The importance of lamellar architecture to obtain ductility in heavily cold-worked pearlitic steels revealed by microbending experiments

Abstract

In-situ microbending experiments were conducted to understand the effect of composite architecture on the deformation behavior and ductility of heavily cold-worked pearlitic steels. Two extreme architectures were deliberately chosen for this purpose: first, a high-pressure torsion-deformed fully pearlitic steel consisting of a nanolayered lamellar arrangement of ferrite and cementite and second, an even further refined state where this lamellar arrangement is transferred to a carbon-decorated ferritic subgrain structure. Despite the enormous strength of these samples, in-situ microbending experiments reveal an astonishing homogeneous deformation capability of nanostructures – much larger than in uniaxial compression or tension. Plastic strains of up to 20% can be realized without severe failure of the specimens. This outstanding ductility seems to be linked to the inherent strain gradient of the bending beams, hindering early initiation and propagation of shear bands. While this holds true for both tested states, the architecture of the pearlitic steels plays a predominant role in this respect. In case of the lamellar architecture homogenous plastic flow can be realized up to significantly larger plastic strains, while shear band and crack formation occur already at lower plastic strains in case of the carbon-decorated subgrain structure.