| The increasing adoption of the new one-step stainless steel production process,known for its simple smelting process and economic benefits in producing 400 series stainless steel,is gaining traction among enterprises.However,the stainless steel smelting process utilizing the TSR furnace,a typical one-step smelting method,faces challenges such as insufficient decarburization capacity,prolonged smelting time during deep decarburization,and high chromium oxidation loss.To address these issues,this study proposes the introduction of CO2 into the TSR furnace to enhance stainless steel smelting.The unique high-temperature physical and chemical properties of CO2 are utilized to strengthen decarburization in the molten steel and improve the stirring performance of the molten pool,thereby increasing chromium recovery and smelting efficiency.Thermodynamic and kinetic analyses are conducted to explore the decarburization and chromium retention performance of CO2,as well as the reaction behavior at the bubble-liquid steel interface during bubble floatation.Under CO2 injection conditions,the relationship between the composition,temperature,and CO partial pressure of the molten steel is established when the decarburization and chromium retention reactions reach equilibrium.Kinetic calculations indicate that the volume of CO2 bubble increases by approximately 1.30 times its initial volume at equilibrium,leading to a 1.19～1.30 times increase in the decarburization rate of the molten steel.Laboratory experiments using a tube furnace reveal that,in high carbon and low chromium content conditions,the use of CO2 instead of N2 increases the decarburization rate of molten steel by 5.56%and reduces chromium oxidation loss by 10.19%.Under medium carbon and high chromium content conditions,increasing the proportion of CO2 replacing N2 from 0 to 100%results in a 12.95%increase in the decarburization rate,while the oxidation loss of chromium decreases from 8.99%to 4.79%as the proportion gradually increases from 0 to 75%.However,complete replacement of N2 with CO2 leads to a slight rise in chromium oxidation loss to 5.81%.Hydraulic and numerical simulations are employed to establish corresponding models for the 70-ton TSR furnace at a steel plant.By incorporating a bubble diameter calculation model and user-defined function(UDF),the impact of increased bubble volume on the flow field and mixing time of the molten pool is investigated when the initial radius of the bottom-blowing CO2 bubble is 3 mm.The hydraulic simulation results demonstrate that the volume increase of CO2 facilitates solute diffusion in the molten pool,resulting in an 8.4～16.5 s reduction in mixing time and significant improvements in the dynamic conditions of the molten pool.Numerical simulation results reveal that the volume increase of CO2 leads to a more uniform velocity distribution of the molten steel,reduces the lowspeed zone near the wall of the molten pool,and decreases the proportion of dead zones by 9.25%～10.82%.Based on the aforementioned theoretical research,a test platform for smelting stainless steel with O2-CO2 injection is constructed using a 70-ton TSR furnace.Relevant industrial tests are conducted,with the results showing that at the end of the DEC5 stage,the test process achieves lower carbon content in the molten steel compared to the original process for different carbon concentration ranges(0<[%C]≤0.1,0.1<[%C]≤0.2,and 0.2<[%C]≤0.3),with reductions of 0.014%,0.008%,and 0.004%respectively.The temperature of the molten steel in the test process is also lower by 8.1 K,5.5 K,and 4.8 K respectively compared to the original process.For 0.1<[%C]≤0.2 and 0.2<[%C]≤0.3,the test process exhibits increased chromium content by 0.185%and 0.409%respectively,accompanied by a decrease in Fe-Si consumption per ton of steel by 1.1 kg and 2.4 kg compared to the original process.However,in cases where 0<[%C]≤0.1,the CO partial pressure of the molten pool exceeds the threshold required for the decarburization and chromium retention reaction,resulting in a 0.055%lower chromium content and an increase of 0.3 kg in Fe-Si consumption per ton of steel.Furthermore,a process model for stainless steel smelting by injecting O2-CO2 into the TSR furnace is established based on metallurgical thermodynamics and dynamics theory.This model accurately calculates and predicts changes in molten steel composition,temperature,and CO partial pressure.The research findings demonstrate a continuous decrease in carbon content throughout the smelting process,with a slower decline rate in the second half of the DEC5 stage.Chromium content shows a continuous increase from the beginning of smelting,with a slight decrease until the DEC4 stage.During the DEC5 stage,chromium content initially rises slightly and then decreases rapidly in the second half,attributed to the CO partial pressure exceeding the theoretical critical value,failing to meet the requirements of the decarburization and chromium retention reaction.Additionally,as the proportion of bottom-blowing CO2 replacing N2 increases from 0 to 100%,the contents of carbon,silicon,and manganese,as well as the temperature,gradually decrease,while chromium content gradually increases.There is a turning point in the change trend of carbon content,chromium content,and temperature before the end of smelting.The turning points occur at 30.5 min,29.5 min,and 28.6 min when the CO2 injection ratios are 0%,50%,and 100%,respectively.The research results presented in this paper provide robust data support for the industrial application and promotion of stainless steel smelting with O2-CO2 injection into the TSR furnace,promoting the further development of the one-step process for stainless steel smelting. |
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