Temperature, at which in the notched bar impact test the transition from a ductile to a brittle fracture indicates. Above the transition temperature brittle fractures are not to be expected, below cleavage fractures have to be reckoned with.
The temperature at which a transition from ductile to brittle fracture takes place in steel. It is usually determined by making a series of Charpy impact tests at various temperatures, the transition temperature is usually taken as the point where 50% of the fracture is brittle.
(1) An arbitrarily defined temperature that lies within the temperature range in which metal fracture characteristics (as usually determined by tests of notched specimens) change rapidly, such as from primarily fibrous (shear) to primarily crystalline (cleavage) fracture. (2) Sometimes used to denote an arbitrarily defined temperature within a range in which the ductility changes rapidly with temperature.