不锈钢的感应焊接有什么特殊要求

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不锈钢的感应焊接有什么特殊要求
Are there any special requirements for induction welding stainless steels?


     Stainless steels present a number of problems. From a mechanical aspect, they have much in common
with high carbon alloy steels, and they require special roll designs to overcome their resistance to cold
forming and to compensate for spring back.

      Because stainless steels have greater hot yield strength, more pressure has to be applied by the weld
rolls to create the weld upset. This can be a serious problem with thin-walled tubing because the thin
material has very little column strength, and cannot transfer the necessary pressure without buckling.
Stainless steels contain between 5% and 20% Chromium, which oxidizes very readily at the temperatures
needed for welding. In fact it is this oxide layer that protects the surface of the metal from corrosion,
giving it its “stainless” properties. Oxide inclusions cause weld defects and they must either be forced out
of the weld, into the bead, or preferably prevented in the first place. The higher the chromium content,
the more difficult it is to weld. Oxidation can be prevented by enclosing the weld area in a low pressure
inert shielding gas such as nitrogen. Simply blowing a jet of nitrogen onto the heated part of the tube is
not very effective because additional oxygen from the surrounding air is usually mixed in with the inert
gas. Oxygen should be displaced from the inside of the tube as well, since air is carried along with the
strip.

      Some tubing manufacturers believe that using a lower welder frequency can improve weld quality, but
the same effect can be achieved by moving either the coil or the impeder or both upstream to provide a
longer heat soak.

wangzhewang2010

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