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dc.contributor.advisorMatlock, David K.
dc.contributor.authorAl-jabr, Haytham M.
dc.contributor.committeememberFindley, Kip Owen
dc.contributor.committeememberSpeer, J. G.
dc.contributor.committeememberSteele, John P. H.
dc.contributor.committeememberVan Tyne, C. J.
dc.date.accessioned2016-06-13T13:56:09Z
dc.date.available2016-06-13T13:56:09Z
dc.date.issued2016
dc.descriptionIncludes bibliographical references.
dc.description2016 Spring.
dc.description.abstractThe effects of microstructure and crystallographic texture in four commercially-produced API X70 pipeline steels and their relation to planar anisotropy of toughness and delamination were evaluated. The experimental steels were processed through either a hot strip mill, a Steckel mill, or a compact strip mill. Different processing routes were selected to obtain plates with potential variations in the microstructure and anisotropic characteristics. Tensile and Charpy impact testing were used to evaluate the mechanical properties in three orientations: longitudinal (L), transverse (T) and diagonal (D) with respect to the rolling direction to evaluate mechanical property anisotropy. The yield and tensile strengths were higher in the T orientation and toughness was lower in the D orientation for all plates. Delamination was observed in some of the ductile fracture surfaces of the impact samples. To further study the splitting behavior and effects on impact toughness, a modified impact test (MCVN) specimen with side grooves was designed to intensify induced stresses parallel to the notch root and thus facilitate evaluation of delamination. Scanning electron microscopy combined with electron backscattered diffraction (EBSD) were used to evaluate the grain size, microstructural constituents, and crystallographic texture to determine the factors leading to delamination and the anisotropy in toughness. The ferrite grain size is mainly responsible for the differences in DBTTs between the L and T orientations. The higher DBTT in the D orientation observed in pipeline steels is attributed to crystallographic texture. The higher DBTT in the D direction is due to the higher volume fraction of grains having their {100} planes parallel or close to the primary fracture plane for the D orientation. An equation based on a new “brittleness parameter,” based on an assessment of grain orientations based on EBSD data, was developed to predict the changes in DBTTs with respect to sample orientation based on grain size and texture. The calculated DBTTs correlated well with the experimental values. The {001}<110> and {113}<110> components are the main preferred orientations that cause brittleness in the D direction, since their {001} planes make an angle less than 20° with the primary fracture plane of the samples oriented in the D direction. It was also concluded that delamination occurs due to banded bainite regions that were oriented such that their {001} planes make a small angle with the rolling plane leading to degradation in crack arrestability. The texture of the banded regions consisted of {001}<110>, {113}<110> or {111}<112> orientations. It was concluded that the {001}<110> and {113}<110> orientations promote splitting because their fracture strengths in the normal direction are low. The {111}<112> orientation has a calculated fracture strength more than twice the {001}<110> and {113}<110> orientations and therefore banded regions with the {111}<112> texture are more susceptible to cleavage fracture perpendicular to the normal direction.
dc.format.mediumborn digital
dc.format.mediumdoctoral dissertations
dc.identifierT 8046
dc.identifier.urihttp://hdl.handle.net/11124/170235
dc.languageEnglish
dc.publisherColorado School of Mines. Arthur Lakes Library
dc.relation.ispartof2016 - Mines Theses & Dissertations
dc.rightsCopyright of the original work is retained by the author.
dc.subjectanisotropy
dc.subjectdelamination
dc.subjectpipeline
dc.subjectsteel
dc.subjecttexture
dc.subjecttoughness
dc.titleInfluence of crystallographic texture in X70 pipeline steels on toughness anisotropy and delamination
dc.typeText
thesis.degree.disciplineMetallurgical and Materials Engineering
thesis.degree.grantorColorado School of Mines
thesis.degree.levelDoctoral
thesis.degree.nameDoctor of Philosophy (Ph.D.)


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