PSI - Issue 53

America Califano et al. / Procedia Structural Integrity 53 (2024) 185–189 Author name / Structural Integrity Procedia 00 (2019) 000–000

186

2

1. Introduction Understanding the fatigue crack-growth behavior of materials is of paramount importance, as it plays a pivotal role in the structural integrity and reliability of various components and structures. Among the materials of interest, 17-4 PH stainless steel has gained significant attention due to its excellent combination of mechanical properties and corrosion resistance (Henry et al., (2021)), making it a preferred choice for numerous engineering applications. In recent years, the advent of AM techniques has revolutionized the way of producing components (Gibson et al., (2021)). As a matter of fact, several types of stainless steel can be nowadays processed via SLM (Afkhami et al., (2019)). The mechanical properties and microstructures of the steels made by AM are influenced by many factors, first and foremost the manufacturing process parameters (Alfieri et al., (2022), De Luca et al., (2021), Sepe et al., (2020), Sepe et al., (2022)). For this reason, it is fundamental to investigate the mechanical and the crack-growth behaviors under different loading conditions (Foti et al., (2023), Karaka ş et al., (2023), Sepe et al., (2021)). In addition, it is necessary to explore the potential advantages and/or challenges posed by materials made by AM in comparison to traditionally wrought ones, in order to broader the knowledge and the applicability in engineering and manufacturing contexts. For the above reasons, the experimental fatigue crack propagation behavior of 17-4 PH stainless steel specimens made both by SLM and traditional rolling is investigated in this work. Tests were carried out using standard compact C(T) specimens tested at R = 0.1 at a frequency of 5 Hz. The main objective was to study the effect of the crack orientation on crack-length vs. number of cycles curves for the differently manufactured

stainless steel specimens. 2. Materials and methods

The raw material consisted into two 17-4 PH stainless steel rectangular plate obtained: i) by means of the SLM technique; ii) by means of traditional rolling technique. The first plate was manufactured using the commercial EOS GP1 (UNS S17400) powder and the printing parameters listed in Table 1 (Caiazzo & Alfieri, (2021)), in full-melting mode, choosing the z-axis as printing direction. As discussed in literature (Califano et al., (2023)), the final plate had sizes of 170 mm x 70 mm x 6.65 mm and allowed to get ten specimens (numbered from 1 to 10): one full specimen was used for metallographic analyses and nine C(T) specimens were used for crack-growth tests. The results for two of the nine C(T) specimens (n. 2 and n. 5) were reported here.

Table 1. Printing parameters used for the manufacturing phase. Parameter Value Operating laser power [W] 195 Operating wavelength [nm] 1030 Linear scanning speed [m ∙ s-1] 1.2 Hatch distance [mm] 0.09 Layer thickness [mm] 0.02 Focused laser diameter [mm] 0.09

The second plate was obtained through the traditional rolling technique and had sizes of 200 mm x 300 mm x 12 mm. After the rolling phase, the plate was milled and the thickness brought to 6.75 mm, then was grinded so to achieve the desired thickness of 6.55 mm. A schematic of the plate with its final dimensions and the specimens is reported in Fig. 1, where the rolling direction was highlighted. From the plate two slices were cut out and six C(T) specimens were extracted from each slice by means of an Electric Discharge Machining (EDM) machine. The specimens extracted from the first slice were characterized by a notch directed transversely to the rolling direction and were indicated as TL1, TL2, etc . On the other hand, the specimens extracted from the second slice were