Evolution of Inclusions in AH32 Shipbuilding Steel Ingots Solidified Under Permanent Magnet Stirring with Different Magnetic Flux Densities

An innovative permanent magnet stirring (PMS) distinguished by high magnetic flux density presents a viable approach to produce AH32 shipbuilding steel with fine and uniform distributed inclusions during solidification. In this work, a PMS model was built to simulate the magnetic and flow characteristics of the steel under various central magnetic flux densities (0, 1000, 1400, 1800 Gs). The simulated results showed that the maximum electromagnetic force escalated from 1.80 to 5.56 kN/m³, and thus, an enhanced flow was introduced with a maximum tangential velocity of 0.12 to 0.31 m/s when the magnetic flux densities increased from 1000 to 1800 Gs. Moreover, the experimental results indicated three typical inclusions of Al₂O₃, MnS, and Al₂O₃–MnS observed in the steel, and distributed more uniformly after PMS with enhanced magnetic flux density. The mean size of inclusions in the center of ingot reduced significantly from 7.2 to 2.5 μm and its number increased from 64 to 85 per mm² when the magnetic density increased to 1800 Gs based on the Aztec Feature results. In addition, the percentages of Al₂O₃–MnS complex inclusions increased from 32.8 to 75.3 pct due to the increasing number of small-sized Al₂O₃ nucleation core for MnS precipitation after enhanced PMS.