Refinement effectiveness of self-prepared (NbTi)C nanoparticles on as-cast 1045 steel

(NbTi) C nanoparticles were prepared using mechanical alloying (MA) and heat treatment process, and the nanoparticles pre-dispersed with Fe powder were introduced to 1045 steel. The microstructure of powders during different ball milling steps and as-casted steels were investigated using optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD) and transmission electron microscope (TEM). The results showed that the added carbides in as-cast steels were mainly composed of three kinds of types: uniform distribution; grain boundary center distribution and chainlike distribution. The uniformly distributed (NbTi) C nanoparticles in the matrix acted as effective heterogeneous nuclei that strongly refined the crystallization microstructure; the grain boundary center distributed particles interacted with the solid-liquid interface, thereby, hindered and restrained the movement of the solid-liquid interface; and the chainlike distributed nanoparticles move with the migration of solid-liquid interface and did not inhibit the interdendritic growth significantly. Compared with the cast steel without (NbTi) C nanoparticles, the modified steels have significantly refined microstructure, improved strength and increased hardness. With the further increase the amount of (NbTi) C nanoparticles, the efficacy of the (NbTi) C nanoparticles for refining crystallization microstructure weakened. (C) 2017 Elsevier Ltd. All rights reserved.