| The development of modern industries and technologies requires steel materials to possess higher qualities and cost performances.As key factors,grades,performances and costs of the product are of great concern to the competitiveness of a manufacturer.Direct alloying using chromium ores in converters can decrease the cost of ferrochrome,increase the heat efficiency of converter process,and protect the environment from the emission of hazardous substances in ferrochrome manufacturing.The direct alloying using chromium ores in an oxidizing atmosphere converter is rarely reported and its thermodynamic mechanism has not been well understood.Based on the manufacture of GCr15 steel using a converter,the existence states,thermodynamic aspects of the reduction of chromium ores were calculated.The optimized reductant ratio and composition of pulverized ores for briquetting were also investigated.The results are important references in choosing processing parameters of the direct alloying.A mathematic model to calculate the valence state of Cr in the CaO-SiO2-MgO-Al2O3-FeOt-CrOx slag system was established and the calculated result was proved by experiments.The calculated results reveal: the oxygen potential is the main factor to affect the valence state of Cr in the given slag system.When lg(PO2/atm)is between-9.56 and-8.79,the main valence state of Cr were bivalent and trivalent at the end of decarbonization in a converter.The average valence of Cr in the slag increases with higher oxygen partial pressure,slag basicity and initial Cr2O3 content,and decreases with the increase of temperature.However,influence of x in CrOx by variation of Al2O3 and Fe O is very limited.Based on the thermodynamic data,thermodynamic state diagrams of Cr oxides,Cr ores,and C,Si,Al which as the reductant in solid state or dissolved in liquid steel were calculated.The result shows C,Si and Al can reduce chromium ore and relevant oxides.The reaction temperature of solid C with chromite and magnochromite were 322? and 52? lower than using dissolved [C] as the reductant,respectively.The activity of slag components and molten steel in GCr15 smelting was calculated using related models.The results show that both CrO and Cr2O3 can be reduced by the rest of [C] in the molten steel.What's more,(CrO)is more easily reduced by [C].In the same thermodynamic conditions,the reduction ability of [Al] is the strongest.Orthogonal experiments(based on different oxidability of slags and adding sequences of reductants)were adopted to investigate the reducing capacity of four mixed reductants: 90%C+20%Si,90%C+20%Al,90%Si+20%Al,and 90%C+10%Si10%Al.The result shows that the reductant 90%C+10%Si10%Al is the best combination.Pulverized chromium ore,coke,and related chemical reagents were mixed and briquetted for experiments.The results reveal low-melting temperature zones were formed within the bulk.With more addition of CaF2 and basicity,the briquettes will smelt faster.But MgO/SiO2 has little little influence on the melting rate.On the other hand,the Cr concentration in steel during the final stage of the reaction can be improved by increasing the basicity and MgO/SiO2 in the briquetted bulk.But CaF2 content has little influence on Cr yield.The result shows that the direct alloying using Cr ore can reduce the cost of GCr15 manufacturing 19.88~30.82 yuan per ton. |
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