JP5458654B2 - Work roll for hot rolling mill and its manufacturing method - Google Patents

Description

  The present invention relates to a work roll used for hot rolling of a metal plate, and more specifically, by reducing the thermal expansion coefficient of the work roll, the expansion of the work roll that occurs as the roll temperature increases during rolling ( The present invention relates to a work roll for a hot rolling mill capable of suppressing (thermal crown) and a manufacturing method thereof.

  In the hot rolling of a metal plate, the temperature of the work roll is higher at the part where the metal plate of the material to be rolled contacts than at the other part, the work roll is locally thermally expanded, and the thermal expansion called a thermal crown is performed. Parts are generated. This thermal crown varies depending on the rolling schedule, the sheet width of the material to be rolled, the temperature, etc., but as will be described later, it affects the sheet passability and the quality of the sheet shape after rolling in hot rolling. .

Hereinafter, the production by hot rolling of a thin steel plate that requires strict quality as a metal plate will be described in detail.
In a production line for hot rolling of thin steel plates, a rolling material called a slab is heated to 1000 to 1300 ° C. and extracted from a heating furnace, and is rolled to a predetermined thickness by a rough rolling machine in a rough rolling process. Next, the steel sheet is successively rolled by a plurality of finish rolling mills arranged continuously in the finish rolling process, rolled into a thin steel plate having a predetermined thickness, and wound into a winder to form a hot coil.

  In the rough rolling process, in order to supply the sheet bar to the finishing mill, the thickness is usually reduced by rolling in 4 to 9 passes from the slab thickness (about 200 to 300 mm) to the sheet bar thickness (about 20 to 60 mm). Is done. The steel material (rolled material) before rolling is called a slab, and the steel material that has passed through a roughing mill is called a sheet bar. Further, the steel material (rolled material) in the rough rolling process is generally called a rough bar, but basically the plate thickness is different. The surface temperature of the sheet bar after rough rolling is about 900 to 1150 ° C. The sheet bar that has undergone rough rolling is cut at the leading end and supplied to the finishing mill row.

  In the finish rolling process, the finish rolling mill row is composed of a plurality of rolling mills, for example, seven stands F1, F2,... It is finished into a thin steel plate having a thickness of about 1.2 to 15 mm, and after being cooled, it is wound around a hot coil by a coiler. A thin steel plate (rolled material) during or after finish rolling is also called a steel strip or stripped.

  Conventionally, as a work roll material for hot finish rolling, a high speed material excellent in wear resistance and rough skin resistance is preferably used, extending the roll exchange period by reducing roll wear, missing the roll surface layer, Effective in improving the surface quality of rolled material by reducing banding (partial peeling). The high-speed material used for the outer layer of these high-speed rolls contains several percent of Cr, Mo, W, V, Co, etc., and has a particularly fine structure that crystallizes hard carbides. And has rough skin resistance.

  However, by using the above-mentioned high-speed composite roll in hot sheet rolling, problems such as wear reduction and surface quality improvement were almost solved, but stable rolling and quality improvement of the plate shape after rolling were improved. There were the following problems in realizing.

  The temperature of the work roll rises due to heat and frictional heat generated from the material to be rolled during hot rolling. As the hot rolling progresses, the average temperature of the work roll becomes about 50 to 100 ° C. in the finish rolling, and the temperature of the barrel central portion in the barrel length direction of the work roll where the steel strip of the material to be rolled is rolled is different. This temperature is higher than that of the barrel end in the barrel length direction of the roll, and a thermal crown is generated as shown in FIG. In FIG. 4, 1 is a work roll 1 and 8 is a steel strip of a material to be rolled. Note that the thermal crown of FIG. 4 is schematically shown, and is exaggerated from the actual one.

  This thermal crown is a phenomenon in which the diameter at the barrel central portion of the work roll in the barrel length direction is larger than that at the barrel end. When rolling a steel strip with a roll with a larger diameter at the center of the roll barrel, the roll gap formed by the upper and lower work rolls becomes smaller at the work roll center, so the center of the steel strip is less than the plate width end. It stretches well, exhibits a so-called belly stretch shape or a mid-stretch shape (center buckling), and the steel strip becomes wavy, so-called flatness deteriorates. The plate crown also deteriorates.

FIG. 3A shows the belly elongation or middle elongation phenomenon that occurred during hot rolling of the finishing mill. As shown in FIG. 3B, when the plate width is narrow, the difference in elongation between the plate width end portion and the plate width central portion is small, and thus it is difficult to form an abdominal stretch shape. However, as shown in FIG. 3 (c), when the plate width is wide, the belly stretch becomes large, and when this belly stretch is rolled in the next stand, a stable plate cannot be formed, and in some cases steel A squeezing (two-sheet biting) may occur in the center of the belt, leading to a rolling accident.
In this way, the thermal crown greatly affects the stable plate-passability in rolling operations and the quality of the plate shape after rolling (flatness and plate crown). Therefore, in hot finish rolling, the work roll reduces the thermal crown. Many have been developed.

Among them, the following techniques are disclosed as techniques relating to a roll for reducing the thermal crown.
In Patent Document 1, a high-speed material having excellent wear resistance and skin roughness resistance can be used as an outer layer material, and stability of the rolling state in hot rolling can be ensured. For the purpose of providing a composite roll for hot rolling excellent in improvement in plate properties, a composite roll in which a high-speed outer layer material is integrated with a shaft material. An iron-based shaft material having an average coefficient of thermal expansion of 11.8 × 10 ⁻⁶ / ° C. or less is used, whereby the average thermal expansion coefficient from room temperature to 200 ° C. in the entire composite roll is 12.0 × 10 ⁻⁶ / ° C. The invention of a composite roll configured as follows is described.

Although the thermal expansion coefficient of the high-speed outer layer material is larger than that of the iron-based shaft material, according to the invention described in Patent Document 1, by limiting the material and composition range of the iron-based shaft material, An iron-based shaft material having an average coefficient of thermal expansion up to 1 ° C. of 11.8 × 10 ⁻⁶ / ° C. or less is used, whereby an average coefficient of thermal expansion from room temperature to 200 ° C. in the entire composite roll is 12.0 × 10 ^{− Since} it is configured to be ⁶ / ° C. or less, it aims to stabilize the rolling state in hot rolling while maintaining the features such as wear resistance, rough skin resistance, and crack resistance by using a high-speed outer layer material. Patent Document 1 describes that the sheet-passability in hot sheet rolling can be greatly improved, particularly as a work roll for hot finishing.

Patent Document 2 also discloses a low thermal expansion composite work composed of an outer layer made of a high-speed material and a shaft made of stainless steel (SUS) having a relatively low thermal expansion coefficient and thermal conductivity at room temperature to 100 ° C. An invention of a roll and its manufacturing technology is described. In this invention, since the thermal conductivity of the shaft member is 0.062 cal / cm · sec · ° C. from room temperature to 100 ° C. and is small, the temperature rise of the shaft member is reduced and the thermal expansion associated therewith is also suppressed. doing. And the composite work roll of this invention is manufactured by welding and forming an outer layer made of a high speed material on the outer periphery of a shaft made of stainless steel (SUS material) by a continuous overlay casting method (same as a continuous casting method), The thermal expansion coefficient of the shaft material from room temperature to 100 ° C. is 12 × 10 ⁻⁶ / ° C. or less, and the heat conductivity of the shaft material from room temperature to 100 ° C. is 0.062 cal / cm · sec · ° C. or less. .

  According to the invention described in Patent Document 2, the thermal crown can be remarkably reduced by using a composite work roll manufactured by continuous overlay casting for hot finish rolling (25% of the conventional), so The plate flatness can be secured at a high level without causing any middle elongation. For this reason, Patent Document 2 describes that it is easy to obtain an appropriate plate profile and that the quality of the rolled plate can be improved.

However, when the above-described conventional composite roll is used as a work roll of a hot finishing rolling mill and thin plate hot rolling is performed, there are the following problems.
As the shaft material described in Patent Document 1, an iron-based shaft material having an average thermal expansion coefficient of 11.8 × 10 ⁻⁶ / ° C. or less from room temperature to 200 ° C. is used. With a work roll configured to have an average coefficient of thermal expansion up to 12.0 × 10 ⁻⁶ / ° C. or less, the thermal crown can be reduced by at most several percent and at most 10% or less. When the plate width returned to 300 mm or more again after hot rolling (the plate width widened by 300 mm or more compared to the previous material), the belly stretch became prominent, and it was not possible to prevent a drawing accident caused by the belly stretch.

  On the other hand, the thermal conductivity at normal temperature to 100 ° C. of the shaft material of the roll described in Patent Document 2 is 0.062 cal / cm · sec · ° C. or less, and the shaft material is made of stainless steel (SUS material). When the composite roll for hot rolling is used as the work roll of a hot finishing mill, the thermal conductivity is low up to the 30th stage in the initial stage of the hot rolling cycle (rolling from the introduction of the polishing roll to the roll replacement). By using stainless steel as the shaft material, heat conduction can be suppressed, so the amount of thermal crown can be suppressed by about 20% compared to general high-speed rolls, but the thermal crown becomes larger after the 50th half of the cycle. There was a problem. This indicates that the temperature of the roll increases with the passage of time and the thermal expansion coefficient increases. In other words, it became clear that the effect of reducing the thermal crown was lost when the hot finish rolling cycle was increased and the rolling time was increased.

There are ferritic, martensitic and austenitic stainless steels, and there is only austenitic stainless steel to achieve a thermal conductivity of 0.062 cal / cm · sec · ° C. or less. The thermal conductivity is about 0.062 cal / cm · sec · ° C., but at room temperature to 100 ° C., the thermal expansion coefficient is larger than 12 × 10 ⁻⁶ / ° C. and 17 × 10 ⁻⁶ / ° C. . This is about 1.4 times as large as that of steel, and is large, so that there is a drawback that the thermal crown becomes large in the latter half of the cycle when the temperature of the shaft rises.

JP 2000-135504 A Japanese Patent No. 4154676

  The present invention suppresses a thermal crown generated in a work roll in hot finish rolling of a metal plate, particularly hot finish rolling of a thin steel plate, thereby enabling a stable and stable rolling. And it aims at providing the work roll for hot rolling mills which can improve the shape quality of the metal plate after rolling, and a thin steel plate, and its manufacturing method.

[1] A composite work roll for a hot rolling mill comprising a shaft member made of carbon steel or alloy steel, an intermediate layer made of Fe-Ni alloy, and an outer layer made of high-speed material, wherein the shaft member is Including a barrel central portion in the barrel length direction, having a recess on the outer periphery of the region that does not reach both ends of the barrel , the intermediate layer is formed in the recess, and the shaft member and the intermediate layer form a cylindrical body, A composite work roll for a hot rolling mill, wherein an outer layer is formed on an outer periphery of a cylindrical body.
[2] The intermediate layer is formed so that the thickness in the vicinity of the center of the barrel central portion of the intermediate layer is the thickest in a section in the trunk length direction passing through the axial center of the shaft member. The composite work roll for hot rolling mills described in 1.
[3] The hot rolling mill according to [1] or [2], wherein a thermal expansion coefficient at normal temperature to 125 ° C. at a barrel central portion of the work roll is 7 × 10 ⁻⁶ / ° C. or less. Composite work role.
[4] The work roll is manufactured by welding and forming an intermediate layer on a shaft material by a continuous casting method, and then forming an outer layer by welding. [1] to [3] Method for producing a work roll for a hot rolling mill.

According to the composite work roll for a hot rolling mill of the present invention, the thermal crown is remarkably reduced by providing an intermediate layer made of Fe-Ni alloy material having a small thermal expansion coefficient in the barrel portion at the center in the barrel length direction. it can.
Therefore, in hot finish rolling of metal plates, especially thin steel plates, the plate can be passed in the state of steel plates with reduced plate stretch (medium elongation) and excellent plate flatness. Improvement (including prevention of drawing accidents) and improvement in the quality of the plate shape (flatness and plate crown) after hot rolling can be brought about. Moreover, according to the manufacturing method of this invention, the composite roll in which the shaft material, each layer, and layers were integrated reliably can be manufactured.

Sectional view in the length direction of the work roll of the present invention The figure which shows the manufacturing apparatus of the work roll of this invention (intermediate layer is welded) The figure which shows the manufacturing apparatus of the work roll of this invention (welding an outer layer) Diagram showing the effect of thermal crown on plate shape (abdominal stretch or medium stretch occurrence) Diagram showing the effect of thermal crown on plate shape (when plate width is narrow) Diagram showing the effect of thermal crown on plate shape (when plate width is wide) Diagram showing the thermal crown generated on the work roll

FIG. 1 is a view showing an example of a composite work roll for a hot rolling mill according to the present invention, and is a sectional view in the trunk length direction passing through the center of the shaft (hereinafter simply referred to as a section in the trunk length direction passing through the shaft center). "Cylinder length cross section"). Here, 1 is a work roll, 2 is a shaft member, 3 is an intermediate layer, and 4 is an outer layer. 5 is a neck portion, and 6 is a journal portion, which is a portion to which a load is applied, and is usually in contact with a bearing in the chock. Reference numeral 7 denotes a torque transmission unit connected to the universal joint. The universal joint (not shown) is connected to a speed reducer and a motor to transmit rolling power.
In the following, a work roll is sometimes simply referred to as a roll.

Since the shaft member 2 forms the intermediate layer 3 between the shaft member and the outer layer 4, the barrel portion has a recess in the outer periphery of the barrel central portion in the barrel length direction, and the diameter of this portion is in the other portion. The diameter is thinner than that. And the intermediate | middle layer 3 is formed in this recessed part, and the shaft material 2 and the intermediate | middle layer 3 make a cylindrical body (round bar-shaped body). In FIG. 1, the intermediate layer 3 is formed in a trapezoidal shape in which the length in the length direction of the portion where the cross section in the length direction is in contact with the outer layer is larger than the length in the length direction of the portion in contact with the shaft member. It goes without saying that the body length direction cross-section of the recesses has the same shape.
The outer layer 4 has a cylindrical shape and is formed on the outer periphery of the shaft member 2 and the intermediate layer 3 to form the outer shape of the barrel portion.
The shaft member 2, the intermediate layer 3, and the outer layer 4 are integrated in a metallic manner.

The material of each member of the roll is described below.
Carbon steel or alloy steel can be used for the shaft material 2, but alloy steel such as chromium molybdenum steel (SCM JIS G4105) and nickel chromium molybdenum steel (SNCM G4103) is preferably used. In the hot finish rolling, a roller having a tensile strength of at least 800 MPa or more is preferable. In order to transmit the rolling power, a high-strength shaft material is required, but a suitable material may be employed depending on the material of the material to be rolled and the rolling conditions.

The intermediate layer is made of an Fe-Ni alloy material containing 32 to 40% by mass of Ni, but is a chemical component consisting of C: 0.1 to 1% by mass, Ni: 32 to 40% by mass, the balance Fe and unavoidable impurities. Is preferred.
In general, Fe—Ni alloys are known to be low thermal expansion materials. When Ni is less than 32% by mass and more than 40% by mass, the amount of expansion becomes large, which is not effective in reducing the thermal crown. Preferably, Ni is 34% by mass or more and 38% by mass or less, and in this range, the thermal expansion coefficient is 1 × 10 ⁻⁶ / ° C. or less from room temperature to 125 ° C.
If C is 0.1% by mass or less, the fluidity during dissolution is lowered and it becomes difficult to join the shaft. If the amount of C increases, the thermal expansion coefficient tends to decrease, but if it exceeds 1% by mass, it becomes brittle and there is a risk that defects inside the roll will occur during rolling.

  Since the outer layer forms a roll surface that comes into contact with the material to be rolled, it is necessary that the outer layer has excellent wear resistance and rough skin resistance. As such a material, a high speed material is conventionally known, and in the present invention, a high speed material is used as the outer layer material.

A preferable chemical component for the outer layer material of the high speed material is C: 1.0 to 2.0.
Mass%, Si: 0.5-1.5 mass%, Mn: 0.5-2.0 mass%, Cr: 3-10 mass%, V: 3-10 mass%, W: 3-10 mass% The balance is substantially Fe and inevitable impurities.

C is necessary for forming carbides for improving wear resistance. If it is less than 1.0%, the amount of crystallized carbide is small, and the wear resistance is lowered. When it exceeds 2.0 mass%, it will precipitate with C single-piece | unit and intensity | strength will fall.
Si is an element necessary as a deoxidizing agent. If it is less than 0.5% by mass, there is no deoxidizing effect, and an oxide is precipitated, so that it becomes brittle. Moreover, when Si exceeds 1.5 mass%, the toughness of a base will fall.
Mn has an action of fixing S, which is an impurity, as MnS together with a deoxidizing action. If it is less than 0.5% by mass, deacidification is poor. If it exceeds 2.0% by mass, retained austenite tends to be generated, and sufficient hardness cannot be maintained stably.
Cr, V, and W each form an intermetallic compound such as MC, M ₄ C ₃ , M ₆ , and M ₂ C (where M is an arbitrary metal element) effective for wear resistance when less than 3% by mass. In addition, if each exceeds 10% by mass, these carbides are excessive, which is inconvenient.

Next, the form of the intermediate layer of the roll of the present invention shown in FIG. 1 will be described.
In the present invention, an intermediate layer made of an Fe—Ni alloy material having a low coefficient of thermal expansion in the range of room temperature to 125 ° C. is formed in order to suppress thermal crown generated during hot rolling. As shown in FIG. 4, this thermal crown is usually the largest at the center of the barrel center in the barrel length direction and gradually decreases toward the barrel end in the barrel length direction. The thermal crown at the center of the barrel in the direction must be effectively reduced.

For this reason, as shown in FIG. 1, the intermediate layer does not need to be formed over the entire length of the barrel length L in the barrel length direction, and includes a barrel central portion in the barrel length direction between the shaft member and the outer layer. It is formed in a region that does not reach the part. Therefore, the concave portion in which the intermediate layer of the shaft material is formed does not need to be formed over the entire length of the barrel length L in the barrel length direction, and includes the central portion of the barrel in the barrel length direction and the shaft material in a region that does not reach both ends of the barrel. It will form in the outer periphery of.
Furthermore, in order to effectively reduce the thermal crown at the center of the barrel, the intermediate layer has the thickest thickness near the center of the barrel center in the barrel length direction and in the vicinity of both ends in the barrel length direction. 1 is made trapezoidal as shown in FIG. 1, for example, as described in detail below, so that the vicinity of both ends in the body length direction is smaller than the thickness near the center of the center part in the body length direction. It is preferable to taper.

  In the form of the present invention shown in FIG. 1, the intermediate layer is formed in a recess in the outer periphery of the shaft member, including the barrel central portion in the barrel length direction and not reaching both ends of the barrel. In the direction cross section, the length B in the body length direction of the portion in contact with the outer layer is formed to be trapezoidal so as to be larger than the length A in the length direction of the portion in contact with the shaft member (that is, the portion in contact with the outer layer). The body length direction length B corresponds to the trapezoid bottom side length, and the body length direction length A of the portion in contact with the shaft member corresponds to the trapezoid upper side length). For this reason, since the both ends of the trunk | drum length direction of an intermediate | middle layer are tapering, the thermal crown of the area | region of the barrel center part of a work roll is reduced more effectively.

  The shape of the intermediate layer is not limited to a trapezoidal cross section in the roll body length direction as shown in FIG. 1, but as described above, the vicinity of both ends in the body length direction of the intermediate layer is tapered. It is preferable. Further, the intermediate layer may be formed so that a portion in contact with the shaft member in the body length direction cross section of the intermediate layer has an arc shape, and the vicinity of both end portions in the body length direction of the intermediate layer may be tapered.

In FIG. 1, d ₁ is the diameter of the region A of the longitudinal section of the shaft member ₂ , d ₂ is the diameter of the barrel portion where the recess of the shaft member is not formed, d ₃ is the diameter of the work roll, and L is Each barrel length is shown. Therefore, the thickness of the intermediate layer in the region A is (d ₂ −d ₁ ) / 2.
Moreover, the center of A and B shall correspond with the center of the barrel center part of a trunk | drum length direction.

Next, a manufacturing method will be described.
As already described, after processing a material made of chrome molybdenum steel (SCM JIS G4105) or nickel chrome molybdenum steel (SNCM G4103) specified by JIS into a shaft material within the above-mentioned suitable range, Using a continuous casting apparatus shown in 2 (a) and FIG. 2 (b), a work roll is manufactured by a continuous casting method.

2 (a), the continuous Ikake device, high-frequency heating device upper portion is provided so as to surround a funnel-shaped upper mold 9 and the mold 9 in which the lower is matched to the diameter d ₂ of the shaft member with the funnel 11 and the cooling device 10. The cooling device 10 is an annular body having a hollow inside, and the inner diameter of the annular body is the same as the diameter of the lower part of the mold 9, that is, d ₂ , and is coaxially disposed in contact with the mold. The cooling device 10 is provided with an inlet and an outlet for cooling water (not shown) so that the cooling water continuously flows through the cavity of the cooling device.

Continuous casting is performed in two stages.
Using the apparatus described in FIG. 2 (a), the first-stage continuous casting method is performed as follows.
A shaft member having a recess is inserted into the mold 9. It is preferable to heat the mold 9 in advance from the high-frequency heating device 11. Then, while pouring the melted intermediate layer material, the shaft member 2 is lowered by an elevating mechanism (not shown) in the lower direction. In conjunction with this lowering, the melt of the intermediate layer material is also lowered, cooled by the cooling device 10 and rapidly solidified. Then, after cooling to room temperature, the shaft member in which the concave portion is filled with the intermediate layer is turned into a cylindrical body (round bar-like body) having a diameter d ₂ by lathe processing.

Next, the second stage is performed by a continuous casting apparatus shown in FIG. The configuration of this continuous casting apparatus is basically the same as that used in the first stage, but the inner diameters of the mold 9 and the cooling device 10 are the same as the roll diameter (outer diameter) d _{3 of the} present invention. And larger than their inner diameter in the first stage. Further, a closing plate (not shown) is fixed to the lower part of the shaft member so that the molten metal does not flow out from the lower part of the mold in an unsolidified state during pouring.

In the second stage, the shaft member having the diameter d ₂ manufactured in the previous stage and having the concave portion filled with the intermediate layer is coaxially set in the mold 9. Then, the melted outer layer material is poured, and the shaft material is lowered and rapidly solidified in the same manner as in the first stage.

  As described above, a roll is manufactured by a two-stage continuous casting method. At this time, the shaft member, the intermediate layer, and the outer layer are reliably integrated with each other by this solidification. In order to relieve the internal stress generated after the rapid solidification, annealing is performed at 400 to 600 ° C. for 6 to 24 hours, and then the neck 5 and the journal portion 6 are rolled by machining to complete the roll. The barrel part is finished to an appropriate roughness by polishing. If the thickness of the outer layer material is large, the thermal crown becomes large, and if the thickness is thin, the roll life is shortened because the diameter is short. Therefore, in the hot finishing rolling mill for thin steel plates, the range of 100 mm to 200 mm is preferable.

  In the above-described embodiment of the present invention, an Fe—Ni alloy material having a very small thermal expansion coefficient is used as the intermediate layer material, and a section in the barrel length direction is shown in FIG. 1 at the barrel central portion in the barrel length direction. Because the outer layer uses a conventional high-speed material with good wear resistance and rough skin resistance, the thermal expansion of the outer layer is the same as the conventional one, but the overall roll is the size of the thermal crown. Can be reduced to about ½ of the conventional case.

The work rolls of Examples 1 to 7 of the present invention were manufactured by the continuous casting apparatus shown in FIG. The shaft material 2 is an SCM420 material, and the intermediate layer 3 is a Fe-Ni alloy material having a chemical composition of C: 0.2% by mass, Ni: 36% by mass, the balance Fe and unavoidable impurities. Formed to go. Subsequent machining, the diameter _{d 2} is set to 500 mm. The intermediate layer has a trapezoidal shape as shown in FIG. The thickness of the intermediate layer is in the range of 175 to 215 mm. Barrel length L is 2300 mm, C: 1.5% by mass, Si: 0.75% by mass, Mn: 1.2% by mass, Cr: 5
Mass%, V: 5 wt%, W: subjected to Ikake an outer layer material made of high-speed steel material consisting of 4 wt% and the balance Fe and unavoidable impurities, the work roll diameter d ₃ after processing was 800 mm.

For the work roll of the comparative example, an outer layer material made of a high speed material having the same chemical composition as that of Examples 1 to 7 of the present invention was cast using the SCM420 material as the shaft material 2 by a normal continuous casting method. Then, after heat treatment, it was air-cooled and post-machined to produce.
In the work roll of Conventional Example 1, SUS304, which is the following chemical component, was used for the shaft member 2. Its chemical components are C: 0.05% by mass, Cr: 18.5% by mass, Ni: 8.2% by mass, Si: 0.32% by mass, Mn: 0.4% by mass, the balance Fe and inevitable impurities It is. Conventional Example 2 uses low alloy steel for the shaft material, and the conditions are the same as those in the example shown in Patent Document 1 where the thermal expansion coefficient is the smallest. The chemical composition of the shaft material is C: 0.46% by mass, Cr: 0.2% by mass, P: 0.011% by mass, Si: 0.5% by mass, Mn: 1.12% by mass, balance Fe and Inevitable impurities.
The work rolls of the conventional examples 1 and 2 are both casted on the shaft material of the above chemical component by the continuous casting method with the outer layer material made of a high speed material having the same chemical composition as the inventive examples 1 to 7 and the comparative example, Next, after heat treatment, it was manufactured by machining.
The inventive examples 1 to 7, the comparative example, and the conventional examples 1 and 2 were all air-cooled after holding the heat treatment at 550 ° C. for 12 hours.
Table 1 shows the configuration of the work rolls of the present invention example, the conventional example, and the comparative example.

In order to evaluate the degree of thermal crown of Work Rolls of Invention Examples 1-7, Comparative Examples, and Conventional Examples, the diameter (outer diameter) of the center of the barrel central portion in the barrel length direction of the work roll was measured, and the following Thus, the thermal expansion coefficient in normal temperature -125 degreeC was compared. In the operation of hot finish rolling of a thin steel plate, the work roll has a temperature of about 50 to 100 ° C., and generally does not exceed 125 ° C. Therefore, it is sufficient to consider the thermal expansion coefficient from room temperature to 125 ° C. is there.
For each work roll, the outer diameter of the barrel central portion of the barrel of the work roll in the normal temperature state before charging the furnace and the outer diameter of the center of the roll barrel central portion of the work roll after being held in a furnace at a temperature of 125 ° C. for 48 hours The coefficient of thermal expansion was determined based on the measured value. Table 2 shows the results.
A in Table 2, _B, already mentioned for _d 1, d _2.

In the present invention example, the thermal expansion coefficient of the present invention example 1 having the thickest intermediate layer is the smallest, and is 4.97 × 10 ⁻⁶ / ° C. Further, the thermal expansion coefficient of Invention Example 7 having the smallest intermediate layer thickness is the largest, which is 6.65 × 10 ⁻⁶ / ° C., which is lower than 7.00 × 10 ⁻⁶ / ° C. And the thermal expansion coefficient of a work roll is so small that the thickness of an intermediate | middle layer becomes large.

On the other hand, in the comparative example, the chemical components of the shaft material and the outer layer material are the same as those of Examples 1 to 7 of the present invention, but since there is no intermediate layer having a small thermal expansion coefficient, the thermal expansion coefficient is 12.50 × 10 ⁻⁶ / ° C. It is significantly higher than 7.00 × 10 ⁻⁶ / ° C. And in Conventional Example 1, the chemical components of the outer layer material are the same as those of Invention Examples 1 to 7, but SUS304 having a large thermal expansion coefficient is used for the shaft material and there is no intermediate layer having a small thermal expansion coefficient. The thermal expansion coefficient is 14.50 × 10 ⁻⁶ / ° C., which is further increased, and is significantly higher than 7.00 × 10 ⁻⁶ . Since this was heated in the furnace for a long time, the temperature of the shaft material SUS304 was also about the same as the furnace temperature, and the expansion coefficient of SUS304 was large. Conventional Example 2 uses low alloy steel for the shaft material, and is different from Conventional Example 1 in this respect. However, although the coefficient of thermal expansion is slightly small, it is 10.50 × 10 ⁻⁶ / ° C., which is still higher than 7.00 × 10 ⁻⁶ / ° C.

As described above, in the work rolls of Examples 1 to 7 of the present invention, the thermal expansion coefficient at the center of the barrel center at room temperature to 125 ° C. is lower than 7.00 × 10 ⁻⁶ / ° C.
Thus, it was confirmed that Examples 1 to 7 of the present invention can significantly reduce the body length direction thermal crown of the work roll in the temperature range of room temperature to 125 ° C. as compared with Comparative Examples and Conventional Examples 1 and 2.
It goes without saying that the hot finish work roll of the present invention is effective even if the material to be rolled is a metal plate other than steel.

1: Work roll 2: Shaft material 3: Intermediate layer 4: Outer layer 5: Neck part 6: Journal part 7: Torque transmission part 8: Metal plate (steel strip)
9: Mold 10: Cooling device 11: High frequency heating device

Claims (4)

A composite work roll for a hot rolling mill comprising a shaft member made of carbon steel or alloy steel, an intermediate layer made of Fe-Ni alloy, and an outer layer made of high-speed material, wherein the shaft member is in the barrel length direction. Including a central portion of the barrel and having a recess in the outer periphery of the region that does not reach both ends of the barrel , the intermediate layer is formed in the recess, and the shaft member and the intermediate layer form a cylindrical body. A composite work roll for a hot rolling mill, characterized in that an outer layer is formed on the outer periphery of the roll.   2. The intermediate layer according to claim 1, wherein the intermediate layer is formed so that the thickness in the vicinity of the center of the barrel central portion of the intermediate layer is the thickest in a section in the barrel length direction passing through the axial center of the shaft member. Composite work roll for hot rolling mill. 3. The composite work roll for a hot rolling mill according to claim 1 , wherein a thermal expansion coefficient at normal temperature to 125 ° C. at a barrel central portion of the work roll is 7 × 10 ⁻⁶ / ° C. or less. The hot roll according to any one of claims 1 to 3 , wherein a work roll is manufactured by welding and forming an intermediate layer on a shaft member by a continuous casting method and then further forming an outer layer by welding. A method for producing a work roll for a rolling mill.