retempering

Retempering is a secondary heat-treatment applied to steel after an initial tempering step. It involves heating tempered steel to an additional tempering temperature, or adjusting the tempering temperature in a subsequent cycle, in order to refine the material’s properties and relieve residual stresses that may have developed during later processing such as machining, forming, or welding.

Purpose and effects

The main goal of retempering is to achieve a better balance of hardness and toughness for the intended service conditions. Retempering can help relieve tensile or localized stresses, improve dimensional stability, and reduce brittleness introduced by subsequent work. The exact effect depends on the alloy and the temperatures used; hardness typically decreases with tempering while toughness and ductility can improve. In some cases, retempering is used to correct an over-tempered condition or to homogenize microstructure after nonuniform heating.

Process considerations

Retempering temperatures are chosen based on the alloy composition and the target properties. The steel is heated in a controlled furnace to the selected tempering temperature, held for a specified time to allow diffusion and stress relief, and then cooled, usually in air or in a furnace. Some applications use a two-stage schedule with different tempering temperatures to fine-tune hardness and toughness. The effectiveness of retempering depends on accurate temperature control and knowledge of the material’s heat-treatment response.

Applications and limitations

Retempering is used for carbon and alloy steels, particularly tools and high-strength components, when post-tempering processing has altered performance. It is not universally beneficial; excessive or inappropriate retempering can lead to unwanted softening and reduced wear resistance. As with any heat treatment, decisions should be based on material data and service requirements.

See also: tempering, quench and temper, heat treatment of steels.