Simultaneously enhanced strength and toughness of cast medium carbon steels matrix composites by trace nano-sized TiC particles

Abstract

A great challenge in producing TiC reinforced metal matrix composites is encountered to directly add TiC particles into molten steel during casting owing to floating of nano-sized TiC on molten steels and agglomeration. As such, this work proposes a novel strategy using pre-distribution in situ nano-sized TiC/Al master alloy to fabricate 45 steel matrix composites reinforced with trace nano-sized TiC particles while without changing the original casting process; this strategy can effectively avoid the aforementioned challenge. The average grain sizes of as-cast and heat-treated 45 steel with 0.018 wt% nano-sized TiC particles remarkably decrease from 14.75 μm to 9.51 μm respectively to 8.77 μm and 5.46 μm respectively, which is attributed to that the nanoparticles provide effective nucleation sites and inhibit grain growth. Furthermore, adding trace nano-sized TiC particles significantly enhances their strength and toughness. The 45 steel matrix composites reinforced with 0.054 wt% nano-sized TiC particles exhibits the best tensile mechanical properties with yield strength of 624 MPa, ultimate strength of 920 MPa, elongation of 23.8% and impact toughness of 50.21 J/cm2, which are 19%, 13%, 10% and 38% respectively higher than the 45 steel. The strengthening and toughening mechanisms of 45 steel by nano-sized TiC are attributed to grain boundary strengthening, work hardening and dispersion strengthening. The strategy proposed in this work may provide a promising method for enhancing steel performances for industrial productions.