Superduplex stainless steels have seen increasing use in past decades in applications that require both excellent mechanical properties and corrosion resistance. The properties of duplex steels depend strongly on their thermal history, which can produce a wide range of austenite to ferrite ratios; whereas optimal properties generally require near 50-50 ferrite-austenite duplex microstructures. Additive manufacturing processes involve large thermal gradients as new material is melted on top of already printed material, and thermal history depends on process parameters. As the equilibrium phase ratio depends strongly on temperature, the result is a wide range of reported phase ratios, ranging from negligible fractions of austenite to greater than 60 %. So it is important to understand and predict how the phase ratio depends on process parameters. We assesses the microstructures in single-bead-thickness walls of SAF 2507 superduplex stainless steel printed using constant process parameters, using the laser metal powder directed energy deposition (LMPDED) additive manufacturing technique. Post-printing microstructural analysis revealed a gradient of austenite phase fraction as a function of distance from the build platform. This data reveals the relation between the thermal history and solid-solid phase transformation of ferrite to austenite during the fabrication process. The thermal history of each position in the wall was modelled by a previous fast numerical simulation (that has been improved in this contribution), and a fast diffusion controlled solid-solid phase transformations model based on semi-analytical methods has been developed. Numerical results for the phase ratios are in reasonable agreement with experimental observations. The proposed simulations strategy is sufficiently fast to enable to adjust the process parameters to achieve a targeted distribution of phase ratio in order to facilitate additive manufacturing of super duplex stainless steels, and a temperature control strategy of the build platform has been proposed on this basis to reach almost uniform near 50-50 phase ratios.