Alを含む溶融亜鉛による鉄の溶食について

Abstract

For the purpose of studying the attack of hot dip galvanizing bath against the kettle and the coating machine, the authors made experiments on attack against various kinds of carbon steels (C: 0.02-0.2%) with molten zinc bath containing aluminum (0-0.3%) at 440-480°C. The results obtained were as follows: (1) In the zinc bath containing no aluminum, the attack on steels due to the reaction of Fe-Zn always conformed to the “Law of parabolic attack”. However, when aluminum was contained in the bath, the reaction of Fe-Zn passed the following three periods: Inhibition period→Acceleration period→Regular period (conforming to the “Law of parabolic attack”). (2) The duration of each of inhibition and accaleration periods was longer with the increase of aluminum content and the drop of bath temperature. (3) The reaction velocity for attack after reaching the regular period increased with the increase of aluminum content and the rise of bath temperature. (4) The iron loss constant in the reaction of regular period in the bath containing aluminum was expressed by the following formula: C=K[Al%]n: where C: Iron loss constant [(g/cm2)2/min.]×10-8, n: Reaction index, K: Reaction coefficient, (Values of n and K varied according to the kind of steels and bath temperature). (5) The activation energy in the reaction of regular period (Q kcal/mol) for the bath containing aluminum was markedly greater than that for the bath containing no aluminum. In other words, the attack on steels with the bath containing aluminum was remarkably accelerated by a slight rise of temperature.