Steel is an iron based element were other elements have been added. The addition of these other element play a significant role in effecting there mechanical properties (hardness, tensile and yield strength, ductility and machinability). The most common element to be added is carbon. The content of carbon in steel ranges from 0.2% to 2.1% depending on the grade. Other elements used are manganese, chromium, vanadium and tungsten. Qualities like hardness, ductility, and tensile strength are controlled by varying the amount of alloying elements and the form of their presence in steel. For example increasing the amount of carbon in steel will make it harder but less ductile.
Carbon (C) – Primary hardening element in steel. Hardness and tensile strength increase as carbon content increases. Ductility and weldability decrease as carbon content increases.
Nickel (Ni)– Is a ferrite strengthener, strengthening and toughening the ferrite phase. Increases strength, impact strength and toughness, impart corrosion resistance in combination with other elements.
Manganese (Mn) – Is beneficial to surface quality of steel. Add to steels tensile strength, and has a significant effect on hardenability in steel. Like carbon it decreases ductility and weldability. Eliminates formation of harmful iron sulfides, increasing strength at high temperatures.
Chromium (Cr) – Added to steel to increase corrosion resistance and oxidation resistance, to increase hardenability and strength, and to increase corrosion resistance at high concentrations. Chromium is generally used with a toughening element like nickel to produce superior mechanical properties.
Tungsten (W) – Increases hardenability particularly at high temperatures due to stable carbides. Refines grain size and interferes with the formation of cementite, allowing martensite to preferentially form at slower quench rates, resulting in high speed steel.
Vanadium (V) – Increases yield strength and the tensile strength of steel. Added in small amounts to significantly increase the strength of steels. Increases creep resistance and impact resistance due to formation of hard vanadium carbides, limits grain size.
Molybdenum (Mo) – Increases hardenability and strength at high temperatures and under dynamic conditions. Enhances the creep strength of steel at elevated temperatures.
Silicon (Si) – One of the principal deoxidizers used in steelmaking. Improves strength, elasticity, acid resistance and promotes large grain sizes which cause increasing magnetic permeability. Less effective than manganese in increasing strength and hardness. Silicon is detrimental to surface quality.
Titanium ( Ti) – Improves strength and corrosion resistance. Used to restrain grain growth and improve toughness. Titanium causes sulfide inclusiuons to be globular rather than in elongated resulting in improved toughness and ductility.
Cobalt (Co) – increases strength at high temperatures and magnetic permeability
Zirconium (Zr) – increases strength and limits grain size. Zirconium also causes sulfide inclusiuons to be globular rather than in elongated resulting in improved toughness and ductility.
Boron (B) – highly effective hardenability agent, improves deformability and machinability. Boron-treated steels are produced to a range of 0.0005 to 0.003%.
Copper (Cu) – Can be detrimental to surface quality. Copper is beneficial to atmospheric corrosion resistance when present in amounts exceeding 0.20%.
Aluminum (Al) – Is used a as a deoxidizer. Aluminum is added to reheated steels to control grain size. It is the most effective alloy in controlling grain growth. Titanium, zirconium, and vanadium are also valuable grain growth inhibitors, but there carbides are difficult to dissolve into solution in austenite.
Chromium – Added to increase corrosion resistance and oxidation resistance, to increase hardenability, or to improve strength. Chromium is normally used with a toughening element such as nickel to produce superior mechanical properties. At least 11% is added to steel so that a hard oxide forms on the metal surface. (this is known as stainless steel)
Tungsten (W) – interferes with the formation of cementite, allowing martensite to preferentially form at slower quench rates, resulting in high speed steel.
Phosphorus (P) – increases strength and hardness and decreases ductility and notch impact toughness of steel. The effects on ductility and toughness are greater in quenched and tempered high-carbon steels. Phosphorus levels are kept to a minimum.
Sulfur (S) – decreases ductility and notch impact toughness especially in the transverse direction. Weldability decreases with increasing sulfur content. Sulfur levels are kept to a minimum.
Nitrogen (N) – makes steel more brittle.