PSI - Issue 79

A. Bacco et al. / Procedia Structural Integrity 79 (2026) 342–347

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2. Material and Methods The material under study is STRENX700E HSS, produced according to EN 10025-6 specifications, with a minimum yield strength of 700 MPa. The chemical composition of the material, provided by the manufacturer, shows a significant silicon content (Si > 0.20%), Table 1, an element known to influence the reactivity of the substrate during the galvanising process and the formation of brittle intermetallic phases in the interface area between the steel and the coating.

Table 1. Chemical composition of Strenx 700E steel.

%max C %max Si %max Mn %max P %max S %max Cr %max Cu %max Ni %max Mo %max B

Material

STRENX700E

0.20

0.60

1.60

0.020

0.010

0.80

0.30

2.0

0.70

0.005

The test pieces were obtained from 3 mm thick hot-rolled sheets, which were then machined to extract the test pieces and create circular notches, Fig. 1. The test pieces were then subjected to a multi-step preparation process before being galvanised: I. degreasing and pickling, with hydrochloric acid (HCl) to remove residual oils from mechanical processing and any oxides; II. rinsing, with water to remove the acids from the previous stage; III. fluxing, using a mixture of zinc chloride (ZnCl), ammonium chloride (NH4Cl) and bismuth chloride (BiCl3) to create a protective barrier that prevents the formation of oxides before galvanising and promotes the metallurgical reaction between steel and zinc, thus improving the adhesion of the coating (Astorre et al., 2000); IV. drying, using hot air to remove all moisture from the samples. Finally, hot-dip galvanising with a Zn–5%Al (Bellini et al., 2019, Jabbar et al., 2023, Kühne et al., 2025) alloy was carried out. The galvanising process was performed under controlled conditions, with a bath temperature of 450°C. The choice of the Zn–5%Al alloy was motivated by its greater resistance to corrosion in marine environments compared to conventional galvanising, as well as its lower tendency to form hydrogen cracks.

Fig. 1. Shape and dimensions of the specimens tested (units in mm).

Fatigue tests were conducted at constant axial load (constant amplitude test) using an electrodynamic testing machine, the StepLab UD40, with a frequency of 40 Hz and a load ratio of R = 0.01. The tests were performed in air at room temperature, until failure or until 5·10 6 cycles were reached as the conventional threshold for infinite life (run-out).