THE EFFECT OF CARBON ON THE CHARPY V-NOTCH DUCTILE-BRITTLE TRANSITION CURVE

The literature on the microstructures and Charpy V-notch ductile-brittle transition curves for normalized or annealed irons and plain carbon steels have been reviewed. Up to about 0.10 wt.% carbon the microstructure has grain and sub-grain structures with a grain boundary carbide and, towards the top of the range, some limited pearlite. From about 0.10 wt. % to about 4.5 wt. % the microstructure consists of pearlite colonies in a matrix of ferrite. From about 4.5 wt. % carbon to the eutectoid composition (0.80 wt. % carbon) the microstructure consists of grain boundary proeutectoid ferrite and pearlite in the rest of each grain. Each type of microstructure leads to a distinguishable type of ductile-brittle transition behavior. A phenomenological model of the transition has been developed in which the Charpy V-notch impact energy is expressed as a function of carbon content and temperature. This model has been shown to describe the main features of the transition but has yet to be fully tested. *Alan A. Johnson (m) has a Ph.D. in metal physics from Imperial College, London University. He ha