JP3412590B2 - Roll for rolling - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rolling roll. Specifically, the present invention relates to a rolling roll that has both excellent wear resistance and accident resistance and does not cause gravity segregation of carbide even when manufactured by a centrifugal casting method.

[0002]

2. Description of the Related Art In recent years, with the progress of hot rolling technology, wear resistance of hot rolling rolls is increased by adding a large amount of V and W to crystallize hard V carbides and W carbides. High-carbon, high-vanadium rolls with significantly improved properties have been developed and are already in practical use. However, this high carbon high vanadium roll is comprehensively evaluated by, for example, resistance to flaw generation and flaw depth control when a rolling accident such as strip breaking, narrowing and bite prevention in a hot rolling mill occurs. Accident resistance is not good, and when a rolling accident occurs, damage such as flaws and dents is severely received. For this reason, the application of high-carbon, high-vanadium rolls to hot-rolling finishing second-stage stands, which tend to have high rolling accident rates, has been particularly delayed.

On the other hand, conventionally, a high alloy grain roll in which fine graphite is deposited on the surface by adjusting the alloy composition has been applied to the latter stage of hot rolling finishing.
The high alloy grain roll is generally manufactured as a composite roll by a centrifugal casting method. Although this high alloy grain roll has excellent accident resistance as compared with the above-mentioned high carbon and high vanadium type roll, it has low abrasion resistance. Therefore, it is desired to improve wear resistance of the high alloy grain roll without deteriorating accident resistance.

As a proposal for improving the wear resistance of high alloy grain rolls, for example, Japanese Patent Laid-Open No. 52-147514 discloses
C: 3.0 to 4.0% (in this specification, "%" means "mass%" unless otherwise specified), Si: 0.5 to 1.0%, Mn: 0.5 to 1.0%, Ni : 3.
A hot rolling roll made of a so-called high alloy grain cast iron material is proposed, which contains 0 to 5.0%, Cr: 1.0 to 3.0%, Mo: 0.2 to 0.8%, and further contains Nb in an amount of 0.2 to 2.5%. There is. The roll for hot rolling according to this proposal, by adding Nb, precipitates a high-hardness Nb double carbide and reduces the amount of cementite, and by refining the structure, the wear resistance is improved. There is. Also,
When the high alloy grain cast iron material according to this proposal is used as the outer layer material of the composite roll by centrifugal casting, the Nb content is
It is said that 1.0 to 2.0% is preferable.

[0005]

However, the present inventor
As a result of extensive studies to improve the wear resistance of high alloy grain rolls, when the high alloy grain cast iron material according to this proposal is used as the outer layer material of the composite roll by centrifugal casting, centrifugal force acting during centrifugal casting is exerted. It was found that Nb double carbide gravity segregation occurs in the obtained composite roll.

Therefore, when this composite roll is applied to, for example, a hot rolling finishing stand, rough skin occurs in the segregated portion of the Nb compound carbide at an early stage, and in order to eliminate this rough skin, wear of the roll base is eliminated. Although the amount is small, it is necessary to remove the composite roll from the post-stand of hot rolling finish and perform roll grinding.

As described above, the hot rolling roll made of so-called high alloy grain cast iron material proposed in Japanese Patent Laid-Open No. 52-147514 has a problem of gravity segregation of carbides produced by the centrifugal casting method. Due to the rough skin caused by this, there is a problem that the characteristic abrasion resistance cannot be sufficiently exhibited.

An object of the present invention is to provide a rolling roll which has both excellent wear resistance and accident resistance and which does not cause gravity segregation of carbide even when manufactured by a centrifugal casting method.

[0009]

When a high alloy grain roll is applied to a post-stand of hot rolling finish, a base having a low hardness in the microstructure is preferentially worn in the final stand. Therefore, by precipitating a hard carbide other than cementite in a matrix made of a high alloy grain cast iron material, it is possible to improve the wear resistance of the matrix itself and to improve the wear resistance of the entire high alloy grain cast iron material. Both are possible. However, as described above, since gravity segregation of carbide occurs when manufactured by the centrifugal casting method, it is important not to cause gravity segregation of precipitated carbide.

On the other hand, one of the reasons why the high alloy grain rolls have better accident resistance than the high carbon and high vandium rolls is that they have graphite having an area ratio of 1 to 3%. Therefore, in order to improve wear resistance while sufficiently maintaining accident resistance of the high alloy grain roll, the area ratio is 1
It is also important to crystallize graphite so that it is ˜3%.

However, in general, alloying elements such as V and Ti which form hard carbides, which are indispensable for improving the wear resistance of high alloy grain rolls, depend on the addition amount thereof, but are not limited to white pig iron. Shows a tendency to change and reduces the area ratio of graphite.

Therefore, the present inventor has conducted further studies in order to achieve both of the trade-off objectives of precipitation of hard carbide and crystallization of graphite having a predetermined area ratio. As a result, conventional high alloy grain cast iron materials have been obtained. By adding at least one of Nb and W and limiting the content of each of Nb and W to a specific relationship, it has both excellent wear resistance and accident resistance, and is manufactured by a centrifugal casting method. It was found that it is possible to provide a rolling roll that does not cause gravity segregation of carbides, and further studies have been completed to complete the present invention.

According to the present invention, at least the work surface is
C: 2.5-3.8%, Si: 0.5-1.5%, Mn: 0.4-1.2
%, Ni: 2.0 to 5.0%, Cr: 1.0 to 3.0%, Mo: 0.1 to
1.2%, Nb: 0.1-2.0% and W: 0.1-3.0
% Nb (%) with containing -0.5 W (%) ≦ 0.95
And a balance of Fe and unavoidable impurities.

In the rolling roll according to the present invention, the work surface has (i) V: 1.0% as an optional additive element.
The following are included and one or two selected from the group consisting of Ti: 0.5% or less and (ii) Co: 3.0% or less are both included.

In the present invention, the "working surface" means the roll surface that comes into contact with the material to be rolled and rolls down the material in the radial direction of the rolling roll. Therefore, the rolling roll according to the present invention includes a composite roll in which the exterior material including the work surface has the above composition, and an integrated roll having the above composition.

[0016]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a rolling roll according to the present invention will be described in detail below. In the following description, the case where the rolling roll is a hot rolling composite roll is taken as an example. First, the reason for limiting the composition of the outer layer material constituting the working surface of the hot rolling composite roll according to the present invention will be described.

(C: 2.5 to 3.8%) C is an element that forms both carbides and graphite, and mainly balances the graphitizing element such as Si and the white pig-making element such as Cr and the cooling rate. The amounts of graphite and cementite are determined by the difference and the like. If the C content is less than 2.5%, the amounts of graphite and cementite will be insufficient, while if the C content exceeds 3.8%, the amounts of graphite and cementite will be too large and brittle. Therefore, in the present invention, the C content is 2.5
% To 3.8%. From the same viewpoint, it is desirable that the lower limit of the C content is 2.8% and the upper limit thereof is 3.5%.

(Si: 0.5 to 1.5%) Si is an element necessary for maintaining the balance of the amounts of graphite and cementite. That is, if the Si content is less than 0.5%, the crystallization amount of graphite will be insufficient, while if the Si content exceeds 1.5%, the crystallization amount of cementite will be insufficient. Therefore, in the present invention, the Si content is limited to 0.5% or more and 1.5% or less. From the same viewpoint, the lower limit of Si content is 0.6% and the upper limit is 1.2%.
It is desirable that

(Mn: 0.4 to 1.2%) Mn is added to harden the matrix and improve wear resistance. However, if the Mn content is less than 0.4%, such an effect is small, while if the Mn content exceeds 1.2%, the toughness decreases. Therefore, in the present invention, the Mn content is limited to 0.4% or more and 1.2% or less.
From the same viewpoint, the lower limit of Mn content is 0.6% and the upper limit is 1.0.
% Is preferable for each.

(Ni: 2.0 to 5.0%) Ni is an element that forms a solid solution in the matrix, and is added to martensite the matrix and harden it. However, when the Ni content is less than 2.0%, such an effect is small. On the other hand, when the Ni content exceeds 5.0%, the amount of retained austenite increases, and the steel is easily cracked during casting. Therefore, in the present invention, the Ni content is 2.0% or more and 5.0% or more.
Limited to: From the same viewpoint, the lower limit of Ni content is 3.
It is desirable that the upper limit is 0% and the upper limit is 4.6%.

(Cr: 1.0 to 3.0%) Cr is an element necessary for stabilizing cementite and maintaining the balance between the amounts of graphite and cementite. However, when the Cr content is less than 1.0%, such an effect is small. On the other hand, when the Cr content exceeds 3.0%, the amount of cementite becomes excessive and the material becomes brittle. Therefore, in the present invention, the Cr content is limited to 1.0% or more and 3.0% or less. From the same viewpoint, it is desirable that the lower limit of Cr content is 1.2% and the upper limit thereof is 2.2%.

(Mo: 0.1 to 1.2%) Mo is added to martensite the matrix and harden it. But Mo
If the content is less than 0.1%, the effect is small.
If the content exceeds 1.2%, the amount of retained austenite increases and cracks easily occur during casting. Therefore, in the present invention,
Mo content is limited to 0.1% to 1.2%. From the same viewpoint, it is preferable that the lower limit of the Mo content is 0.2% and the upper limit thereof is 1.0%.

The outer layer member constituting the working surface of the hot composite roll for rolling of the present invention, in addition to these, by <br/> containing Nb and W, crystallized a double carbide hard in the matrix Let The contents of Nb and W will be described below.

(Nb: 0.1 to 2.0%) Nb is an element that forms hard carbide. However, if the Nb content is less than 0.1%, such an effect is small. On the other hand, if the Nb content exceeds 2.0%, coarse double carbides are crystallized and the crystallization amount of graphite is reduced. Therefore, in the present invention, the Nb content is limited to 0.1% or more and 2.0% or less. From the same viewpoint, the lower limit of the Nb content is desirably 0.3%. The upper limit of the Nb content is preferably 1.4%, more preferably 1.0%.

(W: 0.1-3.0%) W is an element that forms hard carbide. However, when the W content is less than 0.1%, such an effect is small, while when the W content exceeds 3.0%, the effect is saturated and the cost is increased. Therefore, in the present invention, the W content is limited to 0.1% or more and 3.0% or less. From the same viewpoint, the lower limit of the W content is preferably 0.5%, and more preferably 1.0%. Further, the upper limit of the W content is preferably 2.0%, more preferably 1.5%.

(Nb (%) − 0.5 W (%) ≦ 0.95) In the composite roll for hot rolling according to the present invention, Nb and W are
Formula; Nb (%)-0.5 W (%) is 0.95
It is the following. If this value exceeds 0.95, the difference in the crystallization temperature of the primary austenite and the hard carbide is large in the solidification process, and the large difference in specific gravity with the molten steel causes the hard carbide to crystallize, and the gravity of the hard carbide during centrifugal casting When segregation occurs, when it is applied to a post-stand for hot rolling finishing and rolling is performed, rough skin is generated from this gravity segregation portion. Therefore, in the present invention, the value of Nb (%)-0.5 W (%) is limited to 0.95% or less. From the same viewpoint, the value of Nb (%)-0.5 W (%) is preferably 0.90% or less, and more preferably 0.83% or less.

In addition to these, the outer layer material constituting the working surface of the composite roll for hot rolling according to the present invention is V, Ti and
Co may be contained as an optional additional element. Hereinafter, these optional additional elements will be described.

(V: 1.0% or less, Ti: 0.5% or less) V and Ti are elements that form hard carbides, like Nb and W. However, V is a strong whitening element, and when it is added in an amount exceeding 1.0%, the amount of graphite is extremely reduced. Therefore, when V is added, its content is 1.0
It is desirable to limit it to less than or equal to%.

If the Ti content exceeds 0.5%, the graphite shape is deteriorated. Therefore, when Ti is added, its content is preferably limited to 0.5% or less.

(Co: 3.0% or less) Co is an element that forms a solid solution in the matrix and may be added to harden the matrix. However, when the Co content exceeds 3.0%, the effect is saturated and the cost is increased. Therefore, when Co is added, its content is preferably limited to 3.0% or less. Compositions other than the above are Fe and inevitable impurities.

On the other hand, as the inner layer material of the composite roll for hot rolling according to the present invention, a known inner layer material compatible with the outer layer material having the above composition may be used. The composition of such an inner layer material is as follows: C: 2.7-3.5%, Si: 1.5-3.0%,
Mn: 0.3-0.7%, Ni: 0.1-2.0%, Mg: 0.02-0.12
%, The balance Fe and unavoidable impurities are exemplified.

The composite roll for hot rolling according to the present invention having the inner layer material and the outer layer material having such a composition has (a) improved wear resistance, (b) prevention of gravity segregation of hard carbide, and (c) accident resistance. Any maintenance of sex can be achieved. That is, (a) improvement of wear resistance In the outer layer material constituting the working surface of the composite roll for hot rolling according to the present invention, Nb: 0.1 to 2.0% and W: 0.1 to 3.0%.
By adding one or two selected from the group consisting of%, hard carbide is made to exist in the matrix in a form independent of cementite which is a carbide generally possessed by high alloy grain cast iron materials. Thereby, preferential wear of the base can be prevented and wear resistance can be improved.

(B) Prevention of Gravity Segregation of Hard Carbide The outer layer material constituting the working surface of the composite roll for hot rolling according to the present invention is limited to Nb (%)-0.5 W (%) ≤0.95. In the solidification process, the difference in crystallization temperature between primary austenite and hard carbide is small, and the hard carbide having a small difference in specific gravity with molten steel can be crystallized, which allows gravity segregation of hard carbide during centrifugal casting. Can be prevented.

(C) Maintenance of accident resistance In the outer layer material constituting the working surface of the composite roll for hot rolling according to the present invention, the area ratio is 1 to 3% among the elements forming hard carbide. Thus, in order to crystallize graphite, the additive element and its amount are determined. Specifically, Nb: 0.1
.About.2.0% and W: 0.1 to 3.0%, while adding 1 or 2 kinds selected from the group consisting of 0.1 to 3.0%, V is suppressed to 1.0% or less, and Ti is added to 0.5.
% Or less, the graphite is crystallized so that the area ratio is 1 to 3%.

Therefore, the composite roll for hot rolling according to the present invention has excellent wear resistance and accident resistance, and can be applied to, for example, a hot rolling finishing stand.
Rough skin caused by gravity segregation of carbides produced by the centrifugal casting method does not occur in the outer layer material constituting the work surface. Therefore, it is possible to significantly extend the period from application to the hot rolling finishing latter stage stand until roll grinding, that is, the roll life, and to improve the wear resistance that the high alloy grain rolls have as an essential feature. It can be fully demonstrated.

[0036]

EXAMPLES The present invention will be described more specifically with reference to examples.

Example 1 having the chemical composition shown in Table 1.
Using 15 kinds of molten metal, this was cast into a mold (rotating on a centrifugal casting machine) (inner diameter 400 mm, length 2000 mm) at a casting temperature of 1340 ° C with a wall thickness of 100 mm (casting amount: 1320 kg). Then, it was used as the outer layer material of the high alloy grain roll.

[0038]

[Table 1]

After cooling these outer layer materials and subjecting them to a predetermined heat treatment, Sample No. 1 to Sample No. 15 were cut out from the central portion and analyzed for radial component distribution, wear resistance, microstructure (carbide segregation). Existence) and accident resistance were investigated. The results are also shown in Table 1.

The wear resistance is determined by the sliding wear method of the two discs of the mating material (carbon steel) and the test piece. The mating material is heated to 800 ° C and the test piece is rotated at a peripheral speed of 60 m / min while being water cooled. Let
The slip ratio between the test piece and the mating material is 5%, and the load is 300.
The test was performed up to 20000 rotations in kg, and then the wear test for measuring the wear amount of the test piece was performed to evaluate. A wear amount of 43 (mg / mm) or less was regarded as acceptable.

Further, the accident resistance is a method in which a rectangular parallelepiped test piece is pressed against a high-speed rotating disk of a counterpart material (carbon steel) for 15 seconds and then immediately water-cooled, and after a test with a load of 200 kg,
It was evaluated by conducting a thermal shock test for measuring the depth of cracks generated in the test piece. Crack depth 1.5 (m
m) The following were accepted.

Sample No. 1 to Sample No. 8 in Table 1 are examples of the present invention satisfying all the conditions of the present invention.
o.9 to Sample No. 15 are comparative examples that do not satisfy the conditions of the present invention.

FIG. 1 is a graph showing the Nb content and the W content of sample No. 1 to sample No. 15 in Table 1. The numbers in the figure indicate sample numbers.

Sample No. 1 to Sample No. 8 have improved wear resistance,
Prevent gravity segregation of hard carbide and maintain accident resistance,
Both were able to be achieved.

On the other hand, in all of Sample No. 9 to Sample No. 15, Nb-0.5 W exceeded 0.95, so that gravity segregation of hard carbide occurred.

Particularly, sample No. 11 to sample No. 13 and sample
In No.15, the Nb content exceeds 2.0%, so
In the abrasion test, the coarse hard carbide was chipped off, resulting in deterioration of abrasion resistance as compared with the inventive examples. Further, similarly, Sample No. 11 to Sample No. 13 and Sample No. 15 all have a Nb content of more than 2.0%, so that the graphite content is reduced, so that the sample is more resistant to thermal shock tests than the present invention. Accidentality has deteriorated.

(Example 2) A molten metal for an outer layer material having a chemical composition shown in Table 2 was cast into a mold of a centrifugal casting machine rotating at a centrifugal force of 135 G at a casting temperature of 1320 ° C to obtain a wall thickness of 100 mm (casting). Included amount
4200kg) After casting and completely solidifying, the rotation of the mold was stopped, and 1360 of molten metal for the inner layer material having the chemical composition shown in Table 2 was cast.
By casting at a casting temperature of ℃, the outer layer material and inner layer material are completely welded and integrated, resulting in a product body diameter of 758 mm, body length of 25
A composite roll for hot rolling having a length of 00 mm and a total length of 5550 mm was manufactured. Then, after the composite roll for hot rolling was completely cooled, the mold mold was disassembled. After that, a predetermined heat treatment was performed to obtain the roll of the present invention, the comparative roll (1) and the comparative roll (2).

[0048]

[Table 2]

The rolls of the present invention, the comparative roll (1) and the comparative roll (2) were cut at the center of the roll body to analyze the component distribution in the radial direction, investigate the microstructure and test the material (wear resistance). And accident resistance).

FIG. 2 is a graph showing Nb and W contents depending on the distance from the roll surface of the roll of the present invention. As shown in the graph of FIG. 2, in the roll of the present invention, both the Nb amount and the W amount are made uniform in the radial direction.

On the other hand, FIG. 3 is a graph showing the Nb amount depending on the distance from the roll surface of the comparative roll (1). As shown in the graph of FIG. 3, in the comparative roll (1), the amount of Nb is unevenly distributed on the roll surface side in the radial direction, and it is found that the amount is not uniform.

FIG. 4 shows the roll of the present invention and the comparative roll.
For each of (1), the metallographic structure of the roll surface,
It is a photograph showing a metal structure within 50 mm from the surface. Figure 4
Therefore, the roll of the present invention, the roll surface portion and from the surface
It can be seen that gravity segregation of Nb and W double carbides does not occur in any of the 50 mm interiors. In contrast,
It is clear that gravity segregation of Nb double carbide occurs in the comparative roll (1).

Table 3 shows the rolls of the present invention and comparative rolls.
(2) The results of each material test (wear resistance and accident resistance) are shown. The test criteria are the same as in Example 1 described above. It can be seen from Table 3 that the roll of the present invention has about 30% better wear resistance and about the same accident resistance as the comparison roll (2).

[0054]

[Table 3]

It can be seen from this example that improvement of wear resistance, prevention of gravity segregation of hard carbide and maintenance of accident resistance could be achieved at the same time.

(Modified Embodiment) In the description of the embodiments and examples, the case where the rolling roll is for hot rolling is taken as an example. However, the rolling roll according to the present invention is not limited to hot rolling, but is also applied to cold rolling.

In the description of the embodiments and examples,
The case where the rolling roll is a composite roll is taken as an example. However, the present invention is not limited to the composite roll, and is similarly applied to the integrated roll. In this case, the single roll material for the outer layer material used in the description of the embodiments and the examples may constitute the rolling integral roll.

[0058]

As described in detail above, according to the present invention, a rolling roll having both excellent wear resistance and accident resistance and which does not cause gravity segregation of carbide even when manufactured by a centrifugal casting method. Could be provided. Therefore, by applying this rolling roll to a hot rolling finishing latter stage stand, which tends to have a high rolling accident occurrence rate, the life of the rolling roll can be extended and the manufacturing cost of the steel material can be greatly reduced. The significance of the present invention having such an effect is extremely remarkable.

[Brief description of drawings]

FIG. 1 is a graph showing the Nb content and the W content of Sample No. 1 to Sample No. 15 in Example 1.

FIG. 2 is a graph showing Nb and W amounts according to the distance from the roll surface of the roll of the present invention in Example 2.

FIG. 3 is a graph showing the Nb amount depending on the distance from the roll surface of the comparative roll (1) in Example 2.

FIG. 4 is a photograph showing the metallographic structure of the roll surface and the metallographic structure within 50 mm from the surface of each of the inventive roll and the comparative roll (1) in Example 2.

─────────────────────────────────────────────────── ─── Continuation of front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) C22C 38/00-38/60 C22C 37/08 B21B 27/00

Claims (3)

(57) [Claims] 1. At least the work surface, in mass%, C: 2.5-3.8%, Si: 0.5-1.5%, Mn: 0.4-1.2%, Ni: 2.0-5.0%, Cr: 1.0-3.0%, Mo. : 0.1 to 1.2%, Nb: 0.1 to 2.0% and W: 0.1 to 3.0%, and the following formula (1) is satisfied, with the balance being Fe and inevitable impurities. Roll for rolling. Nb (%) −0.5 W (%) ≦ 0.95 ・ ・ ・ ・ ・ (1) 2. The work surface further comprises V: 1.0% by mass.
The rolling roll according to claim 1, further comprising one or two selected from the group consisting of the following and Ti: 0.5 mass% or less. 3. The work surface further comprises Co: 3.0 mass%.
The rolling roll according to claim 1 or 2, further comprising: