The influencing mechanisms of banded structure, nonmetallic inclusions and grain size on transverse impact toughness are systematically analyzed aiming at such problems as great fluctuation of transverse impact property and unstable low-temperature toughness of H beam SM490YB for ocean engineering. The Mn segregation and spheroidized inclusions are effectively inhibited, grains are refined as well as microstructure homogenization is realized through adopting such comprehensive measures as composition optimization, modified inclusions with Ca treatment, low superheat continuous casting as well as controlled rolling and cooling. The transverse impact energy at -20 ℃ is improved, fluctuation is reduced, banded structure is improved, spheroidization effect of inclusions are obvious and grains are refined for H beam with specification of H300×300 with treatment of optimum technology.
| 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 |