Issues with chromed suspension pieces?

[Mark Worthington]

My rear suspension has chrome-plated drag links, lower arms, and top links. It looks great, but now I'm thinking about taking it apart to address two potential concerns, one that I'm aware of and another that I'm not sure is a problem.

In Engineer To Win, Carroll Smith wrote that he doesn't like chrome-plated suspension pieces (he didn't say why) but went on to say that when he does encounter them, he he washes the tubes out with a mild baking soda solution to neutralize any residual plating-bath acids, dries them thoroughly, then sprays liberal amounts of WD40 inside to inhibit corrosion. Mine don't appear to have been treated in this manner by the former owner of my kit (who arranged for the chromeplating), and the pieces appear to have come straight from the plating shop. There was significant corrosion on the female threads that I cleaned out with a tap before I could thread the rod ends in. I did spray the insides with WD40, but did not use any sort of a solution to neutralize residual acids. I didn't worry about it too much because I would think that, in the absence of any more moisture, the corrosion would have progressed to where it is now and stopped.

Then a few weeks ago I was advised that chrome-plated suspension pieces should be heat treated after they are plated to provide "embrittlement relief." Again, I doubt any such heat treatment was carried out by the previous owner. If this is a genuine concern, I'll address it, as rear suspension component failure is fundamentally an issue of safety.

I'm hoping that someone can provide me with some solid tech on embrittlement relief and the need for post-plating heat treatment.

[Brian Magee]

Hi Mark

The main reason that chrome plating is not used on race car suspension is because the plating can hide cracks in the tube and is therefore not liked by scrutineers. Most cars use nickel plating which does not hide cracks.

Brian.

[Mark Worthington]

Interesting, Brian. I would've thought the chrome would actually make it easier to spot cracks.

[David Morton]

Mark,
I was advised against chrome on any suspension parts when I was fitting Rose joints. If the Zinc Chromate has not been purged completely there would be a real chance of corrosion within any welds and I would hazard a guess that short of X-raying or Dye penetrant (or both) on each welded point, your fears of failure at any welded point may well become a reality. IMHO I doubt that any heat treatment short of welding (again)would set your mind at rest and if it were me, I would use them as a pattern and fabricate some replacements.
Dave M

[Mark Worthington]

Not really what I wanted to hear, Dave, but I respect your opinion.

I've heard of suspension failures on some GTDs and Tornados...were those pieces chromed?

[David Morton]

Mark,
That might be a more suitable question for the GTD40 club and see if there have been any. As for other makes, equally I have no information. I've heard of 'upright' failures but they are not the issue in question. I think the previous comment made about chrome hiding the cracks is valid. Most of the wishbones and suspension that I see being made in 20g or 22g for race cars is only treated with Keyfoss before it goes into service, and it never lasts very long before its damaged anyway(thats why they are being made in the first place!).
I think you are face with a value judgement - is the cost of examining/checking/replacing the affected parts that high compared with the overall cost of your investment and labour? Using them as a pattern, the costs may not be as high as you imagine. Its not rocket science after all and any decent fab. shop could make them without a gold plated price.(sorry - wrong analogy !!)
Dave M

[Gary Gibbs]

I knew this sounded familiar. There is a phenomena called "Hydrogen Embrittlement" that can be caused in some cases by chrome plating steel.

I did a quick search on google using "chrome hydrogen embrittlement" and found many links including:

http://www.nmfrc.org/crarchive/feb02a.cfm
http://www.finishing.com/1600-1799/1747.html
http://www.nhra.com/dragster/1999/is...echnology.html

[MK -IV J6]

Mark
IMHO you should NOT use these pieces. Remake them. If these break they can kill you literaly.
Best

[norman falkiner]

GOOD ADVICE If in doubt throw them out.We do not want to start a new topic on chromed suspension failures.

[J What?]

Hydrogen embrittlement usually takes place over a longer period of time.I had an old Hawk formula ford with chromed trailing arms and it made it quite difficult to check for cracks as the chrome cracks and you can not see what the underlying surface looks like. Simply nickel plating is not the answer. Typical chroming is a copper, nickel, chrome process all of which are applied electrically and therefore add to the possibility of hydrogen embrittlement. The correct type of nickel is electroless nickel. If you ask a plater if he does electroless nickel and he hesitates, find another plater. Most chrome shops do not do it.

[Rick Muck- Mark IV]

Virtually no sactioning bodies will allow chrome plated suspension pieces anymore. Even NASCAR that "high tech" leader banned chrome for the wheels as they could not be properly inspected and the Hydrogen embrittlement became a real concern. Most competition cars today have the arms zinc plated or other non corrosive plating. A part that has been nickel or chrome plated must be "normallized" to counteract the Hydrogen embrittlement process. As was pointed out, nickel plating is a step in the chrome process. "Chrome" in and of itself is used as a plating material only to seal and brighten the nickel underneath. When you look at a chromed part you are really seeing the nickel for the shine, the chrome is basically a "sealant" due to the fact that nickel oxidizes quickly.

Rick

[Dan Weilacher]

I agree , inspection on chromed parts could be a problem. Generally your street car parts are way over engineered compared to a race car that you are going to throw away the part after so many miles of hard use like a formula car. The nickel is just polished ,that is correct on the sheen,, compared to the if left just as plated, it looks satin .Here is a 2001 pic of a penske car with "chromed " suspension, so there are real race cars still running with awsome bits out there . Oh i took this pic too [img]/ubbthreads/images/graemlins/cool.gif[/img]

[Mark Worthington]

Thread resurrection.

I picked up some nice new trailing arms for my car that are made of 1 inch OD by 0.095" wall thickness 4130 tubing with 4130 threaded tube adapters at each end. The rear suspension peices I'm replacing are mild steel and have been chromed by the original owner of my RF kit. From the above posts, I've been told that chrome plated suspension bits are a no-no and that unless the pieces were baked after plating that hydrogen embrittlement is a concern. Well, I figured that the car would be primarily a street car and that I'd inspect the suspension and replace with something better as time and funds allowed. So along came this good deal on the trailing arms and the ability to use RH and LH-threaded rod ends at each end for easy adjustment and I took the plunge.

I took them (along with a few other brackets and stuff) over to a plating company today to have them electroless nickle plated. It seems that electroless nickle plating, unlike chrome, will not hide cracks developing in suspension pieces. I was also under the impression that electroless nickle plating, unlike chrome, doesn't lead to hydrogen embrittlement concerns. I was wrong. According to the president of the plating company, the specification he is required to meet for embrittlement relief is to heat the parts to 375 * F for 3 hours, and that this must be done within 30 minutes of when the pieces leave the plating bath.

The plating is going to cost me $100, and another $100 if I want the parts baked because he has to fire up a room-sized oven. He said he can call me when the pieces are in the plating bath so I could fetch them and bring them home and bake them in my oven. Now I'd like to do this right, but I'd also like to save $100 and treat the parts in my oven, but it could be several hours before I pick up the parts and get them home.

How big of a deal is a couple hours delay when it comes to avoiding hydrogen embrittlement? As I understand it, hydrogen embrittlement results from diffusion of hydrogen gas into the metallic grain structure, so it stands to reason that baking the parts as soon as possible limits the extent to which diffusion can occur. It also stands to reason that a longer baking period could offset a reasonable delay in getting the parts baked.

I did some searching and this article is the best tech I've found on the phenomenon. Ironically, it seems that my original mild steel trailing arms are less susceptible to hydrogen embrittlement than my new 4130 trailing arms because the Rockwell hardness value of mild steel is much less.

I appreciate any feedback you might have.

[Lynn]

Mark,

Chrome, in and of itself, is a VERY brittle metal. That is exactly why the chrome is only made an atom or two thick over a thicker nickle plating. If the nickle is not thick enough or the chrome is too thick, the chromium atoms can can migrate into the crystaline structure of the steel (iron) which will cause it to become hardened and brittle. In thinking about this, I believe, that heat treating a chromed part may actually make the situation worse by allowing more chromium atoms to migrate further into the surface. Some atoms can make a crystaline metal stronger if they can form bonds with the metal atoms around them. Carbon in iron makes it much stronger, and we call it steel. Nitrogen can make steel extremely hard and strong; I am sure everyone has heard of nitriting (sp?) of bearing surfaces, etc. Chrome, however, is very inert and doesn't make bonds easily, so the end result when it is within a metal crystal is that it is hardened, but not made stronger. Indeed, because it distorts the regularity of the crystaline structure, it provides a plane of weakness along which the metal can crack and propagate the crack. Not something you would want happening to stressed members of a race car.

As an aside, the cutting edge of materials engineering is working with metal ices, rather than crystals. When metals are rapidly quenched to harden them, they become something like a metal ice, but at a more macro level: there are randomly oriented grains of crystaline structures. With a pure metal ice, there are NO crystaline structures: all the atoms are randomly dispersed. They have developed some superstrong materials with very exotic properties like this.

Regards,
Lynn

[Curtis]

Having been on the SCCA Tech Crew in the 60's,
I can tell you that they did not allow Chrome Wheels.
Were not considered safe.
At least in the NW Region.

Cheers,

Curtis

GT 40K
Woodill Wildfire

[Howard Jones]

Why not just apply a light coat of paint, like the top link here. Sure does make the whole question a lot simpler.

[Lynn]

I would suggest powder coating. They have devoped some chrome powders that look just like chrome. I don't think 350º for 20-30 minutes is going to hurt the links, but be sure to remove any rubber or plastic parts!

If you want to do it yourself, watch Harbor Freight who frequent puts their system on sale at a very reasonable price. That is what I have and it works just fine for what I do. The oven can be a little harder depending on how big the items you want to powder coat are. I just bought a used stove out of the local want ads for like $50. I had already put a 220v outlet in the garage for my TIG welder so that was covered. And, it works great for most things (I did have to take my sway bars to shop that let me use their larger oven.)

Regards,
Lynn

[Peter D]

Another option is ceramic coating - as per exhausts, etc. I got all the suspension bits (incl springs) and the rear clip mounting frame done this way & am very pleased with the look & even happier with the durability. This stuff is bullet-proof - you can whack it with a hammer & all you get is a dent (no chipping, ever). After some heat problems with the paint on the main rear cross-brace, I got this piece done as well - along with the louvred panel on top of the rear clip, mesh grills at the back, aly heat shields in the engine bay, etc.

When it gets a bit dirty, you can wash it down with anything (even thinners), then a quick run over with any metal polish & its back to a new highly polished alloy look.

The following pic is an early one, but it shows most of the ceramic coated bits.

Kind Regards,

Peter D.