<p>This study investigated the effects of heat treatment on the mechanical and fatigue behavior of FCD450 cast iron. Quenching and tempering heat treatment led to a decrease in the graphite spheroidization rate, an increase in pearlite fraction, and a reduction in ferrite content. Tensile testing revealed improved yield and tensile strength, accompanied by reduced elongation, indicating enhanced strength and hardness at the expense of ductility and toughness. High-cycle fatigue tests under various mean stresses and stress ratios revealed that tensile mean stress reduces fatigue life, whereas compressive mean stress increases it. Finally, the mean stress effect was evaluated using the modified Goodman, Gerber parabola, Morrow, Smith-Watson-Topper (SWT), and Walker equations by comparing the distribution of the equivalent stress-life curves to the baseline. Among the models analyzed, the SWT equation demonstrated the closest agreement with the baseline, followed by the modified Goodman, Morrow, Gerber parabola, and Walker equations, in that order.</p>