Abstract not available

Thesis (Ph.D.)--University of Wollongong, 2005. / Typescript. Includes bibliographical references: leaf 153-164.

The effect of initial microstructures of an 0.05 wt.% C low carbon steel, acicular ferrite (AF), Bainite (B), polygonal ferrite (PF), fine polygonal ferrite (FPF), and a microstructure produced by direct strip casting (DSC) (termed SC), on the deformation and recrystallization behaviour of cold rolled low carbon (LC) steel, was investigated. The initially prepared samples with the initial microstructures were cold rolled to 50, 70 and 90% reductions, then annealed isothermally in the temperature range 580 ??? 680 oC. The microstructures and textures produced by deformation and annealing were studied by optical microscopy, XRD, TEM, SEM and EBSD. The initial microstructures were characterized mainly by optical microscopy and EBSD. Using EBSD, the ferrite grain size of the AF, B and SC samples was considerably larger than that found by optical microscopy with a large fraction of low angle grain boundaries (LAGBs) observed within prior austenite grains. All samples exhibited a very weak texture close to random. After cold rolling, the microstructures of AF and SC contained shear bands with PF and FPF generating deformation bands. For AF and SC, the pearlite phase was more extensively elongated in rolling direction compared with PF and FPF. After 90% cold rolling reduction, PF, FPF and SC consist mainly of the texture component and AF and B . It was found that FPF recrystallized most rapidly followed by B, PF and AF with SC recrystallizing orders of magnitude more slowly due to the solution drag caused by its uniformly distributed higher Mn content. Very strong (???-fibre) texture was generated in cold rolled PF followed by FPF, with AF, SC and B generating very weak textures. The texture evolution during annealing 90% reduction PF was examined in further detail. The behaviour of nucleation and grain growth provides strong evidence of orientated nucleation as the dominant factor for CRA texture development in this material.

The effect of initial microstructures of an 0.05 wt.% C low carbon steel, acicular ferrite (AF), Bainite (B), polygonal ferrite (PF), fine polygonal ferrite (FPF), and a microstructure produced by direct strip casting (DSC) (termed SC), on the deformation and recrystallization behaviour of cold rolled low carbon (LC) steel, was investigated. The initially prepared samples with the initial microstructures were cold rolled to 50, 70 and 90% reductions, then annealed isothermally in the temperature range 580 ??? 680 oC. The microstructures and textures produced by deformation and annealing were studied by optical microscopy, XRD, TEM, SEM and EBSD. The initial microstructures were characterized mainly by optical microscopy and EBSD. Using EBSD, the ferrite grain size of the AF, B and SC samples was considerably larger than that found by optical microscopy with a large fraction of low angle grain boundaries (LAGBs) observed within prior austenite grains. All samples exhibited a very weak texture close to random. After cold rolling, the microstructures of AF and SC contained shear bands with PF and FPF generating deformation bands. For AF and SC, the pearlite phase was more extensively elongated in rolling direction compared with PF and FPF. After 90% cold rolling reduction, PF, FPF and SC consist mainly of the texture component and AF and B . It was found that FPF recrystallized most rapidly followed by B, PF and AF with SC recrystallizing orders of magnitude more slowly due to the solution drag caused by its uniformly distributed higher Mn content. Very strong (???-fibre) texture was generated in cold rolled PF followed by FPF, with AF, SC and B generating very weak textures. The texture evolution during annealing 90% reduction PF was examined in further detail. The behaviour of nucleation and grain growth provides strong evidence of orientated nucleation as the dominant factor for CRA texture development in this material.

This study is an initial attempt to investigate the possibility of substituting conventional laboratory destructive testing techniques at Sandvik's strip steel production facilities with the 3MA (Micro-magnetic Multi-parameter Microstructure and Stress Analysis) NDT (nondestructive testing) technique. The interest for the research comes from various problems with the actual destructive testing method. Sandvik manufactures thin strip steel (among other products) and controls the quality of its product by taking samples from the ends of the strip and measuring the sample's material properties in a separate laboratory. Hence, the sample preparation process is time and material consuming, and the results obtained from the laboratory measurements are not always representative of the real values along the whole length of the strip (usually several kilometers). Therefore, the present project involves the correlation between three material properties (Vickers hardness, tensile strength and carbide density) and a selection of micro-magnetic parameters measured with the 3MA-II equipment manufactured by the Fraunhofer IZFP institute. The 3MA-II system is based on four measuring techniques (harmonic analysis, magnetic Barkhausen noise, incremental permeability and Eddy current testing) and is capable of recording up to 41 micro-magnetic parameters. Samples of two different steel grades (composition) were used in the study. The results for hardness and tensile strength (average relative errors of 1.04% and 0.78%, respectively) corroborated the applicability of the 3MA technique to steel strip inspection. Thus, the implementation of this technique would lead to an improvement in the company's energy efficiency and sustainability. However, finding a good correlation between micromagnetic parameters and material properties is not always possible and, in the case of carbide density, no reliable correlation was achieved. So, further experiments are proposed for future studies regarding carbide density and other material properties.

Eutectoid steel strips are designed for the production of parts for intensive use such as clutches, seat slides, and springs as they exhibit<p>excellent strength levels and wear resistance. These properties arise from the unique morphology of lamellar pearlite which can be considered<p>as a self-laminated nanoscale composite. However, a spheroidization annealing step is nowadays necessary to improve the cold forming properties before further cold rolling steps.<p>This thesis is aimed at improving the tensile ductility of the hot rolled products of eutectoid composition in order to eliminate the intermediate<p>annealing step. Two strategies are proposed.<p>The first is to transpose the concept of controlled rolling developed for HSLA to<p>eutectoid steels. Through a strict adjustment of the austenite processing and of the cooling strategy, it is possible to improve the ductility<p>of the final lamellar microstructure. The way the processing parameters influence the hot deformation of austenite, the eutectoid transformation and of the subsequent spheroidization annealing is deeply<p>investigated. It is found that refinement and pancaking of austenite<p>is beneficial as it reduces the pearlite block size improving the total<p>tensile elongation. Accelerated cooling is of paramount importance to<p>achieve fine Interlamellar spacing (ILS), which lead to high strength<p>levels and accelerate spheroidization during subsequent annealing.<p>The second approach involves intercritical or warm deformation. Warm processing of eutectoid steels is first explored by torsion testing<p>and then up-scaled to a pilot rolling-line. The interactions between thermomechanical parameters, rolling forces generated and microstructural<p>evolution are carefully scrutinized. During concurrent hot deformation, spheroidization of cementite takes place almost instantaneously<p>in both torsion and rolling. The restoration processes occurring in the ferrite matrix depends on the strain path and the strain rates. Low strain rates (0,1 s−1) and simple shear promotes the formation of a recrystallized-like HABs network of about 3μm in size.<p>Plane strain compression and high strain rates (10 s−1) leads to the formation of a typical recovered dislocation substructure (LABs) of 1μm in size. During annealing, no recrystallization occurs and the LABs substructure remains stable. This substructure influences drammatically the mechanical properties: the strength is very high and the work-hardening behavior is poor due to high recovery rate in the region close to the LABs. However, due to the presence of spheroidized<p>cementite particles the ductility of warm rolled eutectoid steels is higher than that of ultra fine grained low carbon steels. / Doctorat en Sciences de l'ingénieur / info:eu-repo/semantics/nonPublished

<p dir="ltr">Over the past three to four decades, mechanically stabilized earth (MSE) walls have gained preference over other wall types due to the several advantages that they offer, such as ease of construction, flexibility to accommodate large differential settlements, architectural versatility, and low cost per unit area of wall face. Because of these advantages, several departments of transportation in the United States have adopted MSE walls to serve as abutments for highway and railway bridges. While the response of conventional MSE walls has been studied both experimentally and numerically, comparatively less work has been done to investigate the behavior of MSE walls used as abutments for bridge support. This dissertation presents a case study of the performance of a pile-supported, MSE bridge abutment in Whitestown, Indiana, during construction and while in service. A zone near the middle of the east MSE abutment wall was instrumented with earth pressure cells, strain gauges, inclinometers, and crackmeters to investigate the transfer of dead and live loads from the bridge to the foundation elements (pile cap and piles), and to assess the performance of the MSE abutment wall under these loading conditions. The data was collected continuously, both during and after construction, using multiplexers and dataloggers powered by solar panels. The values of key parameters used in MSE wall design were determined from the instrumentation results and compared with those obtained using design methods available in the literature. In addition, the measured dead loads carried by the instrumented piles were compared with the estimated dead loads used in the design of the MSE abutment. After the bridge was constructed, a live load test was performed by parking twelve triaxle trucks at different locations along the approach to the instrumented MSE abutment as well as on the bridge deck near the abutment. Finally, a series of three-dimensional finite element analyses of MSE walls and pile-supported MSE abutments were performed using a two-surface-plasticity constitutive sand model. The lateral stresses on the back of the wall facing and the reinforcement tensile loads obtained from the FE analyses were found to be in good agreement with those measured at the end of construction of the Whitestown MSE abutment. The results obtained from the FE analyses highlight the influence of wall height, backfill soil type, and pile offset on the magnitude and distribution of the lateral stresses on the back of the wall facing and the maximum tensile loads in the reinforcements.</p>