1. According to thermodynamic calculations, in the initial stage boronizing may occur through a dual mechanism: simultaneous active diffusion of atomic boron and direct reaction resulting in the formation of higher iron borides. 2. It is demonstrated that in powder boronizing the nature of the activator has a pronounced effect on the concentration and character of distribution of pores in the boride layer and hence on the quality of the resultant coating. 3. On the basis of data yielded by thermodynamic calculations and experimental results it is shown that iron oxides can be successfully employed as activators of the powder boronizing process. 4. Experiments have shown that a powder mixture consisting of 80% boron carbide and 20% magnetite is comparable in activity to mixtures with halide activators, but surpasses them in other respects: It possesses good processing characteristics, is nontoxic, shows no sinterability, and is capable of being used repeatedly without regeneration. 5. Mixtures with oxygen transport of boron offer greatest promise for the boronizing of high-alloy stainless steels.