JP2002180176A - High alloy grain cast iron material for hot rolling roll made by centrifugal casting - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high alloy grain cast iron material for a hot rolling roll made by centrifugal casting combining surface roughening resistance and wear resistance. SOLUTION: The high alloy grain cast iron material for a hot rolling roll made by centrifugal casting has a composition, as an external layer material, containing, by mass, 2.7 to 4.0% C, 0.5 to 3.5% Si, 0.2 to 2.0% Mn, 2.5 to 7.0% Ni, 0.5 to 2.5% Cr, 0.2 to 1.0% Mo, 0.001 to 0.50% Co, 0.001 to 0.50% B, 0.001 to 0.50% Al, 0.001 to 0.50% Ti and 0.001 to 0.50% Cu, and the balance Fe with inevitable impurities.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used, for example, for hot rolling of steel molds, thin plates, thick plates, etc., and particularly a high alloy for centrifugally cast hot rolling rolls having excellent wear resistance and surface roughening resistance. It is related to Glen cast iron.

[0002]

2. Description of the Related Art In recent years, in the field of hot rolling of iron and steel, for example, in the form of molds, thin plates, thick plates, etc., there is a high demand for improved quality of rolled products. Sex is required. As an outer layer material of a rolling roll corresponding to these requirements, for example, JP-A-8-92698
No. 6,086,045. This technical content is intended to improve the wear resistance and seizure resistance by coexisting graphite and hard carbide in a gray cast iron material having excellent seizure resistance.

[0003]

However, according to this technique, the amount of graphite crystallized is extremely small because V which has a strong tendency to form white iron is contained at 2% or more, and Si is required to crystallize graphite. Inoculation of 0.1% by mass or more in Si amount is performed using the contained inoculant. For this reason, crystallization unevenness and coarsening of graphite are likely to occur, and when applied to a roll material for hot rolling, there is a problem that the surface roughening resistance is poor, and the current severe rolling operation, that is, high speed, high load, large In order to cope with reduction, etc., the abrasion resistance and surface roughening resistance of the rolling roll are not yet sufficient, and as a result, the user has to improve the basic unit of the roll and simplify the maintenance work of the roll. Expectations are still high. In view of the above background, the present invention seeks to further improve the uniformity and fineness of eutectic carbide and graphite existing around the matrix, and as a result, to significantly improve the abrasion resistance and surface roughening resistance of the rolling roll. Its purpose is to

[0004]

The present invention has solved the above-mentioned problems. The gist of the present invention is as follows: (1) In mass%, C: 2.7 to 4.0%, Si: 0.5
-3.5%, Mn: 0.2-2.0%, Ni: 2.5-
7.0%, Cr: 0.5 to 2.5%, Mo: 0.2 to
1.0%, Co: 0.001 to 0.50%, B: 0.0
01 to 0.50%, Al: 0.001 to 0.50%, T
i: 0.001 to 0.50%, Cu: 0.001 to 0.
A high-alloy grain cast iron material for a hot-rolling roll manufactured by centrifugal casting, comprising 50% and an outer layer material comprising the balance of Fe and unavoidable impurities.

(2) As an outer layer material, further,
W: 0.2 to 2.0%, V: 0.2 to 1.8%, Nb:
The high-alloy grain cast iron material for centrifugally cast hot-rolling rolls according to the above (1), which contains 0.2 to 2.0% of one or more kinds. (3) As an outer layer material, Zr: 0.0% by mass.
01-0.50%, Mg: 0.001-0.50%, C
The high-alloy grain cast iron material for hot-rolling rolls manufactured by centrifugal casting according to claim 1 or 2, which contains one or more of a: 0.001 to 0.50%.

Hereinafter, the present invention will be described in detail. The microstructure of the Glen cast iron material of the present invention is generally composed of a matrix structure of eutectic carbide and graphite and bainite or martensite. In the present invention, in order to make the eutectic carbide and graphite uniform and fine in the microstructure of the grain cast iron, B, Al, Ti
It has been found that it is effective to add a small amount of compound. In addition, simultaneous addition of trace amounts of Cu and Co
It was found to be very effective in strengthening the matrix structure. As a result, the wear resistance and surface roughness resistance of the Glen cast iron roll could be greatly improved.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting each chemical component according to the present invention will be described below. C: 2.7 to 4.0% C is mainly graphite and Fe, Cr, Mo, Nb,
Combines with V, W, etc. to form various carbides. Further, they are dissolved in the matrix to form a bainite or martensite phase. The larger the content, the more effective in improving the wear resistance. However, if the content exceeds 4.0%, graphite or carbide, which is a feature of the present invention, even if a small amount of B, Al, Ti, etc., is contained. Was coarsely crystallized as a primary crystal and uniformity and fineness could not be achieved, so the upper limit was made 4.0%. When the content is less than 2.7%, the amount of carbides is small and wear resistance deteriorates. Therefore, the lower limit is set to 2.7%.

Si: 0.5 to 3.5% Si is added for the purpose of crystallizing graphite. But,
If it is less than 0.5%, the effect is insufficient, and conversely,
If it exceeds 3.5%, the toughness is reduced, so the range is set to 0.5 to 3.5%. Mn: 0.2 to 2.0% Mn is added for the purpose of deoxidation and desulfurization. However, if it is less than 0.2%, the effect is insufficient, and if it exceeds 2.0%, the toughness is reduced, so the range is made 0.2 to 2.0%.

Ni: 2.5 to 7.0% Ni is dissolved in the matrix to stabilize bainite and martensite. For that, 2.5%
It is necessary to contain the above. However, when the content exceeds 7.0%, the amount of retained austenite becomes excessive, and it becomes difficult to secure hardness. Therefore, the range is 2.5 to
It is set to 7.0%. Cr: 0.5 to 2.5% Cr is added for increasing hardenability, increasing hardness, increasing temper softening resistance, stabilizing carbide hardness, and the like. However, if it exceeds 2.5%, the eutectic carbide content will increase too much and the toughness will decrease, so the upper limit is made 2.5%. On the other hand, 0.
If it is less than 5%, the effect of the addition cannot be obtained. Therefore, the range is set to 0.5 to 2.5%.

Mo: 0.2 to 1.0% Mo, like Cr, is added for increasing hardenability, increasing hardness, increasing temper softening resistance, stabilizing carbide hardness, and the like. However, if the content exceeds 1.0%, the eutectic carbide content increases too much and the toughness decreases, so the upper limit was set to 1.0%. On the other hand, if it is less than 0.2%, the effect of the addition cannot be obtained. Therefore, the range is set to 0.2 to 1.0%.

Co: 0.001 to 0.50% Co is a main chemical component of the present invention together with B, Al, Ti, Cu and the like described above. Most of them are dissolved in the matrix to strengthen the matrix. Therefore, it has the effect of improving the hardness and strength at high temperatures. However, 0.0
If it is less than 01%, the effect is insufficient, and if it exceeds 0.50%, the effect is saturated. Therefore, from the viewpoint of economy, it is set to 0.50% or less.

B: 0.001 to 0.50% When B is 0.001% or more, the hardenability is enhanced, the toughness is prevented from being lowered, and the crystallized graphite is uniformly and finely dispersed. However, if it is excessive, the toughness is reduced, so it is necessary to suppress the toughness to 0.50% or less. Al: 0.001 to 0.50% Al forms an oxide in the molten metal, lowers the oxygen content in the molten metal, improves the soundness of the product, and generates the oxide as a crystal nucleus. Coagulated tissue to act,
In particular, it is effective for fine dispersion of eutectic carbide. But,
The effect is 0.001%, but if contained too much, it becomes an inclusion and remains in the product,
The upper limit was set to 0.50%.

Ti: 0.001 to 0.50% Ti forms a solid solution in the eutectic carbide and has an effect of improving wear resistance and finely dispersing the crystallized shape of the eutectic carbide. Further, they are dissolved in the matrix to strengthen the matrix. In order to improve wear resistance, the content must be at least 0.001% or more. However, if it exceeds 0.50%, graphite crystal, which is an important component in the microstructure of high-alloy grain cast iron, is used. Inhibits outflow.

Cu: 0.001 to 0.50% Cu is used to strengthen the base structure and improve the high-temperature hardness.
Along with B, Al, Ti and the like, it is a main chemical component of the present invention. However, if the content is less than 0.001%, the effect is not obtained. On the other hand, if the content exceeds 0.50%, the wear resistance and the crack resistance are reduced and the surface properties of the roll are deteriorated. And

The basic components of the material of the present invention are as described above. However, depending on the size of the roll to which the material is to be applied, the required characteristics of use of the roll, etc., the above-mentioned chemical component of the present invention may be used as other chemical components. In addition to the above, the chemical components described below may be appropriately selected and contained. W: 0.2 to 2.0% W is dissolved in a matrix similarly to Mo to strengthen the matrix, and combines with C to form eutectic carbides such as M ₂ C and M ₆ C. Improves wear resistance. To strengthen the base, it is necessary to contain at least 0.2% or more, but 2.0%
If it exceeds 300, coarse carbides are formed and toughness is reduced. The selection of the addition or non-addition of W may be appropriately determined based on, for example, the size of the roll to be applied, required roll use characteristics, and the like.

V: 0.2-1.8% V combines with C to form a high-hardness MC carbide, improves wear resistance, and is solid-dissolved in the matrix to strengthen the matrix. . 0.2% minimum to strengthen base
The above content is necessary, but if it exceeds 1.8%, the eutectic MC carbide becomes too coarse, leading to a decrease in toughness, and, as described above, inhibits the crystallization of graphite. . The selection of the addition or non-addition of V may be appropriately determined based on, for example, the size of the roll to be applied, required roll use characteristics, and the like.

Nb: 0.2-2.0% Nb hardly forms a solid solution in the matrix, and most forms MC carbide having high hardness, thereby improving wear resistance. However, if the content is less than 0.2%, the effect is insufficient. If the content is more than 2.0%, MC carbides are crystallized as coarse primary dendrites as primary crystals, leading to a decrease in toughness. . The selection of the presence or absence of Nb may be appropriately determined based on, for example, the size of the roll to be applied and the required roll use characteristics.

Zr: 0.001 to 0.50% Zr forms an oxide in the molten metal, lowers the oxygen content in the molten metal, improves the soundness of the product, and reduces the generated oxide. Since it acts as a crystal nucleus, it is effective in refining a solidified structure. However, the effect is 0.001%, but if contained too much, it will become an inclusion and remain in the product, so the upper limit is 0.50%
It was made to become.

Mg, Ca: 0.001 to 0.50% Mg, Ca is an element most contributing to the improvement of the roughening resistance of the rolling roll of the present invention. Mg and Ca are elements having strong deoxidation and desulfurization effects, and generate oxides of MgO and CaO, which are suspended in the molten metal to become nuclei, and microcrystalline uniformly as MC carbide as primary crystals. Further, although the reason is not clear, it has been found that the MC carbide to be crystallized becomes spherical due to an effect expected to be similar to that of graphite of spheroidal graphite cast iron being spherical by the addition of these elements. The effect is recognized when the amount of Mg or Ca is 0.001% or more, respectively. However, if the content exceeds 0.50%, the effect is saturated, and addition of a large amount of an Mg alloy or a Ca alloy is dangerous in terms of work due to severe reaction with the molten metal. Therefore, the ranges of Mg and Ca are set to 0.001 to 0.
50%.

N: 1000 ppm or less N is 1000 ppm or less in order to improve the resistance to rough skin. That is, when the content is 1000 ppm or less, the nucleus growth effect on carbides is suppressed, the amount of spherical primary crystal carbides is reduced, and instead, elongated and fine eutectic carbides are increased, and VC carbides are finely and uniformly dispersed. Thereby, rough skin resistance is reduced. However, if the concentration exceeds 1000 ppm, the effect is lost.
It was set to 0 ppm. Note that the concentration is preferably 500 ppm or less, more preferably 300 ppm. As a method of reduction, it is also effective to use a small amount of N, such as roll scrap or scrap material, which is a raw material of the roll, and to dissolve the raw material in an atmosphere of an inert gas such as Ar in a melting furnace. It is.

O: 500 ppm or less If O is contained in a large amount because it becomes a nonmetallic inclusion and lowers the cleanliness of the material, casting cracks are likely to occur.
Therefore, the reduction amount is set to 500 ppm or less. Note that the concentration is desirably 300 ppm or less, more desirably, 100 ppm. As a reduction method, for example, it is effective to dissolve the raw materials in an atmosphere of an inert gas such as Ar in the melting furnace. P and S are
It is unavoidable to be mixed in from the raw material, and the less the material is, the more preferable it is. Therefore, P: 0.2% or less,
S: 0.1% or less is good.

[0022]

EXAMPLES Examples of the present invention will be described below together with conventional materials. (Example 1) The steel shown in Table 1 was subjected to 1470 in a high-frequency induction furnace.
After melting at a temperature of 100 ° C., the molten metal was 100 mm in diameter and 10 mm in height.
It was cast at 1320 ° C. in a 0 mm sand mold. Thereafter, the test piece was heated at 400 to 450 ° C. for 10 hours and gradually cooled to decompose residual austenite and remove strain, thereby preparing a hot wear test piece. Next, a comparative test was performed using the hot rotary wear tester shown in FIG. In addition, the rolling device 3 which rotates the heating piece 1 and the test piece 2 in a contact state as shown in FIG.
Further, a disk-to-disk type testing machine which surrounds the test piece 2 and has a high-frequency induction heating coil 4 for cooling them, a cooling device 5 and a radiation thermometer 6 was used. The test condition at that time is that the maximum contact stress between both disks is about 25kg
At f / mm ² , the peripheral speed (number of rotations) of the test piece 2 is 720
rpm, and the slip ratio between both disks was 4.5%. The temperature of the heating piece corresponding to the hot-rolled material is 960.
° C, the temperature of the test piece was 650 ° C, and 500 rotations were performed, and the wear amount of the test piece was measured. Thereafter, the surface roughness of the test piece after the wear test was measured.

[0023]

[Table 1]

FIG. 2 is a graph showing the results of measurement of the loss of wear of the materials A to N of the present invention and the materials O to R of the prior art by a hot rotational wear test. FIG. 3 is a view showing the measurement results of the surface roughness of the test piece after the hot rotational wear test of the material of the present invention and the conventional material. As is clear from FIGS. 2 and 3, the materials A to N of the present invention have less abrasion loss compared to the conventional materials O to R, and have a surface as an index for evaluating the resistance to rough skin. The roughness is also small. From the results of the above various tests, it is clear that the material of the present invention, when applied to an actual rolling roll, sufficiently exerts its intended abrasion resistance and surface roughness resistance action and effect.
The result applied to an actual rolling roll will be described.

Example 2 A molten metal having the chemical composition of the present invention shown in Table 2 melted by using a low-frequency induction furnace was used as an outer layer molten metal and incorporated in a horizontal centrifugal casting machine with an inner diameter of 800 mm.
It was cast into a rotary mold having a length of 2000 mm, and after an appropriate time, a molten metal having a chemical composition of ductile cast iron as an inner layer material was injected in several degrees. The melting temperature is 1470 ° C and the casting temperature is 1320 ° C. After casting, the resultant was heated at 430 ° C. for 10 hours and gradually cooled to decompose residual austenite and remove distortion, and then finished. Thereafter, ultrasonic testing was performed to confirm that the roll was a sound rolling roll having no defects. Subsequently, the roll was subjected to actual hot finish rolling. As a result, it was confirmed that, compared to the conventional rolling roll, the basic unit of the roll was improved by about 20% due to the improvement of the wear resistance and the surface roughening resistance, and the effect of the material of the present invention was great.

[0026]

[Table 2]

[0027]

As described above, according to the present invention, B, Al, Ti and the like are used for the purpose of further uniformizing and refining eutectic carbide and graphite in a centrifugally cast hot-rolled gray cast iron material. Is added in a very small amount to greatly improve the wear resistance and the surface roughening resistance. In addition, the addition of a small amount of Cu and Co enhances the matrix structure and improves the wear resistance. This makes it possible to significantly improve the surface roughness resistance and the wear resistance, and to extend the life of the hot rolling roll. As a result, there is an effect that the roll basic unit is greatly improved. Further, there is an effect that the quality of a rolled product is significantly improved by improving the roll performance.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a schematic configuration of a hot rotary wear tester.

FIG. 2 is a view showing a wear loss of a material of the present invention and a conventional material by a rotational wear test.

FIG. 3 is a diagram showing the surface roughness of a material of the present invention and a conventional material after a rotational wear test.

[Description of Signs] 1 Heating piece 2 Test piece 3 Rolling device 4 High frequency induction heating coil 5 Cooling device 6 Radiation thermometer

Claims (3)

[Claims] 1. Mass% as outer layer material: C: 2.7 to 4.0%, Si: 0.5 to 3.5%, Mn: 0.2 to 2.0%, Ni: 2.5 To 7.0%, Cr: 0.5 to 2.5%, Mo: 0.2 to 1.0%, Co: 0.001 to 0.50%, B: 0.001 to 0.50%, Al: 0.001 to 0.50%, Ti: 0.001 to 0.50%, Cu: 0.001 to 0.50%, and the centrifugal layer is composed of an outer layer material composed of Fe and inevitable impurities. High alloy grain cast iron for hot rolling rolls made by casting. 2. The outer layer material further includes: W: 0.2 to 2.0%, V: 0.2 to 1.8%, Nb: 0.2 to 2.0% by mass%. 2. The high-alloy grain cast iron material for centrifugally cast hot rolling rolls according to claim 1, which contains at least one kind or two or more kinds. 3. The outer layer material further comprises, by mass%, Zr: 0.001 to 0.50%, Mg: 0.001 to 0.50%, Ca: 0.001 to 0.50%. The high-alloy grain cast iron material for centrifugally cast hot rolling rolls according to claim 1 or 2, which comprises at least two kinds of grains.