Nitridization

Nitriding is a heat treating process that diffuses nitrogen into the surface of a metal to create a case-hardened surface. These processes are most commonly used on low-carbon, low-alloy steels. They are also used on medium and high-carbon steels, titanium, aluminium and molybdenum. In 2015, nitriding was used to generate unique duplex microstructure (Martensite-Austenite, Austenite-ferrite), known to be associated with strongly enhanced mechanical properties

Typical applications include gears, crankshafts, camshafts, cam followers, valve parts, extruder screws, die-casting tools, forging dies, extrusion dies, firearm components, injectors and plastic-mold tools.

The processes are named after the medium used to donate. The three main methods used are: gas nitriding, salt bath nitriding, and plasma nitriding.

In gas nitriding the donor is a nitrogen rich gas, usually ammonia (NH₃), which is why it is sometimes known as ammonia nitriding. When ammonia comes into contact with the heated work piece it dissociates into nitrogen and hydrogen. The nitrogen then diffuses onto the surface of the material creating a nitride layer. This process has existed for nearly a century, though only in the last few decades has there been a concentrated effort to investigate the thermodynamics and kinetics involved. Recent developments have led to a process that can be accurately controlled. The thickness and phase constitution of the resulting nitriding layers can be selected and the process optimized for the particular properties required.

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