Compression temperature to activate kinking in pearlitic steel

Abstract

The preferable condition for kinking in the compression of pearlitic steel is reported in this study. Spring steel (0.53 wt%C-1.48%Si-0.70%Mn-0.76%Cr–Fe) with a pearlitic structure was compressed at different temperatures ranging from ambient to 600 °C. The deformation microstructure clarified that the kinking occurred more oftenwhen the compression temperature was less than 400 °C. Three-dimensional reconstruction of the scanning electron microscopy images with focused-ion-beam serial sectioning revealed that the kinked structure comprised a band-like sheared area surrounded by the bent structures. The shear strain in the kinked structure is greater than the macroscopic strain applied by compression. A series of measurements of compressive flow stress (strain rate: 0.001/sec to 1/sec) elucidated negative strain rate sensitivity (m-value < 0) at ∼ 300 °C. Strain localization by kinking occurs preferentially at relatively lower temperature because a smaller strain rate sensitivity can promote local plastic instability.