Application of high-basicity mould fluxes for continuous casting of large steel slabs

Abstract

Controlling the formation of longitudinal cracks on hypo-peritectic steel slab surfaces is one of the key challenges in continuous casting worldwide. Based on the production in Chongqing Iron & Steel Co., mould fluxes with high basicity ranging from 1.7 to 1.8 were put forward and the effects of compositions on the basic properties of mould flux were studied in the present paper.After laboratory experiments, a high-basicity mould flux with an increased crystallisation speed to abate the heat-transfer capability in the meniscus area was fully applied in the first steelmaking plant of Chongqing Iron & Steel Co. Using the high-basicity mould flux, for more than 3 million tonnes of slab production, the large longitudinal crack was eliminated and the rate of formation of small longitudinal cracks decreased greatly. During the production process, sticking that impedes the smooth running of continuous casting was infrequent, and the spot check for longitudinal cracks on micro alloy steel surface was simplified in the slab finishing process. Furthermore, since the application effect of mass production is remarkable, the hot charging process is better implemented, and the contract can be accomplished in time. In summary, the problem of longitudinal cracks on hypo-peritectic steel slab surfaces is finally resolved and the high-basicity mould fluxes have become indispensable auxiliary materials during continuous casting of hypo-peritectic steel.

Causes of Corner Cracks in Hypoperitectic Microalloyed Steel Billets

“…However, the corner of the billet is cooled in two dimensions, and the static pressure of the molten steel is very small, resulting in an air gap forming in the corner of the billet (Figure 9a). [26] The air gap causes a large thermal resistance at the corner, and thus, the temperature of the corner rises again. The fine grains on the surface of the corner grow into coarse grains due to the temperature rising (Figure 9b).…”

“…The presence of potassium does not prove that the inclusions originate from mold fluxes. [26] If potassium comes from mold flux, there must be Al and Si distribution in the crack, because most of the components of the mold flux are Al 2 O 3 and SiO 2 (Table S1, Supporting Information). However, there was no obvious distribution of Al in the cracks.…”

The relationship between crystallization and break temperature of mould flux

“…For this study, four typical mould fluxes were selected, namely, mould flux B (billet), LC (low-carbon steel), MC (medium-carbon steel), and UHB (ultra-high basicity [22]). The specific compositions are listed in Table 1.…”

Influence of Al₂O₃/SiO₂ and BaO/Al₂O₃ Ratios on Rheological and Crystallization Behavior of CaO–BaO–Al₂O₃-Based Mold Slags

“…[1][2][3] However, a fully crystalline slag film is not an alternative, as it provides poor lubrication to the solidifying shell. 4) This is a particular issue for the continuous casting of high-Al steel, 5) due to the interfacial reaction between Al in liquid steel and SiO 2 in conventional CaO-SiO 2 -based mold slag induces the transformation of initial silica-based mold slag into alumina-based mold slag, leading to a significant change of slag properties, such as increases in viscosity and crystallization of the slag, which disturb the lubrication and heat…”