Ultrasonic fatigue tests on maraging 300 steel: Under solution annealed, after aging heat treatment and under pre-corrosion attack

Ultrasonic fatigue tests were carried out under continuous cycling on the maraging 300 steel for the following conditions: (A) solution annealed (as received from supplier), (B) after aging heat treatment of 490 °C for 6 h, (C) after pre-corrosion attack, and (D) specimens loaded at 293 MPa at room temperature without failure until 1.0E+10 cycles. The ultrasonic fatigue strength of the four modalities were compared and discussed in regard the crack initiation inclusion, the heat treatment and the testing conditions. Crack initiation and propagation under this fatigue testing modality was analyzed; revealing that ultrasonic fatigue strength is related to internal TiN-inclusions and its parameters of shape and orientation, in regard the uniaxial applied load. Numerical simulations were carried out to investigate the stress concentration of an ellipsoidal void of 150 mm (longer radius), and a TiN ellipsoidal inclusion of same dimensions. In addition, SEM (Scanning Electron Microscope) analysis was carried out on the fracture surfaces to determine the crack initiation and propagation zones.