HELP WANTED welding stainless to mild questions

[shanepren]

Hi guys

Ive searched a few threads already and ive a question for you all.

Ive just started a new job where im required to weld 4mm 312 stainless steel plate to approx 15mm mild steel chassis. The company bought a reel of 312 stainless wire and a bottle of 97.5%argon &2.5% co2.

I was welding today but i cant really seem to get very good penetration and when i do get it penetrated its not sticking to the mild steel sometimes.

What am i doing wrong guys? Do i need a higher wire feed or higher voltage and amps?

I cant get a decent finish on it either


Im not experienced at stainless welding or the setups for it. Ive only ever mig and arc welded mild steel before.


Any help would be great because its really frustrating me

Cheers
Shane

 

[BrokenBiker]

I would suggest trying higher voltage and maybe a touch less wire speed, although if you are unsure of how to set a welder up for various joints maybe you need to sit a course as the joint you describe sounds like it could be structural

 

[Rig Pig]

I think your building in some serious corrosion joining mild to stainless.

 

[shanepren]

Not my choice on materials unfortunately.

Its basically just 25mm stainless 90° angle plate welded directly to the chassis to hold on a clip to hold a wire up off the chassis. Not structural but i still want it done right.

Cheers guys

 

[shanepren]

Oh and probably should of stated access is very tight so thats not helping either

 

[Richard.]

Well a good start is you have got the right dis similar consumables and gas for the job. The trick with welding something really thick to something thin is to set your machine up for the thick stuff . Your gonna need some power for the 15mm. You want to then blast your way into that thick section while wetting the edges of the 4mm. If you want more penetration up the wire speed if you want bead spread up the voltage.

 

[shanepren]

Thanks richard

 

[Dimitri De Spiegeleer]

typically, dissimilar welding is done with 309 or 309LMo, which has a tad higher Nickel content.
312 is some great wire but has other uses. It should stick to the mild steel without problems though, as said before you're probably lacking power (= wire speed).

 

[Richard.]

I would say he has picked the best material because of the current he needs. 309 is a good consumable but at high currents it becomes less ferrite than the 312 so is therefor more prone to cracking.

 

[Dimitri De Spiegeleer]

309 is a good consumable but at high currents it becomes less ferrite than the 312

Didn't know that - will check that out next time I have the chance. Never used 312 for anything else than specialties or small repairs, never at higher currents.

 

[Richard.]

There expensive I know that much the job dose not sound like a critical application and both consumables are suitable. If I was doing it I would go with the 309 as u suggested simply from a cost point of view.

 

[TechnicAl]

309L and 312 are both good for welding stainless to mild steel. 312 has a higher ferrite content and is stronger than 309L. There are applications where one is better than the other. Where the strength is needed for example.
309LMo has the same Ni content as 309L but it also contains Mo. It is designed for cladding mild steel. The clad layer will be diluted by the mild steel and the layer will be similar to 316L. 309LMo isn't really designed for dissimilars. It can be used but there is no advantage.

Higher currents give higher dilution so this could lead to higher ferrite but it depends on the materials being welded.

As for the OP....I didn't know you could get 312 plate. I thought it was only a weld filler metal (and maybe a cast alloy). Do you mean 321?.........to be honest it doesn't really make any difference as its still a dissimilar joint.

 

[Richard.]

Oh yeah I did not see that. I've not heard of a 312 plate. Perhaps he means 321.