Cold model experiments were conducted to investigate the dripping behavior of molten iron in the coke packed bed filled with molten slag. The dripping behavior or dripping rate of pseudo-iron droplets in packed beds filled with immiscible liquid was described well by three comparatively simple mathematical models.
As a fundamental study for clarifying the reduction phenomena of sintered iron ore in a blast furnace, iron oxide (H) and quaternary calcium ferrite (Cf) were prepared and its kinetic behavior at the final stage of reduction with CO–CO2 gas mixture was studied. Reduction rate increased with increasing reduction temperature. Besides, it increased with increasing partial pressure of CO gas. Influence of gas composition on reduction rate is much larger than reduction temperature. From comparisons of weight loss curves of H samples with that of Cf samples, reduction rate of H samples were faster than that of Cf samples in the same conditions. Reduction reaction of H and Cf samples proceeded topochemically at higher temperature (1100°C), and proceeded non-topochemically at lower temperature (<1000°C). Besides, the reduction reaction of samples used CO rich gas proceeded topochemically. Structure of iron layer in H samples were different for temperature and gas composition. On the other hand, structure of iron layer in Cf samples were almost the same in all conditions. Reduction data were analyzed by one interface unreacted core model, chemical reaction rate content kc and effective diffusion coefficient in product layer De were determined. The values of kc had Arrhenius-type temperature dependence, and were approximately same tendency except for Cf samples in near equilibriums gas compositions. The values of De obtained from Cf samples were approximately constant in all conditions.
New needs about on-line analysis of Mn concentration have been arose in association with the decrease of the quantity of slag in the basic oxygen furnace drastically. In the JFE steel, a trial to determine the Mn concentration in molten steel by an atomic absorption spectrometry focusing on the atomic vapor that exists on the molten steel surface has been examined. In this work, the radiant light spontaneously generated from the molten steel surface of a high temperature state was used as a light source. As an experiment result, it was found that direct determination of the Mn concentration in the molten steel by this law was possible since measured Mn absorbance correlated with Mn concentration up to 3% in molten steel.
The hardness of Fe–Cu alloys is known to increase by the precipitation of Cu clusters during thermal aging. We reported previously that the precipitation of Cu clusters accelerate due to the introduction of lattice defects by pre-strain obtained through tensile test or cold rolling, thus reducing the starting temperature of the hardness increase. However, the mechanism has not yet been clarified. In this study, the positron annihilation lifetime and coincidence Doppler broadening techniques have been used to investigate the recovery behavior of lattice defects such as vacancies, vacancy clusters and dislocations as well as the diffusion behavior of Cu atoms of cold rolled and thermally-aged Fe–Cu alloys. Lattice defects were densely introduced when Fe–1.5%Cu alloys were cold rolled at a reduction rate of more than 30%, and vacancies were approximately 20% of the defects. Both vacancies and dislocations were annealed out through the aging process. On the other hand, some dislocations remained even after aging at 550°C, although the vacancies almost disappeared after aging at 300°C. Cu clusters started to precipitate mainly on the dislocations above 200°C in the cold rolled Fe–1.5%Cu alloys. The hardening due to the Cu clusters occurs with the recovery of vacancies. Thus, both vacancies and dislocations accelerate the diffusion of Cu atoms and the precipitation of Cu clusters.
The metallurgical macro- and micro-structure, and the residualstress of the Japanese matchlock gun, fabricated at the late Edo period, have been investigated with an optical microscope, an SEM, an EPMA and an X-ray residual stress meter for estimating the fabricating process and their materials. This gun was fabricated by Udonbari (in Japanese) process, which is similar to that of the Russell's method, tubes was created by the joining together opposite edges of a flat iron strip with an iron core bar. The joining line was wavy. Their residual stress was mainly compressive and the values were from 180 to 280 MPa in the longitudinal direction and from 240 to 380 MPa at the transverse direction. The gun was made of low carbon steel with equiaxed ferrite grains; their grain size was mainly 10 μm partly with 100 μm and exceptionally more than 1000 μm grains. Moreover, we find the special banded structure, consisted of fine ferrite grains bands and large ferrite grains bands. The firing part was fabricated by the joining of five parts for getting the L-shape hole. The female screw was made by forging; therefore the shape was tapered screw and the male screw was cut from a low grade steel bar, confirmed by their macro-structure.
Cold rolled niobium normally shows high planar anisotropy in mechanical properties which causes earing in deep-drawing. Niobium is a bcc refractory metal, but its deformation and recrystallization textures have not been understood sufficiently. In this study, pure niobium sheets have been reduced from 2.0 to 0.5 mm in thickness by four-pass cold rolling. Either symmetric rolling or asymmetric rolling was performed as the cold rolling. The asymmetric rolling was realized by differential-speed rolling with speed ratio of 1.4. Elongated grains with α-fiber and γ-fiber texture components developed by the symmetric rolling. On the other hand, elongated grains are less developed by the asymmetric rolling. Changes in texture and microstructures in symmetric rolling and subsequent annealing are similar to those of α-Fe. During recrystallization after the asymmetric rolling, α-fiber does not develop well and equiaxed microstructure is formed. It is formed that planar anisotropy of r-value, i.e. Δr-value, is improved by the asymmetric rolling subsequently followed by annealing.
Three dimensional numerical analysis model of thermal stress and deformation of slab in reheating furnace was constructed. Using this model, temperature distribution, thermal stress and deformation of 36%Ni–Fe alloy slab showing the unique thermal expansion property, called “Invar ally”, were simulated. During slab reheating, the surface part of the slab is always a high temperature compared with the internal portion. The difference of temperature between surface and center parts of slab causes the difference of thermal expansion, and stress acts on each part of the slab. The magnitude and the direction of stress vary in accordance with plastic deformation through the reheating phase. Tensile stress can be generated on the surface part of the slab during heating. If the tensile stress acting on the surface part is large enough, surface defects may be easily caused. Therefore, it is suggested that attention should be paid to the heating pattern in order to avoid surface defects of 36%Ni–Fe alloy.
The pinning effects of second phase particles on the grain growth of ferrite were studied in an Fe–0.1C alloy containing 5 ppm boron (B). The number and size distribution of Fe3(CB) particles were measured at grain faces, edges and corners by serial sectioning. The particle size was determined from the number of consecutive sections on which the particle was observed. The proportion of particles at each grain boundary site was significantly greater than that of random distribution. The modified Zener theory which assumes that all grain boundaries are pinned by particles could explain the grain size very well, whereas the theory which considers that the pinning of grain boundary corners plays a major role gave a smaller grain size than experiment. Nishizawa et al.'s correlation model accounted well for the number of pinning particles on grain boundaries as well as the grain size. The Hunderi–Ryum's model which takes into accounts pinning of all grain boundary sites gave results close to experiment when a larger proportion of pinning particles at boundary sites than random distribution was incorporated.
The effect of austenite grain size on the fatigue crack growth and arrest behavior of carburized steel was studied. On the fatigue test of same stress amplitude, the fatigue crack initiation of fine austenite grain steels is delayed in comparison with coarse austenite grain steels, but the difference of crack initiation life between fine grain steels and coarse grain steels is very slight against 107 cycles. The improvement of crack arrest property is dominant for increasing fatigue limit by refinement of austenite grain size. The critical stress intensity factor for crack arrest under fatigue tests at the stress amplitude of the each fatigue limit of carburized steels is calculated by considering the effect of compressive residual stress. As a result, it becomes clear that the finer the austenite grain size, the larger becomes the critical stress intensity factor for crack arrest, and crack arrest property is improved remarkably by the refinement of austenite grain size.