WO2015053137A1

WO2015053137A1 - Superhard alloy composite roll and production method therefor

Info

Publication number: WO2015053137A1
Application number: PCT/JP2014/076214
Authority: WO
Inventors: 大島　昌彦; 拓己大畑; 俊二松本; 裕允小湊
Original assignee: 日立金属株式会社
Priority date: 2013-10-09
Filing date: 2014-09-30
Publication date: 2015-04-16
Also published as: JP6421758B2; JPWO2015053137A1

Abstract

A superhard alloy composite roll having: a superhard alloy outer layer and an iron-based alloy inner layer diffusion-bonded therein; a carbon concentrated layer comprising an iron-based alloy having a higher carbon concentration than an inner layer main body, in a surface area of the inner layer adjacent to the bonding boundary with the outer layer; a carbon concentration of 0.7%-1.2% by mass in said bonding boundary of the carbon concentrated layer; and a thickness of 0.5-6 mm.

Description

Cemented carbide composite roll and manufacturing method thereof

The present invention comprises an outer layer excellent in wear resistance, rough skin resistance, etc. and an inner layer excellent in toughness, and is a highly durable cemented carbide composite roll suitable for rolling steel materials such as plate materials, wire materials, bar materials, And a manufacturing method thereof.

Made of tungsten carbide (WC) cemented carbide with excellent wear resistance, rough skin resistance, etc., to meet the demands for higher quality of rolled materials, such as improved dimensional accuracy, and improved productivity by reducing the number of roll change man-hours. Rolls for rolling are used, and cemented carbide rolling rolls having various structures have been proposed.

For example, as shown in FIG. 11, Japanese Patent Laid-Open No. 3-281007 discloses a roll body 105 having a fastening flange portion 103 fixed at both ends and a detachable fastening flange portion 104, and a thermal expansion coefficient of 15 ×. A cemented carbide cylinder fitted to the roll body 105 via

metal ring spacers

111 and 111 and a cylindrical spacer 114 having a thermal conductivity of 0.4 cal / cm · sec · ° C or higher at 10 ^-6 / ° C or higher. A cemented carbide rolling roll having a body 110 is proposed. The tightening force of the tightening

flange portions

103 and 104 is improved by utilizing the thermal expansion of the

ring spacers

111 and 111. However, even with the ring-

shaped spacers

111 and 111 and the cylindrical spacer 114, the adhesion between the cemented carbide cylinder 110 and the roll body 105 is not sufficient with the tightening force by the tightening

flange portions

103 and 104. In addition, the cemented carbide cylindrical body 110 may slip with respect to the roll body 105 during rolling.

In order to solve the problem of the cemented carbide rolling roll having such an assembly structure, a cemented carbide composite roll in which a cemented carbide outer layer and a metal inner layer are diffusion-bonded has been proposed. For example, JP 2001-47111 A discloses a cemented carbide composite roll in which an outer layer member made of a WC-based cemented carbide is metal-bonded to the outer periphery of an inner layer member made of a material having excellent toughness. A cemented carbide composite roll is proposed in which a WC-based cemented carbide intermediate layer having a lower content than the outer layer is provided, and the inner layer member and the intermediate layer are joined via a metal layer. Japanese Patent Laid-Open No. 2001-47111 discloses that the WC has a gradient concentration from the outer layer member to the inner layer member and the physical properties such as the coefficient of thermal expansion and the elastic coefficient are continuously applied from the outer layer member to the inner layer member. It is described that the strength of the boundary joint is improved.

JP 2004-167501 is a cemented carbide composite roll in which a cemented carbide outer layer member is joined to the outer periphery of a steel or iron alloy inner layer member, and has a Young's modulus between the inner layer member and the outer layer member. A composite roll for rolling made of cemented carbide characterized by providing an intermediate layer of 190 GPa or less is proposed. Japanese Patent Laid-Open No. 2004-167501 absorbs strain between the outer layer and the inner layer by setting the Young's modulus of the intermediate layer to 190 GPa or less, and even if the thermal expansion coefficient difference between the outer layer and the inner layer is large, it is excessive in the roll. No residual stress is generated, and it is described that it is possible to avoid and avoid the problem of separation of the boundary joint during roll production. Japanese Patent Application Laid-Open No. 2004-167501 exemplifies Invar alloy and SUS304 as the material of the intermediate layer.

JP 2003-275809 has proposed a composite roll for rolling in which a WC cemented carbide outer layer is directly metal-bonded to the outer periphery of an iron alloy inner layer containing 0.5 mass% or more of C. Japanese Unexamined Patent Publication No. 2003-275809 describes that the obtained cemented carbide composite roll does not have a fragile η phase at the boundary joining portion and has high joining reliability.

However, cemented carbide composite rolls described in JP-A-2001-47111, JP-A-2004-167501, and JP-A-2003-275809, in which a cemented carbide outer layer having excellent wear resistance and an iron-based alloy inner layer are joined. It has been found that there is a possibility that the bonding reliability between the outer layer and the inner layer may not be sufficient to increase the size of the roll as in a hot sheet rolling roll having an outer diameter of 300 mm or more and a roll length of 500 mm or more. Further, when used in more severe rolling conditions, higher bonding strength between the outer layer and the inner layer is required.

Accordingly, an object of the present invention is a cemented carbide composite roll comprising a cemented carbide outer layer excellent in wear resistance, rough skin resistance, and the like and an iron-based alloy inner layer excellent in toughness, both of which have extremely high joint strength. And an efficient manufacturing method thereof.

As a result of earnest research in view of the above-mentioned purpose, by providing a C-enriched layer in advance on the surface of the iron-based alloy inner layer, the outer layer and the inner layer are strengthened without forming a fragile η phase at the joint boundary. It was discovered that they were joined, and the present invention was conceived.

That is, the cemented carbide composite roll of the present invention is a cemented carbide outer layer and an iron-based alloy inner layer that are diffusion-bonded, and the inner layer body in the surface layer region of the inner layer adjacent to the bonding boundary with the outer layer. It has a C-enriched layer made of an iron-based alloy having a higher C concentration.

The thickness of the C concentrated layer is preferably 0.5 to 6 mm.

The C concentration at the junction boundary of the C concentrated layer is preferably 0.7 to 1.2% by mass. It is preferable that the C concentration in the C-concentrated layer gradually decreases from the joining boundary toward the inner layer main body. The reduction rate of the C concentration in the depth direction in the C enriched layer is preferably 0.01% / mm or more.

The tensile strength at the boundary between the outer layer and the inner layer is preferably 600 MPa or more.

The cemented carbide outer layer preferably contains 70 to 88% by mass of WC particles.

In the cemented carbide composite roll of the present invention, the C concentration of the iron-based alloy inner layer body is preferably 0.2 to 0.5% by mass.

The iron-based alloy inner layer preferably contains 1.0% by mass or more in total of at least one selected from the group consisting of Cr, Ni, Mo, V, W, Ti and Nb.

The method of the present invention for producing a cemented carbide composite roll in which a cylindrical outer layer member made of a cemented carbide and an inner layer member made of an iron-based alloy are joined is obtained by carburizing the outer surface of the inner layer member. The member and the inner layer member are diffusion bonded.

The thickness of the carburized layer formed by the carburizing process is preferably 0.5 to 10 mm.

It is preferable to perform the carburizing process by a gas carburizing process.

The inner layer member is disposed inside the outer layer member, and a hollow cylindrical restraining member having a smaller coefficient of thermal expansion than the outer layer member is disposed outside the outer layer member in a temperature range from room temperature to a bonding temperature. The outer layer member, the inner layer member, and the outer layer member so that the outer surface of the inner layer member that is most thermally expanded presses the inner surface of the outer layer member, and the inner surface of the restraining member that is not thermally expanded presses the outer surface of the outer layer member. It is preferable that a gap with the restraining member is set, and the inner surface of the outer layer member and the outer surface of the inner layer member are brought into close contact with each other by heating, so that the outer layer member and the inner layer member are diffusion bonded.

It is preferable that both end portions in the axial direction of the restraining member protrude from both end surfaces in the axial direction of the outer layer member.

It is preferable that the restraining member is thicker than the outer layer member.

The restraining member is preferably made of graphite or ceramics.

It is preferable that the restraining member is formed by coaxially stacking a plurality of ring members.

It is preferable that a reaction preventing material is interposed between the restraining member and the outer layer member.

In the cemented carbide alloy composite roll of the present invention, the cemented carbide outer layer and the iron-based alloy inner layer are joined via the C-concentrated layer, so the joining strength between the outer layer and the inner layer is high. Therefore, even a large rolling roll having an outer diameter of 300 mm or more and a roll length of 500 mm or more can be used for long-term rolling. In addition, when the inner layer member made of an iron-based alloy and the outer layer made of a cemented carbide alloy that have been carburized in advance in the surface layer region are joined by the diffusion joining method or the HIP method, a joining boundary without a fragile η phase can be formed. A cemented carbide composite roll in which an alloy outer layer and an iron-based alloy inner layer are firmly bonded can be obtained.

It is a fragmentary sectional front view which shows the cemented carbide composite roll of this invention. It is a graph which shows C concentration distribution of the cemented carbide composite roll of this invention. It is a flowchart which shows the manufacturing process of the cemented carbide composite roll of this invention. It is sectional drawing which shows the example which manufactures the cemented carbide composite roll of this invention by the diffusion bonding method. FIG. 4 (a) is an enlarged view of a portion A in the bag. It is sectional drawing which shows the diffusion bonding method using the constraining member comprised by the some ring member piled up coaxially. It is sectional drawing which shows the example which manufactures the cemented carbide composite roll of this invention by HIP method. 2 is a cross-sectional view showing a joining experiment of Example 1. FIG. It is a front view which shows a tension test piece. 2 is a graph showing a C concentration distribution from the surface to the inside in the carburized layer of Example 1. FIG. 4 is a graph showing the C concentration distribution from the joining boundary to the inside of the inner layer for joining test pieces 4 and 5 of Example 1. FIG. FIG. 3 is a partial cross-sectional view showing a cemented carbide rolling roll disclosed in Japanese Patent Laid-Open No. 3-281007.

The present invention will be described in detail below with reference to the accompanying drawings. However, the present invention is not limited to these, and can be appropriately changed or improved without departing from the technical idea of the present invention. The description relating to one embodiment of the present invention also applies to other embodiments unless otherwise specified.

[1] Cemented carbide composite roll A cemented carbide composite roll 10 of the present invention that can be used for rolling a rolled material such as steel is composed of a cemented carbide outer layer 1 and a ferrous alloy as shown in FIG. The inner layer 2 is made of an alloy, and a C concentrated layer 3 is provided at the boundary between the outer layer 1 and the inner layer 2. The C-enriched layer is an iron-based alloy having a C concentration of 0.6% by mass or more and has a higher C concentration than the inner layer 2. The outer layer 1 whose surface is in contact with the material to be rolled is required to have excellent wear resistance, rough skin resistance and mechanical strength, and the inner layer 2 constituting the roll shaft whose both ends are supported by bearings (not shown) is a high machine. Strength and toughness are required.

(1) Outer layerThe cemented carbide outer layer 1 of the cemented carbide composite roll of the present invention is a sintered alloy in which hard WC particles are bonded with a metal such as Co, Ni, Cr, Fe, etc. Carbides such as Ta and Nb may be contained. Since the outer layer 1 has high wear resistance and mechanical strength, the average particle size of the WC particles is preferably 3 to 10 μm, the content of the WC particles is preferably 70 to 88% by mass, and more preferably 72 to 85% by mass. preferable. The thickness of the outer layer 1 is preferably set in the range of 5 to 50 mm in consideration of gradual wear due to rolling.

(2) Inner layer The iron-based alloy of the inner layer 2 is preferably steel. In order for inner layer 2 to have sufficient toughness, 0.2 to 0.5 mass% of C and 1.0 mass% or more in total of at least one selected from the group consisting of Cr, Ni, Mo, V, W, Ti and Nb Steel is preferred. When C is less than 0.2% by mass, the inner layer 2 does not have sufficient strength. On the other hand, if C exceeds 0.5% by mass, the toughness of the inner layer 2 is insufficient. The content of other elements may be within the general composition range of steel materials.

Since the inner layer 2 has a larger thermal expansion coefficient than the outer layer 1 made of a cemented carbide having a small thermal expansion coefficient, it needs a transformation expansion characteristic to relieve strain generated by the thermal expansion. If this transformation is a pearlite transformation, due to plastic deformation at a high temperature, a large strain is generated due to a difference in thermal expansion coefficient in the process of cooling to room temperature, which causes roll breakage. For this reason, this transformation must be a bainite transformation or a martensitic transformation that occurs at low temperatures. For this reason, it is preferable that the inner layer contains 1.0% by mass or more in total of at least one selected from the group consisting of Cr, Ni, Mo, V, W, Ti, and Nb. In particular, the Cr content is preferably 0.5 to 1.5 mass%, the Mo content is preferably 0.1 to 0.5 mass%, and the Ni content is preferably 1.5 to 2.5 mass%.

(3) C-enriched layer When the cemented carbide outer layer 1 and the iron-based alloy inner layer 2 are sintered and bonded, the carbon is changed from the cemented carbide outer layer 1 to the inner layer 2 at the bonding interface due to the difference in carbon activity between the two. It is known that the carbon concentration in the outer layer 1 made of cemented carbide decreases due to diffusion. As a result, a η phase, which is a carbide having a low carbon composition, is generated in the cemented carbide and the mechanical strength of the cemented carbide is deteriorated.

As a result of the joining experiment of the outer layer 1 made of cemented carbide and the inner layer 2 made of iron alloy, a C concentrated layer 3 having a C concentration of 0.6% by mass or more was formed near the surface of the inner layer 1 to be joined with the outer layer 1 made of cemented carbide. It has been found that if formed, the diffusion of C from the cemented carbide outer layer 1 to the inner layer 2 can be substantially suppressed, thereby preventing the generation of η phase. Furthermore, since the C enriched layer 3 may be formed very close to the inner layer 2, the toughness of the iron-based alloy inner layer 2 is not impaired.

Thus, by providing the C-concentrated layer 3 near the surface (surface layer) of the inner layer 2 that becomes the boundary with the outer layer 1, the outer diameter of the outer layer 1 is 300 mm or more and the roll length is 500 mm or more. It is possible to obtain a cemented carbide composite roll 10 having an excellent bonding strength.

FIG. 2 shows the C concentration distribution in the region including the C concentrated layer of the cemented carbide composite roll 10 of the present invention. In FIG. 2, the horizontal axis represents the distance from the boundary with the outer layer 1 (the origin is the junction boundary with the outer layer 1), and the vertical axis represents the C concentration. In the cemented carbide composite roll 10 of the present invention, a layer having a C concentration of 0.6% by mass or more from the boundary with the outer layer 1 toward the inner layer 2 is referred to as a C concentrated layer 3. The thickness of the C concentrated layer 3 is preferably 0.5 to 10 mm. If the thickness of the C concentrated layer 3 is less than 0.5 mm, C diffuses to the inner layer 2 side when bonded to the outer layer 1 and the C concentration of the C concentrated layer 3 becomes too low, and the cemented carbide of the outer layer 1 Since the η phase may occur in the inside, it is not preferable. On the other hand, if the thickness of the C enriched layer 3 exceeds 10 mm, the time for carburizing treatment for forming the C enriched layer 3 becomes longer, which is not preferable because the manufacturing cost increases.

In the C concentrated layer 3 of the cemented carbide composite roll 10 of the present invention, when the range from the boundary with the outer layer 1 to 0.5 mm is defined as a region adjacent to the outer layer 1, the C concentration in the adjacent region of the outer layer is 0.7 to 1.2. It is preferable that it is mass%. If the C concentration in the adjacent region of the outer layer is 0.7% by mass or more, there is almost no diffusion of C from the outer layer 1 made of cemented carbide to the inner layer 2, and the generation of η phase in the outer layer 1 made of cemented carbide can be reliably prevented. , The strength reduction can be prevented. On the other hand, if the C concentration in the adjacent region of the outer layer exceeds 1.2% by mass, graphite is generated at the joining boundary, and the strength is lowered, which is not preferable.

In the C enriched layer 3, it is preferable that the C concentration gradually decreases from the boundary with the outer layer 1 toward the inner layer 2. As the physical properties such as Young's modulus, thermal expansion coefficient, and hardness continuously change from the joining boundary toward the inner layer 2, the joining reliability increases.

The tensile strength at the boundary between the outer layer 1 and the inner layer 2 is preferably 600 MPa or more, more preferably 700 MPa or more so that the outer layer 1 and the inner layer 2 do not peel even when used for a long time in rolling. The tensile strength at the boundary between the outer layer 1 and the inner layer 2 can be measured by a tensile test of a test piece including the boundary between the outer layer 1 and the inner layer 2.

[2] Manufacturing method of cemented carbide composite roll
(1) Carburizing treatment FIG. 3 shows a manufacturing process of the cemented carbide composite roll 10 of the present invention. First, carburizing treatment is performed on the outer peripheral surface of a columnar or cylindrical inner layer member 12 made of an iron-based alloy. A solid carburizing method, a liquid carburizing method, or a gas carburizing method can be used for the carburizing treatment, but a gas carburizing method is preferable in order to form a uniform carburized layer. The carburized layer 13 becomes the C concentrated layer 3 after being joined to the outer layer 1, and the C concentration is preferably 0.7 to 1.2% by mass on the outermost surface (outer layer adjacent region). When the C concentration on the surface of the carburized layer 13 is less than 0.7 mass%, the bonding strength with the outer layer 1 is insufficient, and the C concentrated layer 3 may not be formed. On the other hand, if the C concentration on the surface of the carburized layer 13 exceeds 1.2% by mass, graphite may be generated at the bonding boundary with the outer layer, resulting in a decrease in bonding strength. In the carburized layer 13, the C concentration gradually decreases from the surface toward the inside of the inner layer 2.

The thickness of the carburized layer 13 is preferably 0.5 to 10 mm. When the thickness of the carburized layer 13 is less than 0.5 mm, not only the bonding strength with the outer layer is insufficient, but also the C concentrated layer 3 may not be formed at the bonding boundary. On the other hand, it takes an excessive amount of time to form the carburized layer 13 having a thickness of more than 10 mm, which increases the manufacturing cost. A preferable thickness of the carburized layer 13 is 2 to 5 mm.

(2) Joining The outer layer member 11 made of cemented carbide is joined to the inner layer member 12 on which the carburized layer 13 is formed. The joining method is not limited as long as the inner layer member 12 and the outer layer member 11 are joined without a gap, but a diffusion joining method and a hot isostatic pressure (HIP) method are preferably used.

(a) Diffusion Bonding Method FIG. 4 shows a method for producing the cemented carbide composite roll of the present invention by the diffusion bonding method. As shown in FIG. 4, an inner layer member (corresponding to a roll shaft) 12 whose surface is carburized is placed on a base 8. After the cylindrical cradle 9 is placed on the base 8 so as to surround the inner layer member 12, the cylindrical outer layer member 11 is placed on the cylindrical cradle 9. The cradle 9 is preferably made of a material that is inactive with respect to the outer layer member 11, similarly to the restraining member described later. Specifically, the cradle 9 is preferably made of graphite or ceramics. Next, the cylindrical restraining member 16 having a smaller coefficient of thermal expansion than the outer layer member 11 is placed on the base 8 so as to surround the outer layer member 11.

The inner layer member 12, the outer layer member 11, and the restraining member 16 arranged in this way are heated in an inert atmosphere to perform diffusion bonding between the outer layer member 11 and the inner layer member 12. The diffusion bonding temperature is preferably 1000 to 1280 ° C. If the diffusion bonding temperature is less than 1000 ° C, sufficient bonding strength may not be obtained. If the diffusion bonding temperature exceeds 1280 ° C, a η phase is generated in the cemented carbide near the bonding interface, and the bonding strength is reduced. descend. The diffusion bonding temperature is more preferably 1100 to 1280 ° C, and most preferably 1200 to 1260 ° C. The time for maintaining the diffusion bonding temperature may be about 1 to 120 minutes, preferably 30 to 90 minutes. As the inert atmosphere, an inert gas such as N ₂ or Ar, a reducing gas such as H ₂ , or a vacuum can be used.

In the temperature range from room temperature to the diffusion bonding temperature of 1000 to 1280 ° C., the thermal expansion coefficients of the inner layer member 12, the outer layer member 11, and the restraining member 16 must satisfy the relationship of inner layer member 12> outer layer member 11> restraining member 16. Don't be. The thermal expansion coefficient of the iron alloy inner layer member 12 in the range from room temperature to 1000 to 1280 ° C. is about 11 to 15 × 10 ⁻⁶ / ° C., and the thermal expansion coefficient of the cemented carbide outer layer member 11 is 6 About 10 × 10 ^-6 / ° C. Therefore, the thermal expansion coefficient of the restraining member 16 must be sufficiently smaller than these in the temperature range from room temperature to the diffusion bonding temperature.

In order to satisfy such a thermal expansion coefficient condition, the restraining member 16 is preferably made of graphite or ceramics having a thermal expansion coefficient of about 4 to 9 × 10 ⁻⁶ / ° C. Further, the restraining member 16 must sufficiently withstand the diffusion bonding temperature and the diffusion bonding stress, and therefore must have high strength and high rigidity at the diffusion bonding temperature. Furthermore, the restraining member 16 is preferably made of a material that is not bonded to the cemented carbide at the diffusion bonding temperature. Graphite or ceramics also satisfy these conditions. Among them, isotropic graphite having a thermal expansion coefficient of 6 × 10 ⁻⁶ / ° C. or less and a bending strength at 1000 ° C. of 30 MPa or more is particularly preferable.

In consideration of such a difference in coefficient of thermal expansion, the outer surface of the inner layer member 12 that is most thermally expanded by heating sufficiently presses the inner surface of the outer layer member 11, and the inner surface of the restraining member 16 that is least thermally expanded is the outer layer member 11. It is necessary to set a gap G ₁ between the inner layer member 12 and the outer layer member 11 and a gap G ₂ between the outer layer member 11 and the restraining member 16 so as to sufficiently press the outer surface of the member [see FIG. 4 (b)]. . For example, the diameter of the steel inner layer member 12 (thermal expansion coefficient: 13 × 10 ⁻⁶ / ° C.) is 275 mm and the outer layer member 11 made of cemented carbide (thermal expansion coefficient: 8 × 10 ⁻⁶ / ° C.) When the thickness is 69 mm, the gap G ₁ between the outer layer member 11 and the inner layer member 12 is preferably 0.3 to 1.5 mm, and the gap G ₂ between the outer layer member 11 and the restraining member 16 is 1 to 2 mm. Preferably there is. For example, the inner diameter of outer layer member 11 is preferably 276 mm (G ₁ = 1 mm), and the inner diameter of graphite constraining member 16 (thermal expansion coefficient: 5.5 × 10 ⁻⁶ / ° C.) is preferably 346.5 mm (outer layer member 11 ) Because the outer diameter of 345 mm is G ₂ = 1.5 mm).

As described above, the restraint member 16 having a smaller coefficient of thermal expansion than the outer layer member 11 is disposed outside the outer layer member 11, and the thermal expansion of the outer layer member 11 and the inner layer member 12 is restrained by the restraint member 16, so that the inner layer that is most thermally expanded. The outer surface of the member 12 is in close contact with the inner surface of the outer layer member 11 with a surface pressure (bonding surface pressure) necessary for diffusion bonding. This makes it possible to obtain a cemented carbide composite roll with good bonding reliability even when the outer diameter is 300 mm or more and the roll length is 500 mm or more.

As shown in FIG. 4 (a), long the preferably than the total length L ₁ of the total length L ₃ is the outer layer member 11 of the restraining member 16, also the axial end faces 6a of the restraining

member

16, 6b are axial outer member 11 It is preferable that the length D projects from both end faces 1a and 1b. Accordingly, since the outer member 11 can be uniformly constrained between axially opposite ends, uniformly diffusion bonding to the inner layer member 12 over the entire length L ₁ of the outer member 11. For example, when the total length L ₂ of the inner layer member 12 is 800 mm and the total length L ₁ of the outer layer member 11 is 700 mm, D is preferably 10 to 100 mm.

Since the restraining member 16 must sufficiently restrain the outer layer member 11 without being deformed or damaged at the diffusion bonding temperature, it is preferable that the restraining member 16 is sufficiently thicker than the outer layer member 11 in the radial direction. For example, when the diameter T ₂ of the inner layer member 12 is 275 mm and the thickness T ₁ of the outer layer member 11 is 35 mm, the thickness T ₃ of the restraining member 16 is preferably 100 to 150 mm.

As shown in FIG. 5, the constraining member 16 can be configured by stacking a plurality (six in the illustrated example) of relatively short ring members 61 to 66 coaxially in the axial direction. Since the thermal expansion restraining force of the restraining member 16 acts in the radial direction, even if the ring members 61 to 66 separated in the axial direction are used, the thermal expansion restraining effect is the same. Of course, each of the ring members 61 to 66 is preferably made of graphite or ceramics. When manufacturing a cemented carbide composite roll having a length of 500 mm or more, it is preferable to use a plurality of ring members 61 to 66 from the viewpoint of ease of manufacturing.

It is preferable to interpose a reaction preventing material between the restraining member 16 and the outer layer member 11 so that the reaction does not occur even when contacting the outer layer member 11 at the diffusion bonding temperature. As the reaction preventing material, ceramics such as alumina having low reactivity with the outer layer member 11 is preferable. The reaction inhibitor may be in the form of powder or woven fabric. In the case of powder, the slurry may be applied to the outer surface of the outer layer member 11 or the inner surface of the restraining member 16. In the case of a woven fabric shape, the outer layer member 11 may be wound around the outer periphery.

When the outer layer member 11 and the inner layer member 12 are diffusion bonded, the outer layer member 11 becomes the outer layer 1 and the inner layer member 12 becomes the inner layer 2. Further, the carburized layer 13 of the inner layer member 12 becomes the C concentrated layer 3. Thereafter, the restraining member 16 is removed to obtain a cemented carbide composite roll 10 in which the outer layer 1 and the inner layer 2 are integrated. If necessary, a desired portion of the cemented carbide composite roll 10 is machined to obtain a dimension and shape suitable for hot sheet rolling.

(b) Hot isostatic pressure (HIP) method As shown in FIG. 6, an iron-based alloy obtained by putting a cylindrical outer layer member 11 into a cylindrical HIP can body 20 a and then carburizing inside the cylindrical outer layer member 11. The inner layer member 12 is disposed, the

donut plates

20b, 20b covering the end surface of the outer layer member 11 are welded to the cylindrical HIP can body 20a, and the

cup portions

20c, 20c covering the inner layer member 12 are further attached to the

donut plates

20b, 20b. Weld and depressurize the resulting HIP can. Then, the HIP can is put into the HIP device and the HIP process is performed. The HIP temperature is preferably 1100 to 1300 ° C., and the HIP pressure is preferably 100 to 140 MPa.

The outer layer member 11 and the inner layer member 12 are firmly joined by HIP, the outer layer member 11 becomes the outer layer 1, and the inner layer member 12 becomes the inner layer 2. Further, the carburized layer 13 of the inner layer member 12 becomes the C concentrated layer 3. After cooling, the HIP can 20 is removed by machining to obtain a cemented carbide composite roll 10 in which the outer layer 1 and the inner layer 2 are integrated. Also in this case, a desired portion of the cemented carbide composite roll 10 may be machined as necessary. Instead of providing the carburized layer 13, the gap between the outer layer member 11 and the inner layer member 12 may be filled with a powder having a high C concentration. Examples of such high C concentration powder include WC ₅₀ -Co ₅₀ cemented carbide.

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

Example 1
Using a cemented carbide having the composition shown in Table 1, a cylindrical outer layer test piece 31 having an outer diameter of 20 mm and a thickness of 20 mm shown in FIG. 7 was produced. Further, a disk-shaped inner layer test piece 32 having an outer diameter of 30 mm and a thickness of 10 mm shown in FIG. 7 was prepared using an iron-based alloy having the composition shown in Table 2. The inner layer test piece 32 was subjected to gas carburizing treatment to form a carburized layer 13 having a target depth of 4 mm and a target C concentration of 0.75 to 0.9% by mass on the surface. FIG. 9 shows the C concentration distribution from the surface to the inside of the carburized layer 13. The C concentration was measured by cutting out a small sample from the test piece 32 and using a carbon analyzer. As a result of the measurement, the thickness of the carburized layer was about 4 mm, and the maximum value of C concentration (concentration on the surface) was 0.92% by mass. The surface layer portion of the carburized layer 13 was removed by machining to a depth of 0.2 mm.

Notes: (1) The average particle size of the WC particles was 5 μm.

The outer layer test piece 31 and the inner layer test piece 32 are stacked as shown in FIG. 7, and after being placed in a graphite jig 34, they are pressurized from above in a vacuum, diffusion bonded under the conditions shown in Table 3, and bonded test pieces 1 ~ 5 was obtained. Each bonding test piece 1 to 5 was cut and the bonding interface was observed. For the bonding specimens 4 and 5, the C concentration distribution from the bonding boundary to the inner layer was examined. The results are shown in FIG. In Table 3, the C-concentrated layer means that the C concentration is in the range of 0.6% by mass or more.

Note: (1) C concentration on the outermost surface.
(2) C concentration at the boundary with the outer layer.

The η phase at the bonding interface between the inner layer test piece 32 and the outer layer test piece 31 was not observed in the bonding test pieces 1 to 4, but was confirmed in the bonding test piece 5.

Example 2
An outer layer test piece 31 ′ having a composition shown in Table 1 having a diameter of 25 mm × a length of 75 mm and an inner layer test piece 32 ′ made of an iron-based alloy having a composition shown in Table 2 having a diameter of 25 mm × a length of 75 mm (implemented) A carburized layer 13 was formed under the same conditions as in Example 1.). After placing the outer layer test piece 31 ′ and the inner layer test piece 32 ′ in the graphite jig 34 as shown in FIG. 7, the jig 34 is pressed from above in vacuum, and diffusion bonding is performed under the conditions shown in Table 4. The test specimens 1 ′ to 5 ′ were prepared.

A tensile test piece 40 having a shape shown in FIG. 8 (consisting of an outer layer test piece part 41 and an inner layer test piece part 42 having a boundary in the center between the gauge points) was prepared from each of the joining test pieces 1 ′ to 5 ′. . The outer layer test piece portion 41 was formed from the outer layer test piece 31 ', and the inner layer test piece portion 42 was formed from the inner layer test piece 32'. The diameter of the tensile test piece 40 was 6.3 mm, and the gauge distance was 19 mm.

For each of the obtained tensile test pieces 1 to 5 (corresponding to the joining test pieces 1 'to 5'), the tensile strength at the joining boundary was measured by a tensile test. The results are shown in Table 4. As is apparent from Table 4, the tensile strength at the boundary between the outer layer test piece portion 41 and the inner layer test piece portion 42 was 600 MPa or more for the tensile test pieces 1 to 4, but 530 MPa for the tensile test piece 5 It was low. This is considered to be because the η phase was formed at the bonding interface in the bonding test piece 5 '.

Example 3
Using a ferrous alloy having the composition shown in Table 2, a roll shaft-shaped inner layer member 12 having an outer diameter of 276 mm and a total length of 1930 mm was produced. A carburized layer 13 having a target thickness of 4 mm and a target C concentration of 0.75 to 0.9% by mass was formed on the surface of the inner layer member 12 by a gas carburizing method. A test piece was collected from the end of the inner layer member 12, and the C concentration was measured in the depth direction of the carburized layer 13. As a result, it was found that the C concentration distribution was the same as in FIG. Thereafter, the carburized layer 13 was removed by machining by a depth of 0.5 mm.

Further, a hollow cylindrical outer layer member 11 having an outer diameter of 364 mm, an inner diameter of 276 mm, and a total length of 680 mm was manufactured using a cemented carbide having the composition shown in Table 1. Further, a graphite hollow cylindrical restraining member 16 having an outer diameter of 600 mm, an inner diameter of 365.5 mm, and a total length of 800 mm was produced.

As shown in FIG. 4, the inner layer member 12 on which the carburized layer 13 is formed is disposed on the graphite base 8, and the outer layer member 11 is disposed on the outer periphery of the inner layer member 12 with a gap G ₁ (= 1.0 mm). A restraining member 16 was disposed on the outer periphery of the outer layer member 11 with a gap G ₂ (= 1.5 mm). In this arrangement, it was placed in a vacuum furnace and held at 1250 ° C. for 60 minutes for diffusion bonding to produce a cemented carbide composite roll 10.

The end portions of the outer layer 1 and the inner layer 2 in the cemented carbide composite roll 10 were visually inspected, and the entire bonding surface was inspected. As a result, no boundary defect was observed over the entire bonding surface. Further, no peeling between the outer layer 1 and the inner layer 2 was observed.

1: Outer layer
2: Inner layer
3: C thickened layer
8: Base
9: cradle
10: Cemented carbide composite roll
11: Outer layer member
12: Inner layer member
13: Carburized layer
16: Restraint member
20: HIP can
31: Outer layer specimen
32: Inner layer specimen
34: Graphite jig
61-66: Ring member for restraint member
L ₁ : Length of outer layer member
L ₂ : Length of inner layer member
L ₃ : Length of restraint member
D: Length of the restraining member extending from each end of the outer layer member
T ₁ : Thickness of outer layer member
T ₂ : Diameter of inner layer member
T ₃ : Thickness of restraining member
G ₁ : Gap between the outer layer member and the inner layer member
G ₂ : Gap between the outer layer member and the restraining member

Claims

In a cemented carbide composite roll in which a cemented carbide outer layer and an iron-based alloy inner layer are diffusion-bonded, an iron-based alloy having a C concentration higher than that of the inner layer main body in a surface layer region of the inner layer adjacent to a bonding boundary with the outer layer A cemented carbide composite roll having a C-concentrated layer made of
2. The cemented carbide composite roll according to claim 1, wherein the C concentrated layer has a thickness of 0.5 to 6 mm.
3. The cemented carbide composite roll according to claim 1, wherein the C concentration at the joining boundary of the C concentrated layer is 0.7 to 1.2% by mass.
The cemented carbide composite roll according to any one of claims 1 to 3, wherein the C concentration in the C concentrated layer gradually decreases from the joining boundary toward the inner layer main body. Hard alloy composite roll.
5. The cemented carbide composite roll according to claim 4, wherein a reduction rate of the C concentration in the depth direction in the C concentrated layer is 0.01% / mm or more.
6. The cemented carbide composite roll according to claim 1, wherein a tensile strength at a boundary between the outer layer and the inner layer is 600 層 MPa or more.
7. The cemented carbide composite roll according to claim 1, wherein the cemented carbide outer layer contains 70 to 88% by mass of WC particles.
8. The cemented carbide composite roll according to claim 1, wherein the iron-based alloy inner layer body has a C concentration of 0.2 to 0.5 mass%.
The cemented carbide composite roll according to any one of claims 1 to 8, wherein the iron-based alloy inner layer includes at least one selected from the group consisting of Cr, Ni, Mo, V, W, Ti and Nb in total. A cemented carbide composite roll containing 1.0% by mass or more.
In a method of manufacturing a cemented carbide composite roll in which a cylindrical outer layer member made of cemented carbide and an inner layer member made of an iron-based alloy are joined, after carburizing the outer surface of the inner layer member, the outer layer member and the A method comprising diffusion bonding an inner layer member.
11. The method for producing a cemented carbide composite roll according to claim 10, wherein a thickness of the carburized layer formed by the carburizing treatment is 0.5 to 10 mm.
12. The method for producing a cemented carbide composite roll according to claim 10, wherein the carburizing treatment is performed by a gas carburizing treatment method.
The method for producing a cemented carbide composite roll according to any one of claims 10 to 12,
Arranging the inner layer member inside the outer layer member,
A hollow cylindrical restraining member having a smaller coefficient of thermal expansion than the outer layer member in a temperature range from room temperature to a bonding temperature is disposed outside the outer layer member,
The outer layer member and the inner layer member are configured such that the outer surface of the inner layer member that is most thermally expanded by heating presses the inner surface of the outer layer member, and the inner surface of the restraining member that is not thermally expanded presses the outer surface of the outer layer member. And setting a gap with the restraining member,
A method wherein the inner surface of the outer layer member and the outer surface of the inner layer member are brought into close contact with each other by heating, whereby the outer layer member and the inner layer member are diffusion bonded.
14. The method for producing a cemented carbide composite roll according to claim 13, wherein both end portions in the axial direction of the restraining member protrude from both end surfaces in the axial direction of the outer layer member.
15. The method for producing a cemented carbide composite roll according to claim 13, wherein the restraining member is thicker than the outer layer member.
16. The method for producing a cemented carbide composite roll according to claim 13, wherein the restraining member is made of graphite or ceramics.
The method for producing a cemented carbide composite roll according to any one of claims 13 to 16, wherein a reaction preventing material is interposed between the restraining member and the outer layer member.