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[en] The feasibility of preparing high entropy alloys in the Al-Sc-Ti-V-Cr system has been evaluated taking into account the different criteria reported in the literature. Based on such criteria, three Al-Sc-Ti-V-Cr alloys were chosen with contents of each element varying from 10 to 35 at. %, and prepared by arc melting. All alloys exhibit a two-phase dendritic microstructure, with the major dendritic phase being a bcc solid solution enriched in Ti, V, or Cr. Scandium is strongly rejected from the dendrites towards the interdendritic regions to form Al2Sc in the three alloys. The bcc solid solution dendrites become harder with high Ti content and lower with high Cr content. The toughness of the alloys depends on the hardness of the dendrites, with alloys with harder dendrites becoming more brittle. The results indicate that neither empirical criteria used nor THERMOCALC calculus tool can predict properly the formation of a single solid solution nor the nature of the existing phases respectively.
[es]En este trabajo se estudia la posibilidad de preparar aleaciones de alta entropía del sistema Al-Sc-Ti-V-Cr. Para ello se han seleccionado los elementos y la composición utilizando los criterios conocidos y disponibles en la literatura y se han preparado mediante fusión por arco tres aleaciones con contenidos que varían entre el 10 y 35 at.%. Las tres aleaciones tienen una microestructura dendrítica bifásica similar, siendo las dendritas una solución sólida bcc enriquecida en Ti, V o Cr. El escandio aparece únicamente en el espacio interdendrítico formando el intermetálico Al2Sc. La dureza de las dendritas crece con el contenido en Ti y se hace menor a medida que es mayor el contenido en Cr. Además, la tenacidad de las aleaciones depende de la dureza de las dendritas siendo ésta mayor cuanto más blandas son las dendritas. Los resultados obtenidos demuestran que ni los criterios empíricos utilizados ni los cálculos mediante THERMOCALC permiten predecir la formación de una única solución sólida ni la naturaleza de las fases observadas experimentalmente.
[en] Low carbon steel sheets are produced up to 0.5 mm thickness at Pakistan Steel. These sheets are used for different forming operations to produce auto parts, household appliances, car bodies etc. For such application the metal must have high ductility, good forming properties and low yield strength. Hot band from 2-3 mm thickness is cold reduced up to 0.5 mm thickness at reversible cold rolling mill. Then annealed in bell type furnaces with inner height of 4.7 meters, where coils are heated up to lower critical line in controlled atmosphere of nitrogen and hydrogen. The material may fail during subsequent forming operation if the annealing regime at the bell type furnaces is not optimum. Objective of the work undertaken is to produce sheet of good shape up to 0.3 mm thickness and evaluate annealing regime to have intended forming properties. (author)
[en] In this work, the effects of different amounts (5, 10, 20, 40%) of compressive deformation of austenite on the isothermal transformation of bainite in a Fe-Mn-Si-C alloy steel have been investigated. It is found that the prior deformation of austenite retards significantly the bainitic transformation. At the same isothermal transformation temperature, as the amount of prior deformation is higher, the quantity of bainite (which can be obtained after the isothermal transformation is completed) becomes less and it is also more difficult to develop the classical sheaf-like structure. The evidence implies that severe deformation causes mechanical stabilisation of austenite for bainitic transformation. (orig.)
[en] Retainec austenite in high-carbon steels has been determined by means of new computation techniques applied to the processing of X-ray diffraction data. Instead of using the traditional procedure based on the weak (200) reflections of martensite and austenite, intensity measurements of the overlapped (110) peak of martensite and (111) peak of austenite were performed. The separation of the peaks was based on a Pearson VII function, which is capable of describing all diffraction profiles. The accuracy of integrated intensities was then improved with the beneficial effects of higher precision in the calculation of the amount of retained austenite. (author)
[pt]Determinou-se a austenita retida em acos de alto carbono por meio de novas tecnicas de calculo computacional para processamento de dados de difracao de raios-X. Em vez de usar o procedimento tradicional baseado nas fracas reflexoes (200) da martensita e austenita, medidas da intensidade dos picos superpostos da martensita (110) e austenita (111) foram feitas. A separacao dos picos foi baseada na funcao de Pearson VII, a qual e capaz de descrever todos os perfis de difracao. A precisao das intensidades integradas foi entao melhorada com os efeitos uteis de maior precisao no calculo da quantidade de austenita retida. (M.C.K.)
[en] Two different high strength steels (H 85 and 34 Cr Ni Mo 6) were treated by different heat treatment techniques. conventional austenitization treatment (CAT), high temperature austenitization (HTA) and a new technique called duplex treatment (DT) in order to study the effect of these techniques on the microstructure and mechanical properties of these two steels. Testing and investigation of the heat treated specimens of the two steels showed that DT specimens have beneficial microstructural changes as a results of high temperature austenization and fine grain size. They also found to have higher room temperature charpy V-notch impact toughness in comparison with those treated by HTA and CAT. 5 tabs., 34 figs., 60 refs
[en] Liquid phase sintering is a very suitable method for producing P/M (powder metallurgy)parts with very high density near theoretical density. This high alloy P/M steel in the sintered-heat treated condition, is a good material for wear applications. In this research, a high alloy steel with 7% molybdenum and 2% carbon was selected. Sintering of this high carbon-high molybdenum steel occurred at low temperature under liquid phase. Due to high content of carbon and molybdenum, a great amount of molybdenum carbides was formed in the microstructure. After compacting of metal powder mixtures with a pressure of 400 MPa, green compacts were sintered in a furnace with controlled atmosphere (N/sub 2/H/sub 2/) at 1210 deg. C for one hour. After sintering, densities beyond 98% of theoretical density were achieved. To improve mechanical properties, sintered specimens were heat treated. The heat treatment cycle was: austenitizing at 980 deg. c for 15 minutes and tempering at 500 deg. c for one hour. Tensile strength and hardness were 495 MPa and 491 HV30 respectively, which after heat treatment increased to 525 MPa and 560 HV30. Microstructure of above steel was stabilized by heat treating. A continuous ternary eutectic mixture with a laminar structure consisting of gamma-Fe, Fe/sub 2/MoC and Fe/sub 3/C phase formed between the grains. This high alloy P/M steel with a high hardness and good wear properties after nearly full densification, is a good material for severe wear conditions. Occurrence of liquid phase sintering at a relatively low temperature is a considerable advantage of this method. In this way, it is possible to sinter this steel in an ordinary production furnace (e.g., mesh belt type). Rocker arm tip would be a good candidate for this high alloy P/M steel. (author)
[en] Equilibrium concentrations are traditionally calculated with the help of equilibrium constant equations from selected reactions. This procedure, however, is only useful for simpler problems. Analysis of the equilibrium state in a multicomponent and multiphase system necessarily involves solution of several simultaneous equations, and, as the number of system components grows, the required computation becomes more complex and tedious. A more direct and general method for solving the problem is the direct minimization of the Gibbs energy function. The solution for the nonlinear problem consists in minimizing the objective function (Gibbs energy of the system) subjected to the constraints of the elemental mass-balance. To solve it, usually a computer code is developed, which requires considerable testing and debugging efforts. In this work, a simple method to predict equilibrium composition in multicomponent systems is presented, which makes use of an electronic spreadsheet. The ability to carry out these calculations within a spreadsheet environment shows several advantages. First, spreadsheets are available 'universally' on nearly all personal computers. Second, the input and output capabilities of spreadsheets can be effectively used to monitor calculated results. Third, no additional systems or programs need to be learned. In this way, spreadsheets can be as suitable in computing equilibrium concentrations as well as to be used as teaching and learning aids. This work describes, therefore, the use of the Solver tool, contained in the Microsoft Excel spreadsheet package, on computing equilibrium concentrations in a multicomponent system, by the method of direct Gibbs energy minimization. The four phases Fe-Cr-O-C-Ni system is used as an example to illustrate the method proposed. The pure stoichiometric phases considered in equilibrium calculations are: Cr2O3(s) and FeOCr2O3(s). The atmosphere consists of O2, CO e CO2 constituents. The liquid iron, dissolving O, Cr, C and Ni, is modeled with the Unified Interaction Parameter Formalism considering the existence of associates Cr*O and Cr2*O, in order to take into account the strong attractive interaction between Cr and O. The thermodynamic conditions found in the production of low carbon stainless steel are analyzed. The thermodynamic equilibrium between dissolved Cr and O were analyzed at 1873 and 1923 K. The value of the critical chromium in liquid iron is calculated for the temperature of 1873 K. The effects of vacuum level and Ni content on decarburization are shown with the proposed method. In this work, the change of variables to overcome the deficiency of the Solver in applying the generalized reduced gradient method (GRG) is also presented. Spreadsheet results are compared with experimental results from the literature and with results determined with the help of FactSage - a commercial software package for solving chemical thermodynamic problems. From the comparison, it can be seen that spreadsheet results are in satisfactory agreement with all others. In addition, it has been shown simultaneously how spreadsheets can be easily used for metallurgical thermodynamics educational purposes (au)
[en] Iron metal and a low carbon steel have been implanted with nitrogen ions and then post irradiated with alpha carbonitrides formed at the metallic surfaces was determined through the Conversion Eletrons Moessbauer Spectroscopy in 57Fe. Effects of the post bombardment on the retention of the precipitates and their dissolution were determined and are discussed for both materials. (author)
[en] Within the USDOE Fuel Cycle Research and Development Program steel-based alloys have shown promise as potential waste forms for Tc-based waste streams produced from spent fuel processing. Waste stream components are alloyed with steel to create an alloy with a complex microstructure. Surface analytical techniques (SEM, EDS) coupled with long-term corrosion studies and electrochemical techniques have been used to analyze the corrosion behaviour of this material. Due to the complex alloy structure it is difficult to determine which phases are active or passive to corrosion. A microelectrochemical cell system has been employed to isolate and study individual phases and regions to separate their corrosion behaviours. Such analyses lead to a much clearer picture of alloy corrosion processes when coupled with bulk studies. (author)