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    Mechanical and wear behavior of alloyed gray cast iron in the quenched and tempered and austempered conditions
    (01-08-2011)
    Balachandran, G.
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    Vadiraj, Aravind
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    Kazuya, Ekusa
    Three groups of hypereutectic cast irons alloyed with Cu, Ni and microalloying additive like Ti and Nb were examined for its hardness and wear resistance in the austempered (360 °C/3. h) and quenched and tempered conditions at varying tempering temperatures. It is observed that the cast irons in the quenched and tempered condition showed good wear resistance and moderate hardness at 400 °C. This was comparable with the wear resistance in austempered condition. The study also showed that in quenched and tempered condition, increasing Cu content in cast irons improved its wear resistance moderately while increasing Ni content has decreased its wear resistance. The presence of strong carbide formers (Nb, Ti) did not give significant improvement in wear resistance in quenched and tempered condition. Even in austempered alloys, higher Cu content increases its wear resistance and higher Ni content decreases their wear resistance. The austempered alloys showed ausferritic microstructure with 20% austenite phase which enhances wear resistance through transformation induced plasticity effect. On the other hand, the quenched and tempered alloys showed good wear resistance at 400. °C due to fine tempered carbides in the matrix. © 2011 Elsevier Ltd.
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    Structure-property correlation in austempered alloyed hypereutectic gray cast irons
    (15-01-2010)
    Vadiraj, Aravind
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    Balachandran, G.
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    Gopalakrishna, B.
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    Prabhakara Rao, K.
    The austempering behavior of a series of hypereutectic alloyed gray iron compositions with carbon equivalent from 4.37 to 5.14 was studied to understand the influence of microstructure on its mechanical and wear properties. The alloying elements in the alloys included Ni, Mo, Cr and inoculation by micro-constitution of Ti, Nb and Ce. The alloys were austempered at 360 °C and upper bainitic type feathery ferrite was observed in the matrix. While the graphite content determined by optical metallography varied between 16 and 24 vol%. The volume of austenite determined by XRD analysis showed values between 20 and 26%. The ferrite lath size was determined using XRD peak broadening. The tensile property varying between 188 and 270 MPa, showed no significant variation with volume percentage of carbon or austenite in the ausferrite. However the wear rate varying between 0.5 and 2.6 × 10-7 g/Nm, showed a decreasing trend with graphite content attributed to the higher lubricating effect of released carbon during sliding wear. The specific wear rate of hypereutectic alloys, increased with increasing ferrite lath size due to enhanced softer ferrite phase on the sliding surface. The wear rate was found to increase with volume of austenite, austenite carbon content and austenite lattice parameter, which is attributed to increased stability of austenite against strain induced martensite formation and the increased formation of bainitic carbides in the second stage tempering. The various technical aspects in correlating the microstructure with the mechanical and wear properties of hypereutectic austempered gray iron are described. © 2009 Elsevier B.V. All rights reserved.
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    Mechanical and wear behavior of quenched and tempered alloyed hypereutectic gray cast iron
    (01-04-2011)
    Vadiraj, Aravind
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    Balachandran, G.
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    Kazuya, Ekusa
    The effect of tempering temperature (100-600 °C) on the hardness and wear resistance of a series of quenched and tempered hypereutectic alloyed gray cast irons has been studied in this work. Hardness was observed decreases with increase in tempering temperature and this trend is influenced by alloying additions and the volume of graphite flakes. Hardness of alloyed gray irons is also influenced by solid solution strengthening of tempered ferrite and carbide content and their distribution. The wear loss of alloyed cast irons was found to be lowest at a tempering temperature of 100 °C and 400 °C. The optimum tempering temperature is 400 °C with moderate hardness and low wear rate. This has been attributed to strengthening of the matrix at this temperature. Beyond 400 °C, the wear rate increases significantly due to carbide coagulation. © 2010 Elsevier Ltd.
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    Mechanical and wear behaviour of alloyed hypereutectic grey cast iron
    (01-07-2010)
    Vadiraj, A.
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    Balachandran, G.
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    Gopalakrishna, B.
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    Rao, D. V.
    Alloyed grey cast iron is an important automotive material used in clutch and brake applications. In order to understand the influence of microalloying additives on the graphitic morphology, mechanical and wear behaviour, a series of microalloyed cast iron melts were taken. The laboratory scale ingots made were characterised for microstructure, mechanical properties and wear behaviour. All the cast irons made were hypereutectic with a microstructure consisting of class A type graphite in a pearlitic matrix with eutectic grain boundary carbides. The microalloyed cast irons showed two- to threefold improved wear resistance over a base unalloyed material at comparable mechanical strengths. The wear loss was found to be linear with increasing sliding distance, and the wear resistance is attributed to the combined influence of dense pearlitic matrix with carbides and good distribution of graphite flakes. Cast iron microalloyed with Ni (0.62%) with Ce inoculation showed best overall properties compared to other alloys. © 2010 Maney Publishing.
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    Wear behavior of alloyed hypereutectic gray cast iron
    (01-03-2010)
    Vadiraj, Aravind
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    Balachandran, G.
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    Gopalakrishna, B.
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    Venkateshwara Rao, D.
    Alloyed gray cast iron of varying compositions was studied for their wear behavior. In general, the alloyed gray irons studied have higher graphite volume fraction (∼20%) with Type-A graphite flake morphology. Base cast iron showed two to three times higher wear rates than the alloyed gray irons. Tensile strength and wear rates show decreasing trend with increase in graphite and carbide volume fraction. Wear track analysis shows three body abrasive wear mode resulting in debris generation and smudging along the wear tracks. The graphite gets released during sliding to form films along the wear tracks and then forms irregular debris. © 2009 Elsevier Ltd. All rights reserved.
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    Mechanical behaviour of an austempered ductile iron
    (01-10-2010)
    Dhanasekaran, S.
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    Vadiraj, Aravind
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    Balachandran, G.
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    Austempering of a ferrite-pearlitic grade of ductile iron was carried out to assess the potential use of the materialfor crank shaft application reported. A commercial material was austempered at 340?C to realize the properties. The austempered ductile iron gave good strength although the ductility values were lower. The material developed had complete ausferritric structure free of pearlite. The various phase constitution and phase transformation associated with the treatment and during mechanical deformation was examined. Using XRD analysis the volume fraction of the austenite in the matrix was estimated. The various aspects of processing a commercial cast iron during ausetmpering, the phase transformation, microstructural evolution have been examined along with the property of the material. The mechanical behaviour of the material andthe scope for further improvement is discussed. © 2010 TIIM,India.
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    Studies on mechanical and wear properties of alloyed hypereutectic gray cast irons in the as-cast pearlitic and austempered conditions
    (01-02-2010)
    Vadiraj, Aravind
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    Balachandran, G.
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    Gopalakrishna, B.
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    Prabhakara Rao, K.
    The mechanical and wear behavior of a series of as-cast gray iron alloys were compared with properties obtained after austempering at 360 °C. The austempered alloys showed equivalent or moderately enhanced mechanical strength than the as-cast pearlitic gray irons. The specific wear rates of all the austempered alloys decreased significantly by 7-15 times and friction coefficient reduced by 30-50% compared to pearlitic alloyed gray irons. The dry sliding wear studies of as-cast alloys against high carbon 1%Cr through-thickness hardened steel shows that the specific wear rate ranged from 5.6 to 19.1 (×10-7) g/Nm with friction coefficient from 0.55 to 0.7. While, the austempered alloys showed wear rates from 0.5 to 2.6 (×10-7) g/Nm with friction coefficient ranging from 0.23 to 0.4. The improved wear resistance was attributed to the layer wise surface phase transformation associated with strain induced martensite formation of the stabilized austenite in the austempered matrix, lubrication of the interface by the flake graphite and better heat conduction from the rubbing interface by higher volume fraction of the graphite. Cast iron alloyed with Ni shows enhanced mechanical properties and wear resistance. The tensile strength shows decreasing trend with increase in carbon equivalent and graphite volume. The specific wear rate and friction coefficient shows decreasing trend with increase in hardness and graphite flake volume. © 2009 Elsevier Ltd. All rights reserved.
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    Effect of misch metal inoculation on microstructure, mechanical and wear properties of hypoeutectic gray cast irons
    (01-12-2009)
    Vadiraj, Aravind
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    Balachandran, G.
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    Alloyed gray cast irons were made with and without misch metal inoculation (0.1%). The mechanical and wear properties were compared with conventional gray cast iron used for a typical clutch application in heavy commercial vehicles. Alloyed gray iron without misch metal showed higher volume fraction of pearlite (89%) and lower flake graphite (11%). Misch metal inoculated gray irons showed higher volume of flake graphite (15%) with 85% pearlite as matrix. Alloyed gray irons produced tensile strength from 300 to 344 MPa and hardness in the range of 221-247 VHN. Misch metal inoculation has slightly increased the graphite volume (40-60%) with corresponding decrease in strength and hardness (9-13%) in alloyed gray irons. The specific wear rates of all alloyed gray irons are significantly lower (<34%) compared to unalloyed base at two different sliding speeds (1.6 m/s and 2.5 m/s). The friction coefficient is less than 0.4 for alloyed gray irons as against 0.5-0.7 for unalloyed base gray iron at both the sliding speeds. This is attributed to the presence of alloying additives within the matrix which resists adhesive and abrasive wear loss. Among the inoculated alloyed gray irons, the alloy with lower S content (0.08%) showed higher wear rate at higher sliding speed due to lower graphite flake density compared to higher S containing iron (0.12%). This indicates that the wear rate is influenced by the amount of graphite which is released into the interface during sliding to provide lubrication and reduce wear. Inoculation with rare earth misch metal has a positive influence over graphite morphology in gray iron. © 2009 Elsevier Ltd. All rights reserved.
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    Structure and property studies on austempered and as-cast ausferritic gray cast irons
    (01-10-2010)
    Vadiraj, Aravind
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    Balachandran, G.
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    A high-strength and wear-resistant alloyed gray iron with ausferritic microstructure on solidification directly from molten condition could be made in a Ni and Mo alloyed gray cast iron. The as-cast ausferritic cast iron was compared with two conventionally austempered gray iron with and without Ni and Mo additions. The various phase constitution and volume fractions were analyzed using optical, SEM and XRD analyses. The various aspects of the alloy chemistry and processing conditions have been correlated with the microstructure and mechanical properties obtained. The analysis showed that the Ni-Mo alloyed austempered gray iron and the directly as-cast austempered gray iron had similar phase constitutions. The strength of the direct as-cast alloy with ausferritic microstructure was higher than the others due to its higher austenite content and carbide distribution. The wear rate of the conventionally austempered Ni and Mo containing alloy and direct as-cast ausferritic alloys is 20% of the austempered gray iron without Ni and Mo with friction coefficient less than 0.4. © ASM International.