Continuous casting mold powder for high-aluminium steels: low-reactivity lime–alumina (CaO–Al₂O₃) type
Lime–alumina (CaO–Al₂O₃) mould powders for high-aluminium TRIP and TWIP steels · Al–SiO₂ reaction, alumina pickup, lime/alumina ratio, crystallisation and lubrication
This page covers mould powders built on lime and alumina instead of lime and silica, made for casting high-aluminium steels such as TRIP and TWIP grades where aluminium in the steel would otherwise reduce the silica in the flux. Ask three things first: how much alumina pickup the powder has shown on steel with your aluminium content, what lime/alumina ratio and fluxing additions set its viscosity, and what lubrication and crystallisation results the supplier can show.
Lime–alumina (CaO–Al₂O₃-based) mould powders and granules for continuous casting of high-aluminium steels, including TRIP and TWIP grades. Conventional lime–silica (CaO–SiO₂-based) mould fluxes, including fluorine-free and peritectic-grade fluxes, are covered on the Continuous casting mold flux page. Tundish covering fluxes and ladle slag conditioners are outside this page.
CNFX editorial research · Sources checked October 12, 2026 · 4 sources
Limit the reaction between aluminium in the steel and the powder
Cho and co-authors from POSCO, POSTECH, ArcelorMittal Global Research, S&B Industrial Minerals and Stollberg & Samil (ISIJ International, 2013) state that when casting high-aluminium advanced high-strength steels, the reaction between aluminium in the steel and silica in the mould flux changes the viscosity and crystallisation of the mould slag and deteriorates mould lubrication. In trial casts of 1.45% Al TRIP steel on a pilot caster, their lime–alumina based mould fluxes reduced alumina pickup to less than 5%, against 15% for corollary casts with conventional lime–silica fluxes, and gave enhanced lubrication, stable mould heat transfer and slabs with periodic, sound oscillation marks. [1]
A 2023 Materials study states the same mechanism for high-Al TRIP and TWIP steels, where Al in liquid steel reacts with components of the molten flux, especially SiO₂, "dramatically changing" the liquid slag pool and slag films; it also reports that the lubricating effect of CaO–Al₂O₃-based fluxes has been insufficient in casting high-Al steels, with sticking or breakout limiting their industrial application. [2]
Editorial note: ask the supplier for pickup and lubrication results on a steel with an aluminium content close to yours, since the ISIJ figures come from 1.45% Al TRIP steel on a pilot caster. [1]
Give the supplier the steel grade and its Al, Mn, Si and C contents, section size, casting speed, mould oscillation, the alumina pickup you see with your present powder, and any sticker or breakout history.
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Set viscosity and crystallisation with the lime/alumina ratio and fluxing additions
Viscosity of lime–alumina powders depends on the CaO/Al₂O₃ ratio. Seyrek and Thackray (University of Sheffield, 2021) measured CaO–Al₂O₃-based mould fluxes with B₂O₃ by inclined plate test and report that viscosity decreases dramatically as the lime/alumina ratio rises from 1 to 1.5, decreases slightly from 1.5 to 2.5 and becomes stable above 2.5, and that B₂O₃ addition lowers viscosity at ratios of 1.2, 3.3 and 5.5. [4]
The 2023 Materials study used CaO–Al₂O₃–BaO–CaF₂–Li₂O fluxes of 24 wt% CaO, 15 BaO, 10 F, 6 Li₂O, 4.5 B₂O₃ and 2 MgO with 32, 37 or 42 wt% Al₂O₃, the higher levels standing for alumina absorbed from the steel. Adding Al₂O₃ increased the growing speed and thickness of solid slag films measured with a water-cooled copper probe at 1,300–1,400 °C, MgAl₂O₄ spinel precipitated at 10 wt% extra Al₂O₃, and the apparent activation energy of initial devitrified crystallisation fell from 314.16 to 297.32 and 269.46 kJ/mol. [2]
A 2019 Materials study compared a CaO–SiO₂–CaF₂ flux with a CaO–Al₂O₃-based flux of 42 CaO, 42 Al₂O₃, 8 Na₂O and 8 B₂O₃ (mass%): the CaO–Al₂O₃ flux precipitated CaAl₂O₄ and Ca₃B₂O₆, its phases and crystal morphologies did not change between 5 and 50 °C/min cooling, and the authors name the morphology difference between the two families' primary crystals as "probably one of the biggest factors limiting lubrication" with high-Al steel. [3]
Editorial calculation: the CaO/Al₂O₃ mass ratio is 24 ÷ 32 = 0.75 for the 2023 base flux and 24 ÷ 42 ≈ 0.57 with 10 wt% extra alumina, against 42 ÷ 42 = 1.0 for the 2019 flux; both sit at or below the lower end of the 1–1.5 range over which the Sheffield work reports viscosity decreasing dramatically, so ask the supplier for measured viscosity at your ratio. [2][3][4]
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Lime–alumina flux compositions and results from Materials and ISIJ studies
Published compositions come from studies, not commercial grades; use them to frame questions to a supplier.
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Each manufacturer above links to the page on that company's own website where the product is listed, with the date we checked it. How we source and review
· Page last updated 13 October 2026
Buyer questions
Why use a lime–alumina mould powder for high-aluminium steel?
Aluminium in the steel reacts with silica in conventional fluxes and changes the slag; in pilot casts of 1.45% Al TRIP steel, lime–alumina fluxes cut alumina pickup to less than 5% against 15% with lime–silica fluxes (ISIJ International, 2013). [1]
How does the lime/alumina ratio affect viscosity?
Seyrek and Thackray report viscosity decreasing dramatically from a ratio of 1 to 1.5, slightly from 1.5 to 2.5, and staying stable above 2.5. [4]
What limits lime–alumina powders?
Studies report insufficient lubrication, with sticking or breakout, and different primary crystal morphology from lime–silica fluxes. [2][3]
Sources and what still needs a direct check
Sources checked 2026-10-12. The ISIJ International paper reports pilot-caster trials; the Materials and Sheffield papers are laboratory studies. None is a commercial product specification.
