Cast iron is usually divided into steel-making pig iron, cast pig iron and alloy pig iron according to different uses.Steel is divided into carbon steel and alloy steel according to the composition of different elements.Alloy steel is on the basis of carbon steel, in order to improve or obtain some properties and deliberately add appropriate amount of one or more elements of steel, the elements in the addition of a lot of types, mainly chromium, manganese, vanadium, titanium, nickel, molybdenum, silicon.In addition, iron ore is also used as a catalyst for ammonia synthesis (pure magnetite), natural mineral pigments (hematite, specularite, limonite), feed additives (magnetite, hematite, limonite) and precious medicinal stone (magnet), but the amount is very small.Iron and steel products are widely used in various sectors of the national economy and people's life in all aspects, is the basic material necessary for social production and public life.Since the invention of the converter steelmaking method in the middle of the 19th century, steel has been an important structural material, occupies an extremely important position in the national economy, is an important pillar industry of social development, and is an important and widely used metal material in modern industry.Therefore, people often steel, steel output, varieties, quality as a measure of a country's industrial, agricultural and scientific and technological development level of important signs.