Physical and Mathematical Modeling of the Argon-Oxygen Decarburization Refining Process of Stainless Steel

The available studies in the literature on physical and mathematical modeling of the argon oxygen decarburization (AOD) process of stainless steel have briefly been reviewed. The latest advances made by the author with his research group have been summarized. Water modeling was used to investigate the fluid flow and mixing characteristics in the bath of an 18 t AOD vessel, as well as the 'back attack' action of gas jets and its effects on the erosion and wear of the refractory lining, with sufficiently full kinematic similarity. The non rotating and rotating gas jets blown through two annular tuyeres, respectively of straight tube and spiral flat tube type, were employed in the experiments. The geometric similarity ratio between the model and its prototype (including the straight tube type tuyeres) was 1:3. The influences of the gas flow rate, the angle included between the two tuyeres and other operating parameters, and the suitability of the spiral tuyere as a practical application, were examined. These latest studies have clearly and successfully brought to light the fluid flow and mixing characteristics in the bath and the overall features of the back attack phenomena of gas jets during the blowing, and have offered a better understanding of the refining process. Besides, mathematical modeling for the refining process of stainless steel was carried out and a new mathematical model of the process was proposed and developed. The model performs the rate calculations of the refining and the mass and heat balances of the system. Also, the effects of the operating factors, including adding the slag materials, crop ends, and scrap, and alloy agents; the non isothermal conditions; the changes in the amounts of metal and slag during the refining; and other factors were all considered. The model was used to deal with and analyze the austenitic stainless steel making (including ultra low carbon steel) and was tested on data of 32 heats obtained in producing 304 grade steel in an 18 t AOD vessel. The changes in the bath composition and temperature during the refining process with time can be accurately predicted using this model. The model can provide some very useful information and a reliable basis for optimizing the process practice of the refining of stainless steel and control of the process in real time and online.

Surface decarburization characteristics and relation between decarburized types and heating temperature of spring steel 60Si2MnA

The characteristics of complete and partial decarburizations in spring steel 60Si2MnA were systematically investigated, including the microstructure, the hardness gradient, and the formation mechanism. The relation between decarburized types and heating temperature of the steel was comprehensively discussed. It is found that heating temper- ature has an important influence on the decarburized types. With the rise of heating temperature, the decarburized types change from no decarburization to complete decarburization, complete and partial decarburizations, partial decarburiza- tion, and no decarburization.

Forming condition and control strategy of ferrite decarburization in 60Si2MnA spring steel wires for automotive suspensions

The ferrite decarburization behavior of 60Si2MnA spring steel wires for automotive suspensions, including the forming condition and the influence of heating time and cooling rate after hot rolling, was investigated comprehensively. Also, a control strategy during the reheating process and cooling process after rolling was put forward to protect against ferrite decarburization. The results show that ferrite decarburization, which has the strong temperature dependence due to phase transformation, is produced between 675 and 875°C. The maximum depth is found at 750°C. Heating time and cooling rate after rolling have an important influence on decarburization. Reasonable preheating temperature in the billet reheating process and austenitizing temperature in the heat-treatment process are suggested to protect against ferrite decarburization.

Effect of decarburization annealing temperature and time on the carbon content, microstructure, and texture of grain-oriented pure iron

In this study,the effect of decarburization annealing temperature and time on the carbon content,microstructure,and texture of grain-oriented pure iron was investigated by optical microscopy and scanning electron microscopy with electron-backscatter diffraction. The results showed that the efficiency of decarburization dramatically increased with increasing decarburization temperature. However,when the annealing temperature was increased to 825°C and 850°C,the steel's carbon content remained essentially unchanged at 0.002%. With increasing decarburization time,the steel's carbon content generally decreased. When both the decarburization temperature and time were increased further,the average grain size dramatically increased and the number of fine grains decreased; meanwhile,some relatively larger grains developed. The main texture types of the decarburized sheets were approximately the same: {001}<110> and {112~115}<110>,with a γ-fiber texture. Furthermore,little change was observed in the texture. Compared with the experimental sheets,the texture of the cold-rolled sheet was very scattered. The best average magnetic induction(B_(800)) among the final products was 1.946 T.

Decarburization rate of RH refining for ultra low carbon steel

The decarburization behaviors of ultra low carbon steel in a 210-t RH vacuum degasser were investigated under practical operat- ing conditions. According to the apparent decarburization rate constant （Kc） calculated by the carbon content in the samples taken from the hot melt in a ladle at an interval of 1-2 min, it is observed that the total decarburization reaction period in RH can be divided into the quick decarburization period and the stagnant decarburization period, which is quite different from the traditional one with three stages. In this study, the average apparent decarburization rate constant during the quick decarburization period is 0.306 min^-1, and that of the stagnant period is 0.072 min^-1. Increasing the initial carbon content and enhancing the exhausting capacity can increase the apparent decarburization rate constant in the quick decarburization period. The decarburization reaction comes into the stagnant decarburization period when the carbon content in molten steel is less than 14× 10^-6 after 10 min of decarburization.

Mathematical Model of Decarburization of Ultra Low Carbon Steel during RH Treatment

According to the balance of carbon and oxygen, a decarburization model for the RH treatment has been developed. in which the influence of the mass transfer of carbon and oxygen in the liquid steel and the stirring energy (ε) in the vacuum vessel on decarburization rate has been considered. The conclusion that the volumetric coefficients of the mass transfer of carbon is proportional to ε(1.5) is drawn. Industrical experiment proves this model is reliable. The influence of some factors on decarburization rate has been obtained. which can provide directions for RH treatment The decarburization behavior of steel with RH-OB treatment is also studied. The OB-or-not curve, the optimized OB time and OB amount are discussed.

Numerical Simulation of Recirculating Flow and Decarburization in RH Vacuum Refining Degasser

Based on the principle of RH process and the mechanism of decarburization, a three-dimensional mathematical model to represent the flow and decarburization of molten steel was established. The model was verified and the effect of operating parameters on the process was investigated.

Electrochemical Characteristic of Decarburization Reaction

The electrochemical mechanism of the reaction between Fe-C melts and CaO-SiO2-Al2O3-FeOx slag systems has been carried out. The experimental results suggest that the final content of carbon in melt increases as the partial oxygen pressure of gas decreases no matter whether there is electronic conductor or not. However, the final content of carbon in the system with electronic conductor is much lower than that without electronic conductor. It can be deduced that the transfer ability of oxygen in slag is dominated by electrons. When an electronic conductor exists, an easy pathway for the electrons is provided and the oxygen transfer rate is accelerated.

Decarburization mechanism of RH-MFB refining process

The overall decarburization mechanism can be divided into the decarburization in bulk molten steel and floating of CO against static pressure, the decarburization on the surface of argon bubbles and splashing particles. On the basis of each conception the RH-MFB decarburization mathematical model has been built according to the thermodynamic and mass conservation principle, and contributions of every decarburization mechanism were discussed and analyzed.

Influence of Conductivity of Slag on Decarburization Reaction

By altering the electrochemical properties of slag, the decarburization reaction of Fe3+-based slag withFe-C droplet was studied. The results showed that a lot of free electrons and holes exist in the slag containing transition metal oxides (such as TiO2 and Fe2O3). So electronic conduction in the slag increases. Finally, it led to the increment of the decarburization reaction rate between slag and Fe-C droplet, and mass fraction of carbon remaining indroplet decreases to a lower level.

Modeling study on the flow patterns of gas–liquid flow for fast decarburization during the RH process

A water model and a high-speed video camera were utilized in the 300-t RH equipment to study the effect of steel flow patterns in a vacuum chamber on fast decarburization and a superior flow-pattern map was obtained during the practical RH process. There are three flow patterns with different bubbling characteristics and steel surface states in the vacuum chamber： boiling pattern（BP）, transition pattern（TP）, and wave pattern（WP）. The effect of the liquid-steel level and the residence time of the steel in the chamber on flow patterns and decarburization reaction were investigated, respectively. The liquid-steel level significantly affected the flow-pattern transition from BP to WP, and the residence time and reaction area were crucial to evaluate the whole decarburization process rather than the circulation flow rate and mixing time. A superior flow-pattern map during the practical RH process showed that the steel flow pattern changed from BP to TP quickly, and then remained as TP until the end of decarburization.

Numerical Simulation of Decarburization in a Top-Blown Basic Oxygen Furnace

An improved mathematical model to describe the decarburization process in basic oxygen furnaces for steelmaking is presented in this work. This model takes into account those factors or parameters that determine the bath-oxygen impact area, such as the cavity depth, the lance height, the number of nozzles and the nozzles diameter. In the thermal issue, the model includes the targeted carbon content and temperature. The model is numerically solved, and is validated using reported data plant. The oxygen flow rate and the lance height are varied in the numerical simulations to study their effect on the carbon content and decarburization rate.

Study on Diffusion Behavior of 72LX Blooms in the Decarburization Process

To elucidate the diffusion behavior of carbon atoms within the austenite region,the decarbonization of 72LX steel bloom was investigated.Experimental studies were performed to obtain the depth profiles of the decarburized layers within the temperature range of 950-1250℃.The findings show that,within a temperature range of 950-1200℃,both the depth of the decarburization layer of the grain interior(h_(in))and the depth of the decarbonization effect zone of the grain boundary(h_(b))increase concurrently with increasing holding temperatures and times and an inflection point is observed at 1200℃.By measuring the change in the sample diameter before and after the experiment,the change in the radius reduction of h_(Fe) causes by oxidation is obtained.Minimal changes are observed in h_(Fe) when the temperature is below 1050℃.As the temperature increases to 1100℃,a sudden change in h_(Fe) is observed,which corresponds to a rapid increase in oxidation.At temperatures above 1100℃,a more gradual change is observed.From the experimental results,a two-dimensional decarburization mathematical model is established and the carbon diffusion coefficients at different temperatures are obtained by simulation and regression fitting.The simulation values obtain from the carbon diffusion model matched well with the experimental values,thereby confirming the accuracy of the simulation process.

CO_(2)捕集和利用技术的应用与研发进展

由于CO_(2)的过度排放导致了全球严重的气候变化问题,实现碳中和已成为全球各国的共识,碳捕集、利用与封存(CCUS)是实现碳中和的必由路径之一,引起了研究者的广泛关注。中国石化南京化工研究院有限公司长期致力于CO_(2)捕集和利用技术的研发和应用推广工作,已形成低分压烟气碳捕集技术、NCMA(南化复合胺)脱碳技术和催化热钾碱脱碳技术3种成熟碳捕集技术,成功应用于多个工业项目中。同时,在新型碳捕集技术和CO_(2)利用技术领域开展了大量研究,并取得了一定的进展,部分成果达到了国内及国际先进水平。

Inconel 617合金在非纯氦气环境中的高温腐蚀行为研究

Inconel 617合金是高温气冷堆蒸汽发生器的候选材料,在反应堆超高温运行时可能会受到氦气中痕量杂质的腐蚀。为探究合金在高温堆环境中的腐蚀机理,本研究开展了Inconel 617合金在980℃的非纯氦气中的腐蚀实验,对气相以及腐蚀行为进行了分析。通过化学热力学和动力学计算,阐明了合金脱碳的机理,并建立了碳迁移判定模型和脱碳反应预测模型,与实验数据有良好的一致性。在此基础上,研究了预氧化和温度对脱碳反应的影响。研究结果表明,即使杂质含量极低,也会诱发相关的腐蚀行为。降低运行温度可以有效避免合金脱碳,但预氧化的抗脱碳效果不理想。因此,极低杂质含量并非高温堆一回路净化目标,应该根据模型预测和实验分析来选择更加合理的杂质控制方案。

304不锈钢氩氧脱碳精炼过程中炉渣成分预测模型

针对304不锈钢氩氧脱碳(Argon-Oxygen Decarburization,AOD)精炼过程中存在炉渣成分难以测量等问题,本研究综合考虑了顶枪吹氧、供气比例变化、物料熔化速度以及初始渣量对渣-钢反应和精炼炉渣成分的影响,建立了炉渣成分预测模型,并用于计算精炼过程中的炉渣和钢液成分变化。此模型计算的渣成分与钢液硫含量与实测值吻合较好,AOD精炼终点渣中SiO_(2)含量平均偏差为1.434%,CaO含量平均偏差为1.848%,Cr_(2)O_(3)含量平均偏差为0.080%,MnO含量平均偏差为0.016%,钢液终点S含量平均偏差为0.002%。

近二十年宝钢RH装备及技术进步

在汽车板、硅钢、镀锡板、管线钢、船板等高等级品种钢开发和质量提升需求的推动下,近二十年来宝山基地在RH精炼装备、工艺技术及自动化等方面取得了长足的进步,特别在RH真空精炼装备、高效脱碳、低成本处理、顶枪真空加热、夹杂物控制、RH专线化生产、环保耐材、RH智能一键精炼等方面形成了具有自身特点的工艺技术,满足了品种钢开发、质量提升和产能提高的需求。

20Mn2钢链条断裂原因分析

某厂20Mn2钢链条在使用中断裂。为找出链条断裂的原因,检测了断裂链条的化学成分、硬度、显微组织和断口形貌。结果表明:链条表面脱碳严重,导致表面疲劳强度和硬度下降;心部有大量铁素体和氧化物夹杂,导致其力学性能降低。是这两个因素导致链条在使用中断裂。

某涡轮发动机压气机叶片盘开裂的原因分析

某涡轮发动机压气机叶片盘采用13Cr15Ni4Mo3N半奥氏体沉淀硬化不锈钢制造,退火后依次进行了1 040℃水淬、-73℃冷处理、950℃水淬、-73℃冷处理和540℃×4 h时效,热处理后发现开裂。通过化学成分分析、宏观检验、金相检验、X射线衍射、电子背散射衍射和能谱分析研究了叶片盘开裂的原因。结果表明:叶片盘有三种裂纹,即R角处的长裂纹、表面网状裂纹和内部的二次裂纹;R角处长直裂纹主要是叶片过小的R角所致,网状裂纹是氧化脱碳及冷处理过程中产生的表面拉应力所致。

一种新型高强韧弹簧钢的脱碳敏感性

以一种新研发的Si-Cr系高强韧弹簧钢为实验材料,对不同加热和保温条件下该弹簧钢表面脱碳层形貌特征、脱碳敏感性及其影响机理等进行了研究,并从理论上建立了弹簧钢脱碳层深度与保温条件的关系.结果表明:该弹簧钢的总脱碳层深度随加热温度的升高呈先增加后减小的趋势,当加热温度为1100℃时,总脱碳层深度达到最大,约为231.2μm,其脱碳敏感温度为(1100±50)℃;随着保温时间的延长,弹簧钢脱碳层深度增加,且脱碳层深度与保温时间的平方根存在线性关系.与其他Si-Mn系和Si-Cr系弹簧钢相比,该Si-Cr系弹簧钢中由于碳含量较低,硅含量也适当降低,并且添加了适量的Cr和V,有效降低了脱碳敏感性.