Fluoride-free continuous casting mold flux for low-carbon steel

Abstract

The invention provides a fluoride-free continuous casting mold flux for low-carbon steel, comprising, based on weight, Na.sub.2O 5-10%, MgO 3-10%, MnO 3-10%, B.sub.2O.sub.3 3-10%, Al.sub.2O.sub.36%, Li.sub.2O<3%, C 1-3%, and the balance of CaO and SiO.sub.2 as well as inevitable impurities, wherein the ratio of CaO/SiO.sub.2 is 0.81.3. The mold flux has a melting point of 951150 C., a viscosity at 1300 C. of 0.1-0.3 Pa.Math.s, and a crystallization rate of 10-50% as determined according to the method described in the specification for examining crystallization property. The boron-containing, fluoride-free flux developed according to the invention has a moderate crystallization rate, can be used in a crystallizer to control transfer of heat from molten steel effectively, and has been applied successfully in a low-carbon steel slab conticaster with a metallurgical effect that arrives at the level of a traditional fluoride-containing flux to full extent.

Claims

1. A fluoride-free continuous casting mold flux suitable for producing low-carbon steel, consisting of, based on weight, Na.sub.2O 6-9.5%, MgO 3-10%, MnO 3-10%, B.sub.2O.sub.3 3-4%, Al.sub.2O.sub.36%, Li.sub.2O<3%, C 1-3%, the balance of CaO and SiO.sub.2, and inevitable impurities, wherein the weight ratio of CaO/SiO.sub.2 is 0.81.0; wherein the crystallization rate of the mold flux ranges from 22% to 50% as characterized by the proportion of crystals at a section when 50g of the mold flux is melted at 1350 C. and then poured into a steel crucible to be cooled naturally; and wherein said mold flux has melting point and viscosity of heat transfer capability suitable for producing low carbon steel in a continuous casting system.

2. The fluoride-free continuous casting mold flux of claim 1, wherein said MgO is 5-9% by weight.

3. The fluoride-free continuous casting mold flux of claim 1, wherein said MnO is 5-9% by weight.

4. The fluoride-free continuous casting mold flux of claim 1, wherein said Al.sub.2O.sub.3 is 0.5-6% by weight.

5. The fluoride-free continuous casting mold flux of claim 1, wherein said Li.sub.2O is 2.5% by weight.

6. The fluoride-free continuous casting mold flux of claim 1, wherein the said C is 1.3-2.8% by weight.

7. The fluoride-free continuous casting mold flux of claim 1, wherein said melting point is 1010-1150 C. and said viscosity is 0.1-0.3 Pa.Math.s at 1300 C.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 shows a steel crucible for measuring the crystallization property of a mold flux, wherein I refers to steel crucible, and II refers to flux body.

DETAILED DESCRIPTION OF THE INVENTION

(2) The invention will be described in more detail with reference to the following examples. These examples are only intended to describe the most preferred embodiments of the invention without limiting the scope of the invention.

Examples 1-7

(3) The following raw materials (without limitation) were used to prepare a mold flux: limestone, quartz, wollastonite, magnesite clinker, bauxite, soda, borax, borocalcite, manganese carbonate, pigment manganese, lithium carbonate, lithium concentrate, etc.

(4) The above raw materials were ground into fine powder, mixed homogeneously at a target composition, and then pre-melted to form a complex solid solution from these substances and release carbonates and volatiles such as water, etc. A pre-melted material having faster melting speed and better homogeneity was obtained, followed by cooling, breaking and secondary grinding into fine powder having a particle size of less than 0.075 mm. On the ground of compositional deviation, mild adjustment was conducted using the above stated raw materials, wherein the pre-melted material accounted for not less than 70%. Subsequently, a suitable amount of carbonaceous material such as carbon black, graphite and the like was added, mixed mechanically, or treated using a spray drying device to give a granular product flux.

(5) The table below shows the compositions of the mold fluxes of the examples. Compared with the comparative examples, the mold flux of the invention has the same capability of heat transfer as a traditional fluoride-containing flux, such that the problems of unduly high capability of heat transfer of the crystallizer and inability of the caster in achieving normal draw speed, which tended to occur in the comparative examples, are eliminated.

(6) TABLE-US-00001 Comparative Examples Examples {circle around (1)} {circle around (2)} {circle around (1)} {circle around (2)} {circle around (3)} {circle around (4)} {circle around (5)} {circle around (6)} {circle around (7)} Chemical CaO 37 33.5 34.2 33 33 38 35 31 31 composition % SiO.sub.2 33 32 30 33 33.5 29.5 29 38.5 34.5 Al.sub.2O.sub.3 3 4 5 3 3 6 5 0.5 1 MgO 3 3.5 6 8 6 5 3 9 6 MnO 5 4.5 5 5 10 3 5 5 9 Na.sub.2O 9 12 9 8 6 6 9.5 9 9 B.sub.2O.sub.3 4 6.5 7.5 4 4 8 10 3 6 Li.sub.2O 1 0.5 1 2.5 1 1.5 0 1 1 C 2.3 2.4 2.4 2.6 2.0 1.3 2.8 1.8 1.6 CaO/SiO.sub.2 1.12 1.05 1.14 1.00 0.99 1.29 1.21 0.81 0.90 Melting point C. 1045 985 1040 1010 1065 1140 970 1105 1080 Viscosity at 1300 C. 0.20 0.22 0.20 0.18 0.24 0.15 0.12 0.30 0.26 Pa .Math. s Crystallization rate % 3 0 15 45 35 30 10 22 17 Heat transfer capability Excessively Excessively Moderate Moderate Moderate Moderate Moderate Moderate Moderate high high