Filler-free (FF) welding processes namely, Activated Tungsten Inert Gas welding (ATIG), Laser Beam Welding (LBW), and Friction Stir Welding (FSW) were utilized for joining the nuclear grade 9Cr-1Mo-V-Nb ferritic-martensitic steel and 316 L(N) austenitic stainless steel. A comparative investigation was made by assessing the weld geometries, metallurgical features, material mixing proportions, carbon diffusion behaviour, and mechanical properties of the post-weld heat-treated (PWHT) dissimilar weld joints. Geometries of the weld zones were observed with the transverse and longitudinal macrographs. Metallurgical features were examined by optical microscopy (OM) and Scanning electron microscopy (SEM). Three-phase microstructures were identified in the dissimilar weld zones (DWZ). The elemental distributions were identified by Energy-dispersive X-ray spectroscopy (EDAX). The mixing proportions of the dissimilar alloys and the formation of δ-ferrite in the dissimilar heat-affected zones (HAZ) and DWZ were analytically quantified. Moreover, the diffusion activity of carbides/interstitial carbon atoms was examined by Secondary ion mass spectroscopy (SIMS). In the FSW joints, the intermingled microstructures are recorded with high and stabilized hardness values as compared to the DWZ of the ATIG and LBW joints. In the transverse tensile test, all FF joints were failed at the 316 L(N) base metal (BM) region. Tensile and impact testing of all weld metal indicated that, the weld metal region of the LBW joint exhibited higher strength and lower toughness as compared to the ATIG and FSW joints. The presence of untransformed, recrystallized fine equiaxed austenite along and refined martensitic structure arranged in an alternate layers within the weld metal region of FSW joint caused the higher toughness property than the ATIG and LBW joints.

无填料 (FF) 焊接工艺，即活性钨惰性气体焊接 (ATIG)、激光束焊接 (LBW) 和搅拌摩擦焊 (FSW) 用于连接核级 9Cr-1Mo-V-Nb 铁素体-马氏体钢和 316 L(N) 奥氏体不锈钢。通过评估焊后热处理 (PWHT) 异种焊接接头的焊缝几何形状、冶金特征、材料混合比例、碳扩散行为和机械性能，进行了比较研究。用横向和纵向宏观照片观察焊缝区的几何形状。通过光学显微镜 (OM) 和扫描电子显微镜 (SEM) 检查金相特征。在异种焊缝区 (DWZ) 中发现了三相显微组织。通过能量色散 X 射线光谱 (EDAX) 确定元素分布。异种合金的混合比例和异种热影响区 (HAZ) 和 DWZ 中 δ-铁素体的形成被分析量化。此外，通过二次离子质谱（SIMS）检查碳化物/间隙碳原子的扩散活性。在 FSW 接头中，与 ATIG 和 LBW 接头的 DWZ 相比，记录的混合微观结构具有高且稳定的硬度值。在横向拉伸试验中，所有 FF 接头均在 316 L(N) 母材 (BM) 区域失效。所有焊缝金属的拉伸和冲击试验表明，与 ATIG 和 FSW 接头相比，LBW 接头的焊缝金属区域表现出更高的强度和更低的韧性。未转化的存在，