Paul Amaranth asked:
> What's involved
> in the process and what does it do for you? Shot peening I understand,
> but what is nitriding? Any others?
Nitriding is a type of casehardening - i.e. it generates a hardened
layer on the surface of the treated part. It is done by exposing the
part to a nitrogen rich environment at elevated temperatures (typically
around 1000 F/550 C), most commonly using either anhydrous ammonia gas
or an alkali cyanide salt bath. In addition to the hardness of the
nitrides formed in the outer layer, the process also causes physical
growth or expansion of this layer. While this generally requires that
the part be finish machined after the process, it also results in the
surface having residual compressive stresses which serve to increase the
fatigue resistance of the part (this is similar to the effect of shot
peening). It also generally increases the corrosion resistance, but
this is not generally important for a crankshaft. Not all steels
respond well to nitriding, and while I would expect that most steels
used in crankshafts would benefit, they will not all benefit equally. I
doubt that it would be appropriate for use on nodular iron cranks, but
I'm not certain.
There are some other treatments which I have heard of, but am not
familiar with. One which comes to mind is called "Tuftriding", and was
used on some BL cranks. I believe this process works well on at least
some steels which do not respond particularly well to nitriding.
Harry Phinney harry@cv.hp.com
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