The annealed microstructure of low carbon steel
is ferrite and a small amount of pearlite, which has low strength and hardness, good plasticity and toughness. Therefore, it has good cold formability and can be cold formed by crimping, bending, stamping and other methods. This steel has good weldability. Low carbon steel with low carbon content has low hardness and poor machinability. Normalizing can improve its machinability.
Low carbon steel
has great aging tendency, including quenching aging tendency and deformation aging tendency. When the steel cools rapidly from high temperature, the carbon and nitrogen in ferrite are supersaturated. It can also slowly form the carbon and nitrogen of iron at room temperature. Therefore, the strength and hardness of steel are improved, while the plasticity and toughness are reduced. This phenomenon is called quenching aging. Even if low carbon steel is not quenched but air cooled, aging will occur. The carbon and nitrogen atoms in ferrite interact elastically with the dislocations, and the carbon and nitrogen atoms gather around the dislocation line. This combination of carbon and nitrogen atoms and dislocation lines is called old Coriolis air mass (Coriolis air mass). 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. There are obvious upper and lower yield points on the tensile curve of low carbon steel. From the upper yield point to the end of yield extension, there is a surface wrinkle band formed due to uneven deformation on the sample surface, which is called ludes band. Many stamping parts are often scrapped. There are two ways to prevent it. It is a high pre deformation method. The pre deformed steel will also produce ludes belt during stamping after being placed for a period of time. Therefore, the pre deformed steel should not be placed 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 deformation aging caused by the formation of Coriolis gas mass.