JPH05179393A - Combination roll - Google Patents

Abstract

PURPOSE:To develop the combination roll which has an outside layer of the uniform quality of a material and is highly resistant to wear by constituting the roll to be used for rolling, etc., of steel products of the outside layer made of a cast iron contg. a hard metal carbide, an intermediate layer made of a high-carbon cast steel and an inside layer made of a graphite cast iron. CONSTITUTION:The roll for rolling the steel products is made of the combination structure, such as solid roll or sleeve-like roll consisting of the outside layer 1, the intermediate layer 3 and the inside layer 2. The outside layer 1 of the roll is made of the wear resistant cast iron contg., by weight% 1.0 to 3.0% C, 0.1 to 2.0% Si, 0.1 to 2.0% Mn, 3.0 to 10.0% Cr, 0.1 to 9.0% Mo, 1.5 to 10.0% W, 0.5 to 10.0% Co and 3.0 to 10.0% in total of one or two kinds of V and Nb. The intermediate layer 3 is made of the high-carbon cast steel contg. 1.0 to 2.5% C, 0.2 to 3.0% Si, 0.2 to 1.5% Mn, <=4% all of Cr, Ni and Mo, further <=12% in total of W, V and Nb and a small quantity of Co. The inside layer 2 is made of the flake graphite cast iron, spheroidal graphite cast iron or graphite steel.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite roll for rolling steel and the like.

[0002]

2. Description of the Related Art A composite roll is one in which a solid inner layer (axial core portion) formed of a tough material is welded to an outer layer which is a layer used for rolling formed of wear resistant material, and an outer layer 1 as shown in FIG. There is an intermediate layer 3 interposed between the inner layer 2 and the inner layer 2. Note that, as shown in FIG. 2, the cylindrical roll is also called a sleeve roll, and is usually fixed to the roll shaft by shrink fitting or the like, assembled, and then used for rolling.

The intermediate layer 3 is formed to prevent mixing of high alloying elements from the outer layer 1 to the inner layer 2 which would occur when the outer layer 1 and the inner layer 2 are directly welded, and to prevent deterioration of the toughness of the inner layer. It is something. As disclosed in Japanese Patent Publication No. 58-30382 and Japanese Patent Publication No. 61-16415, high chromium cast iron containing 10 to 25% of Cr and seizure resistance have been conventionally used as outer layer materials having excellent wear resistance. A high-chromium cast iron with crystallized graphite is also used.

[0004]

In recent years, rolling conditions have become more severe, and higher wear resistance has been required.
For this reason, as mentioned in the above publication, one or two kinds of Nb and V are added to high chromium cast iron or graphite crystallized high chromium cast iron in a total amount of 2% or less to generate fine carbides as crystal nuclei. As a result, the structure is made finer and denser, and the wear resistance is improved. However, in reality, it cannot be said that the demand for improvement in wear resistance is sufficiently satisfied.

On the other hand, it is considered that a large amount of W should be added to the material in order to greatly improve the wear resistance in steel rolling. However, since the outer layer of the composite roll is mainly cast by centrifugal casting, there is a problem that W is separated due to the difference in specific gravity, segregation occurs in the circumferential direction, and it is difficult to obtain a uniform material. The present invention has been made in view of the above problems, and an object of the present invention is to provide a composite roll for rolling steel and the like, which has an outer layer made of a uniform material having excellent wear resistance.

[0006]

The composite roll of the present invention comprises:
An outer layer and an intermediate layer, and an intermediate layer and an inner layer are welded to each other, and the outer layer has a chemical composition by weight of C: 1.0 to 3.0%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0%, W: 1.5 to 10.0%, V, Nb: 3.0 to 10.0% in total of one or two kinds, Co: 0.5 to 10.0%, and balance balance It consists essentially of Fe and the intermediate layer is C: 1.
It is made of high carbon cast steel having a specific composition containing 0 to 2.5%, and the inner layer is made of flake graphite cast iron, spheroidal graphite cast iron or graphite steel. Further, the outer layer component may contain, in addition to the outer layer alloy component, one or more of Al, Ti, and Zr: 0.01 to 0.50% each, or B: 0.01 to 0.50%.

[0007]

The outer layer of the composite roll of the present invention is made of Cr, M
Oxide, W, Nb, V, Fe and C are bonded to each other to form a high hardness composite carbide in the matrix, and the matrix is strengthened by the action of Co to improve the hardness at normal temperature and high temperature, resulting in wear resistance. It dramatically improves your sex. For this reason,
To ensure the same life as conventional high chromium cast iron,
The thickness of the outer layer may be as thin as about 80 mm or less, that is, about 80% of the conventional thickness, so that the outer layer material containing a large amount of expensive alloy can be used in a small amount. Further, like the high chromium cast iron, the outer layer is subjected to quenching heat treatment to impart high hardness. At this time, the outer layer material according to the present invention has a high hardness and has a higher residual stress as compared with high chromium cast iron and the like, but since the outer layer can be thinned, the residual stress can be suppressed to a low level and the accident resistance can be improved. Can be improved. Also,
Since the casting thickness can be reduced to about 80 mm or less, rapid solidification can be achieved, macro segregation hardly occurs, a fine structure is formed, and abrasion resistance is further improved. On the other hand, even if the outer layer is formed thick, W with a large mass is
%, The segregation is relatively easy to occur. Even if the outer layer is formed by centrifugal casting, macro segregation hardly occurs and the uniformity of the structure is excellent.

Since the intermediate layer is formed between the outer layer and the inner layer by the high carbon cast steel having the specific composition, it is possible to prevent the high alloy component of the outer layer from being mixed into the inner layer and deteriorating its toughness. .. Moreover, since the boundary portion between the intermediate layer and the inner layer is made of a low alloy, the formation of the carbide layer is suppressed, and the boundary strength can be improved. Further, during the austenite heat treatment of the outer layer, it is possible to prevent the temperature rise of the inner layer, and it is possible to heat only the outer layer to a high temperature of 1100 ° C. or higher while preventing deterioration of the toughness of the material of the inner layer. Further, in the composition of the intermediate layer of the present invention, martensite transformation does not occur during quenching of the outer layer, so that even if quenching heat treatment is applied to the outer layer, excessive residual stress does not occur, resulting in excellent accident resistance.

Further, since the inner layer is made of flake graphite cast iron, spheroidal graphite cast iron or graphite steel, that is, a steel material in which graphite is crystallized, the Young's modulus can be about 19000 kg / mm ² or less, and when overloaded. By flattening the roll, the load can be absorbed and accident resistance can be improved. Further, the low temperature strain relief annealing can reduce the residual stress during the heat treatment of the outer layer. In addition, it has excellent thermal conductivity and thus heat dissipation, and can prevent thermal deformation of the roll during rolling. Further, since it has good toughness, it can withstand shocking rolling torque.

[0010]

EXAMPLES First, the outer layer of the composite roll of the present invention was used.
The reasons for limiting the chemical composition of wear-resistant cast iron materials
It In the following, all units of components are% by weight. C: 1.0 to 3.0% C is mainly combined with Fe and Cr to form M₇C₃Mold high
In addition to forming hardness composite carbide, Cr, Mo, V, N
b, combined with W MC type, M₆C type, M₂High hardness such as C type
It also forms complex carbides. This high hardness composite carbide formation
Therefore, a C% of 1.0% or more is required. On the other hand, 3.0
If C is contained in excess of 10%, the amount of carbide increases and it becomes brittle.
Since the crack resistance deteriorates, 3.0% or less
It Si: 0.1-2.0% Since Si is a casting alloy of the present invention, it ensures the flowability of molten metal.
Is an element necessary for, and at the same time, from the raw materials used
 About 0.1% is inevitably contained. But 2.0%
If it exceeds the range, toughness is deteriorated, which is not preferable. Mn: 0.1-2.0% Mn increases the curing ability and also combines with S to form MnS
However, it is an element that prevents embrittlement due to S, and at the same time it is a raw material used.
Therefore, about 0.1% is inevitably contained. But 2.0
%, It is not preferable because the toughness is deteriorated. Cr: 3.0-10.0% Cr combines with C together with Fe, Mo, V, Nb, W,
Improves wear resistance at high temperature by forming high hardness composite carbide
Contribute to the above. In addition, some are solid-solved in the base and hardenable.
And improve wear resistance. Below 3.0%, these effects
There are few fruits, and improvement in wear resistance cannot be expected. On the other hand, 10.0
%, The toughness of the steel will deteriorate.
Absent. Mo: 0.1-9.0% Mo easily combines with C along with Fe, Cr, V, Nb, and W.
And mainly M₇C ₃Mold, M₆C type, M₂C type composite coal
To increase wear resistance by increasing the hardness at room temperature and high temperature.
Contribute to improvement. Mo is effective when added in a small amount compared to W
Exert fruit. In this case, if it is less than 0.1%, the desired wear resistance
Toughness cannot be obtained, while if it exceeds 9.0%, toughness
It is not preferable because it will decrease. W: 1.5-10.0% W is also easily C with Fe, Cr, Mo, V, and Nb.
To form complex carbides,
It contributes to the improvement of abrasion resistance. Expected if less than 1.5%
Wear resistance cannot be obtained, while exceeding 10.0%
And toughness decrease, and heat crack resistance deteriorates.
It Also, it is easy to generate macrosegregation during centrifugal casting.
Let Therefore, it is set to 10.0% or less. V, Nb: One or two in total 0.3-10.0% V is easy to be C together with Fe, Cr, Mo, W like Nb
To form mainly MC-type composite carbides.
It contributes to the improvement of wear resistance by increasing the temperature and high temperature hardness.
Further, this MC type composite carbide is formed in a branch shape in the thickness direction.
Therefore, the plastic deformation of the base is suppressed, the mechanical properties,
Also contributes to the improvement of crack resistance. Single or two
This effect will not appear unless combined with 3.0% or more.
Yes. However, if the addition amount exceeds 10.0%, the toughness is reduced.
And easy to generate macro-segregation during centrifugal casting
Become Therefore, the amount is 10.0% or less. Co: 0.5-10.0% Co is an important element that characterizes the present invention, and the base is modified.
It has a great effect on doing good. Co suppresses diffusion of C
It has a special effect that
Improves toughness by forming a solid solution and improves high temperature hardness and wear resistance.
There is an effect to improve. In addition, Co is an element of a carbide-forming element.
The hardness of the matrix is increased to increase the amount of solid solution in the stenite.
And the tempering resistance increases. To expect these effects
 It is necessary to contain 0.5% or more, but added over 10.0%
However, the effect is saturated and it is an expensive element.
Then, 0.5 to 10.0%. Note that high alloy cast iron materials
When casting by composite casting to make a composite roll,
The distribution of carbides is likely to be non-uniform, and casting conditions are optimized
Of the high alloy material containing Co of the present invention.
In this case, Co is a group that is independent of the formation of carbides as described above.
Greater non-uniformity of carbides as it forms a solid solution in the ground
Nonetheless, the above-mentioned excellent effect can be expected.

In the wear resistant cast iron material of the outer layer of the present invention, the balance is formed by Fe and impurities in addition to the above alloy components. still,
P and S are inevitably mixed in from the raw material, but they are desirable because they make the material brittle, so it is preferable that they are less than P: 0.2%, S: 0.1%
It is better to stop below. The wear-resistant cast iron material of the outer layer according to the present invention contains, in addition to the above alloy components, A of the following composition range:
One, two or more of 1, Ti, and Zr, or those containing B are included. Al, Ti, Zr: 0.01 to 0.50% each Al, Ti, Zr forms an oxide in the melt, reduces the oxygen content in the melt, improves the soundness of the product, and forms the oxide. Acts as a crystal nucleus, which is effective for refining the solidified structure. If it is less than 0.01%, this effect is not sufficient, while if it exceeds 0.50%, it remains as inclusions, which is not preferable. In addition, Al, Ti,
In the present invention, Zr is mainly added to improve wear resistance by refining the cast structure, and is not simply added for degassing. B: 0.01 to 0.50% B combines with oxygen in the molten metal to show a deoxidizing effect. In addition, the effect of refining the solidified structure with the generated oxide as the core,
Also, it has the effect of increasing the hardenability due to B dissolved in the matrix. In the case of a large-mass casting such as a rolling roll, it may be difficult to increase the cooling temperature, but the increased hardenability makes it easier to obtain a hardened structure. If it is less than 0.01, such an effect is not sufficient, while if it exceeds 0.50%, the material becomes brittle, which is not preferable.

Next, the inner layer material of the composite roll of the present invention will be described. The inner layer material is a material in which graphite is crystallized for the following reasons, specifically, flake graphite cast iron (abbreviated as FC), spheroidal graphite cast iron (abbreviated as DCI), graphite steel (abbreviated as SGS).
To use. Reasons for using graphite crystallized material When rolling is used, an overload condition (for example, biting of two plates) cannot be avoided, but the Young's modulus of the outer layer material is 21000.
Since it is as high as ~ 23000kg / mm ² , large stress is generated in the outer layer material. Young's modulus of the middle layer is 20000-23000kgf / mm
Is ^2, since the layer thickness is relatively thin as about 25 to 30 mm, the lower the Young's modulus of the inner layer material to be complexed, during overload,
The flattening of the roll allows the inner layer material to absorb the load.

Therefore, lowering the Young's modulus of the inner layer material increases the safety during use. In order to have a Young's modulus of less than 20000 kg / mm ² , the inner layer material must be crystallized from graphite. The outer layer material contains a special alloy and is tempered 2
Since it is hardened by the secondary hardening phenomenon, it is generally difficult to remove residual stress. Therefore, when the outer layer material is subjected to a hardening heat treatment on the composite roll, a compressive stress is generated in the outer layer and a tensile stress is generated in the inner layer due to expansion due to transformation of the outer layer material. When the tensile stress of the inner layer material becomes excessively large, the inner layer is broken or the boundary portion between the intermediate layer and the inner layer is broken, and the roll is broken.

In order to prevent the destruction, the composite roll may be subjected to strain relief annealing to release the residual stress of the inner layer material. However, high temperature strain relief annealing exceeding 600 ° C causes a decrease in hardness of the outer layer. Therefore, it is necessary to release the residual stress of the inner layer material by low temperature strain relief annealing. For this purpose, the inner layer material is preferably graphite crystallized. In the case of the present invention, the low temperature strain relief annealing can achieve its purpose by the tempering heat treatment of the outer layer. The roll receives heat from the rolled material (around 1000 ° C) during use. To prevent thermal deformation of the roll and maintain a predetermined shape, heat radiation must be good. Therefore, the inner layer must have good heat conduction. Therefore, a graphite crystallized material is suitable as the inner layer material. The roll neck must be strong enough to withstand bending forces and motor torque. Since there are impact loads, toughness is important as well as strength. By crystallizing graphite, toughness can be improved.

Next, the characteristics and preferable composition (unit: wt%) of various inner layer materials forming the inner layer of the composite roll will be described. As described above, the inner layer needs to contain graphite, but when the outer layer and the inner layer are welded, a high alloy component of the outer layer is inevitably mixed. It is necessary to determine the composition in consideration of this point. (1) In the case of FC, FC has good castability and Young's modulus of 10000 to 15000 kg /
Since it is as low as mm ^2, and the graphite is in the form of flakes, residual stress can be easily removed and the thermal conductivity is high. Further, the workability is also good, and when used as the inner layer material of the hollow roll, the inner surface processing is easy. However, since the strength is limited to about 30 kg / mm ² , it is not suitable for composite rolls used under conditions of large rolling load. The solidus of FC with the following composition is 1130-
It is 1170 ° C.

Preferred composition examples and reasons for limitation are shown below. C: 2.5 to 4.0% C is necessary for crystallizing graphite, and if less than 2.5%, the amount of graphite is small. On the other hand, if it exceeds 4.0%, the amount of graphite becomes excessive and the strength decreases. Si: 0.8 to 2.5% Si acts to promote crystallization of graphite, and if it is less than 0.8%, graphitization is insufficient. On the other hand, if it exceeds 2.5%, the base becomes brittle.

Mn: 0.2-1.5% Mn has the function of strengthening the matrix and preventing the damage of S. 0.2
If it is less than%, the effect can hardly be expected. on the other hand,
If it exceeds 1.5%, the material becomes brittle. P and S: 0.2% or less of each P and S are impure elements, so the smaller the better, the better it is to keep the content to 0.2% or less.

Since low-concentration ones are expensive, it is unavoidable to contain them in an amount of about 0.01% or more in consideration of economical efficiency. Ni: 3.0% or less Ni is effective for graphitization and strengthening of the matrix, but 3.0
If it exceeds%, the untransformed structure tends to remain and the strength deteriorates.

Cr and Mo: 2.0% or Less Each Cr and Mo have a strengthening effect on the matrix, but if they are too much, they inhibit graphitization. To strengthen the base, it is desirable to contain 0.1% or more. On the other hand, in order to prevent the inhibition of graphitization, it is necessary to limit the content to 2.0% or less including the amount mixed from the outer layer.

W, V, Nb: 4.0% or less in total These elements are inevitably mixed from the outer layer. W, V, N
b has no effect of improving the material quality of the inner layer. Therefore, these elements are interpreted as impurities, and up to 4% is allowed as a range that does not deteriorate the mechanical properties of the inner layer material. A on the outer layer
In the case of including 1, Ti, Zr, and B, these elements are inevitably mixed in the inner layer through the intermediate layer, but the amount thereof is very small, so that there is almost no problem in terms of material. Further, Co is inevitably mixed, but Co is not particularly limited because it does not deteriorate the material of the inner layer.

In addition to the above components, FC consists essentially of Fe.
Is formed by. The composition range of the molten metal before welding to the intermediate layer, that is, before casting is exemplified below. The composition of the molten metal is determined in consideration of the amount of components mixed from the intermediate layer so that the composition of the inner layer is obtained after welding. C: 2.5 to 4.0%, Si: 0.8 to 2.5%, Mn: 0.2 to 1.5%, P: 0.2% or less, S: 0.2% or less, Ni: 3.0% or less, Cr: 2.0% or less, Mo: 2.0% or less. The balance is substantially Fe (2) DCI. DCI has good castability and Young's modulus of 15000 to 19000 kg.
/ Mm ² and a large amount of graphite. Further, the shape of graphite is spherical, unlike FC, and therefore is excellent in strength and toughness. In addition, the workability is also good. Therefore, it is suitable as an inner layer material. As disclosed in JP-B-59-52930 and JP-B-59-52931, the material is heated and held in the ferrite / austenite coexistence temperature range (780 to 900 ° C) and then rapidly cooled at 200 to 800 ° C / Hr. Then, the matrix structure becomes a two-phase mixed structure of ferrite and pearlite by the heat treatment for converting austenite into fine pearlite. This structure is particularly excellent in the effects of crack development and residual stress removal.
The heat treatment of the two-phase mixed texture may be performed as a heat treatment before the heat treatment for hardening the outer layer of the composite roll. The solidus of DCI having the following composition is 1130-1170 ° C.

Preferred composition examples and reasons for limitation are shown below. C: 2.5 to 4.0%, Si: 1.3 to 3.5%, Mn: 0.2 to 1.5%, P: 0.2% or less, S: 0.2% or less, Ni: 3.0% or less, Cr: 2.0% or less, Mo: 2.0% or less. , W, V, Nb: 4% or less in total, Mg: 0.02 to 0.1
%, Co mixed from the remaining intermediate layer and components other than substantially Fe 2 Si and Mg are the same as in FC, so these two components will be described.

Si is a graphitization promoting element. DCI contains Mg due to spheroidization of graphite. Since Mg is a strong graphitization inhibiting element, 1.3% or more of Si is required to achieve graphitization in the presence of Mg. On the other hand, if it exceeds 3.5%, the matrix becomes brittle and a large amount of ferrite precipitates, resulting in a decrease in strength. Mg has a function of making graphite spherical. 0.02% or more is necessary to obtain the effect. On the other hand, if it exceeds 0.1%, graphitization is hindered and casting defects are easily generated.

The suitable molten metal composition of DCI before welding to the outer layer is illustrated below. C: 2.5 to 4.0%, Si: 1.3 to 3.5%, Mn: 0.2 to 1.5%, P: 0.2% or less, S: 0.2% or less, Ni: 3.0% or less, Cr: 2.0% or less, Mo: 2.0% or less. , Mg: 0.02 to 0.1%, balance substantially Fe (3) SGS Since SGS has a high Young's modulus of 17000 to 20000 kg / mm ² and a small amount of graphite, residual stress is relatively difficult to remove. Also, the castability is not very good, and a large feeder or the like is required. However, its strength is excellent at 40 kg / mm ² or more, and its toughness is also excellent, so it is optimal for rolls used under severe operating conditions under which a large bender load is applied. Also, the solidus line (for SGS with the composition below) is 11
Since it is 70 to 1250 ° C, which is higher than that of FC and DCI, there is an advantage that it is less likely to deteriorate during the austenitizing heat treatment of the outer layer.

Preferred composition examples and reasons for limitation are shown below. C: 1.0 to 2.3%, Si: 0.5 to 3.0%, Mn: 0.2 to 1.5%, P: 0.2% or less, S: 0.2% or less, Ni: 3.0% or less, Cr: 2.0% or less, Mo: 2.0% or less. , W, V, Nb: 4.0% or less in total, Co mixed in from the remaining intermediate layer and components other than substantially Fe C, Si are the same as FC, so these two components will be explained.

C is necessary for crystallizing graphite.
If it is less than 1.0%, crystallization of graphite is unlikely to occur. On the other hand, 2.3%
If it exceeds, the shape of graphite will collapse and the strength will decrease. Si is necessary for graphitization. If it is less than 0.5%, crystallization of graphite becomes difficult, while if it exceeds 3.0%, the matrix becomes brittle.
The suitable molten metal composition of SGS before welding to the outer layer is exemplified below.

C: 1.0 to 2.3%, Si: 0.5 to 3.0%, Mn: 0.2 to 1.5%, P: 0.2% or less, S: 0.2% or less, Ni: 3.0% or less, Cr: 2.0% or less, Mo: 2.0% or less, balance substantially Fe Next, the intermediate layer will be described. The intermediate layer is formed for the purpose of reducing the mixing of the alloy components of the outer layer into the inner layer, but the intermediate layer itself also needs strength of about 30 kg / mm ² . When the strength is insufficient, the boundary between the outer layer and the intermediate layer is broken and the outer layer is peeled off. Therefore, the intermediate layer needs to be made of a material having high strength even if a large amount of alloying components are mixed from the outer layer. For this reason, high carbon cast steel (abbreviated as AD) having the following composition is suitable as the intermediate layer material. Less than,
The composition of the intermediate layer material according to the present invention and the reasons for limitation are shown below. C: 1.0 to 2.5% C contributes to the improvement of strength, but if it is less than 1.0%, the freezing point becomes high and the welding tends to be insufficient. On the other hand, if it exceeds 2.5%, the amount of carbide becomes excessive and the material becomes brittle. Si: 0.2 to 3.0% Si has an action of promoting degassing and an action of improving the flowability of molten metal.
If it is less than 0.2%, such an effect cannot be expected, while 3.0%
If it exceeds, the material becomes brittle. In the high Si region, crystallization of graphite may be observed in relation to the Ni content, but there is no problem in terms of material. Mn: 0.2 to 1.5% Mn is limited to the above range for the same reason as the ductile cast iron as the inner layer material. Ni: 4.0% or less Ni has the function of strengthening the material. However, if it exceeds 4.0%, the action is saturated and an untransformed structure is apt to occur, resulting in deterioration of strength. Cr, Mo: 4.0% or less for each Cr, Mo have the function of strengthening the material. But 4.0
If it exceeds%, the mechanical properties will rather deteriorate. W, V, Nb: 12% or less in total Although these elements have almost no effect on improving the material of the intermediate layer, mixing from the outer layer is inevitable. 12% is acceptable as a range that does not deteriorate the mechanical properties of the intermediate layer material. When the outer layer contains Al, Ti, Zr, and B, these elements also inevitably enter the intermediate layer. in this case,
For the same reason, statistically, including these elements, 12% or less. Co is also inevitably mixed from the outer layer, but it is not particularly limited because it does not deteriorate the material of the intermediate layer.

The components of the intermediate layer material are, in addition to the components described above, the balance being substantially Fe. It should be noted that P and S are impurities and should be as small as possible because they make the material brittle. In the present invention, both of them are preferably kept to 0.2% or less like the inner layer material. still,
The composition range of the molten metal before welding to the outer layer is exemplified below. The composition of the molten metal is determined in consideration of the amount of the components mixed from the outer layer so that the composition of the intermediate layer is obtained after welding.

C: 1.0 to 2.5%, Si: 0.2 to 3.0%, Mn: 0.2 to 1.5%, P: 0.2% or less, S: 0.2% or less, Ni: 4.0% or less, Cr: 4.0% or less, Mo: 4.0% or less, balance substantially Fe In the present invention, 1.0 to 2.5 between the outer layer and the inner layer (axial core).
Since the intermediate layer of% C is provided, it is possible to significantly suppress the harmful alloying elements from being mixed into the inner layer from the outer layer to the inner layer at the time of welding, and the following effects are exhibited.

During the quenching heat treatment of the outer layer, it is preferable to heat the outer layer to 1100 ° C. or higher due to the austenitizing heat treatment. However, even if the outer layer is heated to 1100 ° C. or higher, heat transfer to the inner layer is conducted through the intermediate layer. Therefore, the temperature of the inner layer can be easily suppressed to 1100 ° C. or less by adjusting the amount of heat, and the melting loss of the inner layer can be prevented. The concentration of Cr, Mo, W, and V in the intermediate layer increases due to the welding with the outer layer, but since these elements can be kept lower than in the outer layer, the intermediate layer and the outer layer are more likely to be welded than the outer layer. By welding the intermediate layer and then the inner layer, the alloy concentration in the welded portion of the inner layer can be lowered. Therefore, when the intermediate layer is provided, the carbide layer is hard to form at the boundary with the inner layer, and the boundary strength can be improved.

Most of the intermediate layer according to the present invention undergoes pearlite transformation during the quenching heat treatment of the roll, and the rest undergoes bainite transformation. The martensitic transformation does not occur, or even if it occurs, it is a very small amount. Therefore, there is no large expansion behavior associated with the martensitic transformation, and the residual stress on the roll is not increased. When a large amount of martensitic transformation occurs, a large compressive residual stress (axial direction) acts on the outer and middle layers, and a large tensile residual stress (axial direction) acts on the inner layer in combination with the martensitic transformation of the outer layer. Lucky, the inner layer is pulled and broken.

In the case of the solid roll of the composite roll of the present invention, the outer layer and the intermediate layer are usually centrifugally cast, and then the inner layer (axial core portion) is statically cast therein. Further, in the case of the sleeve roll, the inner layer is centrifugally cast after the outer layer and the intermediate layer. FIG. 3 shows a horizontal centrifugal casting apparatus, in which a centrifugal casting die 4 is rotatably supported by rotating rollers 5 and 5, and molten metal is cast from a weir bowl 6 through a pouring trough 7. Cast in 4 8 is a sand mold for hot water stopper.
In order to cast a solid composite roll, first, the molten outer layer material is cast into a rotating die 4, and after it is solidified, the outer layer is melted.
The molten metal for the intermediate layer is cast on the inner peripheral surface of 1, and the intermediate layer 3 is centrifugally cast. After that, a mold 4 having an outer layer 1 and an intermediate layer 3 therein is erected, and an upper mold and a lower mold for forming a shaft core are continuously provided at both ends thereof to form a stationary mold, and an inner layer is provided inside the mold. Cast the molten metal. In the horizontal centrifugal casting apparatus, since each part of the molten metal cast in the mold moves up and down with each rotation of the mold, there is a change in G, and vibration occurs due to eccentricity and scratches on the rollers and the mold. It is easy to generate, and the components in the cast outer layer material melt easily move. Therefore, when casting a thick outer layer,
Since segregation tends to occur due to the movement of the components, it is usually preferable to cast at a relatively low temperature with the solidification start temperature + 70 ° C or lower. However, since the outer layer material according to the present invention is a high wear resistant material, it is hard to wear and the outer layer may be relatively thin,
The casting thickness is about 80 mm (preferably 55 to 70 mm), and since it is rapidly cooled by the mold, there is almost no risk of segregation even when casting is performed at a temperature higher than the above temperature. The thickness of the outer layer of the product is 50 when considering the melting margin of 20 mm and the machining margin of 10 mm due to the intermediate layer
mm (preferably 25 to 40 mm).

FIG. 4 shows a vertical centrifugal casting apparatus,
An upper die 12 and a lower die 13 are assembled on the upper and lower ends of a centrifugal force casting die 11, and the die is concentrically and mechanically fixed to a rotating base 14. For this reason, the outer layer material molten metal 16 cast into the mold through the weir bowl 15 and ascended to and adhered to the inner surface of the mold 11 by the action of centrifugal force is less susceptible to fluctuations in G and vibration. Therefore, if vertical centrifugal casting is used, segregation is less likely to occur even when casting a thick outer layer, and therefore casting can be performed at higher temperatures, which is effective in improving workability and preventing casting defects due to inclusion of foreign matter. Is. It is needless to say that only the centrifugal force casting die 11 may be fixed to the substrate 14, the outer layer and the intermediate layer may be cast, the upper die and the lower die may be assembled, and the shaft core may be statically cast.

The outer layer wear-resistant cast iron material of the present invention is cast as the outer layer of a composite roll, and then the entire roll is heated from the quenching temperature (austenizing temperature) to 400 to 650 ° C. in a temperature range of 150.
By quenching at a cooling rate of ° C / Hr or higher, a good quenched structure can be obtained. Tempering is 500-600 ℃
It is advisable to carry out once or several times at the above temperature. In the outer layer material according to the present invention, since Mo, W, V, Nb, etc. which are solid-solved in the matrix during the austenitizing heat treatment are precipitated as fine carbides by the tempering heat treatment, a tempering secondary hardening phenomenon occurs,
Excellent in high temperature hardness.

As a heating method for the outer layer, a method of heating the entire roll in a heating furnace, a method of arranging an induction heating coil and a number of gas burners around the outer peripheral surface of the outer layer and rapidly heating only the outer layer by these There is. In the former case, it takes time to raise the temperature, a thick oxide film is formed on the outer layer surface, and the yield of the outer layer decreases. Furthermore, in order to avoid the melting loss of the inner layer of the cast iron material and to heat it, it is necessary to stop the heating at 1100 ° C (desirably 1000 ° C) or less, and thus it is difficult to sufficiently dissolve the carbide in the matrix, There is a problem that it is difficult to obtain sufficient hardness even by the subsequent heat treatment. On the other hand, according to the heating method of only the outer layer, in combination with the formation of the intermediate layer,
Since the outer layer can be reliably kept at 1100 ° C. or higher and the inner layer can be kept at less than 1100 ° C., it is possible to prevent partial melting of the inner layer and strength reduction due to coarsening of crystal grains. Also, since the temperature becomes lower toward the center of the inner layer (axial core), the heat of the outer layer can be released to the inside after heating to the austenitizing temperature, and the cooling rate of the deeper layer of the outer layer can be increased during quenching. it can.

The composite roll of the present invention, whether hot-rolled or cold-rolled, includes a rolling roll for rolling equipment and a pinch roll for auxiliary equipment or a roller for conveying rolled material.
It is applied to rolls and rollers that require abrasion resistance.
As the rolled material, not only iron and steel and non-ferrous metals but also non-metals are targeted. Next, specific examples of the present invention will be described. (1) Centrifugal casting of the molten outer layer material shown in Table 1 into a die for centrifugal force casting with an inner diameter of φ 810 mm, and after the outer layer was completely solidified, the intermediate layer molten metal of the same table was subsequently centrifugally cast to form the outer layer. And the intermediate layer were welded together. The thickness of casting is 65 mm for the outer layer and 30 mm for the middle layer
And The examples are samples Nos. 1 to 6, and the outer layer material of the conventional example of No. 7 is a high chromium cast iron material with improved wear resistance. The unit of composition in the table is% by weight, and the balance is substantially Fe. (2) Wait until the middle layer is completely solidified, stop the rotation of the mold, stand the mold having the outer layer and the middle layer vertically, and connect the upper mold and the lower mold to both ends. The molten metal of the inner layer material (axial core material) shown in the table is cast inside.

[0037]

[Table 1]

(3) After rough-casting the cast composite roll, the rolls of the examples were uniformly preheated to 600 ° C., and then the rolls were arranged horizontally facing each other as shown in FIG. The outer surface of the outer layer was heated while being rotatably supported between the gas burners 21 arranged in parallel at a pitch of 250 mm along the axial direction and rotating the roll. Outer layer surface temperature is 1165
The heating was stopped when the temperature of the inner layer reached 870 ° C. The time required for heating was 250 minutes. In the case of this example, the temperature near the outer peripheral surface of the inner layer was estimated to be 970 ° C. from the temperature data of heat conduction. On the other hand, the conventional roll was austenitized by holding the whole roll at 1050 ° C. for 5 hours. (4) For the rolls of the example and the conventional example, after stopping heating, immediately perform water cooling with spray water to keep the roll surface temperature at 500 ° C.
After quenching to room temperature, it was allowed to cool to room temperature. Then 20 at 550 ℃
The tempering heat treatment for holding the time was repeated twice. The outer layer surface hardness after the heat treatment is shown in Table 2 below. From the table, it can be seen that the outer layer of the example is significantly improved in hardness and excellent in abrasion resistance as compared with that of the conventional example. still,
When the oxidation state of the outer layer surface was observed, the thickness of the oxide layer was about 0.5 mm in the example, whereas it was about 3.0 mm in the conventional example.

[0039]

[Table 2]

(5) After finishing the surface of the cylinder, the welding condition was confirmed by an ultrasonic flaw detection test, and it was found that the welding was good for all rolls. Next, when the roll body was cut and the cross section of the outer layer was visually observed, no segregation of the components was observed in any of the rolls. Table 3 shows the results of analyzing the components in the central portion of the thickness of the intermediate layer and the central portion of the inner layer (axial core portion). From the table, it can be seen that the mixing amount of the outer layer high alloy component in the inner layer is very small in both the example and the conventional example.

[0041]

[Table 3]

(6) Further, Table 4 shows the results of tensile test by collecting tensile test pieces from the inner layer of each sample. From the table, Nos. 1 and 4 to 6 of the examples in which the inner layer is DCI have higher strength than No. 7 of the conventional example, and the conventional example is deteriorated by about 20% as compared with the examples. Is recognized.

[0043]

[Table 4]

[0044]

As described above, in the composite roll of the present invention, the outer layer thereof contains a predetermined amount of Co, and Cr, Mo, W,
Since it is formed of a special cast iron material containing a predetermined amount of V and Nb, the presence of these high-hardness composite carbides can dramatically improve the wear resistance and prevent macrosegregation during casting. Also, since the intermediate layer is formed of high carbon cast steel of a specific composition, it is possible to significantly reduce the mixing of high alloying components from the outer layer to the inner layer, improve the boundary strength, and prevent the martensitic transformation from remaining. It is possible to prevent melting damage and strength reduction of the inner layer during austenitizing heat treatment of the outer layer without increasing stress. Further, since the inner layer is formed of flake graphite cast iron, spheroidal graphite cast iron or graphite steel, the strength and toughness are good, the Young's modulus can be made considerably lower than that of the outer layer, and the flattening of the roll during overload causes the outer layer to become flat. It is possible to prevent excessive stress from being generated, and it is excellent in safety and accident resistance. Furthermore, since it has excellent heat dissipation, thermal deformation is unlikely to occur.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a solid composite roll according to the present invention.

FIG. 2 is a sectional view of a sleeve-shaped composite roll according to the present invention.

FIG. 3 is a cross-sectional view of main parts of a horizontal centrifugal casting device.

FIG. 4 is a sectional view of a main part of a vertical centrifugal casting apparatus.

FIG. 5 is a cross-sectional view showing a heated state of an outer layer of a composite roll.

[Explanation of symbols]

 1 Outer layer 2 Inner layer 3 Middle layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Kimura 64, Nishimukaijima-cho, Amagasaki City, Hyogo Prefecture Kubota Amagasaki Factory (72) Inventor Kei Shikata, Kubota Amagasaki Factory 64 Nishimukojima-cho, Amagasaki City, Hyogo Prefecture Within

Claims (4)

[Claims] 1. A composite roll comprising an outer layer formed of wear-resistant cast iron material, an intermediate layer welded to the inner peripheral surface of the outer layer, and an inner layer welded to the inner peripheral surface of the intermediate layer, The chemical composition of the outer layer is% by weight, C: 1.0 to 3.0%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0%, W: 1.5 to 10.0. %, V, Nb: one or two in total of 3.0 to 10.0%, Co: 0.5 to 10.0%, and the balance substantially consisting of Fe. The intermediate layer has a chemical composition of wt% and C: 1.0 to. 2.5%, Si: 0.2-3.0%, Mn: 0.2-1.5%, Ni: 4.0% or less, Cr: 4.0% or less, Mo: 4.0% or less, W, V, Nb: 12% or less in total, the balance being the outer layer Is composed of Co and substantially Fe, and the inner layer is made of flake graphite cast iron, spheroidal graphite cast iron or graphite steel. Composite roll to. 2. A composite roll comprising an outer layer made of wear-resistant cast iron material, an intermediate layer welded to the inner peripheral surface of the outer layer, and an inner layer welded to the inner peripheral surface of the intermediate layer, The chemical composition of the outer layer is% by weight, C: 1.0 to 3.0%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0%, W: 1.5 to 10.0. %, V, Nb: one or two in total of 3.0 to 10.0%, Co: 0.5 to 10.0%, Al, Ti, Zr: one or more of 0.01 to 0.50% each, and the balance substantially The intermediate layer is made of Fe and has a chemical composition of wt%, C: 1.0 to 2.5%, Si: 0.2 to 3.0%, Mn: 0.2 to 1.5%, Ni: 4.0% or less, Cr: 4.0% or less, Mo. : 4.0% or less, W, V, Nb, Al, Ti, Zr: 12% or less in total, the balance being Co mixed from the outer layer and substantially Fe The inner layer composite roll, characterized in that it is formed by flake graphite cast iron, spheroidal graphite cast iron or graphite steel. 3. A composite roll comprising an outer layer made of wear-resistant cast iron material, an intermediate layer welded to the inner peripheral surface of the outer layer, and an inner layer welded to the inner peripheral surface of the intermediate layer, The chemical composition of the outer layer is% by weight, C: 1.0 to 3.0%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0%, W: 1.5 to 10.0. %, V, Nb: one or two in total of 3.0 to 10.0%, Co: 0.5 to 10.0%, B: 0.01 to 0.50%, and the balance substantially Fe, and the intermediate layer has a chemical composition by weight. %, C: 1.0 to 2.5%, Si: 0.2 to 3.0%, Mn: 0.2 to 1.5%, Ni: 4.0% or less, Cr: 4.0% or less, Mo: 4.0% or less, W, V, Nb, B: 12% or less in total, the balance consisting of Co and substantially Fe mixed from the outer layer, and the inner layer is made of flake graphite cast iron, spheroidal graphite cast iron or graphite steel. Composite roll, characterized in that it is. 4. A composite roll comprising an outer layer made of wear-resistant cast iron material, an intermediate layer welded to the inner peripheral surface of the outer layer, and an inner layer welded to the inner peripheral surface of the intermediate layer, The chemical composition of the outer layer is% by weight, C: 1.0 to 3.0%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0%, W: 1.5 to 10.0. %, V, Nb: one or two in total of 3.0 to 10.0%, Co: 0.5 to 10.0%, Al, Ti, Zr: one or more of 0.01 to 0.50% each, B: 0.01 to 0.50 % And the balance consisting essentially of Fe, and the chemical composition of the intermediate layer is wt%, C: 1.0 to 2.5%, Si: 0.2 to 3.0%, Mn: 0.2 to 1.5%, Ni: 4.0% or less, Cr: : 4.0% or less, Mo: 4.0% or less, W, V, Nb, Al, Ti, Zr, B: 12% or less in total, the balance being Co and actual mixed from the outer layer A composite roll characterized in that it is qualitatively made of Fe and the inner layer is made of flake graphite cast iron, spheroidal graphite cast iron or graphite steel.