Dynamic strain aging of an AISI 1025 steel coil and its relationship with macroscopic responses during the upsetting process

Abstract

In this paper, dynamic strain aging (DSA) of an AISI 1025 steel coil and related strain hardening behavior are described, including their macroscopic effects. A cylinder compression test was conducted for various sample temperatures and strain rates ranging from 20 degrees C to 500 degrees C and 1/s to 20/s, respectively. The experimental flow stress data were indicative of typical DSA, which caused serrated flow; this was verified by the strain hardening rate obtained from the Kocks-Mecking hardening model. The experimental data were mathematically fitted by a simple but general power law model, with piecewise bi-linear functions of sample temperature and strain for both the strength constant and strain rate sensitivity exponent. The flow stresses extracted from JMatPro were used as the theoretical flow stresses for comparison with fitted flow stresses associated with DSA, to characterize the effects. The fitted flow stresses were validated experimentally by compression tests conducted at various sample temperatures and strain rates; the varying conditions had a negligible effect despite the complexities in the flow stress due to DSA. An instability index was proposed to evaluate the macroscopic effect of DSA on upsetting processes in non-isothermal cylinder compression tests. This index was used to quantify the macroscopic plastic deformation behavior of the material with DSA.