Microstructure Transformation Behavior of Oxide Scale of Hot Rolled SPHC Steel for Galvanizing During Heating Process

To analyze microstructure transformation behavior of hot rolled strip scale during heating process in the direct fired section of reduction annealing furnace, the microstructure transformation of oxide scale of hot rolled strip studied by thermal simulation on GLEEBLE3800 test machine. The microstructures of oxide scale at different temperatures were observed by EPMA. When the temperature rised to 530 ℃, the eutectoid Fe preferentially dissolved and iron ions formed. Iron ions diffused into the adjacent Fe3O4 through short range leading to iron ion content in Fe3O4 increasing. The nucleation of Fe1-yO was not found in oxide scale. When the heating temperature was 650 ℃, the eutectoid structure had almost completely reversed, and only the pre-eutectoid structure remained in the whole scale. The structure of the oxide scale had evolved into two la-yers, consisting of the outer Fe3O4 and the inner Fe1-yO until the temperature reached 760 ℃.Pro-eutectoid Fe3O4 and eutectoid structure had transformed into Fe1-yO during heating process. The preferential dissolution of lamellar eutectoid Fe diffused into the adjacent eutectoid Fe3O4 through short range diffusion. © 2021, Materials Review Magazine. All right reserved.