| Summary: | 碩士 === 國立成功大學 === 材料科學及工程學系碩博士班 === 100 === In recent years modern constructions were developed high-rise and large span. For the purpose of getting high strength and thickness steel plate, and for high welding efficiency to increase welding heat input. But high heat input welding process, which will make the heat-affected zone (HAZ) of coarse grains, resulting in toughness and strength decrease. Modified by inclusions of high heat input welding steel, which was the most effective way to enhance its strength and toughness.
This study focused on structure steel inclusion analysis, which was including SM570, SS400, and the magnesium addition of SS400 steels. Analyze the types, sizes, and numbers of inclusions, as well as the interface relationship between inclusion and ferrite. The microstructures of inclusions were observed by field emission SEM. The chemical compositions of the inclusions were analyzed by SEM-EDS. Identified the inclusions structure and analyzed inclusions and ferrite orientation by electron backscatter diffraction (EBSD). Combine the SEM-BEI images and EDS were analyzed through the image analysis software to determine the size and numbers of inclusions.
The inclusions of SM570 steel mainly have titanium nitride, γ-alumina, and α-manganese sulfide. The inclusions of SS400 steel have γ-alumina, and α-manganese sulfide. The inclusions of SS400+Mg steel have magnesium aluminum oxide (MgO•Al2O3), and α-manganese sulfide. According to the size distribution statistics, the inclusions were mainly concentrated below diameter 1μm, and most were single-phase manganese sulfide. Titanium nitride and manganese sulfide have coherent/semi-coherent interface, and the alumina and magnesium aluminum oxide have semi-coherent/incoherent interface.
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