Deformation Twinning Behavior of Twinning-induced Plasticity Steels with Different Carbon Concentrations – Part 2: Proposal of Dynamic-strain-aging-assisted Deformation Twinning

Abstract

In a previous study, the carbon concentration dependence of the deformation twinning behavior in twinning-induced plasticity steels was investigated, which clarified that the deformation twin fraction in the < 144 > tensile orientation did not change with the carbon concentration. In this study, twinning deformation occurred in the Fe-18Mn-1.2C steel at 473 K with a relatively high stacking fault energy of 55 mJ/m 2 . To explain these experimental results, dynamic strain aging of Shockley partials dislocations was proposed as an additional contributing factor to assist the deformation twinning in high-carbon-added austenitic steels. Most abnormalities concerning deformation twinning such as the high stacking fault energy in Fe-Mn-C austenitic steels were interpreted by considering the effect of dynamic strain aging.KEY WORDS: deformation twinning; dynamic strain aging; austenitic steel; electron backscatter diffraction (EBSD).

Overview of Dynamic Strain Aging and Associated Phenomena in Fe–Mn–C Austenitic Steels

“…This consideration provides an answer to the problem of solute carbon, significantly facilitating deformation twinning in high-Mn austenitic steels. 8,15,16,66) For instance, the SFE in the experimental condition shown in Fig. 7(d) is 55 mJ/m 2 , which is significantly higher than the general upper limit of SFE for the occurrence of twinning in austenitic steels (30-40 mJ/m 2 ).…”

“…A significant amount of deformation twins was not observed immediately after the onset of serrated flow, e.g., at 10% tensile strain. 15) However, as shown in Fig. 7(e), a considerable amount of deformation twins appears after further plastic deformation, e.g., at 20% tensile strain.…”

“…The onset of deformation twinning is delayed when the flow stress decreases because further work hardening is required to satisfy the critical stress for twinning. In addition, as will be explained in detail in section 5, the authors have proposed that deformation twining can be promoted through dislocation separation by the dislocation pinning effect of carbon 15,16) and by reduction in critical resolved shear stress for twinning associated with carbon-enhanced dislocation planarity.…”

“…15,16) Unlike in other crystal systems such as BCC, deformation twinning in FCC occurs after significant plastic deformation. 43) That is, the major difference between FCC twinning and stress-assisted ε-martensitic transformation in Fe-Mn-C austenitic steels is based on whether the activation of plasticity mechanism requires a pre-plastic strain given by dislocation slip deformation.…”

“…With increase in SFE, the effect of DSA significantly contributes to work hardening in Fe-high Mn steels containing a high concentration of carbon. 15,16) Unlike the twinning effect, the relationship between DSA and work hardening has rarely been discussed from a comprehensive viewpoint. In order to comprehensively understand the work hardening in highMn high-C steels with SFE higher than 20 mJ/m 2 , we must summarize the primary factors affecting the DSA in the steel series reported in previous papers.…”