1,720,965 research outputs found
A sigma particles dissolution model with application to duplex and superduplex stainless steels forged components
No full textSigma phase in well known as a detrimental precipitate which reduces the mechanical and chemical properties of forged components with particular reference to toughness and corrosion resistance. For this reason, temperatures and times of a sigma phase dissolution heat treatment have to be accurately chosen. The optimum choice has to lead to a complete dissolution of the precipitates in the shortest time without compromising the microstructure of the component. In order to reach this goal, both an accurate prediction of the thermal history in all the points of the component (by numerical simulation) and an accurate knowledge of sigma particles dissolution kinetics are needed.
In this paper, the dissolution mechanism of sigma particles is studied with particular reference to duplex and superduplex stainless steels forged components. It was found that sigma phase dissolution kinetics is mainly influenced by Cr and Mo grain boundary diffusion
Numerical and experimental study of pre-forging heating process of heavy-section steel blocks
No full textIn forging and rolling processes, methane used in heating furnaces represents the main cost item. For this reason, it is important to reduce its consumption without negatively affecting the quality of final products. By means of experimental investigations (thermo-couples measurements and infrared camera analyses) coupled to a simplified thermal numerical model, it has been possible to study the complete thermal evolution of low carbon steel ingots of various diameters during the heating stage carried out in methane ovens. By evaluating of both experimental and numerical results, the heating cycle has been optimized. Three main aspects were taken into account: the final quality of forgings, energy and heating time reduction. The potential for significant savings in terms of energy and cycle time have been finally evaluated
Sigma phase precipitation modelling in a UNS S32760 superduplex stainless steel
No full textSigma phase precipitation is known to have detrimental effects on mechanical and corrosion properties in stainless steels. Accordingly, heat treatments and welding must be performed carefully. For this reason, computer models which predict the evolution of secondary phases with the temperature are very useful for a good planning of industrial heat treatments or welding. A semiempirical model, based on the pioneer work of Wilson and Nilsson, describing the microstructural evolution of UNS S32760 superduplex stainless steels was developed. The computer model, based on the modified Johnson–Mehl–Avrami (JMA) type of equation, uses information from isothermal experiments of -phase transformation and predicts the transformation kinetics during a cooling process. A good agreement was found between the predicted (CCT)-diagram and the experimental tests
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Appropriate Similarity Measures for Author Cocitation Analysis
Full text linkWe provide a number of new insights into the methodological discussion about author cocitation analysis. We first argue that the use of the Pearson correlation for measuring the similarity between authors’ cocitation profiles is not very satisfactory. We then discuss what kind of similarity measures may be used as an alternative to the Pearson correlation. We consider three similarity measures in particular. One is the well-known cosine. The other two similarity measures have not been used before in the bibliometric literature. Finally, we show by means of an example that our findings have a high practical relevance.information science;Pearson correlation;cosine;similarity measure;author cocitation analysis
Recent advances in dissolution kinetics of sigma phase in duplex stainless steels
No full textSigma phase is well known as a detrimental phase that causes considerable reduction in plasticity and corrosion resistance of duplex stainless steels (DSS). From a practical viewpoint, the occurrence of this phase as early as in the production process with associated brittleness, constitutes a problem of paramount importance. For this reason, the precipitation kinetics of sigma phase was extensively studied in literature. On the contrary, less attention has been paid to investigate the microstructure evolution of DSS during heating, which is of primary importance when a thermal treatment must be planned. As a matter of fact, any undissolved precipitates or chemical non-uniformity in the parent phase greatly affect both the material properties at room temperature and the subsequent precipitation process during cooling. Starting from a kinetic dissolution model recently published in literature, recent advances in dissolution kinetics of sigma phase in duplex stainless steels are presented in this work
Chromium nitrides effects on low temperature impact toughness and durability of duplex stainless steels forgings.
No full textThe chromium nitrides effects on duplex stainless steels low temperature impact toughness and durability were investigated. A duplex rolled ring was cut as different blocks, and different Cr2N amounts were obtained by trial heat treatments, with the solution annealing furnace temperature set at low and high levels, 1040 and 1140 °C respectively, and the transfer time ranging between 5 and 120 s in order to prevent the σ phase formation. Micrographic examinations, low temperature Charpy impact tests and durability assessments were carried out on specimens sampled from the blocks cores. The material strength was evaluated by hardness tests.
The results showed how an increase in transfer time allows the N diffusion in the austenite phase, reducing the nitrides quantity in the ferrite phase. A synergistic effect between the transfer time and the solution annealing temperature on the amount of intermetallic particles was observed. Clear effects of the Cr2N presence on both material low temperature impact toughness and pitting corrosion resistance were found
Effect of microstructure and test temperature on impact toughness of superduplex stainless steel UNS S32760.
No full textSuperduplex stainless steels (SDSSs) are very attractive materials, combining high mechanical properties with improved corrosion resistance. However, these steels present technical limitations because they experience the precipitation of various intermetallic phases occurring in the temperature range of 600-1000°C. The high level of alloying elements, such as Cr and Mo, accelerates the precipitation of intermetallic phases, which are the responsible of embrittlement.
In the present study, isothermal heat treatments were performed in the temperature range of 800 to 1000°C, with different ageing times, on an UNS S32760 superduplex stainless steel. The evolution of mechanical properties has been followed by means of Charpy impact tests performed at different temperatures. Total and instantaneous impact energy has been evaluated using an instrumented drop tower equipped with a strain gauge. Microstructural evolution in the material was also carried out. The results of the impact tests evidence the deleterious effect of secondary phases at room temperature, and even more at lower temperatures. A correlation between the impact properties and the different amount of precipitates has been established
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