在18，27 μm冲击振幅下对Q420qD/20MnMoNb厚板异种钢T型焊接接头焊趾区进行超声冲击处理，分析了不同冲击振幅下焊趾处的显微组织、残余应力以及显微硬度，并与超声冲击前的进行了对比。结果表明：超声冲击处理后焊趾表层出现塑性变形层、大量位错及较高残余压应力，晶粒细化，硬度提高。当超声冲击振幅由18 μm增至27 μm，塑性变形层深度由约120 μm增大至144 μm，亚晶尺寸进一步细化至约25 nm，位错密度进一步增大至约2.48×10¹⁴ m^-2；表面残余压应力增大至约433 MPa，其影响深度增大至约1 410 μm；表面硬度增大至约400 HV，硬化层深度增加至约900 μm。

Ultrasonic impact was conducted on the weld toe region of Q420qD/20MnMoNb thick plate dissimilar steel T-type welded joints with 18, 27 μm impact amplitudes, and the microstructure, residual stress and microhardness at the weld toe were analyzed under different impact amplitudes, and compared with those before ultrasonic impact. The results show that after ultrasonic impact, a plastic deformation layer, a lot of dislocations and a high compressive stress appeared on the surface layer of the weld toe, the grains were refined, and the hardness increased. When the ultrasonic impact amplitude increased from 18 μm to 27 μm, the depth of the plastic deformation layer increased from about 120 μm to 144 μm, the subcrystalline was further refined to about 25 nm in size, and the dislocation density increased to about 2.48×10¹⁴ m^-2; the residual compressive stress on the surface increased to about 433 MPa and its affected depth increased to about 1 410 μm; the surface hardness increased to about 400 HV and the depth of hardening layer increased to about 900 μm.