Brittle to ductile transition – An engineer’s point of view

•Main results of BDT analysis vs. scale of analysis are summarized.•Engineering/phenomenological interpretation of BDT is proposed.•BDT results from stress assisted thermally activated nature of dislocation activity.

Knowledge of mechanisms and governing parameters of various modes of damage to structural materials is very important in numerous aspects of practical physical metallurgy–steel production, manufacture of welded joints with required properties, or identification of damage causes in industrial accidents. The apparently simple task of finding a literature source with clear physical–metallurgical interpretation of the reasons for BDT (brittle-to-ductile transition) in steel and other body-centered cubic metals was found to be quite an intricate problem, since an unequivocal and comprehensive theoretical concept of BDT is still missing. Based on the main results of a literature survey a phenomenological explanation of the existence of BDT is presented.