Effect of Cooling Method on Microstructure and Mechanical Properties of Hot-Rolled C-Si-Mn TRIP Steel

 The controlled cooling technology following hot rolling process is a vital factor that affects the final microstructure and mechanical properties of the hot-rolled transformation induced plasticity (TRIP) steels. In the present study, low alloy C-Si-Mn TRIP steel was successfully fabricated by hot rolling process with a 450 hot rolling mill. To maximize the volume fraction and stability of retained austenite of the steel, two different cooling methods (air-cooling and ultra-fast cooling “AC-UFC” and ultra-fast cooling, air-cooling and ultra-fast cooling “UFC-AC-UFC”) were conducted. The effects of the cooling method on the microstructure of hot-rolled TRIP steel were investigated via optical microscope, transmission electron microscope and conversion electron Mssbauer spectroscope. The mechanical properties of the steel were also evaluated by conventional tensile test. The results indicated that ferrite and bainite in the microstructure were refined with the cooling method of UFC-AC-UFC. The morphology of retained austenite was also changed from small islands distributing in bainite district (obtained with AC-UFC) to granular shape locating at the triple junction of the ferrite grain boundaries (obtained with UFC-AC-UFC). As a result, the TRIP steel with a content of retained austenite of 1152%, total elongation of 32% and product of tensile strength and total elongation of 27552 MPa·% was obtained.     

Continuous casting of steels in Japan

The effective pair potentials of molten AgBr, CuBr, CuI and RbBr have been obtained from measured structural information by solving the modified hypernetted-chain (MHNC) equation coupled with a predictor–corrector method, recently proposed for a binary system. The usefulness of the pair potentials obtained in this work was suggested by reproducing the particular pre-peak in the partial structure factor of Cu–Cu pair in molten CuBr and CuI, because such pre-peak couldnot be given while using the model potentials previously proposed for these two molten salts. Some characteristic features in these four molten salts were also detected in the bridge function, which was introduced to the MHNC equation as a many-body interaction contribution.     

Characterization of Catalase from Psychrotolerant Psychrobacter piscatorii T-3 Exhibiting High Catalase Activity

A psychrotolerant bacterium, strain T-3 (identified as Psychrobacter piscatorii), that exhibited an extraordinarily high catalase activity was isolated from the drain pool of a plant that uses H(2)O(2) as a bleaching agent. Its cell extract exhibited a catalase activity (19,700 U·mg protein(-1)) that was higher than that of Micrococcus luteus used for industrial catalase production. Catalase was approximately 10% of the total proteins in the cell extract of the strain. The catalase (PktA) was purified homogeneously by only two purification steps, anion exchange and hydrophobic chromatographies. The purified catalase exhibited higher catalytic efficiency and higher sensitivity of activity at high temperatures than M. luteus catalase. The deduced amino acid sequence showed the highest homology with catalase of Psycrobacter cryohalolentis, a psychrotolelant bacterium obtained from Siberian permafrost. These findings suggest that the characteristics of the PktA molecule reflected the taxonomic relationship of the isolate as well as the environmental conditions (low temperatures and high concentrations of H(2)O(2)) under which the bacterium survives. Strain T-3 efficiently produces a catalase (PktA) at a higher rate than Exiguobacterium oxidotolerans, which produces a very strong activity of catalase (EktA) at a moderate rate, in order to adapt to high concentration of H(2)O(2).     

Thermal depoling and relaxation property of (Na,K)NbO3 system

(Na,K)NbO₃ ceramics was synthesized by an ordinal solid state reaction method. Thermally stimulated depolarization current (TSDC) pattern of the poled ceramics was measured. Electrically poled Na_0.5K_0.5NbO₃ ceramics generated anomalous large discharge current at around 370 °C during the heating step due to the thermal relaxation of oxygen vacancy. The oxygen vacancy piled up around electrodes and formed the electrically inhomogeneous structure in the ceramics. In addition, the anomalous current of K-riched ceramics was larger than that of Na-riched one. This result suggested that the equilibrium composition of NaNbO₃–KNbO₃ system was near to Na-riched composition against Na_0.5K_0.5NbO₃.     

Ultrafast dynamics of surface-enhanced Raman scattering due to Au nanostructures

Ultrafast dynamics of surface-enhanced Raman scattering (SERS) was investigated at cleaved graphite surfaces bearing deposited gold (Au) nanostructures (～10 nm in diameter) by using sensitive pump-probe reflectivity spectroscopy with ultrashort (7.5 fs) laser pulses. We observed enhancement of phonon amplitudes (C═C stretching modes) in the femtosecond time domain, considered to be due to the enhanced electromagnetic (EM) field around the Au nanostructures. Finite-difference time-domain (FDTD) calculations confirmed the EM enhancement. The enhancement causes drastic increase of coherent D-mode (40 THz) phonon amplitude and nanostructure-dependent changes in the amplitude and dephasing time of coherent G-mode (47 THz) phonons. This methodology should be suitable to study the basic mechanism of SERS and may also find application in nanofabrication.     

Porous ceramics mimicking nature—preparation and properties of microstructures with unidirectionally oriented pores

Porous ceramics with unidirectionally oriented pores have been prepared by various methods such as anodic oxidation, templating using wood, unidirectional solidification, extrusion, etc. The templating method directly replicates the porous microstructure of wood to prepare porous ceramics, whereas the extrusion method mimics the microstructures of tracheids and xylems in trees. These two methods are therefore the main focus of this review as they provide good examples of the preparation of functional porous ceramics with properties replicating nature. The well-oriented cylindrical through-hole pores prepared by the extrusion method using fibers as the pore formers provide excellent permeability together with high mechanical strength. Examples of applications of these porous ceramics are given, including their excellent capillary lift of over 1 m height which could be used to counteract urban heat island phenomena, and other interesting properties arising from anisotropic unidirectional porous structures.     

PCE-based fast path control in multi-domain photonic networks

We discuss issues for controlling an optical path in large-scale photonic networks, and introduce an inter-domain path control system based on Path Computation Elements (PCEs). In the system, maximum flow information enables the load balancing of traffic, and Path Key scheme preserve the confidentiality of internal topology information among carrier networks. Based on the experimental results, we show the path setup in the introduced system is significantly faster than the manual path setup among domains in current carriers' networks. For the additional reduction of the path setup time, we propose the domain-wise paralleled signaling method. We also show that decreasing the number of nodes per domain makes path setup faster in the introduced system with deployment of the proposed signaling method.     

Strengthening of Porous Alumina by Pulse Electric Current Sintering and Nanocomposite Processing

Porous Al₂O₃ and SiC–dispersed-Al₂O₃ (Al₂O₃/SiC) nanocomposites with improved mechanical properties were fabricated using pulse electric current sintering (PECS). Microstructures with fine grains and enhanced neck growth, as well as high fracture strength, could be achieved via PECS of Al₂O₃. The incorporation of fine SiC particles into an Al₂O₃ matrix significantly increased the fracture strength of porous Al₂O₃. Based on microstructural observations, it was revealed that the refinement of Al₂O₃ grains and neck growth occurred by PECS and nanocomposite processing.     

High-Accuracy Analysis of Beams of Bimodulus Materials

Recently, several authors have treated the problems of bending of beams of bimodulus materials. The present paper, applies Levinson beam theory, which includes shear deformation and warping of the cross section, to bending analysis of thick rectangular beams with bimodulus materials. Many numerical results are obtained by use of the transfer matrix approach and compared with the methods of Bernoulli-Euler beam theory, Timoshenko beam theory, and Levinson beam theory with various boundaries. Also, the neutral-surface location and displacements for beams of bimodulus materials are calculated.     

Molecular dynamics study of surface effect on martensitic cubic-to-tetragonal transformation in Ni–Al alloy

Molecular dynamics (MD) study of martensitic transformation (MT) in nickel and aluminum alloy is performed. The behavior focused on is transformation between crystalline structures from B2 cubic cell to body-centered tetragonal cell, which is simply realized by uniaxial tensile loading. The potential function used is Finnis–Sinclair type having only single energy minimum where B2 structure exists. The availability of this specific many-body potential for stress-induced MT phenomena under uniaxial loading is fully discussed. In MD simulations, martensite phase is induced by tensile stress or strain in the atomic system, as predicted by a potential energy map. It is understood that the characteristic of the potential energy function with regard to deformation is crucial for MT studies and investigating energy-strain or stress–strain map is worthwhile. The MT behavior in the atomic system occurs during a plateau region of stress–strain (S–S) curve of the whole specimen, that is typical for experimental superelastic or shape-memory alloys under uniaxial loading. It is found that, during each MT event, large jump of atomic strain is observed. Owing to single energy minimum, the atomic system shows almost perfect recovery in S–S curve, where the graph comes completely back to initial state after unloaded. Besides, the present paper focuses on surface effect for MT behavior. Since the surface effect is dominant in MT phenomena especially in microscopic specimens, a novel computational scheme for stabilizing condition in which uniaxial loading is always applied together with arbitrary periodic boundary condition(s) is devised. By comparing one-, two-, and three-dimensional models under uniaxial loading, it is recognized that the nucleation behavior depends strongly on the existence of free surface region (including corner edge). When there is no surface, a chaotic nucleation of martensite is observed. On the other hand, the free surface induces first martensite because of less constraint in tensile deformation of unit cells. It is confirmed that the tendency toward MT nucleation corresponds to yield stress or strain of the specimen. In order to define and detect martensite structure as for each atom, an atomic strain measure (ASM) with our own formation is introduced. It is shown that the ASM is very effective to distinguish martensite bct unit structure from others.