In order to improve the surface quality of high-strength steel internal thread,enhance the fatigue life and reliability of the thread,the ultrasonic burnishing technology is used to strengthen high-strength steel large-diameter internal thread.The microscopic surface topography,roughness,hardness,residual stress and fatigue life of the thread are detected and compared before and after ultrasonic burnishing by using optical microscope,surface topography measurement instrument,micro hardness tester,stress tes...