Bainitát

Bainitát is a metastable transformation product that forms in steel at temperatures between the nose of the pearlite transformation curve and the martensite start temperature. It is a microstructure consisting of ferrite and iron carbide precipitates. There are two main types of bainite: upper bainite and lower bainite.

Upper bainite forms at higher temperatures within the bainite transformation range and typically appears as aggregates of laths of ferrite that are roughly parallel to each other, with carbide particles precipitating between these laths. The carbides in upper bainite are generally cementite (Fe3C) and tend to be elongated and oriented at an angle to the ferrite laths.

Lower bainite forms at lower temperatures within the bainite transformation range. In lower bainite, the ferrite forms as plates, and the carbide precipitates, also typically cementite, are found within the ferrite plates and are oriented parallel to specific crystallographic planes. This gives lower bainite a distinct feathery or acicular appearance.

The formation of bainite involves a complex interplay of diffusion and shear mechanisms. The exact temperature and time at which bainite forms significantly influence its morphology and properties. Bainitic steels exhibit a good combination of strength and toughness, making them suitable for applications such as structural components, tools, and automotive parts. The properties are generally superior to pearlite and can approach those of tempered martensite in certain conditions.