The influence of long time intercritical heat-treatments (720 to 750 °C) on the impact and tensile properties of ferrite/pearlite steels has been examined. Intercritical annealing enables Mn to diffuse to the α/ γ boundaries and refine the grain-boundary carbides on cooling to room temperature. When the resulting microstructure formed on cooling to room temperature is ferrite/pearlite, this treatment can result in a significant improvement in impact behavior compared to a normalizing treatment. On heating to the intercritical annealing temperature, Mn enrichment of the γ combined with a fast enough cooling rate results in martensite formation. This may be beneficial to both strength and impact behavior at low volume fractions of martensite, but a marked deterioration in impact behavior occurs at high volume fractions, even though grain-boundary carbides remain fine.