Trevor,
Thanks for that great answer. Very intereisting discussion of grain structure and testing methods. Takes me back to the one materials class required when your major is Electriclal Engineering. This brings me to another question. I'm digging down because my next rebuild will most likely include journal welding. If I understand it correctly, forging changes grain size, shape and orientation to increase strength. In a crank, I assume the added strength is for both torsion and bending. So, the question: would 2mm (or, even more) of grain-structure change due to weld penetration make much difference in the overall strength that has been added core-deep by forging?
Sorry if seems I'm trying wear out your fingers with typing.
Richard L.
Yes you are correct.
Metal spraying will yield the strongest crank.
However BSA cranks were way over designed so a moot point about drop in strength due to changes in grain structure caused by the welding.
Get the finished product nitrided and it will be more resistant to failure than it was when new.
Be sure to tell whoever is doing the build up you are going to nitride it as it might make a difference to what they use to do the build up with.
For all I know they could use a nitrogen wire to do the build up so you get a double benefit.