A 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 sample and it affected structure formation during the solidification. The samples solidified under the different electromagnetic conditions were cut and chemically etched for the observation of the macro- and micro-structures. And those were compared each other. Without the imposition of the static magnetic field and the alternating current on the steel, micro-structure was dendrites. On the other hand, the solidified structure under the 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 to 0.3 T, some parts of the solidified structure were equi-axed structure. As the frequency of the 80 A alternating current decreased under the constant magnetic field intensity of 1 T, the solidified structure changed from dendritic structure to equi-axed structure. Grain refinement mechanism 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 electric current increased.

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To investigate the effect of simultaneous addition of Al₂O₃ and MgO on the liquid phase area for the CaO–SiO₂–FeO_x system, liquidus for the CaO–SiO₂–FeO_x–2.5mass%Al₂O₃–2.5mass%MgO system were measured at 1573 K with various oxygen partial pressures by using chemical equilibration technique. By the addition of Al₂O₃ and MgO to the CaO–SiO₂–FeO_x system, the liquid phase area enlarges with the oxygen partial pressure of 1.8×10⁻³ Pa. The liquid phase area separates into two liquid phase areas with the oxygen partial pressure of 0.18 Pa. The liquid phase area shrinks at low SiO₂ region with the oxygen partial pressure of 2.1×10² Pa.

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In the present study, we measured the viscosity change with the melting time (melting temperature: 1873 K, 1773 K or 1673 K, atmosphere: air) of calcium ferrite (CaO·Fe₂O₄(CF)) based slags (CF, CF–5wt%SiO₂ and CF–5wt%Al₂O₃) by the rotating crucible method. Moreover, the viscosity changes were discussed from the viewpoints of the iron oxidation states (Fe²⁺ and Fe³⁺) and the coordination number of Fe³⁺.
Viscosity of the CF based slags decreased with the melting time at all the temperature (1673 K, 1773 K or 1873 K). Viscosities of the slags became constant after the melting time of 120 min at 1873 K and at 1773 K. In the case of the melting at 1673 K, the viscosity of the slags became constant after 240 min. The results of the chemical analysis indicated that the oxidation state of iron ions in the quenched CF slag was not changed during the viscosity measurements. We could not directly observe the change in the coordination structure of Fe³⁺ in CF based slags during the melting time, because the CF based slag could not be vitrified due to the limitation of quenching rate in the present study. However, the data of the viscosity and the structural information for 40CaO–40SiO₂–20Fe₂O₃ (mol%) slag indicated that the coordination structure of Fe³⁺ strongly affect the viscosity of iron-containing slags. The decreases in the viscosity of the CF based slags would be also controlled by the change in the coordination number of Fe³⁺.

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In this paper, the concept of grading of the feed ores has been used for the purpose of evaluation of the compactness of the briquettes. Fuller curve, the most popular ideal grading curve, has been considered. Ideal grading curves can lead to the maximum extent of compaction in the briquettes, ensuring highest strengths of the briquettes. The strength of the briquettes from a given fine ore mix has been assessed in relation to the extent of shift of the grading curve for the feed mix, from its ideal Fuller curve. Two parameters, namely, root mean square deviation (RMSD) and coefficient of uniformity (CU) have been used as the measure of the shifts from the corresponding Fuller curves. Mathematical equations have been derived to establish the correlations between the shatter strengths and hot compressive strengths with RMSD and CU. It is observed from the current work that closeness of a feed mix to its Fuller curve can provide satisfactory strength of the briquettes, but the incremental benefit in strength of the briquettes is reduced progressively with closeness to Fuller curve. This approach can be used to produce briquettes of significantly high strength through selective and optimised grading of the feed mixes.

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Since the solid flow in blast furnace is composed of each particle motion, the discontinuous phenomena of burden descending can be occasionally observed. Understanding of the solid flow is important for blast furnace operation. Discrete Element Method (DEM) can offer the behavior for each particle of burden in the furnace. Three dimensional analysis of solid motion containing the ununiform region became possible with using DEM.
In the present study, a blast furnace of 2000 m³ inner volume with 16 tuyeres was taken as the object for the simulation. Firstly, the stream line of solid, velocity variation and stress field in blast furnace were simultaneously analyzed by using the characteristic of DEM on each particle movement. Especially, the transient behavior on velocity and stress distribution during charging and slipping were calculated. The fundamental characteristics of burden descending became clear. Secondly, this study has focused on the asymmetric phenomena in the blast furnace on the basis of the above results. In this calculation, number of active tuyere was intentionally varied. The stress network showed the remarkable change in this case. Moreover, it was found that many local slips between particles were distributed in the bosh and they concentrated on the region nearby the active raceway due to the weakened stress. The stress network is closely related the particle velocity distribution. The consumption rate of coke in the tuyere significantly affected on the circumferential uniformity. Totally, the discontinuous burden descending and the characteristic of particle movement were essentially understood.

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The effect of CaF₂ and Na₂O on the sulfide capacity of the CaO–SiO₂–CaF₂–MgO_satd.(–Na₂O) slags for hot metal desulfurization was investigated at 1623 and 1723 K by taking the role of MgO as an important refractory component into account. The liquidus line of the MgO-saturated system was similar to the CaO–SiO₂–CaF₂ ternary slag system. The silica content for the 2CaO·SiO₂-saturation was slightly decreased with MgO saturation. Although the sulfide capacity at MgO-saturation is lower than that of the CaO_satd.–SiO₂–CaF₂ slag system, it is greater than the ternary slag system saturated with 2CaO·SiO₂ phase. This suggests that MgO can increase the activity of free O²⁻ ions under conditions of relatively low CaO activity. Near the composition of 3CaO·SiO₂-saturation, MgO decreased the sulfide capacity of the slag because MgO is less basic than CaO in highly basic compositions. In addition, the addition of 5 mass% Na₂O significantly increases the sulfide capacity of the MgO-saturated slag especially in the composition of low ‘CaO+CaF₂’. This suggests that the input amounts of ‘CaO+CaF₂’ can be reduced from 95 to 75 mass% for maintaining the sulfide capacity of 0.01 at 1623 K, which is important considering the reduction of CaO and CaF₂ consumption in hot metal desulfurization process with MgO saturation.

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The 3D-microstructure in 9SMn28 free-cutting steel under water cooling condition was simulated based on the finite element–cellular automaton method with convection and porosity, and the simulated results are consistent with that of the experiment. The casting of 9SMn28 alloy is a stepwise solidification mode under water cooling condition. Convection is mainly made of buoyancy-driven flows and feeding flows in perpendicular direction of the solid–liquid interface. Convection is the reason of shaggy on free surface; it can decrease pipe shrinkage and columnar grain zone. Flow field plays an importance role in even temperature field and irregulation porosity morphology. The simulated result of pipe shrinkage is consistent with that of this experiment; the simulated result of porosity is identical with that of this experiment basically.

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Effects of Al addition on as-cast γ-austenite grain structure in 0.2wt%C–0.035wt%P steel with Al concentration ranging from 0.04 to 1.04 wt% were studied by means of furnace cooling and casting experiments. In the furnace cooling experiment with a cooling rate of 0.03°C/s, the as-cast γ grain structure consisted of equiaxed grains and the γ grain size was not affected by the increase in Al concentration up to 0.54 wt%. In the casting experiment of the sample with 0.04 wt% Al, on the other hand, the as-cast γ grain structure consisted of Coarse Columnar Grain (CCG), Fine Columnar Grain (FCG) and Equiaxed Grain (EG) regions, sequentially, from the mold side to the center of the ingot. The increase in Al concentration leads to increase in the fraction of FCG region at the expense of both CCG and EG regions. Even in the samples with high Al concentrations, AlN particles were rarely found and also Al segregation did not occur substantially. Instead, P segregated in interdendritic regions. The concentration of the segregated P increased from the CCG region to the FCG region. It was suggested based on a thermodynamic calculation that the segregation of P is enhanced by Al addition and the high P concentration stabilizes the high temperature phase such as liquid or δ-ferrite, depending on Al concentration at lower temperatures. This stabilized high temperature phase is considered to retard the γ grain boundary migration. Therefore, the increase of FCG region and the decreases of CCG and EG regions due to Al addition should be attributable to pinning effect of the stabilized high temperature phase.

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The effect of solute drag on recovery and recrystallization during hot deformation of Nb microalloyed steels has been modeled using a newly developed microstructure model. The model is based on dislocation theory and the calculated dislocation density determines the driving force for recrystallization. Subgrains act as nuclei for recrystallization and have to reach a critical size and configuration in order for recrystallization to start. In the model, the solute drag effect of Nb in solution is described. Nb retards both dislocation and grain boundary movement giving retardation in both recovery and recrystallization. Calculations were compared to experimental results from axisymmetric compression tests combined with stress relaxation. In order to model the effect of solute drag, the experiments were carried out at temperatures where precipitation of Nb(C, N) should not occur. The calculated flow stresses for the compression tests show good fit with experimental data. Also, the calculated results of the relaxation tests show good agreement with experimental data.

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The microstructure and mechanical properties of a Nb bearing weld metal under different normalizing processes had been evaluated and analyzed. The results showed that there was a great difference between the microstructure and mechanical properties of the as-welded and the as-normalized weld metals, and that the normalizing process played an important role in determining the microstructure and mechanical properties of a Nb bearing weld metal. The microstructure of the weld metal was converted from a columnar grain structure in the as-welded state into equiaxed grain, and the degenerated pearlite and NbC precipitates were observed in the weld metal after a 920°C normalizing treatment. Corresponding to the microstructure, the normalized weld metal had lower yield and tensile strengths, higher elongation and higher −20°C impact energy than the as-welded weld metal. With the prolonging of the holding time at the normalizing temperature of 920°C, the grain size in the weld metal remained almost constant, while the size of NbC precipitate increased. The mechanical properties of the weld metal showed no obvious change with the increasing holding time. With an increase of the normalizing temperature, the quantity of the NbC particles decreased and the proportion of Widmanstatten ferrite microstructure in the weld metal increased, which caused the yield and tensile strengths to increase obviously, while the elongation and impact toughness decreased significantly. When normalizing at 1200°C, the NbC particles in the weld metal disappeared due to dissolution and the twin subplates were formed in the Widmanstatten ferrite.

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The fabrication of transparent Ti-containing mesoporous silica thin films (Ti-MSTFs) showing highly hydrophilic properties was achieved on quartz and Al alloy substrates by using a sol–gel/spin-coating technique. The presence of the mesoporous structure and titanium oxide species which exist in an isolated and tetrahedrally-coordinated state within the silica framework was observed by XRD and DRUV–vis measurements. The surface wettability on the Ti-MSTFs was also investigated based on the water contact angle measurement. Water contact angles on Ti-MSTFs on quartz and Al alloy substrates were extremely low values of 5° and 8° even under dark conditions, respectively, which were much smaller than those on original substrates. These observations indicate that highly hydrophilic surfaces were formed both on quartz and Al alloy substrates by coating with Ti-MSTFs. It can be interpreted that the capillary condensation due to the mesoporous structure and the presence of isolated titanium oxide species as adsorption sites of water contributed to the appearance of the high hydrophilicity. Furthermore, the irradiation of UV-light led to the decrease in water contact angles on Ti-MSTFs and it was found that Ti-MSTFs exhibited the photoinduced superhydrophilic properties.

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Internal oxidation of Fe–Cr alloys were investigated in dry and humid atmospheres at temperatures of 973 and 1073 K in order to clarify the effect of humidity on the oxygen permeability in internal oxidation zone. The oxygen partial pressure in the chamber was fixed by Fe/FeO powder mixture. The calculated oxygen permeability increases linearly with increasing Cr concentration in the alloys, both at 973 and 1073 K. Moreover, the presence of humidity enhanced the oxygen permeability compared with that under dry condition. The oxygen permeability through IOZ in humid atmosphere is larger than that in dry atmosphere as a factor of 1.2.

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Fe–3.2%Si steel from a commercial source supplied in the form of fully recrystallized sheet was selectively thinned to produce foils of different thicknesses which separated the subsurface layers in which the η texture dominated, from the central layer of γ texture. Goss oriented grains were more frequent in the sub-surface layers, but were also present in the central portion of the material. Annealing these foils at ~1000°C produced Goss texture in the surface foil, and {111}‹hkl› in the central foil. From these experiments it is clear that Goss secondaries grow easily in the η layer, but not in the γ layer and this was proved in a sequential heating experiment. A search of the misorientations between Goss oriented primary recrystallised grains in the η oriented volumes, for the most likely CSLs, i.e., Σ5 and Σ13a, proved to be unsuccessful. Some were found, but not in sufficient numbers to provide a satisfactory explanation for the formation of Goss secondaries. It is suggested however, that if CSLs are important in the selection of Goss secondaries, that Si segregation has also to be considered, for this will be less in special boundaries and thus provide less solute drag.

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The microstructure evolution at interfaces of a layer-integrated steel sheet constructed by ferritic (SPCC) and martensitic stainless (SUS420J2) steel layers, which were bonded through a cold-rolling and subsequently annealed at 1000°C, has been investigated using scanning transmission electron microscopy combined with energy dispersive X-ray spectroscopy. We find that microstructures around the SPCC/SUS420J2 interfaces are significantly reconstructed during a short-time annealing at 1000°C followed by quenching into water, and the resultant ferrite/martensite interface is found to be extended into the SPCC side from the original cold-rolled interface. Occurrence of such interface migration can be reasonably explained as due to a martensitic transformation across the composition-gradient interface that is caused by element diffusions during annealing at 1000°C. These microstructural characteristics are discussed by comparing with our recent observations of austenite (SUS304)/martensite (SCM415) interface microstructures (Hayashi et al., ISIJ Int., 49 (2009), 1406), which are formed via the same rolling/annealing procedures, aiming to provide a common aspect on how the strong bonding between the hetero-interfaces can be achieved in the layer-integrated steels.

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It is very important to study the incubation time of alloys as it has direct relation to precipitation kinetics and affects morphology of structure. In spite of many efforts of scientists to develop methods to find incubation time, it is still difficult to measure experimentally. In addition, there is need to develop an approach to analyze existing data for many steels. On the other hand, high nitrogen steels have received a lot of attention for their unique properties, however, there is no clear model developed to predict its precipitation kinetics. In present work, Cr₂N age-precipitation in high nitrogen austenitic steels is simulated using neural network (NN) analysis. The feed forward neural network with a back propagation algorithm was built to obtain the constitutive relation of Cr₂N age precipitation with alloying elements and aging temperature. The simulated results show that the NN model can correctly reproduce the precipitation behavior of the steel. An analysis of model predictions and experimental data is presented.

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In the present paper, the precipitation behavior of secondary phases in Lean Duplex Stainless Steel (LDX) 2101 had been studied. The alloy has a typical ferritic-austenitic duplex structure after solution treatment. Isothermal ageing treatments were carried out over the temperature range from 700 to 850°C for the period between 2 min and 1440 min. Cr₂N-type nitrides were formed as the main product of precipitates, together with small amount of Cr₂₃C₆-type carbides. Increase of N content and decrease of Cr and Mo contents in the steel had led to the absence of σ-phase. Due to the solid solution strengthening by interstitial atoms, the hardness value of austenite was measured to be higher than that of ferrite. With increasing the isothermal ageing time, precipitates were observed to be preferentially nucleated at the δ/γ interface and grown toward the δ phase. The δ/γ interfce migrated from the precipitate particles into δ phase, leaving the precipitates behind along the original interfaces, which could increase the size of the secondary austenite (γ′) phase and decrease the hardness of both austenite and ferrite. Inside γ′ phase, the hardness was measured to increase from about 3.20 GPa at the original interface to about 3.75 GPa at the newly formed interface of δ/γ′. The isothermal kinetics for the precipitation of secondary phases was measured to obey the JMAK-type law. The TTT (time-temperature-transformation) curve was constructed based on the measurements, which seems to have resulted from the overlap of two different precipitated products. The average impact energy at room temperature for the sample after solid solution treatment was measured to be 105 J. When 2% secondary phases were precipitated during ageing, the impact energy decreased to about 43 J, reduced by about 59% as compared with the as-annealed sample, indicating that formation of secondary phases can result in dramatic decrease of steel toughness.

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Tensile specimens of 10B22 (22MnB5) sheet steels were austenitized, quenched to martensite, and tempered at temperatures between 150 and 520°C for various times. The heat treated specimens were charged with 1.7 ppm hydrogen and immediately tested. Fracture surfaces were examined by field emission scanning electron microscopy. As-quenched martensitic specimens exhibited the most severe embrittlement and failed by stress-controlled cleavage fracture at low stresses. The initiation of hydrogen-induced fracture in specimens tempered between 150 and 350°C was consistent with glide plane decohesion, and coarse inclusion particles served as sources of hydrogen for circular areas of hydrogen-induced cleavage. Specimens tempered at 460 and 520°C showed little sensitivity to hydrogen embrittlement. The progression of decreased sensitivity to hydrogen-induced fracture with increasing tempering temperature correlates with the reduction in dislocations, the principal hydrogen traps, and the formation of cementite particles, considered to be ineffectual traps, with increased tempering. Very small amounts of intergranular fracture were observed, only in as-quenched specimens, confirming that boron has little effect on hydrogen embrittlement of hardened low-carbon steels.

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The fatigue behavior and mechanical properties of Dual Phase Austempered Ductile Iron (Dual Phase ADI) containing 20, 50, and 70% ausferrite were studied and compared to ductile irons with fully ferritic and ADI matrices. The results indicate that as the amount of ausferrite increases, tensile strength, yield stress, fracture toughness and fatigue resistance increase significantly, if compared to fully ferritc ductile irons. The elongation diminishes; nevertheless all Dual Phase ADI matrices have a deformation until failure that satisfies the minimum value required by ASTM A 536 standard for ferritic ductile iron. All tensile properties of the samples containing 20% ausferrite, located in the last to freeze zones, increased; and so did the endurance limit about 25%. The fact that Dual Phase ADI could offer a wide range of mechanical properties, as a function of the relative percentage of free ferrite and ausferrite, led to the assumption that it could be used in safety parts, thereby replacing ductile irons with other matrices.

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Iron-based metal foam has several advantages over aluminum alloy foam, such as high strength and low cost. However, iron foam does not have high porosity and uniform pore size. It is known that both the decrease in the interfacial tension between molten iron and pores and the increase in the viscosity of the melt contribute to the stabilization of pores. The objective of this study is to investigate the effect of the addition of chromium and tungsten oxide (Cr₂O₃ and WO₃) powders, which are expected to act as stabilizers, on the porosity and pore size of iron foam. Blended powders of pure iron, 3.0 mass% graphite, 0.5 mass% Fe₂O₃, and a certain amount of additives were compacted. The additives used were Cr₂O₃ and WO₃, whose composition ranged from 0.0 to 5.0 vol%. The porosity and the average pore size of the iron foam were measured after heating the precursor at 1563 K. The porosity decreased slightly with increasing additive content. Although the addition of Cr₂O₃ and WO₃ powders led to a decrease in the pore size, the amount of additives did not affect the average pore size. The addition of Cr₂O₃ particles to the precursor led to the formation of a Cr₂O₃ layer on the pore surface of the iron foam and a change in microstructure of the obtained iron foam. On the other hand, the addition of WO₃ particles did not result in the formation of a WO₃ layer on the pore surface.

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Previous studies have pointed out that some quantity of ferritic stainless steel scrap is mixed with carbon steel scrap, thus resulting in the accumulation of chromium in carbon steel products. Chromium substance flow accounts for 97% of its consumption in Japan. This paper describes the analysis chromium substance flow in stainless steel, other alloy steels, and carbon steel in Japan. The analysis was carried out using dynamic modeling. To classify the different kinds of alloys, stainless steel is subdivided into 13Cr, 18Cr, Cr–Ni, and Cr–Ni–Mo. Heat-resistant steel, structural alloy steel, bearing steel, and spring steel are also considered as steel alloys that include chromium. Carbon steel is classified into BOF (basic oxygen furnace) carbon steel and EAF (electric arc furnace) carbon steel to reflect differences in the raw materials from which they are composed. It was found that in-use stocks of chromium in the forms of stainless steel and other alloy steel in 2005 were 3.4 and 0.7 Tg, respectively. Other chromium stock as an alloying element in carbon steel was estimated as being 0.7 Tg in 2005, and it is dissipated in the carbon steel cycle. From the results of the dynamic model, the rates of ferritic stainless steel and other alloy steel recovered as carbon steel were approximately 40 and 80%, respectively, in 2005. Chromium accumulation in EAF carbon steel was dynamically analyzed from 1990 to 2030. On the basis of the assumption that future steel demand will be the same as the current demand, it is predicted that the mean chromium content in EAF carbon steel will gradually increase and reach 0.24% in 2030.

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