JPH06179947A - Composite roll made by centrifugal casting - Google Patents

Abstract

PURPOSE:To obtain a composite roll made by centrifugal casting in which wear resistance and crack resistance are combined by integrating an external layer material having a specified compsn. constituted of C, Si, Mn, Cr, Mo, W, V, Nb and Fe and a shaft material made of cast iron by fusing. CONSTITUTION:By a centrifugal casting method by which excellent productivity and cost effectiveness are obtainable an external layer material and a shaft material of common cast iron or ductile cast iron good in toughness are integrated by fusing to obtain a composite roll. At this time, the componental compsn. of the external layer material is constituted of a one contg. 1.5 to 3.5% C, <=1.5% Si, <=1.2% Mn, 5.5 to 12.0% Cr, 1.0 to 8.0% Mo, >1.0 to 4.0% W, 3.0 to 10.0% V and 0.6 to 7.0% Nb, furthermore contg., at need, one or more kinds among <=2.0% Cu, <=5.5% Ni, <=10.0% Co, <=2.0% Ti, <=2.0% Zr and <=0.1% B and satisfying V+1.8Nb<=7.5C-6.0%, Mo+3.0W<=14.0 and 0.2<=Nb/V<=0.8, and the balance Fe with inevitable impurities.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a centrifugally cast composite roll having both wear resistance and crack resistance.

[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 a high Cr cast iron or Ni grain cast iron in which cementite type carbide is crystallized as an outer layer material. The inner layer material is manufactured by a centrifugal casting method using gray cast iron or ductile cast iron having good toughness.

However, due to severer rolling conditions and demand for improved productivity in rolling, it is required to provide rolling rolls having further wear resistance and crack resistance.

Under such circumstances, for example, Japanese Patent Laid-Open No. 60-124
No. 407 and Japanese Patent Application Laid-Open No. 61-177355 propose to use high V cast iron as the outer layer material of a conventional centrifugal casting roll.

[0005]

However, in the rolling roll using high V cast iron as the outer layer material of the centrifugal casting roll, V carbide having a small specific gravity is segregated by centrifugal separation,
The characteristics in the outer layer of the roll become uneven in the thickness direction. This tendency is remarkable as the outer layer thickness of the large roll increases, and there is a problem that it cannot withstand use as a practical roll.

Incidentally, Japanese Unexamined Patent Publication (Kokai) No. 58-87249 and Japanese Unexamined Patent Publication (Kokai) No. 1-96355 propose roll materials to which cast steel, which is highly alloyed like high speed steel, and cast iron are applied. However,
Japanese Patent Laid-Open No. 58-87249 is intended for shrink-fitting or assembling rolls, and slippage between the outer layer and the shaft material that occurs during rolling poses a problem. Further, Japanese Patent Application Laid-Open No. 1-96355 can only be applied to a special manufacturing method other than the centrifugal force casting method, such as a special overlay welding method, which is problematic in terms of productivity and economy.

That is, when a rolling roll is manufactured, it is possible to remarkably improve the wear resistance by adding a large amount of V to the outer layer of the rolling roll, but the productivity and the economical efficiency are most excellent at the time of manufacturing the composite roll. However, when the centrifugal casting method which is generally carried out is adopted, there is a problem that the segregation of carbides occurs due to the centrifugal separation and the predetermined characteristics cannot be obtained uniformly.

According to the present invention, by optimizing the alloy components forming the outer layer and limiting the carbide composition, even if a centrifugal casting method having excellent productivity and economical efficiency is applied, segregation does not occur. An object of the present invention is to provide a centrifugally cast composite roll having uniform cracking resistance and crack resistance.

[0009]

The present invention according to claim 1 is a centrifugally cast composite roll comprising an outer layer material and a shaft material of ordinary cast iron or ductile cast iron fused and integrated with the outer layer material. , The outer layer material is C: 1.5 to 3.5%, Si: 1.5
% Or less, Mn: 1.2% or less, Cr: 5.5 to 12.0%, M
o: 1.0 to 8.0%, W: over 1.0 to 4.0%, V: 3.0 to 1
0.0%, Nb: 0.6 to 7.0%, and the following (1)
Expressions (2), (3) are satisfied, and V + 1.8Nb ≤ 7.5 C-6.0 (%) (1) Mo + 3.0W ≤ 14.0 (2) 0.2 ≤ Nb / V ≤ 0.8 (3) The balance is Fe and inevitable impurities.

The present invention according to claim 2 is a centrifugally cast composite roll comprising an outer layer material and a shaft material of ordinary cast iron or ductile cast iron fused and integrated with the outer layer material, the outer layer material comprising: C: 1.5 to 3.5%, Si: 1.5% or less, Mn: 1.
2% or less, Cr: 5.5 to 12.0%, Mo: 1.0 to 8.0%,
W: over 1.0 ~ 4.0%, V: 3.0 ~ 10.0%, Nb: 0.6 ~
7.0%, Cu: 2.0% or less, Ni: 5.5% or less,
Co: 10.0% or less, Ti: 2.0% or less, Zr: 2.0% or less, B: 0.1% or less, and at least one selected from the following formulas (1) and (2) , V + 1.8Nb ≤ 7.5 C-6.0 (%) (1) Mo + 3.0W ≤ 14.0 (2) 0.2 ≤ Nb / V ≤ 0.8 (3) Residual Fe and inevitable impurities It is made up of:

According to a third aspect of the present invention, in the present invention according to the first or second aspect, an intermediate layer is further provided between the outer layer material and the shaft material, and an outer layer material is provided through the intermediate layer. The shaft material and the shaft material are integrally welded.

[0012]

The reason for limiting the content of alloying elements in the outer layer material of the composite roll of the present invention and the limiting formula for the amounts of V, Nb, and C will be described.

C: 1.5 to 3.5% C is an essential element for forming a hard carbide which improves the wear resistance of the outer layer material of the roll, and is required to be 1.5% or more.
%, The crack resistance will drop significantly, so the upper limit is
3.5%

Si: 1.5% or less Si is added as a deoxidizing agent and an element necessary for ensuring castability, but if it exceeds 1.5%, the crack resistance decreases, so the upper limit is made 1.5%.

Mn: 1.2% or less Mn is necessary for the same purpose as the above Si, but 1.
If it exceeds 2%, the crack resistance is deteriorated, so that it is not preferable and the upper limit is made 1.2%.

Cr: 5.5 to 12.0% Cr forms carbides and is an element necessary for improving wear resistance, and is added in an amount of 5.5% or more. If it exceeds 12.0%, V and Nb targeted by the present invention are added. If added, wear resistance deteriorates, so the upper limit is made 12.0%.

Mo: 1.0 to 8.0%, W: more than 1.0 to 4.0% Mo forms a carbide similarly to Cr and is effective in improving wear resistance, as well as hardenability and temper softening resistance of the matrix. It is required to be 1.0% or more because it improves and is effective in strengthening the base structure, but if it exceeds 8.0%, the crack resistance decreases, so the upper limit is made 8.0%.

Like W, W forms carbides and is effective in improving wear resistance, and is also effective in improving the hardenability and temper softening resistance of the matrix and is effective in strengthening the matrix structure.
It is necessary to add more than 1.0%, but if it exceeds 4.0%, the crack resistance deteriorates, so the upper limit is made 4.0%.

Further, when adding Mo and W in combination, (M
When o + 3.0 W) exceeds 14.0%, the shape of the eutectic carbide becomes needle-like or rod-like and the crack resistance remarkably decreases, so Mo + 3.0 W ≦ 14.0%.

Ni: 5.5% or less, Co: 10.0% or less Ni is added to improve the hardenability and strengthen the matrix structure, but if it exceeds 5.5%, an unstable structure such as the presence of residual γ is formed. Therefore, it is not preferable and the upper limit is set to 5.5%.

Co is added to stabilize the structure at high temperatures, but if it exceeds 10.0%, its heat resistance improving effect is saturated, so the upper limit is made 10.0% from the economical point of view.

Cu: 2.0% or less Cu is added to strengthen the matrix structure and improve the high temperature hardness, but if Cu exceeds 2.0%, the surface properties of the roll are deteriorated and the wear resistance and crack resistance are improved. The upper limit is set to 2.0% because it will decrease.

Ti: 2.0% or less, Zr: 2.0% or less,
B: 0.1% or less Ti, Zr, and B are added to suppress the formation of coarse eutectic carbides and improve wear resistance and crack resistance. However, when Ti and Zr exceed 2.0%, V, Nb The upper limit is 2.0 because it deteriorates the shape of the composite carbide and conversely reduces wear resistance.
%, And if B exceeds 0.1%, it segregates at the grain boundaries to reduce crack resistance, so the upper limit is made 0.1%.

V: 3.0-10.0%, Nb: 0.6-7.0% V, Nb is the most important essential element in the present invention,
These combined additions and content limiting conditions are the greatest features of the present invention.

V is a hard MC that is most effective in improving wear resistance
Or, it is an essential element for forming M ₄ C ₃ carbide, and 3.0% or more is necessary to exert its effect.
%, The crack resistance decreases and manufacturing problems occur, so the upper limit is made 10.0%.

Nb, like V, is a hard MC effective for wear resistance.
Formed carbides are formed, but if added alone, they become coarse lumpy carbides and their effect cannot be obtained, and crack resistance becomes a problem.

Therefore, the relationship between the amount of C and the hardness of the base material when V and Nb are added in combination, the hot wear ratio between the outer layer and the inner layer due to the carbide distribution of the centrifugally cast ring material, and the heat Maximum crack depth and Nb, V in impact test
The results of examining the relationship with the content ratio Nb / V of are shown in FIGS. 1 and 2, respectively.

From FIG. 1, it is clear that V + 1.8 Nb≤7.5 C-6.0 (%) must be satisfied in order to obtain the hardness Hs 75 or more required for the wear-resistant hot rolling roll. .

In the experiment of FIG. 1, Si: 0.3%, Mn:
25mmY which was cast a molten metal containing 0.4%, Cr: 6.2%, Mo: 3.2%, W: 1.5% and varying C, V, Nb.
-For the blocks, samples that had been subjected to 1050 ° C quenching treatment and 550 ° C tempering treatment were used.

Further, it is necessary to satisfy 0.2 ≤ Nb / V ≤ 0.8 in order to obtain a uniform outer layer material even when manufactured by the centrifugal casting method from Fig. 2 and not to impair crack resistance. It became clear that there is.

In FIG. 2, "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).
w) and the ratio (Iw / Ow), and the “maximum depth of thermal shock cracks” is the maximum depth of cracks generated in the thermal shock test.

In the experiment of FIG. 2, C: 2.3%, Si:
0.3%, Mn: 0.5%, Cr: 6.5%, Mo: 2.6%,
A ring sample with a wall thickness of 100 mm obtained by centrifugal force casting (140 G) containing a melt containing W: 1.3%, V: 5.2% and Nb: 0 to 7.0% was quenched at 1050 ° C and tempered at 550 ° C. The applied sample was used.

The wear test was conducted by heating the mating material to 800 ° C. by the sliding wear method of a two-disc of a mating material of φ190 × 15 and a test material of φ50 × 10, and pressing the test material under a load of 100 kgf to 800 rpm. Rotation was carried out at a slip rate of 3.9% to measure the wear loss after 120 minutes.

The thermal shock test was conducted by pressing a 55 × 40 × 15 plate-shaped test piece against a roller rotating at 1200 rpm under the conditions of a load of 150 kgf and a contact time of 15 s, and the test piece was generated. The crack length was measured.

[0035]

【Example】

(Example 1) Molten metal having the chemical composition shown in Table 1 (material of the present invention: B
.About.E, comparative materials: A, F to Q) were cast by centrifugal force casting, a ring sample having a wall thickness of 100 mm was prototyped, and Shore hardness, hot wear and thermal shock tests were conducted.

[0036]

[Table 1]

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 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.

The results of the wear test and the thermal shock test are shown in Table 2.
Shown in. According to Table 2, the material of the present invention has the same hardness as the conventional Ni-Glen material (A material), but the wear resistance,
It is recognized that the crack resistance is significantly improved.

[0040]

[Table 2]

Further, since the comparative materials F to P are out of the limitation of the present invention, the hardness of the F material is low due to the low C content, and the segregation of carbide reduces the wear resistance of the outer layer. ,
With respect to the G material, segregation of carbide reduces the wear resistance of the outer layer, the H material has a reduced crack resistance, and the I material has insufficient hardness. In addition, the J material has an excessive amount of C and thus has low crack resistance, the K material has an excessive amount of Si, which has poor crack resistance, and the L material has an excessive amount of Mn and therefore has an excellent crack resistance. Wear resistance and crack resistance of the M material decrease due to excessive Cr content, and crack resistance decreases of the N material due to excessive Mo content, and V content of the O material is insufficient. Wear resistance and crack resistance are reduced due to
Since the V content of the material is excessive, the crack resistance is lowered, and the Q material of the material is excessive, and the crack resistance is degraded.

A composite roll having an outer layer and an inner layer having the compositions shown in Table 3 and having a cylinder diameter of 670 mm and a cylinder length of 1450 mm was manufactured by the following procedure. The molten metal for the outer layer material was melted in a low frequency melting furnace, and the molten metal for the outer layer material was cast into a centrifugal casting mold rotating at a centrifugal force of 140 G to a thickness of 75 mm at 1490 ° C. Twenty minutes after the casting of the outer layer material, the rotation of the mold was stopped to erect the mold, and 35 minutes after the casting of the outer layer, the molten metal for the inner layer material was cast. After cooling to room temperature, dismantling the mold and performing rough processing, 1050
A heat treatment was carried out by quenching from ℃, and then tempering at 550 ℃. After heat treatment, inspections such as ultrasonic flaw detection were performed, but it was a sound roll with no defects, the outer layer thickness after finishing was 45 mm, and the surface hardness was 78-82 Shore hardness.
Met.

[0043]

[Table 3]

As a result of using the above composite roll for an actual hot strip mill finishing stand, as shown in FIG. 4, the use result of the conventional nickel-glen cast iron roll was greatly exceeded. In addition, the surface of the roll was not roughened, and good results were obtained.

In the practice of the present invention, when forming a composite roll using the material of the present invention shown in Table 1 as an outer layer material,
An intermediate layer as in Example 2 described later may be provided between the outer layer and the inner layer.

(Example 2) A molten metal having the chemical composition shown in Table 4 (materials of the present invention: B to H, comparative materials A and IL) was cast by centrifugal force casting to produce a ring sample having a wall thickness of 100 mm as a prototype. ,
Shore hardness, hot wear and thermal shock tests were performed.

[0047]

[Table 4]

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

The results of the wear test and the thermal shock test are shown in Table 5. According to Table 5, the material of the present invention has a hardness comparable to that of the conventional Ni-Glen material (material A), but it is recognized that both wear resistance and crack resistance are remarkably improved.

[0051]

[Table 5]

Further, since the comparative materials I to L are out of the limitation of the present invention, the material I has an excessive Cu content, so that the wear resistance and crack resistance are deteriorated, and the material J has an excessive W content. Therefore, segregation of carbide reduces wear resistance on the outer layer side, and K material has T
Since the amounts of i and B are excessive, the wear resistance and crack resistance are deteriorated, and the wear resistance of the L material is deteriorated because the amount of Zr is excessive.

A composite roll having an outer layer, an intermediate layer, and an inner layer having the compositions shown in Table 6 and having a cylinder diameter of 670 mm and a cylinder length of 1450 mm shown in FIG. 3 was manufactured by the following procedure. The molten metal for the outer layer material was melted in a low frequency melting furnace, and the molten metal for the outer layer material was cast into a centrifugal casting mold rotating at a centrifugal force of 140 G to a thickness of 75 mm at 1490 ° C. Immediately after solidification of the outer layer material,
It was cast at 40 ° C to a thickness of 40 mm. After this intermediate layer is completely solidified, the rotation of the mold is stopped, the mold is erected,
40 minutes after the casting of the outer layer material, the molten metal of the inner layer material was cast at 1450 ° C. After cooling to room temperature, the mold was disassembled, rough processing was performed, quenching was performed from 1050 ° C., and then tempering was performed at 550 ° C. for tempering. After heat treatment, inspections such as ultrasonic flaw detection were performed, but no defects occurred at the boundary between the outer layer and the intermediate layer and at the boundary between the intermediate layer and the inner layer, and the internal properties were sound, and the outer layer thickness after finishing was It was 45 mm, and the surface hardness was 78 to 82 in Shore hardness.

[0054]

[Table 6]

As a result of using the above-mentioned composite roll in an actual hot strip mill finishing stand, the use result of the conventional nickel-grain cast iron roll was greatly exceeded. In addition, the surface of the roll was not roughened, and good results were obtained.

In the practice of the present invention, when forming a composite roll using the material of the present invention shown in Table 4 as the outer layer material,
The intermediate layer may not be provided between the outer layer and the inner layer.

[0057]

As described above, according to the present invention, productivity,
Even if the centrifugal casting method with excellent economical efficiency is applied, it is possible to obtain a centrifugally cast composite roll excellent in wear resistance and crack resistance without segregation and the like.

[Brief description of drawings]

FIG. 1 is a diagram showing the influence of the combined addition amount of V and Nb and the C amount on the hardness of a base material.

FIG. 2 is a hot wear ratio between an outer layer and an inner layer due to a carbide distribution of a centrifugally cast ring material, and a Nb and V content ratio Nb which affects the maximum crack depth in a thermal shock test.
It is a diagram which shows the influence of / V.

FIG. 3 is a vertical sectional view of a composite roll according to a second embodiment.

FIG. 4 is a diagram showing rolling results of the composite rolls manufactured in Examples 1 and 2 in an actual mill in comparison with those of conventional rolls.

Claims (3)

[Claims] 1. A centrifugally cast composite roll comprising an outer layer material and a shaft material of ordinary cast iron or ductile cast iron fused and integrated with the outer layer material, wherein the outer layer material is C: 1.5 to 3.5%, Si : 1.5% or less, Mn: 1.2% or less, Cr: 5.5 to 12.0%, Mo: 1.0 to 8.0%, W: 1.
Over 0 ~ 4.0%, V: 3.0 ~ 10.0%, Nb: 0.6 ~ 7.0%
And satisfy the following formulas (1), (2), and (3), and V + 1.8Nb ≤7.5 C-6.0 (%) (1) Mo + 3.0W ≤14.0 (2) 0.2 ≤ Nb / V ≦ 0.8 (3) A centrifugally cast composite roll characterized by comprising the balance Fe and inevitable impurities. 2. A centrifugally cast composite roll comprising an outer layer material and a shaft material of ordinary cast iron or ductile cast iron fused and integrated with the outer layer material, wherein the outer layer material is C: 1.5 to 3.5%, Si : 1.5% or less, Mn: 1.2% or less, Cr: 5.5 to 12.0%, Mo: 1.0 to 8.0%, W: 1.
0 over ~ 4.0%, V: 3.0 ~ 10.0%, Nb: 0.6 ~ 7.0
%, Cu: 2.0% or less, Ni: 5.5% or less, C
o: 10.0% or less, Ti: 2.0% or less, Zr: 2.0% or less, B: 0.1% or less, and one or more selected from, and the following formulas (1) and (2): , V + 1.8Nb ≤ 7.5 C-6.0 (%) (1) Mo + 3.0W ≤ 14.0 (2) 0.2 ≤ Nb / V ≤ 0.8 (3) Residual Fe and inevitable impurities A composite roll made by centrifugal casting characterized by comprising 3. An intermediate layer is provided between the outer layer material and the shaft material,
The centrifugally cast composite roll according to claim 1 or 2, wherein the outer layer material and the shaft material are welded and integrated via the intermediate layer.