Meaning of annealing, normalizing, tempering and quenching of seamless steel pipe

- Mar 05, 2019-

     There are a lot of friends on the seamless steel pipe annealing, normalizing, tempering, quenching does not understand the meaning, if these concepts confusion in the use of materials production process not likely to cause back late consequences. Therefore, a proper understanding of the meaning of each of seamless steel pipe heat treatment is particularly important. Here we take a look seamless steel pipe heat treatment process:

①heat treatment:

A. heating: heating below Ac1 is mainly to stabilize the steel structure and eliminate internal stress.

The heating above Ac3 is mainly for austenitizing steel.

B. insulation: the purpose is uniform heating temperature of the steel tube, in order to get a reasonable heating organization.

C. cooling: the cooling process is the key process of heat treatment of steel tubes, which determines the microstructure and mechanical properties of steel tubes after cooling.

Commonly used cooling methods are: furnace cooling, air cooling, oil cooling, water cooling, etc.

② steel normalizing: refers to a steel pipe is heated above the austenitizing temperature, holding time, and then flat in the air 
uniformly slowly cooled, thereby obtaining a stable organization process 
the main purpose of: steel grain refinement , uniform internal organization, change the residual stress state, the steel pipe to improve overall performance. 
Main functions: reducing or eliminating tissue steel strip during deformation and a mixed crystal formed; 
eliminate excessive carbide eutectoid steel mesh in order to facilitate the spheroidizing annealing; 
prior to use as in C quenching steel and alloy steel pretreatment, the tissue to a uniform grain refinement, the quenching step reduces defects in the steel pipe produced; 
for low-C and low alloy steels used in place of annealing in order to improve the cutting performance of conventional construction steel pipe as undemanding the final heat treatment and the like.

③ annealing steel: the steel is heated to a temperature above or below the critical point (the Ac1 or the Ac3), and After an incubation period, and then allowed to cool slowly to obtain an approximate equilibrium organization process, and then divided into recrystallization annealing, fully annealed, isothermal degradation, spheroidizing annealing and stress relief. 
C is generally high, and low-alloy steel pipe, it is necessary to reduce the hardness and strength by annealing, to improve the plasticity, stress and eliminate uneven crystal structure refinement, in order to facilitate machining steel and steel for the final heat treatment laid tissue basis.

 tempering the steel pipe: heating the steel to a certain temperature below Ac1 for a period of time, then cooling the steel tube in a certain way to obtain a relatively stable state of the process.

The main purpose is to improve the plasticity and toughness of the steel pipe, so that the steel pipe can obtain good comprehensive mechanical properties, reduce or eliminate the residual internal stress of the steel tube during quenching and stabilize the size of the steel tube, so that the organization of the steel pipe will not change during the use.

After the steel tube is tempered, air cooling is usually adopted. To prevent the steel pipe from re producing internal stress, it should be cooled slowly. For steel tubes with high tempering brittleness, quick cooling should be adopted after tempering, such as oil cooling.

Steel tube tempering is generally divided into: low tempering 150~250 degrees.

Tempering at 350~500 C

High temperature tempering at 500~650 C

seamless steel pipe

⑤ steel Quenching: heating the steel pipe to the Ac3 above 30 ~ 50 ℃, after incubation period of rapid cooling the steel pipe obtained by the process of the tissue M and B. 
M generally have high hardness and brittleness, A is rapidly cooled product. 
Quenching the steel structure after addition to M, B A small amount of residues, which are unstable tissue. 
After quenching the steel pipe, the internal heat is generated stress and stress, may be eliminated and generally improved by tempering, quenching (Q + T) performance of steel can be greatly improved.

⑥ solution treatment: the essence of steel quenching process, but the higher the temperature of the solution treatment. A solution treatment is mainly used for stainless steel tube, which aims to reduce the hardness and strength of the steel, improve the ductility and toughness of steel, and to improve the corrosion resistance and overall performance of the finished steel pipe, reaches a predetermined standard or user requirements.

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