Iron-carbon alloy contains small amounts of elements from steelmaking processes such as manganese, silicon, sulfur and phosphorus. It is also known as manufacturing steels since its area of use is the construction and manufacturing sector.  All the properties of carbon steels are directly related to their structure, depending on the amount of carbon they contain. Hardness, yield and tensile strength of steels increase with increasing carbon content, while ductility (% elongation and % sectional shrinkage) and impact strength properties decrease. Increasing the amount of carbon (depending on these properties) plays a decreasing role in the plastic deformability of steels. On the other hand, as a very important and effective element in martensitic transformation, it makes it possible to harden steels by the mechanism we call quenching. The increase in the amount of carbon has an adverse effect on the water absorption ability and weldability of steel. Low carbon steels can be divided into three groups according to their carbon content.  Low Carbon Steels: Steels containing up to 0.20% carbon can be included in this group. It is also known as mild steels due to its mechanical properties. Low carbon steels account for the largest amount of world steel production. In particular, flat products and steel bars and profiles used in the construction industry and basic structures are classified as low carbon steels. Low carbon steels, due to their low carbon content, cannot be sufficiently hardened in mass by heat treatment. However, surface hardening processes such as hardening, cementation, nitriding, etc. can harden their surfaces. Usage Areas and Features: It can be used in the manufacture of bolts, nuts, machine parts that can be rehabilitated, taking part in the building and construction industry. They can be hardened by surface hardening processes.  Medium Carbon Steels: Steels in this group are steels containing between 0.20-0.60% carbon. They have moderate mechanical properties depending on the amount of carbon. The most important feature of steels in this group is that they can be hardened sufficiently by heat treatment. In this respect, the application areas of medium carbon steels are special. These steels are especially preferred by the machinery manufacturing industry. Machinability and formability are lower than low carbon steels. The welding capability of steels in this group is also lower than that of low carbon steels. Because the uncontrolled thermal effects that occur during welding cause the structural change of the steel to be uncontrolled. This can lead to defects in the materials. For this reason, special care must be taken when welding medium carbon steels, especially those containing alloying elements.  High Carbon Steels: These are steels containing more than 0.60% carbon. Normally, they are steels with high strength and low ductility. They gain high hardness due to hardening by heat treatment. In this respect, they are resistant to abrasion and have cutting properties. Their machinability and formability are lower than low and medium carbon steels. Their welding capabilities are also low and can be welded with more specialized 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% according to the iron-carbon balance diagram, this value is limited to 1.2-1.4% in practice. In particular, high carbon steels can absorb water more easily than low and medium carbon steels and the hardness of the resulting martensitic structure is higher.  Usage Areas and Features: It is used in the production of tools such as shafts, bolts, nuts, spiral and leaf springs, scissors, cutting simple tools, punches, bucket gears, grader blades, high-strength machine parts, files, cutters, wood saws. It is suitable for hardening by heat treatment.