Effect of Refractory on Nonmetallic Inclusions in Si–Mn‐Killed Steel

Abstract

Some laboratory experiments are carried out to study the effect of different refractories on the original and exogenous inclusions in Si-Mn-killed steel. As expected, it is found that Al 2 O 3 refractory causes high melting points of both SiO 2 -Al 2 O 3 -MnO system and SiO 2 -Al 2 O 3 -CaO system inclusions, while MgO crucible reduces the melting points of both systems of inclusions to a certain extent. The purity of MgO refractory is crucial for tire cord steel grades, and even 0.3% of Al 2 O 3 impurity in refractory results in an evident increase (by 10%-20%) of Al 2 O 3 content in the inclusions. Similar to Al-killed steel grades, MgO·Al 2 O 3 spinel can also be stable in Si-Mn-killed steel due to the effect of MgO refractory, and MgO and Al 2 O 3 inclusions can transform into MgO·Al 2 O 3 spinel. These inclusions should be strictly controlled during refining process. High-purity and high-quality MgO refractory as well as high-quality alloys are recommended for Si-Mn-killed steel grades, and Al 2 O 3 -based refractory should be avoided.

Formation, Evolution and Removal of MgO·Al₂O₃ Spinel Inclusions in Steel

“…This argument is also applicable for both dissolved Mg and dissolved Ca. The formation of spinel on alumina in Si-Mn-killed steel grades 52) is an evidence to support this argument, because the Al content in Si-Mn-killed steel grades is very low, and the reactions of Eqs. (18) and (21) are not applicable.…”

“…This is a direct evidence that spinel inclusions generate from alumina inclusions. At the same time, some laboratory experiments 20,49,52) were also designed to confirm the formation of spinel using alumina sticks and rods, and a relatively uniform spinel layer can still be found as shown in Fig. 3.…”

“…(3) describes the transformation of MgO inclusions into spinel inclusions. Many researchers 4,10,15,16,52) used these two equations to consider the stability of spinel inclusions in steel. This method is named as border lines method by Zhang et al 36) Park and Todoroki et al 9,67) introduced the calculation details and also summarized some thermodynamic data used for the calculations.…”

Formation Mechanisms and Three-dimensional Characterization of Composite Inclusions in Low Aluminum Steel Deoxidized by Silicon

“…The inclusions in the silicon deoxidized steel were mostly SiO 2 , Al 2 O 3 -SiO 2 , SiO 2 -MnO and MnO-SiO 2 -Al 2 O 3 . [15][16][17][18][19] The composite inclusions such as CaO-SiO 2 , MgO-Al 2 O 3 -SiO 2 and other composite inclusions with more complicated compositions were found in calcium-treated or magnesium-treated steel. 20) Besides, MnS wrapped Al-Si-O-Mn composite inclusions were found in some types of steel.…”

Reaction Mechanism of CA6, Al2O3 and CA6-Al2O3 Refractories with Refining Slag

“…The slag corrosion will destroy the structure of the refractory and reduce the service life [ 4 , 5 , 6 , 7 ]. More importantly, under the continuous scouring effect of molten steel, the dislodged refractory and the corrosion products would enter the molten steel to form exogenous large size inclusions [ 8 , 9 , 10 , 11 , 12 , 13 , 14 , 15 , 16 , 17 ], which will have a fatally harmful effect on the purity of the molten steel and the quality of the final products [ 17 , 18 , 19 , 20 ]. Therefore, in order to eliminate the introduction of exogenous inclusion and to increase the service life of the refractories, it is absolutely essential to study corrosion behavior between the refractory and refining slag.…”