Carbon steel
Carbon structural steel has many impurities and non-metallic inclusions, but it is easy to smelt, good in manufacturability, cheap in price, and large in output. (Steel with more harmful impurities such as sulfur and phosphorus) is mainly used for manufacturing engineering structural parts and stress Steel for small machine parts. Therefore, it is widely used. Carbon structural steel is usually rolled into steel plates and various profiles (round steel, square steel, flat steel, angle steel, channel steel, I-beam, steel bars, etc.) for building structures such as factories, bridges, and ships [1] .
According to the quality of steel, it can be divided into ordinary carbon steel and high-quality carbon steel. ⑴ Ordinary carbon structural steel, also known as ordinary carbon steel, has wide restrictions on carbon content, performance range, and content of phosphorus, sulfur and other residual elements. In China and some countries, it is divided into three categories according to the guarantee conditions of delivery: Class A steel (Class A steel) is the steel with guaranteed mechanical properties. Class B steel (Class B steel) is steel with a guaranteed chemical composition. Special steel (C-type steel) is a steel that guarantees both mechanical properties and chemical composition, and is often used to manufacture more important structural parts. China currently produces and uses the most A3 steel (Class A No. 3 steel) with a carbon content of about 0.20%, which is mainly used for engineering structures. Some carbon structural steels also add trace amounts of aluminum or niobium (or other carbide-forming elements) to form nitrides or carbide particles to limit grain growth, strengthen the steel, and save steel. In China and some countries, in order to meet the special requirements of professional steel, the chemical composition and properties of ordinary carbon structural steel have been adjusted, thus developing a series of professional steel of ordinary carbon structural steel (such as bridges, buildings, Steel bars, steel for pressure vessels, etc.). ⑵Compared with ordinary carbon structural steel, high-quality carbon structural steel has lower content of sulfur, phosphorus and other non-metallic inclusions. According to the different carbon content and application, this kind of steel can be roughly divided into three categories: ① less than 0.25% C is low carbon steel, especially 08F and 08Al with carbon content less than 0.10%, because of its good deep It is widely used for deep drawing parts such as automobiles, cans, etc. because of its punchability and weldability. 20G is the main material for making ordinary boilers. In addition, low carbon steel is also widely used as carburizing steel for machinery manufacturing. ② 0.25-0.60% C is medium carbon steel, which is mostly used in the quenched and tempered state to make parts in the machinery manufacturing industry. ③ More than 0.6% C is high carbon steel, which is mostly used in the manufacture of springs, gears, rolls, etc. According to the different manganese content, it can be divided into two steel groups with ordinary manganese content (0.25-0.8%) and higher manganese content (0.7-1.0% and 0.9-1.2%). Manganese can improve the hardenability of steel, strengthen ferrite, and improve the yield strength, tensile strength and wear resistance of steel. Usually, the mark "Mn" is added after the grade of steel with high manganese content, such as 15Mn and 20Mn, to distinguish it from carbon steel with normal manganese content.
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