An alternative method of gas boriding applied to the formation of borocarburized layer

The borocarburized layers were produced by tandem diffusion processes: carburizing followed by boriding. An alternative method of gas boriding was proposed. Two-stage gas boronizing in N2–H2–BCl3 atmosphere was applied to the formation of iron borides on a carburized substrate. This process consisted in two stages, which were alternately repeated: saturation by boron and diffusion annealing. The microstructure and microhardness of produced layer were compared to those-obtained in case of continuous gas boriding in H2–BCl3 atmosphere, earlier used. The first objective of two-stage boronizing, consisting in acceleration of boron diffusion, has been efficiently implemented. Despite the lower temperature and shorter duration of boronizing, about 1.5 times larger iron borides' zone has been formed on carburized steel. Second objective, the absolute elimination of brittle FeB phase, has failed. However, the amount of FeB phase has been considerably limited. Longer diffusion annealing should provide the boride layer with single-phase microstructure, without FeB phase.

► Alternative method of gas boriding in H2-N2-BCl3 atmosphere was proposed.
► The process consisted in two stages: saturation by boron and diffusion annealing.
► These stages of short duration were alternately repeated.
► The acceleration of boron diffusion was efficiently implemented.
► The amount of FeB phase in the boride zone was limited.