Utilization of small coke in the blast furnace was carried out to improve the permeability in the lower part of the blast furnace. However, at high small coke rates, it was thought that some small coke continues to exist in the lower part of the blast furnace because the small coke charging rate is larger than the gasification reaction rate of the small coke. Therefore, the effect of the small coke rate on permeability in the lower part of the blast furnace was investigated. At high small coke rates, residual small coke with a reduced particle size counted to exist in the lower part of the blast furnace after the coke gasification reaction, and the average particle diameter of the coke and the void fraction of the coke packed bed in the lower part of the blast furnace decreased. It was estimated that the increase in the pressure drop of the coke packed bed in the lower part of the blast furnace was larger than the decrease in pressure drop in the cohesive zone, and as a result, the pressure drop in the lower part of the blast furnace increased.
Various types of brick masonry are used in the handling and treatment of hot materials in steelmaking processes. Although trouble related to damage of the bricks and joints is an important issue, it is difficult to predict and prevent damage of brick masonry because masonry is characterized by heterogeneity, nonlinearity and nonequilibrium. In this paper, the brick masonry in a coke oven is studied as an example, and a method of deformation prediction under external force is developed as a basic study. First, a compression test of a sample consisting of two bricks with one mortar joint is performed. Second, a part of a heating flue of a coke oven made of bricks is constructed as a test sample, and brick masonry deformation under external force is measured experimentally. Third, a model of the same heating flue in the experiment is prepared, and a numerical elasto-plastic analysis is carried out using the total strain rotating crack model based on the measured mechanical properties. Finally, the experimental and numerical deformation results are compared. The results validated this method of predicting masonry deformation.
In the current trend, a low carbon operation of blast furnace is going to make liquid permeability severe condition due to thinning of coke layer around cohesive zone. An iron carburization reaction is one of the most important reactions at the cohesive zone, because an enhancement of the reaction has a positive possibility to improve a metal dripping behavior from cohesive zone. Although it is thought ash of carbonaceous material has a negative effect on the reaction, there is not enough correctly focused knowledge on behavior of the ash in iron carburization reaction. In this study, several kinds of carbonaceous material samples with ash remove treatment by acid solution were prepared. The carbonaceous material samples were applied for “in-situ” observation of molten iron formation behavior due to iron carburization reaction under a constant heating rate condition with inert gas atmosphere. It was found that the acid treatment decreased not only amount of the ash in the carbon samples but also Na concentration of the ash. Decreasing of ash content in carbonaceous material decreased initial Fe-C liquid formation temperature because obstruction on reaction area of iron carburization reaction was decreased. Decreasing of Na content in ash caused changing of molten ash’s properties, increasing of melting temperature and decreasing of wettability to iron and carbon. In case of without the acid treatment, it was thought molten ash could behave as a barrier at a reaction interface of iron carburization due to good wettability from lower temperature than initial Fe-C liquid formation temperature.
A low carbon operation is an unfavorable situation for liquid permeability around cohesive zone, because liquid volume will increase against solid coke in there. In order to keep a healthy operation with this technique, information of wetting behavior between liquid iron and coke should be correctly understood. However, there is not enough information about wetting behavior between them, because of many difficulties about wettability measurement from an active reaction between iron and carbonaceous materials. In this study, a sessile drop method with molten sample injection system was applied to measurement of wetting behavior between liquid iron and carbonaceous material at 1673 K for excluding reaction between samples before starting measurement. Carbonaceous material’s substrates were made from mixture powder of graphite and alumina by hot press at 1873K. From the results, following knowledge was revealed. Molten iron samples un-saturated with carbon showed bigger values of contact angles, 110°~120°, at initial stage, than apparent constant values of them, 85°~100°, at latter stage. It indicated a reaction between iron and carbonaceous materials had obvious effect on wetting behavior between them due to decrease an interfacial energy during the reaction. Mixed alumina powder in the substrate prevented to wetting behavior of iron sample on carbonaceous materials, and they changed their apparent constant contact angles from 115° to 130°. The alumina powder had effects on not only wetting behavior but also reaction between iron and carbonaceous materials.
Recently, interest in the art of dephosphorization in steelmaking has turned toward relatively lower basicity slag saturated with a [2CaO・SiO2-3CaO・P2O5] solid solution rather than CaO-saturated slag. In this work, laboratory experiments were carried out in order to investigate the change of the phosphorus-concentrated phase in low basicity slag. Phosphorus-containing slag was added onto 10 kg of hot metal, and its basicity was lowered through the desiliconization reaction of the hot metal at 1573 K.
EPMA observation of the slag after the experiment showed different mineral phases corresponding to the slag basicity (mass%CaO) / (mass%SiO2). When basicity was larger than 0.8, the phosphorus-concentrated phase (P-phase) was observed but was different from the solid solution phase in the initial slag. When basicity was lower than 0.8, the P-phase was not observed, and phosphorus was distributed through the slag at a low concentration. These results would reflect decomposition of the P-phase and formation of homogeneous liquid slag.
Based on a thermochemical consideration with the phase diagram of the [CaO-SiO2-FeO] system, the dissolution of the P-phase observed in the present experiment would be due to the slag composition approaching the SiO2 saturated region and a resulting decrease in CaO activity. From the viewpoint of the phase diagram of the [CaO-SiO2-P2O5] system, lowering the slag basicity to CaO・SiO2 saturation would come to coexistence of a higher P-phase such as 5CaO・SiO2・P2O5 or even 3CaO・P2O5, which would lead to an increase in the driving force for phosphorus transfer from slag to metal (so-called rephosphorization) at lower slag basicity.
It is well known that a formation of band segregation in products manufactured by centrifugal casting process is strongly influenced by shearing flow behavior in lidquid-solid coexisting regions of metals. However, it is difficult to observe or measure what happens in the process because the preocess is carried out under high temperatures and the material is usually opaque. Therefore, we tried to observe the shearing flow behavior in the vicinity of solidification front in the centrifugal casting process by using flow and solidification simulations based on a particle method. We simulated flow and solidification behaviors in the process with growing solidification shells which rotate with the mold, and investigated the influence of rotating speed on the shearing flow behavior of the metal. As a result, the shearing flow behavior was well evaluated by spectral analysis of the velocity gradient around the solidification front. The shearing flow behavior is strongly influenced by the fluctuation of free surface and the apparent viscosity of fluid phase.
The effect of Si on the oxidation resistance of high purity Nb containing 19% Cr ferritic stainless steels have been investigated by means of isothermal heating at temperatures up to 1273 K in air and, the structures of scale and the scale/metal interface were investigated with FE-SEM and FE-TEM. The results are as follows:
Si improved the oxidation resistance, as reported in previous studies. Si addition of about 0.1% improved the limit of the oxidation resistance more than 100 K. The presence of an amorphous SiO2 layer was found between the Cr2O3 scale and the metal. This layer might act as an oxidation resistance barrier. In the Si-free steel, a NbO2 layer formed under Cr2O3 scale, and the Fe2Nb- free region formed in the vicinity of the surface. On the other hand, when Si was added, the formation of NbO2 layer was suppressed. In case of 1%Si, no NbO2 layer formed and the Fe2Nb-free region was eliminated. In addition, Fe particles were present in the Cr2O3 scale in the Si-added steel.
Fe-Zn intermetallic compound (IMC) coatings with various volume fractions of constituent phases, such as Γ, Γ1, δk, and δp, were deformed to reveal the mechanism responsible for the delamination of IMC coatings. From the fracture surfaces of coating layers subjected to tensile stress, it was clarified that Γ phase is brittle due to its weak grain boundaries. Under compressive stress, cracks propagated along either Γ/Γ1(δk) or Γ/steel interfaces from the pre-existing vertical cracks which were presumably formed during fabrication process. It is demonstrated that the former route initiates an inclined crack in the δk phase layer and results in the delamination of the IMC coating. The transition in the crack propagation path from Γ/steel to Γ/Γ1(δk) interface was observed as the thickness of the Γ layer increased. Without Γ1 phase, the transition was found for thicker Γ layer than that observed with Γ1 phase. The weakness of the Γ grain boundary was found to play an important role in deflecting the Γ/Γ1(δk) interface crack to Γ/steel interface, and hence enhance the resistance to delamination.
Deep learning by convolution neural network (CNN) was applied to recognize a microstructure of steels. Three typical CNN-models such as LeNet5, AlexNet, and GoogLeNet were examined their accuracy of recognition. In addition to a model, an effect of learning rate, dropout ratio, and mean image subtraction on recognition accuracy were also investigated. Through this study, the potency of deep learning for microstructural classification is demonstrated.
Carbonization behavior of biomass in the rapid carbonization/pulverized process using heat storage materials was experimentally examined. Biomass samples were charged into a rotary kiln-type electric furnace with stainless balls. Obtained biomass chars were evaluated by means of gasification test in CO2 atmosphere using a thermal gravimetry. The char was classified into two type, “fine” and “coarse”, by particle size.
“Coarse” char contracted with increasing holding temperature. Crashing of biomass char was observed at the holding temperatures over 600°C and fine char was formed. Melted structure was observed on the surface of “coarse” char indicating rapid heating. Yields of the total char are decreased with increasing holding temperature due to vaporization of volatile matters like tar. On the other hand, the yield of “fine” char is increased with increasing rotation speed when carbonization reaction sufficiently proceeded.
The char obtained by the present carbonization experiment at between 600 and 800°C for 10 min showed similar gasification property with CO2 to that prepared by normal carbonization at 800°C for 1 h.
Steel of Japanese swords has been produced with Tatara process from iron sand and charcoal. Carbon dissolved in steel was absorbed from wooden charcoal fuel during the production of the steel. From the decay of 14C activity in the steel, the 14C age of Japanese sword can be determined. The 14C ages of 4 Japanese swords were measured with accelerator mass spectrometry and calibrated to calendar years. Each 14C age provided plural calendar year periods with definite probabilities, and one of the periods agreed with the production year of each sword that was determined from the sword master’s name cut in the grip of his sword after taking the age range of charcoal used for steel production and usage for several generations of the same names of sword masters into account.