Effect of Ce-La on inclusion evolution in Al-killed high strength steel

Abstract

The mechanism of inclusion evolution after rare earth addition based on oxide metallurgy was investigated experimentally and using thermodynamic calculations, where Ce-La was added to Al-killed high strength steel during Ruhrstahl-Heraeus refining to modify the oxide inclusions within the steel. The typical inclusions observed before Ce-La addition were spherical magnesium aluminate spinel inclusions. And fewer individual Al2O3 inclusions and Al2O3–TiOx inclusions were also observed. The addition of Ce-La led to transformation of MgO · Al2O3 spinel inclusions to (Ce,La)2O3, (Ce,La)2O2S and (Ce,La)2O2S + MgO · Al2O3 inclusions. Thermodynamic calculations indicated that Ce-La combined with dissolved oxygen and sulfur in molten steel to form rare earth inclusions, while the remainder of the Ce and La modified MgO · Al2O3 to (Ce,La)2O3 and (Ce,La)2O2S.

Effect of rare earth on inclusion evolution and corrosion resistance of HRB400E steel

“…The reaction formulas of the main rare earth inclusions and their standard Gibbs free energies are listed in Table 2. [ 18,27,28 ]…”

“…The reaction formulas of the main rare earth inclusions and their standard Gibbs free energies are listed in Table 2. [18,27,28] The Gibbs free energy of each reaction formula was calculated using Equations ( 1)- (3).…”

“…Related first-order interaction parameters used in this calculation have been listed in Table 3. [27,29,30] The change in Gibbs free energy during the chemical reactions to form rare earth inclusions (the ratio of Ce to La in the alloy was 1:3) at 1600°C according to the reactions and activity coefficients of each element is shown in Figure 6 The formation of rare earth inclusions is related to the Gibbs free energy and affected by mutual transformation. Therefore, the mutual transformation between the rare earth inclusions was further calculated, as shown in Table 4.…”

Effect of Rare‐Earth La on Inclusion Evolution in High‐Al Steel

“…[ 20–22 ] Wang et al [ 23,24 ] investigated the effect of La on inclusions in steel containing As and reported that the evolution route of inclusions in the La–O–S–As system was La 2 O 3 → La 2 O 2 S → La 2 O 2 S–LaAsO 4 → LaAsO 4 . Geng et al [ 25 ] reported that Ce–La could transform MgO·Al 2 O 3 spinel inclusions to (Ce, La) 2 O 3 , (Ce, La) 2 O 2 S, and (Ce, La) 2 O 2 S + MgO·Al 2 O 3 inclusions in Al‐killed high‐strength steel. Gong et al [ 26 ] observed that MnS and Al 2 O 3 –MnS inclusions could be modified into La–O–S, La–S, and other La‐containing complex inclusions.…”

“…It is generally accepted that the type of inclusion treatment by rare‐earth elements is related to the S/O ratio and the added amount of rare‐earth elements. [ 19,25,27–31 ] However, fundamental studies on inclusion evolution treated using rare‐earth elements in high‐Al steels are considerably scarce.…”