CONTROL OF MICROSTRUCTURE OF FE-B MICROCRYSTALLINE MATERIALS

The correlations between hardness, microstructure and heat-treatment c ondition of Fe-B microcrystalline materials were systematically invest igated. The means of controlling microstructure by adjusting compositi on and, thus, the type of boride was also explored. It was established that the grain size of the matrix phase was determined by the volume fraction of dispersive boride particles, and their size follows the fo rmula: D(max) = 4/3 rBAR/f and, in turn determines hardness which obey s the Hall-Petch relation: H(V) = H(O) + kd-1/2. It was also found tha t the size of the boride particles increases exponentially with increa sing temperature and linearly with the fourth root of holding time. M3 B2 has a lower coarsening rate than M2B; therefore, promoting M3B2 and inhibiting M2B is an effective measure to stabilize the microcrystall ine structure under hot exposure.