JP2007038289A - Outer layer for rolling roll, and rolling roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an outer layer for a rolling roll having excellent wear resistance and rough surface resistance, capable of suppressing flattening of the roll by providing a high modulus of longitudinal elasticity to the outer layer, excellent in rolling consistency, and relatively low in manufacturing cost, and a rolling roll using the same. <P>SOLUTION: The outer layer a for the rolling roll has a structure in which 20-60% MC carbide in terms of the area ratio and carbides of M<SB>2</SB>C, M<SB>6</SB>C and M<SB>7</SB>C<SB>3</SB>of 0-5% in total with the size of ≥1 μm in terms of the circle-equivalent-diameter are dispersed in a base of the Vickers hardness of Hv550-900, and the modulus of longitudinal elasticity is ≥ 240 GPa. <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 abrasion resistance and skin roughness resistance, and particularly used in a finishing row of a hot sheet rolling mill with less flatness of the roll. It is suitable as a work roll and its outer layer material.

  Important properties that determine the productivity of rolling are the wear resistance and rough surface 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 addition, when the surface roughness resistance is poor, irregularities are generated on the roll surface, and this is transferred to the material to be rolled, thereby impairing the surface quality of the material to be rolled. In order to prevent these problems, the rolls must be replaced frequently, resulting in a decrease in rolling mill productivity due to increased 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 roll size.

Therefore, a high-speed alloy containing a large amount of alloy elements such as Cr, Mo, W, and V as an outer layer material (rolling layer) for rolling rolls intended to meet the demands of wear resistance and rough skin resistance. Is used. 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.

  On the other hand, in recent years, the application of high-pressure rolling in a hot rolling finishing row is progressing with the aim of improving mechanical properties by refining the crystal grains of steel. In such a mill, the rolling load increases, so that roll wear, that is, an increase in the amount of roll wear and early roughening of the roll surface occur. In addition, due to the high rolling load, flatness occurs on the surface of the roll, which causes slip. When these phenomena occur, stable rolling becomes difficult.

  In order to solve such a problem, various rolls have been conventionally proposed.

  For example, Patent Document 1 discloses a composite roll for hot rolling incorporated as working rolls in three rolling mills behind a finishing tandem rolling mill group that continuously hot-rolls a strip or steel plate, and the diameter of the roll 250 to 620 mm, the longitudinal elastic modulus to 200 to 260 GPa, and the chemical component of the outer layer in terms of mass ratio: C: 1.0 to 3.0%, Si: 0.2 to 2.0%, Mn: 0.2 to 2.0%, V: 3.0 to 10.0%, Cr: 3.0 to 10.0%, and one or two of Mo and W are contained in an amount of 2.0 to 10.0% And the composite roll for hot rolling which consists of remainder Fe and an unavoidable impurity is described.

  According to Patent Document 1, in hot strip continuous rolling, an operating roll having a high friction coefficient with a rolled steel material, low wear, and no flattening or yield damage is provided. High-productivity and economical rolling can be achieved by performing high-pressure rolling in a group.

  Moreover, in patent document 2, in the composite roll for hot rolling integrated in the rolling machine of three backs of the continuous hot rolling mills which carry out hot continuous rolling of a steel plate, in the circumference | surroundings of the core material which consists of steel-based materials, 10% to 50% carbide and / or nitride powder with Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W metal in mass%, C: 0.5 to 1.5%, Si: 0 1 to 2.0%, Mn: 0.1 to 2.0%, Ni: 0.1 to 2%, Cr: 0.5 to 10%, Mo: 0.1 to 2% or more The outer layer material is formed by sintering the remaining Fe and the iron-based powder composed of inevitable impurities, the diameter of the composite roll made of the outer layer material is 250 to 620 mm, and the longitudinal elastic modulus is 240 GPa or more. A composite roll for hot rolling is described.

  According to Patent Document 2, the conventional iron-based cast material naturally has a limit in elastic modulus, but the carbide of the present invention has a high elastic modulus, and by utilizing this in large quantities, it has high elasticity as a roll material. A coefficient can be given.

JP 2002-346613 A JP 2004-148321 A

  In recent years, there has been an increasing demand for rolls with excellent flatness and wear resistance, and with low flatness that facilitate stable rolling. For example, in the finish line of a hot sheet rolling mill that produces a fine-grained structure hot-rolled steel sheet, the amount of rolling reduction has increased dramatically compared to conventional rolling, in addition to improved wear resistance and rough skin resistance, In particular, rolls with less flatness are required.

  Here, Patent Document 1 does not disclose means for controlling the longitudinal elastic modulus of the hot-rolling composite roll. Moreover, it is not considered to increase the longitudinal elastic modulus and suppress roll flatness by optimizing the components of the metal structure of the outer layer. In addition, the amount of MC carbide that contributes to wear resistance is comparable to that of conventional high-speed rolls, and it is difficult to meet the demand for further improvement of wear resistance.

  Patent Document 2 discloses an outer layer material obtained by sintering carbide and / or nitride powder of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, and W metal and iron-based powder. In the obtained composite roll, the mixing ratio of the powder of the outer layer material, the roll diameter, and the range of the longitudinal elastic modulus are described. According to Patent Document 2, a high longitudinal elastic modulus of 240 GPa or more is imparted by using a large amount of these carbides or nitrides. However, it is not considered to control the amount, type and distribution state of carbides contained in the outer layer metallographic structure. In addition, these carbides and nitrides are extremely expensive and require a great number of man-hours for the sintering process, so that the manufacturing cost is higher than that of a melting process such as centrifugal casting.

The present invention has excellent wear resistance and rough skin resistance, suppresses roll flatness by imparting a high longitudinal elastic modulus to the outer layer material, has excellent rolling stability, and is relatively inexpensive to manufacture. An object of the present invention is to provide a simple rolling roll.

  Since the metal carbide in the roll outer layer material has a higher longitudinal elastic modulus than that of the base, the longitudinal elastic modulus is improved by containing a large amount thereof. Furthermore, the present inventors have found that an unprecedented high longitudinal elastic modulus can be obtained by controlling the amount, type and distribution state of the metal carbide.

  That is, the outer layer material for rolling rolls of the present invention is 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 longitudinal elastic modulus is 240 GPa or more. Features.

Further, 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, and M ₂ C, M _{6 having} a circle equivalent diameter of 1 μm or more. It is a structure in which 0 to 5% of the total amount of C and M ₇ C ₃ carbides is dispersed, and has a longitudinal elastic modulus of 240 GPa or more.

  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.

  An average equivalent circle diameter of MC carbide in the structure of the outer layer material is 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. It is characterized by.

  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.

  MC carbide has higher hardness than other carbides and contributes to improvement of wear resistance. In addition, MC carbide is stable at high temperature and hardly metal-bonds with the material to be rolled, and therefore exhibits an excellent effect 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. In addition, the greatest feature of the present invention is that the longitudinal elastic modulus is increased by containing a large amount of MC carbide. MC carbide has a higher longitudinal elastic modulus than that of Fe-based matrix, and is effective in improving the longitudinal elastic modulus of the outer layer material. Among MC carbides, for example, the longitudinal elastic modulus of VC carbide is about 270 GPa, and that of NbC carbide is about 340 GPa, which is larger than the base of about 200 to 220 GPa. MC carbide of the present invention, when the area ratio is less than 20%, the increase in wear resistance and longitudinal elastic modulus is insufficient, and when the MC carbide exceeds 60% in area ratio, the seizure resistance improving effect is saturated, Toughness is significantly reduced. 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 preferably has a longitudinal elastic modulus of 240 GPa or more. In addition, the outer layer material of the present invention specifies the dispersion form of MC carbide, thereby significantly increasing the longitudinal elastic modulus compared to conventional high-speed smelted material, suppressing the flatness of the roll surface, and improving the stability of rolling. Can be improved. A more preferable range of the longitudinal elastic modulus is 250 GPa or more, and a more preferable range is 260 GPa or more.

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. If the total of these carbides exceeds 3% 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.

  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 a 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.

  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 coated portions) are MC carbides having an equivalent circle diameter of 15 μm or more, and symbol b (black coated 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, MC carbide b of less than 15 μm is excluded from the measurement object, and the shortest distance between adjacent MC carbides a in MC carbide a of 15 μm or more existing on the straight line L is 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). Note that X is any other 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.

  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 material of the inner layer material is not particularly limited. For example, when a steel-based material having an inner layer material having a longitudinal elastic modulus of about 210 GPa is used, the roll as a whole can exhibit higher rigidity due to a synergistic effect with the outer layer material having a high longitudinal elastic modulus of the present invention. Further, when a ductile material having an inner layer material having a longitudinal elastic modulus of about 180 GPa is used, plate shape control by roll bending or the like can be facilitated even when the outer layer material having a high longitudinal elastic modulus of the present invention is used. Thus, the inner layer material may be appropriately selected according to the application and purpose. 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 roll using the same exhibit excellent wear resistance, rough skin resistance and rolling stability in general work rolls for rolling. In particular, work rolls used for high-pressure rolling in the finishing row of hot sheet rolling mills exhibit extremely excellent wear resistance, rough skin resistance and rolling stability, improving productivity in rolling mills, Contributes to reduction and quality improvement of the material to be rolled.

  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 casting mold for centrifugal force casting, and casting the centrifugal force to concentrate MC carbide on the inner surface side in 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 longitudinal elastic modulus of each test material was measured. The longitudinal elastic modulus was measured by a free resonance natural vibration method using a test piece obtained by processing a specimen into a width of 10 mm, a length of 60 mm, and a thickness of 1.5 mm.

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 of 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 carbides, the total area ratio AA (%) of M ₂ C, M ₆ C and M ₇ C ₃ carbides having an equivalent circle diameter of 1 μm or more, and MC carbides 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.

  Sample No. of the present invention. The longitudinal elastic moduli of 1 to 5 were all 240 GPa or more. Particularly, those having a large area percentage of MC carbides were significantly higher than those of conventional materials. This is largely due to the fact that MC carbide is dispersed and distributed in an area ratio of 20% or more.

  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.

  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.

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.

  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.

  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 roll using the same exhibit excellent wear resistance, rough skin resistance and rolling stability in general work rolls for rolling. In particular, work rolls used for high-pressure rolling in the finishing row of hot sheet rolling mills exhibit extremely excellent wear resistance, rough skin resistance and rolling stability, improving productivity in rolling mills, Contributes to reduction and quality improvement of the material to be rolled.

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.

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)

An outer layer material for rolling rolls having a structure in which MC carbide is dispersed in an area ratio of 20 to 60% in a base having a Vickers hardness of Hv 550 to 900 and having a longitudinal elastic modulus of 240 GPa or more. 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 by having a longitudinal elastic modulus of 240 GPa or more. 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. It is formed by centrifugal casting, The outer layer material for rolling rolls according to any one of claims 1 to 12. A rolling roll formed using the outer layer material for a rolling roll according to any one of claims 1 to 13.