Martempering – Definition, Benefits, Applications

Martempering, also known as hot bath quenching, is a heat treatment process for steel. It is a special process that is only used when distortion and high residual stresses play a role. In this process, the parts are quenched from the austenitizing temperature in a hot bath oil, fluidized bed or molten salt just above the martensite starting temperature Ms. As a result, the core and the edge zone of the parts are brought to and maintained at almost the same temperature. The workpiece is removed from the quenching medium after a sufficient holding time. The workpiece is then quenched further, usually with air cooling at room temperature. The advantage of air cooling is that it prevents the formation of thermal stresses. This heat treatment method is more expensive than other quenching or tempering processes, as the quenching oils used have to be specially mixed from quality base materials and extensive antioxidants.

The benefits of martempering

Hot martempering is a process that is similar to conventional quenching methods, with the difference that it reduces the residual stress and distortion in steel parts. This minimizes the formation of cracks during quenching, improves the absorbed impact energy and achieves higher fatigue resistance. These properties are achieved through lower thermal gradients during quenching. In addition, the martensite transforms evenly, which is also a positive factor.

On which parts and materials is martempering applied on?

As martempering reduces the thermal residual stresses of steel workpieces, it is mainly used when parts with complex geometries, different weights and changes in cross-section need to be hardened.

As the main advantage of hot bath hardening is the elimination of cracks and the reduction of distortion, alloy steels are more suitable for this application. However, any steel grade that responds to oil quenching can be martensitically hardened.

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