PSI - Issue 33

Julio A. Ruiz Vilchez et al. / Procedia Structural Integrity 33 (2021) 658–664 Author name / Structural Integrity Procedia 00 (2019) 000–000

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Fig. 5. Ultrasonic fatigue endurance of maraging steel 300, for three stress levels: 389, 486, and 585 MPa.

Discussion The values of fatigue endurance of maraging 300, under room temperature, load ratio R = -1 and without control of environmental humidity, were observed associated with a nonmetallic inclusion of type Ti(N,C). Figure 6 presents the fracture superficial paths of two testing specimens; the first one loaded at 389 MPa (a), and the second at 585 MPa (b). Thermic effect is clear observed along the superficial crack path for the high applied load (Figure 6b), which confirm that crack propagation in this steel may be associated with both: internal and superficial effects, which would be enhanced with the increasing of applied load. If crack initiation was localized inside the specimen, superficial effects modify the fatigue endurance of this steel, particularly for high applied load and without cooling system.

Fig. 6. Fracture superficial paths of two testing specimens: 389 Mpa (a), and 585 MPa (b) In Figure 7 are shown the fracture surfaces of two specimens loaded at 389 Mpa and 585 MPa. Concentric circular zones are observed for both cases, where at the center of these zones is localized the crack initiation inclusion. All tested specimens present an interior crack initiation inclusion of type Ti(N,C), and are not at the subsurface, but deeply inside the specimen.