Outer layer material for hot rolling rolls and composite rolls for hot rolling

Abstract

To provide a hot-rolling roll outer layer material with excellent resistance to skin roughness and wear resistance.SOLUTION: A hot-rolling roll outer layer material has a composition satisfying: a mixed entropy ΔSmix of 0.0110 kJ / (mol×K) or more, expressed by a predetermined formula (1); a mixed enthalpy ΔHmix of -25.0 kJ / mol or more and 5.0 kJ / mol or less, expressed by a predetermined formula (2); and an average melting point Tm,ave of 1830K or less, expressed by a predetermined formula (3).SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an outer layer material for rolling rolls and a composite roll for rolling, both suitable for hot rolling. [Background technology]

[0002] In recent years, the demand for high-quality steel sheets has increased, and consequently, there is a need to improve hot rolling technology for steel sheets. Therefore, there is a strong demand for improved characteristics of hot rolling rolls used in hot rolling equipment that come into contact with the steel sheets, particularly improved wear resistance. To solve these problems and improve wear resistance, high-speed steel rolls are used, which are based on high-speed steel, a type of tool steel, and contain carbide-forming elements such as V, Cr, Mo, and W. These rolls incorporate large amounts of hard carbides such as V-type MC carbides, Mo and W-type M2C carbides, and Cr-type M7C3 carbides (where M represents the metallic element that forms the carbide), thereby improving hardness.

[0003] Conventionally, various technologies have been disclosed to improve the above-mentioned wear resistance. For example, Patent Document 1 discloses a technology for a rolling mill roll made of an Fe-based alloy containing, by mass%, C: 1.0-2.6%, Cr: 4.0-10.0%, Mo: 5.0-10.0%, W: less than 5.0%, and V: 3.0-8.0%, satisfying 12.0% ≤ 2Mo + W ≤ 20.0%, 2Mo / W ≥ 3.0, and 0.2% ≤ C - 0.24V ≤ 0.7%. This technology is said to generate MC, M4C3, M2C, and M6C carbides, which particularly contribute to wear resistance, within an optimal range, thereby obtaining a rolling mill roll with excellent wear resistance.

[0004] Furthermore, Patent Document 2 states that, in mass%, C: 0.7~3.6%, Si: 0.2~2.5%, Mn: 0.2~2.0%, Cr: 2.0~10%, Mo: 0.2~10%, V: 2.0~10%, B: 0.001~0.50%, Al: 0.001~0.50%, Ti: 0.001~0.50%, Zr: 0.001~0.50%, Cu: 0 A technology for an outer layer material for a rolling mill composite roll is disclosed, which contains 0.001-0.50% of magnesium, 0.001-0.50% of magnesium, 0.001-0.50% of magnesium, 0.001-0.50% of calcium carbonate, with the remainder being Fe and unavoidable impurities, and further containing one or more of the following: 0.1-10% of Ni, 0.2-10% of W, 0.2-10% of Nb, and 0.2-10% of Co. This technology allows for the creation of a microstructure in which MC carbides crystallize finely, uniformly, and spherically, thereby providing an outer layer material for a rolling mill composite roll with excellent wear resistance.

[0005] Patent Document 3 discloses a technology for a composite roll for hot rolling that has a chemical composition consisting of C: 1-3%, Si: 0.4-3%, Mn: 0.3-3%, Ni: 1-5%, Cr: 2-7%, Mo: 3-8%, V: 3-7%, and B: 0.01-0.12% by mass, with the remainder being Fe and unavoidable impurities, and satisfies the relationship expressed by formula (1): Cr / (Mo+0.5W)<-2 / 3[C-0.2(V+1.19Nb)]+11 / 6 (wherein W=0 and Nb=0 if the optional components W and Nb are not included), and contains 1-15% MC carbide, 0.5-20% carbonobide, and 0.5-20% Mo-based carbide by area ratio. This allows for the creation of composite rolls for hot rolling with excellent wear resistance due to the use of MC carbides.

[0006] Patent Document 4 describes a group of materials containing, by mass, C: 1.50-2.70%, Si: 0.3-3%, Mn: 0.1-3%, Ni: 0.1-2.5%, Cr: 4.0-7.0%, Mo: 4.1-8.0%, V: 5.0-10.0%, W: 0-0.4%, Nb: 0.1-3.0%, N: 0.005-0.15%, B: 0-0.05%, and further comprising Co: 0.1-5%, Zr: 0.01-0.5%, Ti: 0.05-0.5%, and Al: 0.001-0.5%. A technology is disclosed for a wear-resistant centrifugal casting composite roll for rolling, comprising an Fe alloy containing at least one selected from the above, with the remainder being substantially Fe and unavoidable impurities, where the ratio V / Nb (mass%) of V content to Nb content (mass%) is 1 to 20.0, and the C-bal, expressed by the following formula: C-bal = C% - 0.2 × V% - 0.06 × Cr% - 0.063 × Mo% - 0.033 × W% - 0.13 × Nb% [where C%, V%, Cr%, Mo%, W%, and Nb% are the mass%) content of C, V, Cr, Mo, W, and Nb, respectively], is 0 to 0.28. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2004-183085 [Patent Document 2] Japanese Patent Publication No. 2002-161331 [Patent Document 3] International Publication No. 2015 / 045984 [Patent Document 4] Japanese Patent Publication No. 2020-022989 [Non-patent literature]

[0008] [Non-Patent Document 1] Akira Takeuchi;Materials Transactions,Vol.46,No.12(2005) [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, with the increasing demand for high-quality steel sheets and the advancement of hot rolling technology, the properties required of hot rolling rolls are becoming increasingly stringent, with strong demands not only for wear resistance but also for surface roughness resistance. The technologies described in Patent Documents 1 to 4 improve the wear resistance of hot rolling rolls by optimizing the amount of carbide produced and controlling the carbide morphology. However, the matrix of the hot rolling roll material is composed of tempered martensite and bainite, and since the hardness of the matrix is ​​lower than that of the carbide, the matrix is ​​more susceptible to wear than the carbide. As wear of the matrix progresses, the matrix can no longer support the carbide, causing chipping of the carbide. As a result, irregularities occur between the chipped and non-chipped areas, and these irregularities on the roll surface are transferred to the rolled material, causing poor quality of the steel sheet product.

[0010] This invention has been made in view of the above circumstances, and aims to provide an outer layer material for hot rolling rolls that is excellent in terms of surface roughness resistance and abrasion resistance. [Means for solving the problem]

[0011] The inventors of this invention conceived of a method to solve the problem of surface roughness caused by the hardness difference between the carbides and the matrix of hot-rolling rolls. This method utilizes the "cocktail effect" of high-entropy alloys, which has been actively researched in recent years, to form a uniform structure with minimal hardness differences near the surface of the hot-rolling rolls, thereby achieving high hardness. The cocktail effect utilizes the emergence of physical properties that exceed the predicted values ​​according to mixing laws, resulting from the nonlinear interactions between various constituent atoms.

[0012] The inventors of this invention have conducted a detailed investigation into the relationship between chemical composition and hardness and have found the following: Specifically, the chemical composition is optimized so that the mixing entropy, mixing enthalpy, and the average melting point calculated from the melting points of the pure elements and the composition ratio of each element are within an appropriate range. This makes it possible to manufacture a hot-rolling roll outer layer material that is castable and exhibits improved surface roughness resistance and wear resistance.

[0013] Based on these findings, the present invention has been further studied and completed. That is, the gist of the present invention is as follows.

[0014] [1] The mixing entropy ΔS represented by the following formula (1) mix is 0.0110 kJ / (mol×K) or more, and the mixing enthalpy ΔH represented by the following formula (2) mix is -25.0 kJ / mol or more and 5.0 kJ / mol or less, and the average melting point T represented by the following formula (3) m,ave is a roll outer layer material for hot rolling having a component composition that satisfies 1830 K or less.

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[0015] The present invention provides an outer layer material for hot-rolling rolls that is excellent in terms of surface roughness resistance and abrasion resistance. According to the present invention, it is possible to provide an outer layer material for hot rolling rolls and a composite roll for hot rolling that has excellent surface roughness resistance and abrasion resistance, by suppressing surface roughness caused by the difference in hardness between the carbides and the base material of the hot rolling roll. [Brief explanation of the drawing]

[0016] [Figure 1] Figure 1 is a schematic diagram illustrating the hot rolling abrasion test. [Modes for carrying out the invention]

[0017] The advantage of high-entropy alloying is that, when the constituent elements are multi-component, for example, five or more elements (five types), and the elemental content approaches equidistant proportions, the effect of the entropy term on the stability of the alloy during mixing in the so-called Gibbs free energy equation increases, allowing it to exist stably in a solid solution state. Furthermore, because the crystal structure is formed with various elements with different atomic radii, latent strain is generated in the lattice, resulting in a high hardness of the matrix. Various components were added to obtain these effects.

[0018] The hot rolling roll outer layer material of the present invention has a mixed entropy ΔS represented by formula (1). mix The concentration is 0.0110 kJ / (mol×K) or greater, and the mixed enthalpy ΔH is expressed by equation (2). mix The average melting point T is between -25.0 kJ / mol and 5.0 kJ / mol, and is expressed by equation (3). m,ave It is characterized by having a component composition in which the average melting point T is 1830K or less. m,ave It is calculated from the melting points of pure elements and their compositional ratios.

[0019]

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[0020]

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[0021]

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[0022] Equations (1) and (2) are based on empirical rules commonly used in the design of high-entropy alloys. As a result of our diligent research, we have determined that ΔS, expressed in equation (1), is a parameter. mix ΔH expressed by equation (2) mix , T represented by equation (3) m,ave We found that a high-hardness, high-entropy alloy can be obtained when the above range is satisfied. Equation (3) is a parameter set to determine the melting point at which it can be dissolved, and T is expressed in equation (3). m,ave We found that it is possible to cast within the above range.

[0023] ΔS mix If ΔS is less than 0.0110 kJ / (mol×K), it becomes difficult to form a high-entropy alloy, and the benefits of high-entropy alloying cannot be obtained. As a result, the solid solution cannot be stabilized, and it is strongly influenced by the elements it contains, which can result in insufficient hardness being obtained, or even if high hardness is achieved, the alloy may become brittle. If sufficient hardness is not obtained, the wear resistance deteriorates. Also, even if high hardness is achieved, if the alloy is brittle, surface chipping is more likely to occur, and the resistance to surface roughness deteriorates. Therefore, ΔS mix The pressure should be 0.0110 kJ / (mol×K) or higher. ΔS mix The concentration is preferably 0.0120 kJ / (mol×K) or higher, and more preferably 0.0130 kJ / (mol×K) or higher. Also, ΔS mix The upper limit is not particularly limited, but one example is ΔS mix It is less than or equal to 0.0200 kJ / (mol×K).

[0024] ΔH mix If the ΔH is less than -25.0 kJ / mol or greater than 5.0 kJ / mol, it becomes difficult to form a high-entropy alloy, and the benefits of high-entropy alloying cannot be obtained. As a result, the solid solution cannot be stabilized, and it is strongly influenced by the elements it contains, resulting in insufficient hardness being obtained, or even if high hardness is achieved, the alloy may become brittle. If sufficient hardness is not obtained, the wear resistance deteriorates. Also, even if high hardness is achieved, if the alloy is brittle, surface chipping is more likely to occur, and the resistance to surface roughness deteriorates. Therefore, ΔH mix The concentration shall be between -25.0 kJ / mol and 5.0 kJ / mol. ΔH mix It is preferably -23.0 kJ / mol or higher, and more preferably -20.0 kJ / mol or higher. Also, ΔH mix The concentration is preferably 4.0 kJ / mol or less, and more preferably 2.0 kJ / mol or less.

[0025] Furthermore, in the present invention, ΔH ij The value was obtained by referring to the value in Non-Patent Document 1.

[0026] T m,ave When the temperature exceeds 1830K, melting becomes difficult, or even if melting is possible, it cools and solidifies during pouring, making casting impossible. This prevents the manufacture of outer layer material for hot-rolling rolls and the evaluation of its properties. Therefore, T m,ave The temperature should be 1830K or lower.

[0027] Furthermore, in this invention, for example, the following values ​​were used as the melting points of the pure elements for the following elements. Al:933.15[K], Co:1768.15[K], Ni:1728.15[K], Si:1685.15[K], Ti:1939.15[K], V:2190 .15[K], Cr:2130.15[K], Fe:1809.15[K], Cu:1358.15[K], Mo:2896.15[K], W:3680.15[K]

[0028] The component composition of the outer layer material for the hot rolling roll of the present invention is the mixed entropy ΔS represented by formula (1). mix , mixed enthalpy ΔH represented by equation (2) mix and the average melting point T represented by equation (3) m,ave It is sufficient if it satisfies the above range.

[0029] Specifically, an example of the above component composition is a component composition containing five or more elements. More specifically, an example of a component composition containing three elements, Al, Co, and Ni, and two or more elements selected from Si, Ti, V, Cr, Fe, Cu, Mo, and W is an example of such a composition.

[0030] A preferred composition is one in which, in atomic percent, Al: greater than 0% and 25.0% or less, Co: greater than 0% and 35.0% or less, Ni: greater than 0% and 35.0% or less, and further containing two or more elements selected from Si: greater than 0% and 25.0% or less, Ti: greater than 0% and 25.0% or less, V: greater than 0% and 25.0% or less, Cr: greater than 0% and 35.0% or less, Fe: greater than 0% and 35.0% or less, Cu: greater than 0% and 45.0% or less, Mo: greater than 0% and 30.0% or less, and W: greater than 0% and 15.0% or less, with the remainder being unavoidable impurities. The reasons for this are explained below. In the following, atomic percent will be simply written as % unless otherwise specified. Also, content refers to the atomic percent content of the element in question relative to the entire alloy.

[0031] Al: more than 0% and less than 25.0% Al has a relatively large atomic radius compared to elements such as Fe, Co, and Ni, and its inclusion in the crystal lattice together with these elements creates potential strain within the lattice, which is effective in increasing hardness. However, when the Al content exceeds 25.0%, the alloy tends to become brittle. Furthermore, Al that is not in solid solution causes a decrease in hardness, and variations in elemental distribution occur, leading to large variations in Vickers hardness (hardness differences) in the outer layer material of hot-rolling rolls. Therefore, an Al content of more than 0% and 25.0% or less is preferable. An Al content of 24.0% or less is more preferable, and 22.0% or less is even more preferable. In addition, an Al content of 0.1% or more is more preferable, 2.0% or more is even more preferable, and 5.0% or more is even more preferable.

[0032] Co: more than 0% and less than 35.0% Co is preferably included in the composition because it increases the effect of the entropy term on the stability of the alloy and stabilizes the solid solution. However, if the Co content exceeds 35.0%, the entropy term decreases, and the high-entropy alloying tends to become unstable. Therefore, a Co content of more than 0% and 35.0% or less is preferable. A Co content of 34.0% or less is more preferable, and 32.0% or less is even more preferable. Furthermore, a Co content of 0.1% or more is more preferable, 8.0% or more is even more preferable, and 10.0% or more is even more preferable.

[0033] Ni: more than 0% and less than 35.0% Ni, like Co, increases the effect of the entropy term on alloy stability and stabilizes the solid solution, so its inclusion in the composition is preferable. However, when the Ni content exceeds 35.0%, the high-entropy alloying tends to become unstable. Therefore, a Ni content of more than 0% and 35.0% or less is preferable. A Ni content of 34.0% or less is more preferable, and 32.0% or less is even more preferable. Furthermore, a Ni content of 0.1% or more is more preferable, 8.0% or more is even more preferable, and 10.0% or more is even more preferable.

[0034] In one example of a preferred component composition of the present invention, in addition to the components described above, two or more elements selected from Si: greater than 0% and 25.0% or less, Ti: greater than 0% and 25.0% or less, V: greater than 0% and 25.0% or less, Cr: greater than 0% and 35.0% or less, Fe: greater than 0% and 35.0% or less, Cu: greater than 0% and 45.0% or less, Mo: greater than 0% and 30.0% or less, and W: greater than 0% and 15.0% or less may be included. When these elements are included, the crystal lattice is composed of elements with different atomic radii, and potential strain is generated in the lattice, making it easier to achieve high hardness and stabilizing the high-entropy alloying. For this reason, it is preferable to include two or more elements selected from Si, Ti, V, Cr, Fe, Cu, Mo, and W within the above content range. Note that ΔS mix ΔH mix , T m,ave The elements and their quantities are adjusted as appropriate so that they fall within an appropriate range.

[0035] Furthermore, the range of content of the components included when two or more elements selected from Si, Ti, V, Cr, Fe, Cu, Mo, and W are included is shown below. If Si is present, the Si content is greater than 0%, preferably 0.1% or more, more preferably 2.0% or more, and even more preferably 4.0% or more. Also, if Si is present, the Si content is 25.0% or less, preferably 24.0% or less, and more preferably 22.0% or less. If Ti is present, the Ti content is greater than 0%, preferably 0.1% or more, more preferably 2.0% or more, and even more preferably 4.0% or more. Also, if Ti is present, the Ti content is 25.0% or less, preferably 24.0% or less, and more preferably 22.0% or less. If V is present, the V content is greater than 0%, preferably 0.1% or more, more preferably 2.0% or more, and even more preferably 5.0% or more. Also, if V is present, the V content is 25.0% or less, preferably 24.0% or less, and more preferably 22.0% or less. If Cr is present, the Cr content is greater than 0%, preferably 0.1% or more, more preferably 5.0% or more, and even more preferably 10.0% or more. Also, if Cr is present, the Cr content is 35.0% or less, preferably 32.0% or less, and more preferably 28.0% or less. If Fe is present, the Fe content is greater than 0%, preferably 0.1% or more, more preferably 2.0% or more, and even more preferably 5.0% or more. Also, if Fe is present, the Fe content is 35.0% or less, preferably 32.0% or less, and more preferably 30.0% or less. If Cu is present, the Cu content is greater than 0%, preferably 0.1% or more, more preferably 5.0% or more, and even more preferably 10.0% or more. Also, if Cu is present, the Cu content is 45.0% or less, preferably 44.0% or less, and more preferably 42.0% or less. If Mo is present, the Mo content is greater than 0%, preferably 0.1% or more, more preferably 8.0% or more, and even more preferably 10.0% or more. Also, if Mo is present, the Mo content is 30.0% or less, preferably 28.0% or less, and more preferably 26.0% or less. If W is present, the W content is greater than 0%, preferably 0.1% or more, and more preferably 0.4% or more. Also, if W is present, the W content is 15.0% or less, preferably 12.0% or less, and more preferably 8.0% or less. In the example of the preferred component composition described above, two or more elements selected from Si, Ti, V, Cr, Fe, Cu, Mo, and W may be included, but the content of any element not included in this composition may be 0%.

[0036] Remainder: unavoidable impurities In one example of a preferred component composition of the present invention, the remainder other than the components described above can be unavoidable impurities. Examples of unavoidable impurities include P, S, Mg, Zr, REM (rare earth metals), Sn, As, Sb, Bi, Pb, Zn, N, and O. However, within limits that do not impair the effects of the present invention, it is not prohibited to include P, S, Mg, Zr, and REM at 0.03% or less each, Sn, As, and Sb at 0.05% or less each, and Bi, Pb, Zn, N, and O at 0.01% or less each. Here, REM is a collective term for a total of 17 elements including Sc, Y, and lanthanide elements. One or more of these 17 elements can be included as unavoidable impurities, and the REM content refers to the total content of these elements.

[0037] Furthermore, in the example of the preferred component composition of the present invention described above, the total content of Al, Co, and Ni is preferably 35.0 to 82.0% in atomic percent. When the total content of Al, Co, and Ni is within the above range, it becomes easier to create a high-entropy alloy and to stably achieve high hardness. The total content of Al, Co, and Ni is more preferably 38.0% or more in atomic percent, and even more preferably 40.0% or more. Also, the total content of Al, Co, and Ni is more preferably 80.0% or less in atomic percent, and even more preferably 78.0% or less.

[0038] The microstructure of the hot-rolling roll outer layer material of the present invention is not particularly limited. Preferably, the microstructure of the outer layer material has a single crystalline structure. Furthermore, it is preferable that the outer layer material satisfies the following ranges for average Vickers hardness and the range of difference between the maximum and minimum values ​​of the measured Vickers hardness.

[0039] The hot rolling roll outer layer material of the present invention has the above component composition, and the hardness of the outer layer material is preferably 620 HV or more and 850 HV or less, based on an average Vickers hardness measured at 20°C. When the average Vickers hardness is 620 HV or more, the wear resistance is further enhanced. On the other hand, when the average Vickers hardness is 850 HV or less, it becomes easier to grind away cracks formed on the surface of the hot rolling roll during hot rolling. The average Vickers hardness is more preferably 630 HV or more, and even more preferably 650 HV or more. Furthermore, the average Vickers hardness is more preferably 820 HV or less, and even more preferably 800 HV or less. The average Vickers hardness measured at 20°C is determined by taking 25 measurements of the Vickers hardness HV of the test material (outer layer material for hot rolling) under the conditions of 20°C using a Vickers hardness meter (test force: 50 gf), with a diamond indenter, atmospheric conditions, and a load holding time of 10 seconds. The average value of these measurements is then calculated. The Vickers hardness HV is measured at the center of the thickness of the outer layer material for hot rolling.

[0040] Furthermore, it is preferable that the difference between the maximum and minimum Vickers hardness values ​​measured at 20°C as described above for the hot-rolling roll outer layer material of the present invention is 120 HV or less. When the difference is 120 HV or less, it becomes easier to suppress surface roughness caused by the difference in hardness between the carbide and the matrix, which was a problem with conventional hot-rolling roll outer layer materials. More preferably, the difference is 100 HV or less, and even more preferably 80 HV or less.

[0041] Next, preferred manufacturing methods for the hot rolling roll outer layer material and hot rolling composite roll of the present invention will be described.

[0042] A preferred method for manufacturing the hot rolling roll outer layer material of the present invention is to pour molten metal having the above-described component composition of the hot rolling roll outer layer material into a mold and cast it. Specifically, molten metal having the above-described component composition of the hot rolling roll outer layer material is poured into a rotating mold, which is coated on its inner surface with a refractory material mainly composed of zircon to a thickness of 1 to 5 mm, to a predetermined thickness, and then centrifugal casting is performed.

[0043] As an example of a preferred manufacturing method of the present invention, the mixing entropy ΔS of the component composition of the molten metal is determined by formula (1) above. mix The process of calculating the mixed enthalpy ΔH of the component composition using the above formula (2). mix The process of calculating the average melting point T of the component composition using the above formula (3), and m,ave The process includes a step to calculate the mixture entropy ΔS. mix , Mixing enthalpy ΔH mix , average melting point T m,ave However, after confirming that the specified range is met, the molten metal can be poured into the mold to cast the outer layer material for the hot rolling mill roll. Also, the calculated mixing entropy ΔS mix , Mixing enthalpy ΔH mix , average melting point T m,ave If one or more of the following do not meet the specified range, the component adjustment is performed, and the mixed entropy ΔS mix , Mixing enthalpy ΔH mix , average melting point T m,ave The composition can be adjusted to meet a predetermined range. Then, the molten metal after the composition adjustment can be poured into a mold to cast the outer layer material for hot rolling rolls.

[0044] The hot-rolling composite roll of the present invention has a centrifugal-cast outer layer and an inner layer when the outer layer material of the roll is cast by centrifugal casting. The hot-rolling composite roll of the present invention may consist of this outer layer and an inner layer that is welded and integrated with the outer layer. An intermediate layer may be placed between the outer layer and the inner layer. That is, instead of an inner layer that is welded and integrated with the outer layer, an intermediate layer that is welded and integrated with the outer layer and an inner layer that is welded and integrated with the intermediate layer may be used. It is preferable that the inner layer be manufactured by static casting.

[0045] For the inner layer, which is cast by static casting, it is preferable to use spheroidal graphite cast iron or cyanomorphic graphite cast iron (CV cast iron), which have excellent castability and mechanical properties. In centrifugal cast rolls, the outer and inner layers are welded together, and components of the outer layer material are mixed into the inner layer. When carbide-forming elements such as Cr and V contained in the outer layer material are mixed into the inner layer, the inner layer becomes weaker. For this reason, it is preferable to minimize the mixing rate of outer layer material components as much as possible.

[0046] Furthermore, when forming an intermediate layer, it is preferable to use graphite steel, high-carbon steel, hypoeutectic cast iron, etc., as the intermediate layer material. The intermediate layer and the outer layer are welded together, and components of the outer layer material are mixed into the intermediate layer. In order to suppress the mixing rate of outer layer material components into the inner layer, it is preferable to minimize the mixing rate of outer layer material into the intermediate layer as much as possible.

[0047] Based on the above, a composite roll for hot rolling can be obtained having three layers: an outer layer, an intermediate layer, and an inner layer, or two layers: an outer layer and an inner layer. [Examples]

[0048] The present invention will be described in more detail by the following examples, but the present invention is not limited to these examples.

[0049] The material was heated and melted at 1450-1600°C to obtain molten metal with the component composition shown in Table 1. The molten metal was then poured into a Y-shaped keel block mold (rectangular section: 35 mm thick, 230 mm wide, 120 mm high) and cast to produce test specimens No. 1-17 of the present invention and test specimens No. 18-31 of the comparative examples. After cooling, the test specimens were removed and hardness measurements and hot rolling abrasion tests were performed. The test pieces used for the measurements and tests were taken from the center of the wall thickness of the test specimen. m,ave Materials with a temperature exceeding 1830K could not be cast, and therefore, test materials could not be produced.

[0050] Furthermore, the mixing entropy ΔS of the molten metal is calculated using the above formula (1). mix According to equation (2) above, the mixed enthalpy ΔH mix According to equation (3) above, the average melting point T m,aveEach of these was calculated. Then, the calculated mixture entropy ΔS mix , Mixing enthalpy ΔH mix , average melting point T m,ave However, it was confirmed whether or not the predetermined range was met. For the examples of the present invention shown in Table 1, the calculated mixing entropy ΔS mix , Mixing enthalpy ΔH mix , average melting point T m,ave However, if the specified range was met, the molten metal having that component composition was poured into the mold and casting was performed. If the specified range was not met, the component composition was adjusted, and after confirming that the specified range was met, the molten metal having the adjusted component composition was poured into the mold and casting was performed. The component composition and ΔS are shown in Table 1. mix ΔH mix , T m,ave This is the molten metal poured into the mold (i.e., the test material that was prepared).

[0051] Here, using Test Material No. 1, an example of the present invention shown in Table 1, as an example, we can determine ΔS from its component composition. mix ΔH mix , T m,ave I will explain in detail how to find this.

[0052] First, the elements contained in test material No. 1 are Al, Co, Ni, Ti, V, Cr, and Fe, a total of seven types. The order of the elements listed in equations (1), (2), and (3) is not arbitrary, but for calculation purposes, we will treat Al as the first element and Fe as the seventh. From Table 1, x Al =0.167, x Co =0.167, x Ni =0.167, x Ti =0.083, x V =0.082, x Cr =0.167, x Fe = 0.167, and by calculating equation (1), ΔS mix = 0.0158 kJ / (mol × K) is obtained.

[0053] Furthermore, from Non-Patent Document 1, ΔH ij The values ​​in [kJ / mol] are, respectively, ΔH AlCo = -19, ΔHAlNi =-22, ΔH AlTi =-30, ΔH AlV =-16, ΔH AlCr =-10, ΔH AlFe =-11, ΔH CoNi =0, ΔH CoTi =-28, ΔH CoV =-14, ΔH CoCr =-4, ΔH CoFe =-1, ΔH NiTi =-35, ΔH NiV =-18, ΔH NiCr =-7, ΔH NiFe =-2, ΔH TiV =-2, ΔH TiCr =-7, ΔH TiFe =-17, ΔH VCr =-2, ΔH VFe =-7, ΔH CrFe =-1 was adopted. For Test Specimen No. 1, when expanding the right side of Equation (2), ΔH mix =4 × {(x Al × x Co × ΔH AlCo + x Al × x Ni × ΔH AlNi + x Al × x Ti × ΔH AlTi + x Al × x V × ΔH AlV + x Al × x Cr × ΔH AlCr + x Al × x Fe × ΔH AlFe ) + (x Co × x Ni × ΔH CoNi + x Co × x Ti × ΔH CoTi + x Co × x V × ΔH CoV + x Co × x Cr × ΔH CoCr + x Co × x Fe × ΔH CoFe ) + (x Ni × x Ti × ΔH NiTi + xNi ×x V ×ΔH NiV +x Ni ×x Cr ×ΔH NiCr +x Ni ×x Fe ×ΔH NiFe )+(x Ti ×x V ×ΔH TiV +x Ti ×x Cr ×ΔH TiCr +x Ti ×x Fe ×ΔH TiFe )+(x V ×x Cr ×ΔH VCr +x V ×x Fe ×ΔH VFe )+(x Cr ×x Fe ×ΔH CrFe )} and by substituting each, ΔH mix The result is -18.3 kJ / mol.

[0054] As mentioned above, the melting point of a pure element is T m,Al =933.15K, T m,Co =1768.15K, T m,Ni =1728.15K, T m,Ti =1939.15K, T m,V =2190.15K, T m,Cr =2130.15K, T m,Fe Using =1809.15K, and calculating equation (3) from these values ​​and mole fractions, T m,ave =1738K is obtained.

[0055] [Table 1]

[0056] For test pieces cut from the test materials of the present invention example and comparative example, the Vickers hardness HV at 20°C was measured at 25 points using a micro-Vickers hardness tester (test force: 50 gf), and the average value was calculated. In addition, the difference between the maximum and minimum values ​​of the Vickers hardness measured at the 25 points was determined. For the Vickers hardness measurement, a Mitutoyo HM-200 tester was used, and the experiment was conducted in air with a load holding time of 10 seconds. Measurements were also taken with a shift of three indentation widths, resulting in a total of 25 measurements at 5 points vertically and 5 points horizontally.

[0057] The hot rolling abrasion test method was as follows. Ring-shaped test pieces were taken from test materials No. 1 to 31, and hot rolling abrasion test pieces (outer diameter 60 mmφ, width 10 mm, with C1 chamfer) were taken from the ring-shaped test pieces obtained for each inventive example and each comparative example. The hot rolling abrasion test was performed using a two-disc sliding rolling method between the test piece and the mating piece, as shown in Figure 1. The test piece 1 was rotated at 700 rpm while being cooled with cooling water 2, and the mating piece 4 (S45C, outer diameter 190 mmφ, width 15 mm, with C1 chamfer), heated to 800°C by a high-frequency induction heating coil 3, was rolled in contact with the rotating test piece 1 with a load of 686 N in the load direction 7. The rotation direction 5 of the test piece 1 and the rotation direction 6 of the mating piece 4 are the rotation directions in which the tangents at the contact point between the test piece 1 and the mating piece 4 are in the same direction. The abrasion test was conducted for 450 minutes, with the mating piece being replaced every 45 minutes (31,500 rotations of the test piece), for a total of 10 tests (315,000 rotations of the test piece). The average amount of abrasion per test (per 31,500 rotations of the test piece) was calculated. In addition, the test surface of the test piece after the test was observed visually and with a digital microscope to evaluate its resistance to surface roughness. The results are shown in Table 2.

[0058] [Table 2]

[0059] In Table 2, a wear amount of 0.16 g / cycle or less was considered acceptable (excellent wear resistance), and a value greater than 0.16 g / cycle was considered unacceptable. Furthermore, the test surface was observed with a digital microscope at 30x magnification. If irregularities were observed on the test surface, it was considered to have surface roughness, and if no irregularities were observed, it was considered to have no surface roughness. A "no surface roughness" result was considered acceptable (excellent resistance to surface roughness). As is clear from Table 2, the present invention example exhibits excellent wear resistance and resistance to surface roughness. In the present invention example, the difference between the maximum and minimum values ​​of Vickers hardness was small, suppressing irregularities on the test surface caused by variations in Vickers hardness, and no surface roughness was observed, which is caused by the difference in hardness between the carbide and the matrix, as seen in conventional hot-rolling roll outer layer materials.

[0060] Therefore, according to the present invention, it is possible to manufacture an outer layer material for hot rolling stand rolls and a composite roll with excellent wear resistance that suppresses surface roughness caused by the difference in hardness between the carbides and the base material of the hot rolling rolls. As a result, it is also possible to improve the lifespan of the hot rolling rolls and reduce the time loss when rolling is interrupted due to roll trouble, thereby improving the rolling efficiency of the hot rolling stand rolls and increasing the productivity of hot-rolled steel sheets. [Explanation of symbols]

[0061] 1: Test specimen 2: Cooling water 3: High-frequency induction heating coil 4: Opponent's piece 5: Direction of rotation of the test specimen 6: Direction of rotation of the opponent's piece 7: Direction of load

Claims

1. The entropy of mixing ΔS is expressed by the following equation (1). ｍｉｘ If the concentration is 0.0110 kJ / (mol × K) or higher, the mixed enthalpy ΔH is expressed by the following formula (2). ｍｉｘ If the average melting point T is between -25.0 kJ / mol and 5.0 kJ / mol, it is represented by the following formula (3). ｍ，ａｖｅ It has a component composition that satisfies the requirement of 1830K or less. The aforementioned component composition is expressed in atomic percent. Al: 2.0% or more and 25.0% or less, Co: 5.6% to 35.0%, and Ni: Includes 6.4% to 35.0%, moreover, Si: more than 0% and less than 25.0%, Ti: more than 0% and less than 25.0%, V: more than 0% and less than 25.0%, Cr: more than 0% but not more than 35.0%, Fe: more than 0% but not more than 35.0%, Cu: more than 0% and 45.0% or less, Mo: greater than 0% and less than or equal to 30.0%, W: Contains two or more types selected from between 0% and 15.0%. The total content of Al, Co, and Ni is 35.0% to 82.0% in atomic percent. A roll outer layer material for hot rolling, the remainder consisting of unavoidable impurities. [Math 1] Here, R is the gas constant 8.314 × 10⁻⁴ －３ kJ / (mol×K), i means that it is the i-th element when the n elements contained in the component composition are arranged in order, x ｉ This is the mole fraction of the i-th element. [Math 2] Here, ΔH ｉｊ is the mixing enthalpy [kJ / mol] in the liquid phase of an isoatomic alloy in a binary system. i and j mean the i-th and j-th elements when the n elements contained in the component composition are arranged in order, and x ｉ and x ｊ is the mole fraction of the i-th and j-th elements. [Math 3] Here, i means the i-th element when arranging the n kinds of elements contained in the component composition in order, and T ｍ，ｉ is the melting point [K] of the pure element in the i-th element, and x ｉ is the mole fraction of the i-th element.

2. The hot rolling roll outer layer material according to claim 1, wherein the average Vickers hardness measured at 20°C is 620 HV or more and 850 HV or less, and the difference between the maximum and minimum values ​​of the Vickers hardness measured at 20°C is 120 HV or less.

3. A composite roll for hot rolling having two layers, an outer layer and an inner layer, or three layers, an outer layer, an intermediate layer and an inner layer, A composite roll for hot rolling, wherein the outer layer is made of the hot rolling roll outer layer material described in claim 1 or 2.

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