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Why does stainless steel tube turn yellow or black after bright annealing?

Posted by： Hangao    Time：5/13/2024 2:56:24 PM

The yellow color on the surface of stainless steel pipe may be caused by unstable heating temperature. The surface temperature is too high and the internal temperature is insufficient, which may be due to improper annealing temperature control or problems in the temperature zone division design of the annealing furnace. The quality of annealing furnaces on the market is uneven, and the price difference is large, which makes it difficult for users to choose.



Looking for the root cause of the problem from the process and technical perspective, it is found that the user's temperature setting, the surface cleanliness of the stainless steel pipe, and the material may be related.

In order to solve these problems and ensure that the surface of the stainless steel pipe is bright after annealing, the following points need to be noted:

1. The airtightness of the vacuum furnace is crucial, which directly affects the surface finish of the stainless steel pipe. The stuffing box needs to be sealed before and after annealing, and most of the hydrogen leaks out here.

2. The structure of the annealing furnace, the distribution of the temperature zone, and the rationality of the thermal field directly affect the uniformity of the heating of the stainless steel pipe. The stainless steel pipe needs to reach an incandescent state, but it cannot be overly softened or drooped.

3. Ensure that the stainless steel tube itself does not have too much oil or water stains, which will destroy the atmosphere in the furnace and make the purity of the protective gas unable to meet the requirements.

4. Maintain a slightly positive pressure in the furnace atmosphere to prevent air from being sucked back into the furnace. If ammonia is used to decompose the mixed gas, it is usually necessary to maintain a pressure of more than 20kBar.

I hope users can pay attention to the above points. If the stainless steel tube after annealing still does not achieve the expected effect, please feel free to contact our company's technical department.

Guangdong Henkel Technology Co., Ltd.
Recommended reading: Intelligent bright solution equipment
Recommended reading: Stainless steel pipe making machine
Hotline: 189-4243-7326

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