<VV> Nitride Coating Thickness
BobHelt at aol.com
BobHelt at aol.com
Sat May 10 15:59:41 EDT 2014
>From my book and extensive research.....
Finally, the crankshafts were nitrided to increase the surface hardness
and to prevent incipient cracks from being initiated in the fillets.
Chevrolet called this process “Tufftriding.” The nitriding process involved
heating the crank to 1075O F in a liquid cyanide salt environment for a number of
hours. The nitrates in the salt react with the hot steel to increase the
fatigue strength of the surface. The longer the crank is exposed to the
cyanide salt, the greater will be the depth of nitriding. Twenty hours of
exposure produces a hardened depth of about 0.012". While the actual length of
exposure at Chevrolet is unknown, it is thought to have been around four
hours, which would create a depth of about 2-3 thousands of protection. The
actual hardened depth is very thin, and is completely destroyed by regrinding
the crank. However, the reground surfaces can be nitrided again by any
competent shop.
Bob Helt
In a message dated 5/10/2014 9:43:24 A.M. US Mountain Standard Time,
virtualvairs at corvair.org writes:
original message-
Date: Thu, 8 May 2014 08:02:58 -0400 (EDT)
From: Shelrockbored at aol.com
Subject: Nitride Coating Thickness
How thick is the Nitride coating on the crank of a turbo engine?
Is it .015 - .020?
Steve Sassi
LI Corvari
======================================================
I think that is off by at least one decimal for the factory TuffTriding.
The Chevy Power book and others used to warn that more than gentle
polishing would remove the very hard surface case. There is a still beneficial
fatigue resistant layer of compressive stressed material a bit deeper. I'm
pretty Any regrind returns it to base metal in the hardest working regions.
If the regrind can restore (or create) decent filler radiuses then the
crank at least starts with fatigue resistant geometry. Some regrinds ruin an
otherwise good crankshaft.
Dan T
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