JP4823763B2 - Heat treatment furnace and burner port for heat treatment furnace - Google Patents

Description

  The present invention relates to a heat treatment furnace for heating and heat treatment by blowing combustion gas from a burner onto a steel material and the like, and a burner port for a heat treatment furnace used in the heat treatment furnace.

2. Description of the Related Art Conventionally, as one of furnaces for heating steel materials and the like, a heat treatment furnace is used in which a heating burner is provided on a furnace wall and combustion gas of the heating burner is sprayed on the steel material or heated radiatively. As a typical furnace, there is a heat treatment furnace before hot-rolling of wire rods or steel slabs or before plating of continuous molten metal plating.
For example, a continuous hot metal plating line is composed of a heat treatment furnace for heat annealing a cold rolled steel sheet and a hot dipping bath. Specifically, the steel sheet is heated in a reducing atmosphere of an indirect heating type heat treatment furnace, for example, a radiant tube type heat treatment furnace, which is heated in a direct heating type heat treatment furnace in which a high-temperature combustion gas is blown from a burner to a cold rolled steel sheet. To do. In the direct-fired heat treatment furnace, the combustion gas is blown from the reduction burner and heated, so that the steel plate can be rapidly heated and a thin oxide film is formed on the steel plate surface.

This oxide film is reduced in a reducing atmosphere of an indirect heating type heat treatment furnace, and the oxide film on the steel sheet surface is removed to form a steel sheet surface suitable for hot dipping. For this reason, in a continuous molten metal plating line, a facility that uses a combination of a direct-fired heat treatment furnace and an indirect heating heat treatment furnace is generally used.
The steel sheet reduced in the reducing atmosphere of the indirect heating type heat treatment furnace is subsequently soaked in a soaking furnace, then slowly cooled to a predetermined temperature in a slow cooling furnace in the cooling furnace, quenched in the quenching furnace, and molten metal plating Hot dipping is performed in the bath.
The direct heat heating type heat treatment furnace provided in the continuous molten metal plating line has conventionally been constructed of an indefinite refractory or brick, and the burner installed in the furnace wall is an indeterminate refractory. Surrounded by (fireproof castable).

The refractory around the burner was subjected to many years of heat cycle and thermal shock caused by switching between ignition combustion and extinguishing of the burner, and cracks and layered peeling occurred on the wall around the burner. The peeled refractory adhered to the steel plate or was sandwiched between the steel plate and the hearth roll to braze the steel plate.
In addition, since the irregular refractory or brick has a large heat capacity, it takes a long time to start up the furnace (for example, about 8 hours) or cool down for the shutdown (for example, about 24 hours). It was the main cause of sex decline.

As a technique for preventing cracking of the refractory and peeling of the layered structure, as disclosed in Patent Document 1, it is proposed to use a ceramic fiber burner tile that is resistant to thermal shock. As an example disclosed in this patent document 1, a trumpet-shaped or cylindrical burner insertion hole is formed by laminating ceramic fiber blankets in a cross, radial or mosaic shape and expanding on the inner surface side of the furnace formed at the center of the burner tile. In this invention, the fiber tip of the ceramic fiber blanket is positioned to prevent local blowout of fibers in the burner insertion hole, thereby extending the service life.
However, the heating burner generates a high flow rate flame, and the flow rate reaches 50 m / sec. Therefore, the furnace wall of the present invention cannot be said to have sufficient wind resistance, and the ceramic fiber blanket is complicated. Since it is difficult to process and install into a structure and the material cost increases, it is considered that there is a problem as an industrial facility.

In addition, as disclosed in, for example, Patent Document 2, in a conventional square ceramic burner tile, distortion due to thermal stress is generated inside the tile and a crack is generated. Therefore, a ceramic burner tile having a cylindrical two-layer structure is used. Techniques have been proposed that use and extend life. This Patent Document 2 discloses a ceramic burner tile having a cylindrical double layer structure including a ceramic burner tile having an outer cylindrical shape and a circular trumpet shape and a cylindrical sleeve fitted to the ceramic burner tile.
However, such ceramic burner tiles are not sufficient because they do not maintain the straightness of the burner flame and do not describe the heat resistance of the cylindrical ceramic burner port material.

Therefore, for example, as disclosed in Patent Document 3, it is conceivable to apply a sintered body having a bending strength of 500 MPa or more at 1400 ° C. in the atmosphere to the ceramic burner port material.
However, even if the sintered body disclosed in Patent Document 3 is used, a heat treatment furnace or the like for heating and heat-treating a steel material or the like by blowing a combustion gas from a burner is exposed to a higher temperature of 1500 ° C. or higher. Because it is a use environment, long-term durability is inferior, and since the ratio of the grain boundary phase to the main phase (β-Si ₃ N ₄ ) is high, the rate of deterioration due to repeated thermal shock increases and decreases, which is sufficient Instead, a sintered body excellent in long-term durability even at a high temperature of 1500 ° C. or higher has been desired.

JP-A-6-281132 Japanese Utility Model Publication No. 5-17338 JP 2004-59346 A

  Therefore, in the present invention, by applying a sintered body excellent in long-term durability even at a high temperature of 1500 ° C. or higher to the ceramic burner port material, it adheres to the steel plate or is sandwiched between the steel plate and the hearth roll, and the steel plate surface Steel heating type heat treatment furnace capable of preventing cracks and peeling of the furnace wall around the heating burner, which can cause cracks, and shortening the start-up and pause time of the heat treatment furnace, and the heat treatment used in this heat treatment furnace The object is to provide a furnace burner port.

The present inventors paid attention to ceramic fibers having a small heat capacity as a refractory material capable of preventing cracking and peeling of the furnace wall refractory in the heat treatment furnace, and conducted intensive research on using this as a furnace wall refractory material. .
As a result, for heat treatment furnaces before hot rolling, heat treatment furnaces before continuous molten metal plating, etc., ceramic fiber is used as the furnace wall material, and a burner port is installed in the burner insertion hole provided in the furnace wall. When used as a ceramic fiber, the ceramic fiber has excellent heat resistance and high thermal shock resistance, so there is no cracking or flaking on the furnace wall, but there is a problem of aging deterioration of the burner port member. It was found that when the steel plate passing through was swung in the thickness direction in the furnace, the ceramic fiber on the furnace wall and the steel plate contacted to break the ceramic fiber on the furnace wall.

These problems are caused by the fact that at least one of the Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase and Yb ₂ Si ₂ O ₇ phase is 2.5 to 4.8% by mass, Si ₂ outside the burner combustion tube. ₂ to 6.5% by mass of the N ₂ O phase, ₂ to 5% by mass of SiC particles having an average particle size of 0.1 μm or more and 0.7 μm or less, and β-Si ₃ N ₄ and inevitable impurities as the balance Knowing that it can be solved by arranging a silicon nitride ceramic sintered body burner port (cylinder) that has a composition to achieve, and that it can be a sintered body excellent in long-term durability even at a high temperature of 1500 ° C. or higher did.
In addition, by providing the function of a protector by projecting the burner port from the furnace wall surface, the steel plate swung in the thickness direction contacts and protects the tip of the burner port first, so that the ceramic fiber furnace wall and It was found that the contact of can be prevented.

And since ceramic fibers have a smaller heat capacity compared to irregular refractories or bricks, furnaces using ceramic fibers for the furnace walls are used for the time required to raise the temperature for starting up the furnace and for cooling for shutdown. It has been found that the time required can be greatly reduced (less than half).
In addition, the exhaust gas flow velocity blown into the furnace from the heating burner that blows through the dog bone in the furnace reaches 25 m / sec, and there is a problem of blowing the ceramic fiber of the ceramic fiber furnace wall and damaging the furnace wall. Found that the ceramic burner port can serve as an anchor for fixing the ceramic fiber and can be solved.

The present invention has been completed based on these new findings, and the gist of the invention is as follows.
(1) In a heat treatment furnace in which one or more burners are disposed on the furnace wall, at least a furnace wall structure in which ceramic fibers are disposed on the inside of the furnace wall is provided, and a burner is inserted into an insertion hole provided in the furnace wall. And at least one of the Y ₂ Si ₂ O ₇ phase, the Er ₂ Si ₂ O ₇ phase, and the Yb ₂ Si ₂ O ₇ phase is 2.5 to 4.8 mass%, Si ₂ to 6.5% by mass of 2N ₂ O phase, ₂ to 5% by mass of SiC-based particles having an average particle size of 0.1 μm to 0.7 μm, and the remainder of β-Si ₃ N ₄ and inevitable impurities A burner port composed of a silicon nitride ceramic sintered body having the composition as described above is disposed adjacently, and the tip of the burner port is disposed so as to protrude from the inner wall surface of the furnace to the inside of the furnace. Heat treatment furnace.

(2) A burner port support member made of the silicon nitride ceramic sintered body is disposed outside the burner port, and the tip of the burner port support member protrudes from the furnace inner wall surface to the furnace inner side. The heat treatment furnace according to (1), wherein the heat treatment furnace is arranged.
(3) In a heat treatment furnace in which one or more burners are disposed on the furnace wall, the furnace wall structure having ceramic fibers disposed at least inside the furnace wall is provided, and the burner is inserted into the insertion hole provided in the furnace wall. And at least one phase of Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase and Yb ₂ Si ₂ O ₇ phase is 2.5 to 4.8% by mass on the outside of the tip of the burner. ₂ to 6.5% by mass of Si ₂ N ₂ O phase, ₂ to 5% by mass of SiC particles having an average particle size of 0.1 μm to 0.7 μm, and β-Si ₃ N ₄ and inevitable impurities A burner port made of a silicon nitride ceramic sintered body having a composition with the remainder as a balance is fitted, and the tip of the burner port is disposed so as to protrude from the inner wall surface of the furnace to the inside of the furnace. Heat treatment furnace.

(4) The heat treatment furnace according to any one of (1) to (3), wherein the silicon nitride ceramic sintered body has a relative density of 98% or more.
(5) Any one of (1) to (4), wherein the tip of the burner port or the tip of a support member for the burner port is disposed so as to protrude from the inner wall surface of the furnace to the inside of the furnace by 5 mm or more and 30 mm or less. A heat treatment furnace according to any of the above.
(6) At least a furnace wall structure in which ceramic fibers are disposed inside the furnace wall, and disposed adjacent to the inside of the burner of the heat treatment furnace in which the burner is installed in the insertion hole provided in the furnace wall. A burner port for a heat treatment furnace, in which at least one of a Y ₂ Si ₂ O ₇ phase, an Er ₂ Si ₂ O ₇ phase, and a Yb ₂ Si ₂ O ₇ phase is 2.5 to 4.8 mass%, Si _{2 2} to 6.5% by mass of the N ₂ O phase, ₂ to 5% by mass of SiC particles having an average particle size of 0.1 μm or more and 0.7 μm or less, and β-Si ₃ N ₄ and inevitable impurities as the balance A burner port for a heat treatment furnace, characterized by comprising a silicon nitride ceramic sintered body having a composition to achieve.

The heating type heat treatment furnace of the present invention uses ceramic fibers having a small heat capacity and excellent shock resistance and spall resistance on the furnace wall, etc., and also has excellent thermal stability and mechanical stability, and has long-term durability. By using the sintered silicon nitride ceramics as a burner port member, cracks and peeling of the furnace wall around the heating burner can be prevented, and the fragments pass through the furnace due to the wind speed of the burner flame. It does not adhere to the steel plate or become wrinkled due to furnace wall peeling.
In addition, since the time required for starting up and shutting down the furnace can be greatly shortened, productivity can be improved.

The present invention will be described in detail below.
The heating heat treatment furnace has a furnace wall or the like made of an irregular refractory, and a burner installed on the furnace wall is surrounded by an irregular refractory (fireproof castable) or brick.
The refractory around the burner is subjected to many years of heat cycle and thermal shock due to switching between ignition combustion of the burner and extinguishing, cracks and laminar peeling on the wall around the burner, and expulsion due to neck breakage of the anchor brick ) Becomes larger.
In addition, since the refractory has a large heat capacity, it takes a long time to start up the furnace (for example, about 8 hours) or the cooling time for shutdown (for example, about 24 hours), prolonging periodic repairs and improving productivity. There was a problem of inhibiting.

The present invention provides ceramic fibers having a small heat capacity, excellent impact resistance and spall resistance, and Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase and Yb ₂ Si. SiC-based particles having 2.5 to 4.8 mass% of at least one phase of ₂ O ₇ phase, ₂ to 6.5 mass% of Si ₂ N ₂ O phase, and an average particle size of 0.1 μm to 0.7 μm. These problems are solved by using a silicon nitride ceramic sintered body burner port having a composition of 2 to 5% by mass and β-Si ₃ N ₄ and inevitable impurities as the balance.

[First Embodiment]
FIG. 1 is a view exemplarily showing a first embodiment of a furnace wall structure of a direct-fired heat treatment furnace according to the present invention.
As shown in FIG. 1, a furnace wall or the like of a heat treatment furnace in which a steel plate 1 is passed inside has a wind-resistant ceramic fiber 3 against a rising air flow inside the furnace on the furnace inner wall side, and a ceramic fiber outside of the furnace fiber. A blanket material 8 is installed. And the combustion burner 2 is arrange | positioned in the insertion hole of the furnace wall.

When the furnace wall is composed only of ceramic fiber blanket material, the exhaust gas flow velocity from the combustion burner into the furnace and blown through the flue on the inner surface of the furnace reaches 25m / sec. This will blow away the fibers of the wood and damage the furnace wall.
Furthermore, when the inside of the furnace wall is composed of only the wind-resistant ceramic fiber, if the exhaust gas flow rate is about 25 m / sec, which blows through the flue on the inner surface of the furnace, the wind speed can be secured, but the furnace wall burner Since the flow velocity of the combustion gas from the combustion burner in the insertion hole reaches 50 m / second, even the wind-resistant ceramic fiber that comes into contact with the combustion gas flame of the combustion burner has insufficient wind resistance, and the fiber is blown off by the combustion gas flow. As a result, the furnace wall is damaged and the straightness of the flame is impaired.

Therefore, in the first embodiment, as shown in FIG. 1, in order to prevent the occurrence of damage to the furnace wall due to the combustion gas flame of the combustion burner 2, the Y ₂ Si ₂ O ₇ phase and Er ₂ Si _At least one of the ₂ O ₇ phase and the Yb ₂ Si ₂ O ₇ phase is 2.5 to 4.8% by mass, the Si ₂ N ₂ O phase is ₂ to 6.5% by mass, and the average particle size is 0.1 μm or more. Burner port 4 of the sintered silicon nitride ceramics having a composition with 2 to 5% by mass of SiC particles of 7 μm or less and β-Si ₃ N ₄ and unavoidable impurities as the balance, It arrange | positions adjacent to the furnace inner side, and arrange | positions the front-end | tip from the furnace wall surface (panel surface).
Thereby, contact between the burner combustion flame and the ceramic fiber 3 can be prevented by the burner port 4, so that the furnace wall is not damaged.

Moreover, the function of the protector of the furnace wall surface damage by the contact with a ceramic fiber furnace wall and the steel plate 1 can be given by protruding the burner port 4 front-end | tip to the furnace inner side from a furnace wall surface.
Here, the protruding distance L1 of the burner port 4 from the furnace wall surface to the furnace inner side is set to 5 to 30 mm, so that the steel sheet 1 (plate thickness 0.6 to 6.0 mm) passing through the furnace is in the thickness direction. The steel plate 1 is preferable because it contacts the burner port 4 first and does not directly contact the furnace wall ceramic fiber surface.
If the protruding distance is less than 5 mm, the function of the protector cannot be sufficiently provided. On the other hand, if it exceeds 30 mm, unnecessary contact with the steel sheet tends to occur, such being undesirable.

Further, as shown in FIG. 1, at least one of the Y ₂ Si ₂ O ₇ phase, the Er ₂ Si ₂ O ₇ phase, and the Yb ₂ Si ₂ O ₇ phase is added to the outside of the burner port 4 by 2.5-4. 8% by mass, ₂ to 6.5% by mass of the Si ₂ N ₂ O phase, ₂ to 5% by mass of SiC particles having an average particle size of 0.1 μm or more and 0.7 μm or less, and β-Si ₃ N ₄ and A burner port support member 5 made of a silicon nitride ceramic sintered body having a composition with inevitable impurities as the balance may be disposed.
The tip of the burner port support member 5 is also preferably disposed so as to protrude from the inner wall surface of the furnace to the inside of the furnace, and the protrusion distance L2 to the furnace inside is 5 to 5 for the same reason as in the case of the burner port 4. 30 mm is preferable.

In addition, the silicon nitride ceramic sintered body is not limited to the burner port or the burner port support material, but is applied to various protector members that protect the ceramic fiber from contact with the burner body, the outer periphery of the burner tile, and the steel plate. Is also possible.
The ceramic fiber may be composed mainly of alumina-silica having an alumina content of 40 to 75 mass% and a silica content of 25 to 60 mass%, for example.
The heat capacity of the ceramic fiber is about 8.4 to 16.7 × 10 ⁴ J / m ³ · ° C., and the heat capacity of the amorphous castable or brick is about 167.4 to 251.1 × 10 ⁴ J / m ³ · ° C. Compared with, the heat capacity is sufficiently small and the thermal shock resistance is also excellent.

Therefore, if ceramic fiber is used for the furnace wall of the heating heat treatment furnace, the furnace wall and the like are easy to heat and cool, so that the heating temperature for starting up the heating heat treatment furnace and for stopping (extinguishing) The cooling time can be greatly shortened.
That is, in the conventional heat treatment furnace having a refractory structure, for example, it took about 8 hours to start up the heat treatment furnace and about 24 hours to stop, but according to the heat treatment furnace of the present invention, It is possible to start up and pause in about half the time.

In addition, since the ceramic fiber is excellent in thermal shock resistance and spall resistance, it is possible to prevent cracks and layered peeling on the furnace wall.
Furthermore, as shown in FIG. 1, a furnace wall structure in which the ceramic fiber 3 is disposed inside the furnace wall and the ceramic fiber blanket material 8 is disposed outside the ceramic fiber 3 may be employed.
The ceramic fiber blanket is typically formed by molding ceramic fiber into a blanket or felt shape, and a general-purpose material known as a material that can be used for a high-temperature heat insulating material, a furnace ceiling, a furnace wall, or the like is used. be able to.

[Second Embodiment]
FIG. 2 is a view exemplarily showing a second embodiment of the furnace wall structure of the direct fire heating type heat treatment furnace of the present invention. In this way, the tip of the combustion burner 2 may be fitted with a cylindrical burner port 7 to provide a holder function.
That is, as a means for preventing damage to the furnace wall due to partial contact between the burner combustion flame and the ceramic fiber furnace wall, a cylindrical burner port 7 is fitted to the tip of the combustion burner 2 to match the holder function. Can have.

Specifically, a guide pipe 6 for supporting the burner is provided on the outer periphery of the combustion burner 2, and a protrusion 61 is formed on the outer peripheral surface of the guide pipe 6.
On the other hand, a ring-shaped groove 71 is formed on the inner peripheral surface of the burner port 7.
Then, the burner port 7 is held at the tip of the combustion burner 2 by fitting the groove 71 of the burner port 7 to the protrusion 61 of the guide pipe 6.
The tip of the burner port 7 is protruded from the furnace wall surface (panel surface) to provide a protector function as in the case of the burner port described above.
By arranging the burner port 7, the burner combustion flame hits the inner surface of the burner port 7, the straightness of the flow of the combustion flame is maintained, and the burner combustion flame is sprayed in a uniform state on the steel plate 1 in the furnace. Reduction characteristics can be made uniform.

[Material of burner port and support member for burner port]
Further, regarding the selection of the material of the burner ports 4 and 7 and the support member 5 for the burner port, the present inventors have excellent oxidation resistance and thermal shock resistance, high strength and high toughness, and 1500 ° C. or higher. Has developed ceramics with excellent long-term durability even at high temperatures.
Unlike the ceramic sintered body mainly composed of alumina, zirconia, etc., the silicon nitride sintered body has excellent heat resistance and can maintain mechanical strength at high temperatures. I examined that.

However, a conventional silicon nitride sintered body having a low melting point glass phase is inferior in oxidation resistance and thermal shock resistance at high temperatures.
Therefore, the inventors have intensively studied the refinement of the crystal phase and crystal grains constituting the silicon nitride ceramic sintered body. More specifically, the present inventors produced a silicon nitride sintered body composed of various crystal phases and evaluated its characteristics.

As a result, at least one of the Y ₂ Si ₂ O ₇ phase, the Er ₂ Si ₂ O ₇ phase, and the Yb ₂ Si ₂ O ₇ phase is 2.5 to 4.8% by mass, and the Si ₂ N ₂ O phase is 2 to 2%. Silicon nitride having a composition of 6.5% by mass, 2 to 5% by mass of SiC particles having an average particle size of 0.1 μm or more and 0.7 μm or less, and β-Si ₃ N ₄ and unavoidable impurities as the balance Ceramic sintered body has little strength drop from normal temperature to high temperature (about 1500 ℃), excellent in oxidation resistance and thermal shock resistance, static fatigue characteristics due to temperature gradient, etc., and thermal stress fracture resistance due to rapid cooling It has been found that it has excellent properties such as enhancing the properties.

When at least one of the Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase, and Yb ₂ Si ₂ O ₇ phase is less than 2.5% by mass, the liquid at the α → β transition of Si ₃ N ₄ It is not preferable because the phase is too small to sufficiently advance the phase transition and the porosity in the sintered body is increased. When the content exceeds 4.8% by mass, the β-Si ₃ N ₄ crystal grains become coarse or have a low aspect ratio. , The columnar phase is not sufficiently entangled and the strength and toughness are lowered, which is not preferable.
Furthermore, in order to maintain long-term durability at a higher temperature of 1500 ° C. or higher, when the ratio of the grain boundary phase to the main phase (β-Si ₃ N ₄ ) is high, two-phase repetition with slightly different thermal expansion This is not preferable because the rate of deterioration associated with expansion / contraction due to thermal shock increases.
That is, long-term durability at high temperatures can be ensured by setting at least one of the Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase, and Yb ₂ Si ₂ O ₇ phase to 4.8 mass% or less. It was.

Further, when the mass ratio of the Si ₂ N ₂ O phase is less than 2% by mass of the whole, the porosity in the sintered body becomes high and the effect of contributing to the mechanical strength is small, and when it exceeds 6.5% by mass, β-Si _{Since 3} N ₄ crystal grains grow abnormally or are not sufficiently entangled, the strength and toughness are lowered, which is not preferable.
Furthermore, the silicon nitride ceramic sintered body used in the heat treatment furnace of the present invention has the effect of dispersing the SiC fine particles having an average particle size of 0.1 μm or more and 0.7 μm or less to suppress the growth of crystal grains in the parent phase. Structure in which the average crystal grain size of Si ₃ N ₄ (one-line cutting method) is 0.5 to 2 μm, the average aspect ratio is as small as about 1.5 to 10 and the columnar crystal grains of β-Si ₃ N ₄ are intertwined In addition, at least one of the high melting point Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase, Yb ₂ Si ₂ O ₇ phase and Si ₂ N ₂ O phase are finely precipitated at the grain boundaries. Yes.

As described above, high toughness is maintained while maintaining high strength up to high temperature due to the dispersion effect of reducing the ratio of the grain boundary phase to the main phase (β-Si ₃ N ₄ ) and atomizing SiC particles. And having a bending strength of 500 MPa or higher at 1500 ° C. or higher in the atmosphere and a toughness value K _IC of 5 MPa · m ^1/2 or higher.
However, the temperature at which the bending strength of 500 MPa or more can be maintained is not particularly specified, but the strength can be sufficiently maintained up to about 1550 to 1600 ° C.

Here, the Si ₂ N ₂ O crystal phase has the same type of X-ray diffraction pattern as that of the Si ₂ N ₂ O crystal identified by the powder X-ray diffraction method, and is a compound composed of Si ₃ N ₄ and SiO ₂ . Among them, it is the most stable compound in a high-temperature oxidizing atmosphere.
Similarly, the Y ₂ Si ₂ O ₇ crystal phase, the Er ₂ Si ₂ O ₇ phase, and the Yb ₂ Si ₂ O ₇ phase are the Y ₂ Si ₂ O ₇ crystal and Er ₂ Si ₂ identified by the powder X-ray diffraction method. It has the same type of X-ray diffraction pattern as O ₇ crystal and Yb ₂ Si ₂ O ₇ crystal, and is composed of Y ₂ O ₃ and SiO ₂ , Er ₂ O ₃ and SiO ₂ , Yb ₂ O ₃ and SiO ₂ , respectively. Among them, it is the most stable compound in a high-temperature oxidizing atmosphere.

The β-Si ₃ N ₄ crystal phase has the same type of X-ray diffraction pattern as the β-Si ₃ N ₄ crystal shown by JCPDS card 33-1160.
Furthermore, it is composed of at least one phase of Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase, Yb ₂ Si ₂ O ₇ phase, β-Si ₃ N ₄ phase, and Si ₂ N ₂ O phase. The relative density of the silicon nitride sintered body is desirably 98% or more with respect to the theoretical density.
If the relative density is less than 98%, thermal stability and mechanical stability are likely to be insufficient, and there is a high possibility that the effect of improving long-term durability is not observed.

[Method of manufacturing sintered silicon nitride ceramics]
Next, a method for producing a silicon nitride ceramic sintered body used in the heat treatment furnace of the present invention will be described.
As the silicon nitride powder used as a raw material, Si ₃ N ₄ powder having an α-type crystal structure is preferable from the viewpoint of sinterability, but β-type or amorphous Si ₃ N ₄ powder is included. It doesn't matter. In order to obtain a sufficiently high density during sintering, fine particles having an average particle diameter of 1 μm or less are desirable.
Since silicon nitride is a substance having strong covalent bonding and is often difficult to sinter alone, generally a sintering aid is added for densification.

As the sintering aid, at least one of silicon oxide, yttrium oxide, erbium oxide, and ytterbium oxide can be used.
Alternatively, oxynitride (Si ₂ N ₂ O) and complex oxides of silicon oxide, yttrium oxide, erbium oxide, ytterbium oxide (Y ₂ SiO ₅ and Y ₂ Si), which are required to be added in terms of oxides, are added. ₂ O ₇ , Er ₂ SiO ₅ , Er ₂ Si ₂ O ₇ , Yb ₂ SiO ₅ , Yb ₂ Si ₂ O _7, etc.).

As used herein, silicon oxide and yttrium oxide, erbium oxide, etc. at least one ytterbium oxide, a crystalline phase transition from _α-Si 3 _{N 4} phase during sintering the _Si 3 _{N 4} to _β-Si 3 _{N 4} phase It has the function of proceeding in the melt, and further promotes the growth of β-Si ₃ N ₄ columnar phase, thereby improving the high-temperature strength and toughness. The amount of each added is preferably 3 to 7% by mass of silicon oxide, at least one of yttrium oxide, erbium oxide and ytterbium oxide, and 2 to 6% by mass of these composite oxides.

When silicon oxide is less than 3% by mass, the liquid phase formation temperature at the time of sintering temperature rise becomes high and a sufficiently dense sintered body cannot be obtained. However, several mass% of oxidation is applied to the surface layer of the silicon nitride powder used as a raw material. When a physical layer or an oxynitride layer is present, the target sintered body may be obtained even if it is less than 3% by mass.
However, in the case of silicon nitride powder having a normal oxide layer, when silicon oxide is less than 3% by mass, at least one of Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase, Yb ₂ Si ₂ O ₇ phase One phase and Si ₂ N ₂ O phase are not formed.
On the other hand, if the silicon oxide exceeds 7% by mass, at least one phase of Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase, Yb ₂ Si ₂ O ₇ phase and Si ₂ N ₂ O phase are not formed. A relatively low melting point SiO ₂ phase is formed and the mechanical strength at high temperature is lowered, which is not preferable.

When the addition amount of at least one of yttrium oxide, erbium oxide, and ytterbium oxide is less than 2% by mass, melt formation is insufficient, the relative density is less than 98%, and densification does not proceed.
On the other hand, when the addition amount of at least one of yttrium oxide, erbium oxide, and ytterbium oxide exceeds 6% by mass, at least one of the Y ₂ Si ₂ O ₇ phase, the Er ₂ Si ₂ O ₇ phase, and the Yb ₂ Si ₂ O ₇ phase. One phase is not formed, and Y ₂ SiO ₅ phase, Er ₂ SiO ₅ phase, Yb ₂ SiO ₅ phase having relatively low melting points are formed, and the obtained sintered body has high mechanical strength and oxidation resistance at high temperature. Decreases.

At least one of silicon oxide, yttrium oxide, erbium oxide, and ytterbium oxide is preferably fine particles having an average particle diameter of 3 μm or less in order to obtain a homogeneous and high-density sintered body.
These raw material powders used as sintering aids are relatively inexpensive, and are stable ceramic powders that do not deteriorate during the mixing process in water.

As a method for producing and dispersing SiC fine particles having an average particle size of 0.1 μm or more and 0.7 μm or less of the present invention, a rotary pot mill (= Trommel), a planetary ball mill, an attritor, a vibration ball mill, an attrition mill, a rotation・ A method such as a revolving mixed pot mill can be used.
The material of the pot or ball to be used is preferably substantially composed of a main body and a lid of a SiC sintered body. In a pot mill for mass production, a material having a SiC tile attached as a liner may be used.

The crystalline phase of the spherical SiC to be mixed may be either α-SiC type (= 3C) or β-SiC type (= 2H, 4H, 6H, etc.), but sintering is performed in a temperature range of 1770 to 1850 ° C. Therefore, basically, the 6H phase is often identified.
In addition, the wear mixing mass is slightly different depending on the mixing method, the number of rotations, the particle size of other raw material powders, etc., but the wear on the inner wall of the pot: ball wear = 1: 10 to 20 (mass ratio). There are overwhelmingly many.

Therefore, when it is desired to change the mixing amount, it is effective to control the increase or decrease of the ball surface area, that is, the size of the ball diameter in the range of approximately 0.5 mm to 20 mm in addition to the increase or decrease of the ball addition amount.
If the amount is less than 2% by mass, the effect of suppressing the growth of the mother phase crystal grains is poor, and if it exceeds 5% by mass, columnar growth of the mother phase and the toughening due to the intersection of the crystal phases are not preferable.

As a sintering method, various sintering methods such as a pressureless sintering method, a gas pressure sintering method, a hot isostatic pressing sintering method, a hot pressing sintering method, etc. are performed in an atmosphere containing nitrogen gas. A plurality of these sintering methods may be combined.
The reason why sintering is performed in an atmosphere containing nitrogen gas is to suppress the decomposition of Si ₃ N ₄ during sintering. Since Si ₃ N ₄ decomposes at about 1800 ° C. or higher under a nitrogen gas of 0.1 MPa, when sintering at 1800 ° C. or higher, the nitrogen gas pressure is the critical decomposition pressure of Si ₃ N _{4 at} the sintering temperature. Set as above.

In addition, when producing a large thick-walled shaped product, in order to achieve sufficient densification, hot isostatic pressing in a nitrogen gas atmosphere may be further performed after pressureless sintering. More preferred.
As pressureless and hot isostatic pressing sintering conditions, the sintering temperature is desirably 1770 to 1850 ° C.
If the temperature is less than 1770 ° C., a dense sintered body cannot be obtained, and it becomes difficult to generate sufficient residual stress in the vicinity of the solid solution particles, so that a high toughness sintered body cannot be obtained.
On the other hand, at a high temperature exceeding 1850 ° C., β-Si ₃ N ₄ crystal grains become coarse, Si ₂ N ₂ O phase, Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase, Yb ₂ Si ₂ O Strength degradation occurs due to decomposition of the _seven phases, etc., and high hardness and thermal shock resistance cannot be obtained.

In addition, when the holding time is less than 8 hours, the densification does not proceed sufficiently, depending on the thickness of the molded body.
In order to crystallize at least one phase of Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase, Yb ₂ Si ₂ O ₇ phase and Si ₂ N ₂ O phase as grain boundary phases, The temperature lowering rate is preferably 10 ° C./min or less, more preferably 5 ° C./min to 10 ° C./min. When the rate of temperature decrease is lower than 5 ° C./min, the life of the furnace is shortened and the production efficiency is lowered. When the temperature is lower than 10 ° C./min, the Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase, Yb _At least one of the ₂ Si ₂ O ₇ phases and the Si ₂ N ₂ O phase are difficult to generate.

Next, examples of the present invention will be described together with comparative examples. The present invention is not limited to these examples.
(Examples 1-5)
To silicon nitride (Si ₃ N ₄ ) powder (α conversion rate of 97% or more, purity 99.7%, average particle size 0.7 μm),
Yttrium oxide (Y ₂ O ₃ ) powder (average particle size 2.5 μm), erbium oxide (Er ₂ O ₃ ) powder (average particle size 2.4 μm), ytterbium oxide (Yb ₂ O ₃ ) powder (average particle size 1 0.8 μm), yttrium oxide and silicon oxide composite oxide (Y ₂ SiO ₅ ) powder (average particle size 2.9 μm), ytterbium oxide and silicon oxide composite oxide (Yb ₂ Si ₂ O ₇ ) powder (average particle size) A predetermined amount (mass%) shown in Table 1 below, and a silicon oxide (SiO ₂ ) powder (average particle diameter of 1.9 μm) added,
Using purified water or acetone as a dispersion medium,
As the mixing balls, SiC balls having a diameter of 10 mm were used at a ratio of 200 g, which is twice as large as 100 g of all ceramic powder raw materials, and kneaded for 48 hours in a ball mill in which SiC tiles were attached to the inner wall and the lid. The amount of purified water or acetone added was 120 g with respect to 100 g of the ceramic whole powder raw material.
The amount of contamination was determined from the amount of mass reduction of the SiC tile or SiC ball. The average particle diameter of SiC is 0.2 to 0.5 μm, and the mixing amount in each example is as shown in Table 1.
Moreover, in each Example, it compared with the crystal phase ratio calculated | required from an X-ray diffraction pattern. The ratio of various crystal phases was determined according to a calibration curve obtained in advance from the X-ray diffraction peak height. The results are shown in Table 1.

Next, the obtained mixed powder was molded and then sintered. As molding conditions, a pressure of 130 MPa was applied by cold isostatic pressure, and a cylinder having an outer diameter of 140 mm (inner diameter of 100 mm) × height of 150 mm was molded.
For Examples 1 and 2, as sintering conditions, gas pressure sintering was performed for 8 hours at a temperature shown in Table 1 in a nitrogen gas 0.4 MPa pressurized atmosphere, and the temperature was the same at 1550 ° C. when the temperature was lowered. The furnace was cooled for the time shown in Table 1 at the temperature decreasing rate shown in Table 1 until the temperature was maintained and the room temperature.
About Examples 3-5, in the nitrogen gas 0.4MPa pressurization atmosphere, gas pressure sintering of 8 hours holding | maintenance was performed at the temperature shown in Table 1, and cooling at the time of temperature fall to the normal temperature of Table 1 was carried out. After performing, it reheated to 1550 degreeC in nitrogen atmosphere, and after the holding time of Table 1, it stood to cool at the time of temperature fall, and the sintered compact of Examples 1-5 was obtained.

(Comparative Examples 1 and 2)
Comparative Examples 1 and 2 use the same raw materials as in Examples 1 to 5, but the inner walls, lids and balls of the pots were made of Si ₃ N ₄ materials without using SiC materials, and were similarly prepared with purified water or acetone, It is each comparative example when the relative density is less than 98% due to abnormal grain growth (Comparative Example 1), and when the Si ₂ N ₂ O phase and Y ₂ Si ₂ O ₇ phase are not obtained (Comparative Example 2). . These are shown together in Table 1.

(Evaluation methods)
JIS standard bending test pieces were cut out from the sintered bodies obtained in Examples 1 to 5 and Comparative Examples 1 and 2, and mechanical properties were evaluated. The bending strength was measured according to JIS R1601 at normal temperature in the atmosphere and 1500 ° C. The hardness was measured as Vickers hardness at an indentation load of 98N.
For toughness, the fracture toughness value K _IC was measured at room temperature by the SEPB method of JIS R1607. The thermal shock resistance was evaluated based on a rapid cooling temperature difference ΔT at which a bending test piece was heated to a predetermined temperature in the air and then rapidly cooled in water, and the bending strength began to deteriorate. As the oxidation resistance, the bending test piece was heated to 1400 ° C. in the air, held for 64 hours, and evaluated by a mass change amount ΔW per unit surface area.
The sintered body density was measured as a relative density by the Archimedes method. Table 2 shows various properties of the obtained sintered bodies.

(Discussion)
As a result, as shown in Table 2, it was confirmed that the samples according to the examples of the present invention had higher strength at room temperature and higher temperature than the comparative examples, and extremely excellent thermal shock resistance and oxidation resistance.
Moreover, about the heat processing furnace before hot-rolling of the slab which is an actual operation equipment, and the heat-treatment furnace before plating of continuous molten metal plating, the sintered bodies of Examples 1 to 5 and Comparative Examples 1 and 2 above. Each was applied as a burner port 7 in the form shown in FIG. The tip of the burner port 7 protruded 5 mm inside the furnace.

Therefore, the sintered bodies of Examples 1 to 5 and Comparative Examples 1 and 2 were mounted on an actual machine as the burner port 7 and the durability for 2 years was confirmed. The operating conditions of the actual machine were heat treatment of steel sheets exceeding 30,000 tons per month, and the steel sheet passing speed was 100 to 150 m / min.
As a result, when the sintered bodies of Examples 1 to 5 were applied as burner ports, even after two years, damage, surface irregularities due to the formation of an oxide layer, adhesion of scales, and the like were not observed.
On the other hand, when the sintered bodies of Comparative Examples 1 and 2 are applied as burner ports, the strength at normal temperature and high temperature is low, the thermal shock resistance and the oxidation resistance are inferior. Adhesion of surface irregularities and scales due to the formation of layers was observed.

The schematic diagram which shows the inner wall structure of the heat processing furnace which concerns on the 1st Embodiment of this invention. The schematic diagram which shows the inner wall structure of the heat processing furnace which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 ... Steel plate, 2 ... Combustion burner, 3 ... Ceramic fiber, 4, 7 ... Burner port, 5 ... Support member for burner port, 6 ... Guide pipe, 8 ... Blanket material, 61 ... Projection part, 71 ... Groove part

Claims (6)

In a heat treatment furnace in which one or more burners are arranged on the furnace wall,
It comprises a furnace wall structure in which ceramic fibers are disposed at least inside the furnace wall, and a burner is installed in an insertion hole provided in the furnace wall,
Inside the burner furnace,
At least one of the Y ₂ Si ₂ O ₇ phase, the Er ₂ Si ₂ O ₇ phase and the Yb ₂ Si ₂ O ₇ phase is 2.5 to 4.8% by mass, and the Si ₂ N ₂ O phase is ₂ to 6.5. mass%,
2-5% by mass of SiC particles having an average particle size of 0.1 μm to 0.7 μm, and
a burner port composed of a silicon nitride ceramic sintered body having a composition with β-Si ₃ N ₄ and unavoidable impurities as a balance is disposed adjacently; and
A heat treatment furnace characterized in that a tip of the burner port is arranged so as to protrude from the inner wall surface of the furnace to the inside of the furnace. A burner port support member made of the silicon nitride ceramic sintered body is disposed outside the burner port, and
The heat treatment furnace according to claim 1, wherein a tip of the burner port support member is disposed so as to protrude from the inner wall surface of the furnace to the inside of the furnace. In a heat treatment furnace in which one or more burners are arranged on the furnace wall,
It comprises a furnace wall structure in which ceramic fibers are disposed at least inside the furnace wall, and a burner is installed in an insertion hole provided in the furnace wall,
Outside the tip of the burner,
2.5 to 4.8% by mass of at least one of Y ₂ Si ₂ O ₇ phase, Er ₂ Si ₂ O ₇ phase and Yb ₂ Si ₂ O ₇ phase,
₂ to 6.5% by mass of the Si ₂ N ₂ O phase, ₂ to 5% by mass of SiC particles having an average particle size of 0.1 μm to 0.7 μm, and
A burner port composed of a silicon nitride ceramic sintered body having a composition with β-Si ₃ N ₄ and inevitable impurities as the balance is fitted, and
A heat treatment furnace characterized in that a tip of the burner port is arranged so as to protrude from the inner wall surface of the furnace to the inside of the furnace.   The heat treatment furnace according to any one of claims 1 to 3, wherein the silicon nitride ceramic sintered body has a relative density of 98% or more.   The tip of the burner port or the tip of a support member for the burner port is disposed so as to protrude from the inner wall surface of the furnace to the inside of the furnace by 5 mm or more and 30 mm or less. Heat treatment furnace. A heat treatment furnace that is disposed adjacent to the inside of the burner of the heat treatment furnace having a furnace wall structure in which ceramic fibers are disposed at least inside the furnace wall, and a burner is installed in an insertion hole provided in the furnace wall. Burner port for
At least one of the Y ₂ Si ₂ O ₇ phase, the Er ₂ Si ₂ O ₇ phase and the Yb ₂ Si ₂ O ₇ phase is 2.5 to 4.8% by mass, and the Si ₂ N ₂ O phase is ₂ to 6.5. mass%,
2-5% by mass of SiC particles having an average particle size of 0.1 μm to 0.7 μm, and
A burner port for a heat treatment furnace, comprising a sintered silicon nitride ceramics composition having β-Si ₃ N ₄ and unavoidable impurities as a balance.

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