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Medium Manganese Steel: A Promising Candidate for Automotive Applications
No full textOver the last decade, research in the field of advanced high strength steels (AHSS) for automotive applications has undergone a paradigm shift from low manganese (Mn) transformation induced plasticity (TRIP) aided and high Mn twinning induced plasticity (TWIP) steels to medium Mn (3-10 wt.% Mn) TRIP and/or TWIP aided steels. This is primarily due to the unique combination of strength and ductility obtained in medium Mn steels. Medium Mn steels represent the 3rd generation class of advanced high
strength steels (AHSS). These steels supersede the 1st Gen AHSS which shows dismal performance with respect to the requirement of the modern carmakers, at the same time, medium Mn steels are significantly cheaper and are easy to process as compared to the 2nd generation AHSS. These advantages have led to an upsurge in the research of these 3rd Gen AHSS- medium Mn steels since last 10 years. The present article aims to showcase the process of medium manganese steels in terms of mechanical performance and therefore its applicability for automotive applications. An overview of composition, suitable heat treatment and the associated parameters, different processing routes, microstructure, mechanical properties and factors influencing it are presented
Observation of large exchange bias field in Mn rich NiMnAl Heusler alloy thin film
No full textIn the present work exchange bias in Mn rich Ni-Mn-Al film has been studied. The film has been deposited by cosputtering from the targets of Ni, Mn and Al. It exhibits an antiferromagnetic B2 phase at room temperature. At low temperature, magnetization versus temperature (M-T) measurement shows a bifurcation among ZFC and FC curves. Hysteresis (M-H) loops measurements reveal the occurrence of exchange bias phenomenon at low temperature. Large HEB of 2.2 kOe for 20 kOe cooling field has been observed. There occurs a field induced ordering at temperature similar to 50 K reflected as coinciding ZFC (zero-field cooled) and FC (field-cooled) curves at large magnetic field. AC susceptibility measurement indicates the occurrence of cluster glass behaviour at low temperature. The exchange constant obtained from the best fit to the experimental data was found to be Ji approximate to -2 meV. The negative interface exchange constant indicates AFM coupling occurs among the coexisting phases. Exchange bias phenomenon may be associated to the coexistence of antiferromagnetic and ferromagnetic like ordering at low temperature. Cooling field dependence of H-EB and coercive field H-C indicate that an increase in anisotropy and growth of ferromagnetic clusters occurs at high magnetic field
Beneficiation of difficult-to-wash Indian low volatile coking coal fines by Falcon concentrator
Get PDFThe fast depleting reserves of high-grade Indian coking coal and its resultant dependence on import makes the emerging situation a fit case for exploring innovative and high efficacy techniques such as non-conventional gravity-based systems for clean coal recovery viz., advanced centrifugal gravity separators like Falcon concentrators for fine and ultra-fine coal particles processing using enhanced gravitational force. The above methodology has been adopted for low volatile coking (LVC) coal due to the high ash content associated washability characteristics and high near gravity material content. Attempt was made using laboratory Falcon SB40 concentrator for cleaning the LVC coals assaying 32.6% ash. Considering the physical properties, coal petrography and washability studies, as received coal was ground to three size fractions of –500 μm, –250 μm and –150 μm and subjected to separation in Falcon separator. Experiments were conducted using Design Expert software to evaluate the effects of four significant process variables such as feed size, pulp density, gravitational force value and water pressure. The relationship between the response functions (ash content, combustible recovery and separation efficiency) and process variables is presented as empirical model equations. Under the optimum operating conditions, LVC coal was cleaned to 18.4% ash content with 57.8% combustible recovery using Falcon concentrator
Strain-induced microstructural evolution and its implication on high-temperature hot corrosion (HTHC) phenomena in Alloy 617
No full textThe influence of various extents of strain on the microstructure and the high-temperature hot corrosion (HTHC) behavior in Alloy 617 is examined in this study. Electron backscatter diffraction characterization revealed an increase in the spread in the local misorientation zones from the vicinity of boundaries to the grain interiors with the extent of strain. Moreover, the increase in the degree of deformation also increased the connectivity of the random high angle grain boundaries (HAGBs), as corroborated by the fractal analysis, since most of the twin boundaries changed their character from 'special' to 'random' on the application of strain. The HTHC behavior of the as-received and the strained specimens is evaluated by exposing them to a salt mixture (Na2SO4 + NaCl+V2O5) at 1273 K for 24 h. The hot corrosion damage is assessed based on oxide scale characteristics (morphology, thickness, and composition), internal percolation depth, Micro-CT (porosity), and Mott-Schottky (passive film defects) analyses. In-depth characterization of the corroded specimens unveils an improved resistance to HTHC in the highly strained specimens due to the enhanced Cr diffusion through the defects and connected random HAGBs which facilitated the formation of a continuous, and compact Cr-rich oxide film. Importantly, the occurrence of recrystallization and the evolution of the Cr-rich carbides in the strained specimens in the course of the HTHC test increased its likelihood of resisting the aggressive environment for a prolonged duration
Performance characterization and misplacement studies of liquid-solid fluidized bed density separator for coal beneficiation using Taguchi-ANOVA method
No full textCoal preparation plants commonly use density-based separators to remove high-density inorganic matter (rock) from low-density carbonaceous matter (coal). Liquid-solid fluidized bed separators (FBS), segregates particles with different size, shape, and density. Particles with different terminal velocities report to various heights of the fluidization column. This property has been used to beneficiate the low-grade coal particles. As the material systems in mineral processing vary broadly in physical characteristics, misplacement of particles to an undesired destination is a prevalent occurrence. The present work aims at understanding the influence of input variables on the separation performance and particle misplacement in FBS. Quantitative and qualitative analyses of the performance characteristics and misplacement have been studied using Taguchi statistical design and ANOVA. Misplacement and normalized misplacement indexes were calculated to quantify the extent of misplacement during segregation. The optimized mean separation efficiency was obtained at optimized combination of mean particle size of 400 mu m, bed height of 20 cm, superficial velocity of 2.83 cm/s, and overflow tap height of 12 cm, whereas the optimized mean normalized misplacement index was obtained at mean particle size of 400 mu m, bed height of 20 cm, superficial velocity of 2.12 cm/s, and overflow tap height of 12 cm
Extraction and flotation performance evaluation of bio-collector in high ash graphite ore beneficiation
No full textThe rapid depletion of high-grade ores and natural resources, utilization of low-grade ores by beneficiation becomes utmost importance for sustainable development and resource management. The increasing wide range of applications of graphite for electrode, lubricants, refractory applications especially the recent surging electric automobile industry, resulting in significant need of graphite in future. Graphite demand in the energy storage industry is expected to grow faster than today's demand in future. Most of the graphite ore deposits in India are of low grade containing high ash content. Graphite is a naturally hydrophobic mineral and froth flotation process involves separation of minerals based on its surface hydrophobicity. The chemical reagents commonly used in graphite flotation are hydrocarbon oils such as diesel, kerosene along with a frothing agent such as methyl isobutyl carbinol (MIBC) which are non-environment friendly, hazardous and not cost effective while used at large scale industrial processing of the ore. Hence, in this work, a new eco-friendly bio-collector was developed from the exocarp or rind of a shrubaceous plant as an alternate flotation reagent for graphite. The flotation performance efficacy of this bio-collector was evaluated in comparison to the existing practice of diesel-MIBC dual reagent system in graphite flotation. A high ash low-grade graphite ore from eastern India with 84.71% ash and 9.07% fixed carbon was beneficiated by flotation technique for recovering graphite with lower ash content. The ore characterization studies mineralogy (XRD, ore microscopy) and morphology (SEM) reveal that the graphite mineral phase with sheet like appearance was accompanied predominantly by quartz, with minor fractions of biotite, muscovite and kaolinite. The spectral analysis of the developed bio-collector was characterized (FTIR). Under similar flotation test conditions on processing the high ash graphite ore, a final concentrate graphite product with 11.40% ash using diesel & MIBC as flotation reagents and 11.74% ash using bio-collector was obtained which indicates that the developed bio-collector could be a potential replacement for diesel-MIBC reagents being used in graphite processing mineral industries. Also, this bio-collector has an added advantage of being a natural plant based extract with environmental compatibility leading to a step towards clean ore processing
Tensile deformation micro-mechanisms of a polycrystalline nickel base superalloy: From jerky flow to softening
No full textIn this study, efforts were made to elucidate the tensile deformation micro-mechanisms of a polycrystalline nickel-base superalloy used for the fabrication of critical rotating and stationary components of the gas turbine engine under relevant service conditions. The microstructural evolutions during the investigated temperatures and strain-rates are explicitly indicating the divergence in associated tensile responses. The alloy exhibits serrated or jerky flow behavior at 300 and 400 degrees C, whereas, yield strength anomaly (YSA) is observed at 750 degrees C. With further increase in testing temperature, softening mechanisms start dominating and dynamic recrystallization occurs at 930 degrees C. TEM investigation revealed that the serration in the flow curve at 300 degrees C is attributed to the disordering of the secondary.' -precipitates by the leading a/2 dislocation super-partial and refurbishment of order through thermal activation before the trailing super-partial arrives. The YSA observed at 750 degrees C is essentially due to the cross-slip of dislocation super-partials and the presence of dislocation debris
Microwave-assisted infrared thermography: A tool for quality assessment of blast furnace feeds
No full textInfrared thermography is a ubiquitous technique for surface non-contact temperature profile analysis and monitoring. The generated thermograms offer a plethora of applications in non-destructive evaluation (NDE) for detecting inhomogeneities in engineering structures. However, the potential of this technique is still in its infancy for quality assessment of minerals and ores. In steel plants, iron ore and coke are the most important raw materials fed into the blast furnace. The alumina content in iron ore and moisture percentage in coke play a significant role in determining ultimate product quality and blast furnace efficiency. Till date, plant operators have relied on time-consuming and cumbersome chemical analysis methods for quality analysis of ores. The present investigation reveals a microwave-assisted infrared thermography based non-invasive technique for fast and accurate quality evaluation of blast furnace feed material, in terms of alumina content in iron ores and moisture content in coke. The estimation of alumina content is based on the difference in dielectric constants of various iron ore constituents. Moisture analysis in coke involves the utilization of well-known black body radiation. The co-relation factor for the alumina content in iron ore is slightly lower than the moisture content in coke. The basic difference occurs owing to inherent limitation of the technique for two different substances. Such type of novel approach is scanty in open domain literature. This non-invasive, real time, precise and fast technique proved its enormous potential during validation for random plant samples and thus promising to improve feed quality and blast furnace efficiency
A single-step process to leach out rare earth elements from coal ash using organic carboxylic acids
No full textThe ever increasing applications of rare earth elements and their limited primary resources has compelled researchers worldwide to find alternate methods of efficient leaching from various secondary resources, in particular from end of life products. The present research work describes such a process to extract rare earth elements from coal ash using low molecular weight carboxylic acids. Different carboxylic acids, i.e. monocarboxylic (lactic acid), dicarboxylic (malonic acid, succinic acid, tartaric acid) and tricarboxylic acid (citric acid) were used to successfully leach out significant proportion of rare earth elements (up to 62%) from coal ash at the natural pH of the carboxylic acid solutions (pH 1.6-2.3). The carboxylic acid concentration, leaching duration, temperature, and pulp density were optimized for the leaching process. Best leaching efficiency (65% for LREE, 19% for HREE & 62% for total REE) was achieved using 5% tartaric acid solution having natural solution pH 1.8 at 90 degrees C with a leaching duration of 60 min. The leaching efficiency of the different carboxylic acids were in the order of tartaric acid>lactic acid>citric acid>malonic acid>succinic acid. The leaching kinetics of individual rare earth elements was found to be different from each other owing to their different complex formation ability with carboxylic acids. Appreciable selectivity was observed for leaching of rare earth elements over transition metal and main group elements. XRD and electron probe micro analyzer (EPMA) studies revealed that unlike mineral acids, carboxylic acids leached out rare earth elements without damaging the minerology of coal ash, thus providing the opportunity to utilize the treated coal ash for other applications like in cement and bricks industries. Thus, the novelty of the present work lies in efficient and selective leaching of lanthanides from coal ash using only organic acids, which are considered much milder and greener options compared to mineral acids
Effect of constitutive model on residual stress development in the pressure tube rolled joint
No full textBeing one of the most important joints in a pressurized heavy water reactor (PHWR), pressure tube rolled joint is critical during the construction and operation. This joint is formed through the roll expansion process that leads to an interference fit between the Zr 2.5%Nb pressure tube and stainless-steel end fitting. For integrity of this joint, a sufficient pull-out strength and leak tightness must be maintained, while having lower undesirable residual stresses, especially in the transition zone. The roll expansion process parameters are controlled to achieve optimum contact pressure and limit the tensile residual stress. The parameters of this roll expansion process are designed either through experiments or through numerical simulations. One important aspect that is often ignored in the numerical simulations is the effect of material constitutive behavior of the Zr 2.5%Nb alloy, particularly the anisotropic yield behavior and the cyclic stress-strain response. In this paper, these two aspects of constitutive behavior are investigated, using three-dimensional finite element simulations, to understand their influence on the residual stress development in the roll expansion process. The cyclic behavior was modelled using Chaboche nonlinear kinematic hardening model. The model parameters were extracted from low cycle fatigue experiments with the strain amplitude equivalent to that seen in roll expansion process. The results show that constitutive behavior, especially the cyclic behavior, has a significant impact on the residual stress. Anisotropic yielding of the pressure tube was also seen to affect the tensile residual stress and the contact pressure, although to a lesser extent. Finally, after comparison between four combinations of constitutive behavior, a simple isotropic yield with isotropic hardening model is suggested to predict the tensile residual hoop stress in the rolled joint, conservatively