Leo Kestens - Academia.edu (original) (raw)

Papers by Leo Kestens

A detailed understanding of microstructural changes in a sequence of thermomechanical processing ... more A detailed understanding of microstructural changes in a sequence of thermomechanical processing allows the improvement of magnetic properties in FeSi strips. The current contribution considers the texture evolution in non-oriented electrical steels of high Si content. Hot band strips of various textures were subjected to cold rolling and recrystallization annealing. The findings suggest that the crystallographic orientations observed after cold rolling are correlated with the hot band texture. In contrast, the evolution of recrystallization textures was more likely affected both by the hot and cold rolling microstructural features. The evolution of recrystallization textures is discussed on the basis of crystal plasticity calculations while the magnetic properties are correlated with the crystalline anisotropy energy density.

Analytica Chimica Acta, 2010

The influence of temperature on the mechanical behaviour of the heat treatable Aluminium alloy EN... more The influence of temperature on the mechanical behaviour of the heat treatable Aluminium alloy EN AW-6061 has been investigated with a series of tensile tests. It is found that temperature has an effect on both the storage of dislocations and dynamic recovery. The results have been used to fit the dislocation based Nes work-hardening model. Simulations show that the model

Materials Science Forum, 2007

Materials Science Forum, 2005

We report the results of the microstructural characterization of a Ti-bearing IF-steel deformed a... more We report the results of the microstructural characterization of a Ti-bearing IF-steel deformed at high strain rates (≈ 6.10 4 s -1 ) in a split Hopkinson bar. The shock-loading tests were performed in hat-shaped specimens to induce the formation of adiabatic shear bands (ASB). The samples were deformed at 223 K and 298 K. High-resolution electron backscatter diffraction (EBSD) reveals the development of an ultrafine-grained structure within the ASB. A closer inspection reveals the presence of deformation twins in grains adjacent to the shear band. These twins bend towards the ASB suggesting that mechanical twinning occurs before the flow associated to shear banding. The results of microtexture have indicated the presence of a sharp <111> γ-fiber texture in the ASB for both temperatures.

International Conference on Residual Stresses 9 (Icrs 9), 2014

ABSTRACT A new method has been designed to automatically adapt the geometry of the fusion zone of... more ABSTRACT A new method has been designed to automatically adapt the geometry of the fusion zone of a weld according to the temperature calculations when the thermal welding heat source parameters are known. In the material definition in a Finite Element code for welding stress calculations, the fusion zone material has different properties than the base material since, among others, the temperature at which the material is stress free is the melting temperature instead of room temperature. In this work, the fusion zone has been determined by postprocessing the thermal model results. The calculated dimensions of the fusion zone have been used as an input for a user subroutine which automatically creates a Finite Element mesh that separates fusion zone elements and base material elements according to the physical reality. It has been shown that the method allows a more accurate stress prediction in the fusion zone and the heat affected zone close to the fusion line, where residual stresses can be important. Neutron diffraction measurements have been used as a validation of the model.

Materials Science Forum, 1994

Materials Science Forum, 2007

Page 1. Microstructure – Texture Related Toughness Anisotropy of API-X80 Pipeline Steel Orlando L... more Page 1. Microstructure – Texture Related Toughness Anisotropy of API-X80 Pipeline Steel Orlando León García1, a, Roumen Petrov1,2 b, Jin-Ho Bae3, Leo Kestens2,1,c and Ki Bong Kang3 1 Ghent University, Dept. of Metallurgy ...

Materials Science Forum, 2013

ABSTRACT

Materials Science Forum, 2006

The effect of heating rate and annealing time on the microstructure and texture of a commercial 0... more The effect of heating rate and annealing time on the microstructure and texture of a commercial 0.04 %C steel, cold rolled up to 80 %, is studied. Samples have been isothermally annealed at various heating rates (12 ºC/h, 20 ºC/h, 40 ºC/h and 650 ºC/min) and then soaked at 700 ºC for 15 hours. The microstructural evolution of the samples during the heating process and hold period has been followed by optical microscopy, scanning and transmission electron microscopy. The electron back-scattered diffraction technique is used to reveal the texture of the samples. Tensile tests and hardness measurements are correlated with the microstructural features. Results show that (a) recrystallization occurs between 600 and 650 ºC; (b) a "pancake" structure develops during recrystallization at low heating rates without appreciable grain growth; (c) samples heated at 650 ºC/min exhibit an equiaxed grain structure and significant grain growth; (d) only at low heating rates the material develops a strong {111} recrystallization texture, in accordance with the high plastic anisotropy found by mechanical testing.

Materials Science Forum, 2006

An Fe-2%Si alloy, which was designed for electromagnetic applications was submitted to a series o... more An Fe-2%Si alloy, which was designed for electromagnetic applications was submitted to a series of plane strain compression (PSC) tests with reductions of 25, 35 and 75% at temperatures varying from 800 to 1,100°C and at a constant engineering strain rate corresponding to a constant cross velocity of 20 mm/s. The initial structure of the material displayed nearly equi-axed grains with an average size of 80 µm. The as-received texture was characterised by a nearly random cube fibre (<100>//ND) with a relatively weak maximum on the rotated cube component ({001}<110>). After deformation the samples were water quenched in order to avoid post-process static recrystallization events. The microstructures were analysed by orientation imaging microscopy (OIM) revealing that the zone of PSC was restricted to the central layers of the sample but minimally covering 50% of the sample thickness. After deformation at 800°C the conventional lamellar deformation structures were observed on the sections perpendicular to the transverse direction of PSC. At higher deformation temperatures the structure was of a bimodal nature consisting of lamellar deformation bands and equi-axed small grains. The volume fraction of these small equi-axed grains increased from 19.9% after 75%reduction at 800°C to 67.8% after 75% reduction at 1.100°C. After 75% reduction the equi-axed grains exhibited an average size of 10 µm which represents a strong grain refinement with respect to the initial size of 80 µm prior to PSC. Ferrite Silicon steels undergo extensive dynamic recovery during hot working. Dynamic recrystallization (DRX), though, has not yet been reported for these alloys although the present data suggest that a DRX mechanism might be responsible for the remarkable grain refinement after relatively low amounts of strain applied at high temperatures.

Materials Science Forum, 2007

Page 1. Three Dimensional Microstructure–Microtexture Characterization of Pipeline Steel R. Petro... more Page 1. Three Dimensional Microstructure–Microtexture Characterization of Pipeline Steel R. Petrov 1,5*a , O. León Garcìa 2, b , JJL Mulders 3,c , ACC Reis 1, d , Jin-Ho Bae 4,e , L. Kestens 5,1, f and Y.Houbaert 1,g 1 Ghent ...

Materials Science Forum, 2010

Abstract The phase transformation and the final microstructure were studied in a pipeline steel g... more Abstract The phase transformation and the final microstructure were studied in a pipeline steel grade API-X80 by carrying out a number of physical simulations of the industrial hot rolling schedules. The deformation and the cooling parameters were simulated by means ...

Surface and Interface Analysis, 2013

ABSTRACT Sodium silicate solutions, also known as ‘water-glass’, are used for a wide variety of a... more ABSTRACT Sodium silicate solutions, also known as ‘water-glass’, are used for a wide variety of applications. In particular, they are commonly used in pre-treatments of aluminum alloys as cleaners and corrosion inhibitors. Silicate films are known to be promising for corrosion protection and to confer high hydrophilicity. One of the main issues in the study of the formation of silicate films on metal oxides is the complexity of the anionic speciation in aqueous solution. In this work, the mechanism of sodium silicate interaction with porous anodic alumina and its dependence on the solution characteristics is studied by means of Fourier transformed infrared spectroscopy (FTIR). Grazing angle-FTIR and attenuated total reflection-FTIR are used in order to monitor the chemical changes occurring with time on the surface upon silicate adsorption. The effect of the SiO2/Na2O molar ratio and the temperature is studied. The role of rinsing is investigated when the alumina surface is washed in water after the silicate treatment. A chemical description of the phenomena occurring during silicate treatment is given.

Materials Science and Engineering: A, 2010

An experimental study on interstitial free (IF) steel sheets was performed with the objective to ... more An experimental study on interstitial free (IF) steel sheets was performed with the objective to determine the micromechanism(s) governing the void initiation caused by cubic titanium nitride, TiN, particles during tensile deformation. Void initiation was characterized using optical and scanning electron microscopy on samples that were deformed to various elongations. Moreover the development of the particle deformation zone was critically

Materials Chemistry and Physics, 2012

h i g h l i g h t s < The plastic deformation of a silicon containing steel is studied by plane s... more h i g h l i g h t s < The plastic deformation of a silicon containing steel is studied by plane strain compression. < Equiaxed and elongated grains develop in different regions of the sample due to recrystallization. < Texture, by EBSD, is revealed to be similar in either type of grains.

ISIJ International, 2003

RefDoc Bienvenue - Welcome. Refdoc est un service / is powered by. ...

Acta Materialia, 2005

Selective growth effects during primary recrystallization have been widely discussed but so far n... more Selective growth effects during primary recrystallization have been widely discussed but so far no convincing proof has been provided. In the search for a more fundamental understanding of texture formation during the growth stage of static recrystallization, the historic growth experiment by Ibe and Lücke was re-evaluated by making use of modern electron backscattering diffraction equipment. Moreover, the non-random character

Acta Materialia, 2009

... in the literature. One example is the recent work by Vercammen [25] on a Fe–30Mn–3Si–3Al aust... more ... in the literature. One example is the recent work by Vercammen [25] on a Fe–30Mn–3Si–3Al austenitic steel with a SFE of 40 mJ m −2 in which a small cube component was observed after recrystallization annealing. The aim ...

Acta Materialia, 2008

Important technological properties of metal sheets, like formability and particularly deep drawab... more Important technological properties of metal sheets, like formability and particularly deep drawability, are strongly affected by the crystallographic texture. The crystallographic orientation of the deformed grains strongly depends on the deformation path applied. The desirable {1 1 1}//ND texture, which is usually related to good deep drawability, cannot be formed in aluminium alloys by conventional rolling and annealing, although it is known to be a shear texture in face-centred cubic metals. Shear deformation in flat product can be imposed by asymmetric rolling (ASR) in which the diameters of working rolls are different, and in this technique could extend the possibilities for texture control of rolled sheet. The potential of the ASR process is modelled by crystallographic texture models and compared with experimental results.

pmt.usp.br

Resumo A textura (100)< 0vw>, ideal para utilização em motores elétricos, pode ser obtida e... more Resumo A textura (100)< 0vw>, ideal para utilização em motores elétricos, pode ser obtida em um plano perpendicular à direção de solidificação, na zona colunar, de Fe-3, 1% Si. O processo de lingotamento contínuo de tiras (LCT) propicia condições favoráveis para a obtenção desta textura. Além disso, apresenta como vantagem, em relação ao lingotamento convencional, a possibilidade de se obter tiras de 2mm de espessura diretamente a partir do metal líquido. Com o objetivo de produzir amostras com a textura ideal para ...

A detailed understanding of microstructural changes in a sequence of thermomechanical processing ... more A detailed understanding of microstructural changes in a sequence of thermomechanical processing allows the improvement of magnetic properties in FeSi strips. The current contribution considers the texture evolution in non-oriented electrical steels of high Si content. Hot band strips of various textures were subjected to cold rolling and recrystallization annealing. The findings suggest that the crystallographic orientations observed after cold rolling are correlated with the hot band texture. In contrast, the evolution of recrystallization textures was more likely affected both by the hot and cold rolling microstructural features. The evolution of recrystallization textures is discussed on the basis of crystal plasticity calculations while the magnetic properties are correlated with the crystalline anisotropy energy density.

Analytica Chimica Acta, 2010

The influence of temperature on the mechanical behaviour of the heat treatable Aluminium alloy EN... more The influence of temperature on the mechanical behaviour of the heat treatable Aluminium alloy EN AW-6061 has been investigated with a series of tensile tests. It is found that temperature has an effect on both the storage of dislocations and dynamic recovery. The results have been used to fit the dislocation based Nes work-hardening model. Simulations show that the model

Materials Science Forum, 2007

Materials Science Forum, 2005

We report the results of the microstructural characterization of a Ti-bearing IF-steel deformed a... more We report the results of the microstructural characterization of a Ti-bearing IF-steel deformed at high strain rates (≈ 6.10 4 s -1 ) in a split Hopkinson bar. The shock-loading tests were performed in hat-shaped specimens to induce the formation of adiabatic shear bands (ASB). The samples were deformed at 223 K and 298 K. High-resolution electron backscatter diffraction (EBSD) reveals the development of an ultrafine-grained structure within the ASB. A closer inspection reveals the presence of deformation twins in grains adjacent to the shear band. These twins bend towards the ASB suggesting that mechanical twinning occurs before the flow associated to shear banding. The results of microtexture have indicated the presence of a sharp <111> γ-fiber texture in the ASB for both temperatures.

International Conference on Residual Stresses 9 (Icrs 9), 2014

ABSTRACT A new method has been designed to automatically adapt the geometry of the fusion zone of... more ABSTRACT A new method has been designed to automatically adapt the geometry of the fusion zone of a weld according to the temperature calculations when the thermal welding heat source parameters are known. In the material definition in a Finite Element code for welding stress calculations, the fusion zone material has different properties than the base material since, among others, the temperature at which the material is stress free is the melting temperature instead of room temperature. In this work, the fusion zone has been determined by postprocessing the thermal model results. The calculated dimensions of the fusion zone have been used as an input for a user subroutine which automatically creates a Finite Element mesh that separates fusion zone elements and base material elements according to the physical reality. It has been shown that the method allows a more accurate stress prediction in the fusion zone and the heat affected zone close to the fusion line, where residual stresses can be important. Neutron diffraction measurements have been used as a validation of the model.

Materials Science Forum, 1994

Materials Science Forum, 2007

Page 1. Microstructure – Texture Related Toughness Anisotropy of API-X80 Pipeline Steel Orlando L... more Page 1. Microstructure – Texture Related Toughness Anisotropy of API-X80 Pipeline Steel Orlando León García1, a, Roumen Petrov1,2 b, Jin-Ho Bae3, Leo Kestens2,1,c and Ki Bong Kang3 1 Ghent University, Dept. of Metallurgy ...

Materials Science Forum, 2013

ABSTRACT

Materials Science Forum, 2006

The effect of heating rate and annealing time on the microstructure and texture of a commercial 0... more The effect of heating rate and annealing time on the microstructure and texture of a commercial 0.04 %C steel, cold rolled up to 80 %, is studied. Samples have been isothermally annealed at various heating rates (12 ºC/h, 20 ºC/h, 40 ºC/h and 650 ºC/min) and then soaked at 700 ºC for 15 hours. The microstructural evolution of the samples during the heating process and hold period has been followed by optical microscopy, scanning and transmission electron microscopy. The electron back-scattered diffraction technique is used to reveal the texture of the samples. Tensile tests and hardness measurements are correlated with the microstructural features. Results show that (a) recrystallization occurs between 600 and 650 ºC; (b) a "pancake" structure develops during recrystallization at low heating rates without appreciable grain growth; (c) samples heated at 650 ºC/min exhibit an equiaxed grain structure and significant grain growth; (d) only at low heating rates the material develops a strong {111} recrystallization texture, in accordance with the high plastic anisotropy found by mechanical testing.

Materials Science Forum, 2006

An Fe-2%Si alloy, which was designed for electromagnetic applications was submitted to a series o... more An Fe-2%Si alloy, which was designed for electromagnetic applications was submitted to a series of plane strain compression (PSC) tests with reductions of 25, 35 and 75% at temperatures varying from 800 to 1,100°C and at a constant engineering strain rate corresponding to a constant cross velocity of 20 mm/s. The initial structure of the material displayed nearly equi-axed grains with an average size of 80 µm. The as-received texture was characterised by a nearly random cube fibre (<100>//ND) with a relatively weak maximum on the rotated cube component ({001}<110>). After deformation the samples were water quenched in order to avoid post-process static recrystallization events. The microstructures were analysed by orientation imaging microscopy (OIM) revealing that the zone of PSC was restricted to the central layers of the sample but minimally covering 50% of the sample thickness. After deformation at 800°C the conventional lamellar deformation structures were observed on the sections perpendicular to the transverse direction of PSC. At higher deformation temperatures the structure was of a bimodal nature consisting of lamellar deformation bands and equi-axed small grains. The volume fraction of these small equi-axed grains increased from 19.9% after 75%reduction at 800°C to 67.8% after 75% reduction at 1.100°C. After 75% reduction the equi-axed grains exhibited an average size of 10 µm which represents a strong grain refinement with respect to the initial size of 80 µm prior to PSC. Ferrite Silicon steels undergo extensive dynamic recovery during hot working. Dynamic recrystallization (DRX), though, has not yet been reported for these alloys although the present data suggest that a DRX mechanism might be responsible for the remarkable grain refinement after relatively low amounts of strain applied at high temperatures.

Materials Science Forum, 2007

Page 1. Three Dimensional Microstructure–Microtexture Characterization of Pipeline Steel R. Petro... more Page 1. Three Dimensional Microstructure–Microtexture Characterization of Pipeline Steel R. Petrov 1,5*a , O. León Garcìa 2, b , JJL Mulders 3,c , ACC Reis 1, d , Jin-Ho Bae 4,e , L. Kestens 5,1, f and Y.Houbaert 1,g 1 Ghent ...

Materials Science Forum, 2010

Abstract The phase transformation and the final microstructure were studied in a pipeline steel g... more Abstract The phase transformation and the final microstructure were studied in a pipeline steel grade API-X80 by carrying out a number of physical simulations of the industrial hot rolling schedules. The deformation and the cooling parameters were simulated by means ...

Surface and Interface Analysis, 2013

ABSTRACT Sodium silicate solutions, also known as ‘water-glass’, are used for a wide variety of a... more ABSTRACT Sodium silicate solutions, also known as ‘water-glass’, are used for a wide variety of applications. In particular, they are commonly used in pre-treatments of aluminum alloys as cleaners and corrosion inhibitors. Silicate films are known to be promising for corrosion protection and to confer high hydrophilicity. One of the main issues in the study of the formation of silicate films on metal oxides is the complexity of the anionic speciation in aqueous solution. In this work, the mechanism of sodium silicate interaction with porous anodic alumina and its dependence on the solution characteristics is studied by means of Fourier transformed infrared spectroscopy (FTIR). Grazing angle-FTIR and attenuated total reflection-FTIR are used in order to monitor the chemical changes occurring with time on the surface upon silicate adsorption. The effect of the SiO2/Na2O molar ratio and the temperature is studied. The role of rinsing is investigated when the alumina surface is washed in water after the silicate treatment. A chemical description of the phenomena occurring during silicate treatment is given.

Materials Science and Engineering: A, 2010

An experimental study on interstitial free (IF) steel sheets was performed with the objective to ... more An experimental study on interstitial free (IF) steel sheets was performed with the objective to determine the micromechanism(s) governing the void initiation caused by cubic titanium nitride, TiN, particles during tensile deformation. Void initiation was characterized using optical and scanning electron microscopy on samples that were deformed to various elongations. Moreover the development of the particle deformation zone was critically

Materials Chemistry and Physics, 2012

h i g h l i g h t s < The plastic deformation of a silicon containing steel is studied by plane s... more h i g h l i g h t s < The plastic deformation of a silicon containing steel is studied by plane strain compression. < Equiaxed and elongated grains develop in different regions of the sample due to recrystallization. < Texture, by EBSD, is revealed to be similar in either type of grains.

ISIJ International, 2003

RefDoc Bienvenue - Welcome. Refdoc est un service / is powered by. ...

Acta Materialia, 2005

Selective growth effects during primary recrystallization have been widely discussed but so far n... more Selective growth effects during primary recrystallization have been widely discussed but so far no convincing proof has been provided. In the search for a more fundamental understanding of texture formation during the growth stage of static recrystallization, the historic growth experiment by Ibe and Lücke was re-evaluated by making use of modern electron backscattering diffraction equipment. Moreover, the non-random character

Acta Materialia, 2009

... in the literature. One example is the recent work by Vercammen [25] on a Fe–30Mn–3Si–3Al aust... more ... in the literature. One example is the recent work by Vercammen [25] on a Fe–30Mn–3Si–3Al austenitic steel with a SFE of 40 mJ m −2 in which a small cube component was observed after recrystallization annealing. The aim ...

Acta Materialia, 2008

Important technological properties of metal sheets, like formability and particularly deep drawab... more Important technological properties of metal sheets, like formability and particularly deep drawability, are strongly affected by the crystallographic texture. The crystallographic orientation of the deformed grains strongly depends on the deformation path applied. The desirable {1 1 1}//ND texture, which is usually related to good deep drawability, cannot be formed in aluminium alloys by conventional rolling and annealing, although it is known to be a shear texture in face-centred cubic metals. Shear deformation in flat product can be imposed by asymmetric rolling (ASR) in which the diameters of working rolls are different, and in this technique could extend the possibilities for texture control of rolled sheet. The potential of the ASR process is modelled by crystallographic texture models and compared with experimental results.

pmt.usp.br

Resumo A textura (100)< 0vw>, ideal para utilização em motores elétricos, pode ser obtida e... more Resumo A textura (100)< 0vw>, ideal para utilização em motores elétricos, pode ser obtida em um plano perpendicular à direção de solidificação, na zona colunar, de Fe-3, 1% Si. O processo de lingotamento contínuo de tiras (LCT) propicia condições favoráveis para a obtenção desta textura. Além disso, apresenta como vantagem, em relação ao lingotamento convencional, a possibilidade de se obter tiras de 2mm de espessura diretamente a partir do metal líquido. Com o objetivo de produzir amostras com a textura ideal para ...