Development of mould fluxes based on lime–alumina slag system for casting high aluminium TRIP steel

Abstract

With excellent strength and ductility properties, transformation induced plasticity (TRIP) steels are superior to ordinary commercial steels and have great application potential in the automobile industry. However, the continuous casting of TRIP steels is associated with challenges owing to its high aluminium content, approximately 0?5-1?8%. The reaction of aluminium near the steel/slag interface continuously changes the basicity of conventional lime-silica based mould fluxes causing variation in the flux physical properties between the solidifying shell and mould wall. Therefore, the heat transfer process is unstable and the surface quality of the as-cast slab is not guaranteed.To reduce the reactivity of aluminium in TRIP steel during casting, it is suggested to replace the lime-silica based fluxes with a lime-alumina based mould flux, based on laboratory measurements and industrial trials. The trials showed great improvement in the slab surface quality and no depression defect was noticed so far.

Effect of Al Speciation on the Structure of High‐Al Steels Mold Fluxes Containing Fluoride

“…The high concentrations of SiO 2 react with Al to yield controlled performance of the spent CaO–SiO 2 –Al 2 O 3 mold fluxes (SiO 2 ~10–30 mol%, Al 2 O 3 ~5–15 mol%) to meet the demands for high‐Al steels casting . The second method is based on nonreactive mold fluxes, which utilizes novel developed CaO–Al 2 O 3 mold fluxes with concentrations higher in Al 2 O 3 and lower in SiO 2 (SiO 2 < 10 mol%, Al 2 O 3 > 15 mol%) to suppress the slags/steel reaction . Both strategies, however, have their advantages and drawbacks.…”

Non‐Isothermal Crystallization Kinetics of Mold Fluxes Containing Li2O for High Aluminum Steel Casting

“…In recent researches, two different approaches were proposed to improve casting operation and slab surface quality . When current CaO–SiO 2 based mold fluxes with low basicity were used to cast high Al steel, spent fluxes with appropriate physical properties can ensure sufficient lubrication . However, it is difficult to avoid the chemical reactions between mold flux and liquid steel, which may cause the occurrence of cracks, depressions, and deep oscillation marks.…”

Review of Mold Fluxes for Continuous Casting of High‐Alloy (Al, Mn, Ti) Steels

“…However, problems such as thick slag rims, inadequate slag consumption, and breakout prevention (BOP) alarms still existed, which consequently prevent long sequence casting. Furthermore, plant trials, conducted in Wuhan Iron and Steel Company Limited in 2014, showed that increasing the B 2 O 3 content in the mold flux exerted little effect on controlling slag rims and improving lubrication for the reduction of B 2 O 3 .…”