## 5 Discussion
### Role of Microstructural Parameters on Mechanical Behavior  
The presented model combines a large number of microstructural parameters in order to predict the behavior of the material. It is possible to use the obtained model to perform simulations to study the effect of different microstructural parameters on mechanical behavior simply changing the value of these parameters. As a first example, Figure 9 shows the independent behavior of the three phases considered in the model. The simulations were performed under the same conditions used for the fitting. Combining experiments along different directions and at different strain rates allows evaluating how strain rate and crystallographic texture affect the response of each of the phases. In the obtained curves, it is clearly observed how the phases with lower yield stress have a larger strain rate sensitivity. While the bainite phase shows a considerable stress increment at higher strain rates, the effect of high strain rate is much lower on the response of the LCM and MA phases. Regarding crystallographic texture, as happened with the experimental and fitted curves, a larger anisotropy is observed for the HT material, especially in the martensitic phases. This result can be correlated with the initial textures in Figure 4. The bainite texture of the LT material exhibits a more homogeneous \(\gamma\)-fiber, while the martensitic phase of the HT material includes some rotated cube components not present in the LT's ODF which will increase the anisotropy. Another example is given in Figure 10. In each graph, three tensile curves are shown, all corresponding to uniaxial tension along RD at a strain rate of \(0.008\,\mathrm{s}^{-1}\). One of the curves is reproduced in Figure 5. The other two curves are calculated modifying the value of a microstructural parameter of the bainitic phase: grain size, initial dislocation density or carbides fraction. In one of the curves, the original value of the parameter (displayed in Table 3) is doubled, and, in the other one, it is halved. Decreasing the size of the bainite grains makes the material stronger and increasing it makes the material softer, in accordance with the Hall-Petch effect. Grain size also influences the work hardening behavior through Equation (20), but this effect is barely noticed in the graphs. On the other hand, the carbides do not have any effect on the yield stress, but they influence hardening behavior. When the fraction of carbides is higher, the  
Figure 10: Influence of bainite microstructural parameters ((**left**) grain size; (**middle**) carbides fraction; and (**right**) initial dislocation density) on the tensile behavior of the LT and HT materials at a strain rate of \(0.01\,\mathrm{s}^{-1}\) along RD. Figure 9: Tensile diagrams of individual phases in the LT and HT materials under the same loading conditions used in the fitting (cf. Figure 5). strain hardening effect will be higher too. Since, in Equation (20), the term that accounts for the carbides fraction also includes the carbide shape and carbide size, the effect of doubling the carbides fraction will be the same as the effect of halving the carbides size, and vice versa, while the factor that accounts for the shape of the carbides (\(c_{p}\)) will have the same effect as the carbides fraction. In the case of dislocation density, there are two different effects on the tensile response. Increasing the dislocation density implies a higher yield stress, but also a slight reduction of the hardening rate. As expected, the effect of doubling or halving the initial dislocation density is small when compared with the effect of doubling the grain size or carbides fraction (N.B. dislocation density values typically vary between several orders of magnitude, while size or fraction values are much closer). There are many parameters that may be varied too: chemical composition (in particular, carbon content), martensite lath width, grain shape and orientation or crystallographic texture.