JP6516344B1 - Method of producing in-bath roll and in-bath roll - Google Patents

Abstract

[PROBLEMS] To enhance corrosion resistance, high temperature oxidation resistance and high temperature wear resistance to molten aluminum. A roll in a bath used in a metal bath containing at least 50% by mass or more of Al, and the roll surface of the roll in the bath has a two-layer sprayed coating comprising an undercoat layer and a top coat layer. The undercoat layer includes a first boride containing at least WB, WCoB, W2CoB2, and a second boride consisting of at least one of borides of Cr, Zr and Ti, It is a cermet sprayed coating which consists of a cobalt base alloy which remainder does not contain 5 mass% or more of nickel, the said topcoat layer is a ceramic sprayed coating which consists of Al2O3 type oxide, and when said cermet sprayed coating is 100 mass% The content of the first boride is 55% by mass or more and 75% by mass or less, and the content of the second boride is 5% by mass or more and 15% by mass or less The content of B is 5.0% by mass or more and 7.0% by mass or less, and when the ceramic sprayed coating is 100% by mass, the content of Al.sub.2O.sub.3 is 60% by mass or more. I assume. [Selected figure] Figure 1

Description

  The present invention relates to the art of modifying the surface of rolls in a bath used in a molten aluminum bath.

  As a method of forming a plating film on the surface of a steel plate, a method of immersing the steel plate in a pot containing molten aluminum is known. In this pot, a roll (for example, a sink roll, a support roll) in a molten metal bath for continuously plating a steel plate is installed, and generally, on the surface of the roll, molten metal reactivity, corrosion resistance, A protective layer having wear resistance is formed.

In Patent Document 1, an undercoat layer is formed on the surface of a roll in a molten metal bath, and the adhesion state confirmed thereon by X-ray phase analysis is ZrO ₂ · x (x is CaO, Y ₂ O ₃ , MgO , An oxide selected from the group consisting of CeO ₂ , and HfO ₂ ) and a layer consisting of ZrSiO ₄ and / or its decomposition products (ZrO ₂ and SiO ₂ ), which is characterized in that Powder compositions are disclosed. In Patent Document 1, as an undercoat layer, a metal carbide _{(WC, TiC, Cr 3 C} 2, NbC, ZrC, TaC, MoC, VC), metal boride _{(CrB 2, TiB 2, ZrB} 2, MoB ₂ ) and the thing which consists of 1 or more types of ceramic components in metal nitride (MoN, TiN), and 1 or more types in Co, Ni, Cr, Mo, and W are disclosed.

In Patent Document 2, an aqueous solution or slurry of any one or more selected from oxides, borides and nitrides is applied to the surface of the oxide-based ceramic thermal spray coating and the pores in the coating to seal them. It is disclosed to perform hole processing. Furthermore, in the specification paragraph 0026 of Patent Document 2, oxides such as TiO ₂ , ZrO ₂ , SiO ₂ , MgO, and nitrides such as BN in an aqueous solution of chromic acid anhydride, ammonium chromate, ammonium bichromate In addition, a sealing treatment technology is disclosed which is applied to a thermal spray coating and heated and fired.

Japanese Patent Application Laid-Open No. 6-330278 Patent No. 4571250

  The in-bath roll having the constitution of Patent Document 1 was used in a molten aluminum bath, but the corrosion resistance, the high temperature oxidation resistance and the high temperature abrasion resistance to the molten aluminum were not sufficient.

  In particular, in recent years, the rotational speeds of the support roll and the sink roll are often controlled to be lower than the line speed of the steel plate, and are exposed to severe wear environments. There is a strong demand for improvement.

In order to solve the above problems, the in-bath roll according to the present invention is (1) an in-bath roll used in a metal bath containing at least 50% by mass of Al, and on the roll surface of the in-bath roll. A two-layer thermal spray coating comprising an undercoat layer and a topcoat layer is formed, and the undercoat layer comprises a first boride containing at least WB, WCoB, W ₂ CoB ₂ , Cr, Zr and Ti. A cermet spray coating comprising a cobalt-based alloy containing a second boride of at least one of borides and the remainder not containing nickel in an amount of 5% by mass or more, and the top coat layer is Al ₂ O ₃ A ceramic thermal spray coating of a base oxide, wherein the content of the first boride is 55 mass% or more and 75 mass% or less when the cermet thermal spray coating is 100 mass% The content of the second boride is 5% by mass to 15% by mass, the content of B is 5.0% by mass to 7.0% by mass, and 100% by mass of the ceramic thermal spray coating is used. when the content of _Al 2 _{O 3} is characterized in that it is 60 mass% or more.

(2) A friction reducing layer formed on the surface of the top coat layer, the friction reducing layer comprising BN and at least one of TiO ₂ , ZrO ₂ , SiO ₂ , MgO and CaO. When the friction reducing layer is 100% by mass, the content of BN is 20% by mass or more, and the in-bath roll according to the above (1) is characterized.

    (3) The content of the first boride is 64% by mass or more and 70% by mass or less, and the content of the second boride is 7% by mass or more, based on 100% by mass of the cermet sprayed coating. The in-bath roll according to the above (1) or (2), which is 12% by mass or less.

  (4) In the method of manufacturing a roll in a bath according to (1), the cermet sprayed coating is formed by high speed flame spraying, and the ceramic sprayed coating is formed by plasma spraying or high speed flame spraying. It is characterized by

(5) In the method for producing a roll in a bath according to (2), the cermet sprayed coating is formed by high speed flame spraying, and the ceramic sprayed coating is formed by plasma spraying or high speed flame spraying. The friction reduction layer is formed by applying an aqueous solution containing BN and at least one of TiO ₂ , ZrO ₂ , SiO ₂ , MgO, and CaO to the top coat layer, followed by baking. It is characterized by

  ADVANTAGE OF THE INVENTION According to this invention, the roll in a bath excellent in the corrosion resistance with respect to molten aluminum, high temperature oxidation resistance, and high temperature abrasion resistance can be provided.

It is the schematic which shows schematic structure of a hot-dip aluminum plating apparatus. It is the schematic enlarged view in a part of sink roll. It is sectional drawing in a part of protective layer. It is an enlarged photograph of the cross-sectional structure of a round bar thermal spray sample (when almost no corrosion of aluminum is confirmed) It is a magnified photograph of the cross-sectional structure of the round bar spray sample (when erosion of aluminum is confirmed) FIG. 1 is a schematic view of a wear testing device (without metal bath).

First Embodiment
FIG. 1 shows a schematic configuration of a hot-dip aluminum plating apparatus. The hot-dip aluminum plating apparatus includes a pot 11, a sink roll 13 and a support roll 14. A metal bath 12 is stored in the pot 11. The metal bath 12 is a molten metal whose main component is aluminum, and contains zinc etc. in addition to aluminum. Aluminum is contained in the metal bath 12 at least 50% by mass. The sink roll 13 is disposed in the metal bath 12 and changes the transport direction of the steel sheet A. The support roll 14 is provided at a position sandwiching the steel plate A, and stabilizes the passing position of the steel plate A and levelizes the plating adhesion thickness.

  The steel sheet A is immersed in the metal bath 12 and then changed in direction by the sink roll 13, and after the plating adhesion thickness is leveled by the support roll 14, the sheet is discharged to the outside of the pot 11.

  The protective layer formed on the surface of the sink roll 13 will be described in detail with reference to FIGS. 2 and 3. FIG. 2 is a schematic cross-sectional view of a part of the sink roll 13. FIG. 3 is a cross-sectional view of part of the protective layer.

  The sink roll 13 includes a roll main body portion 131, roll shaft portions 132 formed on both end portions of the roll main body portion 131, and a protective layer 133 formed on the base material surface of the roll main body portion 131. The roll shaft portion 132 is rotatably supported by a bearing (not shown). The steel plate A can be conveyed inside and outside the metal bath 12 by rotating the sink roll 13 in the direction of the arrow (see FIG. 1) with the roll shaft portion 132 as the rotation axis.

  The protective layer 133 includes an undercoat layer 133 a and a top coat layer 133 b. Here, in the top coat layer 133 b formed on the undercoat layer 133 a, cracks occur due to thermal expansion when the sink roll 13 is immersed in the metal bath 12 or in a preheating step before immersion. Therefore, since the molten metal in the metal bath 12 reaches the undercoat layer 133a through the cracks, the undercoat layer 133a is required to have corrosion resistance and high temperature oxidation resistance to molten aluminum.

(About the undercoat layer 133a)
The undercoat layer 133a is a cermet spray coating, and is composed of a first boride, a second boride, and a Co-based alloy. As the first boride, W boride containing at least WB, WCoB, W ₂ CoB ₂ is used. The W boride may further contain W boride composed of W, Cr, and B. For the second boride, at least one of Cr boride, Zr boride and Ti boride is used. Since it is at least one type, one of Cr boride, Zr boride and Ti boride may be used to constitute the second boride. Alternatively, the second boride may be formed of two of Cr boride, Zr boride and Ti boride. Furthermore, the second boride may be configured using three species of Cr boride, Zr boride and Ti boride. Among these, a cermet spray coating composed of W boride, Zr boride and Co-based alloy is particularly preferable.

  The present inventors have prevented the erosion of molten aluminum on the substrate by forming the undercoat layer 133a with a cermet spray coating containing a first boride and a second boride in a predetermined ratio. It has been discovered that high temperature oxidation resistance can be obtained. That is, it has been found that the resistance to corrosion and the high temperature oxidation resistance to molten aluminum are significantly enhanced. If the oxidation resistance of the undercoat layer 133a is enhanced, as a result, the oxidation resistance of the roll substrate underlying the undercoat layer 133a is also enhanced.

  The predetermined ratio will be described. The content of the first boride is 55% by mass or more and 75% by mass or less, and the content of the second boride is 5% by mass or more, where the undercoat layer 133a (cermet sprayed coating) is 100% by mass. It is 15% by mass or less. Preferably, the content of the first boride is 64% by mass to 70% by mass, and the content of the second boride is 7% by mass to 12% by mass. When the thermal spray coating is quenched after the thermal spraying, the amorphous non-crystalline phase of either the first boride or the second boride may be included in the undercoat layer 133a.

  When the content of the first boride decreases to less than 55% by mass, the high temperature oxidation resistance and the molten aluminum corrosion resistance become insufficient. When the content of the first boride exceeds 75% by mass, the B content in the cermet sprayed coating may be less than 5.0%, and the molten aluminum corrosion resistance and the high temperature oxidation resistance of the cermet sprayed coating There is a risk that the gender will be insufficient. That is, when the content of the first boride becomes more than 75% by mass, the cermet sprayed coating becomes a W rich coating and the content of B decreases, so that the molten aluminum corrosion resistance of the cermet sprayed coating is insufficient. May be

  When the content of the second boride decreases to less than 5% by mass, the B content in the cermet sprayed coating may become less than 5.0%, and the molten aluminum corrosion resistance of the cermet sprayed coating and the high temperature acid resistance May be insufficient. When the content of the second boride exceeds 15% by mass, the B content in the cermet sprayed coating may become more than 7.0% by mass, and when used for a long time in a high temperature molten metal, the cermet sprays Excess borides are formed in the coating, the hardness of the cermet sprayed coating abnormally increases and the toughness decreases, and as a result, the cermet sprayed coating is likely to be cracked, and erosion of the material due to penetration of molten aluminum or cermet Peeling of the thermal spray coating may occur. In addition, when a crack occurs in the cermet sprayed coating, the area in contact with air increases, and as a result, the high temperature oxidation resistance may be insufficient.

  The inventors of the present invention have separately confirmed that sufficient corrosion resistance against molten aluminum and high temperature oxidation resistance can not be obtained with the undercoat layer 133a formed only of the second boride. That is, the present inventors have found that excellent molten aluminum corrosion resistance and high temperature oxidation resistance can not be obtained unless the undercoat layer 133a is a combination of the first boride and the second boride. did. This point will be clarified in an example described later.

  For a Co-based alloy (100% by mass), for example, Cr: 15% by mass to 35% by mass, W: 10% by mass or less, Fe: 7% by mass or less, C: less than 2% by mass, Ni: 5% by mass Less than, the remainder can use the alloy which consists of Co.

  Here, when 5 mass% or more of Ni is contained in the Co-based alloy, Ni is dissolved in the molten aluminum, in other words, the Co-based alloy as a binder metal is dissolved in the molten aluminum, and the wear resistance is excellent. There is a possibility that the top coat layer 133b may come off from the base material. Therefore, the Co-based alloy should not contain 5% by mass or more of Ni.

The undercoat layer 133a can be formed, for example, by thermally spraying a thermal spray material containing WB, at least one of CrB ₂ , ZrB ₂ , and TiB ₂ , and a Co-based alloy. As the Co-based alloy, a Co-based alloy composed of at least one of W and Fe and Cr can be used. The Co-based alloy may contain Ni, but it needs to be less than 5% by mass. An undercoat layer 133a is formed by spraying the base material surface of the roll body 131 by high velocity oxy-fuel (HVOF) by setting the compounding ratio of the above-mentioned thermal spray materials to an appropriate value. can do. The high speed flame spraying method is a kind of flame spraying method using combustion flames such as high pressure oxygen and hydrocarbon fuel gas, and generates a high speed flame comparable to the explosion spraying method by increasing the pressure in the combustion chamber. be able to. By spraying by high-speed flame spraying, the coating structure of the undercoat layer 133a can be densified. Thereby, the through-pores in the thermal spray coating are extremely reduced, and the penetration of the molten metal into the thermal spray coating can be suppressed.

In addition, by receiving the heat at the time of thermal spraying, a part of the thermal sprayed WB reacts with Co contained in the Co-based alloy to form WCoB and W ₂ CoB ₂ . Also, a small amount of W boride composed of W, Cr and B may be produced. CrB _2, by heat the heat during spraying, some changes to CrB. A part of ZrB ₂ is changed to ZrB by receiving heat during thermal spraying. A part of TiB ₂ is changed to TiB by receiving heat at the time of thermal spraying. That is, when CrB ₂ is sprayed, the undercoat layer 133 a contains CrB and CrB ₂ . When ZrB ₂ is thermally sprayed, the undercoat layer 133 a includes ZrB and ZrB ₂ . When TiB ₂ is thermally sprayed, the undercoat layer 133 a includes TiB and TiB ₂ .

  The preferable thickness of the undercoat layer 133a is 50 μm or more and 300 μm or less. When the thickness of the undercoat layer 133a is less than 50 μm, it is difficult to obtain the above-described effect as the undercoat layer. When the thickness of the undercoat layer 133a exceeds 300 μm, the cost increases.

(About top coat layer 133b)
Since the undercoat layer 133a is insufficient in abrasion resistance, abrasion occurs due to long-term sheet passing. Therefore, the top coat layer 133b excellent in high-temperature wear resistance is formed on the undercoat layer 133a.

The thermal spray coating forming the top coat layer 133 _b is a ceramic thermal spray coating made of an alumina (Al ₂ O ₃ ) -based oxide. This ceramic thermal spray coating is excellent in corrosion resistance to molten aluminum, has a low hardness reduction at high temperatures, and is less susceptible to wear even when exposed to a molten aluminum environment for a long time. The content of alumina (Al ₂ O ₃ ) is 60% by mass or more when the whole of the ceramic sprayed coating is 100% by mass in order to express this effect. The alumina-based oxide may be composed of alumina (Al ₂ O ₃ ) alone, but may contain oxides other than alumina (for example, TiO ₂ , SiO ₂ ). That is, the top coat layer 133 _b may be formed of an alumina-based oxide composed of Al ₂ O ₃ -TiO ₂ and Al ₂ O ₃ -SiO ₂ . Further, the top coat layer 133 _b may be formed of an alumina-based oxide composed of alumina (Al ₂ O ₃ ), Al ₂ O ₃ -TiO ₂ , and Al ₂ O ₃ -SiO ₂ .

  The preferable thickness of the top coat layer 133 b is 30 μm or more and 300 μm or less. When the thickness of the top coat layer 133 b is less than 30 μm, it is difficult to obtain the effects of the top coat layer 133 b described above. When the thickness of the top coat layer 133 b exceeds 300 μm, a crack may occur due to thermal shock during use.

  The top coat layer 133 b can be formed, for example, by thermally spraying a thermal spray powder containing an alumina-based oxide on the undercoat layer 133 a by a plasma spray method. The plasma spraying method is a method using as a heat source a high temperature and high speed plasma generated when a discharge is performed while flowing an inert gas between a pair of electrodes. In general, argon is used as a working gas, and a water-cooled nozzle-like copper anode and a tungsten cathode are used as electrodes. When an arc is generated between the electrodes, the working gas is plasmified by the arc, and a high-temperature, high-speed plasma jet is ejected from the nozzle. The thermal spray powder is charged into the plasma jet and heated to accelerate, whereby the thermal spray powder can be caused to collide with the undercoat layer 133 a to form the top coat layer 133 b. According to the plasma spray method, even a high melting point spray material such as an alumina-based oxide can be formed into a film.

  The topcoat layer 133b may be formed by spraying a thermal spray powder containing an alumina-based oxide onto the undercoat layer 133a by high-speed flame spraying. High speed flame spraying is a type of flame spraying using high pressure oxygen and combustion flames such as hydrocarbon fuel gas. It is possible to generate a high speed flame comparable to a detonation flame spray while being a continuous combustion flame. Since the thermal spray powder collides with the undercoat layer 133a at a high speed, a dense film can be formed. The average particle size of the thermal spray powder is preferably 15 μm or less in order to promote the combustion flame of the thermal spray powder.

Second Embodiment
The present embodiment is a modification of the first embodiment, and a friction reducing layer is formed on the top coat layer 133 b. Thereby, the wear resistance of the top coat layer 133 b can be further enhanced.

The friction reducing layer comprises BN and a predetermined oxide which is less likely to react with molten aluminum under temperature conditions of room temperature to 800 ° C. For the predetermined oxide, for example, one or more of TiO ₂ , ZrO ₂ , SiO ₂ , MgO and CaO can be used. When the friction reducing layer is 100% by mass, the content of BN is 20 mass or more. The upper limit of BN is not particularly limited, but is preferably 50% by mass. If the BN exceeds 50% by mass, the durability of the friction reducing layer may be reduced. By using a friction reducing material containing BN, it is possible to form a friction reducing layer with sliding lubricity on the surface of the ceramic thermal spray coating.

  As a result, the frictional force applied to the ceramic thermal spray coating is reduced, and damage to the ceramic thermal spray coating, surface roughening, and the like can be suppressed more effectively. In addition, the above-mentioned friction reduction layer can be formed by apply | coating the aqueous solution containing the above-mentioned friction reduction material to the topcoat layer 133b, and baking it.

  Here, the present inventors also studied using other nitrides such as TiN, ZrN and VN as the friction reducing material, but discovered that excellent high temperature lubricity can not be obtained without BN. That is, the present inventors discovered that the friction force applied to the ceramic sprayed coating can be more effectively reduced by forming the friction reducing layer using a friction reducing material containing BN of 20% by mass or more. Specifically, it has been found that the roll can be used for a long time even if the conveyance speed of the steel sheet A reaches twice the conveyance speed of the roll. In addition, the sink roll 13 is generally controlled to be slower than the transport speed of the steel plate A (that is, the line speed).

CaO is more thermodynamically stable than Al ₂ O ₃ and, when used with BN, makes the friction reducing layer more durable. The preferred thickness of the friction reducing layer is 5 μm or more and 100 μm or less. When the thickness of the friction reducing layer is less than 5 m, it is difficult to obtain the above-mentioned effect of the friction reducing layer. When the thickness of the friction reducing layer exceeds 100 μm, the friction reducing layer is likely to be cracked, which may cause a problem of chipping and peeling.

  Although the protective layer 133 of the sink roll 13 has been described in the above embodiment, the protective layer 133 of the present invention can also be applied to the support roll 14. Here, in order to absorb the influence of the vibration generated at the time of conveyance of the steel plate A, the support roll 14 is controlled at a speed lower than the line speed of the steel plate A. Specifically, in the case of the support roll 14, since the rotational speed is controlled to be lower than that of the sink roll 13, the wear problem due to the speed difference becomes more remarkable. Therefore, the present invention can be more suitably used for the support roll 14.

Next, the present invention will be described more specifically by showing examples.
Example 1
In order to confirm the molten aluminum corrosion resistance of the undercoat layer, the following molten aluminum corrosion resistance test and high temperature oxidation resistance test were conducted. A round bar spray sample in which a cermet thermal spray coating was formed on Fe base was prepared and immersed in a metal bath for 48 (hours), and then it was withdrawn and the appearance and cross-sectional structure of the round bar spray sample were observed. The bath component of the metal bath was 100% aluminum, and the bath temperature was set to 700 (° C.).

  When the aluminum corrosion was hardly confirmed (see, for example, FIG. 4), the molten aluminum corrosion resistance was evaluated as “very good” as being very good. When the aluminum corrosion was slightly confirmed, the molten aluminum corrosion resistance was evaluated as "good" as being generally good. When a large amount of aluminum corrosion was confirmed (see, for example, FIG. 5), the molten aluminum corrosion resistance was evaluated as “poor” as poor.

  In the high-temperature oxidation resistance test, a test piece on which a cermet sprayed coating is formed is formed, and this is heated with a thermogravimetric measurement device (TG) to obtain information on weight change, up to 600 ° C. in the air. Oxidation resistance performance was evaluated. The reason why the temperature is set to 600 ° C. is that the sink roll is preheated before being immersed in the metal bath 12, and the maximum temperature of this preheat temperature is about 600 ° C.

Tables 1 and 2 show the evaluation results of molten aluminum corrosion resistance and high temperature oxidation resistance. In addition, in the Co-based alloy, Cr: 35% by mass, W: 5% by mass, Fe: 2% by mass, C: less than 2% by mass, alloy 1 consisting of the balance Co, Cr: 25% by mass, W: 10 % By mass, Fe: 1.5% by mass, C: less than 2% by mass, Ni: 1.0% by mass, the balance being an alloy 2 consisting of Co, Cr: 20% by mass, W: 5% by mass, C: 1. 0% by mass, Ni: 2.0% by mass, alloy 3 consisting of the balance Co, Cr: 15% by mass, Fe: 7% by mass, C: 1.3% by mass, Ni: 3.0% by mass, the balance is One of alloy 4 consisting of Co was used. In addition, the layer thickness of the undercoat layer made all 100 micrometers the target value.
From the above test results, by forming an undercoat layer having a content of the first boride of 55% by mass to 75% by mass and a content of the second boride of 5% by mass to 15% by mass. It has been found that corrosion resistance and high temperature oxidation resistance to molten aluminum are combined. In particular, when the content of the first boride is 64% by mass to 70% by mass, and the content of the second boride is 7% by mass to 12% by mass, the above-mentioned effects are significantly enhanced. I understand. Moreover, it turned out that the combination of W boride and Zr boride is particularly excellent from the results of sample Nos. 1 to 6. On the other hand, it has been found that the thermal spray coating in which only the second boride is combined with the Co-based alloy has lower corrosion resistance and high temperature oxidation resistance to molten aluminum as compared with the cermet thermal spray coating of the present invention. The first boride (W boride) consists of WB, WCoB and W ₂ CoB ₂ and Table 1 describes the total content of these borides. Moreover, the total content of CrB and CrB ₂ is described as the content of Cr boride, the total content of ZrB and ZrB ₂ is described as the content of Zr boride, the content of Ti boride The total content of TiB and TiB ₂ is described as

(Example 2)
Co base alloy 5 consisting of Cr: 15% by mass, Fe: 7% by mass, C: 1.0% by mass, Ni: 5.5% by mass, and the remainder being Co: sample No. 23 to 25 of Table 1 The corrosion resistance to molten aluminum was investigated in the same manner as described above, changing to (a Ni-rich Co-based alloy). The same molten aluminum as in Example 1 was used. The results are shown in Table 3.
From the above test results, it was found that the thermal spray coating is corroded by the molten aluminum when the content of Ni contained in the Co-based alloy exceeds 5% by mass.

(Example 3)
The abrasion resistance (abrasion resistance at high temperature) of the top coat layer and the friction reducing layer was confirmed by the abrasion test apparatus of FIG. In the figure, reference numeral 104 denotes a metal bath, in which a sliding shaft 101 bent in two steps is disposed. A plate-like evaluation material 102 was attached to the end of the sliding shaft 101. As a base material of the evaluation material 102, SUS304 was used. An undercoat layer and a topcoat layer were formed on the surface of the substrate of the evaluation material 102. Also, for some samples, a friction reducing layer was formed on the top coat layer. The undercoat layer was formed of the thermal spray coating of sample No. 23 of Example 1. The sliding shaft 101 was reciprocated 48 (hour) in the horizontal direction indicated by the arrow while pressing the mating member 103 supported by the supporting member 105 against the evaluation member 102 in the metal bath 104 with a predetermined load. The bath component of the metal bath 104 was 100% by mass of aluminum, and the bath temperature was set to 700 (° C.). The pressing load was set to 5.0 (kgf). The sliding speed of the sliding shaft 101 was set to 50 (mm / s). The counterpart material 103 was made of SUS304.

The compositions of the topcoat layer and the friction reducing layer were variously changed, and the above-described actual machine evaluation was performed for each. The layer thickness of the top coat layer was set to a target value of 150 μm. The layer thickness of the friction reducing layer was set to a target value of 50 μm. After the test, each evaluation material 102 was cut, and the cross-sectional structure of the cut surface was observed to confirm the thickness change of the top coat layer. Assuming that the thickness of the top coat layer before the test is 100% and the thickness reduction rate after the test is 50% or more, the high-temperature abrasion resistance is evaluated as "poor" as being low, and the thickness reduction rate after the test is 20 % And less than 50% are evaluated as "good" as high temperature abrasion resistance, and when the thickness reduction ratio after the test is less than 20%, "very good" as high temperature abrasion resistance It evaluated by. The test results are shown in Table 4.
Sample No. 38 had no friction reducing layer, and the content of alumina (Al ₂ O ₃ ) contained in the topcoat layer was insufficient at less than 60% by mass, so the high-temperature wear resistance was evaluated as “poor” . On the other hand, in sample Nos. 35 to 37 and 48, since the content of alumina (Al ₂ O ₃ ) was increased to 60 mass% or more, the evaluation of high-temperature wear resistance was improved to “good”. In samples No. 39 to 43, since the friction reducing layer containing BN at 20 mass% or more was formed on the top coat layers of sample Nos. 35 to 37, the evaluation of high-temperature wear resistance was improved to "very good". On the other hand, in samples No. 44 to 46, since the friction reducing layer did not contain BN, the evaluation of the high-temperature wear resistance remained “good”. Moreover, in sample No. 47, since BN contained in a friction reduction layer ran short, evaluation of high temperature abrasion resistance remained "good".

(Example 4)
The above-mentioned samples No. 35 to 38, 48 were respectively immersed in a metal bath to confirm the molten aluminum corrosion resistance of the top coat layer. The bath component of the metal bath was 100% by mass of aluminum, the bath temperature was 700 (° C.), and the immersion time was 48 (hour). After the immersion test, the appearance is observed, and if the top coat layer is found to have a melt damage or if the top coat layer has a crack and the molten aluminum penetrated from the crack shows a melt to the substrate The molten aluminum was evaluated as "poor" as having low corrosion resistance. When the above-mentioned melting loss was not recognized, it evaluated as "good" that molten aluminum corrosion resistance was high.

11 pot 12 metal bath 13 sink roll 14 support roll 131 roll main body part 132 roll shaft part 133 protective layer 133 a undercoat layer 133 b top coat layer

Claims (5)

A roll in a bath used in a metal bath containing at least 50% by mass or more of Al,
On the roll surface of the roll in the bath, a two-layer thermal spray coating comprising an undercoat layer and a top coat layer is formed,
The undercoat layer contains a first boride containing at least WB, WCoB, W ₂ CoB ₂ and a second boride consisting of at least one of borides of Cr, Zr and Ti, and the remainder is It is a cermet thermal spray coating of cobalt-based alloy not containing 5% or more by mass of nickel,
The top coat layer is a ceramic sprayed coating made of an Al ₂ O ₃ based oxide,
The content of the first boride is 55% by mass to 75% by mass, and the content of the second boride is 5% by mass to 15% by mass, based on 100% by mass of the cermet sprayed coating. The content of B is 5.0% by mass or more and 7.0% by mass or less.
The in-bath roll characterized in that the content of Al ₂ O ₃ is 60% by mass or more when the ceramic sprayed coating is 100% by mass. A friction reducing layer formed on the surface of the top coat layer, the friction reducing layer comprising BN and at least one of TiO ₂ , ZrO ₂ , SiO ₂ , MgO and CaO,
The in-bath roll according to claim 1, wherein the content of BN is 20% by mass or more when the friction reducing layer is 100% by mass.   The content of the first boride is 64% by mass to 70% by mass, and the content of the second boride is 7% by mass to 12% by mass, based on 100% by mass of the cermet sprayed coating. The roll according to claim 1 or 2, characterized in that: A method of producing a roll in a bath according to claim 1, wherein
The cermet sprayed coating is formed by high speed flame spraying method,
The method for producing a roll in a bath, wherein the ceramic thermal spray coating is formed by plasma spraying or high speed flame spraying. The method for producing a roll in a bath according to claim 2, wherein
The cermet sprayed coating is formed by high speed flame spraying method,
The ceramic sprayed coating is formed by plasma spraying or high speed flame spraying,
An aqueous solution containing BN and at least one of TiO ₂ , ZrO ₂ , SiO ₂ , MgO, and CaO is applied to the top coat layer and then fired to form the friction reducing layer. The method of producing the in-bath roll.