The 10 most-cited articles in 鐵と鋼 : 日本鐡鋼協會々誌, 2024

This study demonstrates the effect of Ti addition on phase selection and subsequent ferrite-austenite transformation in Fe–22mass%Mn–0.7mass%C alloy, where the austenite is the primary phase in equilibrium. X-ray radiography revealed that the metastable ferrite nucleated as equiaxed grains in the completely melted specimen. During subsequent cooling, the metastable ferrite massively transformed into the austenite in the solid state, forming multiple austenite grains in each metastable ferrite grain. The ferrite-austenite transformation was immediately followed by the coarsening of multiple austenite grains within each former metastable ferrite grain. Typical austenite grain size ranged from 100 to 500 μm. In the specimen after the observation, titanium carbonitride (Ti(C,N)), which acts as heterogeneous nucleation agent for the ferrite, was presented and overlaid manganese spinel (MnAl2O4) or Al-Ti oxide. Because disregistry between such oxides and Ti(C,N) can be relatively low, the oxides facilitated the formation of Ti(C,N) in the melt. Regarding the formation of the oxides, it…

Microsegregation of solute components during the solidification process causes solute pile-up in the liquid phase, which strongly affects the formation behavior of inclusions. However, there is no quantitative evaluation of solute concentration distribution during dendritic growth. In this study, we established an in-situ observation method for quantitative evaluation of solute concentration distribution using model materials with fluorescent reagents to clarify how the solute pile-up progresses due to microsegregation. In addition to evaluating the physical properties of the model materials necessary for this study, a quantitative evaluation of solute concentration distribution during dendritic growth was successfully achieved. Numerical analysis, taking into account the equilibrium partition of solute components and solute diffusion in each phase, reproduced the measured solute concentration distribution in the liquid phase. Thus, the solute concentration distribution was evaluated by the actual measurement and numerical analysis, and it was clarified that a relatively simple…

It is known that the size distribution of inclusions in steels has a significant effect on material properties. The solidification characteristics and TiC formation behaviour of alloy 800H were evaluated both by experiment and simulation in this work. The relationship between dendrite arm spacing and the cooling rate was estimated. TiC particles were observed at the interdendritic region. The size distribution of TiC particles was affected by the solidifacation cooling rate. A solidification analysis using the MPF (Multi-Phase Field) method revealed that TiC formation begins at a solid fraction of 0.79, and solidification accelerates due to TiC formation. It was thought that TiC particles generated in the latter part of solidification aggregate and coalesce without engulfment by the solidified shell. The size distribution of TiC particles was also affected by heat treatment after solidification.

The purpose of this report is to compare the coating structure and corrosion mechanism of newly developed Zn-19%Al-6Mg-Si with conventional Zn-Al-Mg alloy coating Zn-11%Al-3%Mg-0.2%Si. In past papers the corrosion resistance of Zn-Al-Mg alloy coating layers was mainly discussed based on analysis methods that focus on one aspect of early corrosion stage. However, this report focuses on the changes in the corrosion mechanism until the end of the coating lifespan and picks up the factors of the coating layer that contribute to corrosion resistance.

The recovery rate of iron is reduced if iron particles suspended in the refining slag do not sediment. The sedimentation rate of particle iron in the foaming slag is slower than in the slag in the single-phase liquid. Iron particles are especially likely to remain in the foaming slag. To predict the sedimentation rate of iron particles in the slag, it is necessary to derive an accurate viscosity of the foaming slag. However, it is difficult to estimate an appropriate value because the state of gas-liquid multiphase fluid changes the condition with time. Its apparent viscosity varies depending on the measurement method because it is a non-Newtonian fluid. In this study, to understand the sedimentation behavior of iron particles in foaming slag, a gas-liquid multiphase fluid was generated by glycerin solution. Its apparent viscosity was estimated by the Stokes equation using the falling-ball method. The sedimentation rate of stainless steel, titanium, and glass balls with a diameter of 2 mm were measured in a glycerin aqueous solution gas-liquid fluid. The sedimentation rate was…

High phosphate slag fertilizer (SHP) contains phosphorous, calcium, magnesium and silicon, expected to be effective in supplying plant nutrients and improving soil acidity. We clarified the characteristics and effects of the SHP as a fertilizer. Nippon Steel Corporation prepared the SHP prototypes by concentrating phosphorus through high-temperature processing. Five types (SHP12, SHP15, SHP18-1, SHP18-2, SHP27-2) were examined through dissolution test, pot cultivation experiment, and evaluation of improving effect on soil acidity. The SHP12 was insoluble in water but soluble in various acids and most SHP contained more than 95% of acid-soluble phosphate and silicate. Above-ground growth and phosphate uptake of spinach was higher in the SHP12 plot than in no-phosphate, ammonium phosphate and fused phosphate plots, indicating that phosphorus in the SHP12 could be absorbed more easily than the common phosphate fertilizers. Above-ground growth and phosphate uptake of wheat was also high in the SHP12 and SHP15 plots, which was comparable to ammonium phosphate plot. However, the SHP27-2…

In the steel making process, most slags and fluxes often contain solids phase such as CaO. It is well known that the suspension in which solid phase are suspended has higher viscosity than that of pure matrix liquid. Therefore, it is expected that the viscosity of slag containing solid phase will increase. In this study, terminal settling velocity of particle in suspension has been measured. The suspensions consist of silicone oil matrix and polyethylene beads, and the settling particles are bearing balls made of stainless steel. As a result of the higher viscosity of suspension, the terminal settling velocity of bearing ball becomes slower than that in pure silicone oil. It was clarified that the retardation of the terminal velocity and the increasing of drag coefficient depend only on the volume fraction of solid phase (the polyethylene beads) of the suspension, and it is independent of the size of the suspended beads and the viscosity of the matrix liquid. A correlation equation for predicting the drag coefficient of particles in suspension was proposed.

Strain distribution developed during tensile deformation in as quenched martensitic steels with various prior austenite grain sizes (PAGS) was visualized by using digital image correlation method, and then the effect of PAGS on strain distribution was discussed based on the results obtained from SEM/EBSD measurements. The martensitic steels with PAGS ranging from 8 to 110 μm were fabricated by controlling the solution-treated temperature. Carbides were observed in all specimens, suggesting that the auto-tempering occurred during the water quenching. The amount and size of carbide increased with increasing the PAGS. Inhomogeneous microscopic strain distribution in a unit of block was developed by tensile deformation in all specimens, and the strain distribution became rather inhomogeneous with increasing the PAGS. The blocks with the high Schmid factor of habit plane slip system tended to exhibit high strain. It was observed that there were blocks with low Schmid factor but high strain, and such blocks had numerous carbide precipitates, indicating that those blocks were well-tempered…

In the steelmaking process, molten slag is foamed through gas injection and gas generation reactions, and molten iron droplets get mixed and trapped in the slag. A settling velocity of an iron droplet in the foaming slag are very important, because a residence time of an iron droplet in the slag is directly calculated the settling velocity. According to the previous research, the settling velocity is expected to be slower than in regular non-foaming slag. However, it has yet to be quantitatively clarified. This study measured the settling velocities of particles through a foaming liquid of glycerin-water solution. A dimensionless correlation equation for particle settling velocity in the formed liquid was proposed by conducting a dimensional analysis of the experimental data. Using the obtained equation, we have predicted the settling velocity of iron particles in the foaming slag. It was clarified that the settling velocity of iron particles is highly affected by a volume fraction of gas phase in the foaming slag. There is a certain threshold for the velocity, and the velocity…

In the production of high strength steel, it is necessary to improve the inner quality of steel slab. Among of the internal defects, the center segregation deteriorates the ductility and fatigue strength of high strength steel. Therefore, it is necessary to understand the generation mechanism of center segregation and develop the countermeasure technologies. In the center-segregated region of high phosphorous and hyper-peritectic steel slabs, iron-phosphide may be observed. However, the precipitation mechanism of iron-phosphide has not been fully clarified. Therefore, in this study, in order to clarify the formation mechanism of micro- and macro-segregation in the final solidification of CC slab, the melting behavior of the center segregation region of high phosphorous and hyper peritectic steel slab has been investigated by using high temperature observation equipment installed with the image furnace. Additionally, the enrichment of solute in the inter-dendritic region has been analyzed by using micro- segregation model with consideration of delta-gamma transition of steel. Under…