A large portion of ceramics, salt and glass have a property with high electric conductivity at liquid state and with low one at solid state. By making use of such electrical property a direct induction skull melting process was developed to melt and hold those materials, especially with a high melting point and chemical active properties, for avoiding contamination from a crucible. In order to understand the characteristics of melting behavior of the materials in the process the theoretical study on temperature, magnetic and velocity fields which are tightly related with each other is indispensable. In this study a mathematical model taking account of the distributions of temperature, magnetic and velocity fields is developed. The experimental work to melt a NaCl salt has been conducted. The observed evidence in the experiment has been confirmed by the mathematical model.
The carbidization rate of iron ore was thermo-gravimetrically measured and analyzed with CO-CO2 gas mixtures from 873K to 1073K, after it was completely reduced with H2 gas containing sulfur low enough not to form sulfide. The fractional carbidization is defined as the mass gain relative to the mass of carbon required converting whole of iron to cementite, θ-Fe3C. The reaction was composed of three stages: (1) Carbon was supersaturated in α-iron. (2) The fractional carbidization increased linearly after the nucleation of cementite, until it was saturated. The sulfur, which was adsorbed on the pore surface in iron ore, stabilized cementite and prevented free carbon from deposition. (3) However, at 873K and 1073K, free carbon deposited and mass gain was accelerated at a certain fractional carbidization. This phenomenon is a kind of percarbidization of cementite without formation of percarbide, χ-Fe5C2. Carbide was decomposed into free carbon and metal and then iron ore was broken to powder, that is so-called 'metal dusting'. The authors considered that the slope of straight line portion during the growth of carbide is the carbidization rate from 873K to 1023K, which contained no error of mass changes due to reduction and carbon deposition. The carbidization rate was formulated as a function of relative partial pressure of CO and CO2, PCO, PCO2[-]and temperature, which is controlled by the following elementary reactions, CO+_??_=C+O (ad) CO+O (ad)=CO2.
Phase diagrams of Fe, FeO, Fe3O4, Fe2C and Fe3C in CH4-H2-H2O and CO-CO2 gas mixtures were made by using thermodynamic data at every 50°C in the temperature range from 550 to 850°C. On the basis of these diagrams, experimental conditions were determined. The reaction experiments were carried out by using fluidized bed or fixed bed reactor with the sample of two kinds of ore (dense and porous, 0.4-0.5 mm in diameter). The thermodynamic date used can be recommended because the experimental results under some conditions near the main phase boundary agreed well with the estimated one. It was confirmed that Fe3C was produced via Fe3O4 in CO-CO2, gas mixtures at 550°C. However, the reaction rete was very slow. This Fe3C hardly decomposed to Fe and C. When the steam of 5 vol % or more was included in the CH4-H2-H2O gas mixtures. Fe3C was not generated in 0.1 MPa at all.
The carbidization rate of iron ore was thermogravimetrically measured and analyzed in H2-H2S-CO-CO2 gas mixtures from 873K to 1073K, after it was completely reduced in H2-H2S gas mixture. Both gases contained sulfur low enough not to form sulfide. The fractional carbidization, fθ[-], is defined as the mass gain relative to the mass of carbon converting iron to cementite completely, θ-Fe3C. It grew along a parabolic curve without such a nucleation period as the carbidization CO-CO2 system. Then, it grew linearly forming percarbide, χ-Fe5C2 after fθ=0.5. The authors considered that the nucleation resistance of cementite and percarbide was reduced by higher carbon supersaturation than that in CO-CO2 system. It assumed that the carbidization rate was controlled by carburization of metal with CO and the reaction interface decreased linearly with the amount of metal. Thus, the curve was analyzed using the equation of first order reaction: -1n(1-fθ)=Rt, where the carbidization rate, R [s-1] is constant with time. The maximum rate was obtained at about 20 vol% H2 in H2-CO system. This fact agreed with Turkdogan and his co-workers' previous work for carbon deposition. As the results, the author showed the adsorbed OH catalyzed carbidization in the following reaction: CO(g)+OH(ad)=CO2(g)+1/2 H2. Sulfur suppressed the reaction with OH(ad) more strongly than O(ad).
The transfer rate of oxygen from gas phase into liquid iron through molten iron oxide-CaO-SiO2-Al2O3 slags (CaO/SiO2_??_1) at 1600°C was investigated by blowing the oxidizing gas on the slag surface which covered liquid iron. Gas blowing was started after slag was almost equilibrated with liquid iron or from non-equilibrium state. The transfer rate of oxygen into liquid iron was affected by T.Fe content in the slag. During the transfer of oxygen, FeO content in the slag largely increased, but FeO1.5 content in the slag was kept very low. When the initial T.Fe content in the slag was below equilibrium content with liquid iron, the slow deoxidation of liquid iron by the slag and an increase in FeO content in the slag occurred at first. After the FeO content increased up to its equilibrium value with oxygen in liquid iron, the transfer of oxygen into liquid iron was accelerated. A kinetic model was developed based on two films theory. The experimental results were confirmed to be interpreted by this model.
A d.c. bias current driven by the self-bias voltage which is conducted through the r.f.-powered glow discharge plasma varies the emission characteristics drastically, leading to improvement of the detection power in the optical emission spectrometry. By conducting the bias currents of 20-30 mA, the emission intensities of the atomic resonance lines were 10-20 times larger than those obtained with conventional r.f.-powered plasmas. The detection limits for determination of alloyed elements in the Fe-based binary alloy samples were estimated to be 1.6×10-3% Cr for Crl 425.43 nm, 7×10-4% Mn for Mnl 403.10nm, 1.9×10-3% Cu for Cu l 327.40 nm, 1.1x 10-3% Al for All 396.16 nm, and 6.6×10-3% Ni for Ni I 352.45 nm.
The effect of Fe-15%Zn upper coating on stone chipping resistance of galvannealed steel sheet and Zn-Ni electroplated steel sheet was investigated by using gravelometer under the temperature of -20°C after three-coat painting (phosphate, electropaint, primer surfacer and top coat) for automobile outer panel. ( 1 ) The plating/base-steel interface damage diameter by the stone chipping decreases largely by plating Fe-Zn upper coating on zinc alloy coated steel sheets. On the other hand, the electropaint/phosphate interface damage diameter increases by Fe-Zn upper coating. ( 2 ) P-ratio [Phosphophyllite/(Phosphophyllite+ Hopeite)] of phosphate film of zinc alloy plated steel sheets increases by Fe-Zn upper coating. The peeling resistance between electropaint and phosphate film against impact becomes low when P-ratio is high. From these results, the reason why the peeling at plating/steel interface decreases when Fe-Zn upper coating is applied seems as follows: Under the condition where Fe-Zn upper coating is applied to zinc alloy plated steel sheets, the peeling resistance at electropaint/phosphate interface is weaker than that at plating/steel interface, then the peeling occured at interface between electropaint and phosphate, which consumes the kinetic energy of gravel, so peeling at plating/steel interface becomes small.
Intergranular proeutectoid ferrite nucleation in a V-N steel has been examined at isothermal transformation at 600°C with respect to the austenitizing temperatures. While substantial grain growth takes place, the number of intergranular ferrite grains per unit grain boundary area decreases with increasing austenitizing temperatures. Non-stationary increasing rate with time is observed. Overall transformation during isothermal transformation delays after austenitizing at higher temperatures and follows the Johnson-Mehl-Avrami formula for the case of fast grain boundary nucleation. It is discussed that the decrease in the intergranular ferrite nucleation rate associated with higher austenitizing temperatures is partially due to grain boundary structures, not merely to the decrease in the nucleation sites associated with grain growth. Use of high austenitizing temperature is requisite for the intragranular ferrite precipitation.
Mechanical milling using high energy planetary ball mill was applied to Fe-C alloy powders with (ferrite+cementite) two-phase structures to give an ultimate large strain into the powders. Dissolution behavior of cementite during mechanical milling was investigated in relation to ultra grain refining of ferrite matrix, and dissolution capacity of cementite was discussed in terms of carbon content in the powders. Ultra grain refining of ferrite matrix to about 10nm results in full dissolution of cementite in the powders with carbon up to 2 mass% C. Most of carbon, which has been rejected from decomposed cementite, is suggested to segregate at grain boundary to form amorphous layer. Thus, it was proposed that the dissolution limit of cementite depends on both volume fraction of the grain boundary amorphous layer and carbon concentration therein. For example, as the maximum carbon content of the grain boundary amorphous layer was to be about 4.2 mass% C, the dissolution limit of cementite was estimated at 30 vol% from the mass valance for carbon content in the case ferrite grains were refined to around 10 nm. This volume fraction of cementite is just correspondent to that in Fe-2mass%C alloy.
Recent antiearthquake design is on the basis of ultimate state design which aims absorption of earthquake's energy by plastic deformation of buildings. From this point of view, it is required that deformability of buildings' pile should be improved much more. Inside pile, steel bar for prestressed concrete (PC-bar) is used for reinforcement. One of the main factors which affect deformability of the pile is uniform elongation of PC-bar. Therefore it is pointed out that the PC-bar with high uniform elongation is indispensable. It is known that high uniform elongation is attained by dual phase in the case of lower strength steels. But study which treats with high strength steels such as 1420 MPa grade PC-bar is quite few. In this paper, we focus on Si and study the effect of Si on ductility of high strength steels. Finally we found that uniform elongation was improved to 5% by 3.5% Si addition. Improvement on uniform elongation by Si addition is mainly attributed to appearance of ferrite and refinement of carbide.
Tensile tests and fatigue tests have been conducted for laser butt welded joints obtained from the combination of two steels and two plate thicknesses. Tensile and fatigue strengths were evaluated and the effects of type of steels and plate thickness on those strengths were studied on the basis of changes in microstructure, hardness and residual stress. Tensile strength of the joints with the same thickness was lower than that of the joints with different thicknesses and the joints of the same steel showed lower tensile strength than the joints of different steels. All joints were fractured at the location away from the center of the weld zone. Fatigue strength of the joints decreased compared with that of the base metal. The type of steels had no influence on the fatigue strength, while the fatigue strength of the joints were slighlty affected by plate thickness. In the joints with the same thickness, fatigue fracture took place at the location 4 mm to 5 mm away from the center of the weld zone, but in the joints with different thicknesses, at the shoulder between thin and thick plates, i.e. at the weld zone.
Ductile crack initiation behavior of structural steel under cyclic loading was investigated using notched round bar specimens with comparing to monotonic loading. FEM analysis was carried out to determine the effects of equivalent plastic strain and stress triaxiallity on ductile crack initiation. Under cyclic loading, ductile crack initiated at notch tip for all specimens differing in root radius, even for the specimen with root radius of 1.0 mm which crack initiated in the center of the specimen under monotonic loading. In the case of the specimen with large root radius under monotonic loading, it is considered that void growth and coalescence is promoted by a large stress triaxiallity and it leads to ductile crack initiation in the center of the specimen. On the contrary, under cyclic loading or under monotonic loading with small root radius, deformation in the center of the specimen is small, and crack initiated at the notch tip by accumulation of equivalent plastic strain under cyclic loading or concentration of strain at notch tip. It can be stated that, effect of stress triaxiallity on ductile crack initiation at notch tip is small, and crack initiates at notch tip when equivalent plastic strain exceeds a certain level of strain.
Accurate measurement of load is essential in the instrumented impact test. Especially, significant variation in load has been reported in the instrumented Charpy impact test, for example when miniaturized specimens were tested. Load calibration values are evaluated by means of both finite element analyses and experiments. Decrease in specimen thickness results in slight decrease of calibration parameters. This is attributable to strain localization near the region in which strain gages are placed. The results strongly suggest that the system must be calibrated for each different size of specimens to know accurate toughness data.