The brightness of the precision tube after annealing determines the quality of the product. There are many factors that can affect the brightness, and five important factors are listed below:

1. Whether the annealing temperature reaches the specified temperature. Steel heat treatment generally adopts solution heat treatment, which is commonly referred to as “annealing” with a temperature range of 1040~1120℃ (Japanese standard). The stainless steel tube in the annealing zone should be in a white-hot state, but should not soften or sag, which can be observed through the observation hole of the annealing furnace.
2. Annealing atmosphere. Generally, pure hydrogen is used as the annealing atmosphere, and the purity of the atmosphere should be above 99.99%. If another part of the atmosphere is an inert gas, the purity can be lower, but it must not contain too much oxygen or water vapor.
3. Furnace sealing. The bright annealing furnace should be closed and isolated from the outside air. If hydrogen is used as the protective gas, only one exhaust port should be open (used to ignite the discharged hydrogen). The sealing of the furnace can be checked by applying soap water to the joints and gaps of the annealing furnace to see if there is any air leakage. The most likely places for air leakage are the places where the tubes enter and exit the annealing furnace, and the sealing rings at these places are particularly prone to wear and should be checked and replaced regularly.
4. Protective gas pressure. In order to prevent micro-leakage, a certain positive pressure should be maintained in the protective gas in the furnace. If hydrogen is used as the protective gas, the pressure requirement is generally above 20kBar.
5. Water vapor in the furnace. On the one hand, check whether the furnace material is dry. When the furnace is first loaded, the furnace material must be dried. On the other hand, check whether there is too much water residue on the steel tube entering the furnace, especially if there are holes on the tube, make sure not to let water leak in, otherwise the atmosphere in the furnace will be destroyed.