In virtual design of hot stamping, the reliable description of the material flow behaviour is an important input to ensure accurate estimations of the final shapes of parts. Currently, to characterise the hot stamping material’s flow behaviour at elevated temperatures, tensile and upsetting tests are available. The focus of this article is on the determination of the flow curves of manganese-boron steel at elevated temperatures based on upsetting tests. The measurement of material flow properties directly out of the upsetting tests still remains a complex task due to its non-uniaxial nature. Therefore, traditional methods to calculate flow curves out of such measurements are not necessarily appropriate. It requires a method which considers multi-axial stress states as well as non-uniform strain evolution. In that way the calculation of the flow curves is appropriate and it can provide reliable input for simulations of hot stamping. In order to interpret measurements and deduce flow properties more precisely, simulations using Finite Element Method (FEM) of the tests themselves are executed. Indeed in FE-models it is possible to account for complex boundary conditions such as non-uniform temperature fields, non-uniaxial stress states and friction between upsetting die and the specimen during the deformation. With use of inverse optimisation, based on the final geometry of the deformed specimen, Coulomb’s friction coefficient is estimated. It is demonstrated that an almost constant value of the friction coefficient is achieved, even after using many different types of strain hardening to describe the material behaviour in the FE-models. Finally, it is demonstrated that the deduced material flow curves with use of inverse optimisation are more accurate than that of the directly calculated out of experimental results.