335,969 research outputs found
Niukasti seostettujen terästen martensiitin alkulämpötila ja itseispääseminen
No full textAbstractHigh-strength low-alloy martensitic steels provide low-cost environmentally efficient solutions for weight critical engineering. The wider use of such materials will provide energy savings and reduce the carbon footprint of many products. They offer a combination of both good weldability and high strength, which makes them attractive materials for structural applications. During the rapid transformation, the martensite becomes supersaturated with carbon when compared with the equilibrium ferritic state of the steel. However, when low-carbon steels with high martensitic start temperatures (Ms) are quenched, fine carbides can form in the first formed martensite laths. This phenomenon is called auto-tempering. The martensite laths which form at low temperatures remain relatively untempered. Auto-tempered steels exhibit superior toughness and improved formability when compared to steels without auto-tempering. This thesis extends our understanding of auto-tempered martensite in as-quenched low-alloy steels. The tools used were the Gleeble physical simulator for processing the steels, electron microscopy for microstructural characterization, MATLAB to quantify the incidence of carbides in auto-tempered microstructures and Thermo-Calc software to model the microstructure.Chemical inhomogeneity caused by interdendritic microsegregation is shown to have a major influence on the slow onset of martensite. Combining segregation information with the Koistinen-Marburger equation enabled a good prediction of the experimental martensite evolution curves. The effect of hot mounting during metallographic sample preparation on as-quenched low-alloy steels was investigated. It was found that hot mounting caused additional tempering, which was manifested as new carbides appearing in the regions otherwise free of carbides in auto-tempered microstructures. Electron back scattered diffraction revealed that all the untempered regions in the auto-tempered steel were oriented with {100} planes almost parallel to the broad surface of the hot-rolled steel plate. Martensite orientation variant analysis showed that the auto-tempered and the untempered regions were part of the same packet. A custom-built MATLAB image processing tool was used to quantify the fraction of carbides in auto-tempered microstructures and the frequency distribution of degrees of auto-tempering. The Thermo-Calc modules DICTRA and TC-Prisma were used to compare the precipitation and the partitioning kinetics of carbon during the quenching process. The predictions showed satisfactory agreement with the electron microscopy results, which indicated that the Thermo-Calc software can be used to help design new low-alloy martensitic steels.Original papersOriginal papers are not included in the electronic version of the dissertation.Ramesh Babu, S., Ivanov, D., & Porter, D. (2019). Influence of Microsegregation on the Onset of the Martensitic Transformation. ISIJ International, 59(1), 169–175. https://doi.org/10.2355/isijinternational.isijint-2018-424Self-archived versionRamesh Babu, S., Jaskari, M., Järvenpää, A., & Porter, D. (2019). The Effect of Hot-Mounting on the Microstructure of an As-Quenched Auto-Tempered Low-Carbon Martensitic Steel. Metals, 9(5), 550. https://doi.org/10.3390/met9050550Self-archived versionRamesh Babu, S., Nyyssönen, T., Jaskari, M., Järvenpää, A., Davis, T. P., Pallaspuro, S., Kömi, J., & Porter, D. (2019). Observations on the Relationship between Crystal Orientation and the Level of Auto-Tempering in an As-Quenched Martensitic Steel. Metals, 9(12), 1255. https://doi.org/10.3390/met9121255Self-archived versionRamesh Babu, S., Davis, T. P., Haas, T., Jarvenpää, A., Kömi, J., & Porter, D. (2020). Image Processing Tool Quantifying Auto-Tempered Carbides in As-Quenched Low Carbon Martensitic Steels. Metals, 10(2), 171. https://doi.org/10.3390/met10020171Self-archived versionRamesh Babu, S., Jaskari, M., Jarvenpää, A., Davis, T. P., Kömi, J., & Porter, D. (2020). Precipitation Versus Partitioning Kinetics during the Quenching of Low-Carbon Martensitic Steels. Metals, 10(7), 850. https://doi.org/10.3390/met10070850Self-archived versionTiivistelmäSuuren lujuusluokan niukasti seostetut martensiittiset teräkset mahdollistavat kustannustehokkaat ja ympäristövaikutuksia huomioivat ratkaisut sovelluksissa, joissa materiaalin massa on ratkaiseva tekijä. Hyvien hitsattavuusominaisuuksien yhdistyminen korkeaan lujuuteen, tekee niistä houkuttelevan vaihtoehdon rakenteellisten sovellusten materiaaliksi. Nopean faasimuutoksen aikana martensiitin hiilipitoisuus ylittää tasapainon mukaisen ferriitin kylläisyysrajan. Korkean martensiitin alkamislämpötilan omaavia vähähiilisiä teräksiä karkaistaessa, hienojakoisia karbideja voi muodostua ensin muodostuneisiin martensiittisäleisiin. Tätä ilmiötä kutsutaan itseispäästöksi. Alhaisemmissa lämpötiloissa muodostuvissa martensiittisäleissä päästö jää suhteellisesti hyvin vähäiseksi. Itseispäästö parantaa sekä lujuutta että muokattavuusominaisuuksia. Tämä väitöskirja laajentaa niukasti seostettujen ja karkaistujen terästen martensiitin itseispäästön tietämystä.Väitöskirjassa osoitetaan, että kemiallisen koostumuksen epähomogeenisuus, joka johtuu dendriittien välille muodostuvasta mikrosuotaumasta, vaikuttaa huomattavasti martensiitin muodostumisen vaiheittaiseen alkuun. Suotautumasta saadun tiedon yhdistäminen Koistinen-Marburger yhtälöön mahdollisti kokeellisen martensiitin muodostumiskäyrän tarkan ennustamisen. Havaittiin, että kuumanapitus lisää pääsemistä, joka ilmenee uusien karbidien esiintymisenä. Takaisinsironneiden elektronien diffraktion menetelmällä saatu tieto paljasti, että kaikkien niiden alueiden, jotka eivät olleet päässeet, kidetasot {100} olivat lähes kohtisuoria kuumavalssatun teräslevyn valssauspintaan nähden. Martensiitin suuntautumisvariantin analyysi osoitti, että itsepäässeet alueet ja ne alueet, joilla päästöä ei ollut tapahtunut, kuuluivat samaan pakettiin. MATLAB ohjelmistolla toteutettua omaa kuvankäsittelytyökalua käyttäen määritettiin karbidien osuus itsepäässeissä mikrorakenteissa sekä itsepääsemisasteen esiintymistiheysjakaumassa. Thermo-Calc ohjelmiston DICTRA ja TC-Prisma osia käytettiin karkaisun aikaisen hiilen erkautumis- ja jakautumiskinetiikan vertailemiseen. Ennustettu tulos vertautui tyydyttävästi elektronimikroskoopilla saatuihin tuloksiin, mikä viittaa siihen että Thermo-Calc voidaan käyttää.OsajulkaisutOsajulkaisut eivät sisälly väitöskirjan elektroniseen versioon.Ramesh Babu, S., Ivanov, D., & Porter, D. (2019). Influence of Microsegregation on the Onset of the Martensitic Transformation. ISIJ International, 59(1), 169–175. https://doi.org/10.2355/isijinternational.isijint-2018-424Rinnakkaistallennettu versioRamesh Babu, S., Jaskari, M., Järvenpää, A., & Porter, D. (2019). The Effect of Hot-Mounting on the Microstructure of an As-Quenched Auto-Tempered Low-Carbon Martensitic Steel. Metals, 9(5), 550. https://doi.org/10.3390/met9050550Rinnakkaistallennettu versioRamesh Babu, S., Nyyssönen, T., Jaskari, M., Järvenpää, A., Davis, T. P., Pallaspuro, S., Kömi, J., & Porter, D. (2019). Observations on the Relationship between Crystal Orientation and the Level of Auto-Tempering in an As-Quenched Martensitic Steel. Metals, 9(12), 1255. https://doi.org/10.3390/met9121255Rinnakkaistallennettu versioRamesh Babu, S., Davis, T. P., Haas, T., Jarvenpää, A., Kömi, J., & Porter, D. (2020). Image Processing Tool Quantifying Auto-Tempered Carbides in As-Quenched Low Carbon Martensitic Steels. Metals, 10(2), 171. https://doi.org/10.3390/met10020171Rinnakkaistallennettu versioRamesh Babu, S., Jaskari, M., Jarvenpää, A., Davis, T. P., Kömi, J., & Porter, D. (2020). Precipitation Versus Partitioning Kinetics during the Quenching of Low-Carbon Martensitic Steels. Metals, 10(7), 850. https://doi.org/10.3390/met10070850Rinnakkaistallennettu versioAcademic dissertation to be presented with the assent of the Doctoral Training Committee of Technology and Natural Sciences of the University of Oulu for public defence in the OP-Pohjola auditorium (L6), Linnanmaa, on 5 February 2021, at 12 noonAbstract
High-strength low-alloy martensitic steels provide low-cost environmentally efficient solutions for weight critical engineering. The wider use of such materials will provide energy savings and reduce the carbon footprint of many products. They offer a combination of both good weldability and high strength, which makes them attractive materials for structural applications. During the rapid transformation, the martensite becomes supersaturated with carbon when compared with the equilibrium ferritic state of the steel. However, when low-carbon steels with high martensitic start temperatures (Ms) are quenched, fine carbides can form in the first formed martensite laths. This phenomenon is called auto-tempering. The martensite laths which form at low temperatures remain relatively untempered. Auto-tempered steels exhibit superior toughness and improved formability when compared to steels without auto-tempering. This thesis extends our understanding of auto-tempered martensite in as-quenched low-alloy steels. The tools used were the Gleeble physical simulator for processing the steels, electron microscopy for microstructural characterization, MATLAB to quantify the incidence of carbides in auto-tempered microstructures and Thermo-Calc software to model the microstructure.
Chemical inhomogeneity caused by interdendritic microsegregation is shown to have a major influence on the slow onset of martensite. Combining segregation information with the Koistinen-Marburger equation enabled a good prediction of the experimental martensite evolution curves. The effect of hot mounting during metallographic sample preparation on as-quenched low-alloy steels was investigated. It was found that hot mounting caused additional tempering, which was manifested as new carbides appearing in the regions otherwise free of carbides in auto-tempered microstructures. Electron back scattered diffraction revealed that all the untempered regions in the auto-tempered steel were oriented with {100} planes almost parallel to the broad surface of the hot-rolled steel plate. Martensite orientation variant analysis showed that the auto-tempered and the untempered regions were part of the same packet. A custom-built MATLAB image processing tool was used to quantify the fraction of carbides in auto-tempered microstructures and the frequency distribution of degrees of auto-tempering. The Thermo-Calc modules DICTRA and TC-Prisma were used to compare the precipitation and the partitioning kinetics of carbon during the quenching process. The predictions showed satisfactory agreement with the electron microscopy results, which indicated that the Thermo-Calc software can be used to help design new low-alloy martensitic steels.Tiivistelmä
Suuren lujuusluokan niukasti seostetut martensiittiset teräkset mahdollistavat kustannustehokkaat ja ympäristövaikutuksia huomioivat ratkaisut sovelluksissa, joissa materiaalin massa on ratkaiseva tekijä. Hyvien hitsattavuusominaisuuksien yhdistyminen korkeaan lujuuteen, tekee niistä houkuttelevan vaihtoehdon rakenteellisten sovellusten materiaaliksi. Nopean faasimuutoksen aikana martensiitin hiilipitoisuus ylittää tasapainon mukaisen ferriitin kylläisyysrajan. Korkean martensiitin alkamislämpötilan omaavia vähähiilisiä teräksiä karkaistaessa, hienojakoisia karbideja voi muodostua ensin muodostuneisiin martensiittisäleisiin. Tätä ilmiötä kutsutaan itseispäästöksi. Alhaisemmissa lämpötiloissa muodostuvissa martensiittisäleissä päästö jää suhteellisesti hyvin vähäiseksi. Itseispäästö parantaa sekä lujuutta että muokattavuusominaisuuksia. Tämä väitöskirja laajentaa niukasti seostettujen ja karkaistujen terästen martensiitin itseispäästön tietämystä.
Väitöskirjassa osoitetaan, että kemiallisen koostumuksen epähomogeenisuus, joka johtuu dendriittien välille muodostuvasta mikrosuotaumasta, vaikuttaa huomattavasti martensiitin muodostumisen vaiheittaiseen alkuun. Suotautumasta saadun tiedon yhdistäminen Koistinen-Marburger yhtälöön mahdollisti kokeellisen martensiitin muodostumiskäyrän tarkan ennustamisen. Havaittiin, että kuumanapitus lisää pääsemistä, joka ilmenee uusien karbidien esiintymisenä. Takaisinsironneiden elektronien diffraktion menetelmällä saatu tieto paljasti, että kaikkien niiden alueiden, jotka eivät olleet päässeet, kidetasot {100} olivat lähes kohtisuoria kuumavalssatun teräslevyn valssauspintaan nähden. Martensiitin suuntautumisvariantin analyysi osoitti, että itsepäässeet alueet ja ne alueet, joilla päästöä ei ollut tapahtunut, kuuluivat samaan pakettiin. MATLAB ohjelmistolla toteutettua omaa kuvankäsittelytyökalua käyttäen määritettiin karbidien osuus itsepäässeissä mikrorakenteissa sekä itsepääsemisasteen esiintymistiheysjakaumassa. Thermo-Calc ohjelmiston DICTRA ja TC-Prisma osia käytettiin karkaisun aikaisen hiilen erkautumis- ja jakautumiskinetiikan vertailemiseen. Ennustettu tulos vertautui tyydyttävästi elektronimikroskoopilla saatuihin tuloksiin, mikä viittaa siihen että Thermo-Calc voidaan käyttää
Analysis of Babu and Odeh's Model
No full textIn this work, Babu and Odeh���s model for estimating flow rate from partially penetrating systems is studied. A VBA code is written in order to simulate the model and its results are compared against simulations using Eclipse Software. Sensitivity to different parameters is analyzed and an increasing-decreasing behavior as the reservoir���s length is increased is specifically addressed and analyzed.
After simulating different scenarios it is observed that Babu and Odeh���s model predicts that there will be a specific reservoir���s length for which a maximum flow rate will be predicted. An explicit analytical expression is obtained for one of the cases considered in the model.
The results obtained are compared against Eclipse runs, it is observed that the model is reasonably accurate, and that the reservoir���s length at which the maximum flow rate onsets is similar in both cases.
It is concluded that the model is accurate within its simplistic assumptions, but it is in these same assumptions that it might yield very different results than reality itself
The Impact Of The Development Of ICT In Several Hungarian Economic Sectors
No full textAs the author could not find a reassuring mathematical and
statistical method in the literature for studying the effect of
information communication technology on enterprises, the author
suggested a new research and analysis method that he also used to study the Hungarian economic sectors. The question of what
factors have an effect on their net income is vital for enterprises. At first, the author studied some potential indicators related to economic sectors, then those indicators were compared to the net income of the surveyed enterprises. The resulting data showed that the growing penetration of electronic marketplaces contributed to the change of the net income of enterprises to the greatest extent.
Furthermore, among all the potential indicators, it was the only indicator directly influencing the net income of enterprises.
With the help of the compound indicator and the financial data
of the studied economic sectors, the author made an attempt to find a connection between the development level of ICT and
profitability. Profitability and productivity are influenced by a lot of other factors as well. As the effect of the other factors could not be measured, the results – shown in a coordinate system - are not full but informative.
The highest increment of specific Gross Value Added was
produced by the fields of ‘Manufacturing’, ‘Electricity, gas and water supply’, ‘Transport, storage and communication’ and
‘Financial intermediation’. With the exception of ‘Electricity, gas and water supply’, the other economic sectors belong to the group of underdeveloped branches (below 50 percent).
On the other hand, ‘Construction’, ‘Health and social work’ and
‘Hotels and restaurants’ can be seen as laggards, so they got into the lower left part of the coordinate system.
‘Agriculture, hunting and forestry’ can also be classified as a
laggard economic sector, but as the effect of the compound
indicator on the increment of Gross Value Added was less
significant, it can be found in the upper left part of the coordinate system. Drawing a trend line on the points, it can be made clear that it shows a positive gradient, that is, the higher the usage of ICT devices, the higher improvement can be detected in the specific Gross Value Added
Laser transition characteristics of Nd3+-doped fluorophosphate laser glasses
No full textFluorophosphate glasses of composition P2O5-K2O-MgO)-A1(2)O(3)-A1F(3) and P2O5-K2O-MgO-A1(2)O(3)-BaF2 were prepared with different Nd3+ ion concentrations. The absorption and emission spectra in the UV-VIS-NIR region were measured for these glasses. Judd-Ofelt analysis has been carried out using the absorption spectra of 1.0 mol% Nd3+-doped glasses to evaluate the radiative properties for some luminescent levels of the Nd3+ ion. The stimulated emission cross-sections of the F-4(3/2) -> I-4(11/2) laser transition for the present glasses are found to be higher than for other Nd3+-doped glasses. Branching ratio calculations also revealed the potentiality of the F-4(3/2) I-4(11/2) transition for laser action in these glasses. The observed concentration quenching of the lifetime of the 4 F3/2 level is explained as a result of cross-relaxation process between the Nd3+ ions
Dynamics of semi-flexible tethered sheets
No full textThe dynamics of a semi-flexible sheet or tethered membrane in a solvent is studied using the method of stochastic rotation dynamics. Hydrodynamic interactions between different parts of the sheet are naturally included in this method. We confirm the scaling law for the radius of gyration versus sheet size predicted for a self-avoiding tethered membrane. The mean-square displacement shows both sub-diffusive and diffusive behavior similar to linear polymers. In the intermediate scattering function the sub-diffusive behavior appears as stretched exponential which we reproduce in our simulations. Thereby, we confirm an early prediction between the roughness and the sub-diffusion exponent derived from Zimm dynamics (E. Frey, D.R. Nelson, J. Phys. I 1, 1715 (1991)). Finally, we show that the diffusion coefficient of the square sheet is inversely proportional to the edge length of the sheet again in good agreement with theoretical predictions
- …
