KR102228851B1 - Roll outer layer material for rolling and composite roll for rolling - Google Patents

Abstract

A roll outer layer material having remarkably improved wear resistance and a composite roll for rolling are provided. It is a gradient composition in which the W content decreases from the outer circumferential side toward the inner circumferential side in the radial direction, and at the surface of the outer layer material at a position corresponding to the maximum diameter when rolling is used, in mass%, W: 25 to 70%, Co: 5 to 45 %, and further contains C: 0.6 to 3.5%, Si: 0.05 to 3%, Mn: 0.05 to 3%, Mo: 1 to 15%, and the balance is a W-Co-based alloy composed of unavoidable impurities It is a roll outer layer material having a composition. It is preferable that the roll outer layer material is made of a centrifugal casting agent.

Description

Roll outer layer material for rolling and composite roll for rolling

The present invention, as a first embodiment, 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 in particular, to an improvement in wear resistance.

In addition, the present invention, as a second embodiment, 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 in particular, to an improvement in abrasion resistance and reduction of a rolling load. .

[First embodiment]

First of all, in the first embodiment, in recent years, the progress of the rolling technology of a steel sheet is remarkable, and along with it, the use environment of the rolling roll is becoming more severe. In particular, in recent years, the amount of production of steel sheets, such as high-strength steel sheets and thin-walled products, which has a large rolling load and which requires excellent surface quality, is increasing.

For this reason, in a work roll for cold rolling, excellent abrasion resistance and high hardness to handle it are required. Improvement of abrasion resistance is generally achieved by higher alloying of the roll material, but higher alloying may lead to deterioration of the grindability or increase in damage in the event of a roll accident (deterioration of accident resistance). Therefore, it is necessary to use a material that has both grinding properties and accident resistance. In addition, in order to manufacture a steel sheet with excellent surface quality, it is necessary to make the surface properties of the rolls in direct contact with the steel sheet homogeneous and fine. Specifically, as a roll material, cast iron having a high degree of cleanliness and a fine microstructure, It is required to be made of cast steel.

In addition, in the work roll for hot rolling, the occurrence of roll wear or surface roughness makes it inevitable to restrict the rolling schedule in terms of the material and dimensions of the product, and also makes it difficult to reduce the frequency of roll exchange. The decrease in durability of rolls is one of the obstacles to productivity improvement and cost reduction. For this reason, in the work roll for hot rolling, it is required to suppress the occurrence of abrasion and surface roughness, and to improve the internal degree of the roll.

From this point of view, it has been strongly desired to improve the properties of the roll for rolling to be used, in particular, to improve wear resistance. The improvement of abrasion resistance in a rolling roll has become an important subject directly connected to the improvement of the steel plate quality and productivity improvement in manufacture of a steel plate.

In response to the demand for improving the wear resistance of such rolling rolls, for example, as described in Non-Patent Literature 1 and Non-Patent Literature 2, make the composition of the outer layer similar to the composition of high-speed tool steel, and disperse hard carbides in large quantities. High-speed tool steel rolls have been developed that have improved wear resistance significantly. Further, for example, Patent Document 1 describes a composite roll for hot rolling formed by forming an outer layer around a steel-made core by a continuous growth 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% are included, P: 0.08% or less, S: 0.06% or less, B: 0.0500% or less, the balance has a composition consisting of Fe and inevitable impurities, by area ratio It is composed of a structure containing 5 to 30% of granular carbides and 6% or more of non-granular carbides, and is said to have a base phase hardness of 550 or more of Vickers hardness (Hv). In addition, it is said that the outer layer material may further contain 5.0% or less of Ni, 5.0% or less of Co, and 5.0% or less of Nb. Accordingly, by the presence of a predetermined amount or more of non-granular carbide, even if a crack occurs, propagation to the core of the roll is suppressed, heat cracking resistance is improved, and the VC-based rigidity Abrasion resistance is also said to be good in that it contains carbides.

For such a high speed tool steel roll outer layer material, it is necessary to disperse a large amount of hard carbides in a matrix in order to improve abrasion resistance. However, hard carbides produced by a high-speed tool steel composition generally have a lighter specific gravity than a matrix, and are likely to cause segregation during casting. In particular, in the centrifugal casting method, which is a typical casting method for roll outer layers because of its excellent productivity and economy, a phase with a light specific gravity tends to accumulate and segregate inside by centrifugal force, so a high-speed tool steel roll outer layer material is centrifugal casting. It has been considered difficult to manufacture.

However, as a technique for providing a roll outer layer material for rolling excellent in wear resistance and crack resistance in which segregation and the like does not occur even when the centrifugal casting method is applied, in Patent Document 2, C: 1.5 to 3.5%, Si: 1.5% or less, Mn: 1.2% or less, Ni: 5.5% 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 a roll outer layer material containing V 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.

In addition, in Patent Document 3, in terms of 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 further contains Nb and V so that the content of Nb, V and C satisfies a specific relationship, and the ratio of Nb and V is in a specific range. It is described. By setting it as such a composition, segregation in the roll outer layer material is suppressed even if a centrifugal casting method is applied, abrasion resistance and crack resistance are improved, and it is said that it greatly contributes to the productivity improvement of hot rolling.

In addition, in Patent Document 4, a centrifugal cast composite roll is described. The centrifugal cast composite roll described in Patent Document 4 consists of an outer layer and an inner layer of cast iron or cast steel, and the outer layer is in 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 of the alloy component and the balance satisfying Fe and unavoidable impurities It has a composition consisting of. In the technique described in Patent Document 4, _{crystallization of M 6} C-type carbides that are likely to cause aggregation or segregation is suppressed, and it is possible to make an outer layer in which only MC-type + M ₇ C ₃ type carbides are precipitated, and is produced by a centrifugal casting method. It is said that it can be done.

In addition, for example, in Patent Document 5, a centrifugal cast outer layer material for rolling rolls is described. The centrifugal cast outer layer material for rolling rolls described in Patent Document 5 has a composition containing, in mass%, C: 4.5 to 9%, Si: 0.1 to 3.5%, Mn: 0.1 to 3.5%, and V: 18 to 40%, and is preferably In other words, it is supposed to have a structure in which MC carbide is dispersed by 20 to 60% by area ratio by area ratio in a base having Vickers hardness of HV 550 to 900. In the technique described in Patent Document 5, by actively using centrifugal casting segregation in which MC carbides with a small specific gravity are concentrated on the inner surface side, and after centrifugal casting, cutting so that only the layer enriched with MC carbides remains, the roll outer layer with many MC carbides It is said that it can be reliably formed at low cost.

As a material having very excellent wear resistance, cemented carbide has been known from a long time ago. As a cemented carbide, for example, as described in Non-Patent Document 3, tungsten carbide (WC) is generally formed and sintered together with Co as a binder.

As a technique in which such a cemented carbide is applied to a rolling roll, there are descriptions in Patent Document 6, Patent Document 7, Patent Document 8, Patent Document 9, Patent Document 10, and the like.

Patent Document 6 describes a tungsten carbide-based cemented carbide for hot rolling rolls and hot rolling guide rolls. In the technology 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% by weight or less, It is a tungsten carbide-based alloy in which the total sum of cobalt, nickel, and chromium is 12 to 65% by weight. Patent Document 6 describes an example in which such a carbide alloy is applied to a roll for hot rolling of a common steel material (wire rod).

In addition, Patent Document 7 describes a roll for hot wire rod made of a cemented carbide. In the technique described in Patent Literature 7, the cemented carbide used is WC having an average particle diameter of 1 µm to 5 µm, or a hard carbide phase in which a part of WC is substituted with at least one type of TiC, TaC, and NbC by 10% by weight or less. And, a ternary alloy bonded phase, wherein Cr in the bonded phase is 0.30 or less with respect to the sum of Ni and Co, and is 0.05 or more with respect to the total bonded phase, and further Ni is in the sum of Ni and Co It is made of a cemented carbide with a polarization potential of 0.33 to 0.90, and a polarization potential of 0.3 V or more with respect to cooling general industrial water. By using such a carbide alloy, it is said that a roll for hot wire rods excellent in surface roughness resistance is obtained.

In addition, in Patent Document 8, a cemented carbide formed by bonding an outer layer made of a cemented carbide to the outer periphery of an inner layer made of a steel-based or iron-based material through an intermediate layer, and the intermediate layer is formed using WC raw material powder having an average particle diameter of 3 μm or less. A composite roll for rolling made of an alloy is described. And it is said that it is preferable to make the content of the WC particle of an intermediate layer into 70% or less by weight ratio. Accordingly, it is said that a roll for rolling made of a cemented carbide having excellent abrasion resistance and high reliability in strength can be obtained.

In addition, Patent Document 9 discloses a rolling roll made of a cemented carbide having high strength and reliability by forming an outer layer of a carbide alloy having excellent abrasion resistance and providing an intermediate layer made of a carbide alloy containing WC and Ni. have.

In addition, in Patent Document 10, on the outer periphery of the inner layer made of a steel-based material or an iron-based material, R = σc(1-ν)/Eα (however, σc: flexural strength, ν: Poisson's ratio, E: Young's modulus, α: thermal expansion coefficient) of a thermal shock coefficient R of 400 or more is described in which an outer layer made of a cemented carbide is bonded to each other to form a cemented carbide composite roll for sheet rolling. Accordingly, it is said that the abrasion resistance and the inner surface roughness of the roll are improved, and the occurrence and progress of thermal cracking during a rolling accident are suppressed.

[Second Embodiment]

In addition, in the second embodiment, in recent years, the progress of the rolling technology of the steel sheet has been remarkable, and along with it, the use environment of the rolling roll has become remarkably severe. In particular, in recent years, the amount of production of steel sheets, such as high-strength steel sheets and thin-walled products, which has a large rolling load and which requires excellent surface quality, is increasing.

Therefore, in the work roll for cold rolling, excellent wear resistance and high hardness to withstand it are required. The improvement of abrasion resistance is generally achieved by higher alloying of the roll material, but the higher alloying may lead to deterioration of the grinding properties or increase in damage in the event of a roll accident (deterioration of accident resistance). It is necessary to make it with materials that combine. In addition, in order to manufacture a steel sheet with excellent surface quality, it is necessary to make the surface properties of the rolls in direct contact with the steel sheet homogeneous and fine. Specifically, as a roll material, cast iron having a high degree of cleanliness and a fine microstructure, Cast steel is required.

In addition, in the work roll for hot rolling, the occurrence of roll wear or surface roughness makes it inevitable to restrict the rolling schedule in terms of the material and dimensions of the product, and also makes it difficult to reduce the frequency of roll exchange. The decrease in the content of the product has become one of the difficulties in improving productivity and reducing costs. For this reason, in the work roll for hot rolling, it is required to suppress the occurrence of abrasion and surface roughness, and to improve the internal degree of the roll.

From this point of view, it has been strongly desired to improve the properties of the roll for rolling to be used, in particular, to improve wear resistance. The improvement of abrasion resistance in a rolling roll has become an important subject directly connected to the improvement of the quality of a steel plate and the improvement of productivity in manufacture of a steel plate.

In addition, in the automotive field in recent years, weight reduction of a vehicle body by the application of a high-strength material is in progress from the viewpoint of improving fuel economy, and it is considered that the application of a high-strength material is further advanced in the future. When the high-strength material is rolled, the surface layer portion of the rolling work roll in contact with the rolled material elastically deforms, and the contact area (or contact arc length) between the surface layer of the rolling work roll and the material to be rolled increases, and the rolling load ( The rolling pressure acting from the material to be rolled on the rolling work roll) increases. When the rolling load is excessive, there is a problem that the dimensional accuracy of the material to be rolled decreases or the minimum rollable sheet thickness is limited.Therefore, a roll outer layer material for rolling that is difficult to elastically deformed and has a high Young's modulus is required. .

Regarding the demand for improving the wear resistance of the rolling roll, for example, as described in Non-Patent Literature 1 and Non-Patent Literature 2, the outer layer composition is set to a composition similar to that of the high-speed tool steel, and hard carbides are dispersed in a large amount to achieve wear resistance. Significantly improved high speed tool steel rolls have been developed. Further, for example, Patent Document 1 describes a composite roll for hot rolling formed by forming an outer layer around a steel core material by a continuous growth 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% are included, P: 0.08% or less, S: 0.06% or less, B: 0.0500% or less, the balance has a composition consisting of Fe and inevitable impurities, by area ratio It is composed of a structure containing 5 to 30% of granular carbide and 6% or more of non-granular carbide, and the known hardness is said to have a Vickers hardness (HV) of 550 or more. In addition, it is said that the outer layer material may further contain 5.0% or less of Ni, 5.0% or less of Co, and 5.0% or less of Nb. Accordingly, even if cracks occur due to the presence of a predetermined amount or more of non-granular carbides, propagation to the core of the roll is suppressed, heat crack resistance is improved, and abrasion resistance is also good in that VC-based hard carbides are included. have.

In such a high speed tool steel roll outer layer material, it is necessary to disperse a large amount of hard carbides in a matrix for improving wear resistance. However, hard carbides produced by a high-speed tool steel composition generally have a lighter specific gravity than a matrix, and are likely to cause segregation during casting. In particular, in the centrifugal casting method, which is a typical casting method for roll outer layers because of its excellent productivity and economy, since the phase with light specific gravity is easy to accumulate and segregate inside by centrifugal force, it is difficult to manufacture the high speed tool steel roll outer layer material by the centrifugal casting method. It has been considered difficult.

However, as a technique for providing a roll outer layer material for rolling excellent in wear resistance and crack resistance in which segregation and the like does not occur even when the centrifugal casting method is applied, in Patent Document 2, C: 1.5 to 3.5%, Si: 1.5% or less, Mn: 1.2% or less, Ni: 5.5% 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, wherein the content of Nb, V, and C satisfies a specific relationship, and further describes a roll outer layer material containing the ratio of Nb and V in a specific range.

In addition, in Patent Document 3, in terms of 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 further contains Nb and V so that the content of Nb, V and C satisfies a specific relationship, and the ratio of Nb and V is in a specific range. It is described. By setting it as such a composition, segregation in the roll outer layer material is suppressed even if a centrifugal casting method is applied, abrasion resistance and crack resistance are improved, and it is said that it greatly contributes to the productivity improvement of hot rolling.

In addition, in Patent Document 4, a centrifugal cast composite roll is described. The centrifugal cast composite roll described in Patent Document 4 consists of an outer layer and an inner layer of cast iron or cast steel, and the outer layer is in 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 of the alloy component and the balance satisfying Fe and unavoidable impurities It has a composition consisting of. According to the technique described in Patent Document 4, _{the crystallization of M 6} C-type carbides that are likely to cause aggregation or segregation is suppressed, and it is possible to make an outer layer in which only MC-type + M ₇ C ₃ type carbides precipitate, and thus it can be produced by a centrifugal casting method. Has been.

In addition, for example, in Patent Document 5, a centrifugal cast outer layer material for rolling rolls is described. The centrifugal cast outer layer material for rolling rolls described in Patent Document 5 has a composition containing, in mass%, C: 4.5 to 9%, Si: 0.1 to 3.5%, Mn: 0.1 to 3.5%, and V: 18 to 40%, and is preferably In other words, it has a structure in which MC carbide is dispersed in an area ratio of 20 to 60% in a matrix having a Vickers hardness of HV550 to 900. In the technique described in Patent Document 5, by actively using centrifugal casting segregation in which MC carbides with a small specific gravity are concentrated on the inner surface side, and after centrifugal casting, cutting so that only the layer enriched with MC carbides remains, the roll outer layer with many MC carbides It is said that it can be reliably formed at low cost.

As a material having very excellent abrasion resistance and a high Young's modulus, cemented carbide has been known from a long time ago. 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 rolling roll, there are descriptions in Patent Document 6, Patent Document 7, Patent Document 8, Patent Document 9, Patent Document 10, and the like.

Patent Document 6 describes a tungsten carbide-based cemented carbide for hot rolling rolls and hot rolling guide rolls. In the technology 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% by weight or less, It is a tungsten carbide-based alloy in which the total sum of cobalt, nickel, and chromium is 12 to 65% by weight. Patent Document 6 describes an example in which such a cemented carbide is applied to a roll for hot rolling of an ordinary steel material (wire material).

In addition, Patent Document 7 describes a roll for hot wire rod rolling made of a cemented carbide. In the technique described in Patent Literature 7, the cemented carbide used is WC having an average particle diameter of 1 µm to 5 µm, or a hard carbide phase in which a part of WC is substituted with at least one type of TiC, TaC, and NbC by 10% by weight or less. And, a ternary alloy bonded phase, wherein Cr in the bonded phase is 0.30 or less with respect to the sum of Ni and Co, and is 0.05 or more with respect to the total bonded phase, and further Ni is in the sum of Ni and Co It is made of a cemented carbide with a polarization potential of 0.33 to 0.90, and a polarization potential of 0.3 V or more with respect to cooling general industrial water. By setting it as such a carbide alloy, it is said that it becomes the roll for hot wire rods which are excellent in inner surface roughness property.

Further, in Patent Document 8, an outer layer made of a cemented carbide is bonded to the outer periphery of an inner layer made of a steel-based material or an iron-based material through an intermediate layer, and the intermediate layer is formed using WC raw material powder having an average particle diameter of 3 μm or less. A composite roll for rolling made of a cemented carbide is disclosed. And it is said that it is preferable to make the content of the WC particle of an intermediate layer into 70% or less by weight ratio. Accordingly, it is said that a roll for rolling made of a cemented carbide having excellent abrasion resistance and high reliability in strength can be obtained.

In addition, Patent Document 9 discloses a rolling roll made of a cemented carbide having high strength and reliability by forming an outer layer of a carbide alloy having excellent abrasion resistance and providing an intermediate layer made of a carbide alloy containing WC and Ni. have.

In addition, in Patent Document 10, on the outer periphery of an inner layer made of a steel-based material or an iron-based material, R = σc(1-ν)/Eα (however, σc: section strength, ν: Poisson's ratio, E: Young's modulus, α: thermal expansion) A composite roll made of a cemented carbide for plate rolling is disclosed by bonding an outer layer made of a cemented carbide having a thermal shock coefficient R expressed as a coefficient) of 400 or more. Accordingly, it is said that the abrasion resistance and the inner surface roughness of the roll are improved, and the occurrence and progress of thermal cracking during a rolling accident are suppressed.

Japanese Published Patent Publication No. Hei04-141553 Japanese Published Patent Publication No. Hei04-365836 Japanese Published Patent Publication No. Hei 05-1350 Japanese Laid-Open Patent Publication No. Hei 08-60289 International application WO2006/030795 Japanese Patent Publication No. 57-6502 Japanese Patent Publication No. 58-39906 Japanese Laid-Open Patent Publication No. 2004-243341 Japanese Unexamined Patent Publication No. 2006-175456 Japanese Laid-Open Patent Publication No. 2004-268140

Kamata et al.: Hitachi Review Vol. 72, No. 5(1990), p69 Hashimoto et al.: Steelmaking Research No. 338 (1990), p62 By Kaizo Monma: 「Steel Materials Revised Edition」Practical School Publication (1981), p.368 Matsunaga et al.: Analysis Technology for Longer Roll Life (1999), p11 Hashimoto et al.: Shinnittetsu Gibo No. 355 (1995), p76

[First embodiment]

However, in the first embodiment, in the technique described in Patent Document 1, since the outer layer is formed by a continuous growth method around a steel core, there is a problem that productivity is low and cost is high. In addition, in the techniques described in Patent Documents 2 and 3, it is said that the content of Nb, V, and C is mainly limited to a specific range, and MC-type carbide is uniformly dispersed to improve abrasion resistance and crack resistance. _{However, in practice, since a considerable amount of M 7} C ₃ type carbide or M ₆ C type carbide containing a large amount of Cr or Mo is also present, further improvement of the properties is sufficient only from the viewpoint of uniformly dispersing the MC type carbide. Can't. In addition, in the technique described in Patent Document 4, in order _{to suppress the crystallization of M 6} C-type carbides that are likely to cause aggregation or segregation, Mo+W: is limited to 10.0% or less, thereby making it possible to manufacture a roll outer layer material by a centrifugal casting method. I'm doing it. However, limiting the Mo and W content has left a problem with the recent demand for further improvement in wear resistance.

In addition, in the production of rolling rolls using the centrifugal casting method, the increase in the amount of carbide-forming elements such as Mo, V, W, etc. is due to the fact that the formed carbides are light, so that the formed carbides are accumulated on the inner surface side and aggregated at the boundary with the inner layer. In addition, there was a concern that the bonding strength of the boundary may be lowered.

In addition, in the technology described in Patent Document 5, although the abrasion resistance of the roll is improved, it requires the operation of removing the outer surface side area with fewer MC-type carbides, and the yield is very low, the advantage of the centrifugal casting method of high productivity and low cost. There was a problem of losing money.

In addition, the technology described in Patent Document 6 or Patent Document 7 using a cemented carbide targets small rolls for wire rod rolling, and this technology is used to manufacture large rolls such as cold rolling rolls and hot rolling rolls. It is difficult to apply it as it is. Further, since HIP treatment, which is an expensive process compared to the centrifugal cast product, is required, there is a problem that the manufacturing cost is high even for a small product.

The technologies described in Patent Document 8, Patent Document 9, and Patent Document 10, which use a carbide alloy as an outer layer material of a roll for sheet rolling, all assume the sintering-HIP method for forming the outer layer material, and the manufacturing cost is very high. There is a problem left. In addition, these techniques use soft Co or Ni as a binder, and there is also a problem that dents and flaws (recesses) are easily generated during rolling, and practical use is not in progress.

In the first embodiment, an object of the present invention is to solve the problems of the prior art, and to provide a roll outer layer material having excellent wear resistance and excellent abrasion resistance compared to the prior art, and a composite roll for rolling using the same, at low cost. It is done.

[Second Embodiment]

In addition, in the technique described in Patent Document 1 in the second embodiment, since the outer layer is formed by the continuous growth method around the steel core, there is a problem that productivity is low and cost is high. In addition, in the techniques described in Patent Documents 2 and 3, it is said that the content of Nb, V, and C is mainly limited to a specific range, and MC-type carbide is uniformly dispersed to improve abrasion resistance and crack resistance. _{However, in practice, since a significant amount of M 7} C ₃ type carbide or M ₆ C type carbide containing a large amount of Cr or Mo is also present, further improvement of the properties is sufficient only from the viewpoint of uniformly dispersing the MC type carbide. Can not. In addition, in the technique described in Patent Document 4, in order _{to suppress the crystallization of M 6} C-type carbides that are likely to cause aggregation or segregation, Mo+W: is limited to 10.0% or less, thereby making it possible to manufacture a roll outer layer material by a centrifugal casting method. I'm doing it. However, limiting the Mo and W content has left a problem with the recent demand for further improvement in wear resistance.

In addition, 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 lighter than that of the molten metal forming the matrix, and thus the generated VC The hard carbide of the system accumulates on the inner surface side and aggregates at the boundary with the inner layer, and there is a concern that the bonding strength of the boundary may decrease.

In addition, in the technology described in Patent Document 5, although the abrasion resistance of the roll is improved, it requires the operation of removing the outer surface side area with fewer MC-type carbides, and the yield is very low, the advantage of the centrifugal casting method of high productivity and low cost. There was a problem of losing money.

In addition, the technology described in Patent Document 6 or Patent Document 7 using a cemented carbide targets small rolls for wire rod rolling, and this technology is used to manufacture large rolls such as cold rolling rolls and hot rolling rolls. It is difficult to apply it as it is. Further, since HIP treatment, which is an expensive process compared to the centrifugal cast product, is required, there is a problem that the manufacturing cost is high even for a small product.

The technologies described in Patent Document 8, Patent Document 9, and Patent Document 10, which use a carbide alloy as an outer layer material of a roll for sheet rolling, all assume the sintering-HIP method for forming the outer layer material, and the manufacturing cost is very high. There is a problem left. In addition, these techniques use soft Co or Ni as a binder, and there is also a problem that dents and flaws (recesses) are easily generated during rolling, and practical use is not in progress.

In the second embodiment, the present invention solves the problems of the prior art, and has a remarkably improved abrasion resistance and Young's modulus compared to the prior art, and a roll outer layer material having excellent wear resistance and rolling load reduction effect, and a composite roll for rolling using the same It aims to provide inexpensive.

[First embodiment]

First of all, in the first embodiment, in order to achieve the above-described problem, the present inventors have made it possible to manufacture a rolling roll having a very high wear resistance equivalent to that of a cemented carbide by a centrifugal casting method with excellent productivity and economy. About the condition, it carefully examined. As a result, if the hard carbide can be concentrated and concentrated on the outer surface side of the roll by using the centrifugal force acting on the molten metal and the crystalized phase during centrifugal casting, the abrasion resistance of the roll for rolling made of centrifugal casting is An idea came to what could be remarkably improved. Further, in order to concentrate and thicken hard carbides on the outer surface side of the roll during centrifugal casting, according to further investigation, carbides having a greater specific gravity than the liquid phase from the liquid phase in which the centrifugal force is acting are primary phases. The thought came to me that I had to find the conditions that could be determined as.

That is, when a carbide having a specific gravity larger than that of the liquid phase crystallizes in the liquid phase in which the centrifugal force is acting, a centrifugal force in the outer circumferential direction acts on the carbide. At that time, if the carbide and the γ phase around it are not eutectic solidification, and the carbide can be directly crystallized from the liquid phase as a primary crystal, the carbide is easily moved and accumulated on the outer circumference side, since the circumference of the carbide is still liquid. You can do it.

As a carbide-forming element that satisfies such conditions, attention was paid to W, which has a large specific gravity, and it was thought to contain a large amount of it, and various casting experiments were repeated, and state diagram calculations were utilized.

(1) When a molten metal containing 0.6% by mass or more of C in a W-Co-based alloy containing a large amount of W with a high specific gravity, the M ₆ C-type carbide enriched with W appears as a primary crystal,

(2) When such a molten W-Co-based alloy is cast by centrifugation, a _{structure in which the M 6} C-type carbide crystallized as a primary crystal segregates at a high concentration on the outer surface side of the outer layer material is obtained.

Found.

Further, it has been recognized that when the alloy to be used is an Fe-based alloy, the formation of W-based eutectic carbide is promoted, and _{the appearance of the M 6 C-type carbide as a primary crystal is inhibited.} In addition, by making the alloy used as a W-Co-based alloy that increases the activity of carbon, the formation of W-based eutectic carbide is suppressed, and the M ₆ C-type carbide enriched with W appears in a large amount as a primary crystal in the molten metal. In addition, when the amount of C is less than 0.6% by mass, the primary M ₆ C-type carbide does not appear. On the other hand, when the amount of C exceeds 3% by mass, the liquidus temperature becomes too high, making it difficult to dissolve and cast. Since the MC type carbide and the M ₂ C type carbide which are very fragile grow and become coarsened, it is recognized that roll breakage is easily caused, respectively.

The present invention has been completed by further investigation based on such recognition. That is, the gist of the present invention is as follows.

(1) W-Co-based alloy roll outer layer material for rolling, wherein the W content is inclined composition decreasing in the radial direction from the outer periphery of the roll toward the inner periphery, and the outer layer surface at a position corresponding to the maximum diameter when rolling is used , By 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%, Roll outer layer material having a composition in which the remainder is made of unavoidable impurities.

(2) In addition to the above composition, one or two or more selected from Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, and Nb: 0.1 to 3% in mass% The roll outer layer material for rolling according to (1) to be contained.

(3) The roll outer layer material for rolling according to (1) or (2), further containing 0.05 to 3% Ni: by mass% in addition to the above composition.

(4) The roll outer layer material for rolling according to any one of (1) to (3), wherein the roll outer layer material for rolling is a centrifugal casting product.

(5) A rolling composite roll comprising an outer layer and an inner layer welded and integrated with the outer layer, wherein the outer layer is the outer roll material for rolling according to any one of (1) to (3).

(6) 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, wherein the outer layer is the roll outer layer material for rolling according to any one of (1) to (3). Composite roll for rolling.

(7) The composite roll for rolling according to (5) or (6), wherein the outer layer is made of centrifugal casting.

[Second Embodiment]

In addition, in the second embodiment, in order to achieve the above-described problem, the present inventors produced a rolling roll having a very high wear resistance and a high Young's modulus equivalent to that of a cemented carbide by a centrifugal casting method excellent in productivity and economy. About the conditions to make it possible, I carefully examined. As a result, if the hard carbide can be concentrated and concentrated on the outer surface side of the roll by using the centrifugal force acting on the molten metal and the crystallization phase during centrifugal casting, the wear resistance of the roll for rolling made of centrifugal casting will be remarkably improved. I thought about what I could do. Further, in order to concentrate and thicken hard carbides on the outer surface side of the roll during centrifugal casting by further investigation, carbides having a specific gravity greater than that of the liquid phase from the liquid phase in which the centrifugal force is acting can be crystallized as primary crystals. The thought came to me to discover the conditions that existed. In addition, it was found that in order to improve the Young's modulus, the amount of W and Mo dissolved in the base should be increased in addition to densely concentrating and thickening hard carbides on the outer surface side of the roll.

That is, when a carbide having a specific gravity larger than that of the liquid phase crystallizes in the liquid phase in which the centrifugal force is acting, a centrifugal force in the outer circumferential direction acts on the carbide. At that time, if the carbide and the γ phase around it are not solidified in a process, and the carbide can be directly crystallized from the liquid phase as a primary crystal, the carbide can be easily moved and accumulated on the outer circumference side because the circumference of the carbide is still liquid. .

As a carbide-forming element that satisfies such conditions, attention was paid to W, which has a large specific gravity, and it was thought to contain a large amount of it, and various casting experiments were repeated, and state diagram calculations were utilized.

(1) When a molten metal containing 0.6% by mass or more of C in a W-Co-based alloy containing a large amount of W with a high specific gravity, the M ₆ C-type carbide enriched with W appears as a primary crystal,

(2) When such a molten W-Co-based alloy is cast by centrifugation, a _{structure in which the M 6} C-type carbide crystallized as a primary crystal segregates at a high concentration on the outer surface side of the outer layer material is obtained.

Found.

Further, it has been recognized that when the alloy to be used is an Fe-based alloy, the formation of W-based eutectic carbide is promoted, and _{the appearance of the M 6 C-type carbide as a primary crystal is inhibited.} In addition, by making the alloy used as a W-Co-based alloy that increases the activity of carbon, the formation of W-based eutectic carbide is suppressed, and the M ₆ C-type carbide enriched with W appears in a large amount as a primary crystal in the molten metal. In addition, when the amount of C is less than 0.6% by mass, the primary M ₆ C-type carbide does not appear. On the other hand, when the amount of C exceeds 3% by mass, the liquidus temperature becomes too high, making it difficult to dissolve and cast. Since the MC type carbide and the M ₂ C type carbide which are very fragile grow and become coarse, it is recognized that roll breakage is easily caused, respectively.

The present invention was completed by further examination based on such recognition. That is, the gist of the present invention is as follows.

(1) An outer layer of a roll made of W-Co-based alloy, whose W content decreases in the radial direction from the outer circumference of the roll toward the inner circumference of the roll, and becomes a surface layer at a position corresponding to the maximum diameter when rolling is used. Ash, by 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%, , In addition, W, Co, Mo, and Fe content satisfies the following equation [1], and the remaining roll outer layer material having a composition consisting of unavoidable impurities.

1.2≤(%W+%Mo)/(%Co+%Fe)≤9.0　　　[1]

Here, %W, %Mo, %Co, and %Fe are the content (mass%) of each element.

(2) The roll outer layer material for rolling according to (1), wherein the Young's modulus of the outer layer material serving as the surface layer at a position corresponding to the maximum diameter at the time of use of the rolling is 270 GPa or more and 500 GPa or less.

(3) In (1) or (2), in addition to the above composition, in mass%, Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, Nb: 0.1 to 3 Roll outer layer material containing 1 type or 2 or more types selected from %.

(4) The roll outer layer material for rolling according to any one of (1) to (3), further containing 0.05 to 3% Ni: by mass% in addition to the composition.

(5) The roll outer layer material for rolling according to any one of (1) to (4), wherein the roll outer layer material for rolling is a centrifugal casting material.

(6) A rolling composite roll 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 decreases in a radial direction from the outer circumferential side of the roll toward the inner circumferential side. The outer layer material which is a composition and becomes a surface layer at a position corresponding to the maximum diameter when rolling is used, in 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 content of W, Co, Mo, and Fe satisfies the following equation [1], and the remainder is for rolling having a composition consisting of unavoidable impurities Composite roll.

1.2≤(%W+%Mo)/(%Co+%Fe)≤9.0　　　[1]

Here, %W, %Mo, %Co, and %Fe are the content (mass%) of each element.

(7) The composite roll for rolling according to (6), wherein the Young's modulus of the outer layer material serving as the surface layer at a position corresponding to the maximum diameter at the time of using the rolling is 270 GPa or more and 500 GPa or less.

(8) In (6) or (7), in addition to the above composition, in terms of mass%, Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, Nb: 0.1 to 3 A composite roll for rolling containing one or two or more selected from %.

(9) The composite roll for rolling according to any one of (6) to (8), further containing 0.05 to 3% Ni: by mass% in addition to the composition.

(10) 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, wherein the outer layer is made of a W-Co-based alloy, and the W content is from the outer periphery of the roll to the inner periphery. The outer layer material which is a surface layer at a position corresponding to the maximum diameter at the time of rolling is a gradient composition decreasing in the radial direction toward and is, in 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%, Fe: 5 to 40%, and the content of W, Co, Mo, and Fe is the following formula [1] A composite roll for rolling having a composition that satisfies and the remainder is composed of inevitable impurities.

group

1.2≤(%W+%Mo)/(%Co+%Fe)≤9.0　　　[1]

Here, %W, %Mo, %Co, and %Fe are the content (mass%) of each element.

(11) The composite roll for rolling according to (10), wherein the Young's modulus of the outer layer material serving as the surface layer at a position corresponding to the maximum diameter at the time of rolling use is 270 GPa or more and 500 GPa or less.

(12) In (10) or (11), in addition to the above composition, in terms of mass%, Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, Nb: 0.1 to 3 A composite roll for rolling containing one or two or more selected from %.

(13) The composite roll for rolling according to any one of (10) to (12), further containing 0.05 to 3% Ni: by mass% in addition to the composition.

(14) The composite roll for rolling according to any one of (6) to (13), wherein the outer layer is made of centrifugal casting.

In the first embodiment, according to the present invention, a rolling roll suitable as a hot rolling or cold rolling roll, having remarkably excellent abrasion resistance, particularly a centrifugal cast rolling roll, can be manufactured at low cost and easily. Yes, it has a remarkable effect in the industry.

In addition, according to the second embodiment, according to the present invention, a roll for rolling suitable as a roll for hot rolling or cold rolling, having remarkably excellent abrasion resistance and rolling load reduction effect, particularly a roll for rolling made of centrifugal casting, is inexpensive. In addition, it can be easily manufactured and exhibits a remarkable industrial effect.

1 is a tissue photograph showing a scanning electron microscope structure in Example 1. FIG. (a) is sleeve No. 13 (test material No. 13), and (b) is sleeve No. 5 (test material No. 5).
2 is an explanatory diagram schematically showing an outline of a wear test in Example 1. FIG.
3 is a schematic diagram illustrating an example of a composite roll in the present invention.
Fig. 4 is a schematic diagram of a cross section of a composite roll for explaining an example of a rolling composite roll comprising an outer layer in the present invention and an inner layer welded and integrated with the outer layer.
Fig. 5 is a schematic diagram of a cross section of a composite roll for explaining an example of a rolling composite roll comprising an outer layer in the present invention, an intermediate layer welded and integrated with the outer layer, and an inner layer welded and integrated with the intermediate layer in the present invention.
6 is a tissue photograph showing a scanning electron microscope structure in Example 2. FIG. (a) is sleeve No. 13, and (b) is sleeve No. 5.
7 is an explanatory diagram schematically showing an outline of a wear test in Example 2. FIG.
8 is a schematic diagram of a composite roll for evaluating rolling load in Example 2. FIG.

Hereinafter, a first embodiment and a second embodiment in the present invention will be described with reference to the respective drawings.

[First embodiment]

The roll outer layer material for rolling of the present invention is made of centrifugal casting. "Centrifugal cast roll outer layer material for rolling" means that it is a roll outer layer material for rolling in a state manufactured using the centrifugal casting method which has been conventionally used as a manufacturing method of rolling rolls. Roll outer layer material for rolling manufactured by using a centrifugal casting method ("centrifugal casting agent" roll outer layer material for rolling) has conventionally been used as a "material" from a rolling roll manufactured by a manufacturing method other than that. It can be clearly distinguished, and furthermore, specifying the roll outer layer material for "centrifugal casting" rolling by structure or characteristic requires a great deal of effort, and is impractical.

The outer layer of the roll for rolling of the present invention is made of a W-Co-based alloy, has an inclined composition in which the W content decreases in the radial direction from the outer circumferential side of the roll toward the inner circumferential side, and the outer layer surface at a position corresponding to the maximum diameter when rolling is used. In this mass%, W: 25 to 70%, Co: 5 to 45% are included, and further C: 0.6 to 3.5%, Si: 0.05 to 3%, Mn: 0.05 to 3%, Mo: 1 to 15% is included, and the balance has a composition consisting of inevitable impurities. In addition, it is preferable that the above-described composition is satisfied at a position in the radial direction corresponding to at least 20% of the volume on the outer surface side with respect to the total volume of the outer layer material. For example, in the case of a sleeve having an outer diameter of 250 mm and an inner diameter of 140 mm, it is preferable to satisfy a position of at least 9 mm in the radial direction toward the inner circumferential side from a position corresponding to the maximum diameter at the time of rolling use.

In addition, "the outer layer material surface at a position corresponding to the maximum diameter in rolling use" refers to a layer formed on the outer surface of the outer layer material while being cast (a portion where the molten metal is rapidly cooled and solidified by contact with the mold). It refers to the outer layer surface at the position corresponding to the maximum diameter of the roll diameter of the product provided for rolling use, that is, the outer layer surface at the position corresponding to the maximum diameter that can be used as a product (roll outer layer material). Say. Specifically, "the outer layer material surface at a position corresponding to the maximum diameter in rolling use" means that the layer formed on the outer surface of the outer layer material is removed by grinding, and the maximum diameter of the roll diameter of the product provided for rolling use is applied. It is set as a position corresponding to the range representing at least 20% of the volume of the outer surface side with respect to the total volume of the outer layer material in the radial direction from the outer layer material surface at the corresponding position toward the inner circumferential side.

In addition, the composition analysis of the outer layer material surface may be performed by instrument analysis such as fluorescence X-ray analysis or emission spectral analysis, or as a destructive test, but from the position including the outer layer material surface, the thickness in the radial direction of the roll A block-shaped sample of less than 10 mm may be collected, and the sample may be subjected to chemical analysis, or any may be used.

First, the reason 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 described as %.

C: 0.6 to 3.5%

C is an element having an action of forming a hard carbide by bonding with W and carbide-forming elements such as Mo, Cr, V, and Nb, and improving abrasion resistance. Depending on the amount of C, the shape of the carbide, the amount of crystallization, and the crystallization temperature change. When the C content is 0.6% or more, the M ₆ C-type carbide is crystallized as a primary crystal, and a structure that segregates on the outer surface side at the time of centrifugal casting is obtained, and abrasion resistance is improved. In addition, when the content of C is less than 0.6%, the _{amount of M 6} C-type carbide crystallized as a primary crystal is insufficient, and abrasion resistance decreases. On the other hand, if the C content exceeds 3.5% and is contained in a large amount, it becomes difficult to manufacture as an outer layer material, and M ₂ C carbide or MC carbide which is very fragile is generated and coarsened, resulting in roll breakage during rolling. It becomes easy to do. From such a point, C was limited to the range of 0.6 to 3.5%. Further, preferably, C is 1.0 to 3.0%. More preferably, C is 1.2 to 2.8%.

Si: 0.05 to 3%

Si is an element that acts as a deoxidizing agent and also has a known strengthening effect. In order to obtain such an effect, it is necessary to contain 0.05% or more of Si. On the other hand, even if Si contains more than 3%, the effect is saturated, and graphite flakes appear, resulting in a decrease in toughness. For this reason, Si was limited to the range of 0.05 to 3%. In addition, Si is preferably 0.1 to 2%. More preferably, Si is 0.2 to 1.8%.

Mn: 0.05 to 3%

Mn is an element having an action of fixing S as MnS and detoxifying S, which adversely affects the material. In addition, Mn contributes to the improvement of hardenability by being employed in the base. In order to obtain such an effect, it is necessary to contain 0.05% or more of Mn. On the other hand, even if it contains more than 3% of Mn, the above-described effect is saturated, and material deterioration is caused. For this reason, Mn was limited to the range of 0.05-3%. Further, preferably, Mn is 0.1 to 1%. More preferably, Mn is 0.2 to 0.8%.

Mo: 1 to 15%

Mo is a carbide-forming element that combines with C to form carbide.In the present invention, in particular, in the present invention, it is dissolved in hard M ₆ C-type carbide, which is an ultra-crystalline carbide enriched with W, to strengthen the carbide, thereby increasing the breaking resistance of the roll outer layer material. It has an action of letting go. In addition, Mo improves the hardening property during heat treatment, and contributes to an increase in the hardness of the roll outer layer material. In addition, Mo is an element heavier than Co and has an effect of not inhibiting or promoting centrifugation of the primary carbide toward the outer surface side. In order to obtain these effects, it is necessary to contain 1% or more of Mo. On the other hand, when Mo is contained in a large amount exceeding 15%, hard and brittle carbides mainly formed of Mo appear, and abrasion resistance deteriorates. For this reason, Mo was limited to the range of 1-15%. Further, Mo is preferably 2 to 10%. More preferably, Mo is 4 to 10%.

W: 25-70%

W is the most important element in the present invention, and is an alloy composition containing 25% or more in a large amount. Thereby, it is _{possible to make a large amount of hard M 6} C-type carbide enriched with W as a primary crystal, and a roll outer layer material for rolling with remarkably improved wear resistance. In addition, when the W content is less than 25%, it becomes difficult to obtain the roll outer layer material for rolling excellent in abrasion resistance as the object of the present invention. On the other hand, when the content of W exceeds 70%, the M ₆ C-type carbide coarsens and becomes brittle, and the melting point of the molten metal increases, making it difficult to dissolve or cast. For this reason, W was limited to the range of 25 to 70%. In addition, W is preferably 30 to 65%. More preferably, W is 35 to 55%.

Co: 5 to 45%

Co, together with W, is an important element in the present invention. By containing Co in a large amount with W, the activity of C increases, and the _{appearance of hard carbides (M 6} C type, M ₂ C type, MC type, etc.) enriched with W as a primary crystal is promoted. , It contributes to the improvement of the wear resistance of the roll outer layer material for rolling. In order to obtain such an effect, it is necessary to contain 5% or more of Co. On the other hand, when Co is contained in a large amount exceeding 45%, the γ phase is stabilized and the matrix becomes soft, and when used as a rolling roll, a bundle of dents and scratches (concave portions) is caused, and abrasion resistance is achieved. Remarkably decreases. For this reason, Co was limited to the range of 5 to 45%. Further, preferably, Co is 10 to 40%. More preferably, Co is 15 to 35%.

Although the above-described component is a basic component, in addition to the basic composition, one or two or more selected from Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, and Nb: 0.1 to 3%, And/or Ni: 0.05 to 3% may be selected and contained as necessary.

One or two or more selected from Fe: 5-40%, Cr: 0.1-10%, V: 0.1-6%, Nb: 0.1-3%

All of Fe, Cr, V, and Nb are carbide-forming elements, and are elements having an action of solidifying the carbide to strengthen the carbide, and may contain one or two or more of them selected as necessary.

Fe is dissolved in the carbide and dissolved in the base, contributing to the strengthening of the base, and has an effect of preventing the generation of dents and flaws (recesses) when used as a rolling roll. In order to obtain such an effect, it is preferable to contain Fe 5% or more. On the other hand, when Fe contains more than 40%, the amount of hard M ₆ C-type carbides appearing as primary crystals decreases, the fragile M ₃ C-type carbides increase, and abrasion resistance decreases. For this reason, when it contains, it is preferable to limit Fe to 5 to 40% of range. Further, more preferably, Fe is 10 to 35%. More preferably, Fe is 12 to 30%.

The mechanism by which the matrix of the W-Co-based alloy is strengthened by the inclusion of Fe in the matrix is not clear at this point, but the γ-phase stabilization action by Co is offset by the α-phase stabilization action by Fe. Either because the strength has increased, or because the α-phase stabilizing action of Fe is large, the matrix becomes a hard martensite or bainite structure, or a structure in which additional fine carbides are precipitated appears in the matrix. It is thought that the strengthening of the base occurred.

Cr, as a strong carbide-forming element, mainly forms eutectic carbide and has an effect of improving the strength of the formed carbide. Since eutectic carbide is crystallized in the gap of the _{primary M 6} C-type carbide, it acts to strengthen the gap of the _{M 6 C-type carbide as a result.} Further, Cr also has an action of suppressing the appearance of graphite. Since the W-Co-based alloy has a high C activity coefficient, graphite tends to appear, and when graphite appears, the toughness decreases. In order to suppress the appearance of graphite and stably use it as a rolling roll, in the present invention, it is preferable to contain Cr as necessary. In order to obtain such an effect, it is preferable to contain Cr of 0.1% or more. On the other hand, when Cr contains more than 10%, a large amount of Cr-based eutectic carbides appear and the toughness decreases. For this reason, when it contains, it is preferable to limit Cr to 0.1-10% of range. Further, more preferably, Cr is 1 to 8%. More preferably, Cr is 1.5 to 7%.

V is an element that combines with C to form hard VC (MC-type carbide including Mo, Nb, Cr, W, etc.), and the formed MC-type carbide is crystallized as primary crystal, and W is concentrated M ₆ C-type carbide. is a nucleus of the crystallization, to promote the emergence of the M ₆ C type carbide has a function of dispersing the finer M ₆ C type carbide at a high density. In order to obtain such an effect, it is preferable to contain V in an amount of 0.1% or more. On the other hand, if V is contained in a large amount exceeding 6%, even if it contains a large amount of W, the low specific gravity V-type MC-type carbide increases and becomes coarse, and is centrifuged on the inner surface side of the roll outer layer material during centrifugal casting. do. _{Therefore, the amount of hard M 6} C-type carbide on the outer surface side is insufficient, and the abrasion resistance at the time of use of the roll outer layer material is deteriorated. Further, when a large amount of the V-type MC-type carbide centrifuged on the inner surface side decreases, the strength of the boundary between the inner roll layer and the intermediate layer decreases. For this reason, when it contains, it is preferable to limit V to 0.1-6% of range. Further, more preferably, V is 1 to 5%. More preferably, V is 1.5 to 4%.

Nb has a very high bonding strength with C and is a strong carbide-forming element, and it is easy to form a composite carbide with V or W. Such a composite carbide of Nb and V and W are, is the crystallization nuclei of M ₆ C type carbide han W is a thickening, which crystallized as the Primary, promotes the appearance of M ₆ C type carbide, finer M ₆ C type carbide It has the effect of dispersing in high density. In order to obtain such an effect, Nb needs to contain 0.1% or more. On the other hand, when a large amount of Nb exceeds 3%, a low-density Nb-based MC-type carbide is formed and coarsened. During centrifugal casting, the carbide is easily centrifuged on the inner side of the roll outer layer material, and the outer layer material The amount of MC-type carbide on the inner surface side increases. Further, when the amount of the MC-type carbide centrifuged on the inner surface side of the outer layer material increases, the quality of the inner surface side decreases, such as a decrease in the strength of the boundary between the roll inner layer and the intermediate layer. For this reason, in the case of containing, it is preferable to limit Nb to the range of 0.1 to 3%. Further, more preferably, Nb is 0.5 to 2%. More preferably, Nb is 0.6 to 1.8%.

Ni: 0.05 to 3%

Ni is an element having an effect of improving the quenchability, and can be contained as necessary, for example, in order to eliminate the lack of quenchability in a large roll. In order to obtain such an effect, it is preferable to contain Ni at least 0.05%. In addition, when the impurity level is less than 0.05%, the effect is not recognized. On the other hand, when the Ni content exceeds 3%, the γ phase is stabilized, and the desired quenchability cannot be secured. For this reason, when it contains, it is preferable to limit Ni to 0.05-3% of range. More preferably, Ni is 0.1 to 2.5%.

The balance other than the above-described components is made of unavoidable impurities. Examples of inevitable impurities include P, S, N, and B. Further, since P segregates at grain boundaries and exerts an adverse effect such as embrittlement of the material, it is preferable to reduce it as an impurity as much as possible, but it is acceptable if it is 0.05% or less. In addition, S, like P, segregates at the grain boundary and has an effect such as embrittlement of the material, so it is preferable to reduce it as an impurity as much as possible, but if it is 0.05% or less, a part of it is combined with Mn to form a sulfide-based inclusion. Because it exists and becomes harmless, it is acceptable. In addition, N is mixed in about 0.01% to 0.1% as an impurity, as long as it is usually dissolved. However, if it is contained at this level, the effect of the present invention is not affected. 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 addition, B may be mixed from scraps of raw materials for melting or casting flux and contained as an unavoidable impurity element. B is dissolved in a carbide or a base to change the properties of the carbide, or dissolved in a base to affect the quality of the base, resulting in quality variation in some cases. For this reason, it is preferable that B is reduced as much as possible, but if it is 0.1% or less, the effect of the present invention is not adversely affected. Here, it is preferable to adjust the total amount of the inevitable impurity elements to less than 1%.

Next, a preferable manufacturing method of the roll outer layer material for rolling of the present invention will be described.

In the present invention, from the viewpoint of productivity and manufacturing cost, the roll outer layer material for rolling is manufactured by using a centrifugal casting method in which a casting mold is rotated. Accordingly, it is possible to manufacture a roll outer layer material for rolling excellent in abrasion resistance at low cost.

First, the molten metal having the above-described roll outer layer material composition is poured into a rotating mold to have a predetermined thickness, followed by centrifugal casting to obtain a roll outer layer material for rolling. In addition, in general, in order to protect the mold, a refractory material mainly made of zircon or the like is coated on the inner surface of the mold. Further, in the present invention, it is preferable to perform centrifugal casting by adjusting the rotational speed so that the centrifugal force becomes 120 to 250G. By applying a high centrifugal force, it is possible to increase the dispersion density of the hard carbide having a high density on the outer surface side.

In the present invention, the obtained outer roll material for rolling is a single sleeve, and a shaft member is fitted thereto to form a rolling roll. For example, as shown in Fig. 3, the roll outer layer material for rolling may be heat-shrink-fitted to a shaft material (roll shaft) made of made of forged carbon steel to form a composite roll. In addition, the obtained outer roll material for rolling is a sleeve having an intermediate layer integrated by welding and integrally formed therein, and may be formed as a roll for rolling by fitting a shaft material thereto. In addition, the intermediate layer is preferably formed by pouring the molten metal of the intermediate layer composition and centrifugal casting while rotating the mold, during or after solidification of the roll outer layer material. Examples of the intermediate layer material include graphite steel, 1 to 2 mass% C high carbon steel, hypoeutectic cast iron, and the like. In addition, the shaft material of these rolling rolls is not particularly limited, but it is preferable to use separately manufactured forged steel products (shafts), cast steel products (shafts), and cast iron products (shafts).

Further, in the present invention, the outer layer of the roll for rolling is used as an outer layer, and a composite roll comprising an inner layer integrated by welding with the outer layer (for example, refer to the schematic view of the cross section of the composite roll in FIG. 4), or the above The outer layer of the roll for rolling may be used as an outer layer, and a composite roll composed of an intermediate layer welded and integrated with the outer layer, and an inner layer welded and integrated with the intermediate layer (for example, see a schematic diagram of a cross section of the composite roll in FIG. 5). .

In the case of forming the intermediate layer, it is preferable to perform centrifugal casting by pouring the molten metal of the intermediate layer composition while rotating the mold, during or after solidification of the roll outer layer material. Further, as the intermediate layer material, it is preferable to use graphite steel, high carbon steel of 1 to 2 mass% C, sub-eutectic cast iron, or the like. The intermediate layer and the outer layer are integrally welded, and the components of the outer layer are mixed into the intermediate layer within a range of about 10 to 90%. From the viewpoint of suppressing the mixing amount of the outer layer component into the inner layer, it is preferable to reduce the mixing amount of the outer layer component 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, the rotation of the mold is stopped to erect the mold, and then the inner layer material is statically cast. Here, as the inner layer material to be statically cast, it is preferable to use nodular graphite cast iron, vermicular graphite cast iron (CV cast iron), etc., which are excellent in castability and mechanical properties. In addition, in a composite roll in which there is no intermediate layer and the outer layer and the inner layer are integrally welded, the components of the outer layer material are often mixed in the inner layer in an amount of about 1 to 10%. W, Cr, V, etc. contained in the outer layer material are strong carbide-forming elements, and when these elements are incorporated into the inner layer, the inner layer becomes brittle. For this reason, in the present invention, it is preferable to suppress the mixing ratio of the outer layer component to the inner layer to less than 5%.

It is preferable that the said outer roll material for rolling and the composite roll for rolling are heat-treated after casting. Heat treatment is a process of heating at 1000 to 1200°C and maintaining for 5 to 40 hours, then cooling in a furnace, air cooling or air blast cooling, and heating and maintaining at 400 to 600°C. It is preferable to set it as the process of performing the process of cooling at least once. In addition, the hardness of the roll outer layer material for rolling and the composite roll for rolling of the present invention is preferably adjusted within the range of 79 to 100HS depending on the application. It is recommended to adjust the heat treatment after casting so that such hardness can be stably secured.

[Second Embodiment]

The roll outer layer material for rolling of the present invention is made of centrifugal casting. "Centrifugal cast roll outer layer material for rolling" means that it is a roll outer layer material for rolling in a state manufactured using the centrifugal casting method which has been conventionally used as a manufacturing method of rolling rolls. Roll outer layer material for rolling manufactured by using the centrifugal casting method ("Centrifugal casting agent" roll outer layer material for rolling) is clearly distinguished as "water" from rolling rolls manufactured by other manufacturing methods. In addition, specifying the "centrifugal casting agent" roll outer layer material for rolling by structure or characteristic requires a great deal of effort and is impractical.

The roll outer layer material for rolling of the present invention is made of a W-Co-based alloy, has an inclined composition in which the W content decreases in the radial direction from the outer circumferential side of the roll toward the inner circumferential side, and becomes a surface layer at a position corresponding to the maximum diameter in rolling use. The outer layer material contains, in mass%, W: 25 to 70%, Co: 5 to 45%, and further C: 0.6 to 3.5%, Si: 0.05 to 3%, Mn: 0.05 to 3%, Mo: 1 It contains -15%, and the content of W, Co, Mo, and Fe satisfies the following formula [1], and the balance has a composition consisting of unavoidable impurities. In addition, it is preferable that the above-described composition is satisfied at a position in the radial direction corresponding to at least 20% of the volume on the outer surface side with respect to the total volume of the outer layer material. For example, in the case of a sleeve having an outer diameter of 250 mm and an inner diameter of 140 mm, it is preferable to satisfy a position of at least 9 mm in the radial direction toward the inner circumferential side from a position corresponding to the maximum diameter at the time of rolling use.

1.2≤(%W+%Mo)/(%Co+%Fe)≤9.0　　　[1]

Here, %W, %Mo, %Co, and %Fe are the content (mass%) of each element, and when they are not contained, they are set to 0.

In addition, the term "outer layer material that becomes the surface layer at a position corresponding to the maximum diameter in rolling use" means a layer formed on the outer surface of the outer layer material while being cast (a part where the molten metal is rapidly cooled by contact with the mold and solidified, etc.) ) Is removed by grinding, and it refers to the outer layer material that becomes the surface layer at a position corresponding to the maximum diameter of the product roll diameter provided for rolling use. That is, it refers to an outer layer material having a thickness of at least 9 mm in the radial direction to become a surface layer at a position corresponding to the maximum diameter that can be used as a product (roll outer layer material).

In addition, the composition analysis of the outer layer material serving as the surface layer may be performed by instrument analysis such as fluorescence X-ray analysis or emission spectroscopic analysis, or as a destructive inspection, but from the position containing the outer layer material serving as the surface layer, the roll diameter A block-shaped sample having a thickness of less than 10 mm in the direction may be collected, and the sample may be subjected to chemical analysis, or any may be used.

First, the reason 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 described as %.

C: 0.6 to 3.5%

C is an element having an action of forming a hard carbide by bonding with W and carbide-forming elements such as Mo, Cr, V, and Nb, and improving abrasion resistance. Depending on the amount of C, the shape of the carbide, the amount of crystallization, and the crystallization temperature change. When C is 0.6% or more, the M ₆ C-type carbide is crystallized as a primary crystal, a structure that segregates on the outer surface side during centrifugal casting is obtained, and abrasion resistance is improved. In addition, when C is less than 0.6%, the _{amount of M 6} C-type carbide crystallized as a primary crystal is insufficient, and abrasion resistance decreases. On the other hand, if C is contained in a large amount exceeding 3.5%, it becomes difficult to manufacture as an outer layer material, and because very fragile M ₂ C carbide or MC carbide is generated and coarsened, roll breakage occurs during rolling. It becomes easy to do. From such a point, C was limited to the range of 0.6 to 3.5%. Further, preferably, C is 1.0 to 3.0%. More preferably, C is 1.2 to 2.8%.

Si: 0.05 to 3%

Si is an element that acts as a deoxidizing agent and also has a known strengthening effect. In order to obtain such an effect, Si needs to contain 0.05% or more. On the other hand, even if Si contains more than 3%, the effect is saturated, flake graphite appears, and toughness decreases. For this reason, Si was limited to the range of 0.05 to 3%. In addition, Si is preferably 0.05 to 2%. More preferably, Si is 0.2 to 1.8%.

Mn: 0.05 to 3%

Mn is an element having an action of fixing S as MnS and detoxifying S, which adversely affects the material. In addition, Mn is employed in the base and contributes to the improvement of qualitative properties. In order to obtain such an effect, it is necessary to contain Mn 0.05% or more. On the other hand, even if it contains more than 3% of Mn, the above-described effect is saturated, and material deterioration is caused. For this reason, Mn was limited to the range of 0.05-3%. Further, preferably, Mn is 0.1 to 1%. More preferably, Mn is 0.2 to 0.8%.

Mo: 1 to 15%

Mo is a carbide-forming element that combines with C to form carbide.In the present invention, in particular, in the present invention, it is dissolved in hard M ₆ C-type carbide, which is an ultra-crystalline carbide enriched with W, to strengthen the carbide, thereby increasing the breaking resistance of the roll outer layer material. It has an action of letting go. In addition, Mo improves the hardening property during heat treatment, and contributes to an increase in the hardness of the roll outer layer material. In addition, Mo is an element heavier than Co, and has an effect of not inhibiting or promoting centrifugation of the primary carbide to the outer surface side. In order to obtain these effects, Mo needs to contain 1% or more. On the other hand, when Mo is contained in a large amount exceeding 15%, hard and brittle carbides mainly composed of Mo appear, and abrasion resistance deteriorates. For this reason, Mo was limited to the range of 1 to 15%. Further, preferably, Mo is 2 to 10%. More preferably, Mo is 4 to 10%.

W: 25-70%

W is the most important element in the present invention, and is an alloy composition containing 25% or more in a large amount. Thereby, it is _{possible to make a large amount of hard M 6} C-type carbide enriched with W as a primary crystal, and a roll outer layer material for rolling with remarkably improved wear resistance. On the other hand, when the W content exceeds 70%, the M ₆ C-type carbide becomes coarse and fragile, and the melting point of the molten metal increases, making it difficult to dissolve or cast. For this reason, W was limited to the range of 25 to 70%. Further, preferably, W is 30 to 65%. More preferably, W is 35 to 55%.

Co: 5 to 45%

Co, together with W, is an important element in the present invention. By containing Co in a large amount with W, the activity of C increases, and the _{appearance of hard carbides (M 6} C type, M ₂ C type, MC type, etc.) enriched with W as a primary crystal is promoted. , It contributes to the improvement of the wear resistance of the roll outer layer material for rolling. In order to obtain such an effect, it is necessary to contain 5% or more of Co. On the other hand, when Co is contained in a large amount exceeding 45%, the γ-phase is stabilized and the matrix becomes soft, and when used as a rolling roll, a bundle of dents and scratches (concave portions) is caused, and abrasion resistance remarkably decreases. do. For this reason, Co was limited to the range of 5 to 45%. Further, preferably, Co is 10 to 40%. More preferably, Co is 12 to 35%.

Although the above-described component is a basic component, in addition to the basic composition, one or two or more selected from Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, and Nb: 0.1 to 3%, And/or Ni: 0.05 to 3% may be selected and contained as necessary.

One or two or more selected from Fe: 5-40%, Cr: 0.1-10%, V: 0.1-6%, Nb: 0.1-3%

All of Fe, Cr, V, and Nb are carbide-forming elements, and are elements that have an action of strengthening the carbide by solid solution in the carbide, and may contain one or two or more kinds, selected as necessary.

Fe is dissolved in the carbide and dissolved in the base, contributing to the strengthening of the base, and has an effect of preventing the generation of dents and flaws (recesses) when used as a rolling roll. In order to obtain such an effect, it is preferable to contain Fe 5% or more. On the other hand, when Fe contains more than 40%, the amount of hard M ₆ C-type carbides appearing as primary crystals decreases, the fragile M ₃ C-type carbides increase, and abrasion resistance decreases. For this reason, when it contains, it is preferable to limit Fe to 5 to 40% of range. Further, more preferably, Fe is 10 to 35%. More preferably, Fe is 12 to 30%.

The mechanism by which the matrix of the W-Co-based alloy is strengthened by containing Fe in the matrix is not clear at this point, but the γ-phase stabilization action by Co is canceled out by the α-phase stabilization action by Fe, and as a result, known It is because the strength has increased, or because the α-phase stabilizing effect of Fe is large, the matrix becomes a hard martensite or bainite structure, or a structure in which additional fine carbides precipitated appears in such a matrix. It is thought that the reinforcement phenomenon occurred.

Cr, as a strong carbide-forming element, mainly forms eutectic carbide and has an effect of improving the strength of the formed carbide. Since eutectic carbide is crystallized in the gap of the _{primary M 6} C-type carbide, it acts to strengthen the gap of the _{M 6 C-type carbide as a result.} Further, Cr also has an action of suppressing the appearance of graphite. Since the W-Co-based alloy has a high C activity coefficient, graphite tends to appear, and when graphite appears, the toughness decreases. In order to suppress the appearance of graphite and stably use it as a rolling roll, in the present invention, it is preferable to contain Cr as necessary. In order to obtain such an effect, it is preferable to contain Cr 0.1% or more. On the other hand, when Cr contains more than 10%, a large amount of Cr-based eutectic carbides appear and the toughness decreases. For this reason, when it contains, it is preferable to limit Cr to 0.1-10% of range. Further, more preferably, Cr is 1 to 8%. More preferably, Cr is 1.5 to 7%.

V is an element that combines with C to form hard VC (MC-type carbide including Mo, Nb, Cr, W, etc.), and the formed MC-type carbide is crystallized as primary crystal, and W is concentrated M ₆ C-type carbide. and the extrusion of the core, facilitating the occurrence of the M ₆ C type carbide has a function of dispersing the finer M ₆ C type carbide at a high density. In order to obtain such an effect, it is preferable to contain V by 0.1% or more. On the other hand, if V is contained in a large amount exceeding 6%, even if it contains a large amount of W, the low specific gravity V-type MC-type carbide increases and becomes coarse, and is centrifuged on the inner surface side of the roll outer layer material during centrifugal casting. . _{Therefore, the amount of hard M 6} C-type carbide on the outer surface side is insufficient, and the abrasion resistance at the time of use of the roll outer layer material is deteriorated. Further, when a large amount of the V-type MC-type carbide centrifuged on the inner surface side decreases, the strength of the boundary between the inner roll layer and the intermediate layer decreases. For this reason, when it contains, it is preferable to limit V to 0.1-6% of range. Further, more preferably, V is 1 to 5%. More preferably, V is 1.5 to 4%.

Nb has a very high bonding strength with C and is a strong carbide-forming element, and it is easy to form a composite carbide with V or W. This is the crystallization nucleation of W One M ₆ C type carbide thickening, which crystallized as the Nb and V and W the complex carbide is invited of, it promotes the appearance of the M ₆ C type carbide, finer M ₆ C type carbide It has the effect of dispersing in high density. In order to obtain such an effect, Nb needs to contain 0.1% or more. On the other hand, when a large amount of Nb exceeds 3%, a low specific gravity Nb-based MC-type carbide is formed and coarsened. During centrifugal casting, the carbide is easily centrifuged on the inner surface side of the roll outer layer material, and the outer layer The amount of MC-type carbide on the inner surface side of the material increases. Further, when the amount of the MC-type carbide centrifuged on the inner surface side of the outer layer material increases, the quality of the inner surface side decreases, such as a decrease in the strength of the boundary between the roll inner layer and the intermediate layer. For this reason, in the case of containing, it is preferable to limit Nb to the range of 0.1 to 3%. Further, more preferably, Nb is 0.5 to 2%. More preferably, Nb is 0.6 to 1.8%.

Ni: 0.05 to 3%

Ni is an element having an effect of improving the quenchability, and may be contained as necessary, for example, in order to eliminate the lack of quenchability in a large roll. In order to obtain such an effect, it is preferable to contain Ni by 0.05% or more. In addition, when Ni is less than 0.05%, which is an impurity level, the effect is not recognized. On the other hand, when Ni is contained in an amount exceeding 3%, the γ phase is stabilized, and desired quenchability cannot be secured. For this reason, when it contains, it is preferable to limit Ni to 0.05-3% of range. More preferably, Ni is 0.1 to 2.5%.

The balance other than the above-described components is made of unavoidable impurities. Examples of inevitable impurities include P, S, N, and B. In addition, since P segregates at grain boundaries and exerts adverse effects such as embrittlement of the material, it is preferable to reduce it as an impurity as much as possible, but it is acceptable as long as P is 0.05% or less. In addition, S, like P, segregates at the grain boundaries and embrittles the material, so it is preferable to reduce it as an impurity as much as possible. However, if S is 0.05% or less, some of it is combined with Mn and sulfide Since it exists as a system inclusion and becomes harmless, it is acceptable. In addition, N is mixed in about 0.01% to 0.1% as an impurity, as long as it is usually dissolved. However, if it is contained at this level, there is no effect on the effect of the present invention. However, since N may generate gas defects at the boundary between the outer layer and the intermediate layer or the inner layer of the composite roll, N is preferably limited to less than 0.07%. In addition, B may be incorporated as an inevitable impurity element by mixing from scrap of a melting raw material or a casting flux. B is dissolved in a carbide or a base to change the properties of the carbide, or dissolved in a base to affect the quality of the base in some cases, resulting in quality deviation. For this reason, it is preferable that B is reduced as much as possible, but when B is 0.1% or less, the effect of the present invention is not adversely affected. Here, the inevitable impurity element described above is preferably adjusted to less than 1% in total.

In addition, the outer layer material serving as the surface layer at a position corresponding to the maximum diameter at the time of rolling use in the present invention contains the above composition, and the content of W, Co, Mo, and Fe satisfies the following equation [1].

1.2≤(%W+%Mo)/(%Co+%Fe)≤9.0　　　[1]

Here, %W, %Mo, %Co, and %Fe are the content (mass%) of each element, and when they are not contained, they are set to 0.

When (%W+%Mo)/(%Co+%Fe) becomes 1.2 or more, a large amount of hard carbides are accumulated, and the amount of W and Mo dissolved in the matrix also increases. It becomes a Young's modulus of 270 ㎬ or more. In the case of a conventional high-speed tool steel-based roll, the Young's modulus of the surface layer in contact with the rolled material is about 220 to 235 GPa (for example, see Non-Patent Documents 4 and 5), and the Young's modulus is 270 GPa or more, the elasticity of the roll surface layer. The effect of reducing the rolling load by suppressing the deformation is obtained. Even if (%W+%Mo)/(%Co+%Fe) is less than 1.2, if the above composition range is satisfied, a roll outer layer material for rolling excellent in wear resistance is obtained, but since the Young's modulus is less than 270 GPa, a remarkable rolling load reduction effect is obtained. I don't lose. On the other hand, in order to make (%W+%Mo)/(%Co+%Fe) more than 9.0, it is necessary to add a large amount of expensive W and Mo, which is economically disadvantageous, so (%W+%Mo)/ (%Co+%Fe) made 9.0 the upper limit. Further, as a result of the intensive examination of the present inventors, when (%W+%Mo)/(%Co+%Fe) satisfies the above formula [1], the sum of the high capacities of W and Mo in the base is 3.5% or more, and 270 It has been confirmed that the Young's modulus of GPa or more can be obtained. Control of (%W+%Mo)/(%Co+%Fe) may be adjusted by the composition of the molten metal, the casting temperature at the time of centrifugal casting, and the centrifugal force. Further, preferably, (%W+%Mo)/(%Co+%Fe) is 4.8 or more and 7.8 or less.

In addition, in order to exhibit an excellent rolling load reduction effect in the roll outer layer material of the present invention, it is preferable that the Young's modulus of the outer layer material serving as a surface layer at a position corresponding to the maximum diameter at the time of rolling use is 270 GPa or more and 500 GPa or less. As described above, in the case of a conventional high-speed tool steel-based roll, if the Young's modulus of the surface layer in contact with the rolled material is about 220 to 235 GPa (for example, see Non-Patent Documents 4 and 5), and the Young's modulus is 270 GPa or more. , The rolling load reduction effect by suppressing the elastic deformation of the roll surface layer is obtained. However, in order to make the Young's modulus larger than 500 GPa, it is necessary to contain a large amount of alloying elements, which is economically disadvantageous, so that the Young's modulus is preferably 270 GPa or more and 500 GPa or less.

The Young's modulus is measured by taking a compression test piece or a tensile test piece from an outer layer material at a position corresponding to the maximum diameter at the time of rolling use, and calculating it from the gradient at the time of elastic deformation in a compression test or a tensile test, or a non-destructive measurement method such as an ultrasonic method. It may be measured as.

Next, a preferable manufacturing method of the roll outer layer material for rolling of the present invention will be described.

In the present invention, from the viewpoint of productivity and manufacturing cost, the roll outer layer material for rolling is manufactured by using a centrifugal casting method in which a casting mold is rotated. Accordingly, it is possible to manufacture a roll outer layer material for rolling excellent in abrasion resistance at low cost.

First, the molten metal having the above-described roll outer layer material composition is poured into a rotating mold so as to have a predetermined thickness, followed by centrifugal casting to obtain a roll outer layer material for rolling. In addition, in general, in order to protect the mold, a refractory material mainly made of zircon or the like is coated on the inner surface of the mold. Further, in the present invention, it is preferable to perform centrifugal casting by adjusting the rotational speed so that the centrifugal force at a position corresponding to the maximum diameter at the time of rolling use becomes 120 to 250 G. By applying a high centrifugal force, the dispersion density of the hard carbide having a large specific gravity can be increased on the outer surface side.

In the present invention, the resulting roll outer layer material may be a single sleeve, and a shaft material may be fitted thereto to form a rolling roll (see, for example, Fig. 8). In addition, the obtained outer roll material for rolling is a sleeve having an intermediate layer integrated by welding on the inner side thereof, and a shaft member is fitted thereto to form a rolling roll. In addition, the intermediate layer is preferably formed by pouring the molten metal of the intermediate layer composition and centrifugal casting while rotating the mold, during or after solidification of the roll outer layer material. Examples of the intermediate layer material include graphite steel, 1 to 2 mass% C high carbon steel, subeutectic cast iron, and the like. In addition, the shaft material of these rolling rolls is not particularly limited, but it is preferable to use separately manufactured forged steel products (shafts), cast steel products (shafts), and cast iron products (shafts).

In the present invention, in the present invention, the outer layer of the roll for rolling is used as an outer layer to form a composite roll consisting of an inner layer integrated by welding with the outer layer, or the outer layer of the roll for rolling is used as an outer layer, and an intermediate layer in which the outer layer is welded and integrated with the outer layer. Or, it may be a composite roll comprising the intermediate layer and the inner layer formed by welding.

In the case of forming the intermediate layer, it is preferable to perform centrifugal casting by pouring the molten metal of the intermediate layer composition while rotating the mold, during or after solidification of the roll outer layer material. Further, as the intermediate layer material, it is preferable to use graphite steel, high carbon steel of 1 to 2 mass% C, sub-eutectic cast iron, or the like. The intermediate layer and the outer layer are integrally welded, and the components of the outer layer are mixed in the intermediate layer within a range of about 10 to 90%. From the viewpoint of suppressing the mixing amount of the outer layer component into the inner layer, it is preferable to reduce the mixing amount of the outer layer component into the intermediate layer as much as possible.

In general, the inner layer is formed by stopping the rotation of the mold after the outer layer or the intermediate layer is completely solidified, and then erecting the mold, and then statically casting the inner layer material. Here, it is preferable to use spherical graphite cast iron, caterpillar graphite cast iron (CV cast iron), and the like, which are excellent in castability and mechanical properties, as the inner layer material to be statically cast. In addition, in a composite roll in which there is no intermediate layer and the outer layer and the inner layer are integrally welded, the components of the outer layer material are often mixed in the inner layer in an amount of 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 incorporated into the inner layer, the inner layer becomes brittle. For this reason, in the present invention, it is preferable to suppress the mixing ratio of the outer layer component to the inner layer to less than 5%.

It is preferable that the said outer roll material for rolling and the composite roll for rolling are heat-treated after casting. Heat treatment involves heating at 1000 to 1200°C and holding for 5 to 40 hours, then cooling in the furnace, air cooling or air cooling, and heating and maintaining at 400 to 600°C and cooling at least once. It is preferable to use the treatment. In addition, the hardness of the roll outer layer material for rolling and the composite roll for rolling of the present invention is preferably adjusted within the range of 79 to 100HS depending on the application. It is recommended to adjust the heat treatment after casting so that such hardness can be stably secured.

Example

[Example 1]

First, examples in the first embodiment described above will be described.

The molten metal of 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 a centrifugal casting method. In addition, the casting temperature was 1450 to 1550°C, and the centrifugal force was set to 140 to 220 G by the gravity drainage. In some test materials (melted metal No.S), since remarkable carbide segregation to the inner surface occurred, 60 G was set for the purpose of reducing this segregation. After casting, reheating to 1050 to 1200°C and holding for 10 hours, then quenching treatment to cool to 100°C or less, and tempering treatment to cool by heating and holding at 400 to 560°C are repeated once or twice. did. Accordingly, 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. In addition, the commercially available centrifugal cast outer layer composition used as a roll for hot finish rolling of steel (high speed tool steel roll composition: 2.2% C-0.4% Si-0.4% Mn-5.3% Cr-5.2% Mo-5.6% V -1.1% Nb) of molten metal (melt No.V) was melted, a sleeve-shaped roll outer layer material was cast in the same manner, and heat treatment was performed after casting to obtain a test material (hardness 85HS), and a conventional example (test material No. 22).

From the test material subjected to the heat treatment, a test piece for composition analysis and a test piece for abrasion test were taken. In addition, test material No. 19 was very fragile, and it was very difficult to collect the test material.

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

Table 2 shows the obtained results.

In addition, the abrasion test piece (outer diameter 60 mm phi x 10 mm width) was taken from the test piece after the above-described heat treatment so that the center of the width of the abrasion test piece became a position of 10 mm in the radial direction from the outer surface of the test material. In addition, as shown in FIG. 2, the wear test was performed by a two-disc sliding transmission method of a test piece (wear test piece) and a mating material (material: S45C, outer diameter 190 mmφ×width 15 mm).

In the abrasion test, while cooling the test piece with water, a counterpart heated at 850°C was pressed with a load of 980 N to a test piece rotating at a rotation speed: 700 rpm (peripheral speed: 2.1 m/s), while sliding rate: Electricity was carried out to 14.2%. The mating member was updated every 21000 times the number of transmissions of the test piece, and the rotation was performed until the cumulative number of rotations reached 168,000. After the end of the test, the wear loss of the wear test piece was investigated. For the obtained wear loss, the wear loss of the conventional example (test material No. 22) was taken as the standard (1.0), and the ratio of the wear loss of each test material to the standard (: wear resistance ratio = (abrasion loss of the conventional example)/( Abrasion loss of the test material)) was calculated and abrasion resistance was evaluated. When the abrasion resistance is 3 or more, the symbol ``◎'', when the abrasion resistance is 2 or more and less than 3 are indicated by the symbol ``○'', when the abrasion resistance is less than 2 are indicated by the symbol ``×'', and the symbol ◎ is very good, and the symbol ○ is Good and symbol × were evaluated as inferior, respectively.

Table 3 shows the obtained results.

In Example 1, all of the examples of the present invention have a wear resistance ratio of 2.1 or more, and abrasion resistance is significantly improved compared to the conventional example (high speed tool steel roll). On the other hand, in the comparative examples outside the scope of the present invention, cracks occur during the test, or the wear resistance ratio is less than 2, so that there is little improvement in wear resistance compared to the conventional examples.

In addition, the structure was observed and shown in Fig. 1 for the examples of the present invention (No. 13, No. 5). A test piece for tissue observation was collected so that a position of 5 mm in the radial direction from the outer surface of the test material after the heat treatment was an 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 a primary carbide (M _{6 C-type carbide enriched with W).} In the example of the present invention, it can be seen that the primary carbide is dispersed at a high density on the outer surface side of the test material (sleeve-shaped roll outer layer material).

In addition, for reference, for test material No. 11 (invention example), a position of 18 mm (18 mm position) and a position of 38 mm in the radial direction from the outer surface of the test material (sleeve-shaped roll outer layer material) after heat treatment ( 38 mm position), a test piece for composition analysis having a size of 5 mm in the radial direction and 10 mm×10 mm in a plane parallel to the outer surface was taken from the position. Then, the composition at each position was analyzed by chemical analysis. The obtained results were also listed in Table 2.

In addition, for test material No. 11 (example of the present invention), the test surface of the abrasion test piece is at a position of 18 mm (18 mm position) in the radial direction from the outer surface of the test material after heat treatment and a position in the range of 38 to 48 mm A wear test piece was taken so that it might become (38 mm position). In the same manner as in the above-described conditions, an abrasion test was performed to measure the wear loss. The obtained results were also listed in Table 3.

From Table 2, on the outer surface of the test material (sleeve-shaped roll outer layer material), W is mainly concentrated, a position 18 mm away from the outer surface in the radial direction (18 mm position), and a position 38 mm away in the radial direction from the outer surface. At (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 inclined. Therefore, as can be seen from Table 3, at a position of 18 mm in the radial direction (18 mm position) and a position 38 mm apart (38 mm position) from the outer surface, the area up to 10 mm in the radial direction from the outer surface Compared to that, abrasion resistance is lowered.

[Example 2]

Next, examples in the second embodiment described above will be described.

The molten metal of the composition shown in Table 4 was dissolved 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 a centrifugal casting method. In addition, the casting temperature was 1450 to 1550°C, and the centrifugal force was set to 140 to 220 G by the gravity drainage. In some test materials (melted metal No.S), since remarkable carbide segregation to the inner surface occurred, 60 G was set for the purpose of reducing this segregation. After casting, reheating to 1050 to 1200°C and holding for 10 hours, then quenching treatment to cool to 100°C or less, and tempering treatment to cool by heating and holding at 400 to 560°C are repeated once or twice. did. Accordingly, 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. In addition, the commercially available centrifugal cast outer layer composition used as a roll for hot finish rolling of steel (high speed tool steel roll composition: 2.2% C-0.4% Si-0.4% Mn-5.3% Cr-5.2% Mo-5.6% V -1.1% Nb) of molten metal (melt No.V) was melted, similarly, a sleeve-shaped roll outer layer material was cast, and heat treatment was performed after casting to obtain a test material (hardness 85HS), and a conventional example (test material No. 22).

From the test material subjected to the heat treatment, a test piece for composition analysis, a test piece for abrasion test, a test piece for Young's modulus measurement, and a roll test piece for rolling load evaluation were taken. In addition, test material No. 19 was very fragile, and it was very difficult to collect the test material.

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

Table 5 shows the obtained results.

In addition, the abrasion test piece (outer diameter 60 mm phi x 10 mm width) was taken from the test piece after the above-described heat treatment so that the center of the width of the abrasion test piece became a position of 10 mm in the radial direction from the outer surface of the test material. In addition, as shown in FIG. 7, the abrasion test was performed by a two-disc sliding transmission method of a test piece (wear test piece) and a mating material (material: S45C, outer diameter 190 mmφ×width 15 mm).

In the abrasion test, while cooling the test piece with water, the counter piece heated at 850°C was press-contacted with a test piece rotating at a rotational speed of 700 rpm (circumferential speed: 2.1 m/s) with a load of 980 N, while rolling at a sliding rate of 14.2%. The mating member was updated every 21000 times the number of transmissions of the test piece, and the rotation was performed until the cumulative number of rotations reached 168,000. After the end of the test, the wear loss of the wear test piece was investigated. For the obtained wear loss, the wear loss of the conventional example (test material No. 22) was taken as the standard (1.0), and the ratio of the wear loss of each test material to the standard (: wear resistance ratio = (abrasion loss of the conventional example)/( Abrasion loss of the test material)) was calculated and abrasion resistance was evaluated. The case where the wear resistance ratio was 3 or more was evaluated as "◎", the case where the wear resistance ratio was 2 or more and less than 3 was evaluated as "○", and the case where the wear resistance ratio was less than 2 was evaluated as "×". In addition, the symbol ◎ indicates very good, the symbol ○ indicates good, and the symbol × indicates inferiority, respectively.

The Young's modulus measurement test piece (φ16×5 mm thickness) is ground 5 mm in the radial direction from the outer surface of the test material after the above-described heat treatment, and 5 mm in the radial direction from the outer surface after grinding, and φ 16 in a plane parallel to the outer surface. A test piece having a size of mm was taken. Using the obtained test piece, the Young's modulus was measured by an ultrasonic method.

Further, the above-described heat-treated test material was ground 10 mm in the radial direction from the outer surface to obtain a roll test piece (outer diameter 230 mmφ×width 40 mm) having the surface after grinding as an outer surface, as shown in FIG. After shrinking heating and fitting to a shaft material made of carbon steel forged steel to obtain a composite roll for evaluation of rolling load, the composite roll was installed in a 4Hi thin-plate cold rolling mill (backup roll: outer diameter 500 mmφ×body length 40 mm), and tensioned. The rolling load at the time of cold rolling with a 20% reduction in sheet thickness was measured using a steel sheet having a strength of 590 MPa (board width 20 mm, sheet thickness 1.5 mm x length 20 m) as a material to be rolled. From the results, based on the rolling load of test sample No. 22, which is a conventional example, the amount of reduction in the rolling load of each roll test piece relative to the standard (=100-rolling load of the test material/rolling load of the conventional example × 100) was calculated, When the rolling load was reduced by 10% or more, it was said that the effect of reducing the rolling load was recognized.

Table 6 shows the obtained results.

In Example 2, all of the examples of the present invention have a wear resistance ratio of 2.1 or more, and abrasion resistance is significantly improved compared to the conventional example (high speed tool steel roll), and the rolling load is reduced by 10% or more compared to the conventional example. It shows an excellent rolling load reduction effect. On the other hand, in the comparative examples outside the scope of the present invention, cracks occur during the test, or the wear resistance ratio is less than 2, so that the improvement in wear resistance is less compared to the conventional examples, or the Young's modulus is less than 270 GPa, so the rolling load reduction effect is small. .

Further, the structure was observed and shown in Fig. 6 for the examples of the present invention (No. 13, No. 5). A test piece for tissue observation was taken so that a position of 5 mm in the radial direction from the outer surface of the test material after the heat treatment was an 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 a primary carbide (M _{6 C-type carbide enriched with W).} In the example of the present invention, it can be seen that the primary carbide is dispersed at a high density on the outer surface side of the test material (sleeve-shaped roll outer layer material).

In addition, for reference, for test material No. 11 (invention example), a position of 18 mm (18 mm position) and a position of 38 mm in the radial direction from the outer surface of the test material (sleeve-shaped roll outer layer material) after heat treatment ( 38 mm position), a test piece for composition analysis having a size of 5 mm in the radial direction and 10 mm×10 mm in a plane parallel to the outer surface was taken from the position. And the composition at each position was analyzed by chemical analysis. The obtained results were also listed in Table 5.

In addition, for test material No. 11 (example of the present invention), the test surface of the abrasion test piece is at a position of 18 mm (18 mm position) in the radial direction from the outer surface of the test material after heat treatment and a position in the range of 38 to 48 mm A wear test piece was collected so as to be (38 mm position), a wear test was performed in the same manner as in the above-described conditions, and the wear loss was measured. The obtained results were also listed in Table 6.

From Table 5, on the outer surface of the test material (sleeve-shaped roll outer layer), mainly W is concentrated, a position 18 mm away from the outer surface in the radial direction (18 mm position), and a position 38 mm away in the radial direction from the outer surface. At (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 inclined. Therefore, as can be seen from Table 6, at a position of 18 mm in the radial direction (18 mm position) and a position 38 mm away (38 mm position) from the outer surface, an area up to 10 mm in the radial direction from the outer surface Compared to that, abrasion resistance is lowered.

Claims (21)

As a roll outer layer material for rolling made of W-Co base alloy,
W content is an inclined composition that decreases in the radial direction from the outer circumferential side of the roll toward the inner circumferential side, and the outer layer material surface at a position corresponding to the maximum diameter at the time of rolling use is in 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%
A roll outer layer material for rolling having a composition including, wherein the balance is made of inevitable impurities. The method of claim 1,
In addition to the above composition, the roll outer layer material for rolling further contains at least one of the following (A) and (B) in mass%.
(A) One or two or more selected from Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, Nb: 0.1 to 3%
(B) Ni: 0.05 to 3% The method according to claim 1 or 2,
The roll outer layer material for rolling is a roll outer layer material for rolling, which is a centrifugal casting material. A rolling composite roll comprising an outer layer and an inner layer welded and integrated with the outer layer,
The composite roll for rolling, wherein the outer layer is the roll outer layer material for rolling according to claim 1 or 2. 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,
The composite roll for rolling, wherein the outer layer is the roll outer layer material for rolling according to claim 1 or 2. The method of claim 4,
A composite roll for rolling in which the outer layer is made of centrifugal casting. The method of claim 5,
A composite roll for rolling in which the outer layer is a centrifugal cast. A roll outer layer material made of a W-Co-based alloy, whose W content is an inclined composition that decreases in the radial direction from the outer periphery of the roll toward the inner periphery, and the outer layer material that becomes the surface layer at a position corresponding to the maximum diameter when rolling is used, has a mass %in,
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: contains 1 to 15%,
Further, the roll outer layer material having a composition in which the content of W, Co, Mo, and Fe satisfies the following formula [1], and the remainder is composed of unavoidable impurities.
group
1.2≤(%W+%Mo)/(%Co+%Fe)≤9.0 [1]
Here, %W, %Mo, %Co, and %Fe are the content (mass%) of each element. The method of claim 8,
The outer layer material of a roll for rolling, wherein the Young's modulus of the outer layer material serving as the surface layer at a position corresponding to the maximum diameter when using the rolling is 270 GPa or more and 500 GPa or less. The method according to claim 8 or 9,
In addition to the above composition, the roll outer layer material for rolling further contains at least one of the following (A) and (B) in mass%.
(A) One or two or more selected from Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, Nb: 0.1 to 3%
(B) Ni: 0.05 to 3% The method according to claim 8 or 9,
The roll outer layer material for rolling is a roll outer layer material for rolling, which is a centrifugal casting material. The method of claim 10,
The roll outer layer material for rolling is a roll outer layer material for rolling, which is a centrifugal casting material. A rolling composite roll 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, the W content is an inclined composition that decreases in the radial direction from the outer circumferential side of the roll toward the inner circumferential side, and the outer layer material serving as the surface layer at a position corresponding to the maximum diameter at the time of rolling use is mass% in,
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: contains 1 to 15%,
Further, a rolling composite roll having a composition in which the content of W, Co, Mo, and Fe satisfies the following formula [1], and the remainder is composed of unavoidable impurities.
group
1.2≤(%W+%Mo)/(%Co+%Fe)≤9.0 [1]
Here, %W, %Mo, %Co, and %Fe are the content (mass%) of each element. The method of claim 13,
A composite roll for rolling in which the Young's modulus of the outer layer material serving as the surface layer at a position corresponding to the maximum diameter when using the rolling is 270 GPa or more and 500 GPa or less. The method of claim 13 or 14,
In addition to the above composition, the composite roll for rolling further contains at least one of the following (A) and (B) in mass%.
(A) One or two or more selected from Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, Nb: 0.1 to 3%
(B) Ni: 0.05 to 3% 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,
The outer layer is made of a W-Co-based alloy, the W content is an inclined composition that decreases in the radial direction from the outer circumferential side of the roll toward the inner circumferential side, and the outer layer material serving as the surface layer at a position corresponding to the maximum diameter at the time of rolling use is mass% in,
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%,
Fe: contains 5 to 40%,
Further, a rolling composite roll having a composition in which the content of W, Co, Mo, and Fe satisfies the following formula [1], and the remainder is composed of unavoidable impurities.
group
1.2≤(%W+%Mo)/(%Co+%Fe)≤9.0 [1]
Here, %W, %Mo, %Co, and %Fe are the content (mass%) of each element. The method of claim 16,
A composite roll for rolling in which the Young's modulus of the outer layer material serving as the surface layer at a position corresponding to the maximum diameter when using the rolling is 270 GPa or more and 500 GPa or less. The method of claim 16 or 17,
In addition to the above composition, the composite roll for rolling further contains at least one of the following (A) and (B) in mass%.
(A) One or two or more selected from Fe: 5 to 40%, Cr: 0.1 to 10%, V: 0.1 to 6%, Nb: 0.1 to 3%
(B) Ni: 0.05 to 3% The method according to any one of claims 13, 14, 16 and 17,
A composite roll for rolling in which the outer layer is made of centrifugal casting. The method of claim 15,
A composite roll for rolling in which the outer layer is made of centrifugal casting. The method of claim 18,
A composite roll for rolling in which the outer layer is made of centrifugal casting.

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