| 1. |
- Jagodzińska, Katarzyna, 1990-
(författare)
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Energy and material recovery from high-ash waste through pyrolysis
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Undoubtedly, the past practices of profit maximisation by all means, which fuelled swift industrialisation and urbanisation, left behind a legacy of non-sanitary old landfills polluting the environment. These, together with active landfills supplied with tremendous streams of waste produced annually, are a loose cannon calling for action. Specifically, this action is the transition to resource- and energy-efficient economy model – the so-called circular economy.The circular economy approach includes the closing of material loops by both: i) the recycling of pre- and post-consumer residues and ii) the mining of existing landfills, treated as material stocks. Following this, the possibility of energy and material recovery from two types of high-ash waste was investigated within this thesis. The first type of waste is a fine residue from the shredding of the mixture of industrial and municipal metallic waste with end-of-life vehicles (the so-called 'shredder fines'), which represents the aforementioned pre-and post-consumer residues. The second type of waste is excavated waste from an old landfill, and its recovery falls within the latter way of closing the material loops mentioned above.For the purpose of energy and material recovery, the aforementioned waste was subjected to thermochemical processes, namely pyrolysis and pyrolysis with in-line catalytic decomposition of the produced pyrovapours (volatile pyrolysis products). This thesis consists of four studies on that matter.The research within this thesis started with the characterisation of excavated waste fractions to preliminarily assess their potential further applications. The fractions are characterised by significant contamination with heavy metals (mainly Hg and Pb) and chlorine. Furthermore, they are characterised by highly heterogeneous compositions, reflected in a high complexity of the formed pyrovapours. However, in order to maximise the fractions' utilisation ratio, their collective pyrolysis in the form of refuse-derived fuel (RDF) was proposed for further studies.Following the above, the second study performed within the thesis aimed at the characterisation of the products from excavated RDF pyrolysis. The pyrovapours obtained at 500°C and 600°C showed potential for further catalytic upgrading to higher-quality products. Given the above, a study on the in-line catalytic decomposition of the pyrovapours from excavated RDF pyrolysis was performed. The process was aimed at the production of a H2-rich gas along with carbon nanotubes (CNTs). The study investigated the influence of the catalyst composition, its synthesis method, and catalytic bed temperature on the H2 and CNTs yields. Eventually, the bimetallic Fe-Ni/Al2O3 catalyst prepared using the sol-gel method showed the best performance as it tripled the H2 conversion rate (in comparison to the case without using a catalyst) and yielded 76 mg/gsample_daf CNTs of promising characteristics. Nevertheless, further research on this process is necessary to optimise it and to assess its feasibility subsequently.The final study included in the thesis focused on enhancing metals recovery from shredder fines by subjecting them to torrefaction (low-temperature pyrolysis). The process results in partial decomposition of the so-called 'fluff' (textiles fibres with plastic, wood and rubber particles in which metal particles are entangled), which interferes with the sorting techniques. Therefore, torrefaction seems to be a promising way of liberating metal particles from shredder fines so that metals can be recycled.
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| 2. |
- Yang, Hanmin, 1992-, et al.
(författare)
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Carbon-negative valorization of biomass waste into affordable green hydrogen and battery anodes
- 2023
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Ingår i: International journal of hydrogen energy. - : Elsevier BV. - 0360-3199 .- 1879-3487.
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The global Sustainable Development Goals highlight the necessity for affordable and clean energy, designated as SDG7. A sustainable and feasible biorefinery concept is proposed for the carbon-negative utilization of biomass waste for affordable H2 and battery anode material production. Specifically, an innovative tandem biocarbon + NiAlO + biocarbon catalyst strategy is constructed to realize a complete reforming of biomass pyro-vapors into H2+CO (as a mixture). The solid residues from pyrolysis are upgraded into high-quality hard carbon (HCs), demonstrating potential as sodium ion battery (SIBs) anodes. The product, HC-1600-6h, exhibited great electrochemical performance when employed as (SIBs) anodes (full cell: 263 Wh/kg with ICE of 89%). Ultimately, a comprehensive process is designed, simulated, and evaluated. The process yields 75 kg H2, 169 kg HCs, and 891 kg captured CO2 per ton of biomass achieving approx. 100% carbon and hydrogen utilization efficiencies. A life cycle assessment estimates a biomass valorization process with negative-emissions (−0.81 kg CO2/kg-biomass, reliant on Sweden wind electricity). A techno-economic assessment forecasts a notably profitable process capable of co-producing affordable H2 and hard carbon battery anodes. The payback period of the process is projected to fall within two years, assuming reference prices of 13.7 €/kg for HCs and 5 €/kg for H2. The process contributes to a novel business paradigm for sustainable and commercially viable biorefinery process, achieving carbon-negative valorization of biomass waste into affordable energy and materials.
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| 3. |
- Wen, Yuming, 1994-
(författare)
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Towards a Sustainable Biomass and Waste Refinery Based on Pyrolysis Combined with a Pretreatment Process
- 2022
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Some of the naturally accumulated biomass and the massive production of waste by human activities have caused serious environmental problems. The degradation of biomass and waste is one of the main greenhouse gasses (GHG) emission sources. Pyrolysis is a technique that can convert the organic feedstock into char, bio-oil, and gas at 350 - 800 °C and in the absence of oxygen. The diversity of the pyro-products makes pyrolysis one of the most promising techniques for biomass and waste refineries. One of the main challenges of the technique is that the unfavorable physical and/or chemical properties of the feedstock would increase the energy and cost required for the whole refinery process. Combining feedstock pretreatment with a pyro-refinery has the potential to make the entire process more efficient from a cost, energy, and climate perspective. In this thesis, the performance of the peat moss pyrolysis is firstly investigated. It was found that it has a potential to convert peat moss into fuels through pyrolysis. Thereafter, beach-cast seaweed is further considered as a feedstock for the process, which is a high-ash content biomass. Three refinery processes were designed and simulated based on the pyrolysis results. Results showed that it was necessary to have a washing pretreatment for the beach-cast seaweed pyro-refinery. The implementation of washing pretreatment could decrease the direct energy for the whole process from 1485.8 to 1121.0 MJ for treating one ton of dry beach-cast seaweed. The further life cycle assessment (LCA) analysis showed that using the pyro-refinery process with washing pretreatment to treat one ton of dry beach-cast seaweed for the electricity production had the lowest cumulated energy demand (CED). Specifically, it has a value of -3.0 GJ and the lowest global warming potential within a 100-year time frame (GWP100) with a value of -790.9 kg CO2eq compared to the other scenarios of producing liquid biofuel and syngas. Digestate from anaerobic digestion (AD) requires proper treatment. The third work of this thesis compares the pyrolysis behavior of the organic fraction of municipal solid waste (OFMSW) and its digestate. It was found that the AD process could decrease the pyrolytic activation energy of OFMSW. Due to digestate’s higher ash content, the char yield rate of digestate was higher than that of OFMSW. On the other hand, the yield rates of bio-oil and gas of OFMSW pyrolysis were higher than that of its digestate. The moisture content of the digestate is hard to be removed by traditional mechanical dewatering techniques due to digestate’s hydrophilic properties. Thus, the use of a pretreatment combined with hydrothermal carbonization (HTC) and mechanical dewatering has the potential to contribute to the digestate pyro-refinery. In the last work, the effect of HTC on the kinetics and thermodynamics of the agricultural waste digestate (AWD) pyrolysis was investigated. It was revealed that the HTC pretreatment could decrease the pyrolytic activation energy of AWD from 182.9 - 274.4 kJ/mol to 144.6 - 205.2 kJ/mol. Bench-scale pyrolysis experiments, process simulations, and LCA were then conducted based on the kinetic prediction results. In the process simulations and LCA, four scenarios of AWD refinery with different pretreatment combinations with HTC and mechanical dewatering were designed. It was found that the different pretreatment processes could benefit the designed AWD refinery for different targets. The implementation of both HTC and mechanical dewatering pretreatment for refinery based on a 650 °C-pyrolysis presented the lowest CED value of 10.3 GJ for treating one ton of AWD. The least emission of carbon dioxide equivalents (-843.3 kg) was achieved in the case of using a 650 °C-pyrolysis temperature with the pretreatment with only a dewatering process when treating 1-ton dry AWD.
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| 4. |
- Compañero, Reinol Josef, 1987-
(författare)
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Recirculation of scrapped resources : The role of material information in enhancing the sustainability of recycling
- 2024
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Industries have responded to the climate change problem by positioning their activities as compatible with concepts such as the Circular Economy. Conveying the idea of maximizing and keeping the resources in a manner that aligns with the principles of sustainable development, the endorsements for implementing circularity measures has arguably become a boon for businesses. Firms that have traditionally consumed both primary and anthropogenic resources in the production of materials used in infrastructure, transportation, and other technological requirements are in a special position. On the one hand, their products are needed for societal development. But on the other hand, their activities emit considerable amounts of greenhouse gases.The steel industry is a classic example where material and energy resource savings are achieved when the End-of-Life (EoL) products are recycled. However, these assumed efficiencies are provisional to scrap being a suitable replacement for ore-based resources. The replacement of primary (i.e. purer) - with secondary (i.e. contaminated) as feedstock for production depends heavily on a recycling system’s capability to deal with the complexity of the ferrous scrap streams that society is generating. More specifically, in reference to recovering the material identity through characterization and sorting that lessens or avoids the current practice of either diluting contaminants or compensating for insufficient alloying through addition of primary resources.This present thesis takes a critical look at the use of scrap with the view that recycling is a technical process that is carried out by enterprises. The impression that recycling consequently replaces the use of primary resources is scrutinized, with consideration of scrap as a characteristically appropriate, but innately challenging feedstock to use. Case studies focusing on the Swedish scrap-based production context revealed that the recycling system actors operate and transact on the basis ofscrap’s quality, which in turn was interpreted as being multidimensional and dependent on each actor’s preferences. The alignment of economic and environmental interests connected with scrap utilization was found to be limited, with companies preferring the use of primary resources when scrap is no longer suitable.The idea of suitability was then ascribed to compositional information regarding scrap and tested at two levels: having access to partial or full information. The former is what is achieved through the current scrap handling in the reverse loop while the latter is an idealized situation where the exact chemistry of the scrap is known. An optimization program was then used to simulate steel recycling where the scenarios tested were designed to focus on the response of the production model to the scrap chemistry of the input materials. The results obtained showed an overall decrease in production costs and an increase in the proportion of scrap used in production. In most cases, this was attributed to the flexibility to allocate scrap based on its composition to the closest matching target products.Finally, additional interviews with industry practitioners further clarified established, company-based protocols for dealing with the lack of information and provided insights with regard to opportunities for increasing scrap utilization. An analysis of the responses suggested that there are contextual differences when it comes to practices by each company, and even attitudes, towards anthropogenic resources. Ultimately, the insights from this thesis lend support to the need of enterprises to address the trade-offs related to scrap utilization and lead to enhanced sustainability in steel recycling.
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| 5. |
- Akbarnejad, Shahin, 1978-
(författare)
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Mathematical and Experimental Study on Filtration of Solid Inclusions from Molten Aluminium and Steel
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Aluminum and steel have been the most produced metal and alloy, respectively, for many years. Their extensive use in various industries, their fundamental role in our everyday life, and their excellent recycling characteristics are the major driving forces for development of their production towards more sustainable processes. A successful integration and application of molten metal filtration from unwanted inclusions in production processes could result in reducing scrap, rework and would provide a cleaner molten metal which could lead to production of metallic materials with enhanced mechanical properties. Filtration of aluminum melts by ceramic foam filters is an established process in aluminum industry. Ceramic filters are also used in steel foundries to remove inclusions from the melt prior to casting to the mold. However, the use of ceramic filters is either limited to specific types of alloys or casts or to specific filters with large pores and openings. As a result, utilization of ceramic filters in the steel industry has limitations in capturing inclusions, where specifically small size inclusions may not be captured. This research work aims at contributing to the global effort in developing the molten metal production processes to become more sustainable and to increase the quality of the final product. To be specific, it is aimed at shedding more light into filtration applications and the use of ceramic filters for removal of solid non-metallic inclusions from molten aluminum and steel. Thus, permeability characteristics of single 30, 50, and 80 Pore Per Inch (PPI) alumina Ceramic Foam Filter (CFF) grades as well as stacks of three 30, three 50, and three 80 PPI alumina CFF grades were both experimentally and numerically obtained and studied. This provides the information needed to estimate the pressure required to prime and/or push the molten aluminum through the filters. The pressure could either be built up by gravitational or other forces. It has been shown recently that it is possible to prime such filters with electromagnetic forces and filter solid inclusions from molten aluminum. Lastly, physical refining of molten steel from solid alumina inclusions through monolithic extruded square-celled alumina ceramic filter was investigated and studied with a developed mathematical Computational Fluid Dynamics (CFD) model as well as the particle trajectories of inclusions in the size range of 1 to 100 [µm]. The experimentally obtained permeability characteristics as well as the obtained pressure gradient profiles of the single 30, 50, and 80 PPI CFFs were compared to previous research findings from the literature. Overall, a good agreement between the current and previous findings was found. It was also shown that fluid bypassing should be avoided during permeability experiments, otherwise deviations as high as 60% may occur. It was also revealed that similar permeability characteristics for the stacked filters, compared to single filters, could be achieved. However, an about three times higher pressure gradient or pressure needs to be applied when using a stack of three identical PPI filters compared to using single filters. The numerical simulations also validated the experimental findings of the permeability experiments. The CFD simulations and particle trajectories of the solid alumina inclusions in molten steel through the monolithic alumina filter revealed that it was possible to capture all particles larger than 50 [µm]. However, it was not possible to capture all particles smaller than 50 [µm] due to the applied simulation approach as well as current simulation limitations in the software.
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| 6. |
- Al-Saadi, Munir, 1965-
(författare)
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Thermomechanical Processing of Nickel-Base Alloy 825
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Alloy 825 material was studied using a Gleeble-3800 thermosimulatorby performing single-hot compression experiments.Optical microscopy and electron backscatter diffraction wereutilized to characterize the microstructure. Dynamicrecrystallization is not considerable in the as-cast alloy anddislocation recovery is deemed to be dominant. Based on thisfinding, the effect of adding trace amounts of alloying additionson the mechanical properties of cast alloy 825 was studied, withemphasis on whether or not dynamic recrystallization occurred.The results show that dynamic recrystallization was moreprevalent under all test conditions in samples containing a traceamount of magnesium, but not for the conventional alloy.However, alloying with trace magnesium did not lead to animprovement of the mechanical properties. Instead, processingmaps for hot forging of conventional Alloy 825 were required toidentify optimal working parameters and to achieve dynamicrecrystallization. The hot deformation behavior of cast Alloy 825was characterized by using dynamic materials modelling of hotcompression data. The results show that the maximum powerdissipation efficiency is over 35%. The highest efficiency isachieved in the temperature range of 1100 ℃ - 1250 ℃ and instrain rates in the range of 0.01 ≤ strain rate / s ≤ 0.1. The optimumprocessing parameters for good strain hardening are obtained inthe temperature range between 950 ℃ and 1100 ℃ with strainrates of 0.3 ≤ strain rate/ s ≤ 10.0. In addition, the influence of thedeformation level on the recrystallization and microstructuralchanges in Alloy 825 during hot forging operations attemperatures between 950 °C and 1200 °C was studied. Themaximum yield strength and ultimate tensile strength wereobtained after forging to achieve a true strain of 0.9 were 413 MPa and 622 MPa , respectively, with a ductility of 40%.However, Alloy 825 is often supplied as annealed bars.Therefore, the effect of the forging strain magnitude andsubsequent annealing on the microstructure, strengtheningmechanisms and room temperature mechanical properties wereinvestigated to assess the suitability of current industrialpractice. The results showed that the majority of strengtheningwas attributed to grain refinement, the dislocation densities thatarise due to the large forging strain, and due to solid solutionstrengthening. The results of calculations are in excellentagreement with experimental data, with less than 1% difference.These results can be used by future researchers and industry topredict the strength of Alloy 825 and similar alloys, especially inmaterial after a completed hot forging operation.
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| 7. |
- Bölke, Kristofer
(författare)
-
IronArc a New Process for Pig Iron Production : A Numerical and Experimental Investigation Focusing on Mixing
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- I den här studien så var syftet att undersöka omrörningen och relaterade fenomen i den nyutvecklade IronArc processen. Processen använder sig av gasinjektion genom plasmageneratorer för att smälta och reducera en slagg bestående av järnoxid. Både penetrationsdjupet hos gasen och omrörningstiden undersöktes under olika förhållanden för att de är viktiga parametrar för processen. Undersökningen har gjorts både genom experiment och Computational Fluid Dynamics (CFD).Först utvecklades en nerskalad modell i akrylplast av IronArc pilot reaktorn i skala 1:3, där både penetrationsdjupet och omrörningstiden bestämdes för ett system med luft och vatten genom fysiska experiment. Sedan så skapades en matematisk modell för att beskriva penetrationen av luft injicerat i vatten. Den validerade modellen användes sedan för att beskriva penetrationsdjupet av den injicerade gasen i slaggen för pilotreaktorn. Vidare så utvecklades en ny metod för att bestämma omrörningstiden i pilotreaktorn med slagg som flytande medium. Slaggen undersöktes också både med hjälp av ljusoptiskt mikroskop (LOM) och även genom beräkningar i Thermo-Calc. Detta gjordes för att undersöka huruvida slaggen är i smält tillstånd då processen körs. Ytterligare en matematisk modell utvecklades sedan för att beskriva omrörningen i den nedskalade modellen av akrylplast med luft och vatten. Samma CFD modell användes för att beskriva omrörningen i pilotreaktorn, där modellen validerades mot de tidigare resultaten från de fysiska experimenten med slagg i pilotreaktorn. Slutligen så utfördes ytterligare försök i pilotreaktorn för att bestämma omrörningstiden, men med vatten istället för slagg. Det bör även nämnas att det enbart var luft som injicerades utan att gasen värmdes upp i plasmageneratorn, då vattnet skulle evaporerat om man värmt gasen.Den genomsnittliga omrörningstiden för den nerskalade modellen där luft injicerades i vatten bestämdes till 7,6 s och 10,2 sekunder för respektive homogeniseringsgrad på 95% och 99%. Detta gjorde då ett inlopp användes med ett gasflöde på 282 NLmin-1 användes. Det visade sig att den genomsnittliga omrörningstiden ökade med 15,8% för 95% homogenisering och 17,6% för 99% homogeniseringsgrad då 3 inlopp användes för samma gasflöde. Penetrationsdjupet visade på ett pulserande beteende med ett maximum och minimum värde för respektive undersökt gasflöde.Penetrationsdjupet för experimentet med gas injicerat i vatten kunde beskrivas korrekt med CFD modellen, där Euler-Euler metoden bestämde penetrationsdjupet av experimentet inom en noggrannhet på 86%. Det visade sig också att denna metod reducerade beräkningstiden jämfört med den andra testade Volume of Fluid (VOF) modellen. Penetrationsdjupet av gas i slagg predikterades till 0.3 m, vilket motsvarar radiens läng i reaktorn.Resultaten visade att möjligt att experimentellt bestämma omrörningstiden i pilotreaktorn genom att addera ett spårämne (MnO2 pulver) till slaggen och ta kontinuerliga prover. Mer specifikt så var tiden för att homogenisera badet under 10 sekunder efter att spårämnet tillsatts. Både LOM (Ljusoptiskt Mikroskop) observationerna och Thermo-Calc beräkningarna indikerade att det var rimligt att anta att slaggen är i smält tillstånd under körning.Den predikterade omrörningstiden för den numeriska modellen för luft-vatten systemet var 7,5 sekunder och överensstämmer med experimentresultaten med 1,3%. omrörningstiden bestämdes till 6.5 sekunder för simuleringen av pilotreaktorn och det stämmer överens med resultaten från experimenten i pilotskalan som visade att omrörningstiden var under 10 sekunder. Även resultaten från experimenten då omörningstiden bestämdes 8,5 och 14 sekunder för 95 % och 99% homogeniseringsgrad, då reaktorn var vattenfylld.Denna undersökning av den nya IronArc-processen har gett värdefull information om omrörningen som kan användas i designbeslut för en framtida storskalig järnframställningsprocess.
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| 8. |
- De Colle, Mattia
(författare)
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Experimental studies to overcome the recycling barriers of stainless-steel and BOF slags
- 2022
-
Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis presents several studies aimed at improving the recycling of steel slag. The studies are based on a first evaluation of the state-of-the-artof the recycling applications both with respect to their possibilities and limitations. In addition, an analysis that highlights several properties of allkinds of ferrous slags, such as bulk chemical composition and common mineral phases, is presented to aid the discussion. Specifically, the studiespresented in this thesis cover two main topics: a new recycling application for stainless-steel slags and a theoretical study on the hydration offerropericlase, which is a mineral often present in basic oxygen furnace slags. Most of the studies presented in this thesis focus on the exploration of anew use of stainless-steel slags, aimed at increasing their recycling rate. In fact, this kind of materials are the most problematic slags to recycle, asmost are not viable for most of the state-of-the-art applications. Therefore, the potential to use them as a substitute for lime in the neutralization ofacidic waste waters is investigated. The studies cover a wide range of trials, from test performed at both laboratory and industrial scale with acidicwaste waters collected from stainless-steel plants, to more fundamental studies on the dissolution of slag minerals in acid environment. Overall,the substitution of lime with stainless-steel slags is proved to be successful both in terms of the obtained final pH values as well as in terms ofobtaining an efficient removal of metal ions dissolved in waters. In the last part of the thesis, a theoretical study on the hydration offerropericlase is conducted. This study proposes a possible technical solution to reduce the volumetric expansion of steel slags, which containhigh percentages of periclase. Specifically, it is seen that ferropericlase with high percentages of FeO adsorbs less water. Thus, they expand lesscompared to regular periclase. Therefore, the formation of such a phase during the solidification of slag can provide a higher volumetric stability,which is highly beneficial when the material later is employed in outdoors applications
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| 9. |
- Du, Hongying, 1991-
(författare)
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Evaluations of Non-metallic Inclusionsin Ca-treated Steels and Their Effect on the Machinability
- 2021
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In recent decades, a considerable development of steel with respect to the performance of steel has taken place, which also has resulted in large challenges to process these steel grades. Therefore, it is essential to make suitable modifications of non-metallic inclusions (NMI) in the steelmaking process and to have a good control of its characteristics to meet the target mechanical properties and to obtain a good machinability. Based on a case of 316L stainless steel trials with a calcium modification to improve the machinability of steel, the influence and contribution of different NMIs on the machinability were discussed. First, based on the Thermo-Calc calculation results with respect to the appropriate range of Ca additions, steel is produced by an additional Ca treatment at the end of the ladle treatment. In order to evaluate non-metallic inclusions and their influence on machinability tests, steel samples were collected from rolled bars produced by the conventional production route (316R) and an experimental trial with Ca treatment (316Ca). The metal chips generated during the machining test were also collected for the evaluation of chip breakability and NMIs characteristics after machining. In addition, the Electrolytic extraction (EE) technology is used to extract NMIs from steel and chip samples. Then, a three-dimensional (3-D) study is performed on the inclusions collected on a membrane filter using a scanning electron microscope (SEM) equipped with energy-dispersive X-ray spectroscopy (EDS). The morphology, size, number, frequency, and composition of non-metallic inclusions are studied. Four main types of inclusions were found in the 316Ca steel: Type I (elongated MnS), Type II (oxy-sulfides with hard oxide cores), Type III (soft elongated oxides), and Type IV (hard undeformed oxides).The results show that the morphologies of NMIs in stainless steel chips were significantly changed after cutting. Overall, three different main shapes of NMIs were found: i) Group I having similar shapes, ii) Group II stretched inclusions having very thin film-like (Group II-a) and fractured stretched morphologies (Group II-b), and iii) Group III brittlely fractured inclusions. The total areas of MnS and SO inclusions in the secondary deformation zone of the chips were significantly increased (by up to 2-3 times) compared to that of the reference steel sample before the cutting test. It was found that the morphologies of NMIs during machining depend on the location in chips, the workpiece material, as well as the applied cutting speed. This results in different temperatures and metal matrix deformation degrees during machining. In addition, the chip breakability and chip tool contact length of the reference steel and the experimental steel were evaluated and compared with the characteristics of NMIs in the two steels. A new weight-measurement-based method was developed. The results show that the 316Ca steel generally has a better machinability compared to the reference 316R steel. However, the chip-tool contact length results show that the modification of NMIs for machinability improvements is only beneficial in some machining processes. The 316R steel was preferred at low cutting speeds, whereas the 316Ca steel was preferred at high cutting speeds. The different characteristics of NMI in the various cutting conditions and materials lead to different behaviors and functions of NMI during processing. Finally, the possible application of PDA/OES in the steelmaking process was also evaluated. This online survey method developed in the industry during recent years provides a high possibility for implementing a rapid screening of the NMI content and shows the potential of establishing an online control of NMI during the processing of steel.
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| 10. |
- GUO, SHUO, 1987-
(författare)
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Evaluation of Non-Metallic Inclusions after Deformation and Their Effect on the Machinability of Steel
- 2022
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- The presence of non-metallic inclusions (NMIs) have critical effects on both the mechanical properties and machinability of steels. In the present thesis, one focus is to study the characteristics of deformed sulfides (MnS) for a stainless steel (3R65) and a tool steel (42CrMo4). Three groups of MnS inclusions were detected in the samples taken after deformation of the steel: i) type RS (sulfides with a Rod-like geometry), ii) type PS (sulphides with a plate-like geometry) and iii) type OS (oxy-sulfides). Here, the elongated inclusions present in both stainless and tool steels were studied more in detail using SEM to determine the tendency for the inclusions to break. The results showed that three types of elongated MnS inclusions could be identified, namely UU, UB and BB. Here, ‘U’ represents the unbroken edge(s) of inclusion and ‘B’ represents the broken edge(s) of an inclusion. The presence of these three types of inclusions in samples collected both before and after a heat treatment was studied and the results showed that the heat treatment had a very small effect on the morphologies of the elongated MnS inclusions for both stainless steels (containing <0.1 mass % C) and tool steels (containing 0.42 mass % C). In the second part of the thesis, the characteristics of chips after machining of a 157REM Ce-treated steel and a 157C reference steel was studied. Furthermore, the effect of the NMIs on the chip breakability during machining was determined. The results show that a Ce modification of a 157C steel transforms the NMIs from large size elongated inclusions to small size inclusion with a spherical shape. This leads to an improved machinability of 157C steels. In addition, a newly developed weight distribution of chips (WDC) method, based on the chip weight measurements, was used to determine the tendencies for breaking of chips. The results of this investigation showed that the chips that were obtained from the machining of 157C and the 157REM steels could be classified into the following three types: i) type I chips (with a geometry containing one arc) and having a weight of less than 0.08 g, ii) type II chips (with a geometry containing two arcs) and having weights between 0.08 g and 0.15 g, and iii) type III chips (with a geometry containing three or more arcs) and having weights larger than 0.15 g. From industrial experience, it is known that a high amount of small type I chips will lead to a good chip breakability. The results from the machining test show that the fraction of type I chips from machining of the 157REM steel (65 %) is smaller than from machining of the 157C reference steel (80 %) when using a lower feed rate of 0.4 mm/rev. However, when using a higher feed rate of 0.5 mm/rev, 40 % of the chips belong to type I small chips for the 157REM steel and 14 % for the 157C steel. Based on the conditions used in this study and the obtained results, the following is clear in order to reach the best machinability: i) it is most advantageous to use the 157C steel when using a lower feed rate of 0.4 mm/rev and ii) it is most advantageous to use the 157REM steel when using a higher feed rate of 0.5 mm/rev.
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