Harmful impurities in steels: negative effects and ways to combat them

Harmful impurities in steels are chemical elements and compounds that, when present in small quantities, have a significant negative effect on its structure and physical and mechanical characteristics. These impurities can enter steel as a result of the processes of smelting, forming or processing raw materials.

Sulfur and phosphorus are harmful impurities in steels and alloys

Sulfur and phosphorus are considered the main harmful impurities. They significantly degrade the properties of materials and make them unsuitable for use in some industries.

Sulfur reduces the plasticity and viscosity of the material and increases its tendency to crack (red brittleness) during hot processing (rolling, forging, stamping). Its increased content is allowed only in steels used for the manufacture of irresponsible structures.

Phosphorus also reduces the plasticity of alloys, since the type of its crystal lattice, the structure and size of atoms differ significantly from gland, nickel and other metals.

The negative effects of sulfur and phosphorus include the following:

• increased brittleness — sulfur and phosphorus contribute to the formation of a brittle phase in steel or alloy, which leads to a decrease in the strength and impact strength of the material;
• reduced corrosion resistance — these chemical elements contribute to the formation of compounds that accelerate corrosion processes, which leads to rapid destruction of the material;
• deterioration of plasticity — harmful impurities cause the formation of heterogeneities in the alloy structure, which reduces the plasticity of the material and reduces its ability to deform without cracking;
• decrease in thermal stability — phosphorus and sulfur can cause the formation of new crystalline phases, which leads to a decrease in the alloy's ability to maintain its mechanical properties when the operating temperature rises;
• poor weldability — an increased content of harmful impurities contributes to the formation of new undesirable compounds in the welding zone, which leads to the formation of defects and cracks in this area.

Gaseous harmful contaminants

Even small amounts of oxygen, hydrogen, or nitrogen can have a drastic negative effect on material properties. The increased nitrogen or oxygen content helps to reduce the viscosity and plasticity of steel, and also leads to the formation of non-metallic foreign inclusions that degrade the mechanical properties of the alloy. The presence of hydrogen makes steel brittle and can lead to the formation of internal cracks called flocins.

Methods to combat harmful contaminants

The main way to reduce the negative impact of harmful impurities is to add special ones alloying elements, capable of binding sulfur, phosphorus and other substances, thereby reducing their content in the alloy and improving the mechanical characteristics of the material. Manganese and silicon are among the useful additives, which are able to effectively deoxidize steel and make it more durable.

Another method of combating harmful impurities is strict quality control of the raw materials used. This makes it possible to avoid phosphorus, sulfur and other elements entering the alloys and to maintain the physical and mechanical properties of materials at the required level.

Harmful impurities in precision alloys

Precision alloys used in high-precision products require special attention to their chemical composition. Limiting the sulfur and phosphorus content in such alloys is crucial to ensure high accuracy and product reliability.

Thanks to their own spectral laboratory, PZPS engineers can clearly supervise the amount of harmful impurities and other chemical elements in manufactured products. This makes it possible to obtain steels and alloys with an accurate chemical composition and optimal physical and mechanical characteristics, which ensures the reliability, strength and durability of finished products.