| Summary: | 碩士 === 義守大學 === 材料科學與工程學系碩士在職專班 === 100 === The purpose of this study is to observe the effects of different cooling condi-tions on the formation of the spike-like spangles, with the conditions set and samples obtained directly in the production process. The main operation parameter of this study is the volume of cooling air in No.1 and No.2 up-leg coolers.
When the volume of cooling air increased from 179m3/min to 288m3/min, the length of the spike-like spangles on both sides of the steel sheet shortened, with their frequency of appearance reduced accordingly. Observations under optical micro-scope revealed that the long, rectangular parts of a spike-like spangle showed an equiaxed grain structure, while the slender, needle-like ones on the sides showed a columnar grain structure. The grain sizes of the equiaxed and columnar crystals were found to be unaffected by different cooling rates, with no significant difference in their respective elemental compositions. Micro hardness tests showed that areas of spike-like spangles were harder than those of normal ones. The main factor con-tributing to a higher hardness is the much smaller grain size of the spike-like spangle.
Results from salt spray tests showed no significant difference in corrosion re-sistance between spike-like spangles and normal ones.
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