JP2018039047A - Rolling roll outer layer material with high abrasion resistance and rolling compound roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a roll outer layer material having high abrasion resistance and a rolling compound roll including the same.SOLUTION: A roll outer layer material has an inclined composition with a W content reducing in a radial direction from an outer peripheral side of a roll toward an inner peripheral side thereof. An outer layer material surface at a position corresponding to a maximum diameter when used being rolled has a composition containing W:25-70%, Co:5-45%, C:0.6-3.5%, Si:0.05-3%, Mn:0.05-3% and Mo:1-15% in mass%, and an inevitable impurity as a remaining part. A carbide area ratio of the outer layer material surface is 45-90%. A rolling compound roll also preferably contains one or more selected from Fe:5-40%, Cr:0.1-10%, V:0.1-6% and Nb:0.1-3% in mass%, and more preferably satisfies expression [1]: 0.6≤%Fe/%Co≤1.5 [1], where %Fe and %Co are respectively the content (mass%) of Fe and Co.SELECTED DRAWING: None

Description

  The present invention relates to a roll outer layer material for rolling suitable for hot rolling or cold rolling and a composite roll for rolling using the same, and more particularly to improvement of wear resistance.

  In recent years, the progress of rolling technology of steel sheets has been remarkable, and accordingly, the usage environment of rolling rolls has become more severe. In particular, the production of steel sheets that require a large rolling load and require excellent surface quality, such as high-strength steel sheets and thin-walled products, has been increasing recently.

  For this reason, a work roll for cold rolling is required to have excellent wear resistance and high hardness. In general, the wear resistance is improved by making the roll material highly alloyed. However, when the alloying is made high, the grindability is deteriorated or the damage caused by a roll accident is increased (decrease in accident resistance). Therefore, it is necessary to use a material that has both grindability and accident resistance. Furthermore, in order to produce a steel sheet with excellent surface quality, it is necessary to make the surface properties of the roll in direct contact with the steel sheet uniform and fine. Specifically, the roll material is highly clean and fine. It is required to make cast iron and cast steel having a fine microstructure.

  In addition, in the work roll for hot rolling, the occurrence of roll wear and rough surface makes it difficult to limit the rolling schedule due to the material and dimensions of the product, and it is difficult to reduce the frequency of roll replacement. Degradation is one of the bottlenecks in improving productivity and reducing costs. For this reason, in the work roll for hot rolling, it is requested | required that generation | occurrence | production of abrasion and rough skin should be suppressed and the durability of a roll should be improved.

  For these reasons, there has been a strong demand for improving the properties of the rolling rolls used, particularly for improving wear resistance. Improvement of wear resistance in a roll for rolling is an important issue directly related to improvement of steel plate quality and productivity in the production of steel plates.

  In response to the demand for improving the wear resistance of such rolling rolls, for example, as described in Non-Patent Document 1 and Non-Patent Document 2, the outer layer composition is similar to the high-speed tool steel composition, and hard carbides are used. A high speed roll has been developed in which a large amount of is dispersed to significantly improve wear resistance. Further, for example, Patent Document 1 describes a hot roll composite roll in which an outer layer is formed around a steel core by a continuous overlaying method. In the composite roll for hot rolling described in Patent Document 1, the outer layer material is, by weight, C: 1.0 to 4.0%, Si: 3.0% or less, Mn: 1.5% or less, Cr: 2 to 10%, Mo : 9% or less, W: 20% or less, V: 2 to 15% included, P: 0.08% or less, S: 0.06% or less, B: 0.0500% or less, and the composition composed of the balance Fe and inevitable impurities However, the hardness of the base is said to have a Vickers hardness (Hv) of 550 or more, which is composed of a structure containing 5-30% granular carbide and 6% or more non-particulate carbide in area ratio. The outer layer material may further contain Ni: 5.0% or less, Co: 5.0% or less, and Nb: 5.0% or less. Thereby, even if cracks occur due to the presence of a predetermined amount or more of non-particulate carbide, it is suppressed from progressing to the deep part of the roll, heat crack resistance is improved, and VC-based hard carbide is included. The wear resistance is also good.

  Such a high-speed roll outer layer material needs to disperse a large amount of hard carbide throughout the matrix in order to improve wear resistance. However, hard carbides produced with a high-speed composition generally have a lighter specific gravity than the base, and are likely to cause segregation during casting. Especially in the centrifugal casting method, which is a typical casting method for roll outer layer material because of its excellent productivity and economy, the phase with light specific gravity tends to accumulate and segregate inside due to centrifugal force. It has been considered difficult to manufacture by a centrifugal casting method.

  However, as a technique for providing a roll outer layer material for rolling with excellent wear resistance and crack resistance that does not cause segregation even when a centrifugal casting method is applied, Patent Document 2 discloses, in mass%, C: 1.5- Including 3.5%, Si: 1.5% or less, Mn: 1.2% or less, Ni: 5.5% or less, Cr: 5.5-12.0%, Mo: 2.0-8.0%, V: 3.0-0.0%, Nb: 0.5-7.0% In addition, a roll outer layer material containing Nb and V such that the contents of Nb, V, and C satisfy a specific relationship and the ratio of Nb and V is within a specific range is described.

  Patent Document 3 discloses that in mass%, C: 1.5 to 3.5%, Si: 1.5% or less, Mn: 1.2% or less, Cr: 5.5 to 12.0%, Mo: 2.0 to 8.0%, V: 3.0 to 10.0. %, Nb: 0.5 to 7.0%, and Nb and V are contained so that the contents of Nb, V and C satisfy a specific relationship, and the ratio of Nb and V falls within a specific range. A roll outer layer material is described. By adopting such a composition, segregation in the roll outer layer material is suppressed even when the centrifugal casting method is applied, and wear resistance and crack resistance are improved, which greatly contributes to improvement in hot rolling productivity. .

Patent Document 4 describes a centrifugal cast composite roll. The centrifugal cast composite roll described in Patent Document 4 is composed of an outer layer and an inner layer of cast iron or cast steel, and the outer layer is, by weight, C: 1.0 to 3.0%, Si: 0.1 to 3.0%, Mn: 0.1 to 2.0%. , Cr: 2.0 to 10.0%, Mo: 0.1 to 10.0%, V: 1.0 to 10.0%, W: 0.1 to 10.0%, and Mo + W: 10.0% or less satisfy the alloy composition and the balance from Fe and inevitable impurities It has the composition which becomes. According to the technique described in Patent Document 4, crystallization of M ₆ C type carbides that are likely to cause aggregation and segregation is suppressed, and an outer layer in which only MC type + M ₇ C ₃ type carbides precipitate can be formed. It can be manufactured with.

  Further, for example, Patent Document 5 describes a centrifugal cast outer layer material for a rolling roll. The centrifugal cast outer layer material for rolling rolls described in Patent Document 5 contains, in mass%, C: 4.5 to 9%, Si: 0.1 to 3.5%, Mn: 0.1 to 3.5%, V: 18 to 40%. It has a composition, and preferably has a structure in which MC carbides are dispersed in an area ratio of 20 to 60% in a Vickers hardness (Hv) base of 550 to 900. In the technique described in Patent Document 5, MC carbide with a small specific gravity is concentrated on the inner surface side, and positively utilizes centrifugal casting segregation. After centrifugal casting, cutting is performed so as to leave only a layer in which MC carbide is concentrated. For example, it is said that an outer layer of a roll containing many MC carbides can be reliably formed at low cost.

As a material having extremely excellent wear resistance, a cemented carbide has been known for a long time. As a cemented carbide, for example, as described in Non-Patent Document 3, tungsten carbide (WC) is generally molded and sintered together with Co as a binder.
As a technique in which such a cemented carbide is applied to a roll for rolling, Patent Document 6, Patent Document 7, Patent Document 8, Patent Document 9, Patent Document 10, and the like are described.

  Patent Document 6 describes a tungsten carbide base cemented carbide for a hot rolling roll and a hot rolling guide roll. In the technique described in Patent Document 6, the weight ratio of chromium to the sum of cobalt and nickel is 1/1 to 1/99, the weight ratio of cobalt to nickel is 9/1 to 1/9, and tungsten carbide is 88 weights. %, A tungsten carbide based alloy having a total of 12 to 65% by weight of cobalt, nickel and chromium. Patent Document 6 describes an example in which such a cemented carbide is applied to a roll for hot rolling of a normal steel material (wire material).

  Patent Document 7 describes a hot wire rolling roll made of cemented carbide. In the technique described in Patent Document 7, the cemented carbide used is replaced with WC having an average particle diameter of 1 μm to 5 μm, or a part of WC is replaced by 10% by weight or less with one or more of TiC, TaC, and NbC. It consists of a hard carbide phase and a ternary alloy binder phase, and Cr in the binder phase is 0.30 or less with respect to the sum of Ni and Co, and 0.05 or more with respect to the total binder phase, and further Ni is The cemented carbide has a polarization potential of 0.33 to 0.90 with respect to the sum of Ni and Co, and a polarization potential of 0.3 V or more with respect to cooling general industrial water. By setting it as such a cemented carbide, it is supposed that it will become the roll for hot wire materials excellent in the skin-resistance roughness.

  Patent Document 8 discloses that an outer layer made of cemented carbide is joined to an outer periphery of an inner layer made of a steel or iron-based material via an intermediate layer, and the intermediate layer has a mean particle size of 3 μm or less. A rolling composite roll made of cemented carbide formed using powder is described. Further, the content of WC particles in the intermediate layer is preferably set to 70% or less by weight. Thereby, it is said that the roll for cemented carbide rolling excellent in abrasion resistance and highly reliable in strength can be obtained.

  In Patent Document 9, an outer layer is formed of a cemented carbide having excellent wear resistance, and an intermediate layer made of a cemented carbide containing WC and Ni is provided to provide a highly reliable cemented carbide. An alloy rolling roll is disclosed.

  Further, Patent Document 10 discloses that R = σc (1-ν) / Eα (where σc: bending strength, ν: Poisson's ratio, E: Young's modulus on the outer periphery of the inner layer made of steel or iron-based material. , Α: thermal expansion coefficient), a composite roll made of cemented carbide for sheet rolling in which an outer layer made of a cemented carbide satisfying a thermal shock coefficient R of 400 or more is described. As a result, the wear resistance and roughness resistance of the roll are improved, and the occurrence and development of thermal cracks during rolling accidents are suppressed.

Japanese Unexamined Patent Publication No. 04-141553 Japanese Patent Laid-Open No. 04-365836 JP 05-1350 A Japanese Patent Laid-Open No. 08-60289 International application WO2006 / 030795 Japanese Patent Publication No.57-6502 Japanese Patent Publication No.58-39906 JP 2004-243341 A JP 2006-175456 A JP 2004-268140 A

Kamada et al .: Hitachi Review Vol. 72, No. 5 (1990), p.69 Hashimoto et al .: Steel Research No. 338 (1990), p62 Kazuma Kazama: “Steel Material Science Revised Edition” Jikkyo Publishing (1981), p368

However, the technique described in Patent Document 1 has a problem that productivity is low and cost is high because an outer layer is formed around a steel core by a continuous overlaying method. In the techniques described in Patent Documents 2 and 3, mainly, the contents of Nb, V and C are limited to a specific range, and MC type carbides are uniformly dispersed to improve wear resistance and crack resistance. It is said. In reality, however, there are considerable amounts of M ₇ C ₃ type carbides and M ₆ C type carbides that contain a large amount of Cr and Mo, so that further improvement in properties can be achieved only from the viewpoint of uniformly dispersing MC type carbides. That's not enough. In the technique described in Patent Document 4, Mo + W is limited to 10.0% or less in order to suppress crystallization of M ₆ C-type carbides that are likely to cause aggregation and segregation. Making it possible. However, limiting the contents of Mo and W has left a problem for the recent demand for further improvement in wear resistance.

  In the production of rolling rolls using the centrifugal casting method, the increase in the amount of carbide forming elements such as Mo, V, and W is because the specific gravity of the generated VC-based hard carbide is lighter than the molten metal forming the base, There was a concern that the generated VC-based hard carbide accumulates on the inner surface side and aggregates at the boundary with the inner layer, leading to a decrease in bonding strength at the boundary.

  Further, in the technique described in Patent Document 5, although the wear resistance of the roll is improved, it requires an operation of removing the outer surface region where the MC type carbide is reduced, and the yield is very low. There was a problem that the superiority of the centrifugal casting method of productivity and low cost was lost.

  The techniques described in Patent Document 6 and Patent Document 7 using cemented carbide are intended for small rolls for wire rod rolling, and this technique can be used as a cold rolling roll or a hot rolling roll. It is difficult to apply as it is to the manufacture of a large roll. In addition, since HIP processing, which is an expensive process compared with centrifugal casting products, is required, there is a problem that manufacturing costs are high even for small products.

  The techniques described in Patent Document 8, Patent Document 9, and Patent Document 10 that use cemented carbide as an outer layer material for a roll for sheet rolling assume that the outer layer material is formed by a sintered-HIP method. Therefore, the problem that the manufacturing cost is extremely high remains. In addition, these techniques use soft Co or Ni as a binder, and there is a problem that dents (recesses) are easily generated during rolling, and the practical application has not progressed.

  The present invention solves such problems of the prior art, and provides a roll outer layer material excellent in wear resistance, which has significantly improved wear resistance compared to the prior art, and a composite roll for rolling using the roll at low cost. Objective.

  In order to achieve the above-mentioned problems, the present inventors have made it possible to manufacture a rolling roll having extremely high wear resistance similar to that of cemented carbide by a centrifugal casting method that is excellent in productivity and economy. We studied diligently. As a result, if the hard carbides can be concentrated and concentrated on the outer surface side of the roll by utilizing the centrifugal force acting on the molten metal and the crystallization phase during centrifugal casting, the wear resistance of the centrifugal casting roll is reduced. I came to think that the sex could be remarkably improved. And by further study, in order to concentrate and concentrate hard carbide on the outer surface side of the roll during centrifugal casting, carbide having a specific gravity larger than that of the liquid phase is selected from the liquid phase in which centrifugal force is acting. I came up with the idea of finding the conditions that allow crystallization as primary crystals.

  That is, when a carbide having a specific gravity larger than that of the liquid phase is crystallized in the liquid phase in which the centrifugal force is acting, the centrifugal force acts in the outer circumferential direction on the carbide. At that time, if the carbide and the surrounding γ phase do not eutectic solidify and the carbide can be crystallized directly from the liquid phase as the primary crystal, the carbide is still in the liquid phase, so the carbide easily moves to the outer peripheral side, It can be accumulated.

As a carbide forming element that satisfies such conditions, paying attention to W with a large specific gravity, and also thinking of containing a large amount of it, repeating various casting experiments, utilizing phase diagram calculation etc.,
(1) When a molten metal containing 0.6 mass% or more of C in a W-Co based alloy containing a large amount of W having a large specific gravity, M ₆ C type carbide enriched in W appears as primary crystals. ,
(2) When such a W-Co based alloy melt is centrifugally cast, a structure form in which M ₆ C type carbides crystallized as primary crystals segregate at a high concentration on the outer surface side of the outer layer material is obtained.
I found.

It has been found that if the alloy used is an Fe-based alloy, the formation of W-type eutectic carbide is promoted, and the appearance of M ₆ C type carbide as the primary crystal is inhibited. In addition, by using a W—Co-based alloy that increases the carbon activity as the alloy used, the formation of W-type eutectic carbide is suppressed, and M ₆ C type carbide enriched with W in the molten metal is the first. When the C content is less than 0.6% by mass, the primary crystal M ₆ C type carbide does not appear. On the other hand, when the C content exceeds 3% by mass, the liquidus temperature increases. It has been found that, since it becomes too high, melting and casting become difficult, and MC-type carbides and M ₂ C-type carbides that are very fragile grow and become coarse, which easily causes roll breakage.

The present invention has been completed based on such findings and further studies. That is, the gist of the present invention is as follows.
(1) W-Co-based alloy roll outer layer material for rolling, which has a gradient composition in which the W content decreases in the radial direction from the outer circumference side of the roll toward the inner circumference side, and corresponds to the maximum diameter during rolling use. The outer layer material surface at the position is mass%, W: 25 to 70%, Co: 5 to 45%, C: 0.6 to 3.5%, Si: 0.05 to 3%, Mn: 0.05 to 3%, Mo: 1 to A roll outer layer material for rolling, characterized in that it contains 15%, the balance is composed of inevitable impurities, and the carbide area ratio on the surface of the outer layer material is 45% or more and 90% or less.
(2) In (1), in addition to the above composition, it is further selected by mass% from Fe: 5-40%, Cr: 0.1-10%, V: 0.1-6%, Nb: 0.1-3% A roll outer layer material for rolling, comprising one or two or more types.
(3) A rolling roll outer layer material having the above composition and satisfying the following formula [1] in (2):
0.6 ≦% Fe /% Co ≦ 1.5 [1]
Here,% Fe and% Co are the contents (mass%) of Fe and Co, respectively.

(4) The roll outer layer material for rolling according to any one of (1) to (3), further containing Ni: 0.05 to 3% by mass% in addition to the above composition.
(5) The rolling roll outer layer material according to any one of (1) to (4), wherein the rolling roll outer layer material is made by centrifugal casting.
(6) A composite roll for rolling comprising an outer layer and an inner layer welded and integrated with the outer layer, wherein the outer layer is made of a W-Co-based alloy, and the W content is directed from the outer peripheral side of the roll toward the inner peripheral side. The outer layer material surface at a position corresponding to the maximum diameter when using rolling is mass%, W: 25-70%, Co: 5-45%, C: 0.6-3.5% Si: 0.05 to 3%, Mn: 0.05 to 3%, Mo: 1 to 15%, the balance is composed of inevitable impurities, and the carbide area ratio on the surface of the outer layer material is 45% or more 90 % Of a composite roll for rolling.
(7) In (6), in addition to the above composition, it is further selected by mass% from Fe: 5-40%, Cr: 0.1-10%, V: 0.1-6%, Nb: 0.1-3% One type or two or more types of rolled composite rolls.
(8) A composite roll for rolling according to (7), wherein the composition has the above composition and the contents of Fe and Co satisfy the following formula [1].
0.6 ≦% Fe /% Co ≦ 1.5 [1]
Here,% Fe and% Co are the contents (mass%) of Fe and Co, respectively.

(9) The rolling composite roll according to any one of (6) to (8), further containing Ni: 0.05 to 3% by mass% in addition to the above composition.
(10) A rolling composite roll comprising an outer layer, an intermediate layer welded and integrated with the outer layer, and an inner layer welded and integrated with the intermediate layer, wherein the outer layer is made of a W-Co based alloy and contains W In the gradient composition in which the amount decreases in the radial direction from the outer peripheral side of the roll toward the inner peripheral side, the outer layer material surface at the position corresponding to the maximum diameter during rolling use is mass%, W: 25 to 70%, Co: 5 to 45%, C: 0.6 to 3.5%, Si: 0.05 to 3%, Mn: 0.05 to 3%, Mo: 1 to 15%, and the balance is composed of inevitable impurities, and the outer layer A composite roll for rolling, characterized in that the carbide area ratio on the material surface is 45% or more and 90% or less.
(11) In (10), in addition to the above composition, it is further selected by mass% from Fe: 5-40%, Cr: 0.1-10%, V: 0.1-6%, Nb: 0.1-3% One type or two or more types of rolled composite rolls.
(12) A composite roll for rolling according to (11), wherein the composition has the above composition and the contents of Fe and Co satisfy the following formula [1].
0.6 ≦% Fe /% Co ≦ 1.5 [1]
Here,% Fe and% Co are the contents (mass%) of Fe and Co, respectively.
(13) The rolling composite roll according to any one of (10) to (12), further containing Ni: 0.05 to 3% by mass% in addition to the above composition.
(14) The composite roll for rolling according to any one of (6) to (13), wherein the outer layer is made of centrifugal casting.

  According to the present invention, a roll for rolling excellent in wear resistance, particularly suitable for a hot rolling or cold rolling roll, particularly a roll for centrifugal casting, can be manufactured at low cost and easily. There are remarkable effects in the industry.

It is a structure | tissue photograph which shows the scanning electron microscope structure | tissue in an Example. (A) is sleeve No. 13 and (b) is sleeve No. 5. It is explanatory drawing which shows typically the outline | summary of the abrasion test in an Example. It is a schematic diagram of the composite roll for a rolling test.

  The roll outer layer material for rolling of the present invention is made by centrifugal casting. As used herein, “centrifugal rolling roll outer layer material” means a rolling roll outer layer material that has been manufactured using a centrifugal casting method that has been conventionally used as a rolling roll manufacturing method. To do. Roll outer layer material for rolling manufactured using the centrifugal casting method ("centrifugal casting" outer layer material for rolling roll) is conventionally referred to as "things" with rolling rolls manufactured by other manufacturing methods. It can be clearly distinguished, and specifying the outer layer material of the roll made of “centrifugal casting” by structure and characteristics is laborious and impractical.

  The roll outer layer material for rolling of the present invention is made of a W-Co-based alloy and has a gradient composition in which the W content decreases in the radial direction from the outer peripheral side of the roll toward the inner peripheral side, and corresponds to the maximum diameter during rolling use. The surface of the outer layer material at the position to be included includes W: 25-70%, Co: 5-45%, C: 0.6-3.5%, Si: 0.05-3%, Mn: 0.05-3%, Mo: 1-15% is included, the balance is composed of inevitable impurities, and the carbide area ratio on the surface of the outer layer material is 45% or more and 90% or less. The composition and carbide area ratio described above are used in rolling if the sleeve has a radial position corresponding to at least 20% of the volume on the outer surface side relative to the total volume of the outer layer material, for example, an outer diameter of 250 mm and an inner diameter of 140 mm. It is preferable to satisfy even a position of at least 9 mm in the radial direction from the position corresponding to the maximum diameter at the time toward the inner peripheral side.

  Here, “the surface of the outer layer material at the position corresponding to the maximum diameter during rolling use” is a layer formed on the outer surface of the outer layer material as cast (the molten metal is rapidly cooled by contact with the mold and solidified. The surface of the outer layer material at the position corresponding to the maximum diameter of the product roll diameter that is used for rolling for the first time, that is, the position corresponding to the maximum diameter that can be used as a product (roll outer layer material). The outer layer material surface.

  Further, the composition analysis of the outer layer material surface can be performed by instrumental analysis such as fluorescent X-ray analysis or emission spectroscopic analysis. Either a block sample having a diameter of less than 10 mm may be collected and subjected to chemical analysis.

  First, the reasons for limiting the composition of the roll outer layer material for rolling of the present invention will be described. Hereinafter, the mass% related to the composition is simply expressed as%.

C: 0.6-3.5%
C is an element having an action of combining with W and a carbide-forming element such as Mo, Cr, V, and Nb to form a hard carbide and improve wear resistance. Depending on the amount of C, the form of carbide, the amount of crystallization, and the crystallization temperature change. When C is 0.6% or more, an M ₆ C type carbide is crystallized as an initial crystal, and a structure form segregating to the outer surface side during centrifugal casting is obtained, and wear resistance is improved. If C is less than 0.6%, the amount of M ₆ C-type carbide crystallized as primary crystals is insufficient, and the wear resistance is reduced. On the other hand, if the content exceeds 3.5%, it becomes difficult to produce as an outer layer material, and M ₂ C carbides and MC carbides that are very fragile are formed and coarsened, and therefore roll breakage is likely to occur during rolling. Therefore, C is limited to the range of 0.6 to 3.5%. In addition, Preferably it is 1.0 to 3.0%.

Si: 0.05-3%
Si is an element that acts as a deoxidizer and also has a matrix strengthening action. In order to acquire such an effect, 0.05% or more of content is required. On the other hand, if the content exceeds 3%, the effect is saturated, and flake graphite appears and the toughness is lowered. For this reason, Si was limited to the range of 0.05 to 3%. In addition, Preferably it is 0.1 to 2%.

Mn: 0.05-3%
Mn is an element having an action of fixing S as MnS and detoxifying S that adversely affects the material. Further, Mn contributes to improving hardenability by dissolving in the base. In order to acquire such an effect, it is necessary to make it contain 0.05% or more. On the other hand, even if the content exceeds 3%, the above-described effects are saturated and the material is deteriorated. For this reason, Mn was limited to the range of 0.05 to 3%. In addition, Preferably it is 0.1 to 1%.

Mo: 1-15%
Mo is a carbide-forming element that forms a carbide by combining with C. In the present invention, in particular, in the present invention, solid carbide dissolves in a hard M ₆ C-type carbide that is a primary crystal carbide enriched in W to strengthen the carbide. , Has the effect of increasing the fracture resistance of the roll outer layer material. Mo also improves the hardenability during heat treatment and contributes to the increase in hardness of the outer layer material of the roll. Furthermore, Mo is an element heavier than Co, and has an effect of not inhibiting or promoting the centrifugal separation of primary crystal carbide to the outer surface side. In order to obtain these effects, a content of 1% or more is required. On the other hand, if the content exceeds 15%, Mo-based hard and brittle carbides appear and wear resistance decreases. For this reason, Mo was limited to the range of 1 to 15%. In addition, Preferably it is 2 to 10%. More preferably, it is 4 to 10%.

W: 25-70%
W is the most important element in the present invention, and has an alloy composition of 25% or more. As a result, a large amount of hard M ₆ C-type carbide enriched with W can appear as a primary crystal, and a roll outer layer material for rolling with significantly improved wear resistance can be obtained. On the other hand, if the content exceeds 70%, the M ₆ C-type carbide becomes coarse and brittle, and the melting point of the molten metal rises, which makes it difficult to melt and cast. For this reason, W was limited to the range of 25 to 70%. In addition, Preferably it is 30 to 65%. More preferably, it is 40 to 55%.

Co: 5-45%
Co, together with W, is an important element in the present invention. By containing a large amount of Co together with W, the activity of C increases, and a large amount of hard carbides (M ₆ C type, M ₂ C type, MC type, etc.) enriched with W are used as primary crystals. Appearance is promoted and contributes to the improvement of the wear resistance of the outer layer material of the roll for rolling. In order to obtain such an effect, it is necessary to contain 5% or more of Co. On the other hand, if the content exceeds 45%, the γ phase is stabilized, the base becomes soft, and when used as a roll for rolling, frequent occurrence of indentations (recesses) is caused, and the wear resistance is remarkably reduced. . For this reason, Co was limited to the range of 5 to 45%. In addition, Preferably it is 10 to 40%. More preferably, it is 12 to 35%.

The above components are basic components, but in addition to the basic composition, Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, Nb: 0.1 to 3% were selected. You may contain 1 type (s) or 2 or more types and / or Ni: 0.05-3% as needed as needed.
One or more selected from Fe: 5-40%, Cr: 0.1-10%, V: 0.1-6%, Nb: 0.1-3%
Fe, Cr, V, and Nb are all carbide-forming elements, elements that have the effect of strengthening the carbide by solid solution in the carbide, and can be selected as necessary to contain one or more kinds. .
Fe dissolves in the carbide and also in the base, contributes to strengthening of the base, and has an effect of preventing formation of dents (recesses) when used as a rolling roll. In order to acquire such an effect, it is preferable to contain 5% or more. On the other hand, if the content exceeds 40%, the amount of hard M ₆ C-type carbide appearing as primary crystals decreases, the number of brittle M ₃ C-type carbides increases, and wear resistance decreases. For this reason, when it contains, it is preferable to limit Fe to the range of 5 to 40%. In addition, More preferably, it is 10 to 35%.

  The mechanism by which the base of the W-Co-based alloy is strengthened by containing Fe in the base has not been clarified at this time, but the α-phase stabilization action by Fe offsets the γ-phase stabilization action by Co. As a result, the strength of the base has increased, or the α-phase stabilization effect of Fe is large, and the base has a hard martensite or bainite structure, or even finer carbides have precipitated in such a base. We believe that a base strengthening phenomenon has occurred, such as the appearance of an organization.

Cr is a strong carbide-forming element and has the effect of mainly forming eutectic carbides and improving the strength of the formed carbides. The eutectic carbides crystallize in the gaps between the primary crystals of the M ₆ C type carbide, and as a result, act to strengthen the gaps of the M ₆ C type carbides. Cr also has an action of suppressing the appearance of graphite. W-Co based alloys have a high activity coefficient of C, so that graphite is likely to appear. When graphite appears, toughness decreases. In order to suppress the appearance of graphite and use it stably as a roll for rolling, in the present invention, it is preferable to contain Cr as necessary. In order to acquire such an effect, it is preferable to contain 0.1% or more. On the other hand, if the content exceeds 10%, a large amount of Cr-based eutectic carbide appears and the toughness decreases. For this reason, when it contains, it is preferable to limit Cr to 0.1 to 10% of range. In addition, More preferably, it is 1 to 8%.

V is an element that combines with C to form hard VC (MC-type carbide containing Mo, Nb, Cr, W, etc.). The formed MC-type carbide crystallizes as the primary crystal and W is concentrated. It becomes a crystallization nucleus of the converted M ₆ C type carbide, promotes the appearance of M ₆ C type carbide, and further has a function of dispersing fine M ₆ C type carbide at high density. In order to acquire such an effect, it is preferable to make it contain 0.1% or more. On the other hand, if it contains more than 6% in a large amount, even if it contains a lot of W, the low specific gravity V-type MC type carbide increases and becomes coarse and is centrifuged to the inner surface side of the roll outer layer material during centrifugal casting. The Therefore, the amount of hard M ₆ C type carbide on the outer surface side is insufficient, and the wear resistance when using the roll outer layer material is lowered. Further, when the amount of V-based MC type carbide centrifuged at the inner surface side becomes large, the boundary strength with the inner layer of the roll or the intermediate layer is lowered. For this reason, when it contains, it is preferable to limit V to 0.1 to 6% of range. In addition, More preferably, it is 1 to 5%.

Nb has a very high bonding strength with C and is a strong carbide forming element, and easily forms a composite carbide with V and W. Such a composite carbide of Nb and V or W becomes a crystallization nucleus of M ₆ C type carbide enriched with W, which is crystallized as a primary crystal, promotes the appearance of M ₆ C type carbide, and further refines. It has the effect of dispersing high density M ₆ C type carbide. In order to obtain such an effect, the content of 0.1% or more is required. On the other hand, a large content exceeding 3% forms a low specific gravity Nb-based MC type carbide and becomes coarse, and during centrifugal casting, the carbide is easily separated into the inner surface side of the roll outer layer material, and on the inner surface side of the outer layer material. The amount of MC type carbide increases. Moreover, the MC type carbide that is centrifuged to the inner surface side of the outer layer material, when the amount increases, the quality of the inner surface side decreases, for example, the boundary strength between the inner layer of the roll and the intermediate layer decreases. For this reason, when it contains, it is preferable to limit Nb to 0.1 to 3% of range. In addition, More preferably, it is 0.5 to 2%.

Ni: 0.05-3%
Ni is an element that has the effect of improving hardenability, and can be contained as necessary, for example, to solve the shortage of hardenability in large rolls. In order to acquire such an effect, it is preferable to contain 0.05% or more. In addition, the effect is not recognized if it is less than 0.05% which is an impurity level. On the other hand, if the content exceeds 3%, the γ phase is stabilized and the desired hardenability cannot be ensured. For this reason, when it contains, it is preferable to limit Ni to 0.05 to 3% of range.

  The balance other than the above-described components consists of inevitable impurities. Examples of inevitable impurities are P, S, N, and B. Note that P is segregated at the grain boundary and has an adverse effect such as embrittlement of the material. Therefore, it is desirable to reduce P as much as possible, but 0.05% or less is acceptable. S, like P, is segregated at the grain boundaries and has the effect of embrittlement of the material, so it is desirable to reduce it as an impurity. However, if it is 0.05% or less, part of it is Mn. Since they combine to exist as sulfide inclusions and are rendered harmless, they are acceptable. Further, N is mixed as an impurity by about 0.01 to 0.1% if it is a normal solution. However, this content does not affect the effects of the present invention. However, N is preferably limited to less than 0.07% because gas defects may be generated at the boundary between the outer layer and the intermediate layer or the inner layer of the composite roll. In some cases, B is mixed from scrap of melting raw material or casting flux and contained as an unavoidable impurity element. B may be dissolved in carbides or bases to change the properties of the carbides, or may be dissolved in bases to affect the hardenability of the bases, thereby fostering quality variations. For this reason, it is preferable to reduce B as much as possible, but if it is 0.1% or less, the effect of the present invention will not be adversely affected. Here, it is preferable to adjust the above inevitable impurity elements to less than 1% in total.

Furthermore, in the present invention, the carbide area ratio on the surface of the outer layer material at the position corresponding to the maximum diameter during rolling is required to be 45% or more and 90% or less. If the carbide area ratio is less than 45%, it is difficult to enjoy the effect of improving wear resistance because there are many bases, and if the carbide area ratio is more than 90%, the amount of base serving as a binder is small, so it is easy to break. It becomes very difficult to manufacture a roll for rolling. Therefore, the carbide area ratio is limited to 45% or more and 90% or less. The carbide area ratio may be controlled by adjusting the composition of the outer layer material of the roll to the above-described range and the molten metal temperature or centrifugal force during centrifugal casting. The higher the molten metal temperature during centrifugal casting, the slower the solidification progress in the mold of the centrifugal casting machine, and the time over which hard M ₆ C carbides enriched in W can move to the outer surface side by centrifugal force. Since there is a large margin, the density of the carbide on the outer surface side tends to increase. Moreover, since the centrifugal separation of the hard M ₆ C type carbide with concentrated W is promoted as the centrifugal force increases, the density of the carbide on the outer surface side tends to increase.

In the present invention, it is preferable that Fe and Co are contained in the above-described range, and the content of Fe and Co satisfies the following formula [1].
0.6 ≦% Fe /% Co ≦ 1.5 [1]
Here,% Fe and% Co are the contents (mass%) of each element.
When% Fe /% Co is in the range of 0.6 to 1.5, the matrix is transformed into a hard structure such as martensite or bainite during the heat treatment, and the hardness of the matrix is remarkably increased, so that the wear resistance is improved. On the other hand, if% Fe /% Co is out of the above range, the matrix does not transform during heat treatment and remains γ phase, so it is soft and inferior in wear resistance. May occur.

Next, the preferable manufacturing method of this invention roll outer-layer material for rolling is demonstrated.
In the present invention, from the viewpoint of productivity and manufacturing cost, the roll outer layer material for rolling is manufactured using a centrifugal casting method in which a casting mold is rotated. Thereby, the roll outer layer material for rolling excellent in abrasion resistance can be manufactured at low cost.

  First, molten metal having the above-described roll outer layer material composition is poured into a rotating mold so as to have a predetermined thickness, and centrifugally cast to obtain a roll outer layer material for rolling. In general, in order to protect the mold, the inner surface is generally covered with a refractory material mainly composed of zircon or the like. In the present invention, it is preferable to perform centrifugal casting by adjusting the number of rotations so that the centrifugal force at a position corresponding to the maximum diameter during rolling is 120 to 250 G. By applying a high centrifugal force, it is possible to increase the dispersion density of the hard carbide having a large specific gravity on the outer surface side.

  In the present invention, the obtained rolling roll outer layer material may be used as a rolling roll by fitting a shaft material into a single sleeve. Moreover, the obtained roll outer layer material for rolling may be formed as a roll for rolling by providing an intermediate layer welded and integrated on the inner side thereof, fitting a shaft member therein as a sleeve having the intermediate layer. The intermediate layer is preferably formed by pouring molten metal having an intermediate layer composition and centrifugal casting while rotating the mold after the outer layer material of the roll is solidified or completely solidified. Examples of the intermediate layer material include graphite steel, 1-2% by mass C high carbon steel, hypoeutectic cast iron, and the like. In addition, although the shaft material of these rolls for rolling is not specifically limited, It is preferable to set it as the forged steel product (shaft) manufactured separately, a cast steel product (shaft), and a cast iron product (shaft).

  Further, in the present invention, the above-described rolling roll outer layer material is an outer layer, and a composite roll comprising an inner layer fused and integrated with the outer layer, or the above-described rolling roll outer layer material is an outer layer, and the outer layer is welded integrally. It is good also as a composite roll which consists of the intermediate | middle layer which changed to the inside layer which welded and integrated with this intermediate | middle layer.

  In the case of forming the intermediate layer, it is preferable that the outer layer material of the roll is solidified or completely solidified, and then the molten metal having the intermediate layer composition is poured and centrifugally cast while rotating the mold. As the intermediate layer material, it is preferable to use graphite steel, 1-2% by mass C high carbon steel, hypoeutectic cast iron or the like. The intermediate layer and the outer layer are integrally welded, and the outer layer component is mixed in the intermediate layer in a range of about 10 to 90%. From the viewpoint of suppressing the amount of the outer layer component mixed into the inner layer, it is desirable to reduce the amount of the outer layer component mixed into the intermediate layer as much as possible.

  In general, the inner layer is formed by static casting of the inner layer material after the outer layer or the intermediate layer is completely solidified and then the rotation of the mold is stopped and the mold is set up. Here, it is preferable to use spheroidal graphite cast iron, worm-like graphite cast iron (CV cast iron), etc. excellent in castability and mechanical properties as the inner layer material to be statically cast. In a composite roll in which there is no intermediate layer and the outer layer and the inner layer are integrally welded, the component of the outer layer material is often mixed into the inner layer by about 1 to 10%. W, Cr, V, and the like contained in the outer layer material are strong carbide forming elements, and when these elements are mixed into the inner layer, the inner layer is weakened. For this reason, in the present invention, the mixing rate of the outer layer component into the inner layer is preferably suppressed to less than 5%.

  The rolling roll outer layer material and the rolling composite roll described above are preferably subjected to heat treatment after casting. Heat treatment is performed at 1000 to 1200 ° C and held for 5 to 40 hours, then cooled in the furnace, cooled by air or blast air, and further cooled and held at 400 to 600 ° C once or more. It is preferable to perform the treatment. In addition, it is preferable to adjust the hardness of the roll outer layer material of the present invention and the composite roll for rolling within the range of 79 to 100 HS according to the application. It is recommended to adjust the heat treatment after casting so that such hardness can be secured stably.

  The molten metal having the composition shown in Table 1 was melted in a high frequency induction furnace, and a sleeve-shaped roll outer layer material (outer diameter: 250 mmφ, radial thickness: 55 mm) was cast as a test material by centrifugal casting. The casting temperature was 1450 to 1550 ° C., and the centrifugal force was 140 to 220 G as a multiple of gravity. In some test materials (melt No. S), significant carbide segregation occurred on the inner surface, so 60 G was used for the purpose of reducing this segregation. The test materials 24 and 25 are made of molten metal having the same composition (melt No. X), but the test material 24 is cast with a centrifugal force of 140 G and the test material 25 with a centrifugal force of 220 G.

  After casting, reheat to 1050 to 1200 ° C and hold for 10 hours, then quenching to cool to 100 ° C or lower and tempering to heat, hold and cool to 400 to 560 ° C, repeated once or twice did. Thereby, the hardness at a position of 5 mm in the thickness direction from the outer surface of the test material was adjusted to approximately 85 to 100 HS. It should be noted that the composition of a commercially available centrifugal cast outer layer material used as a roll for hot finish rolling of steel (high-roll composition: 2.2% C-0.4% Si-0.4% Mn-5.3% Cr-5.2% Mo-5.6 % V-1.1% Nb) melted (molten metal No. V), and a sleeve-shaped roll outer layer material was cast in the same manner and heat-treated after casting to obtain a test material (hardness 85HS). Test material No. 22).

  A test piece for composition analysis, a test piece for wear test, and a roll test piece were collected from the test material subjected to the heat treatment. Test material No. 19 was very fragile and it was very difficult to collect the test material.

  The specimen for composition analysis was ground 5 mm in the radial direction from the outer surface of the test material after the heat treatment described above, 5 mm in the radial direction from the outer surface after the grinding, and 10 mm × 10 mm in a plane parallel to the outer surface. A specimen of a size was collected. Each component element was analyzed using the obtained test piece. The analysis method was chemical analysis, C was a combustion method, Si and W were gravimetric methods, Mn, Cr and Mo were atomic absorption methods, Co was a volumetric method, Fe was a volumetric method or atomic absorption method.

In addition, a test piece having a diameter of 5 mm from the outer surface of the test piece after the heat treatment described above in the radial direction and a surface parallel to the outer surface and having a size of 10 mm × 10 mm is collected, and the surface of 10 mm × 10 mm is mirror-polished, and then aqua regia It was corroded with (hydrochloric acid: nitric acid = 3: 1) and observed with an optical microscope. The observation magnification was 250 times, the region of 450,000 μm ² was observed, and the carbide area ratio (= total carbide area / 450000 × 100) was measured.

The obtained results are shown in Table 2.
In addition, the wear test piece (outer diameter 60 mmφ × width 10 mm) is such that the center position of the width of the wear test piece is 10 mm in the radial direction from the outer surface of the test material after the heat treatment described above. Collected. As shown in FIG. 2, the wear test was performed by a two-disk sliding rolling method of a test piece (wear test piece) and a mating material (material: S45C, outer diameter 190 mmφ × width 15 mm).

  In the wear test, the sliding rate is 14.2 while the test piece rotating at 700 rpm (peripheral speed: 2.1 m / s) is pressed against the test piece rotating at 850 ° C with a load of 980 N while the sample is cooled with water. %. The mating material was updated every 21000 times of rolling of the test piece and rolled until the cumulative number of rotations reached 168000. After the test, the wear loss of the wear test piece was investigated. With respect to the obtained wear loss, the wear loss of the conventional example (test material No. 22) is taken as the standard (1.0), and the ratio of the wear loss of each test material to the standard (the wear resistance ratio = (wear loss of the conventional example) / (Abrasion loss of the test material)) was calculated and the wear resistance was evaluated. A case where the wear resistance ratio was 3 or more was evaluated as “◎”, a case where the wear resistance ratio was 2 or more and less than 3, was evaluated as “◯”, and a case where the wear resistance ratio was less than 2 was evaluated as “x”.

  In addition, each of the roll test pieces (outer diameter 230 mmφ x width) using the above-mentioned heat-treated test materials No. 1 and No. 22 as the raw material, and grinding the outer surface by 10 mm in the radial direction from the outer surface. As shown in FIG. 3, after rolling into a shaft made of carbon steel forged steel to form a composite roll for rolling test, the composite roll was converted into a 4Hi thin plate cold rolling mill (backup roll: It was installed on an outer diameter of 500mmφ x body length of 40mm, and cold rolled with a sheet thickness reduction rate of 20% using a steel sheet with a tensile strength of 590MPa (sheet width 20mm, sheet thickness 1.5mm x length 20m) as the material to be rolled. The wear loss of each composite roll at this time was measured, and the wear resistance ratio was calculated to evaluate the wear resistance.

  The obtained results are shown in Tables 3 and 4.

  In all of the examples of the present invention, the wear resistance ratio is 2.1 or more, and the wear resistance is remarkably improved as compared with the conventional example (high-speed roll). On the other hand, in the comparative example that is out of the scope of the present invention, cracking occurs during the test, and the wear resistance ratio is less than 2, so that the wear resistance is less improved than the conventional example.

In addition, a structure | tissue is observed about this invention example (No.13, No.5), and it shows in FIG. A specimen for tissue observation was collected so that the position 5 mm in the radial direction from the outer surface of the test material after heat treatment was the observation surface, and observed with a scanning electron microscope (magnification: 250 times) to obtain a reflected electron image . It is confirmed that the white region is primary crystal carbide (M ₆ C type carbide in which W is concentrated). In the example of the present invention, it can be seen that primary crystal carbides are dispersed at high density on the outer surface side of the test material (sleeve-shaped roll outer layer material).

  For reference, for test material No. 11 (example of the present invention), 18 mm position (18 mm position) and 38 mm position (38 mm position) in the radial direction from the outer surface of the heat-treated test material (sleeve roll outer layer material) Then, a specimen for composition analysis having a size of 5 mm in the radial direction from the position and 10 mm × 10 mm in a plane parallel to the outer surface was collected. And the composition in each position was analyzed by chemical analysis. The obtained results are also shown in Table 2.

  In addition, for test material No. 11 (example of the present invention), the test surface of the wear test piece was 18 mm in the radial direction from the outer surface of the test material after heat treatment (18 mm position) and 38 to 48 mm in the range (38 mm). The wear test piece was collected so as to be at the position), and the wear test was performed in the same manner as described above to measure the weight loss. The obtained results are also shown in Table 3.

  From Table 2, W is concentrated mainly on the outer surface of the test material (sleeve-shaped roll outer layer material), a position 18 mm away from the outer surface in the radial direction (18 mm position), and 38 mm away from the outer surface in the radial direction. At the same position (38 mm position), the ratio of W decreases, the ratio of Co, Fe, etc. increases, and it can be seen that the composition is clearly gradient. Therefore, as can be seen from Table 3, the wear resistance is 18 mm in the radial direction from the outer surface (18 mm position) and 38 mm away (38 mm position) compared to the area from the outer surface to 10 mm in the radial direction. It is falling.

  In addition, from the test materials No. 24 and No. 25, even when molten metal with the same composition is used, the wear conditions are improved by optimizing the manufacturing conditions such as centrifugal force and increasing the carbide area ratio of the outer surface. It can be seen that it is possible to Test material No. 24 had a centrifugal force of 140 G, the carbide area ratio on the outer surface was 48%, Test material No. 25 had a centrifugal force of 220 G, and the carbide area ratio on the outer surface was 73%. The wear resistance ratios of test materials No. 24 and No. 25 are 2.4 and 3.3, respectively. By optimizing the manufacturing conditions, it is possible to improve the wear resistance even when using molten metal of the same component. Become.

  Also, test material No. 16 (molten metal No. P), test material No. 26 (molten metal No. Y), test material No. 27 (molten metal No. Z), test material No. 28 (molten metal No. AA) This is a test material in which% Fe /% Co on the outer surface is changed by changing the amount of Fe and Co with the same content of elements other than Fe and Co in the molten metal. In test materials No. 16 and No. 28,% Fe /% Co on the outer surface is 1.4 and 0.7, respectively, and satisfies the above formula [1]. Test materials No. 26 and No. 27 have% Fe /% Co on the outer surface of 0.5 and 1.7, respectively, and do not satisfy the formula [1]. From Table 3, the test materials No.16 and No.28 in which% Fe /% Co satisfies the formula [1] are more resistant to wear than the test materials No.26 and No.27 that do not satisfy the formula [1]. It can be seen that the roll outer layer material for rolling superior in wear resistance can be obtained by setting% Fe /% Co within the range of the above-mentioned formula [1].

  Table 4 shows the results of producing roll test composite rolls using the test materials No. 1 and No. 22 and evaluating the wear resistance. Also in the rolling test using the composite roll for rolling, it was confirmed that the wear resistance was improved as compared with the conventional roll.

Claims (14)

  A roll outer layer material for rolling made of a W-Co-based alloy, wherein the outer layer has a gradient composition in which the W content decreases in the radial direction from the outer peripheral side of the roll toward the inner peripheral side, and corresponds to the maximum diameter during rolling use. The material surface is mass%, W: 25-70%, Co: 5-45%, C: 0.6-3.5%, Si: 0.05-3%, Mn: 0.05-3%, Mo: 1-15% An outer layer material for rolling rolls, characterized in that the balance has a composition consisting of inevitable impurities, and the carbide area ratio on the surface of the outer layer material is 45% or more and 90% or less.   In addition to the above composition, in addition to mass, one or more selected from Fe: 5-40%, Cr: 0.1-10%, V: 0.1-6%, Nb: 0.1-3% The roll outer layer material for rolling according to claim 1, comprising: The roll outer layer material for rolling according to claim 2, wherein the composition has the composition and the contents of Fe and Co satisfy the following formula [1].
Record
0.6 ≦% Fe /% Co ≦ 1.5 [1]
Here,% Fe and% Co are the contents (mass%) of Fe and Co, respectively.   The roll outer layer material for rolling according to any one of claims 1 to 3, further comprising Ni: 0.05 to 3% by mass% in addition to the composition.   The rolling roll outer layer material according to any one of claims 1 to 4, wherein the rolling roll outer layer material is made by centrifugal casting. A composite roll for rolling comprising an outer layer and an inner layer welded and integrated with the outer layer,
The outer layer is made of a W-Co-based alloy, and the W layer has a gradient composition in which the W content decreases in the radial direction from the outer peripheral side of the roll toward the inner peripheral side, and the outer layer material surface at a position corresponding to the maximum diameter during rolling is used. , W: 25-70%, Co: 5-45%, C: 0.6-3.5%, Si: 0.05-3%, Mn: 0.05-3%, Mo: 1-15% A composite roll for rolling having a composition consisting of inevitable impurities and a carbide area ratio of 45% to 90% on the surface of the outer layer material.   In addition to the above composition, in addition to mass, one or more selected from Fe: 5-40%, Cr: 0.1-10%, V: 0.1-6%, Nb: 0.1-3% The composite roll for rolling according to claim 6, comprising: The composite roll for rolling according to claim 7, wherein the composite roll has the composition and the content of Fe and Co satisfies the following formula [1].
Record
0.6 ≦% Fe /% Co ≦ 1.5 [1]
Here,% Fe and% Co are the contents (mass%) of Fe and Co, respectively.   The composite roll for rolling according to any one of claims 6 to 8, further comprising Ni: 0.05 to 3% by mass% in addition to the composition. A composite roll for rolling comprising an outer layer, an intermediate layer welded and integrated with the outer layer, and an inner layer welded and integrated with the intermediate layer,
The outer layer is made of a W-Co-based alloy, and the W layer has a gradient composition in which the W content decreases in the radial direction from the outer peripheral side of the roll toward the inner peripheral side, and the outer layer material surface at a position corresponding to the maximum diameter during rolling is used. , W: 25-70%, Co: 5-45%, C: 0.6-3.5%, Si: 0.05-3%, Mn: 0.05-3%, Mo: 1-15% A composite roll for rolling having a composition consisting of inevitable impurities and a carbide area ratio of 45% to 90% on the surface of the outer layer material.   In addition to the above composition, in addition to mass, one or more selected from Fe: 5-40%, Cr: 0.1-10%, V: 0.1-6%, Nb: 0.1-3% The composite roll for rolling according to claim 10, comprising: The composite roll for rolling according to claim 11, wherein the composite roll has the composition and the content of Fe and Co satisfies the following formula [1].
Record
0.6 ≦% Fe /% Co ≦ 1.5 [1]
Here,% Fe and% Co are the contents (mass%) of Fe and Co, respectively.   The composite roll for rolling according to any one of claims 10 to 12, further comprising Ni: 0.05 to 3% by mass in addition to the composition.   The composite roll for rolling according to any one of claims 6 to 13, wherein the outer layer is made of centrifugal casting.