Before we talk about the Melonite® process, it’s important to understand that you must complete all machine work to be performed on parts prior to treatment. The finished surface is extremely hard and makes modification of parts after Melonite treatment impractical. High Speed steel cutting tools will be destroyed trying to cut through Melonite.
MELONITE is a thermochemical treatment for improving surface properties of metal parts. It exhibits predictable and repeatable results in the treating of low and medium carbon steels, alloy steels and stainless steels. The process has many stages, from the pre-treatment-cleaning, to pre-heat furnace, to the Melonite salts, quench salts and water rinses.
The MELONITE process is not a coating. It is a process that introduces nitrogen and carbon into the surface of the metal. It produces high wear resistant as well as improved lubricity. The service life of steel tools and parts is extended. Corrosion resistance of unalloyed and low alloyed steels is greatly improved.
The MELONITE process increases fatigue strength about 30-80% on parts made of alloyed steels. The hardness is maintained up to about 930°F and extends the surface life of steel tools and components which are exposed to heat.
During the MELONITE process, which takes place between 900°F and 1075°F. A two-part nitride layer consisting of a monophase compound layer and a diffusion layer is formed. Total depth ranges from 0.008-0.040″, depending on the composition of the base material and treating time. Hardness in the compound layer ranges from approximately HV 700 on alloyed steels.
A unique feature of salt bath nitrocarburized layers (melonite) is the monophase compound layer, with a nitrogen content of 6-9% and a carbon content of around 1%. Compared with double phase nitride layers which have lower nitrogen concentrations, the monophase layer is more ductile and gives better wear and corrosion resistance by improvement with case hardening.
In metallographic analysis the compound layer is clearly definable from the diffusion layer as a lightly etched layer. A porous area develops in the outer zone of the compound layer. The case hardness of the compound layer measured on a cross-section is up to about 1600 HV on high chromium steels. Treatment duration of 1-2 hours usually yield compound layers about 0.0004″ to 0.0008″. The higher the alloy content, the thinner the layer for the same treatment cycle.
Corrosion resistance of Melonite is exceptional. Salt spray tests show that Melonite can go nearly four times longer without rust spots developing than with nickle plating.
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