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Quantitative Characterization of Processing-Microstructure-Properties Relationships in Pressure Die-Cast Mg AlloysLee, Soon Gi 06 July 2006 (has links)
The central goal of this research is to quantitatively characterize the relationships between processing, microstructure, and mechanical properties of important high-pressure die-cast (HPDC) Mg-alloys. For this purpose, a new digital image processing technique for automatic detection and segmentation of gas and shrinkage pores in the cast microstructure is developed and it is applied to quantitatively characterize the effects of HPDC process parameters on the size distribution and spatial arrangement of porosity. To get better insights into detailed geometry and distribution of porosity and other microstructural features, an efficient and unbiased montage based serial sectioning technique is applied for reconstruction of three-dimensional microstructures. The quantitative microstructural data have been correlated to the HPDC process parameters and the mechanical properties. The analysis has led to hypothesis of formation of new type of shrinkage porosity called, gas induced shrinkage porosity that has been substantiated via simple heat transfer simulations. The presence of inverse surface macrosegregation has been also shown for the first time in the HPDC Mg-alloys. An image analysis based technique has been proposed for simulations of realistic virtual microstructures that have realistic complex pore morphologies. These virtual microstructures can be implemented in the object oriented finite elements framework to model the variability in the fracture sensitive mechanical properties of the HPDC alloys.
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Optical emission from electric arc furnacesAula, M. (Matti) 19 January 2016 (has links)
Abstract
The main cause of temperature and composition fluctuations in the electric arc furnace (EAF) process is the scrap used as a raw material. Process conditions in EAF can vary significantly from heat to heat because there is no accurate information of scrap composition. Due to harsh process conditions, there are currently few sensors available for direct on-line measurement of the EAF process.
In this work new information about stainless steelmaking EAF process conditions is sought with optical emission spectrum measurement. The measurement system relies on transportation of the light emitted from the measured furnace to a remotely situated spectrometer.
Analysing the slag composition from the arc emission spectrum was tested in the laboratory and on a pilot scale. The laboratory measurements indicate that changes in the amount of CrOx and MnO in the slag have the highest impact on optical emission spectra. The pilot scale measurements show that the Cr2O3 content of the slag can be measured from the arc emission spectrum using suitable reference lines with an average absolute error of 0.62 %-points and a standard deviation of 0.49 %-points.
The results from measurements at Outokumpu Stainless Oy, Tornio Works, indicate that measurement of the optical emission spectrum from industrial EAF is feasible in a practical sense, and can be used in analysing of EAF atmosphere, scrap melting and slag surface. Furthermore, the results of industrial measurements indicate that the atoms in the arc plasma mainly originate from the slag. The measurement of scrap melting could be potentially used in EAF control in optimization of arc voltages and second scrap bucket charging. The potential use of slag CrOx measurements is in optimization of reductant additions as well as defining the further processing of EAF slag. / Tiivistelmä
Valokaariuunien ohjaus on perinteisesti ollut uunioperaattorin käsissä. Valokaaariuuniprosessin on-line mittaukseen on olevassa vähän menetelmiä johtuen uunin hyvin haastavaista olosuhteista.
Tässä työssä on tutkittu optiseen emissiospektroskopiaan perustuvaa menetelmää uuden jatkuva-aikaisen tiedon tuottamisessa valokaariuuniprosessista. Mittausjärjestelmä perustuu valon keräämiseen mitattavasta uunista valokuidun avulla, joka johtaa valon analysoitavaksi etäälle prosessista sijoitettuun spektrometriin. Mittauksia suoritettiin laboratorio-, pilot- ja tehdas-mittakaavassa.
Valokaariuunin kuonan koostumuksen analysointia testattiin laboratorio- ja pilot-mittakaavan uuneilla. Laboratoriomittaukset osoittivat että kuonan komponenteista CrOx ja MnO ja vaikuttavat eniten mitattuun emissiospektriin. Pilot-mittakaavan kokeissa havaittiin, että kuonan Cr2O3-pitoisuutta voidaan mitata valokaaren emissiospektristä 0,62 %-yksikön keskimääräisellä absoluuttisella virheellä ja 0,49 %-yksikkön hajonnalla.
Teollisella valokaariuunilla suoritetuista mittauksista havaittiin että optisen emissiospektrin mittaus voidaan suorittaa ilman ylitsepääsemättömiä teknisiä esteitä. Mittauksen tuloksia voidaan puolestaan käyttää kaasufaasin reaktioiden, romun sulamisen ja kuonapinnan ominaisuuksien arvioinnissa. Valokaaren emissiospektrin analyysi osoitti, että valokaaren plasman komponentit ovat pääosin peräisin kuonasta, joka mahdollistaa kuonan koostumuksen arvioinnin valokaaren emissiospektrin perusteella. Romun sulamisen mittausta voidaan prosessinohjauksessa käyttää jänniteportaiden ja toisen korin panostuksen optimointiin. Kuonan kromipitoisuuden mittaamista voidaan puolestaan käyttää pelkistinaineiden lisäyksen optimointiin ja kuonan jatkokäsittelyn valintaan.
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