Abstract
The yielding of a high Mn twinning-induced plasticity steel was examined in three fine-grained specimens recrystallized at 700°C for 5 min with different cooling conditions. While the stress-strain curves of furnace-cooled and air-cooled specimens exhibit a stress drop at yielding, the drop was not observed in the water-quenched specimen. A simple analysis of the displacement data indicates the occurrence of localized deformation at the beginning of the plastic deformation in the three tensile specimens with different cooling conditions. The localized deformation of all three specimens was confirmed as Lüders strain by digital image correlation (DIC) analysis. Based on this observation, the role of yielding behavior on the strain hardening rate evolution at an early stage of the tensile deformation was discussed.
Highlights
Twinning-induced plasticity (TWIP) steel is one of the representative austenitic steels developed originally for formable automotive sheet applications (Kim et al, 1989; Grässel et al, 2000)
Its dislocation accumulation kinetics is accelerated (Jeong et al, 2011). It results in a higher strain hardening rate (SHR) at small strains in the fine-grained specimen than in the coarse-grained specimen, whereas the rate is reversed with further strain (Gutierrez-Urrutia and Raabe, 2012; Kang et al, 2016; Tian et al, 2017)
Corresponding Kernel average misorientation (KAM) maps for the furnace cooling (FC), air cooling (AC), and water quenching (WQ) samples were shown in Figures 2A,B,C, 2, respectively
Summary
Twinning-induced plasticity (TWIP) steel is one of the representative austenitic steels developed originally for formable automotive sheet applications (Kim et al, 1989; Grässel et al, 2000). Due to the deformation twinning, a large strain hardening is known to be available in the high Mn austenitic steel, resulting in attractive combinations of ultimate tensile strength (UTS) and total elongation (TE) (Bouaziz and Guelton, 2001; Gil Sevillano, 2009). Its dislocation accumulation kinetics is accelerated (Jeong et al, 2011) It results in a higher strain hardening rate (SHR) at small strains in the fine-grained specimen than in the coarse-grained specimen, whereas the rate is reversed with further strain (Gutierrez-Urrutia and Raabe, 2012; Kang et al, 2016; Tian et al, 2017). The total strain hardening capability does not vary much with the grain size, the higher SHR maintained to the large strain region in the coarse-grained specimen improves its ductility
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