Behavior of alumina-magnesia complex inclusions and magnesia inclusions on the surface of molten low-carbon steels

Abstract

It is well known that alumina inclusions on the surface of molten Al-killed steel quickly attract each other to form clusters. On the other hand, alumina-magnesia complex inclusions on the surface of molten low-carbon steel with a high oxygen content have a much weaker tendency to form clusters. In the present work, the reason for the different behaviors of the two types of inclusions was analyzed in detail. A confocal scanning laser microscope was used to carry out the experiment of in-situ observation of the two types of inclusion on the molten pool. The first type of inclusion was 93 mass pct alumina-7 mass pct magnesian, obtained in a Mg-added Al-killed steel. The second type of inclusion was nearly pure magnesia, obtained in a Mg-killed steel. The attractive force between a pair of inclusions, for both cases, was found to be approximately 1O Ϫ17 to 10 Ϫ16 N and one-tenth of that between a pair of alumina inclusions. The various effects of contact angle, surface tension, and oxygen content of the steel melt on the attractive force are discussed in detail from the viewpoint of the capillary force.

Interactions between Exogenous Magnesia Inclusions with Endogenous Inclusions in a High Alloyed Steel Melt

“…Upon earlier investigations by applying the same steel melt, [6] the exogenous alumina particles attract the endogenous particles with real attractive forces of 1 Â 10 À16 up to 1 Â 10 À15 N. Comparing both groups of result, it turns out that the real attraction forces of the exogenous MgO particles are much smaller than that of the exogenous Al 2 O 3 particle. The extracted results are in an excellent agreement with the experiments of magnesia and alumina particles in the low-carbon steel as reported by Kimura et al, [22] in which they have observed the one-tenth smaller attraction forces of MgO (10 À19 N to 10 À18 N) in comparison to the attraction forces of alumina (10 À18 N to 10 À17 N). In fact, they argued that the different contact angle of MgO (90 ) and Al 2 O 3 (120 ) to their molten low carbon steel can be recognized as the major reason for the weaker magnesia tendency for coagulation.…”

Effect of Mg Addition on the Evolution of Inclusions in Al–Ca Deoxidized Melts

“…4,32,33) By using in-situ CSLM observation, Kimura et al found that alumina-magnesia complex inclusions on the surface of molten steel have a much weaker tendency to aggregate and to form clusters than alumina inclusions. 34,35) It is probably a good idea that the inclusions after calcium treatment can be refined through magnesium addition. Once the addition time is appropriate, the residual large inclusions are refined, which can improve the final quality of steel.…”

“…The size of inclusions reduces to 2 μm probably due to the modification of the contact angle and interfacial tension between inclusions and molten iron. The work of Kimura et al 34,35) can approve it indirectly. The reason for this interesting phenomenon is complicated, and it should be paid more attention in the following research.…”

Effect of trace magnesium addition on the characteristics of mechanical properties in high strength low alloy steel

“…It was therefore concluded that trace Mg was good for the refinement of inclusions. Through in-situ observation experiments with a confocal scanning laser microscope, Kimura et al [3] have measured the attractive force between a pair of inclusions such as alumina-magnesia complex inclusions, magnesia and alumina inclusions, and their studies shown that the attractive force between a pair of inclusions, for alumina-magnesia complex inclusions and magnesia, was found to be approximately 10 -17 to 10 -16 N and one-tenth of that between a pair of alumina inclusions, which may be a mechanism of Mg-containing inclusions not easily to aggregate in liquid steel.…”