Core hardness
Core hardness is the hardness in the center of a hardened part, away from the surface. It affects toughness and fatigue strength.
Physical-Chemical Mechanism of Action
Core hardness results from heat-treated metal structures, especially in steels. In the hardening process, the material is heated to a high temperature and then rapidly cooled, forming a glass-hard structure like martensite.
Metallurgical Relevance & Welding Risks
Uneven core hardness can lead to cracks and fracture in the component. If martensite content is too high (too fast cooling), the material becomes hard and prone to hot cracking. Too slow cooling can lead to a too-soft core structure, reducing toughness.
Shop Practice & Instructions
To ensure uniform core hardness, it is crucial to maintain the correct cooling conditions. This involves using cooling water or gases at the right temperature and with the proper quenching method. The time and temperature of the hardening medium and the cooling rate must be precisely met to achieve optimal core hardness.