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Outline
Aiming at the bright band color difference on the upper surface occurring during the production of wide low-carbon deep-drawing steel for automotive outer panels on the electro-galvanizing line, a systematic study was carried out by means of optical microscopy, SEM, EDS and metallographic analysis. The results showed that the defect was caused by abnormally coarse grains in the surface layer of the cold-rolled substrate, leading to abnormal crystallization during electro-galvanizing. The areas with abnormal electroplating crystallization appeared as small bright spot defects, and a large number of bright spots macroscopically manifested as bright band color difference. Through comprehensive defect inspection and process analysis, it was determined that the high hot rolling coiling temperature and excessive wrapper roll pressure during coiling resulted in coarse grains in the surface layer of the hot-rolled strip, and the heredity of the hot-rolled microstructure led to coarse grains in the surface layer of the cold-rolled substrate. By reducing the coiling temperature from 750 ℃ to 710 ℃ and optimizing the wrapper roll pressure parameters, the defect was successfully eliminated, and the process optimization had no significant effect on the microstructure and properties of the finished product.
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| 科 Family | 属数 Number of genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) | 属 Genus | 种数 Number of species | 占总种数比例 Percentage of total species (%) |
|---|---|---|---|---|---|---|
| 鹅膏菌科Amanitaceae | 2 | 11 | 5.26 | 鹅膏菌属 Amanita | 10 | 4.78 |
| 小菇科 Mycenaceae | 2 | 12 | 5.74 | 丝盖伞属 Inocybe | 5 | 2.39 |
| 多孔菌科 Polyporaceae | 8 | 14 | 6.70 | 蜡蘑属 Laccaria | 5 | 2.39 |
| 红菇科 Russulaceae | 3 | 23 | 11.00 | 小皮伞属 Marasmius | 6 | 2.87 |
| 小菇属 Mycena | 11 | 5.26 | ||||
| 光柄菇属 Pluteus | 5 | 2.39 | ||||
| 红菇属 Russula | 17 | 8.13 | ||||
| 栓菌属 Trametes | 5 | 2.39 |
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