FACTORS AFFECTING BRIGHT ANNEALING OF STAINLESS STEEL TUBES

Posted by LUCY ZHANG on May 5th, 2019

There are many influence factors of bright annealed stainless steel tubing, this paper lists five important factors for your reference.

1. Whether the annealing temperature reaches the specified temperature
The heat treatment of stainless steel is usually solid solution heat treatment, that is what people usually called annealing, the temperature range of 1040~1120 (Japanese standard).You can also look through the observation hole of the annealing furnace, the stainless steel tube in the annealing zone should be in incandescent state, but no softening droop appears.

2. Annealing atmosphere
Pure hydrogen is regarded as anneal atmosphere commonly, atmosphere purity had better be 99.99% above, if another part in atmosphere is inert gas, purity also can a bit lower, but it  absolutely cannot contain excessive oxygen water vapor.

3. Bright annealing furnace should be closed and isolated from the outside air; using hydrogen as a shielding gas, only one vent is vented (used to ignite the exhausted hydrogen). It can be checked by wiping in the annealing furnace with soap water in the joint gap to see whether the air run, one of the most likely places for gas to escape is where the annealing furnace enters the pipe and where the pipe comes out. The sealing ring in this place is particularly prone to wear and tear, so it should be checked and changed frequently.

4. Protect gas pressure
In order to prevent micro-leakage, the protective gas in the furnace should maintain a certain positive pressure, if it is hydrogen protective gas, the general requirements of more than 20kBar.

5. On the one hand, check whether the furnace material is dry, furnace material must be dried for the first furnace charging, Secondly, whether the stainless steel tube into the furnace remains too much water, especially if there are holes in the pipe, do not leak into it, or it will destroy the atmosphere of the stove.

It should be noted that basically these, normally, after the furnace, stainless steel tube should be back about 20 meters and start to shine, which is bright reflective.