Issue 78

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

used only for qualitative microstructural characterization, and fracture micromechanisms were not identified. Systematic fracture-surface SEM examination across all experimental conditions was not performed. The observed SEM differences may also be influenced by factors related to the manufacturing and thermomechanical history of the chain material, such as local cooling-rate variations, deformation history, microstructural banding, chemical segregation or the position from which the specimens were extracted within the chain link. However, since the manufacturing history, spatial microstructural distribution and local chemical variations were not systematically investigated in this study, these factors cannot be identified as definitive causes. They should therefore be considered as possible contributing factors to the observed specimen-to-specimen variability. In addition, the selected cross-sectional fields do not represent the complete spatial microstructural distribution of each specimen. Accordingly, the SEM findings are limited to qualitative near-fracture microstructural characterization. his study experimentally evaluated the combined effects of seawater corrosion, notch timing and test temperature on the Charpy V-notch impact behaviour of AISI 1008 steel extracted from the base material of galvanized marine chain links. Based on the obtained results, the following conclusions can be drawn: 1) The uncorroded AISI 1008 chain steel exhibited a pronounced temperature-dependent impact response. The absorbed energy decreased sharply as the test temperature was reduced from 23 °C to − 40 °C, indicating a substantial reduction in impact resistance and energy absorption capacity over the investigated temperature range. 2) A considerable scatter in absorbed impact energy was observed even in the uncorroded reference condition. This finding suggests that factors other than corrosion exposure may have contributed to the Charpy response, including specimen to-specimen material variability within the chain-link material. However, the present observations do not identify a definitive cause for the within-group scatter. 3) The influence of seawater exposure on the mean Charpy impact response became more apparent after 30 days of immersion. At 0 °C, the specimens exposed to seawater and substitute seawater for 30 days exhibited lower mean absorbed impact energies than the uncorroded reference specimens. The 10-day results showed considerable scatter and should therefore be interpreted cautiously rather than as evidence of improved impact performance after short term exposure. 4) Seawater produced higher corrosion mass loss than substitute seawater under comparable exposure durations. This indicates that coastal seawater may represent a more severe corrosion environment than substitute seawater under static immersion conditions. However, the difference in absorbed impact energy between seawater and substitute seawater was not proportional to the difference in mass loss. 5) Corrosion mass loss showed a weak negative correlation with absorbed impact energy; however, the relationship was not statistically significant ( r = -0.140, p = 0.544, R 2 = 0.020). Therefore, corrosion mass loss alone was not sufficient to reliably predict the Charpy impact performance within the present dataset. The measured impact response may depend on multiple parameters, including corrosion condition, notch condition, test temperature and specimen-to specimen material variability. 6) The two notch-timing conditions exhibited different mean absorbed energies and levels of scatter, but the direction of the trend was not consistent at 0 and 23 °C. Direct exposure of the notch root to seawater did not produce a consistently higher or lower absorbed energy under all investigated conditions. Therefore, notch timing should be considered together with test temperature, corrosion history and local material variability when evaluating the impact response of the chain steel. 7) Hardness showed a weak negative correlation with absorbed impact energy, but the relationship was not statistically significant ( r = -0.156, p = 0.387, R 2 = 0.024). Thus, the measured hardness variation alone was insufficient to explain the observed scatter in absorbed impact energy. Stereomicroscope observations highlighted differences in macroscopic fracture-surface appearance, while near-fracture cross-sectional SEM highlighted local ferrite–pearlite heterogeneity, pearlite distribution and discontinuity-like features in selected regions. Because the SEM observations were not performed on the actual fracture surfaces, they cannot identify the fracture micromechanisms or establish a direct causal relationship between the observed cross-sectional features and absorbed impact energy. 8) From a structural integrity perspective, the results show that the impact resistance of the investigated marine chain steel cannot be assessed only by average corrosion loss or average hardness values. Local corrosion condition, notch state, low-temperature loading and possible local material variability should also be considered when evaluating the damage tolerance and reliability of chain components operating in marine environments. T C ONCLUSIONS

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