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Heat treatment Classification of steel pipe (Part two)
- May 29, 2018 -

According to different heating temperature of steel tube, combined with different cooling rate of steel tube, it is divided into normalizing, annealing, tempering, quenching and other processes. Normalizing: Refinement of austenite grain, uniform internal structure and change of residual stress State, improve the comprehensive performance of steel pipe. To reduce the formation of steel tube in the deformation process of banded structure and mixed crystal (but not to eliminate the segregation in the steel and the inclusions caused by the banded tissue); To eliminate the reticular carbide in the hypoeutectoid, which is propitious to spheroidization annealing, is used as pretreatment before quenching of medium carbon steel and alloy structure, so as to refine the grains to make the microstructure homogeneous, 

Reduce the pipe defects produced by quenching process, for low carbon steel and low alloy steel pipe to replace annealing, improve the cutting performance of steel pipe, also can be used as the final heat treatment of ordinary steel pipe. Annealing: It is divided into recrystallization annealing, complete annealing, isothermal annealing, spherical annealing and elimination of residual stress annealing. 

General high carbon, low alloy and alloy steel pipe, the need to reduce its hardness and strength by annealing, improve plasticity, eliminate internal stress and uneven organization, refinement of crystalline microstructure, in favor of the machining of steel pipe and the final heat treatment for steel pipe laying the foundation. Tempering, generally divided into low-temperature tempering (150-250°c), medium temperature tempering (350-500°c), and High-temperature tempering (500-650°c). To improve the plasticity and toughness of the steel pipe, so that the steel pipe to obtain good comprehensive mechanical properties, reduce or eliminate the steel pipe in the quenching of residual stress and stabilize the steel pipe size, so that the steel pipe in the use of the process does not change. 

Tempering generally use air cooling, in order to prevent the steel pipe to produce internal stress, should be slow cooling; for high-temperature tempered brittle steel pipe, after tempering should be used for rapid cooling, such as oil cold. Quenching: The metal material heats up to the austenite Ac3 line above 30-50°c, after the heat preservation time causes the steel tube to cool quickly and obtains the martensite or the Bainite the craft process. Heat stress and tissue stress can be produced after quenching of steel tube, which is usually eliminated and improved by tempering. 

The combination of quenching and tempering (quenched and tempered) can make the comprehensive performance of steel greatly improved. Other processes, such as solid solution treatment and protection of gas heat treatment.