JP3280270B2 - Roll for hot rolling - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolling roll having remarkably excellent wear resistance and free from segregation of carbides even when manufactured by a centrifugal casting method.

[0002]

2. Description of the Related Art In recent years, hot rolling technology has been remarkably advanced, and even in a hot rolling roll, wear resistance is markedly increased by adding a large amount of V and W to produce hard V carbide and W carbide. High-performance rolls (hereinafter referred to as high-speed rolls) having an outer layer material having an improved high-speed tool steel composition have been developed (for example, JP-A-1-96355, JP-A-6-145888, JP-A-4-80344, JP-A-4-80344). 5-1350, JP-A-5-5155, JP-A-8-
35033, etc.), and some of them are being put to practical use. However, the use environment of rolls is becoming increasingly severe from the viewpoint of improving the quality of rolled products and efficient production, and at the same time, the requirements for the surface quality of rolled steel sheets are becoming stricter, and the wear resistance is further increased. There has been a demand for improved rollability and roll surface quality.

[0003]

SUMMARY OF THE INVENTION
Since various types of alloy components such as V, W, Mo, and Cr are added, a plurality of different types of carbides (MC, M ₆ C, M ₇ C ₃ , M ₂ C) are added according to the amount of each element added. , M ₃ C) crystallize out. Further, as the alloying element is added in a large amount, the amount of carbide increases, and there is a possibility that the wear resistance is further improved in a preferable composition range. However, when a large amount of various types of carbides are generated in order to improve the wear resistance of the casting roll, solidification segregation of the carbides becomes remarkable based on differences in the crystallization timing and specific gravity of each carbide, and hot rolling is performed. A segregation pattern was generated on the roll surface during the process, and particularly when used as a roll for the subsequent stage of the finishing mill, there was a problem that the surface quality of the steel sheet to be rolled was deteriorated.

[0004] When a high-speed roll is manufactured by a centrifugal casting method, which is advantageous in terms of cost, a tendency of segregation of carbides is further increased due to the long centrifugal force and solidification time. On the other hand, if high-speed rolls are manufactured by the welding overlay method or the continuous casting overlay method (manufacturing cost is large), the outer layer material is rapidly solidified without applying centrifugal force. Although segregation is suppressed, there is a problem that the roll manufacturing cost is significantly increased. Due to such a problem, it has been difficult to produce a high-speed roll with further improved wear resistance.

An object of the present invention is to significantly improve abrasion resistance,
It is, of course, to provide a high-performance high-speed roll in which carbides do not segregate even when manufactured by an economically excellent centrifugal casting method.

[0006]

The roll for hot rolling according to the present invention according to the present invention has a weight ratio of C: 2.4 to 2.9.
%, Si: 1% or less, Mn: 1% or less, Cr: 12 to 18
%, Mo; 3 to 9%, V; 3 to 8%, Nb; 0.5 to 4%
, And simultaneously satisfy the following expressions (1) and (2): 0.27 ≦ Mo (%) / Cr (%) <0.7 (1) C (%) + 0.2 · Cr (%) ≦ 6.2 .. (2) An outer layer composed of the remaining Fe and inevitable impurities.

The hot-rolling roll according to the present invention according to the second aspect of the present invention has a weight ratio of C: 2.4 to 2.9%, Si: 1% or less, Mn: 1% or less, Cr: 12 to 18%, Mo; 3-9
%, V; 3 to 8%, Nb; 0.5 to 4%, and
The following expressions (1) and (2) are simultaneously satisfied, and 0.27 ≦ Mo (%) / Cr (%) <0.7 (1) C (%) + 0.2 · Cr (%) ≦ 6.2 (2) Remaining Fe And an unavoidable impurity, particularly having an outer layer in which W is less than 1%.

The hot-rolling roll according to the present invention according to claim 3 is, by weight ratio, C: 2.4 to 2.9%, Si: 1% or less.
Bottom, Mn: 1% or less, Cr: 12-18%, Mo: 3-9
%, V; 3 to 8%, Nb; 0.5 to 4%, and
The following formulas (1) and (2) are satisfied at the same time, and 0.27 ≦ Mo (%) / Cr (%) <0.7 (1) C (%) + 0.2 · Cr (%) ≦ 6.2 ... (2) The balance consists of Fe and unavoidable impurities, and is MC type
13-30% of total area ratio of carbide and M7C3 type carbide
It has an outer layer containing it.

The hot-rolling roll according to the present invention according to claim 4 is, by weight ratio, C: 2.4 to 2.9%, Si: 1% or less.
Bottom, Mn: 1% or less, Cr: 12-18%, Mo: 3-9
%, V; 3 to 8%, Nb; 0.5 to 4%, and
The following formulas (1) and (2) are satisfied at the same time, and 0.27 ≦ Mo (%) / Cr (%) <0.7 (1) C (%) + 0.2 · Cr (%) ≦ 6.2 ... (2) The balance consists of Fe and unavoidable impurities, and is MC type
13-30% of total area ratio of carbide and M7C3 type carbide
Containing, the area ratio of M7C3 type carbide is more than 6%
It has layers.

[0010] The roll for hot rolling according to the present invention according to claim 5 is, by weight ratio, C: 2.4 to 2.9%, Si: 1% or less.
Bottom, Mn: 1% or less, Cr: 12-18%, Mo: 3-9
%, V; 3 to 8%, Nb; 0.5 to 4%, and
The following formulas (1) and (2) are satisfied at the same time, and 0.27 ≦ Mo (%) / Cr (%) <0.7 (1) C (%) + 0.2 · Cr (%) ≦ 6.2 ... (2) The balance of Fe and unavoidable impurities, especially the W content
Is less than 1%, and MC type carbide and M7C3 type carbonization
It has an outer layer containing 13 to 30% of the total
It is something that has been done .

[0011] The hot-rolling roll according to the present invention according to claim 6 is, by weight ratio, C: 2.4 to 2.9%, Si: 1% or less.
Bottom, Mn: 1% or less, Cr: 12-18%, Mo: 3-9
%, V; 3 to 8%, Nb; 0.5 to 4%, and
The following formulas (1) and (2) are satisfied at the same time, and 0.27 ≦ Mo (%) / Cr (%) <0.7 (1) C (%) + 0.2 · Cr (%) ≦ 6.2 ... (2) The balance of Fe and unavoidable impurities, especially the W content
Is less than 1%, and MC type carbide and M7C3 type carbonization
Containing 13 to 30% of the total area ratio of M7C3
The area ratio of the object is 6% or more.

The present invention according to claim 7 provides the invention according to claims 1 to 6
A roll for hot rolling consisting of an outer layer according to any of the above and an inner layer of spheroidal graphite cast iron or graphite steel welded and integrated,
The inner layer is, by weight ratio, C: 2.5 to 4.0%, Si: 1.5 to 3.
5%, Mn: 1.5% or less, Ni: 5% or less, Cr: 3%
In the following, Mo: 3% or less, V: 3% or less, Nb: 2% or less, with the balance being Fe and unavoidable impurities.

[0013] The present invention described in claim 8 provides the invention according to claims 1 to 7.
A hot-rolling roll having an intermediate layer between the outer layer and the inner layer according to any one of the above, wherein the outer layer and the inner layer are welded and integrated through the intermediate layer, wherein the intermediate layer has a weight ratio of C 0.8 to 3.
0%, Si; 0.3 to 3.0%, Mn; 1.5% or less, Ni;
5% or less, Cr: 10% or less, Mo; 4% or less, V: 5%
In the following, Nb; 3% or less is contained, and the balance is composed of Fe and inevitable impurities.

According to a ninth aspect of the present invention, in the hot rolling roll according to the eighth aspect of the present invention, the mixing ratio of the intermediate layer to the inner layer material is further restricted to a range of 5 to 20%. It was made.

According to a tenth aspect of the present invention, in the hot rolling roll according to the eighth or ninth aspect, the mixing ratio of the outer layer to the intermediate layer material is further restricted to a range of 5 to 50%. It is something to do.

The present invention described in claim 11 provides the invention according to claims 1 to
In any one of the above 10, the one or more layers constituting the roll for hot rolling contain 6% or less of Co.

The present invention described in claim 12 is the first invention.
A hot-rolling roll obtained by centrifugally casting the outer layer according to any one of the first to eleventh aspects.

Here, the "outer layer mixing ratio into the intermediate layer material" is a value for controlling how much the components of the outer layer are mixed into the casting composition of the intermediate layer by re-dissolving the outer layer during the casting of the intermediate layer. It is.

That is, focusing on a certain element, the component ratio of the outer layer of the roll is (a weight%) and the casting component ratio of the intermediate layer is (b
% By weight), and when the component ratio of the intermediate layer of the roll after casting is (c% by weight), the “outer layer mixing ratio to the intermediate layer material” is defined as follows.

[0020]

(Equation 1)

The “ratio of mixing the intermediate layer into the inner layer material” is
This is a value for controlling how much the components of the existing intermediate layer are mixed into the casting composition of the inner layer due to the re-dissolution of the existing intermediate layer during the casting of the inner layer.

That is, focusing on a certain element, the component ratio of the roll intermediate layer is (c weight%) and the casting component ratio of the inner layer is (d
% By weight), and when the component ratio of the inner layer of the roll after casting is (e% by weight), the “ratio of mixing the intermediate layer into the inner layer material” is defined as follows.

[0023]

(Equation 2)

It should be noted that as an element to be considered when calculating the mixing ratio, an element such as Cr, Mo, or Si that is unlikely to segregate is desirable.

The terms "outer layer material" and "inner layer material"
The term "water before casting" means "outer layer" and the term "inner layer" means "after solidification".

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION

(A) Reasons for limiting alloy elements in outer layer (Technical concept and characteristics of the present invention) In the present invention, [a] prevention of segregation of carbide, [b] remarkable improvement in wear resistance, [c] prevention of roll breakage, Are simultaneously studied from the following viewpoints to solve the problems of conventional rolls at once in a hot rolling high-speed roll having an outer layer of a high Cr-Mo composition containing V and Nb. A suitable composition has been found.

[A] Prevention of segregation of carbides (a) In order to prevent segregation of carbides, the difference between the crystallization timing (crystallization temperature) of austenite and carbides during the solidification process is small, and the difference in specific gravity between molten steel and steel. It has been found that it is effective to crystallize small carbides or not to crystallize various types of carbides.

(B) The conditions for obtaining a high-speed roll with remarkably improved wear resistance are as follows: extremely hard MC-type carbide and M ₆ C, M ₇ C ₃ , M ₂₃ C ₆ , M ₂ C which are quasi-hard phases. , M ₃
It has a metal structure in which a large amount of eutectic carbide such as C is present. Here, the more eutectic carbide that is a quasi-hard phase, the more the wear resistance improves, but when the type of eutectic carbide increases,
Since the segregation of carbides is promoted as described above, it is important to design an alloy composition in which various types of eutectic carbides do not eutectic.

(C) Prevention of Segregation of Eutectic Carbide If the composition is made of high C and high Cr, the Cr-based carbide mainly composed of M ₇ C ₃ can be uniformly dispersed as a colony-like eutectic carbide in the metal structure. , High Cr cast iron. Using this as a hint, we have found a method of suppressing carbide segregation by using M ₇ C ₃ -type carbide as the quasi-hard phase of high-speed rolls.

In the present invention, M ₇ C ₃ is mainly used as the quasi-hard phase.
C: 2.4 to 2.9%, and Cr: 12 to 18% were selected as the preferable composition ranges in which the type carbides are largely crystallized. However, even in this composition range, C and Cr have the formula;
(%) + 0.2 · Cr ( %) when added beyond 6.2 numerical values calculated by the needle-like Cr carbide will crystallize out in addition to the colony-like M ₇ C ₃ type carbide described above It has been found. When a roll is centrifugally cast with a composition in which acicular Cr carbides are crystallized, colony-like carbides and acicular carbides segregate, so a limiting formula: C (%) + 0.2 · Cr
(%) ≦ 6.2 was set.

In general, high-strol contains W, but when W is added, carbide different from M ₇ C ₃ type (M
₅ C, M ₂ C, etc.), which may segregate. Further, since the specific gravity of W is remarkably large, the difference in specific gravity between the molten metal and the carbide is enlarged to further promote the segregation of the carbide (specific gravity of each element → W; 19.3, Fe; 7.9, Cr; 7.2, Mo;
10.2) as well as deteriorating wear resistance. Therefore, in the present invention, W should not be added in such an amount that W-based carbides appear.

(D) Prevention of segregation of MC-type carbides MC-type carbides mainly composed of V have a lower specific gravity than molten metal. Therefore, when centrifugally cast, there is a problem that MC carbides are centrifuged based on a difference in specific gravity. .

In order to suppress the centrifugal separation of MC type carbide,
It is effective to increase the specific gravity of the MC type carbide to reduce the specific gravity difference from the molten metal. In the present invention, V-based M
High specific gravity elements Nb and Mo (specific gravity → V
C; 5.7, V; 6.1, Nb; 8.6, Mo; 10.2) to modify the MC-type carbide into a composite carbide having a large specific gravity and not to add W which has an effect of increasing the specific gravity of the molten metal. The method prevented centrifugation of MC-type carbides. The preferred composition to achieve this is V;
%, Nb: 0.5-4%, Mo; 3-9%.

[B] Significant improvement in wear resistance In order to exhibit wear resistance as a high-speed roll, MC is required.
A type carbide is essential, and in order to further improve wear resistance, it is necessary to have a large amount of a stronger eutectic carbide. In the present invention, in order to further remarkably improve the wear resistance of the high-speed roll under the above-described restriction conditions related to segregation, an appropriate amount of MC carbide and M ₇ C ₃ type carbide are introduced, and MC carbide is introduced. M ₇ C ₃ type carbide was strengthened. That is, in order to improve the wear resistance, the total of the MC carbide and the M ₇ C ₃ type carbide is required to be 13% or more. In order to make these carbides appear, a preferable composition is to use C as a carbon source at 2.4% to 2.9%. %, V; 3-8% and N
b; By containing 0.5 to 4%, the appearance of the composite type MC carbide of V and Nb, is intended to contain 12 to 18% of Cr in order to further reveal the appropriate amount of M ₇ C ₃ type carbide. However, it was not possible to stably remarkably improve abrasion resistance only by limiting the composition described above. Therefore,
Investigations have been made to improve the wear resistance within a range that does not promote segregation, and it has been found that the above-mentioned MC carbide and Cr carbide are modified by the proper blending of Mo, thereby significantly improving the wear resistance. That is, by containing 3 to 9% of Mo,
Mo is enriched in the MC carbide and the Cr carbide, and each carbide is reformed into a tough composite carbide. Here, it is necessary to increase the amount of added Mo as the amount of Cr increases.
(%) / Cr (%), it was found that the abrasion resistance would not be improved unless the value was 0.27 or more.
0.27 ≦ Mo (%) / Cr (%) was set. In addition, Mo
If the value calculated by (%) / Cr (%) exceeds 0.7,
Since it was found that Mo became excessive and Mo-based eutectic carbides appeared in large quantities and promoted segregation of carbides and caused deterioration of wear resistance, the limiting formula: Mo (%) /
Cr (%) <0.7 was set. In addition, even if Mo / Cr is 0.7 or less, Mo-based carbides crystallize or Mo / Cr
If the value is 0.7 or less, there is no adverse effect on the roll characteristics.

[C] Prevention of Roll Breakage When a composite high-speed roll in which the amount of carbide is remarkably increased in order to improve the wear resistance is manufactured, the roll may be broken after casting. The cause of the breakage is that if the amount of carbide in the outer layer becomes excessively large, the coefficient of expansion decreases significantly (because the coefficient of linear expansion of the carbide is low, the outer layer containing a large amount of carbide has a small coefficient of linear expansion). This is because the difference in the amount of thermal expansion / contraction increased and the thermal stress of the roll became excessive. Based on this finding, a study was made on the limit carbide amount that suppresses the breakage of the composite roll. As a result, MC-type carbide and M ₇ C
It has been found that it is necessary to reduce the total area ratio of type ₃ carbide to 30% or less.

(1) The carbide content of the outer layer of the roll in the present invention is determined as follows.・ The total of the MC type carbide and the M ₇ C ₃ type carbide in the outer layer is 13 to 30% in area ratio. In order to obtain excellent wear resistance, the MC type carbide and the M ₇ C type
The total of type ₃ carbides must be at least 13% in area ratio. However, if the sum of the area ratios exceeds 30%, the roll is likely to break.

The area ratio of the M ₇ C ₃ type carbide in the outer layer is 6%
The total of MC type carbide and M ₇ C ₃ type carbide is 13 ~
It was 30%, and, together with the wear resistance is remarkably improved when M ₇ C ₃ type carbide is contained in an area ratio above 6%, also improved surface properties of the roll or rolled steel plate. Further, there is also an effect of suppressing the thermal expansion of the roll and improving the sheet passing property. M
₇ C ₃ type carbide area ratio of the effect can not be obtained with less than 6%.

(2) The composition of the roll outer layer in the present invention is determined as follows. C: 2.4 to 2.9% C is an element essential for carbide formation for improving the abrasion resistance of the roll. If it is less than 2.4%, the amount of carbides is insufficient, so that excellent wear resistance cannot be obtained. On the other hand, if the content exceeds 2.9%, the amount of carbides becomes excessive, and segregation of carbides occurs.

Cr: 12-18%, C (%) + 0.2Cr
(%) ≦ 6.2 Cr makes a proper amount of colony-shaped M ₇ C ₃ carbide appear,
It is necessary to add 12% or more to improve abrasion resistance and skin roughness resistance. If it is less than 12%, Cr carbide will be insufficient, and wear resistance will deteriorate and roll surface roughness will occur. If the content exceeds 18% or the value calculated by C (%) + 0.2 · Cr (%) exceeds 6.2, needle-like Cr carbides are crystallized and carbide segregation occurs. It causes the surface quality to deteriorate.

Mo: 3 to 9%, 0.27 ≦ Mo (%) / C
r (%) <0.7 Mo will enhance their carbides and concentrated to MC carbides and M ₇ C ₃ carbide, has the effect of greatly improving the wear resistance of the roll. At the same time, it has an effect of suppressing segregation of MC carbide. In order to obtain these effects, Mo must be 3% or more, and satisfy 0.27 ≦ Mo (%) / Cr (%). On the other hand, if Mo exceeds 9% or Mo
If the value calculated by (%) / Cr (%) exceeds 0.7,
A large amount of Mo-based carbides appears, which promotes segregation of the carbides and significantly reduces wear resistance.

V: 3 to 8%, Nb: 0.5 to 4% V is an essential element for forming a hard MC carbide and obtaining a certain level of wear resistance as a high-speed roll. To achieve this effect, 3% or more is required.
%, The melting point of the molten metal is increased and the fluidity of the molten metal is lowered, which causes a problem in roll production.

Nb is also an MC carbide forming element, and has the effect of enriching Mo in MC carbide. By adding Nb, the MC carbide is made tougher (V, Nb, M
o) It is modified to a C-based composite MC carbide to significantly improve wear resistance. In addition, since the specific gravity approaches the specific gravity of the molten metal by forming the composite MC carbide, segregation of the MC carbide is suppressed. To obtain this effect, Nb must be 0.5% or more. However, if it exceeds 4%, Nb-based carbides are independently crystallized and promote segregation of carbides. (The preferred ranges are V; 4 to 6% and Nb; 1 to 2%.)

Si: 1% or less Si is added as a deoxidizing material and for ensuring castability. The preferred lower limit of Si is 0.1% or more. Even if it exceeds 1%, the effect is saturated.

Mn: 1% or less Mn is added to fix S in the molten steel as MnS and to remove the adverse effect of S. The preferred lower limit of Mn is 0.1% or more. Even if it exceeds 1%, the effect is saturated.

W: less than 1% In the present invention, the addition of W not only has no effect of improving wear resistance, but also has an adverse effect of promoting segregation of carbides.
It is not preferable to add W. Even if it is inevitably contained from dissolved raw materials, it is necessary to change the dissolved raw materials so as not to exceed 1%, preferably not to exceed 0.5%, in order to minimize the adverse effects. .

Ni: less than 1.5% Ni is not an essential element of the present invention, but may have an effect of improving the quenchability and expanding the operation range at the time of quenching the roll. However, if the content exceeds 1.5%, the effect is saturated and the formation of unstable residual γ is promoted, so the upper limit is made 1.5%.

Co: 6% or less Co is not an essential element of the present invention, but may be added because it has a function of stabilizing the structure at high temperatures and has an effect of reducing the coefficient of thermal expansion. . However, the effect of improving the abrasion resistance of the roll of the present invention, the surface roughness resistance is small,
Since the merit for improving the roll characteristics is low, the upper limit is set at 6% from the viewpoint of economy.

(3) The roll production in the present invention is defined as follows. -Inner layer: Spheroidal graphite cast iron or graphite steel It is preferable to apply a high-strength material excellent in castability and workability to the inner layer. Considering practicality, it is preferable to select spheroidal graphite cast iron when manufacturing a solid integrated roll, and to select graphite steel when manufacturing a cylindrical sleeve roll.

When the outer layer and the inner layer of the roll are directly welded and integrated, a large amount of the alloy component of the outer layer may be mixed into the inner layer, and the inner layer may become hard and embrittled. In this case, hard embrittlement of the inner layer becomes remarkable. In such a case, it is preferable to provide an intermediate layer between the outer layer and the inner layer in order to suppress the alloy component of the outer layer from being mixed into the inner layer. It is not necessary to strictly define the components of the intermediate layer. However, in order to prevent hard embrittlement of the inner layer due to mixing of the alloy components of the outer layer into the inner layer, Cr and M
The content of alloying elements such as o, V and Nb must be lower than that of the outer layer, and in order to ensure castability, the molten metal for the intermediate layer contains 0.5% or more of C and 0.5% or more of Si. Preferably.

(4) The intermediate layer and the inner layer of the composite roll (product) of the present invention contain a higher alloying element content because the outer layer alloy components are mixed. Remarkably high alloying of each layer causes roll breakage due to embrittlement. Therefore, the alloy composition of each layer in the composite roll product is preferably set in the following range.

Intermediate layer C: 0.8-3.0%, Si: 0.3-3.0%, Mn; ≦ 1.5
% Ni; ≤ 5%, Cr; ≤ 10%, Mo; ≤ 4% V; ≤ 5%, Nb; ≤ 3%

Inner layer C: 2.5 to 4.0%, Si: 1.5 to 3.5%, Mn: ≦ 1.5
%, Ni; ≤ 5% Cr; ≤ 3%, Mo; ≤ 3%, V; ≤ 3%, Nb; ≤ 2
%

(B) Reasons for Restriction of Alloy Elements in Inner Layer and Intermediate Layer In the composite roll (three-layer roll) of the present invention, the outer layer inner surface and the inner layer are interposed between the outer layer, the intermediate layer and the inner layer in a metallurgical manner. It is essential to mix the layer material and to mix the inner layer material with the inner surface side of the intermediate layer.

However, the outer layer must not be mixed excessively until the excellent toughness of the inner layer and the intermediate layer is impaired.

In the present invention, the intermediate layer is provided to suppress the mixing of the outer layer into the inner layer. However, the outer layer is mixed into the inner layer via the intermediate layer.

Therefore, in the present invention, it has been found that the mixing ratio of the outer layer to the intermediate layer material is optimally 5 to 50%. If it is less than 5%, casting defects such as unwelding or inclusions are likely to occur at the boundary between the outer layer and the intermediate layer, and the soundness of the boundary cannot be ensured. On the other hand, if it exceeds 50%, a large amount of carbide-forming elements (especially Cr) contained in the outer layer is mixed, and the toughness of the intermediate layer is impaired.

In the present invention, it has been found that the mixing ratio of the intermediate layer to the inner layer material is optimally set to 5 to 20%. If it is less than 5%, casting defects such as unwelding or inclusions are likely to occur at the boundary between the intermediate layer and the inner layer, and the soundness of the boundary cannot be ensured. On the other hand, if it exceeds 20%, the effect of improving the bonding state between the inner layer and the intermediate layer is not only saturated, but also a large amount of carbide-forming elements (especially Cr) contained in the intermediate layer are mixed into the inner layer, and the inner layer becomes significantly embrittled. This causes the roll to break.

That is, the mixing ratio of the outer layer to the intermediate layer material and the mixing ratio of the intermediate layer to the inner layer material are restricted within the above ranges, and the composition of the intermediate layer material and the inner layer material are selected in consideration of the increase in the components due to the interlayer mixing. Just do it.

The preferred composition of the inner layer and the intermediate layer of the roll product is as follows. [Inner layer] By providing the intermediate layer, the incorporation of Cr in the outer layer into the inner layer can be greatly reduced as compared with the case without the intermediate layer, but this incorporation of Cr cannot be completely prevented. Therefore, it is necessary to select the chemical component of the inner layer material and its component ratio in consideration of the increase in Cr%.

C: 2.5 to 4.0% When C is less than 2.5%, the amount of graphite is reduced, and shrinkage cavities are easily generated. On the other hand, if the content exceeds 4.0%, it becomes fragile, so it is specified in the range of 2.5 to 4.0%.

Si: 1.5 to 3.5% If the content of Si is less than 1.5%, the amount of graphite decreases and a large amount of cementite precipitates, so that the material becomes hard and brittle. on the other hand,
If it exceeds 3.5%, the amount of graphite becomes too large and the strength is deteriorated. Therefore, it is specified in the range of 1.5 to 3.5%.

Mn: 1.5% or less Mn is effective in suppressing the harm of S. However, if it exceeds 1.5%, the material becomes brittle. Therefore, the content is specified in the range of 1.5% or less. If the content is less than 0.3%, the effect is not sufficient.

Ni: 5.0% or less Ni increases the strength, but there is no remarkable effect even if the content exceeds 5.0%. Therefore, it is specified in the range of 5.0% or less. If the content is less than 0.3%, the effect is insufficient.

Cr: 3% or less Even if the intermediate layer is provided, it is inevitable that a certain amount of Cr is mixed into the inner layer. If the content exceeds 3%, the amount of cementite increases, and the material strength and toughness are remarkably deteriorated.

Mo: 3% or less Mo has the effect of increasing the base hardness, but if it exceeds 3%, it becomes brittle and uneconomical, so it is made 3% or less.

V: 3% or less, Nb: 2% or less Nb and V uniformly disperse fine carbides, improve the strength of the inner layer, and abrasion resistance of the shaft of the roll composed of the inner layer of the roll. Also improve.

However, when the content of V exceeds 3% and the content of Nb exceeds 2%, the castability of the inner layer is remarkably deteriorated and the hard embrittlement becomes remarkable, so that the content is limited.

Co: 6% or less Co has the effect of reducing the coefficient of thermal expansion, and thus has the effect of preventing the breakage of the roll due to thermal stress. However, even if added over 6%, the effect hardly increases. No, so the upper limit is 6
%.

P: 0.1% or less P increases the fluidity of the molten metal, but is preferably 0.1% or less in order to make the material brittle.

S: 0.04% or less S must be kept low because it inhibits spheroidization of graphite, and is preferably 0.04% or less.

[Intermediate Layer] The intermediate layer has a function of suppressing the deterioration of the toughness of the inner layer due to the carbide-forming element (especially Cr) contained in the outer layer being mixed into the inner layer.

C: 0.8 to 3.0% C is dissolved in the matrix to secure the strength. C content is 0.
If it is less than 8%, the effect is insufficient, while if it exceeds 3.0%, carbides increase and toughness deteriorates. Therefore, C is defined as 0.8 to 3.0%.

Si: 0.3 to 3.0% Si is required to be at least 0.3% in order to suppress hard embrittlement and ensure castability. Even if added in excess of 3.0%, the effect saturates. Therefore, it is specified as 0.3 to 3.0%.

Mn: 1.5% or less Mn has the effect of improving the material strength, but the effect is saturated even if it exceeds 1.5%, so the content is set to 1.5% or less.

Ni: 5% or less Ni is effective for securing strength and toughness, but the effect is saturated even if it exceeds 5%, so it was limited to 5% or less.

Cr: 10% or less Cr is desirably low because it forms carbide and embrittles the material. Even when the amount of Cr in the outer layer is extremely high, it must be 10% or less.

Mo: 4% or less Mo is an important element similar to Ni in terms of securing toughness. However, even if it exceeds 4%, the material is embrittled.

V: 5% or less, Nb: 3% or less V and Nb have an effect of improving the strength of the intermediate layer. However, if V exceeds 5% and Nb exceeds 3%, microscopic shrinkage cavities are easily formed in the intermediate layer, and the strength of the intermediate layer is significantly deteriorated.

Co: 6% or less Co has the effect of reducing the coefficient of thermal expansion, and thus has the effect of preventing the breakage of the roll due to thermal stress. However, even if added over 6%, the effect hardly increases. No, so the upper limit is 6
%.

P: not more than 0.05% P increases the fluidity of the molten metal, but the lower the better, because it makes the material brittle, the more preferable it is 0.05% or less.

S: 0.03% or less S, like P, makes the material brittle, so the lower the content, the better, and the content is preferably 0.03% or less.

As the deoxidizing agent, Al, Ti, Zr or the like may be used in an amount of 0.1% or less.

When the composition of the intermediate layer and the inner layer after solidification satisfies the above ranges, excellent material properties of the intermediate layer and the inner layer can be obtained. In the case of the present invention, the content of V and Nb mixed into the inner layer from the outer layer has the effect of improving the mechanical properties of the spheroidal graphite cast iron or graphite steel as the inner layer as compared with general spheroidal graphite cast iron or graphite steel. is there. this is,
This is because V and Nb have a crystal grain refining action and contain an appropriate amount of V and Nb, which are hardenable elements, so that a very fine bainite matrix can be obtained by high-temperature heat treatment. In the case of the roll of the present invention, this effect allows the roll to be used for higher-load rolling than before.

(Method of Measuring Carbide Area Ratio) The roll material of the present invention mainly comprises MC, M ₇ C ₃ and M ₂ C or M
_{There are 6} C-type carbides. Incidentally, since the Cr content is large, there is almost no M ₃ C type carbide.

The method for identifying carbides and the method for measuring the amount (area ratio) of carbides in the present invention are described below. 1. Measurement of Total Carbide Content (Area Ratio) When the sample surface is mirror-finished and polished and immersed in a 5% nitric acid alcohol solution, hydrochloric acid-picric acid alcohol solution or aqua regia, the base is corroded. When the corroded surface is observed with an optical microscope, the base portion looks black and the carbides look white. Therefore, the total carbide amount (area ratio) was measured by a method of measuring the area of the white portion using an image analyzer. (If the base is not sufficiently blackened by corrosion, the corroded surface is evenly painted with a black pencil, and the surface is lightly wiped with gauze or the like to make black (base) and white (carbide) clear. )

2. Measurement of the amount (area ratio) of MC-type carbides MC-type carbides appear gray under an optical microscope when they are left mirror-finished (no-etch). In this state, the area (area ratio) of the MC type carbide was measured by measuring the area of the gray part with an image analyzer.

3. Carbides of M ₂ C and M ₆ C type of the measurement sample surface (area ratio) is mirror finish polishing, 3 by Murakami reagent 5
After ₂ seconds of corrosion, the M ₂ C and M ₆ C type carbides are colored black. In this state, the amount (area ratio) of the M ₂ C and M ₆ C type carbides was measured by measuring the area of the black portion with an image analyzer.

4. Measurement of M ₇ C ₃ type carbide amount (area ratio) M ₇ C ₃ type carbide amount = total carbide amount− (MC type carbide amount +
M ₂ C and M ₆ C type carbide)

5. The total amount of MC-type carbide and M ₇ C ₃ -type carbide (area ratio) Total amount = amount of carbide of total amount of carbide -M ₂ C and M ₆ C-type MC-type carbide and M ₇ C ₃ type carbide

6. In the component of the roll outer layer of the present invention,
The amount of M ₂ C or M ₆ C type carbide increases as the composition becomes higher and the composition becomes higher. However, if the total carbide area ratio does not exceed 40%, problems such as segregation do not occur.

[0091]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A centrifugally cast roll according to the present invention has the above-described structure, and a method of manufacturing this roll will be described with reference to an example shown in FIG.

First, the molten metal for forming the outer layer 1 is cast into a metal mold which is rotated on a centrifugal casting machine and has a refractory material coated on the inner surface. Cast 2 in. After the two layers, that is, the outer layer 1 and the intermediate layer 2 are completely solidified, the mold is set upright, and the inner layer 3 is cast from above,
The outer layer 1, the intermediate layer 2, and the inner layer 3 are completely metallurgically bonded to form an integral roll. The outer layer 1 and the intermediate layer 2
Even if both of them are not completely solidified, the inner layer 3 may be cast by an appropriate method in which the inner surface is partially solidified in a horizontal or inclined manner.

(Example 1) A sample having a thickness of 100 mm was centrifugally cast with a molten metal having the chemical composition shown in Table 1 corresponding to the outer layer of the roll. By observing the structure of the cross section of the sample, the presence or absence of carbide segregation was determined. Next, quenching from 1050 ℃, 550 ℃
After the tempering treatment, a test piece for measuring the carbide area ratio and a wear test piece were prepared. The carbide area ratio was determined using an image analyzer to determine the amount of carbide having a maximum diameter of 1 μm or more. The abrasion test is a sliding wear method of two disks of the mating material (S45C) and the test piece.
Rotate at 800rpm to reduce the slip rate between the test piece and the mating material to 14.2%
For 15 minutes with a load of 100 kg. After this test was performed 12 times while changing the mating material, the wear amount of the test piece was measured.

[0094]

[Table 1]

As an example of the presence or absence of carbide segregation, the material of the present invention
FIG. 1 shows the carbide structure of (A-9), and FIG. 2 shows the carbide structure of the comparative material (C-8). In the material of the present invention, carbides appearing white are uniformly dispersed in the thickness direction of the sample, and thus have a preferable structure as a rolling roll. On the other hand, in the comparative example containing excessive C or Cr, the needle-like carbide and the colony-like carbide are separated and segregated in the thickness direction, and when used as a rolling roll, the surface quality of the rolled steel sheet is deteriorated.

Table 2 and FIG. 3 show the presence or absence of carbide segregation and the amount of wear in each sample.

[0097]

[Table 2]

The material of the present invention has no carbide segregation.
It shows extremely good wear resistance.

The comparative materials B-1 and B-2 are examples in which the amount of Mo deviates beyond the limit range, and the carbide is segregated and the wear resistance is deteriorated.

The comparative materials C-1 to C-3 deviate from the component limitation range of the present invention on the assumption that C or Cr is insufficient, and are examples deviating from the limitation range of the present invention due to insufficient amount of carbide. No segregation of carbides was observed, but the wear resistance was significantly degraded. Comparative material C-1 also lacks Mo / Cr.

The comparative material C-4 is an example in which Mo / Cr is insufficient and deviates from the limited range of the present invention, and segregation of carbide is not recognized, but wear resistance is significantly deteriorated.

The comparative materials C-5 to C-8 are examples in which the amount of C or Cr is excessive and deviated from the component limitation range of the present invention, and carbides are segregated. Among them, C-6 lacks Mo and thus deviates from the component limitation range and Mo / Cr limitation range of the present invention, and the wear resistance is significantly deteriorated.

The comparative material C-9 has a C + 0.2Cr value of 6.2.
Is exceeded, carbides are segregated, and Mo and Mo / C
Due to the shortage of r, the wear resistance has also been significantly deteriorated.

(Example 2) 2.8C-15Cr-based composition and M
A Y-type keel block having a thickness of 30 mm was melted with a molten metal having a chemical composition shown in Table 3 in which Mo / Cr was changed by changing the amount of o, quenched from 1050 ° C, and tempered at 550 ° C. . By observing the structure of the sample, the presence or absence of needle-like carbides causing carbide segregation was determined. The abrasion test is a sliding wear method of the two disks of the mating material (S45C) and the test piece.
The sample was rotated at 0 rpm and rolled under a load of 100 kg for 15 minutes with a slip ratio of 14.2% between the test piece and the mating material. After this test was performed 12 times while changing the mating material, the wear amount of the test piece was measured.
Table 4 shows the wear amount of each sample and the presence or absence of needle-like carbide. The materials of the present invention (Nos. 3 to 5) have extremely excellent wear resistance, and no needle-like carbides are observed. On the other hand, Mo / Cr is 0.
The wear resistance of the comparative material (No. 1 and 2) less than 27 is significantly deteriorated, and the wear resistance of the comparative material (No. 6) having an excessive amount of Mo deteriorates with the appearance of acicular carbide. There was found.

[0105]

[Table 3]

[0106]

[Table 4]

(Example 3) The outer layer material, the intermediate layer material and the inner layer material having the compositions shown in Table 5 were melted to obtain a body diameter of 670 mm, a body length of 1450 mm,
Was manufactured by the following procedure. The outer layer material was cast in a mold rotating at a centrifugal force of 140 G to a thickness of 75 mm. Immediately after the outer layer was solidified, an amount of the intermediate layer material equivalent to a thickness of 40 mm was cast on the inner surface of the outer layer, so that the inner surface of the outer layer was redissolved and integrally welded to the intermediate layer. After the intermediate layer was solidified, the rotation of the mold was stopped, and the outer layer-intermediate layer-inner layer was integrally welded by casting the inner layer material. After cooling until the surface temperature of the outer layer became 60 ° C. or less, the mold was disassembled.

Comparative Roll The comparative roll deviated from the component limitation range of the present invention due to excessive amounts of C and Cr, and the carbide area ratio of the outer layer (MC and M ₇ C
(Total ₃ ) is 32.4%, which is a roll outside the limited range of the present invention. After dismantling the mold, the comparative roll broke from the inner layer during standing.

Roll of the Present Invention The roll of the present invention was subjected to a heat treatment of quenching from 1050 ° C. and then tempering at 500 ° C. after dismantling the mold. After the heat treatment, inspections such as ultrasonic flaw detection were also performed, but there were no defects such as a back cavity in the intermediate layer and the vicinity thereof, and the internal properties were sound.

[0110]

[Table 5]

As a result of using the above-mentioned roll of the present invention in an actual hot-rolling finishing mill, as shown in FIG. 4, excellent wear resistance far exceeding the use results of the conventional roll was confirmed.
In addition, the surface of the roll was not roughened, and very good results were obtained.

(Example 4) As an example of the present invention, an intermediate layer material and an inner layer material having the chemical compositions shown in Table 6 were dissolved (analytical values of the outer layer material indicate the results of chemical analysis of the product). Long
A 1450 mm composite roll was manufactured by the following procedure.

[0113]

[Table 6]

(1) A molten metal equivalent to a wall thickness of 75 mm was cast as an outer layer in a mold rotating at a centrifugal force of 140 G.

(2) 11 to 15 minutes after completion of casting of the outer layer material, an intermediate layer material having a thickness of 40 mm is cast on the inner surface of the outer layer to re-dissolve the inner surface of the outer layer, and to be integrated with the intermediate layer. Welded.

(3) The rotation of the mold was stopped 40 to 46 minutes after the casting of the outer layer was completed, and the outer layer-intermediate layer-inner layer were integrally welded by casting the inner layer material.

(4) After cooling the surface temperature of the outer layer to 60 ° C. or lower, the mold was disassembled.

(5) As a heat treatment, quenching from 1000 ° C.
Tempering was performed at ℃. The heat treatment was completed for each roll without causing any breakage. In addition, the body was inspected by an ultrasonic flaw detection method. As a result, there was no defect such as a back pocket in the intermediate layer and the vicinity thereof, and the internal properties were sound. Next, cut out the body end of each roll,
The middle part of the thickness of the intermediate layer and the inner layer (from the boundary between the intermediate layer and the inner layer)
(The position 30 mm inside) was checked, and the tensile strength was measured. Table 7 shows their chemical compositions and tensile strengths. The chemical composition of the intermediate layer and the inner layer of the roll of the present invention falls within the above-mentioned preferred component range, and the tensile strength of each layer satisfies 500 MPa or more, which is sufficient for a composite roll.

[0119]

[Table 7]

Example 5 (Tables 8 to 10) Rolls having a product body diameter of 820 mm, a body length of 2400 mm, and a total length of 5300 mm were produced. (1) A molten metal having an outer layer thickness of 100 mm was cast at 1430 ° C. into a mold rotating on a centrifugal casting machine.

(2) Twenty minutes after the start of casting the outer layer, a molten metal having a thickness of 40 mm was placed in a rotary mold at 1500 ° C. as an intermediate layer.
Cast in.

(3) 47 minutes after the start of casting the outer layer, the outer layer and the intermediate layer are completely solidified.

(4) Thereafter, the mold is set upright, ductile cast iron as an inner layer material is cast from above at 1400 ° C., and the mold is completely filled, heated and covered with a heat insulating material.

(5) After being completely cooled, the roll was taken out of the mold and subjected to heat treatment and machining to obtain a roll of the final product.

As a result of ultrasonic flaw detection and cutting inspection of the roll body, the average thickness of the outer layer was 83 mm due to the casting of the intermediate layer. The average thickness of the intermediate layer was 33 mm. Then, the outer layer, the intermediate layer, and the inner layer were completely metallurgically bonded to each other, and histological continuity was observed.

Table 8 shows the chemical compositions of the outer layer, the intermediate layer, and the inner layer at the molten metal stage.

[0127]

[Table 8]

The chemical composition after solidification of the outer layer, the intermediate layer and the inner layer of the roll cast with the composition shown in Table 8 is as shown in Table 9.

[0129]

[Table 9]

Table 10 shows a comparison between the mechanical properties of the intermediate layer of the roll of the present invention and that of the conventional roll of the same size.

[0131]

[Table 10]

The rolls of the present invention having the compositions shown in Tables 8 and 9 have remarkably excellent wear resistance by optimizing the alloy components forming the outer layer and limiting the carbide composition. Excellent, in addition to the outer layer without carbide segregation even when manufactured by the centrifugal casting method, the inner layer uses the toughest ductile cast iron of cast iron-based material, providing an intermediate layer between the outer layer and the inner layer, They can be completely metallurgically bonded to give a high performance centrifugally cast roll.

Example 6 (Tables 11 to 13) Rolls having a product diameter of 680 mm, a length of 2050 mm, and a total length of 5800 mm were produced. (1) As an outer layer, a molten metal having a thickness of 80 mm was cast at 1420 ° C. into a mold rotating on a centrifugal casting machine.

(2) 16.5 minutes after the casting of the outer layer was started, an amount of molten metal equivalent to a thickness of 40 mm was placed in a rotary mold as an intermediate layer.
Cast at 1490 ° C.

(3) After 42 minutes from the start of casting the outer layer, the outer layer and the intermediate layer are completely solidified.

(4) Thereafter, the mold is set upright, ductile cast iron as an inner layer material is cast from above at 1400 ° C., and the mold is completely filled, heated and covered with a heat insulating material.

(5) After being completely cooled, the roll was taken out of the mold and subjected to heat treatment and machining to obtain a roll of a final product.

As a result of ultrasonic inspection and cutting inspection of the roll body, the average thickness of the outer layer was 67 mm due to casting of the intermediate layer. Then, the outer layer, the intermediate layer, and the inner layer were completely metallurgically bonded to each other, and histological continuity was observed.

Table 11 shows the chemical compositions of the outer layer, the intermediate layer, and the inner layer at the molten metal stage.

[0140]

[Table 11]

The chemical composition of the outer layer, the intermediate layer and the inner layer of the roll cast with the composition shown in Table 11 after solidification is as shown in Table 12.

[0142]

[Table 12]

The mechanical properties of the intermediate layer of the roll of the present invention and those of the conventional roll of the same size can be described as follows.
As shown in Table 13.

[0144]

[Table 13]

In the rolls of the present invention having the compositions shown in Tables 11 and 12, the alloy components for forming the outer layer are optimized and the carbide composition is limited, whereby the wear resistance is remarkably excellent, and the economical efficiency is further improved. Excellent, in addition to the outer layer without carbide segregation even when manufactured by the centrifugal casting method, the inner layer uses the toughest ductile cast iron of cast iron-based material, providing an intermediate layer between the outer layer and the inner layer, They can be completely metallurgically bonded to give a high performance centrifugally cast roll.

[0146]

Industrial Applicability According to the present invention, a high-performance roll that exhibits extremely excellent wear resistance even under extremely severe rolling conditions in recent years and further improves the surface quality of a rolled steel sheet has been developed, which has excellent economical efficiency. It is possible to manufacture by a casting method, and it is possible to improve the productivity of the rolled steel sheet and reduce the manufacturing cost. The present invention can be applied to a cylindrical sleeve roll.

In addition, according to the present invention, by optimizing the alloy component forming the outer layer and limiting the carbide composition,
The outer layer is free from carbide segregation even when manufactured by the economically superior centrifugal casting method, and the inner layer is made of the toughest ductile cast iron of cast iron material. An intermediate layer can be provided between the inner layer and the metallurgical connection between them to form an integral high performance centrifugal cast roll.

[Brief description of the drawings]

FIG. 1 is a micrograph showing a metal structure (carbide structure) of a material of the present invention.

FIG. 2 is a micrograph showing a metal structure (carbide structure) of a comparative material.

FIG. 3 is a diagram showing the presence or absence of carbide segregation and the amount of wear.

FIG. 4 is a schematic diagram showing rolling results in an actual mill.

FIG. 5 is a schematic view showing a roll of the present invention.

────────────────────────────────────────────────── ─── Continued on the front page (51) Int.Cl. ⁷ Identification code FI C22C 38/00 302 C22C 38/00 302E 38/26 38/26 (72) Inventor Koji Yuda 1-1-1, Kawasakicho, Handa-shi, Aichi Prefecture Address Kawasaki Steel Corporation Chita Works (56) References JP-A-8-73977 (JP, A) JP-A-7-224356 (JP, A) JP-A-8-81731 (JP, A) 5-339673 (JP, A) JP-A-5-313118 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 37/00 B21B 27/00 B22D 13/02 502 C22C 37 / 06 C22C 38/00 301 C22C 38/00 302 C22C 38/26

Claims (12)

(57) [Claims] 1. A weight ratio of C: 2.4 to 2.9%, Si: 1
% Or less, Mn; 1% or less, Cr; 12 to 18%, Mo;
9%, V; 3 to 8%, Nb; 0.5 to 4%, and simultaneously satisfy the following expressions (1) and (2): 0.27 ≦ Mo (%) / Cr (%) <0.7 (1) C (%) + 0.2 · Cr (%) ≦ 6.2 (2) A roll for hot rolling having an outer layer composed of a balance of Fe and unavoidable impurities. 2. C: 2.4 to 2.9% by weight, Si; 1
% Or less, Mn; 1% or less, Cr; 12 to 18%, Mo;
9%, V; 3 to 8%, Nb; 0.5 to 4%, and simultaneously satisfy the following expressions (1) and (2): 0.27 ≦ Mo (%) / Cr (%) <0.7 (1) C (%) + 0.2 · Cr (%) ≦ 6.2 (2) A roll for hot rolling having an outer layer composed of a balance of Fe and unavoidable impurities and having a W content of less than 1%. 3. A weight ratio of C: 2.4 to 2.9%, Si: 1
% Or less, Mn; 1% or less, Cr; 12 to 18%, Mo;
9%, V; 3 to 8%, Nb; 0.5 to 4%, and simultaneously satisfy the following expressions (1) and (2): 0.27 ≦ Mo (%) / Cr (%) <0.7.・ ・ ・ ・ (1) C (%) + 0.2 ・ Cr (%) ≦ 6.2 ・ ・ ・ ・ ・ (2) The area ratio of MC type carbide and M7C3 type carbide is composed of the balance of Fe and unavoidable impurities . In total
A roll for hot rolling having an outer layer containing 13 to 30%. 4. A weight ratio of C: 2.4 to 2.9%, Si: 1
% Or less, Mn; 1% or less, Cr; 12 to 18%, Mo;
9%, V; 3 to 8%, Nb; 0.5 to 4%, and simultaneously satisfy the following expressions (1) and (2): 0.27 ≦ Mo (%) / Cr (%) <0.7.・ ・ ・ ・ (1) C (%) + 0.2 ・ Cr (%) ≦ 6.2 ・ ・ ・ ・ ・ (2) The area ratio of MC type carbide and M7C3 type carbide is composed of the balance of Fe and unavoidable impurities . In total
Contains 13 to 30% and the area ratio of M7C3 type carbide is 6% or less
A roll for hot rolling having an outer layer contained therein. 5. A weight ratio of C: 2.4 to 2.9%, Si: 1
% Or less, Mn; 1% or less, Cr; 12 to 18%, Mo;
9%, V; 3 to 8%, Nb; 0.5 to 4%, and simultaneously satisfy the following expressions (1) and (2): 0.27 ≦ Mo (%) / Cr (%) <0.7. ... (1) C (%) + 0.2 · Cr (%) ≤ 6.2 ... (2) Consisting of the balance of Fe and unavoidable impurities, especially the W content
Is less than 1%, and the MC type carbide and the M7C3 type carbide are in the total area ratio.
A roll for hot rolling having an outer layer containing 13 to 30%. 6. A weight ratio of C: 2.4 to 2.9%, Si: 1
% Or less, Mn; 1% or less, Cr; 12 to 18%, Mo;
9%, V; 3 to 8%, Nb; 0.5 to 4%, and simultaneously satisfy the following expressions (1) and (2): 0.27 ≦ Mo (%) / Cr (%) <0.7. ... (1) C (%) + 0.2 · Cr (%) ≤ 6.2 ... (2) Consisting of the balance of Fe and unavoidable impurities, especially the W content
Is less than 1%, and the MC type carbide and the M7C3 type carbide are in the total area ratio.
Contains 13 to 30% and the area ratio of M7C3 type carbide is 6% or less
A roll for hot rolling having an outer layer contained therein. 7. A hot-rolling roll comprising the outer layer according to claim 1 and an inner layer of spheroidal graphite cast iron or graphite steel welded and integrated, wherein the inner layer has a weight ratio of C; 2.5 to 4.0%, Si; 1.5 to 3.
5%, Mn: 1.5% or less, Ni: 5% or less, Cr: 3%
A roll for hot rolling, containing Mo: 3% or less, V: 3% or less, Nb: 2% or less, and the balance being Fe and unavoidable impurities. 8. A hot rolling roll having an intermediate layer between the outer layer and the inner layer according to claim 1, wherein the outer layer and the inner layer are welded and integrated through the intermediate layer. The intermediate layer is, by weight, C: 0.8 to 3.0%, Si: 0.3 to 3.0%.
3.0%, Mn: 1.5% or less, Ni: 5% or less, Cr: 10
%, Mo; 4% or less, V: 5% or less, Nb; 3% or less, and a roll for hot rolling comprising the balance of Fe and inevitable impurities. 9. The hot-rolling roll according to claim 8, wherein the mixing ratio of the intermediate layer to the inner layer material is regulated within a range of 5 to 20%. 10. The hot-rolling roll according to claim 8, wherein the mixing ratio of the outer layer to the intermediate layer material is restricted to a range of 5 to 50%. 11. The method according to claim 1, wherein
Co is added to at least one of the layers constituting the hot-rolling roll.
% For hot rolling. 12. A hot-rolling roll obtained by centrifugally casting the outer layer according to claim 1. Description: