Spheroidal Graphite Irons (SGIs) have graphite particle inclusions in an iron matrix. The matrix structure controls overall mechanical properties, and the graphite morphology plays a vital role in crack initiation and propagation behavior. High silicon Solution Strengthened Ferritic (SSF) SGIs are developed to provide higher strength with excellent ductility. In SSF SGIs, graphite nodules shape has a key role in damage micromechanisms. The graphite nodule growth morphology can go through transitions to form degenerated graphite particles other than spheroidal graphite nodules in SGI microstructure. Additional thermal and mechanical processes influence SGI microstructure affecting mechanical properties and damage micromechanisms. Most of the damage mechanism studies on SGI were focused on the role of spheroidal graphite nodules on the stable crack propagation region. In this work, microstructure and properties of different SGI grades were compared, and EN-GJS-500-14 SSF SGI was further deep cold rolled and thermal cycled to study the effect of these processes on the material microstructure. Tensile and fatigue damage mechanisms were studied in detail to understand the role of different forms of graphite particles in SGI microstructure. The microstructure characterization result and damage mechanisms were formulated in a Representative Volume Element (RVE) model, and then to multiscale SGI material microstructure model. Microstructure studies and nanoindentation test results showed that the general microstructure of as-cast, deep cold rolled (DCR) and thermal cycled SGI can be characterized by graphite morphology, matrix composition and its phase properties. In DCR process, plastic hardening of the ferrite matrix was obvious. The large plastic flow of the ferrite matrix caused subsurface graphite particles to appear as a surface crack, which must be considered in graphite particles characterization. In thermal cycling process, the graphite-ferrite interface state was the most susceptible region in the microstructure, which needs to be included in microstructure characterization.In the tensile test, the matrix-nodule interface decohesion and plastic deformation of the ferrite matrix were the dominant damage mechanisms. Less influenced by nodule shape, graphite particles showed decohesion from the ferrite matrix at the overall stress of 400 MPa to 420 MPa, which is close to the yield stress of the material. In a separately performed Fatigue Crack Initiation (FCI) and Fatigue Crack Propagation (FCP) tests, the graphite particle shape plays a decisive role in crack initiation and propagation. In the crack initiation region, degenerated iii