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The causes for lower qualified rate of transverse low temperature impact toughness at -20 ℃ of SM490YB hot-rolled H beam for offshore oil platform are analyzed with such instrument and equipment as the optical microscope, scanning electron microscope and energy spectrometer. The results showed that the poorer low temperature impact toughness of test steel was caused by large Al2O3 inclusion, harder bainite structure, coarse grain and banded structure in the steel. The transverse low temperature impact toughness at -20 ℃ of test steel is improved obviously and qualified rate of impact at -20 ℃ is increased from 80% to 100% by reducing carbon content of test steel as well as optimizing smelting and rolling processes so that the grain size and inclusions of test steel are refined as well as types of microstructure are optimized.
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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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