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To investigate the microstructural and mechanical properties of 1 000 MPa grade ultra-high strength steel submerged arc welding welded joints for hydroelectric engineering, the microstructure of different regions of the welded joint was characterized using scanning electron microscopy (SEM). Mechanical properties of the welded joint were determined through tensile testing, impact testing, and bending testing. The results reveals that, the weld metal of the root pass and fill passes is composed of columnar, dendritic, and equiaxed grains, with a microstructure dominated by acicular ferrite and a small amount of granular bainite. The heat-affected zone (HAZ) exhibits multiple typical regions, including a critical coarse grain zone and a coarse grain zone near the fusion line along the thickness direction. Away from the weld, fine grain zones and critical zones are observed, with a microstructure primarily consisting of granular bainite, M-A constituents, and lath martensite. The weld metal of the cap pass exhibits typical columnar grains with a microstructure primarily composed of acicular ferrite. The HAZ of the cap pass includes coarse grain, fine grain, critical, and subcritical zones. Due to the absence of subsequent welding passes, no critical coarse grain zone is formed, and the microstructure is primarily composed of lath martensite, granular bainite, and M-A constituents. The average tensile strength of the welded joint reaches 980 MPa grade, the low-temperature impact absorption energy of the weld zone and the HAZ at –40 ℃ is 118.7 J and 149.3 J (at T/4), 67.0 J and 154.0 J (at T/2), respectively. No cracks appear in the lateral bending.
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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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