Abstract The present study concerns the development of a new pack-boriding process which is simple, economical, original and industrially reliable. Three agents essential for the formation of satisfactory boride surface layers have been defined: an activator (BF 3 gas), an oxide moderator (silica: acid-washed sand) and a boriding agent (finely powdered boron carbide diluted with SiC). In the laboratory and industrial reactors, the BF 3 gas passes first through silica ( T > 450 °C) and then through a layer of boron carbide containing the samples (900 < T < 1100 °C). Gaseous phase boriding is also possible with the same reactants; the samples are placed immediately after the boron carbide layer, either directly in the gas stream or in a bed of SiC. The results obtained on carbon steels are satisfactory (single-phase acicular Fe 2B). The boride layer also adheres well to high chromium steels but unsatisfactory results are obtained with very highly alloyed steels such as 18-10 stainless steel.