Morphological Characterization of Fe2B Borided Layers on AISI 9254 Steel Using Reused Boron Paste: A Classical and Fractal Approach

Boriding is a widely used thermochemical treatment to improve surface hardness and wear resistance in steels used in demanding mechanical applications. However, boronizing processes using new boron paste increase costs and generate waste, creating a need for more sustainable alternatives. In this context, the reuse of dehydrated boron paste has proven effective in the formation of Fe2B layers on AISI 9254 steel. In this study, AISI 9254 steel was boronized using reused dehydrated boron paste at 1173 K, 1223 K, and 1273 K for 3600, 7200, 10,800, and 14,400 s. Optical microscopy revealed layer thicknesses ranging from 16.07 μm to 69.35 μm. X-ray diffraction confirmed the formation of single-phase Fe2B, while EDS indicated elemental redistribution within the layer. The Vickers microhardness profile characterized the mechanical behavior, and the adhesion force showed HF1-HF2 ratings. The activation energy for boron diffusion in Fe2B was calculated at 106.567 kJ mol−1. Auto-affine analysis verified the fractal nature of interface growth, with a scale ω(d) according to ω(δ)∼δH. These results confirm that reused paste allows the formation of Fe2B layers, supporting sustainable boronization strategies with controlled interfacial evolution.