As the industry develops, higher levels of mechanical properties of steel materials are required. Especially, brake disk for railway trains and valve seat in NPP request high strength toughness combination. To improve strength and toughness, Nb, Mo and Ti was added to AISI4130 steel. Studies on the change of strength and impact toughness according to Ti content that induces acicular ferrite were limited to 0.05wt.% or less. In this research, results on microstructure and mechanical properties behavior according to extraordinary wide range of Ti content (0~0.12wt %) in brake disc and valve seat steel are introduced. Samples were subjected to the quenching-tempering heat treatment, and bainite morphology and acicular ferrite formation were observed through OM, SEM, ESBS and TEM analysis. Using EBSD, the behavior of the ferrite block as an effective grain was analyzed in detail, and various types of ferritic steel microstructures such as Acicular Ferrite, Granular Bainite, Bainitic Ferrite and Polygonal Ferrite were quantitatively analyzed according to Ti content. The change in the direction of crack propagation was observed through the fracture surface analysis of the impact tested specimens. Through this study, the mechanism of the mechanical properties change according to the Ti content was investigated and the optimum Ti alloy level is suggested.