Mild to Stainless weld strength

[smashweld]

would uing the standard wire/gas (ferromax7)used for mild to join mild and stainless compromise the strength or just the corrosion resistance/look of the weld?

Fairly sure the stainless is 304

.....reason for asking is have a job to do that’s usually 3mm mild to 6mm mild. The 3mm part has always been mild but on this truck the rear frame is stainless

 

[TechnicAl]

If you use mild steel wire the weld will probably be stronger than both the mild steel and the 304L......but it will also be more brittle.....I dont mean brittle like cast iron just by comparison to the other two.........freeze it and it may snap with a british standard hammer blow

 

[smashweld]

Thanks...what would be the proper method?

Ideally want to use the mig but have an old oil cooled stick welder and 200a tig

 

[TechnicAl]

You would normally use whats known as a Dissimilar Rod.....probably the most common being 309|L.......its overalloyed so the dilution results in something similar to 304L.

 

[Richard.]

All methods will do it but some probably more practical than others. Mig being the least because you’ll need a reel of 309 (expensive) and a bottle of 98/2
At least for tig and MMA you could possibly sponge a couple of rods
I’ll give you a few 309’s or 312’s tig rods if it’s just for a one off job no problem.

 

[smashweld]

Cheers for the offer Richard... need some other consumables anyway tho so will get the 309s along with the other stuff.

I've found some old rods that I think are dissimilar rods but the coating pings off them when they get hot so will just buy the right thing!

 

[smashweld]

Would a 2.5mm 309L electrode be the right size? Or3.2 for 3mm to5mm vertical? Hardly ever use the stick welder...

..there’s already some mild steel box welded to the stainless frame (that’s getting replaced) I cut out a bit of the weld with a grinder, it doesn’t spark as much when cutting/grinding mild but sticks to a magnet...does that sound like a 309 rod/wire was used there?

 

[smashweld]

....found some rods marked 309L-17 at the back of my dads boiler cupboard! What does the 17 indicate?

Tested them out....any idea what causes the little black crater type things?! The slag is pretty hard to get off...helmet down when chipping like!

 

[sjp001]

Sorry if mistaken... Are those craters the hammer marks from you chipping the slag off?

 

[smashweld]

That’s why I mentioned slag But at the same time doesn’t seem like it should be happening and wondering what’s causing it

 

[TechnicAl]

The weld should be non magnetic but you may get a pull from the mild steel behind it
309L-17 is the correct rod but they are an acid rutile which makes the arc very soft with minimal pen and they are also prone to porosity....dry them....probably about 150 oC for 30 mins should do it

 

[smashweld]

hmmm, the bit of weld I cut out was definitely magnetic, would the mild steel kind of bleed in to the weld? not that this matters much now, just curious what it's been welded with before

I'd rather just get new rods if there's something better tho, especially if there's a better rod for vertical runs

solved the crater marks problem by using the chisel type end of the hammer

 

[Richard.]

If your welding stainless onto mild steel then expect some dilution and in turn expect some magnetic pull. As Al said 309 is the correct consumable for stainless to steel.
It’s over alloyed with chromium to ensure your joint meets the minimum 12% with dilution which will give you an austenitic joint.
Some stainless grades are magnetic which If your joining one of those again will explain the magnetic pull.
Pull a fresh rod out the box and hold a magnet to the rod. There should be no attraction from a 309.

 

[smashweld]

the stainless I want to weld to def isn't magnetic...my torch won't stick to it

are these 309l-17 rods suitable for vertical/overhead or is there another rod that would make the job easier? Didn't have much joy with v up or down but might just need practice/settings adjusted...

when I say better rod I mean a better 309 variant btw

 

[TechnicAl]

If your welding stainless onto mild steel then expect some dilution and in turn expect some magnetic pull. As Al said 309 is the correct consumable for stainless to steel.
It’s over alloyed with chromium to ensure your joint meets the minimum 12% with dilution which will give you an austenitic joint.
Some stainless grades are magnetic which If your joining one of those again will explain the magnetic pull.
Pull a fresh rod out the box and hold a magnet to the rod. There should be no attraction from a 309.

The wire might show a slight pull due to the work hardening its been subjected to....but it will be slight...unless you have the British Gas type magnet that will probably attract the Moon.....(B Gas use a magnet to reject claims under their maintenance scheme....sludge is excluded)

The intention of using 309L is that the weld wont crack which could happen with some other steels

 

[TechnicAl]

Do you know the brand of rods?
they should be OK but it depends which one it is....the 309L-17 doesnt tell the whole story

 

[smashweld]

I'd have to look on the box...I think it's just a sticker on the plastic box from a welding supplies place tho rather than the manufacturers

 

[Rig Pig]

Isn't corrosion going to be an issue? Stainless and carbon steel make a nasty little battery.

 

[TechnicAl]

Isn't corrosion going to be an issue? Stainless and carbon steel make a nasty little battery.

only if the atmosphere is corrosive....the designer should take that into account

 

[Rig Pig]

only if the atmosphere is corrosive....the designer should take that into account

Sadly they seldom do!