Rehardening

Rehardening is a heat treatment process aimed at restoring or increasing a material’s hardness after it has become softened by previous processing, wear, or aging. It is commonly applied to metals, especially steels, but can also involve ceramics and some polymers in specialized contexts.

In steel, rehardening often follows a loss of hardness caused by tempering, deformation, or extended use. The typical approach is re-austenitizing the steel by heating to a temperature that forms austenite, holding to dissolve existing phases, and then quenching to transform the austenite back into martensite. A subsequent tempering step may be used to achieve a desired balance of hardness and toughness. Some tools and components are rehardened in localized regions using surface methods, such as induction hardening or flame hardening, to reestablish a hard surface while preserving a softer interior.

Surface rehardening methods extend the life of parts subject to wear at the surface, including gears, shafts, and cutting edges. Carburizing, nitriding, or other surface-pocusing treatments can create a hard, wear-resistant outer layer without fully hardening the entire cross-section.

Process considerations include potential distortion, cracking, grain growth, and embrittlement from multiple cycles. The choice of method depends on material composition, geometry, desired final properties, and economic factors. Hardness is typically verified through standard tests such as Rockwell or Vickers along with microstructural analysis.

Rehardening is one option among heat treatment strategies, used to restore wear resistance and extend component life, or to refresh a worn edge, often in combination with or as an alternative to other surface-hardening techniques.