| Medium and low carbon ferrochrome is widely used in producing stainless steel and chromium alloy steel, liquid-phase decarburization of high-carbon ferrochrome is gradually limited by environmental protection because of metallurgical chrome slag is a kind of harmful solid waste produced in the productive process. Therefore, solid-phase decarburization technology of high carbon ferrochrome is becoming more and more attention.The effect of different heating fields on microstructure of the material was studied, which provided evidence for special effects of microwave heating field. In this paper, high-carbon ferrochrome powders(HCFP) with addition of calcium carbonate powders(CCP) was studied, HCFP decarburized in solid-state was comparatively researched after heating by microwave and conventional field. The phase composition and structure of HCFP after decarbonization by two heating method was comparatively studied through carbon content analysis, metallographic structure analysis, electron probe microscopic analysis and XRD analysis. The differences of HCFP decarburized in solid-state was studied between microwave field and conventional heating field. The mechanism of HCFP heating by microwave and its advantages was also studied, proves that microwave field can significantly improve the diffusivity of the carbon in HCFP. It can greatly improve the conditions of thermodynamics and dynamics of solid-state decarburization. The main conclusions of this paper as follows:(1) The Metallographic organization structure of HCFP are mainly bulky white lumps phase (Cr,Fe)7C3as the matrix phase, occupied more than80%of the total phase, as well as small amounts of gray irregular shape phase (Cr,Fe)23C6fill in (Cr,Fe)7C3matrix phase in the middle. Due to larger grain of (Cr,Fe)7C3and more carbon content, carbon solid phase migration needs more energy.(2) The lattice parameter of Cr7C3:a=0.452nm, b=0.695, c=1.212, crystal cell volume is0.3807nm3. In Cr7C3crystal, the position of the carbon atoms is in the triangular prism of chromium atoms, bond strength and density of Cr7C3is high, belongs to the thermodynamic stability structure, has the very high hardness at the same time. The lattice parameter of Cr23C6:a=1.058nm, crystal cell volume is0.2935nm3. In Cr23C6crystal, the position of the carbon atoms is in the quartet of prism of chromium atoms, bond strength of Cr-C is significantly less than the Cr7C3, relative density is less than Cr7C3too, theory hardness is also less than Cr7C3, thermodynamic stability is lower than Cr7C3naturally.(3) HCFP mixed with CCP heated to900℃,1000℃,1100℃,1200℃and holding for60min respectively by microwave heating, the decarbonization percentage was far higher than that of by muffle furnace heating. Visible, by microwave heating, it do not need to high temperature and long time of heat preservation can achieve very good effect on decarburization.(4) When heated by conventional field, the decarburization reaction requires higher temperature,(Cr,Fe)23C6-CrFe in high carbon ferrochrome powders generate less, grow slowly, segregate seriously and distributed very unevenly; while heated by microwave filed, the generation of (Cr,Fe)23C6-CrFe requires relatively lower temperature, has a fast reaction velocity, distributed uniform.(5) By calculation, whether the bonds of Cr7C3to the mixture of covalent bond, ionic bond and metallic bonding keys, and present the gold properties, and electronic polarization relaxation of Cr7C3is the main cause of electromagnetic waves loss. At the same time, the activity of carbon atoms and its diffusion difficulty is the key factors that influencing the solid phase decarburization rate, and the diffusion capacity of carbon atoms under microwave heating is increased significantly, greatly improve the solid phase decarburization reaction conditions of thermodynamics and dynamics.(6) The oxidation degree of decarburization material accelerates when the temperature is increasing. The smaller particle size is, the more serious oxidation degree will be. However, the oxidation degree of materials under microwave heating field is significantly less than that of conventional heating field. This shows that the diffusion rate of the carbon in high-carbon ferrochrome powders is faster than the rate of oxidation. Microwave heating has good antioxidation during the process of decarbonization. It can better suppress the oxidation of the decarburization ferrochrome powders.(7) There was still a lot of CaCO3undecomposed when heated to900℃and hold for60min by conventional heating. CaCO3completely decomposed when the temperature was1000℃. While heated by microwave field, CaCO3almost completely decomposed at900℃and hold for60min. By conventional heating to900℃, not only appeared Cr2O3but also generated a small amount of CaCr2O4, while heated by microwave field, CaCr2O4occurred at1000℃but not900℃. There were a lot of oxide phases CaCr2O7and Ca(CrO2)2appeared at1100℃by conventional heating. There was no new oxide appeared that heated to1100℃by microwave. There was CaCr2O7appeared at1200℃. It further prove that the rate of carbon diffusion in HCFP by microwave heating is much higher than that of conventional heating indeed, which greatly reduced the oxidation degree of the materials. |
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