Electromagnetic sensor to detect the unbalanced flow in CC strand by using the magnetic transformation just below CC mold has been proposed, noticing that the narrow face of slab has been cooled at beneath of mold and surface temperature rapidly decreases to Curie temperature (Tc). Laboratory experiments have been performed to verify the principle of the proposed sensor, which is composed of primary and secondary solenoid coil. The obtained experimental results showed that the relationship between the surface temperature of slab and induced electric voltage could be explained by Curie-Weiss law, when AC magnetic field has been imposed on the slab surface. Moreover, plant tests have been conducted by installing the sensor just below the narrow face of mold. It can be found that the proposed sensor have potential to measure surface temperature under severe conditions and detect the unbalanced flow in CC strand.

Friction property of the case hardening steel subjected to excess vacuum carburizing and subsequent severe plastic deformation and induction hardening was evaluated by the traction test. The purpose of this study is to clarify the effect of fine microstructure on the friction property, focusing on the interaction between the fine microstructure and the lubricating oil additives. The vacuum carburizing treatment is performed at the hyper-eutectoid composition of 1.0 mass% C. Subsequently, the carburized surface was formed the white layer by the surface-nanostructured wearing (SNW) process, and the specimen having the initial microstructure was subjected to induction hardening. The microstructure of the condition with SNW was finer compared to that with SNW-less. According to the traction test, traction coefficient (μ) in the specimen having the fine microstructure on the rolling contact surface decreased. Therefore, it was found that the decrease of μ could be achieved by the application of high-density lattice defects (grain boundaries in this study). After the test, the rolling contact surface of the specimen with fine microstructure became smooth, and the surface showed high reactivity with the lubricating oil additives and formed the compound film of Fe-O-P system having a fine, spherical morphology. The surface roughness was improved by the presence of the wear particles on the surface. Therefore, it was thought that the μ was decreased because the transition to a mild friction condition was caused due to the dispersion of the contact pressure.

In a molten zinc bath in a continuous galvanizing line, top dross particles crystallize as Fe₂Al₅ intermetallic compound containing Zn, which causes the surface defect of the final products by easily adhering to steel sheets. The present study focused on the analysis of crystal structure of the top dross by simultaneously exploiting first principle calculation and synchrotron X-ray diffraction of top dross prepared in a laboratory. The following results were obtained: The first principle calculation on top dross suggested that two Al atoms in the partially occupied four Al sites of Fe₂Al₅ based on the crystal structure proposed by Mihalkovič et al. were replaced by two Zn atoms. In addition, Al atoms in the two kinds of partially occupied Al sites in Fe₂Al₅ proposed by Burkhardt et al. was equally replaced by Zn atoms. The propose crystal structure of top dross was verified by the X-ray diffraction profile analysis using RIETAN-FP simulation as well as the experimentally determined lattice constant of Zn containing top dross.

Duplex stainless steels have ferrite and austenite microstructures, which have material properties that are different. The strength level and hydrogen diffusion constant of the phases are different; therefore, it is expected that the microscopic stress and hydrogen concentration distribution are inhomogeneous. Assuming that hydrogen-induced cracking occurs at locally stress-concentrated and hydrogen accumulated locations, it is important to take into consideration the influence of the microstructure in the evaluation of hydrogen-induced cracking. In order to observe crack locations at the microstructural scale, a slow strain rate test of hydrogen-charged specimen was performed and the cross section of the specimen was observed after the test. Hydrogen-induced cracks were mainly found in the ferrite phase. In order to clarify the contribution of the stress and hydrogen concentration distribution to the initiation of hydrogen-induced cracks, a numerical simulation was performed. A microstructural-based finite element model consisting of ferrite and austenite phases was designed based on the micrograph of the duplex stainless steel used. Stress–strain curves of the ferrite and austenite phase were set and macroscopic tension was applied to calculate the microscopic stress distribution. Incorporating the stress distribution into hydrogen diffusion simulation as one of driving forces, the microscopic distribution of hydrogen concentration was calculated. From the simulation results, stress concentration and hydrogen accumulation occurred at ferrite phase or ferrite/austenite boundary. This tendency corresponds closely to the experimentally observed results; therefore, the above approach can be applied to the evaluation of hydrogen-induced cracking at the microstructural scale.

Duplex stainless steels and their deposited weld metal have ferrite and austenite microstructure, which have material properties that are different. In addition, the microstructure of the base metal and weld metal are clearly different; therefore, it affects the hydrogen diffusion and accumulation, and hydrogen-induced cracking behavior at the microstructural scale. In this study, the influence of the microstructure on hydrogen-induced cracking behavior of duplex stainless steel weld metal was investigated. Specimens of duplex stainless steel weld metal were prepared and slow strain rate tensile test was performed after hydrogen charging. Cracks were observed at boundaries of ferrite and austenite phases. In order to clarify the stress and hydrogen concentration distribution at the microstructural scale, a microstructure-based finite element simulation was performed. A finite element model based on a cross sectional observation of the microstructure was designed to calculate the stress and hydrogen concentration distribution. The simulation result showed that the hydrogen accumulation occurs at ferrite/austenite boundaries, which corresponded to the locations where cracks were observed in the experiment. On the other hand, the hydrogen concentration at the accumulation site in the weld metal was low compared to that in the base metal. Therefore, the influence of the phase fraction and the stress-strain curves of the ferrite and austenite phases on the hydrogen concentration was investigated by the proposed numerical simulation. It was demonstrated that both the phase fraction and stress-strain curves have significant influence on the microscopic distribution of hydrogen concentration.