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URN etd-0816107-170924 Statistics This thesis had been viewed 3651 times. Download 3035 times. Author Chao-Jan Huang Author's Email Address No Public. Department Materials Engineering Year 2006 Semester 2 Degree Master Type of Document Master's Thesis Language zh-TW.Big5 Chinese Page Count 85 Title Study on Mechanical and Ultrasonic Properties of SUS 403 Martensitic Stainless Steel after TMT Treatments Keyword TMT Martensite stainless steels ultrasonic ultrasonic Martensite stainless steels TMT Abstract SUS 403 martensitic stainless steels is commonly used in high stress parts such as nuclear power plant. This research has used thermal mechanical treatment (TMT) to improve the disadvantages of coarse grain size of SUS 403 stainless steels. In general, finer grain sizes have several advantages on mechanical properties, such as increasing ultimate tensile strength, ductility, hardness and impact toughness. Also, the degree of grain fineness can result in the difference in ultrasonic responses because the sound waves traveling in the material interact with grain boundaries which show up the variation of ultrasonic velocity and ultrasonic attenuation. Thus, the purpose of this study is to explore the possibility that grain size refinement of SUS 403 by TMT processing and the relationship between its mechanical properties and ultrasonic characteristics.
It was found that the as-received SUS 403 was composed of ferrite and martensite phases with high chromium alloy carbides at grain boundary. After austenitization at 1010℃ for 2hrs, the carbides was dissolved into matrix. In addition, the grain sizes were refined with the increase of the rolled amount. The average grain size is 60~100µm for 20% rolled material and 10~20µm for 40% rolled material as compared to the as-received (>100µm). Moreover, the mechanical properties consisting of tensile strength, ductility, hardness and impact toughness were all improved when the grain sizes were refined.
From the experimental results, it was also found that the carbides reappeared after tempering at 300℃~600℃. In particular, tempering at 500℃, fine alloy carbides were precipitated from martensite resulting in secondary hardening of this material. However, elongation decreased. Higher temperature tempering (>600℃) could increase impact toughness and ultimate tensile strength but hardness decrease. It is because martensite was decomposited to form ferrite.
In the case of ultrasonic properties, it was found that ultrasonic velocity decreased and ultrasonic attenuation increased with the refinement of grain size. Moreover, it was found that the second hardening occurred at the ultrasonic velocity of 5888~5894m/s for 20% rolled material and of 5886m/s for 40% rolled material; and its ultrasonic attenuation is 0.130054dB/mm for 20% rolled material and 0.134408dB/mm for 40% rolled material, respectively.
Advisor Committee Cheng-Hsun Hsu - advisor
Files Date of Defense 2007-07-26 Date of Submission 2007-08-17