合金化溶融亜鉛めっき鋼板の耐パウダリング性に及ぼすめっき皮膜構造の影響

抄録

Effect of coating structure on powdering resistance of galvannealed steel sheet was investigated and the followings are clarified.
1)Higher galvannealing temperature deteriorates powdering resistance. But slower cooling from higher temperature (500550°C) improves powdering resistance.
2)In the case of lower galvannealing temperature (=440°C), the powdering resistance is rather good, although the cooling rate doesn't affect powdering resistance.
3)Exfoliation of galvannealed steel sheet after tensile test correlates with amount of powdering evaluated from draw bead test.
4)Γ₁-phase (Fe₅Zn₂₁) is formed along the interface of coating galvannealed at lower temperature (≤500°C) or cooled slowly from high galvannealing temperature.
5)The decrease of Γ₁ ratio [Γ₁/(Γ+Γ₁)] deteriorates powdering resistance.