Heat treatment processes

Published:  08 June, 2018

Q: Several heat treatment processes are available for gears, what’s the difference between them? The answer to this month’s trouble shooter question is provided by Dennis Lawson, gear expert with R. A. Rodriguez.

A: For many applications, heat treatment is essential for improving both the surface and core hardness of the gear, enhancing its ability to withstand tensile stress, improve strength and reduce wear and tear. These processes can be to treat the whole gear or just focused on the teeth themselves and among the most common are carburizing, induction hardening and nitriding.

Carburizing is a heat treatment performed to create a hard, wear-resistant surface of low carbon steel but it should be noted that the precision of carburized gears declines in the process so to maintain gear accuracy, grinding is essential.

The same caveat applies to gears that are induction hardened. This form of heat treatment is most often used for hardening teeth on gears made from steel containing more than 0.35% carbon. It is particularly suitable for strengthening large gears that cannot be carburized.

Nitriding is performed to harden the gear surface by introducing nitrogen to produce a very hard, but super smooth surface finish. It is commonly used for steel alloys that include aluminium, chrome and molybdenum as they enhance the hardening process. It gives a hardness higher than carburizing and induction hardening but the hardened layer is thinner. Importantly though, as the temperature for nitriding is relatively low – up to 600°C as opposed to 800°C for other processes – it causes no quenching cracks or distortion.

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