Salt Bath Nitriding is a ferritic nitrocarburizing process
which involves the diffusional addition of both nitrogen and carbon to the
ferrous surface at temperatures within the ferritic phase. This process is
preferred for improving tribological and surface properties of ferrous
components in addition to improving fatigue strength. Salt Bath Nitriding is a
non-pollutive bath operating through alkali metal cyanates. The operating
temperature of salt bath is 1000° F. - 1075° F., well with in the ferritic
phase of ferrous materials, thus allowing the process to be performed on
finished parts. During the process both nitrogen and carbon are liberated at the
surface of the ferrous component. These nitrogen and carbon atoms form a
compound layer at the surface and a deep diffusion zone beneath the surface. The
compound layer provides lubricating properties to the surface and are extremely
useful in areas where use of conventional lubricants are ineffective.
The compound zone formed is predominantly epsilon
carbonitride having a thickness of about .00015" to .001". This zone
is mainly dependent on carbon and alloy content of the substrate. The more
compact the compound zone, the higher the hardness will be. The process can
provide a layer with good resistance to scuffing and fatigue. In addition there
is a very high concentration of nitrogen compound and diffusion zones even after
a short treatment time. The epsilon nitride at the surface offers resistance to
two forms of wear. The treated components resist adhesive wear as the scuffing
or "picking up" is suppressed. They also provide some resistance to
abrasive wear. Treated components get increased fatigue strength, since higher
Nitriding potential gives a greater diffusion zone. The hardness that can be
obtained in the treatment depends on the presence of alloying elements as well
as core hardness of the component. The presence of small amounts of porosity at
the surface increases the scoring and seizure resistance. The process by nature
is non-pollutive and all ferrous materials can be treated with minimum
distortion and virtually no effect on core properties. Treated components have
greater resistance to corrosion as well as cavitational erosion. Corrosion
resistance is greatly increased due to the Oxidation step of the process. This
also produces a cosmetically appealing matte black finish.