In situ observation of dissolution of cementite in steel

SUMMARY The mechanisms of dissolution of cementite particles in steel have been studied in situ by high voltage electron microscopy. This method permits direct, continuous observations of the process and provides new information which has not been obtained without this technique. During dissolution of cementite particles in austenite at about 770°C, dislocation helices, loops and complex dislocation configurations are formed from the interfaces of the particles. Dissolution of cementite in ferrite during decarburization at about 700°C also causes the formation and movement of dislocations. However, in contrast to the case of dissolution in austenite, the emission of dislocation loops and helices has not been observed. The migration of crystallographic and noncrystallographic interfaces has been observed during the ferrite to austenite transformation. The noncrystallographic interface is apparently attracted to the cementite particles. The migration rate of the noncrystallographic interfaces is five to ten times faster than that of the crystallographic interface.