In automotive industries, development of new steels with desirable strength, ductility and toughness has been a hot research topic. Recently, low stacking fault energy (SFE) austenitic high Mn steels, which is regarded as a very attractive alloying element, has attracted a great deal of attention driven by the weight reduction and energy and materials saving in this industrial cluster [1
]. Particularly, the application of a new generation of high Mn steels with Al and Si additions, called twinning induced plasticity (TWIP) steel, has been confirmed to efficiently realize weight reduction and energy saving due to their good mechanical properties to facilitate the down size of part dimension and size [3
]. Greatly influenced by the content of chemical composition including Mn, Al and Si, various deformation mechanisms called TWIP and phase transformation induced plasticity (TRIP) effect related to the evolution of microstructure and crystallographic texture components should be considered as an important issue to be explored and addressed in the deformation process [3
In terms of low-to-moderate SFE, Grässel et al. [9
] observed that the extensive deformation twins play a dominant role for the austenitic high Mn steels alloyed with Si and Al. It is proposed that the TWIP effect significantly influences the hardening behavior at macroscopic level through the interaction of dislocations gliding hindered by twinning boundaries when the Mn content is more than 25 wt %; the Al content is about 3 wt %; the Si content is between 2 wt % and 3 wt %; and the C content is low [9
]. The impressive strain-hardening of TWIP steels is caused by various strengthening mechanisms, mainly consisting of dislocations glide and twinning [9
], dynamic strain ageing [10
] and TRIP-effect [11
]. Among these mechanisms, twinning has been seriously taken into account and quantified to explain the strain hardening of TWIP steels, including the texture hardening [12
], the dynamic Hall–Petch hardening [13
] and the Basinski-type hardening [14
]. However, there is still no consensus on the fundamental mechanisms of strain hardening in TWIP steels and the abovementioned studies strongly depend on the microstructural characteristics of twinning, but this issue is still under debate. Thus, it is essential to determine the location and distribution of twinning first. On the other hand, the deformation twins, which are regarded as an important lattice defect of TWIP steels, strongly affects the microscopic evolution especially for the crystallographic texture development in plastic deformation [15
]. From the perspective of deformation mechanism, a remarkable characteristic associated with the deformation twins is the sudden reorientation of crystallites, leading to the preferred crystallographic orientation or texture component. Subsequently, the evolution of crystallographic texture contributes to strengthening generally via slip activities, known as texture hardening, to enhance the mechanical properties such as high strength and good ductility [16
]. Through the thickness addition of nano-twins, the accumulation of the twin volume fraction could make contribution to crystallographic texture evolution [10
], but how the deformation twins affect the strain hardening via the texture development in the course of deformation has not yet been extensively explored. Consequently, it is necessary to investigate the texture components and deformation twins’ nucleation position first in the large plastic deformation process to establish a close connection among deformation twins, crystallographic texture components and strain hardening. However, this relationship has not been explored in greater depth and needs an in-depth investigation to correlate the microstructural characteristics of twinning and textural evolution with strain hardening, particularly for the Fe-Mn-Si-Al TWIP steels.
Since the anisotropy associated crystallographic texture is important in plastic deformation processing [5
], it is indispensable to know more about the relation between crystallographic texture evolution and the microstructure formation and evolution. Currently, most studies on TWIP steels are focused on this relationship of Fe-Mn-C and Fe-Mn-Si-Al steels [18
] and the investigations are more on the effect of crystallographic texture on deformation twins. Earlier experimental investigations detailing the uniaxial tensile loading of fine-grained Fe-Mn-C TWIP steel have revealed that the development of the pronounced <111> fiber in the tensile direction facilitates the formation of deformation twins and maintains the strain hardening rate at a high level [20
]. However, the influence of twinning on texture development needs to be paid more attentions. For the Fe-Mn-Al-C TWIP steels, Souza et al. suggested that the texture transition from copper to brass texture was observed at higher reduction influenced by deformation twins with strong similarity to that found in Fe-Mn-C TWIP steels [21
]. However, this issue should be investigated for Fe-Mn-Si-Al TWIP steels. Compared with Fe-Mn-C TWIP steels, the texture of Fe-Mn-Si-Al TWIP steels shows a great difference in tensile deformation process due to the lower magnitude of the activated twin systems [22
]. Furthermore, Saleh et al. proposed that the texture measurement of Fe-Mn-Si-Al TWIP steels subjected to the uniaxial tension demonstrated the characteristic double fiber texture for FCC materials, with a relatively stronger <111> and a weaker <100> partial fiber parallel to the tensile axis [23
]. However, a detailed explanation of texture transition affected by twinning has not been studied in these studies.
Based on the long-range interactions of individual grains with the polycrystalline aggregate [24
], another widely used approach for predicting crystallographic texture is the viscoplastic self-consistent (VPSC) plasticity model. Through applying predominant twin reorientation (PTR) schemes [25
] and CP (crystal plasticity) model proposed by Kalidindi [26
] to deal with the twinning evolution, a VPSC model was presented by Prakash et al. [27
] to investigate the influence of deformation twins on the crystallographic texture development after tensile loading. However, compared with Kalidindi model, a limited correspondence between the experimental texture intensity and the simulated one obtained by the simulation using VPSC model and considering PTR scheme was concluded. Consequently, Saleh et al. [23
] applied a modified VPSC model to assess the contributions of perfect and/or partial slip, twinning and latent hardening to evolution of the crystallographic texture in TWIP steels and overcame the limited correspondence between experiment and simulation via proper description of hardening parameters of various deformation systems. However, this “mean-field” approach for VPSC model has limitation as there is no sufficient information about the specific interaction between the individual grain and its neighboring grains [28
]. Considering this limitation, a non-homogenization scheme based CPFE method was proposed to represent the intragranular microstructure and grain orientations. Furthermore, this approach facilitates taking into account the grain morphology of metallic materials in microstructural simulation [30
]. To model the relationship between crystallographic texture and deformation twins’ evolution, Dancette et al. [32
] employed a “full-field” and experimental dataset based CPFE analysis to provide an improved prediction of the texture development in uniaxial tension at macroscopic scale, and the relation between the volume fraction of twins inside the individual grains and crystallographic texture at the grain level were confirmed via EBSD measurement and CPFE simulation. The introduced crystal plasticity (CP) model proved that it gives an improved texture prediction compared to the Taylor model for the deformation at higher strain.
In the present study, the grain morphology, crystal orientation and crystallographic texture evolution of Fe-30Mn-3Si-2Al TWIP steel under the uniaxial tensile deformation was studied via EBSD measurement, especially for the deformation twins’ nucleation position and intra- and intergranular deformation. The corresponding CPFE model considering slip and twinning interactions was then proposed. Subsequently, the simulations using Voronoi based polycrystalline RVE microstructure with crystal orientations were conducted to investigate the evolution of hardening behavior associated with slip and twinning activity and further to discuss the effect of twinning on hardening and crystal orientation, as well as the stability of the crystallographic texture development. This study links the mechanical behaviors with microstructural change and texture evolution during deformation thereby provides an accurate prediction of the shape of forming parts in deformation processing of TWIP steels.