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Melonizing Process


Dear Sir,

I am looking for a process called Melonizing, can anyone inform us about this process? How to do that and things like that.


Aravind Addagudi
- Hyderabad, Andhra Pradesh, India


I found the following information on Internet (from website of Burlington Engineering) Melonite and Melonite QPQ

"Melonite™ and Melonite QPQ™ are thermochemical processes intended for the case hardening of iron based metals. These processes are categorized as molten salt bath ferritic nitrocarburizing. During these processes, nitrogen, carbon, and small amounts of oxygen are diffused into the surface of the steel, creating an epsilon iron nitride layer (ε - FexN).

A degraded form of this nitride layer (gamma prime: γ′ - Fe4N) is obtained during plasma or gas nitriding. The nitride layer is composed of two principle zones. Zone 1, called the compound or "white" layer, extends to a case depth of ~0.0004" to 0.0008". The compound layer is porous, which lends to the lubricity of the finish, and hard (~700HV to 1600HV). Zone 2, called the diffusion zone, extends to a case depth of ~.004" to 0.008".

In addition, small quantities of substrate carbon are pulled from deeper within the substrate toward the surface. The diffusion zone demonstrates a decreasing gradient concentration of carbon and particularly nitrogen as the gradient extends deeper into the surface of the substrate. This property yields a tough outer surface or shell, yet alloys the material to retain ductility, thereby lending to the overall strength of the material.

Resulting properties from these chemical and structural composition changes are increased surface hardness, lower coefficient of friction, enhanced surface lubricity, improved running wear performance, increased sliding wear resistance, and enhanced corrosion resistance. Naturally, the alloy of the substrate will influence which properties are principally affected and to what extent they are affected."

Francesca Assone
electroplating shop - Torino, Italy

We have an in-depth article about Kolene's QPQ process in our on-line library.

Ted Mooney,
Ted Mooney, P.E.
Striving to live Aloha - Pine Beach, New Jersey

The process is called Melonite and is a proprietary process. It is a salt bath Ferritic Nitrocarburize procedure which uses a cyanide base. The process is accomplished at temperature around 1050F. It is usually (but not in all cases) applied to low alloy steels to form a surface generally of iron nitrides. I have written a book called Practical Nitriding and Ferritic Nitrocarburizing [affil link on Amazon] which addresses this subject.

David Pye
- Meadville, Pennsylvania

Can someone suggest an alternative to Melonizing. we need to "harden" steel cylinders in ASTM 106 Grade C material and the original specification calls for Melonizing. However most heat treat vendors have declined to do Melonizing.

Zal Cooper
- Satara, MA, India
October 22, 2011

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