Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
6 results
Search Results
Item Determination of wetting behavior, spread activation energy, and quench severity of bioquenchants(2007) Prabhu, K.N.; Fernandes, P.An investigation was conducted to study the suitability of vegetable oils such as sunflower, coconut, groundnut, castor, cashewnut shell (CNS), and palm oils as quench media (bioquenchants) for industrial heat treatment by assessing their wetting behavior and severity of quenching. The relaxation of contact angle was sharp during the initial stages, and it became gradual as the system approached equilibrium. The equilibrium contact angle decreased with increase in the temperature of the substrate and decrease in the viscosity of the quench medium. A comparison of the relaxation of the contact angle at various temperatures indicated the significant difference in spreading of oils having varying viscosity. The spread activation energy was determined using the Arrhenius type of equation. Oils with higher viscosity resulted in lower cooling rates. The quench severity of various oil media was determined by estimating heat-transfer coefficients using the lumped capacitance method. Activation energy for spreading determined using the wetting behavior of oils at various temperatures was in good agreement with the severity of quenching assessed by cooling curve analysis. A high quench severity is associated with oils having low spread activation energy. © 2007 THE MINERALS, METALS & MATERIALS SOCIETY and ASM INTERNATIONAL.Item Heat transfer during quenching and assessment of quench severity - A review(ASTM International, 2010) Prabhu, K.N.; Fernandes, P.In the heat treatment of steel, quenching is done to prevent ferrite or pearlite formation and allows formation of bainite and martensite. For a particular grade of steel, the effectiveness of quenching depends on the cooling characteristics of the quenching medium. The cooling rate is not a constant throughout the quenching process; instead it varies depending upon the various stages that occur during the quenching process. Knowledge of heat transfer during various stages of quenching and kinetics of wetting of the quench medium is fundamental to the understanding of the relationship between material, quench medium, microstructure, and properties. In this paper the characteristics of various quench media, the effect of process parameters on quenching, mechanisms of thermal transport, methods of assessing severity of quenching, and techniques of estimation of heat transfer coefficients are reviewed. An attempt is also made to highlight the importance of wetting kinetics of liquid media on quenching. Copyright © 2009 by ASTM International.Item Heat transfer during quenching and assessment of quench severity-A review(2009) Prabhu, K.N.; Fernandes, P.In the heat treatment of steel, quenching is done to prevent ferrite or pearlite formation and allows formation of bainite and martensite. For a particular grade of steel, the effectiveness of quenching depends on the cooling characteristics of the quenching medium. The cooling rate is not a constant throughout the quenching process; instead it varies depending upon the various stages that occur during the quenching process. Knowledge of heat transfer during various stages of quenching and kinetics of wetting of the quench medium is fundamental to the understanding of the relationship between material, quench medium, microstructure, and properties. In this paper the characteristics of various quench media, the effect of process parameters on quenching, mechanisms of thermal transport, methods of assessing severity of quenching, and techniques of estimation of heat transfer coefficients are reviewed. An attempt is also made to highlight the importance of wetting kinetics of liquid media on quenching. Copyright © 2009 by ASTM International.Item 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.Item 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.Item Comparative study of heat transfer and wetting behaviour of conventional and bioquenchants for industrial heat treatment(2008) Fernandes, P.; Prabhu, K.N.An investigation was conducted to study the suitability of vegetable oils as bioquenchants for industrial heat treatment. The study involved the assessment of the severity of quenching and wetting behaviour of conventional and vegetable oil quench media. Quench severities of sunflower, coconut and palm oils were found to be greater than mineral oil. The quench severity of aqueous media is greater than oil media although their wettability is poor as indicated by their higher contact angles. A dimensionless contact angle parameter defined in this work is found to be a better parameter to compare the wetting behaviour with heat transfer. © 2007 Elsevier Ltd. All rights reserved.