. Especially high carbon steels can take water more easily than low and medium carbon steels and the hardness of the martensitic structure obtained is higher.
USAGE AREAS AND PROPERTIES OF CARBON STEELS