JP2007125562A - Composite roll for rolling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite roll for rolling which has exceedingly excellent wear resistance, and in which an external layer and an internal layer are soundly deposited. <P>SOLUTION: The composite roll for rolling contains an external layer α having chemical components comprising, by mass, >4.5 to 9.0% C, >0.1 to 3.5% Si, >0.1 to 3.5% Mn and >18.0 to 40.0% V, and the balance Fe with inevitable impurity elements, an intermediate layer δ formed on the inside face of the external layer and composed of an Fe-based alloy having chemical components comprising 0.5 to 3.0% C, 0.1 to 3.0% Si and 0.1 to 3.0% Mn, and an internal layer γ formed on the inside face of the intermediate layer and composed of flake graphite cast iron, spheroidal graphite cast iron, graphite steel or cast steel. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a composite roll for rolling using an outer layer material for rolling rolls having extremely excellent wear resistance, and is particularly suitable as a work roll used in a finishing row of a hot sheet rolling mill.

  In recent years, there has been a demand for further improvements in productivity and roll unit consumption in rolling mills, and in particular, work rolls used in hot sheet rolling mills are required to have high wear resistance. More recently, for example, to improve the mechanical properties of the material to be rolled as represented by ultrafine grained steel and the like, high-load operation has been gradually increasing in the rolling process, It is desired to dramatically improve the wear resistance.

  For this reason, centrifugal cast high speed rolls having an outer layer of high speed alloy manufactured by centrifugal casting are used as rolling rolls intended to meet the demand for improved wear resistance. This high-speed outer layer material contains a large amount of alloy elements such as Cr, Mo, W, and V, and its structure contains hard carbides. The high-speed outer layer material is obtained by increasing the hardness by these hard carbides and obtaining high hardness at room temperature and high temperature by the alloy elements in the matrix.

  As a conventional technique of this type, for example, Patent Document 1 discloses that the chemical components are by weight, C: 1.0 to 3.0%, Si: 0.1 to 3.0%, Mn: 0.1 to 2 0.0%, Cr: 2.0 to 10.0%, Mo: 0.1 to 10.0%, V: 1.0 to 10.0%, W: 0.1 to 10.0% In addition, a solid or hollow centrifugal cast composite roll is described which is composed of an alloy layer satisfying the formula Mo + W ≦ 10.0% and an outer layer composed of Fe and impurities as the balance, and an inner layer of cast iron or cast steel.

  According to Patent Document 1, among alloy components such as Cr, V, Mo, and W to be added to ensure wear resistance to be imparted to the outer layer material, the content of Mo and W is set to an optimum range, and the outer layer This prevents segregation of the carbides while ensuring wear resistance, and prevents uneven roll wear and rough skin in actual rolling.

  In Patent Document 2, C: 3.5 to 5.5%, Si: 0.1 to 1.5%, Mn: 0.1 to 1.2%, Cr: 4.0 to 12.0%, A hot-rolling tool steel characterized by Mo: 2.0 to 8.0%, V: 12.0 to 18.0%, the balance Fe and inevitable impurities is described. The hot rolling tool steel is described to contain Nb: 8.0% or less, and further Ni: 5.5% or less. Moreover, in the outer layer material for centrifugal force casting rolls made of hot rolling tool steel, an outer layer material for centrifugal force casting rolls satisfying 0.2 ≦ Nb / V is described.

  According to Patent Document 2, it is possible to obtain tool steel for hot rolling that has both wear resistance, crack resistance, and seizure resistance, and does not cause damage to the surface of the counterpart material when used as a tool. In addition, an outer layer material for rolling rolls that does not cause segregation or the like even when subjected to centrifugal casting can be obtained.

  Patent Document 3 discloses that C: 0.8 to 1.9% on the inner surface of the outer layer of a high-speed cast iron material having a C content of 2.0 to 3.2% (% by weight, hereinafter the same), Si: 3.0% or less, Mn: 2.0% or less, Cr: 6.0% or less, Mo: 5.0% or less, W: 5.0% or less, V: 5.0% or less, the balance substance In particular, an intermediate layer made of Fe is welded and integrated, and C: 0.2-0.8%, Si: 0.2-3.0%, Mn: 0.2-2. 0%, Cr: 1.5% or less, Mo: 1.0% or less, W: 1.0% or less, V: 1.5% or less, provided that Cr + Mo ≧ 0.3%, with the balance being substantially Fe An inner layer of a cast steel material made of the above is welded and integrated, and the high-speed cast iron material constituting the outer layer is C: 2.0 to 3.2%, Si: 0.1 to 2.0%, Mn: 0 0.1-2.0%, Cr: 3-10%, 2 × Mo + W: 5-22%, V: 3-8 %, And the balance is substantially composed of Fe.

  According to Patent Document 3, the welded state with the outer layer, the intermediate layer, and the inner layer is good, the outer layer has a predetermined wear resistance, and the inner layer can have a predetermined toughness. A quality roll for rolling steel can be manufactured.

JP-A-8-60289 JP-A-9-256108 Japanese Patent Laid-Open No. 9-209071

  As a means for improving the wear resistance of a rolling roll, it is generally known to increase the hardness of the roll material by containing a large amount of alloy elements that combine with C and C to form a metal carbide. Among the alloy elements, V, in particular, combines with C to form a hard MC type carbide and improve wear resistance. Nb also forms MC-type carbides like V and improves wear resistance.

However, when a molten metal containing excessive V or Nb is subjected to centrifugal force casting, segregation due to centrifugal separation occurs. For example, in Patent Document 1, when V exceeds 10.0%, the carbide formed in the case of centrifugal casting is light and floats on the inner surface, and the carbide corresponding to the content on the outer surface of the outer layer material used for rolling. Is not included. Such a phenomenon is likely to occur when the molten metal cast into the centrifugal casting mold solidifies to crystallize the MC type carbide in the primary crystal. The primary crystal MC type carbide are lighter specific gravity relative to a specific gravity of 6 g / cm ³ degree and the melt remaining liquid (specific gravity of about 7~8g / cm ^3), excess by the crystallizes centrifugal force for separating the inner surface is there.

  When C, V, and Nb exceed a certain range, primary MC type carbides are formed from the molten metal, and various ranges are reported as primary crystal projection phase diagrams. For example, in a CV primary crystal projection phase diagram made of Fe and an alloy, MC type carbides are crystallized in the primary crystal in the region where C is 2.5% or more and V is 9.5% or more by mass%. Has been reported. Moreover, in the C—Nb primary crystal projection phase diagram made of an Fe-based alloy, MC type carbides crystallize in the primary crystal in the region where C is 1.5% or more and Nb is 4.0% or more by mass%. Has been reported. Therefore, the conventional outer layer material for rolling rolls cast by centrifugal force restricts the content of C, V and Nb in order to suppress primary crystal MC type carbides and prevent segregation.

  In addition, means for preventing segregation due to centrifugation by increasing the specific gravity of the carbide has been proposed. For example, in Patent Document 2 described above, VC carbide has a specific gravity smaller than that of the mother molten metal, and segregates when centrifugal casting is performed. Nb forms a composite carbide {V, Nb} C with V, and increases the specific gravity as compared with a carbide of V alone. Thus, it is described that segregation due to centrifugation is prevented. Further, it is described that in order to obtain a uniform outer layer material for rolls when manufactured by the centrifugal casting method, 0.2 ≦ Nb / V must be satisfied. On the other hand, if V exceeds 18.0%, the effect of improving the seizure property is saturated and there is a risk of producing problems such as poor dissolution. Nb forms composite carbides {V, Nb} C with V, but it is described that when it exceeds 8.0%, production problems such as poor dissolution occur.

  In addition, when forming the inner layer on the inner surface of the outer layer to which such a large amount of alloy component is added, welding defects such as shrinkage cavities and carbide segregation occur between the outer layer and the inner layer, or a large amount of from the outer layer to the inner layer. There was a problem that the toughness of the inner layer deteriorated due to the mixing of alloy components. Patent Document 3 describes that when the composite roll having an outer layer of a high C material and an inner layer of a low C material is produced by centrifugal casting, the above problem can be suppressed by providing an intermediate layer. However, there is no description about the case where the amount of alloy in the outer layer, particularly C and V, is particularly large as in the present invention, and there is no description about the thickness of the intermediate layer.

  Thus, in order to drastically improve the wear resistance of the conventional centrifugally cast high-speed outer layer material, a large amount of V and Nb may be added. However, as described above, it is actually very difficult to manufacture. is there. Further, when the amount of carbides of V and Nb is increased, the wear resistance is excellent, while segregation occurs on the inner surface of the outer layer material due to the specific gravity of the carbide, and carbide segregation occurs at the welded portion with the inner surface. It becomes difficult to weld the inner layer material.

  Accordingly, the present invention aims to provide a composite roll for rolling in which the problems in the conventional high speed outer layer material made by centrifugal casting are solved, the wear resistance is remarkably excellent, and the outer layer and the inner layer are welded soundly. .

  The composite roll for rolling of the present invention is particularly characterized in that an intermediate layer of an Fe-based alloy is provided between an outer layer to which an alloy amount such as C, V, etc. is added significantly and an inner layer made of cast iron or cast steel. There is. In the present invention, the optimum C, Si, Mn component range of the intermediate layer was found, and the optimum intermediate layer thickness was defined.

    That is, the composite roll for rolling of the present invention has a chemical composition of mass%, C: more than 4.5% and 9.0% or less, Si: more than 0.1% and 3.5% or less, Mn: 0.00%. More than 1% and 3.5% or less, V: more than 18.0% and less than 40.0%, the outer layer composed of the remaining Fe and inevitable impurity elements, and the chemical components formed on the inner surface of the outer layer are in mass %, C: 0.5 to 3.0%, Si: 0.1 to 3.0%, Mn: 0.1 to 3.0% of an intermediate layer made of an Fe-based alloy, and the intermediate layer And an inner layer made of flake graphite cast iron, spheroidal graphite cast iron, graphite steel, or cast steel.

  The intermediate layer has a thickness of 5 mm or more in a cross section perpendicular to the roll axis direction.

  Further, any one of Cr: more than 1.0% and 15.0% or less, Mo: more than 0.5% and 10.0% or less, and W: more than 1.0% and 40.0% or less in the outer layer. It contains a seed or two or more kinds.

A part or all of V in the outer layer is substituted with Nb in a range satisfying the following formula (1) in mass%.
18.0% <V% + 0.55 × Nb% ≦ 40.0% (1)

Further, the outer layer satisfies the following expression (2).
0 <C% −0.2 × (V% + 0.55 × Nb%) ≦ 2.0%. . . (2)

  Further, the outer layer is characterized by containing one or two of Ni: 2.0% or less and Co: 10.0% or less in mass%.

  Further, the outer layer is characterized by containing one or two of Ti: 0.5% or less and Al: 0.5% or less in mass%.

  First, the reason for limiting the chemical component (% by mass) of the outer layer in the present invention will be described. In addition, the chemical component of the outer layer of the present invention is not a molten metal component but a component of the outer layer in the final roll product.

C: More than 4.5% and not more than 9.0% C is an essential element that contributes to wear resistance by combining with alloy elements such as V or Nb to form MC type carbides. Further, the remainder mainly contributes to wear resistance by strengthening the matrix by solid solution or precipitation with alloy elements in the matrix. When C is 4.5% or less, the amount of MC type carbide is insufficient, and sufficient wear resistance cannot be obtained. On the other hand, if C exceeds 9.0%, the total amount of carbides becomes excessive and crack resistance deteriorates.

Si: more than 0.1% and 3.5% or less Si acts as a deoxidizer in the molten metal. When Si is 0.1% or less, the deoxidation effect is insufficient and casting defects are likely to occur. Moreover, when it exceeds 3.5%, it will embrittle. A preferable range is 0.2 to 2.5%, and a more preferable range is 0.2% to 1.5%.

Mn: More than 0.1% and 3.5% or less Mn is effective when deoxidation of molten metal or S, which is an impurity, is fixed as MnS and exceeds 0.1%. When Mn exceeds 3.5%, retained austenite is likely to be generated, and the hardness cannot be stably maintained, and wear resistance and rough skin resistance are likely to be deteriorated. A preferable range is 0.2 to 2.5%, and a more preferable range is 0.2 to 1.5%.

V: more than 18.0% and not more than 40.0% V is an important element of the present invention that mainly bonds with C to form MC type carbide. One of the features of the present invention is that the outer layer material contains a very large amount of MC type carbide. When V is 18.0% or less, the amount of MC type carbide is insufficient, and sufficient wear resistance cannot be obtained. On the other hand, if V exceeds 40.0%, MC type carbides become excessive and the base becomes insufficient. If the base is insufficient, crack resistance deteriorates because the crack propagates through the carbide in the structure and expands.

Cr: more than 1.0% and not more than 15.0% Cr dissolves in the matrix and improves hardenability, and partly bonds with C in the matrix and precipitates as ultrafine carbides to strengthen the matrix. When Cr is 1.0% or less, the effect of strengthening the base cannot be obtained sufficiently. On the other hand, if it exceeds 15.0%, carbides other than MC type carbides such as M ₇ C ₃ are particularly increased or coarsened, and crack resistance is lowered. A more preferable range of Cr is 3.0% to 9.0%.

Mo: more than 0.5% and 10.0% or less Mo dissolves in the matrix and enhances hardenability, and partly bonds with C in the matrix and precipitates as ultrafine carbides to strengthen the matrix. Further, a part of Mo forms MC type carbide together with V, Nb and the like. When Mo is 0.5% or less, the effect of strengthening the base cannot be sufficiently obtained. On the other hand, if it exceeds 10.0%, carbides other than MC type carbides such as M ₃ C and M ₆ C are particularly increased or coarsened, and crack resistance is lowered. A more preferable range of Mo is more than 0.5% and not more than 5.0%.

W: More than 1.0% and 40.0% or less W is solid-solved in the matrix to enhance hardenability, and partly bonds with C in the matrix and precipitates as ultrafine carbides to strengthen the matrix. Further, a part of W forms MC type carbide together with V, Nb and the like. If W is 1.0% or less, the effect of strengthening the base cannot be obtained sufficiently. On the other hand, when it exceeds 40.0%, carbides other than MC type carbides such as M ₆ C are generated or excessively increased, and crack resistance decreases. A more preferable range of W is 5.0% to 40.0%, and further preferably 5.0% to 20.0%.

  In order to obtain a base necessary for fully exhibiting the wear resistance, the outer layer material of the present invention contains at least one kind or two or more kinds of Cr, Mo or W which are base strengthening elements. Is desirable.

18.0% <V% + 0.55 × Nb% ≦ 40.0%
Nb has the same effect as V in that it forms MC type carbides. Since Nb can be replaced by an equivalent formula at 0.55 × Nb% per 1% by mass based on the atomic weight ratio, part or all of V included in the range of the previous formula can be replaced with Nb. .

0 <C% −0.2 × (V% + 0.55 × Nb%) ≦ 2.0%
When the value of C% −0.2 × (V% + 0.55Nb%) is 0 or less, the amount of MC type carbide cannot be obtained sufficiently, and V and Nb become excessive in the base, and the hardness of the base It cannot be obtained and wear resistance is reduced. On the other hand, if the value of C% −0.2 × (V% + 0.55Nb%) exceeds 2.0%, carbides other than MC type carbides are formed or increased, and crack resistance is deteriorated.

  Moreover, the following components can be selectively added to the outer layer material of the present invention in accordance with the use and usage method of the roll for rolling.

Ni: 2.0% or less Ni dissolves in the base and is effective in improving the hardenability of the base. When Ni exceeds 2.0%, the base austenite is stabilized, and the base hardness cannot be sufficiently obtained.

Co: 10.0% or less Co dissolves in the base and has the effect of strengthening the base. In addition, the hardness of the base can be maintained even at high temperatures. If Co exceeds 10.0%, the toughness decreases. On the other hand, since Co is expensive, the content may be determined in consideration of economy and use conditions.

Ti: 0.5% or less Ti acts as a deoxidizer in the molten metal, and also has the effect of combining with N to form nitrides and forming MC type carbide nuclei and making the MC type carbides fine. A part of it is combined with C to become a part of MC type carbide. A Ti effect of 0.5% or less is sufficient.

Al: 0.5% or less Al acts as a deoxidizer in the molten metal and has the effect of making the MC carbide fine. If it exceeds 0.5%, the hardenability is deteriorated, and it is difficult to obtain sufficient base hardness.

  Next, the intermediate layer of the present invention will be described. The outer layer of the present invention is a high alloy component in order to ensure wear resistance. Therefore, when the outer layer and the inner layer are joined, alloy components are mixed from the outer layer to the inner layer, and toughness deteriorates. In addition, since the outer layer is a high alloy component, a large amount of carbides of V and Nb exist, and particularly when centrifugal casting is performed, segregation occurs on the inner surface of the outer layer material due to the specific gravity of the carbide, and the welded portion with the inner surface Since an unevenly distributed carbide layer is generated, it is difficult to weld the outer layer material and the inner layer material. Therefore, by interposing the intermediate layer between the outer layer and the inner layer, mixing of the alloy components into the inner layer and the carbide layer are suppressed, thereby strengthening the welding between the outer layer and the inner layer. The reason for limiting the component (mass%) of the intermediate layer will be described below. In addition, the component of the intermediate | middle layer of this invention is not a molten metal component but the component of the intermediate | middle layer in a final roll product.

C: 0.5 to 3.0%
C contributes to improving the strength, but if it is less than 0.5%, the welding tends to be insufficient, and defects such as cast holes are likely to be generated at the boundary between the intermediate layer and the outer layer or the inner layer. On the other hand, if C exceeds 3.0%, carbides are excessive and the strength tends to be lowered. A more preferable range of C is 0.8 to 2.4%.

Si: 0.1-3.0%
Si acts as a deoxidizer in the molten metal. When Si is 0.1% or less, the deoxidation effect is insufficient and casting defects are likely to occur. On the other hand, if it exceeds 3.0%, the hardenability is lowered and embrittled, so that it is not suitable as an intermediate layer. A more preferable range of Si is 0.2 to 1.5%, and a more preferable range is 0.2% to 1.0%.

Mn: 0.1 to 3.0%
Mn is effective when deoxidation of molten metal or S, which is an impurity, is fixed as MnS and exceeds 0.1%. If Mn exceeds 3.0%, it tends to become brittle and unsuitable as an intermediate layer. A more preferable range of Mn is 0.2 to 1.5%, and a more preferable range is 0.2 to 1.0%.

  In addition to the above, alloy elements such as Ni, Cr, Mo, W, V, Nb, Co, Ti, and Al may be mixed in the intermediate layer depending on the purpose. In addition, when the thickness of the intermediate layer in a cross section perpendicular to the roll axis direction is less than 5 mm, the mixed alloy elements are not uniformly distributed in the intermediate layer, and poor welding such as carbide segregation is likely to occur. A more preferable range of the thickness of the intermediate layer is 10 to 50 mm. If it exceeds 50 mm, defects in the intermediate layer itself tend to occur and cause toughness deterioration.

  For the inner layer of the composite roll for rolling of the present invention, in order to obtain a sound weld between the intermediate layer and the inner layer, a tough material such as cast iron alloys such as spheroidal graphite cast iron and flake graphite cast iron, graphite steel and cast steel Is desirable. Moreover, about the intermediate | middle layer of the composite roll for rolling of this invention, you may provide a some intermediate | middle layer according to the use and the objective.

  The composite roll for rolling of the present invention exhibits excellent wear resistance in all work rolls for rolling. In particular, the work rolls used in the finishing rows of hot sheet rolling mills exhibit extremely excellent wear resistance, contributing to the improvement of productivity and the roll basic unit in the rolling mill.

  FIG. 1 is a cross-sectional view of a composite roll for rolling formed by centrifugal casting according to the present invention. The outer layer material of the present invention concentrates the primary MC type carbide on the inner surface side by casting molten metal adjusted to a chemical composition for crystallizing primary MC type carbide into a casting mold for centrifugal force casting and centrifugal force casting. Formed layers. In FIG. 1, part a is a layer in which primary MC type carbides are concentrated. The second part is an intermediate layer. Part C is the inner layer. The part B is the other part. The composite roll for rolling can be obtained by removing the portion shown in FIG. 1 by cutting or the like. That is, the portion A of the layer enriched with the primary MC type carbide was used as the rolling layer.

  Examples of the outer layer of the present invention (test materials No. 1 to 5) were formed by centrifugal casting. And the site | part corresponded to (a) part of FIG. 1 was investigated. Moreover, the comparative example (test material No. 6-7) and the prior art example (test material No. 8) were formed by centrifugal casting. Each specimen was subjected to heat treatment after quenching at 1000 to 1200 ° C. and tempering at 500 to 600 ° C. three times. These specimens were subjected to chemical component analysis and a wear test using a rolling wear tester. Moreover, the test piece for fracture toughness values was taken out from these test materials as evaluation of crack resistance, and the fracture toughness value KIC was measured.

  FIG. 2 shows a schematic view of a rolling wear tester. In FIG. 2, the rolling wear tester includes a rolling mill 1, a heating furnace 4 that preheats the rolled material S, a cooling water tank 5 that cools the rolled material S, a winder 6 for the rolled material S, and a tension controller 7. Consists of Test rolls 2 and 3 are incorporated in the rolling mill 1. A test roll was prepared from the above-described test material, and a small sleeve roll having an outer diameter of 60 mm, an inner diameter of 40 mm, and a width of 40 mm was used. A test roll is incorporated in the rolling wear tester, and the test conditions are rolling material: SUS304, rolling reduction: 25%, rolling speed: 150 m / min, rolling temperature: 900 ° C., rolling distance: 300 m / time, roll cooling: water cooling The number of rolls: The test was performed by a quadruple type. After rolling, the depth of wear generated on the surface of the test roll was measured with a stylus type surface roughness meter.

  Table 1 shows examples of outer layer materials for rolling rolls according to the present invention (test materials No. 1 to 5), comparative examples (test materials No. 6 to 7), and conventional examples (test material No. 8). 1 shows chemical components (mass%) and wear test results analyzed from part A. In addition, Formula (1) in Table 1 is a value of V% + 0.55 × Nb%, and Formula (2) is a value of C% −0.2 × (V% + 0.55 × Nb%). .

  Here, in FIG. 1 shows a metallographic structure. In FIG. 8 shows the metal structure. In FIG. 3, the part that appears white is MC type carbide, and the black part is the base. In FIG. 4, white fine-grained portions are MC-type carbides, other white portions are non-MC-type carbides, and black portions are bases. It turns out that this invention material contains MC type carbide | carbonized_material abundantly compared with the conventional material.

  Sample No. of the present invention. The wear amount of 1 to 5 is the test material No. It is less than half compared to 8, and the wear resistance is extremely good. Moreover, it was found that the material of the present invention has a fracture toughness value KIC that is higher than that of the conventional material and is excellent in crack resistance.

  Sample No. of Comparative Example No. 6 has values of C% and C% −0.2 × (V% + 0.55 × Nb%) outside the scope of the present invention, and although the fracture toughness value KIC is better than the present invention, the wear resistance Is extremely inferior.

  Sample No. of Comparative Example No. 7 has values of V%, Cr%, V% + 0.55 × Nb% outside the scope of the present invention, and wear resistance is inferior to that of the present invention. Moreover, the fracture toughness value KIC is also inferior.

  Next, the intermediate layer of the composite roll for rolling of the present invention was examined. Table 2 shows chemical components (% by mass) in the final product of the intermediate layer. Specimen No. 11 to 13 are intermediate layer materials of the present invention. Specimen No. 14, no. 15 is a comparative example. Reference numeral 16 denotes spheroidal graphite cast iron which is a conventional inner layer material. Using these materials, the following welding test was performed.

  The outer layer used in the welding test is the material No. 1 of the present invention shown in Table 1. It was set to 1. No. For Nos. 11 to 15, No. 1 in Table 1 using a mold having an inner diameter of 500 mm and a length of 1200 mm and a centrifugal casting machine. After injecting a melt prepared so as to become the outer layer shown in FIG. The molten metal prepared so that it might become an intermediate | middle layer shown to 11-15 was inject | poured. Thereafter, the mold in which the outer layer and the intermediate layer were injected was taken out from the centrifugal casting machine, placed vertically in the pit, and the inner layer melt made of spheroidal graphite cast iron was injected from the lower part of the mold to produce a composite roll.

  No. For No. 16, molten metal was injected using a mold having an inner diameter of 500 mm and a length of 1200 mm and a centrifugal casting machine. After a predetermined time has passed, the mold in which the outer layer is injected is taken out from the centrifugal casting machine, placed vertically in the pit, and the inner layer melt made of spheroidal graphite cast iron is injected from the lower part of the mold, Manufactured.

  The test roll was naturally cooled together with the mold, and disassembled when the roll reached room temperature, and the test roll material was taken out. A portion with a small amount of carbide (the portion shown in FIG. 1) in the body portion of the roll material was removed by lathe processing to produce a test roll having an outer diameter of 350 mm and a body length of 600 mm. After performing an appropriate heat treatment on the test roll, a disc-shaped material (material including a roll outer layer, an intermediate layer, and an inner layer) was cut out from the center of the roll body by sticking, and various test pieces were collected from the disc-shaped material.

  Among the test pieces, confirmation of the soundness of the welded portion and the thickness of the intermediate layer were measured. No. In 11-15, the boundary tension test between an outer layer and an intermediate | middle layer was done. No. For No. 16, a boundary tensile test between the outer layer and the inner layer was performed.

As shown in Table 2, the test material No. The boundary of 11-13 was welded normally, and boundary strength was 48 kg / mm < ² > or more, and it turned out that it is suitable for an intermediate | middle layer. On the other hand, the test material No. In No. 14, it is recognized that there are a large amount of cast holes in the boundary portion, poor welding occurs, and the boundary strength is very low. Further, the test material No. 15 and no. No. 16 showed a large amount of carbide segregation around the boundary, and the boundary strength was very low.

  FIG. 5 is a schematic cross-sectional view showing various forms of the composite roll for rolling of the present invention. (A) of FIG. 5 is a solid roll consisting of the outer layer i, the intermediate layer d, and the inner layer c of the present invention. FIG. 5 (b) shows a hollow sleeve roll comprising the outer layer i, the intermediate layer d, and the inner layer c of the present invention. F is a hollow part. FIG. 5 (c) shows a hollow sleeve roll made of an outer layer (i), an intermediate layer (d) and an inner layer (c) according to the present invention fitted to a metal shaft material (e). The outer layer (a) referred to here is the same as the layer (i) where MC carbide is concentrated in FIG.

  Moreover, when the composite roll for rolling of this invention was manufactured and actually rolled, it has confirmed that very outstanding abrasion resistance was exhibited.

  The composite roll for rolling of the present invention exhibits excellent wear resistance in all work rolls for rolling. In particular, the work rolls used in the finishing rows of hot sheet rolling mills exhibit extremely excellent wear resistance, contributing to the improvement of productivity and the roll basic unit in the rolling mill.

It is a figure for demonstrating the composite roll for rolling formed by centrifugal force casting of this invention. It is the schematic of a rolling wear tester. Sample No. of the present invention. 1 is a structural photograph of 1 of an optical microscope. Sample No. of conventional material 8 is a structural photograph of the optical microscope. It is a schematic sectional drawing which shows the example of the various form of the composite roll for rolling which concerns on this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling wear test machine, 2 Test roll, 3 Test roll, 4 Heating furnace,
5 Cooling water tank, 6 Winder, 7 Tension controller, S Rolled material,
(B) MC type carbide centrifugal concentrating layer, site excluding Lo, (c) inner layer,
D Intermediate layer, E Shaft material, F Hollow part

Claims (7)

Chemical component in mass%, C: more than 4.5% and 9.0% or less, Si: more than 0.1% and 3.5% or less, Mn: more than 0.1% and less than 3.5%, V : The outer layer containing more than 18.0% and less than 40.0%, the balance being Fe and inevitable impurity elements, and the chemical components formed on the inner surface of the outer layer are in mass%, and C: 0.5-3. An intermediate layer made of an Fe-based alloy containing 0%, Si: 0.1-3.0%, Mn: 0.1-3.0%, flake graphite cast iron formed on the inner surface of the intermediate layer, A composite roll for rolling comprising an inner layer made of spheroidal graphite cast iron, graphite steel, or cast steel. The composite roll for rolling according to claim 1, wherein the intermediate layer has a thickness of 5 mm or more. Further, any one of Cr: more than 1.0% and 15.0% or less, Mo: more than 0.5% and 10.0% or less, and W: more than 1.0% and 40.0% or less in the outer layer. The composite roll for rolling according to claim 1 or 2, comprising seeds or two or more kinds. The composite roll for rolling according to any one of claims 1 to 3, wherein a part or all of V in the outer layer is replaced with Nb in a range satisfying the following formula (1) by mass%.
18.0% <V% + 0.55 × Nb% ≦ 40.0% (1) Furthermore, the said outer layer satisfies the following (2) Formula, The composite roll for rolling in any one of Claims 1-4 characterized by the above-mentioned.
0 <C% −0.2 × (V% + 0.55 × Nb%) ≦ 2.0%. . . (2) Furthermore, the said outer layer is a mass%, and contains any 1 type or 2 types of Ni: 2.0% or less and Co: 10.0% or less, The Claim 1-5 characterized by the above-mentioned. Composite roll for rolling. Furthermore, the said outer layer is a mass%, and contains any 1 type or 2 types of Ti: 0.5% or less and Al: 0.5% or less, The Claim 1 characterized by the above-mentioned. Composite roll for rolling.