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Effet d'une pré-déformation sur l'endommagement anisotrope d'un acier pour pipeline de grade API X100 / Prestrain effect of anisotropic ductile damage in API grade X100 line pipe steelShinohara, Yasuhiro 03 March 2014 (has links)
Dans le cadre de cette étude, l’influence de la pré-déformation sur l’anisotropie du comportement plastique et sur la ténacité d’un acier API X100 pour pipeline a été abordée. Une étude expérimentale approfondie de la microstructure, des propriétés mécaniques et de l’endommagement du matériaux a été mise en oeuvre. Un modèle phénoménologique anisotrope combinant les écrouissagesisotrope et cinématique a été développé dans l’objectif de rendre compte du comportement ductile de cet acier à haute résistance. De plus, un modèle d’endommagement anisotrope a été établi pour représenter l’effet de pré-déformation sur la ductilité et la ténacité de cet acier. L’application des modèles à la flexion sous contrainte illustre, par exemple, l’effet négatif de la pré-déformation sur la charge limite (Moment de flexion maximum) supportée avant flambement du pipe. / In this thesis the influence of prestrain on anisotropic ductility and fracture toughness has been evaluated for API grade X100 line pipe steel. A omprehensive experimental investigation of microstructure, mechanical properties and fracture mechanisms has been carried out. A phenomenological model combining isotropic and kinematic hardening with anisotropic yield function has been developed, in order to represent anisotropic hardening behavior of the high strength steel. Additionally, a damage model incorporating anisotropic damage has been established for representation of prestrain effect on ductility and toughness of the X100 steel. The developed models could predict the bending capacity and the ductile fracture toughness of the cold-formed line pipes.
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Optimising the transformation and yield to ultimate strength ratio of Nb-Ti micro-alloyed low carbon line pipe steels through alloy and microstructural controlTang, Zhenghua 21 July 2007 (has links)
Thinner walled (about 6 mm thickness) line pipe steels for smaller diameter pipelines tend to have a relatively high ratio of yield strength to ultimate tensile strength (YS/UTS) of 0.93 or higher. This study focused on the effect of the microstructures, prior deformation in the austenite, cooling rate, coiling simulation and the additions of some micro-alloying elements on the YS/UTS ratio of a currently produced Nb-Ti and some experimental Nb-Ti-Mo line pipe steels. The experimental research included the design of the chemical compositions for five experimental alloys, simulation of the controlled hot rolling process, the determination of the strain-free as well as the strain affected continuous cooling transformation (CCT) diagrams, phase identification and quantitative assessment of the microstructures by optical microscopy, scanning electron microscopy (SEM) and transmission electron microscopy (TEM), the latter especially on shadowed carbon extraction replicas and, tensile tests etc. This study indicated that the transformed microstructures of the alloys were a mixture of acicular ferrite plus polygonal ferrite and the volume fraction of acicular ferrite varied from 46.3 to 55.4%. Molybdenum additions did not markedly affect the formation of acicular ferrite after hot rolling and rapid cooling. The microstructural details of the acicular ferrite were successfully revealed by TEM on shadowed extraction replicas. This technique was useful to distinguish the acicular ferrite from the polygonal ferrite through a more smooth surface relief after etching in 2% Nital of the little etched polygonal ferrite whereas the deeper etched acicular ferrite showed parallel sets of internal striations. This made it possible to measure the volume fraction of acicular ferrite in the mixed microstructures of acicular ferrite and polygonal ferrite. The continuous cooling transformation behaviors of two alloys with no molybdenum and with 0.22% Mo were constructed with no prior deformation as well as with prior deformation of the austenite. Molybdenum additions shifted the strain-free CCT diagram towards longer times and expanded the region in which acicular ferrite formed from a cooling rate range of 0.3 to 5 ºCs-1 (Mo-free) to 0.1 to 15 ºCs-1 (with 0.22% Mo). However, its effect was significantly overshadowed by prior deformation in the austenite. The strain affected CCT diagrams for both alloys appear to be similar. The prior deformation had a stronger effect on the CCT diagram than molybdenum additions and promoted acicular ferrite formation, whereas it suppressed the formation of bainite. The prior deformation had two effects in acicular ferrite formation: it promoted nucleation and suppressed its growth and, therefore, resulted in a finer overall grain size. The effect on the YS/UTS ratio at various cooling rates ranging from 1 to 34, 51, 54 or 60 ºCs-1 was investigated in three cases: (i) without prior deformation and coiling simulation, (ii) with no prior deformation but with coiling simulation at 575 and 600 ºC and, (iii) with prior deformation of 33% reduction in the austenite below the Tnr followed by coiling simulation at 575 ºC for 1 hour. It was determined that the YS/UTS ratio was a function of the microstructure and cooling rate in the case treatment (i)) without any coiling simulation and prior deformation. The coarse bainite or acicular ferrite, which was formed at high cooling rates, raised the YS/UTS ratio under conditions of no deformation prior to the transformation. The yield strength and ultimate tensile strength also increased with an increase in cooling rate. With coiling conditions (treatment (ii)), the ratio was not sensitive to the cooling rate or the microstructure for the reference Mo-free alloy #6 because the coiling allows recovery of dislocations, thereby decreasing the difference in dislocation density that had arisen between a low and a high cooling rate. The YS/UTS ratio ranged from 0.75 to 0.8 after a simulated coiling at 575 ºC and from 0.76 to 0.78 after a coiling simulation at 600 ºC. Prior deformation (treatment (iii)) in the austenite raised the ratio from 0.81 to 0.86. However, the YS/UTS ratio was not sensitive to cooling rate after coiling at 575 ºC for 1 hour in the cases with and without prior deformation in the austenite. Deformation with a 33% reduction below the Tnr prior to the transformation increased the yield strength more than the ultimate tensile strength, leading to a high YS/UTS ratio that ranged from 0.81 to 0.86. The prior deformation, therefore, had a stronger effect on the YS/UTS ratio than the microstructure. Towards cache optimization in finite automata / Thesis (PhD (Metallurgical Engineering))--University of Pretoria, 2007. / Materials Science and Metallurgical Engineering / PhD / unrestricted
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The Susceptibility of Electric Resistance Welded Line Pipe to Selective Seam Weld CorrosionRitchie, Porter 07 October 2020 (has links)
No description available.
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