Effect of deformation on the austenite-to-ferrite transformation in a plain carbon and two microalloyed steels

Isothermal compression tests were carried out on three steels: (i) a plain C, (ii) a Mo, and (iii) a Mo-Nb-V microalloyed grade in order to study the effect of deformation on the austenite-to-ferrite transformation. Dynamic TTT (DTTT) curves were determined, which show clearly the extent to which deformation accelerates the decomposition of austenite. The latter effect is diminished by the addition of the alloying elements Mo, Nb, and V and is further reduced as the temperature is increased. The substitutional elements Mo, Nb, and V appear to reduce the nucleation rate through reduction of the austenite grain boundary energy. The growth rate is also reduced by these elements, apparently through the solute drag-like effect. The microstructural results indicate that the ferrite formed under dynamic conditions becomes more homogeneous and finer when the strain rate or the temperature is increased. Under static conditions, increasing the prestrain or the prestraining strain rate accelerates the γ-to-α transformation and reduces the mean grain size of the ferrite, although the highest transformation rate is still associated with the dynamic case.     

High temperature deformation of oxidized β-Zr-Mo alloys

The flow properties of β-phase Zr-Mo alloys were investigated by means of compression testing in a nominally pure (10 ppm O₂) argon atmosphere. Experiments were carried out in the strain rate range 10^-1 to 10^-5 s^-1 and from 900 to 1000°C. The stress-strain curves were unusual in that they exhibited a continuous decrease in flow stress with strain, after little or no work hardening. A further unusual feature of the data was that the flow stress in interrupted tests increased with delay time in all the alloys. By contrast, crystal bar Zr, tested under the same atmosphere, exhibited neither flow softening nor significant interruption hardening, but deformed in a conventional manner. The results obtained from X-ray investigations, as well as from interrupted tests and from tests carried out in a more purified atmosphere, indicated that the occurrence of both interruption hardening and flow softening was associated with the formation of an oxygen stabilized a-layer on the outer surface of the β-sample. Growth of the hard α-layer during annealing produces strengthening while its decrease in volume during deformation produces softening. A model, based on the assumption that the hard α-phase shares the load applied to the sample, was developed, and its predictions agree satisfactorily with the experimental observations. The extreme sensitivity of Zr-Mo alloys to trace amounts of oxygen is attributed to the presence of liquid molybdenum oxides in the surface scale, which leads to rapid oxygen transport. The stress sensitivity of the strain rate in these alloys decreases from 4.0 to 3.4 as the molybdenum concentration is increased from 0 to 6 pct, for both the yield and the steady-state regimes of flow. The alloy flow stress increases with molybdenum concentration approximately as C^0.4, and it is apparent that the molybdenum atoms do not act as individual obstacles to flow, but are likely to lead to strengthening by indirect means.     

Continuous cooling transformation temperatures determined by compression tests in low carbon bainitic grades

The transformation behaviors of six steels containing microalloying additions of B, Nb, and Mo were investigated under continuous cooling conditions. Continuous cooling compression (CCC) tests were employed to study the effects of chemical composition (mainly, Nb, Mo, and B) and deformation parameters (reheat temperature, prestrain, and holding time) on the transformation temperatures (A _r3 and B _s). It was found that for the Mo-Nb-B, Mo-B, and B steels, the transformation temperatures are relatively stable, and vary in a range of about 20 °C when the reheat temperature is changed from 900 °C to 1200 °C. Both the stress-temperature curves and the associated microstructures show that transformation in the Mo-Nb-B steel is basically of the γ-to-B type; i.e., the resulting microstructure is low carbon bainite. By contrast, for the Nb-B steels, the transformation temperatures vary significantly when the reheat temperature is changed. The concentration of boron in solution strongly affects the transformation behavior of this type of steel. In the Nb-48B steel, the latter is of the γ-to-B type, while in grades with either higher (Nb-64B) or lower (Nb-15B) boron concentrations, it is mainly of the γ-to-α type. Large Fe₂₃(C,B)₆ particles, which were found at low reheat temperatures and long holding times, are considered to be responsible for raising the transformation temperatures.     

Similarities between lime and limestone in wet—dry scrubbing

Lime is utilized as a sorbent in most commercial wet—dry scrubbing processes for SO₂ control, while limestone is not considered to be sufficiently reactive for such a purpose. Faced with the fact that limestone is potentially the least expensive sorbent for SO₂ control, a study was conducted to uncover ways to increase the reactivity of this sorbent in order to use it in wet—dry scrubbing applications. The study was focused on a comparison of the reactivity of lime and limestone during the dry reaction period. The conditions which have a major impact on the reactivity include the sorption capacity of water vapour, the BET surface area, the relative humidity and the sorbent utilization. The experiments revealed several similarities between the two sorbents, which led to a number of ways to obtain increased limestone acitivity.     

Über die Vermeidung des Austretens von Steinkohlenteeröl aus imprägnierten Leitungsmasten

Zusammenfassung In vielen F?llen zeigen Leitungsmaste, die mit Steinkohlenteer?l impr?gniert wurden, die unangenehme Erscheinung des Austretens von Teer?l. Es wurden Untersuchungen durchgeführt, die das Vermeiden dieses Schwitzens der Maste zum Ziel hatten. Modellversuche, bei denen mit Glaskapillaren gearbeitet wurde, zeigten, da? eine Dampfbehandlung brauchbare Resultate liefern k?nnte. In einer Versuchsanlage wurden sodann Rundholzabschnitte impr?gniert und anschhe?end einer Dampfbehandlung von etwa 30 bis 70 min Dauer bei einer Temperatur von 120°C ausgesetzt. Erw?hnt wird ferner die D?mpfung mittels Kohlenwassertoffen, mit deren Hilfe eine weitere Temperaturerh?hung durchaus m?glich w?re. Die erhaltenen Ergebnisse waren zufriedenstellend, so da? nach entsprechender Beobachtungszeit und zus?tzlicher Prüfung durch Infrarotbestrahlung an eine praktische Einführung der Methode gedacht werden konnte. Erst mit beginnendem Frühjahr stellten sich erneut Absonderungserscheinungen von Teer?l ein, die dazu führten, da? inzwischen mit Untersuchungen an unterkühlten H?lzern begonnen wurde. Endgültige Ergebnisse hierzu liegen noch nicht vor.—Schlie?lich wird noch ein vermeintlich sch?digender Einflu? des D?mpfprozesses auf die Festigkeitseigenschaften des Holzes in Erw?gung gezogen, der jedoch auf Grund neuerer Untersuchungen nicht erwartet werden kann. Mitteilungen aus dem Forschungslaboratorium der Pfleidererwerke.     

High-throughput data analysis for detecting and identifying differences between samples in GC/MS-based metabolomic analyses

In metabolomics, the objective is to identify differences in metabolite profiles between samples. A widely used tool in metabolomics investigations is gas chromatography-mass spectrometry (GC/MS). More than 400 compounds can be detected in a single analysis, if overlapping GC/MS peaks are deconvoluted. However, the deconvolution process is time-consuming and difficult to automate, and additional processing is needed in order to compare samples. Therefore, there is a need to improve and automate the data processing strategy for data generated in GC/MS-based metabolomics; if not, the processing step will be a major bottleneck for high-throughput analyses. Here we describe a new semiautomated strategy using a hierarchical multivariate curve resolution approach that processes all samples simultaneously. The presented strategy generates (after appropriate treatment, e.g., multivariate analysis) tables of all the detected metabolites that differ in relative concentrations between samples. The processing of 70 samples took similar time to that of the GC/TOFMS analyses of the samples. The strategy has been validated using two different sets of samples: a complex mixture of standard compounds and Arabidopsis samples.     

Automatic tube-current modulation in CT--a comparison between different solutions

In this study, tube-current modulation systems on two different CT equipments have been evaluated: Care Dose from Siemens and Auto mA from GE Medical Systems. Care Dose modulates the tube current in the xy-plane during rotation whereas Auto mA modulates the tube current in the z-direction. xy-Plane modulation was investigated by using an elliptic Polymethylmethacrylate phantom and a CTDI-ion chamber. To investigate modulation in the z-direction, an anthropomorphic dosimetry phantom (Atom) was used. Tests performed with and without tube-current modulation were compared with respect to absorbed dose and image quality. In the anthropomorphic phantom measurements, the dose savings were 15% using Care Dose and the photon starvation artefacts were negligible. Using Auto mA the absorbed dose depends on the chosen noise level. Image noise becomes more constant throughout the patient but photon starvation artefacts remain. We conclude that the two tube-current modulation techniques show different dose advantages and image quality artefacts.     

Scatter correction of transmission near-infrared spectra by photon migration data: quantitative analysis of solids

The scope of this work is a new methodology to correct conventional near-infrared (NIR) data for scattering effects. The technique aims at measuring the absorption coefficient of the samples rather than the total attenuation measured in conventional NIR spectroscopy. The main advantage of this is that the absorption coefficient is independent of the path length of the light inside the sample and therefore independent of the scattering effects. The method is based on time-resolved spectroscopy and modeling of light transport by diffusion theory. This provides an independent measure of the scattering properties of the samples and therefore of the path length of light. This yields a clear advantage over other preprocessing techniques, where scattering effects are estimated and corrected for by using the shape of the measured spectrum only. Partial least squares (PLS) calibration models show that, by using the proposed evaluation scheme, the predictive ability is improved by 50% as compared to a model based on conventional NIR data alone. The method also makes it possible to predict the concentration of active substance in samples with other physical properties than the samples included in the calibration model.