PSI - Issue 30

M.M. Kantor et al. / Procedia Structural Integrity 30 (2020) 45–52 M. М . Kantor et al. / Structural Integrity Procedia 00 (2020) 000–000

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Fig. 3. The correlation between minimal KCU values, � spl. and the number of splittings.

Described features pointed at quasi-cleavage character of fracture mechanism, as shown by Herø et al. (1975), Krishnadev et al. (1981). Thus, the formation of splittings could also be considered as a feature of low carbon microalloyed steels fractures in DBT region. The investigation of plastic zone microstructure of specimens fractured in DBT region revealed microcracks formation both under ductile fracture surfaces and under fracture surfaces containing splittings. The nature of microcracks was assessed by means of EBSD, Fig. 4.

Fig. 4. Microstructure under ductile fracture surface (left) and under fracture surface containing splitting (right). EBSD: (a), (b) BS maps; (c), (d) IPF maps.

Microcracks in plastic zone under ductile fracture surfaces occurred as main crack side branches, Fig. 4 (a). Crack tips of such microcracks were commonly blunted. Pattern quality maps, describing the soundness of crystal lattices, showed significant deterioration of BS parameter (dark areas). The formation of completely changed strongly deformed refined (5,2 µm) microstructure and development of deformation substructure (high amount of