JP2715217B2 - Centrifugal casting composite roll - Google Patents

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 abrasion resistance and crack resistance.

[0002]

2. Description of the Related Art Conventionally, a roll for hot rolling which requires abrasion resistance is a composite roll composed of an outer layer and an inner layer. The inner layer material is manufactured by a centrifugal casting method using gray cast iron or ductile cast iron having good 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.

[0004] Under such circumstances, for example, Japanese Patent Laid-Open No. 60-124
No. 407 and JP-A-61-177355 propose the use of high-V cast iron as the outer layer material of a conventional centrifugal casting roll.

[0005]

However, in a rolling roll using high-V cast iron as an outer layer material of a centrifugal casting roll, V carbide having a small specific gravity segregates due to centrifugal separation.
Characteristics in the outer layer of the roll become uneven in the thickness direction. This tendency is remarkable as the thickness of the outer layer of a large roll increases, and there is a problem that the roll cannot be used as a practical roll.

Incidentally, Japanese Patent Application Laid-Open Nos. 58-87249 and 1-96355 propose a rolled material using cast steel or cast iron which is made of a high alloy like high speed steel. However,
JP-A-58-87249 is directed to shrink-fitting or assembling rolls, and there is a problem of slippage between the outer layer and the shaft material during rolling. Japanese Patent Application Laid-Open No. 1-96355 can apply only a special manufacturing method other than the centrifugal force casting method such as a special casting overlaying method, and has problems in productivity and economy.

[0007] That is, in the production of a rolling roll, it is possible to significantly improve the wear resistance by incorporating a large amount of V in the outer layer of the roll, but the most excellent productivity and economical efficiency in the production of a composite roll. If the centrifugal casting method generally used is adopted, there is a problem that segregation of carbides occurs due to centrifugal separation and predetermined characteristics cannot be obtained uniformly.

According to the present invention, the wear resistance which does not cause segregation even when a centrifugal casting method excellent in productivity and economy is applied by optimizing the alloy component forming the outer layer and limiting the carbide composition. It is an object of the present invention to provide a composite roll made of centrifugal casting having uniformity and crack resistance.

[0009]

The present invention according to claim 1 is a composite roll made by centrifugal casting comprising an outer layer material and a shaft material of ordinary cast iron or ductile cast iron which is welded and integrated with the outer layer material. The outer layer material is as follows: C: 1.5 to 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 satisfies the following expressions (1) and (2): V + 1.8Nb ≦ 7.5 C−6.0 (%) (1) 0.2 ≦ Nb / V ≦ 0.8 .. (2) The balance is made of Fe and unavoidable impurities.

According to a second aspect of the present invention, there is provided a composite roll made by centrifugal casting comprising an outer layer material and a shaft material of ordinary cast iron or ductile cast iron welded and integrated with the outer layer material, wherein the outer layer material comprises: C: 1.5-3.5%, Si: 1.5% or less, Mn: 1.2% or less, Cr: 5.5-12.0%, Mo: 2.0-8.0%, V: 3.0-
10.0%, Nb: 0.6 to 7.0%, Ni: 5.5% or less, and satisfy the following expressions (1) and (2), and V + 1.8Nb ≦ 7.5 C−6.0 (%)… (1) 0.2 ≦ Nb / V ≦ 0.8 (2) The balance is made up of Fe and unavoidable impurities.

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

[0012]

The reasons for limiting the content of alloying elements in the outer layer material of the composite roll of the present invention and the limiting formulas 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 for improving the wear resistance of the outer layer material of the roll, and is required to be 1.5% or more.
%, Crack resistance is significantly reduced.
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%, crack resistance is reduced, so the upper limit is made 1.5%.

Mn: 1.2% or less Mn is necessary for the same purpose as that of the Si described above.
If it exceeds 2%, the crack resistance deteriorates, so that the upper limit is undesirably set to 1.2%.

Cr: 5.5 to 12.0% Cr forms a carbide 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 which are the object of the present invention are added. When added, the wear resistance deteriorates, so the upper limit is made 12.0%.

Mo: 2.0 to 8.0% Mo forms carbides like Cr and is effective for improving wear resistance, and also improves the hardenability and temper softening resistance of the matrix and strengthens the base structure. To be effective, 2.0% or more is required. However, if it exceeds 8.0%, crack resistance decreases, so the upper limit is made 8.0%.

Ni: 5.5% or less Ni is added to improve hardenability and strengthen the matrix structure. However, if it exceeds 5.5%, an unstable structure such as the presence of residual γ is formed. 5.5%.

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

V is a hard MC which is most effective for improving wear resistance.
Or an essential element for forming M ₄ C ₃ carbide, and it is necessary to have 3.0% or more to exhibit its effect.
%, Crack resistance deteriorates and production problems occur, so the upper limit is made 10.0%.

Nb is also a hard MC effective for abrasion resistance like V.
Carbides are formed, but if added alone, they become coarse and massive carbides, and not only the effect cannot be obtained, but also crack resistance becomes a problem.

Therefore, the relationship between the amount of carbon on the base metal hardness when V and Nb are added in combination, the hot wear ratio between the outer layer and the inner layer caused by the carbide distribution of the centrifugally cast ring material, and the heat Maximum crack depth and Nb, V in impact test
1, 2, 3, and 4 show the results of examining the relationship with the content ratio Nb / V.

From FIG. 1 and FIG. 2, it is clear that V + 1.8 Nb ≦ 7.5 C−6.0 (%) must be satisfied in order to obtain the required hardness Hs of 75 or more as a wear-resistant hot rolling roll. It became.

The experiment of FIG. 1 shows that Si: 0.5%, Mn:
0.5%, Cr: 6.8%, Mo: 3.2%, C,
A 25 mm Y / block cast from a molten metal with varied V and Nb was subjected to a 1000 ° C. normalizing process and a 550 ° C. tempering sample. The experiment of FIG. 2 was performed with 0.5% Si and 0.5% Mn.
25mmY cast from 5%, Ni: 2.7%, Cr: 7.2%, Mo: 3.5%, and molten C, V, Nb
-Samples which had been subjected to a 1000 ° C. normalizing treatment and a 550 ° C. tempering treatment were used.

3 and 4, a uniform outer layer material can be obtained even when manufactured by centrifugal casting, and 0.2 ≦ Nb / V ≦ 0.8 is satisfied in order not to impair the crack resistance. It became clear that we needed to do that.

3 and 4, the "wear ratio (inner layer / outer layer)" refers to the wear amount (Iw) of the test piece taken from the inner layer side of the ring material and the wear amount of the test piece taken from the outer layer side. (Iw / Ow) with respect to (Ow), and the “thermal shock crack maximum depth” is the maximum crack depth generated in the thermal shock test.

The experiment of FIG. 3 shows that C: 2.5%, Si:
0.5%, Mn: 0.5%, Cr: 6.5%, Mo: 3.5%,
A 100-mm thick ring sample obtained by centrifugal casting (140 G) a molten metal containing V: 5.4% and Nb: 0-8.0%, and subjected to 1000 ° C. normalizing treatment and 550 ° C. tempering treatment. The experiment shown in FIG. 4 was performed using C: 2.7% and Si: 0.6%.
%, Mn: 0.5%, Ni: 3.2%, Cr: 7.4%, M
o: A ring sample with a thickness of 100 mm obtained by centrifugal casting (140 G) a molten metal containing 3.7%, V: 5.8%, and Nb: 0 to 7.5% was subjected to 1000 ° C normalizing treatment and 550 ° C tempering. A treated sample was used.

In the abrasion test, the mating material was heated to 800 ° C. in a two-disk sliding wear method of a mating material of φ190 × 15 and a test material of φ50 × 10, and the test material was pressed at 800 rpm with a load of 100 kgf. At a slip rate of 3.9%, and the wear loss after 120 minutes was measured.

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

Further, as the heat treatment conditions applied to the roll material of the present invention, after austenitizing at 1000 to 1150 ° C., controlled cooling is performed so that the structure after cooling becomes bainite. Therefore, the cooling conditions differ depending on the composition, shape, and size of the target roll material. In the experiments of FIGS. 1 to 4 described above, both the normalizing (air cooling after austenitizing) and the quenching (quenching after austenitizing) are possible because the size of the material to be heat-treated is small. In addition, tempering is performed by selecting the optimal conditions in the range of 500 to 600 ° C.

The centrifugally cast composite roll of the present invention does not necessarily need to contain the above-mentioned Ni.

[0032]

EXAMPLES (Example 1) A molten metal having the chemical composition shown in Table 1 (materials of the present invention: BF, R,
S, comparative materials: A, G to Q) were cast by a centrifugal casting method (140G), a ring sample having a thickness of 100 mm was prototyped, and shore hardness, hot wear and thermal shock tests were performed.

[0033]

[Table 1]

The abrasion test was carried out under the same conditions as described above, by taking test pieces of φ50 × 10 from the inner layer side and the outer layer side of the ring material, respectively.

In the thermal shock test, the above-mentioned plate-like test piece was sampled from the outer layer side of the ring material, and was subjected to the same conditions.

Table 2 shows the results of the wear test and the thermal shock test.
Shown in According to Table 2, the hardness of the material of the present invention is about the same as that of the conventional Ni-grain material (material A),
It can be seen that both the crack resistance and remarkably improved.

[0037]

[Table 2]

Further, since the comparative materials G to Q are out of the scope of the present invention, the wear resistance of the outer layer of the G material is reduced due to segregation of carbide, and the hardness of the H material is insufficient. The crack resistance is reduced, the wear resistance of the outer layer is reduced due to segregation of carbides together with the insufficient hardness of the material I, and the hardness of the material J is insufficient. Further, the K material has an excessive amount of C and thus has a low crack resistance, the L material has an excessive amount of Si and has a low crack resistance, and the M material has an excessive amount of Mn and has a low crack resistance. The N material has an excessive amount of Cr, so the wear resistance and crack resistance are reduced.
If the amount is excessive, the crack resistance is reduced, and the P material is insufficient in the V amount, so that the wear resistance and the crack resistance are reduced,
Since the Q material has an excessive V content, the crack resistance is reduced.

The outer layer having the composition shown in Table 3 (represented by R among the materials B to F, R, and S in Table 1), an intermediate layer, and an inner layer were provided. Diameter 670 mm, trunk length 1450
mm composite roll was manufactured by the following procedure. The melt of the outer layer material is melted in a low-frequency melting furnace, and the melt of the outer layer material is placed in a centrifugal casting mold rotating at a centrifugal force of 140 G at 1490 ° C to a thickness of 75 mm.
mm. Immediately after the outer layer material was solidified, the molten metal in the intermediate layer was cast at 1540 ° C. to a thickness of 40 mm. After the intermediate layer has completely solidified, the rotation of the mold is stopped, the mold is erected, and the inner layer material is melted 1450 minutes after casting the outer layer material.
Cast at ° C. After cooling to room temperature, the mold was disassembled, subjected to rough working, quenched from 1050 ° C., and then subjected to a heat treatment of tempering at 550 ° C. After heat treatment, inspections such as ultrasonic flaw detection were performed, but no defects were generated at the boundary between the outer layer and the intermediate layer and the boundary between the intermediate layer and the inner layer, the internal properties were sound, and the outer layer thickness after finishing processing was The surface hardness was 78-82 in Shore hardness.

[0040]

[Table 3]

As a result of using the above composite roll in an actual hot strip mill finishing stand, as shown in FIG. 6, the use performance of the conventional nickel grain cast iron roll was greatly exceeded. In addition, good results were obtained without any problem such as rough surface of the roll surface.

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,
The above-described intermediate layer is not necessarily provided.

Example 2 A molten metal having the chemical composition shown in Table 4 (materials of the present invention: BF, S,
T, U, V, comparative materials: A, GR) were centrifugally cast (14
0G), a ring sample having a thickness of 100 mm was prototyped and subjected to Shore hardness, hot abrasion and thermal shock tests.

[0044]

[Table 4]

The abrasion test was carried out under the same conditions as described above by collecting test pieces of φ50 × 10 from the inner layer side and the outer layer side of the ring material.

In the thermal shock test, the above-mentioned plate-like test piece was sampled from the outer layer side of the ring material, and was subjected to the same conditions.

Table 5 shows the results of the wear test and the thermal shock test.
Shown in According to Table 5, the hardness of the material of the present invention is almost the same as that of the conventional Ni-grain material (material A),
It can be seen that both the crack resistance and remarkably improved.

[0048]

[Table 5]

Since the comparative materials G to J are out of the scope of the present invention, the hardness of the G and J materials is insufficient, and
For materials, the wear resistance of the outer layer decreases due to segregation of carbides,
The crack resistance of the material I is reduced. Further, regarding the comparative materials K to R, cracking resistance is reduced because the K material has an excessive C content, the crack resistance is reduced because the L material has an excessive Si content, and the M material is Mn. If the amount is too large, the crack resistance is reduced. The N material has an excessive amount of Ni, so the hardness, abrasion resistance, and crack resistance are reduced. The O material has an excessive amount of Cr, and the abrasion resistance is excessive. , The crack resistance is reduced, the P material has an excessive amount of Mo, so the crack resistance is reduced, and the Q material is insufficient in the V amount, so the wear resistance and crack resistance are reduced. Since the amount of V is excessive, the crack resistance is reduced.

Outer layer having the composition shown in Table 6 (U among materials B to F, S, T, U and V in Table 4 was adopted as a representative)
A composite roll having an inner layer, a body diameter of 670 mm and a body length of 1450 mm was produced by the following procedure. The molten metal of the outer layer material was melted in a low-frequency melting furnace, and the molten outer layer material was cast into a centrifugal casting mold rotating at a centrifugal force of 140 G at 1490 ° C. to a thickness of 75 mm. Twenty minutes after the casting of the outer layer material, the rotation of the mold was stopped, the mold was allowed to stand upright, and the molten material of the inner layer material was cast at 1420 ° C. 35 minutes after the outer layer casting. After cooling to room temperature, dismantle the mold,
After roughing, quenching from 1050 ° C, then 550
A heat treatment for performing tempering at ℃ was performed. After heat treatment, inspections such as ultrasonic flaw detection were performed. The roll was a sound roll having no defects, the outer layer thickness after finishing was 45 mm, and the surface hardness was 78 to 82 in Shore hardness.

[0051]

[Table 6]

As a result of using the composite roll in an actual hot strip mill finishing stand, as shown in FIG. 6, the use performance of the conventional nickel-grain cast iron roll was greatly exceeded. In addition, good results were obtained without any problem such as rough surface of the roll surface.

In the practice of the present invention, when forming a composite roll using the material of the present invention shown in Table 4 as an outer layer material,
An intermediate layer as in the first embodiment may be provided between the outer layer and the inner layer.

[0054]

As described above, according to the present invention, productivity,
Even if a centrifugal casting method with excellent economy is applied, a composite roll for rolling excellent in wear resistance and crack resistance free from segregation or the like can be obtained.

[Brief description of the drawings]

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagram showing the influence of a composite addition amount of V and Nb and a C amount on a base metal hardness.

FIG. 2 is a graph showing the effect of the composite addition amount of V and Nb and the C amount on base metal hardness.

FIG. 3 is a graph showing a hot wear ratio between an outer layer and an inner layer caused by a carbide distribution of a centrifugally cast ring material, and a content ratio Nb of Nb and V on a maximum crack depth in a thermal shock test.
FIG. 3 is a diagram showing the effect of / V.

FIG. 4 is a view showing a hot wear ratio between an outer layer and an inner layer caused by a carbide distribution of a centrifugally cast ring material, and a content ratio Nb of Nb and V on a maximum crack depth in a thermal shock test.
FIG. 3 is a diagram showing the effect of / V.

FIG. 5 is a longitudinal sectional view of the composite roll according to the first embodiment.

FIG. 6 is a diagram showing rolling results of the composite rolls manufactured in Examples 1 and 2 in an actual mill compared with those of a conventional roll.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical display location C22C 38/48 C22C 38/48 // B22D 13/02 502 B22D 13/02 502R 19/16 19 / 16 F G

Claims (3)

(57) [Claims] A composite roll made by centrifugal casting comprising an outer layer material and a shaft material of ordinary cast iron or ductile cast iron which is welded and integrated with the outer layer material, wherein the outer layer material has C: 1.5 to 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 satisfies the following expressions (1) and (2): V + 1.8Nb ≦ 7.5 C−6.0 (%) (1) 0.2 ≦ Nb / V ≦ 0.8 ... (2) A centrifugally cast composite roll characterized by the balance comprising Fe and unavoidable impurities. 2. A centrifugally cast composite roll comprising an outer layer material and a shaft material of ordinary cast iron or ductile cast iron welded and integrated with the outer layer material, wherein the outer layer material has C: 1.5 to 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%, Ni: 5.5% or less, and satisfy the following expressions (1) and (2), and V + 1.8Nb ≦ 7.5 C−6.0 (%)… (1) 0.2 ≦ Nb / V ≦ 0.8 (2) A centrifugally cast composite roll characterized by the balance consisting of Fe and unavoidable impurities. 3. An intermediate layer between the outer layer material and the shaft material,
The composite roll made by centrifugal casting according to claim 1 or 2, wherein the outer layer material and the shaft material are welded and integrated through the intermediate layer.