The Solid Solution Strengthening is part of Strengthening Mechanisms courses. The Strengthening Mechanisms is part of the Ferrous Metallurgy set of courses. In this course, the definition of strengthening by addition will be presented and used to estimate alloying elements in the strengthening steel. After that, the atomic arrangements in metals will be introduced. An interactive 3D model will be showed to study the metallic crystal structures like FCC and HCP. Then, solid solution will be presented and different elements apart from iron and carbon will be showed. After that, the substitutional solid solution will be exhibited. Then, the crystal lattice distortion will be explained and how substitutional solutes affect strength increase will be studied. Then, the mechanism of compressibility, chemical valency differences and size factor will be introduced. At the end of this module, the electronegativity will be defined. Finally, the theoretical treatments and empirical data will be related mathematically, and the linearisation effects will be evaluated.