JP2000160277A - Composite roll - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composite roll which has an outer layer excellent in wear resistance and having uniform material quality capable of preventing the occurrence of uneven wear and uneven surface roughness due to macrosegregation at roll surface. SOLUTION: This composite roll consists of an outer layer 1 formed of wear resistant cast iron material, an intermediate layer 2 welded to the inside peripheral surface of the outer layer 1, and an inner layer 3 welded to the inside peripheral surface of the intermediate layer 2, and the outer layer 1 and the intermediate layer 2 are cast centrifugally. The outer layer 1 has a chemical composition consisting of, by weight, 1.0-3.0% C, 0.1-2.0% Si, 0.1-2.0% Mn, 0.1-4.5% Ni, 3.0-10.0% Cr, 0.1-9.0% Mo, 1.5-10.0% W, 0.01-0.50% Al, 0.5-10.0% Co, 3.0-10.0%, in total, of either or both of V and Nb, and the balance essentially Fe. Further, other than these alloy components, 0.01-0.50% of Ti, Zr, and B can be incorporated into the outer layer.

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 rolling use layer formed of a wear-resistant material, or 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 in order to prevent high alloying elements from being mixed into the inner layer 2 from the outer layer 1 and prevent deterioration of the toughness of the inner layer, which occurs when the outer layer 1 and the inner layer 2 are directly welded.

Hitherto, as disclosed in JP-B-58-30382 and JP-B-61-16415, high chromium cast iron containing 10 to 25% of Cr has been known as an outer layer material having excellent wear resistance. Graphite-crystallized high chromium cast iron with improved seizure resistance is 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 types of Nb and V are added in a total of 2% or less to high chromium cast iron or graphite crystallized high chromium cast iron, 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 the circumferential direction, and it is difficult to obtain a uniform material. In view of the above technical background,
If the outer layer of the composite roll is formed of a special cast iron material containing predetermined amounts of Cr, Mo, W, V, and Nb, the presence of these high-hardness composite carbides can dramatically improve wear resistance. The inventors of the present invention have found that such an effect can be obtained, and that macro segregation is unlikely to occur during casting.

However, when the above outer layer was further studied, as described above, it was found that Cr, Mo, W, V,
Nb-containing cast iron material has a high hardness composite carbide and can dramatically improve wear resistance. However, when it is manufactured by centrifugal casting, macro segregation peculiar to centrifugal casting is performed. If this is applied to the outer layer of the composite roll and rolled, a new problem to be solved arises in that unevenness in wear and unevenness in surface roughness due to macrosegregation on the roll surface has arisen. The present invention has been made in view of such a problem, and an object of the present invention is to provide a composite roll for steel rolling and the like having an outer layer of a uniform material which has excellent wear resistance and has solved the above-mentioned problem. .

[0007]

According to the present invention, there is provided a composite roll comprising:
An outer layer formed of a 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, and the outer layer and the intermediate layer In the composite roll formed by casting, the outer layer has a chemical composition in weight% of C: 1.0 to 3.0%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Ni: 0.1 to 4.5%, Cr: 3.0%. 10.0%, Mo: 0.1 to 9.0%, W: 1.5 to 10.0%, Al: 0.01 to 0.50%, Co: 0.5 to 10.0%, V, Nb: 3.0 to 10.0% in total of one or two types, and the balance It is characterized by being substantially composed of Fe (claim 1).

In the composite roll of the present invention, each of Ti and Zr in each of the chemical composition of claim 1 is replaced with 0.01 or less of Fe.
一種 0.50% is added to one or two of them (claim 2). The invention of claim 3 further comprises B: 0.01 to 0.50 instead of part of Fe in the chemical composition of claim 2. In addition.

[0009]

The outer layer of the composite roll according to the present invention was centrifugally cast using various alloys to find the optimum composition for the outer layer of the composite roll from the viewpoint of not only wear resistance but also macrosegregation. , Mo, W, V, Nb,
By adding special elements such as Al, Ti, Zr, and B, the wear resistance was remarkably improved, and a roll outer layer material having uniform surface properties without macrosegregation could be obtained. Here, the first feature of the important operation of the present invention is that Cr, Mo,
A second characteristic feature of the present invention is that, in centrifugal casting of a cast iron material containing W, V, and Nb, the content at which abrasion resistance is dramatically improved by a high hardness composite carbide formed by these alloys is obtained. Is that Al is mainly used and alloys such as Co, Ti, Zr, and B are added so as to prevent macro segregation even in centrifugal casting.

Regarding the second point, in particular, Al which has been conventionally used only as a deoxidizing material or as a material for refining the structure of a special material is replaced by macrosegregation in centrifugal casting due to its high alloy. The macro segregation is improved by the following mechanism by containing it in a cast iron material that is easily generated. That is, Al, Co, Ti, Z
r and B combine with oxygen during melting to form an oxide, and Mo,
In addition to preventing loss of elements important for the performance of the outer layer of the present invention, such as W, V, and Nb, Cr, Mo, W, V, and Nb containing these oxides as nuclei for solidification in the molten metal at the early stage of solidification.
To form a high hardness composite carbide. As a result, a finely dispersed high hardness composite carbide is obtained, and the wear resistance is improved.

On the other hand, since the high-hardness composite carbide is smaller than the specific gravity of the molten metal, it moves to the inner surface side of the outer layer in the molten metal having a low solid fraction at the early stage of solidification, and causes macrosegregation. . When particles move through the molten metal, they receive resistance from the surroundings that is proportional to the square of the particle diameter, but the centrifugal force acting on the particles is proportional to the cube of the particle diameter. As the diameter of the composite carbide particles becomes smaller, the ratio S / V of the surface area S to the volume V of the particles becomes larger, the resistance becomes larger, the movement in the molten metal by centrifugal force becomes less likely to occur, and the macro is unique to centrifugal casting. Segregation is improved.

In the composite roll of the present invention, an intermediate layer is formed between the outer layer and the inner layer by, for example, a high-carbon cast steel having a chemical composition described later. Can be prevented 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 the carbide layer is suppressed, and the boundary strength can be improved. In addition, during the austenite heat treatment of the outer layer of the specific composition of the present invention, it is possible to prevent the temperature of the inner layer from rising, and to prevent the deterioration of the toughness of the inner layer material, while heating only the outer layer to a high temperature of 1100 ° C or more. it can. Also, if the composition of the intermediate layer as in the examples described later, martensitic transformation does not occur at the time of quenching of the outer layer, or even if it occurs in a small amount, even if subjected to a quenching heat treatment to the outer layer, excessive residual stress will occur. Without occurring
Excellent in accident resistance.

Further, when the inner layer of the embodiment described later is formed of flaky 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 reduced to about 19000 kgf / mm ² or less. It is possible to absorb the load by flattening the roll at the time of overload, thereby improving 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.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the outer layer of the composite roll of the present invention
Reasons for limiting the chemical composition of wear-resistant cast iron used for steel
Will be explained. Hereinafter, all units of the components are% by weight. C: 1.0 to 3.0% C mainly combines with Fe and Cr to form M₇C_ThreeMold height
Hard, complex carbides are formed, and Cr, Mo, V, N
b, combined with W, MC type, M₆C type, M_TwoHigh hardness such as C type
Also forms complex carbides. This high hardness composite carbide formation
Therefore, a C% of 1.0% or more is required. Meanwhile, 3.0
%, The amount of carbide increases and the material becomes brittle.
And the crack resistance deteriorates.
You. 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
 About 0.1% is inevitably contained. But 2.0%
If it exceeds, the toughness is reduced, which is not preferable. 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.
From about 0.1% is inevitably contained. But 2.0
%, It is not preferable because toughness is reduced. Ni: 0.1-4.5% 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 less than 0.1%, such effects cannot be obtained, while
If the content exceeds 4.5%, retained austenite increases.
Thus, it becomes difficult to obtain high hardness. In the case of 0.1% Ni or more,
Cooling from quenching temperature to 400-650 ℃
If the rate is 100 ° C./Hr or more, a quenched structure can be obtained. Cr: 3.0-10.0% 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. Some harden as solid solution in the base
And improve wear resistance. Below 3.0%, these effects
The result is small, and improvement of abrasion resistance cannot be expected. On the other hand, 10.0
% Is preferable because it causes deterioration of toughness.
Absent. Mo: 0.1 to 9.0% Mo easily bonds with C together with Fe, Cr, V, Nb, and W
And mainly M₇C _ThreeType M₆C type, M_TwoC-type composite coal
And harden at normal and high temperatures
Contribute to improvement. Mo is less effective than W
Demonstrate fruit. In this case, the expected wear resistance is less than 0.1%
To obtain toughness, while if it exceeds 9.0%, toughness
It is not preferable because it decreases. W: 1.5 to 10.0% W is also easy with C together with Fe, Cr, Mo, V, and Nb.
To form composite carbides, and
It contributes to the improvement of wear resistance. Less than 1.5% is expected
Wear resistance cannot be obtained, while exceeding 10.0%
And lower toughness, worsening heat crack resistance
You. In addition, it tends to generate macro-segregation during centrifugal casting.
Let Therefore, the content is set to 10.0% or less. Al: 0.01 to 0.50% Al is usually used as a "deoxidizer".
Therefore, lower the O concentration in the molten metal,
Prevents loss of easily oxidizable alloy elements such as Mo, W, and V
Stop. On the other hand, Al oxide becomes the core of solidification in the molten metal and
Fine tissue is obtained. In the case of high-speed steel, this Al oxide
MC-type charcoal is used because high-hardness MC carbides are crystallized as nuclei.
Is finely dispersed, which contributes to abrasion resistance and
S / V increases due to dispersion, and transfer due to centrifugal force.
To reduce segregation under centrifugal casting.
You.

Here, in the above formula, "S" indicates the surface area of the MC type carbide particles, and "V" indicates the volume. When the particles move through the molten metal, they receive a resistance from the surroundings that is proportional to the square of the diameter of the particles. On the other hand, since the centrifugal force is proportional to the cube of the particle diameter, the smaller the particle diameter, the more easily the centrifugal force is affected. From the above points, Al
Although almost no annual ring-shaped segregation (band-like segregation) peculiar to centrifugal force casting is recognized, if the content is less than 0.01%, such an effect is not sufficient, while if it exceeds 0.50%, the same is true.

Co: 0.5-10.0% Co is an important element characterizing the present invention, and has a great effect in improving the matrix. Co has a special effect of suppressing the diffusion of C, and has the effect of increasing the toughness by forming a solid solution in the matrix irrespective of the formation of carbides, and also improving the high-temperature hardness and wear resistance. Further, Co increases the solid solution amount of the carbide-forming element in austenite, so that the hardness of the matrix and the tempering resistance increase. To expect these effects
Although the content of 0.5% or more is necessary, even if added over 10.0%, the effect is saturated and it is an expensive element, so the content is made 0.5 to 10.0%. In addition, when casting a high alloy cast iron material by centrifugal force casting and manufacturing a composite roll,
The distribution of carbides is likely to be non-uniform, and it is necessary to optimize the casting conditions.However, in the case of the high alloy material containing Co of the present invention, Co is transferred to the base regardless of carbide formation as described above. Since the solid solution forms, the above-mentioned excellent effects can be expected without increasing the non-uniformity of the carbide.

Co also has the effect of suppressing the change of the molten metal,
It improves the deterioration of the weldability as described below when using Ti or Zr. Co is also effective in improving annual ring-shaped segregation peculiar to centrifugal casting. V, Nb: 0.3 to 10.0% in total of one or two kinds V, like Nb, easily combines with C together with Fe, Cr, Mo, and W to form mainly MC type composite carbides, and at room temperature and high temperature. Increases hardness and contributes to improvement of wear resistance.
Further, since the MC-type composite carbide is formed in a branch shape in the thickness direction, it suppresses plastic deformation of the matrix and contributes to improvement of mechanical properties and crack resistance. Such an effect is unlikely to be exhibited unless it is added alone or in combination of two or more and 3.0% or more. However, when the addition amount exceeds 10.0%, the toughness is reduced, and at the time of centrifugal casting, macro segregation is easily generated. Therefore, the content is set to 10.0% or less.

One or two kinds of Ti and Zr each of 0.01 to 0.50% Each of Ti and Al similarly forms oxides in the molten metal.
Although it has the effect of refining the solidification structure and consequently improving the annual ring-shaped segregation in centrifugal casting as with Al,
i is too strong in oxidation tendency, so that the surface of the molten metal is oxidized before centrifugal force casting to deteriorate castability, or the inner surface of the rotating outer layer is oxidized after centrifugal force casting, and the intermediate layer Alternatively, the weldability with the inner layer deteriorates. For this reason, it is necessary to use it together with Al for the purpose of refining the structure and improving annual ring segregation.

Zr is the same as Ti, and is used together with Al. As described above, Ti and Zr are required to exhibit the above effects.
At least 0.01 to 0.50% of each is required. B: 0.01 to 0.50% B combines with oxygen in the molten metal to exhibit a deoxidizing effect. In addition, there is an effect of refining a solidified structure with the generated oxide as a nucleus, and contributes to improvement of annual ring-shaped segregation like Al. In addition, it has an effect of increasing hardenability due to 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 a hardened structure is easily obtained due to an increase in hardenability. If it is less than 0.01, such effects are not sufficient, while if it exceeds 0.50%, the agent becomes brittle, which is not preferable.

In the wear-resistant cast iron material of the outer layer of the present invention, the remainder is formed of Fe and impurities in addition to the above alloy components. still,
P and S are inevitably mixed in from the raw material, but are preferably as small as possible because the material becomes brittle. P: 0.2% or less, S: 0.1%
It is better to stop below. 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 reason, specifically, flaky graphite cast iron (F
C), spheroidal graphite cast iron (abbreviated as DCI), and graphite steel (abbreviated as SGS). When using rolling, the occurrence of an overload condition (for example, biting of two plates) is inevitable, but the Young's modulus of the outer layer material is 21000.
Since it is as high as 223000 kgf / mm ² , a large stress is generated in the outer layer material. Young's modulus of middle class is 20000 ~ 23000kg
It is a f / mm ^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, at the time of overload, absorbing the load towards the inner layer member by flattening the roll I can do it. Therefore, it is better to lower the Young's modulus of the inner layer material.
Increase safety during use. In order to obtain a Young's modulus of less than 20000 kgf / mm ² , the inner layer material must be crystallized graphite. The outer layer material contains a special alloy.
Since it is hardened by the secondary hardening phenomenon, it is generally difficult to remove residual stress. For this reason, when the outer 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 material. If the tensile stress of the inner layer material is excessive, breakage of the inner layer and breakage at the boundary between the intermediate layer and the inner layer occur, leading to breakage of the roll. To prevent fracture, 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 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 rolls and maintain the required 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 preferable 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 together, the incorporation of a high alloy component in the outer layer necessarily occurs. It is necessary to determine the composition in consideration of this point. (1) In case of FC FC has good castability and Young's modulus is 10,000-15000kgf.
/ Mm ² and the morphology of graphite is easy to remove residual stress and high in thermal conductivity. Also, the workability is 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 kgf / mm ² , it is not suitable for a composite roll used under the condition of a large rolling load. The solidus of FC 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% 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 effect of strengthening the matrix and preventing the harm of S. 0.2
%, The effect is hardly 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 ones are 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 of the matrix.
%, The untransformed structure tends to remain, and the strength is deteriorated. Cr and Mo: 2.0% or less each Cr and Mo have the effect of strengthening the matrix, but too much inhibits the graphitization. In order to strengthen the base, it is desirable to add 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.

The total of W, V and Nb is 4.0% or less. These elements are inevitably mixed from the outer layer. W, V,
Nb 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 they do not degrade the mechanical properties of the inner layer material. Although the outer layer material of the present invention contains Al, Co, Ti, Zr, and B, these elements are inevitably mixed into the inner layer via the intermediate layer, but are trace amounts. It doesn't matter.

FC is, in addition to the above components, substantially the balance of Fe
It is formed by The composition range of the molten metal before welding to the intermediate layer, that is, before casting is shown below. The molten metal composition is mixed with the components from the intermediate layer so that the above-mentioned inner layer composition is obtained after welding.
The amount is determined in consideration of the amount. 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 a Young's modulus of 15,000 to 19,000 k.
gf / mm ² and a large amount of graphite. Furthermore, since the form of the graphite is spherical unlike the FC, the graphite 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 (780 to 900
(° C.), rapidly cooled at 200 to 800 ° C./Hr, and heat-treated to make austenite fine pearlite, whereby the matrix structure becomes a two-phase mixed structure of ferrite and pearlite. This structure is particularly excellent in crack growth and in removing residual stress. 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 solidus 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 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: 0.02-0.1
%, And the balance The other components are substantially the same as those of FC except for FeSi and Mg.

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. Meanwhile, 3.5%
If it exceeds, the matrix becomes brittle, a large amount of ferrite is precipitated, and the strength decreases. Mg has a function of spheroidizing graphite. 0.02% or more is required to obtain the effect. 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 exemplified 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 in the case of Fe (3) SGS SGS has a high Young's modulus of 17,000 to 20,000 kgf / mm ² and a small amount of graphite, so that residual stress is relatively difficult to remove. Also, the castability is not very good, and a large feeder or the like is required. However, it has an excellent strength of 40 kgf / mm ² or more and is excellent in toughness, so it is most suitable for rolls used under severe operating conditions where a large bender load is applied. In addition, solid-phase wire (SG of the following composition)
(In the case of S) is 1170 to 1250 ° C., which is higher than that of FC and DCI.

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 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, and Nb are 4.0% or less in total, and the balance is substantially the same as that for FC except for Fe C and Si. Therefore, these two components will be described.

C is necessary for crystallizing graphite.
If it is less than 1.0%, crystallization of graphite hardly occurs. Meanwhile, 2.3%
If the ratio exceeds the above, the graphite shape is broken and the strength is reduced. Si is necessary for graphitization. If it is less than 0.5%, graphite crystallization becomes difficult, 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, Cr: 2.0% or less, Mo: 2.0% or less, balance substantially Fe Next, an intermediate layer used in the embodiment of the present invention will be exemplified.
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 has a thickness of 30%.
A strength of about kgf / mm ² or more is required. If the strength is insufficient, the boundary between the outer layer and the intermediate layer breaks, and the outer layer peels off. Therefore, the intermediate layer needs to be made of a material having high strength even if a large amount of alloy components are mixed in from the outer layer. For this reason, a high carbon cast steel (abbreviated as AD) having the following composition is suitable as the intermediate layer material. Hereinafter, the composition of the intermediate layer material suitable for use in the embodiment of the present invention and the reason for limitation will be described. C: 1.0 to 2.5% C contributes to the improvement of the strength, but if it is less than 1.0%, the freezing point increases, and the welding tends to be insufficient. On the other hand, if it exceeds 2.5%, the amount of carbides becomes excessive and the material becomes brittle. Si: 0.2 to 3.0% Si has a function of accelerating degassing and a function of improving flowability of molten metal.
If it is less than 0.2%, such effects cannot be expected, while 3.0%
If it exceeds, the material becomes brittle. In the high Si region, crystallization of graphite may be observed depending on the Ni content, but there is no problem with the 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 effect of strengthening the material. However, when the content exceeds 4.0%, the effect is saturated and an untransformed structure is apt to be generated, and the strength is deteriorated. Cr and Mo: 4.0% or less each Cr and Mo have an effect of strengthening the material. But 4.0
%, The mechanical properties deteriorate rather. W, V, Nb: 12% or less in total These elements have little effect on improving the material of the intermediate layer, but mixing from the outer layer is inevitable. Up to 12% is allowed as long as the mechanical properties of the intermediate layer material are not deteriorated. In addition, Al, Co, Ti, Zr, B
, These elements inevitably also enter the intermediate layer. In this case, for the same reason, the total is 12% or less including these elements.

The components of the intermediate layer material are, in addition to the components described above, the remainder substantially formed 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 embodiment of the present invention, it is preferable that both P and S be 0.2% or less as in the case of the inner layer material. 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 components mixed in 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 In the embodiment of the present invention, the balance is substantially between the outer layer and the inner layer (axial portion).
Since the intermediate layer of 1.0 to 2.5% C is provided, the harmful alloy element in the inner layer can be significantly 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, it is preferable to heat the outer layer 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. Since the heat treatment is performed, the temperature of the inner layer can be easily suppressed to 1100 ° C. or less by adjusting the amount of heat, and the melting of the inner layer can be prevented. The intermediate layer has a higher concentration of Cr, Mo, W, V, and Nb due to welding with the outer layer, but since these elements are still kept lower than the outer layer,
Welding the intermediate layer and the inner layer after welding the outer layer and the intermediate layer can lower the alloy concentration at the welded portion of the inner layer than when directly welding the outer layer and the inner layer. 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 embodiment of the present invention undergoes pearlite transformation during the quenching heat treatment of the roll,
Further, the rest 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 does not increase. When a large amount of martensitic transformation occurs, it is combined with the martensitic transformation of the outer layer, and a large compressive residual stress (axial direction) acts on the outer and intermediate layers, and a correspondingly large residual tensile stress (axial direction) acts on the inner layer. And the inner layer is pulled and broken.

[0036]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the case of a composite roll of the present invention, in the case of a solid roll, usually, an outer layer and an intermediate layer are subjected to centrifugal casting, and then an 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 fed from a dam 6 via a pouring gutter 7 to a mold. Cast into 4 Numeral 8 denotes a sand mold for hot water.
To cast a solid composite roll, first, the molten outer layer material is cast into a rotating mold 4, and after it has solidified, the outer layer material is cast.
The intermediate layer material melt is cast into the inner peripheral surface of 1 and the intermediate layer 3 is centrifugally cast. Thereafter, a mold 4 having an outer layer 1 and an intermediate layer 3 is erected, and an upper mold and a lower mold for forming a shaft core portion are connected at both ends thereof to form a stationary mold. What is necessary is just to cast a molten metal. In the horizontal centrifugal casting apparatus, since each part of the molten metal cast in the mold moves up and down every time the mold rotates, there is a variation in G, and vibration is caused by eccentricity and scratches of the rollers and the mold. It is easy to occur and the components in the cast outer layer material melt are easy to move. For this reason, when casting a thick outer layer,
Since the segregation is likely to occur due to the movement of the components, it is usually preferable to perform the casting at a relatively low temperature at a solidification starting temperature of about + 70 ° C. or less. However, since the outer layer material according to the present invention is a highly wear-resistant material, it is difficult to wear, and the outer layer may be relatively thin,
Up to a casting thickness of about 80 mm (preferably 55 to 70 mm), it is rapidly cooled by a mold, so that there is almost no risk of segregation even when casting at a temperature higher than the above temperature. The product outer layer thickness 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 assembled at the upper and lower ends of a centrifugal casting mold 11, and the mold is mechanically fixed concentrically to a 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 centrifugal force is less susceptible to fluctuations and vibrations of G. Therefore, if vertical centrifugal casting is used, segregation hardly occurs even when casting a thick outer layer, so that casting can be performed at a higher temperature. It is. It is needless to say that only the centrifugal force casting mold 11 may be fixed to the base 14, the outer layer and the intermediate layer may be cast, the upper mold and the lower mold may be assembled, and the shaft portion may be statically cast.

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

As a method for heating the outer layer, a method in which the entire roll is put into a heating furnace to heat, a method in which an induction heating coil and a number of gas burners are arranged around the outer peripheral surface of the outer layer, and only the outer layer is rapidly heated by these. There is. In the former case, it takes time to raise the temperature, a thick oxide film is formed on the surface of the outer layer, and the yield of the outer layer decreases. Furthermore, to avoid melting of the inner layer of the cast iron material and heat it, it is necessary to stop heating at 1100 ° C (preferably 1000 ° C) or less, which makes it difficult to form a solid solution of carbides in the matrix. There is a problem that it is difficult to obtain sufficient hardness by the subsequent heat treatment. On the other hand, according to the heating method of only the outer layer, coupled with the formation of the intermediate layer,
Since the outer layer can be reliably stopped at 1100 ° C. or higher and the inner layer can be stopped at less than 1100 ° C., it is possible to prevent partial melting of the inner layer and reduction in strength due to coarsening of crystal grains. In addition, since the temperature decreases toward the center of the inner layer (axial portion), 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 may be any type of hot rolled or cold rolled roll, such as a roll for rolling equipment and a pinch roll for ancillary equipment or a roller for conveying rolled material.
Applied to rolls and rollers that require abrasion resistance.
The rolled material includes not only steel and non-ferrous metals but also non-metals. [Specific Examples] (1) The melt of the outer layer material shown in Table 1 was centrifugally cast in a centrifugal casting mold having an inner diameter of 1040 mm, and after the outer layer was completely solidified, the melt of the intermediate layer material shown in the same table was continuously cast. The outer layer and the intermediate layer were welded by centrifugal casting. Casting thickness is 70mm for outer layer, middle layer
25 mm. In the examples, samples Nos. 1 to 6 and No. 7
The outer layer material of No. 7 is a high chromium cast iron material with improved wear resistance, and the outer layer material of document No. 7 does not contain Al. The composition unit in the table is% by weight, and the balance is substantially Fe. (2) Wait until the intermediate layer is completely solidified, stop the rotation of the mold, stand the mold with the outer layer and the middle layer inside vertically, and connect the upper mold and lower mold at both ends. The inner layer material (shaft core material) shown in the same table was also cast into the interior.

[0041]

[Table 1]

(3) After roughing the cast composite roll, the roll of the embodiment was uniformly preheated to 600 ° C., and then, as shown in FIG. It was rotatably supported between gas burners 21 arranged in parallel at 250 mm pitch along the axial direction, and the surface of the outer layer was heated while rotating the roll. Heating was stopped when the outer layer surface temperature reached 1170 ° C and the temperature at the center of the inner layer reached 830 ° C. The time required for heating was 300 minutes. Based on the heat conduction temperature data, in this case, the temperature near the outer peripheral surface of the inner layer was estimated to be 960 ° C. On the other hand, with respect to the conventional roll, the entire roll was kept at 1050 ° C. for 5 hours to austenitize. (4) For the rolls of the examples and the conventional example, after stopping the heating, spray water cooling was immediately performed, and the roll surface temperature was set to 500 ° C.
And then allowed to cool to room temperature. Then at 550 ° C for 20
The tempering heat treatment for keeping the time was repeated twice. The outer layer surface hardness after the heat treatment was as shown in Table 2 below. From the table, it can be seen that the outer layer of the example has remarkably improved hardness and excellent abrasion resistance as compared with that of the conventional example. still,
Observation of the oxidation state of the outer layer surface revealed that the thickness of the oxide layer was about 0.5 mm in the example and about 3.0 mm in the conventional example.

[0043]

[Table 2]

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

[0045]

[Table 3]

(6) The outer layer material was cut out from the excess length at the trunk end, and the base hardness (micro Vickers hardness) and the high temperature hardness (Vickers hardness) were measured. As a result, as shown in Table 4, both the base hardness and the high-temperature hardness are excellent as compared with the conventional example, and it is desirable that the material is desirable as the outer layer material of the composite roll in terms of abrasion resistance and skin roughness resistance. I understand. In particular, it has been found that the roll is suitable as an outer layer material of a hot rolling roll having a large heat load, particularly a hot thin roll rolling roll in the steel industry. Table 4 shows the reduction rate of the high-temperature hardness at 600 ° C. [(high-temperature hardness at 600 ° C.) / Normal-temperature hardness × 100].

[0047]

[Table 4]

Further, Table 5 shows the specific wear amount in the Ogoshi type abrasion test on the basis of the high chromium cast iron material (Sample 7). Samples 1 to 6 show good wear resistance. .

[0049]

[Table 5]

[0050]

As described above, in the composite roll of the present invention, the outer layer is formed of Cr, Mo, W, V, Nb, Co and Al.
By using a special cast iron material having a specific chemical composition obtained by adding a predetermined amount of a special element such as, a remarkable effect was exhibited when used as a roll material. That is, Cr, Mo, W,
The outer layer cast iron material of the composite roll containing V and Nb has a high hardness composite carbide and can dramatically improve wear resistance. However, when manufactured by centrifugal casting, it is unique to centrifugal casting. Macrosegregation occurs, and when applied to the outer layer of the composite roll and subjected to rolling, there is a problem that unevenness in wear and surface roughness due to macrosegregation on the roll surface can be caused. From the viewpoint of not only wear properties but also macro-segregation, the optimum composition as the outer layer of the composite roll is searched for and centrifugal casting experiments are conducted by combining various alloys, and by adding special elements such as Al, the wear resistance is dramatically improved. It was possible to provide a roll outer layer material having improved and uniform surface properties without macro segregation.

Particularly important points of the present invention are that Cr, Mo,
In centrifugal casting of a cast iron material containing W, V, Nb,
The content in which abrasion resistance was significantly improved by the high hardness composite carbides formed by these alloys was determined, and Co, Ti, Zr, and Al were mainly used to prevent macrosegregation even in centrifugal casting. A remarkable effect was obtained in that an alloy such as B was added. By the way, if we explain the latter,
Macro segregation by including Al, which was conventionally used only as a deoxidizing material or as a material for refining the structure of special materials, in a cast iron material that tends to cause macro segregation in centrifugal casting due to its high alloy. Is improved.

That is, Al, Co, Ti, Zr, and B are engaged with oxygen in the molten metal to form oxides, and Mo, W, V, Nb
In addition to preventing the loss of elements important for the performance of the outer layer of the present invention, it is also possible to form a high hardness composite carbide of Cr, Mo, W, V, Nb with these oxides as nuclei of solidification in the molten metal at the early stage of solidification. Form. As a result, a finely dispersed high hardness composite carbide is obtained, and the wear resistance is improved.

[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

────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] February 7, 2000 (2000.2.7)

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Full text

[Correction method] Change

[Correction contents]

[Document Name] Statement

[Title of the Invention] Composite roll

[Claims]

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 rolling use layer formed of a wear-resistant material, or 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 in order to prevent high alloying elements from being mixed into the inner layer 2 from the outer layer 1 and prevent deterioration of the toughness of the inner layer, which occurs when the outer layer 1 and the inner layer 2 are directly welded.

Hitherto, as disclosed in JP-B-58-30382 and JP-B-61-16415, high chromium cast iron containing 10 to 25% of Cr has been known as an outer layer material having excellent wear resistance. Graphite-crystallized high chromium cast iron with improved seizure resistance is 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 types of Nb and V are added in a total of 2% or less to high chromium cast iron or graphite crystallized high chromium cast iron, 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 the circumferential direction, and it is difficult to obtain a uniform material. In view of the above technical background,
If the outer layer of the composite roll is formed of a special cast iron material containing predetermined amounts of Cr, Mo, W, V, and Nb, the wear resistance can be drastically improved due to the presence of these high hardness composite carbides. The present inventors have found that macro segregation is less likely to occur during casting, and have obtained a certain effect.

However, when the above outer layer was further studied, as described above, it was found that Cr, Mo, W, V,
Nb-containing cast iron material has a high hardness composite carbide and can dramatically improve wear resistance. However, when it is manufactured by centrifugal casting, macro segregation peculiar to centrifugal casting is performed. If this is applied to the outer layer of the composite roll and rolled, a new problem to be solved arises in that unevenness in wear and unevenness in surface roughness due to macrosegregation on the roll surface has arisen. The present invention has been made in view of such a problem, and an object of the present invention is to provide a composite roll for steel rolling and the like having an outer layer of a uniform material which has excellent wear resistance and has solved the above-mentioned problem. .

[0007]

According to the present invention, there is provided a composite roll comprising:
An outer layer formed of a 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, and the outer layer and the intermediate layer In the composite roll formed by casting, the outer layer has a chemical composition in weight% of C: 1.0 to 3.0%, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Ni: 0.1 to 4.5%, Cr: 3.0%. 10.0%, Mo: 0.1 to 9.0%, W: 1.5 to 10.0%, Al: 0.01 to 0.50%, Co: 0.5 to 10.0%, V, Nb: 3.0 to 10.0% in total of one or two types, and the balance It is characterized by being substantially composed of Fe (claim 1).

In the composite roll of the present invention, each of Ti and Zr in each of the chemical composition of claim 1 is replaced with 0.01 or less of Fe.
一種 0.50% is added to one or two of them (claim 2). The invention of claim 3 further comprises B: 0.01 to 0.50 instead of part of Fe in the chemical composition of claim 2. In addition.

[0009]

The outer layer of the composite roll according to the present invention was centrifugally cast using various alloys to find the optimum composition for the outer layer of the composite roll from the viewpoint of not only wear resistance but also macrosegregation. , Mo, W, V, Nb,
By adding special elements such as Al, Ti, Zr, and B, the wear resistance was remarkably improved, and a roll outer layer material having uniform surface properties without macrosegregation could be obtained. Here, the first feature of the important operation of the present invention is that Cr, Mo,
A second characteristic feature of the present invention is that, in centrifugal casting of a cast iron material containing W, V, and Nb, the content at which abrasion resistance is dramatically improved by a high hardness composite carbide formed by these alloys is obtained. Is that Al is mainly used and alloys such as Co, Ti, Zr, and B are added so as to prevent macro segregation even in centrifugal casting.

Regarding the second point, in particular, Al which has been conventionally used only as a deoxidizing material or as a material for refining the structure of a special material is replaced by macrosegregation in centrifugal casting due to its high alloy. The macro segregation is improved by the following mechanism by containing it in a cast iron material that is easily generated. That is, Al, Co, Ti, Z
r and B combine with oxygen during melting to form an oxide, and Mo,
In addition to preventing loss of elements important for the performance of the outer layer of the present invention, such as W, V, and Nb, Cr, Mo, W, V, and Nb containing these oxides as nuclei for solidification in the molten metal at the early stage of solidification.
To form a high hardness composite carbide. As a result, a finely dispersed high hardness composite carbide is obtained, and the wear resistance is improved.

On the other hand, since the high-hardness composite carbide is smaller than the specific gravity of the molten metal, it moves to the inner surface side of the outer layer in the molten metal having a low solid fraction at the early stage of solidification, and causes macrosegregation. . When particles move through the molten metal, they receive resistance from the surroundings that is proportional to the square of the particle diameter, but the centrifugal force acting on the particles is proportional to the cube of the particle diameter. As the diameter of the composite carbide particles becomes smaller, the ratio S / V of the surface area S to the volume V of the particles becomes larger, the resistance becomes larger, the movement in the molten metal by centrifugal force becomes less likely to occur, and the macro is unique to centrifugal casting. Segregation is improved.

In the composite roll of the present invention, an intermediate layer is formed between the outer layer and the inner layer by, for example, a high-carbon cast steel having a chemical composition described later. Can be prevented 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 the carbide layer is suppressed, and the boundary strength can be improved. In addition, during the austenite heat treatment of the outer layer of the specific composition of the present invention, it is possible to prevent the temperature of the inner layer from rising, and to prevent the deterioration of the toughness of the inner layer material, while heating only the outer layer to a high temperature of 1100 ° C or more. it can. Also, if the composition of the intermediate layer as in the examples described later, martensitic transformation does not occur at the time of quenching of the outer layer, or even if it occurs in a small amount, even if subjected to a quenching heat treatment to the outer layer, excessive residual stress will occur. Without occurring
Excellent in accident resistance.

Further, when the inner layer of the embodiment described later is formed of flaky 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 reduced to about 19000 kgf / mm ² or less. It is possible to absorb the load by flattening the roll at the time of overload, thereby improving 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.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the outer layer of the composite roll of the present invention
Reasons for limiting the chemical composition of wear-resistant cast iron used for steel
Will be explained. Hereinafter, all units of the components are% by weight. C: 1.0 to 3.0% C mainly combines with Fe and Cr to form M₇C_ThreeMold height
Hard, complex carbides are formed, and Cr, Mo, V, N
b, combined with W, MC type, M₆C type, M_TwoHigh hardness such as C type
Also forms complex carbides. This high hardness composite carbide formation
Therefore, a C% of 1.0% or more is required. Meanwhile, 3.0
%, The amount of carbide increases and the material becomes brittle.
And the crack resistance deteriorates.
You. 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
 About 0.1% is inevitably contained. But 2.0%
If it exceeds, the toughness is reduced, which is not preferable. 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.
From about 0.1% is inevitably contained. But 2.0
%, It is not preferable because toughness is reduced. Ni: 0.1-4.5% 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 less than 0.1%, such effects cannot be obtained, while
If the content exceeds 4.5%, retained austenite increases.
Thus, it becomes difficult to obtain high hardness. In the case of 0.1% Ni or more,
Cooling from quenching temperature to 400-650 ° C
If the rate is 100 ° C./Hr or more, a quenched structure can be obtained. Cr: 3.0-10.0% 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. Some harden as solid solution in the base
And improve wear resistance. Below 3.0%, these effects
The result is small, and improvement of abrasion resistance cannot be expected. On the other hand, 10.0
% Is preferable because it causes deterioration of toughness.
Absent. Mo: 0.1 to 9.0% Mo easily bonds with C together with Fe, Cr, V, Nb, and W
And mainly M₇C _ThreeType M₆C type, M_TwoC-type composite coal
And harden at normal and high temperatures
Contribute to improvement. Mo is less effective than W
Demonstrate fruit. In this case, the expected wear resistance is less than 0.1%
To obtain toughness, while if it exceeds 9.0%, toughness
It is not preferable because it decreases. W: 1.5 to 10.0% W is also easy with C together with Fe, Cr, Mo, V, and Nb.
To form composite carbides, and
It contributes to the improvement of wear resistance. Less than 1.5% is expected
Wear resistance cannot be obtained, while exceeding 10.0%
And lower toughness, worsening heat crack resistance
You. In addition, it tends to generate macro-segregation during centrifugal casting.
Let Therefore, the content is set to 10.0% or less. Al: 0.01 to 0.50% Al is usually used as a "deoxidizer".
Therefore, lower the O concentration in the molten metal,
Prevents loss of easily oxidizable alloy elements such as Mo, W, and V
Stop. On the other hand, Al oxide becomes the core of solidification in the molten metal and
Fine tissue is obtained. In the case of high-speed steel, this Al oxide
MC-type charcoal is used because high-hardness MC carbides are crystallized as nuclei.
Is finely dispersed, which contributes to abrasion resistance and
S / V increases due to dispersion, and transfer due to centrifugal force.
To reduce segregation under centrifugal casting.
You.

Here, in the above formula, "S" indicates the surface area of the MC type carbide particles, and "V" indicates the volume. When the particles move through the molten metal, they receive a resistance from the surroundings that is proportional to the square of the diameter of the particles. On the other hand, since the centrifugal force is proportional to the cube of the particle diameter, the smaller the particle diameter, the more easily the centrifugal force is affected. From the above points, Al
Although almost no annual ring-shaped segregation (band-like segregation) peculiar to centrifugal force casting is recognized, if the content is less than 0.01%, such an effect is not sufficient, while if it exceeds 0.50%, the same is true.

Co: 0.5-10.0% Co is an important element characterizing the present invention, and has a great effect in improving the matrix. Co has a special effect of suppressing the diffusion of C, and has the effect of increasing the toughness by forming a solid solution in the matrix irrespective of the formation of carbides, and also improving the high-temperature hardness and wear resistance. Further, Co increases the solid solution amount of the carbide-forming element in austenite, so that the hardness of the matrix and the tempering resistance increase. To expect these effects
Although the content of 0.5% or more is necessary, even if added over 10.0%, the effect is saturated and it is an expensive element. In addition, when casting a high alloy cast iron material by centrifugal force casting and manufacturing a composite roll,
The distribution of carbides is likely to be non-uniform, and it is necessary to optimize the casting conditions.However, in the case of the high alloy material containing Co of the present invention, Co is transferred to the base regardless of carbide formation as described above. Since the solid solution forms, the above-mentioned excellent effects can be expected without increasing the non-uniformity of the carbide.

Co also has the effect of suppressing the change of the molten metal,
It improves the deterioration of the weldability as described below when using Ti or Zr. Co is also effective in improving annual ring-shaped segregation peculiar to centrifugal casting. V, Nb: 0.3 to 10.0% in total of one or two kinds V, like Nb, easily combines with C together with Fe, Cr, Mo, and W to form mainly MC type composite carbides, and at room temperature and high temperature. Increases hardness and contributes to improvement of wear resistance.
Further, since the MC-type composite carbide is formed in a branch shape in the thickness direction, it suppresses plastic deformation of the matrix and contributes to improvement of mechanical properties and crack resistance. Such an effect is unlikely to appear unless added alone or in combination of two or more to 3.0% or more. However, when the addition amount exceeds 10.0%, the toughness is reduced, and at the time of centrifugal casting, macro segregation is easily generated. Therefore, the content is set to 10.0% or less.

One or two kinds of Ti and Zr each of 0.01 to 0.50% Each of Ti and Al similarly forms oxides in the molten metal.
Although it has the effect of refining the solidification structure and consequently improving the annual ring-shaped segregation in centrifugal casting as with Al,
i is too strong in oxidation tendency, so that the surface of the molten metal is oxidized before centrifugal force casting to deteriorate castability, or the inner surface of the rotating outer layer is oxidized after centrifugal force casting, and the intermediate layer Alternatively, the weldability with the inner layer deteriorates. For this reason, it is necessary to use it together with Al for the purpose of refining the structure and improving annual ring segregation.

Zr is the same as Ti, and is used together with Al. As described above, Ti and Zr are required to exhibit the above effects.
At least 0.01 to 0.50% of each is required. B: 0.01 to 0.50% B combines with oxygen in the molten metal to exhibit a deoxidizing effect. In addition, there is an effect of refining a solidified structure with the generated oxide as a nucleus, and contributes to improvement of annual ring-shaped segregation like Al. In addition, it has an effect of increasing hardenability due to 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 a hardened structure is easily obtained due to an increase in hardenability. Such effects are not sufficient at less than 0.01, whereas more than 0.50%, the wood
The quality becomes brittle, which is not preferable.

In the wear-resistant cast iron material of the outer layer of the present invention, the remainder is formed of Fe and impurities in addition to the above alloy components. still,
P and S are inevitably mixed in from the raw material, but are preferably as small as possible because the material becomes brittle. P: 0.2% or less, S: 0.1%
It is better to stop below. 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 reason, specifically, flaky graphite cast iron (F
C), spheroidal graphite cast iron (abbreviated as DCI), and graphite steel (abbreviated as SGS). When using rolling, the occurrence of an overload condition (for example, biting of two plates) is inevitable, but the Young's modulus of the outer layer material is 21000.
Since it is as high as 223000 kgf / mm ² , large stress is generated in the outer layer material. The Young's modulus of the middle layer is 20000-23000kgf / mm ²
However, since the layer thickness is relatively thin, about 25 to 30 mm, if the Young's modulus of the inner layer material to be composited 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. For a Young's modulus of less than 20000 kgf / 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. Therefore, when the composite roll is subjected to a heat treatment for curing the outer layer material, 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 is excessive, breakage of the inner layer and breakage at the boundary between the intermediate layer and the inner layer occur, leading to breakage of the roll.

In order to prevent breakage, 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 made of graphite crystallized. In the case of the present invention, the purpose of the 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, characteristics and preferable compositions (unit: wt%) of various inner layer materials forming the inner layer of the composite roll will be described. As described above, it is necessary that the inner layer contains graphite, but when the outer layer and the inner layer are welded, mixing of a high alloy component of the outer layer necessarily occurs. It is necessary to determine the composition in consideration of this point. (1) In case of FC FC has good castability and Young's modulus of 10,000 to 15,000 kgf /
Since it is as low as ² mm2 and the morphology of graphite is flaky, removal of residual stress is easy and thermal conductivity is high. Also, the workability is 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 kgf / mm ² , it is not suitable for a composite roll used under the condition of a large rolling load. The solid phase line of FC having the following composition is 1130
~ 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 effect of strengthening the matrix and preventing harm of S. 0.2
%, The effect is hardly 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 low-grade ones are expensive,
Considering economy, the content of about 0.01% or more will be inevitable.

Ni: 3.0% or less Ni is effective for graphitization and strengthening of the matrix.
%, The 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 graphitization. In order to make 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.

The total of W, V and Nb is 4.0% or less. 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. Although the outer layer material of the present invention contains Al, Co, Ti, Zr, and B,
These elements are inevitably mixed into the inner layer via the intermediate layer, but since they are trace amounts, they hardly cause a problem in the 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 the 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 a Young's modulus of 15,000 to 19000 kgf.
/ Mm ^2, which is high in graphite content. Further, the form of the graphite is
Unlike FC, since it is spherical, it has excellent strength and toughness. Also, the workability is good. Therefore, it is suitable as an inner layer material. In addition, Japanese Patent Publication No. 59-52930,
As disclosed in Japanese Unexamined Patent Publication No. 59-52931, after heating and holding in a ferrite-austenite coexisting temperature range (780 to 900 ° C), the steel is rapidly cooled at 200 to 800 ° C / Hr, and a heat treatment for turning austenite into fine pearlite is performed. The structure is a two-phase mixed structure of ferrite and pearlite.

This structure is particularly excellent in the effect of crack propagation and the effect of removing residual stress. The heat treatment of the two-phase mixed texture is as follows:
What is necessary is just to perform as a heat treatment before hardening heat treatment of the outer layer of a composite roll. The solidus 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 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: 0.02-0.1
%, And the balance The other components are substantially the same as those of FC except for FeSi and Mg.

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. 0.02% or more is required to obtain the effect.
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 described 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 in the case of Fe (3) SGS SGS has a high Young's modulus of 17,000 to 20,000 kgf / mm ² ,
Further, since the amount of graphite is small, the residual stress is relatively difficult to remove. Also, the castability is not very good, and a large feeder or the like is required. However, since the strength is as excellent as 40 kgf / mm ² or more and the toughness is also excellent, it is most suitable for a roll used under severe use conditions in which a large bender load is applied. In addition, the solid phase line (in the case of SGS having the following composition)
Since the temperature is 1170 to 1250 ° C., which is higher than that of FC or DCI, there is an advantage that the outer layer hardly deteriorates in the heat treatment for austenitizing.

Preferred composition examples and the 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, and Nb are 4.0% or less in total, and the balance is substantially the same as that of FC except for Fe C and Si.

C is necessary for crystallizing graphite.
If it is less than 1.0%, crystallization of graphite hardly occurs. Meanwhile, 2.3%
If the ratio exceeds the above, the graphite shape is broken and the strength is reduced. Si is necessary for graphitization. If it is less than 0.5%, graphite crystallization becomes difficult, 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, Cr: 2.0% or less, Mo: 2.0% or less Next, the intermediate layer used in the embodiment of the present invention will be exemplified.
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 has a thickness of 30%.
A strength of about kgf / mm ² or more is required. If the strength is insufficient, the boundary between the outer layer and the intermediate layer breaks, and the outer layer peels off. Therefore, the intermediate layer needs to be made of a material having high strength even if a large amount of alloy components are mixed in from the outer layer.

For this reason, a high carbon cast steel (abbreviated as AD) having the following composition is suitable as the intermediate layer material. Hereinafter, the composition of the intermediate layer material suitable for use in the embodiment of the present invention and the reason for limitation will be described. C: 1.0 to 2.5% C contributes to the improvement of the strength, but if it is less than 1.0%, the freezing point increases, and the welding tends to be insufficient. On the other hand, if it exceeds 2.5%, the amount of carbides becomes excessive and the material becomes brittle.

Si: 0.2-3.0% Si has a function of accelerating degassing and a function of improving flowability of molten metal.
If it is less than 0.2%, such effects cannot be expected, while 3.0%
If it exceeds, the material becomes brittle. In the high Si region, crystallization of graphite may be observed depending on the Ni content, but there is no problem with the 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 effect of strengthening the material. However, when the content exceeds 4.0%, the effect is saturated and an untransformed structure is apt to be generated, and the strength is deteriorated. Cr and Mo: 4.0% or less each Cr and Mo have an effect of strengthening the material. But 4.0
%, The mechanical properties deteriorate rather. W, V, Nb: 12% or less in total These elements have little effect on improving the material of the intermediate layer, but mixing from the outer layer is inevitable. Up to 12% is allowed as long as the mechanical properties of the intermediate layer material are not deteriorated. In addition, Al, Co, Ti, Zr, B
, These elements inevitably also enter the intermediate layer. In this case, for the same reason, the total is 12% or less including these elements.

The components of the intermediate layer material are, in addition to the components described above, the remainder substantially formed 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 embodiment of the present invention, it is preferable that both P and S be 0.2% or less as in the case of the inner layer material. 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 components mixed in 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 In the embodiment of the present invention, the balance is substantially between the outer layer and the inner layer (axial portion).
Since the intermediate layer of 1.0 to 2.5% C is provided, the harmful alloy element in the inner layer can be significantly suppressed from being directly mixed from the outer layer to the inner layer during welding, and the following effects can be obtained.

At the time of quenching heat treatment of the outer layer, the outer layer is preferably heated to 1100 ° C. or higher for austenitizing heat treatment. Since the heat treatment is performed, the temperature of the inner layer can be easily suppressed to 1100 ° C. or less by adjusting the amount of heat, and the melting of the inner layer can be prevented. The intermediate layer has a higher concentration of Cr, Mo, W, V, and Nb due to welding with the outer layer, but since these elements are still kept lower than the outer layer,
Welding the intermediate layer and the inner layer after welding the outer layer and the intermediate layer can lower the alloy concentration at the welded portion of the inner layer than when directly welding the outer layer and the inner layer. 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 embodiment of the present invention undergoes pearlite transformation during the quenching heat treatment of the roll,
Further, the rest 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 does not increase. When a large amount of martensitic transformation occurs, it is combined with the martensitic transformation of the outer layer, and a large compressive residual stress (axial direction) acts on the outer and intermediate layers, and a correspondingly large residual tensile stress (axial direction) acts on the inner layer. And the inner layer is pulled and broken.

[0039]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In the case of a composite roll of the present invention, in the case of a solid roll, usually, an outer layer and an intermediate layer are subjected to centrifugal casting, and then an 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 fed from a dam 6 via a pouring gutter 7 to a mold. Cast into 4 Numeral 8 denotes a sand mold for hot water.
To cast a solid composite roll, first, the molten outer layer material is cast into a rotating mold 4, and after it has solidified, the outer layer material is cast.
The intermediate layer material melt is cast into the inner peripheral surface of 1 and the intermediate layer 3 is centrifugally cast. Thereafter, a mold 4 having an outer layer 1 and an intermediate layer 3 is erected, and an upper mold and a lower mold for forming a shaft core portion are connected at both ends thereof to form a stationary mold. What is necessary is just to cast a molten metal. In the horizontal centrifugal casting apparatus, since each part of the molten metal cast in the mold moves up and down every time the mold rotates, there is a variation in G, and vibration is caused by eccentricity and scratches of the rollers and the mold. It is easy to occur and the components in the cast outer layer material melt are easy to move. For this reason, when casting a thick outer layer,
Since the segregation is likely to occur due to the movement of the components, it is usually preferable to perform the casting at a relatively low temperature at a solidification starting temperature of about + 70 ° C. or less. However, since the outer layer material according to the present invention is a highly wear-resistant material, it is difficult to wear, and the outer layer may be relatively thin,
Up to a casting thickness of about 80 mm (preferably 55 to 70 mm), it is rapidly cooled by a mold, so that there is almost no risk of segregation even when casting at a temperature higher than the above temperature. The product outer layer thickness 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 assembled at the upper and lower ends of a centrifugal casting mold 11, and the mold is mechanically fixed concentrically to a 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 centrifugal force is less susceptible to fluctuations and vibrations of G. Therefore, if vertical centrifugal casting is used, segregation hardly occurs even when casting a thick outer layer, so that casting can be performed at a higher temperature. It is. It is needless to say that only the centrifugal force casting mold 11 may be fixed to the base 14, the outer layer and the intermediate layer may be cast, the upper mold and the lower mold may be assembled, and the shaft portion may be statically cast.

The outer-layer wear-resistant cast iron material of the present invention, after being cast as the outer layer of the composite roll, cools the entire roll from a quenching temperature (austenitizing temperature) to a temperature range of 400 to 650 ° C. by 150.
By quenching at a cooling rate of at least C / Hr, a good quenched structure can be obtained. Tempering 500 ~ 600 ℃
It is good to carry out once or several times at the above temperature. In the outer layer material according to the present invention, Mo, W, V, Nb, Ti, Zr, and the like dissolved in the matrix during the austenitizing heat treatment precipitate as fine carbides by the tempering heat treatment, and the tempering secondary hardening phenomenon occurs. Excellent in high temperature hardness.

As a method for heating the outer layer, a method in which the entire roll is put into a heating furnace to heat, a method in which an induction heating coil and a large number of gas burners are arranged around the outer peripheral surface of the outer layer, and only the outer layer is rapidly heated by these. There is. In the former case, it takes time to raise the temperature, a thick oxide film is formed on the surface of the outer layer, and the yield of the outer layer decreases. Furthermore, to avoid melting of the inner layer of the cast iron material and heat it, it is necessary to stop heating at 1100 ° C (preferably 1000 ° C) or less, which makes it difficult to form a solid solution of carbides in the matrix. There is a problem that it is difficult to obtain sufficient hardness by the subsequent heat treatment. On the other hand, according to the heating method of only the outer layer, coupled with the formation of the intermediate layer,
Since the outer layer can be reliably stopped at 1100 ° C. or higher and the inner layer can be stopped at less than 1100 ° C., it is possible to prevent partial melting of the inner layer and reduction in strength due to coarsening of crystal grains. In addition, since the temperature decreases toward the center of the inner layer (axial portion), 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 may be any of hot rolled and cold rolled rolls, such as a roll for rolling equipment and a pinch roll for ancillary equipment or a roller for conveying rolled material.
Applied to rolls and rollers that require abrasion resistance.
The rolled material includes not only steel and non-ferrous metals but also non-metals. [Specific Examples] (1) The melt of the outer layer material shown in Table 1 was centrifugally cast into a centrifugal casting mold having an inner diameter of 1040 mm, and after the outer layer was completely solidified, the melt of the intermediate layer shown in the table was centrifuged. The outer layer and the middle layer were welded by force casting. The pouring amount was 70 mm for the outer layer and 25 mm for the intermediate layer. The examples are samples Nos. 1 to 6, and the outer layer material of No. 7 is a high chromium cast iron material having improved wear resistance.
The outer layer material does not contain Al. The composition unit in the table is% by weight, and the balance is substantially Fe. (2) Wait until the intermediate layer is completely solidified, stop the rotation of the mold, stand the mold with the outer layer and the middle layer inside vertically, and connect the upper mold and lower mold at both ends. The inner layer material (shaft core material) shown in the same table was also cast into the interior.

[0044]

[Table 1]

(3) After rough processing of the cast composite roll, the roll of the embodiment was uniformly preheated to 600 ° C., and then the roll was placed horizontally opposed to the roll 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 rolls. Outer layer surface temperature is 1170
Heating was stopped when the temperature of the inner layer reached 830 ° C. The time required for heating was 300 minutes. From the heat conduction temperature data, it was estimated that the temperature near the outer peripheral surface of the inner layer was 960 ° C in this case. On the other hand, with respect to the conventional roll, the entire roll was kept at 1050 ° C. for 5 hours to austenitize. (4) For the rolls of the examples and the conventional example, after stopping the heating, spray water cooling was immediately performed, and the roll surface temperature was set to 500 ° C.
And then allowed to cool to room temperature. Thereafter, tempering heat treatment at 550 ° C. for 20 hours was repeated twice. The outer layer surface hardness after the heat treatment was as shown in Table 2 below. From the table,
It can be seen that the outer layer of the example has a remarkable improvement in hardness and is superior in abrasion resistance as compared with that of the conventional example. 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 3.
It was remarkable about 0mm.

[0046]

[Table 2]

(5) After finishing the body surface, the welding condition was confirmed by an ultrasonic flaw detection test. As a result, 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. Table 3 shows 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 portion). From the table, it can be seen that the mixing amount of the outer layer high alloy component in the inner layer is extremely small in both the example and the conventional example.

[0048]

[Table 3]

(6) The outer layer material was cut out from the excess length of the trunk end, and the base hardness (micro Vickers hardness) and the high temperature hardness (Vickers hardness) were measured. As a result, as shown in Table 4, both the base hardness and the high-temperature hardness are excellent as compared with the conventional example, and it is desirable that the material is desirable as the outer layer material of the composite roll in terms of abrasion resistance and skin roughness resistance. I understand. In particular, it has been found that the roll is suitable as an outer layer material of a hot rolling roll having a large heat load, particularly a hot thin roll rolling roll in the steel industry. Table 4 shows the rate of decrease in high-temperature hardness at 600 ° C. [(normal-temperature hardness at 600 ° C.) / Normal-temperature hardness × 10.
0].

[0050]

[Table 4]

Further, Table 5 shows the specific wear amount in the Ogoshi type abrasion test based on the high chromium cast iron material (Sample 7). Samples 1 to 6 show good wear resistance. .

[0052]

[Table 5]

[0053]

As described above, in the composite roll of the present invention, the outer layer is formed of Cr, Mo, W, V, Nb, Co and Al.
By using a special cast iron material having a specific chemical composition obtained by adding a predetermined amount of a special element such as, a remarkable effect was exhibited when used as a roll material. That is, Cr, Mo, W,
The outer layer cast iron material of the composite roll containing V and Nb has a high hardness composite carbide and can dramatically improve wear resistance. However, when manufactured by centrifugal casting, it is unique to centrifugal casting. Macrosegregation occurs, and when applied to the outer layer of the composite roll and subjected to rolling, there is a problem that unevenness in wear and surface roughness due to macrosegregation on the roll surface can be caused. From the viewpoint of not only wear properties but also macro-segregation, the optimum composition as the outer layer of the composite roll is searched for and centrifugal casting experiments are conducted by combining various alloys, and by adding special elements such as Al, the wear resistance is dramatically improved. It was possible to provide a roll outer layer material having improved and uniform surface properties without macro segregation.

Particularly important points of the present invention are that Cr, Mo,
In centrifugal casting of a cast iron material containing W, V, Nb,
The content in which abrasion resistance was significantly improved by the high hardness composite carbides formed by these alloys was determined, and Co, Ti, Zr, and Al were mainly used to prevent macrosegregation even in centrifugal casting. A remarkable effect was obtained in that an alloy such as B was added. By the way, if we explain the latter,
Macro segregation by including Al, which was conventionally used only as a deoxidizing material or as a material for refining the structure of special materials, in a cast iron material that tends to cause macro segregation in centrifugal casting due to its high alloy. Is improved.

That is, Al, Co, Ti, Zr and B engage with oxygen in the molten metal to form oxides, and Mo, W, V, Nb
In addition to preventing the loss of elements important for the performance of the outer layer of the present invention, it is also possible to form a high hardness composite carbide of Cr, Mo, W, V, Nb with these oxides as nuclei of solidification in the molten metal at the early stage of solidification. Form. As a result, a finely dispersed high hardness composite carbide is obtained, and the wear resistance is improved.

[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.

[Description of Signs] 1 outer layer 2 inner layer 3 intermediate layer

Continuing from the front page (72) Inventor Akira Okabayashi 64, Nishimukaijima-cho, Amagasaki-shi, Hyogo Prefecture Inside Kubota Amagasaki Plant Co., Ltd. Inventor Takashi Shikata 64 Nishimujima-cho, Amagasaki City, Hyogo Prefecture Kubota Amagasaki Plant Co., Ltd.

Claims (3)

[Claims] 1. An outer layer formed of a wear-resistant cast iron 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. In the composite roll formed by centrifugal casting of the intermediate layer, the outer layer has a chemical composition of 1.0 to 3.0% by weight, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Ni: 0.1 to 4.5% by weight. %, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0%, W: 1.5 to 10.0%, Al: 0.01 to 0.50%, Co: 0.5 to 10.0%, V, Nb: One or two kinds of total 3.0 to 10.0% 10.0%, and the balance substantially consisting of Fe. 2. An outer layer formed of a wear-resistant cast iron 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. In the composite roll formed by centrifugal casting of the intermediate layer, the outer layer has a chemical composition of 1.0 to 3.0% by weight, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Ni: 0.1 to 4.5% by weight. %, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0%, W: 1.5 to 10.0%, Al: 0.01 to 0.50%, Co: 0.5 to 10.0%, V, Nb: One or two types of total 3.0 to 10.0% 10.0%, Ti, Zr: A composite roll characterized by being composed of one or two of each of 0.01 to 0.50% and the balance substantially of Fe. 3. An outer layer formed of a wear-resistant cast iron 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. In the composite roll formed by centrifugal casting of the intermediate layer, the outer layer has a chemical composition of 1.0 to 3.0% by weight, Si: 0.1 to 2.0%, Mn: 0.1 to 2.0%, Ni: 0.1 to 4.5% by weight. %, Cr: 3.0 to 10.0%, Mo: 0.1 to 9.0%, W: 1.5 to 10.0%, Al: 0.01 to 0.50%, Co: 0.5 to 10.0%, V, Nb: One or two kinds of total 3.0 to 10.0%, Ti, Zr: one or two of each 0.01 to 0.50%, B: 0.01 to 0.50% and the balance substantially consisting of Fe.