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.

Vanadium recovery from stone coal through roasting and flotation

A new process for vanadium recovery from stone coal by roasting-flotation was investigated based on the mineralogy. The process comprised four key steps： decarburization, preferential grinding, desliming and flotation. In the decarburization stage, roasting at 550 ℃ effectively avoided the negative effect of the carbonaceous materials in raw ore and generation of free CaO from calcite decomposition during roasting. Through preferential grinding, the high acid-consuming minerals were enriched in the middle fractions, while mica was enriched in the fine and coarse fractions. Through flotation, the final concentrate can be obtained with V2O5 grade of 1.07% and recovery of 83.30%. Moreover, the vanadium leaching rate of the final concentrate increased 13.53% compared to that of the feed. The results reveal that the decarburization by roasting at 550 ℃ is feasible and has little negative impact on mica flotation, and vanadium recovery from stone coal is conducive to reducing handling quantity, acid consumption and production cost.

Optimization of an Existing Coal-fired Power Plant with CO²Capture

Nowadays, the worsening environmental issue caused by CO2 emission is greatly aggravated by human activity. Many CO2 reduction technologies are under fast development. Among these, monoethanolamine (MEA) based CO2 capture technology has been paid great attention. However, when connecting the CO2 capture process with a coal-fired power plant, the huge energy and efficiency penalty caused by CO2 capture has become a serious problem for its application. Thus, it is of great significance to reduce the related energy consumption. Based on an existing coal-fired power plant, this paper proposes a new way for the decarburized retrofitting of the coal-fired power plant, which helps to improve the overall efficiency of the power plant with less energy and efficiency penalty. The decarburized retrofitting scheme proposed will provide a new route for the CO2 capture process in China.

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.

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.

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.

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.

A process model for BOF process based on bath mixing degree

The process model for BOF process can be applied to predict the liquid steel composition and bath temperature during the whole steelmaking process. On the basis of the traditional three-stage decarburization theory, the concept of mixing degree was put forward, which was used to indicate the effect of oxygen jet on decarburization. Furthermore, a more practical process model for BOF steelmaking was developed by analyzing the effect of silicon, manganese, oxygen injection rate, oxygen lance height, and bath temperature on decarburization. Process verification and end-point verification for the process model have been carried out, and the verification results show that the predic- tion accuracy of carbon content reaches 82.6% （the range of carbon content at the end-point is less than 0. 1wt%） and 85.7% （the range of carbon content at end-point is 0. 1wt% -0.7wt%） when the absolute error is less than 0.02wt% and 0.05wt%, respectively.

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.

Analysis of oxide layer structure in nitrided grain-oriented silicon steel

The production of low-temperature reheated grain-oriented silicon steel is mainly based on the acquired inhibitor method.Due to the additional nitriding process,a high nitrogen content exists in the oxide layer,which changes the structure of the oxide layer.In this study,the structure of the surface oxide layer after nitriding was analyzed by scanning electron microscopy(SEM),electron back-scattered diffraction(EBSD),glow discharge spectrometry(GDS),and X-ray diffraction(XRD).The size and orientation of ferritic grains in the oxide layer were characterized,and the distribution characteristics of the key elements along the thickness direction were determined.The results show that the oxide layer of the steel sample mainly comprised particles of Fe2SiO4 and spherical and lamellar SiO2,and Fe4N and fcc-Fe phases were also detected.Moreover,the size and orientation of ferritic grains in the oxide layer were different from those of coarse matrix ferritic grains beneath the oxide layer;however,some ferritic grains exhibited same orientations as those in the neighboring matrix.Higher nitrogen content was detected in the oxide layer than that in the matrix beneath the oxide layer.The form of nitrogen enrichment in the oxide layer was analyzed,and the growth mechanism of ferritic grains during the oxide layer formation is proposed.

Coordinated control of carbon and oxygen for ultra-low-carbon interstitial-free steel in a smelting process

Low residual-free-oxygen before fmal de-oxidation was beneficial to improving the cleanness of ultra-low-carbon steel. For ultra-low-carbon steel production, the coordinated control of carbon and oxygen is a precondition for achieving low residual oxygen during the Ruhrstahl Heraeus （RH） decarburization process. In this work, we studied the coordinated control of carbon and oxygen for ultra-low-carbon steel during the basic oxygen furnace （BOF） endpoint and RH process using data statistics, multiple linear regressions, and thermodynamics computations. The results showed that the aluminum yield decreased linearly with increasing residual oxygen in liquid steel. When the mass ratio of free oxygen and carbon （[O]/[C]） in liquid steel before RH decarburization was maintained between 1.5 and 2.0 and the carbon range was from 0.030wt% to 0.040wt%, the residual oxygen after RH natural decarburization was low and easily controlled. To satisfy the requirement for RH decarburization, the carbon and free oxygen at the BOF endpoint should be controlled to be between 297 × 10^6 and 400 × 10^-6 and between 574 × 10^-6 and 775 × 10^-6, respectively, with a temperature of 1695 to 1715℃ and a furnace campaign of 1000 to 5000 heats.

Age-hardening of surface aged hardening alloy

Steel T8 treated by plasma surface decarburizing was alloyed by the Xu Tec process with Co,W and Mo. An alloyed layer of Fe Co W Mo with low carbon content was formed on the surface of the high carbon steel, thus an advanced gradient composite was produced. The specimens then were treated by the solution and aging treatments. The characteristics of age hardening of the alloying layer were studied. The hardness of the surface layer increases from HV200 to HV1 200 after the solution treatment at 1 190 ℃ and aging at 400 ℃ for 30 min. The results show that the surface aged high speed steel possesses not only high surface hardness, but also enough bulk strength. [

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.

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.

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.

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.

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.

Mathematical Modeling of the Vacuum Circulation Refining Process of Molten Steel

The available studies in the literature on mathematical modeling of the vacuum circulation (RH) refining process of molten steel have briefly been reviewed. The latest advances obtained by the author with his research group have been summarized. On the basis of the mass and momentum balances in the system, a new mathematical model for decarburization and degassing during the RH and RH KTB refining processes of molten steel was proposed and developed. The refining roles of the three reaction sites, i.e. the up snorkel zone, the droplet group and steel bath in the vacuum vessel, were considered in the model. It was assumed that the mass transfer of reactive components in the molten steel is the rate control step of the refining reactions. And the friction losses and drags of flows in the snorkels and vacuum vessel were all counted. The model was applied to the refining of molten steel in a multifunction RH degasser of 90 t capacity. The decarburization and degassing processes in the degasser under the RH and RH KTB operating conditions were modeled and analyzed using this model. Besides, proceeded from the two resistance mass transfer theory and the mass balance of sulphur in the system, a kinetic model for the desulphurization by powder injection and blowing in the RH refining of molten steel was developed. Modeling and predictions of the process of injecting and blowing the lime based powder flux under assumed operating modes with the different initial contents of sulphur and amounts of powder injected and blown in a RH degasser of 300 t capacity were carried out using the model. It was demonstrated that for the RH and RH KTB refining processes, and the desulphurization by powder injection and blowing in the RH refining, the results predicted by the models were all in good agreement respectively with data from industrial experiments and practice. These models may be expected to offer some useful information and a reliable basis for determining and optimizing the technologies of the RH and RH KTB refining and desulphurization by powder injection and blowing in the RH refining and for controlling the processes.

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.

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.