There are two kinds of deformation processing boundaries of heavy forgings in metallurgy, which are the recrystallization temperature of metal. Plastic deformation below recrystallization temperature is cold working; Plastic processing above recrystallization temperature is hot processing.
The plastic deformation of forging metal is cold working. When the deformation processing is higher than the recrystallization temperature, the dynamic recrystallization will also be carried out at the same time of deformation. During the cooling process after deformation, the towel will continue to recrystallize. This deformation is called hot working. For example, the recrystallization temperature of lead is - 33 ℃. Even at room temperature, the plastic deformation of lead is hot working. For example, the recrystallization temperature of tungsten is about 1188 ℃. Even at the high temperature of 1000 ℃, the deformation T of tungsten is still cold working. It can be seen that the difference between the two deformation processes is not whether the metal is heated during deformation, but what temperature it is heated to. This temperature limit is the recrystallization temperature value of a specific metal.
These two kinds of deformation processing have their own characteristics. Cold working can achieve higher precision and lower surface roughness, and has the effect of processing and hardening. However, the deformation resistance is large, and the one-time deformation is limited, while the hot working is the opposite. Therefore, hot working is mainly used for forging rough and large blanks of parts with complex shapes, hot rolling ingots into steel, etc. Cold working is mainly used for parts and blanks with small section size and low surface roughness value, such as cold head of standard parts, cold stamping, drawing of thin-walled cylindrical parts, etc. When the surface roughness value is low, it can be used in combination. For example, cold rolled steel plates are first hot rolled and then cold rolled.