Abstract: Aiming at the stress relief tempering process after vacuum electron beam welding of 30CrMnSiNi2A ultra-high strength steel structural parts, effect of repeated tempering on microstructure and mechanical properties of lock bottom welded joints in the final heat treatment state was studied.The test results showed that after once and thrice stress relief tempering, tensile properties of welded parts in the final state were slightly improved in comparison with the raw materials of 30CrMnSiNi2A after direct final heat treatment, and tensile properties of the weld were slightly higher than those of the base metal.The final microstructure of raw materials, once stress relief tempered weldments and thrice stress relief tempered weldments was strip martensite, and there was no significant difference in microstructure and composition except for slight changes in microstructure uniformity and martensite morphology.Compared with the fatigue limit of base metal, the fatigue limit of once stress relief tempered joint was reduced by 11%, and that of thrice stress relief tempered joint was reduced by 18%.Highlights:(1)Influence of stress relief tempering on tensile and fatigue properties of joints was mastered.(2)Combined with the microstructure analysis, the influence mechanism was studied.