JPH06256888A - High-speed steel series cast iron containing graphite and composite roll - Google Patents

Abstract

PURPOSE:To produce a high-speed steel series cast iron material low in a friction coefficient and in which the progress of cracks is hard to occur and to provide a composite roll whose outer layer is formed by the cast iron material. CONSTITUTION:The graphite-crystallized high-speed steel series cast iron material is constituted of a chemical compsn. contg., by weight, 1.8 to 3.6% C, 1.0 to 3.5% Si, 0.1 to 2.O% Mn, 2.0 to 10% Cr, 0.1 to 10% Mo, 0.1 to 10% W and total 1.5 to 10% of one or two kinds of V and Nb, and the balance substantial Fe. At this time, 0.5 to 10.0% Co or one or two kinds among 0.01 to 0.50% Al, 0.01 to 0.50% Ti and 0.01 to 0.50% Zr or 0.01 to 0.50% B may be incorporated in addition to the same alloy components.

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, as disclosed in Japanese Patent Laid-Open No. 4-176840, a high speed cast iron material having the following chemical composition (wt%) is known. 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%, V or Nb, one or two total: 3.0 to 10.0%, balance substantially Fe Fe-containing high speed cast iron material containing Mo, W and V has excellent characteristics at high temperature and has a structure Since it has high hardness crystallized carbides such as VC, M ₂ C, and M ₆ C, it has extremely good wear resistance and rough surface 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 in which an intermediate layer is welded therebetween.

[0003]

However, the conventional high-speed cast iron material has a large friction coefficient, and as a result, there are problems such as an increase in rolling load, an unbalance in stripability, and heat generation. The stripability means the ease of separation of the rolled plate from the roll surface.If this is not the case, the rolled plate adheres to the roll surface, hinders smooth running, and meanders. Overlap and surface damage such as wrinkles occur. Also,
When an excessive load is applied to the roll during rolling, there is a problem that microcracks generated on the surface of the roll easily propagate inside the outer layer after that, and in extreme cases, the outer layer is broken.

The present invention has been made in view of the above problems,
An object of the present invention is to provide a high-speed cast iron material and a composite roll having an outer layer formed of the cast iron material, which has a low friction coefficient and is less likely to cause cracks to develop.

[0005]

The high-speed cast iron material having graphite of the present invention has a chemical composition of wt%, C: 1.8-3.6%, Si: 1.0-3.5%, Mn:
0.1 to 2.0%, Cr: 2.0 to 10%, Mo: 0.1 to 10%, W:
0.1 to 10%, V, Nb: One or two kinds, 1.5 to 10% in total, and the balance being substantially Fe. At this time, in addition to the above alloy components, Co: 0.5 to 1
0.0 wt% or Al: 0.01 to 0.50 wt%, Ti: 0.01 to
One or two of 0.50 wt% and Zr 0.01 to 0.50 wt% or B: 0.01 to 0.50 wt% can be contained.

In the composite roll of the present invention, if necessary, an intermediate layer is cast on the inner surface of the outer layer, and the 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, or the intermediate layer and the inner layer. In a composite roll in which and are welded to each other, the outer layer is formed of a high-speed cast iron material having graphite on the surface, the intermediate layer is an adamite material, and the inner layer is formed of a casting steel material having toughness. . The inner layer is preferably made of a graphite crystallized material composed of flake graphite cast iron, spheroidal graphite cast iron or graphite steel, and the intermediate layer has C: 1.0-2.
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,
Due to the presence of a high hardness composite carbide in which Nb, V, Fe and C are bonded to each other in the matrix, and by strengthening the matrix with Co, the hardness at room temperature and high temperature is improved and wear resistance is dramatically improved. To do. Furthermore, since C and Si are specified in a specific range, graphite has an area ratio of 0.1 in the structure.
Approximately 7.0% crystallizes and precipitates, and the action of this graphite can alleviate the impact load, prevent the development of cracks, and reduce the friction coefficient and improve the seizure resistance.

By using a high speed cast iron material containing graphite as the outer layer material of the composite roll, the excellent characteristics of the material can be exhibited during rolling, the rolling load and the friction heat are reduced, and the strip running property is improved. It is possible to provide a rolling roll capable of suppressing the progress of cracks. Since this rolling roll has good seizure resistance due to the action of graphite, it is also suitable as a cold rolling roll.

Further, by forming the intermediate layer between the outer layer and the inner layer using the adamite material, it is possible to prevent the high alloy component of the outer layer from being mixed into the inner layer and deteriorating its toughness. it can. Further, since the boundary portion between the intermediate layer and the inner layer is made of a low alloy, the formation of the carbide layer is suppressed, and the boundary strength can be improved. In addition, it is possible to prevent the temperature rise of the inner layer during the austenite heat treatment of the outer layer, and prevent the deterioration of the toughness of the inner layer material, while only the outer layer is 1100 ° C.
It can be heated to the above high temperature. Further, since martensitic transformation does not occur during quenching of the outer layer, even if the outer layer is subjected to quenching heat treatment, excessive residual stress does not occur, resulting in excellent accident resistance.

Further, by forming the inner layer from flake graphite cast iron, spheroidal graphite cast iron or graphite steel, that is, a steel material in which graphite is crystallized, combined with the presence of graphite in the outer layer, it is excellent in heat conductivity and hence heat dissipation, and is rolled. It is possible to prevent thermal deformation of the roll at that time. Further, the Young's modulus can be made considerably lower than that of the outer layer, and it is possible to prevent excessive stress in the outer layer due to flattening of the roll during overload.

[0011]

EXAMPLES First, the reasons for limiting the chemical composition of the high speed cast iron material having graphite of the present invention will be explained. Hereinafter, the unit of all components is wt%. C: 1.8 to 3.6% C mainly combines with Fe and Cr to form a M ₇ C ₃ type high hardness composite carbide, and also contains Cr, Mo, V, N.
It also combines with b and W to form high hardness composite carbides such as MC type, M ₆ C type and M ₂ C type. Further, due to the action of Si, which is a graphitization-promoting element described later, and by heat treatment, fine graphite is formed and crystallizes and precipitates in the structure. If it is less than 1.8%, the amount of carbides will decrease and graphite will almost disappear.
If the content exceeds 3.6%, the amount of carbide and the amount of graphite become excessive and the material becomes brittle.

Si: 1.0 to 3.5% Si is an element necessary for securing the flowability of molten metal and crystallizing and precipitating graphite. If it is less than 1.0%, the action is insufficient, while if it exceeds 3.5%, graphite is not formed. The area ratio exceeds 7%, resulting in excessive wear starting from graphite and deterioration in wear resistance. In order to promote crystallization of graphite, it is preferable that the amount of Si before casting is made lower than the above-mentioned range of components, inoculation is performed at the time of casting, and the components of the final product are adjusted to be within the above range.

Mn: 0.1-2.0% Mn is an element which increases the hardening ability and which combines with S to form MnS to prevent embrittlement due to S. At the same time, about 0.1% is inevitably contained from the raw materials used. To be done. But 2.0
%, It is not preferable because the toughness is deteriorated. Cr: 2.0-10% Cr combines with C together with Fe, Mo, V, Nb, W,
It forms a high hardness composite carbide and contributes to the improvement of wear resistance at high temperatures. In addition, some of them form a solid solution in the matrix to improve hardenability and wear resistance. If it is less than 2.0%, these effects are small, while if it exceeds 10%, toughness is deteriorated, which is not preferable.

Mo: 0.1-10% Mo easily bonds with C along with Fe, Cr, V, Nb and W.
And mainly M₇C ₃Mold, M₆C type, M₂C type composite coal
To increase wear resistance by increasing the hardness at room temperature and high temperature.
Contribute to improvement. Mo is effective when added in a small amount compared to W
Exert fruit. In this case, if less than 0.1%, the effect is excessive.
On the other hand, if it exceeds 10%, the toughness decreases, which is preferable.
No

W: 0.1 to 10% Similarly, W also easily combines with Fe, Cr, Mo, V, and Nb to form C to form a composite carbide, which increases the hardness at room temperature and high temperature and contributes to the improvement of wear resistance. To do. If it is less than 1.5%, the desired wear resistance cannot be obtained, while if it exceeds 10.0%, the toughness is lowered and the heat crack resistance is deteriorated. Also, it facilitates the generation of macrosegregation during centrifugal casting. Therefore, it should be 10.0% or less.

V, Nb: One or two kinds in total of 1.5 to 10% V easily binds to C together with Fe, Cr, Mo and W similarly to Nb to form mainly MC type composite carbide, It contributes to the improvement of wear resistance by increasing the room temperature and high temperature hardness.
Further, since this 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 be exhibited unless 1.5% or more is added alone or in combination of two kinds. However, if the addition amount exceeds 10%, the toughness is deteriorated, and macro segregation is likely to occur during centrifugal casting.

The high-speed cast iron material according to the present invention is formed of Fe and the unavoidably mixed impurities in addition to the above alloy components. In addition, P and S are inevitably mixed from the raw material, but it is desirable to reduce P and S because it makes the material brittle.
It is better to keep it below 2% and S: 0.1% or less. In the cast iron material of the present invention, in addition to the alloy components, if necessary,
Co: 0.5 to 10.0%, and / or A in the following composition range
One, two or more of 1, Ti, and Zr, or / and B: 0.01 to 0.50% can be contained.

Co: 0.5 to 10.0% Co has a great effect on improving the base. Co is C
Has a special effect of suppressing the diffusion of carbon and 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 the austenite, so that the hardness of the matrix and the tempering resistance increase. In order to expect these effects, 0.5% or more must be contained, but 10.
Even if added in excess of 0%, the effect is saturated and it is an expensive element, so 0.5 to 10.0% is specified. Incidentally, when casting a high-alloy cast iron material by centrifugal 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 Co-containing high alloy material of the present invention, Co dissolves in the matrix irrespective of the formation of carbides as described above, so that the non-uniformity of carbides is reduced. The above-mentioned excellent effects can be expected without increasing the size.

Al, Ti, Zr: 0.01 to 0.50% Al, Ti, Zr each form an oxide in the molten metal, which lowers the oxygen content in the molten metal and improves the soundness of the product. Since the oxide thus formed acts as a crystal nucleus, it is effective in refining the solidified structure. If it is less than 0.01%, this effect is not sufficient, while if it exceeds 0.50%, it remains as inclusions, which is not preferable. In addition, Al, T
In the present invention, i and Zr are added mainly for the purpose of improving the wear resistance by refining the cast structure, and are not added simply for the purpose of degassing.

B: 0.01 to 0.50% B exhibits a deoxidizing effect by combining with oxygen in the molten metal. In addition, the effect of refining the solidified structure with the generated oxide as the core,
Also, it has the effect of increasing the hardenability due to B dissolved in the matrix. In the case of a large-mass casting such as a rolling roll, it may be difficult to increase the cooling temperature, but the increased hardenability makes it easier to obtain a hardened structure. If it is less than 0.01%, such an effect is not sufficient, while if it exceeds 0.50%, the material becomes brittle, which is not preferable.

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, high-grade cast iron, ductile cast iron, graphite steel, cast steel, and other steel materials for casting having high toughness are used. In particular, the former three, which are graphite crystallized materials, are suitable. This is because, in combination with the presence of the graphite in the outer layer, the thermal conductivity and hence the heat dissipation are excellent, and the thermal deformation of the roll during rolling can be prevented. In addition, since the Young's modulus of these graphite crystallized iron and steel materials is about 19000 kg / mm ² or less, the load is absorbed by the flattening of the rolls when overloaded, and the accident resistance can be improved. Further, the low temperature strain relief annealing can easily reduce the residual stress during the heat treatment of the outer layer. Further, since it has good toughness, it can withstand shocking rolling torque. Hereinafter, preferable composition examples (wt%) of high-grade cast iron, ductile cast iron, and graphite steel are shown. (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 mixed from the outer layer or the intermediate layer and substantially Fe Incidentally, when the outer layer contains Al, Ti, Zr, these elements are also included. It mixes into the inner layer from the outer layer or through the intermediate layer, but since it is a very small amount, there is almost no problem in terms of material. The composition of the molten metal before casting is determined so as to be the above composition after welding, and an example of the composition is 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. A suitable molten metal composition before casting 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 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 mixed from outer layer or intermediate layer and substantially Fe In addition, the suitable molten metal composition before casting is illustrated below.

C: 1.0 to 2.3%, Si: 0.5 to 3.0%, Mn: 0.2 to 1.5%, P: 0.2% or less, S: 0.2% or less, Ni: 3.0% or less, Cr: 2.0% or less, Mo: 2.0% or less, balance: Substantially Fe Next, the intermediate layer will be described. The intermediate layer is formed for the purpose of reducing the mixing of the alloy components of the outer layer into the inner layer, but the intermediate layer itself must have a strength of about 30 kg / mm ² . If the strength is insufficient, the boundary between the outer layer and the intermediate layer is broken, 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 alloying components are mixed 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 shown.

C: 1.0 to 2.5% C contributes to the improvement of strength, but if it is less than 1.0%, the freezing point becomes high and the welding tends to be insufficient. On the other hand, if it exceeds 2.5%, the amount of carbide becomes excessive and the material becomes brittle. Si: 0.2-3.0% Si has an action of promoting degassing and an action of improving the flowability of molten metal.
If it is less than 0.2%, such an effect cannot be expected, while 3.0%
If it exceeds, the material becomes brittle. In the high Si region, crystallization of graphite may be observed in relation to the Ni content, but there is no problem with the material.

Mn: 0.2-1.5% Mn is limited to the above range for the same reason as that of the ductile cast iron as the inner layer material. Ni: 4.0% or less Ni has the function of strengthening the material. However, if it exceeds 4.0%, the action is saturated and an untransformed structure is apt to occur, resulting in deterioration of strength.

Cr and Mo: 4.0% or Less Each Cr and Mo have the function of strengthening the material. But 4.0
If it exceeds%, the mechanical properties will rather deteriorate. W, V, Nb: 12% or less in total Although these elements have almost no effect on improving the material of the intermediate layer, mixing from the outer layer is inevitable. 12% is acceptable as a range that does not deteriorate the mechanical properties of the intermediate layer material. When the outer layer contains Al, Ti, Zr, and B, these elements also inevitably enter the intermediate layer. in this case,
For the same reason, statistically, including these elements, 12% or less. Co is also inevitably mixed from the outer layer, but it is not particularly limited because it does not deteriorate the material of the intermediate layer.

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

C: 1.0 to 2.5%, Si: 0.2 to 3.0%, Mn: 0.2 to 1.5%, P: 0.2% or less, S: 0.2% or less, Ni: 4.0% or less, Cr: 4.0% or less, Mo: 4.0% or less, balance: Fe When a 1.0 to 2.5% C intermediate layer is provided between the outer layer and the inner layer (axial core), harmful alloying elements in the inner layer are deposited from the outer layer to the inner layer during welding. In addition to being able to greatly suppress the direct mixture into the, the following effects.

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

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

As a method for casting the composite roll, as is well known, an outer layer and, if necessary, an intermediate layer are cast by a die centrifugal casting method, and then a solid inner layer is statically cast therein.
When the sleeve-shaped roll is cast, the inner layer may of course be centrifugally cast. In the centrifugal casting method, the rotation axis of the cylindrical mold is horizontal in the horizontal direction, oblique in the diagonal direction,
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 with each rotation of the mold, there is a change in G, and the eccentricity of the roller and the mold causes Vibration is likely to occur due to scratches, and the components in the cast outer layer material melt are likely to move. For this reason, when a thick outer layer is cast, segregation is likely to occur due to the movement of components, so it is usually preferable to cast at a relatively low temperature below the solidification start temperature of about + 70 ° C. However, since the outer layer material according to the present invention is a highly wear-resistant material, it is hard to wear, and the outer layer may be relatively thin, and it is rapidly cooled by a mold until the casting thickness is about 80 mm (desirably 55 to 70 mm). Therefore, there is almost no risk of segregation even when casting is performed at a temperature higher than the above temperature. The thickness of the outer layer of the product is about 50 mm (desirably 25 to 40 mm) considering the melting margin of 20 mm and the machining margin of 10 mm.

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

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

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

The high speed cast iron material having graphite of the present invention is
Not only rolling composite rolls for hot rolling or cold rolling, but also rolls for which abrasion resistance is required, such as pinch rolls or rollers for transporting rolled material in rolling auxiliary equipment,
Although it is suitable as an outer layer material for 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 machine parts that require abrasion resistance.

Next, specific examples of the present invention will be given. 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. In the examples, Sample Nos. 1 to 9 are No. 10 conventional high-speed roll materials. The unit of composition in the table is% by weight, and the balance is substantially Fe.

[0039]

[Table 1]

(2) Tissue observation test pieces were collected from each sample,
The microstructure was observed under a microscope to measure the area ratio of crystallized graphite. The results are shown in Table 2. From the table, graphite is crystallized in an area ratio of 0.7 to 3.8% in the examples, but no graphite crystallization was observed in the conventional high speed wear-resistant material.

[0041]

[Table 2]

(3) Next, after holding each sample at 1100 ° C. for 1 hour, it is quenched by forced air cooling and then at 540 ° C. for 10 hours.
The tempering heat treatment of hr was repeated 3 times. The results of measuring the surface hardness of each sample are also shown in Table 2. From the table, it is presumed that the examples and the conventional examples have substantially the same hardness, and the alloys of the examples also have excellent wear resistance. (4) Further, a friction test piece was sampled from each sample, and the friction coefficient was measured by the Falex test. In the Falex test, a test piece is rotated and is nipped and pressed by a pair of V blocks (material stainless steel SUS430), and the friction coefficient and seizure property are examined by 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 outer layer molten metal shown in Table 3 was centrifugally cast into a die for centrifugal force casting having an inner diameter of 810 mm, and in Sample Nos. 13 and 14, after the outer layer was completely solidified, the middle of the same table was obtained. The molten layer material 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 middle 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 inner layer having the outer layer and the middle layer was erected vertically, and the upper mold and the lower mold were connected in series at both ends, and shown in the same table together. Inner layer material (core material) Cast molten metal.

[0043]

[Table 3]

(3) After roughing the cast composite rolls, after uniformly preheating to 600 ° C., the rolls are placed between gas burners that are horizontally opposed to each other and are arranged in parallel at a pitch of 250 mm along the roll axial 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 part of the inner layer reached 120 ° C and 900 ° C. The time required for heating was 180 minutes. In the case of this example, the temperature near the outer peripheral surface of the inner layer was estimated to be 1030 ° C from the temperature data of heat conduction. (4) Immediately after the heating was stopped, spray water cooling was performed, the roll surface temperature was rapidly cooled to 500 ° C, and then allowed to cool to room temperature. After that, a tempering heat treatment of holding 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 layer of the example has high hardness and excellent wear resistance. Further, when the microstructure of the body surface was observed, graphite having an area ratio of 1.5 to 3.5% was recognized.

[0045]

[Table 4]

(5) After finishing the surface of the cylinder, the welding condition was confirmed by an ultrasonic flaw detection test. The welding was good for all rolls. Next, when the roll body was cut and the cross section of the outer layer was visually observed, segregation of the components was not observed in any of the rolls. Table 5 shows the results of analysis of the components in the central portion of the thickness of the intermediate layer and the central portion of the inner layer (axial core portion). From the table, it can be seen that in the example in which the intermediate layer is provided, the mixing amount of the outer layer high alloy component in the inner layer is very small.

[0047]

[Table 5]

(6) From the above results, when the roll of the embodiment is used in the hot strip mill finishing stage, it has excellent wear resistance, good stripping property, and can suppress the temperature rise of the roll. Is expected.

[0049]

The high-speed cast iron material having graphite of the present invention has a high hardness composite carbide in which Cr, Mo, W, Nb, V, Fe and C are mutually bonded in the matrix.
Further, by strengthening the base with Co, the hardness at normal temperature and high temperature is improved, and the wear resistance is dramatically improved. Furthermore, since C and Si are specified in a specific range, graphite crystallizes and precipitates in the structure, and the action of this graphite can alleviate the impact load and prevent the development of cracks. The friction coefficient is reduced and the seizure resistance is improved.

The composite roll using the high speed cast iron material having the above graphite as the outer layer material can exhibit the excellent characteristics of the material at the time of rolling, reduce the rolling load and friction heat, and have the stripability. It is possible to improve and suppress the progress of cracks. Further, since it 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 significantly reduce the mixing of high alloy components from the outer layer to the inner layer, and it is possible to improve the boundary strength. ,
Since the martensite transformation does not occur, the residual stress is not increased, and further, it is possible to prevent melting loss and strength reduction of the inner layer during the austenitizing heat treatment of the outer layer.

Further, by forming the inner layer with a graphite crystallized material composed of flake 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 excessive stress in the outer layer due to the flattening of the roll when overloaded, resulting in excellent safety and accident resistance.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hiroyuki Kimura Inventor Hiroyuki Kimura 64 Nishimukojima-cho, Amagasaki City, Hyogo Prefecture Kubota Amagasaki Plant

Claims (8)

[Claims] 1. The chemical composition is wt%, C: 1.8-3.6%, Si: 1.0-3.5%, Mn:
0.1 to 2.0%, Cr: 2.0 to 10%, Mo: 0.1 to 10%, W:
0.1 to 10%, V, Nb: One or two in total of 1.5 to 10%, and the balance being substantially Fe, which is a high-speed cast iron material having graphite. 2. In addition to the alloy components of claim 1, Co: 0.5
A high-speed cast iron material having graphite containing up to 10.0 wt%. 3. In addition to the alloy components of claim 1, 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. In addition to the alloy components of claim 1, B: 0.01-
A high-speed cast iron material having graphite containing 0.50 wt%. 5. A composite roll in which an inner layer is cast on the inner surface of the outer layer and both are welded together, wherein the outer layer comprises:
A composite roll formed of the high-speed cast iron material having graphite described in 3 or 4, wherein the inner layer is formed of a steel material for casting having high toughness. 6. A composite roll in which an intermediate layer is cast on the inner surface of the outer layer, the 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. It is formed of a high-speed cast iron material having graphite described in 2, 3, or 4, the intermediate layer is formed of an adamite material, and the inner layer is formed of a tough steel material for casting. Composite roll. 7. The iron-and-steel material forming the inner layer is flake graphite cast iron,
The composite roll according to claim 5, which is made of spheroidal graphite cast iron or graphite steel. 8. The adamite material according to claim 6 has a chemical composition of wt%, 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, W, V, Nb: 12% or less in total, and the balance being substantially Fe.