Normalizing, also known as normalizing, is the metal heat treatment process of heating the workpiece to Ac3 or Accm above 30~50℃, after a period of heat preservation, taking it out of the furnace and cooling it in the air with water, spray or blow air. The aim is to refine grain and homogenize carbide distribution.
The main application of normalizing are: (1) for low carbon steel, after normalizing hardness is slightly higher than annealing, toughness is also better, can be used as a pretreatment of cutting. ② For medium carbon steel, can replace the quenching and tempering treatment as the final heat treatment, can also be used as the preparation treatment before surface quenching by induction heating method. ③ Used in tool steel, bearing steel, carburized steel, etc., can reduce or inhibit the formation of network carbide, so as to obtain good microstructure required by spheroidizing annealing. ④ Used for steel casting, can refine the as-cast structure, improve the cutting performance. ⑤ For large forgings, can be used as the final heat treatment, so as to avoid large cracking tendency during quenching. ⑥ For nodular cast iron, improve the hardness, strength, wear resistance, such as used in the manufacture of cars, tractors, diesel engines crankshaft, connecting rod and other important parts. A normalization before spheroidizing annealing of eutectoid steel can eliminate the network of two cementite, in order to ensure that all spheroidizing cementite annealing.
After normalizing, the structure of hypoeutectoid steel is F+S, eutectoid steel is S, eutectoid steel is S+ secondary cementite, and is discontinuous.
The types of steel heat treatment are divided into integral heat treatment and surface heat treatment. The commonly used integral heat treatment is annealing, normalizing, quenching and tempering; Surface heat treatment can be divided into surface hardening and chemical heat treatment.
Normalizing is the heat treatment process of heating steel parts to 30-50℃ above the critical temperature, and cooling in static air after proper time of heat preservation. The main purpose of normalizing is to refine the microstructure, improve the properties of steel, and obtain a near equilibrium microstructure.
Compared with annealing process, the main difference is that the cooling rate of normalizing is slightly faster, so the production cycle of normalizing is short. Therefore, when annealing and normalizing can also meet the performance requirements of parts, normalizing should be selected as far as possible. Most medium and low carbon steel billets are generally treated with positive heat. Alloy steel billets are usually annealed. If normalizing is used, due to the faster cooling speed, the hardness after normalizing is higher, which is not conducive to cutting.
Annealing is a process of heat treatment of metals, in which the metal is slowly heated to a certain temperature, held long enough, and then cooled at a suitable rate. The purpose is to reduce hardness and improve machinability; Eliminate residual stress, stabilize size, reduce deformation and crack tendency; Refine grain, adjust microstructure, eliminate microstructure defects.
It is to soften the material or workpiece after casting, forging, welding or cutting, improve plasticity and toughness, homogenize the chemical composition, remove residual stress, or obtain the desired physical properties. There are many annealing processes with different purposes, such as recrystallization annealing, isothermal annealing, homogenization annealing, spheroidization annealing, stress removal annealing, recrystallization annealing, as well as stabilization annealing, magnetic field annealing and so on.
1. Metal tools lose their original hardness when they are heated.
2, the metal material or workpiece heating to a certain temperature and lasting for a certain time, so that slowly cooling. Annealing can reduce the hardness and brittleness of metal and increase the plasticity. Also called braising.
Recrystallization annealing (complete annealing)
Applied to alloys where solid phase transition (recrystallization) occurs during equilibrium heating and cooling. The annealing temperature is a temperature above or within the phase transition temperature range of the alloy. Heating and cooling are slow. A phase change recrystallization occurs in the alloy during heating and cooling, so it is called recrystallization annealing, often referred to as annealing.
Heat the steel parts to a temperature slightly higher than Ac1, hold for a certain period of time with the furnace cooling to 550~600℃ out of the air cooling heat treatment process is called stress relief annealing. Stress reduction heating temperature is low, no organizational transformation in the annealing process, mainly suitable for blank and machined parts, the purpose is to eliminate residual stress in blank and parts, stable workpiece size and shape, reduce parts in the process of cutting and use of deformation and crack tendency.