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  • 1.
    Sjögren, Torsten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Influences of the Graphite Phase on Elastic and Plastic Deformation Behaviour of Cast Irons2007Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The amount and morphology of the graphite phase largely controls the resulting properties of cast iron. For instance, in flake graphite cast irons the mechanical properties are low while the thermal conductivity is high. This is in contrast with spheroidal graphite cast irons where the mechanical properties are high and the thermal conductivity is low. These differences are due to the different graphite morphologies and must be accounted for in the design work and material selection of cast iron components. In this work the influence of the graphite phase on the elastic and plastic deformation behaviour of cast irons has been studied.

    The material grades studied originate from castings for marine diesel engine piston rings with different chemical analyses. Two groups of pearlitic cast iron materials were studied; one with differences in graphite morphology and one with grey irons that differed in graphite content. For these different material grades the mechanical properties were correlated to microstructural parameters. In addition to standard uniaxial tensile tests, acoustic emission measurements were used for the study of deformation.

    When studying the modulus of elasticity of the cast iron it was found that the modulus of elasticity of the inherent graphite phase depends on the roundness of the graphite particles and is due to the strong anisotropy of the graphite phase. A linear correlation between nodularity and the modulus of elasticity of the graphite phase was derived. This correlation made it possible to account for the anisotropy of the graphite phase in the model used. By applying the linear function when modelling the effective modulus of elasticity, a high accuracy between experimental and theoretical values was achieved.

    Another factor affecting the elastic response when subjecting a cast iron component to tensile load was found to be the plastic deformation that actually occurs at very low strains for all of the studied cast iron grades. It was observed that the plastic deformation in the low strain elastic region, quantified by using acoustic emission measurements, increased linearly with decreasing modulus of elasticity. These measurements showed that the amount of plastic deformation in the elastic region was largely controlled by the graphite morphology. It was concluded that as the roundness of the graphite particles increases, the plastic deformation activity in the elastic region decreases.

    The plastic deformation activity continued linearly into the pronounced plastic region of the tensile tests. A decrease in roundness or increase in graphite fraction resulted in an increase of the amount of plastic deformation and the strain hardening exponent. A

    dependence between strength coefficient and graphite fraction was observed. Models for the flow curves for pearlitic cast irons were developed and shown to accurately reproduce the observed experimental curves.

    The surveys performed and conclusions from this thesis will be helpful in the design of new cast iron materials.

    List of papers
    1. High Performance Piston Rings for Two-Stroke Marine Diesel Engines
    Open this publication in new window or tab >>High Performance Piston Rings for Two-Stroke Marine Diesel Engines
    2004 (English)In: Proceedings // 24th CIMAC World Congress on Combustion Engine Technology, 2004Conference paper, Published paper (Other academic)
    Abstract [en]

    The piston ring is a key component in a marine combustion engine. High mechanical loads, relatively high temperatures and corrosive gases and liquids influence its performance in terms of sealing capacity, wear of cylinder liner and the ring itself. Base material of the ring, coating technology and ring geometry design are discussed in the article.

    When tailoring cast iron materials suitable as piston ring base material two parameters are of importance; the morphology of the graphite and the constituents of the matrix. To optimize the properties of the cast iron a compromise is needed to achieve a satisfactory performance of the piston rings.

    Daros Piston Rings AB is currently developing a second generation of chromium-ceramic coating the so called Z-chrome. The objective of this project has been to increase the maximum operating temperature of the coating and leave the other characteristics of the coating unaffected. The difference between the commercial Daros coating Tritor® and the Z-chrome is the ceramic component included in the coated layer.

    Insufficient conformability of piston ring and liner geometry may produce a large local cylinder wall pressure which will destroy the oil film leading to uncontrolled wear and scuffing. Lack of conformability can also produce leakage paths for the combustion gases. Therefore a correct ring shape is of utmost importance. A new design philosophy designated OPCORE® has been developed and is presented here.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14415 (URN)
    Conference
    24th CIMAC World Congress on Combustion Engine Technology, June 7-11, Kyoto, Japan
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    2. Comparison of Mechanical Properties in Flake Graphite and Compacted Graphite Cast Irons for Piston Rings
    Open this publication in new window or tab >>Comparison of Mechanical Properties in Flake Graphite and Compacted Graphite Cast Irons for Piston Rings
    2004 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 17, no 2, p. 65-71Article in journal (Refereed) Published
    Abstract [en]

    Cast iron is often used as the piston ring material in marine diesel engines. The mechanical properties of cast irons are to a great extent governed by the size, distribution and shape of the incorporated graphite particles. In a set of experiments, the mechanical properties of a pearlitic grey cast iron and a pearlitic compacted graphite cast iron are compared. Both cast iron grades have a eutectic composition. The experiments confirm the importance of micro-yielding of the matrix at the tip of the graphite particles on the macroelastic behaviour of the studied cast irons. This applies especially for the flake graphite cast iron where the graphite tip is sharper and the matrix bridges between the graphite particles are shorter than in the case of the compacted graphite cast iron resulting in micro-yielding at the graphite tip at a very low macro-stress and macro-strain. The high local stresses at the graphite tips also result in the opening of the graphite cavities which is much more severe in the flake graphite cast iron than in the compacted graphite cast iron. The mechanical properties of the eutectic flake graphite cast iron are largely affected by the size and amount of the graphite particles. The smaller the graphite particles (faster solidification) in the microstructure, the lower the values of the mechanical properties. In compacted graphite cast iron, the macro-elastic behaviour is influenced by the matrix and the overall coarseness of the microstructure to a greater extent and the effect of the incorporated graphite particle size is much less pronounced.

    Keywords
    Mechanical properties, Eutectic pearlitic cast iron, Graphite shape, compacted graphite, Flake graphite, Micro-yelding
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14416 (URN)10.1179/136404604225017474 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    3. Modelling the Effect of Graphite Morphology on the Modulus of Elasticity in Cast Irons
    Open this publication in new window or tab >>Modelling the Effect of Graphite Morphology on the Modulus of Elasticity in Cast Irons
    2004 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 17, no 5, p. 271-279Article in journal (Refereed) Published
    Abstract [en]

    Nine grades of pearlitic cast iron containing different graphite morphologies (from flake, compacted and spheroidal) have been studied. The parameters investigated include the graphite aspect ratio, nodularity, graphite size and modulus of elasticity. These parameters have been correlated and compared with different existing bound and model equations. It has been found that the modulus of elasticity of the graphite phase increases as the aspect ratio and nodularity of the graphite increases, i.e.flake graphite gives a lower modulus of elasticity than spheroidal graphite. The experimental values of the modulus of elasticity show good agreement to bound and model equations, although flake graphite cast irons show higher deviation from the modelled values. An equation for the correlation between the graphite modulus of elasticity and the nodularity is presented. Introducing this linear correlation into an existing model for the determination of the effective modulus of elasticity gives a continuous function, including all grades of cast irons, with a very good agreement with experimental values. The modulus of elasticity of cast irons can be accurately predicted from both bound and especially model equations, using the aspect ratio and nodularity of the contained graphite particles. The fit is improved by using a modulus of elasticity of the graphite phase that is based on the graphite morphology, considering that the modulus of elasticity of the graphite is different in the basal and prismatic planes.

    Keywords
    Cast iron, Modulus of elasticity, Graphite morphology, Graphite aspect ratio, Compacted graphite, Flake graphite, Spheroidal graphite, Modelling
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14417 (URN)10.1179/136404604225022694 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    4. Studying Elastic Deformation Behaviour of Cast Irons by Acoustic Emission
    Open this publication in new window or tab >>Studying Elastic Deformation Behaviour of Cast Irons by Acoustic Emission
    2005 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 18, no 4, p. 249-256Article in journal (Refereed) Published
    Abstract [en]

    The deformation of metallic materials includes both an elastic and a plastic deformation. In the case of cast irons, the elastic region becomes less pronounced as the graphite changes from spheroidal to flake shaped, as observed in nodular and grey cast iron, respectively. The present study aims to correlate the shape of the graphite phase with the deformation behaviour, where the plastic deformation and other strain accommodating events are quantified by measurements of the acoustic emission events occurring in the interior of the material at loading. It also aims to explain how the appearance of cast iron stress–strain curves depends on the graphite morphology where, for instance, spheroidal graphite cast irons exhibit a seemingly linear elastic behaviour in contrast to flake graphite cast irons. The present study includes a series of pearlitic cast iron material grades with differences in nodularity and carbon equivalent, respectively. It is shown that as the roundness of the graphite phase increases, the ability to absorb energy increases. The measured acoustic emission indicates that plastic deformation occurs in the seemingly linear elastic region regardless of the cast iron grade, i.e. no cast iron grade exhibits perfect linear elasticity. The plastic deformation rate in the elastic region increases as the roundness of the graphite decreases and as the carbon equivalent increases. It is shown that the plastic deformation governs the resulting modulus of elasticity in all kind of cast irons, i.e. the modulus of elasticity decreases as the yielding of the material increases. The present study improves the understanding of the deformation behaviour in the elastic region of different cast irons. The survey shows that acoustic emission testing is a useful method when studying the deformation behaviour of cast irons.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14418 (URN)10.1179/136404605225023117 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    5. The Effect of Graphite Fraction and Morphology on the Plastic Deformation of Cast Irons
    Open this publication in new window or tab >>The Effect of Graphite Fraction and Morphology on the Plastic Deformation of Cast Irons
    2007 (English)In: Metallurgical and materials transactions. A, ISSN 1073-5623, Vol. 38, no 4, p. 840-847Article in journal (Refereed) Published
    Abstract [en]

    The plastic deformation behavior of cast irons, covering the majority of graphite morphologies, has not been comprehensively studied previously. In this investigation, the effect of graphite morphology and graphite fraction on the plastic deformation behavior of pearlitic cast irons has been evaluated. The investigation is based on tensile tests performed on various different cast iron grades, where the graphite morphology and volume fraction have been varied. Pearlitic steel with alloying levels corresponding to the cast irons were also studied to evaluate how the cast iron matrix behaves in tension without the effects of the graphite phase. It is concluded that as the roundness of the graphite phase increases, the strain hardening exponent decreases. This demonstrates that the amount of plastic deformation is higher in the matrix of lamellar cast iron grades compared to compacted and nodular cast iron grades. Furthermore, this study shows that the strength coefficient in flake graphite cast irons increases as the graphite fraction decreases due to the weakening effect of the graphite phase. This study presents relationships between the strain hardening exponent and the strength coefficient and the roundness and fraction of the graphite phase. Using these correlations to model the plastic part of the stress-strain curves of pearlitic cast irons, we were able to calculate curves in good agreement with experimentally determined curves, especially for gray cast irons and ductile iron.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14419 (URN)10.1007/s11661-007-9115-8 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2010-05-31
    6. Modelling the Effect of Graphite Morphology on the Deformation Behaviour of Cast Irons
    Open this publication in new window or tab >>Modelling the Effect of Graphite Morphology on the Deformation Behaviour of Cast Irons
    2006 (English)In: Eighth International Symposium on Science and Processing of Cast Iron, SPCI8, October 16-19, Beijing, China, 2006Conference paper, Published paper (Other academic)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14420 (URN)
    Available from: 2007-04-20 Created: 2007-04-20
    7. Modeling and Simulation of Elastic Properties in Cast Compacted Graphite Iron Engine Block
    Open this publication in new window or tab >>Modeling and Simulation of Elastic Properties in Cast Compacted Graphite Iron Engine Block
    2006 (English)In: MCWASP Conference XI, May 28-June 2, Opio, France, 2006Conference paper, Published paper (Refereed)
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14421 (URN)
    Available from: 2007-04-20 Created: 2007-04-20
    8. Study of the Mechanical and Thermal Properties of Pearlitic and Ferritic Cast Iron Matrices
    Open this publication in new window or tab >>Study of the Mechanical and Thermal Properties of Pearlitic and Ferritic Cast Iron Matrices
    2007 (English)In: GiessereiforschungArticle in journal (Refereed) Submitted
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14422 (URN)
    Available from: 2007-04-20 Created: 2007-04-20
  • 2.
    Sjögren, Torsten
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Modelling the Effect of Graphite Morphology on the Modulus of Elasticity in Cast Irons2004In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 17, no 5, p. 271-279Article in journal (Refereed)
    Abstract [en]

    Nine grades of pearlitic cast iron containing different graphite morphologies (from flake, compacted and spheroidal) have been studied. The parameters investigated include the graphite aspect ratio, nodularity, graphite size and modulus of elasticity. These parameters have been correlated and compared with different existing bound and model equations. It has been found that the modulus of elasticity of the graphite phase increases as the aspect ratio and nodularity of the graphite increases, i.e.flake graphite gives a lower modulus of elasticity than spheroidal graphite. The experimental values of the modulus of elasticity show good agreement to bound and model equations, although flake graphite cast irons show higher deviation from the modelled values. An equation for the correlation between the graphite modulus of elasticity and the nodularity is presented. Introducing this linear correlation into an existing model for the determination of the effective modulus of elasticity gives a continuous function, including all grades of cast irons, with a very good agreement with experimental values. The modulus of elasticity of cast irons can be accurately predicted from both bound and especially model equations, using the aspect ratio and nodularity of the contained graphite particles. The fit is improved by using a modulus of elasticity of the graphite phase that is based on the graphite morphology, considering that the modulus of elasticity of the graphite is different in the basal and prismatic planes.

  • 3.
    Sjögren, Torsten
    Linköping University, Department of Mechanical Engineering, Engineering Materials. Linköping University, The Institute of Technology.
    The influence of graphite morphology on the elastic behaviour of cast irons2005Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    The morphology of the graphite phase largely controls the resulting properties of different grades of cast iron. In flake graphite cast irons, the mechanical properties are low while the thermal conductivity is high. In contrast, with spheroidal graphite cast irons, the mechanical properties are high while the thermal conductivity is low. These differences must be accounted for in the design work of diesel engines when choosing the material grade of different components. In this work the influence of graphite morphology on the deformation behaviour of cast irons has been studied with an emphasis on the elastic region.

    The studied material grades originated from castings for marine diesel engine piston rings with different chemical analyses. This gave rise to six material grades with different nodularities and three material grades with different carbon equivalents. For these different material grades the mechanical properties were determined and the deformation behaviour was examined by means of mechanical testing and acoustic emission measurements. These data were correlated to microstructural parameters.

    When studying the modulus of elasticity it was found that the modulus of elasticity of the inherent graphite phase depends on the roundness of the graphite particles and is due to the different elasticity in the two main crystallographic directions of the graphite lattice. The graphite particles are structured in different ways in flake graphite and spheroidal graphite, which gives rise to different stiffness at loading. The modelling and experiments support the observation that the average modulus of elasticity of the graphite phase depends on the morphology. This improves the understanding of the differences in the modulus of elasticity of the different studied material grades. The correlation between the modulus of elasticity of the graphite phase and the bulk nodularity of the cast iron specimen was found to be linear. This linear function was used when modelling the effective modulus of elasticity of the different cast iron grades with very high accuracy between experimental and theoretical values.

    Another factor affecting the elastic response when subjecting a cast iron component to tensile load was found to be the plastic deformation that actually occurs at very low strains for all of the studied cast iron grades. lt was found that the plastic deformation in the low strain, elastic region governs the modulus of elasticity of cast irons. The plastic deformation in the seemingly elastic region was quantified by using acoustic emission measurements. These measurements showed that the amount of plastic deformation in the elastic region was largely controlled by the graphite morphology. It was concluded that, as the roundness of the graphite particles increases, the plastic activity in the elastic region decreases and the energy absorption ability increases.

    List of papers
    1. High Performance Piston Rings for Two-Stroke Marine Diesel Engines
    Open this publication in new window or tab >>High Performance Piston Rings for Two-Stroke Marine Diesel Engines
    2004 (English)In: Proceedings // 24th CIMAC World Congress on Combustion Engine Technology, 2004Conference paper, Published paper (Other academic)
    Abstract [en]

    The piston ring is a key component in a marine combustion engine. High mechanical loads, relatively high temperatures and corrosive gases and liquids influence its performance in terms of sealing capacity, wear of cylinder liner and the ring itself. Base material of the ring, coating technology and ring geometry design are discussed in the article.

    When tailoring cast iron materials suitable as piston ring base material two parameters are of importance; the morphology of the graphite and the constituents of the matrix. To optimize the properties of the cast iron a compromise is needed to achieve a satisfactory performance of the piston rings.

    Daros Piston Rings AB is currently developing a second generation of chromium-ceramic coating the so called Z-chrome. The objective of this project has been to increase the maximum operating temperature of the coating and leave the other characteristics of the coating unaffected. The difference between the commercial Daros coating Tritor® and the Z-chrome is the ceramic component included in the coated layer.

    Insufficient conformability of piston ring and liner geometry may produce a large local cylinder wall pressure which will destroy the oil film leading to uncontrolled wear and scuffing. Lack of conformability can also produce leakage paths for the combustion gases. Therefore a correct ring shape is of utmost importance. A new design philosophy designated OPCORE® has been developed and is presented here.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14415 (URN)
    Conference
    24th CIMAC World Congress on Combustion Engine Technology, June 7-11, Kyoto, Japan
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    2. Comparison of Mechanical Properties in Flake Graphite and Compacted Graphite Cast Irons for Piston Rings
    Open this publication in new window or tab >>Comparison of Mechanical Properties in Flake Graphite and Compacted Graphite Cast Irons for Piston Rings
    2004 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 17, no 2, p. 65-71Article in journal (Refereed) Published
    Abstract [en]

    Cast iron is often used as the piston ring material in marine diesel engines. The mechanical properties of cast irons are to a great extent governed by the size, distribution and shape of the incorporated graphite particles. In a set of experiments, the mechanical properties of a pearlitic grey cast iron and a pearlitic compacted graphite cast iron are compared. Both cast iron grades have a eutectic composition. The experiments confirm the importance of micro-yielding of the matrix at the tip of the graphite particles on the macroelastic behaviour of the studied cast irons. This applies especially for the flake graphite cast iron where the graphite tip is sharper and the matrix bridges between the graphite particles are shorter than in the case of the compacted graphite cast iron resulting in micro-yielding at the graphite tip at a very low macro-stress and macro-strain. The high local stresses at the graphite tips also result in the opening of the graphite cavities which is much more severe in the flake graphite cast iron than in the compacted graphite cast iron. The mechanical properties of the eutectic flake graphite cast iron are largely affected by the size and amount of the graphite particles. The smaller the graphite particles (faster solidification) in the microstructure, the lower the values of the mechanical properties. In compacted graphite cast iron, the macro-elastic behaviour is influenced by the matrix and the overall coarseness of the microstructure to a greater extent and the effect of the incorporated graphite particle size is much less pronounced.

    Keywords
    Mechanical properties, Eutectic pearlitic cast iron, Graphite shape, compacted graphite, Flake graphite, Micro-yelding
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14416 (URN)10.1179/136404604225017474 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    3. Modelling the Effect of Graphite Morphology on the Modulus of Elasticity in Cast Irons
    Open this publication in new window or tab >>Modelling the Effect of Graphite Morphology on the Modulus of Elasticity in Cast Irons
    2004 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 17, no 5, p. 271-279Article in journal (Refereed) Published
    Abstract [en]

    Nine grades of pearlitic cast iron containing different graphite morphologies (from flake, compacted and spheroidal) have been studied. The parameters investigated include the graphite aspect ratio, nodularity, graphite size and modulus of elasticity. These parameters have been correlated and compared with different existing bound and model equations. It has been found that the modulus of elasticity of the graphite phase increases as the aspect ratio and nodularity of the graphite increases, i.e.flake graphite gives a lower modulus of elasticity than spheroidal graphite. The experimental values of the modulus of elasticity show good agreement to bound and model equations, although flake graphite cast irons show higher deviation from the modelled values. An equation for the correlation between the graphite modulus of elasticity and the nodularity is presented. Introducing this linear correlation into an existing model for the determination of the effective modulus of elasticity gives a continuous function, including all grades of cast irons, with a very good agreement with experimental values. The modulus of elasticity of cast irons can be accurately predicted from both bound and especially model equations, using the aspect ratio and nodularity of the contained graphite particles. The fit is improved by using a modulus of elasticity of the graphite phase that is based on the graphite morphology, considering that the modulus of elasticity of the graphite is different in the basal and prismatic planes.

    Keywords
    Cast iron, Modulus of elasticity, Graphite morphology, Graphite aspect ratio, Compacted graphite, Flake graphite, Spheroidal graphite, Modelling
    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14417 (URN)10.1179/136404604225022694 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
    4. Studying Elastic Deformation Behaviour of Cast Irons by Acoustic Emission
    Open this publication in new window or tab >>Studying Elastic Deformation Behaviour of Cast Irons by Acoustic Emission
    2005 (English)In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 18, no 4, p. 249-256Article in journal (Refereed) Published
    Abstract [en]

    The deformation of metallic materials includes both an elastic and a plastic deformation. In the case of cast irons, the elastic region becomes less pronounced as the graphite changes from spheroidal to flake shaped, as observed in nodular and grey cast iron, respectively. The present study aims to correlate the shape of the graphite phase with the deformation behaviour, where the plastic deformation and other strain accommodating events are quantified by measurements of the acoustic emission events occurring in the interior of the material at loading. It also aims to explain how the appearance of cast iron stress–strain curves depends on the graphite morphology where, for instance, spheroidal graphite cast irons exhibit a seemingly linear elastic behaviour in contrast to flake graphite cast irons. The present study includes a series of pearlitic cast iron material grades with differences in nodularity and carbon equivalent, respectively. It is shown that as the roundness of the graphite phase increases, the ability to absorb energy increases. The measured acoustic emission indicates that plastic deformation occurs in the seemingly linear elastic region regardless of the cast iron grade, i.e. no cast iron grade exhibits perfect linear elasticity. The plastic deformation rate in the elastic region increases as the roundness of the graphite decreases and as the carbon equivalent increases. It is shown that the plastic deformation governs the resulting modulus of elasticity in all kind of cast irons, i.e. the modulus of elasticity decreases as the yielding of the material increases. The present study improves the understanding of the deformation behaviour in the elastic region of different cast irons. The survey shows that acoustic emission testing is a useful method when studying the deformation behaviour of cast irons.

    National Category
    Engineering and Technology
    Identifiers
    urn:nbn:se:liu:diva-14418 (URN)10.1179/136404605225023117 (DOI)
    Available from: 2007-04-20 Created: 2007-04-20 Last updated: 2013-11-28
  • 4.
    Sjögren, Torsten
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Holmgren, D.
    Rinvall, M.
    Study of the Mechanical and Thermal Properties of Pearlitic and Ferritic Cast Iron Matrices2007In: GiessereiforschungArticle in journal (Refereed)
  • 5.
    Sjögren, Torsten
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Svensson, Ingvar L.
    Högskolan i Jönköping, JTH, Maskinteknik.
    Modelling the Effect of Graphite Morphology on the Deformation Behaviour of Cast Irons2006In: Eighth International Symposium on Science and Processing of Cast Iron, SPCI8, October 16-19, Beijing, China, 2006Conference paper (Other academic)
  • 6.
    Sjögren, Torsten
    et al.
    Högskolan i Jönköping, JTH, Maskinteknik.
    Svensson, Ingvar L.
    Högskolan i Jönköping, JTH, Maskinteknik.
    Studying Elastic Deformation Behaviour of Cast Irons by Acoustic Emission2005In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 18, no 4, p. 249-256Article in journal (Refereed)
    Abstract [en]

    The deformation of metallic materials includes both an elastic and a plastic deformation. In the case of cast irons, the elastic region becomes less pronounced as the graphite changes from spheroidal to flake shaped, as observed in nodular and grey cast iron, respectively. The present study aims to correlate the shape of the graphite phase with the deformation behaviour, where the plastic deformation and other strain accommodating events are quantified by measurements of the acoustic emission events occurring in the interior of the material at loading. It also aims to explain how the appearance of cast iron stress–strain curves depends on the graphite morphology where, for instance, spheroidal graphite cast irons exhibit a seemingly linear elastic behaviour in contrast to flake graphite cast irons. The present study includes a series of pearlitic cast iron material grades with differences in nodularity and carbon equivalent, respectively. It is shown that as the roundness of the graphite phase increases, the ability to absorb energy increases. The measured acoustic emission indicates that plastic deformation occurs in the seemingly linear elastic region regardless of the cast iron grade, i.e. no cast iron grade exhibits perfect linear elasticity. The plastic deformation rate in the elastic region increases as the roundness of the graphite decreases and as the carbon equivalent increases. It is shown that the plastic deformation governs the resulting modulus of elasticity in all kind of cast irons, i.e. the modulus of elasticity decreases as the yielding of the material increases. The present study improves the understanding of the deformation behaviour in the elastic region of different cast irons. The survey shows that acoustic emission testing is a useful method when studying the deformation behaviour of cast irons.

  • 7.
    Sjögren, Torsten
    et al.
    Daros Piston Rings AB.
    Svensson, Ingvar L.
    Division of Component Technology, Jönköping University, Jönköping, Sweden.
    The Effect of Graphite Fraction and Morphology on the Plastic Deformation of Cast Irons2007In: Metallurgical and materials transactions. A, ISSN 1073-5623, Vol. 38, no 4, p. 840-847Article in journal (Refereed)
    Abstract [en]

    The plastic deformation behavior of cast irons, covering the majority of graphite morphologies, has not been comprehensively studied previously. In this investigation, the effect of graphite morphology and graphite fraction on the plastic deformation behavior of pearlitic cast irons has been evaluated. The investigation is based on tensile tests performed on various different cast iron grades, where the graphite morphology and volume fraction have been varied. Pearlitic steel with alloying levels corresponding to the cast irons were also studied to evaluate how the cast iron matrix behaves in tension without the effects of the graphite phase. It is concluded that as the roundness of the graphite phase increases, the strain hardening exponent decreases. This demonstrates that the amount of plastic deformation is higher in the matrix of lamellar cast iron grades compared to compacted and nodular cast iron grades. Furthermore, this study shows that the strength coefficient in flake graphite cast irons increases as the graphite fraction decreases due to the weakening effect of the graphite phase. This study presents relationships between the strain hardening exponent and the strength coefficient and the roundness and fraction of the graphite phase. Using these correlations to model the plastic part of the stress-strain curves of pearlitic cast irons, we were able to calculate curves in good agreement with experimentally determined curves, especially for gray cast irons and ductile iron.

  • 8.
    Sjögren, Torsten
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Vomacka, Peter
    Svensson, Ingvar L.
    Linköping University, Department of Management and Engineering, Energy Systems. Linköping University, The Institute of Technology.
    Comparison of Mechanical Properties in Flake Graphite and Compacted Graphite Cast Irons for Piston Rings2004In: International Journal of Cast Metals Research, ISSN 1364-0461, Vol. 17, no 2, p. 65-71Article in journal (Refereed)
    Abstract [en]

    Cast iron is often used as the piston ring material in marine diesel engines. The mechanical properties of cast irons are to a great extent governed by the size, distribution and shape of the incorporated graphite particles. In a set of experiments, the mechanical properties of a pearlitic grey cast iron and a pearlitic compacted graphite cast iron are compared. Both cast iron grades have a eutectic composition. The experiments confirm the importance of micro-yielding of the matrix at the tip of the graphite particles on the macroelastic behaviour of the studied cast irons. This applies especially for the flake graphite cast iron where the graphite tip is sharper and the matrix bridges between the graphite particles are shorter than in the case of the compacted graphite cast iron resulting in micro-yielding at the graphite tip at a very low macro-stress and macro-strain. The high local stresses at the graphite tips also result in the opening of the graphite cavities which is much more severe in the flake graphite cast iron than in the compacted graphite cast iron. The mechanical properties of the eutectic flake graphite cast iron are largely affected by the size and amount of the graphite particles. The smaller the graphite particles (faster solidification) in the microstructure, the lower the values of the mechanical properties. In compacted graphite cast iron, the macro-elastic behaviour is influenced by the matrix and the overall coarseness of the microstructure to a greater extent and the effect of the incorporated graphite particle size is much less pronounced.

  • 9.
    Sjögren, Torsten
    et al.
    Linköping University, Department of Management and Engineering, Engineering Materials . Linköping University, The Institute of Technology.
    Wessén, Magnus
    Högskolan i Jönköping, JTH, Maskinteknik.
    Svensson, Ingvar L.
    Högskolan i Jönköping, JTH, Maskinteknik.
    Schäfer, Wilfried
    Schäfer.
    Modeling and Simulation of Elastic Properties in Cast Compacted Graphite Iron Engine Block2006In: MCWASP Conference XI, May 28-June 2, Opio, France, 2006Conference paper (Refereed)
  • 10.
    Sjögren, Torsten
    et al.
    Research & Develepment, Daros Piston Rings AB, Mölnlycke.
    Wigren, P.
    Research & Develepment, Daros Piston Rings AB, Mölnlycke.
    Wilhelmsson, F.
    Research & Develepment, Daros Piston Rings AB, Mölnlycke.
    Vomacka, Peter
    Research & Develepment, Daros Piston Rings AB, Mölnlycke.
    High Performance Piston Rings for Two-Stroke Marine Diesel Engines2004In: Proceedings // 24th CIMAC World Congress on Combustion Engine Technology, 2004Conference paper (Other academic)
    Abstract [en]

    The piston ring is a key component in a marine combustion engine. High mechanical loads, relatively high temperatures and corrosive gases and liquids influence its performance in terms of sealing capacity, wear of cylinder liner and the ring itself. Base material of the ring, coating technology and ring geometry design are discussed in the article.

    When tailoring cast iron materials suitable as piston ring base material two parameters are of importance; the morphology of the graphite and the constituents of the matrix. To optimize the properties of the cast iron a compromise is needed to achieve a satisfactory performance of the piston rings.

    Daros Piston Rings AB is currently developing a second generation of chromium-ceramic coating the so called Z-chrome. The objective of this project has been to increase the maximum operating temperature of the coating and leave the other characteristics of the coating unaffected. The difference between the commercial Daros coating Tritor® and the Z-chrome is the ceramic component included in the coated layer.

    Insufficient conformability of piston ring and liner geometry may produce a large local cylinder wall pressure which will destroy the oil film leading to uncontrolled wear and scuffing. Lack of conformability can also produce leakage paths for the combustion gases. Therefore a correct ring shape is of utmost importance. A new design philosophy designated OPCORE® has been developed and is presented here.

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