Effect of heat treatment on microstructure and properties of 1045 steel modified with (NbTi)C nanoparticles

Heat treatment is an important mean to obtain excellent properties of all kinds of metal materials. The microstructure of 1045 steel modified with (NbTi)C nanoparticles was studied by means of optical, scanning electron, and transmission electron microscopy techniques. The effects of (NbTi)C nanoparticles in as-cast, normalized, as well as quenched and tempered (Q&T) steel were determined. The metallographic results showed that the normalized steel had a finer grain size than the as-cast steel. Tensile tests results showed that the strength and elongation of as-cast steel were significantly improved after heat treatment. Normalized steel showed a higher elongation and Q&T steel exhibited a higher strength. Under the same heat treatment condition, (NbTi)C nanoparticles modified 1045 steel showed a similar elongation with the base metal, whereas, the strength and hardness were evidently improved. The improved properties of the modified steel can be attributed to the refinement of the microstructure and uniform dispersion of (NbTi)C nanoparticles. Theoretical calculations of the strengthening contributions to different strengthening mechanisms indicated that particle strengthening plays a key role in strength improvement.