A ferrous alloy is formed with a Fe--Cr stainless steel having a Vickers hardness of 400 or more as a substrate and a Fe--Al diffusion layer having a thickness of 2 to 50 .mu.m. The diffusion layer contains at least 90 vol % of an intermetallic compound of Al and Fe relative to a total volume of the diffusion layer. The Al content included within a depth of at least 2 .mu.m of the diffusion layer is 35 to 65% by weight based upon total weight of a region of the diffusion layer ranging up to the thickness of at least 2 .mu.m. It is preferred to use as the substrate a precipitation-hardening stainless steel comprising 66 to 81.9 wt % of Fe, 15 to 20 wt % of Cr, 3 to 13 wt % of Ni, and one element selected from 3 to 6 wt % of Cu, 0.5 to 2 wt % of Al, and 0.01 to 0.2 wt % of a total of C and N, or a high carbon stainless steel comprising 73 to 89.9 wt % of Fe, 10 to 19 wt % of Cr, 0.1 to 1.2 wt % of C, and less than 3 wt % of Ni. The ferrous alloy may be used for sliding parts such as gears or bearings, and blades of electric shavers or hair clippers.