JP2000144302A - Centrifugally cast composite roll excellent in seizuring resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a centrifugally cast composite roll composed of an external layer small in the segregation of components or the like, low in a friction coefficient, excellent in crack resistance and wear resistance and having high tensile strength and an internal layer having sufficient tensile strength. SOLUTION: This centrifugally cast composite roll is the one in which the external layer has a compsn. contg., by mass, 2.3 to 3.0% C, 2.0 to 3.0% Si, 0.1 to 2.0% Mn, 0.5 to 3.0% Cr, 1.5 to 5.0% Mo, 7.0 to 10.0% Ni, 1.0 to 5.0% V, 0.5 to 3.0% Nb, 0.0050 to 0.0800% B and 0.0050 to 0.0500% rare earth metals and also satisfying 4.30 to 0.33Si-0.047Ni+ 0.0055 (Si+Ni)<=3.4, Mo/Cr>=1.0 and 0.2<=Nb/V<=1.0 and furthermore contains graphite. The internal layer is composed of common cast iron or ductile cast iron, and the external layer and the internal layer are welded and integrated. Moreover, on a space between the external layer and the internal layer, an intermediate layer may be formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite roll for hot rolling, and more particularly, to an outer layer formed of a high-speed cast iron material,
The present invention relates to a centrifugally cast composite roll having both excellent wear resistance and crack resistance and improved seizure resistance.

[0002]

2. Description of the Related Art Ni-glen cast iron, adamite, high-Cr cast iron and the like have been conventionally used as a material for a hot rolling roll. However, recently, in order to further improve the wear resistance of the roll, a high-speed tool steel (high-speed) material utilizing precipitation of MC type carbide, which is a carbide such as Mo, W, V, is used as the roll material. It has become.

[0003] For example, Japanese Patent Application Laid-Open No. 4-176840 discloses that, as a material for a roll, C: 1.0 to 3.0% and Si: 0.
1 to 2.0%, Mn: 0.1 to 2.0%, Cr: 3.0 to 10.0%, M
O: 0.1 to 6.0%, W: 1.5 to 10.0%, one or two or more of V and Nb, 3.0 to 10.0% in total, and a high-speed cast iron material comprising the balance of Fe and unavoidable impurities is disclosed. I have. However, the material described in Japanese Patent Application Laid-Open No. H4-176840, when a roll using a centrifugal casting method is an inexpensive manufacturing method, segregation of components in the roll radial direction, changes in the structure occurs. .

[0004] To solve such a problem, roll materials have been developed which can be applied to an inexpensive centrifugal casting method. For example, Japanese Unexamined Patent Publication No. 4-365836 discloses that C: 1.5 to
3.5%, Si: 1.5% or less, Mn: 1.2% or less, Ni: 5.5%
Below, Cr: 5.5 to 12.0%, Mo: 2.0 to 8.0%, V: 3.0
-10.0%, Nb: 0.6-7.0%, and the following (5)
A roll for rolling that satisfies the equation V + 1.8Nb ≦ 7.5 C−6.0 (5) and the following equation (6): 0.2 ≦ Nb / V ≦ 0.8 (6), with the balance being Fe and unavoidable impurities. An outer layer material is disclosed. This roll outer layer material does not show any segregation of components or change in the structure in the radial direction of the roll despite the application of the centrifugal casting method, and is excellent in both wear resistance and crack resistance. However, it has been found that a composite roll using this outer layer material for a rolling roll has a high coefficient of friction of the roll, which may cause problems such as an increase in rolling load and occurrence of flaws on a product surface due to frictional heat generation during rolling. did.

In order to solve such a problem, a roll material in which graphite is present in a high-speed material and a composite roll having this roll material as an outer layer have been proposed in order to reduce the friction coefficient. For example, JP-A-6-256888 discloses that, in terms of wt%, C: 1.8 to 3.6%, Si: 1.0 to 3.5%, M:
n: 0.1 to 2.0%, Cr: 2.0 to 10%, Mo: 0.1 to 10%,
W: 0.1 to 10%, V, Nb: 1.5 to 1 or 2 in total
10%, or even Co: 0.5 to 10.0%, or Al: 0.
01 to 0.50%, Ti: 0.01 to 0.50%, Zr: 0.01 to 0.50%
A high-speed cast iron material containing one or two or B: 0.01 to 0.50%, the balance substantially consisting of Fe and having graphite, and a composite roll using the high-speed cast iron material as an outer layer material have been proposed. I have. JP-A-6-256889 discloses a high-speed cast iron material containing 0.5 to 10.0% of Ni in addition to the composition of a graphite-containing high-speed cast iron material described in JP-A-6-256888. Composite roles have been proposed.

Japanese Patent Application Laid-Open No. 6-335712 discloses that, by weight, C: 2.0 to 4.0%, Si: 0.5 to 4.0%, and Mn: 0.1 to 4.0%.
1.5%, Ni: 2.0 to 6.0%, Cr: 1.0 to 7.0%, V: 2.
0 to 8.0%, the balance being Fe and impurity elements, having a base structure, a metal structure of 0.5 to 5% by area of graphite and 0.2 to 10% by area of cementite. Rolls for cold rolling have been proposed.

Japanese Patent Application Laid-Open No. 8-209299 discloses that
C: 2.0 to 4.0%, Si: 1.0 to 5.0%, Mn: 0.1 to
2.0%, Cr: 0.1-6.0%, Mo: 0.1-6.0%, V: 0.
A high seizure-resistant hot-rolling roll material containing 1 to 6.0% and Ni: 1.0 to 8.0%, with the balance being Fe and impurity elements, has been proposed. By adjusting the roll material to the above-described composition, crystallization of graphite is promoted and seizure resistance is improved.

Japanese Patent Application Laid-Open No. 9-170041 discloses that the outer layer material contains 2.5 to 4.7% of C, 0.8 to 3.2% of Si, and 0.1 to 0.1% of Mn.
2.0%, Cr: 0.4-1.9%, Mo: 0.6-5.0%, V: 3.
0 to 10.0%, Nb: 0.6 to 7.0%, and 2.0+
0.15V + 0.10Nb ≦ C (%), 1.1 ≦ Mo / Cr, 0.2 ≦ Nb /
V ≦ 0.8, the balance being Fe and impurity elements,
Disclosed is a centrifugally cast roll in which graphite is used, the intermediate layer material is made of graphite steel, the shaft core material is made of ductile cast iron, and the outer layer material is welded and integrated with the shaft core material through the intermediate layer material. .

[0009]

The use of an outer layer material in which graphite is crystallized prevents the drawback of the conventional high-speed cast iron roll material from increasing the rolling load and resulting deterioration in the surface quality of the product. In addition, it is possible to suppress the progress of cracks caused by an excessive load. However, as described in JP-A-6-256888, JP-A-6-256889,
JP-A-6-335712, JP-A-8-209299, and JP-A-9-170041, when a roll having graphite having a composition described in JP-A-9-170041 is manufactured by centrifugal casting, centrifugal separation causes
There remains a problem that the form and distribution of the type carbide and the form of graphite change in the thickness direction of the outer layer, and the roll characteristics change with the wear of the roll. In particular, there was a problem that the wear resistance of the roll was significantly deteriorated depending on the graphite form. Further, in a composite roll in which a high-speed cast iron roll material is used as an outer layer material and a shaft core material is ductile cast iron, there is a problem that the strength of the shaft core material is reduced. Further, in the composite roll described in JP-A-9-170041, an intermediate layer is formed, but there is a problem in the homogeneity of the outer layer material.

Furthermore, it is expected that the introduction of graphite into the outer layer material will lower the tensile properties of the outer layer material.
Since a tensile stress is generated on the surface of the roll during hot rolling by rapid heating and quenching, it is necessary to increase the tensile strength of the outer layer material from the viewpoint of roll surface cracking. Further, in a composite roll using ductile cast iron as an inner layer material, a measure for preventing a decrease in tensile strength of the inner layer material has been demanded.

[0011] Therefore, there still remains a problem to be solved for stably producing a high-quality composite roll having graphite in the outer layer using the centrifugal casting method. The present invention has been made in view of the above-mentioned prior art, and the outer layer material having less segregation of components and the like, a low coefficient of friction, excellent crack resistance, excellent wear resistance, and high tensile strength even when a centrifugal casting method is applied. And an inner layer material having sufficiently high strength.

[0012]

Means for Solving the Problems Among the above-mentioned problems, the present inventors have found that the use of graphite is effective in reducing the friction coefficient and improving the seizure resistance. The crystallization of graphite in the outer layer material for casting rolls was studied. Graphite acts as a solid lubricant, reduces the coefficient of friction, and improves the seizure resistance of the roll. However, if the content is too large or the form is flaky, the wear resistance and tensile strength are reduced. Therefore, control of graphite content and control of graphite morphology are important. The crystallization amount of graphite is as follows: C, which is its element, Si, Ni, which has the action of promoting graphite crystallization, Cr, which suppresses crystallization of graphite and turns into white iron, and combines with C before graphite crystallizes to form C. It is determined by the contents of V and Nb to be consumed. Therefore, the present inventors have found that Cr, V, and Nb are added in large amounts and effective C
In the outer layer material for rolls in which the amount is low, it has been conceived that the adjustment of the amounts of Si and Ni is important for the crystallization of graphite.

At first, the present inventors have found that Nb: 1.5 mass%,
V: 3.5mass%, B: 0.0200mass%, C content is changed in the range of 2.3-3.8mass%, and further, Si and Ni content are changed in cast iron of composition, it affects graphite crystallization.
An experiment was conducted on the effect of the amounts of Si and Ni. The presence or absence of the crystallization of graphite is arranged based on the relationship between the C content and the calculated eutectic value y, and the results are shown in FIG. Incidentally, the calculated eutectic value y is y = 4.30-0.
This equation is expressed by 33Si-0.047Ni + 0.0055 (Si + Ni) and can estimate the change in the amount of eutectic C in which γ and graphite are crystallized from the liquid phase L.

From FIG. 1, it can be seen that crystallization of graphite can be expected when the C content is in the range of 2.3 to 3.8 mass%, when the calculated eutectic value y is 3.4%.
In the following cases, if it exceeds 3.4, crystallization of graphite will not be observed. From this, the present inventors have found that it is necessary to adjust the amounts of Si and Ni so that the calculated eutectic value y becomes 3.4 or less in order to sufficiently crystallize graphite.

Next, the present inventors have studied means for preventing a reduction in the abrasion resistance of the roll outer layer material due to graphite crystallization. The wear resistance of high-speed cast iron roll material is hard MC
Maintained by type carbide. Here, the MC type carbide is a general term for a carbide in which a metal atom such as V, Nb, W, Mo, Ti, Hf or the like and a C atom are bonded. In high-speed cast iron rolls, VC, WC, NbC, etc. are used as MC type carbides. However, when WC is used, quenching and tempering by high-temperature heating are required, so that ductile cast iron having a low melting point, which is widely used in centrifugally cast composite rolls, cannot be used as a shaft material. For this reason, recently, VC crystallized during the solidification process of molten metal has been mainly used. Even when VC is mainly used as the MC type carbide, the crystallization of graphite inevitably lowers the wear resistance. Therefore, it is important to strengthen the crystallized carbide in order to compensate for the decrease in wear resistance.

The inventors of the present invention have studied the toughening of carbides and have found that Cr and Mo toughen carbides and strongly affect wear resistance. The present inventors have found that C: 2.8 mass%, Si: 2.5 mass%, Mn: 0.5 mass%.
%, Nb: 1.5 mass%, V: 3.5 mass%, Ni: 8.0 mass%
Cr: 2.0-3.0 mass%, Mo: 0.5-5.0 mass
% Was melted and cast into a 50 mm thick keel block and solidified. After the solidification, a tempering treatment at 500 ° C. was performed to obtain a disc-shaped test piece (φ50 × 10 mm). A wear resistance test was performed using these disc-shaped test pieces.

The abrasion resistance test was carried out using a two-disk hot abrasion tester under the following conditions. A disk-shaped test piece having a rotation speed of 800 rpm was pressed against a mating material (φ190 × 15 mm) heated to 800 ° C. under a load of 100 kgf, and was rolled for 120 minutes at a slip ratio of 3.9%. After the test, the wear loss of the disc-shaped test piece was measured and evaluated for wear resistance. The results are shown in FIG. 2 in the relationship between the loss on wear and Mo / Cr.

FIG. 2 shows that when Mo / Cr is 1.0 or more, the loss of wear is reduced. For this reason, in order to improve the wear resistance, it is preferable to adjust the contents of Mo and Cr so that Mo / Cr is 1.0 or more. Next, the present inventors examined suppression of tissue segregation by centrifugation. When using VC as MC type carbide,
Since the VC has a specific gravity smaller than that of the molten metal, the VC agglomerates and segregates inside the outer layer material due to centrifugal separation, thereby causing tissue segregation. Therefore, first, as shown in Japanese Patent Laid-Open No.
It is necessary to adjust the Nb content according to the V content so as to become a composite carbide of (V, Nb) C to reduce tissue segregation by centrifugation due to the difference in specific gravity between VC and molten metal I thought that.

The present inventors have found that C: 2.8 mass%, Si: 2.5 m
ass%, Mn: 0.5mass%, Cr: 2.0mass%, Mo: 3.0mass
s%, V: 1.0 to 5.0 mass%, Nb: 0 to 5.0 mass%
The wear resistance was investigated using a ring material (wall thickness: 85 mm) obtained by centrifugally casting (140 G) a molten metal having a s% range and a changed Nb / V ratio. After solidification, the ring material was subjected to a tempering treatment at 550 ° C., and disk-shaped test pieces (φ50 × 10 mm) were collected from the outer surface side and the inner surface side of the ring material. Using these disk-shaped test pieces, the same wear resistance test as described above was performed.

From the results, the ratio of the wear amount WR ₀ of the test piece on the outer surface side to the wear amount WR ₁ of the test piece on the inner surface side, WR ₀ / WR
FIG. 3 shows the relationship between ₁ and Nb / V. From FIG. 3, Nb / V indicates that the wear amount on the outer surface side and the inner surface side is almost equal.
Is 0.2 or more. It has been found that by setting the Nb / V ratio to 0.2 or more, tissue segregation by centrifugation from the viewpoint of abrasion resistance is within a range in which there is no problem.

However, in a component system of a high-speed cast iron roll in which graphite is crystallized, centrifugal separation of carbide cannot be completely suppressed only by increasing the specific gravity of MC type carbide.
Therefore, the present inventors, in addition to increasing the specific gravity of the MC-type carbide, relatively early after the crystallization of the MC-type carbide from the molten metal, γ slightly larger specific gravity than the molten metal MC
It has been conceived that if the crystallization is performed in such a manner as to adhere to the type carbide, that is, the crystallization temperature of the MC type carbide and the crystallization temperature of γ are made close to each other, the centrifugal separation of the MC type carbide can be suppressed.

The present inventors have found that to reduce the temperature difference between the crystallization temperature of MC type carbide and the crystallization temperature of γ, C,
V, Nb content is reduced and the crystallization temperature of MC type carbide is lowered,
It has been found that it is important to reduce the amounts of C and Cr to increase the crystallization temperature of γ. From such studies, the present inventors, in order to suppress carbides due to centrifugation, segregation of the structure, low friction coefficient, high wear resistance, to obtain a high-strength outer layer material for centrifugal casting rolls, the present inventors, Si, Ni After adjusting the amount to properly crystallize the graphite, adjust the Mo / Cr and Nb / V to increase the toughness and specific gravity of the carbide, and further adjust the amount of each component to the appropriate range to obtain MC-type carbide. The technical idea that it is important to reduce the difference between the crystallization temperature of γ and the crystallization temperature of γ and to make the base structure bainite or martensite is important.

Further, the present inventors have studied the reduction in strength of the inner layer material that occurs when the inner layer material is ductile cast iron. As a result, it was found that the decrease in the strength of the inner layer material was caused by the disorder of the graphite form of the inner layer material and the formation of flakes, and the change of the graphite form from spherical to flake was determined by the spheroidizing treatment. It was concluded that the Mg treatment performed as not functioning well. The present inventors, in order not to hinder the spheroidizing effect of graphite by Mg treatment, it is necessary to sufficiently deoxidize the outer layer material so that oxygen is not dissolved from the outer layer material in the ductile cast iron as the inner layer material. I thought. Focusing on Al, which is a deoxidizing element,
It has been found that it is better to adjust the Al content to an appropriate amount in the range of 0.010 to 0.080 wt%.

The present invention has been completed based on the above findings and further studies. That is, the present invention is a composite roll in which an outer layer and an inner layer are welded and integrated with each other, wherein the outer layer has a mass% of C: 2.3 to 3.0%,
Si: 2.0 to 3.0%, Mn: 0.1 to 2.0%, Cr: 0.5 to 3.0
%, Mo: 1.5 to 5.0%, Ni: 7.0 to 10.0%, V: 1.0 to
5.0%, Nb: 0.5-3.0%, B: 0.0050-0.0800%, RE
M: 0.0050-0.0500%, Al: 0.010-0.080%
And the following equations (1), (2) and (3): 4.30−0.33Si−0.047Ni + 0.0055 (Si + Ni) ≦ 3.4 (1) Mo / Cr ≧ 1.0 (2) 0.2 ≦ Nb / V ≦ 1.0 (3) (where, Si, Ni, Mo, Cr, Nb, V: Si, Ni, Mo, Cr,
Nb and V (contents of each element (mass%)), the balance is composed of a centrifugally cast outer layer material having a composition of Fe and unavoidable impurities, and the inner layer is made of ordinary cast iron or ductile A centrifugally cast composite roll having excellent seizure resistance characterized by being formed of cast iron. In the present invention, it is preferable that the centrifugally cast outer layer material further contains, in addition to the composition, W: 1.5% or less in mass%, and in the present invention, the graphite has an area ratio of 0.5% or less. Preferably, it is contained in an amount of up to 5%. Further, it is preferable that the base structure of the outer layer material for the centrifugal casting roll of the present invention be a structure substantially composed of bainite or martensite, or a mixed structure thereof.

The present invention is also a composite roll in which an intermediate layer is disposed between an outer layer and an inner layer, and the outer layer and the intermediate layer and the intermediate layer and the inner layer are welded and integrated with each other. mass%, C: 2.3-3.0%, Si: 2.0-3.0
%, Mn: 0.1-2.0%, Cr: 0.5-3.0%, Mo: 1.5-
5.0%, Ni: 7.0-10.0%, V: 1.0-5.0%, Nb: 0.
5-3.0%, B: 0.0050-0.0800%, REM: 0.0050-0.
0500%, Al: 0.010 to 0.080%, and the following expressions (1), (2) and (3): 4.30−0.33Si−0.047Ni + 0.0055 (Si + Ni) ≦ 3.4 (1) Mo / Cr ≧ 1.0 (2) 0.2 ≦ Nb / V ≦ 1.0 (3) (Si, Ni, Mo, Cr, Nb, V: Si, Ni, Mo, Cr,
Nb, V, the content of each element (mass%)), the balance consists of a composition consisting of Fe and unavoidable impurities, and is formed of a centrifugally cast outer layer material having graphite, and the intermediate layer is
A centrifugally cast composite roll excellent in seizure resistance, characterized in that the inner layer is formed of graphite steel and the inner layer is formed of ordinary cast iron or ductile cast iron. In the present invention, it is preferable that the centrifugally cast outer layer material further contains, in addition to the above composition, mass% and W: 1.5% or less,
Further, in the present invention, the graphite is contained in an area ratio of 0.5 to 5%.
% Is preferred. Further, it is preferable that the base structure of the outer layer material for the centrifugal casting roll of the present invention be a structure substantially composed of bainite or martensite, or a mixed structure thereof.

[0026]

First, the reasons for limiting the chemical composition of the centrifugally cast outer layer material used in the centrifugally cast composite roll of the present invention will be described. In addition, unless otherwise specified,% is:
mass%. C: 2.3 to 3.0% C is an important element that forms a hard carbide for improving the abrasion resistance of the outer layer material of the roll and crystallizes graphite in the base structure. In the present invention, the content is 2.3% or more. Need. On the other hand, when the content exceeds 3.0%, the crystallization temperature of γ is too low, and segregation of the MC type carbide by centrifugation is promoted. For these reasons, C is limited to the range of 2.3 to 3.0%.

Si: 2.0% to 3.0% Si acts as a deoxidizing agent for the molten metal, further enhances the castability of the molten metal, and promotes the crystallization of graphite. If the Si content is less than 2.0%, the crystallization of graphite will be insufficient. On the other hand, when the content exceeds 3.0%, the amount of graphite crystallized becomes too large, and the form of graphite becomes flaky, and the wear resistance and the tensile strength decrease. For this reason, Si is limited to the range of 2.0 to 3.0%. In addition, from the viewpoint of graphite crystallization amount, preferably 2.5 to
3.0%.

Mn: 0.1-2.0% Mn acts as a deoxidizing agent for the molten metal and further combines with S to form Mn.
It has the effect of forming S and preventing embrittlement due to S. Such an effect is observed at a content of 0.1% or more, but 2.0%
If the content exceeds 2, crack resistance is reduced. For this reason, Mn
Was limited to the range of 0.1 to 2.0%. The content is preferably 0.3 to 1.0% from the viewpoints of workability and economy.

Cr: 0.5-3.0% Cr combines with C to form carbides and has a function of improving the wear resistance by forming a solid solution in the matrix. Such an effect is observed at a content of 0.5% or more, while 3.0%
If the content is more than Cr, since Cr is a very strong white iron-forming element, the crystallization of graphite during the solidification process is suppressed, the amount of carbide increases, and the tensile strength decreases. Therefore, Cr is 0.5-3.0%
Limited to the range. In addition, from a viewpoint of abrasion resistance, it is preferably 1.0 to 2.0%.

Mo: 1.5 to 5.0% Mo, like Cr, is an element having the function of forming carbides, strengthening the matrix and carbides, improving wear resistance and improving crack resistance. 1.5% of such effects
Although the above content is recognized, the content exceeding 5.0% reduces crack resistance and toughness. For this reason, Mo is 1.5 to 5.
Limited to the 0% range. The content is preferably 2.5 to 4.0% from the viewpoint of roll characteristics and economy.

Ni: 7.0-10.0% Ni is an element that forms a solid solution in the matrix, enhances the quenchability, strengthens the matrix and promotes the crystallization of graphite, and has a low C content.
In the outer layer material of the present invention, which has many elements that bind to C, such as Nb and V, and has a small effective C content of the molten metal, it is an important element for properly crystallizing graphite. If the Ni content is less than 7.0%, no crystallization of graphite is observed, while if it exceeds 10.0%, a large amount of stable austenite remains and wear resistance is reduced. For this reason, Ni was limited to the range of 7.0 to 10.0%.
In addition, from a viewpoint of stable production, it is preferably 8.0 to 9.0%.

V: 1.0 to 5.0% V combines with C to form a hard MC-type carbide (MC or M ₄ C ₃ ) and effectively acts to improve wear resistance. Such an effect is observed when the content is 1.0% or more, but when the content exceeds 5.0%, the crystallization temperature of the MC type carbide becomes too high, segregation occurs by centrifugation, and further, crack resistance decreases and Production problems such as poor dissolution may occur. Therefore, V
Is limited to the range of 1.0 to 5.0%. In addition, from a viewpoint of abrasion resistance, it is preferably 2.5 to 4.0%.

Nb: 0.5-3.0% Nb forms complex carbide (V, Nb) C with V, increases the specific gravity of the formed carbide, and reduces segregation by centrifugation due to the difference in specific gravity with the molten metal. Has the effect of This effect is observed when the Nb content is 0.5% or more, but when the Nb content exceeds 3.0%, the crystallization temperature of the MC-type composite carbide (V, Nb) C becomes too high, and the Segregation occurs, and further, there arises manufacturing problems such as a decrease in crack resistance and poor dissolution. For this reason, Nb is limited to the range of 0.5 to 3.0%.

B: 0.0050 to 0.0800% B enhances hardenability and forms B nitride to act as a crystallization nucleus of graphite. In the present invention, in order to increase the amount of graphite, it is added for the purpose of increasing the crystallization nuclei of graphite. For this purpose, B needs a content of 0.0050% or more. On the other hand, when the content exceeds 0.0800%, the amount of graphite is rather reduced. For this reason, B was limited to the range of 0.0050 to 0.0800%. Preferably, from the viewpoint of the amount of graphite,
It is 0.015 to 0.04%.

REM: 0.0050-0.0500% REM has the effect of spheroidizing graphite, and this action is 0.00
REM content greater than 50% is permissible, but REM content greater than 0.0500% reduces graphite and increases carbide content. For this reason, REM was limited to the range of 0.0050-0.0500%. In consideration of the effect and economy, preferably, 0.015
~ 0.030%.

Al: 0.010 to 0.080% Al is an element that acts as a deoxidizing agent and is one of the important elements in the present invention. In the outer layer material, as a deoxidizing agent, the soundness of the outer layer material is improved, and the oxide has the effect of refining the solidified structure of the cast iron. When injecting the inner layer material into the outer layer shell formed by centrifugal casting, remelting a part of the outer layer shell, welding and integrating the inner layer material and the outer layer material into a composite roll,
The outer layer material is sufficiently deoxidized so that oxygen does not dissolve in the inner layer material from the outer layer material and does not deteriorate the spheroidizing effect of the Mg treatment in the inner layer material. Therefore, in the present invention, the content of Al is required to be not less than 0.010%. However, if the content of Al exceeds 0.080%, the cleanliness is reduced and the surface defects of the outer layer during use are frequently generated. For this reason, Al was limited to the range of 0.010 to 0.080%.

4.30−0.33Si−0.047Ni + 0.0055 (Si + Ni) ≦ 3.4 (1) Left side of equation (1), y = 4.30−0.33Si−0.047Ni + 0.0055
(Si + Ni) is a formula for estimating the amount of eutectic C in which graphite + γ is crystallized from the liquid phase L, and is a value called a calculated eutectic value. If the calculated eutectic value y exceeds 3.4, crystallization of graphite cannot be expected as shown in FIG. For this reason, the amounts of Si and Ni, which are elements that promote graphite crystallization, are adjusted so that the calculated eutectic value y becomes 3.4 or less. In addition, y is preferably 3.1 to 3.2.

Mo / Cr ≧ 1.0 (2) In the present invention, the Mo / Cr ratio is adjusted in order to compensate for the decrease in wear resistance due to crystallization of graphite by toughening the carbide. (2)
As shown in the equation, by setting Mo / Cr to be 1.0 or more, the wear resistance is improved (FIG. 2). Preferably, Mo / Cr is
1.2 to 1.8.

0.2 ≦ Nb / V ≦ 1.0 (3) In the present invention, in order to increase the specific gravity of the MC type carbide (here, VC), the Nb content is adjusted in accordance with the V content, and the VC is reduced by (V , N
b) A composite carbide of C to reduce segregation due to centrifugation due to the difference in specific gravity from the molten metal. If Nb / V is less than 0.2, tissue segregation occurs due to centrifugation, and the roll material is not uniform. On the other hand, when Nb / V exceeds 1.0, crack resistance deteriorates. Figure 4 shows the effect of Nb / V on crack resistance.
Shown in

FIG. 4 shows that C: 2.8 mass%, Si: 2.5 mass
%, Mn: 0.5mass%, Cr: 2.0mass%, Mo: 3.0mass%
V: 1.0 to 5.0 mass%, Nb: 0 to 5.0 mass%
Centrifugal casting of molten metal with the Nb / V ratio changed to the range of
G) The results of investigating the thermal shock characteristics (crack resistance) using the ring material (wall thickness 85 mm) obtained as described above. 55 after solidification
After tempering at 0 ° C., a plate-like test piece (55 × 40 × 15 mm) was collected from the outer surface side of the ring material. Using these plate-shaped test pieces, the roller rotating at 1200 rpm for 15
c After pressure welding, the substrate was immediately cooled with water, and a thermal shock test was performed to observe the presence or absence of cracks. Crack resistance was evaluated based on the crack depth. The load at the time of pressure welding is 150k
gf.

FIG. 4 shows that when Nb / V exceeds 1.0, the crack depth increases and the thermal shock resistance (crack resistance) decreases. From this, Nb / V is calculated as shown in equation (3).
It was limited to the range of 0.2 to 1.0. Preferably, 0.4
~ 0.8. W: 1.5% or less W combines with C to form carbides and contributes to the improvement of abrasion resistance.
Segregation by centrifugation occurs. For this reason, W is preferably limited to 1.5% or less.

In the outer layer material of the roll of the present invention, the balance other than the above components is composed of Fe and unavoidable impurities. Inevitable impurities include P, S, As, and Bi.
As and Bi are desirably reduced as much as possible in order to deteriorate the material, but P: 0.05% or less, S: 0.02% or less, A
s: 0.015% or less, Bi: 0.015% or less is acceptable. In addition, Ti and Zr have an effect of refining the solidified structure, and Co has an effect of toughening the matrix and does not impair the effects of the present invention. In addition, when it contains, it is preferable that Ti: 1.0% or less, Zr: 1.0% or less, Co: 5.0% or less.

The outer layer material suitable for the composite roll of the present invention preferably has a base structure of bainite or martensite, or a mixed structure thereof. With a structure other than bainite or martensite, high tensile strength (tensile strength: 600 MPa or more) cannot be secured. The outer layer material suitable for the composite roll of the present invention desirably has a structure containing graphite in an area ratio of 0.5 to 5%. If the area ratio of graphite is less than 0.5%, the friction coefficient cannot be reduced. When the area ratio of graphite exceeds 5%, the wear resistance and the tensile strength decrease. Further, in the outer layer material suitable for the composite roll of the present invention, the carbides have an area ratio of
It is desirable to make it 40% or less. If the amount of carbide exceeds 40%, problems such as a decrease in crack resistance and tensile strength occur.

As for the method of casting the composite roll, after the outer layer having the above composition is cast by the centrifugal mold casting method, or further, the intermediate layer is cast by the centrifugal mold casting method, and then the solid inner layer is formed therein. Cast still. When a sleeve-shaped roll is cast, it goes without saying that the inner layer may also be cast by a centrifugal casting method. The centrifugal casting method may be any of a horizontal type in which the rotation axis of a cylindrical mold is horizontal, an oblique type in an oblique direction, and a vertical type in a vertical direction.

In the composite roll of the present invention, the inner layer material forming the inner layer is ordinary cast iron (high-grade cast iron) or ductile cast iron. It is preferable that the composition of the inner layer material after welding is adjusted to the following composition before casting such that the following composition is obtained. The composition of ordinary cast iron is as follows: mass%, 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, Cr: 2.0% or less, Ni: 3.0% or less, Mo: 2.
0% or less, with the balance being substantially Fe. In addition, as a balance, in addition to Fe, trace amounts of Al and N mixed from the outer layer and the intermediate layer.
b, V, REM, and B are included.

The composition of the ductile cast iron is mass%
And C: 2.5 to 4.0%, Si: 1.5 to 3.5%, Mn: 0.2 to
1.5%, P: 0.2% or less, S: 0.2% or less, Cr: 2.0%
Hereafter, Ni: 3.0% or less, Mo: 2.0% or less, Mg: 0.02-0.
1%, with the balance being substantially Fe. The balance is Fe
In addition, trace amounts of Al, Nb, V mixed from the outer layer and intermediate layer
REM and B are included.

In the composite roll of the present invention, an intermediate layer may be provided between the inner layer and the outer layer in order to prevent alloy components of the outer layer, particularly Cr, from being mixed into the inner layer and deteriorating the strength and toughness. it can. The intermediate layer itself requires a certain level of strength. 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 have a composition that does not decrease the strength even when a large amount of alloy element is mixed in from the outer layer. For this reason, the intermediate layer material is preferably made of graphite steel.

The composition of the intermediate layer material is as follows:
2.0%, Si: 1.6-2.4%, Mn: 0.2-1.0%, P:
0.2% or less, S: 0.2% or less, Cr: 3.0% or less, Ni: 1.
0% or less, Mo: 1.0% or less, and the balance is substantially Fe.
The composite roll made by centrifugal casting of the present invention is subjected to a process including a quenching-tempering process or a tempering process after casting to obtain a product.

[0049]

EXAMPLES (Example 1) A molten metal for an outer layer having a composition shown in Table 1 was melted, and an outer layer having a thickness of 100 mm was cast by a centrifugal casting method (145G). After the outer layer has solidified, stand the mold vertically,
An inner layer material (ductile cast iron) melt having the composition shown in Table 1 was injected from above. The inner surface temperature and solidification time of the outer layer and the melt temperature of the inner layer material were determined by solidification heat transfer analysis so that the remelting allowance of the outer layer was 15 mm. After complete solidification, the roll was removed from the mold, heat treated (tempering at 500 ° C.) and machined into a composite roll of the final product. The dimensions of the composite roll are a product body diameter φ685 mm, a body length 2380 mm, and a total length 5815 mm.

From these composite rolls, test specimens were collected,
Shore hardness tests, hot wear tests, thermal shock tests, and tensile tests were performed. Disk-shaped test pieces of φ50 × 10 mm were collected from the outer layer surface side and inner layer side of these composite rolls. The wear test uses these disc-shaped test pieces,
Rotate the counter material (φ190 x 15mm) heated to 800 ° C.
A disc-shaped test piece at 800 rpm was pressed into contact with a load of 100 kgf and rolled for 120 minutes at a slip rate of 3.9%. After the test, the wear loss of the disc-shaped test piece was measured and evaluated for wear resistance. The coefficient of friction was determined from the radius and load of the test piece during the wear test, and the torque acting on the test piece.

Plate-shaped test pieces (55 × 40 × 15 mm) were collected from the outer layer surface side of these composite rolls. In the thermal shock test,
These plate-shaped test pieces are applied to rollers rotating at 1200 rpm.
After pressure contact for 15 seconds, the mixture was directly cooled with water and observed for the occurrence of cracks. Crack depth generated (thermal crack depth)
Was used to evaluate the crack resistance. The load at the time of pressure welding is 150k
gf.

The tensile test was performed using a round bar test piece (φ10 × 50 m) taken from the surface side of the outer layer of the composite roll and the center of the inner layer.
m) was used to determine the tensile strength. The hardness test was measured on the surface of the outer layer of the composite roll using a Shore hardness tester. Table 2 shows the results.

[0053]

[Table 1]

[0054]

[Table 2]

All of the examples (A1 to A4) of the present invention have low wear loss and excellent abrasion resistance, have a low friction coefficient of 0.36 or less and have a low friction coefficient, and have a shallow thermal crack depth and excellent crack resistance. In addition, the centrifugally cast composite roll has a high tensile strength of at least 620 MPa and a small segregation of the structure in the depth direction of the outer layer material, and is excellent in material uniformity. In addition, there is no deterioration of the tensile strength of the inner layer material, and the centrifugal casting composite roll has a high inner layer strength.

On the other hand, in the comparative examples out of the range of the present invention, any one of the wear resistance, friction coefficient, crack resistance and tensile strength of the outer layer material was deteriorated, and the uniformity of the material was poor.
Further, in some of the comparative examples, deterioration of the inner layer strength was observed. In Comparative Example No. B1, the C content was outside the range of the present invention, and the amount of graphite was too large, the wear resistance was reduced, and carbide segregation occurred, resulting in low uniformity of the material. In Comparative Example No. B2, the Ni content was outside the range of the present invention, no crystallization of graphite was observed, and the friction coefficient was as high as 0.56. Further, the tensile strength of the inner layer material is reduced due to the low Al content of the outer layer material and insufficient deoxidation. Comparative Example N
In o.B3, the tensile strength of the inner layer material is low due to the low Al content of the outer layer material and insufficient deoxidation. In Comparative Example No. B4, the V, Nb content of the outer layer material was out of the range of the present invention, the segregation of carbides was remarkable, and the crack resistance was lowered. (Example 2) A molten metal for an outer layer having a composition shown in Table 3 was produced, and an outer layer having a thickness of 100 mm was cast by centrifugal casting (145G). After the outer layer was solidified, the molten metal for the intermediate layer shown in Table 3 was further melted and poured into a mold, and the outer layer was re-melted by 15 mm, and a 40 mm thick intermediate layer was cast by centrifugal casting.
Thereby, the outer layer and the intermediate layer are welded and integrated. After the solidification, the mold is set upright, and the inner layer material (ductile cast iron) having the composition shown in Table 3 is poured from above, and the mold is completely filled so that the remelting allowance is 15 mm. Covered with wood. After complete solidification, the roll was removed from the mold, heat treated (tempering at 500 ° C.) and machined to form a composite roll of the final product. The dimensions of the composite roll are a product body diameter φ685 mm, a body length 2380 mm, and a total length 5815 mm.

From these composite rolls, test pieces were taken from the outer layer material in the same manner as in Example 1, and subjected to a Shore hardness test, a hot wear test, a thermal shock test, and a tensile test.
As for the inner layer material, a tensile test piece was sampled from the center of the inner layer and the tensile strength was measured in the same manner as in Example 1. Similarly, a tensile test piece was sampled from the intermediate layer, and the tensile strength was measured.
Table 4 shows the results.

[0058]

[Table 3]

[0059]

[Table 4]

The inventive example (A5) is excellent in abrasion resistance, low in friction coefficient, shallow in thermal crack depth, excellent in crack resistance, and high in tensile strength, and moreover, in the depth direction of the outer layer material. This is a centrifugally cast composite roll that is excellent in material uniformity without segregation. Further, by forming the intermediate layer between the outer layer and the inner layer, the mixing of the outer layer material into the inner layer material is reduced, and the decrease in the strength of the inner layer material is further reduced.

[0061]

As described above, according to the present invention, there is little segregation of components and structures, etc., excellent in material uniformity, low friction coefficient, high crack resistance, high wear resistance, and high tensile strength. A centrifugally cast composite roll composed of an outer layer material having strength and an inner layer having sufficient tensile strength can be provided at a low cost, and has an industrially significant effect.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the C content affecting graphite crystallization and a calculated eutectic value y.

FIG. 2 is a graph showing the effect of Mo / Cr on the amount of wear.

FIG. 3 is a graph showing the ratio of the wear amount (WR ₀ ) on the surface side of the outer layer material to the wear amount (WR ₁ ) on the inner layer side, and the effect of Nb / V on WR ₀ / WR ₁ .

FIG. 4 shows the effect of Nb / on the crack depth in the thermal shock test.
6 is a graph showing the effect of V.

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) B22D 19/16 B22D 19/16 F C22C 37/04 C22C 37/04 BC 37/08 37/08 Z 37/10 37 / 10 Z

Claims (5)

[Claims] 1. A composite roll in which an outer layer and an inner layer are welded and integrated with each other, wherein the outer layer is mass%, C: 2.3 to 3.0%, Si: 2.0 to 3.0%, Mn: 0.1 to 2.0%, Cr: 0.5 to 3.0%, Mo: 1.5 to 5.0%, Ni: 7.0 to 10.0%, V: 1.0 to 5.0%, Nb: 0.5 to 3.0%, B: 0.0050 to 0.0800%, REM: 0.0050 to 0.0500%, Al : A centrifugally cast outer layer material containing 0.010 to 0.080%, and satisfying the following formulas (1), (2) and (3), comprising a balance of Fe and unavoidable impurities, and further comprising graphite: Wherein the inner layer is made of ordinary cast iron or ductile cast iron, and is a centrifugally cast composite roll having excellent seizure resistance. Note 4.30−0.33Si−0.047Ni + 0.0055 (Si + Ni) ≦ 3.4 (1) Mo / Cr ≧ 1.0 (2) 0.2 ≦ Nb / V ≦ 1.0 (3) where Si , Ni, Mo, Cr, Nb, V: Si, Ni, Mo, Cr, N
b, V, content of each element (mass%) 2. A composite roll in which an intermediate layer is disposed between an outer layer and an inner layer, and the outer layer and the intermediate layer and the intermediate layer and the inner layer are welded and integrated with each other.
C: 2.3 to 3.0%, Si: 2.0 to 3.0%, Mn: 0.1 to 2.0%, Cr: 0.5 to 3.0%, Mo: 1.5 to 5.0%, Ni: 7.0 to 10.0%, V: 1.0 to 5.0% , Nb: 0.5-3.0%, B: 0.0050-0.0800%, REM: 0.0050-0.0500% Al: 0.010-0.080%, and satisfies the following equations (1), (2) and (3). , Consisting of a composition consisting of the balance Fe and inevitable impurities, further formed of a centrifugally cast outer layer material having graphite, the intermediate layer is formed of graphite steel, and the inner layer is formed of ordinary cast iron or ductile cast iron. Centrifugal casting composite rolls with excellent seizure resistance. Note 4.30−0.33Si−0.047Ni + 0.0055 (Si + Ni) ≦ 3.4 (1) Mo / Cr ≧ 1.0 (2) 0.2 ≦ Nb / V ≦ 1.0 (3) where Si , Ni, Mo, Cr, Nb, V: Si, Ni, Mo, Cr, N
b, V, content of each element (mass%) 3. The seizure resistance according to claim 1, wherein the centrifugally cast outer layer material further contains, in addition to the composition, mass% and W: 1.5% or less. Centrifugal casting composite roll. 4. The centrifugally cast composite having excellent seizure resistance according to claim 1, wherein the centrifugally cast outer layer material contains the graphite in an area ratio of 0.5 to 5%. roll. 5. The centrifugally cast outer layer material according to claim 1, wherein a base structure of the outer layer material is substantially composed of bainite or martensite, or a mixed structure thereof. Composite roll.