JP2006346744A - Outer layer material for rolling roll and rolling roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an outer layer material for rolling roll and a rolling roll thereby, which reduces heat conductivity of the outer layer material, has excellent wear resistance and accident resistance, can suppress growth of thermal crown, and also exhibits superb sheet-passing performance. <P>SOLUTION: The outer layer material for rolling roll (a second layer in the figure) has a structure comprising a matrix having a Vickers hardness of Hv 550-900 with dispersed MC carbide of 20-60% by area ratio and M<SB>2</SB>C, M<SB>6</SB>C and M<SB>7</SB>C<SB>3</SB>carbides of 0-5% in total amount, and has a heat conductivity of 25 W/m×K or less at 300°C. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an outer layer material for a rolling roll and a rolling roll using the same, and is excellent in wear resistance and accident resistance, and in particular, excellent in sheet-passability of a material to be rolled, and finishing a hot sheet rolling mill. It is suitable as a work roll used in a row and its outer layer material.

  An important characteristic that determines the productivity of rolling is the wear resistance of the rolling roll. 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 order to prevent this, the rolls must be replaced frequently, resulting in a decrease in rolling mill productivity due to an increase in the frequency of rolling operation interruptions, an increase in the cost required for roll surface grinding, and the amount of roll surface grinding. There arises a problem that the roll basic unit is reduced due to an increase in the number of rolls.

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 material (rolling layer) for rolling rolls intended to meet the demand for wear resistance. Yes. 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.

  Moreover, in the finishing line of a hot sheet rolling mill that rolls steel sheets and the like, in particular, sheet passability and accident resistance are required. If the plateability is poor, the material to be rolled has meandering, middle elongation, ear elongation, and the like, and problems such as deterioration in quality and yield due to shape defects occur. When meandering or middle elongation occurs, the frequency of occurrence of rolling trouble called “drawing” in which the end of the material to be rolled is rolled by two sheets for some reason increases. In this squeeze accident, the material to be rolled is wound around the roll, and the rolling must be stopped. At this time, cracks are generated on the roll surface due to thermal stress and local high pressure due to a squeeze accident. If the accident resistance is poor, the cracks may extend to the deep part of the roll, resulting in roll breakage (spoling).

  There are various factors that affect the sheet-passing property, but as a result of the characteristics of the roll, there is a thermal expansion deformation of the rolling roll, so-called thermal crown. The thermal crown means that the roll surface temperature rises due to heating from the material to be rolled or frictional heat with the roll, causing the roll to undergo thermal expansion deformation. Generally, in the thermal crown, the temperature in the vicinity of the central portion in the axial direction of the roll is higher than that in the vicinity of the end portion, and the vicinity of the central portion in the axial direction of the roll expands more. When the thermal crown exceeds the range of rolling control, the roll gap near the central portion in the axial direction of the roll becomes small, so that the sheet passing property deteriorates.

  Therefore, various means for suppressing the thermal crown have been proposed in the past in order to improve the plate passing property.

For example, in Patent Document 1, in a composite roll for hot rolling in which an outer layer is welded and formed on the outer periphery of a shaft by continuous overlay casting, the shaft has a thermal expansion coefficient of 12 × 10 ⁻⁶ at room temperature to 100 ° C. The composite roll for hot rolling which is below / ° C is described. In addition, it is described that the thermal conductivity of the shaft material from room temperature to 100 ° C. is 0.12 cal / cm · sec · ° C. (50.2 W / m · K) or less.

  Moreover, in patent document 1, it is weight% as a preferable outer layer, C: 1.0-4.0%, Si: 0.2-3.0%, Mn: 0.1-1.5%, Cr: 2 to 12%, Mo: 9% or less, V: 3 to 15%, W: 20% or less, and a high speed material substantially consisting of Fe is described. Furthermore, in addition to the above elements, one or more of Ni: 5% or less, Co: 10% or less, Nb: 5% or less, Ti: 5% or less, Zr: 5% or less are added. Has been.

  According to Patent Document 1, by reducing the thermal expansion coefficient and thermal conductivity of the shaft material of the composite roll to an appropriate range, the thermal crown of the composite roll can be reduced and the plate flatness can be secured at a high level. .

  Patent Document 2 describes a composite roll composed of an outer layer, an intermediate layer, and a core material, in which the thermal conductivity of the material of the intermediate layer is 100 W / m · K or more. And it is described that an intermediate | middle layer consists of an age-hardening copper alloy or an age-hardening aluminum alloy.

  In Patent Document 2, as preferable outer layers, C: 0.4 to 2.0%, Cr: 1 to 20%, Mo: 0 to 10%, W: 0 to 20%, V: 0 to 10% , Co: 0 to 20%, and a high speed material composed of the balance Fe is described.

  According to Patent Document 2, by using a material having high thermal conductivity for the intermediate layer, the diffusion of heat in the direction of the body length of the roll is promoted, and the temperature rise at the center of the body of the roll is reduced. The growth of the thermal crown due to the temperature difference in the roll length direction of the roll can be suppressed by increasing the amount of temperature rise at the roll end of the roll.

  Patent Document 3 includes an outer layer and a core material, and the thickness of the outer layer is the thickest at or near the center in the roll drum length direction, and from the center or near the end in the roll drum length direction. The composite roll for rolling characterized by becoming thin as it goes to is disclosed.

In Patent Document 3, as a preferable outer layer, the alloy component of the outer layer material is C: 1.0% to 3.0% by weight, Si: 3.0% or less, Mn: 1.5% or less, Cr : High-speed material composed of 12% or less, Mo: 10% or less, W: 20% or less, V: 3% to 10%, Co: 10% or less, and the balance Fe. Moreover, it is described that the linear expansion coefficient of this high-speed material is about 10 × 10 ⁻⁶ / ° C.

Patent Document 4 is a composite roll for hot rolling having an intermediate layer between an outer layer and an inner layer manufactured by centrifugal casting, and the outer layer and the inner layer are welded and integrated through the intermediate layer, The said outer layer is C: 1.5-2.6% by weight ratio, Si: 0.1-2.0%, Mn: 0.1-2.0%, Cr: 7-15%, Mo: 2 0.5 to 10%, V: 3 to 10%, Nb: 0.5 to 5%, 0.27 ≦ Mo (%) / Cr (%) ≦ 0.8, Cr (%) / C ( %) ≧ 3.3 at the same time, having a composition comprising the balance Fe and inevitable impurities, and having an average coefficient of thermal expansion of 11.5 × 10 ⁻⁶ / ° C. from room temperature to 300 ° C. A composite roll for hot rolling in which the average thermal expansion coefficient of the inner layer from room temperature to 500 ° C. is 13.5 × 10 ⁻⁶ / ° C. or less is described.

  Further, in Patent Document 4, the inner layer has a weight ratio of C: 2.5 to 4.0%, Si: 1.5 to 3.5%, Mn: 0.3 to 2.0%, Cr: 0.3 to 8.0%, Mo: 0.5 to 4.0%, V: 0.1 to 1.0%, Nb: 0.5% or less, Ni: 1.5% or less, Mg: 0 0.02 to 0.08%, and the balance Fe and inevitable impurities are described.

  Further, the intermediate layer is, by weight ratio, C: 1.5-3%, Si: 0.5-3.5%, Mn: 0.2-2%, Cr: 1.0-6.0% , Mo: 1.0 to 6.0%, V: 3% or less, Nb: 2% or less, Ni: 2% or less, and balance Fe and inevitable impurities.

  According to Patent Document 4, the coefficient of thermal expansion can be reduced by increasing the Cr and Mo contents of the high-speed outer layer material, adding V and Nb in combination, and optimizing the amounts of C, Cr and Mo. It has been found that. Reduces the thermal expansion coefficient of the inner layer material from the viewpoint of improving the wear resistance, rough skin resistance and accident resistance, and stably producing composite rolls with low outer layer thermal expansion coefficient and low residual stress. It is the conclusion that needs to be done.

Japanese Patent Laid-Open No. 10-192916 JP-A-10-230307 JP 2000-288606 A JP 2000-303135 A

  As seen in these known examples, it has been proposed to suppress the growth of the thermal crown from all points of view.

  However, Patent Document 1 attempts to reduce the thermal crown of the roll by suppressing the thermal expansion coefficient and thermal conductivity of the shaft material. For this reason, the suppression of the thermal conductivity of the outer layer material that is most susceptible to heat during rolling is insufficient. Further, it is not considered to reduce the thermal crown from the viewpoint of suppressing the thermal conductivity of the outer layer material and reducing the temperature increase in the vicinity of the central portion in the axial direction of the roll and in the interior thereof.

  Moreover, patent document 2 tries to suppress the thermal crown of a roll by interposing the intermediate layer with high heat conductivity. For this reason, like patent document 1, suppression of the heat conductivity of outer-layer material itself is inadequate. Moreover, in patent document 2, since the temperature rise of an inner layer (core material) increases through an intermediate layer with high thermal conductivity, the thermal expansion amount of the roll itself increases. Since such a roll tends to continuously increase the roll diameter during rolling, the amount of rolling control such as a roll gap increases and rolling tends to become unstable. In addition, since a low-melting-point alloy other than iron such as a copper alloy or an aluminum alloy is used for the intermediate layer, it is difficult to manufacture and the manufacturing cost is likely to increase. Further, when a copper alloy or the like is used for the intermediate layer, recycling as an iron source becomes extremely difficult.

  In Patent Document 3, it is necessary to make the outer layer and the core material have specially shaped cross-sectional structures, respectively, and the manufacturing is extremely complicated and the manufacturing cost is likely to increase. Further, it is not considered to reduce the thermal crown from the viewpoint of suppressing the thermal conductivity of the outer layer material and reducing the temperature increase in the vicinity of the central portion in the axial direction of the roll and in the interior thereof.

Patent Document 4 attempts to lower the thermal expansion coefficient by optimizing the components of the outer layer material, and the thermal expansion coefficient of the outer layer material is 10.3 to 11.2 × 10 ⁻⁶ / ° C. Table 2), which contributes to the suppression of thermal expansion of the outer layer material. However, it is not considered to reduce the thermal crown from the viewpoint of suppressing the thermal conductivity of the outer layer material and reducing the temperature increase in the vicinity of the central portion of the roll and in the inside thereof.

  The present invention focuses on the thermal conductivity of the outer layer material and aims to reduce this by means of technical means different from the prior art, and has excellent wear resistance and accident resistance as well as a thermal crown. An object of the present invention is to provide an outer layer material for rolling rolls that suppresses growth and is excellent in sheet passing properties and a rolling roll using the same.

  The thermal crown in the rolling roll is manifested by the amount of thermal expansion of the roll being different depending on the temperature difference between the central portion in the axial direction of the roll and the end portion, and having a convex shape in the axial direction of the roll. That is, the thermal crown appears when the temperature in the vicinity of the central portion in the axial direction of the roll becomes higher. In recent years, with the aim of improving the productivity of rolling, the time continuously used for one rolling tends to increase drastically by, for example, an increase in the number of rolling or continuous rolling. In such a mill, the processing heat generated on the roll surface is more transferred to the inside, and the temperature inside the roll near the central portion in the axial direction of the roll rises more easily, so that the thermal crown tends to increase. Therefore, the present inventors reduced the heat transfer by reducing the heat transfer near the center in the axial direction of the roll of the outer layer material itself constituting the roll use layer on the surface side of the roll and to the inside of the roll, and the growth of the thermal crown. I tried to suppress it.

  Further, the outer layer material and the inner layer material constituting the roll expand according to the thermal expansion coefficient, but generally the thermal expansion coefficient increases as the temperature becomes higher. Therefore, reducing the heat transfer to the inside of the roll and suppressing the temperature rise is preferable for suppressing the thermal crown from the viewpoint of further suppressing the thermal expansion of the roll.

  As a result of earnest research on the factors affecting the thermal conductivity of the outer layer material, the present inventors have come to the idea that optimization of the components of the metal structure as well as optimization of the chemical composition have a large effect on the thermal conductivity. In addition, the MC carbide, which has a low thermal conductivity, is uniformly dispersed in a large amount in the metal structure of the outer layer material, thereby providing excellent wear resistance and thermal conductivity compared to conventional high-speed outer layer materials. It was found that can be reduced.

  That is, the outer layer material for rolling rolls of the present invention has a structure in which MC carbide is dispersed in an area ratio of 20 to 60% on a base having a Vickers hardness of Hv550 to 900, and a thermal conductivity at 300 ° C. is 25 W / m. -K or less.

In addition, the second outer layer material for rolling rolls of the present invention is based on a base having a Vickers hardness of Hv 550 to 900, MC carbide is 20 to 60% in area ratio, M ₂ C, M _{6 having an} equivalent circle diameter of 1 μm or more. It is a structure in which 0 to 3% of the total amount of C and M ₇ C ₃ carbides is dispersed, and the thermal conductivity at 300 ° C. is 25 W / m · K or less.

  In the present invention, a region not containing MC carbide having an equivalent circle diameter of 15 μm or more in the structure of the outer layer material does not exceed 150 μm in inscribed circle diameter.

  An average inter-particle distance between MC carbides having an equivalent circle diameter of 15 μm or more in the structure of the outer layer material is 10 to 40 μm.

  The average equivalent circle diameter of MC carbide in the structure of the outer layer material is preferably 10 to 50 μm.

  The ratio (G / H) of the average inter-particle distance (G) between MC carbides having an equivalent circle diameter of 15 μm or more in the structure of the outer layer material to the average equivalent circle diameter (H) of MC carbides is 2 or less. Is desirable.

  Moreover, the outer layer material for rolling rolls of the present invention has a chemical component of mass%, C: more than 2.5% and 9.0% or less, Si: more than 0.1% and 3.5% or less, Mn: 0 More than 1% and 3.5% or less, V: more than 11.0% and 40.0% or less, and the balance Fe and unavoidable impurity elements.

  Further, in the outer layer material, the chemical component is mass%, Cr: more than 1.0% and 15.0% or less, Mo: more than 0.5% and less than 20.0%, and W: more than 1.0% and 40%. It is characterized by containing any one or more of 0.0% or less.

Further, in the chemical component of the outer layer material of the present invention, a part of the V is substituted with Nb in a range satisfying the following formula (1) in mass%.
11.0% <V% + 0.55 × Nb% ≦ 40.0% (1)

Furthermore, the following expression (2) is satisfied.
0 <C% −0.2 × (V% + 0.55 × Nb%) ≦ 2.0% (2)

  Further, it is characterized by containing one or two of Ni: 2.0% or less and Co: 10.0% or less in mass%.

  Furthermore, it is characterized by containing any one or two of Ti: 0.5% or less and Al: 0.5% or less by mass%.

  Moreover, the outer layer material for rolling rolls of the present invention is formed by centrifugal casting. Furthermore, it is a rolling roll formed using the outer layer material for rolling rolls of the present invention.

First, the structural elements of the outer layer material for rolling rolls of the present invention will be described.
The base is a portion excluding carbides such as MC carbide, and is mainly composed of Fe and alloy elements, and the hardness changes due to transformation by heat treatment, precipitation of very fine carbides in the base, and the like. When the hardness of the base is Vickers hardness and less than Hv550, the wear resistance is lowered. From the viewpoint of improving the wear resistance, it is desirable that the hardness of the base is high, but if it exceeds Hv900, the toughness of the base decreases. A more preferable range of the hardness of the base is Hv650-850. A more preferable range is Hv650-750.

  The greatest feature of the present invention is to control the dispersion form of MC carbide. Since MC carbide has a lower thermal conductivity than an Fe-based matrix, it is effective for reducing the thermal conductivity of the outer layer material. Among MC carbides, in particular, the thermal conductivity of VC carbide is about 4 W / m · K, and that of NbC carbide is about 14 W / m · K, which is extremely small compared to the base of about 30 to 50 W / m · K. On the other hand, the thermal conductivity of WC carbide is not preferable because it is about 35 W / m · K. The most preferable MC carbide is mainly composed of V, but a part or all of the MC carbide may be substituted with Nb. Further, the alloy components contained in the MC carbide may contain W, Mo, Cr, Fe, etc., but it is desirable that the total amount of V and Nb occupy 50% or more.

  MC carbide has a higher hardness than other carbides, and contributes to an improvement in wear resistance. Furthermore, MC carbide is stable at high temperatures and hardly metal-bonds with the material to be rolled, and therefore exhibits excellent effects in improving seizure resistance. Since MC carbide tends to become granular, it has a characteristic that there is little decrease in toughness even if it is contained in a large amount. The MC carbide of the present invention has insufficient wear resistance and seizure resistance when the area ratio is less than 20%, and if MC carbide exceeds 60% by area ratio, the effect of improving seizure resistance is saturated and toughness is reduced. It drops significantly. Therefore, MC carbide is preferably 20 to 60% in terms of area ratio. A more preferable area ratio is 30 to 50%.

  The outer layer material of the present invention has a thermal conductivity at 300 ° C. of 25 W / m · K or less. The outer layer material of the present invention can achieve a significantly lower thermal conductivity by specifying the MC carbide dispersion form. Thereby, the temperature rise near the axial direction center part of a roll and its inside can be reduced, the growth of a thermal crown can be suppressed, and plate | board property can be improved. A more preferable range of thermal conductivity at 300 ° C. is 23 W / m · K or less, and a more preferable range is 21 W / m · K or less.

In the outer layer material of the present invention, the total amount of M ₂ C, M ₆ C and M ₇ C ₃ carbides having a circle equivalent diameter of 1 μm or more can be dispersed in an area ratio of 0 to 5%. M ₂ C and M ₆ C carbides mainly contain a large amount of Mo and W, and M ₇ C ₃ carbides are a carbide mainly containing a large amount of Cr. These are carbides having hardness next to MC carbides, but are coarse and easily distributed in a network. When carbides other than these MC carbides are contained excessively, cracks during a rolling accident easily propagate these carbides, and toughness decreases. When the sum of these carbides exceeds 5% in terms of area ratio, the carbides become coarse and the rough skin resistance and toughness deteriorate. The smaller the number, the better. The area ratio may be 0%. A more preferable area ratio is 0 to 1%. The outer layer material of the present invention may contain a small amount of various carbides other than MC, M ₂ C, M ₆ C, and M ₇ C ₃ carbides.

  In the structure of the outer layer material of the present invention, it is preferable that the region not containing MC carbide having an equivalent circle diameter of 15 μm or more does not exceed 150 μm in inscribed circle diameter. When the MC carbide has an equivalent circle diameter of less than 15 μm, the effect of improving the seizure resistance inherent to the MC carbide cannot be expected. In addition, the inscribed circle diameter of the region not including MC carbide having an equivalent circle diameter of 15 μm or more is set to 150 μm or less. If there is a region larger than the inscribed circle diameter, variation in the distribution of MC carbide cannot be ignored. Larger and inferior in seizure resistance. It is more preferable that the region not including MC carbide having an equivalent circle diameter of 15 μm or more does not exceed 120 μm in inscribed circle diameter. Furthermore, it is more desirable not to exceed 80 μm.

  In the structure of the outer layer material of the present invention, the average interparticle distance between MC carbides having an equivalent circle diameter of 15 μm or more is preferably 10 to 40 μm. If the distance between the average particles is smaller than this, the MC carbide aggregates too much, and micro unevenness due to the difference in wear occurs between the portion where the MC carbide is large and the portion where the MC carbide is small, thereby impairing the rough skin resistance. When the average inter-particle distance is larger, the variation in the distribution of MC carbides becomes so large that it cannot be ignored, and the seizure resistance is poor. The average interparticle distance between MC carbides having an equivalent circle diameter of 15 μm or more is more preferably 20 to 30 μm.

  In addition, in the structure of the outer layer material of the present invention, it is desirable that the average equivalent circle diameter of the dispersed MC carbide is 10 to 50 μm. During rolling, the roll surface is exposed to high heat from the rolled steel sheet. In particular, when the heat load is high, the roll surface is affected by heat by about 10 μm, and the roll base is softened, which causes deterioration of the wear resistance and rough skin resistance of the roll. When the average equivalent circle diameter of MC carbide is less than 10 μm, MC carbide cannot support the above-mentioned softened base, and wear resistance and rough skin resistance deteriorate. On the other hand, when it exceeds 50 μm and becomes coarse, the effect of improving seizure resistance is saturated and toughness is lowered. A more preferable range of the average equivalent circle diameter of the MC carbide is 10 to 40 μm, and more preferably 15 to 30 μm.

  In the structure of the outer layer material of the present invention, the ratio (G / H) between the average inter-particle distance (G) between MC carbides having an equivalent circle diameter of 15 μm or more and the average equivalent circle diameter (H) of MC carbides is It is desirable that it is 2 or less. The outer layer material of the present invention contains a large amount of MC carbide having excellent wear resistance and is excellent in wear resistance. On the other hand, MC carbide tends to aggregate during production. When the MC carbide aggregates, microscopic unevenness due to a difference in wear occurs in a portion where the MC carbide is large and a portion where the MC carbide is small, which is a cause of impairing the rough skin resistance. When this G / H value exceeds 2, MC carbide tends to agglomerate, and 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. A more preferable value of G / H is 1.5 or less.

Here, the equivalent circle diameter in the present invention will be described. FIG. 1 shows a conceptual diagram of the equivalent circle diameter. The equivalent circle diameter represents the diameter of a circle having the same area as the object (in this case, a carbide). In FIG. 1, when the area of the measuring object E is A, the circle equivalent diameter D is the diameter of the circle B corresponding to the area equal to the area A of the measuring object, and is represented by the equation (3).
Equivalent circle diameter D = √ (A × 4 / π) (3)

  Thus, the equivalent circle diameter D of the MC carbide of the present invention and the average equivalent circle diameter H of the MC carbide obtained by averaging them were obtained.

  The inscribed circle diameter of the region not including MC carbide having an equivalent circle diameter of 15 μm or more in the present invention will be described. FIG. 2 shows a conceptual diagram of the inscribed circle diameter in a region not including MC carbide having an equivalent circle diameter of 15 μm or more.

In FIG. 2, symbols a, a1, a2, a3, and a4 (white coating portions) are MC carbides having a circle equivalent diameter of 15 μm or more, and symbol b (black coating portion) is an MC carbide having an equivalent circle diameter of less than 15 μm, symbol e Is a portion excluding MC carbides a and b, and is a region where the base and M ₂ C, M ₆ C and M ₇ C ₃ carbides exist. In this case, the inscribed circle diameter of the present invention is drawn innumerably on the surface of the region e. As shown in FIG. 2, the inscribed circle diameter d inscribed in all of the MC carbides a1 to a4 of 15 μm or more excluding the MC carbide b of less than 15 μm from the measurement object is the inscribed circle diameter in the present invention. .

The average interparticle distance between MC carbides having an equivalent circle diameter of 15 μm or more in the present invention will be described. FIG. 3 shows a conceptual diagram of the average interparticle distance. In FIG. 3, symbol a (white coated portion) represents MC carbide having an equivalent circle diameter of 15 μm or more, symbol b (black coated portion) represents MC carbide having an equivalent circle diameter of less than 15 μm, and symbol e excludes MC carbides a and b. This is a region where the base and M ₂ C, M ₆ C and M ₇ C ₃ carbides exist. In this case, in an arbitrary straight line L, the MC carbide b of less than 15 μm is excluded from the measurement object, and the shortest distance between adjacent MC carbides a in the 15 μm or more MC carbide a existing on the straight line L When the line segment is Ln (n is the number of line segments), the average inter-particle distance G is expressed by Expression (4). X is another arbitrary straight line, and the average interparticle distance G is obtained in the same manner as the straight line L.
Average interparticle distance G between MC carbides with equivalent circle diameters of 15 μm or more G =
(Σ (L ₁ + L ₂ +... + L _n )) / n (4)

  Next, the reason for limiting the chemical component (mass%) of the outer layer material for rolling rolls of the present invention will be described. The chemical component of the outer layer material of the present invention is not the component of the molten metal, but indicates the chemical component of the outer layer material in the final product.

C: More than 2.5% and not more than 9.0% C is an essential element that contributes to wear resistance by forming MC carbide mainly by combining with alloy elements such as V or Nb. Further, C that does not bond with the alloy element mainly contributes to wear resistance by strengthening the matrix by solid solution or precipitation with the alloy element in the matrix. If C is 2.5% or less, the amount of MC carbide is insufficient and sufficient wear resistance cannot be obtained. On the other hand, if C exceeds 9.0%, the amount of carbide becomes excessive and the thermal crack resistance deteriorates. The C content is more preferably more than 3.5% and not more than 9.0%, still more preferably more than 4.5% and not more than 9.0%.

Si: more than 0.1% and 3.5% or less Si acts as a deoxidizer in the molten metal. When Si is 0.1% or less, the deoxidation effect is insufficient and casting defects are likely to occur. Moreover, when it exceeds 3.5%, it will embrittle. The Si content is more preferably 0.2 to 2.5%, and still more preferably 0.2 to 1.5%.

Mn: More than 0.1% and 3.5% or less Mn is effective when deoxidation of molten metal or S, which is an impurity, is fixed as MnS and exceeds 0.1%. When Mn exceeds 3.5%, retained austenite tends to be generated, and the hardness cannot be stably maintained, and the wear resistance is likely to deteriorate. A more preferable Mn content is 0.2 to 2.5%, and further preferably 0.2 to 1.5%.

V: more than 11.0% and not more than 40.0% V is an important element of the present invention which mainly bonds with C to form MC carbide. One of the features of the present invention is that the outer layer material contains a very large amount of MC carbide. When V is 11.0% or less, MC carbide is insufficient and sufficient wear resistance cannot be obtained. On the other hand, if V exceeds 40.0%, MC carbide becomes excessive and toughness deteriorates. The V content is more preferably more than 15.0% and not more than 40.0%, still more preferably more than 18.0% and not more than 40.0%.

Cr: more than 1.0% and 15.0% or less Cr dissolves in the matrix to improve hardenability, and part of it combines with C in the matrix and precipitates as ultrafine carbide to strengthen the matrix. . When Cr is 1.0% or less, the effect of strengthening the base cannot be obtained sufficiently. On the other hand, if it exceeds 15.0%, carbides other than MC carbide such as M ₇ C ₃ carbide particularly increase, coarsen or crystallize in a network, and heat cracking resistance deteriorates. A more preferable Cr content is 3.0 to 9.0%.

Mo: more than 0.5% and not more than 20.0% Mo dissolves in the matrix and enhances hardenability, and partly bonds with C in the matrix and precipitates as ultrafine carbides to strengthen the matrix. Furthermore, a part of Mo forms granular carbide together with V, Nb and the like. When Mo is 0.5% or less, the effect of strengthening the base cannot be sufficiently obtained. On the other hand, if it exceeds 20.0%, carbides other than MC carbides such as M ₂ C and M ₆ C are particularly increased, coarsened or crystallized in a network, and heat cracking resistance is deteriorated. A more preferable Mo content is 2.5 to 20.0%, and further preferably 2.5 to 10.0%.

W: More than 1.0% and 40.0% or less W is solid-solved in the base part to improve hardenability, and partly bonds with C in the base and precipitates as ultrafine carbide to strengthen the base part. To do. Furthermore, a part of W forms granular carbide together with V, Nb and the like. If W is 1.0% or less, the effect of strengthening the base cannot be obtained sufficiently. On the other hand, if it exceeds 40.0%, carbides other than MC carbide such as M ₆ C and M ₂ C are particularly increased, coarsened or crystallized in a network, and heat cracking resistance is deteriorated. A more preferable W content is 5.0 to 40.0%, and further preferably 5.0 to 20.0% or less.

  The outer layer material of the present invention may contain at least one kind or two or more kinds of Cr, Mo or W, which are base strengthening elements, in order to obtain a base necessary for sufficiently exhibiting the wear resistance. desirable.

11.0% <V% + 0.55 × Nb% ≦ 40.0% (1)
Nb has the same action as V in that it forms MC carbides. When V is 1.0% in mass%, Nb is equivalent to V at 0.55 × Nb% in mass% from the atomic weight ratio. Therefore, a part of V can be replaced with Nb within the range of the formula (1).

0 <C% −0.2 × (V% + 0.55 × Nb%) ≦ 2.0% (2)
When the value of C% −0.2 × (V% + 0.55Nb%) is 0 or less, the amount of MC carbide cannot be obtained sufficiently, and V and Nb become excessive in the base, and the hardness of the base is obtained. The wear resistance decreases. When the value of C% −0.2 × (V% + 0.55Nb%) exceeds 2.0%, carbides other than MC carbides such as M ₂ C, M ₆ C, and M ₇ C ₃ carbides In particular, it increases, becomes coarse or crystallizes in a network, and heat cracking resistance deteriorates.

  Moreover, according to the use and usage method of a rolling roll, the following components can be suitably added to the outer layer material of the present invention.

Ni: 2.0% or less Ni dissolves in the base and is effective in improving the hardenability of the base. If Ni exceeds 2.0%, the base austenite is stabilized, and the base hardness cannot be sufficiently obtained.

Co: 10.0% or less Co dissolves in the base portion and has the effect of strengthening the base. In addition, the hardness of the base can be maintained even at high temperatures. If Co exceeds 10.0%, the toughness decreases. On the other hand, since Co is expensive, it is desirable to determine the content in consideration of economy and use conditions.

Ti: 0.5% or less Ti acts as a deoxidizer in the molten metal, and also has an effect of combining with N to form a nitride, forming a nucleus of granular carbide, and making the granular carbide fine. Part of it is combined with C to become part of granular carbide. A Ti effect of 0.5% or less is sufficient.

Al: 0.5% or less Al acts as a deoxidizer in the molten metal and has an effect of making the granular carbide fine. If it exceeds 0.5%, the hardenability is deteriorated, and it is difficult to obtain sufficient base hardness.

  The outer layer material for rolling rolls of the present invention is preferably formed by a centrifugal casting method, and the outer layer material for rolling rolls formed by centrifugal force casting of the present invention will be described. FIG. 4 is a view for explaining an outer layer material for rolling rolls formed by centrifugal casting according to the present invention. The outer layer material of the present invention forms a concentrated layer of MC carbide on the inner surface side by casting molten metal adjusted to a chemical composition for crystallizing primary MC carbide into a casting mold for centrifugal force casting and centrifugal casting. Can be obtained. In FIG. 4, a portion is a layer in which MC carbides are concentrated and concentrated. The part B is the other part and is a layer in which MC carbide is poor. The part C is a hollow part formed by centrifugal casting. After centrifugal casting, the portion shown in FIG. 4 is removed by cutting or the like, and the portion shown in FIG. 4 is obtained, that is, the outer layer material for a roll according to the present invention. That is, the portion A of the layer in which MC carbides are concentrated is used as a rolling use layer.

Further, in the composite rolling roll in which the outer layer material of the present invention is formed on the outer periphery of the inner layer material, the thermal crown is further suppressed by using the inner layer material having a small thermal expansion coefficient in order to suppress the thermal expansion of the inner layer material. The plate property is improved. When the average thermal expansion coefficient of the inner layer material from room temperature to 300 ° C. exceeds 12 × 10 ⁻⁶ / ° C., the thermal crown is likely to increase, and the plate passing property is deteriorated. The inner layer material preferably has an average coefficient of thermal expansion of 12 × 10 ⁻⁶ / ° C. or less at room temperature to 300 ° C., and particularly preferably ductile cast iron. In the composite rolling roll, one or more intermediate layers may be provided between the outer layer material and the inner layer material of the present invention. Furthermore, the rolling roll of the present invention may be a solid or hollow roll formed with the outer layer material of the present invention, and may be configured by fitting a sleeve having the outer layer material of the present invention to a shaft material.

  The outer layer material for rolling rolls of the present invention and the rolling rolls using the same exhibit excellent wear resistance and sheet-passability in general work rolls for rolling. In particular, the work rolls used in the finishing rows of hot sheet rolling mills exhibit extremely excellent wear resistance and sheet passing properties, contributing to the improvement of productivity and the roll basic unit in rolling mills.

  The outer layer material of the present invention is formed by casting molten metal adjusted to a chemical composition for crystallizing primary granular carbide into a centrifugal casting mold, and centrifugally casting to concentrate MC carbide on the inner surface side of the mold. Layer was formed. Specimen No. Examples 1 to 5 are embodiments of the present invention, which are formed by centrifugal casting according to the present invention, and are collected from a portion corresponding to the above-mentioned portion a in FIG. In addition, specimen No. Nos. 6 to 8 are comparative examples, specimen Nos. Reference numerals 9 and 10 are conventional examples. Specimen No. No. 6 is formed by stationary casting. 7-10 were formed by centrifugal casting.

  The collected specimen No. 1-8 and no. No. 10 was subjected to heat treatment after quenching at 1000 to 1200 ° C. and tempering at 500 to 600 ° C. three times. In addition, specimen No. No. 9 was heated at 400 to 500 ° C. after casting and subjected to residual austenite decomposition and strain relief heat treatment. Each specimen was processed into various specimen shapes after these heat treatments. These test materials No. Table 1 shows 1 to 10 chemical components (% by mass). Here, formula (1) in Table 1 is a value of V% + 0.55 × Nb%, and formula (2) is a value of C% −0.2 × (V% + 0.55 × Nb%). . Moreover, the chemical component of the outer layer material in Table 1 indicates not the component of the molten metal but the chemical component of the outer layer material in the final product.

  Next, the thermal conductivity of each sample material at 300 ° C. was measured. The thermal conductivity was measured by a laser flash method using a test piece obtained by processing the specimen to a diameter of 10 mm and a thickness of 1 mm.

  Moreover, the average thermal expansion coefficient in normal temperature-300 degreeC of each test material was measured. The thermal expansion coefficient was measured using a test piece obtained by processing the specimen into 8 mm × 8 mm × 17 mm, and the average thermal expansion coefficient at room temperature to 300 ° C. was measured using a thermal stress strain measuring device (SSC / 5200 manufactured by Seiko Electronics Industry Co., Ltd.). ).

Furthermore, the total area ratio of M ₂ C, M ₆ C and M ₇ C ₃ carbides, the maximum value of the inscribed circle diameter of the region not including MC carbides having an equivalent circle diameter of 15 μm or more, Vickers hardness of the base, MC The average equivalent circle diameter of carbide and the average interparticle distance of MC carbide having an equivalent circle diameter of 15 μm or more were measured.

  In addition, as an evaluation of wear resistance and rough skin resistance, the wear amount and roughness of a wear test using a rolling wear tester are measured. A seizure resistance evaluation is a measurement of a seizure area ratio by a frictional thermal shock test. The fracture toughness value KIC was measured.

  The area ratio of MC carbide was determined by first polishing the specimen material and then corroding the MC carbide in black by electrolytic corrosion in an aqueous potassium dichromate solution, followed by an image analysis device (SPICCA- manufactured by Nippon Avionics Co., Ltd.). II) and measured.

In addition, the area ratio of M ₂ C, M ₆ C and M ₇ C ₃ carbides is determined by first polishing the specimen to a mirror surface and then corroding it with Murakami's reagent, so that M ₂ C, M ₆ C, and M ₇ C _{After the 3} carbides were corroded black or colored black or gray, they were measured using an image analyzer. 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 easily discriminated, were measured.

  In these image analyses, the area ratio was measured in a field of view corresponding to 0.23 mm × 0.25 mm of the specimen. This measurement was performed for any 20 visual fields of each test material, and the average value was obtained.

  The average equivalent circle diameter of MC carbide was determined by first mirror-polishing the test material and then corroding MC carbide in black by electrolytic corrosion in an aqueous potassium dichromate solution, followed by an image analyzer (manufactured by Nippon Avionics Co., Ltd.). Measurement was performed using SPICCA-II). The measurement range of the image analysis was such that one visual field corresponds to 0.23 mm × 0.25 mm of the test material, and each test material was measured for 20 arbitrary visual fields, and the average value of the measured values was obtained.

The average interparticle distance between MC carbides having an equivalent circle diameter of 15 μm or more is that the specimen is first mirror-polished and then the base is corroded with a picric alcohol solution. When observed with an optical microscope, the matrix appears dark gray, the MC carbides appear light gray, and the M ₂ C, M ₆ C, and M ₇ C ₃ carbides appear white. In this way, the average interparticle distance of MC carbide having an equivalent circle diameter of 15 μm or more is measured using an optical microscope texture photograph of 200 × magnification of an arbitrary 1.0 mm × 1.5 mm surface of the test material sample. did.

In order to measure the inscribed circle diameter in a region not containing MC carbide having an equivalent circle diameter of 15 μm or more, the specimen is first mirror-polished and then the base is corroded with a picric acid alcohol solution. When observed with an optical microscope, the matrix appears dark gray, the MC carbides appear light gray, and the M ₂ C, M ₆ C, and M ₇ C ₃ carbides appear white. In this way, an optical microscope texture photograph of a magnification of 100 times on an arbitrary 2.0 mm × 3.0 mm surface of the test material sample was prepared, and the maximum value of the inscribed circle diameter of the present invention was measured.

  The Vickers hardness of the base was measured in a load range of 50 g to 200 g using a Vickers hardness tester after mirror-polishing the specimen and slightly corroding the base with a picric acid ethanol solution. The average value was calculated | required about arbitrary five places for each test material.

  FIG. 5 shows a schematic view of a rolling wear tester. In FIG. 5, the rolling wear tester includes a rolling mill 1, a heating furnace 4 for preheating the rolled material S, a cooling water tank 5 for cooling the rolled material S, a winder 6 for the rolled material S, and a tension controller 7. Consists of Test rolls 2 and 3 are incorporated in the rolling mill 1. A test roll was prepared from each of the above-described test materials, and a small sleeve roll having an outer diameter of 60 mm, an inner diameter of 40 mm, and a width of 40 mm was used. A test roll is incorporated in the rolling wear tester, and the test conditions are rolling material: SUS304, rolling reduction: 25%, rolling speed: 150 m / min, rolling temperature: 900 ° C., rolling distance: 300 m / time, roll cooling: water cooling The number of rolls: The test was performed by a quadruple type. After rolling, the depth of wear and the ten-point average roughness (Rz) generated on the surface of the test roll were measured with a stylus type surface roughness meter.

  FIG. 6 shows a schematic diagram of a frictional thermal shock tester. In this test, the weight 9 is dropped on the rack 8 to rotate the pinion 10 and bring the biting material 12 into strong contact with the test material 11. By this test, the test material 11 is indented, and the biting material adheres to and adheres to a part or the entire surface thereof. The seizing area ratio is obtained by dividing the seizing adhesion area by the indentation area in percentage. This test was performed twice for each specimen, and the average of the seizure area ratio was determined.

  The fracture toughness value KIC was measured by taking a test piece for measuring the fracture toughness value KIC from each specimen and performing a test based on ASTM E399. The measurement was performed on two test pieces for each specimen, and the average value was obtained.

Table 2 shows the results of various measurements. That is, the area ratio (%) of MC carbide having an equivalent circle diameter of 1 μm or more, the total area ratio AA (%) of M ₂ C, M ₆ C and M ₇ C ₃ carbides, and the MC carbide having an equivalent circle diameter of 15 μm or more. Value BB (μm) of the inscribed circle diameter of the region not containing the heat, thermal conductivity DD (W / m · K) at 300 ° C., average thermal expansion coefficient CC from normal temperature to 300 ° C. (× 10 ⁻⁶ / ° C.) , MC carbide average particle distance G (μm) with equivalent circle diameter of 15 μm or more, MC carbide average circle equivalent diameter H (μm), Vickers hardness of base (Hv), wear amount (μm), surface roughness Rz (μm), seizure area ratio (%), and fracture toughness value KIC (kg / mm ^3/2 ) are shown.

  In FIG. 1 shows a metallographic structure. In FIG. 7, the white part is MC carbide, and the black part is the base. Specimen No. 1 shows that MC carbide is distributed in high concentration.

  In FIG. 6 shows the metal structure. In FIG. 8, the white part is MC carbide and the black part is the base. Specimen No. 6 shows that MC carbide is partially unevenly distributed.

FIG. 9 shows a specimen No. of a conventional high-speed roll material. 10 metallographic structures are shown. In FIG. 9, white fine-grained portions are MC carbides, white mesh-like portions are M ₂ C, M ₆ C, and M ₇ C ₃ carbides, and black portions are bases. Specimen No. 10 shows that MC carbides are partially unevenly distributed and M ₂ C, M ₆ C, and M ₇ C ₃ carbides are distributed in a network.

  FIG. 10 shows a comparative diagram of thermal conductivity. 10, the horizontal axis represents temperature (° C.) and the vertical axis represents thermal conductivity (W / m · K). 1 (example of the present invention), No. 1 6 (Comparative Example), No. 10 (conventional example).

  Sample No. of the present invention. The thermal conductivities at 300 ° C. of 1 to 5 are all 25 W / m · K or less, and the thermal crown can be significantly suppressed. This is largely due to the fact that MC carbide is dispersed and distributed in an area ratio of 20% or more. Especially, when the area ratio of MC carbide exceeds 30%, it can be seen that the thermal conductivity at 300 ° C. is 21 W / m · K or less and the effect is exhibited.

  The amount of wear is the same as the test material No. 9 and no. It is less than half compared to 10, wear resistance is extremely good, and fracture toughness value KIC is also higher than that of conventional materials, and it has accident resistance. Moreover, the average thermal expansion coefficient in normal temperature-300 degreeC is No. of a comparative example and a prior art example. It is lower than 6-10, and it is possible to further exhibit the effect of suppressing the thermal crown.

  Comparative Example No. 6, the region not including MC carbide having an equivalent circle diameter of 15 μm or more exceeds 150 μm in inscribed circle diameter, and the average inter-particle distance (G) between MC carbides having an equivalent circle diameter of 15 μm or more, and the MC carbide The ratio (G / H) to the average equivalent circle diameter (H) is outside the range of the present invention exceeding 2 and the roughness and seizure area ratio are less than those of the conventional materials, and the rough skin resistance and seizure resistance are Inferior.

  Comparative Example No. 7 is C%, Ni%, the value of formula (2), the area ratio of MC carbide, the base hardness, the average equivalent circle diameter of MC carbide is outside the scope of the present invention, and the equivalent circle diameter is 15 μm or more. The ratio (G / H) between the average inter-particle distance (G) between MC carbides and the average equivalent circle diameter (H) of MC carbides exceeds 2, and the amount of wear and seizure area ratio are conventional materials. The wear resistance and seizure resistance are inferior. Furthermore, the thermal conductivity at 300 ° C. exceeds 25 W / m · K, and the growth of the thermal crown cannot be sufficiently suppressed.

Comparative Example No. 8 is V%, Cr%, the value of formula (1), the value of formula (2), the area ratio of MC carbide, the total area ratio of M ₂ C, M ₆ C and M ₇ C ₃ carbide of the present invention The ratio (G / H) of the average inter-particle distance (G) between MC carbides having an equivalent circle diameter of 15 μm or more and the average equivalent circle diameter (H) of MC carbides exceeds 2 (G / H). Yes, the roughness and KIC are lower than the conventional materials, and the rough skin resistance and toughness are inferior. Further, the thermal conductivity at 300 ° C. exceeds 25 W / m · K, and the thermal crown is not sufficiently suppressed.

  No. of the conventional example. 9 is V%, Ni%, the value of the formula (1), the area ratio of MC carbide, the average equivalent circle diameter of MC carbide is outside the scope of the present invention, and between MC carbides having an equivalent circle diameter of 15 μm or more. The ratio (G / H) between the average interparticle distance (G) and the average equivalent circle diameter (H) of MC carbide exceeds 2, and the wear resistance is inferior to that of the present invention material. Further, the thermal conductivity at 300 ° C. exceeds 25 W / m · K, and the thermal crown is not sufficiently suppressed.

  When the rolling roll was manufactured using the outer layer material for the rolling roll of the present invention and actually rolled, it was confirmed that it was excellent in wear resistance, rough skin resistance and seizure resistance.

  The outer layer material for rolling rolls of the present invention and the rolling rolls using the same exhibit excellent wear resistance and sheet-passability in general work rolls for rolling. In particular, the work rolls used in the finishing rows of hot sheet rolling mills exhibit extremely excellent wear resistance and sheet passing properties, contributing to the improvement of productivity and the roll basic unit in rolling mills.

It is a figure for demonstrating a circle equivalent diameter. It is a figure for demonstrating an inscribed circle diameter. It is a figure for demonstrating the distance between average particle | grains. It is a figure for demonstrating the outer-layer material for rolling rolls of this invention. It is the schematic of a rolling wear tester. It is the schematic of a friction thermal shock tester. Sample No. of the present invention. 1 is a metallographic photograph taken by an optical microscope. Sample No. of Comparative Example 6 is a metallographic photograph of the optical microscope of No. 6. Sample No. of conventional example It is a metallographic photograph by 10 optical microscopes. It is a comparison figure of thermal conductivity.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Rolling wear test machine, 2 Test roll, 3 Test roll, 4 Heating furnace,
5 Cooling water tank, 6 Winder, 7 Tension controller, S Rolled material,
8 racks, 9 weights, 10 pinions, 11 test materials,
12 Biting material, A Area of the object, B circle, D circle equivalent diameter,
E measurement object,
a (a1, a2, a3, a4) MC carbide having an equivalent circle diameter of 15 μm or more,
b MC carbide with an equivalent circle diameter of 15 μm or less, c inscribed circle, d inscribed circle diameter,
e Region excluding MC carbides a and b, L arbitrary straight line,
L1, L2, L3 Interparticle distance, b MC carbide centrifuge concentrated layer,
Part excluding Loi, C Hollow part

Claims (14)

A rolling roll having a structure in which MC carbide is dispersed in an area ratio of 20 to 60% on a base having a Vickers hardness of Hv550 to 900, and a thermal conductivity at 300 ° C. is 25 W / m · K or less. Outer layer material. Dispersed in a base having a Vickers hardness of Hv 550 to 900 in an amount of 20 to 60% of MC carbide in an area ratio and 0 to 5% in total amount of M ₂ C, M ₆ C and M ₇ C ₃ carbide having a circle equivalent diameter of 1 μm or more. An outer layer material for a rolling roll, characterized in that the thermal conductivity at 300 ° C. is 25 W / m · K or less. The outer layer material for rolling rolls according to claim 1 or 2, wherein a region not including MC carbide having an equivalent circle diameter of 15 µm or more in the structure does not exceed 150 µm in inscribed circle diameter. The outer layer material for rolling rolls according to any one of claims 1 to 3, wherein an average inter-particle distance between MC carbides having an equivalent circle diameter of 15 µm or more in the structure is 10 to 40 µm. The outer layer material for rolling rolls according to any one of claims 1 to 4, wherein an average equivalent circle diameter of MC carbide in the structure is 10 to 50 µm. A ratio (G / H) of an average inter-particle distance (G) between MC carbides having an equivalent circle diameter of 15 μm or more in the structure to an average equivalent circle diameter (H) of the MC carbide is 2 or less. The outer layer material for rolling rolls according to any one of claims 1 to 5. The outer layer material has a chemical content of mass%, C: more than 2.5% and 9.0% or less, Si: more than 0.1% and 3.5% or less, Mn: more than 0.1% and 3.5% The outer layer material for rolling rolls according to any one of claims 1 to 6, characterized in that it contains V: more than 11.0% and 40.0% or less, and consists of the remaining Fe and unavoidable impurity elements. Further, any one of Cr: more than 1.0% and not more than 15.0%, Mo: more than 0.5% and not more than 20.0% and W: more than 1.0% and not more than 40.0% 1 The outer layer material for rolling rolls according to claim 7, comprising seeds or two or more species. 9. The outer layer material for rolling rolls according to claim 7, wherein a part of the V is substituted with Nb in a range satisfying the following formula (1) in mass%.
11.0% <V% + 0.55 × Nb% ≦ 40.0% (1) Furthermore, the following (2) Formula is satisfied, The outer layer material for rolling rolls in any one of Claims 7-9 characterized by the above-mentioned.
0 <C% −0.2 × (V% + 0.55 × Nb%) ≦ 2.0% (2) The rolling roll according to any one of claims 7 to 10, further comprising, in mass%, any one or two of Ni: 2.0% or less and Co: 10.0% or less. Outer layer material. Furthermore, in mass%, it contains any 1 type or 2 types of Ti: 0.5% or less and Al: 0.5% or less, For the rolling roll in any one of Claims 7-11 characterized by the above-mentioned. Outer layer material. The outer layer material for rolling rolls according to any one of claims 1 to 12, wherein the outer layer material is formed by centrifugal casting. A rolling roll formed using the outer layer material for a rolling roll according to any one of claims 1 to 13.