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J Duszczyk - One of the best experts on this subject based on the ideXlab platform.
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computer simulated and experimentally verified isothermal extrusion of 7075 aluminium through continuous ram speed variation
Journal of Materials Processing Technology, 2004Co-Authors: J Zhou, L Li, J DuszczykAbstract:Abstract The conventional aluminium extrusion process is run at constant ram speed, leading to quality inconsistency along the length of the extruded product and even to Hot Shortness as a result of continued temperature evolution. In the present work, computer simulation of the process at varying ram speed was performed in order to determine the conditions to prevent the extrudate temperature from rising excessively. To maintain the maximum workpiece temperature around 500 and 480 °C corresponding to two initial microstructural states of 7075 aluminium billets, two ram speed profiles were derived from the simulation results of a series of conventional extrusion runs. The predetermined ram speed profile commenced at a relatively high value at the beginning of an extrusion cycle and decreased exponentially with ram displacement as soon as the maximum workpiece temperature reached the target value. The simulations showed that with these ram speed profiles the continued temperature increase normally occurring during conventional extrusion could be effectively inhibited. This was verified experimentally by measuring the extrudate temperature continuously using a thermocouple in the die close to the bearing and also using a multi-wavelength pyrometer behind the die. With the predetermined ram speed profiles, the fluctuations of the maximum workpiece temperature could be controlled within a range of 10 °C. The time taken to extrude each billet could be significantly shortened. In addition, the die face pressure remained stable, which would also favour the consistency of the quality of the extruded product.
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3d fem simulation of the whole cycle of aluminium extrusion throughout the transient state and the steady state using the updated lagrangian approach
Journal of Materials Processing Technology, 2003Co-Authors: J Zhou, J DuszczykAbstract:Abstract Aluminium extrusion involves the generation of free surface, thermal effects, large deformations and complex geometries. The established finite element method (FEM)-based 3D simulation tools using the updated Lagrangian approach, or the Eulerian approach or the arbitrary Lagrangian Eulerian approach all have limitations in describing the process that develops from the transient state to the steady state before reaching the end when the steady state is disturbed. As a result, the simulation of aluminium extrusion performed so far has been restricted to simple geometries, small length-to-diameter (L/D) ratios, the beginning stage or steady-state conditions. This paper reports on an unprecedented attempt to simulate an entire cycle of aluminium extrusion from a billet with an L/D ratio of 4 to a solid cross-shaped profile, using the DEFORM 3D software based on the updated Lagrangian approach. Simulation successfully predicts a complete extrusion pressure/ram displacement diagram that begins with a pressure breakthrough and ends with another pressure rise due to the inhibition of metal flow by the rigid dummy block. The developments of velocity, effective strain and temperature inside the deforming billet indicate that the process is non-steady, even in the steady state, as a result of continuous heat generation and sticking condition at the billet–container interface. The non-steady characteristics are reflected in the expanding deformation zone and shrinking dead metal zone. Simulation also reveals the patterns of the maximum temperature variations in the workpiece and in the tooling, due to heat generation and exchange. Even at a relatively low ram speed of 2 mm/s, the maximum temperature of the workpiece, after an initial steep rise, increases gradually till the end of the process, which may well lead to the occurrence of Hot Shortness. On the basis of these results, a change of the conventional mode of aluminium extrusion is recommended, which at present operates almost all at a constant ram speed and often begins with a uniform billet temperature across the aluminium extrusion industry in the world.
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fem analysis of aluminium extrusion through square and round dies
Materials & Design, 2000Co-Authors: T Chanda, J Zhou, J DuszczykAbstract:Abstract Understanding the state of stress, strain and the temperature of an aluminium alloy going through a die during extrusion is of great importance for running the aluminium extrusion process, because they are closely related to the surface quality of the extruded products, throughput and scrap rate. It has been made clear that surface tearing is mainly caused by excessive local tensile stresses at the surface of the extrudate and Hot Shortness is due to the heat generated during the process that brings the extrudate temperature above the incipient melting point of the billet material. Both the state of stress and the temperature are complicatedly related to the extrusion conditions including initial billet temperature, ram speed, reduction ratio, friction at the interfaces, deformation resistance of the billet material, die geometry, as well as thermal characteristics of the billet material and the tooling. The practical means to accurately measure the stress, strain and temperature is yet quite limited. In the present work, 3D FEM simulation of the aluminium extrusion process was performed to determine the state of stress, strain and the temperature of a commercial aluminium alloy going through square and round dies. It has been found that at the same process conditions, the state of stress in the aluminium alloy going through a round die is more favourable than going through a square die, especially at a high reduction ratio. The magnitude of the tensile stress component at the corners of the square extrudate is much higher than at the surface of the round extrudate, which makes the square extrudate more tearing prone. Simulation also reveals that while temperature evolution during the process is similar for both of the die shapes, temperature rise across the section is prominent, especially at sharp corners of the square extrudate. This has been ascribed to the non-uniform metal flow through the square die.
J Zhou - One of the best experts on this subject based on the ideXlab platform.
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computer simulated and experimentally verified isothermal extrusion of 7075 aluminium through continuous ram speed variation
Journal of Materials Processing Technology, 2004Co-Authors: J Zhou, L Li, J DuszczykAbstract:Abstract The conventional aluminium extrusion process is run at constant ram speed, leading to quality inconsistency along the length of the extruded product and even to Hot Shortness as a result of continued temperature evolution. In the present work, computer simulation of the process at varying ram speed was performed in order to determine the conditions to prevent the extrudate temperature from rising excessively. To maintain the maximum workpiece temperature around 500 and 480 °C corresponding to two initial microstructural states of 7075 aluminium billets, two ram speed profiles were derived from the simulation results of a series of conventional extrusion runs. The predetermined ram speed profile commenced at a relatively high value at the beginning of an extrusion cycle and decreased exponentially with ram displacement as soon as the maximum workpiece temperature reached the target value. The simulations showed that with these ram speed profiles the continued temperature increase normally occurring during conventional extrusion could be effectively inhibited. This was verified experimentally by measuring the extrudate temperature continuously using a thermocouple in the die close to the bearing and also using a multi-wavelength pyrometer behind the die. With the predetermined ram speed profiles, the fluctuations of the maximum workpiece temperature could be controlled within a range of 10 °C. The time taken to extrude each billet could be significantly shortened. In addition, the die face pressure remained stable, which would also favour the consistency of the quality of the extruded product.
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3d fem simulation of the whole cycle of aluminium extrusion throughout the transient state and the steady state using the updated lagrangian approach
Journal of Materials Processing Technology, 2003Co-Authors: J Zhou, J DuszczykAbstract:Abstract Aluminium extrusion involves the generation of free surface, thermal effects, large deformations and complex geometries. The established finite element method (FEM)-based 3D simulation tools using the updated Lagrangian approach, or the Eulerian approach or the arbitrary Lagrangian Eulerian approach all have limitations in describing the process that develops from the transient state to the steady state before reaching the end when the steady state is disturbed. As a result, the simulation of aluminium extrusion performed so far has been restricted to simple geometries, small length-to-diameter (L/D) ratios, the beginning stage or steady-state conditions. This paper reports on an unprecedented attempt to simulate an entire cycle of aluminium extrusion from a billet with an L/D ratio of 4 to a solid cross-shaped profile, using the DEFORM 3D software based on the updated Lagrangian approach. Simulation successfully predicts a complete extrusion pressure/ram displacement diagram that begins with a pressure breakthrough and ends with another pressure rise due to the inhibition of metal flow by the rigid dummy block. The developments of velocity, effective strain and temperature inside the deforming billet indicate that the process is non-steady, even in the steady state, as a result of continuous heat generation and sticking condition at the billet–container interface. The non-steady characteristics are reflected in the expanding deformation zone and shrinking dead metal zone. Simulation also reveals the patterns of the maximum temperature variations in the workpiece and in the tooling, due to heat generation and exchange. Even at a relatively low ram speed of 2 mm/s, the maximum temperature of the workpiece, after an initial steep rise, increases gradually till the end of the process, which may well lead to the occurrence of Hot Shortness. On the basis of these results, a change of the conventional mode of aluminium extrusion is recommended, which at present operates almost all at a constant ram speed and often begins with a uniform billet temperature across the aluminium extrusion industry in the world.
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fem analysis of aluminium extrusion through square and round dies
Materials & Design, 2000Co-Authors: T Chanda, J Zhou, J DuszczykAbstract:Abstract Understanding the state of stress, strain and the temperature of an aluminium alloy going through a die during extrusion is of great importance for running the aluminium extrusion process, because they are closely related to the surface quality of the extruded products, throughput and scrap rate. It has been made clear that surface tearing is mainly caused by excessive local tensile stresses at the surface of the extrudate and Hot Shortness is due to the heat generated during the process that brings the extrudate temperature above the incipient melting point of the billet material. Both the state of stress and the temperature are complicatedly related to the extrusion conditions including initial billet temperature, ram speed, reduction ratio, friction at the interfaces, deformation resistance of the billet material, die geometry, as well as thermal characteristics of the billet material and the tooling. The practical means to accurately measure the stress, strain and temperature is yet quite limited. In the present work, 3D FEM simulation of the aluminium extrusion process was performed to determine the state of stress, strain and the temperature of a commercial aluminium alloy going through square and round dies. It has been found that at the same process conditions, the state of stress in the aluminium alloy going through a round die is more favourable than going through a square die, especially at a high reduction ratio. The magnitude of the tensile stress component at the corners of the square extrudate is much higher than at the surface of the round extrudate, which makes the square extrudate more tearing prone. Simulation also reveals that while temperature evolution during the process is similar for both of the die shapes, temperature rise across the section is prominent, especially at sharp corners of the square extrudate. This has been ascribed to the non-uniform metal flow through the square die.
Calvo Muñoz Jessica - One of the best experts on this subject based on the ideXlab platform.
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Efecto de los elementos residuales e impurezas en la ductilidad y mecanismos de fragilización en caliente de un acero de construcción 0.23C-0.9Mn-0.13SI
Universitat Politècnica de Catalunya, 2006Co-Authors: Calvo Muñoz JessicaAbstract:El agrietamiento transversal en la superficie de los productos de colada continua es un problema que sigue provocando el rechazo de algunos de estos productos con las correspondientes pérdidas energéticas y económicas. A pesar de que el problema se ha conseguido minimizar para algunas calidades de acero, el reciclaje de chatarra, práctica cada vez más frecuente por sus beneficios económicos y medioambientales, está incorporando nuevos retos, especialmente en lo que se refiere a la aparición de grietas superficiales. El origen del agrietamiento para estos aceros se relaciona con el aumento en elementos residuales e impurezas que se introducen durante el reciclaje y son difíciles de eliminar.Para conocer la influencia de estos elementos residuales e impurezas en el agrietamiento transversal, se evaluó la ductilidad en caliente de un acero de construcción 0.23C-0.9Mn-0.13Si con Cu y Sn como residuales y alto S. La ductilidad en caliente fue evaluada a partir de la reducción del área (%RA) de probetas ensayadas a tracción a temperaturas entre 650ºC y 1100ºC. La velocidad de deformación elegida para los ensayos fue 5·10-3s-1. Estas condiciones están en el intervalo de las que se dan durante el desdoblado, etapa crítica para la aparición de grietas. Las curvas de %RA en función de la temperatura se completaron con el estudio fractográfico y metalográfico de las probetas.Durante los ensayos se varió la temperatura de austenización mediante recalentamientos a 1100ºC y a 1330ºC. Otra serie de ensayo consistió en la fusión y solidificación in-situ de las probetas. Además, se trabajó con el material en dos condiciones iniciales: colada (probetas extraídas de una palanquilla) y laminada (probetas extraídas de varilla corrugada). Un acero con una composición base similar pero sin elementos residuales fue evaluado con fines comparativos.Las curvas de ductilidad en caliente fueron muy parecidas independientemente de la temperatura de recalentamiento, sin embargo, cuando el acero se ensayó en su condición laminada el valle de ductilidad obtenido fue más estrecho. Por otro lado, los mecanismos de fragilización variaron con la temperatura de recalentamiento y no con la condición inicial del material. Las fracturas tras recalentamientos a 1100ºC fueron interdendríticas y se relacionaron con las microsegregaciones de solidificación. Recalentamientos a 1330ºC originaron fracturas interganulares.Las inclusiones de MnS, así como las segregaciones de S parecen tener un papel importante en este comportamiento. El efecto del S sólo puede ser evaluado adecuadamente cuando las probetas se solidifican in-situ para poner en solución el S que se encontrara formando MnS. Los resultados obtenidos mediante estas condiciones experimentales presentaron pozos de ductilidad más anchos que los obtenidos en condiciones de recalentamiento. Por otro lado, las fractografías muestran la gran tendencia al "Hot Shortness" que tiene el acero. Éste mecanismo de fragilización que actúa a muy altas temperaturas estaría debilitando los espacios interdendríticos a menores temperaturas. Al comparar el comportamiento del acero industrial con el del acero limpio, lo primero que se ve es que el pozo de ductilidad es significativamente más estrecho para éste último. Así, el único mecanismo de fragilización identificado consiste en la concentración de la deformación en una fina capa de ferrita que se forma rodeando la austenita a temperaturas entre Ae3 y Ar3. El cálculo de las microsegregaciones de solidificación indica que los elementos con más tendencia a enriquecer el último líquido en solidificar son el P y el S. Éste último además parece el responsable de la fragilidad del acero cuando se ensaya en condiciones de recalentamiento, tal y como se pudo determinar por espectroscopía Auger. A pesar de que no se ha podido demostrar, en Sn podría tener también un papel importante en las segregaciones intergranulares.Transverse cracking in the surface is a problem related to the continuous casting steelmaking route. Its incidence has been minimized for several steel grades, but it is very sensitive to operational or compositional variations. In particular, the production of steel from scrap, which has great economic and environmental advantages, has introduced new challenges. The high incidence of transverse cracking for these steel grades is related to their high contents on residual elements which are introduced during the recycling and are difficult to eliminate.The influence of residual elements and impurities on the transverse cracking susceptibility has been studied for a structural steel 0.23C-0.9Mn-0.13Si with high Cu and Sn as residuals, as well as high S. The evaluation was done by means of Hot tensile tests. The reduction area (%RA) of the samples tested to fracture was taken as a measure of the Hot ductility, and therefore, of the sensitivity of the steel to present transverse cracking. The analysis of the fracture surfaces and metallographies of the samples allowed the identification of the different embrittling mechanisms that could take place depending on the thermomechanical conditions. During the tests, samples were first reheated to 1100ºC or 1330ºC, or in- situ melted. Then, they were tested at temperatures ranging from 650ºC to 1100ºC. The strain rate was 5×10-3s-1, close to the ones that take place during the unbending operation in continuous casting. The steel was tested for two initial conditions of the material: the as-cast (samples were machined from a billet), and the as-rolled (samples were machined from a corrugated bar). Moreover, another steel residual free was evaluated for comparison purposes.The Hot ductility curves (%RA vs. Temperature) were similar after different reheating treatments, but ductility troughs appeared narrower when the steel was tested in the as-rolled condition. However, fracture surfaces showed different features depending on the reheating temperature. On one side, the reheating treatment at 1100˚C promoted a mixture of intergranular and interdendritic brittle fracture. The interdendritic component of the fracture was related to microsegregations taking place during the solidification of the steel. On the other side, brittle samples tested after a reheating treatment at 1330˚C showed completely intergranular features.MnS inclusions, as well as S segregations, seemed to have a very important role in the Hot ductility behaviour of the steel. Since S forms particles with high melting points, samples had to be cast in-situ in order to put all S back into solution and then evaluate its effect on the Hot ductility. For samples cast in-situ, the ductility troughs are wider than the ones obtained for reheated samples. Moreover, the fractographies of in-situ melted samples showed the high tendency of the steel to embrittle through "Hot Shortness". This mechanism that would act at very high temperatures could also be the responsible of the brittle behaviour of the steels at testing temperatures.The ductility troughs for the clean steel were significantly narrower than the ones for the industrial steel at any testing condition. The only embrittling mechanism identified for the clean steel was the concentration of the deformations at a ferrite layer formed surrounding the austenite grains at temperatures between Ae3 and Ar3.The composition of the last solidifying liquid was calculated according to microsegregation models. The calculations showed that P and S are the elements with the highest tendency to microsegregate and thus, the last solidifying liquid is enriched in these elements. By means of Auger spectroscopy the S was proved to be the embrittling element under reheating conditions. Though it could not be verified, special attention should be paid to Sn due to its tendency to segregate intergranularly.Postprint (published version
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Efecto de los elementos residuales e impurezas en la ductilidad y mecanismos de fragilización en caliente de un acero de construcción 0.23C-0.9Mn-0.13SI
Universitat Politècnica de Catalunya, 2006Co-Authors: Calvo Muñoz JessicaAbstract:El agrietamiento transversal en la superficie de los productos de colada continua es un problema que sigue provocando el rechazo de algunos de estos productos con las correspondientes pérdidas energéticas y económicas. A pesar de que el problema se ha conseguido minimizar para algunas calidades de acero, el reciclaje de chatarra, práctica cada vez más frecuente por sus beneficios económicos y medioambientales, está incorporando nuevos retos, especialmente en lo que se refiere a la aparición de grietas superficiales. El origen del agrietamiento para estos aceros se relaciona con el aumento en elementos residuales e impurezas que se introducen durante el reciclaje y son difíciles de eliminar.Para conocer la influencia de estos elementos residuales e impurezas en el agrietamiento transversal, se evaluó la ductilidad en caliente de un acero de construcción 0.23C-0.9Mn-0.13Si con Cu y Sn como residuales y alto S. La ductilidad en caliente fue evaluada a partir de la reducción del área (%RA) de probetas ensayadas a tracción a temperaturas entre 650ºC y 1100ºC. La velocidad de deformación elegida para los ensayos fue 5·10-3s-1. Estas condiciones están en el intervalo de las que se dan durante el desdoblado, etapa crítica para la aparición de grietas. Las curvas de %RA en función de la temperatura se completaron con el estudio fractográfico y metalográfico de las probetas.Durante los ensayos se varió la temperatura de austenización mediante recalentamientos a 1100ºC y a 1330ºC. Otra serie de ensayo consistió en la fusión y solidificación in-situ de las probetas. Además, se trabajó con el material en dos condiciones iniciales: colada (probetas extraídas de una palanquilla) y laminada (probetas extraídas de varilla corrugada). Un acero con una composición base similar pero sin elementos residuales fue evaluado con fines comparativos.Las curvas de ductilidad en caliente fueron muy parecidas independientemente de la temperatura de recalentamiento, sin embargo, cuando el acero se ensayó en su condición laminada el valle de ductilidad obtenido fue más estrecho. Por otro lado, los mecanismos de fragilización variaron con la temperatura de recalentamiento y no con la condición inicial del material. Las fracturas tras recalentamientos a 1100ºC fueron interdendríticas y se relacionaron con las microsegregaciones de solidificación. Recalentamientos a 1330ºC originaron fracturas interganulares.Las inclusiones de MnS, así como las segregaciones de S parecen tener un papel importante en este comportamiento. El efecto del S sólo puede ser evaluado adecuadamente cuando las probetas se solidifican in-situ para poner en solución el S que se encontrara formando MnS. Los resultados obtenidos mediante estas condiciones experimentales presentaron pozos de ductilidad más anchos que los obtenidos en condiciones de recalentamiento. Por otro lado, las fractografías muestran la gran tendencia al "Hot Shortness" que tiene el acero. Éste mecanismo de fragilización que actúa a muy altas temperaturas estaría debilitando los espacios interdendríticos a menores temperaturas. Al comparar el comportamiento del acero industrial con el del acero limpio, lo primero que se ve es que el pozo de ductilidad es significativamente más estrecho para éste último. Así, el único mecanismo de fragilización identificado consiste en la concentración de la deformación en una fina capa de ferrita que se forma rodeando la austenita a temperaturas entre Ae3 y Ar3. El cálculo de las microsegregaciones de solidificación indica que los elementos con más tendencia a enriquecer el último líquido en solidificar son el P y el S. Éste último además parece el responsable de la fragilidad del acero cuando se ensaya en condiciones de recalentamiento, tal y como se pudo determinar por espectroscopía Auger. A pesar de que no se ha podido demostrar, en Sn podría tener también un papel importante en las segregaciones intergranulares.Transverse cracking in the surface is a problem related to the continuous casting steelmaking route. Its incidence has been minimized for several steel grades, but it is very sensitive to operational or compositional variations. In particular, the production of steel from scrap, which has great economic and environmental advantages, has introduced new challenges. The high incidence of transverse cracking for these steel grades is related to their high contents on residual elements which are introduced during the recycling and are difficult to eliminate.The influence of residual elements and impurities on the transverse cracking susceptibility has been studied for a structural steel 0.23C-0.9Mn-0.13Si with high Cu and Sn as residuals, as well as high S. The evaluation was done by means of Hot tensile tests. The reduction area (%RA) of the samples tested to fracture was taken as a measure of the Hot ductility, and therefore, of the sensitivity of the steel to present transverse cracking. The analysis of the fracture surfaces and metallographies of the samples allowed the identification of the different embrittling mechanisms that could take place depending on the thermomechanical conditions. During the tests, samples were first reheated to 1100ºC or 1330ºC, or in- situ melted. Then, they were tested at temperatures ranging from 650ºC to 1100ºC. The strain rate was 5×10-3s-1, close to the ones that take place during the unbending operation in continuous casting. The steel was tested for two initial conditions of the material: the as-cast (samples were machined from a billet), and the as-rolled (samples were machined from a corrugated bar). Moreover, another steel residual free was evaluated for comparison purposes.The Hot ductility curves (%RA vs. Temperature) were similar after different reheating treatments, but ductility troughs appeared narrower when the steel was tested in the as-rolled condition. However, fracture surfaces showed different features depending on the reheating temperature. On one side, the reheating treatment at 1100˚C promoted a mixture of intergranular and interdendritic brittle fracture. The interdendritic component of the fracture was related to microsegregations taking place during the solidification of the steel. On the other side, brittle samples tested after a reheating treatment at 1330˚C showed completely intergranular features.MnS inclusions, as well as S segregations, seemed to have a very important role in the Hot ductility behaviour of the steel. Since S forms particles with high melting points, samples had to be cast in-situ in order to put all S back into solution and then evaluate its effect on the Hot ductility. For samples cast in-situ, the ductility troughs are wider than the ones obtained for reheated samples. Moreover, the fractographies of in-situ melted samples showed the high tendency of the steel to embrittle through "Hot Shortness". This mechanism that would act at very high temperatures could also be the responsible of the brittle behaviour of the steels at testing temperatures.The ductility troughs for the clean steel were significantly narrower than the ones for the industrial steel at any testing condition. The only embrittling mechanism identified for the clean steel was the concentration of the deformations at a ferrite layer formed surrounding the austenite grains at temperatures between Ae3 and Ar3.The composition of the last solidifying liquid was calculated according to microsegregation models. The calculations showed that P and S are the elements with the highest tendency to microsegregate and thus, the last solidifying liquid is enriched in these elements. By means of Auger spectroscopy the S was proved to be the embrittling element under reheating conditions. Though it could not be verified, special attention should be paid to Sn due to its tendency to segregate intergranularly
Yb Kang - One of the best experts on this subject based on the ideXlab platform.
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A Novel Technology to Develop a Nickel-Enriched Layer on Slab Surface by Utilizing NiO-Containing Synthetic Powder
'Indiana University Press (Project Muse)', 2018Co-Authors: Tae-in Chung, Jw Cho, Yb KangAbstract:Cu, as one of the typical tramp elements, is known to cause Hot Shortness during reheating of slabs followed by Hot rolling of sheet products. In order to prevent such harmful aspects, a new idea is proposed by using synthetic powders containing NiO in the mold flux during continuous casting of the slab. During the casting, NiO is reduced and absorbed on initial solidified steel shell, and a Ni-rich layer is developed near the surface region of the slab. According to the proposed idea, it is expected that both the Cu solubility and the melting temperature of Cu-segregated region would increase considerably by virtue of Ni-rich layer, which is believed to play an important role to prevent the Cu Hot Shortness. A series of laboratory-scale experiments were carried out in order to confirm the reduction and the absorption of Ni into the steel matrix. It was observed by SEM-EDS and FE-EPMA that a Ni-enriched layer, as thick as a few hundred mu m, formed near the surface of the slab. Also, a number of laboratory-scale heat treatment tests under oxidizing atmosphere showed that the samples with the Ni-enriched layer had a decreased Cu enrichment at the interface between scale and steel, compared to a case without Ni-rich layer. A pilot-plant-scale steel slab (medium carbon steel containing 0.3 wt pct Cu) was obtained in a continuous casting process with the NiO-containing mold flux, and a Ni-enriched layer was also observed. It was concluded that the use of NiO in the mold flux is a promising new approach for suppressing the Hot Shortness of Cu-containing steel, without an expensive addition of Ni to the whole steel matrix.open10
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A Novel Technology to Develop a Nickel-Enriched Layer on Slab Surface by Utilizing NiO-Containing Synthetic Powder
'Springer Science and Business Media LLC', 2018Co-Authors: Tae-in Chung, Jw Cho, Yb KangAbstract:Cu, as one of the typical tramp elements, is known to cause Hot Shortness during reheating of slabs followed by Hot rolling of sheet products. In order to prevent such harmful aspects, a new idea is proposed by using synthetic powders containing NiO in the mold flux during continuous casting of the slab. During the casting, NiO is reduced and absorbed on initial solidified steel shell, and a Ni-rich layer is developed near the surface region of the slab. According to the proposed idea, it is expected that both the Cu solubility and the melting temperature of Cu-segregated region would increase considerably by virtue of Ni-rich layer, which is believed to play an important role to prevent the Cu Hot Shortness. A series of laboratory-scale experiments were carried out in order to confirm the reduction and the absorption of Ni into the steel matrix. It was observed by SEM-EDS and FE-EPMA that a Ni-enriched layer, as thick as a few hundred mu m, formed near the surface of the slab. Also, a number of laboratory-scale heat treatment tests under oxidizing atmosphere showed that the samples with the Ni-enriched layer had a decreased Cu enrichment at the interface between scale and steel, compared to a case without Ni-rich layer. A pilot-plant-scale steel slab (medium carbon steel containing 0.3 wt pct Cu) was obtained in a continuous casting process with the NiO-containing mold flux, and a Ni-enriched layer was also observed. It was concluded that the use of NiO in the mold flux is a promising new approach for suppressing the Hot Shortness of Cu-containing steel, without an expensive addition of Ni to the whole steel matrix.open110Nsciescopu
C J Van Tyne - One of the best experts on this subject based on the ideXlab platform.
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surface Hot Shortness of 1045 forging steel with residual copper
Journal of Materials Processing Technology, 2005Co-Authors: L G Garza, C J Van TyneAbstract:Abstract Hot-Shortness is brittleness in metals during high temperature deformation. In this study, surface Hot-Shortness of 1045 steels with residual copper was investigated. Eight 1045 steels with differing copper contents, from 0.09 to 0.39% (by weight), were tested. High strain rate compression tests of pre-bulged samples were used to simulate forging deformation conditions. It was found that oxidation time and temperature are critical parameters for the control of Hot-Shortness. The testing was divided into two stages: stage one, in which the steels were oxidized at different temperatures from 1100 to 1200 °C for 10 and 30 min and subsequently deformed to determine the critical temperature where the surface cracking becomes severe; and stage two, in which the steels were oxidized for 1, 3, 5, and 7 min at their critical temperature, and then deformed. In the stage one testing, all steels oxidized for 10 min and subsequently deformed exhibited a critical temperature. The critical temperature decreased with decreasing copper content, from 1160 °C for the steel with the highest copper content to 1110 °C for the steel with the lowest copper content. A simple model based on copper enrichment and depletion along surface grain boundaries is presented to explain these observations. Steels oxidized for 30 min and subsequently deformed did not exhibit severe cracking at any temperature, but the steel with the highest copper content that was deformed at 1140 °C exhibited cracking. In stage two testing, the results were less consistent. The steels with high copper content (0.39–0.32%) exhibited maximum cracking at shorter times, while for the steels with medium copper content (0.30–0.21%) the maximum cracking occurred at longer times. No steel exhibited cracking when oxidized at 1200 °C and subsequently deformed. The study shows that steels have a critical temperature at which cracking is severe. Steels oxidized and deformed above the critical temperature did not exhibit Hot-Shortness surface cracking. Hence, a forging practice that both maintains and deforms the steel above the critical temperature could reduce or eliminate surface Hot-Shortness due to residual copper.