A thesis submitted to the Faculty of Engineering in
fulfilment of the requirements for the degree of Master of
Technology in Mechanical Engineering
2005 / The objective of this project was to monitor the high temperature creep behaviour of 441
stainless steel. Two different alloys of 441 were investigated; the main difference
between them being the Niobium content. Particularly imporlant to the project was how
the Niobium content and grain size affected the creep resistance of the material.
Creep tests were performed using purpose built constant load creep test rigs. Initially the
rigs were not suitable for the testing procedures pertaining to this project. This was due to
persistent problems being experienced with regards the reliability and reproducibility of
the rigs. After various modifications were made the results produced from the rigs were
consistent.
Creep test data was used in order to determine the mechanism of creep that is operative
within the material (at a predetermined temperature) under a predetermined load.
Particular attention was paid to the resulting stress exponents. in order to identify the
operative creep mechanism. The identification of the operative creep mechanisms was
also aided by microscopical analysis. This analysis was also necessary to monitor how
the grain size had altered at various annealing temperatures.
Heat treatment was used as a method to alter the high temperature strength and
microstructure of the material. Heat treatments were performed at various temperatures
in order to determine the ideal temperature to promote optimum creep resistance of 441.
All heat treatments were performed in a purpose designed and built high temperature salt
bath furnace. The commissioning of the salt bath formed part of the objectives for this
project.
Sag testing was also conducted, using purpose built sag test rigs. It was necessary to
design and manufacture a sag test rig that could be comparable to the industry accepted
method of sag testing known as the two-point beam method, as this method is believed to
produce inconsistent results.
Conclusions have been drawn from the results of the data and from previous research on
the subject matter.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:cput/oai:localhost:20.500.11838/1249 |
| Date | January 2005 |
| Creators | Cain, Victoria |
| Publisher | Cape Peninsula University of Technology |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Rights | http://creativecommons.org/licenses/by-nc-sa/3.0/za/ |
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