Welding stainless steel

[Just for fun]

So playing around with some unknown Stainless steel. I have welded some thicker stainless steel before without any issues, ok well at least without the black blobs on the backside. I don't have any way of purging the back side. But what is causing those big dark lumps? I didn't keep track of the exact amps I was using. But low amps between 35 and 50 amps. 1/16" materal, 1/16 tungsten, #6 cup, 15 cfm argon and 1/16 filler rod.

Front side


Back side


35 Amps no filler rod


Back side, no filler.

Tim

 

[682bear]

The lumps on back are where the puddle melted through the thin material and formed a bubble under the material...

Caused by either too many amps, or moving too slowly, or both. Either way, there was more heat applied than the material could handle.

-Bear

 

[erikmannie]

I don’t have very much experience with welding stainless, but my guess is that the black is oxidation due to oxygen (from the air, obviously) present back there while it was hot.

Try welding with the weldment very flat (e.g. clamped down) against a welding table, or figure out a way to purge the back side.

I use a dual argon flowmeter for backpurging Ti:

SPARC Dual Output Argon Flow Meter & Regulator CGA580

Dual Argon Flow Meter & Regulator by SPARC available for purchase today. Perfect for MIG and TIG Welding. The pressure gauge goes from 0 to 4000 psi. The output flow is adjustable from 0-60CFH. The tank input fitting is a CGA-580 style, so it fits all argon, helium, nitrogen, and argon/CO2 mixed...

sparcwelders.com

 

[jwmelvin]

Sugaring is the term for the heavily oxidized metal on the i shielded back side. If you can’t purge with argon then you may try Solar Flux.

Why You Should Use SOLAR FLUX

The Problem When welding stainless steel (or one of the high nickel alloys (Inconel, Monel, etc.), the shielding gas or the flux in the electrode only protects the FRONT of the weld. You must use s…

solarflux.wordpress.com

 

[Just for fun]

Thanks guys,

682bear, I kind of figured it all had to do with heat and/or speed and the lack of shielding. I'm new to tig welding and have never seen it bubble up like that before.

Erikmannie, I have looked into the dual argon flow meters in the past, just never made it a priority. I guess it's time to look at it again.

Jwmelvin, Thanks for the pro tip on the solar flux.

 

[Cadillac]

Cooked it!

 

[jakes_66]

Yup, sugared through for sure. It's very common on thin materials, don't worry you didn't do anything wrong. It's a simple fact that you must deal with when welding thin stainless steel. In fact any material will do it to one degree or another. Any high temperature metal in contact with atmospheric oxygen will oxidize readily.

At work our welders work with these conditions every day. Every fabricator has a selection of jigs and fixtures to handle back-purging any variety of situations and positions as well as a handy roll of high temperature tape to seal them up and attach!

 

[Just for fun]

One more little test weld, I clamped my coupon to a piece of aluminum, 35 amps. Looks better, still not good but at least now I know what's going on.

 

[Ulma Doctor]

with stainless steel, the black lumps are Carbide Precipitation
with the aluminum, it is aluminum oxide precipitation

lower welding temperatures or advancing the weld pool quicker is a good place to start
if you stay in one spot too long, the parent metal melts all the way through

 

[Lo-Fi]

You may be welding with the amperage too low.

Welding "cool" makes you stay in one place longer waiting for a decent puddle and end up pumping pump far more heat in than you would if you'd had more amps and worked faster. Moving quickly is so, so important when welding thin stuff, but it's not easy! MIG with stainless wire is much easier to get a decent joint and not cook the other side (without back purging), for what it's worth.