Black Codiac Overview
BLACK CODIAC produces two distinguishable microstructural zones: a shallow, hard ductile surface case made up of
epsilon iron nitride and, beneath it a relatively deep diffusion layer, which is
essentially nitrogen in solid solution. The surface, or compound layer contains
compounds of iron, oxygen, 7-9% nitrogen and approximately 1% carbon. This intermetallic
iron-nitride compound forms during the diffusion of atomic nitrogen when the solubility of
nitrogen at the surface is exceeded. The nitriding potential of the Black Codiac bath is
designed and controlled to produce a specific nitride, i.e. epsilon iron nitride, Fe3N,
which is the predominant phase in the compound zone. Thickness of the compound zone
depends primarily on treatment time and the carbon and alloy content of the base material:
the higher the carbon and/or alloy content, the thinner the reactive area. However, the
average Black Codiac cycle produces a compound layer
.0004" to .0008" deep.
The compound layer is highly resistant to wear, seizure and corrosion. It is durable
practically up to the temperature at which it was generated and has a room temperature
hardness in the range of HV 550-1000, depending on the material.
Typically, the nitrogen penetrates the ferrous matrix to a depth of .020" to
.040" to form the diffusion zone. Both depth and hardness are heavily influenced by
the material: the higher the nitride-forming element content of the steel, the lower the
nitrogen penetration, given equal processing time. Unalloyed steels which are cooled
slowly or reheated after processing may experience some nitrogen precipitation from solid
solution, thus forming needles of gamma prime iron nitride, Fe4N, in the nitrogen-rich
region of the diffusion layer. The total nitriding depth will be approximately two to
three times as deep as the needle depth, depending on the material.
Low to medium Carbon steels
Black Codiac improves the fatigue and wear
characteristics of these materials so significantly that entirely new design concepts have
developed around the process. Parts formed from these steels consistently out perform like
components made from steels that are far more costly in terms of both material and
machining. Where the part is already low carbon, Black Codiac will extend service life 100-500% or allow weight reductions with no compromise of service
life.
Black Codiac for 90 minutes produces a compound
zone 0.0004" to 0.0008" in depth, with a 0.020" to 0.040" nitrogen
diffusion zone beneath. The tough, non-brittle compound zone is responsible for greatly
improved resistance to wear, galling, seizing and corrosion. Improvements in fatigue
resistance and endurance are credited to the diffusion zone, where nitrogen in solid
solution minimizes fatigue failures.
Stainless and other austenitic steels
Wear and gall-resisting properties are key benefits to Black Codiac these metals, although a 1-2 hour treatment also heightens fatigue
endurance by 25-35% in most grades. Austenitic steels develop an extremely hard and
complex compound zone distinctive from all other ferrous materials, typically 0.0007"
to 0.0009" thick, and a diffusion zone of approximately 0.003" deep.
Corrosion and wear resistance
What Black Codiac did for metals performance... QPQ does for surface quality. QPQ starts with Kolene's highly successful salt bath nitriding
process. Black Codiac follows with a proprietary KQ500 oxidizing salt bath post-treat and finishes with mechanical polishing and
reimmersion in KQ500.
This quench-polish-quench (QPQ) sequence after liquid nitriding gives most ferrous
metals a surface conditioning that protects against corrosion and wear better than hard
chrome or nickel plating. Corrosion resistance achieved through QPQ outperforms 12-micron
(0.0005") hard chromium electroplating by ratios up to 20:1 and 20-micron
(0.0008") nickel plating by a factor of 8:1. A.S.T.M. standard corrosion protection
for .001 is 1000 hours salt spray and 2000 hours salt spray protection can be achieved
with Black Codiac.
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