nitrocarburizing

Nitrocarburizing is a surface hardening treatment in which nitrogen and carbon are diffused into the outer layers of ferrous alloys to form a hard diffusion zone beneath a superficial nitride-containing layer. The process increases surface hardness and wear resistance while preserving the toughness of the core material.

Common variants include gas nitrocarburizing, salt-bath nitrocarburizing, and plasma (ion) nitrocarburizing. Gas nitrocarburizing uses ammonia-containing atmospheres at temperatures typically around 520–570 C; salt-bath nitrocarburizing employs molten nitriding/carbiding salts at similar temperatures; plasma nitrocarburizing utilizes a glow discharge in nitrogen- and hydrocarbon-bearing gases, often at lower pressures. Treatment times range from about 30 minutes to several hours. After treatment, a diffusion zone enriched with nitrogen and carbon, overlain by a compound layer dominated by iron nitride (epsilon-Fe2-3N), forms. A post-treatment oxidation or sealing step may be applied to enhance corrosion resistance.

Properties and benefits of nitrocarburizing include increased surface hardness (often in the 600–900 HV range, depending on alloy and process), improved wear and fatigue resistance, and reduced friction when lubricants are present. Corrosion resistance can be modestly improved, especially with subsequent oxidation or sealing. The method typically produces a shallow case, allowing dimensional stability and good integrity in complex shapes.

Applications span automotive components such as gears, shafts, cams, and fasteners, as well as machine tools and hydraulic components. Limitations include potential decarburization of certain steels, the use of hazardous salts in some variants, and the need for controlled post-treatments to maximize corrosion resistance.