The structure of alloys of boron-rich corner of Fe–В–C phase diagram

The structure and microdurometric characteristics of the Fe–В–С alloys in the range of high concentration of boron (>16.0 wt. % B) and low concentration of carbon (0.1 wt. % С) were investigated in this work. The methods of quantitative metallographic, X-ray, differential thermal, fluorescent spectral and microdurometric analyses were applied. Carbon was established to dissolve completely in phase constituents of the investigated alloys, forming solid solutions based on iron borides FeB, FeB2, FeB~4 or FeB~19. It was suggested the existence of one eutectic transformation between borides FeB2 and FeB~4 as well as two peritectic transformations between borides FeB and FeB2 or FeB~4 and FeB~19 correspondingly in the studied concentration range. The formation of boride FeB~4 was explained by its stabilization in the presence of carbon in the alloys. After annealing in vacuum at 900 C for 10 hours with following quenching, the structure became coarser, but no traces of phase decomposition were revealed in the most alloys. Microhardness of the phases observed in the structure of the investigated alloys increased in the following sequence: FeB→FeB2→FeB~4→FeB~19.