| Summary: | 碩士 === 義守大學 === 材料科學與工程學系碩士班 === 97 === It’s well known that weather resistant steels are important for the application as rail, cabinet, leaf spring etc. Besides, the purity of the molten steel is the impurity element content in molten steel, but in the molten steel the impurity elements is called inclusions. Due to the huge deformation ratio of steels by the manufacturing the morphology of inclusions plays affecting role on the properties of steel such as workability, toughness. Most inclusions are Al2O3、MnS、AlN、SiO2、CaO etc.The study investigates the influences of doping rare-earth element on microstructural evolution of weather resistant steels. Doping was performed in a high-vacuum furnace using Ce element (0.034wt%、0.068wt%and0.120wt%), as rare earth element. Heat treatment parameters employed in this study was 1250oC accompanying with different holding times (30,120, and 240 min). The microstructural characterization and phase constitution of the resulting surfaces were carried out by metallography, scanning electron microscope (SEM/EDS). The results show that the amounts of the inclusions increase accompanying with the adding content of Ce element. Comparing the inclusions at RT and after re-heating treatment, the inclusions are smaller after re-heating than at RT. The morphologies of the inclusions are not change a lot. The inclusions are shrunk to 3.5~4 μm after re-heating at 1250℃ just for 0.5 hour, to 2.5~3.5μm after re-heating for 2hours and to 2~3 μm for 4 hours.
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