JP2007160391A - Rolling roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a rolling roll having improved wear resistance by remarkably improving its hardness while maintaining the toughness of the external layer, and exhibiting excellent wear resistance, roughening resistance and recessed flaw resistance by improving its high temperature hardness by a technical means different from the conventional technique. <P>SOLUTION: The external layer for a rolling roll has a structure in which MC carbides are dispersed in 20 to 60% by area ratio, and is characterized in that the Vickers hardness Hv of the matrix at room temperature is 550 to 900, and also, the Vickers hardness Hv of the external layer at room temperature is >1,000. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to hot and cold rolling rolls, and in particular, has an outer layer (rolling layer) that is excellent in wear resistance, rough skin resistance, and dent resistance, particularly hot thin plate rolling. It is suitable for work rolls in the finishing row of machines.

  The wear resistance and rough surface resistance of the rolling roll are important characteristics that determine the productivity of rolling. If the wear resistance is poor, the roll surface is worn early and the dimensional accuracy of the material to be rolled is impaired. In addition, when the surface of the rolling roll is worn unevenly due to contact with the material to be rolled and rough skin occurs, the rough surface is transferred to the rolled material and the surface appearance of the rolled material is impaired. In order to prevent these problems, the rolls must be replaced frequently, and the rolling mill's productivity is reduced due to the increased frequency of rolling operations, the cost required for roll surface grinding is increased, and the amount of roll surface grinding is reduced. There arises a problem that the roll basic unit decreases due to the increase. In particular, in sheet rolling, the surface quality of sheet products is strict, and a high roll roughness resistance is required for rolling rolls used in finishing rows of rolling mills.

Therefore, a high-speed alloy containing a large amount of alloy elements such as Cr, Mo, W, and V has been used as an outer layer for rolling rolls (a layer used for rolling) that has been designed to meet the demands of wear resistance and rough skin resistance. in use. The structure contains M ₇ C ₃ type carbide containing a large amount of Cr (M represents a metal element, the same applies hereinafter), M ₂ C type carbide and M ₆ C type carbide containing a lot of Mo and W, and a lot of V. It contains metal carbide such as MC type carbide. Among the alloying elements, V and Nb in particular form MC carbides with extremely high hardness of Vickers hardness of about Hv 2400-3200, and contribute significantly to the improvement of wear resistance.

  Here, in the sheet rolling mill, a multi-stage mill having an intermediate roll or a backup roll is common. Although this multi-stage mill is excellent in controlling the plate shape, when various foreign substances generated during rolling are sandwiched between an intermediate roll or backup roll that contacts the work roll, the rolling load is concentrated on the foreign substances. For this reason, the work roll of the part which pinched | interposed the foreign material is dented locally, and wrinkles generate | occur | produce. When this dent wrinkle occurs in the work roll, it is transferred to the material to be rolled, and the surface quality of the material to be rolled is extremely lowered. Further, if rolling is continued with the dents in the work roll, cracks may develop from the dents to the inside of the roll due to rolling stress, and the work roll may be spalled.

  In addition, on the surface of the work roll for hot rolling, the temperature at the portion in contact with the rolled material is estimated to rise to about 600 ° C. Under such a high temperature, in the conventional high-speed alloy, the surface of the work roll is softened, and the above-described dents are likely to become deeper. On the other hand, when the roll surface exceeds 600 ° C., the roll surface tends to plastically flow. When plastic flow occurs on the roll surface, streaky skin roughness occurs, strip-like peeling (banding) of the black skin (scale) film formed and attached to the roll surface, and seizure of the material to be rolled, resulting in rough skin resistance. It becomes easy to deteriorate. Furthermore, the roll surface becomes softer as the temperature increases, and the wear resistance deteriorates. For these reasons, it is desirable that the work roll for hot rolling has a high hardness at high temperatures.

  Various means for improving the dent resistance and the hardness at high temperature of the outer layer for rolling rolls have been proposed in the past for such problems.

  For example, in Patent Document 1, the chemical composition is expressed in terms of% by weight, C: 2.45 to 4%, Si: 1 to 2.5%, Mn: 0.6 to 2%, Ni: 0.3 to 1.5%, Cr: 6 to 8% , Mo: more than 11% and 15% or less, W: 10-20%, V: 5-10%, Co: 12-16%, the balance consists of Fe and inevitable impurities, high hardness and high wear A work roll for multi-stage rolling that has resistance and is excellent in dent resistance is disclosed.

In Patent Document 1 [0014], carbides forming elements such as Cr, Mo, W, and V are dissolved in the base and MC and M ₆ C type carbides are precipitated by high-temperature tempering to increase the hardness. . Also, the total amount of Mo and W is preferably in the range of (2Mo + W) from 30% to 50%, and the preferable range of the total amount of Mo, W and Co is (2Mo + W + Co) is from 42% to 66%. %, It has a wide quenching temperature range and a high tempering temperature of 100 to 600 ° C. and a high hardness of HRC68 or higher. In addition to MC, M ₆ C, and M ₇ C ₃ , it is described that the martensite and retained austenite metal structures improve high hardness, high wear resistance, and dent resistance.

Patent Document 2 discloses a steel plate having a mean particle size of 5 to 30 μm and uniformly dispersed in martensite, bainite or pearlite base at an area ratio of 5 to 40% and having no coarse carbide exceeding 100 μm. A hot rolling roll is disclosed. In addition, it is described that the primary carbide is M ₆ C or MC, and M is mainly Mo and is one or more of Fe, Cr, Mn, Ti, Nb, V and W. Yes. Further, it is described that the primary carbide has a Vickers hardness of 1500 or more, the substrate has a Vickers hardness of 500 to 1000, and the roll has an average Vickers hardness of 600 to 1000.

  Further, in the lower right column on page 2 of Patent Document 2, since the roll surface becomes 500 ° C. or higher, the hardness of the substrate is reduced, and abrasive wear due to slippage is caused. At this time, if there is a hard primary carbide, the abrasive wear due to the slip is prevented, and the wear resistance is governed by this balance. On the other hand, since the roll surface is water-cooled, the brittle carbide cracks due to thermal fatigue due to repeated heating and cooling, and the carbides eventually fall off. It is described that when carbides fall off, the abrasive wear prevention effect disappears and the wear of the substrate progresses, and the abrasive wear is again prevented and repeated by the newly appearing carbide.

  Furthermore, the higher the hardness of the carbide, the greater the effect of preventing abrasive wear. If the size of the carbide is large, thermal cracks are likely to occur and fall off early. In addition, it is described that when the amount of the carbide is too large, the base material cannot hold the carbide sufficiently, so that it is inappropriate.

  In Patent Document 3, C: 1.5 to 3.0%, Si: 0.3 to 2.5%, Mn: 0.3 to 1.0%, Cr: 2.0 to 10.0%, Mo: 2.0 to 8.0%, W: 2 to 8.0 by weight percent %, V: 2.0 to 8.0%, Co: 3.0 to 10.0%, Ni: 1.0 to 4.0%, Y: 1.0 to 10.0%, the balance being substantially Fe, It is disclosed.

  In Patent Document 3 [0022], the amount of hard primary carbide is controlled by appropriately suppressing the contents of Cr, Mo, W, and V in the as-cast structure by using the material having the above component composition. By appropriately adding Co, fine secondary carbides can be precipitated to sufficiently strengthen the matrix, and by adding an appropriate amount of Ni together, It is described that it is possible to eliminate the lowering of the insertability, and thus it is possible to sufficiently improve the wear resistance in hot rolling and to sufficiently improve the crack resistance. Further, the measurement result of the high temperature hardness in FIG. 2 discloses that the Vickers hardness at 600 ° C. is Hv 600 or more.

  Examples of a method for producing a rolling roll whose outer layer is formed of a high-speed alloy include a centrifugal casting method, a continuous casting overlay method, and a powder sintering method. Of these manufacturing methods, the centrifugal casting method is the most common from the viewpoints of the degree of freedom of product dimensions and economy. However, when a molten metal containing a large amount of V and Nb is subjected to centrifugal casting, MC carbide segregates on the inner surface side by centrifugal separation. Various centrifugal rolls made by centrifugal casting have been disclosed.

In Patent Document 4, in mass%, C: 1.0 to 3.0%, Si: 0.1 to 3.0%, Mn: 0.1 to 2.0%, Cr: 2.0 to 10.0%, Mo: 0.1 to 10.0%, V: 1.0 to 10.0 %, W: 0.1 to 10.0%, Mo + W ≦ 10.0%, and a solid or hollow centrifugal cast composite roll comprising an outer layer having a composition comprising the balance Fe and impurities and an inner layer of cast iron or cast steel. This document describes that when V exceeds 10.0% by mass, light carbide segregates to the inner surface side by centrifugal casting, and the amount of carbide is small on the outer surface of the outer layer used for rolling. This phenomenon is likely to occur when the molten metal is primary and crystallizes granular carbides. The primary grain carbide has a specific gravity of about 6 g / cm ³ and is lighter than the molten metal (specific gravity: about 7 to 8 g / cm ³ ), so it moves to the inner surface side by centrifugal force.

  In order to prevent segregation due to centrifugal separation by increasing the specific gravity of carbide, Patent Document 5 includes C: 3.5 to 5.5%, Si: 0.1 to 1.5%, Mn: 0.1 to 1.2%, Cr: 4.0 to 12.0. %, Mo: 2.0 to 8.0%, V: 12.0 to 18.0%, the balance Fe and unavoidable impurities are proposed. Since VC has a small specific gravity, it segregates by centrifugal casting, but Nb forms composite carbide (V, Nb) C having a large specific gravity with V, thus preventing segregation of carbides due to centrifugal separation.

JP-A-6-192791 JP-A-3-404 JP 2000-254715 A JP-A-8-60289 JP-A-9-256108

  Although the said patent documents 1-3 improve the dent resistance and the hardness at the time of high temperature of the outer layer for rolling rolls, there exists an inadequate point for a problem solution.

Patent Document 1 discloses that a large amount of M ₆ C carbide is formed by including a large amount of Mo and W, and that the hardness of the base is increased by including a large amount of Co to improve wear resistance and dent resistance. Improve sexiness. However, a large amount of M ₆ C carbide and an increase in matrix hardness both reduce toughness, so the applied roll application is extremely limited.

Patent Document 2 is characterized by carbides mainly composed of Mo, but stable carbides mainly composed of Mo are M ₆ C and M ₂ C, and only a part of them is dissolved in MC. That is, it is difficult for metallurgy to obtain MC carbide mainly composed of Mo.

In addition, a large amount of M ₆ C carbide is easily dispersed in the form of a network and lowers toughness. In addition, when a large amount of M ₆ C is added to add a large amount of Mo, the amount of Mo contained in the base increases and the toughness decreases. In addition, from the viewpoint of the fracture toughness of the entire roll, the base Vickers hardness is limited to 1000 or less, and the average Vickers hardness of the entire roll is limited to 1000 or less, so the effect of improving the obtained wear resistance is limited. The

  Patent Document 3 contains Y, but Y is a rare earth metal and is extremely expensive. Y partially dissolves in the matrix and forms an intermetallic compound with iron and other metals to harden the matrix, but the intermetallic compound decreases the toughness of the matrix.

As seen in these patent documents, increasing the M ₆ C carbide tends to cause a decrease in toughness. On the other hand, MC carbide has higher hardness than M ₆ C carbide, is easily dispersed in a granular form, and there is little decrease in toughness even if it is contained in a large amount. However, with the aim of obtaining a large amount of MC carbide, when a large amount of V and Nb is added to the molten metal, MC carbide is formed in the primary crystal from the molten metal, and the MC outer layer is uniformly contained and obtains a uniform dispersion. Is extremely difficult.

  As described in Patent Documents 4 and 5, if V and Nb are added excessively in the centrifugal casting method, MC carbide segregates on the inner surface side, and the MC carbide obtained on the roll surface side actually used is limited. The

  The present invention improves the wear resistance by significantly improving the hardness while having the toughness of the outer layer, and further improves the high temperature hardness by a technical means different from the conventional technique, thereby providing excellent wear resistance. An object of the present invention is to provide a rolling roll that exhibits high resistance, rough skin resistance, and dent resistance.

  The inventors of the present invention have studied the dispersion form and chemical composition of MC carbide that are desirable for stably obtaining a Vickers hardness of the outer layer at room temperature of Hv1000 or higher and a Vickers hardness of the outer layer at 600 ° C. of Hv500 or higher.

  That is, various test pieces having different types, amounts, distribution forms, and base hardnesses of carbides were prepared as outer layer materials, Vickers hardness at room temperature was measured, and the correlation was investigated. As a result, when MC carbide has an area ratio of 20% or more, Vickers hardness at room temperature is very high with Hv1000 or more, excellent wear resistance and rough skin resistance, especially effective in improving dent resistance I found out that

  At this time, when the cross-sectional structure of the Vickers indentation part and its peripheral part was confirmed, MC carbides that are densely present with an area ratio of 20% or more are close to each other, and the granular MC carbides are in plastic flow. A deterrent effect can be obtained.

  Further, the Vickers hardness of the outer layer test piece at a high temperature was measured and the correlation was investigated. As a result, the Vickers hardness of all specimens decreases as the temperature rises, but when MC carbide reaches 20% or more in area ratio, it is easy to obtain a high hardness with a Vickers hardness at 600 ° C of Hv500 or more and wear resistance. In particular, it was found to be effective in improving the rough skin resistance during hot rolling.

  In addition, as a result of measuring the fracture toughness value KIC, which is one of the toughness evaluations, for the outer layer specimens with an MC area ratio of 20% or more in MC carbide, the base Vickers hardness is Hv550-900 and the conventional high-speed type It was confirmed that toughness equal to or higher than that of the outer layer material can be secured.

  That is, the rolling roll according to the first aspect of the present invention has a structure in which the outer layer for the rolling roll has an area ratio and MC carbide is dispersed by 20 to 60%, the Vickers hardness of the base at room temperature is Hv 550 to 900, and at room temperature The outer layer has a Vickers hardness exceeding Hv1000.

  The rolling roll according to the second aspect of the present invention has a structure in which the outer layer for the rolling roll has an area ratio and MC carbide is dispersed in an amount of 20 to 60%, the Vickers hardness of the base at room temperature is Hv 550 to 900, and the outer layer at 600 ° C. The Vickers hardness of Hv500 exceeds 500.

  The rolling roll of the third aspect of the present invention has a structure in which the outer layer for the rolling roll has an area ratio and 20 to 60% of MC carbides are dispersed, the Vickers hardness of the base at room temperature is Hv 550 to 900, and the outer layer Vickers at room temperature. It is characterized in that the hardness exceeds Hv1000 and the Vickers hardness of the outer layer at 600 ° C. exceeds Hv500.

  The rolling rolls according to the first to third aspects of the present invention are preferably characterized in that, in the outer layer structure, the maximum inscribed circle diameter of a region not including MC carbide having an equivalent circle diameter of 15 μm or more does not exceed 150 μm. To do.

  In the outer layer structure, an average distance between MC carbides having an equivalent circle diameter of 15 μm or more is 10 to 40 μm.

  In the structure of the outer layer, the MC carbide has an average equivalent circular diameter of 10 to 50 μm.

  In the structure of the outer layer, a ratio (B / A) between an average distance B between MC carbides having an equivalent circle diameter of 15 μm or more and an average equivalent circle diameter A of MC carbides is 2 or less.

In the outer layer, M ₂ C, M ₆ C, and M ₇ C ₃ carbides having an area ratio and an equivalent circle diameter of 1 μm or more are dispersed in a total amount of 0 to 5%.

  The rolling roll according to the fourth aspect of the present invention has a structure in which the outer layer for the rolling roll has an area ratio and MC carbide is dispersed in an amount of 20 to 60%, and in mass%, C: 2.5 to 9%, Si: 0.1 to 3.5. %, Mn: 0.1 to 3.5%, and V: 11 to 40%, the composition is composed of the balance Fe and inevitable impurity elements, and the Vickers hardness of the outer layer at room temperature exceeds Hv1000 .

  The rolling roll of the fifth aspect of the present invention has a structure in which the outer layer for the rolling roll has an area ratio and MC carbide is dispersed in an amount of 20 to 60%, and in mass%, C: 2.5 to 9%, Si: 0.1 to 3.5%, It contains Mn: 0.1 to 3.5%, and V: 11 to 40%, has a composition composed of the balance Fe and inevitable impurity elements, and has a Vickers hardness of the outer layer at 600 ° C. exceeding Hv500.

  The rolling roll of the sixth aspect of the present invention has a structure in which the outer layer for the rolling roll has an area ratio and MC carbide is dispersed in an amount of 20 to 60%, and in mass%, C: 2.5 to 9%, Si: 0.1 to 3.5%, Containing Mn: 0.1-3.5%, and V: 11-40%, having the composition of the balance Fe and inevitable impurity elements, the Vickers hardness of the outer layer at room temperature exceeds Hv1000, and the outer layer at 600 ° C. Vickers hardness exceeds Hv500.

  In the rolling rolls of the fourth to sixth aspects of the present invention, the outer layer is further mass%, and is at least one selected from the group consisting of Cr: 1-15%, Mo: 0.5-20%, and W: 1-40%. It is characterized by containing.

In the outer layer, at least a part of V is substituted with an amount of Nb satisfying the following formula (1).
11% ≦ V% + 0.55 × Nb% ≦ 40% (mass%) (1)

The outer layer further satisfies the following formula (2).
0 ≦ C% −0.2 × (V% + 0.55 × Nb%) ≦ 2% (mass%) (2)

  The outer layer may further contain 2% by mass of Ni and / or 10% or less of Co by mass%.

  The outer layer further contains 0.5% by mass of Ti and / or 0.5% or less of Al.

The outer layer is formed by a centrifugal casting method.
I will.

[1] Structure and properties of outer layer for rolling roll
(1) Base hardness at room temperature The base is mainly composed of Fe and alloy elements, and the hardness changes due to transformation by heat treatment and precipitation of ultrafine carbides. If the hardness of the base at room temperature is Vickers hardness of less than Hv 550, the wear resistance of the outer layer of the roll is insufficient. If it is less than Hv 550, it is difficult to stably obtain a Vickers hardness of the outer layer at room temperature of Hv1000 or higher, or a Vickers hardness of the outer layer at 600 ° C. of Hv500 or higher. From the viewpoint of improving wear resistance, it is desirable that the base is hard, but if it exceeds Hv 900, the toughness of the base decreases. More preferable Vickers hardness of the base is Hv 650 to 850, and more preferably Hv 650 to 750.

(2) Hardness of outer layer at room temperature The outer layer of the roll of the present invention has a Vickers hardness of Hv1000 or more at room temperature. When the Vickers hardness at room temperature is less than Hv1000, the effect of improving the dent resistance is insufficient. On the other hand, there is a limit to the hardness that can be obtained due to the restriction of the base hardness and the restriction of the amount of MC carbide, and the toughness decreases if it is excessively hard. More preferably, the Vickers hardness of the outer layer at room temperature is Hv1000 to 1300, and more preferably Hv1000 to 1150.

(3) Hardness of outer layer at 600 ° C. The outer layer of the roll of the present invention has a Vickers hardness at 600 ° C. of Hv500 or more. When the Vickers hardness at 600 ° C. is less than Hv 500, the effect of improving the rough skin resistance particularly in hot rolling is insufficient. On the other hand, there is a limit to the hardness that can be obtained due to the restriction of the base hardness, the restriction of the amount of MC carbide, and the softening of the base at a high temperature, and if it is excessively hard, the toughness decreases. More preferably, the Vickers hardness of the outer layer at 600 ° C. is Hv 500 to 800, and more preferably Hv 600 to 800.

(4) MC carbide MC carbide, which is granular carbide, has higher hardness than other carbides (M ₂ C, M ₆ C, M ₇ C ₃ carbide, etc.), contributes to improved wear resistance and room temperature. This contributes to an increase in Vickers hardness and improves dent resistance. MC carbide is stable at high temperatures, contributes to an increase in Vickers hardness at a high temperature of, for example, 600 ° C., and exhibits an excellent effect in improving the roughness resistance particularly in hot rolling. When the MC carbide is less than 20% in area ratio, the Vickers hardness of the outer layer at room temperature and 600 ° C. tends to be insufficient, and the effect of improving the wear resistance, dent resistance and rough skin resistance is insufficient. On the other hand, when the MC carbide exceeds 60% in area ratio, the above-mentioned effect is saturated and the toughness of the outer roll layer is remarkably lowered. In addition, since the interval between adjacent granular carbides is narrow and cracks are easily propagated, the thermal crack resistance is deteriorated. Therefore, MC carbide is 20 to 60% in area ratio. A preferred area ratio is 30 to 50%.

(5) Size of MC carbide
The average equivalent circle diameter of MC carbide (granular carbide) is preferably 10 to 50 μm. During hot rolling, the roll comes into contact with the hot rolled steel plate and the base softens to about 10 μm from the surface, so if the average equivalent circle diameter of MC carbide is less than 10 μm, the base cannot sufficiently support the MC carbide, The effect of improving wear resistance and rough skin resistance is insufficient. On the other hand, when the average equivalent circle diameter exceeds 50 μm, the effect of improving the rough skin resistance is saturated and the toughness is lowered. The average equivalent circle diameter of MC carbide is more preferably 10 to 40 μm, and most preferably 15 to 30 μm.

As shown in FIG. 1, the equivalent circle diameter of MC carbide 1 defines the diameter of circle 10 having the same area as MC carbide 1 as D ₁₀ . When the area of MC carbide 1 is S, D ₁₀ = 2 × (S / π) 1/2. The average equivalent-circle diameter of MC carbide is an average of D _10.

(6) Average distance between MC carbides In the structure of the outer layer of the roll of the present invention, the average distance between MC carbides having an equivalent circle diameter of 15 μm or more is preferably 10 to 40 μm. When the average distance between MC carbides is less than 10 μm, the MC carbides are unevenly distributed, microscopic unevenness due to wear difference occurs between the parts with a lot of MC carbides and the parts with little MC carbides, and the rough skin resistance is low. On the other hand, when the average distance between MC carbides is more than 40 μm, variation in MC carbide distribution is so large that it cannot be ignored, and no improvement in seizure resistance is observed. The average distance between MC carbides having an equivalent circle diameter of 15 μm or more is more preferably 20 to 30 μm.

The method for obtaining the average distance between MC carbides will be described with reference to FIG. 2 schematically showing the structure of the outer layer of the roll. This structure contains MC carbide (white) 1a having an equivalent circle diameter of 15 μm or more and MC carbide (black) 1b having an equivalent circle diameter of less than 15 μm. 2 indicates a base (containing M ₂ C, M ₆ C and M ₇ C ₃ carbides). When an arbitrary straight line L is drawn in this structure, MC carbides 1 _a1 , 1 _a2 , 1 _a3 ... 1 _an intersect, and the distances L ₁ , L ₂ , L _3. It is measured. Therefore, the average distance between MC carbides having an equivalent circle diameter of 15 μm or more is determined by [Σ (L ₁ + L ₂ +... + Ln)] / n.

(7) Average distance between MC carbides / average equivalent circle diameter In the structure of the outer layer of the roll of the present invention, the ratio between the average distance B between MC carbides having an equivalent circle diameter of 15 μm or more and the average equivalent circle diameter A of MC carbide ( B / A) is preferably 2 or less. In the outer roll layer of the present invention containing a large amount of MC carbide, MC carbide tends to aggregate. When MC carbide aggregates, micro unevenness due to a difference in wear occurs between a portion with a large amount of MC carbide and a portion with a small amount of MC carbide, thereby impairing rough skin resistance. The B / A ratio indicates the degree of aggregation of MC carbide. When B / A exceeds 2, MC carbides are agglomerated too much. A more preferable B / A ratio is 1.5 or less.

(8) Maximum inscribed circle diameter of the region not including MC carbide In the structure of the outer layer of the roll of the present invention, the maximum inscribed circle diameter of the region not including MC carbide having an equivalent circle diameter of 15 μm or more does not exceed 150 μm. preferable. If the maximum inscribed circle diameter is more than 150 μm, the dispersion of MC carbide distribution is so large that it cannot be ignored. The maximum inscribed circle diameter is more preferably 120 μm or less, and more preferably 80 μm or less.

The maximum inscribed circle diameter of the region not including MC carbide having an equivalent circle diameter of 15 μm or more is obtained as shown in FIG. In the illustrated field, the diameter of the circle equivalent diameter of more than 15 [mu] m MC carbides _{1 a1, 1 a2, 1 a3} , circle 20 inscribed in 1 _a4 is D _20. Similarly, the diameter of a circle inscribed in another MC carbide group is obtained. This operation is performed for a plurality of arbitrary fields of view, and the maximum inscribed circle diameter D ₂₀ max is determined.

(9) Non-granular carbide Non-granular carbide (M ₂ C, M ₆ C, and M ₇ C ₃ carbide) having an equivalent circle diameter of 1 μm or more is dispersed in the roll outer layer of the present invention in a total area ratio of 0 to 5%. You may do it. If the total area ratio of non-granular carbides exceeds 5%, the non-granular carbides coarsen and impair the surface roughness and toughness of the roll, and cracks develop along the non-granular carbides crystallized in a network. As a result, the thermal cracking resistance decreases. The smaller the total area ratio of non-particulate carbide, the better. The total area ratio of M ₂ C, M ₆ C, and M ₇ C ₃ carbide having an equivalent circle diameter of 1 μm or more is more preferably 0 to 3%, and still more preferably 0 to 1%. A small amount of carbides other than MC, M ₂ C, M ₆ C, and M ₇ C ₃ carbides may be included.

[2] Composition of outer layer for rolling roll (mass%)
(1) Essential ingredients
(a) C: 2.5-9%
C is an indispensable element that improves wear resistance mainly by bonding with alloy elements such as V and Nb to form MC carbide. C that does not bind to alloying elements mainly dissolves in the matrix or precipitates very finely, strengthening the matrix. If C is less than 2.5%, the amount of MC carbide is insufficient and sufficient wear resistance cannot be obtained. On the other hand, if C exceeds 9%, the amount of carbide becomes excessive and the heat crack resistance of the outer layer of the roll deteriorates. The C content is preferably 3.5 to 9%, more preferably 4.5 to 9%.

(b) Si: 0.1-3.5%
Si acts as a deoxidizer in the molten metal. If Si is less than 0.1%, the deoxidation effect is insufficient and casting defects are likely to occur. On the other hand, when Si exceeds 3.5%, the outer layer of the roll becomes brittle. The Si content is preferably 0.2 to 2.5%, more preferably 0.2 to 1.5%.

(c) Mn: 0.1-3.5%
Mn has an action of deoxidizing the molten metal and fixing S, which is an impurity, as MnS. Mn
When the content is less than 0.1%, these effects are insufficient. On the other hand, if Mn exceeds 3.5%, retained austenite tends to be generated, the hardness cannot be stably maintained, and the wear resistance is likely to deteriorate. The Mn content is preferably 0.2 to 2.5%, more preferably 0.2 to 1.5%.

(d) V: 11-40%
V is an element mainly bonded to C to form MC carbide. In order to include a large amount of MC carbide in the outer layer of the roll, 11 to 40% of V is necessary. If V is less than 11%, MC carbide is insufficient and sufficient wear resistance cannot be obtained. On the other hand, when V is more than 40%, MC carbide becomes excessive and the toughness of the outer roll layer deteriorates. The V content is preferably 15 to 40% or less, more preferably 18 to 40%.

(e) Nb
Nb has the same action as V in that it forms MC carbides. From the atomic weight ratio, 0.55 × Nb% and V% are equivalent in mass%. Therefore, a part or all of V may be substituted with an amount of Nb satisfying the following formula (1).
11% ≦ V% + 0.55 × Nb% ≦ 40% (mass%) (1)
A more preferable range of (V% + 0.55 × Nb%) is 15% to 40% by mass%, and the most preferable range is 18 to 40%.

Nb preferably satisfies C and V and the following formula (2).
0 ≦ C% −0.2 × (V% + 0.55 × Nb%) ≦ 2% (mass%) (2)
When the value of [C% −0.2 × (V% + 0.55 × Nb%)] is less than 0, MC carbide is not sufficiently obtained, V and Nb are excessive in the base, and sufficient hardness and Abrasion resistance cannot be obtained. On the other hand, when the value of [C% −0.2 × (V% + 0.55 × Nb%)] exceeds 2%, non-particulate carbides such as M ₂ C, M ₆ C, and M ₇ C ₃ carbides are network-like. The crystallization of the outer layer of the roll deteriorates.

(2) Optional components The outer layer may appropriately contain the following elements depending on the use and usage of the rolling roll.

(a) Cr: 1-15%
Cr not only improves the hardenability by dissolving in the matrix, but part of it combines with C and precipitates as ultrafine carbide, strengthening the matrix. If Cr is less than 1%, the effect of strengthening the base cannot be obtained sufficiently. On the other hand, when Cr exceeds 15%, carbides other than MC carbide such as M ₇ C ₃ carbide crystallize in a network shape, and heat crack resistance of the outer layer of the roll deteriorates. A more preferable Cr content is 3 to 9%.

(b) Mo: 0.5-20%
Mo not only improves the hardenability by dissolving in the matrix, but partly bonds with C and precipitates as ultrafine carbide, strengthening the matrix. Part of Mo forms granular carbides. If Mo is less than 0.5%, the effect of strengthening the base cannot be obtained sufficiently. On the other hand, when Mo exceeds 20%, non-particulate carbides such as M ₂ C and M ₆ C crystallize in a network shape, and the heat crack resistance of the outer layer of the roll deteriorates. The Mo content is more preferably 2.5 to 20%, particularly 2.5 to 10%.

(c) W: 1-40%
W dissolves in the base part to improve hardenability, and part of it combines with C to precipitate as ultrafine carbides, strengthening the base. Part of W forms granular carbides. If W is less than 1%, the effect of strengthening the base cannot be obtained sufficiently. On the other hand, when W exceeds 40%, non-particulate carbides such as M ₆ C and M ₂ C crystallize in a network shape, and the heat crack resistance of the outer layer of the roll deteriorates. The W content is more preferably 5 to 40%, particularly 5 to 20%.

  In order to give sufficient abrasion resistance to the outer layer of the roll of the present invention, it is preferable to contain at least one of Cr, Mo and W which are base strengthening elements.

(d) Ni: 2% or less
Ni dissolves in the base and is effective in improving the hardenability of the base. When Ni exceeds 2%, the austenite of the base is stabilized, and the hardening effect of the base is insufficient.

(e) Co: 10% or less
Co dissolves in the base and has the effect of strengthening the base. If Co is contained, the hardness of the base can be maintained even at high temperatures. When Co exceeds 10%, the toughness of the outer roll layer is lowered. Since Co is expensive, it is desirable to determine its content in consideration of economy and use conditions.

(f) Ti: 0.5% or less
In addition to acting as a deoxidizer in the molten metal, Ti combines with N to form nitrides, which serve as the core of granular carbides and has the effect of making the granular carbides fine. Some of them combine with C to form granular carbides. A Ti addition effect of 0.5% or less is sufficient.

(g) Al: 0.5% or less
In addition to acting as a deoxidizer in the molten metal, Al has the effect of making the particulate carbide fine. If Al exceeds 0.5%, the hardenability of the outer layer deteriorates, and sufficient base hardness cannot be obtained.

[3] Centrifugal Casting To produce the outer layer for a rolling roll of the present invention, first, a molten metal adjusted to a chemical composition for crystallizing primary MC carbide is cast into a cylindrical mold and centrifugally cast. In the present invention that utilizes centrifugal separation of MC carbide by centrifugal casting, the molten metal composition is different from the composition of the outer roll layer. In order to obtain the outer layer composition described in [2], the molten metal composition is in mass%, C: 2.2 to 6.0%, Si: 0.1 to 3.5%, Mn: 0.1 to 3.5%, and V: 8 to 22% It consists of the balance Fe and unavoidable impurity elements. Since Nb replaces at least a part of V and is centrifuged as MC carbide by centrifugal casting, an amount of Nb satisfying the following formula (3) can be added to the molten metal.
8% ≦ V% + 0.55 × Nb% ≦ 22% (mass%) (3)

  Preferably, the molten metal composition contains, by mass%, C: 2.5-6.0%, Si: 0.2-1.5%, Mn: 0.2-1.5%, and V: 10-22%, and Nb 10% ≦ V% You may contain only the quantity which satisfy | fills + 0.55xNb% <= 22% (mass%).

  Since optional elements Cr, Mo, Ni, Co and Al are hardly centrifuged, the content in the molten metal may be the same as the content in the outer layer of the roll. Since some of W and Ti are dissolved in the primary crystal MC carbide, they are slightly centrifuged.

  As shown in FIG. 4 (a), during the centrifugal casting in the mold 41, the primary crystal MC carbide 43 having a small specific gravity moves in the molten metal 42 to the inside of the roll in contact with the hollow portion 44. As a result, as shown in FIGS. 4 (b) and 4 (c), the inner peripheral layer 40a enriched in MC carbide, the outer peripheral layer 40b poor in MC carbide, and the concentration gradient in which the area ratio of MC carbide changes. A cylindrical body 40 composed of a layer 40c (synonymous with the intermediate layer 40c. That is, since this is a layer between the inner peripheral layer 40a and the outer peripheral layer 40b, it is referred to as an intermediate layer 40c for convenience in the drawing) is obtained. Next, all of the outer peripheral layer 40b and at least a part of the concentration gradient layer 40c are removed from the cylindrical body 40 by cutting or the like, and the portion where MC carbide is concentrated (mainly the inner peripheral layer 40a) is used as the outer layer for the rolling roll.

  The thicknesses of the outer peripheral layer 40b and the concentration gradient layer 40c are determined by the composition of the molten metal and the centrifugal casting conditions, and can be predicted. Since it is not necessary to remove all of the concentration gradient layer 40c, the depth of the concentration gradient layer 40c to be removed is set in advance. Of course, part of the inner circumferential layer 40a may be removed in order to ensure high wear resistance. For example, as shown in FIG. 4 (c), the thickness Dout of the outer peripheral layer 40b to be completely removed, the removal depth Dim of the concentration gradient layer 40c to be at least partially removed, and, if necessary, partially When the removal depth Din of the inner circumferential layer 40a to be removed is determined experimentally or by simulation based on the composition of the molten metal and the centrifugal casting conditions, the inner depth 40a exposed by cutting the cylindrical body 40 by a depth of Dout + Dim (+ Din). Thickness Do [= Dt + Dout + Dim (+ Din)] of cylindrical body 40 is set so that peripheral layer 40a (or a part of inner peripheral layer 40a + concentration gradient layer 40c) has a desired thickness (target thickness of outer layer) Dt. It can be set in advance. If the cylindrical body 40 having a thickness Do larger than the target thickness Dt of the outer layer is formed by the centrifugal casting method using the existing mold 41, it is easy to cut the cylindrical body 40 by a depth of Dout + Dim (+ Din). In addition, a roll outer layer having a thickness of Dt can be obtained at low cost.

  In the method of the present invention, from the distribution of the MC carbide predicted by the molten metal composition and centrifugal casting conditions, the depth at which the MC carbide area ratio is 20% or more is predicted, and the cylinder is increased by the depth. The body is preferably made to have an outer diameter larger than the target outer diameter of the outer layer.

[4] Inner layer material In the rolling roll having the outer layer of the present invention, in order to obtain sound welding with the outer layer, the inner layer is preferably formed of an alloy having higher toughness than the outer layer. Specifically, the inner layer alloy is preferably cast iron such as spheroidal graphite cast iron or flake graphite cast iron, or graphite steel. In the composite rolling roll, an intermediate layer may be provided between the outer layer and the inner layer. Specifically, the intermediate layer can be formed of an adamite material or the like. The rolling roll may be solid or hollow as long as it has the outer layer of the present invention. Moreover, you may fit the sleeve which consists of an outer layer of this invention to a shaft material.

  The rolling roll of the present invention is a work roll for hot and cold rolling, particularly a work roll used in a finishing row of a hot sheet rolling mill, and exhibits excellent wear resistance and rough skin resistance, and is produced by rolling. This contributes to improving the properties and roll basic unit. In addition, since the MC carbide can be dispersed in a large amount and uniformly using the same centrifugal casting apparatus as in the past by the method of the present invention, the outer layer for rolling rolls having excellent wear resistance, rough skin resistance and seizure resistance is reduced. Can be manufactured at cost.

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

  The molten metal adjusted to the chemical composition (mass%) shown in Table 1 was centrifugally cast in a centrifugal casting mold to produce a cylindrical body. Nos. 1 to 5 are examples of the present invention, Nos. 6 to 8 are comparative examples, and Nos. 9 and 10 are conventional examples. However, the static casting method was used only for No. 6 of the comparative example.

  Among the obtained cylinders, the element distribution and MC carbide distribution in the radial cross section of the cylinders were measured for the cylinders No. 1, No. 3 and No. 10. The element distribution and MC carbide distribution were obtained by cutting a rod-shaped test piece collected in the radial direction of the cylindrical body at intervals of 10 mm and collecting a plurality of samples. And the component analysis and MC carbide | carbonized_material area rate of each sample were measured. The results are shown in FIGS.

  As shown in FIG. 5, in the cylindrical body of Example No. 1 of the present invention, V was as small as 5% by mass in the outer peripheral layer, but was as large as 25% by mass or more in the inner peripheral layer, and W was also substantially in the outer peripheral layer. Although it was as small as 10-15 mass%, it was as large as 20-25 mass% in the inner peripheral layer. C was as low as 2.5% by mass in the outer peripheral layer, but was as high as 5% by mass or more in the inner peripheral layer. Regarding other elements (Cr, Mo), there was almost no concentration distribution in the outer peripheral layer to the inner peripheral layer.

  As shown in FIG. 6, the area ratio distribution of MC carbide showed the same tendency as the V concentration distribution. That is, the area ratio of MC carbide was as low as about 4 to 8% by area in the outer peripheral layer, but was as high as about 35% by area or more in the inner peripheral layer. Therefore, for example, the cylindrical body is cut to a depth (indicated by line A in the figure) including the entire outer peripheral layer and most of the concentration gradient layer, and the portion containing 35% or more area of MC carbide is the outer layer for rolling rolls. It was.

  As shown in FIG. 7, in the cylindrical body of Invention Example No. 3, V was as small as about 6% by mass or less in the outer peripheral layer, but as much as 15% by mass or more in the inner peripheral layer, and C, Nb and W In the outer peripheral layer, the amount was almost as low as 5% by mass or less, but in the inner peripheral layer, it was slightly higher as 8% by mass or more. As for Mo, there was almost no concentration distribution in the outer peripheral layer to the inner peripheral layer.

  As shown in FIG. 8, the area ratio of MC carbide was as low as about 4 area% or less in the outer peripheral layer, but was as high as about 25 area% or more in the inner peripheral layer. Therefore, for example, the cylindrical body is cut to a depth (indicated by a line segment A ′ in the figure) including the entire outer peripheral layer and most of the concentration gradient layer, and a portion containing 25% or more area MC carbide is used for a rolling roll. The outer layer was used.

  In the cylindrical body of Conventional Example No. 10, as shown in FIGS. 9 and 10, there was almost no element concentration distribution between the outer peripheral layer and the inner peripheral layer. MC carbide was less than 8 area% at any depth.

  In the same way as the cylindrical bodies of Example No. 1 and No. 3 of the present invention, the cylindrical bodies of other examples were also removed by cutting or the like until the portion where the MC carbides were concentrated was exposed, and the centrifugal cast outer layer for the roll was formed. Produced.

  Table 2 shows the composition of the obtained outer roll layer. Each roll outer layer was subjected to heat treatment comprising quenching at 1000 to 1200 ° C. and three tempering at 500 to 600 ° C. However, the No. 9 roll outer layer of the conventional example was subjected to residual austenite decomposition and strain relief heat treatment at 400 to 500 ° C. Here, formula (1) in Table 2 is the value of [V% + 0.55 x Nb%], and formula (2) is the value of [C%-0.2 x (V% + 0.55 x Nb%)]. It is.

For the specimen cut out from each roll outer layer, MC carbide area ratio (%), total area ratio AA (%) of M ₂ C, M ₆ C and M ₇ C ₃ with equivalent circle diameter of 1 μm or more, MC The average circle equivalent diameter A (μm) of carbides, the average distance B (μm) between MC carbides with equivalent circle diameters of 15 μm or more, and the maximum value of the inscribed circle diameter in the region not containing MC carbides with equivalent circle diameters of 15 μm or more BB (μm), Vickers hardness of base at room temperature (Hv), Vickers hardness of outer layer at room temperature (Hv), Vickers hardness of outer layer at 600 ° C (Hv), Amount of wear (μm), Surface roughness Rz ( μm) and fracture toughness value KIC (kg / mm ^3/2 ) were measured by the following methods. Table 3 shows the measurement results.

(1) Area ratio of MC carbide Each specimen was mirror-polished and electrolytically corroded with potassium dichromate aqueous solution to corrode MC carbide to black, and then an image analyzer (SPICCA-II manufactured by Nippon Avionics Co., Ltd.) Was used to measure the area ratio (%) of MC carbide in 20 arbitrary fields of view corresponding to a 0.23 mm × 0.25 mm portion of the test piece, and the measured values were averaged.

(2) Total area ratio AA of non-particulate carbides (M ₂ C, M ₆ C and M ₇ C ₃ )
Each specimen is mirror-polished and corroded with Murakami reagent to corrode M ₂ C, M ₆ C and M ₇ C ₃ carbides in black or gray, and then each test is performed using the above image analyzer. The total area ratio (%) of M ₂ C, M ₆ C, and M ₇ C ₃ carbides was measured with 20 arbitrary visual fields corresponding to a 0.23 mm × 0.25 mm portion in the piece, and the measured values were averaged. Note that M ₂ C, M ₆ C, and M ₇ C ₃ carbides having an equivalent circle diameter of 1 μm or more, which are easy to identify, were measured.

(3) MC carbide average equivalent circle diameter A
Each test piece is mirror polished and electrolytically corroded with potassium dichromate aqueous solution to corrode MC carbide in black, and then using the above image analyzer, each test piece has a 0.23 mm × 0.25 mm portion. The average equivalent circle diameter (μm) of MC carbide was measured with 20 arbitrary visual fields corresponding to, and the measured values were averaged.

(4) Average distance B between MC carbides
Each specimen was mirror-polished and the base was corroded with a picric acid alcohol solution. Under this optical microscope observation (200 ×), the base appeared dark gray, the MC carbides appeared light gray, and the M ₂ C, M ₆ C and M ₇ C ₃ carbides appeared white. The average distance (μm) between MC carbides having an equivalent circle diameter of 15 μm or more was measured with 20 arbitrary fields of view corresponding to a 1.0 mm × 1.5 mm portion of each test piece, and the measured values were averaged.

(5) Maximum value BB of the inscribed circle diameter in the area not containing MC carbide
Each corroded test piece was observed with an optical microscope (100 times) in the same manner as in (4), and the equivalent circle diameter was 15 μm in 20 arbitrary fields corresponding to 2.0 mm × 3.0 mm portions of the test piece. The maximum value (μm) of the inscribed circle diameter in the region not containing MC carbide was measured, and the measured values were averaged.

(6) Vickers hardness of base at room temperature Each specimen is mirror-polished and lightly corroded with a picric acid ethanol solution, then, using any Vickers hardness tester, the load is 50 ~ Vickers hardness (Hv) was measured in the range of 200 g, and the measured values were averaged.

(7) Vickers hardness of the outer layer at room temperature and 600 ° C Each test piece cut to 5 mm length × 10 mm width × 5 mm height was mirror-polished and lightly corroded with a picric acid ethanol solution, then a high temperature micro hardness tester (Nikon) The Vickers hardness (Hv) of the outer layer at room temperature was measured at a load of 1000 g at any five locations on the test piece using a QM-2 model manufactured by the company, and the measured values were averaged. Further, using the same hardness meter, the Vickers hardness (Hv) of the outer layer at 600 ° C. was measured at a load of 1000 g at any five locations on the test piece, and the measured values were averaged. At this time, the preheating temperature of the sample was 10 minutes.

(8) Wear depth and surface roughness Rz
As an evaluation of wear resistance and rough skin resistance, using a rolling wear tester schematically shown in FIG. 11, the wear depth (μm) and the ten-point average surface roughness Rz were measured for the roll after rolling. It measured as follows. The surface roughness Rz was measured with a stylus type surface roughness meter.

  The rolling wear tester is a small sleeve roll having an outer diameter of 60 mm, an inner diameter of 40 mm and a width of 40 mm manufactured according to Invention Examples No. 1 to 5, Comparative Examples No. 6 to 8, and Conventional Examples No. 9 and No. 10, respectively. A rolling mill 51 including test rolls 52 and 53, a heating furnace 54, a cooling water tank 55, a winder 56, and a tension controller 57. The rolling wear test conditions were as follows.

Rolled material S: SUS304
Rolling rate: 25%
Rolling speed: 150m / min Rolling temperature: 900 ℃
Rolling distance: 300m
Roll cooling: Water cooling Number of rolls: Quadruple

(9) Fracture toughness value KIC
The fracture toughness value KIC of each specimen was measured according to ASTM E399. The measurement was performed on two test pieces, and the average value was obtained.

  FIG. 12 shows the metal structure of the test piece of Example No. 1 of the present invention. FIG. 13 shows the metal structure of the test piece of Comparative Example No. 6. 12 and 13, the white part is MC carbide, and the black part is the base. Although MC carbide is distributed at a high concentration in the test piece of Invention Example No. 1, it can be seen that the MC carbide is high in the test piece of Comparative Example No. 6, but the concentration distribution is non-uniform. .

FIG. 14 shows the metal structure of the conventional high speed roll material of No. 10. The white fine granular portion is MC carbide, the white mesh portion is M ₂ C, M ₆ C and M ₇ C ₃ carbide, and the black portion is the base. It can be seen that in the roll material of the conventional example No. 10, MC carbides are partially unevenly distributed and M ₂ C, M ₆ C and M ₇ C ₃ carbides are distributed in a network.

  The amount of wear of Invention Examples No. 1 to No. 5 is almost half or less than that of Conventional Examples No. 9 and No. 10, indicating that the wear resistance is extremely good. It can also be seen that Invention Examples Nos. 1 to 5 are superior to Conventional Example No. 10 in both rough skin resistance and toughness.

  FIG. 15 shows the relationship between the area ratio of MC carbide and the value of (V% + 0.55 × Nb%) in the equation (1). The relationship between the two is almost linear, and it can be seen that when (V% + 0.55 × Nb%) is about 15% by mass or more, the area ratio of MC carbide is about 20% or more.

  FIG. 16 shows the Vickers hardness at room temperature to 700 ° C. of Invention Example No. 1, Comparative Example No. 6, and Conventional Example No. 10. In the figure, the horizontal axis indicates the measurement temperature (° C.), and the vertical axis indicates the Vickers hardness (Hv). It can be seen that the inventive examples maintain significantly higher Vickers hardness over the range of room temperature to 600 ° C. compared to the comparative example and the conventional example.

  In the test piece of Comparative Example No. 6, the inscribed circle diameter BB of the region not including MC carbide having an equivalent circle diameter of 15 μm or more exceeds 150 μm, and the average distance B between MC carbides having an equivalent circle diameter of 15 μm or more is The ratio of MC carbide to the average equivalent circle diameter A (B / A) was more than 2. Therefore, it was inferior to rough skin resistance. Further, the Vickers hardness of the outer layer at 600 ° C. is Hv500 or less, and rough skin cannot be sufficiently suppressed.

  In Comparative Example No. 7, the C content, the formula (2), the area ratio of MC carbide, the base hardness, and the average equivalent circle diameter of MC carbide are outside the scope of the present invention, and B / A is 2 It was over. Therefore, it was inferior to abrasion resistance. Further, the Vickers hardness of the outer layer at room temperature is Hv1000 or less, and the Vickers hardness of the outer layer at 600 ° C. is Hv500 or less, and dent wrinkles and rough skin cannot be sufficiently suppressed.

In Comparative Example No. 8, the V content, the formulas (1) and (2), the area ratio of MC carbide, and the total area ratio AA of M ₂ C, M ₆ C, and M ₇ C ₃ carbide are the present invention. It was out of the range and B / A exceeded 2. Therefore, it was inferior to rough skin resistance and toughness. Further, the Vickers hardness of the outer layer at 600 ° C. is Hv500 or less, and rough skin cannot be sufficiently suppressed.

  In Conventional Example No. 9, the V content, the formula (1), the area ratio of MC carbide, and the average equivalent circle diameter of MC carbide were outside the scope of the present invention, and B / A exceeded 2. Therefore, it was inferior to abrasion resistance. Further, the Vickers hardness of the outer layer at room temperature is Hv1000 or less, and the Vickers hardness of the outer layer at 600 ° C. is Hv500 or less, and dent wrinkles and rough skin cannot be sufficiently suppressed.

  The rolling roll of the present invention exhibits excellent wear resistance in all rolling rolls. Further, in cold rolling, it is particularly effective in improving the dent resistance and further in hot rolling, particularly in the rough skin resistance. These effects contribute to the improvement of productivity and the roll basic unit in the rolling mill and to the improvement of the surface quality of the rolled material.

It is the schematic which shows the method of calculating | requiring the circle equivalent diameter of MC carbide | carbonized_material. It is the schematic which shows the method of calculating | requiring the average distance between MC carbide | carbonized_materials. It is the schematic which shows the method of calculating | requiring the maximum inscribed circle diameter of the area | region which does not contain MC carbide. It is the schematic which shows a mode that MC carbide | carbonized_material moves to the inner surface side in the case of centrifugal casting. It is radial direction sectional drawing which shows the centrifugal casting outer layer for rolling rolls of this invention. FIG. 5 is a graph showing the distribution of MC carbide in the AA cross section of FIG. 4 (b). 4 is a graph showing a radial distribution of elements in a centrifugally cast cylindrical body of Example No. 1 of the present invention. 6 is a graph showing the radial distribution of MC carbide in the centrifugally cast cylindrical body of Example No. 1 of the present invention. 4 is a graph showing the radial distribution of elements in a centrifugally cast cylindrical body of Invention Example No. 3. 4 is a graph showing a radial distribution of MC carbide in a centrifugally cast cylindrical body of Invention Example No. 3. It is a graph which shows the radial direction distribution of the element in the centrifugal cast cylindrical body of conventional example No. 10. It is a graph which shows radial direction distribution of MC carbide in the centrifugal cast cylindrical body of conventional example No. 10. It is the schematic which shows a rolling abrasion tester. 4 is an optical micrograph showing the metal structure of the test piece of Invention Example No. 1. 6 is an optical micrograph showing a metal structure of a test piece of Comparative Example No. 6. It is an optical microscope photograph which shows the metal structure of the test piece of the prior art example No.10. It is a graph which shows the relationship between the value of (V% + 0.55xNb%) and the area ratio of MC carbide. It is a graph which shows the relationship between the measurement temperature of a test material and Vickers hardness.

Explanation of symbols

1 MC carbide, 10 circle with the same area as MC carbide,
D equivalent to ₁₀ yen diameter, 2 outer layer roll structure,
la (la1, la2, la3, la4) MC carbide having a circle equivalent diameter of 15 μm or more,
lb MC carbide with an equivalent circle diameter of 15 μm or less, L arbitrary straight line,
L1, L2, L3 Interparticle distance, c inscribed circle, d inscribed circle diameter,
e Region excluding MC carbides a and b, 41 mold, 42 molten metal,
43 primary crystal MC, 44 hollow part, 40 cylindrical body, 40a inner peripheral layer,
40b outer peripheral layer, 40c concentration gradient layer,
51 rolling mill, 52 test roll, 53 test roll, 54 heating furnace,
55 Cooling water tank, 56 Winder, 57 Tension controller,
S rolled material,

Claims (17)

The outer layer for rolling rolls has a structure in which MC carbide is dispersed in an area ratio of 20-60%, the base Vickers hardness at room temperature is Hv 550-900, and the outer layer Vickers hardness at room temperature exceeds Hv1000 A rolling roll. The outer layer for the rolling roll has a structure in which MC carbide is dispersed in an area ratio of 20 to 60%, the Vickers hardness of the base at room temperature is Hv 550 to 900, and the Vickers hardness of the outer layer at 600 ° C exceeds Hv500 A featured rolling roll. The outer layer for the rolling roll has a structure in which the MC carbide is dispersed in an area ratio of 20 to 60%, the Vickers hardness of the base at room temperature is Hv 550 to 900, the Vickers hardness of the outer layer at room temperature exceeds Hv1000, and 600 ° C. A rolling roll characterized in that the outer layer has a Vickers hardness exceeding Hv500. 4. The rolling roll according to claim 1, wherein, in the outer layer structure, a maximum inscribed circle diameter of a region not including MC carbide having an equivalent circle diameter of 15 μm or more does not exceed 150 μm. The rolling roll according to any one of claims 1 to 4, wherein in the outer layer structure, an average distance between MC carbides having an equivalent circle diameter of 15 µm or more is 10 to 40 µm. 6. The rolling roll according to claim 1, wherein in the structure of the outer layer, an average equivalent circle diameter of MC carbide is 10 to 50 μm. The ratio (B / A) of an average distance B between MC carbides having an equivalent circle diameter of 15 μm or more and an average equivalent circle diameter A of MC carbides in the outer layer structure is 2 or less. The rolling roll in any one of 1-6. 8. In the outer layer, M ₂ C, M ₆ C, and M ₇ C ₃ carbides having an area ratio of an equivalent circle diameter of 1 μm or more are dispersed in a total amount of 0 to 5%. The rolling roll as described in crab. The outer layer for the rolling roll has a structure in which the MC carbide is dispersed in an area ratio of 20 to 60%, and in mass%, C: 2.5 to 9%, Si: 0.1 to 3.5%, Mn: 0.1 to 3.5%, and V: A rolling roll comprising 11 to 40%, having a composition composed of the balance Fe and inevitable impurity elements, and having a Vickers hardness of the outer layer at room temperature exceeding Hv1000. The outer layer for the rolling roll has a structure in which the MC carbide is dispersed in an area ratio of 20 to 60%, and in mass%, C: 2.5 to 9%, Si: 0.1 to 3.5%, Mn: 0.1 to 3.5%, and V: A rolling roll comprising 11 to 40%, having a composition consisting of the balance Fe and inevitable impurity elements, and having an outer layer Vickers hardness of Hv500 at 600 ° C. The outer layer for the rolling roll has a structure in which the MC carbide is dispersed in an area ratio of 20 to 60%, and in mass%, C: 2.5 to 9%, Si: 0.1 to 3.5%, Mn: 0.1 to 3.5%, and V: It has a composition of 11 to 40%, balance Fe and inevitable impurity elements, and the outer layer Vickers hardness at room temperature exceeds Hv1000, and the outer layer Vickers hardness at 600 ° C exceeds Hv500 A rolling roll. 12. The outer layer further contains at least one mass selected from the group consisting of Cr: 1 to 15%, Mo: 0.5 to 20%, and W: 1 to 40%. The rolling roll in any one of. 13. The rolling roll according to claim 9, wherein in the outer layer, at least a part of V is substituted with an amount of Nb satisfying the following formula (1).
11% ≦ V% + 0.55 × Nb% ≦ 40% (mass%) (1) The rolling roll according to any one of claims 9 to 13, wherein the outer layer further satisfies the following formula (2).
0 ≦ C% −0.2 × (V% + 0.55 × Nb%) ≦ 2% (mass%) (2) The rolling roll according to any one of claims 9 to 14, wherein the outer layer further contains 2% or less Ni and / or 10% or less Co by mass%. The rolling roll according to any one of claims 9 to 15, wherein the outer layer further contains 0.5% by mass of Ti and / or 0.5% or less of Al by mass%. The rolling roll according to any one of claims 1 to 16, wherein the outer layer is formed by a centrifugal casting method.