Inaug.-diss.--Technische hochschule, Aachen. / "Die arbeit ist gleichzeitig erschienen in band v der Mitteilungen aus dem Kaiser-Wilhelm-institut für eisenforschung zu Düsseldorf." Includes bibliographical references.

Title from PDF of title page (University of Missouri--Columbia, viewed on Feb. 19, 2010). The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file. Dr. J. Erik Loehr, Thesis Supervisor. Includes bibliographical references.

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The present work covers an analysis of the fundamental thermal phenomena which take place when 'buoyant', solid additives are injected into steel or hot metal for deoxidation or desulphurization purposes. For low melting point additives such as aluminum (for steel deoxidation) or magnesium (for hot metal desulphurization), it is found that a solid shell of the melt material will tend to fuse onto the object. Very often, the encasing shell will delay the rapid dispersion of the additive. / Two industrial methods which can be used to improve additive dispersion are the wire feeding and bullet shooting techniques. A thermal analysis of these two processes was carried out in the present study. / Aluminum wires of 6.4 to 15.9 mm in diameter were fed into steel melts while their 'apparent' weights were monitored with a novel piece of equipment. It was determined that the maximum depth of penetration of an aluminum wire fed into molten steel can be expressed as: / (DIAGRAM, TABLE OR GRAPHIC OMITTED...PLEASE SEE DAI) / The thermal aspects of the bullet shooting method were also simulated with the above-mentioned apparatus. It was found that the aluminum was only dispersed when the shell in the vicinity of the ends of a bullet had melted back. Since the time required to melt back the shell is inversely proportional to the superheat of the melt, molten aluminum cores encased in solid shells will resurface if the superheat is too low. It was shown that by selectively applying an appropriate thermal resistance onto the surface of a bullet, this problem can be eliminated.

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The behaviour of second phase particles in molten steel processing vessels was investigated, using the E.S.Z. (Electric Sensing Zone) method, in conjunction with aqueous modelling and molten steel systems. / 1. Slag droplet entrainment/dispersion is an axisymmetric gas injection stirred system was investigated: A tank containing a water-olive oil simulation of stirred ladles of molten steel was used. Extensive numerical predictions of the oil (slag) droplet population distributions within the vessel were also carried out, and reasonable agreement with the experimental data achieved. Droplet dispersions were shown to be time and spatially dependent. / 2. Inclusion separation characteristics in tundishes of continuous steel casting operations were investigated. The mixed reactor model proved to be adequate for predicting particle separation behaviour, proved that the effective upper surface area of the dispersed plug flow region is known, a priori. / 3. An on-line method for the detection and measurement of inclusions in molten steel systems was developed. Inclusion removal rates within an induction furnace, as well as inclusion separation behaviour in a commercial scale tundish for continuous billet casting, were measured.

The rapid thermal cycle involved in fiber laser welding (FLW) generates welds with narrow heat affected zones (HAZs) that contain large microstructural gradients, which make it very difficult to properly elucidate microstructural changes that occur during welding in the HAZ and fusion zone (FZ). Evaluation of the microstructural changes is, nonetheless, vital in order to understand and predict how FLW affects the mechanical properties of welded materials. Dual phase (DP) steels, which are designed to obtain soft ferrite and hard martensite, have gained increasing popularity in structural applications. In this research, the microstructural changes that occur in narrow HAZ and FZ are systematically studied by using a Gleeble thermo-mechanical simulation system and transmission electron microscopy (TEM). It is found that significant microstructural changes occur in the FZ and HAZ, which could result in dramatic changes in the mechanical properties of welded materials. An indication of this is the observation that the microhardness values in the FZ and adjacent HAZ are notably disparate from that in the base metal (BM). Further, cracks were observed in the zinc coating on the HAZs of both HSLA and DP980 steels, which may also have effect on mechanical performance of the welded materials.