Annealing is an integral part of making materials soft as possible, increase ductility and less brittle. The annealing process reduces the hardness and makes the material easier to machine and can be used on stainless steel, cobalt, chrome, high temperature alloys and titanium.
For bright annealing to be effective, tube surfaces must be clean and free of foreign matter. The annealing atmosphere must be relatively free of oxygen (if a bright result is desired). This is accomplished by removing nearly all gas (creating a vacuum) or by displacement of oxygen and nitrogen with dry hydrogen or argon. For common stainless steel alloys, the minimum atmosphere quality required is about -40℃ on a dew point scale (for hydrogen or argon atmosphere).
The matallurgy of bright annealing has been reasonably well defined for some time.
In order to achieve a bright result, the most stable oxide forming element in an alloy in any significant concentration must be reduced at peak temperature and atmosphere quality rather than oxidized. For the common austenitic stainless alloys such as 304L and 316L, the most stable oxide former present in significant concentrations is chromium. As such the oxidation potential of chromium at peak annealing temperatures and atmosphere quality will largely determine whether the stainless will be bright.
Bright annealing is commonly used in the aerospace and medical industries, as well as in military and automotive applications. Vacuum bright annealing produces extremely clean parts, eliminating many steps from the manufacturing process.
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