STRAIN-INDUCED NUCLEATION OF MNS IN ELECTRICAL STEELS

The nucleation of MnS was investigated during the creep of electrical steels. Precipitation start (P(s)) times were measured in the temperature range from 800-degrees-C to 1100-degrees-C. Direct evidence regarding the locations of the nucleation sites was obtained by means of electron microscopy. The results show that both dislocations and grain boundaries act as nucleation sites for such strain-induced precipitation. The experimental data were analyzed using classical nucleation theory, on the basis of which it is demonstrated that nucleation at grain boundaries is dominant at the higher testing temperatures. The P(s) values in this temperature range are determined by the corresponding nucleation rate. As the temperature is decreased, however, nucleation on dislocations becomes more important. This is due to the additional driving force contributed by deformation-induced vacancies, as well as because the higher dislocation densities at the lower temperatures provide a higher density of potential nucleation sites. In addition, the influence of the growth of these particles following nucleation is considered in the analysis pertaining to the P(s) curves.