13 replies to this topic

[Mikey7094]

Hi

 

I'll jump straight to my question: is it a good idea to use stainless steel to repair parts of the body where the subframe bolts to?

 

I've seen a few posts on here about stainless steel in bodywork, and I've heard some possible issues with it (I'd be interested to hear any additions): it's difficult to weld to mild steel, it's not as strong as mild steel, paint might not stick to it properly; and I've heard that it might crack under load, so maybe it's more brittle?  But of course the advantage is it wouldn't rust (as easily).  I'm most bothered by the strength/brittleness issue, particularly for structural bits like the subframe mounting points.

 

I ask this because I would like to repair the lower section of the toeboard in my car, where the front subframe attaches (it has solid mounts).  I have some 1.5mm stainless steel I could use, which I'd have thought should be as strong as the 1.2mm mild steel I believe it's supposed to be, and I've never found welding stainless to mild to be a problem.  But I want to make sure it's right because it's an important bit of the car!

 

Does anyone have any opinions, or indeed knowledge?

 

Thanks

 

Mikey

[sonikk4]

No i think will be the answer there. Trying to get the two different metals to weld is one thing but then there is the question of strength as well.

 

In the event of an accident in theory that part of the toeboard will not deform as it should do and the potential for something else to go instead.

 

The same applies to a lot of these stainless steel bolts you see being sold on Ebay. You have to ask yourself are they rated correctly for the job etc etc. 

[rally515]

I think leaving the original toeboard in place and making it a solid foundation for a stainless steel plate to be bonded in is a much better idea, keeping the two disimilar metals from contacting each other should be a factor as they will react and cause some issues with speeding up the corrosion of the original toeboard.

 

Bonding a plate say 6" across squared on each mounting point, either inside or outside of the cabin will do the job intended equaly. The bonding and bilts when tightend will hold them firmly in place.

 

 

I think as a form of seperation it's a good idea, for example, the rear subframe mounting points on the healboard and boot floor and both areas were two pieces of mild steel are up against each other and effectivly a trap for rust to occur, so maybe a plate between these points would be a good idea as to reduce the chances of rot in these rust prone areas ?  I guess standing the test of time is the only real way to find out wheather or not they'd be of use.

[Cooperman]

Just reinforce with mild steel sheet & it will be fine. If the original floor is cracked, grind out the cracks and weld them up before adding the doubler plate to the inside. Seam weld all around and plug weld as well and no moisture can get in, so paint both sides well and it will last for 'ever'.

[Daz1968]

Zintec sheet may be a compromise if you want to help corrosion resistance, I presume as it's zinc coated you would need a good mask while welding though. I have used this in the past and it welds ok, stainless comes in many grades and not all is suitable for stress areas and the point mentioned above regarding stainless fasteners is also true, I would not used normal stainless bolts on any suspension or steering parts they are not of the correct tensile strength requirements and could fail.

[Mikey7094]

I know using mild steel is fine if painted well - I just have these sheets of stainless, and it seemed like it might be a good idea!  So I guess I would need to know what grade it was before considering using it.

 

The problem is my toeboard is rusty, and certainly not a solid base for anything, so my plan was to cut out the rust and weld in a plate of new (maybe stainless) steel.

 

And I had never thought of what would happen in a crash - I guess I thought if I crash in a Mini I'm finished anyway.  But how do I know that even if I used mild steel it would deform as it should?  There must be different grades of mild steel, so if I bought a sheet of it from a place down the road it might not behave the same as the original panel.

[69k1100]

Galvanic corrosion between mild steel and stainless can be quite sever. If you used stainless your have to ensure there was no electrical contact between the subframe and the stainless, lest the mild steel is eaten away.

Especially on salted roads and a high exposure area like that. And before you think about trying to separate them consider the bolts, it's highly unlikely they won't form an electrical connection.

[Mikey7094]

Well this is much more complicated than I thought...

[Daz1968]

When we have steel framework bolted to stainless steel storage tanks a nylon washer is used under bolt and washers and a nylon shim between the steel and stainless. Not easy to do on a subframe mounting though.

[Archived4]

If you were to do it properly you'd have to use 309 dissimilar wire to weld the two together.

[sonikk4]

To be honest i really would not bother. Dissimilar metal corrosion is a proper headache something which we come across in Civil Aviation a lot. Not as bad as it used to be. We always use a interfay sealant between different metal or various coating to help prevent this. 

[exuptoy]

Working offshore we see this a lot. We use stainless steel cable tray and supports, usually mounted to mild steel girders etc. We have to put rubber pads between the two to prevent galvanic corrosion and insulate bolts where they clamp by using nylon washers.

[rally515]

Working offshore we see this a lot. We use stainless steel cable tray and supports, usually mounted to mild steel girders etc. We have to put rubber pads between the two to prevent galvanic corrosion and insulate bolts where they clamp by using nylon washers.

 

 

Intresting, thanks for that, I know what to do now when I come to do something similar ;)

 

Anything fancy you could link us to to help slow down corrosion ? shouls be some pretty heavy duty paint they use in the sea!

[exuptoy]

There is one like red lead they use 

 

 

Working offshore we see this a lot. We use stainless steel cable tray and supports, usually mounted to mild steel girders etc. We have to put rubber pads between the two to prevent galvanic corrosion and insulate bolts where they clamp by using nylon washers.

 

 

Intresting, thanks for that, I know what to do now when I come to do something similar ;)

 

Anything fancy you could link us to to help slow down corrosion ? shouls be some pretty heavy duty paint they use in the sea!

 

 

to be honest mate, I am a maintenance electrician (used to be construction), I pay no attention whatsoever to the paint they use. Also I'm based on an FPSO (floating production storage and offloading) which is basically a tanker converted to a production vessel.......and it's as rusty as furk! Don't think it's seen any paint since it was in dry dock in 2009!!!! There's never any painting squads on board anyway, at least not like when I was part of the construction squads a few years ago.