High borated stainless steels (HBSSs) are widely used in nuclear field because of excellent neutron-shielding ability. However, coarse network-like borides are prone to be formed in weld joints during welding process, deteriorating the ductility seriously. In this work, electron beam (EB) welding was adopted to join ∼3.5 mm thick HBSSs containing 0.30–2.12 wt. % boron. Benefiting from high energy density, fine γ-Fe matrix and network-like borides were obtained in fusion zone (FZ) and partially molten zone (PMZ) of weld joints. The effects of boron content, heat input and post weld heat treatment (PWHT) on the microstructure, mechanical properties and fracture behaviour of weld joints were investigated. As boron content increased, narrower PMZ was observed in weld joints owing to smaller solidification temperature range. The volume fraction and size of borides in PMZ/FZ raised, enhancing the strength and decreasing the ductility. Meanwhile, the fracture location of weld joints was closer to the interface of PMZ and base metal (BM) during deformation. Higher heat input brought a wider PMZ and larger penetration depth, but hardly changed the size and distribution of borides. Interestingly, it caused a steep slope of interfacial line between PMZ and BM, leading to the fracture along the interface with low ductility. After PWHT, the borides in PMZ/FZ were spheroidized, and the stress localization during deformation was weakened. Consequently, excellent weld joints exhibiting similar mechanical properties with base steels were produced. This systematic work provided a reference for welding other materials containing coarse and brittle secondary phases.

高硼酸不锈钢（HBSSs）因其优异的中子屏蔽能力而被广泛应用于核领域。但在焊接过程中，焊缝处易形成粗大的网状硼化物，严重影响延展性。在这项工作中，采用电子束 (EB) 焊接来连接约 3.5 mm 厚的 HBSS，其中含有 0.30-2.12 wt. % 硼。得益于高能量密度，在焊接接头的熔合区（FZ）和部分熔融区（PMZ）获得了精细的γ-Fe基体和网状硼化物。研究了硼含量、热输入和焊后热处理（PWHT）对焊接接头显微组织、力学性能和断裂行为的影响。随着硼含量的增加，由于凝固温度范围更小，在焊接接头中观察到更窄的 PMZ。PMZ/FZ中硼化物的体积分数和尺寸增加，提高了强度，降低了延展性。同时，焊接接头的断裂位置在变形过程中更接近PMZ与母材（BM）的界面。更高的热输入带来更宽的 PMZ 和更大的穿透深度，但几乎没有改变硼化物的尺寸和分布。有趣的是，它导致 PMZ 和 BM 之间的界面线倾斜陡峭，导致沿界面的断裂具有低延展性。PWHT后，PMZ/FZ中的硼化物球化，变形过程中的应力局部化减弱。因此，产生了具有与基础钢相似的机械性能的优良焊接接头。这项系统性的工作为焊接其他含有粗而脆的二次相的材料提供了参考。