JPH09170040A - High speed steel type cast iron material containing crystallized graphite, excellent in surface roughting resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the surface roughing resistance of a high speed steel type cast iron material containing crystallized graphite, used as an outer layer material for a composite roll for rolling, while securing desired wear resistance. SOLUTION: This high speed steel type cast iron material has a composition consisting of, by weight, 2.5-3.6% C, 1.0-3.5% Si, 0.1-2.0% Mn, <2.0% Cr, 0.1-5.0% Mo, 0.1-5.0% W, 0.5-5.0% Nb, and the balance essentially Fe and containing, if necessary, 0.5-10.0% Co, and further, graphite is crystallized in the structure of this material by 2.0-9.0% by area ratio.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a graphite crystallized high-speed cast iron material suitable as an outer layer material of a composite roll for rolling.

[0002]

2. Description of the Related Art Conventional graphite crystallized high-speed cast iron materials used as outer layer materials for rolling composite rolls are Cr, M
O, V, Nb, W, etc., containing an element forming a high hardness composite carbide (for example, JP-A-6-256889).
Reference).

[0003]

Carbides that crystallize in cast iron have high hardness and greatly contribute to ensuring wear resistance.
On the other hand, since it has a large amount of carbon, it is relatively brittle. Therefore, when hot rolling and temperature lowering are repeated on the roll surface like hot rolling, due to the difference in the thermal expansion coefficient of the cast iron matrix and the carbide, a relatively brittle carbide causes microscopic chipping. easy. Even in cold rolling, the surface temperature of the rolled material rises due to heat generated by friction during rolling, and the temperature rise and fall of the roll surface are repeated, so that microscopic chipping of carbides occurs. Further, when used under a rolling condition under high heat load, fine heat cracks are inevitably generated on the roll surface, and due to the heat cracks, microscopic chipping of carbides is more likely to occur.

Among the carbides, the M ₇ C ₃ type composite carbide formed of Cr and Fe and other components is crystallized in the vicinity of the grain boundaries, so that other M ₆ C type, M ₂
Compared with C-type carbides, microscopic chipping tends to occur particularly easily. The microscopic chipping wear of the carbide causes roughening of the surface of the roll and has a disadvantage of deteriorating the surface properties of the rolled product.

The MC type carbide formed by V and Nb is formed in a branch shape in the thickness direction and suppresses plastic deformation of the matrix, which contributes to not only abrasion resistance but also improvement of mechanical properties. . However, since MC-type carbides start to precipitate at a temperature considerably higher than the graphite crystallization temperature as compared with other carbides, carbon contained in the molten metal is first consumed near the crystallization part of MC-type carbides. As a result, the crystallization of graphite tends to be suppressed. In particular, V tends to preferentially form MC type carbides and prevent crystallization of graphite. Graphite reduces the friction coefficient and relaxes the impact load, so that the M ₇
It has an action of suppressing chipping of C ₃ type carbide. For this reason, if the amount of crystallized graphite is insufficient, it is difficult to suppress chipping of M ₇ C ₃ -type eutectic carbide, and the surface of the roll tends to be rough. An object of the present invention is to provide a graphite crystallized high-speed cast iron material in which the surface of the roll is hard to be rough.

[0006]

In order to achieve the above object, in the high-speed cast iron material of the present invention, the crystallization amount of carbides is set to the minimum amount necessary to secure desired wear resistance. The components are adjusted as described above, and a predetermined amount of graphite is surely crystallized. That is, the crystallization amounts of the M ₇ C ₃ -type eutectic carbide that easily causes microscopic chipping and the MC-type carbide that suppresses graphite crystallization were adjusted to be smaller than those of the conventional cast iron material. It is characterized by

Specifically, the high speed cast iron material of the present invention is
% By weight, C: 2.5 to 3.6%, Si: 1.0 to 3.5
%, Mn: 0.1 to 2.0%, Cr: less than 2.0%, M
o: 0.1 to 5.0%, W: 0.1 to 5.0%, Nb: 0.0.
5 to 5.0%, optionally Co: 0.5 to 10.0%, the balance consisting essentially of Fe, and the crystallization amount of graphite is
The area ratio is within the range of 2.0 to 9.0%. If the crystallized amount of graphite is less than 2.0%, the effect of reducing the friction coefficient and mitigating impact relaxation is insufficient, while if it exceeds 9.0%, the material becomes brittle. It is more desirable to crystallize 5% or more of graphite in order to fully enjoy the above-mentioned effects due to crystallization of graphite.

[0008]

The M ₇ C ₃ type composite carbide is a eutectic carbide,
Cr is an essential component for its formation. Since the graphite crystallized high-speed cast iron material of the present invention has a low Cr content, M ₇ C ₃
There is also little formation of eutectic carbides in the mold. Therefore, microscopic chipping of carbides is reduced, roughening of the roll surface is prevented, and a predetermined surface roughness can be maintained. Further, in the graphite crystallized high-speed cast iron material of the present invention, the element forming MC type carbide is only Nb. Therefore, the formation of MC-type carbides can be suppressed to the necessary minimum amount, so that a desired amount of graphite can be crystallized. Due to the presence of graphite, the impact load is relaxed, and as a result, microscopic chipping of M ₇ C ₃ -type carbide is reduced, and surface roughening can be prevented.

[0009]

[Explanation of reasons for limiting ingredients]

C: 2.5-3.6% C combines with Fe, Cr, Mo, W and Nb to form a high hardness composite carbide. 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. In order to secure a proper amount of carbide and graphite, the content of C is specified to be 2.5 to 3.6%.

Si: 1.0 to 3.5% Si is an element necessary for securing the flowability of molten metal and for crystallizing and precipitating graphite. If the content is less than 1%, the desired effect cannot be obtained. On the other hand, if it exceeds 3.5%, the amount of crystallization / precipitation of graphite becomes excessive, and there is a possibility that the abrasion starting from graphite becomes remarkable. Therefore, the content is 1.0-3.
Specify 5%. In order to promote the crystallization of graphite, it is preferable that the amount of Si before casting is set to be smaller than the above component range, inoculation is performed at the time of casting, and the content is adjusted within the above range with the components of the final product.

Mn: 0.1-2.0% Mn has the function of increasing the curing ability. Further, it is an element effective for forming MnS by combining with S and preventing embrittlement due to S. On the other hand, if the content is too large, the toughness is lowered, so the content is specified to be 0.1 to 2.0%.

Cr: less than 2.0% Cr combines with C together with Fe, Mo, Nb, and W to form mainly M ₇ C ₃ type composite carbide, which increases hardness and improves wear resistance. Contribute. However, under rolling conditions under high heat load, the M ₇ C ₃ type carbide easily causes microscopic chipping due to heat cracks, which causes roughening of the roll surface. Therefore, in the present invention, the content of Cr is specified to be less than 2.0%.

Mo: 0.1-5.0% Mo combines with C along with Fe, Cr, Nb and W to form mainly M ₇ C type, M ₆ C type and M ₂ C type composite carbides. And contributes to the improvement of wear resistance by increasing the hardness. Therefore, it is contained at least 0.1% or more. On the other hand, if the content is too large, it becomes difficult to obtain a predetermined amount of graphite. For this reason. , The upper limit is set to 5.0%.

W: 0.1 to 5.0% Similarly, W also combines with Fe, Cr, Mo, and Nb together with C to mainly form a composite carbide, which increases hardness and contributes to improvement of wear resistance. To do. Therefore, it is contained at least 0.1% or more. On the other hand, if the content is too large, it becomes difficult to obtain a predetermined amount of graphite. For this reason. , The upper limit is set to 5.0%.

Nb: 0.5 to 5.0% Nb combines with Fe, Cr, Mo and W together with C to form mainly MC type carbides, which increases hardness and contributes to improvement of wear resistance. To do. Further, since MC type carbides are formed in a branch shape in the thickness direction and suppress plastic deformation of the matrix, they contribute to improvement of mechanical properties and further crack resistance. Therefore, it is contained at least 0.5% or more. On the other hand, if the content is too large, the carbide easily segregates,
It becomes difficult to obtain a predetermined amount of graphite. Therefore, the upper limit is set to 5.0%.

The high-speed cast iron material of the present invention contains the above components, and the balance is formed of Fe and inevitable impurities. For example, P and S are inevitably mixed in from the raw material, but are preferably as small as possible because they make the material brittle. P: 0.2
%, S: 0.1% or less. Incidentally, the cast iron material of the present invention, in addition to the above alloy components, if necessary,
Co: 0.5 to 10.0% can be contained.

Co: 0.5 to 10.0% Co has a great effect on improving the base. Co has a special action of suppressing the diffusion of C, and forms a solid solution in the matrix irrespective of carbide formation to increase toughness, and also increases hardness to contribute to improvement of 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 obtain these effects, it is preferable to contain 0.5% or more.
On the other hand, even if the content exceeds 10.0%, the effect is saturated, which is economically disadvantageous. Therefore, the upper limit is 10.0% even when it is contained as necessary.

[0018]

BEST MODE FOR CARRYING OUT THE INVENTION The high-speed cast iron material of the present invention is a two-layer composite roll in which an outer layer is welded or shrink-fitted to a solid inner layer or a cylindrical inner layer, or an intermediate layer is formed by casting between the outer layer and the inner layer. It is preferably used as an outer layer material of the three-layer composite roll. A material having high toughness such as high-grade cast iron, ductile cast iron, and graphite steel is used as the inner layer material, and an adamite material is used as the intermediate layer material. The solid composite roll can be manufactured by casting an outer layer and, if necessary, an intermediate layer by a centrifugal force casting method, and then casting the inner layer inside the inner layer. In the case of a sleeve-shaped roll, the inner layer is also made by centrifugal casting. Various methods can be used for the centrifugal casting method, in which the rotation axis of the mold is horizontal, horizontal, oblique, or vertical.

[0019]

EXAMPLES In a high-frequency induction melting furnace, molten alloys having various component compositions shown in Table 1 were melted and subjected to centrifugal casting to obtain hollow cylinders for test purposes. In Table 1, sample Nos. 1 to 3 are examples of the present invention, No. 4 is a comparative example in which Cr is out of the range of the present invention, and No. 5 is V including V and Cr is in the range of the present invention. This is a comparative example that is off.

[0020]

[Table 1]

A test piece for microstructure observation was taken from each cylinder, and the microstructure was microscopically observed to measure the area ratio of crystallized graphite. Table 2 shows the results.

Next, in order to produce a ring for high temperature wear test, a test ring was cut out from each cylinder at right angles to the axis, and the ring was held at 1100 ° C. for 1 hour and then quenched by forced air cooling. Then, the heat treatment of tempering at 540 ° C. for 10 hours was repeated three times. After the heat treatment, the outer diameter and the inner diameter of the test ring were machined and the abrasion test was conducted by the high temperature abrasion tester shown in FIG.

In FIG. 1, the wear test apparatus has a lower test roll (1) and an upper test roll (2) having an outer diameter larger than that of the test roll (1) rotatably arranged in opposite directions. With this configuration, when the pressure roll (2) is rotationally driven while being pressed against the test roll (1), the test roll (1) rotates while slipping due to a difference in diameter. The test roll (1) has a test ring (13) fixed to the body (12) of the shaft (11), and the pressure roll (2) is the body (22) of the shaft (21).
The pressure ring (23) is fixed to the pressure ring (23), and a ridge (24) is formed in the circumferential direction at the center of the pressure ring (23) in the width direction. A high frequency coil (3) is provided on the upper half of the pressure roll (2) so as to surround the ridge (24), and the ridge (24) of the pressure roll (2) is heated during the test. The test roll (1) has a cooling water pipe
Water for cooling is sprayed through (4). The outer diameter of the body (12) of the test roll (1) was 70 mm, and the test ring (13)
Has an outer diameter of 210 mm. In the pressure roll (2), the material of the pressure ring (23) is SS41, and the ridge (24) has an outer diameter of 230 mm and a width of 5 mm. During the test, the ridges (24) of the pressure roll (2) were heated to a temperature of 800 ° C. by the high frequency coil (3) and a load of 3 tons was applied to the test roll (1). Axis (21)
Has a rotation speed of 50 rpm and a rotation time of 60 minutes. After causing wear on the surface of the test ring (13) in the above manner, a surface roughness meter (Surfcom 590A-3D, manufactured by Tokyo Seimitsu Co., Ltd.) was used to test each test ring (13). The surface roughness was measured. The measurement was carried out at 4 arbitrary points on the circumferential surface where the test ring (13) was worn over a length of 3 mm. Table 2 also shows the measurement results at the first to fourth positions and their average values.

[0024]

[Table 2]

The samples No. 1 to No. 3 of the present invention have much better surface roughness than the samples No. 4 and No. 5 of the comparative example, and have wear resistance and rough skin resistance. You can see that it is excellent.

[0026]

The composite roll using the graphite crystallized high-speed cast iron material of the present invention as the outer layer has desired wear resistance and excellent surface roughening resistance during rolling, and is hot-rolled or cold-rolled. It is suitable as an outer layer material of a rolling composite roll for hot rolling.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an outline of a high temperature wear test.

[Explanation of symbols]

 (1) Test roll (2) Pressure roll (3) High frequency coil (4) Cooling water pipe (13) Test ring (24) Ridge

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yutaka Tsujimoto 64 Nishimukojima-cho, Amagasaki City, Hyogo Prefecture Kubota Amagasaki Plant Co., Ltd. (72) Inventor Akori Obayashi 64 Nishimukojima-cho, Amagasaki City, Hyogo Prefecture Kubota Amagasaki Plant Co., Ltd. (72) Inventor Nagamori Morikawa 64 Nishimukojima-cho, Amagasaki City, Hyogo Prefecture Kubota Corporation Amagasaki Plant

Claims (2)

[Claims] 1. C: 2.5 to 3.6% by weight% and S
i: 1.0 to 3.5%, Mn: 0.1 to 2.0%, Cr:
Less than 2.0%, Mo: 0.1 to 5.0%, W: 0.1 to 5.
0%, Nb: 0.5-5.0% and the balance consisting essentially of Fe, and a graphite crystallized high-speed cast iron material with excellent surface roughening resistance. 2. The graphite crystallized high-speed cast iron material according to claim 1, which contains Co: 0.5 to 10.0%.