JP5604900B2 - Immersion member for molten metal bath, molten metal plating apparatus, and method for producing molten metal plated steel sheet - Google Patents

Description

  The present invention relates to a dipping member for a molten metal bath, a method for producing a dipping member for a molten metal bath, a molten metal plating apparatus, and a method for producing a molten metal plated steel sheet.

As a method of obtaining a hot-dip plated steel sheet, the heat-annealed steel sheet is led to a molten metal plating bath such as zinc (Zn) or aluminum (Al) through a snout, the molten metal is plated on the steel sheet, and the steel sheet is passed through a pot roll. The method of pulling up and obtaining a plated steel plate continuously is widely used.
In the plating bath, dross (mainly FeZn ₇ , Fe ₂ Al ₅ ) is generated when iron eluted by dipping the steel plate reacts with the plating metal. The dross floats on the plating bath surface and adheres to the plated steel sheet, causing deterioration of the plating quality, adheres to the immersion member in the bath, causes clogging of piping and rotation failure, or in the bath It erodes the immersion member. Therefore, it is necessary to take measures to prevent dross from adhering to the plated steel sheet, and to periodically replace and maintain the immersion member in the bath.

For example, in Patent Document 1, foreign matter (dross) floating on the inner molten metal bath surface of a cylindrical snout used for maintaining an inert atmosphere is controlled for the flow rate of a metal pump used as a foreign matter removing device. Discloses a method for removing out of the snout.
However, since the pump function is impaired in a short period of time due to melting of the pump member and dross adhesion, the pump member must be replaced or maintained by pickling or the like frequently.

To deal with such a problem, for example, Patent Document 2 discloses a technique for extending the life of a pump member by applying a corrosion-resistant coating to the pump member.
However, in this method, the coating layer is peeled off or the dross is fixed, so that the replacement cycle cannot be sufficiently extended.

  In view of this, an immersion member for a molten metal bath made of a ceramic material to which dross does not easily adhere has been developed (see, for example, Patent Documents 3 and 4).

JP 2003-293107 A JP 2003-328990 A JP 2007-145642 A JP 2008-137844 A

  However, even if the immersion members described in Patent Documents 3 and 4 are used, it is not possible to prevent the dross from adhering to or eroding the immersion member in the bath for a long period of time. There is a demand for the development of a dipping member that further improves the adherability (hardness of dross adhesion to the dipping member) and the erosion resistance in molten metal (hardness of the dipping member to be eroded).

  The object of the present invention is to greatly improve the hard-to-reach property and the erosion resistance, while reducing the frequency of replacement of the immersion member due to foreign matter adhesion and erosion to the immersion member in the molten metal bath, that is, high quality, An object of the present invention is to provide an immersion member for a molten metal bath for producing a molten metal plated steel sheet having excellent appearance and a method for producing the immersion member. In addition, another object of the present invention is to provide a molten metal plating apparatus using the immersion member for the molten metal plating bath as a foreign matter removing apparatus and a method for manufacturing a molten metal plated steel sheet to be plated using the molten metal plating apparatus.

The present inventor made at least 20 mass% or more 70 mass% of silicon nitride (Si ₃ N ₄ ) excellent in heat resistance and impact resistance and boron nitride (BN) which is difficult to wet with molten metal based on the total mass of the ceramic composite material. The structure control and manufacturing method of silicon nitride (Si ₃ N ₄ ) -based ceramic composites blended in an amount of less than or equal to 5% were found, and both the dross refusal property and the erosion resistance in the molten metal bath were achieved.

This invention is made | formed based on such knowledge, The summary is shown below.
(1) An immersion member for a molten metal bath using a silicon nitride (Si ₃ N ₄ ) -based ceramic composite material containing at least 20% by mass to 70% by mass boron nitride (BN) based on the total mass of the ceramic composite material There,
Used for coating members or shaft sleeves on the roll surface of a snout, metal pump, gas lift pump, gas wiping nozzle, or pot roll or guide roll,
The boron nitride (B) in the structure of the silicon nitride (Si ₃ N ₄ ) -based ceramic composite material
N) exists as an aggregate having at least one of a flaky shape and a lamellar shape.
An immersion member for a molten metal bath, characterized in that

( 2 ) The boron nitride (BN) in the structure of the silicon nitride (Si ₃ N ₄ ) -based ceramic composite material has an average center-to-center distance of the boron nitride within twice the average particle diameter of the boron nitride. The immersion member for a molten metal bath according to ( 1 ), wherein the immersion member is dispersed as described above.

(3) said silicon nitride _(Si 3 _{N 4)} the boron nitride (BN) concentration in the tissues of the base ceramic composites, high as the surface layer compared to the inner layer of the silicon nitride _(Si 3 _{N 4)} based ceramic composite material (1) or ( 2 ), The immersion member for molten metal baths is characterized by forming a functionally gradient structure.

( 4 ) Aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), magnesium oxide (MgO), rare earth oxide (as a sintering aid in the silicon nitride (Si ₃ N ₄ ) based ceramic composite RE ₂ O ₃ : RE is a rare earth element), zirconium silicide (ZrSi ₂ ), and titanium silicide (TiSi 2), and contains aluminum oxide (Al
₂ O ₃ ), silicon oxide (SiO ₂ ), magnesium oxide (MgO) and rare earth oxide (RE)
₂ O ₃ ) content is 0.2% by mass or more and 5.0% by mass or less, respectively, and zirconium silicide (ZrSi ₂ ) and titanium silicide (TiSi ₂ ) content is 0.5% by mass or more and 5.
The immersion member for a molten metal bath according to any one of (1) to ( 3 ), characterized in that the content is 0% by mass or less.

( 5 ) In a molten metal plating apparatus in which a heat-annealed steel sheet is led into a molten metal bath via a snout, molten metal plating is applied to the steel sheet, and the steel sheet is pulled up via a pot roll to continuously produce a plated steel sheet. A molten metal plating apparatus, wherein the immersion member for a molten metal bath according to any one of (1) to ( 4 ) is applied to a device for removing foreign matter generated on the inner bath surface of the snout.

( 6 ) The apparatus for removing foreign matter includes a gas diffusion cylinder and a piping member, and the immersion member for the molten metal bath is applied to at least one of the gas diffusion cylinder and the piping member ( 5 ). The molten metal plating apparatus described in 1.

(7) (5) or the method of manufacturing a molten metal coated steel sheet, which comprises using a molten metal plating apparatus according to (6).

According to the present invention, silicon nitride (Si ₃ N ₄ ) excellent in heat resistance and impact resistance and boron nitride (BN) which is difficult to wet with molten metal are blended in the above-mentioned blending amounts. It is possible to obtain a dipping member for a molten metal bath having heat resistance and impact resistance necessary as a dipping member, and having excellent stagnation and erosion resistance. Then, the frequency of replacement of the immersion member due to adhesion or erosion of foreign matter on the immersion member in the molten metal bath is reduced, and stable and high quality, that is, excellent appearance, without frequently stopping the apparatus. A metal-plated steel sheet can be manufactured.

1 is a front sectional view of a molten metal plating apparatus according to an embodiment of the present invention. The figure which looked at the snout inner side bath surface in FIG. 1 from the direction which introduce | transduces a steel plate. Side surface sectional drawing of the molten metal plating apparatus in FIG. The principal part longitudinal cross-sectional view of the inner cylinder pipe of the gas lift pump in FIG. FIG. 5 is a plan sectional view of the gas diffusion cylinder of the inner tube in FIG. 4. The schematic of the component analysis result of the immersion member section concerning one embodiment of the present invention.

Below, the immersion member for molten metal bath which concerns on embodiment of this invention, the manufacturing method of the said immersion member, the molten metal plating apparatus, and the manufacturing method of a molten metal plating steel plate are demonstrated.
Examples of the immersion member for the molten metal bath include a snout, a pot roll, a guide roll, a metal pump, and a gas lift pump. This embodiment demonstrates the case where the immersion member for molten metal baths which concerns on this invention is applied with respect to the gas diffusion cylinder for releasing the gas provided to a gas lift pump. In addition, the immersion member for molten metal baths according to the present invention is not limited to the application mode described in the present embodiment. In addition, a piping member of a gas lift pump, a constituent member of a metal pump (for example, a piping member, a discharge port member, etc. ), A molten metal bath immersion portion of a snout, a gas wiping nozzle, a pot roll and a guide roll (for example, a roll surface covering member, a bearing member, a shaft sleeve, etc.).

FIG. 1 is a front sectional view of a molten metal plating apparatus 1 of the present invention.
The heat-annealed steel plate 2 is immersed in a molten metal plating bath 4 as a molten metal bath from the snout 3 of the molten metal plating apparatus 1. The immersed steel plate 2 is pulled up by a pot roll 5 and a guide roll 6. Thereafter, the amount of plating attached to the steel plate 2 is adjusted by a gas wiping nozzle (not shown).
On the bath surface of the molten metal plating bath 4, dross D as a foreign matter is generated when iron eluted by dipping the steel plate reacts with the plating metal. The dross D is mainly composed of FeZn ₇ and Fe ₂ Al ₅ . Dross D also floats on the inner bath surface of the snout 3 in which the steel plate 2 is immersed. Therefore, dross D adheres to the steel plate 2 and causes the plating quality to deteriorate.
In order to discharge dross D from the inner bath surface of the snout 3 to the outer bath surface of the snout 3, the molten metal plating apparatus 1 is provided with a metal pump (see FIG. 2 or FIG. 3) and a gas lift pump 7 as a foreign matter removing device. Has been.

FIG. 2 is a view when the inner bath surface of the snout 3 is viewed in the direction in which the steel plate 2 is introduced. In FIG. 2, details of the outer portion of the snout 3 are omitted.
As shown in FIG. 2, the discharge port 81 of the metal pump 8 (two discharge ports are provided in the present embodiment) and the suction port 71 of the gas lift pump 7 are connected to the steel plate 2 on the inner bath surface of the snout 3. The molten metal plating apparatus 1 is provided in the vicinity of both ends in the width direction so as to face each other. The molten plating solution from the discharge port 81 of the metal pump 8 to the suction port 71 of the gas lift pump 7 flows in the direction of the arrow shown in FIG.

FIG. 3 is a side sectional view of the molten metal plating apparatus 1.
The metal pump 8 is provided with the discharge port 81 and the suction port 83 for sucking the molten plating solution from the outer bath surface of the snout 3 with respect to the main body tube 82 having a substantially U-shaped cross section. Yes. The molten plating solution sucked from the suction port 83 of the metal pump 8 is discharged from the two discharge ports 81 arranged on the inner bath surface of the snout 3, and the dross D is moved to the suction port 71 of the gas lift pump 7 (FIG. 2). reference). Two discharge ports 81 are provided to move the dross D floating on the front side and the back side of the steel plate 2 (see FIG. 2).

  The gas lift pump 7 is provided with the suction port 71 on the inner liquid surface side of the snout 3 with respect to the outer cylinder tube 72 having a substantially U-shaped cross section, and the melted inhaled on the outer bath surface of the snout 3. A discharge port 73 for discharging the plating solution and dross D to the outer bath surface of the snout 3 is provided.

An inner tube 74 is inserted into the outer tube 72 from the discharge port 73 side of the gas lift pump 7. The inner cylinder pipe 74 includes a gas introduction pipe 741 for introducing gas, a gas diffusion cylinder 742 for discharging the introduced gas, and a connector 743 for connecting the gas introduction pipe 741 and the gas diffusion cylinder 742. It is configured.
One end of the inner tube 74 (the lower end side of the gas diffusion cylinder 742) is inserted so as to reach the upper side of the bottom (substantially U-shaped curved portion) of the outer tube 72.
The other end (not shown) of the inner cylinder pipe 74 (the upper end side of the gas introduction pipe 741) is connected to a gas introduction source (not shown). The type of gas introduced is, for example, nitrogen gas as an inert gas.

FIG. 4 is a longitudinal sectional view showing a main part of the inner cylinder pipe 74 of the gas lift pump.
A gas diffusion cylinder 742 as an immersion member for a molten metal bath is formed in a cylindrical shape with a closed bottom. A plurality of gas discharge holes 742A are formed in the gas diffusion cylinder 742 so as to penetrate in the horizontal direction. The gas discharge hole 742A is for releasing the gas introduced from the gas introduction pipe 741 into the gas diffusion cylinder 742 into the space formed by the gas diffusion cylinder 742 and the outer cylinder pipe 72 as a bubble B. It is.
Here, FIG. 5 is a plan sectional view of the gas diffusion cylinder 742. In this embodiment, three rows of gas discharge holes 742A are formed as shown in FIGS. Among these, two rows are formed with three gas discharge holes 742A arranged vertically, and one row is formed with four gas discharge holes 742A arranged vertically (see FIG. 4). The vertical positions of the gas discharge holes 742A are different between the three rows and the four rows of the gas discharge holes 742A, and the gas can be discharged uniformly. Further, as shown in FIG. 5, when the gas diffusion cylinder 742 is viewed in a plan sectional view, a line segment connecting the center of the gas diffusion cylinder 742 and the gas discharge holes 742A in each row forms an angle of about 120 °. . Note that the position, angle, number, size, and the like of the gas discharge hole 742A are not limited to those shown in this embodiment.

The gas lift pump 7 operates as follows. First, when gas is sent from the gas supply source to the gas introduction pipe 741, the gas is supplied from the lower end of the gas introduction pipe 741 into the gas diffusion cylinder 742. The gas supplied into the gas diffuser cylinder 742 passes through the gas discharge hole 742A and is discharged into a space formed by the gas diffuser cylinder 742 and the outer tube 72. Since the space formed by the outside of the gas diffusion cylinder 742 and the inside of the outer tube 72 is filled with the molten plating solution when the gas lift pump 7 is immersed in the molten plating solution, the gas is discharged from the gas discharge hole. It is discharged as bubbles B from 742A and becomes a mixed fluid together with the molten plating solution. At this time, since the bubbles B rise to try to be released into the atmosphere, a force that causes the mixed fluid to float inside the outer tube 72 works, and a flow in which the molten plating solution rises occurs. In this way, the operation of the gas lift pump 7 is obtained.
The operation of the metal pump 8 and the operation of the gas lift pump 7 are combined, and the dross D floating on the inner bath surface of the snout 3 can be efficiently moved to the outer bath surface of the snout 3.

As described above, the present embodiment applies the immersion member for the molten metal bath according to the present invention to the gas diffusion cylinder.
A plurality of gas discharge holes are formed in the gas diffusion cylinder, but dross easily adheres to the gas diffusion cylinder that has been conventionally used.
Conventionally used gas scattering cylinders are made of SUS (SUS316 or the like) or silicon nitride Si ₃ N ₄ ceramics. The gas dispersion cylinder made of SUS has a property that SUS and molten zinc react to form an alloy, and dross easily adheres to the alloyed portion. The gas diffusion cylinder made of silicon nitride ceramics does not cause alloying, but silicon in the ceramic component reacts with molten zinc to form a ZnSi ₂ film, and dross tends to adhere to this film part.
For this reason, the gas discharge holes of the gas diffusion cylinders that have been used in the past are also easily blocked by the dross. If the gas discharge hole is blocked, the operation of the gas lift pump 7 does not occur. Therefore, it has been necessary to frequently replace and maintain the gas diffusion cylinder.

Therefore, in this embodiment, boron nitride (BN) that is at least difficult to wet with molten metal is added to silicon nitride (Si ₃ N ₄ ) that is excellent in heat resistance and impact resistance, based on the total mass of the ceramic composite material. A silicon nitride (Si ₃ N ₄ ) -based ceramic composite material blended in an amount of mass% or less was molded and applied as a gas diffusion cylinder 742 as an immersion member for a molten metal bath.
The gas diffusion cylinder 742 has heat resistance and impact resistance required as an immersion member, and has a hard-to-reach property and an erosion resistance that are significantly improved as compared with conventional immersion members.
In a silicon nitride (Si ₃ N ₄ ) based ceramic composite, when boron nitride (BN) content is less than 20% by mass, dross easily adheres to the immersion member for the molten metal bath, It is insufficient. Moreover, when the compounding quantity of boron nitride (BN) exceeds 70 mass%, the compounding quantity of silicon nitride (Si ₃ N ₄ ) becomes less than 30 mass%, and the strength of the silicon nitride (Si ₃ N ₄ ) based ceramic composite material Since (heat resistance and impact resistance) is low, the strength as an immersion member for a molten metal bath is insufficient.
More preferably, if the blending amount of boron nitride (BN) is in the range of 30% by mass or more and 50% by mass or less, the mechanical properties such as thermal shock resistance do not change, but the dross susceptibility is long-term. Stabilize.

Further, the silicon nitride (Si ₃ N ₄ ) -based ceramic composite material can include a sintering aid added for the purpose of promoting and stabilizing the sintering during sintering. As sintering aids, oxide-based aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), magnesium oxide (MgO), rare earth oxide (RE ₂ O ₃ : RE is a rare earth element), silicide At least one of zirconium silicide (ZrSi ₂ ) and titanium silicide (TiSi ₂ ) can be added, and plural kinds of sintering aids can also be added. In this embodiment, aluminum oxide (Al ₂ O ₃ ) and yttrium oxide (Y ₂ O ₃ ) are added.
When aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), magnesium oxide (MgO), and rare earth oxide (RE ₂ O ₃ ) are added, the addition amounts are each 0.00% based on the total mass of the ceramic composite material. It is preferable to set it to 2 mass% or more and 5.0 mass% or less. This is because, by setting the addition amount range of such an oxide-based sintering aid, reaction hardly occurs in the molten metal, and sufficient strength (heat resistance and impact resistance) can be secured.
When adding zirconium silicide (ZrSi ₂ ) and titanium silicide (TiSi ₂ ), the addition amount is preferably 0.5% by mass or more and 5.0% by mass or less based on the total mass of the ceramic composite material. It is because it becomes difficult to form a reaction layer with a molten metal by setting it as the addition amount range of such a silicide type sintering aid.
Further, the total addition amount of the sintering aid is preferably 10% by mass or less. It is because heat resistance and corrosion resistance tend to be highly stable by setting the total addition amount range. Further, the ceramic composite material is more excellent by being blended in combination with the oxide-based sintering aid and the silicon compound-based sintering aid within the total addition amount range of the sintering aid. Strength and hard-to-reach property can be obtained.

Further, since the shape of boron nitride (BN) is spherical and difficult to manufacture, in this embodiment, boron nitride (BN) is a thin piece in the structure of a silicon nitride (Si ₃ N ₄ ) -based ceramic composite material. It exists as an aggregate having at least one of a shape and a layer shape. By being present as such an agglomerate, the dross hard-to-retain effect is more reliably imparted, and the strength imparting effect of silicon nitride (Si ₃ N ₄ ) is an agglomerate of boron nitride (BN). It will straddle widely between them, and the strength as an immersion member will be given more reliably.

In the present embodiment, in the structure of boron nitride (BN) -silicon nitride (Si ₃ N ₄ ) -based ceramics composite, boron nitride (BN) has an average distance between the centers of boron nitrides. The dispersion is controlled so as to be within twice the particle diameter.
Even if boron nitride is present as an aggregate in the structure, the dispersion makes it difficult to stay in a stable state. This is based on the reason that boron nitride (BN) has a high stagnation effect.

FIG. 6 is a schematic diagram of a component analysis result of the cross section of the immersion member in the present embodiment. The figure shows elemental analysis (target elements are boron, nitrogen, silicon, oxygen, zinc, and aluminum) using the mapping of the EDAX device for the cross section of the gas diffusion cylinder 742, and the site where boron is present is displayed darkly. The parts that are not to be displayed are displayed lightly. Since the component derived from the boron element in the silicon nitride (Si ₃ N ₄ ) -based ceramic composite material constituting the gas diffusion cylinder 742 is boron nitride (BN), the distribution of the boron element is represented by boron nitride (BN). It can be considered as an existence distribution. On the other hand, it can be considered that silicon nitride (Si ₃ N ₄ ) is mainly present in a portion where boron nitride (BN) does not exist.
Then, in this embodiment, as shown in FIG. 6, in the structure of the silicon nitride (Si ₃ N ₄ ) based ceramic composite, boron nitride (BN) is silicon nitride (Si ₃ N ₄ ) based ceramic. A functionally graded structure is formed in which the boron nitride (BN) concentration is higher in the surface layer than in the inner layer of the composite material.
In this way, since boron nitride (BN) is more present in the surface layer, dross adhesion to the outer surface of the gas diffusion cylinder 742 is further less likely to occur. In the case of the gas diffusion cylinder 742, since the dross contacts the outer surface, if the boron nitride (BN) concentration is increased only on the surface side, silicon nitride (Si ₃ ) is formed on the inner surface in contact with the nitrogen gas (inert gas). Even with a functionally gradient structure in which only N ₄ ) exists, dross adhesion can be prevented.
The observation sample for the immersion member cross-sectional analysis was prepared as follows. The immersion member was embedded and fixed in a resin, the immersion member fixed in the resin was cut to expose a cross section of the immersion member, and the cross section was polished to obtain an observation sample. The polished surface becomes the cross section of the analysis target. The surface oxygen in FIG. 6 is derived from oxygen based on the resin used for fixing the immersion member.

Next, a method for manufacturing the gas diffusion cylinder 742 as the immersion member for the molten metal bath according to the present embodiment will be described.
First, a predetermined amount of silicon nitride (Si ₃ N ₄ ) powder, boron nitride (BN) and, if necessary, a sintering aid are added and mixed to obtain a raw material powder. The blending amount is in the range described above.
Silicon nitride used in the present embodiment _(Si 3 _{N 4)} powder, silicon nitride having a β-type crystal structure _(Si 3 _{N 4)} is a powder. The purity of the silicon nitride (Si ₃ N ₄ ) powder is preferably 99.8% or more.
The silicon nitride (Si ₃ N ₄ ) powder preferably has an average particle size of 2 μm or less, more preferably 0.6 μm or less, from the viewpoint of securing the strength of the sintered body.
The boron nitride (BN) powder used in the present embodiment preferably has an average particle diameter of 10 μm or less, more preferably 8 μm or less, from the viewpoint of reducing the interparticle distance and reducing the influence of the aspect ratio. preferable. The purity of boron nitride (BN) powder is preferably 99.8% or more.

Distilled water, binder (binder), and dispersant are added to the raw material powder consisting of silicon nitride (Si ₃ N ₄ ) powder, boron nitride (BN) and sintering aid as necessary, and kneaded in a ball mill. The resulting slurry is granulated with a spray dryer to obtain a granulated product. The granulated product preferably has an average particle size of about 50 μm.
As the binder, a polyacrylic acid emulsion is used in this embodiment, but polyvinyl alcohol or the like can also be used.
Moreover, although polyacrylic acid ammonium is used for a dispersing agent in this embodiment, polysulfonic acid ammonium etc. can also be used for it. In the structure of boron nitride (BN) -silicon nitride (Si ₃ N ₄ ) based ceramic composite by using ammonium polyacrylate or ammonium polysulfonate, the average center distance of boron nitride is the average particle of boron nitride. The boron nitride (BN) can be controlled to be dispersed so that it is within twice the diameter.
As the granulation method, a stirring granulation method, a fluidized bed granulation method, or the like can be used.
In addition, as a method for measuring the average particle size in the present invention, in addition to the laser method and the sedimentation method, a method for obtaining by image processing by a three-dimensional direct observation method can be adopted, and an average particle size, an aspect ratio, and the like are obtained. Can do.

The granulated product is filled into a molding die composed of a center hole molding die of the gas diffusion cylinder 742 and an outer molding rubber die, and molded by an isostatic press to obtain a cylindrical molded body.
Here, the functionally gradient structure described above can be formed as follows. For example, there is a method in which a cylinder having a multi-layer structure in which the boron nitride (BN) concentration increases from the inside to the outside is integrated before firing by isostatic pressing (CIP) molding. It is done. Specifically, a plurality of kinds of slurries with different raw material powder blends are prepared. Here, the slurry of each composition forms each layer of a multi-layer structure.
Next, a granulated product corresponding to each layer obtained from each slurry based on this formulation is prepared, and each granulated product is filled into a mold and molded at a pressure lower than the subsequent hydrostatic pressure. A cylinder having a single-closed structure (a structure in which one opening of the cylinder is closed) is produced for each layer. At this time, the inner and outer diameter dimensions of the cylinder corresponding to each layer are such that the cylinder corresponding to the layer having a low boron nitride (BN) concentration can be inserted into the cylinder corresponding to the layer having a high boron nitride (BN) concentration. To. Then, the outermost layer of the multi-layered cylinder is arranged such that the layer having the highest boron nitride (BN) concentration is disposed, and the cylinder is sequentially inserted so that the boron nitride (BN) concentration becomes lower. The cylinder is made. Further, the multi-layered cylinder is vacuum-packed (wrapped with a vinyl bag or rubber bag and vacuumed), and then integrated by isostatic pressing (CIP).
Another example is a method in which a cylinder, which is the innermost layer of the cylindrical molded body, is produced, and a slurry having a different boron nitride (BN) concentration is applied to its outer surface stepwise so that the concentration increases toward the outermost layer.
In addition, a functionally graded structure can be formed by applying slurry (sludge) having different compositions in stages into a mold, forming layers for each composition, stacking them, and applying hydrostatic pressure. Moreover, the granulated material obtained from each slurry from which a composition differs in steps is filled in a metal mold | die for every composition, and it shape | molds with a pressure lower than hydrostatic pressure press, and produces a flake. The functional gradient structure can also be formed by laminating the thin pieces in layers and applying hydrostatic pressure.
As the molding method, a die press molding method, an extrusion molding method, or the like can be used. Moreover, these methods can also be combined.

The cylindrical molded body is processed into the shape of the gas diffusion cylinder 742, and the obtained green processed body is degreased at a temperature of 600 ° C. in the atmosphere for 4 hours to obtain a degreased body.
The degreased body is sintered by a normal pressure sintering method to obtain a sintered body. From the viewpoint of volatile decomposition during the sintering of silicon nitride (Si ₃ N ₄ ), the sintering temperature is preferably 1600 ° C. or higher and 1850 ° C. or lower. Further, it is preferable to perform hot isostatic pressing (HIP) at 1550 ° C. or higher and 1800 ° C. or lower as the secondary treatment. Since the silicon nitride (Si ₃ N ₄ ) phase in the sintered body is densified by hot isostatic pressing (HIP), the strength of the immersion member can be increased.
In addition, a normal pressure sintering method, a hot press sintering method, an atmospheric pressure sintering method, or the like can be used as the sintering method. Moreover, these methods can also be combined.
By the pressurization, boron nitride (BN) is oriented in a direction perpendicular to the pressurization direction, so that boron nitride (BN) is spread on the outer surface of the gas diffusion cylinder 742. Therefore, adhesion of dross to the outer surface of the gas diffusion cylinder 742 is less likely to occur.

  Cutting is performed as a finishing process for the sintered body to form a gas discharge hole 742A, and a gas diffusion cylinder 742 is obtained. In this embodiment, the gas diffusion cylinder 742 has an outer diameter of 30 mm, an inner diameter of 10 mm, and a length of 110 mm, and the gas discharge hole 742A has a diameter of 2 mm. However, the dimensions of the gas diffusion cylinder 742 are not limited to those shown in the present embodiment.

According to the present embodiment, the following effects can be achieved.
(1) The ceramic composite member used for the gas diffusion cylinder 742 is made of silicon nitride (Si ₃ N ₄ ), which has excellent heat resistance and impact resistance, and boron nitride (BN) that is difficult to wet with molten metal. Since it is a silicon nitride (Si ₃ N ₄ ) -based ceramic composite material blended by 20 mass% or more and 70 mass% or less on a mass basis, the gas diffusion cylinder 742 has heat resistance and impact resistance necessary as an immersion member for a molten metal bath. However, it has excellent dross refusal and corrosion resistance.

(2) In the structure of boron nitride (BN) -silicon nitride (Si ₃ N ₄ ) based ceramic composite, boron nitride (BN) exists as an aggregate having at least one of a flake shape and a layer shape As a result, it is easy to secure comfort and strength.

(3) The boron nitride (BN) in the structure of the silicon nitride (Si ₃ N ₄ ) -based ceramic composite material is dispersed so that the average center-to-center distance of boron nitride is within twice the average particle diameter of boron nitride. Since it is controlled so as to be performed, the effect of ensuring stable staying stability is produced.

(4) In the silicon nitride _(Si 3 _{N 4)} based ceramic composite material in the tissue, boron nitride (BN), many existing silicon nitride _(Si 3 _{N 4)} as the surface layer of the base ceramic composites of boron nitride (BN) Therefore, dross can be more difficult to adhere to the surface of the gas diffusion cylinder 742.

(5) Since the silicon nitride (Si ₃ N ₄ ) -based ceramic composite material includes a sintering aid, the sintering can be promoted and stabilized during sintering.

(6) Since the raw material powder of the silicon nitride (Si ₃ N ₄ ) -based ceramic composite is granulated using a dispersant and a binder, the workability at the time of forming with an isostatic press is improved. Can be made.

(7) Since the molten metal plating apparatus 1 includes the gas lift pump 7 using the gas diffusion cylinder 742 to which dross does not easily adhere, clogging of the gas discharge holes 742A formed in the gas diffusion cylinder 742 is less likely to occur. The replacement frequency of the gas diffusion cylinder 742 can be reduced. That is, it is possible to stably produce a molten metal plated steel sheet having excellent appearance without frequently stopping the apparatus.

Next, examples of the present invention will be described together with comparative examples, but the present invention is not limited to the description of these examples.
[Offline test]
First, in order to confirm that it is a ceramic composite material that has the required strength and hard-to-hold property as an immersion member for the molten metal bath, the molten metal plating solution taken out from the plating bath of the hot dip galvanizing apparatus that is actually in operation is stored. Evaluation was performed using a simple test bath.
Example 1
The following powder,
・ Silicon nitride (Si ₃ N ₄ ) powder: SN-9 grade
(Denki Kagaku Kogyo, purity 99.8%, average particle size 0.7 μm)
-Boron nitride (BN) powder: GP grade
(Manufactured by Denki Kagaku Kogyo, purity 99%, average particle size 8 μm)
Aluminum oxide (Al ₂ O ₃ ) powder: AL-160SG-3
(Made by Showa Denko, average particle size 0.6μm)
・ Yttrium oxide (Y ₂ O ₃ ) powder: RU-P grade
(Shin-Etsu Chemical Co., Ltd., average particle size 2.2μm)
Zirconium silicide (ZrSi ₂ ) powder: 99.9% purity
(High purity chemical research laboratory, average particle size 2.5μm)
Titanium silicide (TiSi ₂ ) powder: 99.9% purity
(Manufactured by High Purity Chemical Laboratory, average particle size 2.1μm)
Was added in a predetermined amount (mass%) shown in Table 1 to obtain a raw material powder. Next, purified water was added to the raw material powder so that the mass ratio of the raw material powder and purified water was 3: 7. Furthermore, 5% by mass (outer coating) of polyacrylic acid emulsion AS-1800 (manufactured by Toagosei Co., Ltd.) was added as a binder (binder) to the raw material powder. Further, ammonium polyacrylate A-6114 (manufactured by Toa Gosei Co., Ltd.) as a dispersant was added in an amount of 0.5% by mass (outer coating) to the raw material powder.

Then, it mixed with the ball mill, and obtained slurry was granulated with the spray dryer, and it was set as granulated powder. This was hydrostatically pressed (CIP) into a cylindrical shape under a pressure of 140 MPa, and then degreased at 600 ° C. in the atmosphere. With respect to this degreased molded body, in Example 1, the following Examples 4 and 5, and the following Comparative Examples 1, 2 and 3, atmospheric pressure sintering was performed for 8 hours under conditions of a temperature of 1750 ° C. and a pressure of 0.098 MPa. It was. After normal pressure sintering, hot isostatic pressing (HIP) was performed under conditions of a temperature of 1650 ° C. and a pressure of 200 MPa to obtain a sintered body.
On the other hand, in Examples 2 and 3 below and Comparative Examples 4, 5 and 6 below, the degreased compacts were subjected to only normal pressure sintering for 8 hours under conditions of a temperature of 1750 ° C. and a pressure of 0.098 MPa. A ligature was obtained.
The obtained sintered body was cut into a size of Φ30 mm × L120 mm to obtain a test body.

Regarding the provision of the functionally gradient structure, a three-layered cylinder having a boron nitride (BN) concentration increasing from the inside toward the outside is manufactured, and this three-layered cylinder is integrated before firing by isostatic pressing (CIP) molding. We used a method to make it.
Specifically, in Example 1, in order to form the functionally gradient structure, three types of slurries with different blending of raw material powders are prepared step by step as shown in Table 2, and the slurries of the respective blends are layer 1 respectively. -Layer 3 was formed.
Next, a granulated product corresponding to layers 1 to 3 obtained from each slurry based on this formulation is prepared, and each granulated product is filled into a mold, and the pressure is lower than the subsequent hydrostatic pressure pressurization. Three cylinders having a single-closed structure were produced by molding at (10 MPa). At this time, the inner and outer diameters of the three cylinders are different, the cylinder corresponding to the layer 2 can be inserted into the cylinder corresponding to the layer 2, and the cylinder corresponding to the layer 2 is inserted into the cylinder corresponding to the layer 3 Can be interpolated. Each cylinder is interpolated to produce a three-layered cylinder, which is wrapped with a vinyl bag and evacuated, and then this cylinder is hydrostatically pressed (CIP) molded under a pressure of 140 MPa. Turned into.

About the intensity | strength of the obtained test body, it evaluated by room temperature bending strength and Vickers hardness.
The room temperature bending strength was measured according to JIS R 1601.
The Vickers hardness was measured using a Vickers hardness tester with a load of 98 N (10 kgf) and a holding time of 15 seconds.
The evaluation results are shown in Table 3.

The dross refusal property of the test specimen is the presence or absence of dross that adheres to the test specimen that has been immersed in a hot dip galvanizing solution (bath temperature 450 ° C) in a simple test bath for 48 hours and then pulled up from the hot dip galvanizing solution Evaluated by.
The hot dip galvanizing solution used was partially taken out from a hot dip galvanizing apparatus (hot galvanized bath, 0.13 mass% aluminum added) that actually manufactures hot dip metal plated steel sheets, and dross was floating It is what you are doing. During the immersion test, stirring was always performed, and the dross adhered to the surface and brought close to the actual use environment where growth occurred.
The evaluation results are shown in Table 3.

  Observation with an electron microscope with a composition analysis function (device name: electron microscope JXA-8100 with quantitative analysis function, presence forms of boron nitride (BN) of each compounding system determined by JEOL are shown in Table 4. In the case where boron nitride (BN) exists in the form of flakes, layers, or aggregates, the average distance between the centers of boron nitride is dispersed so that it is within twice the average particle diameter of boron nitride. When the functional gradient structure in which the boron nitride concentration is higher in the surface layer than in the inner layer of the test body is formed, “◯” is displayed, and “−” is displayed when it is not applicable.

(Examples 2 to 5) and (Comparative Examples 1 to 6)
-Blending Raw material powders were blended according to Table 1.
-Formation of functionally gradient structure In Example 3, the process for forming the functionally gradient structure was performed in the same manner as in Example 1, but the other Examples 2, 4 and 5 and Comparative Example were performed. The said process was not performed about 1-6.
Sintering was performed under the conditions shown in Example 1 above.
Except for this, test specimens were prepared and evaluated in the same manner as in Example 1. The results are shown in Tables 3 and 4.
Moreover, although not used in Example 1, the detail of the powder used in any of Examples 2-5 and Comparative Examples 1-6 is shown below.
Silicon oxide (SiO ₂ ) powder: Crystallite C5X (manufactured by Tatsumori, average particle size 2.2 μm)
Magnesium oxide (MgO) powder: 99.9% purity
(High purity chemical research laboratory, average particle size 1.2μm)

As Table 3 shows, the test bodies of Examples 1 to 5 were provided with the strength required as an immersion member for a molten metal bath, and no dross was attached in the immersion test.
On the other hand, the test bodies of Comparative Examples 1 and 4 had a large amount of dross attached as a result of the immersion test. In particular, although the specimen of Comparative Example 4 had the strength required as an immersion member for a molten metal bath, dross adhesion occurred because the amount of boron nitride (BN) was as small as 10% by mass.
The test bodies of Comparative Examples 2, 3, 5 and 6 were unable to obtain the strength required as an immersion member for a molten metal bath and could not be used for the immersion test.

[Real machine test]
Next, a dipping member (gas diffusion cylinder) for a molten metal bath according to the present invention was attached to a gas lift pump of a hot dip galvanizing apparatus that was actually operated, and the difficulty of dross occupancy was evaluated.
(Example 6)
Granulation was performed in the same manner as in Example 5, and the granulated powder (particle size 50 μm) was molded by a hydrostatic pressure press with a pressure of 140 MPa in the same manner as in the above embodiment to obtain a cylindrical molded body.
The cylindrical molded body was green processed into the shape of the gas diffusion cylinder 742, and the obtained green processed body was degreased at a temperature of 600 ° C. in the atmosphere for 4 hours to obtain a degreased body.
The degreased body was sintered under normal pressure sintering at a temperature of 1750 ° C. and a pressure of 0.098 MPa for 8 hours, and then sintered by a hot isostatic pressing (HIP) method at a temperature of 1650 ° C. and a pressure of 200 MPa. A sintered body was obtained.
The sintered body was cut as a finishing process to form a gas discharge hole to obtain a gas scattering cylinder. The gas diffusion cylinder had an outer diameter of 30 mm, an inner diameter of 10 mm, a length of 110 mm, and a gas discharge hole diameter of 2 mm. As described in the above embodiment, the gas discharge holes were formed in a total of 10 locations, with two rows with three holes arranged vertically and one row with four rows arranged vertically.

  The obtained gas scattering cylinder was attached to the gas lift pump of the molten metal plating apparatus described in the above embodiment, and continuously molten metal plated steel sheets were produced while flowing nitrogen gas at a flow rate of 20 L / min. The molten metal plating bath was a hot dip galvanizing bath to which 0.13% by mass of aluminum was added, and the bath temperature was 450 ° C.

The dross refusal property to the gas scattering cylinder was evaluated as follows.
The back pressure on the nitrogen gas supply side of the gas lift pump is measured, and when the back pressure exceeds 19.6 MPa (2 kgf / cm ² ), it is determined that dross adheres and the gas discharge hole of the gas diffusion cylinder is clogged, The longer the period from the start of the test to the occurrence of the increase in back pressure, the better the dross refusal. The evaluation results are shown in Table 5.

(Comparative Example 7)
Evaluation was performed in the same manner as in Example 6 except that a gas scattering cylinder made of SUS was used.
(Comparative Example 8)
Evaluation was performed in the same manner as in Example 6 except that the granulation was performed in the same manner as in Comparative Example 1.
These evaluation results are shown in Table 5.

Since the period of Comparative Example 7 was 3 to 4 days and the period of Comparative Example 8 was 5 days, the period of Example 6 was 11.5 to 13 days from the start of the test to the increase in back pressure. It has been found that the immersion member (gas diffusion cylinder) for the molten metal bath according to the present invention is extremely excellent in dross retention and corrosion resistance.
Thus, if the period until the maintenance of the gas diffusion cylinder becomes about twice as long, the replacement frequency of the gas diffusion cylinder is reduced to about one half, and the number of line stops associated with the replacement can be reduced. That is, the molten metal plated steel sheet can be manufactured stably and efficiently.
In addition, after completion | finish of the test of Example 6, when the gas diffusion cylinder was taken out from the hot dip galvanizing bath, the crack of the gas diffusion cylinder did not generate | occur | produce. From this, the immersion member (gas diffusion cylinder) for the molten metal bath according to the present invention is resistant to thermal stress due to thermal shock caused by taking in and out of the hot plating bath and temperature gradient caused by nitrogen gas flow in the gas lift pump. However, it was found that it showed excellent resistance.

  The present invention can be suitably used as an immersion member for a molten metal bath attached to a continuous molten metal plating apparatus such as a steel plate.

DESCRIPTION OF SYMBOLS 1 Molten metal plating apparatus 2 Steel plate 3 Snout 4 Molten metal plating bath (molten metal bath)
5 Pot roll 6 Guide roll 7 Gas lift pump 8 Metal pump 71 Suction port 72 Outer tube 73 Discharge port 74 Inner tube 81 Discharge port 82 Main body tube 83 Suction port 741 Gas inlet tube 742 Gas diffusion cylinder (immersion member for molten metal bath) )
742A Gas discharge hole 743 Connector D Dross B Bubble

Claims (7)

An immersion member for a molten metal bath using a silicon nitride (Si ₃ N ₄ ) -based ceramic composite containing at least 20% by mass to 70% by mass of boron nitride (BN) based on the total mass of the ceramic composite ,
Used for coating members or shaft sleeves on the roll surface of a snout, metal pump, gas lift pump, gas wiping nozzle, or pot roll or guide roll,
The boron nitride (B) in the structure of the silicon nitride ( Si ₃ N ₄ ) -based ceramic composite material
N) exists as an aggregate having at least one of a flaky shape and a lamellar shape.
An immersion member for a molten metal bath, characterized in that The boron nitride (BN) in the structure of the silicon nitride (Si ₃ N ₄ ) -based ceramic composite is dispersed so that the average center-to-center distance of the boron nitride is within twice the average particle diameter of the boron nitride. The immersion member for a molten metal bath according to claim 1, wherein the immersion member is a molten metal bath. The boron nitride (B) in the structure of the silicon nitride (Si ₃ N ₄ ) -based ceramic composite material
The N) concentration forms a functionally graded structure in which the surface layer is higher than the inner layer of the silicon nitride (Si ₃ N ₄ ) -based ceramic composite material, according to claim 1 or 2. Immersion member for molten metal bath. Aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), magnesium oxide (MgO), rare earth oxide (RE ₂ O) as sintering aids in the silicon nitride (Si ₃ N ₄ ) -based ceramic composite. ₃ : RE contains a rare earth element), zirconium silicide (ZrSi ₂ ) and titanium silicide (TiSi 2) at least one kind,
Aluminum oxide (Al ₂ O ₃ ), silicon oxide (SiO ₂ ), magnesium oxide (MgO
) And rare earth oxide (RE ₂ O ₃ ) content of 0.2% by mass to 5.0% by mass, respectively, and zirconium silicide (ZrSi ₂ ) and titanium silicide (TiSi ₂ ) content of 0. It is 5 mass% or more and 5.0 mass% or less, The immersion member for molten metal baths as described in any one of Claim 1- Claim 3 characterized by the above-mentioned. In a molten metal plating apparatus that guides a heat-annealed steel sheet into a molten metal bath through a snout, applies molten metal plating to the steel sheet, and pulls up the steel sheet through a pot roll to continuously produce a plated steel sheet,
A molten metal plating apparatus, wherein the immersion member for a molten metal bath according to any one of claims 1 to 4 is applied to a device for removing foreign matter generated on the inner bath surface of the snout. The foreign matter removing apparatus includes a gas diffusion cylinder and a piping member,
The molten metal plating apparatus according to claim 5, wherein the immersion member for the molten metal bath is applied to at least one of the gas diffusion cylinder and the piping member.   A method for producing a molten metal plated steel sheet, wherein the molten metal plating apparatus according to claim 5 or 6 is used.

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