Everyone deals with steel almost every day, but do you know the classification of steel?
Where did the steel come from?
The main raw material of iron making is iron ore, the main component of iron ore is Fe2O3, without carbon; the second raw material of iron making is coke, part of the coke remains in the molten iron during the ironmaking process, resulting in carbon in the molten iron.
The production of iron and steel is made from iron ore to make pig iron, and pig iron is used as raw material to make steel; the process of steelmaking is mainly the process of carbon removal, and carbon cannot be removed completely. Steel needs a certain amount of carbon to achieve the best performance.
To improve the properties of steel, some alloying elements need to be added based on smelting carbon steel.
Pig iron (cast iron) – C is 2.0 to 4.5%
Steel (carbon steel) – containing C is 0.05 to 2.0%
Wrought iron (pure iron) – containing 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 small amounts of other elements.
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 an iron-carbon alloy. It is the most important and most important metal material in engineering technology.
According to carbon content, it can be divided into:
According to the carbon content, carbon steel is divided into low-carbon steel, medium-carbon steel, and high-carbon steel. With the increase in carbon content, the hardness of carbon steel increases, and 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:
To improve the performance of steel, based on smelting carbon steel, the steel made by adding some alloying elements is alloy steel, such as chromium steel, manganese steel, chromium-manganese steel, chromium-nickel steel, etc. 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. Alloying elements often added to steel are Si, W, Mn, Cr, Ni, Mo, V, Ti, etc.
According to the total content of its alloying elements, it can be divided into:
1) Low alloy steel – the total content of alloying elements is less than or equal to 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 steel is classified according to to 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, knives, etc.
3) Special performance steel: such as stainless steel, heat-resistant steel, etc., with special physical or chemical properties.
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