Stainless suspension bolts ?

[Simon]

Now I'd always thought this was a big no-no as stainless is supposedly more brittle than mild steel, but I've now been told it's all down to the grade of bolt and that some stainless IS tough enough to use in this highly critical area.
Who's right?

ps, this is not a pretty pretty thing, but rather an anti-corrosion concern.

 

[Peter Delaney]

Good question Simon - I had been told the same old stories originally by various "experts", so I played it safe & all my suspension bolts are HTS & ugly. Those that are visible have a coat of silver engine paint, but they just don't look as good as s/s, and they sure will corrode over time.

When I raised the subject of huge trans-Atlantic yachts using s/s everywhere (and probably having shock loads a few orders of magnitude greater than you would get in a car), the "expert's" response was to shrug their shoulders & point out the few notable yachting failures - conveniently ignoring the thousands of non-failures !

Perhaps Trevor Booth could give us all a steer in the right direction on this ?

Kind Regards,

Peter D.

 

[Trevor Booth]

You can use them if you get the correct stainles steel bolt and it is used correctly, why do you think trans-atlantic yachts cost so much. It is not the shock that causes the failure it is fatigue caused by cyclic reversal of the stress. Personally i would not use them. If you want corrosion protection have the bolts electrolous nickel plated. This gives an attractive satin finish as a bonus.
Trevor

 

[Frank Catt]

Its not the bolt that is the problem with the GTD, its the length of the bolt ! It was GTDs practice to install 4 inch long bolts to the suspension connections, the correct length needed BUT it meant that the support on one side of the bracket always coincided with the threaded section of the bolt, so the full force imposed between the suspension and chassis is supported on the thread on one side of the bracket. We buy and install 4.5 inch long bolts, reducing the overall length by 0.5 inch, which means that because of the longer shank length there is correct support to the bolt in the bracket. Frank

 

Quality steel bolts are made from alloys that are designed for more than just high tensile strength.

While some grades of stainless do have high tensile strength, the other material properties are not as good.

Carrol Smith wrote a couple of books about choosing the correct bolts and other hardware for a race car. That will have the full story. I think it's called Prepare to Win, or Design to Win, something like that.

That should be required reading for any "kit car" builder, it will tell you how to find and fix the poorly designed use of fasteners that most kits have.

I like to design for safety under normal conditions, then choose which part should fail in an accident. That is why lots of race cars have shear plates, and making them stronger is wrong.

 

[Gary Gibbs]

[ QUOTE ]

Carrol Smith wrote a couple of books about choosing the correct bolts and other hardware for a race car. That will have the full story. I think it's called Prepare to Win, or Design to Win, something like that.


[/ QUOTE ]

"Nuts, Bolts and Fasteners and Plumbing Handbook" As all of his books it is excellent. I would expect if the bolt diameter, etc. is over designed enough you can get away with SS. It is not typically used in high strength applications. Well plated aircraft bolts do hold up reasonably well.

 

[Chris Martino]

Look into MIL (Military) spec or MS / NAS spec fasteners. They have specific codes and specifications that give you information on everything from the treads to the material and when they may have been superceeded by another. /ubbthreads/images/graemlins/tongue.gif

Chris
RCR

 

[BenL]

[ QUOTE ]
[ QUOTE ]

Carroll Smith wrote a couple of books about choosing the correct bolts and other hardware for a race car. That will have the full story. I think it's called Prepare to Win, or Design to Win, something like that.


[/ QUOTE ]

"Nuts, Bolts and Fasteners and Plumbing Handbook" As all of his books it is excellent. I would expect if the bolt diameter, etc. is over designed enough you can get away with SS. It is not typically used in high strength applications. Well plated aircraft bolts do hold up reasonably well.

[/ QUOTE ]

Carrol Smith wanted to call the book "Screw to Win", but the publisher refused to accept that title. I don't know if they're still available, but it used to be possible to get decals that said "Screw to Win" to place on your copy of "Nuts, Bolts and Fasteners and Plumbing Handbook".

 

[Trevor Booth]

if you get the correct S/S bolt it is equally as good as a SAE grade 5 but can have superior tensile strength. Some S/S are heat treatable and are typically used for exhaust manifold studs, head studs. I have used them for years with no failures but I make my own with rolled UNF threads not machined threads. Some S/S are precipitation hardened and are used for specialised aerospace and aircraft parts and fasteners. The ordinary off the shelf marine S/S bolt is usually a machined bolt and thread,and in most cases 316 grade. Apart from the fact that they have a course (UNC) thread, the machined thread weakens the bolt more so than a rolled thread. You would not use these bolts in a single shear (cantilevered load)application. MIl spec or AN aircraft bolts are not necessarily better than an SAE grade 5 unless you are familiar with them and what bolt to choose. The big difference is a guaranteed consistent quality and strength with superior plating. If you use a vehicle in competition you should replace all critical bolts on a regular basis. Personally I would not go to the extra expense of MIL or AN bolts. You can EN plate ordinary Sae Gr5 bolts at a fraction of the cost if you specifically want corrosion protection.

 

If you are replacing a grade 5 bolt, a good stainless bolt with rolled threads and a good heat treat should be able to do it, because grade 5 is pretty weak. The required tensile strength is 120 KSI with 14% elongation.

Grade 8 is 150 KSI with 12% elongation. That's very hard to match with stainless.

Elongation is the measurement of the fasteners ductility. As the tensile strength goes up, elongation goes down. A bolt with very little elongation will look good untill it snaps. A bolt with more elongation will strech before it breaks and in that stretch area, the diameter of the fastener will be reduced.

If it were easy to make grade 8 bolts, we would only have grade 8 bolts. We have grade 5 because we needed a spec for the cheaper bolts.

With stainless, the elongation is what kills you, it's easy to find a stainless alloy with high tensile strength, but it's very hard to make an alloy with good elongation. I'm sure some one could make a grade 8 stainless bolt, but it will probably loose some of the corosion resistance that stainless is known for and it will be $$$.

 

[Howard Jones]

I would not use SS hardware for "itelkillya" aplications such as suspensions pickup points, shock mounts, rollbar mounts, brake caliper mounts, half shaft hardware, etc. Use grade 9 for this stuff.

I damn near killed myself on a bike because I used a unknown set of handlebars in a rush to get to the grid. Some things just REALLY stick in your mind. That one moment really taught me something about "itelkillya" parts.

Use the good stuff and check them offen.

 

[Trevor Booth]

"SS Hardware" hardware being the operative word. The type of SS bolt you would buy at a hardware store. Unknown quality=unknown result except perhaps "itelkillya". I am not a great fan of Gr9 bolts unless what it is in is rigid. They have been known (as well as gr8) to "pop" the heads off. If you analyse the loads imposed, in these types of cars, a good quality Gr5 will more than likely do the job.

 

[Trevor Booth]

Built 2 rev

From memory,
431 SS heat treatable 150 ksi with around 18%

 

Sure, but it's not cheap.

I found this page:

http://www.howcogroup.com/guide/002/o_431.htm

That says 132ksi, 11% elongation. Any further heat treat is going to increase the tensile strength, but the elongation will decrease.

I think that would be a good replacement for a grade 5. For Grade 8, it would depend on the application.

I certainly would not put those on in an "itelkillya" role unless I had a very good idea of the loads involved.

 

[Mark Worthington]

I used AN fasteners in all my suspension pickup points, although I do have a few M8 stainless steel bolts, some of which are on my front ball joint mounts. Pat Barry had a good post where he listed all the sizes that were needed for an RF. The AN stuff is Cd plated and looks nice.

 

[Dave Bilyk]

I would certainly treat the idea of stainless bolts with great care to make sure that both strength and corrosion factors are correctly addressed. The transatlantic yacht would certainly be the area to get ideas from. The strength factor was already well discussed here. The corrosion issue can be very important with stainless steel since under the right conditions it will corrode very quickly. While carbon steels tend to corrode over, stainless, when it corrodes, is vulnerable to local attack which occurs quickly and deeply, rapidly weakening the bolt. The circumstances which tend to lead to this are generally galvanic effects due to dissimilar metals and the presence of salt water (salting of roads in cold countries, or on the coast) in crevices, and stress.
So I am saying get the best advice and the most appropriate materials according to the level of loading, and the material which the bolt is to mate with.
Other problems can be sacrificial corrosion of the bush due to galvanic action, and where stainless bushes are used, galling.
I am not a metallurgist, but work closely with one, we see all these problems with stainless bolting and other components in pumps. Experience with all these issues in the yachts would make this area the best to get ideas from, but as Trevor said, I wouldn't do it, and as Howard said "itelkillya" if you get it wrong.
image from corrosion.com
regards
Dave

 

[Trevor Booth]

Dave,
Does the picture depict crevice corrosion where the nut was, or is it galvanic close to what the bolt was screwed into? Is the material Martensitic.
Trevor,
PS , Care to update the rear toe in thread?

 

[Dave Bilyk]

Trevor, it was crevice corrosion according to the caption, the metallurgist said it was from corrosion.com, so you may find it and the material there.
I havent forgotten the rear toe in thread, and will update it soon.
regards
Dave

 

[Trevor Booth]

Thanks Dave I shall have a look.

Trevor