PREDICTION OF COMPRESSIVE RESIDUAL STRESSES ACCORDING TO ULTRASONIC NANOCRYSTAL SURFACE MODIFICATION PROCESS VARIABLES OF ALLOY 600

Primary water stress corrosion cracking (PWSCC) has been reported in Alloy 600 components. PWSCC occurs due to a combination of high tensile residual stress, corrosive environment, and susceptible material. Prevention of PWSCC primarily involves mitigating tensile residual stresses. One of the peening techniques, ultrasonic nanocrystal surface modification (UNSM), applies a static load and high frequency ultrasonic vibrations of 20 kHz to the strike pin, generating high compressive residual stresses on the surface. Predicting the variation in compressive residual stress according to process variables is essential for analyzing the prevention of PWSCC. Numerous studies have been conducted to predict compressive residual stresses according to process variables, but research on Alloy 600 is insufficient. The finite element analysis methodology is compared to experimental results. Static load and amplitude are considered as variables. The analysis results are quantitatively analyzed, categorizing into surface residual stress, maximum residual stress, and effective depth. As the static load and amplitude increase, the compressive residual stress becomes larger and affects deeper. Amplitude has a greater influence on magnitude of surface residual stresses than static load.