FR2474481A1 - REFRACTORY CERAMIC MIXTURE - Google Patents

Abstract

THE INVENTION CONCERNS A REFRACTORY CERAMIC MIXTURE BASED ON ALUMINUM OXIDE, ZIRCONIUM OXIDE OR SILICON OXIDE, ADDED WITH CARBON AND BINDERS FOR THE MANUFACTURE OF SUBMERSIBLE CASTING BUSHES OR OTHER MOLDED PARTS. TO COME IN CONTACT WITH LIQUID STEEL. THIS MIXTURE CONTAINS 5 TO 15 BY WEIGHT OF METAL CALCIUM-SILICON AND OR METAL FERROSILICON AND OR BORON NITRIDE. APPLICATION IN PARTICULAR TO THE CONTINUOUS CASTING OF STEEL.

Description

The present invention relates to a refractory ceramic mixture.

  In the production of steel deoxidized by aluminum

  After the deoxidation and alloying of the crude steel, a formation of alumina, which constitutes the oxidized solid phase in the liquid steel, is observed. In the continuous casting operations of the steel, a pouring nozzle immersed in refractory material is used between the distributor and the molds. As the steel travels through this submerged slurry nozzle, part of the alumina contained in the molten steel is deposited on

  this nozzle. Large conglomerates are being formed.

  which are torn from time to time by the steel stream and are included in the steel at the time of solidification of the latter. The submerged casting nozzles of the prior art are composed of a refractory mixture, itself composed of one or more refractory oxides (A12O3, SiO2, ZrO2 inter alia), carbon (graphite, coke, soot) and a binder. This composition is not appropriate for objecting to

  of alumina particles that separate from the steel.

  The aim of the invention is to provide a refractory ceramic mixture for the production of submerged casting nozzles or other molded parts which come into contact with the liquid steel and which is capable of preventing the oxidized suspensions present in the molten steel and which tend to agglomerate, in particular

  alumina, to deposit on the inner surface of the bus-

  casting or other molded parts that come into contact with the liquid steel. The invention proposes for the resolution of this problem a refractory ceramic mixture based on aluminum oxide or zirconium oxide or silicon oxide, with added carbon and binders, for the manufacture of submerged casting nozzles or other molded parts which come into contact with the liquid steel, characterized in that it contains 5 to 15% by weight of calcium-silicon metal -2- and / or ferro-silicon metal and / or nitride of

  boron. The advantage of the refractory mixture according to the invention

  This is because the solid oxidized suspensions present in the steel (for example alumina) undergo a lowering of the melting point in the phase transition between the liquid steel and the refractory, in contact with the refractory wall or parts of this refractory wall. This lowering of the melting point results in the primary solid alumina particle (about 1 to 30 microns in diameter) becoming liquefied after coming into contact with the refractory wall, and

  this fact, does not adhere to this wall.

  The subtance that is part of the refractory part and that acts on the suspension forms with this suspension

  an oxidized melt, that is to say that the fuse point

  slag is below the service temperature.

vice of steel.

  In the examples given below, mention is made of several possible embodiments of the mixture

refractory according to the invention.

Example 1

  A mixture having the following composition is made at 70% by weight, preferably 60% by weight of 15% corundum, preferably from 10% by weight of calcium to 15%, preferably from 25% by weight of graphite to preferably 5% by weight of binder.

  Calcium and silicon metal or calcium

  silicon present in the alloy form contained in this mixture are metallically stable. This stable state is achieved on the one hand, by the temperature of the refractory mixture which is relatively low compared to the temperature of the steel and on the other hand by the

  reducing conditions and the presence of carbon.

  These reducing conditions are transformed into oxidizing conditions at the phase boundaries (mixture

  refractory-air; refractory mixture-steel Iiqmaide}.

  On the one hand, at the air-refractory phase boundary, after the progressive combustion of the carbon, the metal component oxidizes and forms an oxidized mixed phase by combining with the base mixture. This mixed phase certainly undergoes a lowering of the melting point but does not undergo any eroding force, so that no erosion occurs and therefore no wear. At the limit of the refractory-liquid steel phase, after the combustion of carbon, there is a beginning of oxidation of the metallic constituent (calcium, silicon, calcium-silicon) with

steel deoxidized by aluminum.

  This oxidation can occur since, in steel deoxidized by aluminum, calcium still has a deoxidizing action. The mixed oxide of calcium and silicon that is formed acts on the alumina at the phase transition, lowering its melting point and leads to the formation of a liquid mixed oxide at the

phase limit (slag film).

  This slag film is entrained in the bath of the mold because of the eroding action of the liquid steel stream. Here, the slag comes under a

  spheroidal shape and dissociates from steel.

  This process according to the invention leads to deliberate internal wear of the refractory wall and prevents the alumina from being deposited on this wall. The thickness of the wall, as well as the composition of the refractory mixture

  must be related to the casting time envisaged.

  EXAMPLE 2 The following composition is produced: at 70%, preferably 60% of corundum at 15%, preferably at least 10% of boron nitride at 30%, preferably 25% of graphite.

  5 to 15%, preferably 5% binder.

  In this example, boron nitride BN is used which, under oxidizing conditions, is not stable and forms B203. Boron nitride is a fluidifier of alumina (which is present in suspension in steel) and has an effect similar to that which has been described in

Example 1

-4-

Example 3

  The mixture has the following composition: at 70, preferably 60 °; zirconium oxide at 30c, preferably 25%, graphite 5 to 15, preferably ferrosilicon, preferably 5c, binder. Erosion produced in the slag region is combated by the use of this mixing composition

  already known refractory which contains zirconium oxide

minium.

Example 4

  This mixture has the same composition as that of the

  except that the corundum has been replaced by siliceous glass. 40 to 70%, preferably 60,% of 15% silica glass, preferably 10% calcium-silicon at 30%, preferably 25%, 15% graphite, preferably 5% of binder.

Example 5

  This mixture has the same composition as that of the

  2, except that the corundum has been replaced by siliceous glass. at 70% preferably 60% of 15% silica glass, preferably 15% boron nitride 15 to 30%, preferably 25% graphite to 15%, preferably 5% binder.

Example 6

  A mixture similar to that of the example is prepared

  2) but which also contains ferro-silicon.

  40 to 70%, preferably 60% corundum at 15%, preferably 5% calcium-silicon at 15c, preferably 5% boron nitride at 15%, preferably 30% ferro-silicon, preferably 20% graphite

  5 to 15, preferably 5, binder.

k474481 -5--

REVEADICATION

  Refractory ceramic mixture based on aluminum oxide

  zirconium dioxide or silicon oxide, with added carbon and binders for the manufacture of submerged casting nozzles or other molded parts intended to come into contact with the molten steel, this mixture being characterized in that It contains 5 to 15% by weight of calcium-silicon metal and / or

  ferrosilicon metal and / or boron nitride.