JPH0587568B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The present invention relates to a hearth roll for a steel heat treatment furnace and a method for manufacturing the same. [Prior Art] As shown in Fig. 4, a hearth roll installed in a steel heat treatment furnace such as a continuous annealing furnace (furnace atmosphere temperature: approximately 600 to 1000°C) has a shell member (shell) 1.
It has a structure in which axle members 4, 4 are joined to openings at both ends by welding or the like. The above roll shell 1 is SCH22 (0.4C−20Ni−
It is a hollow cylindrical body made of Ni-Cr heat-resistant steel such as 25Cr-Fe). A steel material to be heated, such as a cold-rolled steel plate, charged into the furnace is supported on the surface of the roll shell 1, heated to a predetermined temperature in the process of being transferred through the furnace, and sent out from the exit side of the furnace. [Problems to be Solved by the Invention] The hearth roll in the heat treatment furnace is exposed to the atmosphere in the furnace and is heated to a high temperature (for example, 950 to 980°C). On the other hand, a heated steel material S such as a cold-rolled steel plate is charged into the furnace and supported on the surface of the shell 1.
has a significantly lower temperature than Ciel 1. Therefore, the shell 1 receives a cooling effect due to contact with the heated steel material S, and has a surface area a ₁ in contact with the heated steel material (steel material contact area surface) and a surface area on both left and right sides that does not contact the heated steel material (non-contact surface area). Contact area surface) a ₂
A temperature difference (for example, about 150 to 200°C) is generated between the two. Under continuous furnace operation conditions in which the steel to be heated is repeatedly conveyed, there is a thermal strain caused by the temperature difference between the two surfaces near the boundary between the steel contact area A ₁ and the non-contact area A ₂ on the shell surface. This causes uneven wrinkles. The width dimension of the heated steel material S is, for example, 700 mm depending on the product specifications.
Since the width varies widely from ~1,300 mm, wrinkles occur over a wide area on the surface of the shell 1 during actual furnace operation. Furthermore, since the bending and crushing stress due to the load of the heated steel material acts synergistically with the thermal strain due to the temperature difference, not only the wrinkles described above but also the generation and development of minute cracks inevitably occur. When the above-mentioned roughness such as wrinkles and cracks occurs on the shell surface, the uneven pattern is transferred to the heated steel material carried by the shell and transferred.
This causes the surface quality to be impaired. In addition, the occurrence of wrinkles and cracks on the surface of the shell shortens the continuous service life of the hearth roll, increasing the labor and cost required for its maintenance, and interrupting furnace operation to replace the roll, which reduces furnace operation efficiency. be forced to suffer disadvantages such as declines. The present invention has been made in view of the above, and is effective against rough skin such as wrinkles and cracks on the shell surface, which cause deterioration of the surface quality of heated steel materials, increased burden of roll maintenance, and decrease in furnace operation efficiency. To provide an improved hearth roll that is prevented from being inhibited and a method for manufacturing the same. [Means and effects for solving the problem] The hearth roll for a steel heat treatment furnace according to the present invention has the following features:
It is characterized in that a heat transfer layer made of a high heat conductive metal is laminated and bonded to the inner peripheral surface of a shell made of heat-resistant steel via a brazing filler metal layer. FIG. 1 schematically shows the laminated structure of the shell of the hearth roll of the present invention. 3 is a heat transfer layer made of a high heat conductive metal, and the heat transfer layer 3 is similar to the brazing material layer 2.
It is laminated and bonded to the inner circumferential surface of the shell 1 via. In the hearth roll of the present invention in which the heat transfer layer 3 is laminated and bonded to the inner circumferential surface of the shell 1, the surface of the shell 1 has a steel material contact area surface _a1 and a non-contact area surface that cause the wrinkles and cracks. The temperature difference between a ₂ and the resulting thermal strain is effectively alleviated and eliminated by rapid heat transfer (thermal diffusion) performed through the heat transfer layer 3. Shell 1 of the hearth roll of the present invention is SCH22 similar to that of the conventional hearth roll.
It is a hollow cylindrical body made of Ni-Cr heat-resistant steel, such as Ni-Cr heat-resistant steel. The high heat conductive metal that is the heat transfer layer 3 laminated and bonded to the inner peripheral surface means a metal that has a higher thermal conductivity than the heat resistant steel of the shell 1, and the higher the thermal conductivity, the more preferable it is. When specifically selecting the metal material, an additional condition is imposed that it not cause softening or melting due to thermal effects during actual furnace use (the temperature of the shell reaches, for example, 950 to 980°C). Copper (Cu) is the most suitable typical high heat conductive metal that satisfies these conditions. Copper has a thermal conductivity of
0.923 cal/cm・sec・deg) and heat-resistant steel that forms the shell (its thermal conductivity is approximately 0.07 to 0.08 cal/deg).
cm・sec・deg), and has a high melting point (approximately 1083°C) that can withstand use in an actual furnace. However, the copper is not limited to pure copper, and as understood from the above explanation, effective heat transfer between the steel contact surface A ₁ and the non-contact region surface A ₂ of the shell and the furnace It may contain various elements as alloy components or impurities within a range that ensures a high melting point that can withstand the influence of the internal atmosphere. Therefore, the copper or other high heat conductive metal forming the heat transfer layer referred to in this specification is not limited to pure metal as described above and must be interpreted in a broad sense. The thickness of the heat transfer layer 3 is appropriately determined depending on the thickness of the shell 1 and the operating temperature, but it is preferable that the thickness of the shell 1 is approximately 10 to 30 mm and the heating temperature during use is approximately 950 mm.
In a normal hearth roll having a temperature of ~980°C, when the heat transfer layer 3 is made of copper, the layer thickness may be approximately 15 to 30 mm. In the present invention, the abutting interface between the shell 1 and the heat transfer layer 3 is bonded via the brazing material layer 2. Other methods for forming the laminated bonding structure between the shell and the heat transfer layer 3 include, for example, a method using explosive pressure energy, or a heat transfer layer made of a high heat conductive metal on the inner circumferential surface of the shell 1 by centrifugal casting. However, with the former method, it is difficult to ensure the formation of a reliable bond over a wide area of the interface between the shell 1 and the heat transfer layer 3, and with the latter method, the interface Although it is possible to form a reliable metallurgical bonding relationship throughout the entire structure, material deterioration due to the fusion of the shell material (heat-resistant steel) and the heat transfer layer material (copper, etc.) (embrittlement due to the formation of intermetallic compounds at the interface) etc.) cannot be avoided,
In addition, harmful fumes generated during casting pose health and safety problems. According to the brazing method, a uniform and reliable laminated bonding structure can be formed over the entire circumference and length of the interface between the shell 1 and the heat transfer layer 3 without such problems. Many types of brazing filler metals are known, and it goes without saying that when selecting one, the relationship between the melting point of the heat transfer layer forming material and the actual furnace operating temperature should be considered. That is, the brazing material has a welding temperature lower than the melting point of the high heat conductive metal such as copper that forms the heat transfer layer 3, and has a melting point that does not soften or melt when the hearth roll is used in an actual furnace. It takes. In addition, the heat-resistant steel (SCH2) that forms shell 1
There is a relatively large difference in thermal expansion coefficient between the high heat conductive metal (copper, etc.) forming the heat transfer layer 3 (SCH
22 heat-resistant steel: approx. 14.1×10 ^-6 /℃, copper: 17.1×
10 ^-6 /℃), so the temperature increase and decrease process in the furnace (temperature increase rate: e.g. 70 to 100℃/Hr, temperature decrease rate: e.g.
It is desirable that the material has an intermediate coefficient of thermal expansion to serve as a layer for absorbing and relaxing the thermal stress generated between the two layers at temperatures of 150 to 200° C./Hr). The most suitable brazing filler metal that meets these requirements is nickel brazing filler metal, and as a specific example, JIS
BNi-2 (Cr: 6-8%,
B: 2.75-3.5%, Si: 4-5%, Fe2.5-3.5%,
C: 0.06% or less, P: 0.02% or less, Ni: Bal),
BNi-3 (2: 2.75-3.5%, Si: 4-5%, Fe:
0.5% or less, C: 0.06% or less, P: 0.02% or less,
Ni: Bal), BNi-4 (B: 1.5~2.2%, Si: 3~
4%, Fe: 1.5% or less, C: 0.06% or less, P: 0.02
% or less, Ni:Bal), etc. In addition, brass solders, such as those specified in JIS Z3262, are also available.
BCuZn-6 (Cu46-50%, Ni: 9-11%, Pb:
0.05% or less, Al: 0.01% or less, P: 0.25% or less,
Si: 0.04~0.25%, Zn: Bal), BCuZn-7
(Cu: 46-49%, Ni: 10-11%, Ag: 0.3-1
%, Si: 0.15% or less, Zn: Bal), etc. can also be used. The thickness of the brazing material layer 2 is, for example, 0.1 to 0.5 mm.
The degree is appropriate. Next, a method for manufacturing a hearth roll of the present invention will be explained. The body member is made by thermally spraying a brazing metal layer on the outer peripheral surface of a hollow cylindrical body made of a high heat conductive metal, which becomes the heat transfer layer 3, and then attaches this to a hollow cylindrical body made of heat-resistant steel, which is the shell 1 material prepared separately. Manufactured by inserting the filler metal into an upright position, filling the top opening of the gap between the outer hollow cylinder and the inner hollow cylinder with replenishing brazing filler metal, and then heating and melting the filler filler metal in a vacuum furnace. be done. This will be explained with reference to FIG. 10 is a hollow cylindrical body made of heat-resistant steel (hereinafter referred to as "outer layer cylinder"), 30 is a hollow cylinder made of high heat conductive metal (hereinafter referred to as "inner layer cylinder"), and 20 is an outer circumference of inner layer cylindrical body 30. This is a brazing material layer that covers the surface. The outer layer cylindrical body 10 is typically a hollow cylinder obtained by applying required machining to a centrifugally cast pipe material, and the inner layer cylindrical body 30 is formed by forming a high heat conductive metal plate, such as roll forming. It can be manufactured by forming it into a cylindrical shape using a method and joining the butt surfaces using TIG welding or the like. The brazing material layer 20 on the surface of the inner cylindrical body 30 is formed by a thermal spraying method. Thermal spraying methods include gas spraying, arc spraying, high frequency spraying, plasma spraying, etc., and the brazing filler metal sprayed layer 20 can be suitably formed by gas spraying. The fitting of the inner layer cylindrical body 30 to the outer layer cylindrical body 10 may be carried out by heating the outer layer cylindrical body 10 and expanding its diameter. A brazing filler metal 21 for replenishment is loaded into the upper end opening of the clearance C at the fitting interface between the outer layer cylinder 10 and the inner layer cylinder 30. In the figure, an extra length portion E1 (this portion is cut and removed after soldering is completed) is provided at the upper ends of the outer layer cylinder 10 and the inner layer cylinder 30, and a replenishing brazing material 21 is provided in the annular space V. ing. This brazing filler metal 21 has the role of making up for the lack of brazing filler metal with respect to the clearance C at the fitting interface. In addition,
Reference numeral 40 denotes a base plate member attached to the lower end of the clearance C to prevent the melted brazing material from leaking through the lower end opening of the clearance C. The fitted body of the outer layer cylindrical body 10 and the inner layer cylindrical body 30 is held in an upright position and heated to a predetermined soldering temperature in a vacuum furnace. In the heat treatment, due to the melting of the brazing material sprayed layer 20 applied to the fitting interface and the replenishment effect of the brazing material by melting and flowing down the brazing material 21 at the upper end of the clearance C, the outer layer cylinder is formed over the entire circumference of the fitting interface. The soldering of the body 10 and the inner cylindrical body 30 is achieved. In the above heat treatment, if the fitted body is a long body (for example, about 1500 to 3000 mm in axial length), it is not possible to simply replenish the insufficient brazing material to the fitting interface from the upper end opening of the clearance C. It is difficult to ensure a sufficient replenishment effect down to the lower region. In such a case, in addition to the upper end opening of the clearance, it is preferable to load the replenishing brazing filler metal at one or more locations in the height direction of the clearance. In FIG. 2, 22, 22, . . . indicate examples. The replenishing brazing filler metals 22, 22, . . . are filled into the grooves by forming circumferential grooves 31, 31, . Just do it. The groove 31,
For example, the size of the openings 31, .
2,... may be filled by thermal spraying or filled as a paste brazing material. In addition,
The distance between adjacent grooves is, for example, 200 to 300 mm.
may be used as If such circumferential grooves 31, 31, ... are formed on the inner layer cylinder 30 that becomes the heat transfer layer 3, the uniformity of conductive heat transfer will be impaired and the heat diffusion effect will be inhibited. However, there is no such concern at all; on the contrary, reliable soldering is guaranteed by sufficient supply of brazing material to each part of the fitting interface, and as a result, the shell 1 is reduced by heat transfer through the heat transfer layer 3. See the improvement in the uneven heat mitigation and temperature equalization effect. After completing the soldering of the fitting interface by the above heat treatment, the excess lengths E1 and E2 at both ends are cut and removed, predetermined machining is applied, and this is joined to a separately prepared axle 4 to form a predetermined hearth. Assembled into rolls. [Example] An in-furnace test was conducted using the following rolls A and B as test rolls. [] Test rolls The configurations of the bodies of rolls A and B are as follows. However, in both cases, the outer diameter of the shell is 400 mm and the axial length is 950 mm. Roll A (invention example) Shell: 0.4C-20Ni-25Cr-Fe (equivalent to SCH22) Wall thickness 25 mm Heat transfer layer: Oxygen-free copper, layer thickness 25 mm Brazing metal layer: Nickel wax (7Cr-3B-5Si-3Fe-
0.1C−Ni, BNi−2 equivalent), layer thickness approximately 0.5
mm Roll B (conventional example) Single-layer material made of the same heat-resistant steel as the shell of Roll A above. For each of the rolls A and B, as shown in Fig. 3 [ ] [ ], a thermocouple is placed at a distance L = 450 mm from the axial center position of the body and the center position from the inner circumferential surface side. Meter mounting holes were formed, and thermocouple thermometers A and B were inserted and fixed into each hole. The depth of the mounting hole was set to 1/2 of the shell wall thickness. [] Furnace test Test rolls A and B were placed in a heating furnace (atmosphere gas: 98% N ₂ - 2% H ₂ ), and the cold plate material S was supported on the surface of the body in contact with the cold plate material S. The temperature difference (ΔT) between A and B of shell 1 caused by the cooling effect of was measured. However, cold plate material S is preheated to 350℃.
The temperature was raised to 100% and placed on the surface of the shell. Further, in the test, the ambient temperature was 550°C, and the cold plate material S was placed in a state where the roll temperature was increased to 350°C. The width of the cold plate material S is 400 mm, so the distance l from the edge of the cold plate material S to the thermocouple thermometer B is approximately 250 mm.
It is. The measurement results are shown in Table 1.

[Table] As shown above, in conventional roll B with a heat-resistant steel single-layer shell, the temperature difference (ΔT) between the contact area surface and non-contact area surface of the cold plate material is In contrast, in the roll of the invention example having a heat transfer layer laminated structure, the temperature difference was reduced to almost half due to the heat diffusion effect via the heat transfer layer. [Effects of the Invention] The hearth roll of the present invention, in which a heat transfer layer is laminated and bonded to the inner surface of the shell via a brazing material layer, has a heat transfer layer formed on the inner surface of the shell between the heated steel contact area surface and the non-contact area surface. Since heat diffusion occurs rapidly through the heat transfer layer, the temperature difference generated on the shell surface is significantly smaller than that in conventional hearth rolls. Therefore, the occurrence of wrinkles and cracks on the surface of the shell is suppressed and prevented, and the surface of the shell maintains a smooth and beautiful surface condition for a long period of time. This improves and stabilizes the surface quality of the heated steel material supported on the shell surface and transferred, and also provides effects such as improving the useful life of the hearth roll, reducing roll maintenance, and improving furnace operation efficiency.

[Brief explanation of the drawing]

FIG. 1 is an axial cross-sectional view schematically showing the laminated structure of the body of the hearth roll of the present invention, FIG. 2 is a cross-sectional explanatory diagram of the manufacturing method of the hearth roll of the present invention, and FIG. An explanatory diagram of in-furnace test procedures related to examples,
FIG. 4 is an axial sectional view showing a conventional example. 1: Shell, 2: Brazing metal layer, 3: Heat transfer layer, 1
0: Inner layer cylinder (heat-resistant steel cylinder), 20: Brazing filler metal spray layer, 21, 22: Replenishment brazing filler metal, 30: Inner layer cylinder (high heat conductive metal cylinder), 31: Circumferential groove,
C: Clearance, S: Steel material to be heated.

Claims (1)

[Claims] 1. A hearth roll for a steel heat treatment furnace, characterized in that a heat transfer layer made of a high heat conductive metal is laminated and bonded to the inner peripheral surface of a shell made of heat-resistant steel via a brazing filler metal layer. 2. The hearth roll for a steel heat treatment furnace according to claim 1, wherein the brazing material is nickel wax and the high heat conductive metal is copper. 3. A brazing metal layer is thermally sprayed on the outer circumferential surface of a hollow cylinder (hereinafter referred to as the "inner layer cylinder") made by forming high heat conductive metal plates into a cylindrical shape and joining the abutting surfaces by TIG welding, and separately The prepared hollow cylinder made of heat-resistant steel (hereinafter referred to as the "outer cylinder") is fitted into the upright position, and the replenishing brazing filler metal is applied to the clearance at the fitting interface between the outer cylinder and the inner cylinder. 2. The method of manufacturing a hearth roll for a steel heat treatment furnace according to claim 1, wherein the brazing material is loaded into the upper end opening and then heated and melted in a vacuum furnace to join the fitting interface. 4. A groove is formed around the outer peripheral surface at one or more places in the height direction of the inner layer cylinder, and a brazing metal layer is injected onto the outer peripheral surface, and a groove is formed in the recessed space of the groove. 4. The method of manufacturing a hearth roll for a steel heat treatment furnace according to claim 3, further comprising loading the brazing material and fitting the roll into the outer layer cylinder. 5. The method for manufacturing a hearth roll for a steel heat treatment furnace according to claim 3 or 4, wherein the brazing material is nickel wax and the high heat conductive metal plate is a copper plate.