Isij International最新文献

The O₂ and N₂ mixing top-blowing method could effectively improve the mixing degree and suppress the temperature increase rate of the molten bath in vanadium extraction converter. In this paper, four kinds of top-blowing lances designed by an extra N₂ flow rate and various Mach numbers have been investigated by a series of water experiments and numerical simulations. On the basis of result, the mixing time was first increased and then decreased with the increase of lance height, and the lance height of 1400mm obtained the longest mixing time. There were two high-velocity regions generated by impaction of top-blowing jets and stirring of bottom-blowing bubbles. Simultaneously, there were two low-velocity regions formed by the block of furnace wall, and one low-velocity region formed by the local eddy. Comparing with the current top-blowing lance, all three new kinds of top-blowing lances obviously improved the kinetic condition and impaction cavity area of molten bath, which would further be improved with a larger design Mach number. Therefore, an appropriate top-blowing lance had been selected in the industrial application research, which achieved a shorter melting time and a faster vanadium extraction rate, in contrast to the current lance.

The agglomeration of droplets dispersed in an immiscible liquid is often an issue in metallurgical processes. To determine the effect of wettability on droplet agglomeration, we conducted (1) wettability and (2) agglomeration experiments using immiscible liquid paraffin and glycerin aqueous solution. In the wettability experiment, a droplet of one liquid was settled on the other liquid and its shape was observed. The glycerin droplet was wrapped by liquid paraffin, while the paraffin droplet spread on the surface of the glycerin solution. Therefore, liquid paraffin wetted the glycerin droplet, while glycerin solution did not wet the paraffin droplet. In the agglomeration experiment, after the droplet settled or floated in the other liquid layer to arrive at the boundary between the two liquid layers, we measured the time required for droplet agglomeration in its liquid layer. The agglomeration of paraffin droplets from the glycerin solution was faster than that of glycerin droplets from liquid paraffin, indicating that non-wettability of droplets accelerated agglomeration.

All 61 sticker breakouts and 183 false sticker breakouts were obtained based on the on-line mould monitoring system during the conventional slab continuous casting. The 16-dimensional temperature characteristics and temperature velocity characteristics of the sticker breakout were extracted. The sticker breakout recognition based on the XGBoost forward iterative model was developed and optimized by the mean square error algorithm. The results show that the prediction probability of the sticker breakout after optimization is in the range of 0.72∼1.00. The smallest output value 0.5 higher than that before optimization. When the threshold is set to 0.65, the optimized XGBoost model can correctly predict all sticker breakouts and has a 99.5% accuracy rate. The XGBoost model has a stronger generalization ability and higher prediction accuracy, which promotes the intelligent production of continuous casting.

Gas jet cooling is widely used because the device is simple, oxidation can be prevented, and a uniform cooling capacity can be obtained with thin steel sheets. Because the gas jet cooling ability is affected by the physical properties of the gas such as the mixed gas ratio, a quantitative evaluation of the influence of these factors is very important. However, few studies concerning prediction of the cooling capacity of mixed gas jets in atmospheres with different concentrations have been published.

In this research, the results of experiments and a fluid analysis with an air-helium gas jet in an air atmosphere were compared with the results obtained with Martin's non-dimensional empirical equations. As the nozzle condition, a single round nozzle with a tapered shape was examined. The helium concentrations with respect to air were 0, 20, 50, and 100 vol%, and the pressure conditions were 3 and 5 kPa.

Compared with the experimental results, Martin's equations overestimated the improvement of cooling performance with increasing helium concentrations. In the analysis in the present study, it was found that mixing with ambient air increased as the helium concentration decreased.

The trend of divergence between the experimental and predicted cooling capacity was clearly presented in this research. The results of this study will make it possible to improve the accuracy of predictions of the cooling capacity of impinging gas jets with different concentrations of the atmosphere and the gas jet.

A thermomechanical simulator Gleeble 3800 was used to simulate the thermal cycles experienced by various heat-affected zones (HAZ) during the welding process. The influence of peak temperature (T_p, 500°C~1320°C) on the hardness, microstructure, precipitates, and properties of complex steel 780FB with microalloyed elements Ti, Nb, and V was systematically studied. The contributions of dislocation strengthening, precipitation strengthening, fine grain strengthening, and phase transformation strengthening increments to strength changes of samples after different thermal cycles were quantified, and the calculated results were found to be consistent with the experimental data. Compared with 780FB, there was little change in microstructure and properties when T_p was 500°C. When T_p was 650°C, the increase in VC density from 43/μm² to 288/μm² caused the enhancement of hardness and strength. The precipitation strengthening increment (49.84MPa) played a dominant role in strength improvement. As partial bainite in the microstructure of 780FB transformed into ferrite at T_p of 800°C, the weakening of phase transformation strengthening (-57.5MPa) became the main factor in strength change. The softening and strength reduction further increased when T_p was up to 980°C, as 780FB completely recrystallized and transformed into ferrite and MA islands. The phase transformation strengthening further reduced by 74.75MPa. When T_p was 1320°C, the VC density decreased from 43/μm² to 13/μm², and the (Ti,Nb)C density decreased from 34/μm² to 14/μm², leading to severe grain growth (2.24μm to 19.89μm) and bainite transformation. The decrease in precipitation strengthening (-26.86MPa) and fine grain strengthening (-87.91MPa) counteracted with the increase in phase transformation strengthening (51.62MPa), resulting a slight decrease in hardness and strength.

The heats of fusion of Fe, Ni, and Co were measured using a closed-type aerodynamic levitation method to prevent chemical interactions with the container and oxidation of the samples. The hypercooling limits of these metals were experimentally determined using the correlation between the undercooling temperature and thermal plateau time. The heats of fusion of the metals were obtained as the product of the hypercooling limit and the isobaric heat capacity. The experimentally determined hypercooling limits for Fe, Ni, and Co were 280, 414, and 360 K, respectively. Using these hypercooling limits, the heats of fusion of pure Fe, Ni, and Co were determined as 12.7 ± 2.2 kJ mol^-1, 16.9 ± 5.6 kJ mol^-1, 14.8 ± 2.8 kJ mol^-1, respectively. Notably, these experimentally determined heats of fusion using the closed-type aerodynamic levitation method closely align with the literature values within the range of experimental uncertainty, affirming the reliability of this measurement technique.

Mixed powder of SiO₂ and SiC was heated to produce Si in air by irradiating multi-mode microwave at 2.45 GHz using a porous alumina crucible of sintered cement. SiC generated heat inside the mixture. Mullite layer was produced inside of crucible wall. Molten Si was produced at the apparent temperature between 1550°C and 1600°C during 5400s and 6000s. The apparent temperature was much lower than 1778°C determined thermodynamically. This is the characteristics of microwave that heat generates at the contact points of particles and the pointed parts of the surface in powder. A furnace for producing high-quality Si by microwave heating is proposed.

The carburizing and nitriding, essential surface modification methods for steels, enhance wear, fatigue, and corrosion resistance by forming fine carbides, nitrides, and nanoclusters involving alloy elements. Understanding the interactions between interstitial X (C or N) and substitutional elements M is critical for optimizing these processes and tailoring the material properties to specific applications. This study investigates the interaction energies in diatomic and triatomic clusters involving C/N atoms and substitutional elements of Al, Si, Ti, V, Cr, Mn, Co, Ni, Cu, Zr, Nb, and Mo. Using the first-principles calculations, this study reveals the intricate balance of interactions within these clusters, highlighting how atomic arrangements and specific element combinations can lead to either repulsion or attraction. We found that the interaction energies for triatomic clusters can be represented using a linear combination of interaction energies for diatomic clusters. Stable triatomic clusters comprise the second nearest neighbor M-X interactions for Fe-Ti-N, Fe-V-N, and Fe-Nb-N alloys. This finding was consistent with experimental observations of the monolayer clusters. Our analysis using the multiple linear regression and stratified analysis reveals that the metallic radius of element M influences interaction in M-X clusters: a larger metallic radius causes repulsion in the first nearest neighbor clusters and attraction in the second and third nearest neighbor clusters due to strain relief.

Over many years, mesoscale analysis such as the phase-field method has been the mainstream for numerical simulation of solidification. In contrast, our group has taken the initiative in applying molecular dynamics (MD) simulation to various problems in solidification. In this review, recent advances and contributions of MD simulations for solidification are presented. The primary contribution of MD simulation is the derivation of solid-liquid interfacial properties since it is not easy to measure these properties experimentally with high precision. In addition, recent significant progress in computational environments has dramatically expanded the possibilities of MD simulations for solidification. Now, MD simulations with a scale of billion atoms at the micrometer-scale have become a reality, enabling the exploration of analyses previously dominated by mesoscale methods, such as grain growth and dendrite growth. In particular, the dendrite growth at the micrometer-scale presented here represents the first achievement of directly simulating a typical four-fold symmetrical dendrite structure solely through atomic-scale simulations, to the best of the author's knowledge. Moreover, new attempts at the fusion of data-driven methods and MD simulations are presented in this review, aiming to contribute to the rapid development of the field of solidification in the future.

A new type of online accelerated cooling equipment for seamless steel pipe and its application experiments were introduced in the present work. The equipment can simultaneously cool the inner and outer surface of seamless steel pipes. By using online accelerated cooling process, the mechanical properties of the test steel pipe made of Q345B composition meet the requirements of Q460E steel grade index, with the yield strength of 460~475MPa, the tensile strength of 601~603MPa, the elongation of 21.5~26.5%, and the -40°Cimpact energy of 136J.