Corrosion of press-hardened galvanized steel

Press hardening of hot-dip-galvanized steel sheet yields an innovative product with high strength and reduced weight with drastically increasing industrial importance. This process results in an austenitisation of the steel and a conversion of the 10 μm Zn layer into a 20 μm thick coating consisting of zinc saturated α-iron and Γ-FeZn-phases. A 5-times longer protection is found in cyclic corrosion tests. The mechanism is a combination of the increase of the coating thickness, cathodic protection and the barrier properties of simonkolleite in the corrosion products. Simonkolleite-Zn5(OH)8Cl2, hydrozincite-Zn5(CO3)2(OH)6 and akaganeite-β-FeOOH were identified as corrosion products by XRD, FT-IR and Raman spectroscopy.

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► Corrosion performance of press hardened galvanized steel was studied..
► The thermal–mechanical process forms Zn saturated α-Fe and intermetallic Γ-ZnFe..
► Cathodic protection of this coating slows down corrosion by a factor of 5..
► Simonkolleite, hydrozincite, and akaganeite were identified by IR, Raman and XRD.