There is a strong need in the recent steel industry to urgently develop a simple and sensitive method for the determination of trace elements in iron and steel without using harmful chemicals in the troublesome preconcentration steps taking a lot of skill and time. Stripping voltammetry comprises the preconcentration and the subsequent stripping steps. This is one of the most sensitive methods for the present purpose. This review describes the theoretical concepts, advantages, operational parameters and practical applications to steel analysis of stripping voltammetry.
In order to clarify the bulk breakage mechanism of coke in the lower part of blast furnace, model experiments were conducted based on the conditions that were possible to occur in the above region by considering the reaction form, reaction temperature, reaction degree and impact energy with 6 kinds of 50100 mm diameter coke having different strength and reactivity. In the above region, the bulk breakage of coke is occurred nearly independent of CO2 gasification and seems to be controlled by the pore partition thickness in coke lump. The coke diameter reduction in the above region is decided both by the bulk breakage and the fine generation with abrasion accompanied by 20 mass% CO2 gasification. The former effect is larger and the diameter reduction with bulk breakage of coke having 10070 mm diameter is greater than that of coke having 50 mm diameter. The control technology of pore partition thickness in coke lump will be expected to be researched from now on.
Hydrogen microprint technique is a simple and powerful method to visualize hydrogen behavior in metallic materials by using redox reaction between hydrogen and silver bromide. Polished surface of specimens is covered with nuclear emulsion, and silver particles left on the surface after fixing represent sites of hydrogen emission. If silver particles are unstable during fixing and leave original sites of the reaction with hydrogen, hydrogen behavior can not be accurately analyzed. For the purpose of optimizing the experimental procedure to study hydrogen behavior in steels properly, effects of gelatin hardening on the stability of silver particles were examined in the present study by changing type of photographic fixer and pre-fixing treatment. Fixing specimens with hardening fixer was effective to prevent silver particles from moving to other locations during fixing. Applying hardening fixer, however, made it difficult to observe silver particles that existed in a thick gelatin layer. The optimum procedure was fixing specimens with non-hardening fixer after gelatin hardening by formalin. With this procedure, silver particles were stable during fixing and there was no difficulty in observing silver particles that represented points of hydrogen emission.
Delayed fracture in steel has been correlated with concentration of hydrogen to the point of crack initiation. In the present study, effects of plastic deformation and stress gradient on hydrogen diffusion in carbon steels were studied with hydrogen microprint technique (HMT), which can visualize points of hydrogen emission as silver particles superposed on the microstructure. Three kinds of carbon steels, 0.002% C steel, 0.45% C steel, and 0.85% C steel were prepared and behavior of hydrogen transport was studied during tensile deformation and under bending stress. Hydrogen was transported to the surface with gliding dislocations during tensile plastic deformation in ferrite. In pearlite, however, behavior of hydrogen, which was transported along carbide or carbide-ferrite interfaces, was irrelevant to tensile plastic deformation. Behavior of hydrogen transport under various stress gradient was also studied in 0.002% C steel. Stress was applied by using a fourpoint bending tool, and hydrogen emission was visualized in the area applied with maximal tensile stress. It was demonstrated that even elastic stress gradient promoted hydrogen transport and the amount of hydrogen transport was increased with an increase in stress gradient. Hydrogen transport in the plastically bent specimen is expected to be based on the mixed mechanism, including hydrogen transport by moving dislocation, hydrogen diffusion by stress gradient, and hydrogen diffusion along dislocation core. These factors were separately visualized by applying HMT to the specimens prepared in appropriate testing conditions.
The planer anisotropy of r-value (Δr) is an important property of sheet steels for two piece can use. The effects of cold rolling and temper rolling reduction on Δr are especially large. Δr has a maximum value at the ratio of about 75% single cold rolling reduction. At the higher cold reduction, Δr decreases abruptly for the low carbon steels. On the other hands, Δr become zero at the reduction about 90% for ultra low carbon steels. For the double cold rolling, Δr decrease linearly, independent of cold reduction or carbon content. The tin mill black plate is manufactured at high single cold rolling reduction because of its thin thickness of final products. It is thought that single cold rolling reduction become higher when reduction of gauge is progressed. Therefore, reduction of the carbon content is superior to the conventional ones to achieve the small anisotropy ultra-thin sheets. The r-value and its anisotropy can be explained by the texture using simple Tucker model.
Nickel was electrodeposited from sulfamate baths containing various amounts of thiourea. The effect of S in the deposit on the fatigue properties of electroplated Ni was studied by low-cycle fatigue test and by the observation of the fractured surface of the deposit. The results obtained were as follows: (1) In the deposit of low S content (1.3×10-4mass%), the low-cycle fatigue properties were able to be estimated by the tensile test on the basis of Manson's cogradient law. However, the result of tensile test was not applicable to the deposits of high S content (46×10-4 mass%) because of their poor fatigue properties. (2) The striation was recognized on the fracture surface of the deposit containing 1.3×10-4 mass% S, which suggested that transgranular fracture peculiar to the low-cycle fatigue occurred. On the contrary, the deposit of 46×10-4mass% S was consisted of polycrystal colonies with the polygonal shape (several millimeters in size). Since the strength in colony boundary was lower than that in colony itself, the fracture proceeded along the colony boundary. (3) During annealing, S in the deposits diffused into the boundary between grains recrystallized. Therefore, the fracture might occur along the grain boundary embrittled by S.
Micro-strucure, micro-hardness and micro-absorbed impact energy in the Japanese sword have been investigated to clarify excellent mechanical properties of the Japanese sword. The Japanese sword specimen used in the present research has been made by using TSUKURIKOMI process which combines four kinds of steels; HAGANE (edge), SHINGANE (core), MUNEGANE (back) and KAWAGANE (side) steels, with different carbon contents. By this process, HASAKI (edge) side becomes high carbon steel and MUNE (back) side possesses low carbon steel. The cooling velocity in quenching of the Japanese sword is controlled by TSUCHIOKI treatment which coats the clay thinner in the HASAKI side and thicker in the MUNE side. The HASAKI side is quickly cooled and the MUNE side is slowly cooled. The micro-structure in the HASAKI side shows martensite while the MUNE side shows the coexist structure of ferrite and pearlite. The HASAKI side has a lower value while the MUNE side shows a higher value in the micro absorbed impact energies obtained with the 1.0 and 0.7 mm square miniaturized specimens. It has been shown clearly that the TSUKURIKOMI and the TSUCHIOKI processes give the excellent gradated balance of strength-toughness to the Japanese sword. The ORIKAESHI (folding) forging has an effect both on the carbon content and as quenched hardness in HAGANE steel. The most suitable times of ORIKAESHI cycles which adjust to the carbon content of 0.55-0.60 mass% and hardness of 800HV1 have been determined to be thirteen times. These times of ORIKAESHI cycles correspond to the optimum traditional cycles lying between twelve and fifteen times. The present research from the viewpoint of the metallurgy sheds light on the empirical rule in the traditional Japanese sword processing.
Fatigue crack propagation (FCP) has been studied using CT specimens cut from laser welded butt joints of the coupling of two different steels, cold rolled low carbon steel (SP) and high tensile strength steel (HT). When the FCP direction was parallel to the weld, the FCP rates of the welded specimens characterized in terms of the effective stress intensity factor range were nearly the same as that of the base steel (SP) and thus the weld bead had the same intrinsic FCP resistance as the base steel. When the FCP direction was normal to the weld, FCP rates decreased temporarily within the weld zone. This decrease of FCP rate still existed after allowing for crack closure and was also seen in FCP behaviour of the specimens subjected to stress-relief annealing and in crack closure-free FCP behaviour at a high stress ratio. Fractographic examination revealed that typical fracture mechanism was the mixed mode of intergranular and transgranular fracture in SP plate, while transgranular fracture mode in the weld zone and HT plate.
The effects of alloying elements addition on uniform elongation of tempered martensite has been investigated. Tempered martensite is considered as dual phase structure composed of ferrite matrix and harder second phase: cementite. Cementite volume fraction and morphology were observed by scanning and transmission electron microscopy. Microstrain of ferrite matrix were evaluated by means of X-ray diffraction analysis. It was observed that Carbon addition effectively increased uniform elongation. It was explained that high cementite volume fraction contributed to high uniform elongation. It was also observed that Silicon addition increased uniform elongation remarkably. It was considered that Silicon addition led to refinement of cementite and extremely low microstrain of matrix and both of them contributed to high uniform elongation.
"Tatara" was a traditional box-type furnace in Japan and had produced steel and pig iron directly until 1923. After then, because of the low productivity, Tatara was not commercially operated but only for producing the materials of Japanese sword in little. In 1977 with the blank ages after the World War II, Japan Institute of Art Japanese Sword reconstructed the Tatara furnace, called "Nittoho Tatara". Then, Mr. Yoshizo Abe as a leader "Murage" realized his own technique for the Tatara operation because of the technique transfer only by oral instruction to the Murage's family. The 3rd Tatara operation in 1999 winter has been studied on the effect of fire flame (so called "Hose") and sound from furnace, the color and viscosity of slag (so called "Noro") flowed out from furnace and the condition of tuyers to the productivity of "Kera" including steel (so called "Tamahagane") and pig iron (so called "Zuku"), etc. This operation met the trouble of air blowing to the furnace in the final stage. Though many efforts had been made to recover the stable operation, the activity of furnace was stopped in shorter operation time than the other two operations. From the experiences of the recover, the fundamental treatments to make the operation stable have been cleared and also the reaction mechanisms to produce.