The Surface Strengthening Of Explosion Valve Bolt By Ultrasonic Impact Treatment

Blasting valve is the last barrier to protect the safety of nuclear power plants.The tensionbolt is an important component in the valve in blasting,accident or other necessary emergency relief situations through blasting unit,and high-pressure gas is generated,and the tension bolt is pulled off in the pre-groove,then open the valve cover to realize the pressure relief effect.But in the normal work of nuclear power units,under normal working pressure,tension bolts must maintain good mechanical properties,and fatigue failure does not occur.Ultrasonic impact treatment(UIT)as a new technology of surface deformation strengthening,in recent years has been rapid development and application at home and abroad.At present already from the pure treatment began to improve weld metal workpiece surface and sub-surface can also improve the anti-fatigue performance,anti-stress corrosion resistance and wear resistance,but by ultrasonic impact automation for complex shape parts surface uniform reinforcement is rarely reported.This subject to blasting valve tension bolt groove prejudge as the research object,using ultrasonic impact to strengthen the means of special ultrasonic impact head application of the patented technology with independent intellectual property rights,with the enhanced surface matching the impact needle design,strengthening processing of blasting valve to realize automation of surface tension bolts,complex shape parts-tension bolts the groove hyperboloid uniform hardening.On this basis,the effects of ultrasonic shock amplitude,shock time to strengthen the surface roughness,surface condition,microstructure,microhardness,residual stress and fatigue life,reveals the impact of process parameters on complex double ultrasound influence of surface strengthening effect,won the best shock conditions.The process parameters optimization,the simulation of tension bolt ultrasonic peening treatment,the tensile-tensile fatigue limit stress of bolt specimen impact optimal technical conditions were measured,drawing fatigue S-N curve relationship of tension bolts between stress cycles and stress amplitude before and after the impact,and observe the fatigue fracture surface tension bolt groove through the SEM simulation to prejudge the electron microscope analysis of fatigue fracture morphology of various impact conditions,the process of fatigue fracture occurrence,development,reveals the strengthening process and fatigue property The essential relation and the influence rule provides effective theoretical and experimental support for the improvement of fatigue performance.Specific experimental results are summarized as follows:(1)The impact of amplitude under the same impact time with saturation on the strengthening effect of double curved surface tension bolt groove prejudge,in the process of impact time gradually increased to 10 min,surface roughness,surface micro hardness,microstructure and residual stress has been gradually optimized,basically in shock time occurred at 10 min the best impact,and this impact over time,weaken the effect of shock;(2)In the process of impact strengthening,the impact amplitude 30 ?m than 15 ?m firstly achieves the saturation point of the effect of impact strengthening;(3)The best ultrasonic impact process parameters of the hypersurface are the impact amplitude of 30 ?m and the impact time of 10 min.The fatigue limit of the tension bolts is increased by 11% after applying the optimized process to the impact bolts of the tension bolts.