Molecular dynamics study on the effect of ferrite structure on the mechanical characteristics of pearlite

Abstract

Cold-drawn pearlitic steel wire has a wide range of applications in engineering due to its excellent mechanical properties. However, to date, there is limited understanding of how the internal ferrite phase structure of pearlitic steel wire affects its mechanical properties. The effect of the ferrite phase structure on the deformation mechanism and mechanical properties of pearlite was studied using molecular dynamics methods. The study considered three types of ferrite structures: (1) single-crystal structure, (2) nanocrystalline structure and (3) twinned crystal structure. The study showed that the ferrite structure could alter the deformation mechanism of pearlite during tensile loading by affecting the plastic deformation behaviour of ferrite. When the ferrite is a single-crystal structure, the pearlite undergoes elastic deformation followed by direct fracture failure; when the ferrite is a nanocrystalline structure, the pearlite experiences elastic deformation, elastic-plastic deformation, plastic deformation and then fracture failure in sequence; when the ferrite is a twin structure, the pearlite undergoes elastic deformation, plastic deformation and then fracture failure in sequence. Due to the influence of the deformation mechanism, the mechanical properties of pearlite with different ferrite structures showed a significant difference. Compared to single-crystal ferrite, when the ferrite structure is nanocrystalline, the strength of pearlite decreases significantly, but the ductility is significantly increased. Moreover, the ductility increases as the size of the nanocrystals decreases. Compared to single-crystal ferrite, when the ferrite has a twinned structure, the strength of the pearlite remains unchanged, but the ductility significantly increases. In addition, the ductility increases as the thickness of the twin layers decreases. The research results provide a new approach for further improving the mechanical properties of cold-drawn pearlitic steel wire.