A hvem study of the roles of dislocation movements and vacancy flow during dissolution of cementite in steel

Abstract

Dislocation mechanisms during dissolution of cementite particles in a plain carbon steel have been investigated in situ by high voltage electron microscopy. During dissolution of remaining particles of cementite in austenite above the eutectoid temperature, dislocation helices, loops and complex dislocation configurations in the austenite are formed from the interfaces to the particles. Dissolution of cementite in ferrite during austenitization and decarburization at about 700°C also causes the formation and movement of dislocations in the ferrite matrix. The dislocation movements are somewhat different from those in austenite. The configurations of dislocations depend on the dissolution rate and the shape of the particle. When the dissolution rate is sufficiently slow, the particle dissolves without appreciable formation of helices or loops. The critical misfit at which dislocations nucleate and start to move at the interface between matrix and particle during decarburization is estimated to be in the order of 10 −3. The contribution of dislocation movements as a stress relieving mechanism during dissolution of cementite in ferrite and austenite is also estimated.