Annealing, normalizing, quenching, and tempering of steel pipes

　　Annealing of steel pipe: Heating the steel pipe to a certain temperature and keeping it warm for some time, and then cooling it slowly is called annealing. The annealing of steel pipe is a heat treatment method in which the steel pipe is heated to the temperature at which phase transition or partial phase transition 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 grain, improve the mechanical properties of the steel pipe, and reduce the residual stress; at the same time, it can reduce the hardness, improve 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 over from the previous process but also to prepare for the subsequent process. Therefore, annealing belongs to the heat treatment of semi-finished products, also known as pre-heat treatment.

　　Normalizing of steel pipes: Normalizing is a heat treatment method in which steel pipes are heated above the critical temperature so that all steel pipes are transformed into uniform austenite, and then naturally cooled in air. It can eliminate the reticular cementite of the hyper eutectoid steel pipe. Normalizing the hypereutectoid steel pipe can refine the crystal lattice and improve the comprehensive mechanical properties. It is more economical to replace the annealing process with normalizing for parts with low requirements.

　　Quenching of steel pipe: Quenching is to heat the steel pipe above the critical temperature, keep it warm for some time, and then quickly put it into the quenching agent to make its temperature drop suddenly, and cool it rapidly at a speed greater than the critical cooling speed, to obtain martensite. Master’s method of heat treatment of unbalanced tissue. 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, salt solutions, etc.

　　Tempering of steel pipe: reheating the quenched steel pipe to a certain temperature, and then cooling it by a certain method is called tempering. Its purpose is to eliminate the internal stress generated by quenching, reduce hardness and brittleness, and obtain the expected mechanical properties. Tempering is divided into three categories: high-temperature tempering, medium-temperature tempering, and low-temperature tempering. Tempering is often used in conjunction with quenching and normalizing.