Role of trace nanoparticles in manipulating the widmanstatten structure of low carbon steel

•The reinforced low carbon steels were prepared by using TiC-TiB2/Al master alloy.•The formation of widmanstatten structure was limited.•The grain size reduced and pearlite content increased.•The yield strength, tensile strength and ductility were improved simultaneously.•An E2EM model was utilized to discuss the heterogenous cores by nanoparticles.•The fine-grain, thermal-mismatch and dispersion strengthening mechanisms were discussed.•The toughening mechanisms including fine microstructure and scattering effect were discussed.