kernhardheid

Kernhardheid, or core hardness, is a term used in materials science to describe the hardness of the interior region of a material after it has undergone surface-hardening treatments. It contrasts with the hardness of the outer surface or case, which is typically much higher to provide wear resistance.

In practice, kernhardheid is relevant for components that are produced by processes such as carburizing, nitriding, or induction hardening. These treatments create a very hard outer layer while aiming to preserve a tougher, more ductile core. The core hardness depends on alloy composition, heat treatment parameters, and the thickness of the hardened case.

Assessing kernhardheid involves creating a hardness profile across a cross-section of the part. Indentation tests, such as microhardness (Vickers or Knoop) or nanoindentation, are performed from the surface toward the interior. The results are plotted as hardness versus depth. The core hardness is identified as the plateau value in the inner region, away from the influence of the hard surface layer, or defined at a specified depth according to standards or agreed practice.

The concept is important for balancing wear resistance with toughness. A high surface hardness improves wear performance, while an appropriate core hardness helps resist bending and crack propagation. Factors that influence kernhardheid include carbon content, alloying elements (such as chromium, molybdenum, vanadium), heat-treatment temperatures and quenching rates, and the thickness of the hardened layer. Limitations include spatial variation and the fact that hardness alone does not fully predict performance in fatigue or impact loading.