| A new method has been developed to produce 300 series stainless steel, which is mainly for producing un-refined liquid stainless steel with electrosilicothermic metallurgy. Ferronickel alloy with high silicon and low carbon content named as nickel-silicon ferroalloy is produced in the submerged arc furnace ?SAF? at the first step, then the slag containing chromium oxide and calcium oxide which comes from refining furnace is charged into a shaking ladle together with liquid nickel-silicon ferroalloy for pre-desilication and certain chromium reduction, finally, the liquid alloy with other chromium concentrate and lime is charged into a refining furnace for final desilication to get the un-refined liquid stainless steel. In addition, a reductive dephosphorization before the pre-desilcation process needs to be carried out if necessary. Argon Oxygen Decarburization ?AOD? or Vacuum Oxygen Decarburization ?VOD? process could then be followed to produce planned stainless steel. This process is different from the traditional one since it takes advantage of the characteristics of low grade lateritic ore with high SiO2 content and the utilization of low cost of chromium concentrates.Compared to traditional duplex process and based on mass and energy conservation, the total energy consumption, carbon dioxide emission and raw material cost in the new process could be decreased by about 7.1%,6.2% and 6.3%-7.2%, respectively.According to the solubility of carbon in the molten Fe-Ni-Si alloy, the silicon content of nickel-silicon ferroalloy should be more than 20 mass% so that the carbon content in ferroalloy would be less than 0.5 mass% and the load of decarburization in AOD or VOD will be decreased. The phosphorus content of nickel-silicon ferroalloy containing silicon content more than 20 mass% could be decreased below to 0.03 mass% by using reduction dephosphorization process.In the present study, the phosphorus in the Fe-Ni-Si melt was removed by interface dephosphorization and precipitation dephosphorization process. Compared to interface dephosphrizaion, the precipitation dephosporizaion rate was higher. The interface dephosphorization of Fe-Ni-Si melt by CaO-saturated CaO-CaF2 slag was investigated, from which it was found that the dephosphorization efficiency increases as increasing the silicon content, meanwhile the increase rate becomes rapid when the silicon content is more than 10 mass%. By analyzing the phase compositions of the dephosphorization slag of a high silicon Fe-Ni-Si melt, it was found the dephosphorization products changed with the silicon content for the first time. When Si contents are 10.5 mass%,31.48 mass% and 43.15 mass%. the de-P products are Ca2P2, Ca10+xSi12-2xP16 and 4, respectively. While Si content is 34.71 mass%, the de-P product is 4, and Ca10+xSi12-2xP16 The corresponding dephosphorization reaction can be described as 2x?CaO?+?x+2y?[Si]+2z[P]=x?SiO2?+2?CaxSiyPz?.There are two methods to produce nickel-chromium ferroalloy products, with 1.00 mass% or 0.18 mass% silicon, from nickel-silicon ferroalloy with 20 mass% silicon content. If they are produced by EAF process, the slag basicity must be controlled within 1.0 to 1.4 and 1.4 to 1.61 respectively, and the yield of Cr is about 85.52%-95.16% and 85.21%?-92.14%. respectively, and silicon utilization rate is about 77.74%?-78.70% and 76.80%?78.40%, respectively. If they are produced by EAF-ShakingLadle process, the silicon content in alloy must be controlled within 13.00%?13.43% and 10.25%?10.57% after pre-desilicication.In addition, the empirical correlation of the solubility of carbon and silicon content in the molten Fe-Ni-Si with different ratio of Ni to Fe and the empirical correlation of the interface dephosphorizaiton efficiency and silicon in the Fe-Ni-Si alloy were studied. The phenomenon of rephosphorizaiton was observed and discussed during the reducing dephosphorizaion process and the effect of S content in Fe-Ni-Si melt on the dephosphorization efficiency was also researched. |
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