Vliv fosfátování na výsledné povrchové vlastnosti vybraných konstrukčních ocelí

Abstract

The aim of this thesis was to analyze the influence of chromium content in structural steels on the phosphating process, with a special focus on activation failure and the morphology of the resulting phosphate layer. Six reference materials with graded chromium contents were used, ranging from the lowest (0.053 % Cr) to the highest (1.044 % Cr). Surface morphology was assessed by optical microscopy and SEM, while chemical composition and phase distribution were determined by EDS and XRD. Polarization measurements confirmed the conductive nature of the layers, indicating no significant barrier effect. The results showed that low chromium content promotes the formation of larger activation nuclei and the subsequent development of a compact, fine-grained phosphate layer with prismatic (block-shaped) crystals, whereas higher chromium content leads to surface passivation, fewer and smaller activation sites, and the growth of coarser lamellar or rounded crystals due to the dominance of the phosphophyllite phase. The orientation of samples in the bath was found to affect both the rate and uniformity of the layer’s mass gain.