Improvement of Utilization Ratio of Nanoparticles in Steel and Its Influence on Acicular Ferrite Formation

In the present study, 35MnVS experimental steels containing nanoparticles are manufactured using a vacuum induction furnace (VIF), as well as a vacuum induction levitation furnace (VILF). The differences on the utilization ratio of nanoparticles (URN), inclusion characteristics, and steel microstructure between the original steel and experimental steels are compared. The results reveal that the steel processed with a VILF has a higher URN that helps to form a finer inclusion size range. There is a critical size for each inclusion, and only when the inclusion size is <= the critical value, the inclusions can efficiently induce acicular ferrites (AF). Among the three steels, only the inclusion size range of the VILF steel is less than the critical size which is between approximate to 2.2 and approximate to 5.2 mu. Therefore, the inclusions in VILF steel have a relatively stronger ability on inducing AF, and that is revealed by its microstructure showing large proportions of AF.