Trying to weld stainless

[pnt103]

This newbie needs some advice.

I'm trying to use my SIP Migmate 130T (yes, I know) to weld two stainless steel parts together. One is a ring or hoop made from 0.9mm stainless (316, I think), and the other is a bowl made of 0.5mm stainless, grade unknown. I don't usually have a problem with thin mild steel, and I had no problem welding the ends of the hoop together, but I'm having a real problem tacking the hoop to the bowl. I'm using 0.8mm 308L wire with pure argon.

If I turn the power down, the arc is unstable and spits, and the weld material doesn't stick to the bowl. If I turn it up it spatters a lot without penetrating, or blows a hole in the bowl (or the edge of the hoop). The spatter is fierce enough that twice I've had a blob of weld metal jump away from the arc and weld itself to the side of the bowl a couple of inches away (and had to grind it off).

I don't know exactly what the bowl is made of. It's apparently been drawn rather than spun, the metal is magnetic, very ductile (I could form a flange on another piece of it) and doesn't harden when heated to red and then quenched. I guess it's some sort of ferritic rather than martensitic stainless.

Any suggestions? I've tried playing with the power and wire speed, obviously, and I've taken a file to the surface where I want to weld. Would putting a piece of copper behind the place I want to weld help?

Pete

 

[Robbus]

Can you get 0.6mm wire? That'd definitely help control the current/voltage at the bottom end of things. Even so I'd thought 0.5mm anything would be a nightmare to MIG.

Cheers,
Rob

 

[pnt103]

I don't think the problem is getting the power low enough, it's getting anything to stick to the bowl at all! It just seems to bounce off most of the time.

Pete

 

[malcolm]

Stainless is generally a pain - you'd normally expect increased spatter and welds that don't flow too well.

Though I wonder what the metal actually is - magnets don't normally stick to stainless do they? I'd be guessing some sort of mild steel with other stuff mixed in or some weird plating which could be causing the problem. Isn't chromium plated is it?

 

[Drains]

If it is stainless then it'll be martensitic or ferritic . Austenitic is the common non-magnetic type.

Have a look here. I don't know if it'll solve your problem, but might get you on the way. Not sure what the ductility of your bowl tells you...

With what you're trying to do i'd be more inclined to go the tig route, not least because of the thicknesses you're trying to join. It also gives the option of using relatively cheap dissimilar stainless wires.

If the material was thicker then a high nickel MMA rod might do the trick.

Otherwise.... rivets

 

[pnt103]

Stainless is generally a pain - you'd normally expect increased spatter and welds that don't flow too well.

So I've discovered!

Though I wonder what the metal actually is - magnets don't normally stick to stainless do they?

It depends on the type. This stuff is definitely stainless, and homegenous -- no plating.

 

[pnt103]

If it is stainless then it'll be martensitic or ferritic. Austenitic is the common non-magnetic type.

Have a look here. I don't know if it'll solve your problem, but might get you on the way. Not sure what the ductility of your bowl tells you...

I'd found some similar pages, but not that one. I think the ductility just bolsters the thought that it's one of the common ferritic types often used for kitchen utensils. Like, er, bowls, for example!

With what you're trying to do i'd be more inclined to go the tig route, not least because of the thicknesses you're trying to join.

I don't have access to any TIG, unfortunately. Rivets! Hah! One of my original thoughts was that if it's so ductile, I could cut the hole in the bottom a bit smaller, and form a flange instead of welding a hoop onto it. It turns out my sheet metal skills aren't as skilful as I'd like

I did make one of these by soft-soldering a hoop to a bowl. I'd prefer to avoid solder, though.

I'm wondering how much the problems might be reduced by simple things like making sure the earth is really good, putting a lump of copper (I assume it needs to be well-fitting and a good bit thicker than a flattened piece of plumbing) behind the weld point, making sure it's really clean, and being very careful with the wire feed control. Since the corrosion-resistance isn't a critical consideration for this item, I wonder if mild steel wire would be worth a try? At least I can easily get 0.6mm MS wire, whereas the only SS I can find is 0.8mm.

 

[rtbcomp]

My local scrap metal merchant defines magnetic stainless steel as "chrome steel" and only worth the same as mild steel scrap whereas "genuine" stainless is worth considerable more.

I know you can weld chrome steel as I've seen it done on washing machine drums, dishwashers and sinks. I've seen chrome and SS welded together too, I suspect using TIG though.

 

[petedut]

I am no expert but I taught myself how to weld mostly using Stainless and I have found that the sheilding gas makes a hell of a difference. The best I think is C02/Argon mix and to just take your time on the weld

 

[TechnicAl]

petedut is right, youve got the wrong gas. You need a gas for stainless MIG such as Ar+2.5CO2 or Argon + 1-2% O2. The weld wont wet into the sheet without the "active" ingredient.

 

[matt1978]

He could also use a Ar,He,Co2 mix. But if just Ar/Co2 it should be no more that 2-2.5% Co2.

If any more is used 5% for example, you end up putting carbon into the welded area through the extra Co2 in the gas, in time this can cause the weld to go rusty.

Its probably a 304 SS, a ferritic grade

 

[Rusty]

Welding stainless steel " kills " the chromium in the steel which will cause the weld to rust, silver solder is good tho.

 

[pnt103]

Thanks to petedut, TechnicAl, and Matt1978 for the information about the gas. I'm using little disposable bottles (I've got a pub CO2 cylinder but only for rough stuff) and I don't think I've ever seen one with Argon/O2 or Argon with less than 20% CO2. But it does seem like the weld isn't wetting the base metal, so maybe I need to investigate that further. What's likely to happen if I use 80/20 Ar/CO2?

On the bright side, I had another go today, and managed to get some good welds -- just tacks, but that's all I need -- by carefully adjusting the wire speed and taking emery cloth to the surface where I want to weld and also to where the earth clamp goes.

Pete

 

[rtbcomp]

Another point about stainless welding is what you use to clean the metal prior to welding. There are stainless wire brushes available so you don't contaminate the area.

 

[aametalmaster]

Pure Argon won't wet out on SS, you will just get a big tall bead. You need some co2 added to the mix. I just use my 75/25 ar/co2 mix for SS. I know its not a textbook mixture but it saves me from buying tri mix...Bob

 

[Weldingartisan]

Argosheild light is probably the best price/gas compromise for stainless - also good for general light gauge carbon steel, I believe it's 5% C02. W/A

 

[TechnicAl]

Thanks to petedut, TechnicAl, and Matt1978 for the information about the gas. I'm using little disposable bottles (I've got a pub CO2 cylinder but only for rough stuff) and I don't think I've ever seen one with Argon/O2 or Argon with less than 20% CO2. But it does seem like the weld isn't wetting the base metal, so maybe I need to investigate that further. What's likely to happen if I use 80/20 Ar/CO2?

On the bright side, I had another go today, and managed to get some good welds -- just tacks, but that's all I need -- by carefully adjusting the wire speed and taking emery cloth to the surface where I want to weld and also to where the earth clamp goes.

Pete

With 20% co2 you will oxidise the weld metal and lose some of the anti corrosion properties. If its an Si grade filler wire it will be less detrimental but really you shouldnt exceed the 2.5% and proabably the 5% will be OK for everyday jobs.