This paper aims to explore the microstructure and mechanical properties of 9Cr-3W-3Co steel welded joints. In the experiment, 9Cr-3W-3Co steel samples were welded by vacuum electron beam welding technology (VEBW) without any metal stuff, and all the welding joints were treated by high-temperature tempering at 730∘C for 8 h. The microstructure of welding joints was observed by OM, SEM and TEM; and the mechanical properties of welded joints were analyzed by microhardness test, room-temperature tensile, test impact test and high-temperature creep test. As a result, all the 9Cr-3W-3Co steel samples displayed the microstructure status as martensite under the Scheffler-Schneider prediction model, which conformed to the expectation. After high-temperature tempering, the grains of the welding zone were smaller than the base metal and the composition was tempered lath martensite only. Some of the lath martensite bundles even showed the incomplete polygonal transformation. The M23C₆ carbides and MX phase were distributed continuously along with the lath martensite interfaces, which showed a tendency for further aggregation. The microhardness of the weld zone was slightly higher than the base metal (mean of base metal: 240 HV0.98N, mean of weld zone: 273 HV0.98N and mean of heat affected area: 274 HV0.98N). There was no softening phenomenon observed, and the welding joints maintaining the high intensity. Other mechanical properties like the tensile strength (mean: 750 MPa), yield strength (mean: 707 MPa) and impact toughness (mean of WM: 25.1 J and HAZ: 23.3 J) were also excellent. When the temperature parameter is constant, the time for creep fracture reduces significantly with the increase of the stress; whereas the time for creep fracture decreases significantly as the temperature increases, while the stress parameter is constant.

中文翻译：

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9Cr-3W-3Co钢真空电子束焊接接头的组织和力学性能

本文旨在探讨9Cr-3W-3Co钢焊接接头的显微组织和力学性能。实验中，9Cr-3W-3Co钢试样采用真空电子束焊接技术（VEBW）焊接，不添加任何金属材料，所有焊接接头均经过高温回火处理。730∘C 8 小时。采用OM、SEM和TEM观察焊接接头的显微组织；并通过显微硬度试验、室温拉伸试验、试验冲击试验和高温蠕变试验对焊接接头的力学性能进行了分析。结果，所有9Cr-3W-3Co钢样品在Scheffler-Schneider预测模型下的显微组织状态均为马氏体，符合预期。高温回火后，焊接区晶粒小于母材，成分仅为回火板条马氏体。一些板条马氏体束甚至表现出不完全的多边形转变。他们23C ₆碳化物和MX相沿板条马氏体界面连续分布，呈现进一步聚集的趋势。焊缝区显微硬度略高于母材（母材平均值：240 HV0.98ñ, 焊接区平均值：273 HV0.98ñ平均热影响面积：274 HV0.98ñ). 未观察到软化现象，焊接接头保持高强度。其他机械性能，如抗拉强度（平均：750 MPa）、屈服强度（平均：707 MPa）和冲击韧性（平均 WM：25.1 J 和 HAZ：23.3 J）也很出色。当温度参数不变时，蠕变断裂时间随着应力的增大而显着缩短；而蠕变断裂的时间随着温度的升高而显着减少，而应力参数是恒定的。