Annealing, normalizing, quenching and tempering of steel pipe

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Annealing, normalizing, quenching and tempering of steel pipe

Annealing of steel pipes

Heating the steel pipe to a certain temperature and holding it for a while, and then enabling it to cool slowly, is called annealing. Annealing of steel pipe is a heat treatment method in which the steel pipe is maintained at a temperature at which phase change or partial phase change occurs, and then slowly cooled after heat preservation. The purpose of annealing is to eliminate structural defects, improve the structure, homogenize the composition and refine the grains, improve the mechanical properties of the steel pipe, and reduce residual stress; at the same time, it can reduce the hardness, increase the plasticity and toughness, and improve the cutting performance. Therefore, annealing is not only to eliminate and improve the structural defects and internal stress left by the preceding process but also to prepare for the subsequent process, so annealing is a semi-finished product heat treatment, also known as a pre-heat treatment.

 

Normalizing of steel pipe

Normalizing is a heat treatment method in which the steel pipe is maintained at above the critical temperature so that the steel pipe is completely transformed into uniform austenite, and then naturally cooled in the air. It can eliminate the network cementite of the hypereutectoid steel pipe and can refine the crystal lattice and improve the comprehensive mechanical properties for the normalizing of the hypo eutectoid steel pipe. It is more economical to use normalizing to replace the annealing process for the less demanding parts.

 

Quenching of steel pipes

Quenching is to heat the steel pipe to above the critical temperature, keep it for a while, and then quickly put it in the quenching agent to make its temperature suddenly drop, and then rapidly cool it at a rate greater than the critical cooling rate to obtain an imbalance dominated by martensite The heat treatment method of the organization. Quenching can increase the strength and hardness of the steel pipe but reduce its plasticity. Quenching agents commonly used in quenching are water, oil, alkaline water, and salt solutions.

 

Tempering of steel pipe

The quenched steel pipe is reheated to a certain temperature, and then cooled by a specified method is called tempering. Its purpose is to eliminate the internal stress generated by quenching, decrease the hardness and brittleness, to obtain the expected mechanical properties. There are three types of tempering: high-temperature tempering, medium temperature tempering, and low-temperature tempering. Tempering is mostly used in combination with quenching and normalizing.