Efect of inter‑critical annealing atmosphere on microstructure and subsequent corrosion behavior of hot‑dip galvanized Mn containing high‑strength steel

Abstract

A systematic study is performed on the development of hot-dip galvanized coatings on a Mn-containing high-strength steel sheet by varying the dew point (− 50, − 10, and +10 °C) during inter-critical annealing of the steel strip at 800 °C. It also studies the efect of dew point on the corrosion behavior of the coatings in freely aerated 3.5 wt% NaCl solution. The reducing gas atmosphere consists of 95% N2 and 5% H2, where inter-critical annealing is carried out. Surface oxidation of the steel has a strong efect on the development of sound coating. A defect-free adherent galvanized coating is obtained on the annealed steel surface at a fxed dew point of +10 °C, and it is attributed to the fne and continuous compact Fe-Al crystals compared to galvanized coatings produced at other dew points as well as the highest atomically dense (0002) basal plane. This also leads to the lowest corrosion rate (~0.164 mm y−1, where mm and y stand for millimeter and year, respectively) of the galvanized coating produced at a dew point of +10 °C when compared with galvanized coatings produced at dew points of − 50 °C (~0.279 mm y−1) and −10 °C (~0.259 mm y−1). The lowest corrosion rate of the galvanized specimen developed at +10 °C dew point can be attributed to the uniform and defect-free coating surface, together with the dominance of the more atomically dense (0002) basal plane.