Research On Solid-Phase Decarburization Of High-Carbon Ferromanganese Powders By Microwave Heating

Medium and low carbon ferromanganese alloy is the important raw materials of low carbon alloy steel. With the rapid development of the low carbon alloy steel such as Cr-Mn stainless steel, the demand of medium and low carbon ferromanganese is increasing. Some research progress has been achieved that medium and low carbon ferromanganese alloy is produced using high-carbon ferromanganese. However, now, ferromanganese is decarburized in liquid phase.Because of the relatively high vapor pressure of manganese and great binding energy between manganese and oxygen, the decarburization of ferromanganese in liquid phase exhibits high manganese volatilization loss, severe oxidation and low metal recovery rate. To solve above problems, solid-phase decarburization study of high-carbon ferromanganese powder was conducted. Decarburization thermodynamic calculation was carried out. Characteristics of the temperature rise of high-carbon ferromanganese powder and calcium carbonate powder was studed in microwave heating field. Carbon content was measured by carbon and sulfur analyzer. Microstructures were characterized by X-ray diffractometer (XRD),seanning electron microscope(SEM), electron probe micro-analyzer (EPMA). Electromagnetic properties was investigated by a vector network analyzer.The results show that in thermodynamics it is entirely feasible to utilize O2, CO2 or water vapor as gas decarbonizers for high-carbon ferromanganese, but in aspects of decreasing decarburization temperature and preventing oxidation, CO2 is superior to O2 and water vapor.High-carbon ferromanganese powders exhibit better microwave absorption than calcium carbonate powders. The mixture of high-carbon ferromanganese powders and calcium carbonate powders performs good microwave heating performance. The good microwave absorption property of the mixed material lays the foundation for the solid-phase decarburization of high-carbon ferromanganese powders.The specific heating rate of high-carbon ferromanganese powders heated in microwaves field is 2.07～2.22 ℃·kg-1·kW-1·min-1. Whereas, that is only 1.54～1.78 ℃·kg-1·kW-1·min-1 in conventional heating field. High-carbon ferromanganese powders exhibit a rapid heating rate in the microwave field.The microwave heating method is better than conventional heating method.High-carbon ferromanganese powders were decarburized by microwave heating,carbon content of decarburizated materials decreases with increasing decarburization temperature, holding time and decarburization moler ratio. Compensively, suitable decarburization condition is decarburization temperature of 1000℃, holding time of 60 min and decarburization moler ratio of 1:1.18.High-carbon ferromanganese powders were heated up to 900,1000,1100, and 1200℃ and held for 60 min to be decarburized by microwave heating at decarburization ratios of 76.69%,82.90%,84.11%, and 85.75%, respectively. These ratios are higher than the decarburization ratios used for conventional heating (31.94%,57.23%,58.84%, and 88.02%, respectively) under the same experimental conditions. High-carbon ferromanganese powders were decarburized by microwave heating at lower iron and manganese loss ratios of the sample decarburized than that by conventional heating. Moreover, oxidation degree of the sample decarburized in the microwave heating field is lower that that in the conventional heating field.In the frequency bands from 2 to 18 GHz, the polarization relaxation of HCFCP and the decarburized materials mainly derives from dipole polarization and interfacial polarization and the diamagnetism derives from carbon atoms.At the frequency of 2.45 GHz, the decarburized materials have better ability for absorbing microwaves and the temperature-rise period of high-carbon ferromanganese powders is ascribed to magnetic loss and dielectric loss in microwave fields. As heating temperature and holding time increase, the relative complex permittivity ultimately tends to be stable, demonstrating transformation of (Mn, Fe)xCy to Mn and Fe.Solid-phase decarburization of high-carbon ferromanganese powders is a first-order reaction by microwave heating. Apparent activation energy of solid-phase decarburization is 55.07kJ·mol-1 by microwave heating, however,that of solid-phase decarburization is 107.77kJ·mol-1. under the same decarburization condition by conventional heating.which is far less than that of ordinary carbon gasification reaction and that of solid-phase decarburization under the same decarburization condition by conventional heating.