•Reactor pressure vessel weld material 73 W.•Flow curves from tensile test data and simplified coarse inverse finite element modelling were determined. Results are better than extrapolation of other existing popular models (power law, Voce model)•Tensile flow curves in irradiated and un-irradiated conditions at various temperatures (−100 °C up to room temperature) were obtained.•Application to fracture toughness of irradiated and un-irradiated pre-cracked Charpy V-notch specimens.•The extracted flow curves will be used to model mini compact tension (CT) and 1T-CT geometries in FRACTESUS. The H2020 FRACTESUS project is aimed to validate miniaturized compact tension specimens usage for fracture toughness characterization of irradiated materials. One of the tasks in the project is devoted to the numerical simulations of the 0.16T and 1T-CT specimens and comparison of their stress/strain fields in. For this purpose accurate material flow curves are necessary to derive comparable mechanical response between the numerical models and experiments. This paper presents a simple technique of flow curve extraction from the tensile test using engineering stress–strain data. The proposed method utilizes a coarse meshed Finite Element Model and a manual flow curve data optimization procedure without additional scripting. The robustness of the method was shown on the example of the 73 W weld material in the unirradiated and irradiated states, tested at various temperatures from −100 °C to 125 °C. The obtained numerical flow curves are in a very good agreement with the experimental results. Moreover, the advantages of the proposed method were shown over either the methods based on extrapolation of the predictions of popular models with parameters fitted to prior necking or the method based on fracture diameter measurements. The final validation of the proposed methodology was demonstrated by numerical simulations of fracture toughness tests on precracked Charpy specimens.