Nachhärten

Nachhärten is a post-hardening heat treatment applied to metal components to restore or increase hardness after a prior process has softened the material. It is used when forming, machining, or previous heat treatment reduces hardness or wear resistance. There are two general approaches: bulk re-hardening, where the entire part is heated to the hardening range and then quenched, and surface hardening, where only a surface layer is hardened to provide a hard exterior while maintaining a tougher core. The choice depends on alloy, desired hardness, and dimensional tolerances.

Common methods include re-quenching to the hardening range followed by quenching, and surface methods such as induction hardening, flame hardening, or laser hardening. Nachhärten is often followed by tempering to adjust brittleness and toughness. Applications include gears, shafts, tools, dies, and components that require high wear resistance after deformation or finishing.

Considerations include the risk of distortion due to thermal cycles and residual stresses, the need for precise temperature control, and compatibility with the alloy. Quality control typically involves hardness testing (e.g., Rockwell), microstructure inspection, and sometimes residual stress evaluation. In some industries, Nachhärten is used interchangeably with post-quenching hardening or surface hardening, but definitions vary by context.