JP2708611B2 - Composite roll for cold rolling and production method thereof - Google Patents

Description

The present invention relates to a composite roll for cold rolling, a method for producing the same, and a rolling mill using the same, and in particular, has a high axial strength suitable for cold rolling. The present invention relates to a work roll for a shift type six-high rolling mill, a method of manufacturing the same, and a shift type six-high rolling mill using the same.

[Conventional technology]

In the case of rolls for cold rolling mills, thermal shock is applied to the roll surface due to slip generated between the roll and the material to be rolled during rolling, rolled material being rolled around the roll, etc. Occurs.

Work rolls are required to have excellent wear resistance in order to maintain good rolling, in addition to resistance to the thermal shock.

In order to improve the thermal shock resistance, it is effective to improve the tempering resistance of the roll itself and perform the tempering at a higher temperature.

As described in JP-A-63-60258, conventional work rolls are as follows: C1.2-2.5%, Si0.8-3.0%, Mn ≦ 1%, Cr3.0-
After quenching a roll material composed of 6.0% and Mo0.2% or less, tempering was performed.However, in order to obtain hardness of Hs93 or more, the tempering temperature was set to 160 ° C or less. .

[Problems to be solved by the invention]

In the above prior art, when the tempering temperature is raised to 160 ° C. or higher, the hardness of Hs 93 or higher cannot be obtained, the wear resistance is reduced, and good rolling cannot be maintained in order to improve the heat resistance and thermal shock resistance. Was.

An object of the present invention is to provide a composite structure for cold rolling, in which the core material has excellent toughness, is tempered at a temperature of 300 to 550 ° C., and reduces the residual stress on the outermost surface of the outer layer material to 70 to 120 kg. /
To provide a composite roll for cold rolling excellent in abrasion resistance and thermal shock resistance in which the surface of the outer layer material has a Shore hardness of 93 or more as a compressive stress of ² mm2, a method for producing the same, and a rolling mill using the same. It is in.

[Means for solving the problem]

The composite roll for cold rolling of the present invention is a composite roll for cold rolling in which a core material is covered with an outer layer material, the core material having a Shore hardness of 35 or more and a lower hardness than the outer layer material, and It is made of a low alloy steel having a tensile strength of 60 kg / mm ² or more and an impact value of 1.5 kgm / cm ² or more. The outer layer material is C: 0.8 to 1.5% by weight, Si:
1.0 to 3.0%, Mn: 1.5% or less, Cr: 2.0 to 7.0%, Mo: 1 to 5%,
V: 0.5 to 2.0% and W: made of high alloy steel containing not more than 2.0%, and the outer layer material is built up on the core material by an electroslag overlay method, and only the surface layer portion of the outer layer material is By fountain quenching by heating to a temperature equal to or higher than the austenite transformation point, and by performing sub-zero treatment and tempering at a temperature of 300 to 550 ° C., the surface of the outer layer material has a Shore hardness of 93 or more, and the outer layer material Amount of retained austenite
It is characterized by having a martensite structure of 15% by volume or less and a residual stress on the outermost surface of the outer layer material of a compressive stress of 70 to 120 kg / mm ² .

The method for producing a composite roll for cold rolling of the present invention is a method for producing a composite roll for cold rolling in which the outer periphery of a core material is covered with an outer layer material, wherein the core material has a Shore hardness of 35 or more than the outer layer material. It has a low hardness, and tensile strength of 60 kg / mm ² or more, the impact value
The outer layer material is composed of a low alloy steel of 1.5 kgm / cm ² or more, and C: 0.8 to 1.5%, Si: 1.0 to 3.0%, Mn: 1.5% or less, Cr:
It is made of high alloy steel containing 2.0 to 7.0%, Mo: 1 to 5%, V: 0.5 to 2.0% and W: 2.0% or less, and the outer layer material is built up on the core material by an electroslag overlay method. Heating only the surface layer portion of the outer layer material to a temperature equal to or higher than the austenite transformation point and subjecting it to fountain quenching, followed by sub-zero treatment and 300 to 550
Tempering at a temperature of ℃, the Shore hardness of the surface of the outer layer material is 93 or more, the amount of retained austenite of the outer layer material is 15% by volume or less martensite structure, and the outermost surface of the outer layer material Is characterized by a compressive stress of 70 to 120 kg / mm ² .

The rolling mill according to the present invention is a rolling mill including a cold-rolling work roll and a backup roll that is in contact with and supports the cold-rolling work roll. A cold rolled composite roll covered with a core material having a Shore hardness of 35 or more and a lower hardness than the outer layer material, a tensile strength of 60 kg / mm ² or more, and an impact value of 1.5 kgm / cm ² or more of low alloy steel, and the outer layer material is, by weight, C: 0.8 to 1.5%, Si: 1.0 to 3.0%, Mn: 1.5% or less, Cr: 2.0 to 7.0%, Mo: 1 -5%, V: 0.5-2.0% and W: 2.0
The outer layer material is made of a high alloy steel containing the following, and the outer layer material is built up on the core material by an electroslag overlaying method, and only the surface layer portion of the outer layer material is heated to a temperature equal to or higher than the austenite transformation point and a fountain is used. By performing quenching, sub-zero treatment and tempering at a temperature of 300 to 550 ° C., the outer layer material has a surface having a Shore hardness of 93 or more, and the outer layer material has a retained austenite content of 15% by volume or less. It is a composite roll for cold rolling that has a site structure and has a residual stress at the outermost surface of the outer layer material of 70 to 120 kg / mm ² .

In the case of a roll integrated with the above materials, there is a risk of breakage from the inside due to thermal stress during quenching of the fountain, and since the toughness of the shaft is inferior, it is disadvantageous for net breakage during use. . Therefore, the roll has a composite structure in which the surface layer portion is made of the above-mentioned material, and the core material is made of a tough low-alloy steel.

Further, after providing an outer layer made of a high-speed tool steel on the outer periphery of the core made of a low-alloy steel material, a hot forging process is performed on the outer layer in order to disperse carbide contained in the outer layer and homogenize the structure. Is preferred.

The roll of the present invention is a composite roll composed of a core shaft and an outer layer covering the core shaft. If the entire roll is formed of the high-speed tool steel (that is, an integrated roll of high-speed tool steel) ), There is a danger of internal breakage (cracking) due to thermal stress generated during fountain quenching, and the toughness of the shaft part causes the roll neck part to break easily during use. . Therefore, the composite roll structure as described above was adopted.

As for the quenching process, when the blast cooling or the oil cooling is performed, the compressive residual stress of the surface layer is insufficient even if the above-mentioned material is used. That is, when tempering is performed at a temperature of 300 ° C. or higher after the quenching, it is difficult to obtain a hardness of Hs93 or higher. This is the reason why quenching is performed by fountain cooling in the method of the present invention.

The tempering temperature in the present invention is preferably from 450 to 550 ° C, more preferably from 500 to 550 ° C. In the case of a cold rolling roll, it is said that the surface hardness is required to be approximately Hs90 or more.

As in the present invention, the residual stress in the case where only the outer layer portion is heated to a temperature equal to or higher than the transformation point and quenching treatment is performed by rapid cooling is obtained by superimposing the residual stress due to thermal stress and the residual stress due to transformation stress. If the outer layer is quenched,
Due to the volume shrinkage, a compression plastic strain is generated in a portion of the internal plastic deformation temperature range. As a result, when the internal and external temperatures are cooled down to the same temperature, a compressive residual stress is generated in the outer layer portion and a tensile residual stress is generated in the internal portion. This is residual stress due to thermal stress. In addition, since the specific volume of martensite generated in the outer layer due to the transformation is relatively large, tensile residual stress in the core and compressive residual in the hardened outer layer due to the difference from the specific volume of the core. Stress is generated respectively. As described above, the residual stress caused by the thermal stress and the transformation stress is considerably larger than the residual stress caused by only the martensitic transformation (normally a compressive stress of about 20 kg / mm ² ), and is aimed at in the present invention. And a compressive stress of 70 to 120 kg / mm ² (when sub-zero treatment is applied).

In addition, only the fountain quenching treatment leaves about 40% of austenite, and a sub-zero treatment at a temperature of -50 ° C or lower is performed to promote the decomposition of the retained austenite. Zub-zero treatment is carried out by suspending a roll in a vertical sub-zero treatment tank, and spraying liquid nitrogen onto the roll surface while rotating the roll. The amount of retained austenite after the sub-zero treatment is approximately 15% or less.

After this, when tempering at a temperature of 300 ° C or more,
The amount of retained austenite decreases from the above value of about 15% to about several%. The finally retained austenite serves as a buffer for alleviating the thermal expansion and contraction of the roll surface during use of the roll, and exhibits a function of preventing the occurrence of cracks on the roll surface. Further, if the roll is tempered at a high temperature of 300 to 550 ° C., if the roll is used for cold rolling, if an accident occurs, a high-temperature steel sheet is wound around the roll and the roll temperature is reduced. Even if it rises, crack generation due to decomposition of residual austenite on the roll surface and the like is effectively prevented.

Generally, if tempering is performed at a high temperature of 300 to 550 ° C,
It is known that distortion due to quenching is easily released (relaxation) and the amount of reduction in residual stress is increased. However, the high-speed tool steel used in the present invention contains a large amount of alloying elements such as Si, Cr, Mo, V, etc., which increase the tempering resistance. With tempering at around 500 ° C, the release of distortion is small,
High residual stress can be maintained.

The core material in the present invention is preferably a low alloy steel having a tensile strength of 60 kg / mm ² or more and an impact value of 1.5 kg-m / cm ² or more, and in particular, C 0.5 to 1.0% by weight% and Si 1% or less. , Mn1% or less, Cr1
Forged steel containing up to 5% and 0.5% Mo or less is preferred.

[Action]

The work roll for cold rolling having the above configuration can sufficiently withstand abrasion resistance, surface roughness resistance and toughness even when used for rolling in which large bending is applied. In particular, since the outer layer is welded to the shaft by electroslab remelting, the carbides crystallized from the molten metal rapidly solidify without floating, sedimentation or segregation, and are finely and evenly dispersed in the outer layer. Becomes Thus, the high shape control of the rolled material under high pressure can be performed soundly, and the quality of the surface properties of the rolled material is improved.

The present inventors have pursued experiments and obtained the following findings in order to solve the problems of the prior art and achieve the above object.

The outer layer must be made of semi-high speed steel and heat treated to maintain a hardness of Hs93 or more in order to secure abrasion resistance and skin resistance.

The specification of the chemical composition of the semi-high-speed outer layer is based on the following reason.

C is necessary for forming carbides for improving wear resistance and for securing the base hardness. If the amount is less than 0.5%, the amount of carbides is small and the wear resistance is not sufficient. On the other hand, C is 1.5
%, The amount of reticulated carbides precipitated at the grain boundaries increases, resulting in inferior skin roughness resistance and toughness. In particular, 0.8-
1.2% is preferred.

Si is an element required as a deoxidizing agent, and has a tempering resistance of 1.0% or more. But the amount
If it exceeds 3.0%, embrittlement is likely to occur. In particular, 1.5-2.
5% is preferred.

Mn has an action of fixing S, which is an impurity, as MnS as well as a deoxidizing action. However, if the amount exceeds 1.5%, retained austenite increases and stable hardness cannot be maintained, and toughness decreases. In particular, 0.2 to 1.0% is preferable, and 0.2 to 0.5% is more preferable.

If Cr is less than 2%, the hardenability is poor, and if it exceeds 7%,
This is inconvenient because Cr-based carbides are excessive. In particular,
6% is preferable, and 3.5-5% is more preferable.

Mo and W combine with C to form M ₂ C or M ₅ C-based carbides, respectively, and also form a solid solution in the matrix to strengthen the matrix and improve wear resistance and tempering resistance. However, when the amount is excessive, the amount of M ₆ C-based carbide increases, and the toughness and the skin resistance decrease. The upper limits for Mo and W are 5% and 2%, respectively.
Mo should be at least 1%. Mo is preferably from 1.5 to 4.5%, and W is preferably from 0.1 to 1%, more preferably from 0.15 to 0.5%.

V forms MC carbides and contributes to the improvement of wear resistance.
If it is less than 0.5%, the effect is not sufficient. If it exceeds 2%, the grindability is significantly impaired. In particular, 0.7 to 1.5% is preferable.

Co is an element for forming a solid solution in the matrix and tempering at a high temperature to obtain high hardness, but its effect is sufficient if it is less than 5%.

The semi-high speed steel used for the outer layer of the present invention can contain Ni in addition to the above elements. Since Ni has the effect of improving the hardenability, it can be added in an amount of 5% or less. Exceeding this causes an increase in retained austenite, resulting in a decrease in hardness and a decrease in skin roughness resistance. In particular, 1% or less is preferable, and 0.1 to 0.5% is more preferable.

In the present invention, it is preferable to use a forged steel having Hs 35 or more as the material for the core shaft. That is, when a net stress of 10 kg / mm ² is applied as a nominal stress to the roll of the present invention, the size effect coefficient is 0.8, the surface effect coefficient is 0.9,
Assuming that the notch coefficient is 2.0, the required fatigue limit is 36 kg / mm ² , and in order to obtain it, the hardness is preferably Hs 35 or more.

The nominal stress σ _n in the roll net portion is obtained by the following equation.

M: Bending moment = P · l P: Load applied to the bearing l: Moment arm from the center of the bearing d: Diameter of the shaft portion Also, allowable stress (Allowable Stress) σ _al is obtained by the following equation.

σ _wo : Rotating bending fatigue limit of smooth specimen η: Size effect coefficient = 0.8 ξ: Surface effect coefficient = 0.9 β: Notch coefficient = 2.0 S: Safety factor = 1.3 If σ _al ≧ σ _n , it is considered safe. From the above two equations Becomes

If σ _n = 10 kg / mm ² , then σ _wo ≧ 36 kg / mm ² .

As a method of providing an outer layer on a core shaft, Japanese Patent Publication No. 44903/1988
Patent Application Publication No. JP-A-47-2851 discloses a continuous overlaying method using high-frequency heating, and forming an outer layer by hot isostatic pressing using a powder metallurgy method disclosed in JP-A-47-2851. And an overlay method using an electroslag remelting method disclosed in JP-A-57-2862. Electroslag remelting overlay method is good.

Since heating to the quenching temperature is performed so that only the outer layer material is at or above the austenite transformation point, the toughness of the core material can be kept high even after quenching.

Further, the residual stress in the case of heating only the outer layer material or the austenite transformation point becomes to have been superimposed to be due as the transformation stress due to thermal stress in the outermost surface of the outer layer material 70~120kg / mm ² A compressive stress can be obtained, and a Shore hardness of 93 or more on the surface of the outer layer material can be obtained.

[Example] A roll having a body diameter of 385 mm and a body length of 1480 mm was manufactured as an ingot for a composite roll by an electro-remelting method using a shaft material having a diameter of 300 mm as follows, with an outer diameter of 485 mm.

FIG. 7 is a schematic view of an apparatus for producing a composite roll by the electroslag overlaying method. This device is used for welding machine 9,
It includes an amplifier 17, a power supply wiring 12, a carbon brush 12a, a thermometer for temperature measurement 13, a DC motor 18, and a manipulator 19.
A manipulator 19 is moved by a direct current motor 18 so that a tubular electrode 8, which is a consumable electrode made of high-speed tool steel and supported by a manipulator arm 12b, is moved upward. A low alloy steel core shaft 7 is provided on a surface plate 11. A water-cooled mold 10 is installed concentrically with the core shaft 7, and an annular bottom plate (that is, a mold bottom) 16 is installed near the lower end of the core shaft 7 in a space between the two. The core shaft 7 and the water-cooled mold 10
It is rotated in the circumferential direction. The tubular electrode 8 supported by the manipulator 19 is inserted into the space defined by the core shaft 7 and the water-cooled mold 10, that is, into the melting chamber,
The current supplied between the core shaft 7 and the tubular electrode 8 via the wiring 12 causes the tubular electrode 8 to be dissolved and consumed. When an arc is generated by energization, the slag 15 melts due to its resistance heat, and the molten metal 14 is formed.
The core shaft 7 is cooled and solidified by contact with the surface 10 to form a build-up layer on the surface of the core shaft 7. During this time, the water-cooled mold 10 is moved upward coaxially with respect to the core shaft 7. The slag 15 is always adjusted to a thickness of 50 to 60 mm. Further, the molten metal 14 is prevented from dropping downward by the annular bottom plate 16.

Thus, the cladding layer of the obtained composite roll was not forged at 1100 ° C., and had an outer diameter of 415 mm and an outer layer thickness of 42.5 mm.
Furthermore, the surface hardness of the cladding layer can be set to Hs93 or more by heating the cladding layer at a temperature of 1000 to 1200 ° C., performing fountain quenching, and tempering at a temperature of 300 to 550 ° C.

After heat treatment, finish outer diameter 385m by cutting and polishing
It is cut and polished with a diameter of about 2 to 3 mm so that the diameter becomes m.

The chemical composition of the outer layer material is shown in Table 1 (% by weight). The balance is Fe. The roll was heated at a temperature of 1000 to 1200 ° C., subjected to fountain quenching, and tempered by changing the temperature within a temperature range of 120 to 520 ° C. At this time, the tempering time is 10
~ 20 hours. For comparison, rolls having the same dimensions were manufactured for a conventional 5% Cr forged steel material. Table 1 also shows the chemical components of this material. In the heat treatment, quenching suitable for this material was performed, and tempering was performed by changing the temperature in a temperature range of 120 to 520 ° C. At this time, the tempering time was 10 to 20 hours. The roll of the present invention was made of 0.9% C, 3% Cr forged steel and had a hardness of HS40.

FIG. 8 shows a fountain quenching technique. Roll 20
The outer layer 21, which is a hardfacing layer, is hardened. An annular device including an induction coil 22 as a low-frequency inductor and a water injection cylinder 23 is set so as to surround the outer layer 21 of the roll 20 set vertically. With the low-frequency current flowing through the induction coil 22, the roll 20 is moved downward while being rotated. The outer layer 21 is progressively quenched by being continuously cooled and quenched by the cooling water injected from the water injection cylinder 23 while being heated by the generated induced current. As a result, rapid cooling at a cooling rate of 10 ° C./sec or more is achieved. The cooling rate can be controlled by the amount of the jet water and the jet speed.

Heating to the quenching temperature was performed only on the outer layer 21, and the boundary with the core material was performed so as to be lower than the austenite transformation point.
As a result, the toughness of the core material at the boundary can be kept high.

FIG. 1 shows the relationship between the tempering temperature and the hardness, and FIG. 6 shows the relationship between the tempering temperature and the residual stress. In the case of Example 1 and Comparative Example 1, the quenching temperature was 1060 ° C,
By a method as shown in FIG. 8, low frequency induction heating of only the outer layer portion and progressive quenching by subsequent fountain cooling were performed. Thereafter, a sub-zero treatment at −50 ° C. was performed, and tempering was performed at each temperature. The cooling rate at this time is about 15 ° C / s
It was ec.

Comparing FIG. 1 with FIG. 6, it can be clearly understood that the residual stress contributes to the hardness of the roll surface after tempering. With conventional rolls, tempering to achieve Hs93 hardness is 160 ° C.
However, in the case of Example 1, the temperature was 520 ° C., and it can be seen that the tempering temperature at which the same hardness was obtained as compared with the conventional roll was significantly increased. Further, the residual stress on the roll surface of Example 1 and Comparative Example 1 at a tempering temperature of 500 ° C. was −70.
While greater than kg / mm ^2, in a conventional roll, the residual stress of the roll surface is about -30kg / mm ^2, it can be seen that in One by the present invention can secure a large residual stress.

The amount of retained austenite in Example 1 and Comparative Example 1 was 10 to
It was 15% by volume.

In the case of Comparative Example 1, the hardness is H even when tempered at 500 ° C.
It was s88. This is presumably because the amount of Si is as small as 0.79%.

FIG. 2 shows a comparison of thermal shock resistance between Example 1 and a conventional roll. In the test, the material was sampled from the surface of the roll material after forging, worked, and then quenched. Tempering was performed at 520 ° C. in Example 1 and 160 ° C. for the conventional roll, respectively, and the test was performed. The test method was 14 specimens of 80 mm diameter and 40 mm thickness.
The sample was rotated at 20 rpm, and water cooling was performed while pressing a 20 mm square mild steel material against the test piece with a load of 500 g / mm.

The crack length on the vertical axis in FIG. 2 is the sum of the crack lengths generated on the surface of the test piece. In contrast to the conventional material having a crack length of 54 mm, the tempering temperature at 520 ° C. in Example 1 was used. In this case, the height was 23 mm, which is less than half of the conventional material, and the effectiveness of high-temperature tempering is clear.

FIG. 3 shows a comparison of wear resistance. In the test, the sliding surface is diameter
The same heat treatment was applied to an 18 mm test piece, and the test piece was slid on a # 100 emery paper under a load of 500 g. While the wear amount of the conventional roll is 230 mg, when the tempering temperature is 520 ° C. in Example 1, the wear amount is 120 mg, which is excellent in wear resistance.

The roll having a tempering temperature of 520 ° C. in Example 1 was formed into the shape shown in FIG.
mm, especially stainless steel foil with a thickness of 200 μm or less,
As a result of cold rolling of the steel sheet for thin tin plate, it was confirmed that abrasion resistance more than 5 times as high as that of the conventional integrated roll was obtained. 1 is a rolled material, 2 is a work roll according to the present embodiment, 3 is an intermediate roll, 4 is a back-up roll,
5 is an outer layer material and 6 is a core material. The intermediate roll 3 can be shifted left and right.

〔The invention's effect〕

According to the present invention, the composite roll for cold rolling, 300 to 550
℃ high temperature tempering, and the core material is excellent in toughness,
The residual stress at the outermost surface of the outer layer material of a Shore hardness of the surface of the outer layer material can be 93 or more as a compressive stress of 70~120kg / mm ^2, between excellent cold to wear resistance and thermal shock resistance It is possible to provide a composite roll for rolling, a method for producing the same, and a rolling mill using the same.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the tempering temperature and hardness of the inventive roll and the conventional roll, FIG. 2 is a graph comparing the thermal shock resistance of the inventive roll and the conventional roll, and FIG. FIG. 4 is a graph comparing the wear resistance of a roll according to the present invention with a conventional roll, FIG. 4 is a cross-sectional view of a main part of a work roll according to the present invention, and FIG. FIG. 6 is a graph showing the relationship between the tempering temperature and the residual stress of the roll of the present invention and the conventional roll, and FIG. 7 is a composite roll by the electroslag overlaying method. Fig. 8 and Fig. 8 are schematic diagrams showing a manufacturing apparatus and a fountain quenching method of a rolling roll. 1 ... rolled material, 2 ... composite roll, 3 ... intermediate roll, 4 ... back-up roll, 5 ... outer layer material, 6 ...
Core material, 7: core shaft, 8: tubular electrode, 22: induction coil, 23: water injection cylinder.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasuo Kondo 4026 Kuji-cho, Hitachi City, Ibaraki Prefecture Within Hitachi Research Laboratory, Hitachi, Ltd. (56) References JP-A-59-76696 (JP, A) JP-A-58- 39767 (JP, A) JP-A-53-80350 (JP, A) JP-A-63-60258 (JP, A) JP-A-57-2862 (JP, A) JP-B-53-38686 (JP, B2)

Claims (3)

(57) [Claims] 1. A composite roll for cold rolling wherein an outer periphery of a core material is covered with an outer layer material, wherein the core material has a Shore hardness of 35 or more, a lower hardness than the outer layer material, and a tensile strength. 60 kg / mm ² or more, the impact value becomes a 1.5kgm / cm ² or more low alloy steel, the outer layer material, by weight, C: 0.8~1.5%, Si: 1.0~3.0%, Mn: 1.
5% or less, Cr: 2.0 to 7.0%, Mo: 1 to 5%, V: 0.5 to 2.0% and
W: made of a high alloy steel containing 2.0 or less, and the outer layer material is built up on the core material by an electroslag overlay method, and only the surface layer portion of the outer layer material is heated to a temperature equal to or higher than the austenite transformation point. And then subjected to fountain quenching and sub-zero treatment and tempering at a temperature of 300 to 550 ° C. so that the surface of the outer layer material has a Shore hardness of 93 or more, and the residual austenite amount of the outer layer material is 15% by volume. A composite roll for cold rolling, wherein the composite roll has the following martensite structure and a residual stress at an outermost surface of the outer layer material is a compressive stress of 70 to 120 kg / mm ² . 2. A method of manufacturing a composite roll for cold rolling wherein the outer periphery of a core material is covered with an outer layer material, wherein the core material has a Shore hardness of 35 or more, a lower hardness than the outer layer material, and a tensile strength. Strength 60
kg / mm ² or more, and made of a low alloy steel having an impact value of 1.5 kgm / cm ² or more, and the outer layer material is, by weight, C: 0.8 to 1.5%, Si: 1.0 to 3.0%.
%, Mn: 1.5% or less, Cr: 2.0-7.0%, Mo: 1-5%, V: 0.5-2.
0% and W: high alloy steel containing 2.0% or less, the outer layer material is built up on the core material by an electroslag overlay method, and only the surface layer portion of the outer layer material is heated to a temperature equal to or higher than the austenite transformation point. Heating and quenching with a fountain, followed by sub-zero treatment and tempering at a temperature of 300 to 550 ° C., so that the surface of the outer layer material has a Shore hardness of 93 or more, and the residual austenite amount of the outer layer material is 15% by volume or less. And the residual stress at the outermost surface of the outer layer material is 70 to
A method for producing a composite roll for cold rolling, which has a compressive stress of 120 kg / mm ² . 3. A rolling mill comprising: a work roll for cold rolling; and a backup roll for supporting the cold roll work roll in contact with the work roll, wherein the work roll covers an outer periphery of a core with an outer layer material. A cold rolled composite roll, wherein the core material has a Shore hardness of 35 or more and a lower hardness than the outer layer material, and a tensile strength of 60 kg / mm ² or more, and an impact value of 1.
5 kgm / cm ² or more of low alloy steel, the outer layer material is, by weight, C: 0.8 to 1.5%, Si: 1.0 to 3.0%, Mn: 1.5% or less, Cr: 2.0% or less.
~ 7.0%, Mo: 1 ~ 5%, V: 0.5 ~ 2.0% and W: 2.0 or less, and the outer layer material is overlaid on the core material by an electroslag overlay method. Only the surface layer of the outer layer material is heated to a temperature equal to or higher than the austenite transformation point and subjected to fountain quenching;
By performing tempering at a temperature of 550550 ° C., the outer layer material has a surface having a Shore hardness of 93 or more, the amount of retained austenite of the outer layer material is 15% by volume or less, a martensitic structure, and the outer layer material has 70 to 12 residual stress on the outermost surface
A rolling mill characterized by being a composite roll for cold rolling with a compression stress of 0 kg / mm ² .