Impact of Permanent Magnet Stirring on Inclusion Evolution, Solidification Structure and Mechanical Properties of AH32 Shipbuilding Steel

An experimental investigation has been conducted with respect to the effect of permanent magnet stirring (PMS) under different rotation speeds (0, 60, 180 rpm) on the solidification of AH32 shipbuilding steel by analyzing the inclusion evolution, solidification structure, and mechanical properties. As the rotation speed increased from 0 to 180 rpm, the mean size of inclusions (Al₂O₃, MnS, and Al₂O₃–MnS) reduced significantly from 6.23 to 2.92 μm, their number increased from 49 to 82 n mm⁻² and the ratio of complex inclusions increased from 30.6% to 75.6% in the AH32 steel ingot. Besides, the increasing number of small complex inclusion promotes the formation of acicular ferrite in steel, resulting in an elevation of the area ratio from 10.5% to 27.8%. Furthermore, under a rotation speed of 180 rpm, the mean grain size decreased to 99.4 μm and the frequency of high-angle grain boundaries (HAGBs) increased to 86.1%. In addition, the as-cast AH32 steel exhibited an optimized ultimate tensile strength of 532.0 MPa and an improved elongation of 24.2% after an enhanced PMS, which was attributed to more acicular ferrite, higher HAGBs ratio, and refined grain size.