Measurements have been made of the rate of Fe3C formation from Fe3O4 powder and Fe3O4 single crystals at 773 K and 1023 K under the high pressure of 0.5 and 1.0 MPa by using thermo-gravimetric method. Along with the kinetic study of Fe3C formation, high resolution TEM observation around the interface between Fe3O4 matrix and the formed Fe3C have been carried out to confirm the thermodynamically possible direct Fe3C formation from Fe3O4 without the formation of intermediate metallic Fe. Analysis of the rate results suggests that the reaction mechanism of Fe3C formation was possibly described by the sequential reactions of the conversion of Fe3O4 to Fe3C via intermediate metallic Fe although the metallic Fe existence was not confirmed by TEM observation. This inconsistency was explained by considering the relative reaction rates of Fe3C formation from Fe and Fe formation from Fe3O4. It was also found that not only the carbon activity of more than unity but also the low oxygen potential enough for metallic Fe existence might be required for the Fe3C formation.
The viscosity of the CaO–SiO2–MnO(–CaF2) slags (CaO/SiO2 = 1.0, MnO = 10, 40 mass%) was measured to clarify the effect of CaF2 on the viscous flow of molten slags at high temperatures. Furthermore, the Raman spectra of the quenched glass samples were quantitatively analyzed to investigate the structural role of CaF2 in a depolymerization of silicate networks. The critical temperature of the slags abruptly increased at 15 mass% CaF2, which was confirmed to originate from a crystallization of cuspidine using XRD analysis. The viscosity of the slags continuously decreased by CaF2 addition in the 10 mass% MnO system, whereas the viscosity of the 40 mass% MnO system was not significantly affected by CaF2 addition. The activation energy for the viscous flow of silicate melts decreased by CaF2 addition and its tendency became less significant in the more basic composition, i.e. in the 40 mass% MnO system. The effect of CaF2 on the viscosity of the slags was quantitatively analyzed using micro-Raman spectra of quenched glass samples accompanying with a concept of silicate polymerization index, Q3/Q2 ratio. A polymerization index continuously decreased with increasing content of CaF2 in the 10 mass% MnO system, whereas it was not affected by CaF2 in the 40 mass% MnO system. Consequently, the bulk thermophysical property of the CaO–SiO2–MnO–CaF2 slags was quantitatively correlated to the structural information.
In order to describe the formation of FeS–MnS–CuS0.5 inclusion in γ-Fe, the thermodynamic properties of the FeS–MnS–CuS0.5 system have been investigated at 1473 K. The isothermal section was determined by a chemical equilibration technique. The activities of FeS and CuS0.5 in the liquid phase were determined by equilibrating with carbon saturated iron or molten copper, and the activity of MnS was evaluated by using the Gibbs-Duhem equation with Schuhmann’s tangent intercept procedure. Finally, the composition of solid steel equilibrated with the FeS–MnS–CuS0.5 inclusion was estimated using the determined thermodynamic properties.
The AlN solubility product in liquid iron containing manganese up to 22 mass% were measured by the metal-nitride-gas equilibration technique in the temperature range from 1823 to 1873 K. Manganese significantly increased the AlN solubility product in liquid iron primarily due to the large effect of manganese on the nitrogen solubility. Using the Wagner’s formalism, the experimental results were thermodynamically analyzed to determine the thermodynamic interaction parameters between manganese and aluminum in high Mn–Al alloyed liquid steels as follows;
A mathematical model based on the continuum mechanic concept has been developed to describe the profile of solid particles in an industrial scale blast furnace with respect to the in-furnace conditions and its characteristics such as the shape and size of the deadman. The Navier-Stokes differential equation for multi-phase multi-dimensional space has been used to describe the behavior of existing phases. The surface stress tensor has been defined as an extra term and added to the Navier-Stokes equation to describe the particle-particle interactions. This extra term in the Navier-Stokes equation behave as a breaking force when the particles are sliding down. It is shown that the particles change their profile from a V-shape to a W-shape due to the characteristics of the deadman. Moreover, the velocity magnitude is higher at the outer surface of the deadman for higher grid-slabs in this region than the near-wall cells. However, the situation changes as solid particles moving to even lower level of grid-slabs at the outer surface of the deadman in comparison to near-wall cells. It has also been shown that an increase in the magnitude of the effective pressure reduces the velocity magnitude of descending particles.
An undisturbed drainage of molten liquids from the hearth through the taphole(s) is a prerequisite for smooth operation, with high productivity and long campaign life of the blast furnace. Along with growing blast furnace volumes and production rates the taphole load has significantly increased. Still, the flows of molten iron and slag in the taphole have not received much attention even though several investigators have studied the multiphase drainage phenomena of the hearth. In the present paper a three-dimensional computational fluid dynamics model is developed to study the transient flow behavior of iron and slag in the taphole. The interface shape between iron and slag is simulated by utilizing the volume of fraction method. A short-term tapping process is simulated and the developing flow patterns in the taphole are illustrated. It is demonstrated that both non-stratified and stratified flows can occur at different stages of the tap, where gravity plays an important role for the evolving two-liquid flow patterns. The results of the analysis also show that the slag-iron interface and phase velocity profile are reshaped along the flow direction.
Three-dimensional mathematical model describing simultaneous combustion, fluid flow, heat and mass transfer were established in coupled combustion and coking chambers of a coke oven. Since coupling numerical simulation was time-consuming and hard to get convergence, two kinds of decoupling methods were proposed and performed to simplify the simulation and improve the calculation efficiency. The parallel decoupling method separates the coupled transport phenomena into two independent processes existing in combustion and coking chambers, respectively, with necessary heat flux boundary condition. While the serial decoupling method is, first calculating the steady heat transfer with combustion and fluid flow in combustion chamber, and then using the obtained results as inputs to simulate the unsteady heat transfer from combustion chamber to coking chamber via the inter-wall. As far as the temperature evolution in coking chamber was concerned, these two decoupling numerical methods could supply alternative and efficient ways for numerical simulation of transport phenomena in coupled chambers of a coke oven. It is expected that this work is helpful for decoupling simulations of other similar complicated thermal transport processes in coupled geometry.
The role of COREX shaft furnace plays is similar with that of lump zone in blast furnace, but there are still some differences existed between them, especially the burden distribution. However, the research on burden distribution in COREX shaft furnace is quite few. Therefore, a three dimensional model is established in present work based on Discrete Element Method (DEM), after validated by industrial experiments, the model is used to investigate the burden profiles and distribution along radius in the upper part of COREX shaft furnace, the studied parameters include the distributor angle, rotating speed and length, and the stock line. The results show that the distributor angle affects the burden profile most, stock line is next, while rotating speed and length of distributor are least. The small particles segregate more intensively than large and medium particles. Additionally, it is better to reduce the distributor length and stock line in order to obtain a stable burden distribution along radius.
The agglomeration behaviour of reduced iron, made from magnetite powder by carbothermic reduction, was observed by using the in-situ X-ray transmission observation technique. The iron particles, above 1 mm, were clearly observed as black points. Further, the reduction speed was examined by using the thermogravimetric analysis. The bulk density of the packed powder layer and the grain size distribution of magnetite powder and carbon black powder were changed and the effects of them on the reduction speed and the agglomeration degree were examined. The agglomeration degree was evaluated with diameter of iron particles on the X-ray photographs, taken during heating, and the weight of collected iron particles after the observation experiments. Neither the bulk density of powder layer nor the grain size distribution of powder mixture affected to the reduction speed. The agglomeration degree decreased when the bulk density of the powder layer was increased by compacting. On the other hand, the agglomeration degree was increased when the grain size distribution of powder mixture was widened. Further, the height change of powder layer was also measured on the X-ray photographs and compared with the iron particles appearing behaviour to estimate the microscopic agglomeration behaviour. The mechanisms that grain size distribution affected the agglomeration degree were discussed.
Hot metal desulfurization behavior with dolomite flux was examined in heat treatment tests of pellets and in small-scale and commercial-scale hot metal desulfurization tests by mechanical stirring. In the heat treatment tests of pellets, the Mg gas generation ratio at 1673 K increased as the CaO/MgO ratio increased. The Mg gas generation ratio reached 90% with dolomite, which was 1.4 times higher than that with CaO + MgO at the same CaO/MgO. With calcined dolomite and Al ash, CaO efficiency for hot metal desulfurization at 1673 K was 20–30%, which was around double the results with CaO + MgO and CaO. In the desulfurization slag, sulfur was concentrated not with Mg, but Ca and Al were found in an EPMA analysis and detected as CaS by X-ray diffraction. Desulfurization with calcined dolomite and Al ash is considered to proceed by ① desulfurization by Mg(g) and fixing of MgS as CaS, and ② desulfurization by CaO with Mg de-oxidation. 200 t commercial-scale hot metal desulfurization tests with mechanical stirring were carried out. The obtained Mg efficiency for desulfurization was in the range of 15–25% with Mg consumption of 1–1.3 kg/t as MgO. These results were within the same trend as in other studies using metallic Mg and MgO with Al.
The macro-scale segregation of alloying elements during the casting continues to afflict the manufacturers of steel ingots, despite many decades of research into its prediction and elimination. Defects such as A-segregates are still commonplace, and components are regularly scrapped due to their presence, leading to increased economic and environmental costs. With the growth of the nuclear power industry, and the increased demands placed on new pressure vessels, it is now more important than ever that today’s steel ingots are as chemically homogeneous as possible.This article briefly reviews the development of our current understanding of macrosegregation phenomena during the 20th century, before going on to assess the latest developments in the field of macrosegregation modelling. The aim of the text is to highlight the shortcomings of applying contemporary macromodels to steel-ingot casting, and to suggest practical alternatives. In addition, the experimental characterisation of macrosegregation is explored, and a review of the various techniques currently available is presented.
In the steelmaking and continuous casting (SMCC) production process, the operation time delay often occurs which may lead to planned casting break or processing conflict so that the initial scheduling plan becomes unrealizable. Existing rescheduling methods with disturbances firstly classify the disturbances according to the disturbance type and disturbance quantity only by artificial experience or rules, and then directly adjust initial scheduling plan with corresponding rescheduling method. Those methods don’t analyze the influence degree of disturbances to the initial scheduling plan in detail, so the adjustment degree of initial scheduling plan is always too greater, which leads to the poor continuity and stability of initial scheduling plan. In this paper, the relation among operation time delay, planned casting break and processing conflict is deeply analyzed. Then a novel prediction method for abnormal condition of scheduling plan with operation time delay disturbance in SMCC production process is proposed including disturbance identification of operating time delay based on event-driven mechanism, analysis on charges based on reachability matrix, analysis on influence degree of disturbance and abnormal condition decision of initial scheduling plan. As a result, the real-time application shows that the proposed prediction method can timely and accurately predict the abnormal condition of the scheduling plan with operation time delay disturbance in SMCC production process, which can only adjust the affected charges that must to be rescheduled in the initial scheduling plan and reduce the frequency of complete rescheduling. The initial scheduling plan can also maintain the good continuity and stability.
In the steel strip manufacturing process, a high temperature steel strip at a temperature of more than 800°C is rapidly cooled by circular impinging water jets. The cooling rate is an important parameter that characterizes the desired microstructure and mechanical properties of the steel strip. In the cooling process, the nozzle arrangement of the water jet system can be easily changed as necessary and heat transfer characteristics can be controlled by adjusting the nozzle arrangement. In this study, inline and staggered nozzle arrangements are adopted. By using the numerical method developed in a previous study, cooling behaviors such as the temperature distribution of the plate surface, the cooling history of the plate, and the average heat flux are determined and compared quantitatively for each nozzle arrangement.
Tailored properties in hot press forming process (HPF) were investigated with focus on phase transformation characteristics and deformation behavior of constituent base materials for the Tailor Welded Blank (TWB-HPF) and partial quenching (PQ-HPF) approaches. The former uses sheets with different hardenabilities, which results in graded mechanical properties after HPF. The latter uses a single sheet but different heat treatment conditions, which eventually induce the same effect as the first approach. Preliminary dilatometric experiment was conducted to investigate the phase transformation characteristics of the two base metals for TWB-HPF. U-channel was formed by draw bending with the two approaches. For PQ-HPF, several initial tool temperatures varying from room to 450°C were investigated. Thermo-mechanical finite element (FE) analyses of the HPF process with metallurgical considerations in the constitutive model were performed for parts exhibiting tailored properties. These analyzes included the evaluation of heat transfer characteristics and the microstructure evolutions under HPF conditions. A thermodynamic calculation program was used to determine the thermo-physical, physical and metallurgical properties for various microstructures and temperatures. FE analyzes of the hot press forming with phase transformation considerations were conducted using the commercial software DEFORMTM-3D with the DEFORMTM-HT module. The combined experimental and simulation results provided an understanding, on the one hand, of the role of phase transformation in strengthening the material and reducing springback for the TWB-HPF approach and, on the other hand, of temperature on phase transformation characteristics of HPF steel for the PQ-HPF approach.
In order to produce 316L stainless steel separators with low contact resistivity and low cost, an attempt was made to reduce the contact resistivity of 316L steel by acid treatment. In the present work, the contact resistivity and corrosion resistance of acid-treated 316L stainless steels were investigated. Elemental composition, thickness and structure of the passive film on the steel surface were analyzed with transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS). It is found that the contact resistivity of the stainless steel is closely related to the ratio of Fe in oxide-form in the passive film, irrespectively of the thickness of passive film. When the proportion of Fe in oxide-form to the sum of Fe and Cr in oxide-form, i.e. Feox/(Feox+Crox) is lower than ca. 40 at%, the contact resistivity is reduced to lower than 10 mΩ cm2. Besides, the corrosion resistance of the acid-treated stainless steel having low contact resistivity is very high. Power generation test shows that I – V characteristic and durability of the cell assembled using the acid-treated 316L steel separators of low contact resistivity are equivalent to those of the cell assembled using carbon-coated separators.
Electrochemical hydrogen permeation tests of pure Fe sheets rusted by cyclic corrosion test (CCT) and atmospheric exposure were carried out under controlled temperature and humidity to investigate the influence of atmospheric corrosion on the hydrogen entry behavior. The hydrogen entry into the Fe specimens rusted by CCT increased under wet condition, and the hydrogen entry was increased with the CCT cycle number. During drying process after the wetting, hydrogen entry was further enhanced and a peak of hydrogen current was observed. The peak hydrogen permeation current tended to increase with the growth of rust layer, and the peak value of the hydrogen permeation current became remarkably higher than that at the highest humidity when the rust layer was relatively thick. Similar enhancement of hydrogen entry into an outdoor-exposed specimen was also observed during drying. Drying process after CCT resulted in an increase in hydrogen content of 5 mm-thick steel specimens measured by means of thermal desorption analysis, indicating the enhancement of hydrogen entry during drying process and showing a good agreement with the electrochemical hydrogen permeation test results. It is required to take into consideration the enhanced hydrogen entry to estimate concentration of hydrogen from the environment.
The dynamic continuous-cooling-transformation (CCT) diagrams of Nb–Ti microalloyed steel for four different deformation temperatures of 850, 900, 950 and 975°C were plotted by means of a combined method of dilatometry and metallography. The influence of deformation temperature on continuous cooling transformation behavior and transformation microstructure was elucidated. The reason that the polygonal ferrite transformation field is shifted to the right and moved down as the deformation temperature is increased and the progress of transformation for lowest continuous cooling rate of 0.5°C/s was obviously retarded at the lowest deformation temperature of 850°C was discussed in details based on transformation kinetics and strain-induced precipitation kinetics, respectively. Moreover, the polygonal ferrite grain size for lowest continuous cooling rate of 0.5°C/s can be significantly refined from approx. 15.4 μm to 9.4 μm as the deformation temperature is reduced from 975°C to 850°C. In addition, the empirical equation to calculate γ-α phase transformation start temperature was established, and the calculated Ar3 temperatures are in good agreement with measured ones.
Carbon and manganese combined effect on the mechanical behavior of martensite was characterized and analyzed using literature and new experimental data of various carbon-manganese steels. A synergy effect of carbon and manganese on the martenstite strength and strain hardening was detected and was then taken into account in a specific way in the simplified model, based on a Continuous Composite Approach. Model was adjusted with only one fitting parameter and the obtained results are in good agreement with experimental stress-strain curves.
The applicability of high chromium (Cr) steel as the main structural material in fast breeder reactors (FBR) has been explored to enhance the safety, the credibility and the economic competitiveness of FBR power plants. Vanadium (V) and Niobium (Nb) are believed to improve the high-temperature strength of high Cr steels by precipitating as carbides and/or nitrides, namely fine MX particles, although the long-term efficiency and stability of such precipitation strengthening mechanisms resulting from the fine MX particles have not been clarified yet. The effects of V and Nb on degradation of creep properties were investigated under FBR operating conditions, e.g., at 550°C for 500000 h, and the relationship between the long-term creep properties and microstructural changes was investigated considering the MX particles and the Z-phase. It was found that the optimal V and Nb contents for excellent high Cr steel of FBR grade are 0.2 mass% and <0.01 mass%, respectively, under FBR operating conditions.
We investigated the factors affecting static strain aging under stress in a Fe–22Mn–0.6C twinning-induced plasticity steel at room temperature. The magnitude of strengthening by the static strain aging was estimated by tensile strain holding and subsequent re-loading. Strain holding time, pre-strain, strain rate, external stress, and diffusible hydrogen content were varied to clarify their effects on static strain aging, and the present static strain aging was found to be affected by all of these factors. In this paper, we show the phenomenological laws of the relationship among the factors and the stress increase due to the static strain aging.
Recycling iron–bearing dust from steel mills has gained a considerable attention in the past two decades to recover the valuable metals in dust while improving the sustainability of steel production. As a method for extracting the metals from dust, the reduction of dust–carbon composite agglomerates using a rotary hearth furnace (RHF) has been practiced in the steel industry. The use of low–grade carbonaceous reductants, such as low–rank coal and waste plastic, is of steelmakers’ interest to further enhance the waste recycling using the RHF process. However, applying these materials as reductants has proven to be a challenging task since the impact of the released volatile gas from such reductants on reduction reactions is not predictable. In addition, the reduction kinetics of dust pellet in RHF is more complicated than the reaction behaviour of sintered ore in blast furnace due to the higher furnace temperature, faster reduction and rapid gas evolution inside the agglomerate. To predict the reaction behaviour of the dust–carbon composite in RHF, a mathematical model was developed. The model takes into consideration heat and mass transfer as well as the reduction reaction of iron and zinc oxides, gasification of carbon and release of volatiles. The simulated behaviour of a dust pellet by the proposed model provides beneficial information to promote recycling an expanded range of waste materials in the RHF process. The modelling approach and calculation results are discussed in the present paper.
In order to get a safer and more reproducible slag yard practice, the cooling of slags from stainless steel production in a slag yard was studied. A numerical 1D model was used to predict the spatial and temporal evolution of the temperature in the yard. This model has been validated based on temperature measurements at the surface and in the bulk of an industrial yard consisting of 22 layers. Each new layer initially cools down, but is heated again as additional layers are poured on top. In the bulk of the yard, temperatures of over 1273 K can be maintained throughout the filling of the yard. This temperature is a function of the process parameters. The validated model was used to quantify the influence of the layer thickness and the interval between subsequent layers on the temperature evolution within the yard.