National Metallurgical Laboratory
  • Jamshedpur, Jhanrkhand, India
Recent publications
Hot-rolled high strength steel with ferrite matrix and nano-size precipitation is one of the novel advanced ferrous grades at present. This grade of steel, namely NPS800 (Nano-precipitation strengthened 800 grade) finds application in automobile industry for the manufacture of long member parts of large-capacity vehicles. Apart from the minimum strength level of 800 MPa and ductility over 16%, the steel requires adequate stretch flangeability to prevent a catastrophic failure in service. While the grade achieved the desired tensile strength and ductility as per the stipulated specification, there were incidences of erratic stretch flangeability. Detailed microstructural characterization has been carried out to explore the reasons for variations in stretch flangeability. The study reveals that there is a direct correlation between nature of precipitate distribution and size with stretch flangeability. Pre-dominant interphase-controlled precipitation below ~ 12 nm average size is desirable to obtain desired stretch flangeability. To achieve the typical characteristic of precipitation, Ti/Mo atomic ratio plays an important role.
The displacement reaction technique was used to produce a nanostructured core/shell FeCo/Cu composed of FeCo core and copper (Cu) shell. The formation of the core-shell structure and thickness of the Cu layer is established and determined by analyzing the X-ray diffraction (XRD) pattern. The transmission electron microscope and selected area diffraction pattern analysis corroborate the results of the XRD studies. Magnetic force microscopic studies reveal that the FeCo/Cu particle shows single-domain characteristics. Oxidation studies indicate that Cu serves as a protective layer and provides a better oxidation resistance to the FeCo core even at high temperatures. Heat-treated FeCo/Cu particles show the possibility of tuning the magnetic properties of this core-shell structure to fit specific application requirements.
Mineral processing plants operate in capacity of hundreds/thousands of tons per day. Accordingly, chemical reagents’ usage also increases proportionally. Stringent norms toward environment sustainability question the usage of chemical reagents, especially in large quantities and tailings disposal in open areas. Hence, bioreagents have gained great interest. Froth flotation is by far the most practiced processing route for fines beneficiation and low-grade ore upgradation especially for naturally hydrophobic minerals. Flotation being a physico-chemical separation technique, flotation reagents selection plays a pivotal role in the process performance. A novel environmental-friendly biocollector, an extract from the leaves of Vitex negundo, was used as flotation collector in the present investigation for beneficiating a low-grade graphite ore with 8.67% fixed carbon. A three-factor and three-level Box-Behnken Design (BBD) under Response Surface Methodology (RSM) was employed to study the effects of important process variables such as grinding time, depressant dosage, and collector dosage on the responses, namely, ash percent of final concentrate and its recovery. A final graphite concentrate with 4.24% ash and 14.42% yield was obtained using the developed biocollector by flotation of low-grade graphite ore with 89.47% ash content. The degree of significance of input variables was determined using ANOVA. Regression models for ash content, % of final concentrate, and its %recovery was obtained from BBD analysis. It showed that the grinding time has a significant influence on the process followed by depressant dosage on the grade of final concentrate and collector dosage on its recovery.
In the present study, the operational characteristics of an industrial billet caster were investigated. Two billet moulds were instrumented with Fibre Bragg Grating (FBG)-based temperature sensors and run for their full lives of 320 h each under normal plant conditions doing open casting with oil lubrication. The heat fluxes and temperatures of the mould wall were used to study the peritectic nature of the grades cast. The data from the moulds were also used to understand the main resistances to heat transfer by comparing the variation in mould wall temperatures to the variation in liquid steel temperature through a cast. The impact of mould life on the heat transfer through the mould was also studied by comparing data of similar casting conditions over the whole life of the mould. The instrumented moulds were also used to study sticker breakouts. The classical breakout signatures were obtained in the temperature profiles in the breakout events. It was found that the hot spot associated with the temperature peak was moving down at a speed of around 0.7–0.75 times the casting speed. The usefulness of FBG-based temperature sensors for practical billet caster operations has been shown.
Steel production results in a high magnitude of wastes that are either processed in the plant or sold for by-product generation due to stringent environmental regulations. Approximately 2–4 ton steel slag is generated per ton of crude steel by the steel plant. The major slags being highlighted are blast furnace (BF) slag, Linz-Donawitz (LD) slag, and Laddle-refining (LF) slag. As these slags are obtained primarily from the mixing of iron ore with coke and after a series of high-temperature reactions, metallization of some rare earth elements and rare metals is seen in these slags. This study is aimed to characterize these slag wastes generated from TATA STEEL, India, for the content of strategic and rare earth elements omnipresent by various tools like ICP-MS, SEM, and ED-XRF (equipped with Tornado analysis). BF slag is very rich in Ce (177 ppm), followed by 96 ppm La and 74 ppm Nd, apart from Cs (88 ppm), Sb (118 ppm), Sr (411 ppm), and Zr (337 ppm). Nearly 765 ppm V and 67 ppm Nb are reported in the LD slag. LF slag was analyzed with the presence of 66 ppm Ba, 96 ppm Sb, 48 ppm Nb and 70 ppm Cs. These low tenor raw materials owing to huge tonnage availability can serve as a viable secondary resource for utilization. They would be able to cater the critical metal demand ensuring a zero-waste process as per the economic analysis presented.
In general, the phosphatic rock contains around 0.05 wt% rare earth elements (REEs). The global commercial phosphatic rock output is anticipated to obtain 250 million tons per year, making phosphate rocks a significant source of REEs. The review discusses the geological aspects of phosphate rocks, their availability, and methodologies to convert them to phosphoric acid and ultimately to phosphogypsum. Phosphogypsum (PG) is a high-volume by-product of phosphate-based chemical industries that produce phosphoric acid. Because of the low radioactivity of radionuclide contaminants, roughly 85% of PG is stored in open fields. These PG stacks require enormous land areas, cause substantial upkeep expenses, and may create major environmental damage. Apart from the detailed analysis of metal worth in phosphogypsum, the efforts put forth by researchers in recovering valuable rare earth elements from PG have been discussed. Additionally, the processes for metal separation and purification are also discussed in vogue.
Mechanical and corrosion properties of welded duplex stainless steel (DSS) structures are of paramount consideration in many engineering applications. The current research investigates the mechanical properties and corrosion integrity of duplex stainless-steel weldment in a simulated 3.5% NaCl environment using specially developed novel electrodes without the addition of alloying elements to the flux samples. Two different types of fluxes having basicity indexes of 2.40 and 0.40 were used to coat E1 and E2 electrodes respectively for DSS plate welding. The thermal stability of the formulated flux was evaluated using thermogravimetric analysis. The chemical composition, using optical emission spectroscopy, and the mechanical and corrosion properties of the welded joints were evaluated as per different ASTM standards. X-ray diffraction was used to find out the phases present in the DSS welded joints while a scanning electron equipped with EDS was used for microstructural examination of the weldments. The ultimate tensile strength of welded joints made using the E1 electrode was in the range of 715–732 MPa and that of the E2 electrode was found to be 606–687 MPa. The hardness was increased with increased welding current from 90 to 110 A. The welded joint with E1 electrode coated with basic flux has better mechanical properties. The steel structure in 3.5% NaCl environment possesses substantial resistance to corrosion attack. This validates the performance of the welded joints made by the newly developed electrode. The results are discussed on the basis of the depletion of alloying elements such as Cr and Mo observed from the weldments with the coated electrodes E1 and E2 as well as precipitation of the Cr2N in the welded joints made by E1 and E2 electrodes.
Band engineering is a promising approach that proved successful in enhancing the thermoelectric performance of several families of thermoelectric materials. Here, we show how this mechanism can be induced in the p-type TiCoSbhalf-Heusler (HH) compound to effectively improve the Seebeck coefficient. Both the Pisarenko plot and electronic band structure calculations demonstrate that this enhancement is due to increased density-of-states effective mass resulting from the convergence of two valence band maxima. Our calculations evidence that the valence band maximum of TiCoSb lying at the Γ point exhibits a small energy difference of 51 meV with respect to the valence band edge at the L point. Experimentally, this energy offset can be tuned by both Fe and Sn substitutions on the Co and Sb site, respectively. A Sn doping level as low as x = 0.03 is sufficient to drive more than ∼100% increase in the power factor at room temperature. Further, defects at various length scales, that include point defects, edge dislocations, and nanosized grains evidenced by electron microscopy (field emission scanning electron microscopy (FESEM) and high-resolution transmission electron microscopy (HRTEM)), result in enhanced phonon scattering which substantially reduces the lattice thermal conductivity to ∼4.2 W m-1 K-1 at 873 K. Combined with enhanced power factor, a peak ZT value of ∼0.4 was achieved at 873 K in TiCo0.85Fe0.15Sb0.97Sn0.03. In addition, the microhardness and fracture toughness were found to be enhanced for all of the synthesized samples, falling in the range of 8.3-8.6 GPa and 1.8-2 MPa·m-1/2, respectively. Our results highlight how the combination of band convergence and microstructure engineering in the HH alloy TiCoSb is effective for tuning its thermoelectric performance.
The exploration of mechanical properties and formation of various crystal structures under the mechanically stressed condition has numerous uses for the design of engineering components for electronic instruments, automotive, aerospace, etc. In order to diagnose the stress–strain behaviour and growth coalescence of crystalline structures in single-crystal iron during bi-axial tensile deformation, classical molecular dynamics (MD) simulation has been employed. Two-stage atomistic structural transformations in single-crystal iron are observed. First-stage transformation corresponds to body-centred cubic (bcc) to face-centred cubic (fcc) crystal, whereas the second-phase transformation corresponds to fcc to bcc. To gain further insights, multiple MD simulations have been performed by varying the strain rate of the tensile deformation. Common neighbour analysis, dislocation analysis and stress–strain analysis have been used to precisely characterize the simulation trajectories during simulations. Outcomes of our work will provide additional insights for improved design of engineering components.
Rapid technological modernization has accelerated the replacement of older electronic goods with newer ones, which has led to the generation of huge quantities of discarded electronic items at its end-of-life, known as electronic wastes (e-wastes). The growing quantity of e-wastes has become a major threat to the society as well as environment. On the other hand, e-wastes contain several valuable metals and materials of high economic value, which compels researchers to work in the area for secondary resources for metal recovery. Metal recovery from such secondary resources will not only preserve the primary resources but also reduce the loss of valuable metals/materials, protect the environment from their hazardous effects as well as reduce the demand-supply gap of metals up to some extent. In view of the above, present study is focused on the possible effort to figure out variety of metals present in the component of waste personal computers (WPCs) as well as different recycling processes implemented for the efficient recovery of metals.
The thermomechanical distortion and the evolution of an interface layer with intermetallic phases are the two critical challenges for gas metal arc overlap joining of multimaterial sheets. Two novel analytical methods are proposed following mechanistic principles to estimate the thermomechanical distortion and the interface layer thickness. The analytically estimated results are tested rigorously with the corresponding experimentally measured results for gas metal arc joining of aluminium and steel sheets for different process conditions. Both the thermomechanical distortion and the interface layer thickness are influenced predominantly by the wire feed rate and the resulting heat input. The interface layer thickness and the thermal distortion are found to be the minimum for a heat input of 42.4 J/mm corresponding to the lowest wire feed rate of 4 m/min and the highest travel speed of 10 mm/s. The proposed analytical methods can serve as practical easy-to-use design tools for appropriate selection of process variables in gas metal arc overlapped joining of dissimilar sheets to mitigate the joint distortions and restrict excessive growth of the interface layer.
There is a continuous endeavor to replace bentonite with any other suitable inorganic or organic binders. Organic binders generally burn at around 300–350°C and lose their binding property and cause crumbling in most cases. This study aimed to develop a process to use a suitable organic binder for the development of blast furnace quality pellets using some additives which can overcome the strength loss of pellets during induration. The wastes generated from pulp industries viz. Ca-lignosulphonate (Ca-LS) and Na-lignosulphonate (Na-LS) have been used as binders in hematite ore pellets. To alleviate the strength loss at 300–350°C, lower iron oxide (FeO and Fe3O4) containing materials viz. Linz-Donawitz (LD) sludge and mill scale have been added. FeO and Fe3O4 in these materials will be oxidized at the mild oxidizing atmosphere of the induration strand and initiate diffusion bonding at around 300°C. Therefore, the strength loss due to burning will be compensated by the strength gain due to diffusion bonding. From the experimental study, it has been found that Ca-LS is a better binder than Na-LS and LD-sludge (LDS) is a better additive than mill scale. A combination of 0.4% Ca-LS with 5% LDS addition can prevent strength deterioration at 300–350°C during drying and gives a good-quality pellet in terms of strength, thermal shock resistance, reducibility, reduction degradation, and swelling index, which is comparable with bentonite added pellet. Thus, 04% Ca-LS with 5% LDS shows its good application potential to replace bentonite in hematite ore pelletizing.
The 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.
Elevated temperature sensitization of a 304 stainless steel results in degradation of mechanical properties and becomes prone to premature failure. In the present investigation, sensitization of 304 stainless steel has been done in the temperature range of 500–800 °C. Yield strength, ultimate tensile strength and fracture toughness (KJc) of the sensitized 304 stainless steel specimens were determined by ball indentation technique. Microstructural characteristics were quantified and used in artificial neural network to predict the mechanical properties of the investigated alloy. Neural network was developed with the help of MATLAB toolbox. Best equation was fitted for training, testing and validating the output. Predicted values from the developed model exhibited impressive correlation with experimental data obtained through ball indentation technique as well as with literature reports. The model has proved its distinctive potential in predicting the mechanical properties of sensitized 304 stainless steel, which faces restriction in bulk sampling from original component to perform conventional mechanical test during service exposure.
Elemental partitioning across the precipitate/matrix interface controls the kinetics of precipitate evolution, during growth and coarsening. We present the first comprehensive analysis of evolutions of both the aspects of microstructure, i.e., the size (of nano-scale, ordered, coherent γ′ precipitates) as well as the lattice misfit (between γ and γ′), in light of elemental partitioning, applied to a Ni-based superalloy, HAYNES 282. In this work, eexperimental analyses by atom-probe tomography, transmission electron microscopy, and x-ray diffraction are combined with thermo-kinetic modelling using ThermoCalc® and TC-PRISMA®. The current study has isolated the growth and the coarsening regimes, analyzed the respective kinetics and identified their individual rate controlling processes, for the first time. While Cr and Ti are found to be the rate controlling in the growth regime due to their larger amount of partitioning need, Mo becomes rate controlling in the coarsening regime. From the APT data, it is however clear that diffusion across the interface remains slowest for Mo, both in the growth and the coarsening stages. For the coarsening kinetics, unlike most of the recent literature, we have used the thermodynamic parameter corresponding to the non-dilute, non-ideal γ solid solution phase in the modified LSW rate equation. This approach provides a much realistic prediction, as Ni-based superalloys show significant deviation from ideality. Constrained misfit has been found to be positive and found to decrease with ageing time in the present alloy. Elemental partitioning explained quantitatively the variation in the lattice parameters and the misfit.
This study explores the dual‐slope Coffin–Manson (C–M) behavior of a polycrystalline nickel‐based superalloy, EA, used in turbine engine applications with an emphasis on discerning the micro‐mechanisms responsible for it. The motivation for distinguishing the micro‐mechanisms responsible for bi‐linear C–M behavior stemmed from the earlier evolved comprehensions that state that the fatigue life estimation based on the extrapolation of any single line gives inaccurate results. Transmission electron microscopy (TEM) investigations of fatigue fractured specimens at low strain amplitudes, Δε/2, revealed that dislocations are homogeneously distributed in the γ‐channels and occasionally form networks at γ/γ′ interface. Whereas deformation is heterogeneous at high Δε/2 owing to the complex dislocation reactions. Cr23C6 carbides are precipitated during the high Δε/2 fatigue tests, which act as obstacles for dislocations. The deformation heterogeneity resulting from the dislocation–γ′ precipitate interactions and the dislocation–M23C6 carbide interactions accounts for the dual‐slope C–M behavior. The EA alloy exhibited dual‐slope C–M behavior. Cr23C6 carbides are precipitated during high Δε/2 fatigue test. Deformation is mostly homogeneous at low Δε/2. At high Δε/2, dislocation interactions and carbides cause strain localization. Deformation heterogeneity at high Δε/2 is attributed to bilinearity in C–M plot.
Hot-rolled high-strength steel having ferrite matrix and nano-size precipitation possesses a good combination of strength and ductility, and it finds application in the automobile industry for the manufacture of long member and chassis parts of large-capacity vehicles. Such an application needs steel with high stretch flangeability since there are several drilled or broached holes in the finished component. Apart from an adequate strength level of 800 MPa UTS with a minimum elongation of around 16%, the steel requires a high degree of stretch flangeability to avoid any catastrophic failure during its use. During the commercial production process, sometimes, the steel grade namely NPS800 (Nano-Precipitation Strengthened 800 grade) exhibited brittle fracture in the tensile test specimens as well as during the component manufacture. A detailed study was undertaken to understand the causes of brittle fracture or mixed-mode fracture, despite the steel showing a total elongation of not less than 18%, and the resolution to this problem is explained in this paper. Despite the steel having tensile strength and total elongation as per specification, the performance of steel during component forming was found to be erratic. The steel samples while possessing similar chemical composition and mechanical properties exhibited a variation in stretch formability. The main strengthening mechanism of this new grade being precipitation hardening by nano-precipitates, a detailed study involving microstructural characterization became essential to explain the causes of the incidences of poor stretch flangeability. Our study reveals that the size distribution of nano-precipitate formed at the austenite–ferrite interfaces plays an important role in determining the steel properties such as strength, strain-hardening exponent, stretch flangeability, uniform elongation and post-necking elongation. For the normal finish rolling and coiling temperatures, optimization of chemistry was achieved to obtain the mechanical properties such as strength and ductility in the desired range. It is observed that the fineness of the nano-precipitate is important to achieving a good combination of strength, total elongation, strain-hardening exponent, and post-necking elongation to obtain satisfactory stretch formability. The study on the crack tip opening displacement (CTOD) also confirms the significance of finer precipitates on crack propagation and thereby improving hole expansion ratio (HER). By the study of fracture samples using transmission electron microscopy, the role of large-size precipitates in causing the mixed-mode or brittle failure is explained. The significance of the reduction in area (RA), post-necking elongation, and strain rate sensitivity in achieving a satisfactory HER is established.
Traveling grates (TG) are used as beds over which green pellets are subjected to a series of thermal cycles, namely preheating, induration, and firing to make the pellets suitable for charging in the blast furnaces of an integrated steel plant. In this work, chronic failures of TG links after a service life of 2.5-3 years are investigated. A comparative analysis of failed, used and new TG links was carried out. Fractography of the failed link revealed an intergranular brittle fracture near the surface followed by a transgranular fracture with a signature of decohesion in the bulk of the fracture surface. Microstructural analysis revealed the presence of pre-existing grain boundary chromium carbides (Cr23C6) in the new (unused) link, which can facilitate easy crack initiation and propagation. Furthermore, failed and used TG link revealed the presence of extensive precipitation of needle-like sigma phase confirmed by a combination of X-Ray diffraction and scanning electron microscopy coupled with energy dispersive spectroscopy techniques. Such precipitation of the sigma phase occurs during exposure to a susceptible high-temperature range. The presence of the sigma phase is known to embrittle the austenitic stainless steel and such embrittlement is confirmed by a significant increase in hardness and decrease in Charpy impact toughness of failed and used TG links compared to the new TG link. Thermodynamic and kinetic simulations confirmed a high susceptibility of the existing alloy composition to extensive sigma phase precipitation in a wide temperature range. A new alloy composition with higher nickel (∼30 wt. %) and free from tungsten is proposed to reduce the susceptibility towards in-service embrittlement induced by sigma phase precipitation.
Ti6Al4V ELI (Extra-low interstitial) alloy is quite popular due to its application in the fields of biomedical, aerospace, optics and aeronautic industry, because of its high-strength to weight ratio, anti-corrosive and biocompatibility, and lightweight. This alloy contains low interstitials, which gradually improves mechanical and thermal properties and is thus quite popular as titanium medical-grade. Ultra-precision machining (UPM) of Ti6Al4V ELI alloy is treated as a difficult to cut process due its chemical reactivity with the diamond tool. Also, machining Titanium alloy for precision engineering applications is quite challenging due to tool wear. In this paper, an attempt is made to understand the precipitation effect that occurs at Ti-6Al-4 V ELI alloy surfaces during diamond turning. The precipitation generation highly influences surface finishing and imposes serious precision engineering challenges. Therefore, this paper further attempts to scientifically understand the precipitation effect on surface roughness and surface finishing in UPM of Ti6Al4V ELI alloy, particularly through the integrated analytical and experimental approach. The results show that the generation of precipitates induces cracks, scratch marks and pits, which deteriorate the surface quality. The Surface Roughness (Ra) obtained with significant precipitation is 0.1484 μm during the diamond turning of Ti6Al4V.
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144 members
Dr. Biswaranjan Dhal
  • Metal Extraction and Forming Division
Rajat K. Roy
  • Materials Science and Technology Division
S. Nayar
  • Materials Science and Technology Division
Pratima Meshram
  • Metal Extraction and Recycling Division
Rajneesh Kumar
  • Engineering Division
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