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During the process of manufacturing automobile rims by purchased 420CL steel of one wheel plant in the winter, there is welding deformation cracking at edge of the rims with remained “rolled round edge” of steel coils. The metallographic structure and microhardness of edges with and without cracking of rim are detected with metalloscope and microhardness tester respectively as well as the causes of cracking are analyzed. The values of microhardness of weld seam, coarse grain heat affected zone, fine grain heat affected zone and parent metal at edge of the rims with remained “rolled round edge” of steel coils are 217, 215, 223 and 150 respectively, while those without “rolled round edge” of steel coils are 222, 230, 235 and 220 respectively. The difference of microhardness for welding heat affected zone and parent metal at edge of the rim with cracking is about 70, this is the main cause for cracking of rim. After flash butt welding, the difference of material hardness for welding fine grain heat affected zone and without welding heat effect along edge of rim is too large so that the deformation coordination ability at edge of rim is destroyed and the stress concentration is generated at juncture to cause cracking.
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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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