Research on self-propagating eutectic boriding

In this paper, preliminary research has been undertaken on self-propagating eutectic boriding. The results show that with boron carbide (B4C) as the boriding agent and heated by the energy released by thermite reaction during the process of self-propagating combustion, a layer of eutectic or hypoeutectic structure can be formed on the surface of steel with the thickness of up to 1.5 mm or so. The microstructure of the layer varies with the consumption of the thermite as well as with the alloy composition of the matrix. The phase of the layer consists mainly of α-Fe, Fe3(C,B) and some Fe2B and Fe23(C,B)6. The process of eutectic boriding is as follows: at the high-temperature produced by the thermite reaction, chemical reaction occurs between boron carbide B4C and γ-Fe on the sample surface, with Fe2B, Fe3C produced, which reacts with the γ-Fe immediately. Also, Fe–C–B alloy is produced in the liquid phase, which transforms into eutectic structure at room temperature.