Effect of nanoparticles formed in liquid melt on microstructure and mechanical property of high strength naval steel

•In situ Ti3O5 nanoparticles were produced in steel during solidification.•Ti3O5 nanodispersoids bring an equiaxed grain change in as-cast microstructure.•Ti3O5 nanoparticles act as nucleation sites of precipitates during rolling.•Precipitates increase in size slightly during tempering.•Strength and toughness of steel with nanoparticle can be improved during tempering. Fe-based Ni–Cr–Mo high strength low alloy (HSLA) naval steel B was cast by feeding titanium wire in the melt and simultaneously controlling oxide reaction and solute concentration distribution during deoxidization process, and was then hot-rolled and tempered at temperatures ranging from 450°C to 700°C. Steel A was produced for comparison without titanium wire feeding process. Microstructure and mechanical properties of these two materials were investigated to clarify the interrelations of composition, process, microstructure and mechanical properties. It was found that, titanium oxide (Ti3O5) nanoparticles produce grain refinement as well as inclusion refinement during casting, and can act as nucleation site of carbide precipitation to make finer and denser precipitates during hot-rolling with a slight increase in strength, elongation and toughness compared to steel A in rolling condition. The effect of tempering temperatures on precipitates of steel B indicates that Ti3O5 can restrict growth of carbonitrides and most precipitates coarsen slightly without decreasing elongation and toughness.