Work hardening associated with ɛ-martensitic transformation, deformation twinning and dynamic strain aging in Fe–17Mn–0.6C and Fe–17Mn–0.8C TWIP steels

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

“…These steels are TWIP steels that exhibit an excellent combination of elongation and ultimate tensile strength (UTS) mainly due to deformation twinning. 3,25,26) The solution-treated bars were cut by spark machining to achieve the specimen geometries required for the following experiments.…”

“…In general, deformation twinning is suppressed with increasing stacking fault energy because the nuclear region of deformation twins consists of stacking faults. [1][2][3] The stacking fault energy has been known to increase with increasing temperature 4) and specific solute atom concentration, 1) suppressing deformation twinning. [1][2][3] In particular, carbon is an important solute element affecting twinning behavior in high Mn austenitic steels which is a typical low stacking fault energy material.…”

TWIP Effect and Plastic Instability Condition in an Fe^|^ndash;Mn^|^ndash;C Austenitic Steel

“…Figure 2 shows the engineering stress-strain curves at 123, 173, 223, 273, 294, 373, 423, 473, and 523 K. A considerable amount of work hardening and premature fracture without necking were only observed at 123 K. The serrations on the stress-strain curves are attributed to dynamic strain aging. 6,14,16,17) Serrations were observed at and above 273 K, and became clearer with increasing deformation temperature up to 373 K since dynamic strain aging was promoted by an increase in carbon diffusivity with increasing temperature. In contrast, a further increase in deformation temperature suppressed the serrations, since carbon could follow the dislocation motion, weakening the pinning effect.…”

“…16,17) In Fe-Mn-C austenitic steels, deformation twinning 18) and dynamic strain aging 17) are the dominant phenomena causing temperature dependence of work hardening below 573 K. In this paper, we obtained various stress-strain curves and deformation twin densities by changing the deformation temperature in the Fe-18Mn-1.2C austenitic steel. The steel shows a sufficiently low starting temperature for thermally-induced martensitic transformation (Ms).…”

“…9) Namely, the deformation twin fraction at every plastic strain decreases with increasing stacking fault energy unless the volume fraction is sat- Deformation-induced ε-martensitic transformation was reported to occur in a lower temperature range than that for deformation twinning. 2,16,[24][25][26] Deformation twinning is suppressed when ε-martensitic transformation takes place, since stacking faults are the nuclei of both the deformation twin and ε-martensite. Thus, the deformation-induced ε-martensitic transformation would cause the decrease in twin density with decreasing temperature from 223 to 123 K. The ε-martensite cannot be detected in the present experiments, since ε-martensite that formed at an extremely low temperature transforms reversely when the experimental temperature becomes ambient temperature.…”