Analysis of pore formation and carburizing mechanism of magnetite reduction by CO

To investigate the porosity and expansion mechanism of CO-reduced magnetite, the reduced microstructures of magnetite under conventional heating and microwave heating were compared. The microstructure characteristics of magnetite with various reduction degrees were examined in a 60%CO-Ar reduction atmosphere, and the formation and evolution mechanism of the structure were analyzed in conjunction with the reduction effect. The results indicate that the reduction product of CO reduced magnetite possesses a porous structure. Nevertheless, when the gas diffusion is restricted, the reduction process is sluggish and the porous structure is not readily formed. Microwave heating enhances the gas-phase diffusion capacity, thermodynamic carburizing capacity, and solid-phase carbon-oxygen diffusion capacity, resulting in a higher oxygen loss rate than that of conventional heating. Under the experimental conditions, the lattice shrinkage during the Fe 3 O 4 → Fe 0.88 O transformation and the rapid expansion of Fe 0.88 O → Fe 0.94 O are the causes of the crack. Microwaves facilitate the formation of pores and cracks in the product. This study offers a novel concept for the development of foam steel.