Effect of Permanent Magnet Stirring on MnS Precipitation, Microstructure Evolution, and Mechanical Properties of High-Sulfur Micro-alloyed 49MnVS3 Steel

An experimental investigation has been conducted with respect to the influence of permanent magnet stirring (PMS) under different rotation speeds (0, 50, 150 rpm) with a center magnetic flux density of 1450Gs on the evolution of MnS precipitation, microstructure, and mechanical properties of high-sulfur micro-alloyed 49MnVS3 steel. The thermodynamic calculation results indicated that the MnS began to precipitate in 1419 °C and accounted for more than 84 pct of the total in the final solidification temperature of 1404 °C. The experimental results revealed that when the rotation speed increased from 0 to 150 rpm, the mean length of MnS decreased from 7.2 to 3.2 μm, and the distribution of MnS precipitates was more random and uniform, due to the PMS-enhanced turbulent flow with a magnetic Taylor number of 9.21 × 10⁷. Moreover, the content of the intragranular ferrite (IGF) increased rapidly from 0.3 to 3.1 pct, while the content of grain boundary ferrite (GBF) decreased from 11.2 to 9.2 pct after PMS with the rotation speed increased from 0 to 150 rpm. The increased formation of ferrite is related to the precipitation of (Ti, V, Nb) (C, N) on the edge of more small uniformly distributed MnS. In addition, the tensile strength and toughness of the 49MnVS3 steel are enhanced owing to the beneficial changes of increased small-sized MnS precipitates and promoted the formation of intragranular ferrite.