METHOD AND NOZZLE FOR IMPROVING RESIDUAL STRESS OF METALLIC MATERIAL

摘要

PROBLEM TO BE SOLVED: To effectively impart a compressive residual stress to the surface of a metallic material which is in air in an atmospher equivalent to that in water. SOLUTION: A nozzle 8 has a water flow jet port 9 which is at the central part and a water flow jet port 10 which surrounds the water flow jet port 9. A water flow jets from the water flow jet port 9 and 10 of the nozzle 8 which is in air to a metallic material in air. A water flow 11 which jets from the respective water flow jet ports 10 forms a water region partially in air as if water existed in a virtual water tank about the water flow jet port 9. A water jet 12 for high pressure peening jets from the water flow jet port 9 at a speed higher than a water flow 11 into that water region. The water jet 12 contains cavitation air bubbles and collides against the surface of the metallic material. An impact force produced due to collapsing of the cavitation air bubbles generates a compressive residual stress in the metallic material.