To question about Fe5B3 boride formation in boron-rich Fe–В alloys

Abstract

The structure of boron-rich iron alloys in the concentration range of 9.0–15.0 wt. % В, 0.01–0.17 wt. % C, Fe – the balance (with charge impurities of Si, Al, Mn) was investigated in this work. The methods of metallographic, X-ray, stop-quenching, scanning electron microscopic, energy dispersive, and fluorescent spectral analyses were applied. The FeB- and Fe₂B-based solid solutions are proved to be the major constituents of the investigated alloys. No evidence is found for the possible formation of the Fe₅B₃ boride via peritectic reaction L+FeB→Fe₅B₃ at 1650 K and its further decomposition via eutectoid reaction Fe₅B₃→FeB+Fe₂B at 1410 K. It is shown that the phase under consideration is iron hemiboride alloyed mainly by silicon which peritectically forms from primary crystals of iron monoboride and the rest of liquid at 1650 K. The thermal effect at 1410 K is assumed to be caused by a heat production connected with polymorphic transformation α-FeB→β-FeB in the presence of carbon.