Wire + Arc Additive Manufacturing (WAAM) is a form of directed energy deposition for additive manufacturing of metals. An electric arc is used to melt metal feedstock wire, allowing material deposition in a layer-by-layer fashion. In addition to newly manufacturing workpieces, WAAM could also be applied for the remanufacturing of damaged or worn components, contributing to a more circular economy. Due to high cyclical heat input during the WAAM process, a heterogeneous microstructure arises. In particular, a strong microstructural gradient may exist at the interface between the substrate material and the first deposited layer. As a result, material properties may also vary within this region. Furthermore, the welding wire's alloy may differ from that of the substrate, also contributing to the gradient in the interface region. This poster presents ongoing research to numerically model the effect of mechanical loads at the interface of steel components remanufactured by WAAM, for both static and cyclic (fatigue) loading conditions. Local material properties are characterised by hardness mapping, after which correlations can be used to construct the plastic stress-strain curve based on a hardness value. The interface region is then modelled based on element-wise material assignment. However, the limited accuracy of this approach is revealed after comparison with experimental data from tensile tests instrumented with Digital Image Correlation. Future work will investigate the use of Profilometry-based Indentation Plastometry, a novel technique to directly characterise local stress-strain properties, to replace the hardness map as input for this model. Additionally, an eXtended Finite Element Modelling (X-FEM) framework is used to simulate fatigue loading, again based on a hardness map. Modelling of Compact Tension specimens with notches at different locations relative to the interface indicates a fatigue crack path deviating towards the material with lower Young's modulus. In the future, this model will be experimentally validated.