Low carbon steel performance characteristics
Low carbon steel is a carbon steel with a carbon content of less than 0.25%. Because of its low strength, low hardness and softness, it is also called soft steel. It includes most common carbon structural steels and some high-quality carbon structural steels. Most of them are used for engineering structural parts without heat treatment, and some are carburized and other heat treated for mechanical parts that require wear resistance.
The annealed structure of low carbon steel is ferrite and a small amount of pearlite, which has low strength and hardness, and good plasticity and toughness. Therefore, its cold formability is good, and cold forming can be performed by methods such as hemming, bending, and stamping. This steel also has good weldability. Low carbon steel with carbon content from 0.10% to 0.30% is easy to accept various processing such as forging, welding and cutting. It is often used to manufacture chains, rivets, bolts, shafts, etc.
The annealed structure of low carbon steel is ferrite and a small amount of pearlite, which has low strength and hardness, and good plasticity and toughness. Therefore, its cold formability is good, and cold forming can be performed by methods such as hemming, bending, and stamping. This steel has good weldability. Low carbon steel with low carbon content has low hardness and poor machinability. Normalizing treatment can improve its machinability.
Low carbon steel has a large aging tendency, both a quenching aging tendency and a deformation aging tendency. When the steel cools from high temperature quickly, the carbon and nitrogen in the ferrite are in a supersaturated state, and it can slowly form iron carbonitrides at room temperature, so the strength and hardness of the steel are increased, while the plasticity and toughness are reduced. This phenomenon is called quench aging. Low-carbon steel ages even if it is not quenched and air-cooled. Low-carbon steel undergoes a large amount of dislocation deformation, elastic interaction between carbon and nitrogen atoms in the ferrite and dislocations, and carbon and nitrogen atoms gather around the dislocation line. This combination of carbon, nitrogen atoms and dislocation lines is called the Kirschner air group (Korchell air group). It will increase the strength and hardness of steel and reduce the plasticity and toughness. This phenomenon is called deformation aging. Deformation aging is more harmful to the plasticity and toughness of low carbon steel than quenching aging, and there are obvious upper and lower yield points on the tensile curve of low carbon steel. From the emergence of the upper yield point to the end of the yield extension, a surface wrinkle band due to uneven deformation appears on the surface of the sample, which is called the Ruedesian band. Many stamping parts are often scrapped because of this. There are two ways to prevent this. A kind of high pre-deformation method, the pre-deformed steel will also produce a Ruedesian belt when stamped for a period of time, so the pre-deformed steel should not be left for too long before stamping. The other is to add aluminum or titanium to the steel to form a stable compound with nitrogen to prevent the formation of aging caused by Coriolis air mass.