[chris_seven]

There is so much BS written on this subject it is unbelievable.

There is no doubt that Nickel and Chrome plating does cause hydrogen embrittlement, I am sad to say that it is not a matter of belief it really does happen. The best method to eliminate the effects of hydrogen are shown in UK Defence Standard DEF STAN 03-4/2' and I imagine that there is an ASM Equivalent. I would suggest that you basically need to heat treat at around 200 degC for at least 3 hours and carry out this process within 24 hours of plating.


Also another simple fact is that the deposits produced by electroplating are also highly stressed and generally cracked. it is sometimes said that Hard Chrome is quite tough and compared to decorative chrome this is true but the layer is still in terms of fatigue resistance quite poor. A typical reduction of fatigue threshold stress would be around 50% which is fairly catastrophic when you apply this process to a component that has not been 'stressed' to deal with this issue.

Following grinding of hard chrome it is generally necessary to stress relieve to prevent cracks from propagating too quickly. This will involve heating again to 200 degC for another hour. I would then inspect the crank with magnetic particle tests and assuming all was well de-magnetise.

The stresses produced in Hard Chrome are typically tensile in nature they will always have a negative effect on fatigue life.


It is probably OK on large capacity very slow running diesel cranks which can be locally brush plated but I don't think that a high performance crank is a suitable candidate.

Many Companies also submerged arc weld cranks, again commonly applied to low speed diesel and large capacity slow engines.

IMHO the chances of introducing defects during welding is much too high to take the chance on something like a 911 crank.

You will of course produce distortion during welding and there will be residual stresses produced.

You an reduce these stresses by some basic heat treatment but without significant testing it will be difficult to be 100% confident although it is easy to say that all will be well. The inspection needed to guarantee integrity is far too demanding. There will be little or no scope to determine optimum welding parameters and no back up with any mechanical or fatigue tests to prove that the parameters used are correct.

It will also generally mean that the crank will be unlikely to respond correctly to a Tenifer treatment as applied to a standard crank and this will also mean that a reduction if fatigue life is probable.

I have to say that the number of potential problems that can occur during either of these complex process persuades me that the risk/reward benefits are not convincing.