Within our project we are studying the evolution of stresses in Ni-base superalloy IN718 during annealing heat treatments. This is done by performing in-situ neutron diffraction strain measurements during different heat treatments. In order to calculate stresses from these neutron experiments the diffraction elastic constants of the material under investigation are required at the applied temperatures. The aim of this proposal is to determine these materials parameters, using the high temperature stress rig of ENGIN-X. In-situ measurements on IN718 standardized samples will be performed at different loads and temperatures.