Cleavage fracture micromechanisms in thick-section quenched and tempered S690 high-strength steels

Abstract For structural assessment and optimal design of thick-section high-strength steels in applications under harsh service conditions, it is essential to understand the cleavage fracture micromechanisms. In this study, we assess effects through-thickness microstructure an 80-mm-thick quenched tempered S690 steel, notch orientation, crack tip constraint nucleation propagation via sub-sized opening displacement (CTOD) testing at ?100 °C. The was placed parallel perpendicular rolling direction, analysed by varying a/W ratio: 0.5, 0.25, 0.1. orientation does not play a role, material considered isotropic in-plane. Nb-rich inclusions were observed act as weak microstructural link triggering specimens with lowest CTOD values. While shallow-cracked from top section present larger critical values than deep-cracked ones due stress relief ahead tip, have significant influence middle very detrimental presence inclusions. Some show areas intergranular combined effect C, Cr, Mn, Ni, P segregation along precipitation clusters on grain boundaries. Several deflections high-angle boundaries where neighbouring sub-structure has different Bain axes.