Effect of the morphology of the martensite-austenite phase on fracture of the weld heat affected zone in vanadium and niobium microalloyed steels

In multipass welding, the intercritically reheated coarse grained heat affected zone demonstrates the worst toughness in welded joint, since it contains a high-carbon martensite with some retained austenite, known as M-A phase, which is brittle and associated with the high cooling rates following welding. The purpose of the present work was to explore those aspects of the morphology of the M-A phase which determined the ease or otherwise of crack development in welded vanadium and niobium high strength low alloy steels. Four steels were subjected to heat treatment to simulate the microstructure of an intercritically reheated coarse grained heat affected zone (IC CG HAZ). The toughness of the simulated IC CG HAZ was assessed using both Charpy and CTOD tests. Microstructural features were characterised by scanning and transmission electron microscopy and optical microscopy. Fractographic examination of the Charpy and CTOD specimens were carried out to understand the micromechanism of fracture under different microstructural and test conditions. Evidence of both cracking and debonding of M-A phase and carbides was found, and many of the cracks appeared to develop by linking-up of voids resulting from debonding. The importance of the dihedral angle,2θ, in determining the interfacial energy of the two main morphologies of the M-A phase, blocky and elongated stringer particles , was considered.While both carbides and inclusions were observed, these features appear to have a minor role in determining the degree of toughness of the steels

Vanadium microalloyed steel for thin slab casting and direct rolling

Vanadium microalloyed steels with high yield strength (»600 MPa), good toughness and ductility have been successfully produced in commercial thin slab casting plants employing direct rolling after casting. Because of the high solubility of VN and VC, most of the vanadium is likely to remain in solution during casting, equalisation and rolling. While some vanadium is precipitated in austenite as cuboids and pins the grain boundaries, a major fraction is available for dispersion strengthening of ferrite. Despite a coarse as-cast grain size, significant grain refinement can be achieved by repeated recrystallisation during hot rolling. Consequently, a fine and uniform ferrite grain structure is produced in the final strip. Increasing the V and N levels increases dispersion strengthening which occurs together with a finer ferrite grain size. The addition of titanium to a vanadium containing steel, decreases the yield strength due to the formation of V-Ti(N) particles in austenite during both casting and equalisation These large particles reduced the amount of V and N available for subsequent precipitation of fine (~5nm) V rich dispersion strengthening particles in ferrite

Dispersion strengthening in vanadium microalloyed steels processed by simulated thin slab casting and direct charging: Part I - Processing parameters, mechanical properties and microstructure

A study simulating thin slab continuous casting followed by direct charging into an equalisation furnace has been undertaken based on six low carbon (0.06wt-%) vanadium microalloyed steels. Mechanical and impact test data showed properties were similar or better than those obtained from similar microalloyed conventional thick cast as rolled slabs. The dispersion plus dislocation strengthening was estimated to be in the range 80-250MPa.A detailed TEM/EELS analysis of the dispersion sized sub-15nm particles showed that in all the steels, they were essentially nitrides with little crystalline carbon detected. In the Steels V-Nb, V-Ti and V-Nb-Ti, mixed transition metal nitrides were present. Modelling of equilibrium precipitates in these steels, based on a modified version of ChemSage, predicted that only vanadium rich nitrides would precipitate in austenite but that the C/N ratio would increase through the two phase field and in ferrite. The experimental analytical data clearly points to the thin slab direct charging process, which has substantially higher cooling rates than conventional casting, nucleating non-equilibrium particles in ferrite which are close to stoichiometric nitrides. These did not coarsen during the final stages of processing, but retained their highly stable average size of ~7nm resulting in substantial dispersion strengthening. The results are considered in conjunction with pertinent published literature

Evolution of precipitates, in particular cruciform and cuboid particles, during simulated direct charging of thin slab cast vanadium microalloyed steels

A study has been undertaken of four vanadium based steels which have been processed by a simulated direct charging route using processing parameters typical of thin slab casting, where the cast product has a thickness of 50 to 80mm ( in this study 50 mm) and is fed directly to a furnace to equalise the microstructure prior to rolling. In the direct charging process, cooling rates are faster, equalisation times shorter and the amount of deformation introduced during rolling less than in conventional practice. Samples in this study were quenched after casting, after equalisation, after 4th rolling pass and after coiling, to follow the evolution of microstructure. The mechanical and toughness properties and the microstructural features might be expected to differ from equivalent steels, which have undergone conventional processing. The four low carbon steels (~0.06wt%) which were studied contained 0.1wt%V (V-N), 0.1wt%V and 0.010wt%Ti (V-Ti), 0.1wt%V and 0.03wt%Nb (V-Nb), and 0.1wt%V, 0.03wt%Nb and 0.007wt%Ti (V-Nb-Ti). Steels V-N and V-Ti contained around 0.02wt% N, while the other two contained about 0.01wt%N. The as-cast steels were heated at three equalising temperatures of 1050C, 1100C or 1200C and held for 30-60 minutes prior to rolling. Optical microscopy and analytical electron microscopy, including parallel electron energy loss spectroscopy (PEELS), were used to characterise the precipitates. In the as-cast condition, dendrites and plates were found. Cuboid particles were seen at this stage in Steel V-Ti, but they appeared only in the other steels after equalization. In addition, in the final product of all the steels, fine particles were seen, but it was only in the two titanium steels that cruciform precipitates were present. PEELS analysis showed that the dendrites, plates, cuboids, cruciforms and fine precipitates were essentially nitrides. The two Ti steels had better toughness than the other steels but inferior lower yield stress values. This was thought to be, in part, due to the formation of cruciform precipitates in austenite, thereby removing nitrogen and the microalloying elements which would have been expected to precipitate in ferrite as dispersion hardening particles

Thin films CdS/CdTe solar cells with different activation processes base layer

Shown in this work is the possibility to create industrial technology for production of solar cells FTO/CdS/CdTe. The technology includes annealing in freon processing step for activation of cadmium telluride base layers deposited by thermal vacuum evaporation. Solar cells with efficiency of 7% have been obtained. Structural and morphological researches allowed to identify interrelation between photovoltaic characteristics and features of the recrystalization process in base layers after annealing in freon as compared with the standard chloride treatment

Patient Mistreatment and New Nurse Adjustment: The Role of Rumination and Work Engagement

During organizational entry, newcomers often draw upon internal resources like coworkers and supervisors to navigate their roles. Could external interactions with customers or patients hold the key to newcomer adjustment in certain job contexts? Our study, rooted in the conservation of resources theory, identifies a critical link between mistreatment from external parties and newcomer adjustment – a connection that is explained by rumination and work engagement. Through two studies involving new nurses in China (Study 1: Four-wave cross-lagged panel design, N = 181; Study 2: Four-wave time-lagged design, N = 198), we uncover that mistreatment from patients results in rumination among newcomers, leading to diminished task mastery and role clarity, as mediated by reduced work engagement. This ripple effect of external mistreatment persists even when accounting for internal mistreatment (abusive supervision and coworker incivility). Our results illustrate how negative interactions with external entities can hinder newcomer adjustment – a revelation with far-reaching implications for practitioners and future research

Effectiveness of cervical pessary compared to cervical cerclage with or without vaginal progesterone for the prevention of preterm birth in women with twin pregnancies and a short cervix : Study protocol for a two-by-two factorial randomised clinical trial

Peer reviewedPublisher PD

The distribution of transit durations for Kepler planet candidates and implications for their orbital eccentricities

‘In these times, during the rise in the popularity of institutional repositories, the Society does not forbid authors from depositing their work in such repositories. However, the AAS regards the deposit of scholarly work in such repositories to be a decision of the individual scholar, as long as the individual's actions respect the diligence of the journals and their reviewers.’ Original article can be found at : http://iopscience.iop.org/ Copyright American Astronomical SocietyDoppler planet searches have discovered that giant planets follow orbits with a wide range of orbital eccentricities, revolutionizing theories of planet formation. The discovery of hundreds of exoplanet candidates by NASA's Kepler mission enables astronomers to characterize the eccentricity distribution of small exoplanets. Measuring the eccentricity of individual planets is only practical in favorable cases that are amenable to complementary techniques (e.g., radial velocities, transit timing variations, occultation photometry). Yet even in the absence of individual eccentricities, it is possible to study the distribution of eccentricities based on the distribution of transit durations (relative to the maximum transit duration for a circular orbit). We analyze the transit duration distribution of Kepler planet candidates. We find that for host stars with T > 5100 K we cannot invert this to infer the eccentricity distribution at this time due to uncertainties and possible systematics in the host star densities. With this limitation in mind, we compare the observed transit duration distribution with models to rule out extreme distributions. If we assume a Rayleigh eccentricity distribution for Kepler planet candidates, then we find best fits with a mean eccentricity of 0.1-0.25 for host stars with T ≤ 5100 K. We compare the transit duration distribution for different subsets of Kepler planet candidates and discuss tentative trends with planetary radius and multiplicity. High-precision spectroscopic follow-up observations for a large sample of host stars will be required to confirm which trends are real and which are the results of systematic errors in stellar radii. Finally, we identify planet candidates that must be eccentric or have a significantly underestimated stellar radius.Peer reviewedFinal Accepted Versio

A rapid extraction method for glycogen from formalin-fixed liver

Liver glycogen, a highly branched polymer, acts as our blood-glucose buffer. While past structural studies have extracted glycogen from fresh or frozen tissue using a cold-water; sucrose-gradient centrifugation technique, a method for the extraction of glycogen from formalin-fixed liver would allow the analysis of glycogen from human tissues that are routinely collected in pathology laboratories. In this study, both sucrose-gradient and formalin-fixed extraction techniques were carried out on piglet livers, with the yields, purities and size distributions (using size exclusion chromatography) compared. The formalin extraction technique, when combined with a protease treatment, resulted in higher yields (but lower purities) of glycogen with size distributions similar to the sucrose-gradient centrifugation technique. This formalin extraction procedure was also significantly faster, allowing glycogen extraction throughput to increase by an order of magnitude. Both extraction techniques were compatible with mass spectrometry proteomics, with analysis showing the two techniques were highly complementary. (C) 2014 Elsevier Ltd. All rights reserved

Thermal rho and sigma mesons from chiral symmetry and unitarity

We study the temperature evolution of the rho and sigma mass and width, using a unitary chiral approach. The one-loop pion-pion scattering amplitude in Chiral Perturbation Theory at finite temperature is unitarized via the Inverse Amplitude Method. Our results predict a clear increase with T of both the rho and sigma widths. The masses decrease slightly for high T, while the rho-pion-pion coupling increases. The rho behavior seems to be favored by experimental results. In the sigma case, it signals chiral symmetry restoration.Comment: 5 pages, 5 figures, revtex. References and brief comments added. Final version to appear in Phys. Rev.