Solid state phase transformations in Advanced Steels

In order to achieve progress in Advanced Steels development came more emphasis in solid state phase transformations are received. For achieving the desired mechanical and corrosion resistance properties in Duplex Stainless Steels (DSS), a precise knowledge of the precipitation kinetics of secondary phases, the morphology of the precipitates and effects of the alloying elements on different properties is needed. A complicated chemical composition and the production technology route make each grade of DSS a unique object for a study. Besides, when the market needs to reduce weight and increase product durability by utilizing Advance Strength Steels, a deeper understanding of their transformations is required. The aim of the present work was to study the main features of phase precipitation in diverse Duplex Stainless Steels grades, including Lean Duplex, Standard and Superduplex. Beside analyze the effects of metallurgical features on the properties of DSS and Advanced High Strength Dual Phase (DP) steels. One of the tasks was to study the effects plastic deformation after heat treatment in diverse duplex grades

Impact behaviour of dissimilar AA2024-T351/7075-T651 FSWed butt-joints: effects of Al2O3-SiC particles addition

Dissimilar friction stir welding joints are widely employed in the industrial field due to the excellent microstructural and mechanical properties of the resulting joints. Nevertheless, to further enhance the weld properties, the addition of reinforcement particles on the joint-line during the process has been proven effective for increasing its mechanical performance. In the present investigation, the microstructure and the impact behaviour of FSWed joints between AA2024-T351 and AA7075-T651 aluminium plates were investigated, considering the effect of different process parameters selected through a full factorial 2k design of experiments: both the rotational and translational speed of the tool, as well as the addition of Al2O3-SiC microparticles, were considered as input parameters. Unnotched 10 x 5 x 55 mm impact specimens were tested through an instrumented 50 J Charpy pendulum: total impact energy, the two complementary initiation and propagation energies as well as the peak force were correlated to the adopted process parameters. From the performed analyses, it was found that joints with reinforcing particles are prone to form wormhole defects across the stir zone that not only affect the microstructural development, but also the impact behaviour since they require less energy at break in comparison with joints fabricated without particles addition

Effect of the Addition of Nickel Powder and Post Weld Heat Treatment on the Metallurgical and Mechanical Properties of the Welded UNS S32304 Duplex Stainless Steel

Abstract In this research, the effect of the addition of nickel powder and the application of a post weld heat treatment (PWHT) on the welding properties of the UNS S32304 lean duplex stainless steel were investigated in order to improve the microstructure and mechanical properties. Nickel powder was directly poured inside the joint gap and mixed with the filler metal during the Gas Tungsten Arc Welding (GTAW) process; moreover, the solution heat treatment was performed at 1100 °C for 10 min. The joints were characterized by optical microscopy (OM) and the evolution of the phase percentages in the different zones was studied by means of the image analysis technique. Tensile and hardness tests were carried out on the joints in order to evaluate the improvement of the mechanical properties. The results showed that both the addition of nickel powder during the welding process and the post weld heat treatment made it possible to improve the mechanical properties of the weld joints. PWHT had the best effect in restoring the equal percentage of ferrite and austenite compared to the addition of nickel powder

Microstructural Development in a TRIP-780 Steel Joined by Friction Stir Welding (FSW): Quantitative Evaluations and Comparisons with EBSD Predictions

The present work describes the effect of FSW on the result microstructure in the stir zone (SZ), thermo-mechanically affected zone (TMAZ), heat affected zone (HAZ) and base metal (BM) of a TRIP-780 steel. X-ray diffraction (XRD), optical microscopy (OM) and EBSD were used for determinations retained austenite (RA) in the SZ, It was found that the amount of RA developed in SZ was relatively large, (approximately 11% to 15%). In addition, recrystallization and the formation of a grain texture were resolved using EBSD. During FSW, the SZ experienced severe plastic deformation which lead to an increase in the temperature and consequently grain recrystallization. Moreover, it was found that the recrystallized grain structure and relatively high martensite levels developed in the SZ lead to a significant drop in the mechanical properties of the steel. In addition, microhardness profiles of the welded regions indicated that the hardness in both the SZ and TMAZ were relatively elevated confirming the development of martensite in these regions. In particular, to evaluate the mechanical strength of the weld, lap shear tensile test was conducted; exhibited the fracture zone in the SZ with shear fracture with uniformly distributed elongation shear dimples

Virulence Genes and Phylogenetic Group in Isolates of Escherichia Coli Pathogenic Avian

Avian pathogenic Escherichia coli (APEC) shares virulence attributes with strains of E. coli that cause extraintestinal infections in humans and it is considered that it could cause a zoonosis; therefore, the objective of this work was to determine prevalence in a group of APEC isolates of twelve genes associated with virulence as well as identifying the phylogenetic groups to which they belong. According to the results it was found that one of the isolates harbors 91.6% of the virulence genes analyzed and that most of these have between 7 and 8 of these genes. feoB and iss had the highest prevalence with 95.6% and the genes related to iron acquisition were present in more than 60% of APEC, while those of the ibeA invasin and vat toxin were those that were detected with the lowest prevalence The results showed the great genetic diversity of APEC isolates and suggest that bacterial systems of iron acquisition, as well as those related to resistance to host are fundamental virulence factors in these bacteria, however, the presence The rest of the virulence genes is important, since it provides valuable information for the development of vaccines against avian colibacilosis. It was determined that a high percentage of APEC belongs to the phylogenetic group B1 group from which mainly commensal and pathogenic E. coli strains derive, this result strengthens findings on the evolution of pathogens through the acquisition of virulence genes through the horizontal route.Escherichia coli patogénica aviar (APEC) comparte atributos de virulencia con cepas de E. coli causantes de infecciones extraintestinales en humanos y se considera que pudiera ocasionar una zoonosis por lo cual el objetivo de este trabajo fue determinar en un grupo de aislados de APEC la prevalencia de doce genes asociados a la virulencia así como identificar los grupos filogenéticos a los que pertenecen. De acuerdo a los resultados se encontró que uno de los aislados alberga el 91.6% de los genes de virulencia analizados y que la mayoría de estos tiene entre 7 y 8 de estos genes. feoB e iss tuvieron la mayor prevalencia con un 95.6% y los genes relacionados con la adquisición de hierro estuvieron presentes en más del 60% de APEC, mientras que los de la invasina ibeA y de la toxina vat fueron los que se detectaron con la menor prevalencia. Los resultados mostraron la gran diversidad genética de los aislados APEC y sugieren que los sistemas bacterianos de adquisición de hierro, así como los relacionados con la resistencia a los mecanismos de defensa del hospedero son factores de virulencia fundamentales en estas bacterias, sin embargo, la presencia del resto de genes de virulencia es importante, ya que proporciona información valiosa para el desarrollo de vacunas contra la colibacilosis aviar. Se determinó que un alto porcentaje de APEC pertenece al grupo filogenético B1 grupo del que derivan principalmente cepas de E. coli comensales y patogénicas intestinales, este resultado fortalece hallazgos sobre la evolución de patógenos a través de la adquisición de genes de virulencia mediante la vía horizontal

Solid state phase transformations in Advanced Steels

In order to achieve progress in Advanced Steels development came more emphasis in solid state phase transformations are received. For achieving the desired mechanical and corrosion resistance properties in Duplex Stainless Steels (DSS), a precise knowledge of the precipitation kinetics of secondary phases, the morphology of the precipitates and effects of the alloying elements on different properties is needed. A complicated chemical composition and the production technology route make each grade of DSS a unique object for a study. Besides, when the market needs to reduce weight and increase product durability by utilizing Advance Strength Steels, a deeper understanding of their transformations is required. The aim of the present work was to study the main features of phase precipitation in diverse Duplex Stainless Steels grades, including Lean Duplex, Standard and Superduplex. Beside analyze the effects of metallurgical features on the properties of DSS and Advanced High Strength Dual Phase (DP) steels. One of the tasks was to study the effects plastic deformation after heat treatment in diverse duplex grades.Con lo scopo di ottenere progressi industriali nello sviluppo di Advanced Steels, specie quando le necessità di mercato richiedono una riduzione di peso e un aumento della durabilità è fondamentale una più profonda comprensione delle loro trasformazioni di fase allo stato solido. Nel caso di acciai Inossidabili Duplex (DSS), per raggiungere le proprietà meccaniche desiderate e le proprietà di resistenza alla corrosione, è necessaria la precisa conoscenza della cinetica di precipitazione di fasi secondarie, la morfologia dei precipitati e gli effetti degli elementi alleganti su diverse proprietà. La complessa composizione chimica e la tecnologia di produzione rendono ciascuna tipologia di DSS come un caso di studio unico. L’obbiettivo del presente lavoro è stato quello di studiare le principali caratteristiche delle precipitazioni di fasi secondarie in diversi tipi di acciai inossidabili duplex, comprendendo i Lean Duplex, Standard e altamente legati duplex, ed inoltre di analizzare gli effetti delle caratteristiche metallurgiche sulle proprietà degli Acciai Duplex e Advanced High Strength Steels

Cuidados de enfermería a pacientes en pulmotor

Escuela de Enfermería y Obstetrici

Innovative Coatings for Materials Subjected to Aggressive Environments

Aggressive environments require durable materials or excellent coatings to improve their performance and life service [...