Abstract
(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.
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