How safe is stainless steel?

Been looking at using stainless steel fittings on my GTI as I restore it. However, whilst looking for info on bolt markings I came across this. Basically the guy goes over the various properties of mild and stainless steel and there respective strengths concluding that stainless steel should not used for any critical areas i.e suspension.

His figures show even marine grade stainless steel to only be just as strong as 8.8 strength mild steel. VW bolts for suspension are supplied at the next strength up (10.9). It also appears that stainless steel has a much smaller window in which it starts to deform before ultimately breaking 8O .

I'm sticking with stainless on non-critical areas such as fuel pump brackets, fuel tank straps etc but have shied away from using it on suspension. What are other peoples experiences/knowledge in this area? Is this guy getting carried away with his stats :dontknow:

Cheers

I used a large amount of Stainless  to replace the rusty bolts ,self tappers ,nuts etc on the car . Purchased from Ebay

I'm not 100% certain. I was under impression that stainless was tougher but often if you buy a sheet of steel, then a sheet of stainless (for example) due to cost, the stainless you end up buying (unless you specifiy a thickness) is thinner, thus it will be weaker anyway for this reason alone?

I may be talking out of my backside but it's my thoughts anyway!

In the machinery I'm involved in selling we very occasionally get involved in medical or food applications where certain parts are made in stainless and there aren't any particular strength issues I'm aware of.

Anyway, enough of my 'layman' babbling, perhaps someone with some real experience of this knows here?!

Probably not an issue with bolts and fixings and the like but……

Don't you need to be careful when welding stainless steel, vague memory on my welding course about it giving off nasty fumes. Then again maybe I'm gettting confused with the galvanised stuff  :dontknow:

I know naaaarthing, I know naeeeerthing signor Faaaauuulty :wink:

Have to say I'am a little sceptical about how much of an issue it is. I assumed stainless steel was up to the job, particularly marine grade which I has to stand up to the extreme strain/pressures the sea puts on boats e.t.c.

I'll let you do the road testing though Chudd

i was thinking about stainless steel too in case of engine restoration but i desided to use original nut and bolts-of course they was in very good condition so i replated it with new zinc as original was.i must say it looks very good in my opinion.i would not use stainless in chassis areas,i care about my life and other safety too so.............

I would never use Stainless Steel fasteners on any of the heavy duty components of a car (calipers, chassis, subframes, suspension, any other critical items) because it just doesn't have the shear strength to be safely used.

If VW recommend Grade 10.9, stick with it as they have put a lot of thought into this.

I am going to use Stainless Steel fasteners on my mk1 but they will be used to clean up the look of the car really.  Use them mainly in the engine bay for low load bearing parts

Cheers daddyUK, have decided to go with VW 10.9 steel on critical components, not convinced by stainless now. As you say why would VW (considering their cost cutting tendencies) use 10.9 mild steel if 8.8 mild (equivilant to stainless strength) would have beeen good enough?

The stats given show the best stainless vs 10.9 mild
                                    
Marine Grade Stainless - 116,000psi (tensile strength) 87,000 psi (yield strength)
10.9 Mild Steel             - 151,000psi (tensile strength)  136,000psi (yield strength)

Yield is the point at which the metal starts to deform and tensile the point at which it ultimatley breaks. According to this, the best stainless will have long snapped before 10.9 starts to even deform.

Cheers

Stainless steel is a harder material than mild steel and therefore work hardens (becomes less flexible) and is prone to cracking/failure sooner.

So if used in suspension components, which do flex a little, then the time to failure will be shorter.

The same aplies to exhausts, stainless ones dont rust but how many poeple complain about cracks apearing  8O


If it a low use car stainless will be good as it will not deteriate in the garage, daily driver use mild steal :wink:

Rob  

On the food/medical machinery front stainless is the only option for cleanlenss, but the service schedule would be written to change high stress items more frequently than if they could use mild steal.

why dont you use plated fastners in high tensile? look good , dont rust and still mild steel

concluding that stainless steel should not used for any critical areas i.e suspension.

On that i agree and have edited my post above , i meant that replacing all the pretty and non essential load bearing bolts, nuts, self tappers and screws is a great idea . But leave the big ones alone .

Cheers……..

Why not get originals from VAG if still available? You can get good old stuff replated but I've just got some bits for my Mk2 and they were only 1 or 2 quid each. Strange about my Eibach ARB kit though. They supply a longer shocker bottom bolt for the back to tie the ARB in and it's 8.8.
With you all the way with stainless - I've used it on bikes for 20 years and a mate runs a business supplying it. He's never heard of a failure but I wouldn't use is on critical suspension points and he doesn't recommend it. And if you want it to come undone again use plenty of copperslip!
Barkstar