Recent Advances in Materials Science and Engineering

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Authors: Matias Jaskari, Antti Järvenpää, L. Pentti Karjalainen
Abstract: Typical applications of ferritic stainless steels require good formability of the material that is highly dependent on the processing route. In this study, the effects of the heating rate and peak heating temperature on the texture and deep drawability (R-value) of a 78% cold rolled, stabilized 18Cr (AISI 441) ferritic stainless steel were studied. Pieces of cold rolled sheet were heated in a Gleeble 3800 simulator at the heating rates of 25 °C/s and 500 °C/s to various temperatures up to 1150 °C for 10 s holding before cooling at a rate of 35 °C/s. Microstructures were characterized and the texture of the annealed samples determined by the electron backscatter diffraction method. It was established that the high heating rate of 500 °C/s promotes the nucleation of grains with the near {111}<uvw> orientations during the early state of the recrystallization. The maximum texture intensities were found at {554}<225>. The more effective nucleation of these grains resulted in a finer grain size and an increased intensity of the gamma-fibre texture which led to enhanced R-values. At high peak temperatures, the intense grain growth took place.
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Authors: Mohammed Ali, David A. Porter, Jukka I. Kömi, Mamdouh Eissa, Hoda El Faramawy, M.F. El-Shahat, Taha M. Mattar
Abstract: The cleanness, microstructure and mechanical properties of a newly developed CrNiMoWMnV ultrahigh-strength steel with and without electroslag refining (ESR) with 70% CaF2, 15% Al2O3 and 15% CaO have been studied. This steel was designed and melted in an air induction furnace followed by refining using ESR. Cast ingots with and without ESR were forged at temperatures in the range 1100 - 950 °C. Laser scanning confocal microscopy, field emission scanning electron microscopy electron back scattering diffraction, electron probe microanalysis and X-ray diffraction have been used to investigate the microstructure and non-metallic inclusions (NMIs) of forged ingots produced with and without ESR. Hardness, tensile and Charpy-V impact tests were performed. ESR reduced the total impurity level i.e. O%+ N%+ S% by 26 % and the area fractions and numbers of NMIs by 17% and 7% respectively. The NMIs are classified into four major classes: oxides, sulphides, nitrides and complex multiphase inclusions. The microstructure of the forged and air-cooled bars consisted of martensite with a small fraction of distributed retained austenite, a very small fraction of bainite and finely distributed precipitates. The reduction of impurity levels combined with the microstructural changes brought about by the changes in the chemical composition meant that ESR resulted in a significant improvement in some mechanical properties and a marginal improvement in others.
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Authors: Ahmed Ibrahim Abdel-Aziz, Ahmed S.A. Abou Taleb, Z.M. El-Baradie, Ahmed Ismail Zaky Farahat
Abstract: Friction stir processing (FSP) is a solid-state technique for microstructural modification. The aim of this work is to evaluate the effect of input process parameters of friction stir processing (tool rotational speed rpm, travel speed mm/min) on microstructure and mechanical properties of A384 aluminum alloy. A384 aluminum alloy was cast using conventional stir casting process. The obtained alloy was subjected to friction stir process using different input parameters (rpm, mm/min) with double pass. Water was used as cooling medium during process. The microstructures of investigated alloys were characterized by optical, SEM microscopes, EDS and Map analyzer, while mechanical properties were evaluated by using tensile test. The results indicate that; after friction stir processing, the microstructure of as-cast alloy was greatly improved. Needle-like eutectic Si and Chinese Script a-Fe were modified to fine precipitates. Meanwhile, coarse primary Si and large plate b-Fe phase were dissolved. On the other hand, mapping analysis shows homogenous distribution of different alloying elements through the matrix. The higher values of tensile properties were obtained at 1200 rpm and 80 mm/min. UTS and YS were increased by 98% and50%, respectively. Meanwhile, ductility was approximately three times higher than that of cast alloy.
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Authors: Lamiaa Z. Mohamed, Wafaa A. Ghanem, Omayma A. El Kady, Mohamed. M. Lotfy, Hafiz A. Ahmed, Fawzi A. Elrefaie
Abstract: The oxidation behavior of porous nickel low-chromium alloys containing up to 1 wt%Cr oxidized in air at 1273K for 100 h was investigated. Porous-duplex scale was formed on the 1 wt%Cr pellets while single oxide layers were obtained on the 0.25 and 0.5 wt%Cr pellets. Cavities were formed underneath the NiO scales and also between both layers formed on the oxidized 1 wt%Cr pellets. Accumulation of NiCr2O4 was noticed at the oxide/ metal interface. The growth mechanism of the scales was explained on the basis of molecular oxygen inward migration.
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Authors: Mohamed Zaky Ahmed, Bradley P. Wynne, W. Mark Rainforth, Jonathan P. Martin
Abstract: In the present work, a FEI Sirion FEG-SEM equipped with a Nordlys CCD camera controlled by HKL Channel 5 software has been used to characterize the crystallographic texture of 20mm thick friction stir welded AA6082-T651 and AA5083-O. The crystallogaphic texture has been nvestigated near the top surface of the weld nugget at the shoulder affected region and near the base of the nugget in the probe affected region. The crystallographic texture in the shoulder affected region is complex in terms of determing the local reference frame of deformation and it requires complicated rotations to resemble the ideal simple shear texture. This implies the complex deformation histroy experinced in this region. However, the crystallographic texture in the probe-dominated region is simple shear texture. This implies that the deformation conditions across the whole weld nugget in this region are mianly dominated by the shear deformation generated by the probe rotation with the forward motion of the tool only playing a minor role in determining the local deformation gradient. Alternating bands between (+)and (C) was observed in the NG region of FSWed AA6082. The existence of A component is observed with an existence of strong C texture component which implies that when the C component is strong it can be associated with the A texture components.The crystallographic texture of AA5083 at both the shoulder and the probe dominated region is weak relative to that of the AA6082 .
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Authors: Antti Järvenpää, Matias Jaskari, L. Pentti Karjalainen
Abstract: Lower cold rolling reductions before reversion annealing for the grain size refinement are desired in industrial practice. This study demonstrates the effect of a low (32%) cold rolling reduction on cyclic behavior of a partially reversed (750 °C for 0.1s) structure in a 17Cr-7Ni-N type 301LN austenitic stainless steel and compares it with those of a 63% cold rolled and annealed and with a conventional coarse-grained structure. Stress amplitude and the amount of deformation-induced martensite formed under cyclic loading at the 0.6% total strain amplitude were recorded. The results showed that the partially reversed structure after the 32% cold rolling reduction exhibits the similar cyclic stress amplitude level and slight cyclic hardening as the 63% cold-rolled counterpart does. Even though the grain size refinement remains less effective at the lower reduction, the microstructure consists of higher fractions of strong retained cold-deformed austenite and martensite phases which increase the flow resistance. However, the coarse-grained structure exhibits a much lower initial stress amplitude and much more pronounced cyclic hardening. The susceptibility of austenite to transform deformation-induced martensite is practically similar among these three structures. However, the cyclic hardening is a caused by the formation of deformation-induced martensite, and the difference in the degree of cyclic hardening results from the big difference in the strength of the austenite between the partially reversed fine-grained and coarse-grained structures.
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Authors: Ahmed Hamed, Mamdouh Eissa, Abdelhakim Kandil, Omnia Ali, Taha M. Mattar
Abstract: This work aims at designing and developing low carbon steel alloys to meet the high tensile strength, high ductility and high impact toughness properties. The effect of solid solution mechanism, precipitation hardening, as well as grain refinement were developed with different Manganese content (0.78-2.36wt%) combined with Vanadium(0.008-0.1wt%) and Titanium (0.002-0.072wt%) microalloying additions. The controlled thermo-mechanical treatments and chemical compositions play a big role in developing the microstructure and the corresponding mechanical properties. Therefore, the studied chemical compositions were treated thermo-mechanically by two different ways of changing start and finish forging temperatures with subsequent air cooling. The first way by start forging from 1050 to 830oC and the second from 950 to730oC. The second way of forging process developed finer grain sizes and higher ultimate tensile strengths for all the studied steel alloys. In spite of finer grain sizes, the impact toughness value was lower in the second regime due to detrimental influence of precipitation strengthening in the ferrite. A combination of 544 MPa yield strength, 615 MPa ultimate tensile strength, 20% elongation and 138 Joule impact toughness has been attained.
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Authors: Sanaa S. Abd Elmomen
Abstract: Daily average slag and the corresponding hot metal samples were collected from blast furnace No.3 (1033m3 useful volume) of the Egyptian Iron and Steel Company (EISCO) charged with 100% self- fluxing sinter over a period of two months (from July to August 2015). The analyses of slag and metal were used to investigate the effects of temperature and basicity, defined as CaO/SiO2, on manganate capacity and manganese distribution between slag and metal.
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Authors: Ahmed Ismail Zaky Farahat, Mohamed Kamal El Fawkhry, Ayman M. Fathy, Taha M. Mattar
Abstract: Development of S6 tool steel has been discussed in this research by conducting a bit modification in the chemical composition using aluminum instead of molybdenum, and micro addition of boron to enhance the marteniste structure. Then, the hardenability and thermal stability have been detected in regarding to S6 tool steel. A novel isothermal treatment process has been suggested to enrich the retained austenite, and thereby, it has been tracked by using XRD, optical microscope, and SEM in conjugation with EDS. The effect of retained on the mechanical properties has been determined. The results ensure that aluminum has inhibited the graphite formation through the slow cooling regime. No change of hardenability or thermal stability of S6 tool steel triggered from adding of aluminum and microaddition of boron. In addition, the novel isothermal process leads to enrichment of retained austenite that has significantly affected on the combination of ductility with strength of the newly designed steel.
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