Boronizing of Sintered Iron Compacts with Ferroboron and Sodium Carbonate Mixture

Abstract

The effects of the boronizing temperature and time, the sintered density, and the addition of alloying elements on the formation of the boride layer in sintered irons treated with the mixed powder of 80 wt% Ferroboron and 20 wt% Na²CO³ were investigated by microscopic and SEM's examinations, X-ray diffraction and EPMA's analysis. The following results were obtained.
(1) The microscopic examination and X-ray diffraction showed that the boride layer consisted of two phases of FeB in the outer layer and Fe²B in the inner one.
The thickness of boride layer was independent of the density of sintered iron compact.
(2) The boride layer of sintered Fe and Fe-alloyed compacts increased with increasing boronizing temperatures and times in according with parabolic law.
(3) The rate of growth of the boride layer in sintered Fe-C, Fe-Mo and Fe-Ni compacts was inhibited with increasing the addition of alloying elements.
The EPMA's analysis showed that a very considerable concentration of such as C, Mo and Ni occurred at the interface zone between the boride layer and the matrix.