S45C carbon steel has been solidified under the simultaneous imposition of a static magnetic field in vertical direction and an alternating current having a horizontal component. Thus, an electromagnetic force was excited in the S45C steel sample and it affected structure formation during the solidification. The samples solidified under different electromagnetic conditions were cut and chemically etched for observation of the macro- and micro-structures. Solidified structure in the case neither the static magnetic field nor the alternating current was not imposed was dendritic structure. On the other hand, solidified structure under the simultaneous imposition of the 1 T static magnetic field and the alternating current of 80 A, 2 kHz was equi-axed structure. When the magnetic field intensity was decreased from 1 to 0.3 T, equi-axed structure and dendritic structure co-existed. As the frequency of the 80 A alternating current decreased from 2 kHz to 100 Hz under the constant magnetic field intensity of 1 T, solidified structure changed from equi-axed structure to dendritic one. Mechanism of the structure change is supposed to be breaking dendrites into pieces by convection induced in the sample by the non-uniform distribution of the electromagnetic force, which was intensified as the frequency of the alternating current increased.
The oxidation removal of Sn from carbon saturated iron via Ag phase was tried at 1523K. In addition, the thermodynamic data, which are necessary to know the lowering limit of Sn content in carbon saturated iron by this method, were measured. The distribution ratio between carbon saturated iron and Ag, LSn(mass)(=[mass%Sn](in Ag)/[mass%Sn](in Fe–C)) and the activity coefficient of Sn in carbon saturated iron, γ°Sn(in Fe–C), are determined to be 44 and 12.2 at 1523K, respectively. By using these values, the lowering limit of Sn content in carbon saturated iron is calculated to be 1.3×10−8 mass% in oxygen atmosphere (1 atm) at 1523K under the condition that the activity of SnO2 equals to unity. As the experimental results of Sn oxidation removal from carbon saturated iron via Ag phase, the Sn content of carbon saturated iron is actually reduced to less than 0.001 mass% (estimated to be about 0.0001 mass%) from 3 mass%, and it is found that the Sn in molten iron can be removed by the method proposed in the present study.
In order to improve the metallic iron (M.Fe) productivity of partially reduced agglomerates production in packed bed with air flow, the packed bed of which the carbon composite iron ore green balls were charged lower side and the ordinary raw materials are charged on them, called lower charging, were examined. The M.Fe productivity of lower charging were compared with that of the packed bed in which the carbon composite iron ore green balls were mixed with the ordinary raw materials and charged, called mixed charging. Also, the effect of exhaust gas velocity during sintering was studied. As a result, the M.Fe productivity of lower charging was higher than that of mixed charging because reduced agglomerates placed upper side of the packed bed were easier to be re-oxidized. In addition, when the exhaust gas velocity was too slow, the time for re-oxidization was extended so that the M.Fe productivity decreased. However, when the exhaust gas velocity was too fast, the excess of free C combustion or re-oxidization of reduced agglomerates was caused so that the M.Fe productivity decreased, too. Therefore, there is a exhaust gas velocity which make the M.Fe productivity be highest. In this study, the M.Fe productivity achieved 0.21 M.Fe-t/m2/h with lower charging and 0.19 Nm/s of exhaust gas velocity.
The behaviors of contrasts in backscattered electron (BSE) images of cross-sectional heat-treated steel are studied under various accelerating voltages and take-off angle conditions. Changes in these conditions resulted in dramatic changes in contrasts. Low accelerating voltages and low take-off angles improve surface information and channeling contrasts, whereas high accelerating voltages and high take-off angles enhance bulk information and reduce channeling contrasts, resulting in improved Z contrast. These behaviors can be understood by the ratio of LLE (Low-Loss Electron), which are related to channeling contrasts, to the inelastic BSE components detected. The distribution of these components varies depending on the accelerating voltage and take-off angle, in that the detection ratio of LLE to inelastic BSE increases with decreasing accelerating voltages and take-off angles. The results obtained in this study can be used for obtaining Z and crystallographic information separately in BSE images for the material of interest.
The effects of (C+N) contents on the recrystallization behaviors of Ti added high purity ferritic stainless steels were investigated. Recrystallization and grain growth of Ti added ferritic stainless steels retarded as Ti and (C+N) contents increased. It is considered that the retardation of recrystallization and grain growth in Ti added steels became more significant through the increase in the Ti and C contents accompanied by the increase in the amount of Ti(C, N), which pinned dislocations and grain boundaries.
Microstructure and creep strength at 650°C of two high-Cr ferritic heat resisting steels were investigated. 11Cr steel containing relatively high carbon, aluminum and nickel showed a significant drop in creep strength after 1000 h while 9Cr steel containing relatively low carbon, aluminum and nickel showed a recovery of creep strength after a slight drop. The 11Cr steel contained M23(CB)6, Z phase and relatively coarsened Laves phase as precipitates after 7000 h at 650°C, while the 9Cr steel contained fine MX and ultrafine M6C in addition to M23(CB)6 and Laves phase. Z phase was not found and the growth of Laves phase was retarded in the 9Cr steel. It was concluded that the drop of creep strength in the 11Cr steel was attributed to the coarsened Laves and Z phases and the recovery of the strength in the 9Cr steel to fine MX and M6C. Experimental results on the effects of steel compositions on the stability of precipitates in the steels were thermodynamically consistent with Thermo-Calc calculation results using an existing database. It was suggested that chromium and aluminum increased the kinetics of the formation and coarsening of the precipitates.