Stainless steel tube annealed not bright

Under normal circumstances, the stainless steel tube will be bright after bright annealing in the annealing furnace. If there is no bright situation, it is necessary to check where there is a problem in time, find out the cause and solve it in time, and make records. Here are the main reasons for the lack of brightness:

1. Whether the annealing temperature reaches the specified temperature. The heat treatment of stainless steel generally adopts solution heat treatment, which is commonly called "annealing", and the temperature range is 1040 ~ 1120 ℃ (Japanese standard). You can also observe through the observation hole of the annealing furnace. The stainless steel pipe in the annealing area should be incandescent, but there is no softening and sagging.

2. Annealing atmosphere. Generally, pure hydrogen is used as the annealing atmosphere, and the purity of the atmosphere is better than 99.99%. If the other part of the atmosphere is inert gas, the purity can be a little lower, but it must not contain too much oxygen and water vapor.

3. Tightness of furnace body. The bright annealing furnace shall be closed and isolated from the outside air; if hydrogen is used as the protective gas, only one exhaust port is open (used to ignite the discharged hydrogen). The inspection method can be applied to the joints of the annealing furnace with soapy water to see if there is gas leakage. The most easy place to gas leakage is the place where the annealing furnace enters the pipe and the place where the pipe exits. The sealing ring in this place is particularly easy to wear, so it should be inspected and replaced frequently.

4. Protection gas pressure. In order to prevent micro leakage, the protection gas in the furnace shall be kept at a certain positive pressure. If it is hydrogen protection gas, it is generally required to be more than 20kbar.

5. Water vapor in the furnace. On the one hand, check whether the furnace body material is dry. When the furnace is installed for the first time, the furnace body material must be dried; on the other hand, check whether the stainless steel profile radiator tube entering the furnace has excessive water stains, especially if there are holes on the tube, do not let water leak in, otherwise the furnace atmosphere will be completely broken.

We should pay attention to these basically. Normally, the stainless steel pipe that should be retreated about 20 meters after the furnace is opened will start to light up, which is the kind that lights up.

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