Overhardened

Overhardened is a term used to describe a material, typically metal, that has undergone a heat treatment process intended to increase its hardness, but has been subjected to conditions that result in undesirable properties. This can occur during processes like quenching, where rapid cooling is used to achieve hardness. If the cooling rate is too fast or the material composition is not ideal, internal stresses can build up, or the microstructure can become brittle.

The consequences of overhardening can include reduced toughness, making the material more susceptible to cracking or fracture. In some cases, the material may become so brittle that it is unusable for its intended purpose. This phenomenon is particularly relevant in industries where materials are subjected to significant stress or impact, such as manufacturing, automotive, and aerospace.

Identifying overhardening often involves testing the material's mechanical properties, such as hardness, impact strength, and ductility. Visual inspection might reveal surface cracks. Correcting overhardening may involve further heat treatments like tempering, which reduces hardness slightly but significantly increases toughness by relieving internal stresses and altering the microstructure. Careful control of heating and cooling rates, along with appropriate material selection, are crucial to avoid overhardening in the first place.