Three microalloyed steels were tested under continuous and interrupted loading conditions. These materials consisted of a base steel containing 0.06%C and 1.31%Mn and two further alloys containing single additions of 0.29%Mo and 0.04%Nb. / Double hit compression tests were performed on cylindrical specimens of the three steels at 820, 780 and 740$ sp circ$C within the $ alpha$ + $ gamma$ field. A softening curve was determined at each temperature using the offset method. It was observed that, in the base steel, $ alpha$ recrystallizes more slowly than $ gamma$. The addition of Mo steel retards the recrystallization of the base material; it has a greater influence on $ gamma$ than on $ alpha$ recrystallization. Nb addition has an even greater effect on the recrystallization of the two phases. In this steel, the recrystallization of ferrite was incomplete at the three intercritical temperatures. Furthermore, the austenite remained completely unrecrystallized up to the maximum time involved in the experiments (1 hr). / The progress of ferrite recrystallization was followed on quenched specimens of the three steels by means of quantitative metallography. Most of the data fit an Avrami equation with exponents in the range 2 to 2.5. A departure from this equation was observed for the final stages of the recrystallization process. Growth rate analysis showed that the average growth rate decreased with time for all the experimental materials, this decrease being greatest for the base steel and least for the Nb-containing grade. The nucleation of recrystallization was observed to occur heterogeneously in the microstructure. The interface between ferrite and austenite was the preferred site for nucleation. Measurement of the number and size of recrystallized ferrite grains showed that some grains begin to recrystallize very early, growing to a large size by the end of the process. The total number of grains increased continuously until almost 80% of the volume fraction was recrystallized. After that, due to coalescence, the number of recrystallized grains decreased very rapidly. (Abstract shortened by UMI.)
| Identifer | oai:union.ndltd.org:LACETR/oai:collectionscanada.gc.ca:QMM.74539 |
| Date | January 1990 |
| Creators | Simielli, Eider Alberto |
| 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: 001170718, proquestno: AAINN66387, Theses scanned by UMI/ProQuest. |
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