The transition temperature (English: Nil-ductility temperature NDTT or ductile-brittle transition temperature DBTT ) denotes a temperature between the upper and lower layers of a material in terms of its toughness properties. When cooling below the transition temperature, there is a sharp drop in the impact work that is consumed on a test specimen in the notched impact test .
This is particularly important for standard steels with a body-centered cubic crystal system (krz) , as they become brittle below the transition temperature . The need for the construction of workpieces to be considered from this material with respect to the expected operating temperature.
The transition temperature is influenced by the chemical composition (in particular by the "steel pests" hydrogen and nitrogen ), grain size , heat treatment condition, etc. As this is a continuous transition, various definitions have been worked out (e.g. 27 J in the notched impact test or 50 % Brittle fracture fraction in the Battelle drop weight tear test ).
Historically, this topic was particularly studied in technology when warships of the Liberty class were often lost on their northern route in the Arctic Ocean or even in port, often without enemy action.