Steel is a carbon iron alloy with carbon content between 0.0218% and 2.11%, which we usually refer to with iron as steel. In addition to iron and carbon, there are silicon, manganese, sulfur and other alloy elements such as phosphorus. Their functional features are now described together:

Carbon (Carbon): exists in all steel, is the most important hardening element, help to increase the strength of steel;

Chromium (Chromium): increase wear resistance, hardness, and most importantly, corrosion resistance;

Manganese (Manganese): help to generate texture structure, increase firmness, strength and wear resistance;

Molybdenum (Molybdenum): prevent steel from becoming brittle and maintain the strength of steel at high temperature;

Nickel (Nickle): maintain the strength, corrosion resistance and enhanced toughness of the steel;

Silicon (Silicon): used to maintain the strength of the steel during its production;

Tungsten (Tungsten): to enhance wear resistance;

Vanadium (Vanadium): enhanced wear resistance and ductility;

Phosphorus (Phosphorus): It is a harmful element and can improve the strength and reduces the plasticity and toughness of the steel;

Sulfur (Sulfur): It is a harmful element that makes the steel hot and brittle.

Depending on the chemical composition, the steel can be divided into carbon steel and alloy steel.

Carbon steel: 1) Low Carbon steel —— carbon content ≤ 0.25% 

                      2) Medium Carbon steel —— carbon content 0.25%~0.60% 

                      3) High carbon steel —— carbon content>0.60%;

Alloy steel: 1)Low alloy steel—Total alloy elements≤ 5% 

                  2) Medium alloy steel—Total alloy elements 5%~10% 

                  3) High alloy steel——Total alloy elements >10%。

Stainless steel is a special alloy steel.

Depending on the performance and use, the steel can be divided into structural steel, tool steel and special performance steel. Nowadays, steel has become one of the most used materials in the world with its low price and reliable performance. It is an indispensable component in the construction industry, manufacturing industry and people's daily life. It can be said that steel is the material foundation of modern society.