JP3127650B2 - Tandem rolling mill - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a tandem rolling mill in which a plurality of hot or cold sheet rolling mills are arranged in a line.

[0002]

2. Description of the Related Art In a conventional tandem rolling mill, all continuous rolling mills are usually constituted by four-high rolling mills. For this reason, the sheet crown (sheet thickness distribution in the sheet width direction) and the shape (flatness) of the rolled material are performed by the roll bending device of the four-high rolling mill. However, this alone has limited ability to control the crown and shape of the strip, and thereafter, tandem rolling mills incorporating various high-performance rolling mills have been developed. For example, Japanese Patent Publication No. 53-2140 and Japanese Patent Publication No. 55-2121 disclose a rolling mill having a roll movable in an axial direction, and controlling a sheet crown and a shape by using the roll movement and work roll bending in combination. A tandem rolling mill (see FIG. 3, hereinafter referred to as an HC mill) is disclosed. As a result, it is possible to control a composite shape that cannot be corrected conventionally. Japanese Patent Publication No. Sho 59-41804 discloses a tandem rolling mill composed of only a rolling mill (hereinafter referred to as a cross mill) for controlling a sheet crown and the like by crossing a work roll in a horizontal plane.

A four-high rolling mill capable of using a large-diameter work roll and having a large sheet crown control ability is a rolling mill (hereinafter referred to as a PC mill) in which a work roll and a backup roll are vertically crossed together in a horizontal plane. Kuniaki 58-23161
No. 6,086,045.

In order to control the composite shape, two or more types of shape correcting means having different effects on the thickness distribution pattern in the width direction of the sheet are required. For example, as described in Japanese Patent Publication No. 53-2140, by appropriately combining a means for affecting the distribution shape from the vicinity of the center of the sheet width and a means for intensively applying the effect to the end of the sheet. , The composite shape can be modified.

On the other hand, in the case of work rolls, thermal shock is applied to the surface of the roll due to slip generated between the roll and the rolled material during rolling, and a rolling accident in which the rolled material is wound around the roll. Cracks occur. Work rolls are required to have excellent wear resistance in order to maintain good rolling, in addition to resistance to the thermal shock.

As described in Japanese Patent Application Laid-Open No. 63-60258, a conventional work roll has a C of 1.2 to 2.5% and a Si of 0.8 to 3.3%.
0%, Mn ≦ 1%, Cr 3.0-6.0%, Mo 0.2%
After the quenching of the following roll material, tempering was performed. However, in order to obtain a hardness of Hs 93 or more, the tempering temperature was set to 160 ° C. or less.

[0007] Further, Japanese Patent Application Laid-Open No. 53-80351 discloses that a core material is made to have 1.0 to 3.0% C by electroslag welding.
i 0.5-1.5%, Mn 0.5-1.5%, Cr 3.0-
6.0%, W + 1 / 2Mo 10-20%, Mo ≦ 10
%, W ≦ 18.0%, Co ≦ 5.0%, V0.5-5%,
It is disclosed to manufacture a hot-rolling roll having a hardness of Hs 80 or more by forming 5 to 100 mm of a deposited metal substantially composed of Fe.

[0008] A conventional cold-rolling work roll is disclosed in, for example, Japanese Patent Publication No. 50-7529, C: 0.7-1.
Integral forged steel rolls of 1%, Cr 1.5 to 6% and other steel materials to which Mo, V, etc. are added, or 10% Cr steel materials similar to cold soybean steel JIS SKD-11 were mainly used. . Still another prior art is disclosed in JP-A-62-148004.

[0009]

In order to maximize the controllability of the composite shape, all stands should be made of a 6-stage HC mill capable of reducing the work roll diameter. This also has the advantage of requiring a small rolling load. However, this device has the following disadvantages. In the case of hot rolling, since the rolls come into contact with a high-temperature material in the several stands at the preceding stage, the heat capacity of a small-diameter roll is small and immediately becomes high, and the material of the roll deteriorates. In addition, if the diameter of the former work roll is small, it becomes impossible to bite a material having a large plate thickness. This is the same in cold rolling. For this reason, a work roll having a large diameter is required at the preceding stage of the tandem rolling mill regardless of whether it is hot or cold. The 6-stage HC mill having a large-diameter work roll requires an extremely large apparatus, which leads to an increase in construction costs. Further, the large-diameter work roll is hard to bend, so that the roll bending effect is small, and there is also a disadvantage that the control capability of the sheet crown and the like is small.

A PC mill is a four-high rolling mill capable of using a large-diameter work roll and has a large strip crown control ability. However, a tandem mill in which all stands are composed of PC mills has the following disadvantages. .

First, there is no ability to control the composite shape. That is, in order to control the composite shape, a means for affecting the distribution shape from the vicinity of the center of the plate width and a means for intensively effecting the plate edge are appropriately combined. However, PC
All roll cross effects, including the mill, affect the distribution shape from near the center of the sheet width. Since the work roll bending has a large roll diameter, the effect cannot be applied intensively to the plate edge, and the pattern changes similarly to the roll cross effect. Therefore, in a roll cloth type rolling mill, the composite shape cannot be corrected even when the cloth and the roll bending are used together.

Second, no consideration is given to scratching of the material. In particular, when material flaws occur in the first stage, the flaws are transferred to the subsequent rolls, and the number of rolls to be replaced increases, which has a large effect. For hot rolling,
In the former several stands, the rolls come into contact with the high-temperature material, and it is inevitable that the surface is transformed into a state called black scale. For this reason, black skin is actively attached as a kind of surface coating. This black scale is extremely hard, and there is no particular problem if it is uniformly adhered to the roll. However, in the process of forming black scale immediately after the roll replacement, the sticking was unstable, and the sticking once peeled off and was often caught between the roll and the material, resulting in flaws. For this reason, it is necessary to change the rolls, and the resulting time loss causes a decrease in productivity. Immediately after the roll change, the degree of freedom of the schedule is also limited due to the necessity of rolling a material that tends to have black scale.

[0013] Further, there has hitherto not been a work roll with sufficient abrasion resistance and skin resistance against a PC mill and a cross mill. Some high-speed steels have extremely high wear resistance.
It is used as a work roll for multi-high rolling mills such as a Sendzimir mill and a lone mill, and has excellent performance in abrasion resistance and skin resistance. However, since the toughness is inferior, there is a problem that an integrated roll cannot withstand use as a work roll having a large bending and load. Further, it is difficult to use the conventional integrated forged steel roll for a long time in terms of wear resistance and skin roughness. Therefore, there is a method in which a low alloy steel is used for the core material and a high alloy steel having a higher hardness is provided in the outer layer by electroslag melting, but there is a problem that the overlay layer cannot be formed uniformly on the core material. .

An object of the present invention is to dispose a rolling mill in which a pair of work rolls are crossed with respect to a backup roll, so that a sheet crown control ability and a shape control ability, particularly a composite shape correction ability, are high, and wear resistance is high. It is an object of the present invention to provide a tandem rolling mill which uses a roll having a high surface resistance to prevent scratches and has high productivity due to a high load, and a roll using the same.

[0015]

SUMMARY OF THE INVENTION The present invention is directed to a tandem rolling mill in which a plurality of rolling mills are arranged in series, and a pair of work rolls are turned upside down in a horizontal plane by a certain angle with respect to a backup roll supporting the work rolls. At least one cross mill or / and / or a cross mill for controlling the thickness distribution in the width direction.
And a first rolling mill comprising a PC mill and at least one HC mill having a roll movable in the axial direction and controlling the thickness distribution in the width direction by using both the roll movement and the work roll bending. A second rolling mill, wherein at least one of the first and second working rolls for the rolling mill is a composite in which a layer of a harder wear-resistant high-alloy steel having a higher hardness than the core is formed on the surface of the core. A tandem rolling mill characterized by being made of a material.

[0016] Preferably, the first rolling mill is arranged at least on a leading stand of the plurality of rolling mills.
Preferably, the second rolling mill is arranged at least on a final stand of the plurality of rolling mills. Also,
Preferably, the second rolling mill is disposed at least on a final stand of the plurality of rolling mills, and the first rolling mill is disposed on a stand upstream of the second rolling mill. More preferably, the first rolling mill includes a lubricant supply unit for lubricating between the backup roll and the work roll.

The present invention also relates to a tandem rolling mill in which a plurality of rolling mills are continuously arranged. (A) A pair of work rolls are crossed in a horizontal plane in a direction opposite to each other at a certain angle with respect to a backup roll supporting the work rolls. A first rolling mill composed of a plurality of PC mills and / or cross mills for controlling the thickness distribution in the width direction, and a roll movable in the axial direction. At least one HC for controlling the direction thickness distribution
And (b) a lubricant installed in each of the plurality of first rolling mills for lubricating between a backup roll and a working roll. Supply means; (c) first detection means installed upstream of the plurality of first rolling mills and detecting the presence or absence of a rolling material; and (d) each of the plurality of first rolling mills. (E) control means for controlling the lubricant supply means in accordance with signals from the first and second detection means;
A tandem rolling mill comprising:

In the roll according to the present invention, the core material is made of a low alloy steel having a Shore hardness of 35 or more and lower than the outer layer material, and the outer layer material has a Shore hardness of 80 or more and a residual austenite amount. Is a martensite structure of 15% by volume or less, has a compressive stress of 10 kg / mm ² or more on the outermost surface, and is made of a high alloy steel solidified in the roll axis direction.

According to the present invention, C0.5-1.5% by weight, S
i 0.5 to 3.0%, Mn 1.5% or less, Cr 2 to 10
%, V0.5-2.0%, W1-20% or less, characterized in that a high alloy steel solidified in the roll axis direction is used as an outer layer, and a low alloy steel is used as a core material. According to the present invention, as a core material, C0.5 to 1.0%, Si1% or less, Mn1% or less, C
r1 to 5%, Mo0.5% or less, and is made of a low alloy steel having a lower hardness than the outer layer material and a roundness of 10 mm or less, and the outer layer material has a C of 0.5 to 1.5% by weight. Si0.
5 to 3.0%, Mn 1.5% or less, Cr 2 to 10%, M
It is made of a high alloy steel containing o1 to 10%, V0.5 to 2.0%, and W1 to 20% or less, and is characterized by a weld layer solidified in the roll axis direction. Further, the present invention is made of a high alloy steel containing 5% or less of Ni or 1 to 15% of Co in the outer layer.

The present invention uses a composite roll having a core made of low alloy steel and an outer layer made of high alloy steel having higher hardness than the core, wherein the core has a roundness of 10 mm or less,
The outer layer is an equiaxed crystal having an axial solidification structure.

The above-mentioned roll according to the present invention can be applied not only to a work roll of a cross mill but also to a backup roll of a cross mill, a work roll to a four-high rolling mill and an HC mill, an intermediate roll and a backup roll. The composition and heat treatment of the outer layer material of the intermediate roll and the backup roll are adjusted so that the hardness is lower than that of the work roll.

[0022]

According to the present invention, a first rolling mill comprising a PC mill and / or a cross mill in which a work roll is crossed with a backup roll, and a second rolling mill comprising an HC mill which uses both roll movement and work roll bending. And the rolling mill included in a plurality of rolling mills, thereby controlling the thickness distribution shape from the vicinity of the center of the sheet width, that is, the strip crown, by the roll cross effect of the first rolling mill. The composite shape is corrected by the work roll bending, and high strip crown control ability and composite shape control ability can be exhibited. In particular, when the first rolling mill is arranged at the front stage of the tandem rolling mill and the second rolling mill is arranged at the latter stage of the tandem rolling mill, the crown is controlled at the front stage, the composite shape is corrected at the latter stage, and the high The crown control ability and the composite shape control ability can be exhibited.

Further, since a large-diameter work roll can be used for the first rolling mill, the temperature of the work roll is prevented from increasing, and deterioration of the roll material can be reduced. Further, since a large-diameter work roll is used, a sufficient biting property can be secured for a material having a large plate thickness.

In the case where the first rolling mill is arranged in front of the tandem rolling mill, the work roll of the first rolling mill rotates in a horizontal plane at a certain angle with respect to the reinforcing roll supporting the first rolling mill. There is a slight slip between the two rolls, which causes the rolls to grind each other. Therefore, the roll is always kept clean and does not generate flaws due to black scale.

Further, by providing a lubricant supply means for lubricating between the reinforcing roll and the work roll in the first rolling mill, a roll formed between the work roll and the reinforcing roll when only the work roll crosses is provided. The axial thrust force can be reduced, and an accident due to excessive thrust force can be prevented.

Further, the present invention relates to a method for manufacturing a plurality of first rolling mills (P
(C mill, cross mill) is provided with a lubricant supply means for lubricating between the reinforcing roll and the work roll, a first detecting means for detecting the presence or absence of the rolling material, and detecting the biting of the rolling material. By providing the second detection means and control means for controlling the lubricant supply means based on signals from the first and second detection means, the first rolling mill (P
The supply of the lubricant can be stopped immediately before the material is caught in the C mill and the cross mill, and the supply can be started again after the clogging, whereby the first rolling mill (PC
(Mill, cross mill) is eliminated, and the productivity is improved.

Further, the lubricant supply means for the first rolling mill (PC mill, cross mill) is divided into a plurality of systems, and a lubricant supply source is provided for each of the systems so that the lubricant is supplied in accordance with the lubricant supply location. The concentration or friction reducing ability of
The required amount of lubricant can be reduced while ensuring the required lubrication.

That is, for example, the rolling load tends to be large in the front stand of the tandem mill and small in the rear stand, and the thrust force generated in the first rolling mill (PC mill, cross mill) is almost equal to the rolling load. Because of the proportionality, the front stand has a larger thrust force than the rear stand. Therefore, the first rolling mill (PC mill, cross mill) is divided into a plurality of groups in the flow direction of the rolled material,
The lubricant supply means is divided into a plurality of systems corresponding to the grouping of the first rolling mill (PC mill, cross mill), and a common lubricant supply source is provided for each system. In this case, a high-concentration lubricant is used for the lubricant supply source corresponding to the first rolling mill (PC mill, cross mill) on the upstream side, and the lubricant is supplied to the first rolling mill on the downstream side.
By using a low-concentration lubricant as a lubricant supply source corresponding to a rolling mill (PC mill, cross mill), it is possible to reduce the amount of lubricant used while securing necessary lubrication. Further, the thrust force in the first rolling mill (PC mill, cross mill) at each stand is made uniform, so that unnecessary maintenance time is reduced, leading to an improvement in productivity.

Further, the lubrication state of the rolls in the first rolling mill (PC mill, cross mill) is different between the upper and lower portions, and the amount of roll wear is often different between the upper and lower portions. Generally, since a large amount of cooling water is used in hot rolling, a lubricant is likely to flow in the lower roll. For this reason, the coefficient of friction on the lower side increases and the amount of wear increases. Therefore, the lubricant supply means is changed to the first
Are divided into two systems corresponding to the upper roll and the lower roll of the rolling mill (PC mill, cross mill), and a lubricant supply source is provided for each system. In this case, by using a low-concentration lubricant for the lubricant supply source corresponding to the grouped upper roll and using a high-concentration lubricant for the lubricant supply source corresponding to the lower roll, The amount of lubricant used can be reduced while ensuring lubrication.

Furthermore, the contact pressure distribution between the backup roll and the work roll is higher at the center where the plate is bitten than at the end of the roll. Therefore, the distribution of frictional force in the roll axis direction also becomes higher at the center. Therefore, the nozzle group of the lubricant supply means for the first rolling mill (PC mill, cross mill) is divided into a plurality of groups in the roll axis direction, and the lubricant supply means is divided into a plurality of systems corresponding to the grouping of the nozzle groups. Separately, a lubricant supply source is provided for each system. In this case, a high-concentration lubricant is used for the lubricant supply source corresponding to the group of nozzles at the center of the roll, and a low-concentration lubricant is used for the lubricant supply source corresponding to the nozzle group at the end of the roll. By using, it is possible to reduce the amount of lubricant used while securing necessary lubrication for the first rolling mill (PC mill, cross mill).

The first rolling mill (PC mill, cross mill) is provided with a plurality of systems of lubricant supply means, and each of the plurality of systems of lubricant supply means is provided with a lubricant supply source. It becomes possible to supply a plurality of types of lubricants to the machine. At this time, by using a lubricant having a different concentration for each lubricant supply source of the lubricant supply means of a plurality of systems, when the thrust force is detected and becomes excessive, the lubricant supply system having a large concentration is opened. As a result, it is possible to prevent the occurrence of accidents such as roll seizure due to excessive thrust force, and to prolong the life of the roll.

The roll according to the present invention is made of a high-alloy steel in which an outer layer having a higher hardness than the shaft is formed in a gap formed between the low-alloy steel shaft and a concentrically arranged cooling mold. Inserting the consumable electrode and rotating the shaft and the cooling mold in a circumferential direction to supply an alternating current to the consumable electrode and the shaft from a plurality of locations under the slag bath to melt the consumable electrode. It can be manufactured by a step of forming a molten metal by melting and a step of moving the cooling mold in the axial direction of the shaft to solidify the molten metal and integrally welding the outer layer to the shaft. Further, in the present invention, an outer layer material made of a high alloy steel having a higher hardness than the low alloy steel is provided on the outer periphery of the core material made of a low alloy steel such that the roundness of the core material in the roll axis direction is 10 mm or less. After solidification welding, a quenching step of performing progressive quenching by injecting a liquid or gaseous refrigerant into the heated portion while gradually heating the outer layer material to a temperature not lower than the austenite transformation point, and the outer layer after quenching The material is manufactured by a step of performing a high-temperature tempering treatment to reduce the residual austenite phase of the material to 15% by volume or less.

Further, the above-mentioned high alloy steel is solidified and welded in the roll axis direction to form an outer layer material, and a low alloy steel having a lower hardness than the outer layer material is used as a core material and the roundness thereof is 10 mm or less. After the surface layer is heated to a temperature equal to or higher than the transformation point and quenched, it is preferable to perform tempering at a temperature of 300 to 550 ° C.

According to the present invention, hot forging is performed before the quenching step of the outer layer material, and sub-zero processing is performed after the quenching step and before tempering.

In the above-mentioned rolling mill, all of the work rolls of the PC mill, cross mill and HC mill are formed by a composite roll having a core material made of a low alloy steel and an outer layer made of a high alloy steel having a higher hardness than the core material. The work roll diameter of the first stage stand is at least larger than the work roll diameter of the last stage stand. At least the final stage can have a diameter of 250 mm or more.

In particular, in the present invention, a work roll,
HC provided with an intermediate roll that contacts and supports the work roll, and a backup roll that supports the intermediate roll
The mill is connected in tandem in multiple stages, and at least the work roll of the first stage stand is constituted by a composite roll having a core material made of a low alloy steel and an outer layer made of a high alloy steel having a higher hardness than the core material. Features. The intermediate roll itself can use a composite roll for some or all of the stands, and has a lower hardness than the work roll.

The hardness of the work roll in the present invention is Hs
90-100, Hs of backup roll is 60-7
The number of 0 and the intermediate roll is preferably 70 to 80.

The work roll can be rotated by applying a bend to flatten the material to be rolled, and the intermediate roll can also be rotated by applying a bend. The intermediate roll can be slid left and right, and can be rolled so that the roll end is close to the material to be rolled according to the rolling width.

In the case of a roll integrated with the above-mentioned outer layer material, there is a danger of breakage from the inside due to thermal stress during quenching, and since the toughness of the shaft portion is inferior, the neck breakage during use may be reduced. Disadvantageous. For this reason, the roll has the surface layer portion made of the above-mentioned material, and the core material has a composite structure made of alloy steel having high toughness.

Further, an outer layer made of a high alloy steel material such as a high speed tool steel having a higher hardness is provided on the outer periphery of the core shaft made of a low alloy steel material, and then the carbide contained in the outer layer is dispersed and the structure is changed. It is preferable to apply a hot forging process to the outer layer in order to make the outer layer uniform.

The composite roll of the present invention is a composite roll comprising 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 type of high-speed tool steel) In the case of a roll), there is the danger of internal breakage (cracking) due to the thermal stress generated during quenching, and the inferior toughness of the shaft, Breakage easily occurs. Therefore, the composite roll structure as described above was adopted.

The quenching treatment can be performed by impingement cooling or oil cooling. However, when the compression residual stress of the surface layer is further increased and tempering treatment is performed at a temperature of 300 to 550 ° C. after the quenching treatment, In the method of the present invention for obtaining a hardness of Hs 93 or more, quenching is preferably performed by gas injection or fountain cooling. Air is used for gas injection. The tempering temperature in the present invention is 300 ° C to 550 ° C, preferably 450 ° C to 550 ° C, and 500 ° C to 550 ° C.
C is more preferred. In the case of a cold rolling roll, it is said that a surface hardness of about Hs90 or more is required, and in the case of a hot rolling roll, a surface hardness of about Hs80 to 85 is used.

As in the present invention, the residual stress in the case where only the outer layer portion is heated to the transformation point or higher and the quenching treatment is performed by rapid cooling, the residual stress due to thermal stress and the residual stress due to transformation stress are superimposed. Becomes When the outer layer portion is quenched, compressive plastic strain is generated in a portion of the internal plastic deformation temperature region due to the volume shrinkage. 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 by the transformation is relatively large, the tensile residual stress in the core shaft and the compressive residual stress in the hardened outer layer are different from the specific volume of the core shaft, respectively. Occurs. Thus, residual stress caused by thermal stress and transformation stress is
It is considerably larger than the residual stress caused by only the martensitic transformation (usually about -20 kg / mm ² ).
kg / mm ² to −120 kg / mm ² (when sub-zero treatment is performed). In the high-speed system, a compressive residual stress of -10 kg / mm ² or more can be obtained by gas injection cooling.

Further, only by the quenching treatment, about 40% of austenite remains, and a subzero treatment at a temperature of -50 ° C. or lower is performed to accelerate the decomposition of the retained austenite. The sub-zero treatment is performed by suspending a roll in a vertical sub-zero treatment tank, and injecting 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.

Thereafter, when a tempering treatment is performed at a temperature of 300 ° C. to 550 ° C., the amount of retained austenite becomes about 15
% To about 1 to 5%. The finally retained austenite serves as a buffer for alleviating 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. In addition, if the roll is tempered at a high temperature, if the roll is used for hot rolling, even if a high temperature steel sheet is wound around the roll due to an accident and the roll temperature rises, even if the roll temperature rises, Crack generation due to decomposition of the retained austenite is effectively prevented.

In general, when the tempering treatment is performed at a high temperature, the strain due to quenching is easily released (relaxation).
It is known that the amount of decrease in residual stress increases. However, the high-speed tool steel used in the present invention is composed of alloying elements Si, Cr, Mo, and V that increase the tempering resistance.
Therefore, compared with general low-alloy steel, tempering at a temperature of about 500 ° C. can reduce the release of strain and maintain a high residual stress.

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 1.5 in weight%. 0%,
Si 1% or less, Mn 1% or less, Cr 1 to 5%, Mo0.
Forged steels containing up to 5% are preferred.

The composite roll having the above-described structure can be formed into a higher alloy to increase the hardness even when used in rolling in which a large bending is applied. Therefore, the composite roll has sufficient abrasion resistance, skin roughness resistance, and toughness. It will be durable. In particular, since the roll is a roll in which the outer layer is welded to the shaft by a specific manufacturing method by electroslag remelting, the roundness of the core is as small as 10 mm or less, and the carbide crystallized from the melt is floating, sedimentation, segregation. Because of the rapid solidification without the formation, the particles are finely and evenly dispersed in the outer layer. Thus, high-pressure and high-shape control of the rolled material can be performed soundly, and the quality of the surface properties of the rolled material is improved. As described above, the roundness of the core material is a particular problem in providing a higher alloyed outer layer.
The roundness also depends on the thickness of the outer layer material, so that the non-uniform core roundness causes unbalanced compressive residual stress to be formed during quenching and tempering, and may break during use.

The outer layer is made of a higher alloy in order to secure abrasion resistance and surface roughness resistance.
It is necessary to maintain a hardness of 0 or more.

The chemical composition of the outer layer material is specified for the following reasons.

C is necessary for the formation of carbides for improving the 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, if C exceeds 1.5%, the amount of reticulated carbides precipitated at the grain boundaries increases, resulting in inferior surface roughness and toughness. In particular, 0.8 to 1.2% is preferable for the work roll.

Si is an element necessary as a deoxidizing agent,
0.5% or more, and enhances tempering resistance. However, if the amount exceeds 3.0%, embrittlement is likely to occur. In particular, 1 to 3% is preferable for a work roll, and 1.5%.
~ 2.5% is more preferred.

Mn has a deoxidizing action and an action of fixing S, which is an impurity, as MnS.
If it exceeds, the retained austenite increases and stable hardness cannot be maintained, and the toughness decreases. In particular, for a work roll, 0.2 to 1.0% is preferable, and 0.2 to 0.5%.
% Is more preferred.

If Cr is less than 2%, the hardenability is poor.
If it exceeds 0%, it is inconvenient because the amount of Cr-based carbide becomes excessive. In particular, 3 to 7% is preferable for a work roll.
5-5% is more preferable.

Mo and W are each bonded to C to form M ₂
It forms C or M ₅ C-based carbides and forms 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 of Mo and W should be 12% and 20%, respectively, and the lower limits of W and Mo should be 1% or more. In particular, in the work roll, Mo is preferably 1.5 to 4.5% of semi-high-speed steel or 7 to 10% of high-speed steel, and W is 0.1 to 1% of semi-high-speed steel or 0.5 to 0.5% of high-speed steel. 5% is preferred.

V forms an MC-based carbide and contributes to the improvement of wear resistance. However, if it is less than 0.5%, the effect is not sufficiently obtained.
If it exceeds, the grindability is significantly impaired. In particular, 0.7 to 2.0% is preferable for a work roll.

Co is an element for forming a solid solution in the matrix and tempering at a high temperature to obtain high hardness. However, if it is less than 5%, its effect is insufficient. If it exceeds 15%, the toughness decreases. In particular, 6 to 10% is preferable for a work roll.

In particular, semi-high speed as an outer layer as a work roll contains the aforementioned C, Si, Mn and Cr, and W0.1
-1%, V0.5-2.0% and Mo1-5% or high-speed steel is W0.5-3%, 5-11% or 12-20%, Mo
4 to 12%, V0.5 to 1.5% or 1.5 to 5%, or a combination thereof may contain 4 to 20% Co. In the composition based on Hot, the amount of carbide is large because the amount of carbide considers wear resistance and seizure resistance.
And, the greater the amount of carbide, the harder it is to finish by grinding, the lower the toughness, and the higher the local pressure like a cold work roll, the more difficult it is to withstand. Therefore, as the alloy composition of the cold work roll, the carbide amount (carbon amount) is reduced to the extent that the wear resistance is not impaired, and the matrix is strengthened (martensite, especially tempered martensite) to withstand the local pressure (rolling pressure). I have to. Co is effective for strengthening the matrix, and high hardness can be obtained.

The high alloy steel used for the outer layer of the present invention can contain Ni in addition to the above elements. Since Ni has an 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, it is preferably at most 1%, more preferably 0.1 to 0.5%.

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, the roll of the present invention has a nominal stress of 10 kg.
When a net stress of / mm ² is applied, the size effect coefficient is
Assuming that the surface effect coefficient is 0.9 and 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.

A method of providing an outer layer on the core shaft is disclosed in Japanese Patent Publication No. 44903/1984. A method for forming an outer layer by hot isostatic pressing using a powder metallurgical method disclosed in Japanese Patent Application Laid-Open No. Sho 47-2851, et al. There is a cladding method using an electroslag re-dissolution method disclosed in Japanese Patent Application Laid-Open No. H11-163,036. The electroslag remelting overlay method is particularly preferred.

That is, a consumable electrode made of high-alloy steel such as high-speed steel is inserted into a gap formed between the shaft and the mold arranged concentrically, and the shaft and the cooling mold are circumferentially inserted. Preferably, the consumable electrode is rotated at 1 rpm or more to supply the consumable electrode and the shaft material from a plurality of locations under the slag bath to melt the consumable electrode, and the cooling mold is moved coaxially upward with respect to the shaft material. The outer layer formed by bringing the molten metal into contact with the cooling mold and solidifying it is welded to the shaft. The rotation only needs to be relative to the shaft and the consumable electrode. The eccentricity of the core material can be eliminated by allowing current and heat to flow evenly to each part.

The composite roll according to the present invention can be used as a hot or cold work roll, and in particular, can be used for bending and rolling. And it can be used as a roll for schedule free. In the rolling of carbon steel, the conventional roll life was about 4 to 5 hours. However, the roll of the present invention has a life of 2 to 5 times with a semi-high-speed roll or 5 to 10 times with a high-speed roll. A life of 8 hours to 25 hours or 20 hours to 50 hours can be obtained in the polishing step, and the number of times of polishing can be significantly reduced.

Conventionally, a roll having a diameter of at most about 100 mm could be manufactured with an integrated roll made of high-speed steel. However, in the present invention, a roll having a diameter of 250 to 750 mm can be manufactured and used as it is in a conventional rolling mill.

The composite roll according to the present invention has a core material provided on a surface plate and a mold surrounding the core material, and a pipe-shaped electrode is provided on an outer peripheral portion of the core material with respect to the core material. A composite steel ingot is manufactured by electroslag remelting by arranging concentrically, and has a mechanical transmission mechanism that rotates the core material and the mold in synchronization with each other, and the surface plate vertically rotates the core material. Having a support frame for supporting and fixing the electrode, and having an electrode elevating beam for suspending and raising and lowering the electrode along the columns at both ends, and the column is formed of a composite steel ingot by electroslag remelting fixed by the upper beam. It can be obtained by manufacturing equipment.

[0066]

【Example】

Example 1 In FIG. 1, the tandem rolling mill for hot rolling of the present example has first rolling mills 8 to 11 shown in FIG. The second rolling mill 1 shown in FIG.
2 to 14 are arranged, and the rolled material 1 is provided in the first rolling mills 8 to 11
And is continuously tandem-rolled through the second rolling mills 12 to 14.

As shown in FIG. 2, the first rolling mills 8 to 11 respectively move the pair of work rolls 2 and 3 up and down in a horizontal plane at a certain angle with respect to the reinforcing rolls 6 and 7 supporting the work rolls 2 and 3. The cross mill controls the thickness distribution in the width direction. The rolling mill has reinforcing rolls 2, 3
A lubricant supply device (not shown) is provided for lubricating between the work rolls 6 and 7, and a roll generated between the work rolls 2 and 3 and the reinforcing rolls 6 and 7 when only the work rolls 2 and 3 cross each other. The axial thrust force is reduced. As shown in FIG. 3, each of the second rolling mills 12 to 14 has rolls 4 and 5 which can move in the axial direction. And a so-called HC mill for controlling the shape. In this HC mill, the intermediate rolls 4, 5 are moved in the axial direction, and the reinforcing rolls 6, 7 support it.

The work roll diameter is the same for all stands,
In this embodiment, as shown in FIG. 1, the work roll diameter is smaller in the second rolling mills 12 to 14 in the subsequent stage than in the first rolling mills 8 to 11 in the previous stage. This is because when the diameter of the work roll is small, the work roll bending effect concentrates on the edge of the plate, and the ability to correct the composite shape increases.

In a normal rolling schedule, the rolling reduction of the first stand is the largest. Therefore, if a large plate crown is attached here, it will be difficult to correct it at a subsequent stand. That is, it is necessary to install a rolling mill having a large strip crown correcting ability in the preceding stage including the first stand. In the case of hot rolling, since the rolls come into contact with a high-temperature material in the several stands in the preceding stage, the heat capacity of the small-diameter roll is small and the temperature immediately rises, and the material of the roll deteriorates. In addition, if the diameter of the former work roll is small, it becomes impossible to bite a material having a large plate thickness. For this reason,
A large-diameter work roll is required at the front stage of the tandem rolling mill. However, a six-stage HC mill having a large-diameter work roll requires an extremely large apparatus, which causes an increase in construction costs. Further, the large-diameter work roll is difficult to bend, so that there is a drawback that the roll bending effect is small and the control ability of the sheet crown and the like is small.

In the case of hot rolling, it is inevitable that the rolls come into contact with a high-temperature material in the several stands at the preceding stage and the surface is transformed into a state called black scale. For this reason, black skin is actively attached as a kind of surface coating. This black scale is extremely hard, and there is no particular problem if it is uniformly adhered to the roll. However, in the process of black scale generation immediately after the roll change, the way of sticking is unstable, and the sticking once peels off and gets caught between the roll and the material,
Often it was a flaw. For this reason, it is necessary to change the rolls, and the resulting time loss causes a decrease in productivity. Immediately after the roll change, the degree of freedom of the schedule is also limited due to the necessity of rolling a material that tends to have black scale.

On the other hand, since the thickness of the final stand is small, the deformation in the material width direction at the end of the plate is small, and the flatness at the end of the plate poses a problem. Therefore, it is necessary to install a rolling mill with high ability to correct the composite shape at the final stand.

In this embodiment, the shape of the sheet thickness distribution near the center of the sheet width, that is, the sheet crown, is controlled by the roll cross effect of the first rolling mills 8 to 11 arranged in the preceding stage of the tandem rolling mill. The composite shape is corrected by the roll movement and the work roll bending of the second rolling mills 12 to 14 installed in the first mill. Therefore, the crown control can be effectively performed by the four stands at the front stage, and the high composite shape control ability at the three stands at the rear stage can be exhibited.

Further, since large-diameter work rolls can be used for the first rolling mills 8 to 11, high temperature of the work rolls is suppressed, and deterioration of roll materials can be reduced. Further, since a large-diameter work roll is used, a sufficient biting property can be secured for a material having a large plate thickness.

In the first rolling mills 8 to 11 at the front stage of the tandem rolling mill, the work rolls 2 and 3 rotate while crossing the reinforcing rolls 6 and 7 supporting the work rolls at a certain angle in a horizontal plane. Therefore, there is a slight slip between the two rolls, which causes the rolls 2, 3 and 7, 8 to grind each other. Therefore, the roll is always kept clean and does not generate flaws due to black scale.

As described above, according to the present embodiment, it is possible to provide a tandem rolling mill having high strip crown control ability and high composite shape correcting ability while securing the biting property. In addition, the roll surface is always kept free of flaws, and flaws on the material are extremely reduced, so that the yield is greatly improved. Further, since the roll wear is made uniform, useless roll change time is reduced, leading to an improvement in productivity.

Although the present embodiment has been described as being applied to hot rolling, the same structure can be applied to cold rolling, and the sheet crown control ability, the composite shape control ability,
A similar effect can be obtained with respect to the improvement in biting properties.

In this example, the working rolls of the rolling mills 8 to 14 of the cross mill and the HC mill were obtained as follows.

A roll having a body diameter of 850 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 having a diameter of 665 mm as follows.

FIG. 4 is a schematic view of an apparatus for producing a composite roll by the electroslag overlaying method. This device is
Welding machine 134, Wiring 135, Carbon brush 13
3, including the DC motor 11 and the manipulator 112. The manipulator 112 is moved by the DC motor 111, and the tubular consumable electrode 103, which is a consumable electrode made of high-speed tool steel and supported by the arm 113 of the manipulator, is moved up and down. A core shaft 101 made of a low-alloy steel material is provided on a rotary platen 102. A water-cooled mold 120 is installed concentrically with the core shaft 101, and an annular ignition plate (that is, a mold bottom) 130 is installed near the lower end of the core shaft 101 in a space between the two. The core shaft 101 and the water-cooled mold 20 were rotated at 5 rpm in the circumferential direction. The tubular electrode 3 supported by the manipulator 112 is attached to the core shaft 101.
And the water-cooling mold 120, which is inserted into the space, that is, the melting chamber, and is connected to the core shaft 10 through the wiring 135.
1 is that the tubular electrode 103 is melted and consumed by an alternating current supplied between the tubular electrode 103 and the tubular electrode 103. Five carbon brushes 133 are evenly arranged around the platen 102 around the circumference, and a plurality of wirings are also arranged on the tubular electrodes.
The molten metal 141 is formed by the resistance heating, and the molten metal 141 is formed. The molten metal 141 is cooled and solidified by contact with the water-cooled mold 120, and the uniform overlay 142 is formed on the surface of the core shaft 101.
Is formed. During this time, the water-cooled mold 120 is
1 is moved upward coaxially. Slug 1
40 is constantly adjusted to a thickness of 50 to 60 mm. Further, the molten metal 141 is prevented from dropping downward by the annular bottom plate 130. The current and voltage are melted while being controlled so as to be kept constant, and the thickness of the cladding layer and the depth of penetration into the core material are controlled so as to be constant. Thus, the cladding layer of the obtained composite roll was forged at 1100 ° C. to have an outer diameter of 780 mm and a thickness of the outer layer of 42.5 mm. Further, the hardfacing layer is subjected to quenching and tempering heat treatment, so that the surface hardness Hs90 or more of the hardfacing layer can be obtained.

After the heat treatment, the resultant was cut and polished to a finished outer diameter of about 2 to 3 mm by cutting and polishing. Grinding was performed with a grindstone so that the average surface roughness was about 0.5 μm.

The chemical composition of the outer layer material is C 0.92 by weight.
%, Si 2.40%, Mn 0.30%, Cr 4.14%,
Mo 2.20%, V 1.01%, W 0.32%, balance Fe
It is. The roll was further subjected to a heat treatment of quenching from 1000 ° C to 1200 ° C and tempering at 500 ° C for 10 to 20 hours. The quenching was performed by heating the induction coil and gradually cooling by the fountain. After quenching, a sub-zero treatment at −50 ° C. was performed. As a cooling rate, rapid cooling of about 1 to 10 ° C./sec is obtained. 0.95%, 3% for the shaft material of the roll of the present invention
Cr forged steel was used, its hardness was Hs40, and the amount of retained austenite was 10 to 15% by volume.

The roundness of the roll core material in this example was within 5 to 6 mm in the preliminary test. FIG. 5 is a cross-sectional view of the composite roll.

In this embodiment, a cross mill has been described as the first rolling mill.
A similar effect can be obtained by using a mill.

Embodiment 2 Another embodiment of the present invention will be described with reference to FIG. In this embodiment, the present invention is also applied to hot rolling. In the present embodiment, a first rolling mill (cross mill) 8 shown in FIG. 2 is arranged on the first stand, and a second rolling mill (HC mill) 14 shown in FIG. 3 is arranged on the final seventh stand. Conventional four-high rolling mills 9A to 13A are arranged in the intermediate second to sixth stands.

As described above, in the normal rolling schedule, the rolling reduction of the first stand is the largest, and if a large crown is attached here, it becomes difficult to correct this in the subsequent stands. Therefore, it is necessary to install a rolling mill in the first stand that has a large plate crown correcting capability, a large work roll diameter for the above-described reason, and a capability of keeping the roll surface clean. Further, since the thickness of the final stand is small, the deformation in the material width direction at the end of the plate is small, and the flatness at the end of the plate becomes a problem. Therefore, it is necessary to install a rolling mill having a high ability to correct the end shape of the plate at the final stand. There is no particular problem in the rolling mill during this time even with the conventional model.

In this embodiment, the cross mill shown in FIG. 2 is provided on the first stand, and the HC mill shown in FIG. 3 is provided on the final seventh stand. In addition, it is possible to obtain substantially the same effect as that of the embodiment shown in FIG. The present embodiment is also applicable to cold rolling, and similar effects can be obtained with respect to the sheet crown control ability, the composite shape control ability, and the improvement of the biting property.

In this embodiment, as in Embodiment 1, 4
Work rolls and HC for cross mill and HC mill
A composite roll was used as the intermediate roll of the mill. As a backup roll, an integrated forging roll was used. In addition, various combinations of a cross mill, a four-high rolling mill, and an HC mill can be used. The first and second stages are 4-stage mills, the third and fourth stages are cross mills, and the fifth to seventh stages are HC mills. The first to third stages can be combined with a four-stage mill, the fourth stage with a cross mill, and the fifth stage with an HC mill.

The same effect can be obtained by using a PC mill instead of the cross mill in this embodiment.

Embodiment 3 FIG. 7 shows an example of a configuration relating to a lubricant supply device in hot rolling.

In the first rolling mill (cross mill) shown in FIG. 2, since a thrust force is generated between the reinforcing rolls 2, 3 and the work rolls 6, 7 as described above, the lubricant is supplied during this time. The coefficient of friction has been reduced. However, if the coefficient of friction is too low, slip occurs when the rolled material is caught and rolling becomes impossible. For this reason, it is better that the lubricant supply amount is as small as possible. Further, the supply of the lubricant is stopped immediately before the material is caught, and the supply is started again after the material is caught.

In this embodiment, the first rolling mill 8 shown in FIG.
-11, valves 15-18, nozzles 100-10
7. Tank 38 and pump 39, which are the supply sources of lubricant
Is installed, and is controlled by the valves 15 to 18, the supply amount regulators 22 to 25, and the control device 30 of the lubricant supply device. A rolled material detector 29 is installed on the entry side of the rolling mill group, and detects the presence or absence of the rolled material 1. Rolled material is detected using a thermometer. Each stand is provided with load cells 31 to 34 for detecting the bite of the rolled material.

When the rolled material detector 29 detects that a rolled material has entered, the signal is taken into the control device 30 and a supply stop signal is immediately sent to the supply amount controller 22 of the first stand. The feed speed of each stand is input to the control device 30, the time required for the material to pass between the stands is calculated, and the time is sequentially shifted to send a supply stop signal to the supply controller of the subsequent stand. . On the other hand, it is necessary to restart the supply immediately after biting. For this reason, the jamming is detected by the load cells 31 to 34 installed in each stand, and the supply start signal is supplied to the supply amount adjusters 22 to 2.
5 is output. The lubricant is pumped from a supply tank 38 by a pump 39. As a result, accidents due to excessive thrust force and slip accidents at the time of biting are eliminated,
Productivity is improved.

The same effect can be obtained by using a PC mill instead of the cross mill of this embodiment.

[0094]

According to the present invention, it is possible to provide a tandem rolling mill having high strip crown control ability and composite shape correcting ability while ensuring biting properties. In addition, the roll surface is always kept free of flaws, and flaws on the material are extremely reduced, so that the yield is greatly improved. Further, the roll wear is made uniform, and the time for useless roll change is reduced, leading to an improvement in productivity.

Further, the thrust force in the roll axis direction generated between the work roll and the backup roll of the first rolling mill can be reduced, and an accident due to excessive thrust force can be prevented.

Further, according to the present invention, the supply of the lubricant can be stopped immediately before the material is caught in the first rolling mill, and the supply can be started again after the material is caught. There is no slip accident at the time of slipping, and productivity is improved.

The rolling roll according to the present invention can be sufficiently used in terms of abrasion resistance, skin 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 electroslag remelting, carbides crystallized from the molten metal rapidly solidify without floating, sedimentation or segregation, and are finely and evenly dispersed in the outer layer. Becomes By these, under high pressure of the rolled material,
High shape control can be performed soundly and the quality of the surface properties of the rolled material is improved.

[Brief description of the drawings]

FIG. 1 is a schematic view of a tandem rolling mill according to an embodiment of the present invention.

FIG. 2 shows a first rolling mill shown in FIG. 1 (a rolling mill in which a pair of work rolls are crossed up and down in a horizontal plane by a certain angle with respect to a reinforcing roll supporting the work rolls to control a thickness distribution in a width direction). FIG.

FIG. 3 is a second rolling mill shown in FIG. 1 (a rolling mill having a roll that can move in the axial direction, and controlling a sheet crown and a shape by using both the roll movement and the work roll bending).
FIG.

FIG. 4 is a schematic view of a composite roll manufacturing apparatus using an electroslag overlaying method according to the present invention.

FIG. 5 is a sectional view of a composite roll according to the present invention.

FIG. 6 is a schematic view of a tandem rolling mill according to another embodiment of the present invention.

FIG. 7 is a schematic view of a tandem rolling mill having a lubrication supply device according to the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Sheet material, 2,3 ... Work roll, 4,5 ... Intermediate roll, 6,7 ... Backup roll, 8-11 ... First rolling mill, 12-14 ... Second rolling mill, 15-18,44 ~
47: valve (lubricant supply device), 22 to 25: supply amount regulator, 29: material detector (first detection means), 30: control device, 31 to 34: load cell (second detection means), 3
8, 40, 42, 51, 119, 121 ... tank (lubricant supply source), 60 to 67 ... nozzle, 101 ... core material, 10
Reference numeral 2: core material stationary surface plate, 103: pipe-shaped electrode, 104: first elevating mechanism, 120: mold, 121: inner cylinder, 122:
Outer cylinder, 123 gear, 130 guide plate, 131 bolt, 132 core support frame, 133 carbon brush, 1
42: Overlay layer, 150: Second elevating mechanism, 160: Transmission shaft, 170: First transmission gear, 172: Second transmission gear.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI B21B 27/10 B21B 27/10 B // B21B 37/00 BBH C22C 38/00 301L 37/28 302E 37/38 38/22 37 / 42 38/24 C22C 38/00 301 38/30 302 38/34 38/22 B21B 37/00 BBH 38/24 116J 38/30 116F 38/34 116B 117B (56) References JP-A-5-285504 ( JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 1 / 24,13 / 14 B21B 27/00-27/10 B21B 37/00 C22C 38/00-38/60

Claims (5)

(57) [Claims] In a tandem rolling mill in which a plurality of rolling mills are continuously arranged, a pair of work rolls are crossed in a horizontal plane by a certain angle with respect to a backup roll supporting the work rolls in an up-down direction, and At least one first rolling mill for controlling the distribution, and at least one first rolling mill having a roll movable in the axial direction and controlling the thickness distribution in the width direction by a combination of the roll movement and the work roll bending. A work roll for at least one of the first and second rolling mills, wherein a layer of a harder wear-resistant high alloy steel than the core is formed on the surface of the core. Tandem rolling mill, comprising a composite material. 2. A tandem rolling mill in which a plurality of rolling mills are continuously arranged. (A) A pair of work rolls are crossed in a direction opposite to each other in a horizontal plane by a certain angle with respect to a backup roll supporting the work rolls, and A plurality of first rolling mills for controlling the thickness distribution in the direction and at least one roll having a roll movable in the axial direction and controlling the thickness distribution in the width direction by using the roll movement and the work roll bending together And (b) installed in each of the plurality of first rolling mills,
And (c) at least the work rolls of the first and second rolling mills have a higher hardness, abrasion-resistant high alloy than the core material on the surface of the core material. A tandem rolling mill comprising a composite material having a steel layer formed thereon. 3. A composite roll for metal rolling in which the outer periphery of a core material is covered with an outer layer material, wherein the core material is made of a low alloy steel having a Shore hardness of 35 or more and a lower hardness than the outer layer material, The outer layer material has a martensite structure having a Shore hardness of 80 or more and a residual austenite amount of 15% by volume or less, and has a residual stress at the outermost surface of 10 kg / mm ² or more,
A composite roll for a cross mill, comprising a high alloy steel solidified in the roll axis direction. 4. A composite roll for a cross mill wherein the outer periphery of a core material is covered with an outer layer material, wherein the core material has a weight of C0.5 to 1.0.
%, Si 1% or less, Mn 1% or less, Cr 1-5%, Mo
It is made of a low alloy steel containing 0.5% or less and having a hardness lower than that of the outer layer material and a roundness of 10 mm or less. The outer layer material has a C of 0.5 to 1.5% and a Si of 0.5 to 0.3% by weight. 0%, Mn
1.5% or less, Cr 2 to 10%, Mo 1 to 12%, V
A composite roll for a cross mill, comprising a high alloy steel containing 0.5 to 2.0% and W0.1 to 20% or less and comprising a welded layer solidified in a roll axial direction. 5. A composite roll for a PC mill, wherein the outer periphery of a core material is covered with an outer layer material, wherein the core material has a weight of C0.5 to 1.0.
%, Si 1% or less, Mn 1% or less, Cr 1-5%, Mo
It is made of a low alloy steel containing 0.5% or less and having a hardness lower than that of the outer layer material and having a roundness of 10 mm or less, wherein the outer layer material is C0.5-1.5%, Si0.5-0.5% by weight. 3.0%, M
n1.5% or less, Cr 2 to 10%, Mo 1 to 12%, V
A composite roll for a PC mill, comprising a high-alloy steel containing 0.5 to 2.0% and a W of 0.1 to 20% or less and comprising a welded layer solidified in a roll axial direction.