A newly developed creep method is described for following the kinetics of manganese sulfide precipitation in four electrical steels. The technique was also applied to a Ti steel, in which the precipitation kinetics were previously determined using a stress relaxation method. The resulting creep rate is sensitive to the occurrence of precipitation; thus the slope of the true strain-log(time) curve decreases immediately after the initiation and increases on the completion of precipitation. The precipitation-time-temperature diagrams determined in this way are of classical C shape on all of the tested materials. Because higher dislocation densities and internal stress levels are maintained, the present technique is more effective for monitoring the precipitation events occurring in the ferritic phases and at high temperatures than the previously developed stress relaxation method. / The nucleation sites for precipitation during creep testing were investigated with the aid of electron microscopy. It was concluded that the progress of MnS precipitation can be divided into three stages: nucleation, growth and coarsening. There exists a strong tendency for the nuclei to be formed on dislocations at lower temperatures. However, nucleation at grain boundaries is preferred as the temperature is increased. The classical diffusion-controlled growth theory is not satisfactory for strain-induced MrS precipitation. Thus, a modification was made in such a dynamic case by taking the effects of deformation vacancies into account. The kinetics during the coarsening stage are controlled by both bulk and grain boundary diffusion. / The microstructural examinations revealed that both grain deformation and grain boundary sliding take place in the electrical steels at hot working temperatures. Quantitative evaluations showed that the latter process contributes about one-sixth to one-tenth the total strain under the current experimental conditions. The strong retardation of grain deformation after the occurrence of precipitation is explained in terms of the interfacial pinning of mobile dislocations by these incoherent particles. It is also demonstrated that the finely-dispersed precipitates slow down the boundary sliding rate. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.39266 |
| Date | January 1991 |
| Creators | Sun, Wei Ping |
| Publisher | McGill University |
| Source Sets | Library and Archives Canada ETDs Repository / Centre d'archives des thèses électroniques de Bibliothèque et Archives Canada |
| Language | English |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Format | application/pdf |
| Coverage | Doctor of Philosophy (Department of Mining and Metallurgical Engineering.) |
| Rights | All items in eScholarship@McGill are protected by copyright with all rights reserved unless otherwise indicated. |
| Relation | alephsysno: 001237597, proquestno: NN67821, Theses scanned by UMI/ProQuest. |
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