The effect of austempering parameters on impact and fracture toughness of din 35nicrmov12.5 gun barrel steel

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2005

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Aksu, Engin

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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.

Subject Keywords

Metallurgy.

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http://etd.lib.metu.edu.tr/upload/12606240/index.pdf
https://hdl.handle.net/11511/15209

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Graduate School of Natural and Applied Sciences, Thesis

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Citation Formats

E. Aksu, “The effect of austempering parameters on impact and fracture toughness of din 35nicrmov12.5 gun barrel steel,” M.S. - Master of Science, Middle East Technical University, 2005.