Browsing by Author "Talonen, Juha"
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- Deformation Mechanisms and Strain Hardening of Chrominum-Manganese-Nickel Alloyed Austenitic Stainless Steels
School of Engineering | Master's thesis(2010) Oikari, AinoAustenitic stainless steels are known to strain harden strongly as a result to cold work. Strain hardening is a result of increased amount of dislocation glide obstacles, like other dislocations and mechanical twins, and also due to martensite formation. The aim of this thesis was to study the strain hardening behaviour and deformation-induced microstructures of austenitic stainless steels. The theoretical part of this study discusses different factors that affect deformation mechanisms of austenitic stainless steels. The effect of the stacking fault energy was studied more extensively. Also mechanisms affecting strain hardening of these steels were studied. The focus was on deformation-induced martensite transformation, and the effects of composition, grain size, temperature, stress and strain rate on this phenomenon. Six austenitic stainless steel grades (AISI 304, 301, two heats of 201, 204Cu and 201Cu) were studied in the experimental part of the thesis. Controlled amounts of deformation were induced into the test materials via tensile testing, and the resulting microstructures were studied by optical metallography, X-ray diffraction, FEG/SEM and the electron backscatter diffraction (EBSD) technique. The results indicated that deformation-induced martensite formation significantly increased the strain hardening rates of the most unstable steels. The morphology of the formed alpha'-martensite was seen to follow the known patterns, as alpha'-martensite formed into shear band intersections and spread throughout the grain from there. Epsilon-martensite was detected in the steel 204Cu with X-ray diffraction measurements and by utilizing the EBSD technique. This type of martensite was detected in the shear bands. In this steel, alpha'- and epsilon-martensite were usually found in association with each other, but alpha'-martensite was seen to nucleate also at shear band intersections of any type. The results also indicated that the steel grade 204Cu had the lowest stacking fault energy, as the highest amount of epsilon-martensite was formed into this steel. - Test Circuit For IC Encapsulation Quality
Helsinki University of Technology | Master's thesis(1997) Talonen, Juha