S.E. Offerman
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1
Steel production is essential for modern infrastructure and manufacturing, but remains highly resource- and emission-intensive. Increasing the use of recycled steel scrap is an important route towards more circular and lower-emission steel production. However, scrap streams contain individual pieces with varying chemical compositions, which limits their direct use in high-grade steel production. If residual or alloying elements exceed the limits of a target steel grade, scrap may be down-cycled or diluted with primary raw materials.
This thesis develops and evaluates a recipe-based strategy for scrap sorting that uses piece-level composition data to allocate scrap items to steel recipes. The proposed Sorting Decision Layer is intended to operate between sensor-based sorting equipment and the operator. It evaluates scanned scrap items according to mass, elemental composition, heap capacity, and recipe constraints derived from European Steel Standards. A heap is considered feasible when the mass-weighted average composition of the selected items satisfies the lower and upper elemental limits of a target steel recipe.
Because the allocation problem is highly combinatorial, several heuristic algorithms were developed and tested in a simulation framework using synthetically generated scrap data. Performance was evaluated using item conversion, mass conversion, heap utilisation, and economic value. The results show that a multi-pass greedy algorithm provides the best balance between solution quality and computational efficiency. Further experiments show that increasing heap capacity and the number of heaps improves mass conversion and value creation, but may reduce heap utilisation. A balanced configuration was found around seven heaps with a heap capacity of 12,000 kg, achieving approximately 78% mass conversion and 89% heap utilisation.
Overall, this thesis demonstrates that recipe-based scrap sorting is a promising strategy for increasing the value recovered from steel scrap. By combining sensor-based characterisation, steel recipe constraints, and scalable allocation algorithms, scrap sorting can shift from broad classification towards value-oriented recipe allocation. ...
This thesis develops and evaluates a recipe-based strategy for scrap sorting that uses piece-level composition data to allocate scrap items to steel recipes. The proposed Sorting Decision Layer is intended to operate between sensor-based sorting equipment and the operator. It evaluates scanned scrap items according to mass, elemental composition, heap capacity, and recipe constraints derived from European Steel Standards. A heap is considered feasible when the mass-weighted average composition of the selected items satisfies the lower and upper elemental limits of a target steel recipe.
Because the allocation problem is highly combinatorial, several heuristic algorithms were developed and tested in a simulation framework using synthetically generated scrap data. Performance was evaluated using item conversion, mass conversion, heap utilisation, and economic value. The results show that a multi-pass greedy algorithm provides the best balance between solution quality and computational efficiency. Further experiments show that increasing heap capacity and the number of heaps improves mass conversion and value creation, but may reduce heap utilisation. A balanced configuration was found around seven heaps with a heap capacity of 12,000 kg, achieving approximately 78% mass conversion and 89% heap utilisation.
Overall, this thesis demonstrates that recipe-based scrap sorting is a promising strategy for increasing the value recovered from steel scrap. By combining sensor-based characterisation, steel recipe constraints, and scalable allocation algorithms, scrap sorting can shift from broad classification towards value-oriented recipe allocation. ...
Steel production is essential for modern infrastructure and manufacturing, but remains highly resource- and emission-intensive. Increasing the use of recycled steel scrap is an important route towards more circular and lower-emission steel production. However, scrap streams contain individual pieces with varying chemical compositions, which limits their direct use in high-grade steel production. If residual or alloying elements exceed the limits of a target steel grade, scrap may be down-cycled or diluted with primary raw materials.
This thesis develops and evaluates a recipe-based strategy for scrap sorting that uses piece-level composition data to allocate scrap items to steel recipes. The proposed Sorting Decision Layer is intended to operate between sensor-based sorting equipment and the operator. It evaluates scanned scrap items according to mass, elemental composition, heap capacity, and recipe constraints derived from European Steel Standards. A heap is considered feasible when the mass-weighted average composition of the selected items satisfies the lower and upper elemental limits of a target steel recipe.
Because the allocation problem is highly combinatorial, several heuristic algorithms were developed and tested in a simulation framework using synthetically generated scrap data. Performance was evaluated using item conversion, mass conversion, heap utilisation, and economic value. The results show that a multi-pass greedy algorithm provides the best balance between solution quality and computational efficiency. Further experiments show that increasing heap capacity and the number of heaps improves mass conversion and value creation, but may reduce heap utilisation. A balanced configuration was found around seven heaps with a heap capacity of 12,000 kg, achieving approximately 78% mass conversion and 89% heap utilisation.
Overall, this thesis demonstrates that recipe-based scrap sorting is a promising strategy for increasing the value recovered from steel scrap. By combining sensor-based characterisation, steel recipe constraints, and scalable allocation algorithms, scrap sorting can shift from broad classification towards value-oriented recipe allocation.
This thesis develops and evaluates a recipe-based strategy for scrap sorting that uses piece-level composition data to allocate scrap items to steel recipes. The proposed Sorting Decision Layer is intended to operate between sensor-based sorting equipment and the operator. It evaluates scanned scrap items according to mass, elemental composition, heap capacity, and recipe constraints derived from European Steel Standards. A heap is considered feasible when the mass-weighted average composition of the selected items satisfies the lower and upper elemental limits of a target steel recipe.
Because the allocation problem is highly combinatorial, several heuristic algorithms were developed and tested in a simulation framework using synthetically generated scrap data. Performance was evaluated using item conversion, mass conversion, heap utilisation, and economic value. The results show that a multi-pass greedy algorithm provides the best balance between solution quality and computational efficiency. Further experiments show that increasing heap capacity and the number of heaps improves mass conversion and value creation, but may reduce heap utilisation. A balanced configuration was found around seven heaps with a heap capacity of 12,000 kg, achieving approximately 78% mass conversion and 89% heap utilisation.
Overall, this thesis demonstrates that recipe-based scrap sorting is a promising strategy for increasing the value recovered from steel scrap. By combining sensor-based characterisation, steel recipe constraints, and scalable allocation algorithms, scrap sorting can shift from broad classification towards value-oriented recipe allocation.
In an effort to limit global warming to 1.5 °C by the year 2050, the Ultra Low CO2 Steelmaking (ULCOS) program was launched, from which the HIsarna process was developed by Tata Steel in the Netherlands. This process allows us to refine low-quality iron ore and recycle one of the byproducts of steelmaking, converter slag, as a flux material. These attributes are improvements to the traditional blast furnace and offer a significant reduction in CO2 emissions. However, research on the interaction between converter slag and low-quality iron ore at such high temperatures is limited. The main purpose of this investigation is to compare the impact of converter slag and limestone on the thermal decomposition of low-quality hematite- and goethite-bearing iron ores, particularly focusing on the conversion degree and the products of decomposition. To achieve this, the thermal decomposition of several combinations of the ores with the fluxes added at fractions ranging from 0 to 50 wt.% was first modelled thermodynamically using FactSage software. Laboratory experimentation was conducted to complement these findings, starting with thermogravimetric analysis, followed by heat treatment in a horizontal tube furnace. It was found that there was an increase in liquid phase fraction and slag content with flux addition, with the effects being more pronounced for limestone than converter slag. Additionally, the conversion degree of hematite reduced from ~10% with 0 wt.% flux to ~6.75% and ~7.60% when limestone and converter slag were added at 25 wt.%, respectively. Such a reduction in the conversion degree was attributed to the entrapment of iron in calcium-rich slag phases. Therefore, converter slag was found to be less detrimental to the thermal decomposition of low-quality iron ores, in comparison to the traditional limestone, at 1500 °C, concluding that the use of converter slag as a flux material in HIsarna is promising.
...
In an effort to limit global warming to 1.5 °C by the year 2050, the Ultra Low CO2 Steelmaking (ULCOS) program was launched, from which the HIsarna process was developed by Tata Steel in the Netherlands. This process allows us to refine low-quality iron ore and recycle one of the byproducts of steelmaking, converter slag, as a flux material. These attributes are improvements to the traditional blast furnace and offer a significant reduction in CO2 emissions. However, research on the interaction between converter slag and low-quality iron ore at such high temperatures is limited. The main purpose of this investigation is to compare the impact of converter slag and limestone on the thermal decomposition of low-quality hematite- and goethite-bearing iron ores, particularly focusing on the conversion degree and the products of decomposition. To achieve this, the thermal decomposition of several combinations of the ores with the fluxes added at fractions ranging from 0 to 50 wt.% was first modelled thermodynamically using FactSage software. Laboratory experimentation was conducted to complement these findings, starting with thermogravimetric analysis, followed by heat treatment in a horizontal tube furnace. It was found that there was an increase in liquid phase fraction and slag content with flux addition, with the effects being more pronounced for limestone than converter slag. Additionally, the conversion degree of hematite reduced from ~10% with 0 wt.% flux to ~6.75% and ~7.60% when limestone and converter slag were added at 25 wt.%, respectively. Such a reduction in the conversion degree was attributed to the entrapment of iron in calcium-rich slag phases. Therefore, converter slag was found to be less detrimental to the thermal decomposition of low-quality iron ores, in comparison to the traditional limestone, at 1500 °C, concluding that the use of converter slag as a flux material in HIsarna is promising.
In the semiconductor industry, the ongoing demand for the miniaturization of electronic devices has significantly increased the number of components integrated into a single wafer. Consequently, the dimensions of interconnects in integrated circuits (ICs) must be minimized to connect more transistors. This trend inevitably leads to a substantial rise in current density within the interconnects, posing a major reliability challenge known as electromigration (EM). EM can result in further reliability issues, ultimately causing device failure. Extensive research has been conducted over the past decades to mitigate the impact of EM.
This study focuses on copper (Cu) interconnects, investigating the effect of annealing on their microstructure and the resulting impact on resistivity, with particular emphasis on how the microstructure influences EM. Additionally, the progress of attempting to forming Cu nanotwins via electroplating to resist EM is briefly investigated. Sputtered Cu was annealed at temperatures of 300℃, 400℃, 500℃, and 700℃, and the resulting microstructural variations were characterized by using EBSD. The findings reveal a progressive strengthening of the (111) texture in Cu film and an increase in grain size with higher annealing temperatures. Additionally, a notable decrease in grain boundary length was observed as the annealing temperature increased, correlating with reduced resistivity across the annealed samples. Moreover, the study highlights a elimination of defects and strain within the Cu films with increasing annealing temperatures.
Furthermore, EM measurements were conducted using accelerated tests under conditions of high current stress and high temperature. The variations in the microstructure of Cu films were described, and the correlation between EM mechanisms and microstructural parameters was discussed. To quantify the progress of EM, the drift velocity for each sample was calculated, revealing a trend of slower drift velocities with increasing annealing temperatures. This work provides a unique opportunity to investigate the impact of annealing on the microstructure of Cu interconnects and to study how these changes influence EM performance. The findings contribute to a deeper understanding of EM and enhanced reliability prediction in electronic devices.
Keywords: electromigration, copper interconnects, microstructure, annealing. ...
This study focuses on copper (Cu) interconnects, investigating the effect of annealing on their microstructure and the resulting impact on resistivity, with particular emphasis on how the microstructure influences EM. Additionally, the progress of attempting to forming Cu nanotwins via electroplating to resist EM is briefly investigated. Sputtered Cu was annealed at temperatures of 300℃, 400℃, 500℃, and 700℃, and the resulting microstructural variations were characterized by using EBSD. The findings reveal a progressive strengthening of the (111) texture in Cu film and an increase in grain size with higher annealing temperatures. Additionally, a notable decrease in grain boundary length was observed as the annealing temperature increased, correlating with reduced resistivity across the annealed samples. Moreover, the study highlights a elimination of defects and strain within the Cu films with increasing annealing temperatures.
Furthermore, EM measurements were conducted using accelerated tests under conditions of high current stress and high temperature. The variations in the microstructure of Cu films were described, and the correlation between EM mechanisms and microstructural parameters was discussed. To quantify the progress of EM, the drift velocity for each sample was calculated, revealing a trend of slower drift velocities with increasing annealing temperatures. This work provides a unique opportunity to investigate the impact of annealing on the microstructure of Cu interconnects and to study how these changes influence EM performance. The findings contribute to a deeper understanding of EM and enhanced reliability prediction in electronic devices.
Keywords: electromigration, copper interconnects, microstructure, annealing. ...
In the semiconductor industry, the ongoing demand for the miniaturization of electronic devices has significantly increased the number of components integrated into a single wafer. Consequently, the dimensions of interconnects in integrated circuits (ICs) must be minimized to connect more transistors. This trend inevitably leads to a substantial rise in current density within the interconnects, posing a major reliability challenge known as electromigration (EM). EM can result in further reliability issues, ultimately causing device failure. Extensive research has been conducted over the past decades to mitigate the impact of EM.
This study focuses on copper (Cu) interconnects, investigating the effect of annealing on their microstructure and the resulting impact on resistivity, with particular emphasis on how the microstructure influences EM. Additionally, the progress of attempting to forming Cu nanotwins via electroplating to resist EM is briefly investigated. Sputtered Cu was annealed at temperatures of 300℃, 400℃, 500℃, and 700℃, and the resulting microstructural variations were characterized by using EBSD. The findings reveal a progressive strengthening of the (111) texture in Cu film and an increase in grain size with higher annealing temperatures. Additionally, a notable decrease in grain boundary length was observed as the annealing temperature increased, correlating with reduced resistivity across the annealed samples. Moreover, the study highlights a elimination of defects and strain within the Cu films with increasing annealing temperatures.
Furthermore, EM measurements were conducted using accelerated tests under conditions of high current stress and high temperature. The variations in the microstructure of Cu films were described, and the correlation between EM mechanisms and microstructural parameters was discussed. To quantify the progress of EM, the drift velocity for each sample was calculated, revealing a trend of slower drift velocities with increasing annealing temperatures. This work provides a unique opportunity to investigate the impact of annealing on the microstructure of Cu interconnects and to study how these changes influence EM performance. The findings contribute to a deeper understanding of EM and enhanced reliability prediction in electronic devices.
Keywords: electromigration, copper interconnects, microstructure, annealing.
This study focuses on copper (Cu) interconnects, investigating the effect of annealing on their microstructure and the resulting impact on resistivity, with particular emphasis on how the microstructure influences EM. Additionally, the progress of attempting to forming Cu nanotwins via electroplating to resist EM is briefly investigated. Sputtered Cu was annealed at temperatures of 300℃, 400℃, 500℃, and 700℃, and the resulting microstructural variations were characterized by using EBSD. The findings reveal a progressive strengthening of the (111) texture in Cu film and an increase in grain size with higher annealing temperatures. Additionally, a notable decrease in grain boundary length was observed as the annealing temperature increased, correlating with reduced resistivity across the annealed samples. Moreover, the study highlights a elimination of defects and strain within the Cu films with increasing annealing temperatures.
Furthermore, EM measurements were conducted using accelerated tests under conditions of high current stress and high temperature. The variations in the microstructure of Cu films were described, and the correlation between EM mechanisms and microstructural parameters was discussed. To quantify the progress of EM, the drift velocity for each sample was calculated, revealing a trend of slower drift velocities with increasing annealing temperatures. This work provides a unique opportunity to investigate the impact of annealing on the microstructure of Cu interconnects and to study how these changes influence EM performance. The findings contribute to a deeper understanding of EM and enhanced reliability prediction in electronic devices.
Keywords: electromigration, copper interconnects, microstructure, annealing.
Master thesis
(2024)
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A.P.G. Vercraeye, M.J. Santofimia Navarro, P.M. Martin Saint-Laurence, S.E. Offerman
This study investigates the microstructural evolution of high-carbon quench and partitioning (Q&P) steels and the effect of the chemical composition using techniques such as dilatometry, optical microscopy (OM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). The applied Q&P treatments, starting from full austenitization, were applied to the developed steel, leading to microstructures containing volume fractions of retained austenite between up 0.15-0.30. During the partitioning step, a large fraction of the austenite was sufficiently carbon enriched to be retained at room temperature. In some alloys, depending on chemical composition and fraction of austenite at quench, bainite formation occurred during isothermal holding. Notably, no fresh martensite was formed. The microstructure showed pronounced microstructural banding due to the segregation of alloying elements such as Mn and Si. Solute-rich bands show a coarser microstructure of tempered martensite (TM), relatively large austenite islands and bainite. While solute-lean regions show a finer microstructure of TM and fine film-like retained austenite. Increasing C content resulted in a decrease of the martensite start temperature (𝑀𝑠 ) leading to a higher fraction of untransformed austenite at similar quenching temperatures as well as tetragonal martensite. At higher fractions of untransformed austenite the microstructural difference between solute-rich and solute-lean bands is more pronounced. Alloying elements, such as Mn and Ni, play a critical role in refining the microstructure and stabilising austenite.
...
This study investigates the microstructural evolution of high-carbon quench and partitioning (Q&P) steels and the effect of the chemical composition using techniques such as dilatometry, optical microscopy (OM), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and X-ray diffraction (XRD). The applied Q&P treatments, starting from full austenitization, were applied to the developed steel, leading to microstructures containing volume fractions of retained austenite between up 0.15-0.30. During the partitioning step, a large fraction of the austenite was sufficiently carbon enriched to be retained at room temperature. In some alloys, depending on chemical composition and fraction of austenite at quench, bainite formation occurred during isothermal holding. Notably, no fresh martensite was formed. The microstructure showed pronounced microstructural banding due to the segregation of alloying elements such as Mn and Si. Solute-rich bands show a coarser microstructure of tempered martensite (TM), relatively large austenite islands and bainite. While solute-lean regions show a finer microstructure of TM and fine film-like retained austenite. Increasing C content resulted in a decrease of the martensite start temperature (𝑀𝑠 ) leading to a higher fraction of untransformed austenite at similar quenching temperatures as well as tetragonal martensite. At higher fractions of untransformed austenite the microstructural difference between solute-rich and solute-lean bands is more pronounced. Alloying elements, such as Mn and Ni, play a critical role in refining the microstructure and stabilising austenite.
Essential criteria to a shaving blade include wear resistance, corrosion resistance and a sharp cutting edge. The material selection for improved cutting elements as well as increasing the longevity of the blade would provide benefits not only to the consumer experience of a more efficient shaving performance, but also a more sustainable solution to the recurring disposal of blunt razors.
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Essential criteria to a shaving blade include wear resistance, corrosion resistance and a sharp cutting edge. The material selection for improved cutting elements as well as increasing the longevity of the blade would provide benefits not only to the consumer experience of a more efficient shaving performance, but also a more sustainable solution to the recurring disposal of blunt razors.
Laser surface treatment shows great potential to locally create distinct phases in martensitic steels due to its highly localized laser heat flux. Architectured materials with microstructures of metastable austenite/martensite phases exhibit advanced mechanical properties, such as a better combination of strength and ductility. In addition, the presence of laser-reverted austenite in martensitic microstructure improves the pitting corrosion behavior due to the better corrosion resistance of austenite over the martensite phase. However, the combined microstructure of different phases might lead to the emergence of galvanic corrosion, which deteriorates the general corrosion behavior of the laser-treated materials. These findings suggest that the laser surface treatment affects the general and the localized corrosion behavior differently, which is an interesting prospect that requires further investigation.
Fe-25Ni-0.2C, the material in this study, has the starting martensite formation temperature (Ms) below room temperature due to its high nickel percentage, which is thermodynamically possible to form reverted austenite and remain austenite phases during laser treatment. In this study, a high-power Nd:YAG laser system is utilized to locally create an austenitic region in a cryogenically-formed martensitic Fe-25Ni-0.2C alloy. Optical microscope (OM) and scanning electron microscope (SEM) are used to assess the microstructure prior to and after laser treatment. The observed microstructure is related to the high spatial gradients in peak temperature and the heating rate of localized laser treatment, which governs the formation mechanisms. Moreover, the effect of laser processing parameters, such as laser power (P) and scanning speed (v), on the laser-affected zone (LAZ) is also investigated.
The corrosion behavior is characterized by potentiodynamic polarization tests in a 3.5% NaCl solution. The corroded surface is examined by optical microscope (OM) and the three-dimensional depth measurement of the pit morphology. In this work, both the general and the pitting corrosion behavior are discussed. The results are influenced by the microstructure created by different heat treatments. The effect of localized laser treatment on the corrosion behavior is investigated on a combined microstructure of laser-reverted austenite/bulk martensite, which has a surface fraction of laser-reverted austenite up to nearly 53%.
...
Fe-25Ni-0.2C, the material in this study, has the starting martensite formation temperature (Ms) below room temperature due to its high nickel percentage, which is thermodynamically possible to form reverted austenite and remain austenite phases during laser treatment. In this study, a high-power Nd:YAG laser system is utilized to locally create an austenitic region in a cryogenically-formed martensitic Fe-25Ni-0.2C alloy. Optical microscope (OM) and scanning electron microscope (SEM) are used to assess the microstructure prior to and after laser treatment. The observed microstructure is related to the high spatial gradients in peak temperature and the heating rate of localized laser treatment, which governs the formation mechanisms. Moreover, the effect of laser processing parameters, such as laser power (P) and scanning speed (v), on the laser-affected zone (LAZ) is also investigated.
The corrosion behavior is characterized by potentiodynamic polarization tests in a 3.5% NaCl solution. The corroded surface is examined by optical microscope (OM) and the three-dimensional depth measurement of the pit morphology. In this work, both the general and the pitting corrosion behavior are discussed. The results are influenced by the microstructure created by different heat treatments. The effect of localized laser treatment on the corrosion behavior is investigated on a combined microstructure of laser-reverted austenite/bulk martensite, which has a surface fraction of laser-reverted austenite up to nearly 53%.
...
Laser surface treatment shows great potential to locally create distinct phases in martensitic steels due to its highly localized laser heat flux. Architectured materials with microstructures of metastable austenite/martensite phases exhibit advanced mechanical properties, such as a better combination of strength and ductility. In addition, the presence of laser-reverted austenite in martensitic microstructure improves the pitting corrosion behavior due to the better corrosion resistance of austenite over the martensite phase. However, the combined microstructure of different phases might lead to the emergence of galvanic corrosion, which deteriorates the general corrosion behavior of the laser-treated materials. These findings suggest that the laser surface treatment affects the general and the localized corrosion behavior differently, which is an interesting prospect that requires further investigation.
Fe-25Ni-0.2C, the material in this study, has the starting martensite formation temperature (Ms) below room temperature due to its high nickel percentage, which is thermodynamically possible to form reverted austenite and remain austenite phases during laser treatment. In this study, a high-power Nd:YAG laser system is utilized to locally create an austenitic region in a cryogenically-formed martensitic Fe-25Ni-0.2C alloy. Optical microscope (OM) and scanning electron microscope (SEM) are used to assess the microstructure prior to and after laser treatment. The observed microstructure is related to the high spatial gradients in peak temperature and the heating rate of localized laser treatment, which governs the formation mechanisms. Moreover, the effect of laser processing parameters, such as laser power (P) and scanning speed (v), on the laser-affected zone (LAZ) is also investigated.
The corrosion behavior is characterized by potentiodynamic polarization tests in a 3.5% NaCl solution. The corroded surface is examined by optical microscope (OM) and the three-dimensional depth measurement of the pit morphology. In this work, both the general and the pitting corrosion behavior are discussed. The results are influenced by the microstructure created by different heat treatments. The effect of localized laser treatment on the corrosion behavior is investigated on a combined microstructure of laser-reverted austenite/bulk martensite, which has a surface fraction of laser-reverted austenite up to nearly 53%.
Fe-25Ni-0.2C, the material in this study, has the starting martensite formation temperature (Ms) below room temperature due to its high nickel percentage, which is thermodynamically possible to form reverted austenite and remain austenite phases during laser treatment. In this study, a high-power Nd:YAG laser system is utilized to locally create an austenitic region in a cryogenically-formed martensitic Fe-25Ni-0.2C alloy. Optical microscope (OM) and scanning electron microscope (SEM) are used to assess the microstructure prior to and after laser treatment. The observed microstructure is related to the high spatial gradients in peak temperature and the heating rate of localized laser treatment, which governs the formation mechanisms. Moreover, the effect of laser processing parameters, such as laser power (P) and scanning speed (v), on the laser-affected zone (LAZ) is also investigated.
The corrosion behavior is characterized by potentiodynamic polarization tests in a 3.5% NaCl solution. The corroded surface is examined by optical microscope (OM) and the three-dimensional depth measurement of the pit morphology. In this work, both the general and the pitting corrosion behavior are discussed. The results are influenced by the microstructure created by different heat treatments. The effect of localized laser treatment on the corrosion behavior is investigated on a combined microstructure of laser-reverted austenite/bulk martensite, which has a surface fraction of laser-reverted austenite up to nearly 53%.
Plasticity accompanied by dislocation motion is the essential property of metals. A large number of crystal plasticity models have been developed to predict the mechanical response in the work hardening regime while little attention is paid to pre-yield behavior. In this work, we propose a novel model both pre-yield and post-yield from a discrete dislocation dynamics (DDD) database of 55 DDD realizations. Dislocation density and Frank-Read source height are chosen as microstructural state variables to represent the material state. Flow rule and dislocation multiplication model are in good agreement with DDD results. Discrepancies result from the onset of micro-plasticity in pre-yield. The axial stress-strain response predicted by the novel model is consistent with current DDD data. The evolution equation of source height fails in capturing the evolution in accordance with DDD data, which originates from the inaccuracy brought by indirect extraction of source shape from DDD dislocation networks. Future research recommendations include enlargement of the database, extraction of source shape in situ, and evolution equations for link-based microstructural variables.
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Plasticity accompanied by dislocation motion is the essential property of metals. A large number of crystal plasticity models have been developed to predict the mechanical response in the work hardening regime while little attention is paid to pre-yield behavior. In this work, we propose a novel model both pre-yield and post-yield from a discrete dislocation dynamics (DDD) database of 55 DDD realizations. Dislocation density and Frank-Read source height are chosen as microstructural state variables to represent the material state. Flow rule and dislocation multiplication model are in good agreement with DDD results. Discrepancies result from the onset of micro-plasticity in pre-yield. The axial stress-strain response predicted by the novel model is consistent with current DDD data. The evolution equation of source height fails in capturing the evolution in accordance with DDD data, which originates from the inaccuracy brought by indirect extraction of source shape from DDD dislocation networks. Future research recommendations include enlargement of the database, extraction of source shape in situ, and evolution equations for link-based microstructural variables.
Master thesis
(2020)
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Sahith Kokkirala, J. Sietsma, Han Spijkerman, Mark van Drogen, S.E. Offerman, M.G. Mecozzi
Carburized steel grades are widely used in applications where high hardness at the surface is required in combination with good core toughness as well as high fatigue resistance. The process of carburizing lower to medium carbon steel can generally provide this combination of properties and has been practised for several decades. Such steel is very essential in vehicle power-trains. The carburized 18CrNiMo7-6 pinions are ground to obtain high dimensional precision after the carburization, quenching and tempering heat-treatment process. During the grinding process, thermal damage is developed due to the high localised heat energy at the contact zone of the grinding wheel and pinion. The developed thermal damage is known as grinding-induced burn. The burns are observed when the temperature reaches above the tempering range (i.e. 210 ̊ C) and the intensity of the grinding-induced burn is in relation to the thermo-mechanical effects of the grinding process. The nital etch process is used to identify the burns using ISO 14104:2017 standard and the process detects using the discolouration developed on the burn site caused by the chemical attack. The information about the intensity of detected burns are not known in the nital etch method. However, the intensity of the grinding-induced burns can be measured using magnetoelastic parameter of Barkhausen Noise (BN) technique which functions in relation to the microstructure and stress state of the material. The present study aims to investigate microstructural features of grinding-induced burns of varying BN intensities, to evaluate the service life testing of the thermally damaged pinions and the effect of varying grinding parameters on the generation of grinding-induced burns. The microstructure characterization is done by optical microscope, Vickers hardness, scanning electron microscope, X-ray diffraction and correlate the obtained results with the BN signals. The increased pinion speed and reduced grinding cycles are observed in the favouring of increasing localized heat input at the contact zone of grinding wheel and pinion causing the BN signals to increase. 3 samples of varying intensities of grinding induced burns are detected using BN and are characterized. The obtained results gave a good correlation with the Barkhausen noise signals. As the heating rate at the grinding contact zone increased above the tempering range, the BN signals also increased due to the enhanced domain wall movement with the softer microstructure which is observed due to the retained austenite decomposition and carbon diffusion from the tempered martensitic phase. The further increase in temperature above the austenitization range led to the re-hardening burn. The freshly formed structure is brittle and hard untempered martensite at the surface surrounded by the softer tempering burn which might be detrimental during the pinion functioning. The axle test results of the tempered burn pinion observed the transformation of retained austenite to martensitic structure during the cyclic loading which eventually enhanced the surface properties by increase in hardness from 621 HV1 to 676 HV1 at 0.1 mm depth and generating -600 ± 6.6 MPa compressive residual stress due to the volume expansion. This transformation resulted in the grinding induced burn pinion to survive the axle test without failure.
...
Carburized steel grades are widely used in applications where high hardness at the surface is required in combination with good core toughness as well as high fatigue resistance. The process of carburizing lower to medium carbon steel can generally provide this combination of properties and has been practised for several decades. Such steel is very essential in vehicle power-trains. The carburized 18CrNiMo7-6 pinions are ground to obtain high dimensional precision after the carburization, quenching and tempering heat-treatment process. During the grinding process, thermal damage is developed due to the high localised heat energy at the contact zone of the grinding wheel and pinion. The developed thermal damage is known as grinding-induced burn. The burns are observed when the temperature reaches above the tempering range (i.e. 210 ̊ C) and the intensity of the grinding-induced burn is in relation to the thermo-mechanical effects of the grinding process. The nital etch process is used to identify the burns using ISO 14104:2017 standard and the process detects using the discolouration developed on the burn site caused by the chemical attack. The information about the intensity of detected burns are not known in the nital etch method. However, the intensity of the grinding-induced burns can be measured using magnetoelastic parameter of Barkhausen Noise (BN) technique which functions in relation to the microstructure and stress state of the material. The present study aims to investigate microstructural features of grinding-induced burns of varying BN intensities, to evaluate the service life testing of the thermally damaged pinions and the effect of varying grinding parameters on the generation of grinding-induced burns. The microstructure characterization is done by optical microscope, Vickers hardness, scanning electron microscope, X-ray diffraction and correlate the obtained results with the BN signals. The increased pinion speed and reduced grinding cycles are observed in the favouring of increasing localized heat input at the contact zone of grinding wheel and pinion causing the BN signals to increase. 3 samples of varying intensities of grinding induced burns are detected using BN and are characterized. The obtained results gave a good correlation with the Barkhausen noise signals. As the heating rate at the grinding contact zone increased above the tempering range, the BN signals also increased due to the enhanced domain wall movement with the softer microstructure which is observed due to the retained austenite decomposition and carbon diffusion from the tempered martensitic phase. The further increase in temperature above the austenitization range led to the re-hardening burn. The freshly formed structure is brittle and hard untempered martensite at the surface surrounded by the softer tempering burn which might be detrimental during the pinion functioning. The axle test results of the tempered burn pinion observed the transformation of retained austenite to martensitic structure during the cyclic loading which eventually enhanced the surface properties by increase in hardness from 621 HV1 to 676 HV1 at 0.1 mm depth and generating -600 ± 6.6 MPa compressive residual stress due to the volume expansion. This transformation resulted in the grinding induced burn pinion to survive the axle test without failure.
Zinc vapourisation from sludge wastes under thermal processing conditions
Zinc enrichment in HIsarna flue dust
HIsarna is a new furnace technology in the steel industry, featuring a large reduction of CO2-emissions of up to 80%, and offering larger tolerances for gangue materials. Additionally, it has potential for zinc enrichment in the flue dust, as it can quickly vapourise zinc in the feed material and reject it to the flue dust. Increasing the zinc fraction in the flue dust up to 50% would allow for zinc recovery in the zinc smelters. The larger tolerances of the furnace make it possible to include material streams currently mostly land filled. In this thesis, the focus has been on three of these waste streams, goethite, Blast Furnace (BF) dust, and Basic Oxygen Furnace (BOF) dust. The research focussed on acquiring fundamental knowledge on the behaviour of these waste dusts at high temperatures and various retention times. This will aid their future use as an alternative feed stream material for enriching the HIsarna flue dust with zinc, without compromising the longevity of the furnace or the quality of the steel.
In a literature study, several alternative materials were investigated. Of particular interest are the sludge wastes from the steel industry for their large iron and zinc contents, the sludge waste from the zinc smelters for the same reason, and galvanised steel scrap, possibly in combination with EAF dust. There are a few challenges to overcome, such as the copper concentration in the zinc smelter residues, or the variation in composition and quality of steel scrap. However, these materials were identified as high potential for inclusion in HIsarna. It was found that zinc can effectively be reduced and vapourised from the waste dusts regardless of its mineral form, in case there is carbon. The carbon acts as a reductant for the iron oxides, including zinc ferrite, and for zinc oxide. Goethite does not contain any carbon, however, mixing with BF sludge will allow the vapourisation of zinc. A model is proposed for estimation of the amount of carbon, and by extension BF dust, that is needed to achieve a full reduction of the iron oxides with native carbon sources. This will aid future mixing of these waste streams, allowing more control over the composition of the feed stream.
A competing mechanism to direct reduction of zinc oxide was identified. Zinc oxide can react with S2 gas which forms during the thermal shock treatment, forming a zinc sulfide fine particle. At high temperatures, this intermediate species decomposes over time to release the zinc vapour, however, the exact mechanism could not be deduced from the experiments. The mechanism and timescale was verified at various temperatures, and holds up until 1300 ºC. The timescale shortens significantly when increasing the temperature. Therefore, from the work conducted, it was concluded that the zinc can be effectively removed at a relevant timescale for HIsarna and collected in the flue dust. ...
In a literature study, several alternative materials were investigated. Of particular interest are the sludge wastes from the steel industry for their large iron and zinc contents, the sludge waste from the zinc smelters for the same reason, and galvanised steel scrap, possibly in combination with EAF dust. There are a few challenges to overcome, such as the copper concentration in the zinc smelter residues, or the variation in composition and quality of steel scrap. However, these materials were identified as high potential for inclusion in HIsarna. It was found that zinc can effectively be reduced and vapourised from the waste dusts regardless of its mineral form, in case there is carbon. The carbon acts as a reductant for the iron oxides, including zinc ferrite, and for zinc oxide. Goethite does not contain any carbon, however, mixing with BF sludge will allow the vapourisation of zinc. A model is proposed for estimation of the amount of carbon, and by extension BF dust, that is needed to achieve a full reduction of the iron oxides with native carbon sources. This will aid future mixing of these waste streams, allowing more control over the composition of the feed stream.
A competing mechanism to direct reduction of zinc oxide was identified. Zinc oxide can react with S2 gas which forms during the thermal shock treatment, forming a zinc sulfide fine particle. At high temperatures, this intermediate species decomposes over time to release the zinc vapour, however, the exact mechanism could not be deduced from the experiments. The mechanism and timescale was verified at various temperatures, and holds up until 1300 ºC. The timescale shortens significantly when increasing the temperature. Therefore, from the work conducted, it was concluded that the zinc can be effectively removed at a relevant timescale for HIsarna and collected in the flue dust. ...
HIsarna is a new furnace technology in the steel industry, featuring a large reduction of CO2-emissions of up to 80%, and offering larger tolerances for gangue materials. Additionally, it has potential for zinc enrichment in the flue dust, as it can quickly vapourise zinc in the feed material and reject it to the flue dust. Increasing the zinc fraction in the flue dust up to 50% would allow for zinc recovery in the zinc smelters. The larger tolerances of the furnace make it possible to include material streams currently mostly land filled. In this thesis, the focus has been on three of these waste streams, goethite, Blast Furnace (BF) dust, and Basic Oxygen Furnace (BOF) dust. The research focussed on acquiring fundamental knowledge on the behaviour of these waste dusts at high temperatures and various retention times. This will aid their future use as an alternative feed stream material for enriching the HIsarna flue dust with zinc, without compromising the longevity of the furnace or the quality of the steel.
In a literature study, several alternative materials were investigated. Of particular interest are the sludge wastes from the steel industry for their large iron and zinc contents, the sludge waste from the zinc smelters for the same reason, and galvanised steel scrap, possibly in combination with EAF dust. There are a few challenges to overcome, such as the copper concentration in the zinc smelter residues, or the variation in composition and quality of steel scrap. However, these materials were identified as high potential for inclusion in HIsarna. It was found that zinc can effectively be reduced and vapourised from the waste dusts regardless of its mineral form, in case there is carbon. The carbon acts as a reductant for the iron oxides, including zinc ferrite, and for zinc oxide. Goethite does not contain any carbon, however, mixing with BF sludge will allow the vapourisation of zinc. A model is proposed for estimation of the amount of carbon, and by extension BF dust, that is needed to achieve a full reduction of the iron oxides with native carbon sources. This will aid future mixing of these waste streams, allowing more control over the composition of the feed stream.
A competing mechanism to direct reduction of zinc oxide was identified. Zinc oxide can react with S2 gas which forms during the thermal shock treatment, forming a zinc sulfide fine particle. At high temperatures, this intermediate species decomposes over time to release the zinc vapour, however, the exact mechanism could not be deduced from the experiments. The mechanism and timescale was verified at various temperatures, and holds up until 1300 ºC. The timescale shortens significantly when increasing the temperature. Therefore, from the work conducted, it was concluded that the zinc can be effectively removed at a relevant timescale for HIsarna and collected in the flue dust.
In a literature study, several alternative materials were investigated. Of particular interest are the sludge wastes from the steel industry for their large iron and zinc contents, the sludge waste from the zinc smelters for the same reason, and galvanised steel scrap, possibly in combination with EAF dust. There are a few challenges to overcome, such as the copper concentration in the zinc smelter residues, or the variation in composition and quality of steel scrap. However, these materials were identified as high potential for inclusion in HIsarna. It was found that zinc can effectively be reduced and vapourised from the waste dusts regardless of its mineral form, in case there is carbon. The carbon acts as a reductant for the iron oxides, including zinc ferrite, and for zinc oxide. Goethite does not contain any carbon, however, mixing with BF sludge will allow the vapourisation of zinc. A model is proposed for estimation of the amount of carbon, and by extension BF dust, that is needed to achieve a full reduction of the iron oxides with native carbon sources. This will aid future mixing of these waste streams, allowing more control over the composition of the feed stream.
A competing mechanism to direct reduction of zinc oxide was identified. Zinc oxide can react with S2 gas which forms during the thermal shock treatment, forming a zinc sulfide fine particle. At high temperatures, this intermediate species decomposes over time to release the zinc vapour, however, the exact mechanism could not be deduced from the experiments. The mechanism and timescale was verified at various temperatures, and holds up until 1300 ºC. The timescale shortens significantly when increasing the temperature. Therefore, from the work conducted, it was concluded that the zinc can be effectively removed at a relevant timescale for HIsarna and collected in the flue dust.