Strain-rate-dependent deformation behaviour of high-carbon steel in compression: mechanical and structural characterisation

Abstract

Dual-phase high-carbon steels are of significant interest in mining industries particularly in comminution and rock handling applications where the strain rate varies from very low to very high. The effect of quasi-static strain rate on the deformation behaviour of austenite–martensite high-carbon low-alloy steel is investigated for compression loading in this paper. Experiments were conducted at different compressive strain rates (2.56 × 10−4 to 2.56 × 10−1 s−1), and the subsequent microstructural evolution was characterised by optical microscopy, X-ray diffraction (XRD), scanning electron microscopy and electron backscatter diffraction (EBSD) techniques to establish the structure–property correlation. The experimental results indicated an increase in the yield strength (σy) with the increase in the strain rate due to the rate-dependent dislocation velocities. The strain hardening rate of the material exhibited a decreasing trend with an increase in the true strain values for all the applied strain rates. XRD results indicated the phenomenon of deformation-induced martensitic transformation (DIMT) to be rate dependent, whereas EBSD results showed an increase in the Kernel average misorientation values with increase in the strain rate. The volume fraction of retained austenite was observed to be decreasing with an increase in the engineering strain values irrespective of the applied strain rate. The microscopic features of the fracture surfaces showed the presence of transgranular cracking at low strain rates, whereas predominant intergranular cracks were found at higher strain rates. TEM results indicated the decrease in the lath martensites with increase in the strain rate.