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The small-diameter boiler tube is designed and developed through innovating process design as well as its quality indexes are improved by Inner Mongolia Baotou Steel Special Steel Pipe Co., Ltd. based on the requirements of group company, “break through and improve product quality”. The seamless steel pipe with outer diameter of 51~114.3 mm and wall thickness of 3.5~12 mm is rolled by continuous casting billet of Φ150 mm in the original design of the unit. The demand of small-diameter boiler tube with outer diameter of 38~48 mm and wall thickness of 3.5~8 mm in the boiler tube industry is greater. The seamless steel pipes of two groups of outer diameter produced with the billets of the same diameter is realized and their wall thickness accuracy is -7.14%~9.14% through researching and developing the technology of large tube reducing rate for continuous mill unit as well as producing the seamless steel pipe with outer diameter of 38~48 mm by continuous casting billet of Φ150 mm. When rolling small-diameter boiler tubes made of materials of 25MnG, 15CrMoG and 12Cr1MoVG, there are defects of “straight fold” on inner surface as well as “linear indentation” and “subsurface cracks” on outer surface of steel tube. Their causes are analyzed combining with the deformation process and material characteristics as well as the solutions are formulated so that qualified rate of ultrasonic flaw detection of product is increased from 86.82% to 91.32%. The heat-treatment schedule for small-diameter boiler tubes made of materials of 15CrMoG and 12Cr1MoVG is formulated as well as the mechanical properties of products are stable under this process schedule, which could meet the requirements of GB/T 5310-2017 standard.
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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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