In order to examine the mechanism of the change of CaO and CaS content in inclusion during and after Ca addition, experiments were made with 180Kg of molten steel in MgO crucible at 1873K. Effect of initial sulfer content, Ca consumption and Ca addition pattern on the change of inclusion composition were verified in the experiments. A mathematical model, in which the kinetics of Ca evaporation and the reaction between inclusion and molten steel were considered, was developed to calculate the change of CaO and CaS content in inclusion as function of time. The calculated results coincided with the experimental results. The following reaction mechanism was, thus, estimated: (1) The change of inclusion composition during Ca addition (a) was in the completely reverse way of the change after Ca addition (b) in which [Ca] was vaporized. Al2O3_??_CaO-Al2O3-low CaS_??_CaO-Al2O3-high CaS (2) The way of the change of inclusion composition was influenced by [%S] in spite of no effect of Ca consumption and Ca addition pattern. (3) The above mentioned phenomena depend on the following reversible reaction: CaOinclusion=Ca+O CaOinclusion+S=CaSinclusion+O
Coke supply for ironmaking will sharply decrease in the beginning of the 21st century in Japan, because of the end of service life of coke ovens. For the purpose of extending the life of the oven, deformation of the coke cake and the load on the side wall during pushing were studied by applying an electric furnace equipped with a movable wall. Cake deformation under compressive force was found to proceed in three stages. The coke cake was reduced in length in the pushing direction in the cake deformation stage, and load was generated on the side walls in the high wall load stage. The secondary crack in the cake prevents the load transmission on the wall. The load transmission rate when the pushing stress was 0.19MPa, βp, was controlled by adjusting the maximum fluidity and mean reflectance of the blended coal.
Decrease of the amount of fluxes such as limestone, quartz, and serpentine in the iron are sintering process contributes to decreasing the amount of slag volume in the blast furnace operation aimed at increasing the pulverized coal injection. Therefore, it is important to use those fluxes effectively in the sintering process. To clarify the desirable size of fluxes, the assimilation reaction of fluxes with iron oxide in the air has been evaluated quantitatively. Assimilation ratios of fluxes were evaluated in order, from higher to lower, as limestone, quartz and serpentine. The assimilation ratio of limestone decreased when quartz and serpentine were added to the limestone-Fe2O3 two component system. The assimilation ratio of limestone decreased remarkably when fine serpentine was added to that system. Magnesioferrite ( (Mg, Fe)O·Fe2O3) precipitated around serpentine in the assimilation of serpentine. The assimilation ratio of serpentine was concluded to be lower than that of limestone and quartz based on the assimilation characteristics. The amount of melt decreased because magnesioferrite isolated limestone from the melt when fine serpentine was added.
Matrix dependency of relative sensitivity factors (RSFs) in glow discharge mass spectrometry has been systematically investigated. RSFs were determined using pin-shaped and disk-shaped samples prepared from the same blocks. The matrices are Fe, Ni, Al, Cu and Ti. The numbers of elements (isotopes) whose RSFs were determined in the respective matrices are 40, 35, 24, 36 and 12. Using the method of least square, the RSFs for.respective matrices are compared each other. There exists a strong correlation between the RSFs for the different matrices. Thus, the RSFs for a matrix can be transformed for other matrices by the simple multiplication of appropriate coefficients. However, the coefficient for Al matrix is not equal to the value of the RSF of Al element in the relevant matrices. The five sets of the values of the RSFs after transformation to Fe matrix agree each other. The relative errors for the pin-shaped and the disk-shaped samples are almost within 30% and 20%, respectively. The large error for the pin-shaped samples is probably caused by the minute difference of the shape of the prepared samples. Furthermore, the ion beam intensities for the disk-shaped samples were always higher than those for the pin-shaped samples. The fact will also cause the small error for the disk-shaped samples. For precise analyses, disk-shaped samples are recommended.
A criterion for ductile fracture is applied to the prediction of forming limit in bore-expanding processes of sheet steels. Axisymmetric bore-expanding tests of mild steel and high strength steel sheets using conical-, hemispherical-and flat-headed punches are simulated by the rigid-plastic finite element method. From the calculated distributions and histories of stress and strain in the sheets, the fracture initiation sites and the critical strokes are predicted by means of the ductile fracture criterion. The comparison with the experimental results show that the forming limits due to various types of fracture initiations in the bore-expanding processes are successfully predicted by the present approach.
Due to high productivity of tandem cold rolling mills, it is beneficial to produce not only mild steels but stainless steels by using the process, instead of conventional reverse rolling mills with smaller diameter of work rolls. Requirements to lubricant in order to realize the process are conflicting, which one side oil film thickness is required to be reduced to provide brightness of products, beside too thin film causes seizure and heat stratch. In this study, an O/W emulsion is designed and developed to contend with these conflicting requirements. In order to make oil film thickness at inlet zone of roll bite be thinner, the droplet size is reduced down to about 1μm. Also, kinematic viscosity of base oil is increased up to 320mm2/s, which makes the film stronger and prevent heat stratch, even if the film thickness is reduced. Through laboratory tests and cold rolling tests using a production mill, the superiority of this type of lubricant is clarified and good surface brightness of SUS430 can be obtained with large diameter of work rolls in high speed rolling conditions.
Weathering steel has been widely used in many structures for its good corrosion resistance in unpainted condition, because a dense and tight rust layer naturally formed on the surface exhibits corrosion protectiveness It is, however, known that such a protective rust layer can not be created in the case of usage at seaside area. Thus, a Ca-Ni added weathering steel developed for applications to unpainted steel structures within the coastal area. Two types of outdoor exposure tests were carried out to evaluate its corrosion resistance; one is an ordinary exposure test and another is a sheltered exposure test. The results of these tests show that the amounts of corrosion loss are greater in the case of sheltered exposure tests than for ordinary exposure tests. Furthermore, the difference in the extents of corrosion in two types exposure tests is enhanced, as the amounts of chloride in the atmosphere increased. Larger extents of chloride ions are detected in the samples corroded in the sheltered condition than those in the ordinary test. It was found that Ca-Ni added weathering steel has a better corrosion resistance in such a severe environment, probably because alloying elements such as Ca, Ni contributed to prohibit the penetration of chloride ions to the interface between metal and rust layer.
Fe specimens containing 0.3-0.9 mass% Si were annealed in Pb-Zn melt at 733K. Formation and growth kinetics of Fe-Zn alloy layer on the surfaces of the specimens was examined. A Fe-Zn alloy layer with a continuous and protective structure was formed in the melt containing less than 40 mass% Zn. The Fe-Zn alloy layer consists of δ1 and ζ phases, its thickness increases with annealing time according to a parabolic rate law. A fragmentary δ1 layer composed of small discrete δ1 crystals embedded in a matrix of the η phase was formed in the melt containing more than 40 mass% Zn. Although a coherent δ1 layer exists between the fragmentary δ1 layer and the substrate of the specimen, its thickness is very thin. The Pb-Zn layer on the surface of the alloy layer can be removed if the specimen is immersed in pure Zn melt, but the fragmentary δ1 layer is formed after a short time immersion even though the Fe-Zn alloy layer with the continuous and protective structure previously exists on the surface of the specimen.
After previous result on the solution treated at 1173K for 3.6ks and water quenched (STQ) state, the β phase was retained in alloys containing more than 4mass% Fe. Resistivity of the 515mass% Fe alloys showed the negative temperature dependence. The aging behavior of the quenched Ti-410mass% Fe β alloys with accumulative isochronal aging was investigated by changes in resistivity, hardness, and phase constitution which was identified by X-ray diffractometry. The hardness increases by precipitation of isothermal ω phase and decreases by precipitation of α phase consuming the precipitated ω phase. Above 723K, the hardness of the Ti-46mass% Fe alloys became lower than that of STQ state. In 50K/1.8ks accumulative isochronal aging, the temperature at which precipitation of isothermal ω phase confirmed by X-ray diffractometry increases with increasing Fe content. On the other hand, the influence of Fe content on the temperature ofα phase precipitation is not clear. Precipitation of TiFe can not be detected by the X-ray diffraction in accumulative isochronal aging up to 773K. The increase of resistivity of Ti-8mass% Fe and Ti-10mass% Fe alloys at room temperature observed in the aging up to 523K has been attributed to the phase separation in Fe concentration of β phase or the precursor of isothermal ω phase.
The kinetics of grain boundary migration for low angle <110> tilt boundary with misorientation angle of 6° was experimentally studied at various temperatures between 1200 and 1625K using Fe-3wt%Si solid solution bicrystals by capillarity technique. The migration velocity of the low angle tilt boundary was much smaller than that of the ∑9 coincidence boundary. The driving force and mobility of the moving grain boundary were calculated from the migration velocity, the curvature and the grain boundary energy. According to the calculation, the small migration velocity of the low angle tilt boundary is considered to be due to the small mobility and the small driving force (the grain boundary energy). But the migration mechanism of the low angle tilt boundary was as same as that of the ∑9 coincidence boundary. At the low temperatures, the migration was controlled by the diffusion of Si that interacted with the grain boundary. On the other hand, at the high temperatures, it was controlled by the grain boundary diffusion.
To improve the stretch-flangeability of high-strength TRIP-aided dual-phase (TDP) sheet steels, the effects of second phase morphology ("a network structure : TYPE I" and "an isolated fine and acicular one : TYPE II") on the warm stretch-flangeability were investigated. Excellent stretch-flangeability was achieved in the TDP steels with TYPE II morphology, in which an acicular type of retained austenite was mainly isolated in the ferrite matrix, away from bainite phase. In this steel, void formation in a punched surface layer was considerably suppressed, with relatively large work-hardening. Further, the transformation-induced plasticity (TRIP) due to untransformed retained austenite enhanced the localized ductility on hole-expanding. Significant stretch-flangeability improvement of the TDP steel with TYPE II morphology was obtained by warm punching at 150-200°C and the successive warm expanding at 50-200°C. The latter temperatures increased linearly with increasing Ms of the retained austenite.
An advanced work processing, in-rotating-water spinning method has been applied for intermetallic compound Ni3Al. In this method, which ejects a molten metal jet into the water layer formed on the inner surface of rotating drum, continuous filaments with round cross-section can be directly produced from molten Ni3Al. The effect of spinning conditions, especially spinning temperatures on the continuity and ductility of Ni3Al filament have been examined. Ni3Al filaments are annealed at 1033K and 1323K, and then the microstructures are observed. Only the sound filaments have been tensile tested at room temperature. It is shown that a) the continuous and sound filaments are obtained when the temperature of molten metal ranges from 1900K to 1950K, b) the fine acicular microstructure in just as ejected condition changes to the hyperfine dendrite skeleton structure by 1033K annealing and returns to the coarse γ' single phase before spinning because of recrystallization when further annealed at 1323K, and c) the ultimate tensile strength decreases as the annealing temperature increases, while the ductility increases and shows the maximum elongation by 1033K annealing.
The strength and toughness of a newly developed 0.8C-8Cr cold work tool steel whose composition was controlled to suppress the precipitation of massive eutectic M7C3 carbides were investigated with reference to microstructure and were compared with conventional SKD11. The toughness was evaluated by the area under the stress-strain curve. The tensile strength of the newly developed steel (designated as Mod.SKD11) is about 400MPa higher and the toughness is 1.8 times larger than that of SKD11 throughout a wide range of tempering temperatures. It is revealed from microstructure examination, the fracture surface observation and the estimation of the tensile stress required to generate cleavage crack within M7C3 carbide based on Stroh's theory that superior mechanical properties of Mod.SKD11 are attributed to the refinement and homogeneous distribution of M7C3 carbides that retards the crack generation and prevents the crack growth, respectively.
CrMoV (1Cr-1Mo-0.25V) rotor steel is commonly utilized for high pressure (HP) or intermediate pressure (IP) turbine rotor forgings used at steam temperature up to 566°C. The steel has excellent mechanical properties at elevated temperatures, especially creep rupture strength. Improved toughness of the CrMoV rotors, however, is desired in order to minimize the warm-up time of the turbine system. In this study, a fundamental examination was performed using small laboratory ingots. Optimal chemical composition and heat treatment conditions of developed CrMoV rotor steel were selected to obtain good fracture appearance transition temperature (50%FATT) without loss in the creep rupture strength. Toughness was improved by decreasing the silicon content (VCD : Vacuum Carbon Deoxidation) and increasing hardenability to a level greater than conventional HP rotor forgings. The toughness was also improved by accelerating the cooling rate by oil quenching instead of blast cooling. Based on the knowledge obtained through the fundamental study, actual full size HP/IP rotor forgings were manufactured. As test results, it was verified that these rotor forgings show higher toughness along with excellent creep rupture strength.