Further surface treatment aspects in galvanizing iron single crystals

Hydrogen-atmosphere galvanizing of single-crystal and polycrystal samples of four different types of iron with various surface pretreatments was investigated to more conclusively identify the reaction effects of substrate crystallographic orientation and surface treatment. This work forms part of a broader program, supported by the Canadian Galvanizing Research Association, to investigate the role of various parameters of the steel base in the galvanizing reaction. A relationship between galvanizing reactivity and iron crystallography was established for only the Cambridge iron containing 0.02% silicon. Electropolished crystals of this material showed unusually high reactivity which varied on the principal low-index surfaces, decreasing in the order (111), (110) and (100). Electropolished samples of Cleveland (Armco), Ferrovac E and enamelling iron galvanized normally, independent of crystallographic orientation. Reaction on smooth-surfaced crystals generally proceeded in two stages defined by a rate change near the 2.5-min immersion time. Roughening of the crystal surface by shot blasting reduced the reactivity of the Cambridge iron almost to the level obtained for the "normal" galvanizing materials and largely eliminated the differences related to crystallographic orientation. In supplementary tests, electropolished and mechanically polished Cambridge (110) crystals showed identical orientation related reaction behaviour at short, but not at long, immersion times, depending on the method of galvanizing. X-ray analyses of surface strain in a mechanically polished and hydrogen-annealed Cambridge (110) crystal indicated that no recrystallization had occurred. Thus the crystallographic effect on galvanizing was unchanged. Variable reaction effects found with the Cambridge iron emphasize the importance of the substrate surface in the galvanizing reaction. The exceptionally high response of specific crystallographic orientations may have possible connection with outbursts of iron-zinc alloy growth which frequently occur in galvanized coatings on commercial steels.