Galvanneal Coating of Galvannealed Steel Sheet Fracture Research by Dynamic Tensility

Dynamic tensility experiment has been done to research Galvanneal coating fracture of Galvannealed steel sheet with in-situ SEM observation and Galvanneal coating Fracture has been analysed. It is been thongt that desquamation takes place at the interface of substrate /Γ phase. The Fracture of Γ phase is serrated and its thickness is hundreds of nano-metres. The Fracture shape of Γ phase is different from other phases of of the galvanneal coating.

Formation of Γ Phase on Hot-Dip Galvanized Coating Steel Sheet after Various Heat Treatment

Among those intermetallic phases in Zn-Fe system formed in the hot-dip galvanized coating and/or galvanneal coating, the microstructure of Γ phase was the least mentioned. The Γ phase form in the coating layer is usually too thin to observe by a microscope. However, it has been reported that the performance of coating is closely related to the microstructure of Γ phase. Tokunaga et al. has reported that the cracks were generated from the Γ layer or Γ+δ layer. Y.Lin et al. demonstrates that coherent interface forms between Γ and steel interface on annealed electrogalvanized steel sheets indicating that failure would not occur at this interface.Samples used in this study were lab-made hot-dip galvanized steel sheets. To investigate the microstructure of coating, especially the Γ phase layer, specimens were heated to create the designed layer interface. It was found that the heat-treated conditions ranged from 700°C to 750°C for one hour was appropriate to observe the nucleation and growth of Γ phase layer.