Simultaneously enhanced hardness and toughness of normalized graphite ductile irons by TiC-TiB2 nanoparticles

•The graphite nodules were refined by TiC-TiB2 nanoparticles.•The thermostability of graphite nodules was improved by TiC-TiB2 nanoparticles.•The hardness of as-cast and normalized DI was increased by 3.1% and 7.6%2 nanoparticles.•The impact toughness of as-cast and normalized DI was increased by 50.4% and 42.2%.•Cleavage fracture was transformed into ductile fracture by TiC-TiB2 nanoparticles.