Browsing by Author "Prabhu, N."

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Behavior of Alloying Elements during Electro-Slag Remelting of Ultrahigh Strength Steel
(2012) Bandyopadhyay, T.R.; Rao, P.K; Prabhu, N.
The paper deals with the behavior of principal constituents of an ultrahigh strength steels during ESR. The multiple analyses show no significant variation in the concentrations of silicon, manganese, vanadium, molybdenum, sulphur and phosphorus while concentrations of carbon, chromium, aluminium and titanium in the ESR ingot are found to be within the range of 0.01, 0.12, 0.008 and 0.01% respectively. Silicon and manganese show a loss of 0- 55 and 2-13% respectively whereas the degree of desulphurization is in the range of 0 (in Ar shield) to 52 (in air). The lower carbon and chromium content of the electrode than the aimed value can be corrected by adding ferrochromium in-situ during ESR. The recovery of carbon from FeCr was nearly 100% in most of the melts while the recovery of chromium varied over a fairly wide range. The distributions of carbon and chromium are also uniform along the height and width of ESR ingots. The recovery of the inoculant titanium was relatively low at the bottom of the ingot and it increases with height and reached a constant value above 100-150 mm height. For the same addition of titanium, its recovery decreases during ESR with argon shielding. Metallurgical and Mining Industry.
Behavior of Alloying Elements during Electro-Slag Remelting of Ultrahigh Strength Steel
(2012) Bandyopadhyay, T.R.; Rao, P.K; Prabhu, N.
The paper deals with the behavior of principal constituents of an ultrahigh strength steels during ESR. The multiple analyses show no significant variation in the concentrations of silicon, manganese, vanadium, molybdenum, sulphur and phosphorus while concentrations of carbon, chromium, aluminium and titanium in the ESR ingot are found to be within the range of ± 0.01, ± 0.12, ± 0.008 and ± 0.01% respectively. Silicon and manganese show a loss of 0- 55 and 2-13% respectively whereas the degree of desulphurization is in the range of 0 (in Ar shield) to 52 (in air). The lower carbon and chromium content of the electrode than the aimed value can be corrected by adding ferrochromium in-situ during ESR. The recovery of carbon from FeCr was nearly 100% in most of the melts while the recovery of chromium varied over a fairly wide range. The distributions of carbon and chromium are also uniform along the height and width of ESR ingots. The recovery of the inoculant titanium was relatively low at the bottom of the ingot and it increases with height and reached a constant value above 100-150 mm height. For the same addition of titanium, its recovery decreases during ESR with argon shielding. © Metallurgical and Mining Industry.
Comparison of Cooling Behaviour of Carbon Steels in Polymer, Oil and Carbonated Quench Media
(Springer, 2019) Mathews, N.G.; Pranesh Rao, K.M.P.; Nayak, U.V.; Prabhu, N.
Cooling behaviour of steels in quench media is of great importance as this controls phase transformations, heat transfer and the stress evolution. The heat extraction ability of each quenchant is different because of varying thermophysical properties and wetting behaviour. The quenchants should be selected in such a way that they provide uniform cooling of steel. In the present investigation, quenching experiments were carried out with Inconel 600, EN19, EN24, EN31 steel grades in distilled water, servo oil, carbonated distilled water and 10% PAG. The cooling curve analysis of the quenching process was carried out with temperature data recorded during quenching. This measured temperature–time data were used to estimate the heat flux by inverse modelling without considering the effect of phase transformation. The crack propensity was quantified using the quench uniformity ratio. The hardness distribution observed during quenching in carbonated distilled water was observed to be more uniform compared to other quench media. © 2019, The Indian Institute of Metals - IIM.
Estimation of spatially dependent heat flux transients during quenching of inconel probe in molten salt bath
(2017) Pranesh, Rao, K.M.; Prabhu, N.
Several industrial heat treatment processes, such as martempering and austempering, require a quench bath to be maintained at a temperature ranging between 150 C 600 C. Molten salts, molten alkali, and hot oils are the preferred quenchants for these processes. Molten salts and molten alkali are preferred over hot oil because they possess properties like wide operating temperature range, excellent thermal stability, and tolerance for contaminants. In the present work, the performance of a molten potassium nitrate (KNO3) quench bath was analyzed with an Inconel probe that measured 60 mm in height and 12.5 mm in diameter. The probe was heated to 850 C and subsequently quenched in a bath maintained at 450 C. Cooling curves at different locations of the probe were recorded using the K-type thermocouples inserted into the probe. Spatially dependent transient heat flux at the metal/quenchant interface was estimated using inverse heat conduction technique. The existence of two stages of quenching boiling stage and convection stage was confirmed by analyzing the heat flux. The heat transfer coefficient was calculated based on heat flux obtained by the inverse method. The nonuniformity in heat transfer along the length of the probe was quantified by calculating the range of surface temperatures at each instance. The hardness distribution in an AISI 4140 steel was predicted using the temperature distribution in the Inconel probe and obtained using inverse method. Uneven distribution of hardness predicted in the probe was attributed to the nonuniform cooling of the probe during quenching. Copyright 2017 by ASTM International.
Heat transfer during quenching in graphene and multiwall carbon nanotubes nanofluids under agitated quench conditions
(American Scientific Publishers order@aspbs.com, 2019) Vignesh Nayak, U.; Prabhu, N.
Distilled water and aqueous graphene nanofluids of concentrations 0.01, 0.1 and 0.3 vol.% and MWCNT nanofluids of 0.0003, 0.003 and 0.3 vol.% were used as quench media and studied their heat transfer characteristics. ISO 9950 inconel metal probe was used to obtain the thermal history during quenching. The quenching media were agitated in a standard Tensi agitation system at impeller speeds of 0, 500, 1000 and 1500 rpms. Spatiotemporal heat flux was obtained by inverse heat conduction method. The rewetting characteristics of nanofluids were obtained and compared with distilled water. Heat transfer analysis showed highest mean heat flux of 3.23 MW/m2 and fastest heat extraction with 0.1 vol.% graphene nanofluid. © 2019 by American Scientific Publishers.
Novel chromeno [2,3-b]-pyrimidine derivatives as potential anti-microbial agents
(2010) Sankappa, Rai, U.; Isloor, A.M.; shetty, P.; Vijesh, A.M.; Prabhu, N.; Isloor, S.; Thiageeswaran, M.; Fun, H.-K.
An efficient, microwave irradiated synthesis of novel chromeno[2,3-b]-pyrimidine derivatives was carried out. 2-Amino-3,4-dihydro-2H-chromene-3-carbonitrile was converted into imine using N,N-Dimethylacetaldehyde dimethylacetal to give the core intermediate, which was used for the preparation of chromenopyrimidine library, using acetic acid and different amine in microwave irradiation for 5 min. Structures of newly synthesized compounds were confirmed by spectral studies. Compound 6g was characterized by single crystal X-ray analysis. All the compounds were also screened for their anti-microbial activity. Few of the compounds are found to be potential antimicrobials. 2010 Elsevier Masson SAS. All rights reserved.
Novel chromeno [2,3-b]-pyrimidine derivatives as potential anti-microbial agents
(2010) Sankappa Rai, U.; Isloor, A.M.; Shetty, P.; Vijesh, A.M.; Prabhu, N.; Isloor, S.; Thiageeswaran, M.; Fun, H.-K.
An efficient, microwave irradiated synthesis of novel chromeno[2,3-b]-pyrimidine derivatives was carried out. 2-Amino-3,4-dihydro-2H-chromene-3-carbonitrile was converted into imine using N,N-Dimethylacetaldehyde dimethylacetal to give the core intermediate, which was used for the preparation of chromenopyrimidine library, using acetic acid and different amine in microwave irradiation for 5 min. Structures of newly synthesized compounds were confirmed by spectral studies. Compound 6g was characterized by single crystal X-ray analysis. All the compounds were also screened for their anti-microbial activity. Few of the compounds are found to be potential antimicrobials. © 2010 Elsevier Masson SAS. All rights reserved.
Quench cooling performance-hardness correlation for AISI 1045 and 1090 steels
(ASTM International, 2019) Nayak, U.V.; Prabhu, N.
Heat transfer and microstructure evolution during quenching of AISI 1045 and 1090 steels in vegetable oils was investigated. To simulate the industrial quench heat treatment, reference probes made of medium and high carbon steels were quenched, and heat flux transients were estimated by taking into account the phase transformation. The cooling curves obtained with reference probes made from AISI 1045 and AISI 1090 steels showed kinks indicating enthalpy change accompanied with phase transformations during continuous cooling. This was reflected in the estimated heat flux curves. The section thickness effect on heat flux transients was examined by using probes of diameters 25 mm and 50 mm. The cooling rates measured at various locations across the section diameter of reference probes were related to the hardness using the quench factor technique. The heat transfer characteristics of the quench media, the evolved microstructure, and the resulting hardness were in complete agreement. © 2019 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959.
The effect of multi-walled carbon nanotubes reinforcement and multiple reflow cycles on shear strength of SAC305 lead-free solder alloy
(ASTM International, 2019) Tikale, S.; Prabhu, N.
In this study, the effect of multi-walled carbon nanotubes (MWCNT) reinforcement on joint shear strength and microstructural development of tin-3.0silver-0.5copper (SAC305)/ copper solder joint subjected to multiple reflow cycles was investigated. The MWCNT-reinforced SAC305 solder systems (SAC305-x MWCNT; x = 0.01, 0.05, 0.1, and 0.5 wt.%) were developed by a mechanical dispersion method. The microstructural, mechanical, and melting properties of SAC305 composite solders were evaluated as a function of different wt.% of MWCNT addition. The melting behavior of composite solders was analyzed using differential scanning calorimetry. The morphology and intermetallic compound growth at the solder joint interface were studied using scanning electron microscopy. The copper/solder/ copper micro-lap-shear solder joint specimens reflowed for multiple reflow cycles were systematically characterized to evaluate the joint shear strength. The results showed that the reinforcement in the range of 0.01-0.05 wt.% of MWCNT resulted in the improvement of joint shear strength and better wettability compared to plain SAC305 solder alloy. Amongst all compositions analyzed, SAC305-0.05MWCNT nanocomposite suppressed the intermetallic compound layer growth effectively leading to improvement in the joint shear strength under multiple reflow cycles. © 2019 by ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959
The Effect of Thermal Ageing on Solder/Substrate Interfacial Microstructures During Reflow of Sn–37Pb and Sn–3Ag–0.5Cu
(Springer, 2019) Satyanarayan, S.; Kumarswamy, M.C.; Prabhu, N.
In the current study, the influence of thermal ageing on evolution of microstructures in the interfacial region between solders (Sn–37Pb, Sn–3.5Ag–0.5Cu) and copper substrates was investigated. Pb-containing and Pb-free solders were reflowed on Cu substrates at 230 °C for 15 min and were isothermally aged at 100 °C for 24 h. As-reflowed Sn–Pb solder/Cu substrate interfacial region exhibited continuous and layered type of IMC at the interface, and this IMC morphology changed to scallop type with isothermal ageing. SAC solder/Cu as-reflowed samples showed continuous and needle-shaped Cu6Sn5 and Ag3Sn IMCs at the interface. However, in an isothermally aged condition, plate-shaped Cu6Sn5 and flower-shaped Ag3Sn IMCs were found inside the solder matrix. Scanning electron microscopic (SEM) study showed that the thickness of Cu6Sn5 IMC was higher in reflowed Sn–Pb/Cu region than in SAC/Cu region. © 2019, The Indian Institute of Metals - IIM.
Wettability, Interfacial Intermetallic Growth and Joint Shear Strength of Eutectic Sn–Cu Solder Reflowed on Bare and Nickel-Coated Copper Substrates
(Springer, 2019) Sona, M.; Tikale, S.; Prabhu, N.
In the present study, wettability, interfacial intermetallic growth and shear strength of Sn–Cu eutectic solder solidified on bare as well as nickel-coated copper substrates were examined. Sn–0.7Cu solder was reflowed over the substrate for reflow times ranging from 10 to 500 s at 270 °C. Samples were cooled by quenching in water. The wetting behavior was similar on both the substrates. The corresponding time period to the end of gravity zone (Tgz) was measured from the relaxation curve obtained from wetting studies. Tgz was found to be 25 s for Sn–0.7Cu on bare and 50 s on Ni-coated copper substrates. The intermetallic compound layer thickness was fitted to a growth model to study the growth kinetics. The integrity of solder/substrate joint was assessed by performing ball as well as single-lap joint shear tests. The shear strength was found to be maximum at Tgz for all solder/substrate systems. © 2019, The Indian Institute of Metals - IIM.
Wettability, Interfacial Intermetallic Growth and Joint Shear Strength of Eutectic Sn�Cu Solder Reflowed on Bare and Nickel-Coated Copper Substrates
(2019) Sona, M.; Tikale, S.; Prabhu, N.
In the present study, wettability, interfacial intermetallic growth and shear strength of Sn�Cu eutectic solder solidified on bare as well as nickel-coated copper substrates were examined. Sn�0.7Cu solder was reflowed over the substrate for reflow times ranging from 10 to 500�s at 270��C. Samples were cooled by quenching in water. The wetting behavior was similar on both the substrates. The corresponding time period to the end of gravity zone (Tgz) was measured from the relaxation curve obtained from wetting studies. Tgz was found to be 25�s for Sn�0.7Cu on bare and 50�s on Ni-coated copper substrates. The intermetallic compound layer thickness was fitted to a growth model to study the growth kinetics. The integrity of solder/substrate joint was assessed by performing ball as well as single-lap joint shear tests. The shear strength was found to be maximum at Tgz for all solder/substrate systems. � 2019, The Indian Institute of Metals - IIM.