PSI - Issue 79

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

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1. Introduction In the last years, high-strength steels (HSS) have assumed a central role in various applications where the strength-to-weight ratio is a key requirement (Šmak et al., 2021). This type of steel boasts high strength for the same thickness compared to common steels, making it perfect for applications such as civil infrastructure, offshore platforms, industrial vehicles, and earth-moving machinery. The potential to design light-weight structures with high strength also leads to costs and environment impact reductions. Generally, the high mechanical properties of these steels are obtained through an accurate controlled thermomechanical process, which involves hot rolling followed by heat treatment and tempering. This process results in a homogeneous microstructure with controlled distribution of residual stresses, with benefits in terms of mechanical strength (Kuang et al., 2017). However, like common steels, HSS remain prone to corrosion (Yeomans, 2004), which is a significant problem given the wide range of applications these materials have in corrosive environments, especially in marine or coastal environments where the presence of chlorides accelerates surface degradation. A widely used solution used to protect common steels in corrosive environments is the galvanising process, consisting in the application on the component surfaces of a protective layer of zinc, creating a barrier against the surrounding corrosive environment (Berto et al., 2016). Among the galvanising methods, the hot-dip one is widely used in industrial sectors where high-strength steels are employed: it consists of immersing a suitably treated component in a bath of molten zinc. Thanks to this procedure, it is possible to obtain a component covered with a protective layer of zinc in a relatively simple, quick and inexpensive manner. However, when applied to HSS, hot-dip galvanising presents specific challenges. Alloying elements such as silicon and phosphorus, which are present in significant percentages in the chemical composition of high-strength steels, are added precisely to optimise the thermomechanical process that improves their mechanical properties but at the same time make these steels reactive when in contact with molten zinc. This reactivity can lead to various problems, including sub-optimal adhesion of the zinc layer to the surfaces of the components and the creation of a heterogeneous metal layer that can cause surface discontinuities, residual stresses and embrittlement (Di Cocco et al., 2017, Di Cocco et al., 2014, Ruiz-Lòpez et al. 2019). The protective zinc layer is generally composed of chemical-physical phases that depend on the percentages of zinc and steel that compose it and influence its metallurgy and mechanical properties. Some phases play a mainly protective role, while others improve the adhesion between zinc and steel (Carpinteri et al., 2016, Hasegawa et al., 2020). The reactivity of the material to be galvanised causes these phases to grow uncontrollably during galvanising, favouring the growth of the most fragile phases (Alhamdany et al., 2024a-b, Sánchez et al., 2023, Song et al., 2011). High surface fragility is a significant factor, especially in applications subject to fatigue loads, as particularly fragile areas would promote the initiation of cracks that would expose the underlying material to the corrosive environment, contributing to propagation through the underlying material and thus reducing the life of the components (Prabitz et al., 2021, Ikeda et al., 2025, Guraja et al., 2022). The surface finish conditions that can be obtained with the galvanising of these steels are also significant, as the high reactivity with molten zinc makes it difficult to control parameters such as surface roughness and coating discontinuities caused by the detachment of the zinc layer. HSS components are often characterised by variations in thickness and geometric cut-outs, that affect negatively the fatigue life, as widely investigated in literature (Lipiäinen et al., 2022, Zehsaz et al., 2010). However, when a cut component is galvanised, the cut and the surrounding areas are critical factors in the process as they could be the site of defects and unevenness in the distribution of the zinc layer. In consideration of these issues, the study presented in this document aims to investigate the effect of hot-dip galvanising on the fatigue life of notched and galvanised high-strength steel specimens in order to quantify the effects that the hot-dip galvanising process could have on complex components made of HSS and thus provide useful information for the design and maintenance of galvanised HSS structures exposed to cyclic loads in aggressive environments.