In this study the effects of different austempering times and temperatures on impact
toughness, hardness and fracture toughness properties of 35NiCrMoV12.5 gun barrel
steel are investigated. 300 ° / C, 325 ° / C and 350 ° / C were chosen as austempering
temperatures. Isothermal holding times at these temperatures were chosen as 1 minute,
10 minutes, 1 hour and 10 hours. It was found that, 350 ° / C being an exception,
austempering temperature and impact toughness has an inverse relationship and impact
toughness increases as isothermal holding time increases. However this behavior is valid
until some point. Prolonged transformation times causes toughness to decrease.
Hardness measurements revealed that, as isothermal holding time increases, hardness
decreases. In order to compare the mechanical properties obtained by austempering with
that of conventional cooling and tempering, 400 ° / C was chosen as the tempering
temperature and applied to both charpy impact and fracture toughness specimens. It was
found that conventional cooling and tempering produced tougher structures. Size of the
fracture toughness specimens might have caused an undesired situation such as
incomplete transformation to bainite. Optical and scanning electron microscopy was
used in order to analyze the microstructures obtained after each treatment. It was
observed that the majority of the morphologies occurred is lower bainite. On the other
hand, martensitic structures were observed almost at every temperature.
| Identifer | oai:union.ndltd.org:METU/oai:etd.lib.metu.edu.tr:http://etd.lib.metu.edu.tr/upload/12606240/index.pdf |
| Date | 01 July 2005 |
| Creators | Aksu, Engin |
| Contributors | Atala, Haluk |
| Publisher | METU |
| Source Sets | Middle East Technical Univ. |
| Language | English |
| Detected Language | English |
| Type | M.S. Thesis |
| Format | text/pdf |
| Rights | To liberate the content for public access |
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