Cast duplex austenitic-ferritic (AF) steels are widely used in primary loop of Pressurised Water Reactors (PWR). They offer a good combination of mechanical properties and corrosion resistance. However, at service conditions (about 300°C) and during long times of exposure (more than 10000 h), they are sensitive to thermal aging embrittlement mainly due to the microstructural evolution of ferrite. This is the reason why a good estimate of stresses and strains in the phases are required. To achieve these objectives, different micromechanical models were developed in the past assuming two or three scales in the microstructure. Recent Electron Back-Scatter Diffraction (EBSD) analyses have revealed four scales in the microstructure, which represent the complexity of the microstructure to model, and therefore the main challenge for scale transitions in homogenization models. In the present work, a new microstructure-informed multiscale homogenization scheme is developed. At the first scale, the elastoviscoplastic behavior of single crystals for both phases is modeled using linear elasticity and a viscoplastic crystal plasticity model. An "affine" type formulation based on the first moments of stresses is applied to the inelastic non-linear part of the deformation. Then, at the second scale, an EBSD-informed two-phase austenite/ferrite laminate structure is developed with {110}-type habit planes in ferrite and a Kurdjumov-Sachs orientation relationship (KS-OR) between both phases. At the third scale, the microstructure of the individual primary ferritic grain, the socalled "bicrystal", is then modelled as an aggregate of spherical two-phase laminate structure domains corresponding to the 24 KS-OR variants. The elastoviscoplastic self-consistent scheme (EVPSC) is used through the Translated Fields (TF) homogenization method to obtain the effective behavior at this scale. Here, the same method is applied at the macroscopic scale of an ensemble of primary ferritic grains representing the so-called "poly-bicrystal". At both intermediate scales, EBSD data and analyses are used to physically feed the multiscale model. The results are discussed in terms of local stress/strain responses in ferrite correlated to the different KS-OR variants and habit planes. The effect of primary ferritic grain crystallographic orientation is also studied. Materials parameters corresponding to as received and aged specimen are considered in the discussion of the results.