Effects of deformation induced phase transformation and twinning on the mechanical properties of austenitic Fe-Mn-Al alloys.

Sato, Kazunori; Ichinose, Michiyuki; Hirotsu, Yoshihiko; Inoue, Y.

doi:10.2355/isijinternational.29.868

Cited by 281 publications

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“…The phase transformation is correlated to the stacking fault energy yf,, in the austenitic matrix. Low stacking fault energy (yh 2 20 mJ/m2) favours the y+& phase transformation whereas high stacking fault energy (yk, > 20 mJ/m2) suppresses this phase transformation [9]. Alloys with high yfcc tend to mechanical twinning formation instead of phase transformation.…”

Section: Introductionmentioning

confidence: 99%

Phase Transformations and Mechanical Properties of Fe-Mn-Si-Al TRIP-Steels

et al. 1997

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Abstract. Deformation twinning, martensitic phase transformation and mechanical properties of austenitic wt%Mn alloys with additions of aluminium and silicon have been investigated. Tensile tests were carried out at different strain rates and temperatures. The formation of twins, a'-and c-martensite during plastic deformation was analysed by optical microscopy, X-ray diffraction, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The stacking fault energy y h and the free energy AG"+E for the y +~ phase transformation were calculated using the regular solution model. It is known that additions of aluminium increase yfc, and therefore strongly suppress the y+c transformation while silicon decrease yf,, and sustains the y-E transformation. The y-+c phase transformation takes place in alloys with yk, 5 20 mllm2. The stacking fault energy of the Fe-25Mn-3Si-3A1 alloy was calculated as a function of temperature and related with microstructural changes of the strained sample at different temperatures. These steels with reduced density of about 7,3 g/cm-3 combine high tensile ductility up to 80 % at high strain rates with true tensile strength of about 1000 MPa. The excellent plasticity induced by twinning and additional phase transformation up to extreniely high strain rates of about E = lo3 s-' results in an extraordinary shock resistence and enables deep drawing and backward extrusion operations of parts with complex shapes and high production rates.

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Section: Introductionmentioning

confidence: 99%

Phase Transformations and Mechanical Properties of Fe-Mn-Si-Al TRIP-Steels

et al. 1997

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“…In recent years, for this purpose high-Mn austenitic steels have been developed. Various deformation mechanisms can influence their ductility, such as the transformation-induced plasticity (TRIP), the twinning-induced plasticity (TWIP) 1,2) or the shear band induced plasticity (SIP) effect.…”

Section: Introductionmentioning

confidence: 99%

High Temperature Flow Stress and Recrystallization Behavior of High-Mn TWIP Steels

2007

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The flow stress behavior and recrystallization kinetics in the hot rolling temperature range have been investigated in five Fe-Mn-Al (Mn: 25 wt%, Al: 0-8 wt%) TWIP steels by compression testing on a Gleeble simulator. Results were compared with corresponding properties of carbon and austenitic stainless steels. Microstructures were examined by electron microscopy. The results show that the flow stress level of the TWIP steels is considerably higher than that of low-carbon steels and depended on the Al concentration close to 6 wt%, while the structure is austenitic at hot rolling temperatures. At higher Al contents, the flow stress level becomes significantly lowered due to the presence of ferrite. The static recrystallization kinetics is slower compared to that of carbon steels, but it is faster than typical of Nb-microalloyed or austenitic stainless steels. High Mn content is a reason for the high flow stress as well as for slow softening. Al has a minor role only, but in the case of austenitic-ferritic structure, softening of the ferrite phase occurs very rapidly that also contributes to overall faster softening. The grain size is effectively refined by the dynamic and static recrystallization processes.KEY WORDS: high-Mn steels; Al alloying; austenite; flow stress; recrystallization.ISIJ International, Vol. 47 (2007), No. 6, specimens were compressed in a single hit to the true strain of 0.8 at a constant true strain rate that was varied between 0.005 and 5 s Ϫ1. The SRX kinetics of the steels was studied by the double-hit compression technique using different temperatures (900-1 100°C), strains (0.11-0.4) and strain rates (0.01-5 s Ϫ1). The initial grain size of the steels was about 140 mm, as excluding the annealing twin boundaries. The flow stress at 5 % total reloading strain was adopted in computing the recrystallized fraction to exclude the effect of recovery from the softening data, as described elsewhere.9) Microstructures were examined in an optical microscope (OM) as well as in a scanning electron microscope equipped with an electron back-scattered diffraction device (SEM-EBSD). Results and Discussion Flow Stress and Dynamic RecrystallizationAs examples of the constitutive behavior of the steels, typical true stress-true strain curves for the high-Mn and reference steels are displayed in Fig. 1, as compressed at the strain rates of 0.1 s Ϫ1 and 5 s Ϫ1. In Fig. 1(a), it is seen that at 0.1 s Ϫ1, the 25Mn1Al steel exhibits peak stress behavior, even though the peaks are very broad, particularly at 950°C. The peak strain is rather small, about 0.25, 0.4 and 0.5 at 1 100, 1 000 and 950°C, respectively. 25Mn1Al steel possesses much higher deformation resistance than the low-C steel. Figures 1(b) and 1(c) clearly demonstrate that the flow resistance of high-Mn steels is increased by Mn and Al alloying. The flow stress of 25Mn steel is much higher than those of low-C and Nb-bearing steels, and among the Albearing steels, flow stress increases with Al content up to 3% ( Fig. 1(b)) or up to 6 % ( Fig. 1(c))....

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“…4,5,18) The bar diagram of Fig. 14(a) represents the specific energy absorption E spec of the TWIP steel in comparison with selected conventional deep drawing steels, such as IF-steels (FeP04), bake hardening steels (Z St E 180 BH) and thermomechanically processed steels (Q St E 500 TM), respectively ( Table 2).…”

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confidence: 99%