Genomhärdade

Genomhärdade refers to a class of steels and iron alloys that are hardened uniformly throughout their cross-section by a high-temperature heat treatment, rather than only at the surface. The term is commonly used in Swedish metallurgy to describe through-hardening processes, distinguishing them from surface-hardening methods such as carburizing or nitriding.

The typical through-hardening process involves heating the material to a high austenitizing temperature, followed by quenching to form martensite throughout the entire section. After quenching, tempering is usually performed to adjust hardness and relieve internal stresses. The choice of alloy and carbon content determines the achievable hardness and toughness, and some steels may require additional steps or controlled quenching to minimize distortion or cracking.

Materials commonly through-hardened include certain plain carbon steels and alloy steels, as well as some martensitic stainless steels. The resulting microstructure is martensitic across the component, which provides a combination of high strength and uniform hardness. This makes through-hardened parts suitable for applications demanding consistent wear resistance from surface to core, as well as predictable mechanical properties under load.

Advantages of genomhärdade components include uniform hardness, improved core strength, and reliable performance in demanding applications such as gears, shafts, fasteners, and certain types of bearings and springs. Limitations include potential distortion from rapid cooling, brittleness if over-tempered, and higher processing costs compared with some surface-hardening routes. Selection depends on required hardness, toughness, geometry, and service conditions.

See also: case hardening, martensitic steels, heat treatment, tempering.