JP2835259B2 - High-speed cast iron with graphite and composite roll - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-speed cast iron material having graphite and a composite roll having an outer layer cast from the cast iron material.

[0002]

2. Description of the Related Art As a high wear-resistant cast iron material for casting, a high-speed cast iron material having the following chemical composition (wt%) is known as disclosed in Japanese Patent Application Laid-Open No. 4-176840. C: 1.0 to 3.0%, Si: 0.1 to 2.0%, Mn:
0.1 to 2.0%, Cr: 3.0 to 10.0%, Mo: 0.1 to 6.0%, W:
1.5 to 10.0%, total of one or two of V and Nb: 3.0 to 10.0%, balance substantially Fe Such high-speed cast iron material containing Mo, W, and V has excellent characteristics at high temperatures and a microstructure. Since it contains high hardness crystallized carbides such as VC, M ₂ C, and M ₆ C, it has extremely good wear resistance and skin resistance as a roll material for hot rolling. Therefore, it is used as an outer layer and an inner layer made of a tough material welded to the inner surface thereof, or as an outer layer material of a composite roll having an intermediate layer welded therebetween.

[0003]

However, the conventional high-speed steel cast iron material has a large coefficient of friction, and as a result, there are problems such as an increase in rolling load, an imbalance in sheet passing property, and heat generation. The passability refers to the ease of separation of the rolled plate from the roll surface.If this is bad, the rolled plate adheres to the roll surface, hinders smooth running and meanders. Surface damage such as overlap and wrinkles occurs. Also,
When an excessive load is applied to the roll during rolling, there is a problem that the microcracks generated on the roll surface are liable to spread into the outer layer thereafter, and in severe cases, the outer layer is broken.

[0004] The present invention has been made in view of such a problem.
An object of the present invention is to provide a high-speed cast iron material having a low coefficient of friction and hardly causing cracks to develop, and a composite roll having an outer layer formed by the cast iron material.

[0005]

High-speed steel cast iron having graphite of the invention According to an aspect of the chemical composition in wt%, C: 1.8 ~3.6% , Si: 2.3 ~3.5%, Mn: 0.1 ~2.0%, Cr : 2.0 ~10%, Mo: 0.1 ~10%, W: 0.1 ~10%, V, Nb: contains 1.5 to 10% by one or two of the total, with cast iron the remainder being substantially Fe Yes,
The cast iron material has an area ratio of 1.3 to 7.0% crystallized black.
It is configured to have MC type composite carbide with lead .
At this time, Co: 0.5 to 10.0 wt.
% Or Al: 0.01 to 0.50 wt%, Ti: 0.01 to 0.50 wt%
%, One or two of Zr 0.01 to 0.50 wt%, or B: 0.01 to 0.50 wt%.

In the composite roll of the present invention, an intermediate layer is cast on the inner surface of the outer layer if necessary, an inner layer is cast on the inner surface of the outer layer or the intermediate layer, and the outer layer and the intermediate layer or the inner layer, and the intermediate layer and the inner layer are formed. In the composite roll, the outer layer is formed of a high-speed cast iron material having the above graphite, the intermediate layer is formed of an adamite material, and the inner layer is formed of a casting steel material having toughness. . The inner layer is preferably made of flake graphite cast iron, spheroidal graphite cast iron or a graphite crystallized material made of graphite steel, and the intermediate layer is C: 1.0 to 2.
It is preferable to use an adamite material containing 5% and Si: 0.1 to 1.5%.

[0007]

The high-speed cast iron material of the present invention is made of Cr, Mo, W,
High hardness MC with Nb, V, Fe and C bonded to each other
Due to the presence of composite carbides such as molds in the matrix and the strengthening of the matrix with Co, the hardness at ordinary and high temperatures is improved, and the wear resistance is dramatically improved. Furthermore, in particular C,
Since Si is specified in a specific range, graphite is crystallized and precipitated in the structure at an area ratio of about 1.3 to 7.0%, and the action of the graphite can reduce the impact load and prevent the crack from developing. In addition, the friction coefficient is reduced and seizure resistance is improved.

By using the above-mentioned high-speed cast iron material having graphite as the outer layer material of the composite roll, the excellent characteristics of the material can be exhibited during rolling, and the rolling load and frictional heat can be reduced, and the sheet passing property can be reduced. And a roll for rolling that can suppress the progress of cracks can be provided. Since the rolling roll has good seizure resistance due to the action of graphite, it is also suitable as a roll for cold rolling.

Further, by forming an intermediate layer between the outer layer and the inner layer using an adamite material, it is possible to prevent a high alloying component of the outer layer from being mixed into the inner layer and deteriorating its toughness. it can. Further, since the boundary between the intermediate layer and the inner layer is made of a low alloy, the formation of a carbide layer is suppressed, and the boundary strength can be improved. In addition, during the austenite heat treatment of the outer layer, the temperature of the inner layer can be prevented from rising, and the outer layer alone can be kept at 1100 ° C while preventing the deterioration of the toughness of the inner layer material.
It can be heated to the above high temperature. Further, since martensite transformation does not occur during quenching of the outer layer, even if quenching heat treatment is performed on the outer layer, no excessive residual stress is generated, and the accident resistance is excellent.

Further, by forming the inner layer of flaky graphite cast iron, spheroidal graphite cast iron or graphite steel, that is, a steel material in which graphite has been crystallized, the outer layer has excellent heat conductivity and heat dissipation in combination with the presence of graphite, and has excellent heat dissipation. The thermal deformation of the roll at the time can be prevented. In addition, the Young's modulus can be made considerably lower than that of the outer layer, and it is possible to prevent occurrence of excessive stress in the outer layer due to flattening of the roll at the time of overload.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, the reasons for limiting the chemical composition of the graphite-containing high-speed cast iron material of the present invention will be described. Hereinafter, all the units of the components are wt%. C: 1.8 to 3.6% C mainly combines with Fe and Cr to form an M ₇ C ₃ type high-hardness composite carbide, and Cr, Mo, V, N
Combined with b and W, it also forms high hardness composite carbides such as MC type, M ₆ C type and M ₂ C type. Further, by the action of Si, which is a graphitization promoting element to be described later, and by heat treatment, fine graphite is crystallized and precipitated in the structure. If it is less than 1.8%, the amount of carbides decreases and graphite almost disappears.
If the content exceeds 3.6%, the amounts of carbide and graphite become excessive and the material becomes brittle.

Si: 2.3 to 3.5% Si is an element necessary for securing the fluidity of the molten metal and crystallizing and precipitating graphite. When the content is less than 2.3 %, such an effect is insufficient. The area ratio is excessively greater than 7%, the wear originating from graphite becomes remarkable, and the wear resistance deteriorates. In order to promote the crystallization of graphite, it is preferable that the amount of Si before casting is set to be lower than the above-mentioned component range, inoculation is performed at the time of casting, and the final product component is adjusted to the above-mentioned range.

Mn: 0.1 to 2.0% Mn is an element that increases the hardening ability and combines with S to form MnS and prevent embrittlement due to S. At the same time, about 0.1% is inevitably contained from the raw materials used. Is done. But 2.0
%, It is not preferable because toughness is reduced. Cr: 2.0-10% Cr combines with C together with Fe, Mo, V, Nb, and W,
It forms high hardness composite carbides and contributes to improvement of wear resistance at high temperatures. In addition, a part of the alloy dissolves in the matrix to improve quenchability and wear resistance. If the content is less than 2.0%, these effects are small. On the other hand, if the content exceeds 10%, the toughness is deteriorated, which is not preferable.

Mo: 0.1-10% Mo is easily bonded to C together with Fe, Cr, V, Nb and W.
And mainly M₇C _ThreeType M₆C type, M_TwoC-type composite coal
And harden at normal and high temperatures
Contribute to improvement. Mo is less effective than W
Demonstrate fruit. At this time, the effect is excessive if it is less than 0.1%.
If it exceeds 10%, the toughness will decrease.
I don't.

W: 0.1 to 10% W is also easily combined with C together with Fe, Cr, Mo, V, and Nb to form a composite carbide, and contributes to improving the wear resistance by increasing the hardness at ordinary and high temperatures. I do. If it is less than 1.5%, the desired wear resistance cannot be obtained, while if it exceeds 10.0%, the toughness decreases and the heat crack resistance deteriorates. In addition, at the time of centrifugal casting, macro segregation is easily generated. Therefore, the content is set to 10.0% or less.

V, Nb: 1.5 to 10% in total of one or two kinds V easily bonds with C together with Fe, Cr, Mo, W similarly to Nb to form mainly MC type composite carbide, Increases room temperature and high temperature 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 effects are unlikely to appear unless 1.5% or more is added alone or in combination of two types. However, if the addition amount exceeds 10%, the toughness is reduced, and macrosegregation is easily generated during centrifugal casting.

The high-speed cast iron material according to the present invention is formed of the above alloy components and the balance of Fe and impurities unavoidably mixed therein. In addition, P and S are inevitably mixed from the raw material, but it is preferable that P and S are small as the material becomes brittle.
It is better to keep it below 2% and S: below 0.1%. In the cast iron material of the present invention, in addition to the alloy component, if necessary,
Co: 0.5 to 10.0%, and / or A in the following composition range
One, two or more of l, Ti, and Zr, and / or B: 0.01 to 0.50%.

Co: 0.5 to 10.0% Co has a great effect in improving the base. Co is C
It has a special action of suppressing the diffusion of carbides, has the effect of increasing the toughness by forming a solid solution in the matrix irrespective of the formation of carbides, and 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, the content must be 0.5% or more.
Even if it is added in excess of 0%, its effect is saturated and it is an expensive element. When casting a high alloy cast iron material by centrifugal force casting to produce a composite roll, the distribution of carbides tends to be non-uniform,
Although it is necessary to optimize the casting conditions, in the case of the high alloy material containing Co of the present invention, since Co forms a solid solution in the matrix irrespective of carbide formation as described above, the non-uniformity of the carbide is reduced. The above-mentioned excellent effects can be expected without increasing the size.

Al, Ti, Zr: 0.01 to 0.50% each Al, Ti, and Zr form oxides in the molten metal, reduce the oxygen content in the molten metal, improve the soundness of products, and form Since the formed oxide acts as a crystal nucleus, it is effective in refining the solidification structure. If the content is less than 0.01%, this effect is not sufficient. On the other hand, if it exceeds 0.50%, it remains as inclusions and is not preferable. In addition, Al, T
In the present invention, i and Zr are mainly added for improving the wear resistance by making the casting structure finer, and are not simply added for the purpose of degassing.

B: 0.01 to 0.50% B combines with oxygen in the molten metal to exhibit a deoxidizing effect. In addition, the effect of refining the solidification structure with the generated oxide as the nucleus,
And the effect of increasing the hardenability by B dissolved in the matrix. In the case of a casting having a large mass such as a rolling roll, it may be difficult to increase the cooling temperature, but it is easy to obtain a quenched structure due to an increase in hardenability. If it is less than 0.01%, such effects are not sufficient, while if it exceeds 0.50%, the material becomes brittle, which is not preferable.

The cast iron material of the present invention is used as an outer layer material of a two-layer composite roll in which an outer layer and a solid inner layer or a cylindrical inner layer are welded, or a three-layer composite roll in which an intermediate layer is cast between the outer layer and the inner layer. It is preferably used. As the inner layer material, a steel material for casting having high toughness such as high-grade cast iron, ductile cast iron, graphite steel, cast steel or the like is used. In particular, the former three which are graphite crystallization materials are preferred. This is because, in combination with the presence of graphite in the outer layer, the heat conductivity and thus the heat dissipation are excellent, and thermal deformation of the roll during rolling can be prevented. In addition, since these graphite-crystallized steel materials have a Young's modulus of about 19,000 kg / mm ² or less, the load can be absorbed by flattening the rolls during overload, and the accident resistance can be improved. Further, the residual stress at the time of heat treatment of the outer layer can be easily reduced by the low-temperature strain relief annealing. Moreover, since it has good toughness, it can withstand a shocking rolling torque. Preferred examples (wt%) of high-grade cast iron, ductile cast iron, and graphite steel are shown below. (1) High-grade cast iron 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; W, V, Nb: 4% or less in total; balance: Co and substantially Fe mixed from an outer layer or an intermediate layer. When the outer layer contains Al, Ti, Zr, these elements are also included. It is mixed into the inner layer from the outer layer or through the intermediate layer. The composition of the molten metal before casting is determined so as to have the above-mentioned composition after welding. Examples of the composition are shown below.

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, balance: substantially Fe (2) ductile cast iron C: 2.5 to 4.0%, Si: 1.3 to 3.5%, Mn: 0.2 to 1.5%, P: 0.2% or less, S: 0.2% or less, Ni: 3.0% or less, Cr: 2.0% or less, Mo: 2.0% or less, W, V, Nb: 4% or less in total, Mg: 0.02 to 0.1
%, Balance: Co and substantially Fe mixed from the outer layer or the intermediate layer. Preferred examples of the molten metal composition before casting 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, Mg: 0.02 to 0.1%, balance: substantially Fe (3) graphite steel C: 1.0 to 2.3%, Si: 0.5 to 3.0%, Mn: 0.2 to 1.5%, P: 0.2% or less, S : 0.2% or less, Ni: 3.0% or less, Cr: 2.0% or less, Mo: 2.0% or less, W, V, Nb: 4.0% or less in total, balance: Co and substantially Fe mixed from the outer layer or the intermediate layer The preferred melt composition before casting is exemplified below.

C: 1.0 to 2.3%, Si: 0.5 to 3.0%, Mn: 0.2 to 1.5%, P: 0.2% or less, S: 0.2% or less, Ni: 3.0% or less, Cr: 2.0% or less, Mo: 2.0% or less, balance: substantially Fe Next, the intermediate layer will be described. The intermediate layer is formed for the purpose of reducing the mixing of the alloy component of the outer layer into the inner layer, but the intermediate layer itself needs to have a strength of about 30 kg / mm ² or more. 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, an adamite material having the following composition is suitable as the intermediate layer material. Hereinafter, the composition of the intermediate layer material according to the present invention and the reasons for limitation will be described.

C: 1.0 to 2.5% C contributes to an improvement in strength, but if it is less than 1.0%, the freezing point increases, and welding tends to be insufficient. On the other hand, if it exceeds 2.5%, the amount of carbide becomes excessive and the material becomes brittle. Si: 0.2 to 3.0% Si has 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: 0.2-1.5% 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, Mo: 4.0% or less for each Cr and Mo have the 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. When the outer layer contains Al, Ti, Zr, and B, these elements inevitably enter the intermediate layer. in this case,
For the same reason, the content is set to 12% or less including these elements. In addition, Co is inevitably mixed in from the outer layer, but is not particularly limited because it does not deteriorate the material of the intermediate layer.

In addition to the components described above, the intermediate layer material is substantially composed of Fe. It should be noted that P and S are impurities and are preferably as small as possible because they make the material brittle. In the present invention, both of them are preferably limited to 0.2% or less similarly to the inner layer material. still,
The composition range of the molten metal before welding to the outer layer is exemplified below. The composition of the molten metal is determined in consideration of the amount of 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, balance: Fe When an intermediate layer of 1.0 to 2.5% C is provided substantially between the outer layer and the inner layer (axial part), harmful alloy elements in the inner layer are transferred from the outer layer to the inner layer during welding. In addition to the above, it is possible to significantly suppress the direct mixing into the air, and to achieve the following effects.

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

Most of the intermediate layer according to the present invention undergoes pearlite transformation during the quenching heat treatment of the roll, and the remainder undergoes bainite transformation. No or little martensitic transformation occurs. For this reason, there is no large expansion behavior accompanying the martensitic transformation, and the residual stress on the roll is not increased. When a large amount of martensitic transformation occurs, a large compressive residual stress (axial direction) acts on the outer and intermediate layers in combination with the martensitic transformation of the outer layer, and a correspondingly large tensile residual stress (axial direction) acts on the inner layer. And the inner layer breaks in tension.

As a method of casting a composite roll, as is well known, an outer layer and, if necessary, an intermediate layer are cast by a centrifugal die casting method, and then a solid inner layer is statically cast therein.
When a sleeve-shaped roll is cast, it is a matter of course that the inner layer may be cast by centrifugal force. In the centrifugal casting method, the rotation axis of the cylindrical mold is horizontal horizontal type, diagonal inclined type,
Various vertical vertical methods can be applied.

However, 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 the eccentricity and the eccentricity of the rollers and the mold are increased. Vibration easily occurs due to the scratch, and components in the cast outer layer material melt are easily moved. For this reason, when casting a thick outer layer, segregation is likely to occur due to the movement of the components. Therefore, it is usually preferable to cast at a relatively low temperature at a solidification start 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 hard to be worn, and the outer layer may be relatively thin, and is rapidly cooled by a mold until the casting thickness is about 80 mm (preferably 55 to 70 mm). Therefore, there is almost no risk of segregation even if the casting is performed at a temperature higher than the above temperature. The thickness of the outer layer of the product is about 50 mm (preferably 25 to 40 mm) in consideration of the allowance for melting by the intermediate layer of 20 mm and the allowance for processing of 10 mm.

On the other hand, in the vertical centrifugal casting apparatus, since the centrifugal casting mold is mechanically vertically mounted and fixed concentrically to the rotating base, the outer layer material molten metal cast in the mold is formed. Are less susceptible to fluctuations and vibrations in G. Therefore, if vertical centrifugal casting is used, segregation is unlikely to occur even when casting a thick outer layer, so that casting can be performed at a higher temperature, which is effective in improving workability and preventing casting defects due to inclusion of foreign matter. It is.

The high-speed cast iron material having graphite of the present invention comprises:
After casting as the outer layer of the composite roll, a good quenched structure can be obtained by quenching the entire roll from a quenching temperature (austenitizing temperature) to a temperature range of 400 to 650 ° C at a cooling rate of 100 ° C / Hr or more. it can. Tempering is 5
It may be carried out once or several times at a temperature of 00 to 600 ° C. In the outer layer material according to the present invention, Mo, W, V, Nb and the like dissolved in the matrix during the austenitizing heat treatment precipitate as fine carbides by the tempering heat treatment, and a tempering secondary hardening phenomenon occurs. Excellent. Further, graphite is precipitated in the structure by the tempering heat treatment.

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 outer layer surface, and the yield of the outer layer decreases. Furthermore, in order to avoid the melting of the inner layer of the cast iron material and heat it, the heating must be stopped at 1100 ° C. (preferably 1000 ° C.) or less, which makes it difficult to sufficiently dissolve the carbide 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 more 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 core), the heat of the outer layer can be released to the inside after heating to the austenitizing temperature, and the cooling rate of the outer layer deeper can be increased during quenching. it can.

The high-speed cast iron material having graphite of the present invention comprises:
Rolls requiring abrasion resistance, such as rolls for transporting rolled material in pinch rolls or auxiliary equipment for rolling, as well as rolls for hot rolling or rolling for cold rolling,
Although it is suitable as an outer layer material of a cylindrical member such as a roller, it is needless to say that it can be used not only for such applications but also for various mechanical parts and the like that require abrasion resistance.

Next, specific examples of the present invention will be described. Example A (1) The wear-resistant cast iron material shown in Table 1 was cast at 1425 ° C. in a sand mold having an inner diameter of 120 mm and a depth of 120 mm. The examples are samples Nos. 1 to 9 and are No. 10 conventional high-speed roll materials. The composition unit in the table is% by weight, and the balance is substantially Fe.

[0039]

[Table 1]

(2) Tissue observation specimens were collected from each sample,
The microstructure was observed under a microscope, and the area ratio of the crystallized graphite was measured. Table 2 shows the results. From the table, it can be seen that in the example, graphite was crystallized in an area ratio of 1.3 to 3.8%, but in comparative example 8, it was as small as 0.7%, whereas in the high-speed wear-resistant material of the conventional example 10, no graphite was crystallized. there were.

[0041]

[Table 2]

(3) Next, each sample was held at 1100 ° C. for 1 hour, quenched by forced air cooling, and then quenched at 540 ° C. for 10 hours.
hr tempering heat treatment was repeated three times. Table 2 also shows the results of measuring the surface hardness of each sample. From the table, it is inferred that the examples and the conventional examples have substantially the same hardness, and that the alloys of the examples also have excellent wear resistance. (4) Further, a friction test piece was collected from each sample, and a friction coefficient was measured by a Falex test. The Falex test is a test in which a test piece is pinched and pressed between a pair of V-blocks (stainless steel SUS430) while rotating, and the friction coefficient and seizure are examined based on the magnitude and fluctuation of the rotation torque. The material of the block used this time is S45C. The results are also shown in Table 2. From the table, it can be seen that the wear-resistant material of the example has a reduction effect of 20 to 29% as compared with the conventional example. Example B (1) The melt of the outer layer material shown in Table 3 was centrifugally cast into a centrifugal casting mold having an inner diameter of φ810 mm. In Samples Nos. 13 and 14, after the outer layer was completely solidified, The layer material melt was centrifugally cast to weld the outer layer and the intermediate layer. The casting amount was 70 mm for the outer layer and 25 mm for the intermediate layer. Sample Nos. 11 to 14 are all examples. (2) Wait until the outer or middle layer has completely solidified,
The rotation of the mold was stopped, and the mold having the outer layer alone or the outer layer and the intermediate layer was set up vertically, the upper mold and the lower mold were connected at both ends, and the inside of the mold was shown in the same table. Inner layer material (shaft core material) Molten metal was cast.

[0043]

[Table 3]

(3) After rough processing of the cast composite roll, it is uniformly preheated to 600 ° C., and then the roll is placed between gas burners which are horizontally opposed and arranged in parallel at a pitch of 250 mm along the roll axis direction. Was rotatably supported, and the surface of the outer layer was heated while rotating the roll. Outer layer surface temperature is 1
The heating was stopped when the temperature of the inner layer reached 120 ° C and the temperature of the center of the inner layer reached 900 ° C. The time required for heating was 180 minutes. From the heat conduction temperature data, it was estimated that the temperature near the outer surface of the inner layer was 1030 ° C in this example. (4) After the heating was stopped, spray water cooling was immediately performed, and the roll surface temperature was rapidly cooled to 500 ° C, and then allowed to cool to room temperature. Thereafter, a tempering heat treatment maintained at 550 ° C. for 20 hours was repeated twice. The outer layer surface hardness after the heat treatment was as shown in Table 4 below. From the table, it can be seen that the outer layers of Examples have high hardness and are excellent in wear resistance. Further, when the microstructure of the trunk surface was observed, graphite having an area ratio of 1.5 to 3.5% was recognized.

[0045]

[Table 4]

(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 5 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 in the example in which the intermediate layer was provided, the mixing amount of the outer layer high alloy component in the inner layer was very small.

[0047]

[Table 5]

(6) From the above results, when the roll of this embodiment is used for the finishing stage of the hot strip mill, the roll has excellent abrasion resistance, has good sheet passing property, and can suppress the temperature rise of the roll. Is expected.

[0049]

As described above, in the high-speed cast iron material having graphite of the present invention, a composite carbide of a high hardness MC type or the like in which Cr, Mo, W, Nb, V, Fe and C are mutually bonded is present in the matrix. Therefore, by strengthening the matrix with Co, the hardness at room temperature and high temperature is improved, and the wear resistance is dramatically improved. Furthermore, since C and Si are particularly specified in a specific range , 1.3 to 7.0% of graphite is crystallized in the structure in terms of area ratio, and by the action of the graphite, it is possible to alleviate the impact load and to develop cracks. Is prevented, and the friction coefficient is reduced and seizure resistance is improved.

A composite roll using the above-mentioned high-speed cast iron material having graphite as an outer layer material can exhibit the excellent characteristics of the material at the time of rolling, reduce the rolling load and frictional heat, and improve the threadability. Improvement can be achieved, and the progress of cracks can be suppressed. Further, since the seizure resistance is good due to the action of graphite, it is also suitable as a roll for cold rolling. In addition, by forming an intermediate layer between the outer layer and the inner layer using an adamite material, the mixing of high alloy components from the outer layer to the inner layer can be significantly reduced, and the boundary strength can be improved. ,
Since no martensite transformation occurs, the residual stress does not increase, and furthermore, it is possible to prevent the inner layer from being damaged by erosion or a decrease in strength during the austenitizing heat treatment of the outer layer.

Further, by forming the inner layer from a graphite crystallized material made of flaky graphite cast iron, spheroidal graphite cast iron or graphite steel,
Combined with the presence of graphite in the outer layer, it has excellent thermal conductivity and thus heat dissipation, and can prevent thermal deformation of the roll during rolling,
In addition, the Young's modulus can be made considerably lower than that of the outer layer, and it is possible to prevent the occurrence of excessive stress in the outer layer due to flattening of the roll at the time of overload, and it is excellent in safety and accident resistance.

──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Hiroyuki Kimura 64 Nishimujima-cho, Amagasaki City, Hyogo Prefecture Kubota Amagasaki Plant (56) References JP-A-2-285047 (JP, A) JP-A-63-266043 (JP, A) JP-A-4-176841 (JP, A) JP-A-2-258949 (JP, A) JP-A-6-179947 (JP, A) JP-A-5-31317 (JP, A) ( 58) Field surveyed (Int. Cl. ⁶ , DB name) C22C 37/00-38/60 B21B 27/00

Claims (8)

(57) [Claims] 1. The chemical composition is wt%, C: 1.8 to 3.6%, Si: 2.3 to 3.5%, Mn: 0.1 to 2.0%, Cr: 2.0 to 10%, Mo: 0.1 to 10%, W: 0.1 ~10%, V, Nb: one or two of from 1.5 to 10% and the balance in total are cast iron consisting essentially of Fe, the template iron
The material is made of graphite with an area ratio of 1.3 to 7.0% crystallized.
A high-speed cast iron material having graphite, characterized by having an MC-type composite carbide . 2. The alloy according to claim 1, further comprising Co: 0.5.
High-speed cast iron material containing graphite containing up to 10.0 wt%. 3. The alloy according to claim 1, further comprising Al: 0.01.
~ 0.50wt%, Ti: 0.01 ~ 0.50wt%, Zr: 0.01 ~ 0.50
A high-speed cast iron material having graphite containing one or two of wt%. 4. The alloy according to claim 1, wherein B: 0.01 to
High-speed cast iron material containing graphite containing 0.50 wt%. 5. A composite roll in which an inner layer is cast on the inner surface of an outer layer, and the outer layer is welded to the outer layer.
3. A composite roll formed of a high-speed cast iron material having graphite as described in 3 or 4, wherein the inner layer is formed of a tough casting steel material. 6. A composite roll wherein an intermediate layer is cast on the inner surface of the outer layer, an inner layer is cast on the inner surface of the intermediate layer, and the outer layer and the intermediate layer and the intermediate layer and the inner layer are welded to each other. 2, 3, or 4, wherein the intermediate layer is formed of an adamite material, and the inner layer is formed of a tough steel casting material having toughness. Composite roll. 7. The steel material forming the inner layer is flaky graphite cast iron,
The composite roll according to claim 5, wherein the composite roll is formed of spheroidal graphite cast iron or graphite steel. 8. The adamite material according to claim 6, wherein the chemical composition is wt.%, C: 1.0-2.5%, Si: 0.2-3.0%, Mn: 0.2-1.5%, P: 0.2% or less, S: : Ni: 4.0% or less, Cr: 4.0% or less, Mo: 4.0% or less, W, V, Nb: 12% or less in total, and the balance is substantially Fe.