Function of Alloy Element in Steel

Carbon（C）, the main alloying element of steel; Increases mechanical properties such as strength, hardness, and mechanical resistance. But besides this increase, malleability, ductility, and toughness decrease. In addition, the tensile strength can increase up to a point. The increase in the carbon content in the steel composition reduces the ductility of the material, that is, it causes it to show brittle properties. There is a risk of cracking in high carbon steels due to residual austenite that will occur after the heat treatment is applied. It negatively affects the forging and weldability properties of steel.

Chromium（Cr） is the most commonly used alloying element in steel. The most important feature of the steel is that it adds a stainless feature to the steel thanks to the bright oxide layer it forms on the surface of the steel. There is approximately 12% chromium in the composition of stainless steel. Chrome also increases the hardness thanks to the carbides it creates in the steel. While it increases the tensile strength and heat resistance like carbon, it also decreases the ductility.

Nickel（Ni）may be present in steel materials up to 5% by weight of the composition. Nickel improves the hardness and strength properties of the material without decreasing the ductility and toughness, unlike chromium and carbon. It is widely used in stainless steel.

Manganese（Mn） improves the mechanical properties of steels. It increases the strength and decreases ductility. It increases the malleability by reacting with the sulfur contained in the composition. When viewed from a thermal point of view, it increases the quenching depth. Manganese’s ability to increase hardness and strength also depends on the carbon composition of the material. It may also cause an increase in the weldability of the material.

Silicium（Si） is used as an oxygen and degassing agent during production. It also provides fluidity in casting. It improves the magnetic properties of steel and increases its heat resistance. While it increases the hardenability and wears resistance of the material, it adversely affects the surface quality.

Molybdenum（Mo） is used to prevent temper brittleness in steels containing molybdenum, low chromium, and nickel. It increases the heat resistance of steel. Molybdenum has the effect of increasing the effects of other alloying elements. For this reason, it is popular to be used not alone, but with other alloying elements. Molybdenum combines with carbon to form carbide. Since carbides increase the hardness, it is common to use tool steels.

Vanadium（V） could increases the strength, hardness, and wear resistance of steels. Small amounts of added vanadium can prevent grain coarsening. Tempering and softening processes after heat treatment do not give any results. For this reason, it is widely used in tool steels.

Tungsten（W）increases the wear resistance, hardness, and toughness of steels. It provides hot working and cutting efficiency to the material at high temperatures. For this reason, it is popular in tool steels and high-speed steels. It is preferred to use in the structure of heat-resistant steels.

Cobalt（Co） slows the grain coarsening at high temperatures. Increases the heat resistance of the material and strength at high temperatures. For this reason, it is preferred in tool steels.

Aluminum（Al） is used as a deoxidizer. It has a grain refinement feature, therefore it prevents the growth of austenite grains. Increases aging resistance. For this reason, deep-drawn sheets contain aluminum in their structure.

Copper(Cu) imparts corrosion resistance and hardness properties to steel. But at the same time, it decreases ductility very much. For this reason, it is kept at a maximum of 0.5% in the composition.

Nitrogen(Ni) increases its strength and hardness properties. It increases the hardness by forming nitride in the structure of the steel. It facilitates the machining process. It increases fragility.

Sulfur(S) is an undesirable alloying element other than free-cutting steel. Because it makes the steel brittle. For this reason, the effect is minimized by reacting with manganese. It is desired to be in composition as it facilitates machining in free-cutting steels.

Phosphorus（P） like sulfur, turns steel into brittle. For this reason, phosphorus is also undesirable. It increases the hardenability of the steel. But it causes a huge drop in ductility. This decrease is observed more in high carbon steels.