Improper heat treatment of seamless steel pipes can easily lead to a series of production problems, resulting in a significant reduction in product quality and becoming waste. Avoiding mistakes that are easy to occur during heat treatment is to save costs. What problems should we pay attention to during heat treatment? Let's take a look at the common problems in heat treatment of seamless steel pipes:

① Unqualified steel pipe structure and performance: three elements caused by improper heat treatment (T, t, cooling method).
Weihua structure: The coarse grain A formed by steel under high-temperature heating conditions forms a lamellar F and is distributed on P when cooling. It is an overheated structure, which hurts the comprehensive performance of the steel pipe, especially by reducing the room temperature strength of the steel and increasing its brittleness. The W structure with a lighter degree can be eliminated by normalizing at an appropriate temperature, while the W structure with a heavier degree can be eliminated by secondary normalizing. The secondary normalizing temperature is higher and the secondary normalizing temperature is lower to refine the grains. The F-C equilibrium diagram is an important basis for formulating the heating temperature of the heat treatment of steel pipes. It is also the basis for studying the composition, metallographic structure, and performance of the F-C fusion crystal in the equilibrium state. The supercooling A and other temperature transformation diagrams and the supercooling A continuous cooling transformation diagrams are important bases for formulating the cooling temperature of heat treatment.

② Unqualified steel pipe dimensions: Outer diameter, ovality, and curvature are out of tolerance.
The change in the outer diameter of the steel pipe often occurs in the quenching process, and the outer diameter of the steel pipe increases due to volume changes (caused by organizational changes). The sizing process is often added after the tempering process. Changes in the ovality of the steel pipe: The end of the steel pipe is mainly a large-diameter thin-walled steel pipe.

Steel pipe bending: caused by uneven heating and cooling of the steel pipe, which can be solved by straightening. For steel pipes with special requirements, a warm straightening process (about 550°C) should be used.

③ Surface cracks on the steel pipe: caused by too fast heating or cooling speed and excessive thermal stress. To reduce the heat treatment cracks of steel pipes, on the one hand, the heating and cooling systems of steel pipes should be formulated according to the steel type, and the appropriate quenching medium should be selected; on the other hand, the quenched steel pipes should be tempered or annealed as soon as possible to eliminate their stress.

④ Scratches or hard scratches on the surface of steel pipes: caused by relative sliding between steel pipes and workpieces, tools, and rollers.

⑤ Oxidation, decarbonization, overheating, or overburning of steel pipes. Caused by T↑ and t↑.

⑥ Oxidation of the surface of steel pipes treated with protective gas: The heating furnace is not well sealed, and air enters the furnace. The furnace gas composition is unstable. The quality control of each link of the heating of the tube billet (steel pipe) must be strengthened.