| For solid-phase decarburization of high-carbon ferrochrome powders without slag in microwave field, the better microwave-absorption performances of materials result in the faster heating rate of materials followed by a more thorough reaction. There is a close relation between absorption performances and electromagnetic properties. In addition, the decarburization degree of HCFCP in high-temperature also relies on its solid-phase microstructure to some extent.Due to the distinct discrepancy on cooling rate for different sections of liquated HCFC in industrial large-scale cooling process, the type, structure and electromagnetic performance of solid-phases present relatively complex diversities. In previous studies, however, the effects of cooling rate on phase structure as well as further electromagnetic properties of HCFCP have never been comprehensively reported, remaining a real road-block to the practical applications of microwave in solid-phase decarburization of HCFCP. The solid-phase microstructure and electromagnetic properties of HCFCP cooled in furnace, air atmosphere and water bath respectively were investigated by meansof optic microscope, X-ray diffractometer, electronic probe and the vector network analyzer in the frequency range of 1~18 GHz, followed by a comparison to determine the optimal microwave heating materials and further guide the solid-phase decarburization process in microwave field. As the potential fact of microwave heating by multiple frequency in the future industrial development, other frequencies in the limit of 1-18 GHz are also considered besides 2.45 GHz.(1) The results for solid-phase microstructure show HCFC is mainly composed of primary phase(Cr, Fe)7C3, eutectic phase(Cr, Fe)7C3-CrFe and graphite phase, regardless of which kind of cooling rate mentioned above; With the improvement of cooling rate, grain size of primary phase decreases gradually,while its percentage content shows an increasing trend; The growth of primary phase grain for water-cooled sample is perpendicular to the solidification interface, but that of primary phase grain for furnace-cooled and air-cooled samples is without fixed direction; Due to the non-equilibrium solidification in air-cooled and water-cooled conditions, the formation of peritectic phase(Cr,Fe)23C6 is restrained accompanying metastable eutectic phase(Cr, Fe)23C6-CrFe precipitating out. Flake graphite phase is discovered in primary phase and eutectic phase of furnace-cooled specimen as well as eutectic phase of air-cooled and water-cooled specimens. As the cooling rate increases, the mass ratio of Cr to Fe in(Cr, Fe)7C3 gradually declines, while that for(Cr, Fe)23C6, CrFe goes up,and the distribution of other impurity elements such as Si, Mn, Ti in main phasesis hardly affected by cooling rate.(2) The results for electromagnetic performance show that both the real part and the imaginary part of relative complex permittivity of HCFCP both show an increasing order with a rising in cooling rate under most frequencies. The appearance of negative and resonance peaks in the real and imaginary part respectively result from the polarization and relaxation in the extent of 14~18GHz. For comparison, the relative complex permeability presents an opposite changing tendency. Basing on ferromagnetic resonance theory, the peaks of the imaginary part of relative complex permeability appearing in low and high frequencies are attributed to nature resonance, and the resonant frequency has a positive relation with cooling rate. The reflection loss of furnace-cooled,air-cooled and water-cooled HCFCP with the values of-2.57 dB,-2.38 dB,-2.17 dB severally at 2.45 GHz, could meet the need of microwave heating in principle. By overall consideration, the water-cooled powders is determined the optimal materials for solid-phase decarburization of HCFCP in microwave field,attributed to the higher dielectric loss factor as well as the higher magnetic loss factor. |
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