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

Abstract

A fluoride-free continuous casting mold flux for ultralow carbon steel, comprising the following components in weight percentage: 3-10% of Na.sub.2O, 0-3% of Li.sub.2O, 3-8% of MgO, 5-15% of MnO, 0-8% of BaO, 4-12% of Al.sub.2O.sub.3, and impurities with a content of no more than 2%, the balance being CaO and SiO.sub.2, wherein the ratio of CaO/SiO.sub.2 is 0.8-1.3; the raw materials are mixed and then pre-melted; the pre-melted mold flux requires micro-adjusting according to the component deviation, and the ratio of the pre-melted material is not lower than 70%; then a carbonaceous material of 1-3% by the total weight of the mold flux is added and mixed so as to obtain the finished product mold flux. Said mold flux has a melting point of 1100-1200 C. and a viscosity of 0.2-0.6 Pa.Math.s at 1300 C. A method for preparing a mold flux comprising the following steps: mixing raw materials, pre-melting to obtain a pre-melt; then continuously supplementing raw materials into the pre-melt to obtain a substrate with a desired composition; then adding a carbonaceous material to the substrate and mixing so as to obtain said mold flux. This mold flux is a boron-free and fluoride-free mold flux, can effectively reduce the inclusion defect of blank casting and increase the yield of blank casting.

Claims

1. A fluoride-free continuous casting mold flux for ultralow-carbon steel, comprising the following composition as calculated by weight: Na.sub.2O 3-10%, Li.sub.2O 0-3%, MgO 3-8%, MnO 5-15%, BaO 0-8%, Al.sub.2O.sub.3 4-12%, not more than 2% of impurities, and the balance of CaO and SiO.sub.2, wherein the ratio of CaO/SiO.sub.2 is 0.8-1.3, wherein the mold flux is prepared by the following steps: mixing raw materials Na.sub.2O, Li.sub.2O, MgO, MnO, BaO, Al.sub.2O.sub.3, CaO and SiO.sub.2, conducting a pre-melting treatment to produce a pre-melted substance; and subsequently adding supplementary said raw materials to trim its composition, wherein the pre-melted substance is not less than 70% of a target weight; then, a carbonaceous material is added to afford 1-3% of C based on the total weight of the mold flux; after mixing, a final mold flux is obtained; and wherein the continuous casting mold flux does not contain B.sub.2O.sub.3.

2. The fluoride-free continuous casting mold flux for ultralow-carbon steel according to claim 1, wherein the mold flux has a melting point of 1100-1200 C. and a viscosity at 1300 C. of 0.2-0.6 Pa.Math.s.

3. A fluoride-free continuous casting mold flux product for ultralow-carbon steel, formed by mixing a matrix and 1-3% of a carbonaceous material based on the total weight of the matrix, wherein the matrix comprises the following composition as calculated by weight: Na.sub.2O 3-10%, Li.sub.2O 0-3%, MgO 3-8%, MnO 5-15%, BaO 0-8%, Al.sub.2O.sub.3 4-12%, not more than 2% of impurities, and the balance of CaO and SiO.sub.2, wherein the weight ratio of CaO/SiO.sub.2 is 0.8-1.3; the mold flux product is prepared by the following steps: mixing raw materials comprising Na.sub.2O, Li.sub.2O, MgO, MnO, BaO, Al.sub.2O.sub.3, CaO and SiO.sub.2, conducting a pre-melting treatment to produce a pre-melted substance; and subsequently adding supplementary said raw materials to trim its composition; wherein the matrix meets the following condition: the pre-melted substance is not less than 70% of a target weight and wherein the continuous casting mold flux does not contain B.sub.2O.sub.3.

4. The fluoride-free continuous casting mold flux product for ultralow-carbon steel according to claim 3, wherein the matrix has a melting point of 1100-1200 C. and a viscosity at 1300 C. of 0.2-0.6 Pa.Math.s.

5. A fluoride-free continuous casting mold flux product for ultralow-carbon steel, consisting of a matrix and 1-3% of a carbonaceous material based on the total weight of the matrix, wherein the matrix comprises by weight: Na.sub.2O 3-10%, Li.sub.2O 0-3%, MgO 3-8%, MnO 5-15%, BaO 0-8%, Al.sub.2O.sub.3 4-12%, not more than 2% of impurities, and the balance of CaO and SiO.sub.2, wherein the weight ratio of CaO/SiO.sub.2 is 0.8-1.3; and wherein the continuous casting mold flux does not contain B.sub.2O.sub.3.

6. The fluoride-free continuous casting mold flux product for ultralow-carbon steel according to claim 5, wherein the matrix has a melting point of 1100-1200 C. and a viscosity at 1300 C. of 0.2-0.6 Pa.Math.s.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) The invention will be further illustrated with reference to the accompanying drawings and the following specific examples.

Examples

(2) Raw materials for a mold flux (without limitation): limestone, quartz, glass, cement clinker, wollastonite, bauxite, magnesite clinker, soda, barium carbonate, pigment manganese, manganese carbonate, lithium carbonate, lithium concentrate, etc.

(3) The above raw materials were ground into fine powder, mixed homogeneously according to the matrix composition of the mold flux (i.e. the target composition), and then pre-melted to form a complicated solid solution from these substances and simultaneously release carbonates and volatiles such as water, etc. A pre-melted substance having faster melting speed and better homogeneity was obtained, followed by cooling, pulverizing and secondary grinding into fine powder having a particle size of less than 0.075 mm. Because of the various degrees of loss of the various raw materials during the pre-melting treatment, there was a deviation between the composition and total weight of the fine powder pre-melted substance obtained in the above steps and the target composition and weight. On the ground of the specific deviation, trimming was conducted by supplementing the above raw materials, so as to obtain a matrix having the target composition and the target weight. The pre-melted substance accounted for not less than 70% of the target weight. Subsequently, a suitable amount of a carbonaceous material such as carbon black, graphite and the like was added as desired, mixed mechanically, or treated using a spray drying device to produce a final granular mold flux. The compositions and properties of the final mold fluxes according to the Comparative Examples and Inventive Examples are listed in the table below.

(4) 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)} Chemical CaO 39 40 24.5 32.5 28.5 35.5 34 36 Composition % SiO.sub.2 37 31 30.5 36.5 28.5 32.5 28.5 28 Al.sub.2O.sub.3 3.5 5.5 4 8 9 6 11 12 MgO 13 3.5 7.5 4 7 6 5 3 MnO 1 14 7 9 5 10 12 BaO 8 4 7 6 4 Na.sub.2O 1 8.5 9.5 6 8 7 4 5 B.sub.2O.sub.3 10 Li.sub.2O 0.3 1 1.5 2 2.8 F 4 CaO/SiO.sub.2 1.05 1.3 0.8 0.9 1.0 1.1 1.2 1.29 C 2 1.7 2.9 1.2 1.8 2.2 2.5 2 Melting point 1229 1128 1105 1150 1125 1140 1160 1190 C. Viscosity at 0.29 0.34 0.45 0.6 0.4 0.32 0.27 0.22 1300 C. Pa .Math. s