Rapid Heating Process of High Strength Steel Zinc-Iron Coated Plate and Its Effect on Deformation Characteristic

The high strength steel zinc-iron coated (GA) sheet with the dual functions of barrier protection and cathodic protection has broad application prospects in the field of boron steel hot stamping. The essential issue for the industrial application of the zinc-iron coating sheet for hot stamping is how to achieve the optimal balance between the microstructure, morphology, and protective performance of the coating and the properties of the steel by adjusting the heat treatment process. In this paper, a novel step-type rapid heating process path is presented that can achieve short-time alloying of the coating and less Zn loss while ensuring sufficient austenitization of the matrix. The heating process is divided into two stages. The first stage is called the pre-oxidation process, which is used to promote the formation of a continuous oxide layer on the surface of the coating, thereby effectively inhibiting the loss of zinc at high temperature, and ultimately increasing the effective Zn content of the coating. The second stage is the austenitizing process to ensure the complete austenitization of the matrix. The experimental results show that the average thickness of the fully alloyed coating is increased by 23.3%-28.7% compared with the direct rapid heating process, and the average Zn content is increased by 14.3%-17.2% compared with the radiation heating process. The effect of the rapid heating process on the deformation and cracking of the coating was then investigated. The test results show that when the holding time is 20 s, the deformation temperature to avoid premature fracture of the coating sheet is lower than 750 ℃. When the dwell time is extended to 50 s, the critical forming temperature is increased to 780–820 ℃.