The invention relates to a method of heat treating a cast iron having graphite particles, in particular a cast iron having graphite nodules with a substantially spherical geometry. The method comprises the step of subjecting the cast iron to a first austenitizing temperature, in order to obtain a cast iron having an austenite matrix with a substantially homogeneous carbon content. Subsequently, at least part of the cast iron is subjected to at least a second, different austenitizing temperature in order to change, in at least part of the cast iron, the carbon concentration in a part of the matrix surrounding the (spherical) geometry of the graphite particles. The method yields improved controllability on strength properties characteristics for cast irons including malleable irons, in particular for ductile iron.