Issue 78

A. Sancak et alii, Fracture and Structural Integrity, 78 (2026) 186-206; DOI: 10.3221/IGF-ESIS.78.11

Considering the existing studies, corrosion, fatigue, stress analysis, fracture mechanics, wear, material development and welded-joint performance of mooring chains have been investigated extensively. However, the Charpy V-notch impact response of chain base material after controlled seawater corrosion exposure has received limited attention, particularly when seawater and substitute seawater environments are compared and the effects of test temperature and notch timing are considered together. Moreover, the scatter in absorbed impact energy under nominally identical test conditions remains a key challenge for the structural integrity assessment of marine chain steels, since such variability may be associated not only with corrosion-induced mass loss but also with hardness variation and local microstructural heterogeneity. It should be noted that the investigated AISI 1008 steel was obtained from a commercially available hot-dip galvanized chain product used for anchoring and general securing applications in marine environments. In such applications, the galvanized coating provides surface protection against environmental corrosion, while the low-carbon steel forms the load-bearing substrate. Accordingly, this work focuses on the impact response of the underlying steel substrate after controlled seawater exposure rather than on the protective performance of the galvanized coating. Therefore, the present study experimentally investigates the effects of seawater and substitute seawater exposure, test temperature and notch timing on the Charpy V-notch impact toughness of AISI 1008 steel specimens extracted from the base material of galvanized marine chain links. The impact results are evaluated together with corrosion mass loss and hardness measurements, stereomicroscope observations of the fracture surfaces to compare macroscopic fracture appearance, and near-fracture cross-sectional SEM examinations to highlight local microstructural variability in the investigated low-carbon marine chain steel. Material and chemical composition he material investigated in this study was AISI 1008 low-carbon steel extracted from hot-dip galvanized steel chain links with a nominal diameter of 20 mm, as shown in Fig. 1. Although the original chain links were galvanized, the Charpy V-notch specimens were machined from the base material of the chain links. Thus, the impact behaviour was evaluated for the steel substrate rather than for the zinc-coated surface condition. This approach was selected to examine the intrinsic response of the chain steel after controlled seawater corrosion exposure. The elemental composition of the steel was determined on the prepared specimen surface using an ARL-iSPARK 8860 optical emission spectrometer. The measurements were carried out in accordance with ASTM E415 [31]. The measured elemental composition is listed in Tab. 1. The carbon content was 0.0823 wt.%, confirming the low-carbon character of the investigated steel, while the measured carbon equivalent was 0.2131. T M ATERIALS AND METHODS

wt.%

Element

wt.%

Element

C

0.0823 0.4280 0.1099 0.0109 0.0089 0.2717 0.0141 0.1407 0.1149 0.0272 0.0008 0.0105 0.0002 0.0001 0.0001 0.0001 0.2131

B

0.0004 0.0102 0.0025 0.0011 0.0013 0.0020 0.0096 0.0071 0.0001 0.0022 0.0001 0.0003 0.0066 0.0010 0.0001 98.7746

Mn

N Al Ti

Si

S P

Nb Ca W As Pb Sb Ta Zr Zn Ce La Fe —

Cu Sn Cr Ni Mo

V

Co

Bi

Mg Se Te C eq

— Table 1: Elemental composition of the investigated AISI 1008 chain steel, wt.%.

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