<VV> Nitride Coating Thickness

[BobHelt at aol.com]

>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