JP3468381B2 - Assembling type roll - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roll for assembling type rolling having high wear resistance and seizure resistance and excellent crack resistance, and more particularly to a roll suitable as an operating roll for a continuous hot strip mill. .

[0002]

2. Description of the Related Art Conventionally, an integral type composite roll having a grain cast iron material as an outer layer has been used as a working roll of a continuous hot strip rolling mill. The grain cast iron material contains graphite in its metal structure, and even when a rolling accident, for example, is encountered during rolling, there is less seizure of the rolled material due to the effect of graphite, and the occurrence and development of cracks are compared. It has been used for a long time as a stable material because it is very few. But,
The wear resistance was becoming unsatisfactory with the sophistication of the level required for rolls. Recently, as a material satisfying this requirement, for example, the application of a high wear-resistant roll whose outer layer is a high-speed material disclosed in WO88 / 07594 is spreading. Rolls made of high-speed steel material have dramatically improved wear resistance, and thus have significantly contributed to the improvement of rolling technology, but have not been sufficiently satisfied in terms of seizure resistance and crack resistance.

When a roll for hot rolling encounters, for example, a rolling accident during rolling, it is subjected to strong pressure to seize the material to be rolled, and as a result, cracks are likely to occur and propagate. In addition, when a bite prevention accident is encountered, a crack is likely to be generated and propagate due to the thermal shock. If these cracks grow significantly, the entire roll may be damaged.
In such a case, stopping the rolling operation due to damage to the rolls causes enormous damage, but particularly in the case of expensive rolls made of high-speed material, the damage is further increased.

Since it is uneconomical to remake the entire roll, various prefabricated rolling rolls have been disclosed as being able to replace only the body. For example, Japanese Utility Model Publication No. 45-7640 discloses an assembly type hot rolling working roll in which a sleeve made of a material strong against the occurrence and propagation of thermal cracks is shrink-fitted to an arbor, and is disclosed in Japanese Patent Application Laid-Open No. 50-3922. Consists of an outer layer of high-alloy cast steel and an inner layer of low-alloy tough cast steel, with an outer diameter of 0.4 to 1.2 for the "outer layer thickness / inner layer thickness" ratio.
A large, thick, high-hardness composite sleeve of 1000 mm or more is disclosed in
-86463 gazette discloses that in a work roll for rolling in which the ratio of the neck diameter to the outer diameter of the body and the ratio of the discarded diameter of the body to the outer diameter of the body are specified, the inner diameter of the sleeve is approximately equal to the bearing diameter. Equalized rollable work rolls are disclosed.

On the other hand, Japanese Patent Laid-Open No. 2-30730 discloses a high speed material containing graphite in its metal structure. The material of the publication is 20% or more of the area ratio of graphite and MC in the metal structure.
System, M ₄ C ₃ system, M ₂ C type, and a hard carbide of M ₆ C type, chemical composition in a weight ratio C: 2.5~4%, Si: 2~5 %, Mn: 0.1~1.5
%, Ni: 3 to 8%, Cr: 7% or less, Mo: 4 to 12%, V: 2 to 8%, and a Fe-based alloy that can further contain Co: 2 to 8%, It is used for hot or cold rolling rolls. Further, JP-A 4-191347 discloses a hollow sleeve material for assembling type rolling rolls using a high-speed material containing no graphite, and JP-A 4-344807 discloses a high-speed material containing no graphite as an outer layer, A composite sleeve roll for H-section steel rolling is disclosed in which the inner layer is made of tough cast iron or graphite steel.

[0006] In these conventionally known rolls, consideration is given to improving the wear resistance and seizure resistance as well as the crack resistance in terms of chemical composition or material.
It does not exceed the range of the original properties of the material. Further, there is no disclosure of a prefabricated rolling roll using a composite sleeve made of a high-speed material having an outer layer of graphite and having improved wear resistance, seizure resistance, crack resistance, and economic efficiency.

[0007]

SUMMARY OF THE INVENTION The object of the present invention is to solve the above-mentioned problems of HSS-based material rolls, to exhibit the high wear resistance inherent to HSS-based material rolls, and to have excellent seizure resistance. An object of the present invention is to provide a roll for assembling type rolling that is stable and can be used stably without the risk of roll breakage due to the development of cracks.

[0008]

In order to solve the above-mentioned problems, the present inventor has pursued a high-speed material having graphite as a material to be applied to the outer layer of the composite sleeve for forming the trunk portion, thereby obtaining high wear resistance and seizure resistance. At the same time, we focused on applying a compressive stress to the outer layer in order to obtain resistance to the occurrence and development of cracks accompanying it even if seizure occurs. As for the compressive stress, it is necessary to analyze the case of many rolls used for actual rolling, and as a result of investigation, it is necessary to give more than 200MPa. For this purpose, "cross-sectional area of outer layer / cross-sectional area of inner layer" It was concluded that the value of should be set to 0.7 or less, and as a result, an economical assembling roll for rolling having excellent wear resistance and seizure resistance as well as crack resistance can be obtained.

A first aspect of the present invention is a continuous hot strip rolling mill.
The working roll of the
One of the force casting method, continuous overlay casting method and static casting method
Made by the casting method of C: 2-4% by weight, Si: 0.5-4
%, Mn: 0.1-1.5%, Cr: 1-7%, Mo: 2-10%, V: 2-10
% Chemical constituents and the balance is essentially Fe and unavoidable impurities
Made from the object, the metal structure comprises a 0.5% to 5% of graphite and 0.2 to 10% of the MC carbides and 40% or less of the cementite in the matrix structure and area ratio, hardness HS: 70 or more of the outer layer, the weight C: 0.1 in ratio
A composite sleeve for body part, which is metallically joined to an inner layer of cast steel, forged steel or graphite cast steel containing ~ 2%, is fitted and fixed to the shaft member, and the composite sleeve for body part is perpendicular to the rotation axis. The value of "cross-sectional area of outer layer / cross-sectional area of inner layer" in the cross section is
It is a roll for assembling rolling characterized in that it is 0.7 or less and the inner diameter is not less than the diameter of the bearing portion of the shaft material.

The second invention is that the metal structure of the outer layer of the composite sleeve of the first invention roll is any one of M ₂ C based carbide, M ₆ C based carbide and M ₇ C ₃ based carbide in addition to the MC based carbide. It is an assembling type rolling roll containing the above in an area ratio of 0.2 to 20%.

In a third invention, the outer layer of the composite sleeve of the first invention roll or the second invention roll further has a weight ratio of Ni: 0.2 to.
4%, W: 2-10%, Co: 1-10%, Nb: 1-10%, Ti: 0.01-2
%, B: 0.002 to 0.2% and Cu: 0.02 to 1%.

[0012]

The amount of alloying elements contained in the material of the outer layer of the composite sleeve in the present invention depends on the wear resistance, seizure resistance, crack resistance, hardness and compressive residual stress required for the material of the outer layer.
Limited as follows.

C: 2 to 4 wt% C combines with Cr, V, Mo, W, etc. contained at the same time to form a hard carbide, which contributes to the improvement of wear resistance and at the same time, crystallizes graphite to cause calcination resistance. Necessary for imparting suppleness. C is 1
If it is less than 4% by weight, the amount of hard carbides is insufficient and wear resistance cannot be obtained. If it exceeds 4% by weight, cementite and hard carbides are too much and the toughness is lowered.

Si: 0.5-4 wt% Si is required to be 0.5 wt% or more in order to promote graphitization.
It is also effective as a deoxidizer. However, if it exceeds 4% by weight, the material becomes brittle and the toughness decreases. Further, in order to crystallize graphite, 0.1% by weight or more, preferably 0.1 to 0.
It is necessary to add 8 wt% Si by inoculation. Inoculation Si
If the amount exceeds 0.8% by weight, the inoculant becomes difficult to dissolve in the molten metal and uneven casting structure is likely to occur. The total amount of Si added by this inoculation and the amount of Si originally present in the molten metal becomes the content of Si.

Mn: 0.1 to 1.5 wt% Mn is effective in deoxidizing and desulfurizing the molten metal, and is required to be 0.1 wt% or more. However, if it exceeds 1.5% by weight, retained austenite is likely to be generated in the matrix structure, and it becomes difficult to obtain stable hardness during manufacturing, which is not preferable.

Cr: 1 to 7 wt% Cr is effective in improving the wear resistance because it hardens the matrix structure into bainite or martensite and is required to be 1 wt% or more. However, if it exceeds 7% by weight, not only the toughness of the base structure is deteriorated, but also M ₇ C ₃ system and M ₂₃ C ₆ system carbides are formed, and the formation of harder MC carbides such as VC by V is generated. Since it inhibits, the effect of improving wear resistance is saturated.

Mo: 2 to 10 wt% Mo is a solid solution in the base structure to strengthen the base structure,
Since it combines with C to form M ₂ C-based and M ₆ C-based carbides, it is effective in improving wear resistance, and 2% by weight or more is necessary. However, if it exceeds 10% by weight, crystallization of graphite is inhibited and the generation of harder MC-based carbides such as VC is reduced.

V: 2-10 wt% V combines with C to form VC, that is, MC type carbide. The hardness of VC is HV 2500-3000, which is the hardest among carbides. Therefore, V is an essential element most effective in improving wear resistance. When the amount of V is less than 2% by weight, the amount of VC is insufficient, and 10% by weight
If it exceeds, the crystallization of graphite is inhibited and the material becomes brittle.

The outer layer material of the composite sleeve of the present invention may further contain the following alloying elements, alone or in combination, as alloying elements other than the above. Ni: 0.2-4 wt% Ni is effective for crystallization of graphite and improvement of hardenability of matrix structure. If the content is 0.2% by weight or less, the effect cannot be expected, and if it exceeds 4% by weight, austenite is excessively stabilized, transformation to bainite or martensite having a hard matrix structure becomes difficult, and wear resistance cannot be obtained.

W: 2 to 10 wt% W, similar to Mo, forms a solid solution in the matrix structure and strengthens the matrix structure, and combines with C to form M ₂ C-based and M ₆ C-based carbides. It is effective in improving wear resistance and can be added in an amount of 2% by weight or more. However, if it exceeds 10% by weight, the crystallization of graphite is inhibited and the generation of hard MC-based carbides such as VC is reduced.

Co: 1 to 10 wt% Since Co strengthens the matrix in a high temperature state, it is particularly effective in improving wear resistance and skin roughness when used in hot rolling, and 1 wt% or more is added. it can. However, if the Co content exceeds 10% by weight, the toughness decreases. Co also has the effect of making cementite unstable and making it easy to crystallize graphite.

Nb: 1 to 10 wt% Nb, like V, forms MC type hard carbide. As described above, MC-based carbides are the hardest of the carbides, so Nb is an element effective in improving wear resistance, but when it is excessive, it inhibits crystallization of graphite. Therefore, the amount of Nb added is 1 to 10% by weight.

Ti: 0.01 to 2 wt% Ti bonds with O or N, which are graphitization inhibiting elements, and fixes these elements into oxides or nitrides. If the addition amount is less than 0.01% by weight, no effect can be expected. Also,
Based on the amounts of O and N contained, the upper limit of the amount added is 2% by weight.

B: 0.002-0.2 wt% B makes the carbide fine, but if the addition amount is less than 0.002 wt%, its effect cannot be expected, and if it exceeds 0.2 wt%, the carbide becomes unstable.

Cu: 0.02 to 1 wt% Cu has an action of destabilizing cementite and facilitating crystallization of graphite similarly to Co. If the addition amount is less than 0.02% by weight, the effect cannot be expected, and if it exceeds 1% by weight, the toughness decreases.

Other than the above-mentioned elements, the balance is substantially Fe except impurities. The main elements as impurities are P and S, but it is desirable that P is 0.05% by weight or less and S is 0.03% by weight or less for the same reason to prevent deterioration of toughness.

The results of studies on the metallographic structure that the outer layer material of the composite sleeve for forming the body of the present invention should have are as follows. Graphite: 0.5-5% area% As a result of a seizure test, the amount of graphite is proportional to seizure resistance. If the amount of graphite is less than 0.5% by area, the effect of improving seizure resistance is small, and if it exceeds 5% by area, it is mechanically resistant. The properties are significantly reduced. The particle size of the graphite particles is 5 to 50 μm.

MC-based carbide: 0.2 to 10% by area In order to improve wear resistance, hard carbide must be sufficiently dispersed. Therefore, 0.2 to 10 area% of the hardest MC type carbide is dispersed. If the MC-based carbide is less than 0.2 area%, the wear resistance is not sufficient. On the other hand, it is difficult to disperse the MC-based carbide in excess of 10% by area due to the coexistence with graphite.

Cementite: 40 area% or less Cementite contributes to the improvement of seizure resistance, but since it is a soft carbide, it has little effect of improving wear resistance. For this reason, it is desired to reduce the amount of crystallization, but since it crystallizes at about the same time as graphite, it is actually difficult to crystallize graphite without crystallization of cementite. If cementite is excessive, it decreases toughness, so it must be 40% by area or less.

M ₂ C based carbide, M ₆ C based carbide, M ₇ C ₃ based carbide
Any one or more of the following: 0.2 to 20 area% In addition to the MC-based carbide, these carbides may be further dispersed. If the content of these carbides is less than 0.2 area%, the effect is not sufficiently observed, and if the content exceeds 20 area%, the total area of the carbides including cementite becomes excessive and the toughness decreases.

The composite sleeve of the present invention is preferably manufactured by a centrifugal casting method, but without being particular about this, a continuous overlay casting method, a stationary casting method, or another casting method depending on the situation at that time. Can also be produced.

The hardness of the outer layer of the composite sleeve must be HS: 70 or more. As a result, the wear resistance and seizure resistance originally possessed by the outer layer material are secured, and compressive residual stress is imparted to the outer layer to obtain crack resistance.

The inner layer material of the composite sleeve is C: 0.1 to 2% by weight
Is a cast steel, a forged steel, or a graphite cast steel. In these materials, if C exceeds 2% by weight, the amount of carbide or the amount of graphite becomes excessive, so that the strength required for the inner layer cannot be obtained.
Further, when C is less than 0.1% by weight, the strength is too soft and the required strength cannot be obtained.

The composite sleeve constructed as described above is fitted and fixed to the shaft material constituting the bearing portion or the like to obtain the assembly type rolling roll of the present invention. At this time, if the inner diameter of the composite sleeve, that is, the fitting diameter, is not larger than the diameter of the bearing portion, the fitting of the composite sleeve during the fitting operation becomes difficult, so that it is inevitably limited.

Further, in the composite sleeve, the value of "the cross-sectional area of the outer layer / the cross-sectional area of the inner layer" in the cross section perpendicular to the rotation axis is 0.7.
You need to keep it below. By doing so, the outer layer of the composite sleeve is always subjected to a compressive stress of 200 MPa or more regardless of the diameter of the outer layer used for rolling. As a result, even if a situation occurs in which a tensile stress acts on the surface due to abnormal rolling or the like to cause a crack, it is canceled by the compressive stress, so the occurrence of a crack is prevented. When the compressive stress is less than 200 MPa, cracks easily occur. This compressive stress is a combined stress of the circumferential residual stress of the outer layer originally possessed by the composite sleeve and the circumferential fitting stress acting on the outer layer by fitting.

As described above, the prefabricated rolling roll of the present invention is restricted by the cross-sectional areas of the outer layer and the inner layer of the composite sleeve, that is, the diameter of the body portion. The difference is that it cannot be increased. Aspects of the roll for assembling rolling of the present invention, in order to reduce the cross-sectional area of the outer layer of the composite sleeve, the outer diameter of the outer layer is the same as the conventional roll at the beginning diameter of the start of use and the waste diameter at the end of use is larger than that of the conventional roll. The diameter can be increased or the initial diameter can be decreased to make the discarded diameter equal to that of the conventional roll, or can be appropriately performed depending on the situation at that time.
However, it is preferable to increase the initial diameter in the same manner as the conventional roll to increase the waste diameter, that is, to increase the cross-sectional area of the inner layer of the composite sleeve because the toughness of the composite sleeve can be secured.

[0037]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a sectional view of a roll according to an embodiment of the present invention in the direction of a rotation axis, and FIG. In these figures, a body-forming composite sleeve in which the outer layer 1 and the inner layer 2 are metallically joined is fitted and fixed to the shaft member 3 by shrink fitting with a diameter of the bearing portion 4 or more. A drive unit 5 having a smaller diameter than the bearing unit 4 is provided on the further end side of the bearing unit 4. As an example, shown in Table 1
Targeting the No. 1 and No. 2 continuous hot strip rolling rolls, the assembling type rolling rolls of Examples 1 and 2 and Comparative Examples 1 and 2 for comparing them were manufactured.

[0038]

[Table 1]

Table 2 shows the chemical components of the manufactured composite sleeves. The outer layer material is the component system of the present invention, and the inner layer material is Example 1 and Comparative Example 1 forged steel equivalent to JIS-G-4105 SCM-440, and Example 2 and Comparative Example 2 is graphite cast steel. Also,
The composite sleeves of Example 1 and Comparative Example 1 use the forged steel shaft material formed in a hollow cylindrical shape, for example, a continuous overlay casting method similar to the method described in WO88 / 07594, and compared with Example 2. Example 2 was produced by, for example, a centrifugal casting method similar to the method described in Japanese Patent Laid-Open No. 50-3922.

When casting the material of the outer layer, in order to crystallize graphite, the molten metal before inoculation of each composition was inoculated with an inoculum containing Si. As the inoculant, a Ca-Si alloy is preferable to an Fe-Si alloy because good graphite crystallization can be obtained. In each example, Ca-60% Si alloy was used and inoculated with the amount of Si shown in Table 2. Example 1 and Comparative Example 1 were cast into the molten metal in the refractory frame while casting during the continuous build-up casting operation, and Example 2 and Comparative Example 2 were cast into the molten metal in the hot pan while casting during the centrifugal casting operation. I inoculated.

[0041]

[Table 2]

The cast composite sleeves of the respective examples were subjected to predetermined heat treatment and processing of the specifications shown in Table 3. Hardness of outer layers of these composite sleeves, graphite area ratio, MC carbide area ratio, MC
Table 4 shows the area ratio of other form carbides than the carbides. Table 3
Therefore, in each example, the value of "outer layer cross-sectional area / inner layer cross-sectional area" is 0.7 or less at any outer diameter point, but each comparative example exceeds 0.7 at the initial diameter point, and the composite sleeve It becomes 0.7 or less when the outer diameter of becomes smaller.

[0043]

[Table 3]

[0044]

[Table 4]

Table 6 shows the examination results of the circumferential compressive stress acting on the surface of the outer layer of the assembling rolling roll of each example. This compressive stress is a stress σ ₁₅ that is a combination of the residual stress σ _{11 in} the circumferential direction originally possessed by the outer layer of the composite sleeve and the shrinkage fitting stress σ ₁₂ in the circumferential direction generated by shrink fitting.
Is. Residual stress σ ₁₁ was obtained by manufacturing two composite sleeves, each of which is equivalent to each example, and applying a strain gauge to the part
It is a value measured by the open method after cutting into a block of 0 mm x 40 mm x 40 mm. The shrink-fitting stress σ ₁₂ is a value obtained by calculation using a generally known calculation formula for a thick-walled cylinder based on the specifications shown in Tables 3 and 5. As the shrinkage fitting rate, a value generally adopted for the assembling type rolling roll was used, but the compressive stress is slightly changed by changing this value.

[0046]

[Table 5]

[0047]

[Table 6]

According to Table 6, since all the rolls of the present invention have a compressive stress far exceeding 200 MPa regardless of the diameter of the outer layer used, crack resistance is imparted and the material is originally present. In addition to the existing crack resistance, shrink fitting provides more sufficient crack resistance.
The comparative roll has a smaller outer diameter due to use, and exceeds 200 MPa as it approaches the waste diameter, but it has a large diameter and is less than 200 MPa near the initial diameter at the start of use, so crack resistance cannot be said to be sufficient.

In the above, the crack resistance of the outer layer was paid attention to. Further, in the composite sleeve, the tensile residual stress increases as the thickness of the inner layer becomes thinner, and the inner surface of the composite sleeve, that is, the sintered sleeve, is used during rolling. The shrinkage rate may decrease due to fracture from the fitting surface or plastic deformation. Therefore, we examined the tensile stress in the circumferential direction generated on the inner surface of the composite sleeve.

Table 6 also shows the results of examination of the tensile stress in the circumferential direction acting on the inner surface of the inner layer, that is, the shrink-fitted surface of the roll for assembling type rolling of each example. This tensile stress is due to the residual stress σ in the circumferential direction originally possessed by the inner layer of the composite sleeve.
₂₁ and the shrinkage stress σ ₂₂ in the circumferential direction generated by shrinkage fitting.
And a rolling stress σ _{23 in the} circumferential direction applied by the rolling load during use and a thermal stress σ _{24 in the} circumferential direction also applied by heat, which is a stress σ ₂₅ . The residual stress σ ₂₁ is a value measured by the Sachs method after turning the inner surface of a composite sleeve which is produced separately as in the above example and is equivalent to each example. The shrink fitting stress σ ₂₂ is a value obtained by the same calculation as described above based on the specifications shown in Tables 3 and 5. The shrink fitting rate is also the same as described above.

The rolling stress σ ₂₃ was obtained by the following empirical formula obtained from the experimental results of the model roll. σ ₂₃ = {3.6-0.6 (r ₂ / r ₁ )} ・ {P / (π ・ r ₁・ L)} σ ₂₃ : Rolling stress (= composite stress) (MPa) P: Rolling load (kN) r ₁ : Inner surface radius of composite sleeve [= shrink fitting surface radius] (mm) r ₂ : Outer surface radius of composite sleeve (mm) L: Composite sleeve length [= shrink fitting surface length] (mm)

The thermal stress σ ₂₄ is based on the general thermal stress equation when the temperature distribution T (r) is given, and it is assumed that the temperature of the outer surface becomes higher than the inner surface of the composite sleeve by ΔT ° C. It was calculated by the following formula. σ ₂₄ = {(α ・ E) / (1-ν)} ・ {△ T / 3} ・ {[2r ₂ + r ₁ ) / (r ₂ + r ₁ )} σ ₂₄ : Thermal stress [= synthetic stress ] (MPa) α: Thermal expansion coefficient of composite sleeve = 1.2 × 10 ^-5 (1 / ° C) E: Elastic coefficient of composite sleeve = 21 × 10 ⁴ (MPa) ν: Poisson's ratio of composite sleeve = 0.3 ΔT: Temperature difference between outer surface and inner surface of compound sleeve = 40 (℃) r ₁ : Inner surface radius of compound sleeve [= shrink fitting surface radius] (mm) r ₂ : Outer surface radius of compound sleeve (mm)

The inner layer material of the composite sleeves of Example 1 and Comparative Example 1 of the present invention is forged steel, and the tensile strength is 735 MPa. Similarly, Example 2 and Comparative Example 2 are made of graphite cast steel and have a tensile strength of 588 MPa. Comparing the strength possessed by these inner layer materials with the stress generated on the inner surface of the composite sleeve in Table 6, it can be seen that the rolls of the examples of the present invention are It has a much greater strength compared to it and is therefore safe against fracture. On the other hand, in the comparative example roll, when the outer diameter becomes small due to use and becomes close to the discarded diameter, the residual stress becomes small and the combined stress of the inner surface becomes small, and there is a risk of fracture and plastic deformation of the inner surface. However, since the residual stress is large near the initial diameter at the start of use where the diameter is large, the composite stress becomes equal to or higher than the tensile strength or is close to it, and there is a risk of fracture and plastic deformation of the inner surface.

EFFECTS OF THE INVENTION The assembling type rolling roll of the present invention is excellent in abrasion resistance and seizure resistance inherent in the material, and has sufficient crack resistance and fracture resistance. As a result, even if an abnormal situation occurs during rolling, damage to the rolls is prevented, so that the rolling mill is stopped and the rolls are prevented from being damaged.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a roll according to an embodiment of the present invention in a rotation axis direction.

FIG. 2 is a cross-sectional view of a body part of a roll according to an embodiment of the present invention in a direction perpendicular to a rotation axis.

[Explanation of symbols]

1: Outer layer 2: Inner layer 3: Shaft material 4: Bearing part 5: Drive part

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C22C 1/00-49/14 B21B 27/00

Claims (3)

(57) [Claims] 1. A working roll for a continuous hot strip mill.
The composite sleeve for body part is made by centrifugal casting, continuous overlay
Manufactured by either casting method or stationary casting method
By weight ratio, C: 2-4%, Si: 0.5-4%, Mn: 0.1-1.5
%, Cr: 1~7%, Mo : 2~10%, V: 2 to 10% of the chemical components containing
The balance consists essentially of Fe and unavoidable impurities , and the metal structure has a matrix structure with an area ratio of 0.5 to 5% graphite and 0.2 to 10%.
Of MC-based carbide and 40% or less of cementite, and the hardness is HS: 70 or more of the outer layer, and C: 0.1 to 2% by weight of the cast steel or forged steel or graphite cast steel containing the inner layer is metallically joined The body section composite sleeve is fitted and fixed to the shaft material, and the body section composite sleeve has a value of “outer layer cross-sectional area / inner layer cross-sectional area” of 0.7 or less in a cross section perpendicular to the rotation axis. An assembly type rolling roll having an inner diameter equal to or larger than a diameter of a bearing portion of a shaft material. 2. The metal structure of the outer layer of the composite sleeve for forming a body portion is, in addition to MC type carbide, an area of at least one of M ₂ C type carbide, M ₆ C type carbide and M ₇ C ₃ type carbide. 0.2 to 20 in comparison
%, The prefabricated rolling roll according to claim 1. 3. The outer layer of the composite sleeve for forming the body part further comprises Ni: 0.2 to 4%, W: 2 to 10%, Co: 1 to 10%, Nb: 1 by weight ratio.
~ 10%, Ti: 0.01-2%, B: 0.002-0.2%, Cu: 0.02-1%
2. Any one or more of the above are included.
Alternatively, the prefabricated rolling roll according to claim 2.