On the Tensile Behavior of High-Manganese Twinning-Induced Plasticity Steel

Abstract

High-manganese FeMnC and FeMnAlC austenitic twinning-induced plasticity (TWIP) steel exhibits excellent strain-hardening properties due to the gradual reduction of the mean free path for dislocations glide resulting from deformation twinning. Serrated stress-strain curves are often obtained when this type of steel is tested in a uniaxial tensile test. This phenomenon is due to dynamic strain aging (DSA). It is related to the occurrence of localized Portevin-LeChatelier (PLC) deformation bands. The properties of the PLC bands were accurately determined for a FeMnAlC TWIP steel using a combination of high-sensitivity infrared (IR) thermographic imaging and optical strain analysis carried out in situ during tensile deformation. Strain rate jump tests were conducted at room temperature to measure the instantaneous and steady-state strain rate sensitivity as a function of true stress and true strain. Negative values of the steadystate strain rate sensitivity were measured in both upward and downward jump tests. These measurements explain why FeMnC and FeMnAlC TWIP steels have a limited postuniform elongation. A model for the room-temperature DSA of high-Mn austenitic TWIP steel containing C in solid solution is proposed.

The influence of the nitrogen/nickel‐ratio on the cyclic behavior of austenitic high strength steels with twinning‐induced plasticity and transformation‐induced plasticity effects

“…The metallurgical reason, why such changes of a substitutional element like nickel and, therefore, the balance between nitrogen and nickel does influence the cyclic behavior is not clear at this point. Any attempts of the authors to relate this to e. g. cyclic strain ag- ing for which high-manganese steels are known being susceptible [35][36][37] failed. Still CrNiMnCN0.11 showed a Portevin-Le Chatelier effect at different strain rates and temperatures and such effects cannot be ruled out in total [38].…”

On the Mn–C Short-Range Ordering in a High-Strength High-Ductility Steel: Small Angle Neutron Scattering and Ab Initio Investigation

“…These type-A serrations, which are characterized by a steep rise in stress alternating with plateau-like features, were observed in the stress-strain curves in the X60Mn18 steel recrystallization annealed for 2 min and 30 min in Figure 8. The type-A serrations occur as a result of the generation and propagation of a PLC band [16]. As an indicator of the DSA effect, jerky flow is found as a distinct feature of the tensile curves.…”

“…The type-A serrations occur as a result of the generation and propagation of a PLC band [16]. As an indicator of the DSA effect, jerky flow is found as a distinct feature of the tensile curves.…”

“…The serrated stress-strain curves are the main indicator of the DSA mechanism. It has been suggested that DSA in Fe-Mn-C steels involves the interaction of dislocations [4,16,17] and stacking fault regions [12,13] with point defect complexes that include interstitial C.…”

High Mn TWIP Steels for Automotive Applications

“…The fast dislocation core diffusion has been proposed as an alternatively, to explain this widely observed room temperature DSA (Chen et al, 2007). Detailed DSA studies have been carried out by Chen et al (2007), Kim et al (2009) and Zavattieri et al (2009) for Fe-17-18Mn-0.6%C-1-1.5%Al have analyzed the PLC band properties. They report that the band velocity decreases with strain and that the band strain rate is 15-100 times the applied value.…”