Includes bibliographical references. / An investigation has been carried out on a dual-phase 12 % chromium steel, designated 3CR12, with the aim of developing its composition to improve its properties. By the addition of appropriate alloying elements, it was hoped to produce a fully austenitic structure in the rolling temperature range, and at the same time to enhance the kinetics of the decomposition of austenite so that a fully ferritic structure could be obtained after air cooling. The absence of delta ferrite during hot rolling would eliminate the highly anisotropic structure currently found in 3CR12, whilst accelerating the transformation to alpha ferrite might eliminate the need for an annealing treatment. Volume fraction analysis (VF A) of specimens quenched from a soaking temperature of 1000°C showed that Co, Ni and Cu stabilise austenite, whilst Si and Al have the opposite effect. These results were confirmed by finding the equilibrium transformation temperatures of the decomposition of austenite to ferrite using dilatometry, and by investigating the partition of alloying elements between delta ferrite and austenite at I 000°C using the electron microprobe. The effects of the alloying elements on the kinetics of the transformation were investigated by VF A of specimens transformed from 1000°C, and by the use of dilatometry. Dilatometry was used to find the slowest cooling rate at which the alloy was fully untransformed. It was found that Si and Al enhance the kinetics of transformation, whilst Co, Ni and Cu hinder them. The effect of each element is discussed with respect to three factors: the delta ferrite content prior to the transformation, the temperature range of transformation, and the thermodynamic effects of the element.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:uct/oai:localhost:11427/9224 |
| Date | January 1996 |
| Creators | Jungbacke, Nils Gene |
| Contributors | Knutsen, Robert D |
| Publisher | University of Cape Town, Faculty of Engineering and the Built Environment, Centre for Materials Engineering |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Master Thesis, Masters, MSc |
| Format | application/pdf |
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