In 2013, cracks were found in the radius of the dovetail slots of the rotor rim sheets in generator 1 of Juktan hydro power plant in Västerbotten, Sweden. The cracks were estimated to be too deep to be able to repair and Alstom conducted an investigation on the cause of fracture. The investigation came to the conclusion that the radius was too small and that the new rotor rim sheets should have a six times greater fillet radius. However, it has not been investigated whether the material structure or the manufacturing process may have an impact on the crack initiation and following propagation that is the focus of this report.Parts of the dovetail slots were cut out and characterized with XRF, SEM and LOM. Further mechanical characterizations were done according to Vickers.From the SEM and LOM micrographs a high amount of large (10μm) and cubic particles were found in the microstructure. The micrographs also showed a deformation of the microstructure and the hardness test showed a deformation hardening near the edge where the sheet had been punched. The edge surface of the sheet also had notches.The large and hard particles in the microstructure impair the mechanical properties of the steel. Furthermore, the hardening effect combined with the notches will make a good crack initiation point. Therefore, there is a higher possibility that a crack will initiate in the radius of the dovetail slots where large stresses occur.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:kth-152588 |
| Date | January 2014 |
| Creators | Altzar, Oskar |
| Publisher | KTH, Materialvetenskap |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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