JPH11229072A - High speed steel type cast iron material containing crystallized graphite, excellent in surface roughing resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To secure the high wear resistance of a high speed steel type cast iron material containing crystallized graphite, used as an outer layer material of a composite roll for rolling, and to improve its surface roughening resistance. SOLUTION: This cast iron material has a composition consisting of, by weight, 1.8-3.6% C, 1.0-3.5% Si, 0.1-2.0% Mn, 2.0-10.0% Cr, 0.1-10.0% Mo, 1.0-8.0% V, 0.21-2.0%, in total, of at least one kind among the group of lanthanoide series elements, further at least one kind among <=3.0% Nb, <=2.0% Ti, <=10.0% Ni, and <=5.0% Co, and the balance Fe with inevitable impurities. Other than the alloy components, at least either of 0.01-0.50% Al and 0.01-0.50% Zr, and/or 0.01-0.50% B can be incorporated, if necessary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention 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 A high-speed cast iron having high hardness and excellent wear resistance has been conventionally used as an outer layer material of a composite roll for rolling. The high hardness property of the high-speed cast iron material is due to the contribution of the crystallized carbide. However, the carbide has a large amount of carbon, and on the other hand, has a property of being relatively brittle. For this reason, when the temperature of the roll surface is repeatedly raised and lowered by the heat load as in hot rolling, the relatively brittle carbide is microscopically chipped due to the difference in the coefficient of thermal expansion between the cast iron base and the carbide. Tends to occur. The microscopic chipping wear of the carbide causes the surface of the roll to be rough, and has a disadvantage of deteriorating the surface properties of the rolled product.

[0003] By the way, graphite reduces the coefficient of friction,
It has the effect of reducing the impact load and has the effect of suppressing microscopic chipping of carbides. Therefore, the applicant has proposed that Cr, Mo, V, N
A high-speed cast iron material containing high hardness composite carbide forming elements such as b and W and containing a predetermined amount of Si as a graphitization promoting element has been previously proposed (Japanese Patent Application Laid-Open No. 6-256889). This cast iron material has a structure in which composite carbide and graphite are crystallized.

[0004]

However, in the conventional graphite-crystallized high-speed cast iron material, although microscopic chipping of carbides is greatly suppressed, there is a problem that the graphite peripheral portion is preferentially worn during rolling. there were. When the graphite itself is worn, improvement in the rough surface resistance of the roll surface cannot be expected. The present inventors have noted that in the case of a conventional graphite-crystallized high-speed cast iron material, the average particle size of the crystallized graphite is relatively large, about 20 to 50 μm, and it is possible to reduce the particle size of the graphite. If possible, it was thought that abrasion of graphite could be suppressed as much as possible, and the present invention was reached.

[0005] An object of the present invention is to improve the surface roughening resistance of a high-speed cast iron material having a high hardness composite carbide and graphite in its structure by making the crystallized graphite fine, and to provide excellent wear resistance at high temperatures. It is to ensure the nature.

[0006]

In order to achieve the above object, the graphite-crystallized high-speed cast iron material of the present invention according to claim 1 has a C content of 1.8 to 3.6% by weight. Si: 1.0
To 3.5%, Mn: 0.1 to 2.0%, Cr: 2.0 to 1
0.0%, Mo: 0.1 to 10.0%, V: 1.0 to 8.0
%, Nb: 3.0% or less and / or Ti: 2.0
% Or less and at least one of the lanthanoid element groups in a total amount of 0.221 to 2.0%, with the balance being Fe and unavoidable impurities.

[0007] The graphite-crystallized high-speed cast iron material of the present invention described in claim 2 has a C content of 1.8 to 3.6% by weight,
i: 1.0 to 3.5%, Mn: 0.1 to 2.0%, Cr:
2.0 to 10.0%, Mo: 0.1 to 10.0%, V: 1.0.
0 to 8.0%, further contains Ni: 10.0% or less and / or Co: 5.0% or less, and contains at least one of the lanthanoid element groups in a total amount of 0.221 to 2.0%. , The rest F
e and unavoidable impurities.

The high-speed cast iron material according to the present invention described in claim 3 has a C content of 1.8 to 3.6% and a Si content of 1.0% by weight.
0 to 3.5%, Mn: 0.1 to 2.0%, Cr: 2.0 to 1
0.0%, Mo: 0.1 to 10.0%, V: 1.0 to 8.0
%, Nb: 3.0% or less and / or Ti: 2.0
% And Ni: 10.0% or less and / or Co: 5.0
% Or less and at least one of the lanthanoid element groups in a total amount of 0.221 to 2.0%, with the balance being Fe and unavoidable impurities.

[0009] The graphite-crystallized high-speed cast iron material of the present invention may contain, if necessary, Al: 0.01 to 0.5 in addition to the alloy components.
0%, one or two of Zr: 0.01 to 0.50%,
And / or B: 0.01 to 0.50%. The graphite crystallized in the structure has an average particle size of about 1
0 μm or less, the area ratio is about 0.1 to 7%, the desirable average particle size is about 2 to 8 μm, and the desirable area ratio is about 2 to 4%.
It is.

[0010]

The graphite-crystallized high-speed cast iron material of the present invention comprises C, C
A high-hardness composite carbide in which r, Mo, V, Fe, and Nb, Ti are mutually bonded is present in the matrix, and has high hardness at ordinary and high temperatures and excellent wear resistance. In addition, by containing Ni and Co, the matrix is strengthened and excellent in toughness. The lanthanoid element contained in the cast iron material of the present invention has an action of refining crystallized graphite. In addition, while reducing the amount of MC-type carbide crystallized in primary austenite, it has the function of increasing the amount of MC-type carbide in the eutectic region. Abrasion is improved. The cast iron material of the present invention,
In the structure, a predetermined amount of fine graphite is crystallized, and when used as an outer layer material of a composite roll for rolling, the effect of graphite reduces the impact load and suppresses micro chipping of carbide. Having. In addition, since the average particle size of graphite is reduced, wear originating from graphite is remarkably reduced, and excellent surface roughness resistance is exhibited.

[0011] The graphite-crystallized high-speed cast iron material of the present invention comprises A
The solidification structure is further refined by the inclusion of l and Zr, and the hardenability is improved by the inclusion of B.

[0012]

[Explanation of Reasons for Restricting Components] 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 Mo, V, Nb, Ti
And the like to form a high hardness composite carbide 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 precipitated in the structure. If the content is less than 1.8%, the amount of carbides decreases and a suitable amount of graphite cannot be obtained. On the other hand, if the content exceeds 3.6%, the amounts of carbides and graphite become excessive and the material tends to become brittle. Therefore, the content of C is specified to be 1.8 to 3.6%.

Si: 1.0-3.5% Si is an element necessary for securing the flowability of the molten metal and for crystallizing and precipitating graphite. If the content is less than 1.0%, the desired effect cannot be obtained. On the other hand, if it exceeds 3.5%, the amount of graphite becomes excessive, and there is a possibility that abrasion starting from graphite becomes remarkable. For this reason, the content is specified to be 1.0 to 3.5%. 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 to 2.0% Mn has a 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 reduced. Therefore, the content is specified to be 0.1 to 2.0%.

Cr: 2.0-10.0% Cr combines with C together with Fe, Mo, V, Nb, Ti, etc. to form a high-hardness composite carbide and contributes to improvement of wear resistance at high temperatures. . In addition, a part is dissolved in the matrix to improve hardenability and wear resistance. If the content is less than 2.0%, the effect is small, while if it exceeds 10.0%, it becomes difficult to obtain a suitable amount of graphite. For this reason, the content is specified to be 2.0 to 10.0%.

Mo: 0.1 to 10.0% Mo is combined with C together with Fe, Cr, V, Nb, Ti, etc., and mainly forms a composite of M ₇ C type, M ₆ C type and M ₂ C type. It forms carbides and increases normal and high temperature hardness, contributing to improved wear resistance. However, if it is less than 0.1%, the effect cannot be sufficiently obtained, while if it exceeds 10.0%, a suitable amount of graphite cannot be obtained, which is not preferable. For this reason, the content is defined to be 0.1 to 10.0%.

V: 1.0-8.0% V easily combines with C together with Fe, Cr, Mo, etc. to form mainly MC-type carbides, and increases the hardness at ordinary and high temperatures to improve wear resistance. Contribute to the improvement of Also, this MC
Since the type 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. Therefore, the content is at least 1.0% or more. On the other hand, if the content is too large, the carbide is apt to segregate, and it is difficult to obtain a predetermined amount of graphite. For this reason, the upper limit is specified at 8.0%.

Nb: 3.0% or less and / or Ti: 2.0
% Or less Nb and Ti, like V, easily combine with C to form MC.
Since it forms a type carbide and contributes to improving the wear resistance by increasing the hardness at ordinary and high temperatures, it is desirable to add it together with V. However, if the added amount is too large, the dissolution becomes difficult. Therefore, the upper limit is set to 3.0% or less and 2.0% or less, respectively.

Ni: 10.0% or less and / or Co: 5.
0% or less Ni and Co form a solid solution in the matrix and increase the toughness. Further Co
Increases the high temperature hardness and contributes to the improvement of wear resistance. In addition, since the effect of increasing the solid solution amount of the carbide-forming element in austenite to increase the hardness and tempering resistance of the matrix, it is desirable to include the element. On the other hand, if the content is too large, the amount of retained austenite increases, and it becomes difficult to obtain a tough structure by a subsequent heat treatment. For this reason, the upper limits of the contents are set to 10.0% or less and 5.0% or less, respectively.

Lanthanoid element: At least one of the elements is in a total amount of 0.221 to 2.0%. The lanthanoid element is one of atomic numbers 57 to 71.
5 kinds of rare earth elements, La, Ce, Pr, Nd, Pm,
Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Y
b and Lu mean that each element has a similar outer electron configuration and very similar properties to each other. La, Ce,
Lanthanoid elements such as Nd and Pr have an effect of miniaturizing the crystallized graphite, suppress microscopic chipping of carbides, and are extremely effective in improving the surface roughness resistance of the roll surface. In addition, while reducing the amount of MC-type carbides crystallized in primary austenite, it has the function of increasing the amount of MC-type carbides in the eutectic region. Improves abrasion. In order to exhibit these effects, lanthanoid elements such as La, Ce, Nd, and Pr are contained in an amount of at least 0.21% (when a plurality of types are contained, the total amount is not less than 0.21%).
More preferably, it is at least 25%, even more preferably at least 0.3%. However, when the content is too large, inclusions increase and the cleanliness of the material decreases, which may cause casting defects. For this reason, the upper limit is defined as 2.0% (when a plurality of types are contained, the total amount is 1.8%), but from the viewpoint of cleanliness, it is 1.8%.
% Is more desirable, and 1.6% or less is still more desirable. By the way, when casting iron material, misch metal is usually used as a raw material of a lanthanoid element. When using misch metal, Ce and La occupy about 60 to 80% of the lanthanoid element, and N
d, Pr, trace amounts of Pm, Sm, Eu, Gd, T
b and the like. The lanthanoid element also has the effect of increasing the viscosity of the molten metal. When casting a composite roll for rolling, it is generally performed using centrifugal casting, but when the viscosity in the molten metal increases, weight segregation due to centrifugal separation decreases, so that layer segregation on the outer layer surface side of the roll is performed. Has the advantage of being reduced.

Al and Zr: 0.01 to 0.50% each Al and Zr generate oxides in the molten metal, reduce the oxygen content in the molten metal, improve the soundness of the product, Since the generated oxide acts as a crystal nucleus, it is effective in refining the solidified structure. For this reason, if necessary,
It is desirable to contain. Each element has a content of 0.01.
%, The effect is not sufficient, while 0.5
If the content exceeds 0%, it remains as inclusions and is not preferable. As described above, the addition of Al and Zr is mainly added for the purpose of improving the wear resistance due to the refinement of the cast structure, and is not merely 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 B has an effect of improving hardenability due to B dissolved in the matrix. In the case of a casting having a large mass such as a rolling roll, it may be difficult to increase the cooling temperature. However, the addition of B makes it easier to obtain a good quenched structure due to an increase in hardenability. For this reason, it is added if necessary. However, if the content is less than 0.01%, the effect is not sufficient, and if it exceeds 0.50%, the material becomes brittle, which is not preferable.

The high-speed cast iron material of the present invention contains the above components, with the balance being Fe and impurities unavoidably mixed. For example, P and S are inevitably mixed from the raw material,
The smaller the material, the more preferable it is because the material is brittle.

The cast iron material of the present invention does not contain W which is generally used in this type of cast iron material. W forms carbides, increases hardness and contributes to improvement of wear resistance,
On the other hand, when used as a roll, there is a tendency that iron oxide called black scale is easily generated on the roll surface. If the black scale adheres to the roll surface, the surface roughness of the roll surface deteriorates. For this reason, W is not actively used in the cast iron material of the present invention.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION The high-speed cast iron material of the present invention has 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 formed between an outer layer and an inner layer. It is suitably used as an outer layer material of the formed three-layer composite roll. High grade cast iron, ductile cast iron,
A tough material such as graphite steel is used, and an adamite material is used as an 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. In addition to the centrifugal casting method, a known continuous overlay welding method (Continuous Pouring
Process) can also be used.

In the case of the composite roll using the high-speed cast iron material of the present invention for the outer layer, a predetermined heat treatment is applied to the outer layer after casting. For example, from an austenitizing temperature of 650 to 400
After rapidly cooling the temperature range up to 100 ° C. at a cooling rate of 100 ° C./Hr or more to obtain a good quenched structure, tempering is performed once or several times at a temperature of 500 to 600 ° C.

[0027]

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. The centrifugal casting mold rotation speed was G number 140, casting temperature was 1355 ° C, and the obtained test material was 240 mm in outer diameter, 140 mm in inner diameter, and 200 mm in length.
mm. Next, each test material was heated at 1050 ° C. for 1 hour, quenched at a cooling rate of 600 ° C./Hr, and tempered at 520 ° C. for 10 hours was repeated three times. In Table 1, test No.
Nos. 1 to 11 are examples of the present invention, No. 21 is a comparative example containing no Ce and La, and No. 22 is a comparative example in which the contents of Ce and La are smaller than those specified in the present invention. It should be noted that some of the examples of the present invention contain Pm, Sm, Eu, Gd, and Tb, but their amounts are extremely small and are therefore excluded from the measurement.

◎

[Table 1]

A sample for tissue observation was collected from each test material,
The microstructure was observed under a microscope, and the average particle size and area ratio of the crystallized graphite were measured. Table 2 shows the results. The metal structures of the test materials of Example No. 2 and Comparative Example No. 21 are shown in FIG. 1 and FIG. 2 by micrographs, respectively.

Next, after holding each sample at 1100 ° C. for 1 hour, it is quenched by forced air cooling, and then quenched at 540 ° C. for 10 hours.
After repeating the heat treatment for 3 hours, the sample was heated again to a temperature of 500 ° C., and the surface hardness was measured with a Vickers hardness tester. The results are also shown in Table 2.

The surface roughness was examined in the following manner.
First, a test ring is cut out from each cylindrical body in a direction perpendicular to the axis, the ring is held at 1100 ° C. for 1 hour, quenched by forced air cooling, and then subjected to a heat treatment of tempering at 540 ° C. for 10 hours. Repeated three times. After heat treatment,
Machined the outer and inner diameters of the test ring,
Using a high-temperature abrasion test apparatus shown in FIG. 3, the surface roughness was measured after abrasion was caused on the test ring.

In FIG. 3, the abrasion test apparatus has a lower test roll (1) and a higher press roll (2) having an outer diameter larger than the test roll (1) at the lower stage so as to be rotatable in opposite directions. When the pressure roll (2) is rotated while being pressed against the test roll (1), the test roll (1)
Is configured to rotate while slipping. The test roll (1) has a test ring (13) on the body (12) of the shaft (11).
Is fixed, and the pressure roll (2) is connected to the trunk (2) of the shaft (21).
A pressure ring (23) is fixed to 2), and a ridge (24) is formed in the center in the width direction of the pressure ring (23) in the circumferential direction. The upper half of the pressure roll (2) is provided with a high-frequency coil (3) (shown by phantom lines in FIG. 3) so as to surround the ridge (24).
The ridge (24) of the pressure roll (2) is heated. Test roll (1)
, Water for cooling is sprayed through a cooling water pipe (4). The outer diameter of the body (12) of the test roll (1) is 70 mm,
The outer diameter of the test ring (13) is 210 mm. Pressure roll
In (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, a load of 3 tons was applied to the pressure roll (1). The rotation speed of the shaft (21) was 50 rpm, and the rotation time was 60 minutes. After the surface of the test ring (13) was worn as described above, a surface roughness meter (Surfcom 590A-3D, manufactured by Tokyo Seimitsu Co., Ltd.)
, The surface roughness (Rmax) of each test ring (13)
Was measured. The measurement was performed over a length of 3 mm at any four locations on the circumferential surface where the wear of the test ring (13) occurred. Table 2 also shows the measurement results of the first to fourth positions and their average values.

◎

[Table 2]

As is clear from the results in Table 2, the test materials No. 1 to No. 11 of the present invention were the test materials No. 21 to No. 11 of the comparative examples.
It can be seen that the film has a higher hardness at a temperature of 500 ° C. than that of No. 22. This is because high hardness composite carbide forming elements such as Cr, Mo, V, Nb and / or Ti and La, Ce, N
It is presumed that the eutectic region of the high hardness composite carbide was increased due to the synergistic effect due to the inclusion of lanthanoid elements such as d and Pr. Cast iron material with high hardness at high temperature, when used as the outer layer material of the composite roll for rolling, the roll surface has large abrasion resistance due to contact with the hot rolled material,
Demonstrates excellent wear resistance. The test material containing Ni and Co has a slightly higher high-temperature hardness than the test material not containing them.

Table 2 also shows the test materials No. 1 to No. 1 of the invention examples.
1 indicates that the average particle size of graphite is finer than that of Nos. 21 and 22 of Comparative Examples. This is also La,
This is considered to be due to the effect of containing lanthanoid elements such as Ce, Nd, and Pr. As described above, as a refining effect of graphite, it was confirmed that the test materials No. 1 to No. 11 of the present invention had better surface roughness than the test materials No. 21 and No. 22 of the comparative example. Is shown. Thus, when the high-speed cast iron material of the present invention is used as an outer layer material of a composite roll for rolling,
It can be seen that the surface of the roll has excellent surface roughness resistance. Further, graphite crystallized in an appropriate amount is also favorable in terms of seizure resistance.

In the micrographs of FIGS. 1 and 2, graphite is black. The test material No. 2 of FIG. 1 contains 1.93% in total of Ce and La, whereas the test material No. 21 of FIG. 2 does not contain Ce and La at all, From these comparisons, it can be seen that graphite is refined by the inclusion of Ce and La.

[0037]

The graphite crystallized high-speed cast iron material of the present invention has fine crystallized graphite and has high hardness at high temperatures. Therefore, the composite roll using the cast iron material of the present invention as an outer layer exhibits extremely excellent wear resistance and surface roughness resistance during rolling, and is particularly suitable as an outer layer material of a rolling composite roll for hot rolling. is there.

[Brief description of the drawings]

1 is a drawing-substituting micrograph (× 400) showing the metal structure of Test Material No. 2 which is an invention example.

FIG. 2 is a photomicrograph (× 400) showing a metallographic structure of Test Material No. 21 as a comparative example.

FIG. 3 is an explanatory diagram of an abrasion test apparatus used for examining a rough surface state of a test material surface and causing abrasion on the test material surface under a high temperature condition.

[Explanation of symbols]

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

Claims (5)

[Claims] C. 1.8 to 3.6% by weight of C,
i: 1.0 to 3.5%, Mn: 0.1 to 2.0%, Cr:
2.0 to 10.0%, Mo: 0.1 to 10.0%, V: 1.0.
0 to 8.0%, and Nb: 3.0% or less and / or T
i: 2.0% or less, at least one of the lanthanoid element groups in a total amount of 0.21 to 2.0%, the balance being Fe and unavoidable impurities, and graphite crystallization high speed steel with excellent skin roughness resistance Series cast iron material. 2. In weight%, C: 1.8-3.6%, S
i: 1.0 to 3.5%, Mn: 0.1 to 2.0%, Cr:
2.0 to 10.0%, Mo: 0.1 to 10.0%, V: 1.0.
0 to 8.0%, further contains Ni: 10.0% or less and / or Co: 5.0% or less, and contains at least one of the lanthanoid element groups in a total amount of 0.221 to 2.0%, Balance Fe
And graphite crystallization high-speed cast iron material, which is composed of unavoidable impurities and has excellent surface roughness resistance. 3. 1.8% to 3.6% C by weight, S
i: 1.0 to 3.5%, Mn: 0.1 to 2.0%, Cr:
2.0 to 10.0%, Mo: 0.1 to 10.0%, V: 1.0.
0 to 8.0%, and Nb: 3.0% or less and / or T
i: 2.0% or less, Ni: 10.0% or less and / or C
o: 5.0% or less, at least one of the lanthanoid element group in a total amount of 0.21 to 2.0%, the balance being Fe and unavoidable impurities, and graphite crystallization high speed steel with excellent skin roughness resistance. Series cast iron material. 4. Al: 0.01 to 0.50% and / or Z
r: 0.01 to 0.50%.
The graphite-crystallized high-speed cast iron material according to any one of the above. 5. The graphite-crystallized high-speed cast iron material according to claim 1, containing B: 0.01 to 0.50%.