spot welds rusting

[BEANO2]

Hello

We are getting a lot of rust on one of the products we spot weld. The rust is only on/around the spot welds. Picture is attached.

From my understanding this happens because the heat of the weld in a oxidizing environment (ie open air spot weld/unsheilded) will:

1. burn off the millscale layer exposing bare steel to the environment.
2. change the microstructure of the weld metal/HAZ making it more susceptible to rust.

Can any one else explain this more thoroughly? and if possible suggest any solutions?

Thanks

 

[berkshire]

From your picture, it looks like the parent part has a film of oil or lacquer on it preventing or delaying rust.
The spot weld is burning this off. You would need to re oil or re-spray the part right after spot-welding to prevent this.
B.E.

You are judged not by what you know, but by what you can do.

 

[weldstan]

Is the part coated? IF not, the heat of welding does affect the microstructure and a galvanic mismatch can readily be obtained.