JP2007196257A - Roll for rolling - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a roll for rolling in which problems in the conventional rolling roll are solved, and which has an external layer having excellent wear resistance and roughening resistance, and further having extremely excellent toughness. <P>SOLUTION: The composite roll for rolling has the external layer formed by centrifugal casting in which MC carbides are dispersed by 20 to 50% in area ratio, and fracture toughness value KIC is ≥80 kgf/mm<SP>3/2</SP>. The external layer has a structure where MC carbides having an aspect ratio of ≥2.0 are dispersed in ≥10% by area ratio, and has chemical components comprising, by mass, 2.5 to 7.5% C, 0.1 to 3.5% Si, 0.1 to 3.5% Mn and 11.0 to 30.0% V, and the balance Fe with inevitable impurity elements. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a roll for rolling. The outer layer (rolling use layer) of the rolling roll of the present invention is excellent in wear resistance, rough skin resistance and toughness, and is particularly suitable as a work roll used in a hot rolling mill.

  Important properties that determine the productivity of rolling are the wear resistance and rough surface resistance of the rolling roll. If the wear resistance is poor, the roll surface is worn early and the dimensional accuracy of the material to be rolled is impaired. In addition, if the surface of the rolling roll is worn unevenly due to contact with the material to be rolled or contact with the backup roll, the rough surface is transferred to the material to be rolled and the surface appearance of the material to be rolled is impaired. . In order to prevent these problems, the rolls must be replaced frequently, resulting in a decrease in rolling mill productivity due to an increase in the frequency of rolling operations, an increase in the cost required for roll surface grinding, and the amount of roll surface grinding. There arises a problem that the roll basic unit is reduced due to an increase in the roll size.

Therefore, a high-speed alloy containing a large amount of alloy elements such as Cr, Mo, W, and V has been conventionally used as an outer layer for rolling rolls intended to meet the demands of wear resistance and rough skin resistance. In the structure, M ₇ C ₃ type carbide containing a large amount of Cr (M represents a metal element, hereinafter the same), M ₂ C type carbide and M ₆ C type carbide containing a lot of Mo and W, and a lot of V are contained. It contains metal carbide such as MC type carbide. Increasing these hard metal carbides is effective for improving the wear resistance, but if it is excessively increased, the toughness is lowered and crack resistance is deteriorated. Conventionally, various methods for providing both wear resistance and crack resistance have been proposed.

  In Patent Document 1, 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 tool steel for hot rolling composed of Mo: 2.0 to 8.0%, V: 12.0 to 18.0%, the balance Fe and inevitable impurities is described. In addition, Nb: 8.0% or less and Ni: 5.5% or less are described. Further, it is described that 0.2 ≦ Nb / V is satisfied in the outer layer for centrifugal casting roll made of tool steel for hot rolling.

In Patent Document 2, the chemical components are in weight%, C: 1.0 to 2.6%, Cr: 4.0 to 10.0%, Mo: 5.0 to 10.0%, W: 0 to 0. 5.0%, V: 3.0 to 8.0%, 12.0% ≦ 2Mo + W ≦ 20.0%, 2Mo / W ≧ 3.0, 0.2% ≦ C−0.24V ≦ The outer layer which is an Fe-based alloy satisfying 0.7%, and the hardness of the roll outer layer surface in contact with the rolled material is a Shore hardness of 87 or more, and the fracture toughness value KIC of the outer layer is 75 kgf / mm ^3/2. A rolling roll characterized by the above is described. According to Patent Document 2, M ₇ C ₃ and M ₂₃ C ₆ carbides are relatively low in hardness and cause wear resistance to deteriorate. In addition, M ₇ C ₃ and M ₂₃ C ₆ carbides cause cracks to deteriorate along the grain boundaries, thereby causing crack resistance to deteriorate. Therefore, it is considered necessary to suppress these M ₇ C ₃ and M ₂₃ C ₆ carbides as much as possible.

  In Patent Document 3, C1.3 to 3.5% by weight ratio, Si 2.0% or less, Mn 2.0% or less, Ni 2.0% or less, Cr3.0 to 10.0%, W1.0 to 15 0.0%, Mo1.0-15.0%, V3.0-15.0%, Co10.0% or less, the balance Fe and impurities, high-speed tool steel base having an average particle diameter of 20 to 250 μm Ti, V, W having an average particle diameter of 1/2 to 1/40 of the average particle diameter of the base powder of the high-speed tool steel at 2 to 20% by weight with respect to the whole sintered body by weight ratio It consists of one or more hard particles of Ta, Nb carbide, nitride, or carbonitride, wherein the base powder of the high-speed tool steel and the hard particles are bonded by sintering. A powder high speed tool steel rolling roll is described. Patent Document 3 describes that cracks are selectively propagated through crystal grain boundaries to increase the travel distance of cracks and to improve toughness by releasing strain energy during the progress of cracks. Has been.

  In Patent Document 4, in mass%, C: 1.0 to 1.8%, Si: 0.1 to 1.0%, Mn: 0.1 to 1.0%, Cr: 7.0 to 10% 0.0%, Mo: 2.0-6.0%, V: 1.0-4.0%, the balance consisting of Fe and unavoidable impurities, and an aspect ratio of 1.3 or more in the base A powder high-speed tool steel for rolling rolls having excellent wear resistance and toughness, characterized by containing 4.0 to 9.0% Cr-based carbide in the area ratio, is described. In Patent Document 4, it is described that a coarse Cr-based carbide having a minor axis of 3.0 μm or more relaxes the strain energy and suppresses the crack progress when the crack progresses.

JP-A-9-256108 JP 2004-68027 A JP-A-10-175004 JP 2005-213630 A

In order to improve the wear resistance of the rolling roll, generally, the hardness of the roll material is increased. The high-speed roll material contains high-hardness carbides (MC, M ₂ C, M ₆ C, M ₇ C ₃ ) mainly composed of alloy elements, and has improved wear resistance. Among the alloy elements, V and Nb, in particular, form MC carbide with a very high hardness of Hv 2400 to 3200 in terms of Vickers hardness and contribute to the improvement of wear resistance.

However, when a molten metal containing excessive V or Nb is subjected to centrifugal force casting, segregation due to centrifugal separation occurs. In the above-mentioned Patent Document 1, when V exceeds 10.0%, the carbide formed in the case of the centrifugal casting method is light and floats on the inner surface, and the carbide corresponding to the content on the outer surface of the outer layer used for rolling. Is not included. Such a phenomenon is likely to occur when the molten metal cast into the centrifugal casting mold solidifies and crystallizes granular carbides in the primary crystal. This primary crystal granular carbide has a specific gravity of about 6 g / cm ^3, which is light relative to the molten metal residue (specific gravity 7 to 8 g / cm ³ ), and is separated to the inner surface side by centrifugal force when crystallized excessively. .

  In addition, means for preventing segregation due to centrifugation by increasing the specific gravity of the carbide has been proposed. In the aforementioned Patent Document 1, 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. In addition, it is described that in order to obtain a uniform outer layer 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.

  Thus, in order to drastically improve the wear resistance of the high-speed outer layer formed by centrifugal force casting, a large amount of V and Nb may be added. However, as described above, it is actually very difficult to manufacture. .

There exists a roll for rolling described in patent document 2 as what aims at providing both abrasion resistance and crack resistance. V forms MC, M ₄ C ₃ , which is a hard carbide that contributes most to the improvement of wear resistance. When V exceeds 8.0%, MC and M ₄ C ₃ crystallize in primary crystals due to the balance with the C content, aggregate during solidification, and when used as a rolling roll, MC, which is a hard carbide, It is described that the aggregation segregation of M ₄ C ₃ is not preferable because the material to be rolled is transferred. For these reasons, it is difficult to further improve the wear resistance.

  On the other hand, in the case of the powder HIP method as in Patent Document 3 and Patent Document 4, when a large amount of MC carbide forming elements such as V and Nb are added as the metal powder for the roll outer layer material, the molten metal is gas atomized in the powder manufacturing process. MC carbides crystallize in the molten metal nozzle used in the process and block the nozzle. In order to prevent this, if the nozzle diameter is increased, the particle diameter of the powder becomes coarse, and the size of the MC carbide contained in the powder becomes inhomogeneous. In the HIP sintered alloy using such a powder, the size and distribution of MC carbides are non-uniform, and a difference in wear occurs due to micro segregation between a portion with a large amount of MC carbide and a portion with a small amount of MC carbide, resulting in rough skin.

  The roll described in Patent Document 3 is one that is sintered by adding hard carbide or the like. However, when mixing hard particles with the high-speed tool steel base powder, non-uniform mixing or mixing powder is performed. When the capsule is filled, segregation is likely to occur due to separation due to a difference in physical properties such as specific gravity, and it is difficult to improve the homogeneity.

  Since the roll described in Patent Document 4 contains a small amount of V, it is difficult to generate a large amount of MC carbide, and a Cr-based carbide that is harder than MC carbide and poor in wear resistance is used. Since it is the main component, it is difficult to further improve the wear resistance.

  SUMMARY OF THE INVENTION Accordingly, the present invention aims to provide a rolling roll having an outer layer that is free from problems in conventional rolling rolls and that has excellent wear resistance and rough skin resistance and is extremely excellent in toughness.

  The present inventor casts a molten metal adjusted to a chemical composition for crystallizing primary MC carbide into a casting mold for centrifugal force casting, centrifugal casting, and forms a layer in which MC carbide is concentrated on the inner surface side in the mold. By doing so, it was found that a structure in which MC carbides are rich and uniformly dispersed in the structure can be obtained. This primary MC carbide grows in a rod shape by appropriately selecting casting conditions. When cracks enter the surface of the outer layer, the cracks propagate through MC carbides having high hardness and low toughness. At that time, if the MC carbide is rod-shaped, the crack propagation path meanders, and therefore, it was found that the crack does not reach the deep part of the roll and the toughness is improved as compared with the case where the MC carbide is granular or massive.

That is, the rolling roll according to the present invention has an outer layer formed by centrifugal casting in which MC carbide is dispersed in an area ratio of 20% to 50% and a fracture toughness value KIC is 80 kgf / mm ^3/2 or more. Features.

  In the structure of the outer layer, MC carbide having an aspect ratio of 2.0 or more is dispersed in an area ratio of 10% or more.

  In the structure of the outer layer, a maximum inscribed circle diameter of a region not including MC carbide having an equivalent circle diameter of 15 μm or more does not exceed 150 μm.

  In the outer layer structure, an average distance between MC carbides having an equivalent circle diameter of 15 μm or more is 10 μm to 40 μm.

  In the structure of the outer layer, an average equivalent circle diameter of MC carbide is 10 μm to 50 μm.

  In the structure of the outer layer, a ratio (B / A) between an average distance B between MC carbides having an equivalent circle diameter of 15 μm or more and an average equivalent circle diameter A of MC carbides is 2 or less.

In the outer layer, M ₂ C, M ₆ C, and M ₇ C ₃ carbides having an area ratio and an equivalent circle diameter of 1 μm or more are dispersed in a total amount of 0 to 2%.

  The outer layer base has a Vickers hardness of Hv550 or more.

  The outer layer has a chemical composition of mass%, C: 2.5% to 7.5%, Si: 0.1% to 3.5%, Mn: 0.1% to 3.5%, and V: 11 It is characterized by containing 0.0% to 30.0% and comprising the balance Fe and unavoidable impurity elements.

  The outer layer is further mass%, and is selected from the group consisting of Cr: 1.0% to 9.0%, Mo: 0.5% to 7.5%, and W: 1.5% to 15.0%. It contains at least one kind.

In the outer layer, at least a part of V is substituted with an amount of Nb that satisfies the following formula (1).
11.0% ≦ V% + 0.55 × Nb% ≦ 30.0% (mass%) (1)

The outer layer further satisfies the following formula (2).
0 ≦ C% −0.2 × (V% + 0.55 × Nb%) ≦ 1.3% (mass%) (2)

  The outer layer further contains 2.0% by mass of Ni and / or 5.0% or less of Co by mass%.

  The outer layer further contains 0.5% by mass of Ti and / or 0.5% or less of Al by mass%.

  First, the structural elements of the outer layer of the composite roll for rolling of the present invention will be described.

[1] Structure element MC carbide of outer layer for rolling roll MC carbide, which is granular carbide, has higher hardness and wear resistance than other carbides (M ₂ C, M ₆ C, M ₇ C ₃ carbide, etc.). It contributes to the improvement. If the MC carbide is less than 20% by area ratio, the wear resistance is insufficient. On the other hand, when MC carbide exceeds 50% in area ratio, the toughness of the roll outer layer is significantly lowered. Therefore, the preferable area ratio of MC carbide is 20 to 50%. More preferably, the area ratio is 30 to 50%.

Aspect ratio In the structure of the outer layer, it is preferable that MC carbide having an aspect ratio of 2.0 or more is dispersed in an area ratio of 10% or more. A conceptual diagram of the aspect ratio is shown in FIG. When the MC carbide 1 is sandwiched between _two straight lines ML ₁ and ML ₂ that are parallel to the absolute maximum length ML and the maximum length of the distance between any two points on the circumference of the MC carbide 1 When the shortest distance between the two straight lines is MW, ML / MW is the aspect ratio of the present invention. When cracks enter the surface of the outer layer, the cracks propagate through MC carbides having high hardness and low toughness. At that time, if the MC carbide has an aspect ratio of 2.0 or more, the path of crack propagation meanders, and the crack does not reach the deep part of the roll, improving toughness. On the other hand, as the MC carbide has an aspect ratio of less than 2.0, that is, the MC carbide is more granular, the crack propagation path becomes more linear, and the crack is likely to reach the deep part of the roll. Even when the aspect ratio of MC carbide is 2.0 or more, if the area ratio is less than 10%, the effect of the aspect ratio is not remarkable, and the improvement of toughness is insufficient. Therefore, it is desirable that MC carbide having an aspect ratio of 20 or more is dispersed in an area ratio of 10% or more in the structure of the outer layer of the present invention.

Maximum inscribed circle diameter of region not including MC carbide In the structure of the outer layer of the roll of the present invention, the maximum inscribed circle diameter of the region not including MC carbide having an equivalent circle diameter of 15 μm or more preferably does not exceed 150 μm. When the maximum inscribed circle diameter exceeds 150 μm, the dispersion of MC carbide distribution becomes large, and stable toughness cannot be obtained. The maximum inscribed circle diameter is more preferably 120 μm or less, and more preferably 80 μm or less.

FIG. 2 shows how to obtain the maximum inscribed circle diameter in a region not including MC carbide having an equivalent circle diameter of 15 μm or more. In the illustrated field of view, the diameter of the circle 20 inscribed in the MC carbides la ₁ , la ₂ , la ₃ , la ₄ having an equivalent circle diameter of 15 μm or more is D ₂₀ . Similarly, the diameter of a circle inscribed in another MC carbide group is obtained. This operation is performed for a plurality of arbitrary fields of view, and the maximum inscribed circle diameter D ₂₀ max is determined.

Average distance between MC carbides In the structure of the outer layer of the roll of the present invention, the average distance between MC carbides having an equivalent circle diameter of 15 μm or more is preferably 10 to 40 μm. When the average distance between MC carbides is less than 10 μm, the MC carbides are unevenly distributed, and micro unevenness due to wear difference occurs between the parts with a lot of MC carbides and the parts with little MC carbides, resulting in poor skin roughness resistance. On the other hand, if the average distance between MC carbides exceeds 40 μm, the dispersion of MC carbide distribution becomes large, and stable toughness cannot be obtained. The average distance between MC carbides having an equivalent circle diameter of 15 μm or more is more preferably 20 to 30 μm.

FIG. 3 shows how to determine the average distance between MC carbides. The structure shown in FIG. 3 contains MC carbide (white) la having an equivalent circle diameter of 15 μm or more and MC carbide (black) lb having an equivalent circle diameter of less than 15 μm. 2 indicates a base (containing M ₂ C, M ₆ C and M ₇ C ₃ carbides). Subtracting arbitrary straight line L in this tissue, MC carbides _{la 1, la 2, la 3} ··· la n intersect, the distance _L 1 between these MC _carbides, L _2, L 3 · · · _{L n} Is measured. Therefore, the average distance between MC carbides having an equivalent circle diameter of 15 μm or more is determined by [Σ (L ₁ + L ₂ +... + L _n )] / n.

Size of MC carbide The average equivalent circle diameter of MC carbide (granular carbide) is preferably 10 to 50 μm. During hot rolling, the roll comes into contact with the high-heated rolled steel sheet, and the base softens up to about 10 μm from the surface. Therefore, if the average equivalent circle diameter of MC carbide is less than 10 μm, the base cannot sufficiently support the MC carbide, Abrasion resistance and rough skin resistance are insufficient. On the other hand, when the average equivalent circle diameter exceeds 50 μm, the effect of improving the rough skin resistance is saturated and the toughness is lowered. The average equivalent circle diameter of MC carbide is more preferably 10 to 40 μm, and most preferably 15 to 30 μm.

As shown in FIG. 4, the equivalent circle diameter of MC carbide 1 defines the diameter of circle 10 having the same area as MC carbide 1 as D ₁₀ . When the area of MC carbide 1 is S, D ₁₀ = 2 × (S / π) 1/2. The average equivalent-circle diameter of MC carbide is an average of D _10.

Average MC carbide distance / average equivalent circle diameter In the structure of the outer layer of the roll of the present invention, the ratio of the average distance B between MC carbides having an equivalent circle diameter of 15 μm or more and the average equivalent circle diameter A of MC carbide (B / A ) Is preferably 2 or less. In the roll outer layer of the present invention containing a large amount of MC carbide, MC carbide tends to aggregate. When MC carbide aggregates, the micro unevenness | corrugation by a wear difference will arise in a part with much MC carbide, and a part with few MC carbide | carbonized_materials, and the rough skin resistance will be impaired. The B / A ratio indicates the degree of MC carbide aggregation. If B / A exceeds 2, MC carbides agglomerate excessively, which is not preferable. A more preferable B / A ratio is 1.5 or less.

Non-granular carbide Even if 0 to 2% of non-granular carbides (M ₂ C, M ₆ C and M ₇ C ₃ carbides) having an equivalent circle diameter of 1 μm or more are dispersed in the roll outer layer of the present invention in a total area ratio. good. When the total area ratio of the non-particulate carbide exceeds 2%, the non-particulate carbide coarsens and deteriorates the skin resistance and toughness of the roll, and cracks develop along the non-particulate carbide crystallized in a network. As a result, the thermal cracking resistance decreases. The smaller the total area ratio of non-particulate carbide, the better. The total area ratio of M ₂ C, M ₆ C, and M ₇ C ₃ carbide having an equivalent circle diameter of 1 μm or more is more preferably 0 to 1%. A small amount of carbides other than MC, M ₂ C, M ₆ C and M ₇ C ₃ carbides may be included.

Base Vickers Hardness The base of the outer layer of the present invention is mainly composed of Fe and alloy elements, and the hardness changes due to transformation by heat treatment or precipitation of ultrafine carbides. When the hardness of the base at room temperature is Vickers hardness of less than Hv550, the wear resistance of the outer layer is insufficient. From the viewpoint of improving the wear resistance, it is desirable that the base is hard, but if it exceeds Hv900, the base toughness deteriorates. A more preferable Vickers hardness of the base is Hv650-850.

[2] Chemical composition (% by mass) of outer layer of composite roll for rolling
The reason for limiting the chemical component (% by mass) of the outer layer in the composite roll for rolling of 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.

(1) Essential component (a) C: 2.5% to 7.5%
C is an essential element that improves wear resistance by mainly bonding with alloy elements such as V and Nb to form MC carbides. C that does not bond to the alloy element mainly dissolves in the matrix or precipitates extremely finely, strengthening the matrix. If C is less than 2.5%, the amount of MC carbide is insufficient and sufficient wear resistance cannot be obtained. On the other hand, if C exceeds 7.5%, carbides are excessive and the toughness of the outer roll layer is deteriorated. The C content is preferably 3.5% to 7.5%, more preferably 4.5% to 7.5%.

(B) Si: 0.1% to 3.5%
Si acts as a deoxidizer in the molten metal. If Si is less than 0.1%, the deoxidation effect is insufficient and casting defects are likely to occur. On the other hand, when Si exceeds 3.5%, the outer roll layer becomes brittle. The Si content is preferably 0.2% to 2.5%, more preferably 0.2% to 1.5%.

(C) Mn: 0.1% to 3.5%
Mn has a function of deoxidizing the molten metal and fixing S, which is an impurity, as MnS. When Mn is less than 0.1%, these effects are insufficient. On the other hand, when Mn exceeds 3.5%, retained austenite tends to be generated, the hardness cannot be stably maintained, and the wear resistance is likely to deteriorate. The Mn content is preferably 0.2% to 2.5%, more preferably 0.2% to 1.5%.

(D) V: 11.0% to 30.0%
V is an element that mainly bonds with C to form MC carbide. In order to include a large amount of MC carbide in the outer layer of the roll, 11.0% to 30.0% V is necessary. If V is less than 11.0%, MC carbide is insufficient and sufficient wear resistance cannot be obtained. On the other hand, when V is more than 30.0%, MC carbide becomes excessive and the toughness of the outer roll layer deteriorates. V content is preferably 15.0% to 30.0% or less, and more preferably 18.0% to 30.0%.

(E) Nb
Nb has the same action as V in that it forms MC carbides. From the atomic weight ratio, 0.55 × Nb% and V% are equivalent in mass%. Therefore, part or all of V may be replaced with an amount of Nb that satisfies the following formula (1).
11.0% ≦ V% + 0.55 × Nb% ≦ 30.0% (1)

Nb preferably satisfies C and V and the following formula (2).
0 ≦ C% −0.2 × (V% + 0.55 × Nb%) ≦ 1.3% (2)
When the value of [C% −0.2 × (V% + 0.55 × Nb%)] is less than 0, MC carbides cannot be sufficiently obtained, and V and Nb become excessive in the base, and sufficient hardness is obtained. Satisfaction and wear resistance are not obtained. On the other hand, when the value of [C% −0.2 × (V% + 0.55 × Nb%)] exceeds 1.3%, non-granular such as M ₂ C, M ₆ C, and M ₇ C ₃ carbides. Carbide crystallizes in a network, and the heat crack resistance of the outer layer of the roll deteriorates.

(2) Arbitrary component The outer layer may appropriately contain the following elements depending on the application and usage of the rolling roll.

(A) Cr: 1.0% to 9.0%
Cr not only improves the hardenability by dissolving in the matrix, but part of it combines with C and precipitates as ultrafine carbides, strengthening the matrix. If Cr is less than 1.0%, the effect of strengthening the base cannot be sufficiently obtained. On the other hand, when Cr exceeds 9.0%, carbides other than MC carbide such as M ₇ C ₃ carbide crystallize in a network shape, and the toughness of the outer roll layer deteriorates.

(B) Mo: 0.5% to 7.5%
Mo not only dissolves in the matrix and improves hardenability, but part of it combines with C and precipitates as ultrafine carbides, strengthening the matrix. Part of Mo forms granular carbides. If Mo is less than 0.5%, the effect of strengthening the base cannot be sufficiently obtained. On the other hand, when Mo exceeds 7.5%, non-particulate carbides such as M ₂ C and M ₆ C crystallize in a network shape, and the toughness of the outer layer of the roll deteriorates.

(C) W: 1.0% to 15.0%
W dissolves in the base portion to improve hardenability, and part of it combines with C to precipitate as ultrafine carbides, strengthening the base. Further, a part of W forms MC type carbide together with V, Nb and the like. If W is less than 1.0%, the effect of strengthening the base cannot be sufficiently obtained. On the other hand, when W exceeds 15.0%, carbides other than MC, such as M ₂ C and M ₆ C carbides, crystallize in a network shape, and the toughness of the outer roll layer deteriorates.

  In order to give sufficient abrasion resistance to the outer layer of the roll of the present invention, it is preferable to contain at least one of Cr, Mo and W which are base strengthening elements. Moreover, the following components can be selectively added to the outer layer of the present invention in accordance with the use and usage method of the rolling roll.

(D) Ni: 2.0% or less Ni dissolves in the base and is effective in improving the hardenability of the base. If Ni exceeds 2.0%, the base austenite is stabilized, and the hardening effect of the base is insufficient.

(E) Co: 5.0% or less Co dissolves in the base and has the effect of strengthening the base. If Co is contained, the hardness of the base can be maintained even at a high temperature. When Co exceeds 5.0%, the toughness of the outer layer of the roll decreases. Further, since Co is expensive, it is desirable to determine its content in consideration of economy and use conditions.

(F) Ti: 0.5% or less Ti acts as a deoxidizer in the molten metal, and also has an effect of combining with N to form a nitride, serving as a nucleus of MC carbide, and making the MC carbide fine. Part of it is combined with C to become part of MC carbide. The addition effect of Ti is sufficient to be 0.5% or less.

(G) Al: 0.5% or less Al acts as a deoxidizer in the molten metal and has the effect of making MC carbide fine. When Al exceeds 0.5%, the hardenability of the outer layer is deteriorated, and sufficient base hardness cannot be obtained.

[3] Centrifugal Casting To manufacture the outer layer for a rolling roll of the present invention, first, a molten metal adjusted to a chemical component for crystallizing primary crystal MC carbide is cast into a cylindrical mold and centrifugally cast. In the present invention using centrifugal separation of MC carbide by centrifugal casting, the molten metal component is different from the component of the outer roll layer. In order to obtain the outer layer component described in [2], the molten metal component is in mass%, C: 2.2 to 6.0%, Si: 0.1 to 3.5%, Mn: 0.1 to 0.1%. It contains 3.5% and V: 8.0 to 22.0%, and consists of the balance Fe and inevitable impurity elements.

Since Nb replaces at least a part of V and is centrifuged as MC carbide by centrifugal casting, an amount of Nb satisfying the following formula (3) can be added to the molten metal.
8.0% ≦ V% + 0.55 × Nb% ≦ 22.0% (3)

  Preferably, the molten metal component is, by mass%, C: 2.5 to 6.0%, Si: 0.2 to 1.5%, Mn: 0.2 to 1.5%, and V: 10.0. It may contain ˜22.0% and Nb may be contained in an amount satisfying 10.0% ≦ V% + 0.55 × Nb% ≦ 22.0%.

  Since optional elements Cr, Mo, Ni, Co and Al are hardly centrifuged, the content in the molten metal may be the same as the content in the outer layer of the roll. Since W and Ti are partly dissolved in the primary crystal MC carbide, they are slightly centrifuged.

  As shown in FIG. 5A, during centrifugal casting in the mold 41, the primary MC carbide 43 having a small specific gravity moves in the molten metal 42 to the inside of the roll in contact with the hollow portion 44. As a result, as shown in FIG. 5B and FIG. 5C, the inner peripheral layer 40a enriched in MC carbide, the outer peripheral layer 40b poor in MC carbide, and the concentration gradient in which the area ratio of MC carbide changes. From the layer 40c (synonymous with the inclined layer 40c. That is, since this is a layer between the inner peripheral layer 40a and the outer peripheral layer 40b and the concentration of MC carbide is inclined, it is referred to as an inclined layer 40c for convenience in the drawing) A cylindrical body 40 is obtained. Next, all of the outer peripheral layer 40b and at least a part of the concentration gradient layer 40c are removed from the cylindrical body 40 by cutting or the like, and a portion where MC carbides are concentrated (mainly the inner peripheral layer 40a) is used as an outer layer for a rolling roll.

  Since the thickness of the outer peripheral layer 40b and the concentration gradient layer 40c is determined by the composition of the molten metal and the centrifugal casting conditions, it can be predicted. Since it is not necessary to remove all of the concentration gradient layer 40c, the depth of the concentration gradient layer 40c to be removed is set in advance. Of course, part of the inner circumferential layer 40a may be removed in order to ensure high wear resistance.

  For example, as shown in FIG. 5C, the thickness Dout of the outer peripheral layer 40b to be completely removed, the removal depth Dim of the concentration gradient layer 40c to be at least partially removed, and, if necessary, partially If the removal depth Din of the inner circumferential layer 40a to be removed is determined experimentally or by simulation based on the composition of the molten metal and the centrifugal casting conditions, the inner depth 40a exposed by cutting the cylindrical body 40 by a depth of Dout + Dim (+ Din). The thickness Do [= Dt + Dout + Dim (+ Din)] of the cylindrical body 40 is set so that the circumferential layer 40a (or a part of the inner circumferential layer 40a + the concentration gradient layer 40c) has a desired thickness (target thickness of the outer layer) Dt. It can be set in advance. If the cylindrical body 40 having the wall thickness Do larger than the target thickness Dt of the outer layer is formed by the centrifugal casting method using the existing mold 41, the cylindrical body 40 is easily and easily cut by a depth of Dout + Dim (+ Din). A roll outer layer having a thickness Dt can be obtained at low cost.

  In the method of the present invention, from the distribution of the MC carbide predicted by the molten metal component and centrifugal casting conditions, a depth at which the MC carbide area ratio is 20% or more is predicted, and the cylinder is only by the depth. The body is preferably made to have an outer diameter larger than the target outer diameter of the outer layer.

[4] Roll structure The rolling roll using the outer layer of the present invention may have a solid or hollow structure. Moreover, the rolling roll of the present invention is preferably a rolling roll in which the outer layer and the inner layer of the present invention are joined metallically. In addition, a composite roll in which one layer or two or more intermediate layers are interposed between the outer layer and the inner layer of the present invention is desirable. The sleeve having the outer layer of the present invention may be fitted to the shaft member.

  The rolling roll of the present invention exhibits excellent wear resistance and rough skin resistance in general work rolls for hot and cold rolling, and has extremely excellent toughness, and is particularly used in a hot rolling mill. Exhibits extremely excellent crack resistance in work rolls and contributes to improving productivity and roll basic unit in rolling mills.

  The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.

  The molten metal adjusted to the chemical composition (mass%) shown in Table 1 was centrifugally cast in a centrifugal casting mold to produce a cylindrical body. No. 1-No. 5 is an example of the present invention, No. 5; 6-No. 9 is a comparative example. 10 is a conventional example.

  Among the obtained cylindrical bodies, No. 1, no. 4, no. 6 and no. For 10 cylinders, the element distribution and MC carbide distribution in the radial cross section of the cylinder were measured. The element distribution and MC carbide distribution were obtained by cutting a rod-shaped test piece collected in the radial direction of the cylindrical body at intervals of 10 mm and collecting a plurality of samples. Then, component analysis and MC carbide area ratio of each sample were measured. The results are shown in FIGS.

  As shown in FIG. In the cylindrical body 1, V was as low as about 5% by mass in the outer peripheral layer, but as much as 22% by mass or more in the inner peripheral layer, and W was as low as 2 to 5% by mass in the outer peripheral layer. It was as many as 5-6 mass% in the layer. C was as low as about 2.2 to 2.5% by mass in the outer peripheral layer, but was as high as 5% by mass or more in the inner peripheral layer. For other elements (Cr, Mo), there was almost no concentration distribution in the outer peripheral layer to the inner peripheral layer.

  As shown in FIG. 7, the area ratio distribution of MC carbides showed the same tendency as the V concentration distribution. That is, the area ratio of MC carbide was as low as about 4 to 8 area% in the outer peripheral layer, but was as high as about 33 area% or more in the inner peripheral layer. Therefore, for example, the cylindrical body is cut to a depth (indicated by line A in the figure) including the entire outer peripheral layer and most of the concentration gradient layer, and the portion containing 33% by area or more of MC carbide is the outer layer for rolling rolls. It was.

  As shown in FIG. In the cylindrical body No. 4, V was as small as approximately 6% by mass or less in the outer peripheral layer, but as large as 11% by mass or more in the inner peripheral layer, and Nb was as small as approximately 2% by mass or less in the outer peripheral layer. In the outer peripheral layer, C was as low as about 2.5% by mass or less, but in the inner peripheral layer, it was as high as about 4% by mass or more, and W was also about 1.5% by mass or less in the outer peripheral layer. However, it was slightly more than 1.5% by mass in the inner circumferential layer. For other elements (Cr, Mo), there was almost no concentration distribution in the outer peripheral layer to the inner peripheral layer.

  As shown in FIG. 9, the area ratio distribution of MC carbides showed almost the same tendency as the concentration distributions of V and Nb. That is, the area ratio of MC carbide was poor at approximately 4 to 9% by area in the outer peripheral layer, but was as high as approximately 22% by area or more in the inner peripheral layer. Therefore, for example, the cylindrical body is cut to a depth (indicated by a line segment A ′ in the figure) including the entire outer peripheral layer and most of the concentration gradient layer, and a portion containing 22% or more area MC carbide is used for a rolling roll. Outer layer

  As shown in FIG. In the cylindrical body 6 as well, V was as low as about 5% by mass in the outer peripheral layer, but as much as 25% by mass or more in the inner peripheral layer, and W was as low as approximately 10 to 15% by mass in the outer peripheral layer. In the layer, it was as much as 20 to 255 mass%. C was as low as about 2.5% by mass in the outer peripheral layer, but was as high as 5% by mass or more in the inner peripheral layer. For other elements (Cr, Mo), there was almost no concentration distribution in the outer peripheral layer to the inner peripheral layer.

  As shown in FIG. 11, the area ratio distribution of MC carbides showed the same tendency as the V concentration distribution. That is, the area ratio of MC carbide was as low as about 4 to 8 area% in the outer peripheral layer, but was as high as about 35 area% or more in the inner peripheral layer. Therefore, for example, the cylindrical body is cut to a depth (indicated by line segment A ″ in the figure) including the entire outer peripheral layer and most of the concentration gradient layer, and a portion containing 35% or more area of MC carbide is used for a rolling roll. The outer layer was used.

  Conventional Example No. In the 10 cylinders, as shown in FIGS. 12 and 13, there was almost no element concentration distribution between the outer peripheral layer and the inner peripheral layer. MC carbide was approximately 8 area% or less at any depth.

  Invention Example No. 1, no. 4 and no. Similarly to the cylindrical body of No. 6, the cylindrical bodies of other examples and comparative examples were removed by cutting or the like until the portion where the MC carbides were concentrated was exposed, and an outer layer was produced.

  Table 2 shows the composition of the obtained outer roll layer. Each roll outer layer was heat-treated by quenching at 1000 to 1200 ° C. and tempering 3 times at 500 to 600 ° C. Here, the formula (1) in Table 2 is a value of [V% + 0.55 × Nb%], and the formula (2) is [C% −0.2 × (V% + 0.55 × Nb%)]. Is the value of

For the test piece cut out from each outer layer of the roll, the area ratio (%) of MC carbide, the total area ratio AA (%) of M ₂ C, M ₆ C and M ₇ C _{3 having} an equivalent circle diameter of 1 μm or more, MC The average circle equivalent diameter A (μm) of carbides, the average distance B (μm) between MC carbides with an equivalent circle diameter of 15 μm or more, and the maximum value of the inscribed circle diameter in a region not containing MC carbides with an equivalent circle diameter of 15 μm or more BB (μm), area ratio CC (%) of MC carbide having an aspect ratio of 2.0 or more, Vickers hardness of base at room temperature (Hv), wear amount (μm), surface roughness Rz (μm), and fracture toughness The value KIC (kgf / mm ^3/2 ) was measured by the following method. Table 3 shows the measurement results.

(1) Area ratio of MC carbide Each test piece is mirror-polished and electrolytically corroded with an aqueous potassium dichromate solution to corrode MC carbide in black, and then an image analysis apparatus (Nippon Avionics Corporation, SPICCA-II) Was used to measure the area ratio (%) of MC carbide in 20 arbitrary fields of view corresponding to a 0.23 mm × 0.25 mm portion of the test piece, and the measured values were averaged.

(2) Total area ratio AA of non-particulate carbides (M ₂ C, M ₆ C and M ₇ C ₃ )
Each test piece is mirror-polished and corroded with Murakami reagent to corrode M ₂ C, M ₆ C, and M ₇ C ₃ carbides in black or gray, and then each test is performed using the above image analyzer. The total area ratio (%) of M ₂ C, M ₆ C and M ₇ C ₃ carbides was measured with 20 arbitrary fields of view corresponding to a 0.23 mm × 0.25 mm portion in the piece, and the measured values were averaged. . Note that M ₂ C, M ₆ C, and M ₇ C ₃ carbides having a circle-equivalent diameter of 1 μm or more, which are easy to identify, were measured.

(3) MC carbide average circle equivalent diameter A
Each test piece is mirror-polished, and the MC carbide is corroded to black by electrolytic corrosion with an aqueous potassium dichromate solution. Then, using the above image analysis apparatus, each test piece is 0.23 mm × 0.25 mm. The average equivalent circle diameter (μm) of MC carbide was measured with 20 arbitrary fields of view corresponding to the portion, and the measured values were averaged.

(4) Average distance B between MC carbides
Each specimen was mirror-polished and the base was corroded with a picric acid alcohol solution. Under this optical microscope observation (200 ×), the matrix appeared dark gray, the MC carbides appeared light gray, and the M ₂ C, M ₆ C and M ₇ C ₃ carbides appeared white. The average distance (μm) between MC carbides having an equivalent circle diameter of 15 μm or more was measured with 20 arbitrary fields of view corresponding to a 1.0 mm × 1.5 mm portion of each test piece, and the measured values were averaged.

(5) Maximum value BB of the inscribed circle diameter in the region not including MC carbide
Each corroded test piece was observed with an optical microscope (100 times) in the same manner as in (4), and the equivalent circle diameter was measured in 20 arbitrary fields corresponding to 2.0 mm × 3.0 mm portions of the test piece. Measured the maximum value (μm) of the inscribed circle diameter in a region not containing MC carbide of 15 μm or more, and averaged the measured values.

(6) Area ratio of MC carbide having an aspect ratio of 2.0 or more Each specimen was mirror-polished and electrolytically corroded with potassium dichromate aqueous solution to corrode the MC carbide in black, and then an image analyzer (Nippon Avionics) Using SPICCA-II), the area ratio (%) of MC carbide was measured with 20 arbitrary fields of view corresponding to the 0.23 mm × 0.25 mm portion of the test piece. Were averaged to obtain an MC carbide area ratio. Next, the area ratio of MC carbide having an aspect ratio of less than 2.0 was obtained using an image analysis device in the same manner. From these measurement results, (MC carbide area ratio) − (area ratio of MC carbide having an aspect ratio of less than 2.0) = (area ratio of MC carbide having an aspect ratio of 2.0 or more) was calculated. An area ratio of MC carbide of 0.0 or more was obtained.

(7) Vickers hardness of base at room temperature Each specimen is mirror-polished and lightly corroded with a picric acid ethanol solution, and then a load of 50 to 50 at any five locations on the specimen using a Vickers hardness tester. Vickers hardness (Hv) was measured in the range of 200 g, and the measured values were averaged.

(8) Wear depth and surface roughness Rz
As an evaluation of the wear resistance and the rough skin resistance, the wear depth (μm) and the ten-point average surface roughness Rz for the roll after rolling using a rolling wear tester schematically shown in FIG. It measured as follows. The surface roughness Rz was measured with a stylus type surface roughness meter.

  The rolling wear tester is an example of the present invention. 1-No. 5, Comparative Example No. 6-No. 8. Conventional Example No. 9 and no. 10, a rolling mill 51 comprising test rolls 52, 53 made of small sleeve rolls having an outer diameter of 60 mm, an inner diameter of 40 mm and a width of 40 mm, a heating furnace 54, a cooling water tank 55, a winder 56, A tension controller 57. The rolling wear test conditions were as follows.

Rolled material S: SUS304
Rolling rate: 25%
Rolling speed: 150 m / min Rolling temperature: 900 ° C
Rolling distance: 300m
Roll cooling: Water cooling Number of rolls: Quadruple

(9) Fracture toughness value KIC
The fracture toughness value KIC of each test piece was measured according to ASTM E399. The measurement was performed on two test pieces, and the average value was obtained.

  FIG. 16 shows the metallographic structure of the test piece 1 according to the present invention. The metal structure of the test piece of 4 is shown. In addition, FIG. The metal structure of the test piece of 6 is shown. 15-17, a white part is MC carbide | carbonized_material and a black part is a base. Invention Example No. 1 and no. It can be seen that in the test piece 4, MC carbide is distributed at a high concentration and contains a large amount of MC carbide elongated in a rod shape. On the other hand, Comparative Example No. It can be seen that the MC carbide in the test piece 6 has a high concentration, but a small amount of MC carbide elongated in a rod shape.

FIG. The metal structure of 8 test pieces is shown. The white granular part is MC carbide, the white lamellar (layered) part is M ₂ C, M ₆ C and M ₇ C ₃ carbide, and the black part is the base. Comparative Example No. It can be seen that the specimen 8 has a high concentration of MC carbide but contains a large amount of M ₂ C, M ₆ C and M ₇ C ₃ carbide.

FIG. 10 metallographic structures are shown. The white fine granular portion is MC carbide, the white mesh portion is V, and the black portion is a base. Conventional Example No. 10, it can be seen that MC carbides are partially unevenly distributed and M ₂ C, M ₆ C and M ₇ C ₃ carbides are distributed in a network.

Invention Example No. 1-No. The fracture toughness value KIC of No. 5 is 80 kgf / mm ^3/2 or more, which is the conventional example No. It can be seen that it is larger than 10 by 10 kgf / mm ^3/2 or more. In addition, Invention Example No. 1-No. The amount of wear of No. It is found that the wear resistance is very good, almost half or less than 10. In addition, Invention Example No. 1-No. No. 5 is the conventional example No. in the rough skin resistance. It turns out that it is ten or more.

Comparative Example No. In the test piece of 6, the W content exceeds 15% and is out of the range. The area ratio of MC carbide having an aspect ratio of 2.0 or more was less than 10%, which was outside the scope of the present invention. Therefore, KIC was less than 80 kgf / mm ^3/2 and was inferior in toughness.

Comparative Example No. In the test piece of No. 7, the contents of C, V and Mo and the formula (1) were outside the scope of the present invention, and the area ratio of MC carbide having an aspect ratio of 2.0 or more was less than 10%. Therefore, KIC is less than 80 kgf / mm ^3/2 and the toughness is inferior.

Comparative Example No. In the test piece of 8, the content of Cr and the formula (2) are out of the scope of the present invention, and the total area ratio AA of M ₂ C, M ₆ C and M ₇ C ₃ carbides of 1 μm or more is 2.9%. And out of the scope of the present invention. The area ratio of MC carbide having an aspect ratio of 2.0 or more was less than 10%. Therefore, KIC is less than 80 kgf / mm ^3/2 and is inferior in toughness.

Comparative Example No. In No. 9 test piece, the content of W exceeded 15%, and the area ratio of MC carbide having an aspect ratio of 2.0 or more was less than 10%. Therefore, KIC is less than 80 kgf / mm ^3/2 and is inferior in toughness.

FIG. 20 shows the relationship between the area percentage of MC carbide having an aspect ratio of 2.0 or more and KIC in each test material. It can be seen from the figure that the KIC can achieve 80 kgf / mm ^3/2 or more in the present invention example in which the area ratio of MC carbide having an aspect ratio of 2.0 or more is 10% or more.

  The outer layer of the present invention may be used alone as a rolling roll, but is preferably used as a rolling composite roll as shown in FIG. FIG. 21A shows a solid roll composed of the outer layer 71 and the inner layer 72 of the present invention. FIG. 21B shows a hollow sleeve roll comprising the outer layer 71 and the inner layer 72 of the present invention. Reference numeral 85 denotes a hollow portion. FIG. 21C shows a hollow sleeve roll made of the outer layer 71 and the inner layer 72 of the present invention fitted to a metal shaft 86.

  In addition, by the production method of the present invention, a composite roll for rolling having a roll body having an outer diameter of 310 mm and a length of 500 mm was produced, and when actually rolled, extremely excellent wear resistance and rough skin resistance were exhibited. At the same time, it was confirmed that there was no occurrence of abnormal chipping or cracking and that it could be used stably.

  The composite roll for rolling according to the present invention exhibits excellent wear resistance and rough skin resistance in general work rolls for hot and cold rolling, and has excellent outer layer toughness, especially for work rolls used in hot rolling mills. It has an extremely excellent effect and contributes to the improvement of productivity and the basic unit of roll in the rolling mill.

It is the schematic which shows the method of calculating | requiring the aspect ratio of MC carbide | carbonized_material. It is the schematic which shows the method of calculating | requiring the circle equivalent diameter of MC carbide | carbonized_material. It is the schematic which shows the method of calculating | requiring the average distance between MC carbide | carbonized_materials. It is the schematic which shows the method of calculating | requiring the maximum inscribed circle diameter of the area | region which does not contain MC carbide | carbonized_material. It is the schematic which shows a mode that MC carbide | carbonized_material moves to the inner surface side in the case of centrifugal casting. It is radial direction sectional drawing which shows the centrifugal cast cylindrical body in which the outer layer of this invention was formed. It is a graph which shows distribution of MC carbide in the AA section of Drawing 4 (b). Invention Example No. It is a graph which shows the radial direction distribution of the element in the centrifugal cast cylindrical body of 1. Invention Example No. It is a graph which shows the radial direction distribution of MC carbide | carbonized_material in the centrifugal cast cylindrical body of 1. FIG. Invention Example No. 4 is a graph showing a radial distribution of elements in a centrifugally cast cylindrical body of No. 4; Invention Example No. 4 is a graph showing a radial distribution of MC carbide in a centrifugal cast cylinder of No. 4; Comparative Example No. 6 is a graph showing a radial distribution of elements in a centrifugal cast cylinder of No. 6. Comparative Example No. 6 is a graph showing the radial distribution of MC carbide in the centrifugal cast cylinder of No. 6. Conventional Example No. It is a graph which shows the radial direction distribution of the element in 10 centrifugal cast cylinders. Conventional Example No. It is a graph which shows the radial direction distribution of MC carbide | carbonized_material in 10 centrifugal cast cylinders. It is the schematic which shows a rolling abrasion tester. Invention Example No. It is an optical microscope photograph which shows the metal structure of 1 test piece. Invention Example No. 4 is an optical micrograph showing the metal structure of a test piece of No. 4. Comparative Example No. 6 is an optical micrograph showing the metal structure of a test piece of No. 6. Comparative Example No. 8 is an optical micrograph showing a metal structure of a test piece of No. 8. Conventional Example No. It is an optical microscope photograph which shows the metal structure of 10 test pieces. The relationship between the area percentage of MC carbide having an aspect ratio of 2.0 or more in each specimen and KIC is shown. 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

2 bases, 20 inscribed circle, D ₂₀ inscribed circle diameter, L arbitrary straight line,
L1, L2, L3 interparticle distance,
1 MC carbide, 10 yen, D ₁₀ yen equivalent diameter,
41 mold, 42 molten metal, 43 primary crystal MC carbide, 44 hollow part,
40 cylindrical body, 40a inner peripheral layer, 40b outer peripheral layer, 40c concentration gradient layer,
51 rolling mill, 52 test roll, 53 test roll, 54 heating furnace,
55 Cooling water tank, 56 Winder, 57 Tension controller,
S rolled material,
71 outer layer of the present invention, 72 inner layer, 85 hollow portion, 86 shaft material

Claims (14)

A rolling roll having an outer layer formed by centrifugal casting in which MC carbide is dispersed in an area ratio of 20% to 50% and a fracture toughness value KIC is 80 kgf / mm ^3/2 or more. 2. The rolling roll according to claim 1, wherein MC carbide having an aspect ratio of 2.0 or more is dispersed in an area ratio of 10% or more in the structure of the outer layer. 3. The rolling roll according to claim 1, wherein in the structure of the outer layer, a maximum inscribed circle diameter of a region not including MC carbide having an equivalent circle diameter of 15 μm or more does not exceed 150 μm. The rolling roll according to any one of claims 1 to 3, wherein an average distance between MC carbides having an equivalent circle diameter of 15 µm or more in the structure of the outer layer is 10 µm to 40 µm. The rolling roll according to any one of claims 1 to 4, wherein an average equivalent-circle diameter of MC carbide is 10 µm to 50 µm in the structure of the outer layer. The ratio (B / A) between the average distance B between MC carbides having an equivalent circle diameter of 15 μm or more and the average equivalent circle diameter A of MC carbides in the outer layer structure is 2 or less. The roll for rolling in any one of 1-5. _7. The M ₂ C, M ₆ C, and M ₇ C ₃ carbides having an area ratio of 1 μm or more in terms of area ratio are dispersed in a total amount of 0 to 2% in the outer layer. Roll for rolling according to crab. The roll for rolling according to any one of claims 1 to 7, wherein the outer layer base has a Vickers hardness of Hv550 or more. The outer layer has a chemical composition of mass%, C: 2.5% to 7.5%, Si: 0.1% to 3.5%, Mn: 0.1% to 3.5%, and V: 11 The roll for rolling according to any one of claims 1 to 8, characterized by comprising 0.0% to 30.0%, and comprising balance Fe and inevitable impurity elements. The outer layer is further mass%, and is selected from the group consisting of Cr: 1.0% to 9.0%, Mo: 0.5% to 7.5%, and W: 1.5% to 15.0%. The roll for rolling according to claim 9, comprising at least one kind. The rolling roll according to claim 9 or 10, wherein in the outer layer, at least a part of V is substituted with an amount of Nb satisfying the following formula (1).
11.0% ≦ V% + 0.55 × Nb% ≦ 30.0% (mass%) (1) The said outer layer further satisfy | fills following formula (2), The roll for rolling in any one of Claims 9-11 characterized by the above-mentioned.
0 ≦ C% −0.2 × (V% + 0.55 × Nb%) ≦ 1.3% (mass%) (2) The roll for rolling according to any one of claims 9 to 12, wherein the outer layer further contains, by mass%, 2.0% or less of Ni and / or 5.0% or less of Co. The roll for rolling according to any one of claims 9 to 13, wherein the outer layer further contains, by mass%, 0.5% or less of Ti and / or 0.5% or less of Al.