TIG welding stainless

[Goulton]

I'm only an enthusiastic amateur and over the last few weeks have been doing TIG fabrication in mild steel without problems.

I then moved to doing a small job in stainless steel using the same settings I had used for the mild steel and found that there was a some blackness in the weld and considerably more on the surrounding metal. The blackness was removed easily with a wire brush but I felt it should not be there in the first place.

I was welding 304 stainless with 316 filler as this was the only filler I had.

I may be asking quite the wrong questions but .....

Does stainless need more cleaning than other steels? I had done almost none on the M/S but had had a good go with a S/S wire brush on the stainless. Should I be using a chemical cleaner like Acetone or IPA?

Does stainless need a greater gas flow or a longer post flow?

 

[hotrodder]

Does stainless need more cleaning than other steels?

Should typically need less than hot rolled mild steel which is covered mill scale etc

Does stainless need a greater gas flow or a longer post flow?

The chromium that gives stainless it's properties is VERY reactive at welding temps but it's not a case of needing more gas flow, more a case of it being less tolerant of shielding issues and too much gas flow can make things worse. The primary role of post flow is to protect the tungsten as it cools from white hot. Search the forum for 'purge' for more detail that's specific to stainless

Stainless has relatively poor thermal conductivity i.e. need less amps than for mild steel while ally which has high thermal conductivity needs more amps than steel despite it's lower melting point

Check out the TIG tutorial (link at top of page) which covers things in more detail and for the most part is done using stainless. Then read this thread which follows someone getting to grips with arc length and explains how it effects things (also covered in the tutorial) http://www.mig-welding.co.uk/forum/showthread.php?t=23592&highlight=arc+length

 

[langy]

Difficult without a pic to see but my educated guess would be too much heat and slow travel.

 

[Psymon]

My welds are often black. I just clean them up after. TBH I have not seen a totally clean weld with whatever settings I use. Just thought it was normal and clean the metal after.

 

[langy]

If you get everything just so you should get this finish. But it will take practise

 

[Psymon]

Bet there is a VERY fine line to getting that correct?

 

[Goulton]

Thanks to all for the helpful comments, it looks as if I might be worrying unnecessarily. I would certainly have liked to have had a practice first to get current and speed as correct as possible but sadly I didn't have any spare material, so based things very much on what I had done previously on mild steel

Sorry no pictures as it was a bracket on a stainless silencer and I had to clean up and get it back on the bike as soon as possible as I needed transport.