One of the most important yet not so well understood aspects in polycrystalline materials, without which determination of mechanical properties becomes challenging is the Grain Boundary cohesive strength (GBCS). Since a few decades, a lot of theoretical work has been performed, but all of those have provided only a limited thermodynamic framework for predicting the individual nature of elements present at GBs, which may either improve GB cohesive strength or embrittle GBs. Hence, the understanding of the localised properties of the GBs on the basis of their atomic structure is limited and poses a major challenge towards an accurate prediction of materials’ properties. The present work intends to address this requirement by comprehensive characterisation of GBs for all its macroscopic degrees of freedom. To this end, typical engineering material systems such as steels, susceptible to GB segregation and with very high GB cohesive strength will be utilized. Appropriate heat-treatment procedures will be applied along with selective addition of elements that can either embrittle or reinforce the GBs. Following the heat treatment procedure, systematic analysis of GB microstructures using correlative microscopy methodology, i.e. combining structural information of different types of GBs obtained using Electron Backscattered Diffraction (EBSD) and Electron Channelling Contrast Imaging (ECCI) with 3D near-atomic scale chemical distribution analysis, obtained using Local Electrode Atom Probe (LEAP). This study intends to provide an in-depth understanding of the influence of local atomic structure constituting the microstructural boundaries on the mechanical response as well as on the overall performance of the material.