To evaluate condition and distribution of reduction degree and gas permeability in ore layer, examinations of high temperature properties with various ore layer thickness were executed. Gas permeability begins to decrease from the upper part of ore layer, where melt with more FeO is formed with low reduction degree. Experimental results show that the difference of reduction degree in ore layer of examination of high temperature properties is about 40% at 1200°C. Estimation with mathematical model indicates that difference of reduction degree in ore layer increases with decreasing gas flow rate.
In the production line of steel sheet, surface of steel sheet is oxidized inevitably. So it is required to remove the oxide layer by acid pickling. It is very important for keeping the product quality stable to control the acid concentration in pickling process. With the increase in line speed of steel sheet, the acid concentration of pickling solution changes a lot in short time. Therefore, it makes difficult for a conventional chemical analysis to catch up the change of concentration.
Nowadays, NIR (Near-Infrared spectroscopy) has attracted attention as a rapid analytical method to determine the concentration of solutions. Therefore we carried out examination using NIR to measure the concentration for acid pickling solutions in steel-making process.
The NIR spectra in the region of 9500 cm–1 to 5000 cm–1 include OH bond of stretch first over-tone (6800 cm–1) were used. The OH peak shape of aqueous solutions are altered by the interaction between water and other different species. Total acid and Fe concentration were calculated by multivariate analysis using the NIR spectra of the solution that contains those ion. Furthermore, the multivariate analysis conditions were optimized to improve the correlation between NIR analysis value and the chemical analysis values.
The correlation coefficient between NIR analysis values and chemical analysis values reached 0.98, which is good enough for operation. NIR analyzer enabled to measure multiple components at the same time in 1 minute. This system was also tested at an actual pickling line, and good correlations were obtained.
Material flow of steels with different composition in friction stir welding (FSW) was directly investigated by x-ray radiography. The three-dimensional flow patterns in various FSW conditions were obtained using two pairs of x-ray transmission real-time imaging systems. It revealed that the material flow pattern and the flow rate were tightly connected to the deformation resistance of the steel at process temperature. The material flow zone of the steel with higher carbon content, which has higher deformation resistance, was narrower, and its flow rate was lower than those of the steel with lower carbon content. The shape of the material flow zone around the rotating tool was changed from concentric to ellipse due to the stagnation of the material flow on advancing side (AS) in stir zone (SZ) under the insufficient heat-input FSW condition. Further decrement of the heat-input in FSW led to the defect on AS in SZ. The obtained relationship between the FSW conditions and the flow pattern showed that the lower travel speed of the tool is effective to keep the concentric shape so as not to form the defect for the steel with higher carbon content.
The recrystallization behavior of Cu containing 17% Cr ferritic stainless steel cold-rolled sheets was investigated while evaluating the ε-Cu precipitation behavior during annealing. In the case of Cu in a solid solution before cold rolling, the recrystallization temperature of steel containing more than 1% Cu was high. It was thought that recrystallization was delayed because of the ε-Cu precipitation during annealing. The recrystallization temperature of 1.5%Cu-containing steel with fine ε-Cu precipitation because of aging for a short time before cold rolling was similar to that of Cu in solid solution before cold rolling. In contrast, in the case of coarse ε-Cu precipitation because of aging for long time before cold rolling, the recrystallization temperature decreased and was similar to that of steel with no Cu addition. In addition, the Cu-added steel had a weaker recrystallization texture than the no-Cu steel, but γ-fiber was developed because of aging for a long time before cold rolling. Consequently, the volume fraction and size of ε-Cu precipitation, which caused the recrystallization behavior, were examined quantitatively. The analysis based on the subgrain growth model considering a temperature change in the precipitation state such as the volume fraction and particle diameter using Thermo-Calc. and DICTRA was effective.
In the present study, hardness, elastic modulus and fracture toughness of η-Fe2Al5 (oC24 structure) and θ-FeAl3 (mS102 structure) single phase alloys have been examined by various indentation methods. The average hardness of η and θ phases measured by Vickers indentation are 8.5 GPa and 7.8 GPa, respectively. The hardness variations are approximately 20% in η phase and 15% in θ phase, which are associated with their orientation dependence. A trend was found that the hardness becomes lower close to the  indentation direction in both phases. The elastic moduli of η and θ phases measured by nanoindentation are higher than the modulus of pure Fe (about 200 GPa). The fracture toughness of η and θ phases measured by indentation fracture method are 1.38 and 1.27 MPa·m1/2, respectively. The anisotropy of their toughness was not found in the present measurements.
Machinery parts made from medium carbon steels are sometimes formed after spheroidizing annealing (SA). In order to improve the formability, it is necessary to reduce the yield strength and increase the reduction of area to fracture. In the present study, changes in the mechanical properties of medium carbon steel wire rods after SA were precisely investigated in relation to prior microstructure. In the steels with pearlite, the yield strength was drastically reduced and the reduction of area was raised after SA because of microstructural changes from pearlite to ferrite with dispersed spheroidized cementite. It was also found that the yield strength of ferrite with spheroidizing cementite depended sensitively on cementite-particle spacing as well as ferritic grain size. The reduction of area was, however, reduced as cementite size increased. The yield strength of the rod drawn in advance rapidly dropped after SA over 958 K, which was lower than that of ferrite steels with pearlite. Such changes in the mechanical properties after spheroidizing annealing could be reasonably understood from the difference in distribution of spheroidized cementite particles.