This study investigates the microstructural evolution, mechanical performance, and electrochemical corrosion behavior of nanocrystalline boride layers formed on an Fe-20Cr-5Al ferritic alloy by pack boriding at 950 degrees C for 4 h. X-ray diffraction (XRD) and scanning electron microscopy/energy-dispersive X-ray spectroscopy (SEM/EDS) analyses confirmed the formation of a hierarchical boride layer approximately 80-85 mu m in thickness, consisting of orthorhombic (Fe,Cr)B and tetragonal (Fe,Cr)(2)B phases at the surface and (Fe,Cr)(23)(C,B)(6) carboboride phases in the diffusion zone, the latter attributed to the carbon push-ahead mechanism. Rietveld refinement yielded a quantitative phase fraction of 51.9 wt.%. (Fe,Cr)B, 46.1 wt.% Fe2B, and 2.0 wt.% (Fe,Cr)(23)(C,B)(6), with a theoretical boride layer density of 7.40 g cm(-3). Williamson-Hall analysis yielded an average crystallite size of 50.7 nm and a microstrain of 1.686 & times; 10(-3), confirming the nanocrystalline character of the boride phases. Mechanical evaluation revealed a similar to 9-fold increase in surface hardness in Fe20Cr5Al-B relative to Fe20Cr5Al, reaching 1854 HV (18.18 GPa). Tribological testing demonstrated an similar to 18-fold reduction in wear rate (from 3.29 & times; 10(-4) to 1.82 & times; 10(-5) mm(3)/m) and a 14.5% reduction in the coefficient of friction (0.76 -> 0.65), confirming the effectiveness of the boride layer as a tribological barrier. However, electrochemical analyses in 5 wt.% H2SO4 revealed a paradoxical deterioration in corrosion resistance: despite a noble shift in Ecorr from -0.459 to -0.295 V, the corrosion rate increased similar to 4-fold (from 9.67 & times; 10(-3) to 3.83 & times; 10(-2) mm/year), driven by Al-repulsion-induced passive film loss and micro-galvanic cell formation through micro-crack and porosity networks. These findings emphasize that while pack-boriding is highly effective for tribological enhancement of FeCrAl alloys, minimizing boride layer defects is essential to achieve concurrent corrosion protection in acidic environments.