Elastic Wave Characteristics from Crack Initiation and Propagation of High-Strength Steel (HV550) Immersed in Acetic Acid Solution

In this study, when different bending stresses were applied to cracked specimens of high strength steel (SKD11: HV550) immersed in 0.057M solution of acetic acid (CH3COOH), elastic waves were detected and frequency characteristics were analyzed using time-frequency analysis. The dominant frequency band by the tensile test was approximately 103 kHz, and in the acetic acid solution without stress were approximately 32 kHz and 101 kHz. The dominant frequency bands of the crack specimens in which cracks propagated were three groups of about 30-40 kHz(F1), about 60-85 kHz(F2), and about 100-110kHz(F3). The elastic wave was obtained by corrosion, pitting, crack initiation, and propagation, but no elastic wave was detected during the hydrogen aggregation time. The dominant frequency bands of the crack specimen without crack propagation were two groups of approximately 28-33 kHz(F1) and approximately 94-109 kHz(F3). This is the same as the dominant frequency band in the acetic acid solution under non-stress. The fracture surface showed many traces of pitting and corrosion regardless of the applied stress, and microcracks were observed in Cr carbide.