Issue 78

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

experimental groups (n=33), whereas the mass-loss–energy analysis included the corrosion-exposed specimens for which mass-loss data were available (n=21). The individual values were paired according to the specimen numbering reported in Tabs. 4–6. Simple linear trend lines and the corresponding coefficients of determination ( R 2 ) were included in the scatter plots. For the corrosion mass-loss–energy relationship, simple linear regression was additionally expressed as an exploratory empirical model, with corrosion mass loss as the predictor and absorbed impact energy as the response. The statistical analysis was performed using Python and MS Excel. Corrosion mass loss and corrosion rate calculation Mass measurements were performed to quantify corrosion-induced material loss. Initial masses were recorded before corrosion exposure using a balance with a sensitivity of 0.01 g. After immersion and Charpy impact testing, corrosion products were removed from the specimen surfaces using P500C abrasive paper. The specimens were then weighed again using the same sensitivity, and the mass difference was used to determine corrosion mass loss. The corrosion rate was calculated using the ASTM G31-21 mass-loss approach [34]. Because corrosion products were intentionally retained on the specimens until after impact testing, the mass-loss measurements were performed after the mechanical tests. Therefore, the corrosion-rate results were used primarily to compare the relative severity of corrosion between exposure conditions rather than to represent continuously monitored mass-loss evolution during immersion. Hardness measurements Hardness measurements were performed to determine whether the scatter in absorbed impact energy could be associated with local variation in mechanical resistance. Hardness values were expressed on the HRB scale. Measurements were primarily performed using a TIME HLN-11A portable hardness tester equipped with a standard D-type impact probe. The nominal impact energy of the D-type probe was 11 N·mm, and the impact body mass was 5.5 g. For each specimen, approximately five to seven hardness measurements were taken at different locations, and the values were used to evaluate local and specimen-to-specimen variation. The obtained hardness values were additionally verified using a Wolpert Wilson Rockwell hardness tester on the Rockwell B scale under a 100 kgf ( ≈ 981 N) load. The hardness results were compared within each group and between groups to determine whether specimens with unusually low or high absorbed impact energy also exhibited corresponding hardness deviations. The hardness measurements did not indicate extreme hardness outliers sufficient to explain the observed scatter in Charpy impact energy alone. Therefore, the hardness results were considered together with the corrosion condition and microstructural observations in the interpretation of the impact test results. Macroscopic fracture-surface and near-fracture microstructural examinations Macroscopic and microscopic examinations were performed to support the interpretation of the Charpy impact results. Stereomicroscope observations were carried out using a Nikon SMZ800 stereomicroscope. The fracture surfaces and side surfaces of selected specimens were examined. Fracture-surface observations were used to compare the general fracture morphology of reference and corrosion-exposed specimens, while side-view observations were used to assess the fracture path after impact testing, particularly for the reference specimens tested at different temperatures. Scanning electron microscopy was performed using a Hitachi TM1000 scanning electron microscope. SEM examinations were conducted on selected specimens representing different absorbed-energy levels and exposure conditions. The SEM observations were not performed directly on the fracture surfaces. Instead, cross-sections were prepared from regions approximately 10 mm away from the fracture surface and parallel to the fracture plane. The cross-sectional samples were prepared by sequential grinding and polishing, followed by etching with nital to reveal the ferrite–pearlite microstructure. Before SEM observation, the prepared surfaces were coated with platinum to improve surface conductivity and image quality. Therefore, the SEM examination was used for near-fracture microstructural characterization rather than direct fracture-surface fractography. The observations focused on documenting the ferrite–pearlite microstructure, pearlite distribution, local microstructural heterogeneity and discontinuity-like features, including void-like, pull-out-like and inclusion-like regions. No direct relationship between these features and the actual crack path or fracture micromechanism was inferred. The SEM analysis included specimens from the uncorroded reference condition, specimens exposed to seawater for 30 days and notched after corrosion exposure, and specimens exposed to seawater for 30 days in the pre-notched condition. These observations were compared with the absorbed impact energy, corrosion mass loss and hardness results as complementary evidence of local material variability.

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