Relation between the fatigue and fracture ductile-brittle transition in S500 welded steel joints

The formation and propagation of cracks occur through irreversible dislocation movements at notches, material defects, and grain boundaries. Since this process is partly thermally controlled, the resistance to dislocation movements at low temperatures increases. This slows both fatigue initiation and fatigue crack propagation. From recent experimental data, it can be seen that fatigue crack growth is accelerated below the fatigue transition temperature (FTT) that correlates with the ductile-brittle transition temperature (DBTT) found by well-known fracture mechanics tests, i.e., Charpy impact, fracture toughness, and CTOD. Hence, this study investigates the relation between FTT and DBTT in S500 high-strength steel base material and welded joints at low temperatures using fatigue crack growth, fracture toughness tests as well as scanning electron microscopy. From the tests, an almost constant decrease in fatigue crack propagation rate is determined with decreasing test temperature even below the DBTT. At −100 °C, the fatigue crack propagation rate is about half of the rate observed at room temperature for both base material and weld metal.

Subjects

arctic conditions

weldment fatigue

temperature dependence of material fatigue

fatigue and fracture mechanics testing at low temperatures

fatigue and fracture transitions temperatures

direct-current potential drop method

scanning electron microscopy

fracture toughness testing

structural steel

DDC Class

600: Technik

620: Ingenieurwissenschaften

More Funding Information

This research received no external funding.

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publishedVersion

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https://creativecommons.org/licenses/by/4.0/

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metals-12-00385.pdf

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Relation between the fatigue and fracture ductile-brittle transition in S500 welded steel joints