Unveiling the Effect of Cementite Distribution on the Deformation Behavior of Pearlitic Steel Wires under Micropillar Compression: A Strain-Gradient Crystal Plasticity Approach

Abstract

This study examines the deformation mechanisms in cold-drawn pearlitic steel wires using micropillar compression tests. Scanning electron microscopy (SEM) identified five distinct regions characterized by varying cementite distributions, and nanoindentation tests were subsequently performed in these areas. Additionally, five micropillars were fabricated within these regions using focused ion beam (FIB) techniques. The micropillar compression results reveal a pronounced correlation between the mechanical behavior of micropillars and various microstructural parameters, including the cementite inclination angle (CIA), interlamellar spacing, and ferrite-cementite distribution. Furthermore, strain gradient crystal plasticity finite element analysis (SG-CPFEM) revealed a significant increase in geometrically necessary dislocations (GNDs) at the ferrite-cementite interfaces, which critically influences the effective slip resistance. The simulations also indicated that the presence of a ferrite-cementite interface significantly elevates GND concentrations, impacting the load-displacement behavior. Micropillars with cementite normal to the loading direction showed higher increases in GNDs, while reduced cementite spacings were found to amplify GND formation due to increased strain gradients in the ferrite phase. A shear fracture were predominant in pillars with CIA of 67.5º or higher, while kink band formations were observed in pillars with CIA of 22.5º or lower. The increase in GNDs is influenced by both the CIA and interlamellar spacing, highlighting their critical roles in determining mechanical properties.