Welding Mild steel to Stainless?

[Dr Strangeglove]

Can mild steel be welded to stainless? When it comes to replacing some sills etc that are likely to rust again, would it be possible to use stainless sheet instead?

In mig would be best but if not tig?

If not could you try to explain why so I am not wondering?

Regards

Mick

 

[murex400]

yes it can. but if the sill’s were replaced properly and protected they should last as long as the rest off car,and the price of a sheet of stainless will put you off

 

[mart]

Chemical reaction of stainless & mild steel

I am not a metallurgist, but my understanding is that when stainless steel is in contact with mild steel it can form a chemical reaction . You may wish to google it as there are many different types/grades of stainless steel.

 

[Drains]

I am not a metallurgist, but my understanding is that when stainless steel is in contact with mild steel it can form a chemical reaction . You may wish to google it as there are many different types/grades of stainless steel.

You get a galvanic reaction. Having the stainless there will induce greater corrosion in the mild steel.

It's not uncommon to mix the two in certain circumstances, but on thin bodywork it's dodgy.

If you do do it, use stainless wire, or if MMAing, use a "dissimilar" rod - high nickel content.

 

[aametalmaster]

Sometimes when using thin SS sheetmetal welded to carbon steel the carbon will raise to the SS side while welding and it will still rust. Also when you grind side by side carbon/SS where your grinding wheel touches the SS the wheel will deposit carbon into the SS and it will rust. I would stick to the regular carbon steel for panels...Bob

 

[rtbcomp]

"They" even disapprove of using mild steel wire brushes when cleaning stainless, use a brush with SS bristles instead.

 

[weldequip]

"They"

Ahh... the men in white coats. Where would we all be without them?!
weldequip

 

[matt1978]

Use either a 309 or 312 grade of Stainless filler wire.

 

[rtbcomp]

Ahh... the men in white coats. Where would we all be without them?!
weldequip

I bet you thought "SS" referred to Stainless Steel........well it doesn't........it refers to "Them"

 

[scarecrow]

"They" even disapprove of using mild steel wire brushes when cleaning stainless, use a brush with SS bristles instead.

"They others"

 

[Welderpaul]

You get a galvanic reaction. Having the stainless there will induce greater corrosion in the mild steel.

It's not uncommon to mix the two in certain circumstances, but on thin bodywork it's dodgy.

If you do do it, use stainless wire, or if MMAing, use a "dissimilar" rod - high nickel content.

Mmm Bi-metalic corrosion.

 

[Drains]

Mmm Bi-metalic corrosion.

Sorry. Aye, galvanic's with an electrolyte in between.
Different kind of battery.

 

[Dr Strangeglove]

The idea would be to replace all the inner wheel arches, sills etc with S/S as and when they need work! I can get the things folded etc through contacts at work. It is on a Range Rover so the idea is not to put back mild steel in the areas that are likely to get covered in mud.

Also it would mean that doing the job well was worth that bit more time and effort. The main area of concern is the doorposts as this is an area I would not want to suffer. The inner front wings etc would be (I think) relatively easy if I can get them fabricated OK.

The problem with this vehicle is that it does not do many miles (so it stands around a lot) and will have moisture holding grime on it a lot of the time.

If I know that I would have to watch the areas joined for increased corrosion then I would have to make sure any joints were in areas that could be treated on a regular basis. My concerns were that the materials may melt at different temperatures so making sure the heat was concentrated on one material more than the other?, what type of wire to use (which I think has been answered), what type of gas to use?, the corrosion issue and also any problems with increased “metal fatigue” causing joints to fail?

Obviously material costs come into it but it would be nice to know the job could be done and then forgotten.

 

[oddball90]

How old is the Range Rover, assuming it's atleast 20years old. Is it worth messing with stainless steel, as most of the areas you are going to repair are structual(seat belt mounts, door posts, inner wings and sills). Personally i would just repair to a good standard using mild steel and use waxoyl well and use stoneguard underneath. As the vehicle will still rot in other places, ie Chassis.

 

[Dr Strangeglove]

I understand what you are saying but could it be done? I want the vehicle to last (for many years) as it will do very little mileage. I can look after the chassis with waxoyl like you say, and it should retain its strength without to much attention. The parts that I am more thinking of are the spotwelded parts (especially sills), the wheel arches and some floor parts. I have a friend that could plasma cut the sheet and I can do the DXF drawings for the parts and also fold them using his pressbreak, so with a little effort on my part and the cost of materials (ok more expensive in stainless but if utilised well I could get a lot from a sheet!) I can have them.

This would leave me to concentrate on the parts I can’t replace such as chassis, pillars, bulkhead etc. The replacement parts all have hidden moisture/water traps and are just waiting to start corrosion. I have already put plenty of waxoyl on and inside the chassis, into the sills, etc. (I have also undersealed/waxoyled everything else as well so I have no intention of doing the work for the sake of it)

At the end of the day I will only do it if the material cost will allow, but mainly if it would be plausible in that I would not be creating weak points or possible stress failure points. I suppose what I am saying is which joint is the strongest, mild steel to mild steel OR stainless steel to mild steel. If a mild steel to mild steel joint is 8 out of 10 in regards to strength then where does stainless to mild steel rate?

Thanks for all the replies – keep sharing your knowledge.

Kind regards

Mick

 

[Drains]

Mick, the presence of stainless will cause the m/s to rot. What often happens (and I have seen this a number of times), is that the mild steel section of the stainless to mild steel joint, lets go of the stainless, and the joint fails. Quite literally, the weld falls apart at the m/s to stainless weld joint. This is particularly bad where water (and or seawater) is present, like in the hidden seams of a car (or on a boat)

Without doubt, similar joints are stronger than dissimilar joints (particularly in the long term, as corrosion is always a consideration)

Also, because of the different work-hardening and rigidity properties of m/s and s/s, additional movement and fatigue may be induced in places.

My advice would be, don't mix your metals, unless you absolutely have to. Either all mild steel, or all stainless.

Honestly, using stainless is asking for trouble. It is quite straightforward to use effective coatings such as waxoyl, to retard and protect against long term corrosion.

 

[Drains]

Mmm Bi-metalic corrosion.

After a bit of research, I can confirm that bi-metallic corrosion and galvanic corrosion are one and the same thing. But obviously there are different ways it can occur

 

[mishka]

After a bit of research, I can confirm that bi-metallic corrosion and galvanic corrosion are one and the same thing.

If you're really keen you can measure the voltage across the bimetallic junction to tell you the junction temperature, or to trickle-charge your battery (although I would imagine you won't get too much current out of a SS/MS junction). After all, a thermocouple is just a welded bimetallic junction.

 

[malcolm]

Some good links to threads on other forums from the end of the how to stop rust coming back thread. I'm tempted to try the sacrificial corrosion thing by bolting a lump of zinc to the bottom of my Renault.

 

[Dr Strangeglove]

Thanks for the replies. I will take what you have said on board and look if the stainless aspect would be of any use anywhere before I apply it. If it is somewhere where it could be used using mechanical fixings then I may still think about it.

Regarding the “lump of zinc” thing. I have thought about this as well but like the threads say, you need water for them to take effect. Due to that my thought is that zinc ingots will only really work in the area they are attached so you will need a lot of them or you will have only a small area of protection. The main reason I am asking the question about mild to stainless steel welding is for the sills on a range rover. They are manufactured from flat sheet anyway and I was looking to make the inner and outer sills from stainless, use a “top hat” type folded section to support the floor, then have a removable floor (at least in places – but not too much time has been spent on thinking about this yet as I wanted to know about the welding situation first!). However, as well as waxoyling the sills inside I also thought of putting zinc inside! Again I did not spend too much time on it but my thoughts were this. Where do I get the zinc?, is it in ingots as this would not be suitable. I then thought of granules or shavings. I had a quick look on ebay and found zinc powder!! Now remember I was thinking of this specifically for sills. On them the spot welded (corrosion loving) joint is vertically downward at the bottom of the sill. If you could “blow” powder in here so it settles on the bottom of the void, would this work. The other thing I thought of was mixing the zinc powder in with the waxoyl, but if it was covered would it work (probably not) but it may if the waxoyl was lost (which is when you would need it!

Just a thought.

Thanks for the advice!

Regards

Mick