PSI - Issue 68

Sakari Pallaspuro et al. / Procedia Structural Integrity 68 (2025) 802–808 Pallaspuro S. et al. / Structural Integrity Procedia 00 (2025) 000–000

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Fig. 3. Master Curve plots for the specimens notched at the fusion line / coarse-grained heat-affected zone (HAZ): a) HAZ of the martensitic austenitic DQ&P, b) post-weld heat treated DQ&P HAZ, c) HAZ of the martensitic DQ, and d) post-weld heat treated DQ HAZ. The dashed curves indicate 95 % and 5 % probability limits. 4. Conclusions We studied fracture toughness properties of a low-carbon direct-quenched and partitioned (DQ&P) steel, and its electron-beam welded seam in various configurations. The main outcomes are: • Lath-martensitic microstructure with ~7 vol.% of inter-lath retained austenite (DQ&P) and ~1100 MPa yield strength can have very high room temperature fracture toughness (~200 MPa√m) and good low-temperature toughness with T 0 at -41 °C. • Weld seam with ~3 vol.% of retained austenite has excellent ambient ( ≳ 140 MPa√m) and low-temperature toughness in the as-welded condition, and consequently low T 0 practically on par with the DQ&P base material. • Post-weld heat treatment reduces toughness in all the cases. This is most likely due to lowered amount of residual austenite that can undergo beneficial strain-induced martensite transformation, and possibly due to partial relaxation of residual stresses and detrimental decomposition of retained austenite.