Hardening and softening mechanisms of pearlitic steel wire under torsion

• Published in: Materials in engineering Vol. 59; pp. 397 - 405
• Main Authors: Zhao, Tian-Zhang, Zhang, Shi-Hong, Zhang, Guang-Liang, Song, Hong-Wu, Cheng, Ming
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.07.2014
• Subjects: Cementite; Dislocations; Hardening; Mathematical models; Microstructure; Pearlitic steel wire; Scanning electron microscopy; Softening; Strain hardening; Torsion; Pearlitic steel wire; Hardening; Softening; Torsion
• ISSN: 0261-3069
• DOI: 10.1016/j.matdes.2014.03.029

•Mechanical behavior of pearlitic steel wire is studied using torsion.•Work hardening results from refinement lamellar pearlitic structure.•Softening results from recovery, shear bands and lamellar fragmentations.•A microstructure based analytical flow stress model is established. The mechanical behaviors and microstructure evolution of pearlitic steel wires under monotonic shear deformation have been investigated by a torsion test and a number of electron microscopy techniques including scanning electron microscopy (SEM) and transmission electron microscopy (TEM), with an aim to reveal the softening and hardening mechanisms of a randomly oriented pearlitic structure during a monotonic stain path. Significantly different from the remarkable strain hardening in cold wire drawing, the strain hardening rate during torsion drops to zero quickly after a short hardening stage. The microstructure observations indicate that the inter-lamellar spacing (ILS) decreases and the dislocations accumulate with strain, which leads to hardening of the material. Meanwhile, when the strain is larger than 0.154, the enhancement of dynamic recovery, shear bands (SBs) and cementite fragmentations results in the softening and balances the strain hardening. A microstructure based analytical flow stress model with considering the influence of ILS on the mean free path of dislocations and the softening caused by SBs and cementite fragmentations, has been established and the predicted flow shear curve meets well with the measured curve in the torsion test.