Development of high creep strength microstructures in 9Cr ferritic-martensitic steels through the optimization of the processing or the chemical composition

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, leída el 20-09-2019Actualmente, existe una necesidad de incrementar la temperatura de operación de los aceros ferríticos/martensíticos 9Cr con el objetivo de aumentar la eficiencia de las futuras centrales de generación de energía. Como ejemplo, en el caso de las centrales térmicas, un aumento del 1 % en la eficiencia implica la reducción de 2.4 millones de toneladas de CO2, 2000 toneladas de NOx, 2 000 toneladas de SO2 y 500 toneladas de partículas. La temperatura máxima de operación de los aceros ferríticos/martensíticos 9Cr está en 620 °C debido a su baja estabilidad microestructural a temperaturas más elevadas. La microestructura de estos aceros está compuesta por martensita revenida con una alta densidad de dislocaciones. Durante la fluencia, esta microestructura evoluciona hacía una microestructura más estable de ferrita y precipitados. Esta recuperación de la microestructura produce una caída de la resistencia por una disminución en la densidad de dislocaciones y engrosamiento de las lajas, paquetes y bloques martensíticos. El engrosamiento de estas características microestructurales y la caída en la densidad de dislocaciones está impedido por dos tipos de precipitados, los M23C6 y los MX...Nowadays, there is a need to increase the operation temperature of 9Cr ferritic/martensitic steels to improve the efficiency of future power plants. As an example, in the case of coal fired power plants, an increase of 1 % in the efficiency allows the reduction of 2.4 millions of tons of CO2, 2 000 tons of NOX, and 500 tons of particles. The maximum operation temperature for the 9Cr ferritic/martensitic steels is 620 °C due to their low microstructural stability at higher temperatures. The microstructure of these steels consist in tempered martensite with a high dislocation density. During creep, this microstructure evolves to a more stable microstructure, which consists of ferrite and different kinds of precipitates. The evolution towards this microstructure produces a drop in the creep strength by a decrease in the dislocation density and the coarsening of martensitic laths and blocks. The coarsening of these microestructural features and the drop in the dislocation density is hinded by two kinds of precipitates, M23C6 carbides and MX carbonitrides...Fac. de Ciencias FísicasTRUEunpu

Whole-genome sequence of Acinetobacter pittii HUMV-6483 isolated from human urine

Acinetobacter pittii strain HUMV-6483 was obtained from urine from an adult patient. We report here its complete genome assembly using PacBio singlemolecule real-time sequencing, which resulted in a chromosome with 4.07 Mb and a circular contig of 112 kb. About 3,953 protein-coding genes are predicted from this assembly

Genetic polymorphisms in the cag pathogenicity island of Helicobacter pylori and risk of stomach cancer and high‐grade premalignant gastric lesions

AbstractHelicobacter pylori (Hp) infects the stomach of about half of the human population and is strongly associated with the risk of gastric cancer (GC) and its premalignant precursors. The cag pathogenicity island (cagPAI) is a region of the Hp genome encoding for key molecular machinery involved in the infection process. Following a sequencing study, we selected 50 genetic polymorphisms located in seven cagPAI genes and tested their associations with the risk of advanced gastric premalignant lesions and GC in 1220 subjects from various Latin American populations showing the whole spectrum of phenotypes from gastritis to GC. We found that three polymorphisms of cagA are associated with the risk of advanced gastric premalignant lesions (incomplete intestinal metaplasia [ie, Type 2 and 3] or dysplasia), and that six polymorphisms located in cagA, cagL and cagI were associated with risk of GC. When corrected for multiple testing none of the associations were statistically significant. However, scores built by integrating the individual polymorphisms were significantly associated with the risk of advanced gastric premalignant lesions and GC. These results have the potential of establishing markers for risk stratification in the general population, in view of targeting Hp eradication to high‐risk population groups

Sistematización de experiencias educativas transformadoras

Analizar cómo las instituciones educativas intervenidas posibilitan la construcción de vínculos sociales desde prácticas interculturales que reconozcan la diversidadEste proceso de investigación se fundamenta en los principios de la sistematización de experiencias educativas, en la cual se buscó resaltar aquellas que tenían conexión con procesos de interculturalidad, diversidad e inclusión, en articulación con la sublínea de investigación “Procesos educativos para la diversidad y la transformación cultural” de la Maestría en Educación de la Corporación Universitaria Minuto de Dios. Este informe da cuenta de los hallazgos más representativos de experiencias que se desarrollan en seis regiones diferentes de Colombia. El ejercicio de investigación se lleva a cabo en el marco de la estrategia formativa denominada “Proyectos Sombrilla” para lo cual se consolidó un grupo de 13 investigadores que han adelantado de forma sistemática el ejercicio de investigación que el lector podrá conocer a partir de este informe construido colectivamente por todos los integrantes del equipo. Esta investigación surge a partir del interés de conocer cuáles son los aprendizajes-saberes construidos por las comunidades académicas en el marco de experiencias educativas que apelan a la generación de prácticas interculturales y a la construcción de vínculos sociales con sus comunidades educativas y territoriale

DESARROLLO DE MICROESTRUCTURAS DE ALTA RESISTENCIA A FLUENCIA EN ACEROS FERRÍTICOS MARTENSÍTICOS 9CR A TRAVÉS DE LA OPTIMIZACIÓN DEL PROCESADO O LA COMPOSICIÓN QUÍMICA

Tesis DoctoralNowadays, there is a need to increase the operation temperature of 9Cr ferritic/martensitic steels to improve the efficiency of future power plants. As an example, in the case of coal fired power plants, an increase of 1 % in the efficiency allows the reduction of 2.4 millions of tons of CO2, 2 000 tons of NOX, and 500 tons of particles. The maximum operation temperature for the 9Cr ferritic/martensitic steels is 620 °C due to their low microstructural stability at higher temperatures. The microstructure of these steels consist in tempered martensite with a high dislocation density. During creep, this microstructure evolves to a more stable microstructure, which consists of ferrite and different kinds of precipitates. The evolution towards this microstructure produces a drop in the creep strength by a decrease in the dislocation density and the coarsening of martensitic laths and blocks. The coarsening of these microestructural features and the drop in the dislocation density is hinded by two kinds of precipitates, M23C6 carbides and MX carbonitrides. The coarse M23C6 carbides are rich in Cr and are located on lath, block and prior austenite grain boundaries. The main problem of these carbides is their fast coarsening rate, which limits their ability to inhibit the movement of lath and block boundaries during creep. The another kind of precipitates, the MX, are carbonitrides rich in V and Nb. These precipitates are located within the laths, with a smaller size than that of the M23C6 carbides. The most interesting feature of these precipitates is their high thermal stability. This characteristic makes these precipitates very usefull to pin the dislocations during creep and retard the microstructural degradation. The main objective of this thesis cosists in developing, in these steels, new microstructures with a higher microestructural stability than that of the current microstructures. To achieve this, we have considered the high thermal stability of these MX precipiates and we have assumed that , if we obtain a high number density of MX precipitates within the martensitic laths, the creep strength will be improved considerably. To reach this, we are going to employ two strategies. One of them consists in applying a thermomechanical treatment, in a commercial steel, as an alternative to the existing conventional processing route. The other one consists in developing new steel compositions keeping the existing conventional processing route (which does not include a thermomechanical treatment, as it will be described below). The results obtained by applying the thermomechanical treatment show important improvements in creep strength compared to that for the commercial steel processed by the conventional route. However, linked to this improved creep strength, a considerably drop in creep ductility is observed which limits the use of this processing route. The improvement in creep strength is attributable to the high number density of MX nanoprecipitates. The drop in creep ductility is related to the increase in the prior austenite grain size promoted by the higher austenitization temperature employed during the thermomechanical treatment compared to that used in the conventional processing route

Effect of Rotation Speed and Steel Microstructure on Joint Formation in Friction Stir Spot Welding of Al Alloy to DP Steel

In this work, friction stir spot welding of 5754 aluminum alloy to dual phase steel was investigated using two different ratios of martensite and ferrite (0.38 and 0.61) for steel sheet initial microstructure and varying tool rotation speed (800, 1200 and 2000 rpm). The effect of these parameters on the joint formation was evaluated by studying the plunging force response during the process and the main characteristics of the joint at (i) macrolevel, i.e., hook morphology and bond width, and (ii) microlevel, i.e., steel hook and sheet microstructure and intermetallic compounds. The plunging force was reduced by increased tool rotation speed while there was no significant effect from the initial steel microstructure ratio of martensite and ferrite on the plunging force. The macrostructural characterization of the joints showed that the hook morphology and bond width were affected by the steel sheet initial microstructures as well as by the tool rotation speed and by the material flow driver; tool pin or shoulder. At microstructural level, a progressive variation in the ratio of martensite and ferrite was observed for the steel hook and sheet microstructure. The zones closer to the tool presented a fully martensitic microstructure while the zones away from the tool showed a gradual increase in the ferrite amount until reaching the ratio of ferrite and martensite of the steel sheet initial microstructure. Different types of FexAly intermetallic compounds were found in three zones of the joint; the hook tips, in the hooks close to the exit hole and in the corner of the exit hole. These compounds were characterized by a brittle behavior with hardness values varying from 456 to 937 HV01

Whole-Genome Sequence of Acinetobacter baumannii HUMV-3743, Isolated from a Human Wound Exudate

Acinetobacter baumannii strain HUMV-3743 was obtained from wound exudate from an adult patient. Here, we report its complete genome sequence using Illumina-based sequence analysis, which revealed a genome of 4 Mb, which includes 2 predicted plasmids of 78.9 and 107 kb. A total of 3,881 protein-coding genes are predicted from this assembly.Funding: M.L.-D. holds a contract from the Instituto de Investigación Sanitaria Valdecilla IDIVAL and Universidad de Cantabria (PREVAL16/05). Research in our laboratory is supported by the Instituto de Salud Carlos III, Spain (grant PI16/01103) and the Spanish Network for Research in Infectious Diseases (REIPI RD12/0015), cofinanced by European Development Regional Fund “A way to achieve Europe” ERDF

Creep strength boosted by a high-density of stable nanoprecipitates in highchromium steels

There is a need worldwide to develop materials for advanced power plants with steam temperatures of 700°C and above that will achieve long-term creep-rupture strength and low CO2 emissions. The creep resistance of actual 9-12Cr steels is not enough to fulfil the engineering requirements above 600°C. In this paper, the authors report their advances in the improvement of creep properties of this type of steels by the microstructural optimization through nano-precipitation using two methodologies. 1) Applying a high temperature austenitization cycle followed by an ausforming step (thermomechanical treatment, TMT) to G91 steel, to increase the martensite dislocation density and, thus, the number density of MX precipitates (M = V ,Nb; X = C ,N) but at the expense of deteriorating the ductility. 2) Compositional adjustments, guided by computational thermodynamics, combined with a conventional heat treatment (no TMT), to design novel steels with a good ductility while still possessing a high number density of MX precipitates, similar to the one obtained after the TMT in G91. The microstructures have been characterized by optical, scanning and transmission electron microscopy, EBSD and atom probe tomography. The creep behaviour at 700°C has been evaluated under a load of 200 N using small punch creep tests.The authors would like to thank James Burns for assistance in performing APT sample preparation and running the APT experiments. The authors are grateful for the dilatometer tests by Phase Transformation laboratory and for the SEM microscopy by the Microscopy Lab at CENIM-CSIC. This work contributes to the Joint Programme on Nuclear Materials (JPNM) of the European Energy Research Alliance (EERA).Peer reviewe

Clinical and prognostic comparison between left ventricular transient dyskinesia and a first non-ST-segment elevation acute coronary syndrome

Objectives: Apical ballooning shares features with acute coronary syndromes. Recently, atypical forms have been reported without apical involvement. Usually, the prognostic reports have compared them with ST-segment elevation infarction. Left ventricular transient dyskinesias (LVTD), however, frequently occur without ST-segment elevation and when present, these patients always have open arteries. Our aim was to assess the baseline features, clinical presentation, natural history and compare long-term prognosis in an LVTD-cohort with a first non-ST-segment elevation acute coronary syndrome (NSTEMI) group. Methods: We performed a prospective observational study including consecutive patients in two groups: (i) LVTD group: 62 patients with this syndrome between 2003 and 2007. Inclusion criteria were LV segmental transient motion abnormalities; ECG new alterations and elevated troponin; absence of recent significant head trauma or obstructive coronary artery lesions. (ii) Control group: 169 patients admitted for a first NSTEMI in 2004. Results: Median follow-up was 35 months. Mean age was 65 years. LVTD group included 83.9% females. NSTEMI group was predominantly males. Eleven in-hospital deaths happened in NSTEMI cohort and none in LVTD. Four patients in the LVTD group required readmission and two patients died. In the NSTEMI group, heart failure, unstable angina, myocardial infarction (P<0.001) and death (P=0.11) were more frequent. Cox regression showed that diabetes mellitus, significant onset mitral regurgitation and NSTEMI versus LVTD were found as event-independent predictors. Conclusion: LVTD diagnosis represents a decreased risk of events when compared with classic non-ST-segment acute coronary syndrome, pointing out a different pathophysiologic mechanism.Depto. de FisiologíaFac. de MedicinaTRUEpu