REFRACTORY PLATE FOR A SLIDE GATE VALVE, USE OF A FUSED RAW MATERIAL AS A MATERIAL IN SUCH A PLATE AND A MELTING VESSEL COMPRISING SUCH A PLATE

Abstract

The invention relates to a refractory plate for a sliding shutter for regulating a flow rate of liquid steel, to the use of a melt raw material as material in a plate of this kind and to a melt vessel for receiving liquid steel which has a plate of this kind for regulating a flow rate of liquid steel from the melt vessel.

Claims

1. A refractory plate for a slide gate valve for controlling a flow rate of liquid steel, comprising a fused raw material, wherein the fused raw material comprises the following elements each in a proportion in the range of the following mass fractions: aluminum: 46 to 55% by mass; oxygen: 42 to 49% by mass; carbon: 0.1 to 3% by mass; silicon: 0.1 to 4% by mass.

2. Plate according to claim 1, wherein the fused raw material comprises the phase Al.sub.28C.sub.6N.sub.6O.sub.21.

3. Plate according to claim 1, wherein the fused raw material comprises the phase Al.sub.28C.sub.6N.sub.6O.sub.21 in a proportion in the range from 0.05 to 10% by mass.

4. Plate according to claim 1, wherein the fused raw material comprises the element nitrogen.

5. Plate according to claim 1, wherein the fused raw material comprises the element nitrogen in a proportion of at most 0.3% by mass.

6. Plate according to claim 1, wherein the fused raw material comprises the elements aluminum, oxygen, carbon, silicon and nitrogen in a total proportion of at least 98% by mass.

7. Plate according to claim 1, wherein the fused raw material comprises metallic silicon.

8. Plate according to claim 1, wherein the fused raw material comprises the phase SiC.

9. Plate according to claim 1, wherein the fused raw material comprises the phase corundum.

10. Plate according to claim 1, which comprises the fused raw material in a proportion in the range from 3 to 70% by mass.

11. Plate according to claim 1 in the form of either an unfired or fired carbon bonded product.

12. Plate according to claim 1, which has at least one of the following physical values: Thermal expansion coefficient <9.0*106 K.sup.1; Dynamic modulus of elasticity (Young's modulus) at 1,400 C. in reducing atmosphere (sound travel time measurement) <65 GPa; Cold bending strength >15 MPa; Hot bending strength at 1,400 C. in reducing atmosphere >13 MPa; Work at break Gf at 1,400 C. in reducing atmosphere >250, in particular >300 J/m.sup.2; Nominal notched tensile strength NT at 1,400 C. in reducing atmosphere >5 MPa; Thermal shock parameter R according to Kingery at 1,400 C. >10 K; Thermal shock parameter R.sub.st according to Hasselmann at 1,400 C. >5.5 K*m.sup.1/2.

13. A method comprising: using a fused raw material as raw material in a plate for a slide gate valve, wherein the fused raw material comprises the following elements each in a proportion in the range of the following mass fractions: aluminum: 46 to 55% by mass; oxygen: 42 to 49% by mass; carbon: 0.1 to 3% by mass; silicon: 0.1 to 4% by mass.

14. Melting vessel for receiving liquid steel, wherein the melting vessel comprises at least one plate for controlling a flow rate of liquid steel from the melting vessel, wherein the at least one plate comprises a fused raw material, wherein the fused raw material comprises the following elements each in a proportion in the range of the following mass fractions: aluminum: 46 to 55% by mass; oxygen: 42 to 49% by mass; carbon: 0.1 to 3% by mass; silicon: 0.1 to 4% by mass.

15. Melting vessel according to claim 14 in the form of a ladle or tundish in a continuous casting plant for casting steel.

Description

[0089] Further features of the invention result from the claims and from the following description of an example of an embodiment of the invention.

[0090] All features of the invention may, individually or in combination, be combined with each other as desired.

[0091] An exemplary embodiment of the invention is explained in more detail below.

[0092] The subject of the exemplary embodiment of the invention is a refractory plate in the form of a carbon-bonded refractory slide gate plate based on the raw materials alumina, zircon mullite and the fused raw material according to the invention.

[0093] For the production of the slide gate plate, a batch was provided, which contained the raw materials in the proportions shown in Table 1 below, each in relation to the total mass of the batch:

TABLE-US-00001 TABLE 1 Raw material Mass fraction [% by mass] Fused raw material >1.0 to 3.0 mm 21.1 Fused raw material >0.5 to 1.0 mm 10.6 Fused raw material >0.0 to 0.5 mm 17.3 Alumina <125 m 21.8 Zircon mullite <3.0 mm 16.1 Graphite 3.0 Antioxidants (silicon and SiC) 5.5 Hexamethylentetramine 0.5 Synthetic resin (Novolak) 4.1

[0094] The fused raw material for the batch according to Table 1 was produced as follows.

[0095] First of all, a batch was provided, consisting of 89% by mass of calcined alumina, 8% by mass of fireclay and 3% by mass of graphite. This batch was melted to a melt in an electric arc furnace. The melt was then cooled down to room temperature and the melt solidified. The solidified melt was available in the form of a fused raw material according to the invention. In order to provide this fused raw material in the grain size according to the batch in Table 1, the fused raw material was comminuted and made available by sieving in the grain size according to Table 1.

[0096] The fused raw material had the following elements in the proportions according to Table 2 below, each in relation to the total mass of the fused raw material:

TABLE-US-00002 TABLE 2 Element Mass fraction [% by mass] Aluminum 51.70 Oxygen 46.70 Carbon 0.79 Silicon 0.69 Nitrogen 0.12 Further <0.10

[0097] The mineralogical main phase of the fused raw material was corundum (Al.sub.2O.sub.3) in a proportion of more than 95.4% by mass and in addition the phases Al.sub.28C.sub.6N.sub.6O.sub.21 in a proportion of 2.0% by mass and SiC in a proportion of 1.6% by mass. Other phases, including metallic silicon and traces of Al.sub.4O.sub.4C, were present in a total mass of 1.0% by mass. The figures in % by mass are in each case based on the total mass of the fused raw material.

[0098] In the batch according to Table 1, the raw materials alumina and zircon mullite were present as further main raw materials in addition to the fused raw material according to the invention.

[0099] Graphite was present as the carbon component.

[0100] Metallic silicon and silicon carbide were present as antioxidants.

[0101] Synthetic resin (together with hexamethylenetetramine as hardener) was present in the batch as a coking binder.

[0102] The components of the batch according to Table 1 were intimately mixed in a mixer and then pressed in a press to form the green body of a slide gate plate.

[0103] This slide gate plate was an embodiment of an unfired plate according to the invention in the form of a slide ate plate.

[0104] The green body was then first tempered at 250 C., whereby the volatile components of the binder evaporated.

[0105] The tempered green body was then heated to 1,200 C. in a reducing atmosphere and kept at this temperature for a period of three hours in a reducing atmosphere. During this firing process, the carbon components of the graphite and the binder formed a carbon bond.

[0106] After cooling, an embodiment of a plate according to the invention was provided in the form of a fired, carbon-bonded refractory slide gate plate.

[0107] In order to be able to compare the properties of this exemplary embodiment of a fired slide gate plate according to the invention with the properties of a generic slide gate plate according to the state of the art, a generic fired slide gate plate was produced according to the state of the art. This state of the art slide gate plate was manufactured according to the above exemplary embodiment, but with the only difference that instead of the fused raw material according to the invention, fused alumina according to the state of the art was used.

[0108] The physical properties were then determined on both slide gate plates. Table 3 below shows the physical properties determined, whereby the slide gate plate according to the exemplary embodiment is designated E and the slide gate plate according to the state of the art is designated S.

TABLE-US-00003 TABLE 3 Physical value S E Thermal expansion coefficient [K.sup.1] 8.6 * 10.sup.6 8.8 * 10.sup.6 Modulus of elasticity [GPa] 58.4 62.5 Cold bending strength [MPa] 13 16.1 Hot bending strength [MPa] 11.1 15.1 Work at break [J/m.sup.2] 249 346 Notched tensile strength [MPa] 3.6 6.8 Thermal shock parameter R 7.2 12.5 according to Kingery [K] Thermal shock parameter R.sub.st 5.4 6.0 according to Hasselmann [K*m.sup.1/2]

[0109] The modulus of elasticity is the dynamic modulus of elasticity measured by sound travel time measurement at 1,400 C. under reducing conditions.

[0110] The hot bending strength was measured at 1,400 C. under reducing conditions.

[0111] The work at break is the work at break G.sub.f, which was also measured at 1,400 C. under reducing conditions.

[0112] The nominal notched tensile strength is the nominal notched tensile strength NT at 1,400 C. under reducing conditions.

[0113] The thermal shock parameters R according to Kingery and Rst according to Hasselmann were each calculated on the basis of parameters measured at 1,400 C. under reducing conditions.

[0114] All values were measured and determined according to the above-mentioned standards and literature.

[0115] As can be seen from Table 3, the slide gate plate according to the invention proved to be superior to the standard slide gate plate according to the state of the art with regard to practically all of these values (with the exception of the modulus of elasticity).

[0116] Furthermore, a slide gate plate according to the invention and a state of the art slide gate plate were manufactured according to the above example, but with the difference that both slide plates were soaked with pitch after firing. According to this, the embodiment of the fired slide gate plate according to the invention had a hot bending strength of 34.2 MPa and the fired slide gate plate according to the state of the art had a hot bending strength of 14.4 MPa.

[0117] To determine the corrosion resistance of the slide gate plates (not soaked with pitch), a so-called ITO test was also carried out. In this test, stone segments were cut from the slide gate plate E according to the inventions as well as from the slide gate plate S according to the state of the art and used as part of a furnace lining, on which a corrosion test according to the so-called induction crucible furnace test (ITO test) was carried out as follows: First of all, a furnace was constructed whose refractory lining was made of stone segments on the wall side. In the later slag area, the lining was partially formed from the aforementioned brick segments of slide gate plates E and S. The refractory lining enclosed a circular-cylindrical furnace chamber into which a matching circular-cylindrical metal insert (60 kg steel) was placed. The metal insert was heated to 1,600 C. and melted by coils which were guided in a ring around the outside of the lining. A slag powder (3 kg) with the chemical composition shown in Table 4 below (proportions indicated in relation to the total mass of the slag powder) was added to the molten steel, which melted and formed a slag area with a corrosive slag. The slag reacted in the slag area with the stone segments from the slide gate plates E and S and thereby corrosively damaged them. The stone segments were corroded by the slag for a total of about five hours, with the slag being renewed regularly. The lining was then removed and the degree of corrosion was tested on the stone segments, namely the wear surface.

TABLE-US-00004 TABLE 4 Component of the slag Mass fraction [% by mass] Al.sub.2O.sub.3 10.0 SiO.sub.2 10.1 Fe.sub.3O.sub.4 26.1 CaO 37.6 MnO 11.1 MgO 4.2 F 0.5 S 0.4

[0118] For the determination of the wear, the wear surface of the stone segments from the slide gate plate S was normalized to 100% according to the state of the art and set in relation to the corresponding value for the stone segments from the slide gate plate E according to the invention. The wear surface is the maximum cross-sectional area of the corroded areas of the stone segments. According to this, the wear of the stone segments of the slide gate plate E according to the invention amounted to an average of only 82% of the wear surface of the stone segments from the slide gate plate S according to the state of the art.