JPH09170042A - Roll made by centrifugal casting and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a roll having excellent various mechanical properties and suitable for rolling steel sheets by optimizing alloy components forming its external layer. SOLUTION: This roll is composed of an external layer material 1 and an axial core material 2. The external layer material 1 has optimized alloy components, and by limiting carbides, it has also wear and cracking resistances as well as a low friction coefficient, and in which segregation or the like are not generated and surface roughening resistance is secured even if centrifugal casting is executed. As the axial core material 2, ductile cast iron is used, and it is perfectly welded and integrated with the external layer material 1. Thus, the roller having the above constitution is suitably used for rolling thin steel sheets under severe specification as for the surface properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a centrifugally cast roll having abrasion resistance, crack resistance, and surface roughness resistance, which is suitable for use as a rolling roll or the like, and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, a hot rolling roll required to have wear resistance is a composite roll consisting of an outer layer and an inner layer, and M ₇ C ₃ and M ₃ C carbides are crystallized from the outer layer material. High Cr cast iron, Ni grain cast iron, or inner layer material is manufactured by centrifugal casting as gray cast iron or ductile cast iron having high toughness.

[0003] However, due to the severer rolling conditions and the demand for improved productivity in rolling, there is a demand for a roll for rolling having more wear resistance and crack resistance.

Under these circumstances, a high-speed roll material and a rolling roll using the same have been developed in order to improve the wear resistance.

For example, in Japanese Patent Laid-Open No. 4-365836, C: 1.5-
3.5%, Si: 1.5% or less, Mn: 1.2% or less, Cr:
5.5 to 12.0%, Mo: 2.0 to 8.0%, V: 3.0 to 10.0
%, Nb: 0.6 to 7.0%, and the following formula (1)
(2) V + 1.8 Nb ≤ 7.5 C-6.0 (%) (1) 0.2 ≤ Nb / V ≤ 0.8 (2) Rolling roll outer layer material with balance Fe and unavoidable impurities In addition, there is disclosed a rolling roll outer layer material having both wear resistance and crack resistance, which is free from components and structure segregation inside the outer layer even by centrifugal casting.

Further, in Japanese Patent Laid-Open No. 6-256888, C: 1.8 to 3.
6%, Si: 1.0 to 3.5%, Mn: 0.1 to 2.0%, C
r: 2.0 to 10.0%, Mo: 0.1 to 10.0%, W: 0.1 to 10
%, V, Nb: One or two in total of 1.5 to 10% and the balance substantially consisting of Fe. A high-speed cast iron material having graphite is used as an outer layer material for rolling rolls, which has a low friction coefficient and cracks. Disclosed is an outer layer material for rolling that does not easily develop.

[0007]

The hot rolled product is a slab of 130 to 300 mm thickness produced by continuous casting or lump slab heating in a heating furnace, or it receives as a hot piece, rough rolling and finish rolling machine. Is hot-rolled into a strip with a thickness of 1.0 to 25.4 mm, wound into a coil with a winder (coiler), cooled, and processed in various refining lines to be manufactured.

The finish rolling mill is usually a quadruple rolling mill from 5 to 7
It is a continuous rolling mill arranged in series. Until the 1960s, there were many 6-stand mills, but since the 1940s, we have been improving productivity and responding to larger coils.
Most mills have 7 stands. In this finish rolling, there is a so-called drawing accident in which two sheets are stacked between stands and rolled as they are for some reason. In particular, the probability of occurrence is higher in the latter stages, and this kind of accident is seen in the 7-stand finishing rolling mill after the 5th stand. When this throttling accident is encountered, frictional heat generation due to the abnormal rolling,
The roll surface temperature locally rises due to heat generated during processing, and when cooled with water, thermal shock may cause cracks on the roll surface. This is a squeeze crack. Usually, when a throttling accident is encountered, the roll is changed, and the presence or absence of cracks in the roll that has encountered throttling is investigated. If the presence of cracks is confirmed, the roll is ground until the cracks disappear. This means worsening the roll unit. Further, if the presence of a squeezing crack is overlooked and the roll is reused as it is, the squeezing crack will start as a starting point for the crack to develop, which may cause a spalling accident of the roll. In that case, the line must be stopped for several hours to several tens of hours, which causes great damage.

Conventionally, for the latter stage of finishing, a high-alloy grain roll made by centrifugal casting has been generally used except for a part thereof.
Centrifugal casting high alloy grain rolls have a relatively low crack occurrence rate when encountering a squeeze, and even if cracks occur, the depth is relatively shallow, but the wear resistance is poor. Recently, high-speed rolling rolls are being used in the post-finishing stage as well, but their wear resistance is about 3-5 times better than centrifugally cast high-alloy grain rolls, but the rate of occurrence of drawing is high when encountering drawing. , Also, the depth of cracks is deep. This problem has not been solved in JP-A-6-256888.

Recently, not only the materials but also the specifications for the surface properties of the products have become stricter. For example, in the case of a thin steel plate used for the body of an automobile, in order to secure the image clarity when completed as an automobile, A sound product surface during rolling is required. The same applies to the case of thin steel sheets for electric appliances. Surface properties such as when scratches are left on the product surface due to rolls or scales of the material to be rolled during rolling, or when so-called needle-like scale defects occur when the scale adheres to the product like a wedge is inserted. The problems relating to JP-A-4-365836 and JP-A-6-256888 have not been solved yet.

The present invention has been made in view of the above problems,
While maintaining the abrasion resistance, which is a characteristic of high speed steel rolls,
The purpose is to have both crack resistance and a low coefficient of friction, to prevent segregation and the like even in centrifugal casting and to secure resistance to rough skin.

[0012]

The present invention according to claim 1 is a centrifugal casting roll comprising an outer layer material and a ductile cast iron mandrel fused and integrated with the outer layer material. Material is C: 2.5-4.7%, Si: 0.8-3.2%, M
n: 0.1-2.0%, Cr: 0.4-1.9%, Mo: 0.6-
5.0%, V: 3.0-10.0%, Nb: 0.6-7.0% and satisfy the following formulas (1), (2), (3) and (4), and the outer layer material and A centrifugal casting roll consisting of a shaft core material of ductile cast iron fused and integrated through a layer material,
The outer layer material is C: 2.5 to 4.7%, Si: 0.8 to 3.2%,
Mn: 0.1 to 2.0%, Cr: 0.4 to 1.9%, Mo: 0.6
-5.0%, V: 3.0-10.0%, Nb: 0.6-7.0%, and satisfy the following formulas (1), (2), (3) and (4), and 2.0 +0. 15V + 0.10 Nb ≤ C (%) (1) 1.1 ≤ Mo / Cr (2) Nb / V ≤ 0.8 (3) 0.2 ≤ Nb / V (4) The balance consists of Fe and inevitable impurities. The shaft core material has C: 2.8 to 3.8% and Si: 2.0.
~ 3.0%, Mn: 0.3-1.0%, P: 0.10% or less, S:
0.04% or less, Ni: 0.3 to 2.0%, Cr: 1.5% or less,
Mo: 1.0% or less is contained, and the balance is Fe and inevitable impurities.

According to a second aspect of the present invention, in the centrifugal casting roll according to the first aspect, the outer layer material further comprises Ni: 5.
It is designed to contain 5% or less.

According to a third aspect of the present invention, in the centrifugal casting roll according to the first aspect, the outer layer material further has B: 0.00.
The content is 2 to 0.1%.

According to a fourth aspect of the present invention, in the centrifugally cast roll according to the first aspect, the outer layer material further comprises Ni: 5.
5% or less and B: 0.002 to 0.1% are contained.

The present invention according to claim 5 provides claims 1 to 4.
In manufacturing the centrifugally cast roll described in any one of 1 to 3, the mixing ratio of the outer layer material to the shaft core material is regulated within the range of 5 to 25%.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

(A) Reasons for limiting alloying elements in outer layer material “Having graphite” The amount of crystallized graphite is C, which is the element, the Si which has the effect of crystallizing graphite, the V which consumes C before crystallizing graphite,
It is mainly determined by the amount of Nb, but in the range of the present invention, the area ratio is 0.
2 to 5%. This graphite plays a role of absorbing stress during thermal shock. Further, it plays the role of a solid lubricant, reduces the coefficient of friction, and improves seizure resistance.

C: 2.5 to 4.7% C is an essential element for forming hard carbide which improves the wear resistance of the outer layer material of the roll and for crystallizing it in the matrix as graphite.
2.5% or more is required, but if it exceeds 4.7%, the wear resistance decreases, so the upper limit is 4.7%.

Si: 0.8 to 3.2% Si is added for deoxidation, securing castability and crystallization of graphite, but if it is less than 0.8%, the crystallization effect of graphite is insufficient, while 3.
If it exceeds 2%, the amount of crystallized graphite becomes excessive and wear resistance decreases, so the upper limit is made 3.2%.

Mn: 0.1 to 2.0% Mn is required to be 0.1% or more in order to combine with S mixed as an impurity to form MnS and prevent embrittlement due to S, but if it exceeds 2.0%, crack resistance is high. The upper limit is set to 2.0% because it will decrease.

Cr: 0.4-1.9% Cr forms a carbide to improve wear resistance,
0.4% to strengthen the base and improve crack resistance
The above is necessary, but on the other hand, it is a very strong element of white pig iron 1.
If added in excess of 9%, crystallization of graphite in the solidification process is hindered, so the upper limit is made 1.9%.

Mo: 0.6-5% Mo is effective in improving wear resistance by forming carbides similarly to Cr and improving crack resistance by strengthening matrix structure, and hardenability and temper softening resistance of matrix. 0.6% or more is necessary to effectively improve the crack resistance, but if it exceeds 5%, the crack resistance decreases, so the upper limit is made 5%.

V: 3.0 to 10.0% V is a hard MC (or M ₄ C) most effective for improving wear resistance.
₃ ) It is an essential element for forming carbides (diameter of about several μm), and 3.0% or more is necessary to exert its effect, but if it exceeds 10.0%, crack resistance decreases, dissolution is poor, etc. Therefore, the upper limit is 10.0%.

B: 0.002 to 0.1% B combines with dissolved N to form BN, which serves as a nucleus for crystallization of graphite. The presence of this graphite core makes the crystallized graphite finer and improves the wear resistance, and when the roll wears during rolling, it wears more evenly on the microstructure size, approximately 10 to 100 μm order. As a result, the skin of the rolled product (plate) becomes more beautiful. 0.002 for these effects
% Or more, but if it exceeds 0.1%, the problem of deterioration of crack resistance occurs, so the upper limit is made 0.1%.

Nb: 0.6 to 7.0%, 0.2 ≦ Nb / V (4) The VC carbide has a small specific gravity with respect to the mother molten metal, and segregates when centrifugal casting is performed. Nb is added to prevent this segregation. Nb is V and complex carbide {V, N
b} C is formed, and the specific gravity is increased as compared with the case where the carbide is V alone. This prevents segregation due to centrifugation. Therefore, it is necessary to change the amount of Nb added depending on the amount of V added. From FIG. 1, in order to obtain a uniform outer layer material when manufactured by the centrifugal casting method, 0.2 ≦ Nb / V must be satisfied. Also, since V is 3.0% or more, at least Nb is
0.6% or more will be added. On the other hand, if Nb exceeds 7.0%, manufacturing problems such as poor dissolution will occur, so the upper limit is
It is 7.0%.

In FIG. 1, "wear ratio (inner layer / outer layer)" means the wear amount (Iw) of the test piece taken from the inner layer side of the ring material and the wear amount (O of the test piece taken from the outer layer side).
ratio (Iw / Ow) with w). The test in Figure 1 is C: 4.
0%, Si: 1.2%, Mn: 0.3%, Cr: 0.8%, M
A ring sample with a wall thickness of 100 mm obtained by centrifugal casting (140 G) of o: 2.0%, V: 4.9%, and Nb: 0 to 7.5% was subjected to 1050 ° C normalizing treatment and 550 ° C tempering treatment. Using. And wear test is performed with φ190 x 15 mating material and φ
The sliding wear method of the 2 disk of the test material of 50 × 10 makes the mating material 80
The test material is heated to 0 ° C and rolled with a load of 100 kgf to give 80
Rotation was carried out at 0 rpm, the slip rate was set to 3.9%, and the wear reduction after 120 minutes was measured.

2.0 + 0.15V + 0.10 Nb ≦ C (%) (1) When the roll material of the present invention is solidified, first, {V, Nb} C composite carbide and dendrite are first crystallized, and then graphite, The eutectic structure crystallizes and the solidification is completed. C is V, Nb
Is preferentially consumed by the rest, and the rest becomes graphite and the like.
Formula (1) is a condition that the graphite crystallization is 0.2% or more in area ratio.

1.1 ≦ Mo / Cr (2) This is a conditional expression for preventing the occurrence of needle-shaped scale flaws. From the experiment of Table 1, it was clarified that the formula (2) is in a range where needle-shaped scale flaws do not occur. The rolling experiment in Table 1 is C:
4.1%, Si: 0.9%, Mn: 0.5%, Cr: 0.6, 1.
0, 1.7%, Mo: 0.2-7.0%, V: 4.9%, Nb:
A 1.4% φ90 × 250 cylindrical block was subjected to 1050 ° C normalizing treatment and 550 ° C tempering treatment to a diameter of 70 mm and width of 40
mm rolls were taken. And the thickness of SUS304 is 1.2m
The test was conducted by hot rolling three coils of m 3, width 20 mm and length 600 mm. At a rolling reduction of 40%, a rolling speed of 100 mpm, and a rolling temperature of 1050 ° C, when converted to an actual machine, it corresponds to rolling 315 slabs in the first stage (first stage) of hot rolling finishing. In this test, the coil heated immediately before rolling is descaled. After the test, the surface condition of the material to be rolled was observed and examined for scratches and the presence of scales inserted into the product like wedges.

[0029]

[Table 1]

Nb / V ≦ 0.8 (3) This is a conditional expression for ensuring crack resistance. From the experiment of Fig. 2, it became clear that the formula (3) is in the range where the crack resistance is not impaired. In the experiment of FIG. 2, a test piece taken from the outer layer side of the ring material of the experiment of FIG. 1 was used. Thermal shock test
A 55 × 40 × 15 plate-shaped test piece is pressed against a roller rotating at 1200 rpm for 15 s, and immediately water-cooled to generate cracks. The pressure contact load is 150 kgf. After the test, the test piece was cut and the crack length was measured.

Ni: 5.5% or less Added to improve hardenability. When the roll diameter is small or the roll is a sleeve type and the wall thickness is thin and water quenching or oil quenching is possible, it is not always necessary to add it, but when it is not, addition is preferable.

As for the rolling rolls, the maximum range of solid rolls having a diameter of 1500 mm is set to 5.5% or less so that quenching is possible even in natural cooling where the cooling rate is slow.

In the outer layer material of the present invention, the above N
It is not always necessary to contain i and B.

Further, a molten metal having the chemical structure shown in Table 2 (materials of the present invention: A1 to A12, comparative materials: B1 to B15 were subjected to centrifugal casting (14
0G) to cast a ring sample with a wall thickness of 100 mm,
After the normalizing treatment at ℃ and the tempering treatment at 530 ℃, Shore hardness, hot abrasion, and thermal shock test were conducted.

The wear test was carried out by the same method as the above conditions, by taking test pieces of φ50 × 10 from the inner layer side and the outer layer side of the ring material. The friction coefficient was determined from the radius of the test piece, the load, and the torque acting on the test piece.

[0036]

[Table 2]

The thermal shock test was carried out under the same conditions by collecting the above-mentioned plate-shaped test piece from the outer layer side of the ring material.

A rolling test was conducted from the outer layer side of the ring material to φ70 × 40.
The test piece of 1 was sampled and the same method as the above conditions was used.

Table 3 shows the results of the wear test, thermal shock test and rolling test. According to Table 3, the material of the present invention (A1 ~
A12) satisfies the wear resistance, crack resistance, low friction coefficient, surface roughening resistance, and homogeneity in centrifugal casting at the same time as the comparative material.

[0040]

[Table 3]

In the B1 material, the amount of C added was small and graphite was not crystallized. Therefore, the coefficient of friction is high. In the B2 material, the amount of C added is large and the amount of crystallized graphite is excessive, so that the wear resistance is deteriorated. In the B3 material, the amount of Si added was small and graphite did not crystallize. Therefore, the coefficient of friction is high. B4 material is S
Since the amount of i added is large, the amount of crystallized graphite is excessive.
Abrasion resistance is reduced. Further, since the formula (2) was not satisfied, defects were found on the surface of the product sheet during the rolling test.
The B5 material has a large amount of Mn added, so that the crack resistance is deteriorated. Further, since the formula (2) was not satisfied, defects were found on the surface of the product sheet during the rolling test. Since the B6 material has a small amount of added Cr, its wear resistance is lowered. B7 material is C
Since the amount of r added is too large, white pig iron is formed and graphite does not crystallize.
Therefore, the coefficient of friction is high. Since the B8 material contains too much Mo, the crack resistance is deteriorated. Since the B9 material lacked the V content, the wear resistance was lowered and the crack resistance was also slightly lowered. Since the B10 material has an excessive V content, the crack resistance is deteriorated. Since the B11 material does not satisfy the formula (4), segregation of carbide reduces the wear resistance of the outer layer. Since the B12 material did not satisfy the formula (2), defects were recognized on the surface of the product sheet during the rolling test. Since B13 material does not satisfy the expression (3), crack resistance is deteriorated. B14
Since the B content is not added to the material, the wear resistance is inferior to the A material. Since the B15 material has an excessive B content, the crack resistance is deteriorated.

(B) Reasons for limiting alloying elements in shaft core material In a composite roll, in order to metallurgically bond the outer layer material and the shaft core material, it is essential to mix the inner surface side of the outer layer material and the shaft core material. Is. However, the outer layer material should not be excessively mixed in until the excellent toughness, which is the function of the shaft core material, is impaired.

For this reason, the casting conditions are selected, and the mixing ratio of the outer layer material to the shaft core material (the weight percentage of the outer layer material mixed in the shaft core material with respect to the total weight of the shaft core material molten metal) is set to an appropriate value. Keeping in range is extremely important.

In the present invention, it has been found that it is optimum to regulate this range to 5 to 25%. That is, if it is less than 5%, unwelded or casting defects such as inclusions are likely to occur at the boundary between the intermediate layer material and the shaft core material, and the soundness of the boundary portion cannot be secured. Further, if it exceeds 25%, a large amount of Cr and C, which deteriorate the characteristics of the ductile cast iron that is the axial core material, is mixed in the components of the outer layer material, leading to defective graphite shape of the axial core material and remarkable white pig iron. The function as cast iron declines.

Therefore, the mixing ratio of the outer layer material is regulated within the above-mentioned range of 5 to 25%, and in consideration of the component increase due to this, the chemical composition of the molten metal component is adjusted so that the composition of the mandrel after solidification satisfies the following range It is necessary to select the composition.

C: 2.8 to 3.8% If C is less than 2.8%, the amount of graphite becomes small, and the material characteristics as ductile cast iron cannot be sufficiently exhibited. Meanwhile, 3.
Since it becomes brittle if it contains more than 8%, 2.8-3.8
%.

Si: 2.0 to 3.0% When Si is less than 2.0%, the amount of graphite becomes small and a large amount of cementite precipitates, so that it becomes hard and brittle. Meanwhile, 3.0
%, The amount of graphite becomes too large and the strength is deteriorated. Therefore, it is specified in the range of 2.0 to 3.0%.

Mn: 0.3 to 1.0% Mn is effective in suppressing the damage of S, but if it is less than 0.3%, the effect is not sufficient, and if it exceeds 1.0%,
Since it deteriorates the material, it is specified in the range of 0.3-1.0%.

P: 0.1% or less P increases the fluidity of the molten metal, but makes the material brittle, so P is 0.1% or less.

S: 0.04% or less S inhibits the spheroidization of graphite and must be kept low.

Ni: 0.3 to 2.0% Ni promotes graphitization, but if it is less than 0.3%, its effect is insufficient, and if it exceeds 2.0%, it has no remarkable effect. Therefore, it is specified in the range of 0.3 to 2.0%.

Cr: 1.5% or less As for Cr, the Cr in the outer layer is redissolved and diffused into the shaft core material, and if the content exceeds 1.5%, the material strength deteriorates. The Cr content of Cr is 1.0% or less, and the total of Cr content which is redissolved and diffused from the outer layer is 1.5% or less as a result.

Mo: 1.0% or less Mo has the effect of increasing the matrix hardness, but if it exceeds 1.0%, it becomes brittle and uneconomical. Therefore, the content is made 1.0% or less.

When the composition of the mandrel after solidification satisfies the above range, the function of the ductile cast iron used as the mandrel can be obtained. In the present invention, however, V and Nb mixed in from the outer layer are included to form a composite. There is an advantage that mechanical properties are further improved as compared with general ductile cast iron as a roll shaft core.

By keeping the composition of the mandrel of the mandrel within the above-mentioned range, the formation of carbides is suppressed and, in addition, it has a grain refining effect and is a hardenability improving element. And Nb are contained in appropriate amounts, and a fine bainite matrix structure with extremely few carbides can be obtained by high temperature heat treatment. In the case of the roll of the present invention, this effect allows the roll to be used for higher-load rolling than before.

[0056]

EXAMPLES A centrifugally cast roll according to the present invention has the above-described structure, and a method for producing this roll will be described with reference to an example shown in FIG.

First, after the molten metal for forming the outer layer 1 is cast into a metal mold whose inner surface is coated with a refractory material by rotating on a centrifugal casting machine, the outer layer 1 is completely solidified and then the mold is cast. Is erected vertically, the shaft core material 2 is cast from the upper part, and the outer layer 1 and the shaft core material 2 are completely metallurgically bonded to form an integral roll. Even if the outer layer 1 is not completely solidified, the shaft core material 2 may be cast by an appropriate method in which some of the inner surface is not solidified and they are horizontal or inclined.

(Example 1) (See Tables 4 to 6) A roll having a product body diameter of φ820 mm, a body length of 2400 mm and a total length of 5300 mm was manufactured.

(1) As an outer layer, a molten metal having a wall thickness of 100 mm was cast at a casting temperature of 1380 ° C. in a mold rotating on a centrifugal casting machine.

(2) The outer layer is completely solidified 30 minutes after the casting of the outer layer.

(3) After that, the mold is erected straight, and ductile cast iron as a shaft core material is cast from the upper part at 1410 ° C. to completely fill the mold, raise the water, and cover it with a heat insulating material.

(4) After being completely cooled, the roll was taken out from the mold, heat-treated and machined to obtain a final product roll.

As a result of ultrasonic flaw detection and cutting examination of the roll body, the thickness of the outer layer was 86 mm due to the casting of the shaft core material, and the outer layer and the shaft core material were completely bonded to each other and systematic. Continuity was observed.

Table 4 shows the chemical compositions of the outer layer and the mandrel at the molten metal stage.

[0065]

[Table 4]

The chemical composition of the outer layer and the shaft core of the roll cast with the composition shown in Table 4 after solidification is as shown in Table 5.

[0067]

[Table 5]

The mechanical properties of the shaft core of the roll of the present invention are shown in Table 6 in comparison with those of the conventional roll of the same size.

[0069]

[Table 6]

In the rolls of the present invention having the compositions shown in Tables 4 and 5, by optimizing the alloy components forming the outer layer and limiting the carbide composition, wear resistance, crack resistance, and
Outer layer material that has a low friction coefficient and has excellent resistance to surface roughening that does not cause segregation even when centrifugally cast, and the core material is ductile cast iron, which is the toughest cast iron-based material, The core material can be completely metallurgically bonded to form an integral centrifugal casting roll.

(Example 2) (Tables 7 to 9) Rolls having a product body diameter of 680 mm, a body length of 1,500 mm and a total length of 3,600 mm were manufactured.

(1) As an outer layer, a molten metal having a thickness of 80 mm was cast at a casting temperature of 1380 ° C. in a mold rotating on a centrifugal casting machine.

(2) The outer layer is completely solidified 27 minutes after the casting of the outer layer is started.

(3) After that, the mold is erected straight, and ductile cast iron as a shaft core material is cast from the upper part at 1410 ° C. to completely fill the mold, raise the feeder, and cover it with a heat insulating material.

(4) After cooling completely, the roll was taken out of the mold, heat-treated and machined to obtain a final product roll.

As a result of ultrasonic flaw detection and cutting examination of the roll body, the thickness of the outer layer was 68 mm due to the casting of the shaft core material, and the outer layer and the shaft core material were completely bonded to each other, and the systematic Continuity was observed.

Table 7 shows the chemical compositions of the outer layer and the mandrel at the molten metal stage.

[0078]

[Table 7]

The chemical composition of the outer layer and the shaft core of the roll cast with the composition shown in Table 7 after solidification are as shown in Table 8.

[0080]

[Table 8]

The mechanical properties of the shaft core of the roll of the present invention are shown in Table 9 in comparison with those of the conventional roll of the same size.

[0082]

[Table 9]

In the rolls of the present invention having the compositions shown in Tables 7 and 8, by optimizing the alloy components forming the outer layer and limiting the carbide composition, wear resistance, crack resistance,
While using an outer layer material that has a low friction coefficient and has excellent resistance to surface roughening that does not cause segregation etc. even when centrifugally cast, the ductile cast iron, which is the toughest cast iron-based material, is used for the shaft core material. The mandrel can be completely metallurgically bonded to form a centrifugally cast roll.

(Example 3) (Tables 10 to 12) Rolls having a product cylinder diameter of φ820 mm, a cylinder length of 2400 mm and a total length of 5300 mm were manufactured.

(1) As an outer layer, a molten metal having a wall thickness of 100 mm was cast at a casting temperature of 1380 ° C. in a rotating mold during centrifugal casting.

(2) The outer layer is completely solidified 30 minutes after the casting of the outer layer is started.

(3) Then, the mold is erected straight, and ductile cast iron as a shaft core material is cast from the upper part at 1410 ° C. to completely fill the mold, raise the water and cover it with a heat insulating material.

(4) After completely cooling, the roll was taken out from the mold, heat-treated and machined to obtain a roll of a final product.

As a result of ultrasonic flaw detection and cutting investigation of the roll body, the thickness of the outer layer was 87 mm due to the casting of the shaft core material, and the outer layer and the shaft core material were completely bonded to each other, and the systematic Continuity was observed.

Table 10 shows the chemical compositions of the outer layer and the mandrel in the molten metal stage.

[0091]

[Table 10]

The chemical composition of the outer layer and the shaft core of the roll cast with the composition shown in Table 10 after solidification are as shown in Table 11.

[0093]

[Table 11]

Table 12 shows the mechanical properties of the shaft core of the roll of the present invention in comparison with those of the conventional roll of the same size.
It is like.

[0095]

[Table 12]

In the rolls of the present invention having the compositions shown in Tables 10 and 11, by optimizing the alloy components forming the outer layer and limiting the carbide composition, wear resistance, crack resistance, and a low friction coefficient can be obtained. In addition to using the outer layer material that does not cause segregation even when centrifugally cast and has excellent resistance to surface roughening, the shaft core material is made of the toughest ductile cast iron among cast iron-based materials. Can be completely metallurgically bonded together into a centrifugally cast roll.

(Example 4) (Tables 13 to 15) Rolls having a product barrel diameter of 680 mm, a barrel length of 1500 mm and a total length of 3600 mm were manufactured.

(1) As an outer layer, a molten metal having a thickness of 80 mm was cast at a casting temperature of 1380 ° C. in a mold rotating on a centrifugal casting machine.

(2) The outer layer and the intermediate layer are completely solidified 27 minutes after the casting of the outer layer is started.

(3) Then, the mold is erected straight, and ductile cast iron as a shaft material is cast from the upper part at 1410 ° C., the mold is completely filled, and the mold is filled with hot water and covered with a heat insulating material.

(4) After cooling completely, the roll was taken out from the mold, heat-treated and machined to obtain a final product roll.

As a result of ultrasonic flaw detection and cutting examination of the roll body, the thickness of the outer layer was 67 mm due to the casting of the shaft core material, and the outer layer and the shaft core material were completely bonded to each other and structurally continuous. The sex was recognized.

Table 13 shows the chemical compositions of the outer layer and the mandrel at the molten metal stage.

[0104]

[Table 13]

The chemical composition after solidification of the outer layer and the shaft core of the roll cast with the composition shown in Table 13 is as shown in Table 14.

[0106]

[Table 14]

Table 15 shows the mechanical properties of the shaft core of the roll of the present invention in comparison with those of the conventional roll of the same size.
It is like.

[0108]

[Table 15]

In the rolls of the present invention having the compositions shown in Tables 13 and 14, by optimizing the alloy components forming the outer layer and limiting the carbide composition, wear resistance, crack resistance, and a low friction coefficient can be obtained. In addition to using the outer layer material that does not cause segregation even when centrifugally cast and has excellent resistance to surface roughening, the shaft core material uses the toughest ductile cast iron among cast iron materials, and the outer layer material and the shaft core material Can be completely metallurgically combined to form an integrated centrifugal casting roll.

[0110]

As described above, according to the present invention, by optimizing the alloy components forming the outer layer and limiting the carbide composition, it is possible to combine wear resistance, crack resistance, and a low friction coefficient, and to perform centrifugal casting. Outer layer material that does not cause segregation even if it has excellent surface roughening resistance, and the toughest ductile cast iron among cast iron-based materials is used for the shaft core material, and the outer layer material and the shaft core material are completely metallurgical. It is possible to form a centrifugal casting roll by integrally combining them.

[Brief description of the drawings]

FIG. 1 is a diagram showing the effect of the Nb and V content ratio Nb / V on the hot wear ratio between the outer layer and the inner layer due to the carbide distribution of the centrifugally cast ring material.

FIG. 2 is a diagram showing the effect of the Nb / V content ratio Nb / V on the crack depth in a thermal shock test.

FIG. 3 is a schematic view showing a roll of the present invention.

[Explanation of symbols]

 1 Outer layer material 2 Shaft core material

Claims (5)

[Claims] 1. A centrifugally cast roll comprising an outer layer material and a shaft core material of ductile cast iron fused and integrated with the outer layer material, wherein the outer layer material is C: 2.5-4.7%, Si: 0.8- 3.2%, Mn: 0.1-
2.0%, Cr: 0.4 to 1.9%, Mo: 0.6 to 5.0%,
V: 3.0 to 10.0%, Nb: 0.6 to 7.0%, and satisfies the following formulas (1), (2), (3) and (4), 2.0 + 0.15V + 0.10Nb≤C (%) (1) 1.1 ≤ Mo / Cr (2) Nb / V ≤ 0.8 (3) 0.2 ≤ Nb / V (4) The balance consists of Fe and inevitable impurities, and has graphite. The shaft core material is C: 2.8 to 3.8%, Si: 2.0 to 3.0%, Mn: 0.3 to
1.0%, P: 0.10% or less, S: 0.04% or less, Ni: 0.3
A roll made by centrifugal casting, characterized in that it contains ˜2.0%, Cr: 1.5% or less, Mo: 1.0% or less, and the balance Fe and unavoidable impurities. 2. The centrifugally cast roll according to claim 1, wherein the outer layer material further contains Ni: 5.5% or less. 3. The centrifugal casting roll according to claim 1, wherein the outer layer material further contains B: 0.002 to 0.1%. 4. The centrifugally cast roll according to claim 1, wherein the outer layer material is further Ni: 5.5% or less, B: 0.002-0.
Centrifugal casting roll containing 1%. 5. When manufacturing the centrifugally cast roll according to any one of claims 1 to 4, the outer layer material mixing ratio to the shaft core material is regulated within a range of 5 to 25%. Manufacturing method of casting roll.