Reference on resistance spot weld QC

[trainguy]

All,

I have called for resistance spot welding to join AISI 301 1/2 hard sheet. The parts have come in, and the welds seem to match parameters from spot welding charts (for diameter of the fused zone), such as the one from AWS. However, our client has noted that each weld has a discoloration associated with it, the normally grey/silver sheet seems dark grey with a brownish orange crown around the nugget.

Does this indicate poor welding or incorrect settings?

Pull tests indicate good fusion with one of the sheets having a hole in it after pulling.

What document would help verify adequacy of such welds, esp. with respect to corrosion protection?

Is there a treatment that should be done after the fact to improve the corrosion resistant properties?

I do have access to a welding metallurgist, but I like to ask here first...

Thanks in advance.

 

[metengr]

trainguy;
You have discoloration from surface oxidation caused by the heat of resistance welding in air. Regarding problems with the weld - none mechanical.

Corrosion resistance will be affected because the surface has been oxidized on top of the typical surface oxide layer from heat resulting in so called "temper colors".

Depending on service requirements you may need to do nothing or remove the surface discoloration using scotch brite pads or go to the extent of additional cleaning and passivating. I cannot provide any guidance because you don't state how this will be used in service.

 

[metengr]

Take a look here and see what may apply regarding application and cleaning methods based on service;

http://www.ssina.com/publications/index.htm

 

[trainguy]

metengr,

The component is a passenger railcar side sill (the structural member at the intersection of the side wall and the floor). It does not operate in a coastal/marine environment. It's usually covered by a non-structural skirt that keeps it mostly dry. There could be instances when it gets wet, but I suspect these would be rare.

Scotch brite only?
Scotch brite + add cleaning?
Can I passivate a component that is on a railcar?

For my curiosity, is this a normal consequence of spot welding, or did the welder do something wrong, based on my description?

Thank you!

tg

 

[TVP]

Normal occurrence for spot welding.

 

[metengr]

Leave it alone. No cleaning is necessary.

 

[trainguy]

Much appreciated everyone.

Now I just need to convince the client's rep.

tg

 

[Duwe6]

If it's not in the contract, he can pay for it [assuming that you want to take on the work] When you weld ANYTHING metal in open air [no shielding gas/flux] the metal has to oxidize on the surface.

OAKITE has several good pasivation/pickling solutions that will work.

 

[racookpe1978]

As carbon steel - even not in a salt water environment -> It will still rust over time wherever not painted. Perhaps faster in the area covered by the (non-air-tight/non-humidity-tight) trim and flashing.