JPH09316590A - High speed steel type cast iron material containing crystallized graphite, excellent in wear resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the wear resistance of a high speed steel type cast iron material containing crystallized graphite, used as outer layer material for composite roll for rolling. SOLUTION: This high speed steel type cast iron material has a composition consisting of, by weight, 2.0-3.6% C, 1.5-3.5% Si, 0.1-2.0% Mn, 2.0-7.0% Cr, 0.1-5.0% Mo, 0.1-5.0% W, 0.1-3.0% Ta, 1.5-5.0%, in total, of either or both of V and Nb, and the balance essentially Fe. If necessary, <=10.0% Co can be incorporated into this composition.

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
It contains elements such as o, V, Nb, and W that form complex carbides (see, for example, JP-A-6-256889). This cast iron material has a structure in which graphite and complex carbide are crystallized, and has a low friction coefficient and good seizure resistance due to the action of graphite, and high wear resistance due to the presence of carbide. However, as operating conditions become more severe, materials with higher wear resistance are required.

[0003]

SUMMARY OF THE INVENTION An object of the present invention is to provide a graphite crystallized high speed cast iron material having excellent wear resistance.

[0004]

In order to achieve the above object, the graphite crystallized HSS cast iron material of the present invention, in% by weight,
C: 2.0-3.6%, Si: 1.5-3.5%, Mn:
0.1-2.0%, Cr: 2.0-7.0%, Mo: 0.1
Up to 5.0%, W: 0.1 to 5.0%, Ta: 0.1 to 3.0
%, V, Nb, or a total of 1.5 or 5.0
%, The balance consisting essentially of Fe. The cast iron material of the present invention is C
A high-hardness composite carbide in which r, Mo, W, Ta, Nb, V, Fe, and C are bonded to each other is present in the matrix, and has high hardness at normal temperature and high temperature and excellent wear resistance. Among various carbide-forming elements, the greatest characteristic is that Ta is contained, and Ta is a high hardness MC.
Formed type carbide is formed, but a part of it forms a solid solution in the matrix and its secondary hardening action dramatically improves wear resistance. In the cast iron material of the present invention, graphite is crystallized in the structure in an area ratio of 0.1 to 7%. Due to the action of this graphite, the impact load is relaxed and the development of cracks is prevented, and the friction coefficient Reduction and improved seizure resistance.

The cast iron material of the present invention, if necessary, Co:
It may include up to 10.0%. The base is strengthened by the inclusion of Co.

[0006]

[Explanation of reasons for limiting ingredients]

C: 2.0-3.6% C mainly combines with Fe and Cr to form a M ₇ C ₃ type high hardness composite carbide, and also combines with Mo, V, Nb, W, etc. to form MC. type, M ₆ C-type, to form a high hardness composite carbides of M ₂ C type, and the like. Further, by the action of Si, which is a graphitization promoting element to be described later, and by heat treatment, fine graphite is crystallized and precipitated in the structure. If it is less than 2.0%, the amount of carbides will decrease and a suitable amount of graphite will not be obtained, while if it exceeds 3.6%, the amount of carbides and graphite will be excessive and the material tends to become brittle. Therefore, the content of C is specified to be 2.0 to 3.6%.

Si: 1.5 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 1.5%, 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 the abrasion starting from graphite becomes remarkable. Therefore, the content is specified to be 1.5 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: 0.1-2.0% 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 reduced. Therefore, the content is specified to be 0.1 to 2.0%.

Cr: 2.0-7.0% Cr combines with C together with Fe, Mo, V, Nb, W, etc. to form a high hardness composite carbide and contributes to improvement of wear resistance at high temperature. . In addition, some of them form a solid solution 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 7.0%, it becomes difficult to obtain a suitable amount of graphite. Therefore, the content is specified to be 2.0 to 7.0%.

Mo: 0.1-5.0% Mo combines with C together with Fe, Cr, V, Nb, W, etc., and is mainly a composite of M ₇ C type, M ₆ C type and M ₂ C type. Carbides are formed to increase the hardness at normal temperature and high temperature and contribute to the improvement of wear resistance. Further, Mo exhibits its effect when added in a small amount as compared with W. However, if it is less than 0.1%, the effect cannot be sufficiently obtained, while if it exceeds 5.0%, a suitable amount of graphite cannot be obtained, which is not preferable. Therefore, the content is specified to be 0.1 to 5.0%.

W: 0.1-5.0% W also has C in the same manner as Fe, Cr, Mo, V, Nb, etc.
Combined with, it forms a composite carbide and contributes to the improvement of wear resistance by increasing the room temperature and high temperature 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 suitable amount of graphite. Therefore, the upper limit is set to 5.0%.

Ta: 0.1-3.0% Like V or Nb, Ta combines with C to form a high-hardness MC type carbide, and partly forms a solid solution in the matrix. It contributes to the improvement of abrasion resistance by increasing the secondary curing ability and hardness. If the content is less than 0.1%, these effects are not sufficient, and if the content exceeds 3.0%, the corresponding effects cannot be obtained, making it difficult to obtain a suitable amount of graphite. Become. Therefore, the content is specified to be 0.1 to 3.0%.

V, Nb: One or two kinds in total amount of 1.5
~ 5.0% V and Nb easily combine with C together with Fe, Cr, Mo, W, etc. to mainly form MC type carbides, which contributes to the improvement of wear resistance by increasing hardness at normal temperature and high temperature. To do. Also,
Since this MC 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, V and / or N
b is contained by 1.5% or more. On the other hand, when the content is too large, the carbide easily segregates, and it becomes difficult to obtain a predetermined amount of graphite. Therefore, V and / or Nb
The upper limit of is set to 5.0%.

Co: 10.0% or less The cast iron material of the present invention may contain Co, if necessary. Co has a great effect on improving the base. Co has a special effect of suppressing the diffusion of C, and it forms a solid solution in the matrix regardless of the formation of carbide to increase the toughness, and also contributes to the improvement of the high temperature hardness and the 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. However, even if the content exceeds 10.0%, the effect is saturated and it is economically disadvantageous. Therefore, the upper limit is 10.0% even if it is contained if necessary.

The high-speed cast iron material of the present invention contains the above components, and the balance is formed of Fe and inevitably mixed 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.

[0016]

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 cast between the outer layer and the inner layer. It is preferably 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 the case of the composite roll using the high speed cast iron material of the present invention as the outer layer, the outer layer is subjected to a predetermined heat treatment 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.

[0018]

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 G number of the mold at the time of centrifugal casting was 140, the casting temperature was 1355 ° C., and the obtained test material had an outer diameter of 240 mm, an inner diameter of 140 mm, and a length of 2
00 mm. Next, each test material is heated at 1050 ° C. for 1 hour, quenched at a cooling rate of 600 ° C./Hr, and heated to 520 ° C.
The tempering for 10 hours was repeated 3 times. Test N in Table 1
Nos. 1 to 4 are examples of the present invention, and No. 5 is a comparative example containing no Ta.

The Shore hardness of each test material was measured. For the measurement, 5 points were measured for each sample, and the average thereof was calculated. The test results are shown in Table 2.

A test piece for microstructure observation was taken from each test material, and the microstructure was microscopically observed to measure the area ratio of crystallized graphite. The results are shown in Table 2.

Plate-like test pieces (30 × 50 × 1)
(0 mm) was sampled and the abrasion resistance was examined by a RIKEN-Okoshi rapid abrasion tester. In this test method, a rotating wheel is pressed against a fixed test piece and the specific wear amount (mm ² / kgf) is measured from the depth and width of the wear marks on the surface of the test piece to evaluate wear resistance. is there. The test conditions are as follows. Rotor material: SUJ-2 (HRC59 ~ 61) Initial load: 19kgf Sliding speed: 3.8m / sec Sliding distance: 400m Table 2 shows the test results.

[0022]

[Table 1]

[0023]

[Table 2]

As is clear from the results of Table 2, Samples No. 1 to No. 4 of the present invention have higher hardness than Sample No. 5 of the comparative example, and the specific wear amount. It can be seen that the abrasion resistance is extremely small and the abrasion resistance is excellent. Moreover, since a proper amount of graphite is crystallized, it is also good in terms of seizure resistance.

[0025]

The composite roll using the graphite crystallized HSS cast iron material of the present invention as the outer layer exhibits excellent wear resistance during rolling, and is a composite for rolling for hot rolling or cold rolling. It is suitable as an outer layer material for rolls.

Claims (2)

[Claims] 1. C: 2.0 to 3.6% by weight% and S
i: 1.5 to 3.5%, Mn: 0.1 to 2.0%, Cr:
2.0-7.0%, Mo: 0.1-5.0%, W: 0.1-
5.0%, Ta: 0.1 to 3.0%, V or Nb of one or two kinds in total of 1.5 to 5.0%, the balance being substantially Fe, and having excellent wear resistance Graphite crystallized high speed cast iron material. 2. The graphite crystallized high-speed cast iron material according to claim 1, which contains Co: 10.0% or less.