Stainless & Mild

[busastars]

Right probably been discussed a million times but thought I would ask and hopefully help a few others with this thread.

Tig, stainless & mild. Scratch start DC.

I can tig thick mild easy, ive been playing with 0.8mm steel joints/seam/edge and have just got the nack of that but it took alot of playing with techneque and setup etc.

Now ive done nothing with stainless ever, is there anything to know with welding it, im guessing it needs alot more amps, how about gas flow rate, is it less likely to blow holes, is it easier to get nice welds or just easier to weld ie: will it braze well with minimal filler rod.

 

[hotrodder]

It's not harder or easier than carbon steel, just behaves a bit differently

Stainless is a poor conductor of heat compared with carbon and has a higher co-efficient of expansion- lots of distortion possible if not careful. The poor conduction of heat means less amps are required, start at around 5-10% less than you would for carbon

It's more reactive than carbon when welding- the back of the weld really requires shielding from the atmosphere too, especially full pen welds. Search the forum for 'purging' and you should find several threads on the subject. Unlike mild steel, autogenous (no filler) welds work well with stainless- best reserved for low stress parts obviously

For brazing stainless alloys low temperature alloys containing silver are generally preferred

 

[Normsthename]

Stainless is no more difficult to weld as long as you have the correct Stainless filler Rods
I find that mild steel is sometimes more trouble because it sometimes draws oil out of the metal and can comtaminate the weld
I also use a higher gas flow when welding mild steel
I use a pedal so thin materials are much easier to weld

Andy

 

[busastars]

Just thought I would update this tread. My brother has stainless pipes on his Firestorm which had split, dident want to practice on his pipes as ive never welded stainless before and it is a piece that you can see.

BUT

He said sod it have a go, there about 1.2mm stainless, set the tig to about 20 amp, 1.2mm tungstern, 1mm filler. I dident want it to look like its been welded so with the filler I had it on hand just incase. Had a go and it was a piece of cake, apart from a little colour distortion its hardly noticable.

Now my findings are compaired to doing 0.8mm mild on the edge its nice and easy. From doing this I have plenty of confidence in building a custom stainless pipe for my RSV Mille. Think thats going to be my end of summer project.

So for practice start with 0.8mm mild and everything above that is easy.

 

[dopplershift]

I think you can use 'pickling paste' to remove the burnt colour from the welded area.

But: I have NO experience with any sort of SS welding.

 

[flange jockey]

lads this is sch 10 ,the hot look here, burned,,, is down to the machine being at its lowest setting, im sure that a larger filler wire ie 2.5 would have cooled the cap pool enough to offset this, i didn,t have any. f/j

 

[madkayaker]

good work as usual.

 

[weldequip]

I think you can use 'pickling paste' to remove the burnt colour from the welded area.

You can, but without going to the expense & all the associated hazards, these fellas are good...



No good for getting into nooks & crannies like pickling paste, but excellent for removing thermal bluing wherever you can get with your angle grinder. Don't scratch the workpiece like flap discs either
weldequip

 

[dopplershift]

Sorry... cant really tell from the photo: they're the 'strip and clean' disk things right?

They don't seem to last long for me, and they're bl**dy expensive! But I s'pose you don't have to apply much pressure to remove the burnt colour?

 

[hotrodder]

Stainless steel brush will remove the heat tint too. Trick is to brush the weld while it's still hot- little to no effort required for the usual golds, blues and purples. More heavily oxidised/burnt (grey) welds need a little more elbow grease but as long it's still hot it doesn't take long

Scotchbrite works well unless the weld is burnt- available as 'flap discs' and sanding pads (google SCM abrasives) too

Clean 'n strip abrasives... decent ones are out there but a lot of rubbish too

Pickling paste... not the kindest blend of acids, sometimes it can't be beaten (removes contaminants exposing a fresh, chromium rich layer for maximum corrosion resistance) but unless the entire piece is treated you tend to get 'tide marks'

 

[weldequip]

Trick is to brush the weld while it's still hot

That could just add loads of contaminents resulting in a poor quality weld
weldequip

 

[hotrodder]

Hot, as in not yet cooled to ambient. Not molten!! The heat tint is just a thickened oxide layer, a clean stainless brush just removes this layer (as would other abrasives)!

 

[StainlessBloke]

Whether or not you use pickling paste depends on what you are trying to achieve; the paste will remove the HAZ (heat affected zone) from around the weld - this process enables the chromium layer to replenish itself in atmosphere and ensures the welded area offers the same level of corrosion protection as the rest of the part.

Brushing/grinding at the welded area will remove the discolouration but will do nothing to improve the anti-corrosion properties of the surface.

Not every weld needs the attention of pickling for everyday use, but in areas where corrosion could be a problem (i.e. marine/coastal environments etc) it would be recommended.

I'm aware advertising isn't allowed on the forum (I work for a surface treatment company) so if you want to contact me by private message, I'll happily send you a sample of paste to try out if you like. Hope this doesn't contravene any site rules - if admin are unhappy, please give me a shout.

Cheers.

 

[Weldingartisan]

So is pickling paste a better process than an electronic weld cleaner regarding corrosion? W/A

 

[StainlessBloke]

So is pickling paste a better process than an electronic weld cleaner regarding corrosion? W/A

Not really. As long as the HAZ is treated and the discolouration removed, either way should be equally effective.

 

[rodofgod]

Hi All!

Just to add to StainlessBloke's excellent post about pickling paste, these paste's passivities the weld back to the full corrosion resistance of the original stainless material, not just remove colour! Also worth a mention, is the filler wire or welding consumable, these should, now-a-days, have a 'L' somewhere in their classification to signify Low carbon i.e. TIG filler= ER316L, ER308L

Regards

 

[ksimmons]

We cut or tear a strip of scotch bright to put on the bristles of a stainless wire brush to get into corners if you can't get at it with air tools or don't have them available. Wire brushes work good but they have to be stainless.

 

[StainlessBloke]

We cut or tear a strip of scotch bright to put on the bristles of a stainless wire brush to get into corners if you can't get at it with air tools or don't have them available. Wire brushes work good but they have to be stainless.

As previously mentioned; this won't do anything for preventing corrosion in the future as you're just grinding further contaminants into the surface of the material. Fine for work where cosmetics are all that matter though!

 

[ksimmons]

I'm not sure I follow? The only contaminants that will get into the welds come from using something contaminated with carbon i.e. using a pad that's been used on mild steel or using a mild steel brush. I've worked on food grade equipment for a while now, the only time there's been an issue is when mild steel has been involved.

 

[StainlessBloke]

I'm not sure I follow? The only contaminants that will get into the welds come from using something contaminated with carbon i.e. using a pad that's been used on mild steel or using a mild steel brush. I've worked on food grade equipment for a while now, the only time there's been an issue is when mild steel has been involved.

When you manually grind an area, you're basically 'folding the peaks of the metal flat'. It's a bit hard to describe without a diagram I'm afraid, but imagine the surface in profile looks like a saw blade - basically, you are flattening the teeth down on themselves. This will entrap any dirt/contaminant in the area or airborne particulates and entrap them in the surface of the part. Electropolishing/pickling physically remove an amount of metal - imagine cutting the saw blade teeth off half way down - thus exposing, fresh, untouched substrate to air which enables the passive layer to reform.

I wasn't suggesting that the abrasive process would in itself introduce any contaminant - just that it isn't going to clean the piece and aid the reformation of the passive layer.

Sorry for any confusion caused.