Effect of CaF₂ on Viscosity and Refining Ability of Highly Basic Slags for Duplex Stainless Steel

Abstract

To optimize CaF 2 content in highly basic CaO-18%Al 2 O 3-SiO 2-10%MgO-CaF 2 (%CaO/%SiO 2 = 6, denoted as C/S = 6) refining slags used for the production of Al-killed duplex stainless steel with high cleanliness demand, the effect of CaF 2 content on the viscosity and refining ability of the slags were studied and compared with typical CaF 2-free highly basic CaO-30%Al 2 O 3-SiO 2-10%MgO (C/S = 6) slag. The effect of CaF 2 addition in decreasing slag viscosity becomes less obvious with increasing temperature and CaF 2 content. When CaF 2 content exceeds 10%, slag viscosity only marginally decreases with further increasing CaF 2 content. Both monoxide-CaO and monoxide-MgO phases are precipitated in all the CaF 2-bearing slags. CaF 2 addition slightly increases monoxide-MgO precipitation, but dramatically decreases monoxide-CaO precipitation. Viscosities of the CaF 2-bearing slags were also theoretically calculated and good agreement with the measured values was observed. Moreover, the 6% CaF 2-bearing slag has very close viscosities above 1 833 K but much lower viscosities below 1 833 K, compared with the CaF 2-free highly basic slag. Further evaluation of the 6% CaF 2-bearing slag on steel cleanliness confirms that 6% CaF 2 addition is sufficient for the highly basic CaO-18%Al 2 O 3-SiO 2-10%MgO-CaF 2 (C/S = 6) slag. The mechanism of CaF 2 in decreasing the viscosity of CaF 2-bearing slags was discussed from the viewpoints that CaF 2 behaves as a network breaker and that CaF 2 suppresses the precipitation of solid phases. The first aspect was identified to play a much greater role in decreasing slag viscosity.

The Effect of Ca Pretreatment on the Characteristics of Rare‐Earth Nonmetallic Inclusions in Super‐Duplex Stainless Steel

“…Therefore, the inclusions remained in a semiliquid state. As observed in previous studies, [ 43 ] semiliquid inclusions can also take on a spherical shape (Figure 3b).…”

“…Therefore, the inclusions remained in a semiliquid state. As observed in previous studies, [43] semiliquid inclusions can also take on a spherical shape (Figure 3b). Figure 11 presents the elemental mapping of rare-earth inclusions in the samples taken at 3 and 10 min after Ce addition.…”

Effect of Al₂O₃ on Viscosity and Refining Ability of High Basicity Slag for Heat-resistant Austenitic Stainless Steel

“…Figure 2(a) describes the viscosity variations of SA1-SA5 slags (containing different Al 2 O 3 contents) within the temperature range of 1 753-1 873 K. The viscosities measured by Zheng et al 11) for 55%CaO-9%SiO 2 -18%Al 2 O 3 -10%MgO-8%CaF 2 slag, which has a similar composition to SA3 were also shown in Fig. 2(a).…”

“…Extensive studies have revealed that both Al 2 O 3 and CaF 2 significantly affect slag viscosity. [11][12][13] However, excessive CaF 2 addition will accelerate the corrosion of refractories and induce serious environmental pollution. 13,14) By comparison, appropriate Al 2 O 3 addition can not only enhance the refining effect but also be friendly to the environment.…”

Research Progress of Desulfurization Refining Slag: A Review

“…Bearing steel [88] 50.4 4.3 40.3 5 -Alloy structural steel [89] 47.5 12.5 12. Reproduced with permission.…”