细化钢铁材料晶粒的原理与方法

细化晶粒是控制金属材料组织结构的最重要、最基本的方法,目前,实际应用的成块材料可获得的最细的铁素体晶粒约为5μm。获得细晶粒的方法有利用相变和再结晶的热处理（或形变热处理）,钢液超速冷却,机械合金化,超细粒子烧结和非晶体结晶等。形变热处理对晶粒细化极为有效,已以实验室规模获得了具有小于或等于1μm的超细晶组织的成块材料。本文以形变热处理为中心,介绍了控制轧制、加速冷却的形变热处理（TMCP）,以及形成微细双相组织、亚晶大角度化等细化晶粒的方法,从金相学角度阐述了细化晶粒的原理和方法的现状及最新进展。     

Distribution of double bonds in thermally degraded polyisobutylene

The distribution of double bonds in thermally degraded polyisobutylene was determined quantitatively by using pulsed Fourier transform ¹H n.m.r. spectroscopic analysis. The double bonds in the degraded polymer did not exist in the interior but at the terminal positions of the polymer chain. These olefins were of the terminal trisubstituted and terminal vinylidene types. The content of the former was much greater than that of the latter. This shows that radical chain transfer predominantly occurs at the methylene hydrogen rather than at the methyl groups of the polymer chain. The average number of double bonds per molecule, f, was greater than 1 and tended to be near 2. Thereby most of the degraded polyisobutylene was shown to have two terminal unsaturations per molecule.     

Streptomyces aminopeptidase P: biochemical characterization and insight into the roles of its N-terminal domain

We purified and characterized the aminopeptidase P from Streptomyces costaricanus TH-4 (thAPP). This enzyme has a tetramer structure, a metal-ion preference toward Zn, broad substrate specificity and a narrow pH dependency for activity. The primary structure of thAPP, respectively, exhibits 91% and 65% identity with those of two other APPs-APP I and APP II-from Streptomyces lividans (slAPP I and slAPP II). We next overexpressed the genes encoding thAPP and slAPP II in Escherichia coli and characterized them. Two differences were apparent in their properties: slAPP II formed a dimer, whereas thAPP formed a tetramer; also, the alkaline side pKa for the catalytic action of slAPP II is higher than that of thAPP. Investigation using chimeras of both enzymes revealed that the N-terminal domain is associated with the determination of pKa values for catalytic action and quaternary structure.     

A TEM study on melt-crystallized poly(butylene terephthalate)

A study was made to investigate an optimum condition for ruthenium tetraoxide staining of poly(butylene terephthalate) (PBT) with glass transition temperature as low as ca. 23 degrees C for TEM observation of melt-grown PBT crystals. The morphological study of ultrathin sections prepared based on optimum staining at 25 degrees C for 8 h revealed formation of fringed-micellar crystal nuclei in the early stage and folded-chain fringed-micellar crystals in the later stage of isothermal crystallization at 40 degrees C from melt. The fraction of chain-folded crystals increased with increasing crystallization temperature from the quantitative analysis of crystal thickness in comparison with the reported morphology using the replica method.     

A self-organization learning algorithm for visuo-motor coordination in unstructured environments

In this paper, we propose a learning algorithm for coordinating a robot system where the movement of an arm is controlled through a stereo camera system. Instead of calibrating the usually complex non-linear transformation between the arm and cameras, the algorithm decomposes the whole transformation automatically into local linear transformations and then makes the linearization map recorded by the arm controller. The linearization is carried out by a learning process based on a Kohonen-style self-organization network. To deal with unstructured environments in which some obstacles exist, some virtual forces are introduced for dealing with the high degree of complexity underlying in the transformation. This work was presented, in part, at the International Symposium on Artificial Life and Robotics, Oita, Japan, February 18–20, 1996     

Temperature distribution in Li2O pellets under neutron irradiation

The center temperature of Li₂O pellets under neutron irradiation was measured using an encapsuled pin. The surface temperatures of the pellets and the pellet/cladding heat transfer coefficients were estimated on the basis of the well-known conductivity integral.     

Precision dilatometer analysis of neutron-irradiated nuclear graphite recovery process up to 1673 K

Specimens of two kinds of isotropic nuclear graphite, IG-110U and ETP-10, were neutron-irradiated at fluence of 1.92 × 10²⁴ n/m² (E > 1.0 MeV) at 473 K. The recoveries of the macroscopic lengths of these specimens during isothermal and isochronal annealing at temperatures of up to 1673 K were investigated in a step-wise manner by using a precision dilatometer. The macroscopic lengths after isochronal annealing for 6 h at each temperature decreased gradually as the temperature was increased to 1673 K. The recovery trends of the c-axis and a-axis lattice parameters differed from one another, and from the macroscopic length recovery trends. For the IG-110U specimen, the activation energies (E_a) of macroscopic volume recovery corresponding to annealing at 523–773, 773–923, 923–1073, and 1073–1173 K were found to be 0.15, 0.34, 0.73, and 2.59 eV, respectively. For the ETP-10 specimen, the E_a corresponding to 523–923, 923–1223, and 1223–1373 K were determined to be 0.15, 0.46, and 2.19 eV, respectively. These results indicate that both graphite specimens underwent three or four stages of macroscopic length recovery between 523 K and the annealing temperatures at which their initial lengths were recovered. It is suggested that during the first stage recovery proceeded via the migration of single interstitials along the basal plane and the resulting V-I recombination. In the middle stages, recovery occurred due to the migration of interstitial groups such as C₂ along the basal plane, while in the last stage, it proceeded via through-layer migration of interstitials or migration of single vacancies.     

Hydrogen entry into Fe and high strength steels under simulated atmospheric corrosion

Electrochemical hydrogen permeation tests of Fe sheets under two cyclic corrosion test (CCT) conditions were performed to understand hydrogen entry behavior under atmospheric corrosions. Hydrogen entry into 1300 MPa-class high strength steels under two CCT conditions was also investigated using thermal desorption analysis. One CCT consisted of salt spray, dry and wet stages (Salt Spray CCT; SSCCT), and the other consisted of dry and wet stages after NaCl deposition (Dry–Wet CCT; DWCCT). The corrosion rates of Fe and the steels were almost constant under SSCCT and they decreased under DWCCT with time. Nevertheless, both CCTs resulted in increases in hydrogen permeation current and diffusible hydrogen content with time indicating enhancement of hydrogen entry. Corrosion current monitored by means of an atmospheric corrosion monitoring sensor consisting of Fe anode and Ag cathode decreased obviously under dry stage of the CCTs, whereas hydrogen permeation was high at the beginning of the dry stage. The discrepancy between hydrogen entry and corrosion rate indicates that the hydrogen entry is not directly controlled by corrosion rate. Increase in acidity of underlying rust layer with growth of rust layer monitored using a W/WO₃ electrode is considered to be one of the factors affecting the hydrogen entry efficiency.