FR2488165A1 - SUBMERSIBLE BUSH FOR CONTINUOUS CASTING OF MOLTEN STEEL - Google Patents

Abstract

THE INVENTION CONCERNS CONTINUOUS CASTING STEEL BUSHES. IT RELATES TO A BUSETTE HAVING A REFRACTORY LAYER 11 CONTAINING 10.5 TO 26.5 BY WEIGHT OF CARBON, 70.0 TO 86.0 BY WEIGHT OF ZIRCONIA AND 0.5 TO 15.0 BY WEIGHT OF SILICON AND FERROSILICON AND 3 OF IMPURITIES AT THE MAXIMUM. ITS BODY IS SHAPED AS A REFRACTORY BASED ON ALUMINA-GRAPHITE. APPLICATION TO THE CONTINUOUS CASTING OF STEEL.

Description

The present invention relates to a nozzle

  mergée which can be used for a long time, fixed as a substantially vertical extension of the bottom of a molten steel pouring basket transmitted to it by a pocket, in a mold, during the casting

continuous molten steel.

  A molding powder and a submerged nozzle are commonly used in the continuous casting of the molten steel. For example, a molding powder containing 46% by weight of SiO 2, 6.08% by weight of Al 2 O 3, 36.87% by weight of CaO is added to the mold of the molten steel meniscus in a mold. 8.05% by weight of Na2O, with impurities and a loss on ignition of 5.33% by weight. The

  molding powder melts and goes into the vitreous state when

  that it is heated by molten steel and covers the meniscus of molten steel; simultaneously she enters

  in the spaces formed between the sides of solid steel

  and the inner walls of the mold and covers the surface of a cast bar. Molten steel and the bar

  are thus isolated from the air and protected against oxidation.

  dation. In addition, the layer of molten molding powder absorbs non-metallic inclusions that float

on the meniscus of molten steel.

  On the other hand, a submerged nozzle is fixed as a substantially vertical extension of the bottom of a tundish and its lower part is immersed in the molten steel placed in the mold, through

  the entire aforementioned layer of molten molding powder.

  The molten steel of the tundish goes down into the nozzle and is poured into the mold without being exposed to

  air, except during the beginning of the casting.

  The use of a submerged nozzle and a molding powder thus makes it possible to effectively avoid disadvantages such as the oxidation of molten steel in

  the ingot mold and the cast bar extracted from the

  the emergence of turbulence in molten steel, the trapping of air, molding powder and slag, and molten steel splashing as well as the bar

  casting is very healthy, has excellent quality of

  face as well as a very good internal quality.

  It is known that refractories based on amorphous silica, zirconia graphite and alumina graphite are materials allowing the formation of submerged nozzle of the aforementioned type, and such a nozzle is manufactured by

  putting any of these refractories into a configu-

  as shown, for example, on the

  Figure 1, before cooking for the formation of a body. In this FIG. 1, the reference 1 designates the body of the nozzle, the reference 2 a collar, the reference 3

  a hole or bore and the reference 4 an outlet channel.

  The molten steel which is in a tundish is poured into an ingot mold by the neck 2, the hole 3 and the outlet channel 4 of the nozzle. This, through the hole 3 in which molten steel at high temperature flows, is exposed to a considerable change in temperature and

  to a significant thermal shock especially at the beginning of the

  and, in addition, the hole 3 is eroded by the molten steel. In addition, the portion of the outer surface of the body 1 which is in contact with the layer of molten molding powder is more seriously eroded by the molten steel and the molten molding powder. Given the recent trend to use larger continuous casting facilities, the molten steel of more than five pocket loads

  is often spilled continuously during casting.

  A submerged nozzle must therefore have various properties that give it the necessary resistance to

  severe conditions of use above. Among these

  properties, which have the greatest effect on the service life and should therefore be present, are the peel strength during the early casting of molten steel, the resistance to erosion by molten steel and erosion resistance by melted casting powder. A nozzle that does not have these three properties simultaneously can not withstand continuous casting of molten steel for more than five charges.

pocket in a mold.

  However, all the aforementioned refractories based on amorphous silica, zirconia-graphite and alumina-graphite have advantages and disadvantages, and the manufacture of a submerged nozzle that can withstand the aforementioned severe conditions of use and formed of a single type of refractory chosen from among those who are

  cited, is very difficult. More specifically, refraction

  amorphous silica has a very low dilatation

  thermal resistance and a relatively satisfactory resistance

  erosion by melting powder,

  between 2 and 3 mm per continuous casting cycle of molten steel from a pocket charge. However, the refractory based on amorphous silica is, on the contrary, susceptible to peeling, given the transformation of the silica

  amorphous in use for a long time

  riode, and has a relatively low resistance to erosion

  molten steel, especially when it contains much

  shot of manganese. Refractory made from zirconia-gra-

  phite is resistant to erosion by molten steel

  satisfactory, while resistance to erosion

  melting powder causes problems.

  The refractory based on alumina-graphite has a good resistance to erosion by molten steel. Refractories based on zirconia-graphite and alumina-graphite, both containing graphite, have a thermal conductivity

  high and can therefore withstand the im-

  bearing and significant thermal shocks

  tives. On the other hand, the structure becomes porous by oxidation and / or dissolution of the graphite in the molten steel, and the erosion is caused by the molten steel and the molten molding powder which penetrate into parts.

  by becoming so porous, this constitutes a disadvantage

deny common to these refractory.

  It has already been proposed submerged nozzles

2488 165

  to solve the above problems and to improve

  resistance to erosion by molten steel and the resistance

  erosion by a molten molding powder, which

must have such a nozzle.

  The published Japanese patent application

  No 28 568/74 of 27 July 1974 describes an im-

  mergée for continuous casting, having, in section, the configuration schematically shown in Figure 2 of the accompanying drawings, this nozzle comprising a refractory layer resistant to erosion, formed of a material such as a refractory based on zirconia, disposed on at least the inner surface 8 of a hole 6 and an outlet channel 7 of a nozzle body 5 essentially formed of amorphous silica, the outer portion 9 of the body 5 of the nozzle in contact with a layer of molten molding powder at the inner and outer surfaces of the

  body 5, and the refractories based on zirconia, silica

  zirconia, zirconia-mullite, mullite and chromium oxide are suitable for the formation of this refractory having a high resistance to erosion, this nozzle being called "first known nozzle" in the sequel

of this memoir.

  In this first known nozzle, the body 5

  is essentially formed of amorphous silica. This man

  has a very low coefficient of thermal expansion and erosion resistance by the molten molding powder which is relatively satisfactory as indicated above, but it has a relatively high resistance

  weak to erosion by molten steel.

  In addition, in this first known nozzle, zirconia ZrO 2 which constitutes the main material of

  the refractory layer or refractory layers

  the surface portion marked 8 in the hole 6 of the body 5 and / or the surface portion 9 of the outside of the body 5 has excellent erosion resistance by the melted molding powder. However, during firing, there is a considerable difference between the thermal expansion coefficients of the layers

  refractory 8 and / or 9 having a high thermal expansion

  and the body 5 of the nozzle formed of amorphous silica with a very low coefficient of thermal expansion, so that a flaking may appear both in the body and in parts 8 and / or 9. Obtaining a bu

  submerged sink having no defect is therefore difficult.

  The first known submerged nozzle can therefore

  withstand the harsh conditions of use

  corresponding to a continuous casting of molten steel

  for more than five charges of a pocket.

  Japanese Patent Application Laid-open No. 46,522 / 73 of July 3, 1973 discloses a known second submerged nozzle for continuous casting. According to this patent application, a refractory layer having excellent erosion resistance by the molten molding powder is placed over the entire surface of the nozzle body formed of a refractory having excellent erosion resistance by the melted steel, or on its outer part, in contact with a layer of molten molding powder, so that it is at the outer face of the nozzle body or that it forms a projection on the surface

  external of this body; a refractory based on alumina

  graphite is suitable as a material having an excellent

  resistance to erosion by molten steel, and refraction

  The amorphous silica base is suitable as a material having excellent erosion resistance by melted molding powder. This nozzle is called

  "second nozzle known" in the remainder of this memoir.

  In the second known nozzle, the body of the nozzle is formed essentially of alumina-graphite, as according to the invention described hereinafter. The refractory based on alumina-graphite, as indicated previously, has excellent resistance

erosion by molten steel.

  In addition, in the second known nozzle, the main material of the refractory layer placed on the outer part of the body is amorphous silica. As described previously, amorphous silica has a resistance

  erosion by the melted powder which is

  satisfactory, with poor resistance to erosion by molten steel. In addition, the amorphous silica may exhibit chipping due to its transformation

  in use for a long time.

  Thus, the second known submerged nozzle obtains

  Naked by provision of a refractory layer of amorphous silica of low resistance to erosion by the molten steel to the outer part of the body which is in contact with the layer of molten molding powder poses problems of erosion resistance by the molten steel, and the continuous casting of molten steel of more than five charges of one pocket

  is difficult with such a bûsette.

  The invention relates to a submerged nozzle which,

  during the continuous casting of molten steel, can withstand

  ter to a continuous casting of molten steel for a long time

  duration, corresponding to more than five charges of a pocket.

  The invention thus relates to a submerged nozzle, the outer portion of which is in contact with a layer of molten molding powder on the meniscus of steel.

  melted placed in an ingot mold, during the continuous casting

  bare of molten steel, presents an excellent resistance to erosion not only by the molten steel but especially

by the melted molding powder.

  The invention also relates to a submerged nozzle which can withstand for a long period of use during the continuous casting of a highly oxidizing molten steel,

  for example a weakly deoxidized steel. -

  According to a characteristic of the invention, a

  immersed nozzle for continuous casting of molten steel

  door: - a nozzle body formed of a refractory based on alumina graphite and a refractory layer having excellent resistance to erosion by the molten molding powder, this refractory layer being arranged so that it is integral with the body the nozzle

  and at the outer surface of this body to the

  outer portion thereof which is in contact with a layer of molten molding powder placed on the meniscus of the molten steel when the lower portion of the nozzle is immersed in the molten steel placed in the mold, the submerged nozzle being such that the refractory layer placed on the outer part of the body of the

  nozzle essentially contains weighted percentages

  Roles: carbon C 10.5 to 26.5% zirconia ZrO2 70.0 to 86.0% at least one ingredient selected from the group consisting of 0.5 to 15.0% silicon Si and ferrosilicon Fe-Si impurities 3% maximum

  Other features and advantages of the

  will be better understood when reading the description of

  FIG. 3 is a diagrammatic section of the immersed continuous casting nozzle. FIGS.

  of molten steel produced according to the invention.

  The invention relates to the realization, obtained after very thorough studies, of a submerged nozzle capable of withstanding the continuous casting of molten steel for a long period of use, exceeding five

  loads of a pocket. More specifically, the nozzle

  mergée capable of withstanding the continuous casting of molten steel of more than five charges of a pocket is carried out by forming a refractory nozzle body made of alumina-graphite and by arrangement, in the outside part of the body which, when the nozzle is immersed in the molten steel, is in contact with a layer of molten molding powder placed on the meniscus of the molten steel, a refractory layer containing essentially, in percentages by weight: C 10.5 carbon at 26.5% ZrO 2 zirconia 70.0 at 86.0% at least one ingredient selected from silicon Si and 0.5 to 15.0% ferrosilicon Fe-Si impurities up to 3% so that it is integral with body of the nozzle and at

  level of the outer surface of this body.

  Figure 3 is a schematic sectional view of a submerged nozzle embodiment used for the continuous casting of molten steel, according to the invention. On the face

  3, reference numeral 10 denotes a nozzle body, the reference

  11 a refractory layer placed on the

  external body 10, in contact with a layer 14 of powder -

  of molten casting placed on the meniscus of molten steel 13 in a mold 12, the reference 15 designates a neck of the body 10, the reference 16 a longitudinal hole of the body

  and the reference 17 an outlet channel of the hole 16.

  The molten steel which is in a not shown tundish, is poured into the mold 12 by the neck, the hole 16 and the outlet channel 17, the flow of

  the molten steel being adjusted by a not shown distaff

  sented. The body 10 of the nozzle may be formed of an alumina-graphite refractory having a composition

  known chemical or preferably an aluminum refractory

  mine-graphite having, for example, any of the following chemical compositions: 48.0 to 51.0% by weight of alumina, 19.0 to 21.0% by weight of carbon and 28.0 to 31.0% by weight of other ingredients, or 44.0 to 48.0% by weight of alumina, 25.0 to 28.0% by weight

  carbon weight, and 26.0 to 29.0% by weight of other

  grédients. A refractory based on alumina-graphite pre-

  It has excellent erosion resistance from molten steel and has high thermal conductivity since it contains carbon. Consequently, the hole 16, the outlet channel 17 and the part of the body 10 which is immersed in the molten steel, formed of alumina graphite refractory, are less susceptible to erosion by

  melted steel by being exposed to changes in temperature

  erosion and thermal shocks reduced during the early casting of the molten steel and being protected against chipping.

  The reasons for the chemical composition

  FIG. 1 shows the refractory layer 11 placed outside the nozzle body 10 at the location of the intended contact with the molten molding powder layer 14 as previously described and limited as indicated. (1) Carbon C.

  Carbon C not only increases

  Maintain the thermal conductivity but also reduce the thermal expansion of a refractory. In addition, the

  carbon has the effect of increasing resistance to scale

  age and resistance to wetting by the molten steel of a refractory. However, when the carbon content is less than 10.5% by weight, an advantageous effect as described above can not be obtained. Content

  carbon must therefore be at least 10.5% by weight.

  On the other hand, when this content exceeds 26.5% by weight, the carbon partially oxidizes and dissolves in the molten steel so that the refractory becomes porous. Molten steel and molten casting powder that penetrate into

  parts of the refractory thus become porous

  mention an erosion of zirconia as described later in this memoir. The carbon content should not exceed 26.5% by weight. Carbon can be

  in the form of graphite or amorphous carbon.

(2) ZrO 2 zirconia.

  ZrO2 zirconia is added so that it can

  erosion by molten molding powder as it has excellent erosion resistance by molten molding powder. However, when the zirconia content is less than 70.0% by weight, the desired erosion resistance can not be achieved by the melt molding powder. The zirconia content must therefore be at least 70.0% by weight. On the other hand, given the high thermal expansion of zirconia,

  a zirconia content of greater than 86.0% by weight

  to chipping at the beginning of molten steel casting. The zirconia content should not exceed 86.0% by weight. We can use zirconia

stabilized or not.

  (3) Si silicon and ferrosilicon Fe-Si.

  As mentioned above, carbon has

  to oxidize and dissolve in molten steel. Silicon Si and / or ferrosilicon Fe-Si are added in order to

  to compensate for this inconvenience. More specifically, the silicone

  Cium and / or ferrosilicon oxidize or carbonize to form silica or silicon carbide prior to carbon oxidation. As a result, the tendency of the refractory to become porous under the action of carbon oxidation or by dissolving the carbon in the molten steel can be reduced. However, when the content of silicon and / or ferrosilicon is less than 0.5% by

  weight, one can not obtain the aforementioned advantageous effect.

  Accordingly, the silicon and / or ferrosilicon content should be at least 0.5% by weight. On the other hand, when this silicon and / or ferrosilicon content exceeds 15,0%

  by weight, the above-mentioned content of zirconia is

  reduced so that we can not get the

  resistance to erosion by the molding powder

  due. Consequently, the silicon and / or ferrosilicon content

  licium should not exceed 15.0% by weight.

  We can make a submerged nozzle capable

  to withstand a continuous casting for a period of

  particularly long, exceeding five charges of a ladle of molten steel, during the continuous casting of molten steel

  highly oxidizing agent such as weakly deoxidized steel, by ad-

  addition to the refractory layer 11 of the composition

  aforementioned chemical composition, silicon carbide SiC and / or amorphous silica SiO2 in an amount of between 0.5 and

  8.0% by weight. The reasons are as follows. At the in-

  the ingot mold, the molten steel and the powder of

  molding close to the interface of highly oxidized molten steel

  such as weakly deoxidized steel, and a molding powder have a very high oxidizing activity. As a result, the outer surface of the submerged nozzle which is in contact with the molten steel and the molding powder near the interface of the molten steel and this powder, tends to erode easily. However, the addition of silicon carbide to the refractory layer 11 causes a combination of oxygen and silicon carbide in which the oxygen is contained in the molten steel and the molding powder near the interface, and the silicon carbide is contained in the refractory layer 11, so that the erosion resistance of this layer 11 is

  improved by inhibition of oxidation or dissolu-

  carbon content in this layer 11.

  On the other hand, given the high viscosity of the amorphous silica, the addition of amorphous silica to this refractory layer 11 makes it possible to prevent the entry of oxygen contained in the molten steel and the molding powder near the interface inside the refractory layer 11 and thus improves the erosion resistance of this

  11. It is therefore possible to obtain a submerged nozzle

  able to withstand the continuous casting of highly oxidizing molten steel, such as weakly deoxidized steel, for a long period of use, by addition in addition, in a necessary quantity, of silicon carbide and / or

  amorphous silica to the refractory layer 11.

  However, the desired effect mentioned above can not be obtained when the silicon carbide content and / or

  amorphous silica is less than 0.5% by weight. As a result

  The content of silicon carbide and / or amorphous silica should be at least 0.5% by weight. On the other hand, when the content of silicon carbide and / or amorphous silica exceeds 8.0% by weight, the refractory nature of the layer 11 decreases and thus adversely affects the erosion resistance of this refractory layer 11. Consequently, the content of silicon carbide and / or amorphous silica

  must be at most 8.0% by weight.

  In the case where the body of the nozzle has a thickness of between 20 and 25 mm, a thickness of 15 mm is sufficient for the refractory layer having the aforementioned chemical composition, placed at the outer part of the body of the nozzle which is in contact of the layer of

melted molding powder.

  The nozzle is now described in more detail

  immersed according to the invention with reference to examples.

EXAMPLE 1

  A conventional refractory is used.

  of alumina-graphite as a material for the body 10 of the

  nozzle shown in FIG. 3. A refractor is used.

  with the following composition graphite 15% by weight unstabilized zirconia 75% by weight silicon 10% by weight mixed with pitch and tar constituting binders, as material for refractory layer 11 placed at

  external part of the body 10 which is intended to be

  tact of the layer 14 of molten molding powder. These refractories are shaped by the conventional method of pressing in a mold of rubber and are then baked,

  as shown in FIG. 3, an impregnated nozzle is prepared

  medium having a thickness of 30 mm (the refractory layer II having a thickness of 15 mm), in which a refractory layer 11 having excellent resistance to erosion by the molten molding powder is incorporated in the external part of the body 10, in contact with the layer

14 of molten molding powder.

  A steel cadmium aluminum is then continuously poured, in two bars, at the rate of six charges of a pocket of 250 tons, with the immersed nozzle thus prepared. The refractory layer of the present nozzle

  on the one hand erosion which is only 10 mm maximum.

  By way of comparison, it is also possible to flow continuously in two bars, with the aid of a conventional immersed nozzle (having a thickness of 30 mm) of the type represented in FIG. 1, formed of a single type of refractory based on alumina-graphite, a steel cadmium aluminum, in the form of three loads of a pocket of 250 tons. The outer part of the classic nozzle, which is in contact with the layer of molding powder

  melted, presents on the side a serious erosion

  up to 25 mm and we can not continue

continuous casting.

EXAMPLE 2

  We prepare a nozzle immersed in the same

  conditions than in Example 1, having the same construction

  than the nozzle of Example 1, but formed of a

  fracture containing the following ingredients: graphite 10% by weight ferrosilicon 5% by weight zirconia stabilized with MgO 85% by weight mixed with a phenolic resin constituting a binder, this material forming the refractory layer 11 disposed in the part of the body 10 of the nozzle which is intended to be in contact with the layer 14 of molten molding powder. Then, a steel and cadmium cadmium steel is continuously cast into a bar at the rate of eight charges of a 100 ton bag, using the immersed nozzle thus prepared. The refractory layer 11 of the nozzle has an erosion on the side of 16 mm maximum, allowing convenient use .; For comparison, on the other hand, we perform a

  continuous casting into a bar of steel cadmium-plated

  and silicon, at the rate of three charges of a 100-ton bag, using a conventional submerged nozzle formed of a single type of refractory based on alumina-graphite, as described in Example 1 . The

  Classic submerged nozzle splits by fusion.

EXAMPLE 3

  A submerged nozzle (having a thickness of 35 mm, the refractory layer 11 having a thickness of 20 mm) is prepared under the same conditions as in example 1, with the same construction as the nozzle

  of Example 1, but the refractory contains the ingredients

  alloys: graphite 20.0% by weight zirconia stabilized by 50.0% by weight yttrium oxide zirconia unstabilized-25.0% by weight silicon 1.0% by weight silicon carbide 4.0% by weight mixed with a coal tar constituting a binder, and this material is used for the formation of the refractory layer disposed in the part of the body 10 of the nozzle intended to be in contact with the layer 14 of

melted molding powder.

  Two low-deoxidized steel is then continuously poured in two bars at the rate of five charges of a 300-ton bag, using the immersed nozzle thus prepared. The refractory layer 11 of the nozzle has on one side an erosion of only 1 mm only. As a comparison, on the other hand, a low deoxidized steel is continuously cast in two bars at the rate of two charges of a pocket of 300 tonnes, using a conventional immersed nozzle formed of a single

  type of alumina-graphite refractory, of the type

  Figure 1. The outer part of the classic submerged nozzle which is in contact with the powder of

  melted cast, presents on the side an erosion

  up to 27 mm, so we can not continue

the casting continues.

EXAMPLE 4

  A submerged nozzle (having a thickness of 30 mm, the refractory layer 11 having a thickness of 20 mm) is prepared under the same conditions as in Example 1, this nozzle having the same construction as that of Example 1, set except the refractory which contains the following ingredients: graphite 12.0% by weight zirconia stabilized with MgO 35.0% by weight zirconia stabilized by CaO 25.0% by weight zirconia not stabilized 20.0% by weight silicon 3.0 % by weight amorphous silica 2.0% by weight silicon carbide 3.0% by weight mixed with coal tar forming a binder and this material is used for the formation of the refractory layer 11 disposed in the part of the body 10 intended to be in contact with the layer 14 of molten molding powder. A low deoxidized steel is then continuously poured in two bars at the rate of eight charges of a 340 ton bag, using the immersed nozzle thus prepared. The refractory layer 11 of the nozzle has on its side an erosion of only 16 mm

  maximum, allowing convenient use.

  According to the invention and as previously described in detail, it is possible to produce a submerged nozzle for continuous casting of molten steel capable of withstanding the casting of the molten steel of more than five charges of a pocket, with a duration of use. two to three times longer than that of a classic submerged nozzle, so

  presents useful industrial effects.

  Of course, various modifications may be made by those skilled in the art to the devices which have just been described as examples only.

  non-limiting without departing from the scope of the invention.

Claims (2)

  1. Submerged nozzle for casting   tinue of a molten steel, of the type which comprises:   a body (10) of a nozzle formed of a refraction   alumina-graphite base, having a refractory layer   having an excellent resistance to erosion by a molten molding powder, the refractory layer being arranged so that it is integral with the body of the nozzle and at the outer surface of this body in the external part of the body which is intended to be in contact with a layer of molten molding powder placed   on the meniscus of molten steel, when the inferior part   nozzle of the nozzle is immersed in the molten steel placed in a mold, said immersed nozzle being characterized in that the refractory layer (11) placed at the outer part of the nozzle body essentially contains, in C 10 carbon weight percentages, 5 to 26.5% zirconia ZrO2 70.0 to 86.0% at least one ingredient selected from the group consisting of 0.5 to 15.0% silicon Si and ferrosilicon Fe-Si impurities 3% maximum.   2. Nozzle according to claim 1, characterized   in that the refractory layer (11) further contains, in percentagesponderal, at least one ingredient selected from the group consisting of silicon carbide SiC and amorphous silica SiO2 in an amount between 0.5 and 8.0%.