Improper heat treatment of seamless steel pipes can easily cause a series of production problems, resulting in product quality being greatly compromised and turned into scrap. Avoiding common mistakes during heat treatment means saving costs. What problems should we focus on preventing during the heat treatment process? Let’s take a look at the common problems in the heat treatment of seamless steel pipes:
① Unqualified steel pipe structure and performance: three factors caused by improper heat treatment (T, t, cooling method).
Wei structure: The coarse grains A formed by steel under high-temperature heating conditions form a structure in which flakes F are distributed on P when cooled. It is a superheated structure and hurts the overall performance of the steel pipe. In particular, the normal temperature strength of steel is reduced and the brittleness is increased.
The lighter W structure can be eliminated by normalizing at an appropriate temperature, while the heavier W structure can be eliminated by secondary normalizing. The secondary normalizing temperature is higher, and the secondary normalizing temperature is lower. Chemical grains.
The F-C balance diagram is an important basis for formulating the heating temperature for steel pipe heat treatment. It is also the basis for studying the composition, metallographic structure, and properties of F-C crystals in equilibrium, the temperature transition diagram of supercooling A (TTT diagram) and the continuous cooling transformation of supercooling A. Chart (CCT chart) is an important basis for formulating cooling temperature for heat treatment.
② The dimensions of the steel pipe are unqualified: the outer diameter, ovality, and curvature are out of tolerance.
Changes in the outer diameter of the steel pipe often occur during the quenching process, and the outer diameter of the steel pipe increases due to volume changes (caused by structural changes). The sizing process is often added after the tempering process.
Changes in steel pipe ovality: The ends of steel pipes are mainly large-diameter thin-walled pipes.
Steel pipe bending: caused by uneven heating and cooling of steel pipes, can be solved by straightening. For steel pipes with special requirements, a warm straightening process (around 550°C) should be used.
③Cracks on the surface of steel pipes: caused by excessive heating or cooling speed and excessive thermal stress.
To reduce heat treatment cracks in steel pipes, on the one hand, the heating system and cooling system of the steel pipe should be formulated according to the steel type, and an appropriate quenching medium should be selected; on the other hand, the quenched steel pipe should be tempered or annealed as soon as possible to eliminate its stress.
④ Scratches or hard damage on the surface of the steel pipe: caused by relative sliding between the steel pipe and the workpiece, tools, and rollers.
⑤The steel pipe is oxidized, decarbonized, overheated, or overburned. Caused by T↑, t↑.
⑥ Surface oxidation of steel pipes heat treated with protective gas: The heating furnace is not properly sealed and air enters the furnace. The composition of the furnace gas is unstable. It is necessary to strengthen the quality control of all aspects of heating the tube blank (steel pipe).
Post time: Jan-15-2024