Temperature-Dependence of the Mechanical Responses for Two Types of Twinning-Induced Plasticity Steels
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nning-induced plasticity (TWIP) steels possess an extraordinary combination of ultimate tensile strength (UTS) and uniform elongation (UE).[1–3] Hence, these kinds of steels can be potentially used as structural materials in the automotive industry. During an accident, automobile fabrication materials may experience a high strain rate and high-temperature damage.[4–7] Therefore, it is important to investigate the effects of strain rate and deformation temperature on the mechanical properties of TWIP steels. Previous studies have demonstrated that the dynamic strain aging (DSA) effect in Fe-Mn-C system TWIP steel results in a negative strain rate sensitivity, accompanied with a reduction of the twinning capability.[8–11] On the
H.K. YANG, Y.Z. TIAN, Z.J. ZHANG, and P. ZHANG are with the Materials Fatigue and Fracture Division, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, 72 Wenhua Road, Shenyang 110016, China. Contact e-mail: [email protected] Z.F. ZHANG is with the Materials Fatigue and Fracture Division, Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences and also with the University of Chinese Academy of Sciences, 19 Yuquan Road, Beijing 100049, China. Contact e-mail: [email protected] Manuscript submitted November 14, 2017.
METALLURGICAL AND MATERIALS TRANSACTIONS A
contrary, Fe-Mn-Si-Al TWIP steel without DSA effect exhibits a positive strain rate sensitivity.[12,13] Notably, the deformation temperature can also affect the DSA effect and the subsequent mechanical responses in Fe-Mn-C TWIP steel. Jung et al.[14] reported that a temperature increase could facilitate the DSA effect, and Koyama et al.[15] found that Fe-Mn-C TWIP steel exhibited strong twinning capabilities even at high deformation temperatures of up to 473 K. Numerous works have reported the effect of the deformation temperature on the mechanical properties of TWIP steels.[16–19] To further explore the effect of the deformation temperature on DSA, mechanical properties, and microstructure evolutions, a typical Fe-22Mn-0.6C (wt pct) TWIP steel (with DSA effect) and a reference Fe-30Mn-3Si-3Al (wt pct) TWIP steel (without DSA effect) were selected in this study. The deformation temperature was chosen in the range of 293 K to 443 K, where the DSA phenomenon was observed. The aim of this work is to elucidate the temperature effect on the evolution of the deformation twins (DTs), dislocations, and related mechanical responses in Fe-Mn-C and Fe-Mn-Si-Al TWIP steels. Fe-22Mn-0.6C (wt pct, Fe-Mn-C) and Fe-30Mn3Si-3Al (wt pct, Fe-Mn-Si-Al) ingots were molten in a vacuum induction furnace and then austenitized at 1423 K for 120 minutes to eliminate segregation. Next, these two ingots were hot forged at 1123 K to 1423 K into square rods with a cross section of 25 9 25 mm. Finally, the rods were solution treated at 1273 K for 30 minutes and quenched in water. The grain sizes of the Fe-Mn-C and Fe-Mn-Si-Al steels are, respectively, 27.5 and 31.4 lm, i
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