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.