Bright (BA grade) Stainless Steel Tube Annealing Principle And Requirements

  • By:Iris Liang
  • Date:2021/10/16

The bright annealed stainless steel tube can be widely used in heat exchangers, boilers, condensers, coolers, and heaters.

1. Definition of bright annealing

Bright annealing (BA) refers to the stainless steel material in a closed furnace, heated in a reducing atmosphere of inert gas, ordinary hydrogen, through induction coils, rapid induction heating, and then quickly cooled to about 100 degrees Celsius through a water-cooled tunnel, the outer surface of the stainless steel There is a protective layer. The protective layer can resist corrosion and erosion.

Generally speaking, the surface of the steel pipe is smoother and brighter. Usually, this process is realized by single-tube online bright annealing equipment. The traditional belt muffle furnace not only needs to be preheated, which leads to huge energy consumption; it also has poor airtightness, which causes the pipe to become black after annealing and needs to be pickled.

Hangao Tech (SEKO Machinery)'s intelligent energy-saving online bright induction annealing equipment perfectly solves the shortcomings of the traditional muffle furnace. Moreover, due to the reasonable design, there is no need to reuse hydrogen, and the flow rate is small, only a few liters per minute. And there is a special exhaust gas collection and burner to prevent hydrogen from spreading to the surrounding environment and dangerous accidents.

In the process of bright annealing, some factors are very important to the quality of the steel pipe. If the bright annealing process is improper, it will cause cracks and possibly corrosion. The flexible tube is usually in a bright annealed state.

2. Before bright annealing

The surface of the pipe must be clean, and there must be no other foreign matter or dirt. Anything left on the surface of the pipe will damage the surface of the pipe during processing.

3. Add inert gas

The annealing atmosphere should be oxygen-free, isolate the material, and form a vacuum condition. Insert gas, ordinary dry hydrogen or argon, to get a bright effect.

4. Annealing temperature

The annealing temperature should be determined according to different stainless steel grades. Generally, the annealing temperature of austenitic steel is at least 1040 degrees, and the immersion time is not important. A higher temperature is necessary to have a brighter appearance. The heating should be as fast as possible, slow heating will cause oxidation.

Some ferritic stainless steels require a lower annealing temperature, such as TP439, which cannot be effectively bright annealed, and water quenching will cause the formation of oxide scales.

After bright annealing, enter the final step of sizing and straightening. The surface of the stainless steel tube presents a bright appearance, and the bright annealing tube does not need to be pickled.

5. Purpose and advantages of bright annealing

(1) Eliminate work hardening and obtain satisfactory metallographic structure;

(2) Obtain a bright, non-oxidized, and corrosion-resistant surface;

(3) The bright treatment keeps the rolling surface smooth, and the bright surface can be obtained without post-treatment.




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