The paper presents an experimental and analytical process aimed at establishing correlations between the hardness value and the level of plastic deformation. In these conditions, static tensile tests were performed on the compact specimen. These tests allowed us to determine the KIc fracture toughness, as well as to obtain surfaces generated by the material fracture. In the vicinity of the fracture surfaces, Vickers micro-hardness tests were also performed. Two types of determinations were utilized for normal OLC45 steel and for the annealed OLC45 steel. Significant differences regarding the Vickers values were observed; they were determined by the differences which appeared around the crack.