QUANTIFICATION OF NANO-SIZED PRECIPITATES IN MICROALLOYED STEELS BY MATRIX DISSOLUTION

ABSTRACT Microalloyed steels possess good strength, toughness and excellent weldability, all of which are necessary attributes for oil and gas pipelines in northern climates. These properties are attributed in part to the presence of nano-sized Nb/Ti carbide precipitates. In order to understand the strengthening mechanisms and to optimize the strengthening effects, it is necessary to quantify the size distribution, volume fraction and chemical speciation of these precipitates. However, characterization techniques suitable for quantifying fine precipitates are limited. A matrix dissolution method has been developed to extract the nano-sized precipitates from microalloyed steels. The results from Grade 100 microalloyed steel are presented in this paper. INTRODUCTION It is known that the combination of microalloying additions, such as Nb, Ti and V, to the steel and controlled rolling can enhance the strength and ductility of steel. The improvement of mechanical properties results from the refinement of ferrite grain size, precipitation, solute strengthening and dislocation strengthening. The first three can be expressed mathematically as follows

Effect of bainite morphology on hydrogen trapping in X70 microalloyed steel

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Evolution of the dendritic morphology with the solidification velocity in rapidly solidified Al- 4.5wt.%Cu droplets

International audienceThe microstructure morphology of Al-4.5wt.%Cu droplets formed by the Impulse Atomization technique is investigated. Three-dimensional reconstructions by synchrotron X-ray micro-tomography of several droplets reveal different morphologies in droplets of similar diameter and produced in the same batch. Moreover, microstructural features also indicate that the development of the dendrite arms occurs in some droplets along crystallographic axes instead of the usual directions observed in conventional casting for the same alloy. It has been observed that such an unusual growth direction of the dendrites is directly related to the solidification velocity. We underpin these results by carrying out comparisons with a solidification model. Predictions are used to discuss the change of dendrite growth direction, as well as the existence of a dendrite growth direction range for a given type of droplets. In addition, the effect of the droplet size and the cooling gas on the dendrite growth direction range observed experimentally is also investigated by using the model. 1. Introduction Rapid solidification techniques have been developed as they enable to obtain a wide variety of structures which cannot be formed under conventional solidification processes [1]. They differ by the way to form the liquid as a strip or a droplet and by the method of heat extraction. Atomization techniques are used to make metallic powders which are used for making a desired object by pressing or by sintering [2]. The liquid metal generated as a stream breaks up into droplets by Rayleigh-Plateau instability, which subsequently solidify in a much colder medium. In the Impulse Atomization (IA) technique the liquid is pushed through a nozzle plate to form the liquid streams [3]. In order to deepen the understanding of the microstructure formation in the droplets, synchrotron X-ray micro-tomography was carried out at the European Synchrotron Radiation Facility (ESRF, Grenoble, France). Three-dimensional reconstructions of a large number of droplets were obtained, enabling the inner microstructure of the droplets to be statistically analysed for the first time. In a previous paper, we showed that four distinct morphologies could be identified in droplets of the same size and from the same batch [4]. Such a range of morphologies can be linked to a range of solidification velocities for the droplets. Indeed, while Rappaz and co-workers highlighted the <100

EFFECT OF COLD-WIRE ADDITION IN THE TSAW PROCESS ON MICROSTRUCTURE AND MECHANICAL PROPERTIES OF THE HAZ OF X70 MICROALLOYED PIPELINE STEEL

ABSTRACT Microalloyed steels can achieve a good combination of strength and toughness through appropriate alloy design and thermomechanical controlled processing (TMCP). However, the mechanical properties can deteriorate as a result of the high heat input and thermal cycles that the steel experiences during welding. It is generally accepted that the portion of the heat affected zone (HAZ) adjacent to the fusion line, i.e., the coarse grain heat affected zone (CGHAZ), which is characterized by coarse grains and martensite-austenite (M-A) constituents, is the region with poorer toughness relative to the rest of the steel. In the present research work, modification to the conventional tandem submerged arc welding (TSAW) process is carried out by the addition of a cold wire during welding (CWTSAW), which induces changes to the geometry and properties of the weld joint. Microstructural analysis, mechanical property investigation and geometry analysis indicate overall improvement in the weld and the HAZ properties after cold wire addition. These improvements are explained in terms of an increase in the deposition rate and a decrease in the amount of heat introduced to the weldment. An X70 microalloyed steel was welded using both TSAW and CWTSAW processes. Charpy-V-notch impact testing and microhardness testing showed improvement in the HAZ mechanical properties for CWTSAW samples relative to TSAW samples. Microstructural analysis, using both optical microscopy and scanning electron microscopy (SEM), indicated the formation of finer prior austenite grains (PAG) and less M-A constituent within the CGHAZ of the CWTSAW samples. These improvements are due to lower actual heat introduced to the weldment and a relatively faster cooling rate

Dendrite growth morphologies in rapidly solidified Al-4.5wt.%Cu droplets

International audienceThe impulse atomization process developed at the University of Alberta (Canada) enables metallic powders to be solidified with controlled process parameters and improved properties. In order to investigate the microstructure morphologies in droplets of Al- 4.5wt.%Cu alloys, three-dimensional reconstructions of several droplets are obtained by using synchrotron X-ray micro-tomography, allowing a visualization of the inner microstructure in three dimensions. The analysis of the reconstructed volumes reveals that a wide range of morphology, from highly branched to "finger-bundle", can be obtained for different droplets of similar diameter and produced in the same batch. Unexpectedly for this alloy, microstructural features also indicate that the development of the dendrite arms (primary and of higher orders) occurs in most droplets along crystallographic axes, instead of the usual directions observed in conventional casting technologies

The Changing Landscape for Stroke\ua0Prevention in AF: Findings From the GLORIA-AF Registry Phase 2

Background GLORIA-AF (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients with Atrial Fibrillation) is a prospective, global registry program describing antithrombotic treatment patterns in patients with newly diagnosed nonvalvular atrial fibrillation at risk of stroke. Phase 2 began when dabigatran, the first non\u2013vitamin K antagonist oral anticoagulant (NOAC), became available. Objectives This study sought to describe phase 2 baseline data and compare these with the pre-NOAC era collected during phase&nbsp;1. Methods During phase 2, 15,641 consenting patients were enrolled (November 2011 to December 2014); 15,092 were eligible. This pre-specified cross-sectional analysis describes eligible patients\u2019 baseline characteristics. Atrial fibrillation&nbsp;disease characteristics, medical outcomes, and concomitant diseases and medications were collected. Data were analyzed using descriptive statistics. Results Of the total patients, 45.5% were female; median age was 71 (interquartile range: 64, 78) years. Patients were from Europe (47.1%), North America (22.5%), Asia (20.3%), Latin America (6.0%), and the Middle East/Africa (4.0%). Most had high stroke risk (CHA2DS2-VASc [Congestive heart failure, Hypertension, Age&nbsp; 6575 years, Diabetes mellitus, previous Stroke, Vascular disease, Age 65 to 74 years, Sex category] score&nbsp; 652; 86.1%); 13.9% had moderate risk (CHA2DS2-VASc&nbsp;= 1). Overall, 79.9% received oral anticoagulants, of whom 47.6% received NOAC and 32.3% vitamin K antagonists (VKA); 12.1% received antiplatelet agents; 7.8% received no antithrombotic treatment. For comparison, the proportion of phase 1 patients (of N&nbsp;= 1,063 all eligible) prescribed VKA was 32.8%, acetylsalicylic acid 41.7%, and no therapy 20.2%. In Europe in phase 2, treatment with NOAC was more common than VKA (52.3% and 37.8%, respectively); 6.0% of patients received antiplatelet treatment; and 3.8% received no antithrombotic treatment. In North America, 52.1%, 26.2%, and 14.0% of patients received NOAC, VKA, and antiplatelet drugs, respectively; 7.5% received no antithrombotic treatment. NOAC use was less common in Asia (27.7%), where 27.5% of patients received VKA, 25.0% antiplatelet drugs, and 19.8% no antithrombotic treatment. Conclusions The baseline data from GLORIA-AF phase 2 demonstrate that in newly diagnosed nonvalvular atrial fibrillation patients, NOAC have been highly adopted into practice, becoming more frequently prescribed than VKA in&nbsp;Europe and North America. Worldwide, however, a large proportion of patients remain undertreated, particularly in&nbsp;Asia&nbsp;and North America. (Global Registry on Long-Term Oral Antithrombotic Treatment in Patients With Atrial Fibrillation [GLORIA-AF]; NCT01468701

Reducing the environmental impact of surgery on a global scale: systematic review and co-prioritization with healthcare workers in 132 countries

Abstract Background Healthcare cannot achieve net-zero carbon without addressing operating theatres. The aim of this study was to prioritize feasible interventions to reduce the environmental impact of operating theatres. Methods This study adopted a four-phase Delphi consensus co-prioritization methodology. In phase 1, a systematic review of published interventions and global consultation of perioperative healthcare professionals were used to longlist interventions. In phase 2, iterative thematic analysis consolidated comparable interventions into a shortlist. In phase 3, the shortlist was co-prioritized based on patient and clinician views on acceptability, feasibility, and safety. In phase 4, ranked lists of interventions were presented by their relevance to high-income countries and low–middle-income countries. Results In phase 1, 43 interventions were identified, which had low uptake in practice according to 3042 professionals globally. In phase 2, a shortlist of 15 intervention domains was generated. In phase 3, interventions were deemed acceptable for more than 90 per cent of patients except for reducing general anaesthesia (84 per cent) and re-sterilization of ‘single-use’ consumables (86 per cent). In phase 4, the top three shortlisted interventions for high-income countries were: introducing recycling; reducing use of anaesthetic gases; and appropriate clinical waste processing. In phase 4, the top three shortlisted interventions for low–middle-income countries were: introducing reusable surgical devices; reducing use of consumables; and reducing the use of general anaesthesia. Conclusion This is a step toward environmentally sustainable operating environments with actionable interventions applicable to both high– and low–middle–income countries

Bed behaviour in rotary cylinders with applications to rotary kilns

Two modes of transverse solids motion, slumping and rolling, in rotary kiln operation have been experimentally characterized and mathematically modelled in this study. Other modes of bed behaviour encountered in rotary cylinders; slipping, cascading, cataracting and centrifuging have been formulated mathematically. The models have been verified using experimental observations reported in the literature. An experimental study of those conditions under which the bed changed from slumping to rolling was undertaken and the characteristics of these modes of motion quantified using different types of solids in three horizontal rotary cylinders and a small pilot kiln. A Bed-Behaviour Diagram which is a plot of bed depth versus rotational speed was developed to delineate the various areas of dominance of slumping and rolling and it was shown using this Diagram that bed behaviour observations made on batch cylinders were representative of solids motion in a continuous kiln operation, the effects of bed depth, particle size, particle shape and cylinder diameter on the position of the slumping-rolling boundary were also experimentally investigated. The quantitative characterization of slumping and rolling indicated that a new interpretation of the change in bed motion from slumping to rolling was required.Applied Science, Faculty ofMaterials Engineering, Department ofGraduat