• carbon steels, with admixtures of manganese (max 0,8%), silicon (max 0,4%), phosphorus (max 0,05%) and sulfur (max 0,05%). Additionally, carbon steels may contain small quantities of copper, chromium and nickel resulting from steel scrap, as well as dissolved gases, such as hydrogen, oxygen and nitrogen. In carbon steels, increased contents of carbon increase tensile strength Rm, yield point Re, and hardness; decreases plastic properties – elongation A, contraction Z and impact strength KC. However, the increased carbon content impairs weldability and machinability. In turn, manganese, which appears to be a smelting process residue, enhances steel durability and positively affects weldability. Silicon found in carbon steels comes from deoxidation processes. It enhances steel durability, particularly the elasticity limit, yet deteriorates its weldability. Another harmful admixture is phosphorus. Although it increases tensile strength and hardness, it considerably decreases plastic properties. It also raises the temperature at which steel becomes brittle. In rare instances phosphorus is a desirable admixture when it is supposed to enhance machinability, and with accompanying copper presence it improves corrosion resistance. Similarly to phosphorus, sulfur is regarded as a harmful admixture. It does not dissolve in iron and remains in the form of iron and manganese sulfides. During hot machining, iron sulfides (FeS) cause cracks and tears (at above 800°C). Manganese sulfide (MnS) is hardly fusible and occurs in the form of separate inclusions. With sufficient quantity of manganese, iron sulfides (FeS) are not likely to occur. Among other admixtures, oxygen and hydrogen cause steel brittleness in hot machining (like sulfur), while nitrogen manifests itself as hard and brittle nitrides. Types of carbon steels are divided into three categories: construction steels of different grades, tool steels and those of special properties (easily machinable, free-cutting steels) (Table 1) (Dobrzański L.A., 2002; Rudnik S., 1996).