Effect of Magnesium Content on Precipitation Behavior of TiN-Containing Inclusions in High-Titanium High-Strength Steel

High-temperature melting experiments (1600 degrees C), metallographic microscopy and scanning electron microscopy were used to investigate the morphology, quantity and size of TiN in the center of high-titanium high-strength steels under different Mg content (0 wt.% -> 0.0023 wt.%). The results showed that based on thermodynamic calculations regarding the aluminum-magnesium content relationship during deoxidation product formation, significant amounts of MgAl2O4 are generated even with trace amounts of Mg present in the tested steel. The solidification structures of all tested steels are equiaxed grains when the solidification cooling rate is 0.17 degrees C/s. The average size of equiaxial grain in the tested steels decreased from 320 to 271 mu m, 195 and 101 mu m as the Mg content increased from 0 to 0.0007 wt.%, 0.00014 and 0.0023 wt.%, respectively. MgO and MgAl2O4 precipitate before TiN and have a small lattice mismatch with TiN (0.02 and 5.03%, respectively). As the Mg content in the steel increased from 0 to 0.0007 wt.%, 0.0014 and 0.0023 wt.%, the areal density of TiN in the tested steels increased from 44.4 to 102.4 No./mm2, 129.4 and 144.2 No./mm2, the maximum size of TiN particles decreased from 16.5 to 10.4 mu m, 9.8 and 9.3 mu m, the average size of TiN decreased from 9.1 to 4.2 mu m, 3.3 and 3.1 mu m, and the proportion of TiN precipitated at the grain boundaries decreases from 22.7 to 16.8%, 14.5 and 14.8%, respectively.