Where does steel come from?
The main raw material for ironmaking is iron ore, and the main ingredient of iron ore is Fe2O3, without carbon; The second raw material for ironmaking is coke, and part of the coking carbon remains in the molten iron during the ironmaking process, resulting in carbon in the molten iron.
The production of iron and steel is made of iron ore, and pig iron is used as raw material for steelmaking; The process of steelmaking is mainly the process of carbon removal, and the carbon cannot be removed, and the steel needs to have a certain amount of carbon to achieve the best performance.
In order to improve the performance of steel, on the basis of smelting carbon steel, some alloy elements need to be added.
Pig iron (cast iron) – 2.0 to 4.5% C
Steel (carbon steel) - containing C is 0.05 ~ 2.0%
Wrought iron (pure iron) - contains less than 0.05% C
Iron ore → pig iron → steel
Therefore, steel is an alloy of iron with C (carbon), Si (silicon), Mn (manganese), P (phosphorus), S (sulfur), and a small number of other elements.
Among them, in addition to Fe (iron), the content of C plays a major role in the mechanical properties of steel, so it is collectively referred to as iron-carbon alloy. It is the most important, and the most used metal material in engineering technology.
According to the carbon content, it can be divided into:
According to the different carbon content, carbon steel is divided into low carbon steel, medium carbon steel and high carbon steel, with the increase of carbon content, the hardness of carbon steel increases, the toughness decreases.
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%
According to the total content of alloying elements:
In order to improve the performance of steel, on the basis of smelting carbon steel, adding some alloy elements and refining steel is alloy steel, such as chrome steel, manganese steel, chromium manganese steel, chrome nickel steel and so on. Alloy steel, also known as special steel, has some special properties, such as high hardness, high wear resistance, high toughness, corrosion resistance and so on. Alloy elements often added to steel are Si, W, Mn, Cr, Ni, Mo, V, Ti and so on.
According to the total content of its alloy elements, it can be divided into:
1) Low alloy steel - the total content of alloying elements ≤5%.
2) Medium alloy steel - the total content of alloying elements is 5% to 10%.
3) High alloy steel - the total content of alloying elements > 10%.
Alloy steels are classified according to their use:
1) Alloy structural steel: used as engineering components (pipes and brackets, etc.); Various mechanical parts (shafts, gears, springs, impellers, etc.).
2) Alloy tool steel: used as measuring tools, molds, tools, etc.
3) Special performance steel: such as stainless steel, heat-resistant steel, etc., with special physical properties or chemical properties.