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A diesel engine failed during running, its mileage was only more than 2 743 kilometers. After disassembling, it was found that the needle valve body of high pressure common rail injector of cylinder 6 cracked in axial direction, failure analysis was performed. By means of macroscopic trace analysis, scanning electron microscope fracture analysis, energy spectrum analysis, metallographic analysis and microhardness test, it is pointed out that the main cause for the cracking of needle valve body is the existence of fusiform defect in the matrix of needle valve body head, which is the raw material slag containing Zr, O and other elements. The material of needle valve body is ASP steel, in its production process, when the liquid steel flows through the atomizing nozzle (high density zirconia material), a small part of the nozzle material falls into the liquid steel, forming the slag inclusion. The crack initiates and spreads from the slag inclusion, leading to early fatigue fracture of needle valve body.
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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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