2018 Volume 58 Issue 9 Pages 1623-1628
In the manufacture of high tensile strength sheet steels (HSS) containing Cr and Mn, selective surface oxidation of Cr and Mn affects the wettability of the HSS with molten Zn and leads to coating defects in the hot-dip galvanizing process. Therefore, it is important to clarify the selective surface oxidation behavior of Cr- and Mn-bearing steel from the viewpoint of active utilization of galvannealed HSS.
The focus of the present study is an investigation of the influence of the amount of Cr addition on selective surface oxidation, which is thought to determine the wettability of cold-rolled HSS containing 0–0.6 mass% Cr-1.7 mass% Mn with molten Zn. The wettability was investigated by measuring the contact angle of molten Zn containing 0.14 mass% Al (Zn–Al) on the HSS. Surface and cross-sectional analyses were performed using secondary and transmission electron microscopes. Selective surface oxidation behavior was investigated by glow discharge spectroscopy.
The main results obtained are as follows. The contact angle of Zn–Al on the HSS tended to decrease as the amount of Cr addition increased up to 0.6 mass% due to the increment of MnCr2O4, which is known as Cr–Mn spinel and reacts with molten Al more easily than MnO.
