Microstructure Of High-carbon Ferrochrome Powders With Addition Of Calcium Carbonate Decarburized In Solid-state By Microwave Heating

Medium and low carbon ferrochrome is the indispensable raw material to produce stainless steel and chromium alloy steel, liquid-phase decarburization of high-carbon ferrochrome is gradually limited by environment because of metallurgical chrome slag is a kind of harmful solid waste produced in the preparation process. Quickly solid-phase decarburization of high-carbon ferrochrome powders can be achieved by high-carbon ferrochrome powders with calcium carbonate heating in microwave field, and getting a kind of medium and low carbon ferrochrome powders with CaO. This method can avoid emissions of harmful chromium slag, and it is a simple method of high-carbon ferrochrome solid-phase decarburization. Therefore, it has important significance to study the phase composition and microstructure of this new pattern metallurgy material.In this paper, the microstructure and phase structure of the materials of high-carbon ferrochrome powders with addition of calcium carbonate decarburization in solid-phase by microwave heating was investigated by carbon content analysis, metallographic analysis, electron probe microanalysis(EPMA) and X-ray diffraction(XRD). We research microstructure and phase structure of high-carbon ferrochrome and high-carbon ferrochrome powders with addition of calcium carbonate decarburization in solid-phase by microwave heating, we discuss the rule of materials of high-carbon ferrochrome powders with addition of calcium carbonate decarburization in solid-phase by microwave heating, at the same time, we analyze the oxidation degree and oxide phase of decarburization materials, at last, we can concluded the optimum technological parameters of high-carbon ferrochrome powders with addition of calcium carbonate decarburization in solid-phase by microwave heating. The main conclusions of this paper as follows:(1) The metallography structure of high-carbon ferrochrome is mainly composed of primary phase (Cr,Fe)7C3, peritectic phase (Cr,Fe)23C6, ferrochrome ferrite phase CrFe, and a small amount of graphite phase. The structure of primary phase (Cr,Fe)7C3is mainly coarse and hexagonal columnar idiomorphic and hypidiomorphic crystalline-granular texture; The structure of peritectic phase (Cr,Fe)23C6is mainly peritectic structure (Cr,Fe)23C6-(Cr,Fe)7C3which (Cr,Fe)7C3is wrapped and corroded; The structure of eutectic phase (Cr,Fe)23C6-CrFe exists mainly wormlike of fine-grained and peachlike intertwined each other with relatively small grains; The structure of graphite is mainly fine lamellar flakes-filling structure.(2) Primary phase (Cr,Fe)7C3is accounting for75%in the metallographic structure of high-carbon ferrochrome, which contains mainly coarse grains and has a complete crystal form, requiring a great amount of energy to realize carbon migration in solid phase. Peritectic phase (Cr,Fe)23C6is accounting for1.5%in the metallographic structure of high-carbon ferrochrome, which contains mainly small grains and has a incomplete crystal form and beard like corroded wrapping around (Cr,Fe)7C3, requiring less energy for the migration of carbon in solid phase. Eutectic phase (Cr,Fe)23C6-CrFe is accounting for23%in the metallographic structure of high-carbon ferrochrome, with relatively small grains, complex grain boundary, which is relatively easy for carbon migration in solid phase. The graphite is accounting for0.5%in the metallographic structure of high-carbon ferrochrome, with mainly flakes-filling structure fills in the fissures of eutectic phase (Cr,Fe)23C6-CrFe, which is conductive to the migration of carbon in solid phase. (3) There are low content of iron and silicon and high content of chromium and carbon in primary phase (Cr,Fe)7C3, so it has low carbon activity, and it is not easy to the migration and diffusion of carbon in solid phase; There are low content of chromium and carbon and high content of iron and silicon in peritectic phase (Cr,Fe)23C6, so it has high carbon activity, and it is conducive to the migration and diffusion of carbon in solid phase; There are lowest content of chromium and carbon and highest content of iron and silicon in eutectic phase (Cr,Fe)23C6-CrFe, the high of silicon increase carbon activity, so it is easiest to the migration and diffusion of carbon in solid phase; The emergence of graphite phase is conducive to the migration and diffusion of carbon in solid phase.(4) Cooling rate of liquid high-carbon ferrochrome has a great influence on the organizational structure of the high-carbon ferrochrome. Due to the cooling rate is relatively slow in ingot inside, metallographic structure of high-carbon ferrochrome is mainly composed of coarse primary phase (Cr,Fe)7C3and peritectic phase (Cr,Fe)23C6in ingot inside, requiring a great amount of energy to realize carbon migration; Due to the cooling rate is relatively fast in ingot edge, metallographic structure of high-carbon ferrochrome is mainly composed of small primary phase (Cr,Fe)7C3, peritectic phase (Cr,Fe)23C6and eutectic phase (Cr,Fe)23C6-CrFe in ingot edge, requiring less energy for the migration of carbon. Thermodynamic equilibrium crystallization sequence of liquid high-carbon ferrochrome is changed by cooling rate, and phase selection was happened in crystallize phases, froming equilibrium crystallization sequence of mixed crystal of primary phase and peritectic phase (Cr,Fe)7C3/(Cr,Fe)23C6-(Cr,Fe)7C3to nonequilibrium crystallization sequence of mixed crystal of primary phase/peritectic phase/eutectic phase (Cr,Fe)7C3/(Cr,Fe)23C6/(Cr,Fe)23C6-CrFe area, so lots of eutectic phase (Cr,Fe)23C6-CrFe are found on edge area of high-carbon ferrochrome ingot, phase selection caused by the cooling rate provides a better foundation on the solid phase decarburization of high-carbon ferrochrome powders. (5) Medium and low carbon ferrochrome powders containing CaO can be achieved at short notice by solid-phase decarburization of high-carbon ferrochrome powders with CaO in microwave heating field. Phase of decarburization materials is composed of low-carbon ferrochrome carbide phase, metal chromium ferritic phase and CaO.(6) When the temperature of high-carbon ferrochrome powders with addition of calcium carbonate is heated to900℃by microwave heating, calcium carbonate powders is started to broke down into CaO and CO2, while bulky hexagonal columnar shape (Cr,Fe)7C3firstly react with CO2in boundary of high-carbon ferrochrome powders particles, but (Cr,Fe)7C3hardly react inside of high-carbon ferrochrome powders particles; When temperature of microwave heating is1000℃,(Cr,Fe)23C6and CrFe) extend to particles inside for nucleation and growth in boundary of high-carbon ferrochrome powders particles, part of bulky (Cr,Fe)7C3is decomposed into small broken grains exists in (Cr,Fe)23C6and CrFe new generated phases; When temperature of microwave heating is1100℃, bulky hexagonal columnar shape (Cr,Fe)7C3almost changed into tiny granular (Cr,Fe)23C6and CrFe; When temperature of microwave heating is1200℃, degree of oxidation is serious in decarburization material, which a mass of CrFe was oxidized, chromium iron oxide phase chromium (Cr,Fe)2O3and chromium calcium oxide phase CaCr2O4, CaCr2O7are the main oxide phases in decarburization material.(7) Carbon content of ferrochrome powders reduces quickly with rise of temperature of high-carbon ferrochrome powders with addition of calcium carbonate decarburization in solid-phase by microwave heating, carbon content is drop from original8.16%to5.06%,2.24%,1.71%,1.39%. Carbon-rich carbide phase (Cr,Fe)7C3reduces and mental-rich carbide phase (Cr,Fe)23C6and ferrochrome ferrite phase (CrFe) increasees in decarburization material; At the same time, chromium iron oxide and chrome calcium oxide increases with rise of temperature. Comprehensive consideration, the best effect temperature of high-carbon ferrochrome powders solid-phase decarburization is1100℃in microwave field, which actual carbon content is1.71%, and degree of oxidation is not high.