Refinement of Liquid CaO-Al2O3 Inclusions in Duplex Stainless Steel through Ce Treatment

Solid-liquid-mixed inclusions may be less likely to grow into large-sized inclusions, compared to fully liquid inclusions. To investigate this, liquid CaO-Al2O3 inclusions in duplex stainless steel are modified by adding varying amounts of Ce at 1600 degrees C using a vertical tube furnace, focusing on the modification process and the collision growth behavior of solid-liquid-mixed inclusions. Ce treatment significantly reduces the inclusion size, achieving optimal results at an addition of 256 ppm, where the mean diameter of nonmetallic inclusions decreases from 2.88 +/- 0.13 to 1.98 +/- 0.09 mu m. Furthermore, Ce treatment transforms liquid CaO-Al2O3 inclusions into core-shell-structured solid-liquid-mixed inclusions or solid Ce-O-S inclusions, depending on the Ce addition. As Ce addition increases from 256 to 720 ppm, the average content of Ce2O3 in the inclusions rises from 12.7% to 27.8, while Al2O3 and CaO decrease to 45.2 and 27.0%, respectively. A complex relationship exists between inclusion size and Ce2O3 content, with minimal sizes observed at around 20% Ce2O3. The presence of a solid core in solid-liquid-mixed inclusions effectively reduces their coalescence tendency, and the underlying mechanism is analyzed.