JP3155398B2 - Composite roll - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Composite rolls are obtained by welding a solid inner layer (axial portion) formed of a tough material to an outer layer which is a rolled use layer formed of a wear-resistant material, or an outer layer 1 as shown in FIG. And an inner layer 2 with an intermediate layer 3 interposed. As shown in FIG. 2, the cylindrical roll is also called a sleeve roll, and is usually fixed to a roll shaft by shrink fitting or the like, assembled, and subjected to rolling.

The intermediate layer 3 is formed to prevent the high alloying element from being mixed into the inner layer 2 from the outer layer 1 and to prevent the deterioration of the toughness of the inner layer, which occurs when the outer layer 1 and the inner layer 2 are directly welded. Things. Conventionally, as outer layer materials having excellent wear resistance, Japanese Patent Publication No. 58-30382 and Japanese Patent Publication No. 61-16
As disclosed in Japanese Patent Publication No.
High-chromium cast iron containing 5% and graphite-crystallized high-chromium cast iron with improved seizure resistance are used.

[0004]

In recent years, rolling conditions have become 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 crystallization high chromium cast iron in total of 2% or less, and the fine carbides are generated as crystal nuclei. As a result, the structure is refined and densified, thereby improving the abrasion resistance. However, in reality, it cannot be said that the demand for improvement in wear resistance is sufficiently satisfied.

On the other hand, in order to greatly improve the wear resistance in steel rolling, it is considered that a large amount of W should be added to the material. However, since the outer layer of the composite roll is mainly cast by centrifugal casting, there is a problem that W separates due to a difference in specific gravity, segregation occurs in a circumferential direction, and it is difficult to obtain a uniform material. Therefore, in order to solve the above-mentioned problems, the present inventors have added a composite roll material containing a hard carbide such as VC while strengthening the matrix by adding alloy elements such as Cr, Mo, W, and V. No. 3-34693.

[0006] However, this roll material has good abrasion resistance, but oxide scale called black scale is easily formed on the roll surface thickly, and there is a problem of rough skin when the black scale is peeled off. The present invention provides a composite roll for rolling steel or the like, which maintains the characteristics of the roll material proposed above, that is, has excellent wear resistance, is made of a uniform material, and further has an outer layer having excellent surface roughness resistance. With the goal.

[0007]

According to the present invention, there is provided a composite roll comprising:
The outer layer and the intermediate layer, and the intermediate layer and the inner layer are welded to each other, and the outer layer has a chemical composition of% by weight.
0.7 to less than 1.0%, Si: 0.1 to 2.0%, M
n: 0.1 to 2.0%, Ni: 0.1 to 4.5
%, Cr: 3.0 to 10.0%, Mo: 0.1 to
9.0%, W: 1.5 to 10.0%, V, Nb: 1.5 to 10.0% in total of one or two, Co: 0.5 to
The intermediate layer is made of a high-carbon cast steel having a specific composition containing 1.0% to 2.5% of C, and the inner layer is flake graphite cast iron, spheroidal graphite cast iron. Or, it is formed of graphite steel. In addition to the outer layer alloy component, Al, Ti, Zr: one or more of 0.01 to 0.50% each, and B: 0.01 to 0.50 %.

[0008]

The outer layer of the composite roll of the present invention is made of Cr, M
O, W, Nb, V, Fe and C are bonded together to form a high-hardness composite carbide in the matrix, and the strengthening of the matrix by the action of Co improves the hardness at room temperature and high temperature, resulting in abrasion resistance. Dramatically improved. For this reason,
When securing the same life as conventional high chromium cast iron,
Since the outer layer thickness may be as thin as about 80 mm or less, that is, about 80% of the conventional thickness, the amount of the outer layer material containing a large amount of an expensive alloy can be reduced. Further, the outer layer is subjected to a quenching heat treatment to give high hardness, similarly to high chromium cast iron or the like. At this time, the outer layer material according to the present invention has a high hardness and a high residual stress as compared with a high chromium cast iron or the like.However, since the outer layer can be thinned, the residual stress can be suppressed low, and the accident resistance is improved. Can be improved.
Further, since the casting thickness can be reduced to about 80 mm or less, rapid solidification can be performed, macrosegregation is less likely to occur, and a microstructure is formed, thereby further improving wear resistance. On the other hand, even when the outer layer is formed thick, the large mass W is suppressed to 10% or less. Therefore, even if the outer layer is formed by centrifugal casting in which segregation is relatively likely to occur, macro segregation is unlikely to occur, and the uniformity of the structure is obtained. Excellent in nature.

In particular, since the outer layer of the present invention has a low C% of 0.7 to less than 1.0%, the amount of eutectic carbide which crystallizes at the grain boundary in the final solidification is almost eliminated. Accordingly, eutectic oxides (grain-boundary carbides) are preferentially oxidized in hot rolling, tend to thicken the black scale, and become a propagation path of heat cracks due to repetition of heating and cooling in hot rolling and cause black scale peeling. ) Is excellent in rough skin resistance. The eutectic carbide contains elements such as Fe, Mo, W, and V. On the other hand, it is natural that high-hardness carbides such as VC and NbC are crystallized also in this component system.

Since the intermediate layer is formed between the outer layer and the inner layer by the high-carbon cast steel having a 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. . Further, since the boundary between the intermediate layer and the inner layer is made of a low alloy, the formation of a 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 of the inner layer from rising, and to heat only the outer layer to a high temperature of 1100 ° C. or more while preventing the toughness of the inner layer material from deteriorating. Further, since the intermediate layer composition of the present invention does not undergo martensitic transformation during quenching of the outer layer, even if quenching heat treatment is applied to the outer layer, no excessive residual stress is generated and the accident resistance is excellent.

Further, since the inner layer is formed of flaky graphite cast iron, spheroidal graphite cast iron or graphite steel, ie, a steel material in which graphite is crystallized, the Young's modulus can be reduced to about 19000 kg / mm ² or less. The flattening of the roll absorbs the load and improves the accident resistance. Further, the residual stress at the time of heat treatment of the outer layer can be reduced by the low-temperature strain relief annealing. In addition, it has excellent heat conductivity and heat dissipation, and can prevent thermal deformation of the roll during rolling.
In addition, since it has good toughness, it can withstand a shocking rolling torque.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the composite roll of the present invention is used for the outer layer.
Of the chemical composition of wear-resistant cast steel
You. Hereinafter, all units of the components are% by weight. C: 0.7 to less than 1.0% C combines with Fe, Cr, Mo, V, Nb, W and has high hardness
Form complex carbides. The formation of this high hardness composite carbide
And easily oxidize at high temperatures,
Minimize eutectic carbide (grain boundary carbide) as seeding route
Therefore, C% is less than 1.0% in order to make black scale thin and stable.
Must be full. On the other hand, if C is less than 0.7%,
Defects such as hole defects and foreign matter bites are likely to occur. Si: 0.1 to 2.0% Since Si of the present invention is a cast alloy, the flowability of the molten metal is ensured.
Element necessary for
It is valid. At the same time, about 0.1% of raw materials used
Inevitably contained. However, if it exceeds 2.0%,
This is not preferred because it leads to a reduction in the properties. Mn: 0.1 to 2.0% Mn increases the hardening ability and combines with S to form MnS.
And is an element that prevents embrittlement due to S.
To about 0.1% is inevitably contained. But,
If the content exceeds 2.0%, the toughness is reduced, which is not preferable.
No. Ni: 0.1 to 4.5% Ni is dissolved in the matrix, and the continuous cooling transformation diagram (CCT diagram)
And bainite transformation in isothermal transformation diagram (TTT diagram)
The quenching property is improved by moving the
Even if the cooling rate at the time of insertion is reduced, bainite transformation
Does not occur, large amount of retained austenite is martensite
Due to transformation, high hardness is obtained. Composite as in the present invention
In case of outer layer material of roll, thermal expansion of outer layer and inner layer during quenching
The large thermal stress caused by the difference and the heavy
In the case of cooling, a large heat capacity and a high cooling rate
For those that are difficult to cool, the cooling rate during quenching is slow.
It is very important to obtain a hardened structure at least. This
In this case, if it is less than 0.1%, such an effect cannot be obtained.
On the other hand, if the content exceeds 4.5%, the residual austenite
And it becomes difficult to obtain high hardness. In addition, 0.1% Ni
Above is the temperature from quenching temperature to 400-650 ° C
If the cooling rate over 100 ° C / Hr or more, quenching
Weave is obtained. Cr: 3.0 to 10.0% Cr combines with C together with Fe, Mo, V, Nb, and W,
Abrasion resistance at high temperature by forming high hardness composite carbide
Contribute to the top. Most of them are solid solution in the base and harden
And improve wear resistance. At less than 3.0%
The effect is small, and improvement of abrasion resistance cannot be expected. Meanwhile, 1
If the content exceeds 0.0%, the toughness deteriorates, so it is preferable.
Not good. Mo: 0.1 to 9.0% Mo is easily bonded to C together with Fe, Cr, V, Nb and W.
And mainly M₇C _ThreeType M₆C type, M_TwoC-type composite coal
And form a solid solution in the matrix at room temperature and
And high-temperature hardness to contribute to improvement of wear resistance. Mo is
The effect is exhibited by adding a small amount compared to W. This
If less than 0.1%, the desired wear resistance can be obtained.
On the other hand, if it exceeds 9.0%, the toughness will decrease, which is preferable.
I don't. W: 1.5 to 10.0% W is also easily C with Fe, Cr, Mo, V, and Nb.
To form composite carbides, and
It contributes to the improvement of wear resistance. Less than 1.5%
Wear resistance of the initial stage, while 10.0%
If it exceeds, the toughness decreases and the heat crack resistance deteriorates.
Let it. Also, it tends to generate macro-segregation during centrifugal casting.
Let it go. Therefore, the content is set to 10.0% or less. V, Nb: 1.5 to 10.0% in total of one or two kinds V is as easy as C with Fe, Cr, Mo, W like Nb
To form mainly MC type composite carbide,
It contributes to improvement of wear resistance by increasing temperature and high temperature hardness.
Also, this MC type composite carbide is formed in a branch shape in the thickness direction.
Therefore, plastic deformation of the matrix is suppressed, and mechanical properties and
Contributes to the improvement of crack resistance. One or two
This effect will appear if you do not add more than 1.5%
Peg. However, if the addition amount exceeds 10.0%, the toughness becomes low.
As well as macro segregation during centrifugal casting.
Easier to achieve. For this reason, it is set to 10.0% or less. Co: 0.5-10.0% Co is an important element that characterizes the present invention, and
It has a great effect on improving. Co suppresses the diffusion of C
Has a special effect on the base regardless of carbide formation.
Solid solution increases toughness and improves high temperature hardness and wear resistance.
Has the effect of improving. Co is the carbide-forming element Au.
To increase the amount of solid solution in the stain, the hardness of the matrix
And the tempering resistance increases. To expect these effects
0.5% or more is required, but exceeds 10.0%
The effect is saturated even if added by adding
Therefore, it is set to 0.5 to 10.0%. In addition, high alloy casting
Casting steel materials by centrifugal casting to produce composite rolls
In this case, the distribution of carbides tends to be non-uniform,
Need to be optimized, but the high content of Co
In the case of alloy materials, Co is used to form carbides as described above.
Irrespective of solid solution in the matrix, large non-uniformity of carbide
The above-mentioned excellent effects can be expected without compromising.

The wear-resistant cast steel material of the outer layer according to the present invention comprises the above alloy components and the balance being Fe and impurities. still,
P and S are inevitably mixed from the raw material, but are preferably as small as possible because they make the material brittle. P: 0.2% or less;
It is better to keep it below 1%. The wear-resistant cast steel material of the outer layer according to the present invention includes, in addition to the above-mentioned alloy components, one or more of Al, Ti, and Zr in the following composition range, or a material containing B. Al, Ti, Zr: 0.01 to 0.50% each Al, Ti, and Zr generate oxides in the molten metal, reduce the oxygen content in the molten metal, improve the soundness of products, Since the generated oxide acts as a crystal nucleus, it is effective in refining the solidified structure. If it is less than 0.01%, this effect is not sufficient. On the other hand, if it exceeds 0.50%, it remains as inclusions and is not preferable. A
In the present invention, l, Ti, and Zr are mainly added for improving wear resistance by refining a cast structure.
It is not simply added for the purpose of degassing. B: 0.01 to 0.50% B combines with oxygen in the molten metal to exhibit a deoxidizing effect. In addition, the effect of refining the solidification structure with the generated oxide as the nucleus,
And the effect of increasing the hardenability by B dissolved in the matrix. In the case of a casting having a large mass such as a rolling roll, it may be difficult to increase the cooling temperature, but it is easy to obtain a quenched structure due to an increase in hardenability. If it is less than 0.01, such an effect is not sufficient, while 0.50%
If it exceeds, the material becomes brittle, which is not preferable.

Next, the inner layer material of the composite roll of the present invention will be described. As the inner layer material, a material in which graphite is crystallized for the following reasons, specifically, flaky graphite cast iron (abbreviated as FC), spheroidal graphite cast iron (abbreviated as DCI), graphite steel (abbreviated as SGS)
Is used. Reason for using graphite crystallized material When rolling is used, occurrence of an overload state (for example, biting of two sheets) is inevitable, but Young's modulus of the outer layer material is 210
Since it is as high as 00 to 23000 kg / mm ² , a large stress is generated in the outer layer material. The Young's modulus of the middle layer is 20,000
２３23000 kgf / mm ² , but the layer thickness is 25-3
Since it is relatively thin, about 0 mm, if the Young's modulus of the inner layer material to be compounded is low, the load can be absorbed by the inner layer material by flattening the roll at the time of overload. Therefore, lowering the Young's modulus of the inner layer material increases safety during use. 20
In order to have a Young's modulus of less than 000 kg / mm ² , the inner layer material must be crystallized graphite. The outer layer material contains a special alloy.
Since it is cured by the secondary curing phenomenon, it is generally difficult to remove residual stress. For this reason, when the outer layer material is cured and heat-treated on the composite roll, a compression 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. If the tensile stress of the inner layer material becomes excessive, breakage of the inner layer and breakage at the boundary between the intermediate layer and the inner layer occur, leading to roll breakage. To prevent breakage, the composite roll may be subjected to strain relief annealing to release the residual stress of the inner layer material. But 60
High-temperature strain relief annealing exceeding 0 ° 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 made of graphite crystallized. In the case of the present invention, the purpose of low-temperature strain relief annealing can be achieved by tempering heat treatment of the outer layer. The roll receives heat from the rolled material (around 1000 ° C.) during use. In order to prevent thermal deformation of the roll and maintain a predetermined shape, the 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 neck of the roll must be strong enough to withstand the bending force and motor torque. Since there are shocking loads, toughness is important as well as strength. By crystallizing graphite, the toughness can be improved.

Next, the characteristics and preferred compositions (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, mixing of the high alloy component of the outer layer necessarily occurs. It is necessary to determine the composition in consideration of this point. (1) In the case of FC FC has a good castability and a Young's modulus of 10,000 to 150.
Since it is as low as 00 kg / mm ² and the morphology of graphite is flaky, it is easy to remove residual stress and the thermal conductivity is high. Also,
The workability is also good, and when used as the inner layer material of the hollow roll, the inner surface processing is easy. But strength is 30kg
/ Mm ² is the limit, so it is not suitable for a composite roll used under the condition of a large rolling load. In addition, the solidus of FC of the following composition is 1130-1170 degreeC.

Preferred examples of the composition and reasons for the 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 graphite crystallization, and if less than 0.8%, graphitization is insufficient. On the other hand, if it exceeds 2.5%, the matrix becomes brittle. Mn: 0.2 to 1.5% Mn has an effect of strengthening the matrix and preventing harm of S. 0.
If it is less than 2%, the effect can hardly be expected. on the other hand,
If it exceeds 1.5%, the material becomes brittle. P, S: each 0.2% or less P and S are impurities, and therefore the smaller the better, the better. Since the low-concentration one is expensive, the content of about 0.01% or more will be unavoidable in consideration of economy. Ni: 3.0% or less Ni is effective for graphitization and strengthening the matrix.
If it exceeds 0%, an untransformed structure tends to remain and the strength is deteriorated. Cr and Mo: 2.0% or less each Cr and Mo have a strengthening effect on the matrix, but too much inhibits the graphitization. In order 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 keep 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 inner layer material. Therefore, these elements are interpreted as impurities and are allowed up to 4% as long as the mechanical properties of the inner layer material are not deteriorated. In addition, A
When l, Ti, Zr, and B are contained, these elements are inevitably mixed into the inner layer via the intermediate layer, but are trace amounts, so that there is almost no problem in the material. In addition, Co is inevitably mixed, but is not particularly limited because Co does not deteriorate the inner layer material.

FC is, in addition to the above components, substantially the balance of Fe
Is formed. The composition range of the molten metal before welding to the intermediate layer, that is, before casting is shown below. The composition of the molten metal is determined in consideration of the amount of components mixed in from the intermediate layer so that the inner layer composition is obtained after welding. C: 2.5 to 4.0%, Si: 0.8 to 2.5% M
n: 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 in the case of Fe (2) DCI DCI has good castability and Young's modulus of 15,000 to 19
The amount of graphite is also large at 000 kg / mm ² . Furthermore, since the form of the graphite is spherical unlike FC, it has excellent strength and toughness. Also, the workability is good. Therefore, it is suitable as an inner layer material. As disclosed in JP-B-59-52930 and JP-B-59-52931, ferrite-austenite coexistence temperature range (78).
0-900 ° C), and then 200-800 ° C / Hr
The base structure becomes a two-phase mixed structure of ferrite and pearlite by a heat treatment for rapidly cooling and turning austenite into fine pearlite. This structure is particularly excellent in crack propagation and residual stress removing effect. The heat treatment for forming the two-phase mixed structure may be performed as a heat treatment before the heat treatment for curing the outer layer of the composite roll. The solid phase line of DCI having the following composition is 1130 to
1170 ° C.

Preferred examples of the composition and reasons for the limitation are shown below. C: 2.5 to 4.0%, Si: 1.3 to 3.5%,
Mn: 0.2-1.5%, 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, N
b: 4% or less in total, Mg: 0.02 to 0.1%, Co mixed from the remaining intermediate layer and components other than Fe Si, Mg The reasons for limiting the components are the same as those of FC. explain.

Si is a graphitization promoting element. DCI contains Mg for spheroidizing 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, a large amount of ferrite is precipitated, and the strength decreases. Mg has a function of spheroidizing graphite. To obtain this effect, 0.02% or more is required. On the other hand, if it exceeds 0.1%, graphitization is inhibited and casting defects are easily generated.

A preferred melt composition of DCI before welding to the outer layer is shown below. C: 2.5 to 4.0%, Si: 1.3 to 3.5%,
Mn: 0.2-1.5%, 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.
02-0.1%, balance substantially in the case of Fe (3) SGS SGS has a Young's modulus of 17000-20,000 kg / mm
² and a small amount of graphite, the residual stress is relatively difficult to remove. Further, the castability is not very good, and a large feeder or the like is required. However, the strength is 40kg / m
m ² or more and is excellent also also has excellent toughness,
It is most suitable for rolls used under severe use conditions where a large bender load or the like works. In addition, the solidus wire (S of the following composition)
(In the case of GS) is 1170 to 1250 ° C., which is higher than that of FC or DCI, so that there is an advantage that the outer layer hardly deteriorates in the heat treatment for austenitizing.

Preferred examples of the composition and reasons for the limitation are shown below. C: 1.0 to 2.3%, Si: 0.5 to 3.0%,
Mn: 0.2-1.5%, 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:
Since the reasons for limiting the components other than Co mixed from the remaining intermediate layer and substantially Fe C and Si are the same as those of FC, these two components will be described below.

C is necessary for crystallizing graphite.
If it is less than 1.0%, crystallization of graphite hardly occurs. Meanwhile, 2.
If it exceeds 3%, the shape of the graphite collapses and the strength decreases. S
i is necessary for graphitization. If it is less than 0.5%, it becomes difficult to crystallize graphite, while if it exceeds 3.0%, the matrix becomes brittle. A preferred melt 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
Below, Cr: 2.0% or less, Mo: 2.0% or less, balance substantially Fe Next, the intermediate layer will be described. The middle layer is the outer layer alloy
One of the objectives is to reduce the mixing of components into the inner layer
It is formed by itself, but it is 30kg / mm ^TwoLess than
Above strength is required. If the strength is insufficient, the outer layer and the middle
The boundary with the layer breaks and the outer layer peels off. Therefore, in the middle
High strength material even if a large amount of alloy components are mixed in from the outer layer
Need to be quality. For this reason, as an intermediate layer material
Is preferably a high carbon cast steel (abbreviated as AD) having the following composition.
Hereinafter, the composition of the intermediate layer material according to the present invention and the reasons for limitation will be described. C: 1.0 to 2.5% C contributes to strength improvement, but if it is less than 1.0%, the freezing point is low.
And welding tends to be insufficient. On the other hand, 2.5%
If it exceeds, the carbide becomes excessive and the material becomes brittle. Si: 0.2 to 3.5% Si has a function of accelerating degassing and a function of improving flowability of molten metal.
If it is less than 0.2%, such an effect cannot be expected.
If it exceeds 5%, the material becomes brittle. In the high Si region, N
Crystallization of graphite may be observed depending on the i content
However, there is no problem with the material. Mn: 0.2 to 1.5% Mn is increased for the same reason as the ductile cast iron of the inner layer material.
It is limited to the above-mentioned range. Ni: 4.0% or less Ni has an effect of strengthening the material. However, 4.0%
If it exceeds, the action is saturated and untransformed structure is likely to be generated
And the strength deteriorates. Cr, Mo: 4.0% or less for each Cr and Mo have the effect of strengthening the material. However, 4.
If it exceeds 0%, the mechanical properties will rather deteriorate.
You. W, V, Nb: 12% or less in total These elements have little effect on improving the material of the intermediate layer
However, contamination from the outer layer is inevitable. Intermediate layer material
12% allowable as long as the mechanical properties are not deteriorated
Is done. When the outer layer contains Al, Ti, Zr, and B,
These elements also inevitably enter the intermediate layer. This place
In the case of these, for the same reason, 1
2% or less. Also, Co is inevitably mixed in from the outer layer.
But do not degrade the material of the intermediate layer.
Not.

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

C: 1.0-3.5%, Si: 0.2
To 3.5%, 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, the outer layer and the inner layer (axial core) 1.0) between
Since the 2.5% C intermediate layer is provided, the harmful alloy element in the inner layer can be greatly suppressed from being directly mixed from the outer layer to the inner layer during welding, and the following effects can be obtained.

In the quenching heat treatment of the outer layer, the outer layer is preferably heated to 1100 ° C. or more for austenitizing heat treatment. However, even if the outer layer is heated to 1100 ° C. or more, heat transfer to the inner layer is performed 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,
Melting of the inner layer can be prevented. Although the concentration of Cr, Mo, W, and V in the intermediate layer is increased by welding with the outer layer, these elements are still kept lower than in the outer layer. After welding the intermediate layer, it is better to weld the intermediate layer and the inner layer,
The alloy concentration in the welded portion of the inner layer can be reduced. Therefore, when the intermediate layer is provided, a carbide layer is not easily formed at the boundary with the inner layer, and the boundary strength can be improved.

Further, most of the intermediate layer according to the present invention undergoes pearlite transformation during the quenching heat treatment of the roll, and the remainder undergoes bainite transformation. No or little martensitic transformation occurs. For this reason, there is no large expansion behavior accompanying 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 intermediate layers in combination with the martensitic transformation of the outer layer, and a correspondingly large tensile residual stress (axial direction) acts on the inner layer. And the inner layer is pulled and broken.

In the case of the composite roll of the present invention, in the case of a solid roll, usually, after the outer layer and the intermediate layer are subjected to centrifugal casting, the inner layer (axial portion) is statically cast therein. In the case of a sleeve roll, the inner layer is also centrifugally cast following the outer layer and the intermediate layer. FIG. 3 shows a horizontal centrifugal casting machine, in which a centrifugal casting mold 4 is rotatably supported by rotating rollers 5, 5, and molten metal is poured from a dam 6 via a pouring gutter 7. 4 is cast. Numeral 8 denotes a sand mold for hot water. To cast a solid composite roll, first, the outer layer material melt is cast into a rotating mold 4 and after it has solidified,
The intermediate layer material melt is cast into the inner peripheral surface of the outer layer 1 and the intermediate layer 3 is centrifugally cast. Thereafter, a mold 4 having an outer layer 1 and an intermediate layer 3 therein is erected, and upper ends for forming a shaft core are formed at both ends thereof.
What is necessary is just to form a stationary mold by connecting the lower mold, and to cast the inner layer material molten metal into the inside of the stationary mold. In the horizontal centrifugal casting device,
Since each part of the molten metal cast in the mold moves up and down with each rotation of the mold, there is a variation in G, and vibration is easily generated due to eccentricity and scratches of the rollers and the mold. The components in the molten metal are easy to move. For this reason, when casting a thick outer layer, segregation is likely to occur due to the movement of the components.
It is preferable to perform casting at a relatively low temperature by setting the solidification start temperature to about 70 ° C. or less. However, since the outer layer material according to the present invention has high abrasion resistance, it does not easily wear, and the outer layer may be relatively thin, and the casting thickness is 80 mm (preferably 55 to 70 m).
Since it is rapidly cooled by a mold up to about m), there is almost no risk of segregation even if it is cast at a temperature higher than the above temperature. still,
The thickness of the outer layer of the product is 50 mm (preferably 25 to
40 mm).

FIG. 4 shows a vertical centrifugal casting apparatus.
An upper mold 12 and a lower mold 13 are provided at the upper and lower ends of a centrifugal casting mold 11.
Are assembled, and the mold is mechanically fixed concentrically to the rotating base 14. For this reason, the outer layer material molten metal 16 cast into the mold via the dam 15 and ascending and adhering to the inner surface of the mold 11 by the action of the centrifugal force is less susceptible to fluctuations and vibrations of G. Therefore, if vertical centrifugal casting is used, segregation is unlikely to occur even when casting a thick outer layer, so that casting can be performed at a higher temperature, which is effective in improving workability and preventing casting defects due to inclusion of foreign matter. It is. In addition, centrifugal force casting mold
After fixing only the base 11 to the base 14 and casting the outer layer and the intermediate layer, the upper mold and the lower mold may be assembled, and the shaft portion may be cast by standing.

The outer layer wear-resistant cast steel material of the present invention is cast as an outer layer of a composite roll, and then the entire roll is cooled at a cooling rate of 100 ° C./Hr or more in a temperature range from a quenching temperature (austenitizing temperature) to 400 to 650 ° C. By quenching,
Good quenched structure can be obtained. Tempering is 500
It may be carried out once or several times at a temperature of -600 ° C. In the outer layer material according to the present invention, Mo, W, V, Nb and the like dissolved in the matrix during the austenitizing heat treatment precipitate as fine carbides by the tempering heat treatment, and a tempering secondary hardening phenomenon occurs. Excellent.

As a method of heating the outer layer, a method of heating the whole roll in a heating furnace, a method of disposing 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. Further, in order to avoid the melting of the inner layer of the cast iron material and heat it, 1100 ° C. (preferably 1000 ° C.)
The following heating must be stopped, and it is difficult to form a solid solution of the carbide in the matrix. Therefore, there is a problem that it is difficult to obtain a sufficient hardness 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, the outer layer can be reliably stopped at 1100 ° C. or more and the inner layer at less than 1100 ° C. Can be prevented from lowering in strength due to coarsening. In addition, since the temperature decreases 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 outer layer deeper can be increased during quenching. it can.

The composite roll of the present invention has abrasion resistance such as a hot roll, a pinch roll or a transport roller.
It is applied to rolls and rollers that require rough surface resistance. Next, specific examples of the present invention will be described. (1) For centrifugal casting molds with an inner diameter of φ1040 mm, see Table 1.
The outer layer material melt of Table 2 is centrifugally cast, and after the outer layer is completely solidified, the intermediate layer material melt of the same table is centrifugally cast,
The outer layer and the intermediate layer were welded. The casting amount is thick and the outer layer 70
mm and the intermediate layer was 25 mm.

In the examples, the sample No. 1 to No. 4 and the comparative example is Sample No. 5-No. No. 8, this is an example of Japanese Patent Application No. 3-34693. Nine conventional outer layer materials are high chromium cast iron materials having improved wear resistance.
The composition unit in the table is% by weight, and the balance is substantially Fe. (2) After the intermediate layer is completely solidified, the rotation of the mold is stopped, the mold having the outer layer and the intermediate layer is set up vertically, and the upper mold and the lower mold are connected at both ends. The inner layer material (shaft core material) shown in the same table was also cast into the interior.

[0034]

[Table 1]

[0035]

[Table 2]

(3) After the cast composite roll is roughly processed, the roll of the embodiment is uniformly preheated to 600 ° C., and then, as shown in FIG. It was rotatably supported between gas burners 21 arranged in parallel at a pitch of 250 mm along the axial direction, and the surface of the outer layer was heated while rotating the roll. The heating was stopped when the surface temperature of the outer layer reached 1170 ° C and the temperature at the center of the inner layer reached 830 ° C. The time required for heating was 300 minutes. From the heat conduction temperature data, in the case of this example, the temperature near the inner peripheral surface was estimated to be 960 ° C. On the other hand, with respect to a conventional roll, the entire roll was kept at 1050 ° C. for 5 hours to austenitize. (4) For the rolls of the example, the comparative example, and the conventional example,
After the heating was stopped, spray water cooling was immediately performed, the roll surface temperature was rapidly cooled to 500 ° C., and then left to cool to room temperature. afterwards,
Tempering heat treatment maintained at 550 ° C. for 20 hours was repeated twice. The outer layer surface hardness after the heat treatment was as shown in Table 3 below. From the table, it can be seen that the outer layers of Examples and Comparative Examples have remarkably improved hardness and excellent wear resistance as compared with those of the conventional examples. When the oxidation state of the outer layer surface was observed, the thickness of the oxide layer was significantly thinner in the example than in the conventional example.

[0037]

[Table 3]

The following experiment was conducted on the peeling and flaws of the black scale. 1. 1. High temperature wear test: Test piece (φ300 × 50), mating material SS41 (φ290 × 50) Conditions Heating temperature of partner material: 800 ° C Experiment time: 5 hours Water cooling temperature: 40 ° C Result Surface condition of the test piece-The test piece surface of the example had a beautiful glossy skin, but the test piece surface of the comparative example showed uneven adhesion and scratches on the scale, and partial peeling of the scale Was also seen.

In the conventional example, black scale peeling and flaws were remarkably observed. (5) After finishing the body surface, the welding condition was confirmed by an ultrasonic flaw detection test, and the welding was good for all rolls. Next, the roll body was cut and the cross section of the outer layer was visually observed. As a result, no segregation of components was observed in any of the rolls. Tables 4 and 5 show the results of analyzing the components at the center of the thickness of the intermediate layer and at the center of the inner layer (axial core). From the table, Examples and Comparative Examples,
It can be seen that the amount of the outer layer high alloy component mixed in the inner layer is very small in both the conventional examples.

[0040]

[Table 4]

[0041]

[Table 5]

(6) Further, a tensile test piece was collected from the inner layer of each sample and subjected to a tensile test. The results are shown in Table 4. From the table, the inner layer has the No. of the embodiment of DCI. Nos. 1, 3 and 4 have higher strength than No. 7 of the conventional example, and the conventional example shows about 20% deterioration compared to the example.

[0043]

[Table 6]

[0044]

As described above, in the composite roll of the present invention, the outer layer contains a predetermined amount of Co, and contains Cr, Mo, W,
Since it is formed of a special cast steel material containing predetermined amounts of V and Nb, the wear resistance can be remarkably improved by the presence of these high hardness composite carbides, and macro segregation hardly occurs during casting. In particular, the outer layer of the present invention has a thickness of 0.7-1.
Since the C content is as low as less than 0%, the amount of eutectic carbide crystallized at the grain boundary in the final solidification is almost eliminated. Therefore, eutectic oxides (grain-boundary carbides) that are preferentially oxidized in hot rolling, tend to thicken the black scale, and cause peeling of the black scale along with the propagation path of heat cracks by repeated heating and cooling in the hot rolling ) Is excellent in rough skin resistance. In addition, since the intermediate layer was formed from a high-carbon cast steel having a specific composition, the mixing of high alloy components from the outer layer to the inner layer can be significantly reduced, and the boundary strength can be improved,
Since no martensite transformation occurs, the residual stress does not increase, and furthermore, it is possible to prevent the inner layer from being damaged by erosion or a decrease in strength during the austenitizing heat treatment of the outer layer. In addition, since the inner layer is made of flake graphite cast iron, spheroidal graphite cast iron or graphite steel, the strength and toughness are good, and the Young's modulus can be considerably lower than that of the outer layer. It is possible to prevent excessive stress from being generated, and it is excellent in safety and accident resistance. Furthermore, since it is excellent in heat dissipation, thermal deformation hardly occurs.

[Brief description of the drawings]

FIG. 1 is a 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 sectional view of a main part of a horizontal centrifugal casting apparatus.

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 composite roll outer layer heating state.

[Explanation of symbols]

 1 outer layer 2 inner layer 3 middle layer

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiroaki Katayama 64 Nishimujimajima-cho, Amagasaki City, Hyogo Prefecture Inside Kubota Amagasaki Plant (72) Inventor Hiroyuki Kimura 64-Nishimujimajima Town, Amagasaki City, Hyogo Prefecture Inside Kubota Amagasaki Plant ( 56) References JP-A-5-132738 (JP, A) JP-A-1-208437 (JP, A) JP-A-64-31951 (JP, A) JP-A-63-213641 (JP, A) JP-A-63-157836 (JP, A) JP-A-56-62950 (JP, A) JP-A-58-193343 (JP, A) JP-A-4-66649 (JP, A) JP-A-3-64429 (JP) JP-A-5-148510 (JP, A) JP-A-5-179391 (JP, A) JP-A-5-179392 (JP, A) JP-A-5-179393 (JP, A) 5-179394 (JP, A) JP-A-5-31318 (JP, A) JP-A-2-258949 (JP, A) JP-A-62-266043 (JP, A) JP-A-2-285047 (JP, A) JP-A-57-57862 (JP, A) JP-A-5-132735 (JP) JP-A-5-31507 (JP, A) JP-A-4-141553 (JP, A) JP-A-4-197054 (JP, A) JP-B 3-28501 (JP, B2) JP-B 5-67697 (JP, B2) Special Table Hei 5-500536 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B21B 27/00 C22C 37/00 C22C 37/06

Claims (4)

(57) [Claims] 1. A composite roll comprising: an outer layer formed of a wear-resistant cast steel material; an intermediate layer welded to an inner peripheral surface of the outer layer; and an inner layer welded to an inner peripheral surface of the intermediate layer. The outer layer has a chemical composition in weight%, C: 0.7 to less than 1.0%, Si: 0.1 to 2.0.
%, Mn: 0.1 to 2.0%, Ni: 0.1 to 4.5
%, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0
%, W: 1.5 to 10.0%, V, Nb: 1.5 to 10.0% in total of one or two, Co: 0.5 to 10.0%, and the balance substantially Fe The intermediate layer has a chemical composition in weight%, C: 1.0 to 2.5%, Si: 0.2 to 3.5%, Mn: 0.2 to 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 consisting of Co and substantially Fe mixed from the outer layer, A composite roll wherein the inner layer is formed of flaky graphite cast iron, spheroidal graphite cast iron or graphite steel. 2. A composite roll comprising: an outer layer formed of a wear-resistant cast steel material; an intermediate layer welded to an inner peripheral surface of the outer layer; and an inner layer welded to an inner peripheral surface of the intermediate layer. The outer layer has a chemical composition in weight%, C: 0.7 to less than 1.0%, Si: 0.1 to 2.0.
%, Mn: 0.1 to 2.0%, Ni: 0.1 to 4.5
%, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0
%, W: 1.5 to 10.0%, V, Nb: 1.5 to 10.0% in total of one or two, Co: 0.5 to 10.0%, Al, Ti, Zr: One or more of each of 0.01 to 0.50% and the balance substantially consist of Fe. The intermediate layer has a chemical composition in weight%, C: 1.0 to 2.5%, Si : 0.2 to 3.5
%, 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: total Less than 12%,
A composite roll for steel rolling, characterized in that the balance is made of Co and substantially Fe mixed from an outer layer, and the inner layer is made of flake graphite cast iron, spheroidal graphite cast iron or graphite steel. 3. A composite roll comprising: an outer layer formed of a wear-resistant cast steel material; an intermediate layer welded to an inner peripheral surface of the outer layer; and an inner layer welded to an inner peripheral surface of the intermediate layer. The outer layer has a chemical composition in weight%, C: 0.7 to less than 1.0%, Si: 0.1 to 2.0.
%, Mn: 0.1 to 2.0%, Ni: 0.1 to 4.5
%, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0
%, W: 1.5 to 10.0%, V, Nb: 1.5 to 10.0% in total of one or two, Co: 0.5 to 10.0%, B: 0.01 to 0.
50% and the balance substantially consist of Fe. The intermediate layer has a chemical composition by weight of C: 1.0 to 2.5%, Si: 0.2 to 3.5%, 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, with the remainder mixed from the outer layer Wherein the inner layer is made of flaky graphite cast iron, spheroidal graphite cast iron or graphite steel. 4. A composite roll comprising: an outer layer formed of a wear-resistant cast steel material; an intermediate layer welded to an inner peripheral surface of the outer layer; and an inner layer welded to an inner peripheral surface of the intermediate layer. The outer layer has a chemical composition in weight%, C: 0.7 to less than 1.0%, Si: 0.1 to 2.0.
%, Mn: 0.1 to 2.0%, Ni: 0.1 to 4.5
%, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0
%, W: 1.5 to 10.0%, V, Nb: 1.5 to 10.0% in total of one or two, 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 substantially Fe
The intermediate layer has a chemical composition in weight%, C: 1.0 to 2.5%, Si: 0.2 to 3.5%, 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, with the balance of Co and A composite roll substantially comprising Fe, wherein the inner layer is formed of flake graphite cast iron, spheroidal graphite cast iron, or graphite steel.