Common Chemical Elements of Steel and Their Roles in The Formation of Steel

Steel has nowadays become one of the most used materials in the world due to its low price and reliable performance. As the material basis of modern society, it is an indispensable component in the construction industry, manufacturing industry and people's daily life.  

Steel is a general term for iron-carbon alloys with a carbon content between 0.02% and 2.11%. The chemical composition of steel can vary greatly, containing common chemical elements including manganese, phosphorus, silicon, sulfur and other elements. Steel with a carbon content of less than 1.7% is called carbon steel. In actual production, steel often contains different combinations of chemical elements according to different uses.

Carbon(C): 

As the carbon content in steel increases, the yield point and tensile strength increase, but the plasticity and impact resistance decrease. When the carbon content exceeds 0.23%, the welding performance of the steel deteriorates. Therefore, low-alloy structural steel used for welding contains carbon. The amount generally does not exceed 0.20%. High carbon content will also reduce the atmospheric corrosion resistance of steel, and high-carbon steel in open-air stockyards will easily rust. In addition, carbon can increase the cold brittleness and aging sensitivity of steel. 

Silicon (Si):

Silicon is added as a reducing agent and deoxidizer during the steelmaking process, so killed steel contains 0.15-0.30% silicon. If the silicon content in steel exceeds 0.50-0.60%, silicon is considered an alloying element. Silicon can significantly increase the elastic limit, yield point and tensile strength of steel, so it is widely used in spring steel. Adding 1.0-1.2% silicon to quenched and tempered structural steel can increase the strength by 15-20%. Silicon is combined with molybdenum, tungsten, chromium to improve corrosion resistance and oxidation resistance, and can be used to make heat-resistant steel. Low carbon steel containing 1-4% silicon has extremely high magnetic permeability and is used in the electrical industry to make silicon steel sheets. Increased silicon content will reduce the welding performance of steel.

Manganese(Mn):

In the steelmaking process, manganese is a good deoxidizer and desulfurizer. Generally, steel contains 0.30-0.50% manganese. When more than 0.70% is added to carbon steel, it is called "manganese steel". Steel with a higher amount of manganese than ordinary steel not only has sufficient toughness, but also has higher strength and hardness since manganese improves the hardenability and hot working performance of the steel. Despite that, excessive manganese content will weaken the corrosion resistance of steel and reduce welding performance.

Phosphorus(P):

Phosphorus is a harmful element, but phosphorus can increase the fluidity of molten iron. This is because sulfur lowers the melting point of pig iron, so some products often contain higher phosphorus. However, the presence of phosphorus makes iron harder and more brittle. Excellent pig iron should contain less phosphorus. The phosphorus content can sometimes reach 1.2% in order to increase fluidity.

Sulfur (S):

Sulfur is also a harmful element under normal circumstances. It causes the steel to become hot brittle, reduces its ductility and toughness, and causes cracks during forging and rolling. Sulfur is also detrimental to welding performance, reducing corrosion resistance. Therefore, the sulfur content is usually required to be less than 0.055%. Adding 0.08-0.20% sulfur to steel can improve the machinability and is usually called free-cutting steel.

Chromium (Cr):

In structural and tool steels, chromium can significantly increase strength, hardness and wear resistance, but at the same time reduce plasticity and toughness. Chromium can also improve the oxidation resistance and corrosion resistance of steel, so it is an important alloy element of stainless steel and heat-resistant steel. 

Nickel (Ni):

Nickel can increase the strength of steel while maintaining good plasticity and toughness. Nickel has high corrosion resistance to acids and alkalis, and has anti-rust and heat resistance at high temperatures. However, since nickel is a scarce resource, other alloying elements should be used instead of nickel-chromium steel.

Molybdenum (Mo):

Molybdenum can refine the grains of steel, improve hardenability and thermal strength properties, and maintain sufficient strength and creep resistance at high temperatures (long-term stress at high temperatures will cause deformation, which is called creep). Adding molybdenum to structural steel can improve mechanical properties. It can also inhibit the brittleness of alloy steel caused by fire.

Titanium (Ti):

Titanium is a strong deoxidizer in steel. Aside from reducing aging sensitivity and cold brittleness, it can make the internal structure of steel dense and refine the grain force, thus improving welding performance. Adding appropriate titanium to chromium 18 nickel 9 austenitic stainless steel can avoid intergranular corrosion.

Vanadium(V):

Vanadium is an excellent deoxidizer for steel. Adding 0.5% vanadium to steel can refine the structure grains and improve strength and toughness. The carbide formed by vanadium and carbon can improve hydrogen corrosion resistance under high temperature and pressure. 

Tungsten (W):

Tungsten has a high melting point and a large specific gravity. It is an alloy element of your life. Tungsten and carbon form tungsten carbide, which has high hardness and wear resistance. Adding tungsten to tool steel can significantly improve the red hardness and thermal strength.

Niobium (Nb):

Niobium can refine the grains and reduce the overheat sensitivity and temper brittleness of steel, as well as improve the strength, but the plasticity and toughness are reduced. Adding niobium to ordinary low alloy steel can improve its resistance to atmospheric corrosion and hydrogen, nitrogen, and ammonia corrosion at high temperatures. Niobium improves welding properties. Adding niobium to austenitic stainless steel can prevent intergranular corrosion.

Copper (Cu):

Copper can improve strength and toughness, especially atmospheric corrosion resistance. The disadvantage is that it is prone to thermal brittleness during hot processing, and the plasticity is significantly reduced when the copper content exceeds 0.5%. When the copper content is less than 0.5%, it has no effect on weldability.

Aluminum (Al):

Aluminum is a commonly used deoxidizer in steel. Adding a small amount of aluminum to steel can refine the grains and improve impact toughness. Aluminum also has anti-oxidation and anti-corrosion properties. The combination of aluminum, chromium and silicon can significantly improve the high-temperature peeling performance and high-temperature corrosion resistance of steel. The disadvantage of aluminum is that it affects the hot processing performance, welding performance and cutting performance of steel.

Nitrogen (N):

Nitrogen can improve the strength, low-temperature toughness and weldability of steel, and increase aging sensitivity.

Rare earth (Xt):

Rare earth elements refer to the 15 lanthanide elements with atomic numbers 57-71 in the periodic table of elements. Adding rare earths to steel can change the composition, shape, distribution and properties of inclusions in the steel, thereby improving various properties of the steel, such as toughness, weldability, and cold working properties.

The above concludes the common chemical elements of steel and how they play their parts in the formation of steel. It is recommend to ask for Mill Test Certificates(MTC) from the factories before placing orders to know the detailed chemical composition of the steel. An MTC is a document that certifies that a product has undergone specific testing and meets relevant standards. These tests may involve various aspects such as physical properties, chemical properties, electrical properties, etc. The specific aspects to be tested will be determined based on the type and use of the product. Mill Test Certificate is an important guarantee of product quality and an important proof that the product meets relevant standards. MTC is of great significance to both producers and consumers.

At Baowu Special steel, we have always been able to provide the MTC asked by our clients who need to feel more reassured placing orders overseas, which is one of the reasons why the number of clients of Baowu Special steel has been growing rapidly!