超高温高圧キャビテーションによるNi-Cr-Mo鋼の表面改質

抄録

SNCM630 is a material having particularly high strength among SNCM steels, and it is used for an engine member to be a connecting rod or a crank rod. Improvement of fatigue strength of materials is required, because the number of repetition stress quickly reaches the fatigue limit in the high-speed engine section. In this study, improvement of compressive residual stress on sample surface was investigated by applying ultrasonic wave to water jet cavitation (WJC) which is a technique of mechanical surface modification. Moreover, the authors compared it with conventional water jet cavitation (WJC) processing technology. WJC technology leads to the generation of high pressure when the cavities within the water collapse near the surface when a water jet ejected by a nozzle impacts a metal surface. This pressure causes a slight deformation of the impacted surface region and introduces compressive residual stress due to the elastic constraints of the underlying and surrounding metal. If ultrasonic irradiation is applied to WJC bubbles with diameters of several hundred microns, the bubbles are subjected to alternating high and low sound pressures, which leads to high pressures and a high-temperature reaction field. This technique is referred to as multifunction cavitation (MFC). Compressive residual stress was applied to each processed specimen surface. Moreover, improvement of corrosion resistance was observed in after MFC processing.