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Thermodynamic calculation software Thermo-Calc was used to calculate the influence of the change of Nb and Ti content on the precipitation behavior of carbon nitride, the composition of 1 800 MPa hot-formed steel was determined. The equilibrium phase diagram, the precipitation temperature of the main precipitated phase, the change of element content with temperature and the growth behavior of the precipitated phase were calculated, the basic data of the main phase composition and phase transformation characteristics were obtained. The mechanical properties and 3 point bending properties of microalloy 1 800 MPa hot stamping steel have been tested. The test results show that the steel has good toughness. The microstructure of the hot formed steel after quenching was characterized by Electron Back Scattering Diffraction (EBSD). The characterized results show that the small austenitic grains and small martensitic blocks are the main causes for the high toughness of the 1 800 MPa hot formed steel. Finally, the delayed fracture sensitivity of the hot-formed steel was measured by hydrogen filling and slow drawing method. The measured results show that the hot stamping steel has excellent delayed fracture sensitivity when the hydrogen filling time is less than 2 h.
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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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