This study investigates the eddy current testing (ECT) technique to assess microstructural changes in S235 low carbon steel after cold rolling. Specimens of varying thicknesses (12 mm, 8 mm, and 6mm) were analyzed to evaluate the impact of deformation on such properties as dislocation density, grain texture, and hardness. Metallographic studies using light microscopy were performed, supplemented by dislocation density measurements via transmission electron microscopy (TEM). The ECT results demonstrated that microstructural changes, particularly cold-work hardening and grain elongation, significantly influenced the phase angle of impedance. Lower penetration depths were more sensitive to surface changes, highlighting the capacity of ECT for detecting nearsurface deformation. This work establishes a robust, non-destructive methodology for characterizing manufacturing-induced microstructural changes in heat-resistant steels, with applications in quality control and material performance evaluation.