Journal Articles

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Author: search.filters.author.Prabhu, K.N.Subject: search.filters.subject.Quenching

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    Effect of surface roughness on metal/quenchant interfacial heat transfer and evolution of microstructure
    (Elsevier Ltd, 2007) Prabhu, K.N.; Fernandes, P.
    In the present work, the effect of surface roughness on heat transfer rates in various quenchants was determined. The heat flux transients at the probe/quenchant interface were estimated by inverse modeling of heat conduction during end quenching of stainless steel probes with three different surface roughness (grooved, Ra = 3.0 and 1 ?m). Heat transfer during quenching was correlated with the hardness obtained for medium carbon AISI 1060 steel specimens. The effect of surface roughness on heat transfer rate during quenching in water and brine was significant for rough surface whereas its effect on heat transfer rate is only marginal in high viscosity oil quenchants. A fully martensitic structure was observed with grooved surface subjected to water quenching. With a smooth surface a mixed microstructure was obtained. The oil quenched specimens were found to be less sensitive to surface roughness. © 2005 Elsevier Ltd. All rights reserved.
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    Effect of section size and agitation on heat transfer during quenching of AISI 1040 steel
    (2007) Fernandes, P.; Prabhu, K.N.
    In the present work an attempt has been made to determine the heat flux transients during quenching of Ø28 mm × 56 mm height and Ø44 mm × 88 mm height AISI 1040 steel specimens during lateral quenching in brine, water, palm oil and mineral oil. The heat flux transients were estimated by inverse modeling of heat conduction. The variation of heat flux transients with surface temperature for different quenching media is investigated. Higher peak heat flux transients are obtained for 28 mm diameter specimen than 44 mm diameter specimen during quenching in aqueous media. However quenching with oil media shows opposite results. Agitation of quenching medium increases the peak heat flux during the quenching of steel specimen in all the quenching media. Peak hardness is obtained at the surface and with smaller diameter specimens during agitation. © 2006 Elsevier B.V. All rights reserved.
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    Nanoquenchants for industrial heat treatment
    (2008) Prabhu, K.N.; Fernades, P.
    The present work outlines the possibility of using nanofluids for industrial heat treatment. Development of nanoquenchants having (i) high quench severity for enhancement of heat transfer for thick sections with low quench sensitivity and (ii) low cooling severity for thin sections with high quench sensitivity would be extremely useful to the heat treating community. The temperature dependent heat transfer coefficient and the wettability of the medium are the two important parameters that can be used to characterize a nanoquenchant to assess its suitability for industrial heat treatment. © 2007 ASM International.
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    Severity of quenching and kinetics of wetting of nanofluids and vegetable oils
    (2009) Jagannath, V.; Prabhu, K.N.
    In the present work, the suitability of vegetable oil blends with mineral oil and alumina based nanofluids as quench media for industrial heat treatment was investigated. Sunflower oil, palm oil, and mineral oil were used for preparing the blends. Alumina based nanofluids of varying concentrations ranging from 0.01-4 % were used. The size of alumina particles was about 50 nm. The severity of quenching and heat transfer coefficients were estimated during quenching of copper probes. Heat transfer coefficients were estimated using a lumped heat capacitance model. The static contact angle was measured on copper substrates having a surface texture similar to the probes used for estimation of heat transfer coefficients. A dynamic contact angle analyzer was used for this purpose. The measured contact angles of nanofluids on copper were high compared to oils, indicating poor wetting by quench media that are polar in nature. Wetting characteristics had a significant effect on heat transfer coefficients estimated during quenching. Copyright © 2009 by ASTM International.
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    Comparison of Grossmann and lumped heat capacitance methods for assessment of heat transfer characteristics of quench media
    (2011) Prabhu, K.N.; Ali, I.
    The suitability of Grossmann and lumped heat capacitance (LHC) methods for estimation of quench severity of nanofluids, brine solutions and a laboratory detergent based medium was investigated. The study involved the assessment of the effect of section thickness of the probe on heat transfer coefficients for different quench media. Computer aided cooling curve analysis during quenching of type 304 stainless steel probes was carried out. The measured thermal history data were used to estimate heat transfer coefficients by Grossmann and LHC methods. The LHC method based on a 10 mm diameter stainless steel probe was found to be applicable for characterising media having quench severity less than 20 m-1. Although Grossmann method is based on the concept of average heat transfer coefficient, it can be used for quench media having varying severity of quenching. Grossmann method is found to be more sensitive to the effect of section thickness on heat transfer. © 2011 IHTSE Partnership.
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    Characterisation of water base copper nanoquenchants by standard cooling curve analysis
    (2011) Ramesh, G.; Prabhu, K.N.
    Water base copper nanofluids having concentrations varying from 0?001 to 0?1 vol.-% were prepared and used as quench media for immersion quenching. Cooling curve analyses were carried out by using a standard ISO/DIS 9950 quench probe. An inverse heat conduction model is employed to estimate the metal/nanoquenchant interfacial heat flux transients from the measured temperature field and thermophysical properties of the quench probe material. The addition of copper nanoparticles had a significant effect on the occurrence of the vapour blanket stage and nucleate boiling stage. Furthermore, all six cooling curve parameters were found to be altered by adding nanoparticles to water. The contact angle of water decreased from 67 to 39° by adding 0?1 vol.-% of copper nanoparticles indicating the improved wettability of nanofluids. The heat flux curve shows a maximum initially then drops rapidly during quenching. The peak cooling rate and heat flux of water increased by adding copper nanoparticles up to 0?01 vol.-%. Both parameters decreased with further increase in concentration of nanoparticles. The results suggest that the quench severity of water could be altered by adding copper nanoparticles. © 2011 IHTSE Partnership.
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    Effect of addition of aluminum nanoparticles on cooling performance and quench severity of water during immersion quenching
    (ASTM International, 2012) Ramesh, G.; Prabhu, K.N.
    In the present work, the effect of the addition of aluminum nanoparticles in concentrations varying from 0.001 to 0.5 vol. % on the cooling performance and quench severity of water during immersion quenching is investigated. The results of cooling curve analyses show that an increase in nanoparticle concentration increased the cooling rates at critical temperatures up to 0.05 vol. % and decreased them thereafter. The transition from the vapor blanket stage to the nucleate boiling stage was also altered by quenching in nanofluids. A finite difference heat transfer program was employed to generate cooling curves at different values of heat transfer coefficient from thermo-physical properties of the quench probe material. A Grossmann H quench severity versus cooling rate curve was established, and from this curve, the H factors of prepared nanofluids were estimated. An increase in nanoparticle concentration up to 0.05 vol. % resulted in an increase of the H value of water from 63 m -1 to 93 m-1, and any further increase in the concentration of nanoparticles resulted in a decrease in H. The results suggest both the enhancement and the deterioration of the cooling performance of water by the addition of aluminum nanoparticles. Copyright © 2012 by ASTM International.
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    Effect of addition of aluminum nanoparticles on cooling performance and quench severity of water during immersion quenching
    (2012) Ramesh, G.; Prabhu, K.N.
    In the present work, the effect of the addition of aluminum nanoparticles in concentrations varying from 0.001 to 0.5 vol. % on the cooling performance and quench severity of water during immersion quenching is investigated. The results of cooling curve analyses show that an increase in nanoparticle concentration increased the cooling rates at critical temperatures up to 0.05 vol. % and decreased them thereafter. The transition from the vapor blanket stage to the nucleate boiling stage was also altered by quenching in nanofluids. A finite difference heat transfer program was employed to generate cooling curves at different values of heat transfer coefficient from thermo-physical properties of the quench probe material. A Grossmann H quench severity versus cooling rate curve was established, and from this curve, the H factors of prepared nanofluids were estimated. An increase in nanoparticle concentration up to 0.05 vol. %resulted in an increase of the H value of water from 63 m 1 to 93 m 1, and any further increase in the concentration of nanoparticles resulted in a decrease in H. The results suggest both the enhancement and the deterioration of the cooling performance of water by the addition of aluminum nanoparticles. Copyright © 2012 by ASTM International.
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    Effect of boundary heat transfer coefficient and probe section size on cooling curves during quenching
    (ASTM International, 2012) Ramesh, G.; Prabhu, K.N.
    In the present work the effect of boundary heat transfer coefficient and section size of quench probe material on cooling curves was investigated by using finite difference heat transfer based SolidCast software. Simulations were carried out at different combinations of heat transfer coefficient and quench probe diameter and thermal history at the geometric center of the probe was estimated to generate cooling curves. Simulation results show that both boundary heat transfer coefficient and quench probe diameter had a significant effect on the average cooling rate. A relationship between Grossmann quench severity (H), thermal conductivity of material, size of the probe, and average cooling rate was established. By using this model, for a known quench medium, probe size, and material it is possible to predict the average cooling rate of the probe. On the other-hand, for a given material and required cooling rate, cooling severity required from the quench media could be predicted and accordingly an appropriate quench medium can be selected. © 2012 by ASTM International.
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    Wetting Behavior and Heat Transfer of Aqueous Graphene Nanofluids
    (Springer New York LLC barbara.b.bertram@gsk.com, 2016) Nayak, U.V.; Prabhu, K.N.
    Aqueous graphene nanofluids having concentrations 0.01, 0.1, and 0.3 vol.% were used as heat transfer media during quenching of ISO 9950 inconel alloy probe. Contact angle measurements were carried out to assess the wettability of graphene nanofluids. Nanofluids showed better wettability compared to base water with over 16% reduction in their contact angles. The cooling performance of the quench media was assessed by cooling curve analysis during quenching of an instrumented inconel probe from 860 °C into the quench medium. Recorded temperature readings showed longer vapor phase stage during quenching with nanofluids. The severity of nanofluids was found to be lower relative to water. During quenching with nanofluids, the estimated spatiotemporal heat flux transients at the metal/quenchant interface showed that more heat was removed during the vapor phase stage of cooling. The present study brings out the possibility of using stable water-graphene nanoplatelet suspensions for quench heat treatment of steel components requiring cooling severity between water and oil/polymer quenchants. © 2016, ASM International.