JP6191913B2 - Centrifugal cast composite roll and manufacturing method thereof - Google Patents

Description

  The present invention relates to a composite roll made of centrifugal cast having a composite structure in which an outer layer formed by centrifugal casting and a tough inner layer are welded and integrated, and a manufacturing method thereof.

  As shown in FIGS. 1 and 2, the hot rolling composite roll 10 includes an outer layer 1 in contact with the rolled material and an inner layer 2 made of a material different from the outer layer 1 welded to the inner surface of the outer layer 1. The inner layer 2 includes a body core portion 21 welded to the outer layer 1, and a driving side shaft portion 22 and a driven side shaft portion 23 that extend integrally from the body core portion 21 to both sides. A clutch portion 24 used for driving torque transmission is integrally provided at the end of the driving side shaft portion 22. A convex portion 25 necessary for handling the composite roll 10 and the like is integrally provided at the end of the driven side shaft portion 23. The clutch portion 24 has an end surface 24a and a pair of flat cutout surfaces 24b, 24b that engage with driving means (not shown), and the convex portion 25 has an end surface 25a. The driving side shaft portion 22 and the driven side shaft portion 23 need to be machined to form a bearing portion, a neck portion, and the like.

  As such a composite roll 10 for hot rolling, there is a composite roll having a composite structure in which an outer layer 1 made of centrifugal cast having excellent wear resistance and accident resistance and an inner layer 2 made of tough ductile cast iron are welded and integrated. Widely used. In the hot rolling roll 10, when damage such as wear and roughening generated in the surface layer portion of the outer layer 1 due to thermal and mechanical loads due to contact with the rolled material progresses, the surface quality of the rolled material deteriorates. The composite roll 10 that has been worn and roughened is replaced with a composite roll 10 having no damage on the outer layer surface, and the outer layer 1 of the composite roll 10 removed from the rolling mill is re-polished to remove the damaged portion. The composite roll 10 after the re-grinding is again assembled in a rolling mill and used for rolling. If the composite roll 10 is frequently exchanged, the rolling must be interrupted frequently, so that productivity is hindered.

  In order to minimize the interruption of rolling, the wear resistance of the outer layer 1 in contact with the rolled material has been improved. When the service life of the composite roll 10 is extended as the wear resistance of the outer layer 1 is improved, it is also important to improve the wear resistance of the clutch portion 24 fastened to the torque transmission coupling. If the clutch portion 24 is significantly worn, the composite roll 10 cannot be used even if the outer layer 1 is not worn.

  As a composite roll for hot rolling with improved wear resistance of the clutch part, Patent Document 1 discloses an outer layer made of high-speed tool steel, an inner layer made of carbon steel or low alloy steel of C: 0.2 to 1.2% by weight, and In a composite roll for hot rolling having a shaft portion, C: 2.5-3.5%, Si: 1.6-2.8%, Mn: 0.3-0.6%, P <0.05%, S <0.03%, Ni <0.5 on a weight basis , Cr <0.2%, Mo <0.5%, and Mg: 0.02 to 0.05%, the remainder consisting of Fe and other inevitable components, and a clutch part made of spheroidal graphite cast iron with a graphite area ratio of 5 to 15% Discloses a composite roll for hot rolling in which the end portion of the shaft portion is cast. However, the wear resistance of the clutch portion is still insufficient. In addition, since the clutch portion is cast at the end of the shaft portion, there is a problem that a casting defect such as a foreign object bite is likely to occur at the boundary between the two. Furthermore, it is necessary to process the surface to be casted flat, to set a mold around the casted part, or to melt and cast the spheroidal graphite cast iron for the clutch part different from the inner layer. There is also a problem that the cost increases.

  In addition, if the driving side shaft portion 22 and the driven side shaft portion 23 are formed of the same hard material, the driven side shaft portion 23 that does not require the same degree of hardness as the driving side shaft portion 22 becomes harder than necessary, and the workability is improved. There is a problem of deterioration.

JP-A-6-304612

  Accordingly, an object of the present invention is to provide a centrifugal cast composite roll in which the wear resistance of the driving side shaft portion is improved while maintaining the workability of the driven side shaft portion, and a manufacturing method thereof.

  As a result of diligent research in view of the above object, the present inventors have appropriately determined (a) the rising speed of the molten metal surface for the inner layer to be poured into the stationary casting mold after the outer layer is formed by centrifugal casting. By controlling, Cr, Mo, and V or Cr, Mo, V, and Nb in the outer layer can be mixed more than the driven side shaft portion than the driven side shaft portion, so that the driving side shaft portion is driven side shaft. It was discovered that (b) a high-hardness driving side shaft portion has excellent wear resistance, and a non-hard driven side shaft portion has good workability. I came up with it.

The first centrifugal cast composite roll of the present invention is a centrifugal cast composite roll in which an outer layer formed by a centrifugal casting method and an inner layer made of ductile cast iron are welded and integrated, and the outer layer is at least Cr on a mass basis. : Fe-based alloy containing a chemical composition containing 3.0 to 10.0%, Mo: 2.0 to 10.0%, and V: 5.8 to 10.0%, the inner layer includes a trunk core portion welded to the outer layer, and the barrel A driving-side shaft portion and a driven-side shaft portion that integrally extend from both ends of the core portion, and the total amount of Cr, Mo, and V at the end portions of both the shaft portions is 0.15 to 2.0 mass%, and The total amount of Cr, Mo and V at the end of the driving side shaft is 0.2 mass% or more greater than the total amount of Cr, Mo and V at the end of the driven side shaft .

A second centrifugal cast composite roll of the present invention is a centrifugal cast composite roll in which an outer layer formed by a centrifugal casting method and an inner layer made of ductile cast iron are welded and integrated, and the outer layer is at least Cr on a mass basis. : Fe-based alloy containing a chemical composition containing 3.0 to 10.0%, Mo: 2.0 to 10.0%, and V and Nb: 6.5 to 10.0% in total, the inner layer includes a body core portion welded to the outer layer , Having a driving side shaft portion and a driven side shaft portion integrally extending from both ends of the trunk core portion, and the total amount of Cr, Mo, V and Nb at the end portions of both shaft portions is 0.15 to 2.0 mass %, And the total amount of Cr, Mo, V and Nb at the end of the drive side shaft is 0.2% by mass or more than the total amount of Cr, Mo, V and Nb at the end of the driven side shaft It is characterized by that.

  The outer layers of the first and second centrifugal cast composite rolls further contain C: 1.0-3.0%, Si: 0.3-2.0%, Mn: 0.1-1.8%, and Ni: 0-3.5% on a mass basis. Is preferred.

  The outer layers of the first and second centrifugally cast composite rolls are further W: 0 to 10.0%, Ti: 0.003 to 5.0%, Al: 0.01 to 2.0%, Zr: 0.01 to 0.5%, and Co: on a mass basis. You may contain at least 1 type of 0.1 to 10%.

The method for producing a centrifugal cast composite roll according to the present invention includes (1) centrifugal casting of the outer layer with a rotating centrifugal casting cylindrical mold, and (2) raising the cylindrical mold having the outer layer, and upper and lower ends thereof. An upper mold and a lower mold each communicating with the outer layer are provided to constitute a stationary casting mold, (3)
A step of casting a molten metal for the inner layer into a cavity constituted by the upper mold, the outer layer, and the lower mold, and the rising speed of the molten metal surface in the upper mold is 100 mm / second or less, and the lower mold And it is smaller than the rising speed of the molten metal surface in the outer layer.

  In the centrifugal cast composite roll of the present invention, Cr, Mo and V, or Cr, Mo, V and Nb in the outer layer are mixed more in the drive side shaft portion having the clutch portion than in the driven side shaft portion. The drive side shaft portion is sufficiently hard and has excellent wear resistance, and the driven side shaft portion is not too hard and is easy to machine. Therefore, the centrifugally cast composite roll of the present invention has a significantly improved service life and good workability. The centrifugal cast composite roll of the present invention having such characteristics is obtained by controlling the rising speed of the molten metal surface for the inner layer to be poured after the outer layer is formed, so that the production method is efficient, Contributes to a significant reduction in the manufacturing cost of centrifugal cast composite rolls.

It is a schematic sectional drawing which shows the composite roll for hot rolling. FIG. 2 is a partial perspective view showing a clutch part side of the hot-rolling composite roll of FIG. It is sectional drawing which shows an example of the casting_mold | template used for manufacture of the composite roll made from a centrifugal casting of this invention. It is sectional drawing which shows an example of the casting_mold | template used for manufacture of the composite roll made from a centrifugal casting of this invention. It is sectional drawing which shows the other example of the casting_mold | template used for manufacture of the composite roll made from a centrifugal casting of this invention.

  Embodiments of the present invention will be described in detail below, but the present invention is not limited to them, and various modifications may be made without departing from the technical idea of the present invention. Unless otherwise specified, when “%” is simply described, it means “mass%”.

  The first and second centrifugal cast composite rolls of the present invention both have the structure shown in FIG. The only difference between the first centrifugal cast composite roll and the second centrifugal cast composite roll is the composition of the outer layer. That is, V in the outer layer of the first centrifugal cast composite roll is (V + Nb) in the outer layer of the second centrifugal cast composite roll. Therefore, first, the outer layer composition of the first centrifugal cast composite roll will be described, and only the above differences will be described for the second centrifugal cast composite roll.

[1] Centrifugal cast composite roll
(A) Outer layer
(1) Composition of the outer layer of the first centrifugal cast composite roll The outer layer of the first centrifugal cast composite roll is at least Cr: 3.0 to 10.0%, Mo: 2.0 to 10.0%, and V: 5.8 to It consists of a Fe-based alloy containing a chemical composition containing 10.0%. The outer layer preferably further contains C: 1.0 to 3.0%, Si: 0.3 to 2.0%, Mn: 0.1 to 1.8%, and Ni: 0 to 3.5% on a mass basis.

(a) Cr: 3.0 to 10.0% by mass
Cr is an effective element for maintaining the hardness and maintaining the wear resistance by making the base a bainite or martensite. If Cr is less than 3.0% by mass, the amount that dissolves in the inner layer is insufficient, and the wear resistance of the clutch portion is insufficient. On the other hand, if the Cr content exceeds 10.0% by mass, the toughness of the base structure decreases. The Cr content is preferably Cr: 4.0 to 7.0% by mass.

(b) Mo: 2.0 to 10.0% by mass
Mo combines with C to form hard carbides (M ₆ C, M ₂ C), increasing the hardness of the outer layer and improving the hardenability of the matrix. Mo also produces tough and hard MC carbides together with V and Nb to improve wear resistance. If Mo is less than 2.0% by mass, the amount that dissolves in the inner layer is insufficient, and the wear resistance of the clutch portion is insufficient. On the other hand, if Mo exceeds 10.0% by mass, the toughness of the outer layer deteriorates. The Mo content is preferably Mo: 4.0 to 8.0% by mass.

(c) V: 5.8 to 10.0% by mass
V is an element that combines with C to form hard MC carbide. This MC carbide has a Vickers hardness Hv of 2500 to 3000 and is the hardest of the carbides. When V is less than 5.8% by mass, not only the amount of MC carbide precipitated is insufficient, but also the amount of melt into the inner layer is insufficient, resulting in insufficient wear resistance of the clutch part. On the other hand, when V exceeds 10.0% by mass, MC carbide with a low specific gravity is concentrated inside the outer layer due to centrifugal force during centrifugal casting, and not only the MC carbide radial segregation becomes significant, but also MC carbide becomes coarse. The alloy structure becomes rough, and the surface becomes rough during rolling. The V content is preferably V: 6.0 to 10.0% by mass, and more preferably V: 6.0 to 8.0% by mass.

(d) Total amount of Cr, Mo and V The total amount of Cr, Mo and V at the end portion of the shaft portion is 0.15 to 2.0 mass% in both shaft portions, and Cr, Mo and V in one shaft portion The difference between the total amount of Cr and the total amount of Cr, Mo and V in the other shaft portion is 0.2% by mass or more. The outer layer Cr, Mo and V content is Cr: 3.0 to 10.0%, Mo: 2.0 to 10.0%, V: 5.8 to 10.0%, adjusting the pouring conditions of the inner layer ductile cast iron, By mixing a specific amount of carbide-forming elements such as Mo and V into the inner layer, the base structure of the shaft portion made of the inner layer material is solid-solution strengthened, carbide is formed, and the shaft portion is hardened. If the total amount of Cr, Mo, and V at the end of the shaft is less than 0.15% by mass for both shafts, the wear resistance of the clutch is insufficient. If it exceeds 2.0% by mass, the amount of carbides produced is too much, so that it becomes brittle and the shaft portion may be broken. The total amount of Cr, Mo and V at the end of the shaft is more preferably 0.2 to 1.8% by mass for both shafts. The contents of Cr, Mo and V at the end of the shaft part are calculated by chemical analysis by collecting a sample from the end surface of the shaft part or a range within 100 mm from the end surface of the shaft part in the roll axis direction. In addition, the shaft part contains at least one of Cu: 0.1-1.0%, P: 0.03-0.1%, Ni: 0.5-2.5%, Mn: 0.5-1.5% to further improve wear resistance, etc. You may let them.

  The difference between the total amount of Cr, Mo and V at the end portion of one shaft portion and the total amount of Cr, Mo and V at the end portion of the other shaft portion is set to 0.2% by mass or more. The total amount of Cr, Mo and V at the end of the shaft portion is relatively large, i.e., the amount of the carbide forming elements Cr, Mo and V in the outer layer mixed into the inner layer is larger than that of the other shaft portion, By using the driving side shaft portion in which the clutch portion is formed, the wear resistance of the clutch portion can be enhanced. Conversely, the total amount of Cr, Mo, and V at the end of the shaft is relatively small, that is, the amount of carbide-forming elements Cr, Mo, and V in the outer layer mixed into the inner layer is smaller than that of the other shaft. Since the driven side shaft portion is not provided with the clutch portion, the driven side shaft portion is not harder than the drive side shaft portion and can be processed more easily than the drive side shaft portion. The difference between the total amount of Cr, Mo and V at the end of one shaft portion and the total amount of Cr, Mo and V at the end of the other shaft portion is more preferably 0.25% by mass or more.

(2) Composition of the outer layer of the second centrifugally cast composite roll The outer layer of the second centrifugally cast composite roll has at least Cr: 3.0 to 10.0%, Mo: 2.0 to 10.0%, and V and Nb: It consists of a Fe-based alloy containing a chemical composition containing 6.5 to 10.0% in total (except when Nb is 0%). The outer layer preferably further contains C: 1.0 to 3.0%, Si: 0.3 to 2.0%, Mn: 0.1 to 1.8%, and Ni: 0 to 5.0% on a mass basis. The chemical composition of the outer layer of the second centrifugal cast composite roll differs from the chemical composition of the outer layer of the first centrifugal cast composite roll only in that it is the total amount of V and Nb. Therefore, only the total amount of V and Nb will be described in detail below.

(a) V and Nb: 6.5 to 10.0% in total
Like V, Nb combines with C to form hard MC carbide. Nb, combined with V and Mo, solidifies in MC carbide and strengthens MC carbide, improving the wear resistance of the outer layer. The NbC-based MC carbide has a smaller difference from the molten metal density than the VC-based MC carbide, thereby reducing the segregation of the MC carbide. If the total amount of V and Nb is less than 6.5% by mass, the amount that dissolves in the inner layer is insufficient, and the wear resistance of the clutch portion is insufficient. On the other hand, when the total amount of V and Nb exceeds 10.0% by mass, MC carbide having a low specific gravity is concentrated inside the outer layer due to the centrifugal force during centrifugal casting, and not only the radial segregation of MC carbide becomes significant, but also MC The carbides become coarse and the alloy structure becomes rough, and the surface becomes rough during rolling. More preferably, V and Nb: 6.5 to 8.5% by mass in total.

(3) Composition common to the outer layers of the first and second centrifugal cast composite rolls
(a) C: 1.0 to 3.0% by mass
C combines with V, Nb, Cr, Mo and W to form hard carbides, contributing to the improvement of the wear resistance of the outer layer. When C is less than 1.0% by mass, the amount of hard carbide crystallized is too small to provide sufficient wear resistance to the outer layer.

  On the other hand, if C exceeds 3.0% by mass, the toughness of the outer layer is reduced by excessive carbides, and crack resistance is reduced. The content of C is preferably C: 1.0 to 2.8% by mass.

(b) Si: 0.3 to 2.0 mass%
Si reduces oxide defects by deoxidation of the melt. If Si is less than 0.3% by mass, the deoxidizing action of the molten metal is insufficient and oxide defects are likely to occur. On the other hand, if Si exceeds 2.0% by mass, the alloy matrix becomes brittle and the toughness of the outer layer decreases. The Si content is preferably Si: 0.3 to 1.8% by mass.

(c) Mn: 0.1-1.8% by mass
In addition to the deoxidizing action of the molten metal, Mn has an action of fixing S as an impurity as MnS. If Mn is less than 0.1% by mass, these effects are insufficient. On the other hand, even if Mn exceeds 1.8% by mass, further effects cannot be obtained. The Mn content is preferably Mn: 0.1 to 1.6% by mass.

(d) Ni: 0 to 3.5% by mass
Ni improves the hardenability of the base tissue. When Ni exceeds 3.5% by mass, retained austenite becomes excessive and transformation to bainite or martensite becomes difficult. The Ni content is preferably Ni: 0 to 3.3 mass%.

(4) Arbitrary composition The outer layer of the centrifugally cast composite rolling roll of the present invention may contain at least one of the following elements in addition to the above essential composition requirements.

(a) W: 0 to 10.0% by mass
W combines with C to form hard M ₆ C and M ₂ C carbides and contributes to improved wear resistance of the outer layer. It also has the effect of reducing the segregation by increasing the specific gravity by dissolving in MC carbide. However, if W exceeds 10.0% by mass, the network carbide of M ₆ C becomes excessive and the toughness decreases. The W content is preferably W: 0.1 to 8.0% by mass.

(b) Mo and W: Total 3.5-10.0 mass%
Like Mo, W combines with C to produce hard carbides (M ₆ C, M ₂ C), increasing the hardness of the outer layer and improving the hardenability of the matrix. Mo and W together with V and Nb produce tough and hard MC carbides and improve wear resistance.

  If the total amount of Mo and W is less than 3.5% by mass, the amount that dissolves in the inner layer is insufficient, and the wear resistance of the clutch portion is insufficient. On the other hand, when the total amount of Mo and W exceeds 10.0% by mass, the toughness of the outer layer deteriorates. More preferably, Mo and W: 4.5 to 8.0 mass% in total.

(c) Ti: 0.003 to 5.0 mass%
Ti combines with N and O to form an oxide or nitride. Ti oxides or nitrides are suspended in the melt and become nuclei, which refine and homogenize MC carbides. However, if Ti exceeds 5.0% by mass, the viscosity of the molten metal increases and casting defects are likely to occur. Therefore, when adding Ti, the preferable content is 5.0 mass% or less. On the other hand, when Ti is less than 0.003 mass%, the effect of addition is insufficient. The Ti content is preferably 0.003 to 3.0 mass%.

(d) Al: 0.01 to 2.0 mass%
Al combines with N and O to form oxides or nitrides, which are suspended in the molten metal to form nuclei, and MC carbides are crystallized finely and uniformly. However, if Al exceeds 2.0% by mass, the outer layer becomes brittle, leading to deterioration of mechanical properties. Therefore, the preferable content of Al is 0.2% by mass or less. The content of Al is preferably Al: 0.01 to 1.0% by mass.

(e) Zr: 0.01 to 0.5 mass%
Zr combines with C to form MC carbide, improving the wear resistance of the outer layer. Moreover, since the Zr oxide produced | generated in the molten metal acts as a crystal nucleus, the solidification structure becomes fine. It also increases the specific gravity of MC carbide and prevents segregation. However, when Zr exceeds 0.5% by mass, inclusions are generated, which is not preferable. On the other hand, when Zr is less than 0.01% by mass, the effect of addition is insufficient. The content of Zr is preferably Zr: 0.01 to 0.1% by mass.

(f) Co: 0.1-10.0 mass%
Co is an element effective for strengthening the base organization. However, when Co exceeds 10% by mass, the toughness of the outer layer decreases. Therefore, the content of Co is preferably 10% by mass or less. On the other hand, if Co is less than 0.1% by mass, the effect of addition is insufficient. The Co content is preferably Co: 0.1 to 6.0% by mass.

(5) Structure of the outer layer of the first and second centrifugal cast composite rolls In any of the first and second centrifugal cast composite rolls, the outer layer is composed of carbides other than the base, MC carbide, and MC carbide (M ₂ C , M ₆ C, etc.).

(B) Inner layer
(1) Distribution of carbide-forming elements As shown in FIGS. 1 and 2, the inner layer 2 includes a body core portion 21 welded to the outer layer 1, and a driving side shaft portion integrally extending from both ends of the body core portion 21. 22 and a driven side shaft portion 23. Regarding the diffusion of “Cr, Mo, V, and Nb” from the outer layer 1 to the inner layer 2, in the case of the first centrifugal cast composite roll, the Nb content is zero, so that “Cr, Mo, and V” It shall mean diffusion. Therefore, in the following description, the first and second centrifugal cast composite rolls are not distinguished, and are simply referred to as the centrifugal cast composite rolls of the present invention.

  When producing a composite roll made by centrifugal casting according to the present invention, when the melt of ductile iron that becomes the inner layer is cast during or after solidification of the outer layer formed by the centrifugal casting method, the inner surface of the outer layer is remelted, and this ductile for inner layer When the cast iron pouring conditions are adjusted, carbide forming elements (Cr, Mo, V and Nb) in the outer layer 1 are mixed into the inner layer 2 at a predetermined ratio, and the driving side shaft portion 22 and the driven side shaft portion 23 Is strengthened by solid solution, and the hardness is increased by the formation of carbides.

In the present invention, the total content of Cr, Mo and V at the ends of both the driving side shaft portion 22 and the driven side shaft portion 23 is 0.15 to 2.0 mass%, and one driving side shaft portion 22 and the other driven side are driven. The difference in the total content of Cr, Mo and V with respect to the side shaft portion 23 needs to be 0.2% by mass or more. Here, “the end portion of the driving side shaft portion 22” refers to a range within 100 mm from the end face 24a. Further, “the end portion of the driven shaft portion 23” refers to a range within 100 mm from the end face 25a. The contents of Cr, Mo, V, and Nb are obtained by chemical analysis of samples collected from the drive side shaft portion 22 and the driven side shaft portion 23 within the above range.

  If the total amount of Cr, Mo, V and Nb at both ends of both shaft portions 22 and 23 is less than 0.15 mass%, the wear resistance of the clutch portion 24 is insufficient. On the other hand, if the total amount of Cr, Mo, V, and Nb exceeds 2.0 mass%, the generated carbide becomes too much, so both shaft portions 22 and 23 become brittle. The total amount of Cr, Mo, V and Nb at the end portions of both shaft portions 22 and 23 is more preferably 0.2 to 1.8 mass%.

  The difference between the total amount of Cr, Mo, V and Nb at the end of one shaft portion and the total amount of Cr, Mo, V and Nb at the end of the other shaft portion is set to 0.2 mass% or more. By setting the shaft portion of the one where the total amount of Cr, Mo, V and Nb is large (the amount of carbide forming elements mixed from the outer layer 1 to the inner layer 2 is large) as the driving side shaft portion 22 having the clutch portion 24, The wear resistance of the clutch portion 24 can be increased. In addition, the driven side shaft portion is formed by setting the shaft portion with the smaller total amount of Cr, Mo, V, and Nb (the amount of the carbide-forming element mixed from the outer layer 1 to the inner layer 2 is small) as the driven side shaft portion 23. 23 is harder than the drive side shaft portion 22 and is easy to process. The difference in the total amount is preferably 0.25% by mass or more.

(2) Composition of ductile cast iron for inner layer In the final product composite roll, ductile cast iron for inner layer is C: 2.3 to 3.6%, Si: 1.5 to 3.5%, Mn on the basis of mass in addition to Cr, Mo, V and Nb. : 0.2-2.0%, and Ni: 0.3-2.0%. In addition to these elements, Al used as a deoxidizer is 0.1% or less, Cu, Sn, As or Sb for improving hardness is 0.5% or less, and B, Ca, Na mixed from flux or refractory material or Zr may be contained in an amount of 0.2% or less. Further, as impurities, S, P, N and O may be contained in a total of about 0.1% or less. The preferable chemical composition of the ductile cast iron for the inner layer is C: 2.3 to 3.6%, Si: 1.5 to 3.5%, Mn: 0.2 to 2.0%, Ni: 0.3 to 2.0%, Cr: 0.05 to 1.0%, Mo: 0.05 to 1.0%, W: 0 to 0.7%, V: 0.05 to 1.0%, and Nb: 0 to 0.7%, Mg: 0.01 to 0.08%, the balance being substantially Fe and inevitable impurities. In addition, each element in the outer layer also contains less than 1%.

(C) Intermediate layer The present invention utilizes the fact that Cr, Mo, V, and Nb of the outer layer 1 are mixed into the driving side shaft portion 22 and the driven side shaft portion 23 during casting of the inner layer 2, but it is necessary. Accordingly, an intermediate layer may be provided between the outer layer 1 and the inner layer 2. The preferable chemical composition of the intermediate layer is C: 0.8-3.2%, Si: 0.3-2.0%, Mn: 0.1-1.8%, Ni: 0-3.0%, Cr: 0.1-5.0%, Mo: 0- 6.0%, W: 0-5.0%, V: 0-6.0%, and Nb: 0-3.0%. In addition, each element in the outer layer also contains less than 1%.

  When the melt of the intermediate layer is cast, the inner surface of the outer layer 1 is re-melted and mixed into the intermediate layer, so that Cr, Mo, V, and Nb are mixed into the intermediate layer. Since the inner surface of the intermediate layer is redissolved when the inner layer 2 is cast, Cr, Mo, V and Nb mixed in the intermediate layer from the outer layer 1 are mixed in the inner layer. Therefore, even when the intermediate layer is formed, the effect of the present invention can be obtained in the same manner. In order to ensure the movement of Cr, Mo, V and Nb from the outer layer 1 to the inner layer 2, the average thickness of the intermediate layer is preferably 1 to 70 mm, more preferably 3 to 50 mm. .

[2] Method for Producing Centrifugal Cast Composite Roll FIG. 3 and FIG. 4 show an example of a stationary casting mold used for casting the inner layer 2 after centrifugal casting of the outer layer 1 with the cylindrical mold 30 for centrifugal casting. . The stationary casting mold 100 includes a cylindrical mold 30 having an outer layer 1 on the inner surface, and an upper mold 40 and a lower mold 50 provided at upper and lower ends thereof. The inner surface of the outer layer 1 in the cylindrical mold 30 has a cavity 60a for forming the body core portion 21 of the inner layer 2, and the upper die 40 has a cavity 60b for forming the driven side shaft portion 23 of the inner layer 2. The lower mold 50 has a cavity 60c for forming the drive side shaft portion 22 of the inner layer 2. The centrifugal casting method may be any of horizontal type, inclined type and vertical type.

  When the upper mold 40 and the lower mold 50 are assembled above and below the cylindrical mold 30, the cavity 60a in the outer layer 1 communicates with the cavity 60b of the upper mold 40 and the cavity 60c of the lower mold 50, and the entire inner layer 1 is integrally formed. A cavity 60 is configured. 31 and 33 in the cylindrical mold 30 are sand molds. Further, 42 in the upper mold 40 and 52 in the lower mold 50 are each a sand mold. The lower mold 50 is provided with a bottom plate 53 for holding the inner layer molten metal.

  As shown in FIG. 3 and FIG. 4, a cylindrical mold 30 in which the outer layer 1 is centrifugally cast is placed upright on the lower mold 50 for forming the driving side shaft portion 22, and is driven on the cylindrical mold 30. An upper mold 40 for forming the side shaft portion 23 is installed to constitute a stationary casting mold 100 for forming the inner layer 2.

  In the stationary casting mold 100, as the outer layer formed by centrifugal casting is solidified during or after solidification, as the ductile cast iron melt for the inner layer 2 is injected into the cavity 60 from the upper opening 43 of the upper mold 40, the cavity 60 The inner surface of the molten metal gradually rises from the lower mold 50 to the upper mold 40, and the inner layer 2 including the driving side shaft portion 22, the trunk core portion 21, and the driven side shaft portion 23 is integrally cast. At that time, the inner surface portion of the outer layer 1 is remelted by the heat quantity of the molten metal, and Cr, Mo, V, and Nb in the outer layer 1 are mixed into the inner layer 2.

  In the method of the present invention, the rising speed of the molten metal surface in the upper mold 30 for forming the driven side shaft portion 23 is 100 mm / second or less, and the lower mold 40 for forming the driving side shaft portion 22 and the trunk core portion 21 are formed. It is made smaller than the rising speed of the molten metal surface in the cylindrical mold 30 (outer layer 1) for use. Thus, Cr, Mo, V, and Nb that have come out of the outer layer 1 re-dissolved by pouring up to the core portion 21 remain at a predetermined degree on the drive side shaft portion 22 and the trunk portion 21, and are formed by the upper mold 40. Intrusion into the driven side shaft portion 23 is suppressed.

  When the rising speed of the molten metal surface in the upper mold 40 exceeds 100 mm / second, the molten metal in the lower mold 40 and the cylindrical mold 30 and the molten metal in the upper mold 40 are mixed by the stirring of the molten metal by pouring, The amount of Cr, Mo, V, and Nb in the driving side shaft portion 22 and the trunk core portion 21 mixed into the driven side shaft portion 23 becomes excessive. The rising speed of the molten metal surface in the upper mold 40 is preferably 10 to 100 mm / second, and more preferably 20 to 90 mm / second.

  Not only is the rate of rise of the molten metal surface in the upper mold 40 less than 100 mm / second, but is smaller than the rate of rise of the molten metal surface in the lower mold 50 and the molten metal surface in the cylindrical mold 30 (outer layer 1). By doing so, Cr, Mo, V and Nb in the outer layer 1 can be efficiently mixed in the drive side shaft portion 22 and the trunk core portion 21 and Cr mixed in the drive side shaft portion 22 and the trunk core portion 21 , Mo, V, and Nb can be effectively suppressed from being re-mixed into the driven side shaft portion 23 by the stirring of the molten metal. The rising speed of the molten metal surface in the upper mold 40 is preferably 50 to 150 mm / second smaller than the rising speed of the molten metal surface in the lower mold 50 and the rising speed of the molten metal surface in the cylindrical mold 30 (outer layer 1). Further, the rising speed of the molten metal surface in the lower mold 50 and the rising speed of the molten metal surface in the cylindrical mold 30 (outer layer 1) are not particularly limited as long as there is no problem with pouring, but practically 100 to 200 mm. / Sec is preferred. The rising speed of the molten metal surface in the lower mold 50 and the rising speed of the molten metal surface in the cylindrical mold 30 (outer layer 1) may be the same, or the former may be larger. Here, the rising speed of the molten metal surface in the upper mold 40, the rising speed of the molten metal surface in the lower mold 50, and the rising speed of the molten metal surface in the cylindrical mold 30 (outer layer 1) are average rising speeds respectively. .

  As described above, not only adjusting the content of Cr, Mo, V and Nb contained in the outer layer 1, but also the rising speed of the molten metal surface in the upper mold 40, the rising speed of the molten metal surface in the lower mold 50, and By adjusting the rising speed of the molten metal surface in the cylindrical mold 30 (outer layer 1), it is possible to control the amount of Cr, Mo, V and Nb mixed into the driving side shaft portion 22 and the driven side shaft portion 23. Specifically, the total amount of Cr, Mo, V, and Nb at the end of the drive side shaft portion 22 formed by the lower die 50 where the rising speed of the molten metal surface is large is the driven side shaft formed by the upper die 40. More than the total amount of Cr, Mo, V and Nb at the end of the portion 23, the difference being 0.2 mass% or more. Therefore, the wear resistance of the clutch portion 24 formed at the end of the drive side shaft portion 22 can be improved. On the other hand, the driven side shaft portion 23 has a smaller total amount of Cr, Mo, V and Nb, and therefore can be processed more easily than the drive side shaft portion 22.

  In the present invention, there is a difference in the content of Cr, Mo, V and Nb between one shaft portion and the other shaft portion, and in particular, the drive side shaft portion is harder than the driven side shaft portion. Although it is optimal to provide a difference in the content of the above elements, the driven side shaft portion may have a higher hardness than the drive side shaft portion depending on the use and required performance of the roll.

  FIG. 5 shows another example of a mold used in the method of the present invention. The mold 110 includes a portion 71 corresponding to the cylindrical mold 30 for forming the outer layer 1 and the trunk core portion 21, a portion 72 corresponding to the upper die 40 for forming the driven side shaft portion 23, and a drive side shaft portion 22 formed. This is a mold in which a portion 73 corresponding to the lower mold 50 for use is integrally formed. Reference numerals 71a, 72a, and 73a denote sand molds. Thus, the mold 110 serves as both a centrifugal casting mold and a stationary casting mold. After the outer layer 1 is centrifugally cast using the mold 110, the entire mold 110 having the outer layer 1 formed on the inner surface is erected, and the ductile cast iron melt for the inner layer 2 is poured from the upper opening 74.

  When forming the intermediate layer, after forming the intermediate layer on the inner surface of the outer layer 1, the cylindrical mold 30 is erected in the case of the mold shown in FIG. 4, and the mold 110 is erected in the case of the mold shown in FIG. Then, the molten ductile iron for the inner layer 2 is poured from the upper opening.

  The present invention will be described in detail by the following examples, but the present invention is not limited thereto.

Examples 1-3 and Comparative Examples 1 and 2
A cylindrical mold 30 (inner diameter 800 mm and length 2500 mm) having the structure shown in FIG. 3 was placed in a horizontal centrifugal casting machine, and the outer layer 1 was centrifugally cast using a molten metal having the composition shown in Table 1. After the outer layer 1 is solidified, a cylindrical mold 30 with the outer layer 1 (outer layer thickness 90 mm) formed on the inner surface is erected to form a hollow lower mold 50 (inner diameter 600 mm and length) for forming the drive side shaft portion 22. The cylindrical mold 30 is erected on the 1500 mm), and the hollow upper mold 40 (inner diameter 600 mm and length 2000 mm) for forming the driven shaft portion 23 is erected on the cylindrical mold 30. A stationary casting mold 100 shown in FIG. 4 was constructed.

  A molten ductile iron having the composition shown in Table 1 was poured into the cavity 60 of the stationary casting mold 100 from the upper opening 43. The molten metal surface of the ductile cast iron rises in the order of the lower mold 50 for forming the driving shaft 22, the cylindrical mold 30 for forming the trunk core 21 (outer layer 1), and the upper mold 40 for forming the driven shaft 23. did. In this manner, an integral inner layer 2 including the driving side shaft portion 22, the trunk core portion 21, and the driven side shaft portion 23 was formed inside the outer layer 1.

  After the inner layer 2 was completely solidified, the stationary casting mold 100 was disassembled and the composite roll was taken out and tempered at 500 ° C. Thereafter, the outer layer 1, the driving side shaft portion 22, and the driven side shaft portion 23 were processed into predetermined shapes by machining, and the clutch portion 24 and the convex portion 25 were formed. As a result of performing ultrasonic inspection on each composite roll thus obtained, it was confirmed that the outer layer 1 and the inner layer 2 were welded in a sound manner.

Example 4
After forming an intermediate layer (intermediate layer thickness 20 mm) having the composition shown in Table 1 on the inner surface of the outer layer 1, a composite roll was formed in the same manner as in Example 1 except that the cylindrical mold 30 was erected. As a result of ultrasonic inspection, it was confirmed that the outer layer 1, the intermediate layer, and the inner layer 2 were welded in a sound manner.

  For Examples 1 to 4 and Comparative Examples 1 and 2, the casting temperature of the outer layer, the inner layer and the intermediate layer, and the lower mold 50 for forming the driving side shaft portion 22, the cylindrical mold 30 for forming the trunk portion 21, and the driven side Table 2 shows the average rising speed of the inner layer molten metal surface in the upper mold 40 for forming the shaft portion 23. The average rising speed of the inner layer molten metal surface was calculated by measuring the weight of the inner layer molten metal and measuring the casting time. Further, the Cr, Mo, V, and Nb contents were analyzed for the samples cut out from the end surface 24a of the driving side shaft portion 22 and the end surface 25a of the driven side shaft portion 23. The results are shown in Table 3.

The composite rolls of Examples 1 to 4 and Comparative Examples 1 and 2 were used for rolling in an actual machine with a rolling tonnage of 250,000 tons in the final stand of the hot strip mill finish row of plain steel rolling, and the wear resistance of the clutch portion 24 was Was evaluated according to the following criteria. The results are shown in Table 4.
○: The wear resistance of the clutch part was good.
X: The composite roll could not be used due to excessive wear of the clutch part.

  In Examples 1 to 4, the rising speed of the molten surface of the ductile cast iron in the upper mold 40 for forming the driven side shaft portion 23 is 100 mm / second or less, and the lower mold 50 for forming the driving side shaft portion 22 The rise speed of the melt surface of the ductile cast iron and the rise speed of the melt surface of the ductile cast iron in the cylindrical mold 30 (outer layer 1) for forming the trunk portion 21 were smaller. Therefore, the total amount of Cr, Mo, V and Nb at the end of the drive side shaft portion 22 and the total amount of Cr, Mo, V and Nb at the end of the driven side shaft portion 23 are both 0.15 to 2.0 mass%. It was within the range, and the former was 0.2 mass% or more more than the latter.

  On the other hand, in the comparative examples 1 and 2, the rising speed of the molten iron surface of the ductile iron in the upper mold 40 is the rising speed of the molten iron surface of the ductile iron in the lower mold 50 and the cylindrical mold 30 (outer layer 1). Although it was smaller than the rising speed of the melt surface of the ductile cast iron, it was over 100 mm / sec. Therefore, the total amount of Cr, Mo, V and Nb at the end of the drive side shaft portion 22 and the total amount of Cr, Mo, V and Nb at the end of the driven side shaft portion 23 are both 0.15 to 2.0 mass%. Although within the range, the difference between the two was less than 0.2% by mass.

  Comparing Example 2 and Comparative Example 1 in which the total amount of Cr, Mo, V, and Nb at the end of the drive side shaft 22 is close, Example 2 is the end of the drive side shaft 22 compared to Comparative Example 1. The difference between the total amount of Cr, Mo, V, and Nb in and the total amount of Cr, Mo, V, and Nb at the end of the driven shaft portion 23 was large. Therefore, both of the hardness of the clutch portion 24 of the drive side shaft portion 22 was sufficient, but the driven side shaft portion 23 of Example 2 is good because mixing of Cr, Mo, V and Nb is suppressed. In contrast, the driven side shaft portion 23 of Comparative Example 1 was hard due to the large amount of Cr, Mo, V, and Nb mixed therein, and the machining time was significantly long.

  Similarly, when comparing Example 3 and Comparative Example 2 in which the total amount of Cr, Mo, V, and Nb at the end of the drive side shaft portion 22 is close, the hardness of the clutch portion 24 of the drive side shaft portion 22 is Although sufficient, the driven-side shaft portion 23 of Example 3 had good workability, whereas the driven-side shaft portion 23 of Comparative Example 2 was hard and the processing time was significantly longer.

1 outer layer, 2 inner layer, 10 composite roll, 21 trunk core part, 22 drive side shaft part,
23 Driven shaft, 24 Clutch, 25 Convex, 30 Mold, 40 Upper mold, 50 Lower mold

Claims (6)

A centrifugal cast composite roll in which an outer layer formed by a centrifugal casting method and an inner layer made of ductile cast iron are welded and integrated, wherein the outer layer is at least Cr: 3.0 to 10.0%, Mo: 2.0 to 10.0%, And V: an Fe-based alloy containing a chemical composition containing 5.8 to 10.0%, the inner layer being welded to the outer layer, and a driving side integrally extending from both ends of the trunk core A shaft portion and a driven side shaft portion , the total amount of Cr, Mo and V at both ends of the shaft portion is 0.15 to 2.0 mass%, and Cr, Mo and A centrifugal cast composite roll characterized in that the total amount of V is 0.2 mass% or more greater than the total amount of Cr, Mo and V at the end of the driven shaft portion . A centrifugal cast composite roll in which an outer layer formed by a centrifugal casting method and an inner layer made of ductile cast iron are welded and integrated, wherein the outer layer is at least Cr: 3.0 to 10.0%, Mo: 2.0 to 10.0%, And V and Nb: Fe-based alloy containing a chemical composition containing 6.5 to 10.0% in total, the inner layer integrally extending from the core part welded to the outer layer and both ends of the core part A drive-side shaft portion and a driven-side shaft portion , and the total amount of Cr, Mo, V and Nb at both ends of the shaft portions is 0.15 to 2.0 mass%, and the end portion of the drive-side shaft portion A centrifugal cast composite roll characterized in that the total amount of Cr, Mo, V, and Nb is 0.2 mass% or more greater than the total amount of Cr, Mo, V, and Nb at the end of the driven shaft portion . The composite roll made by centrifugal casting according to claim 1 or 2, wherein the outer layer is further based on mass: C: 1.0 to 3.0%, Si: 0.3 to 2.0%, Mn: 0.1 to 1.8%, and Ni: 0 to 3.5. A composite roll made of centrifugal casting, characterized by containing The composite roll made by centrifugal casting according to any one of claims 1 to 3, wherein the outer layer is further based on mass: W: 0 to 10.0%, Ti: 0.003 to 5.0%, Al: 0.01 to 2.0%, Zr: 0.01 to A composite roll made of centrifugal cast, characterized by containing at least one of 0.5% and Co: 0.1 to 10%. A centrifugal cast composite roll in which an outer layer formed by a centrifugal casting method and an inner layer made of ductile cast iron are welded and integrated, wherein the outer layer is at least Cr: 3.0 to 10.0%, Mo: 2.0 to 10.0%, And V: an Fe-based alloy containing a chemical composition containing 5.8 to 10.0%, wherein the inner layer is welded to the outer layer, and a shaft portion integrally extending from both ends of the trunk core portion. And the total amount of Cr, Mo and V at the ends of both shaft portions is 0.15 to 2.0 mass%, and the sum of Cr, Mo and V between one shaft portion and the other shaft portion In a method for producing a composite roll made by centrifugal casting having a difference in amount of 0.2% by mass or more , (1) centrifugal casting the outer layer with a rotating centrifugal casting cylindrical mold, and (2) the cylindrical shape having the outer layer For standing casting, elevate the mold and provide upper and lower molds communicating with the outer layer at the upper and lower ends respectively. (3) having a step of casting a molten metal for the inner layer into a cavity constituted by the upper mold, the outer layer, and the lower mold, and the rising speed of the molten metal surface in the upper mold is 100 mm The method is characterized by being less than the rising speed of the molten metal surface in the lower mold and the outer layer at a speed of less than / sec. A centrifugal cast composite roll in which an outer layer formed by a centrifugal casting method and an inner layer made of ductile cast iron are welded and integrated, wherein the outer layer is at least Cr: 3.0 to 10.0%, Mo: 2.0 to 10.0%, And V and Nb: Fe-based alloy containing a chemical composition containing 6.5 to 10.0% in total, the inner layer integrally extending from the core part welded to the outer layer and both ends of the core part And the total amount of Cr, Mo, V and Nb at the ends of both shaft portions is 0.15 to 2.0 mass%, and between one shaft portion and the other shaft portion, In the method of producing a composite roll made of centrifugal casting in which the difference in the total amount of Mo, V and Nb is 0.2% by mass or more , (1) centrifugally casting the outer layer with a rotating cylindrical mold for centrifugal casting, (2) The cylindrical mold having the outer layer is erected, and an upper die and a lower die that communicate with the outer layer are provided at the upper and lower ends, respectively. And (3) a step of casting a molten metal for the inner layer into a cavity constituted by the upper mold, the outer layer, and the lower mold, and a molten metal surface in the upper mold The method is characterized in that the ascending speed is 100 mm / second or less and is smaller than the ascending speed of the molten metal surface in the lower mold and the outer layer.