JP2974226B2 - 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, and the outer layer material is a high Cr cast iron or a Ni grain cast iron in which a cementite-based carbide is crystallized. 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 C: 1.5-3.5%, Si: 1.5%
% Or less, Mn: 1.2% or less, Cr: 5.5 to 12.0%, M
o: 2.0 to 8.0%, V: 3.0 to 10.0%, Nb: 0.6 to 7.
0%, N: 0.08% or less, Co: 10.0% or less, Cu:
2.0% or less, W: 1.0% or less, Ti: 2.0% or less, Z
r: 2.0% or less, B: 0.1% or less
Containing at least one species and satisfying the following formulas (1) and (2), V + 1.8Nb ≦ 7.5 C−6.0 (%) (1) 0.2 ≦ Nb / V ≦ 0.8 (2) The balance consists 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 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%
Hereinafter, N: 0.08% or less, Co: 10.0% or less, Cu:
2.0% or less, W: 1.0% or less, Ti: 2.0% or less, Z
r: 2.0% or less, B: 0.1% or less
Containing at least one species and satisfying the following formulas (1) and (2), V + 1.8Nb ≦ 7.5 C−6.0 (%) (1) 0.2 ≦ Nb / V ≦ 0.8 (2) The balance consists 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 carbides and is an element necessary for improving wear resistance. Cr 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 a carbide similarly to Cr and is effective in improving wear resistance, and also improves the hardenability of the matrix and the resistance to tempering and softening, and strengthens the matrix 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%.

N: 0.08% or less N is an element inevitably contained, but if the amount is too large, when a composite roll is formed, pore-like defects are formed at the boundary between the outer layer and the inner layer (shaft) or at the boundary between the outer layer and the intermediate layer. The upper limit is set to 0.08% because it easily occurs.

Ni: 5.5% or less, Co: 10.0% or less Ni is added to improve hardenability and strengthen the base structure. However, 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 a high temperature, but if it exceeds 10.0%, the effect of improving the heat resistance is saturated, so the upper limit is made 10.0% from the viewpoint of economy.

Cu: 2.0% or less, W: 1.0% or less Both Cu and W are added for strengthening the base structure and improving the high-temperature hardness, but when Cu exceeds 2.0%, the surface properties of the roll deteriorate. In addition, the upper limit is set to 2.0% in order to lower the wear resistance and crack resistance, and the upper limit is set to 1.0% because W is an element having a large specific gravity and if added in excess, promotes segregation of V-based carbide by centrifugal separation.

Ti: 2.0% or less, Zr: 2.0% or less,
B: 0.1% or less Both Ti, Zr, and B are added to suppress the formation of coarse eutectic carbides and improve wear resistance and crack resistance. However, if Ti and Zr exceed 2.0%, V, Nb The upper limit is 2.0 because the shape of the composite carbide deteriorates and the wear resistance decreases.
If B exceeds 0.1%, B segregates at the grain boundaries and lowers the 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 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 abrasion 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 hard MC which is 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 due to 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 FIGS. 1 and 2, it is apparent 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: 0.3%, Mn:
0.4%, Cr: 6.2%, Mo: 2.8%, Co: 4.0%,
N: 1050 ° C. quenching treatment of a 25 mm Y-block cast from a molten metal containing 0.05% and having varied C, V, and Nb.
Using a sample that has been tempered at 550 ° C., the experiment in FIG. 2 was performed using Si: 0.4%, Mn: 0.4%, Ni: 1.5%, and Cr: 6.%.
A 25 mm Y- alloy containing 1%, Mo: 2.8%, Co: 3.2%, N: 0.06%, and casting a molten metal in which C, V and Nb are changed.
The blocks were subjected to 1050 ° C. normalizing treatment and 550 ° C. tempering treatment.

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

In FIGS. 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: 2.2%, Si:
0.3%, Mn: 0.4%, Cr: 6.3%, Mo: 2.8%,
V: 5.1%, Co: 4.1%, Nb: 0 to 6.0%, N: 0.
A 1050 ° C quenching treatment was performed on a 100-mm-thick ring sample obtained by centrifugal casting (140 G) a molten metal containing 06%.
Using the sample subjected to tempering at 550 ° C., the experiment of FIG. 4 shows that C: 2.3%, Si: 0.4%, Mn: 0.5%, Ni:
1.2%, Cr: 6.2%, Mo: 3.2%, V: 5.4%, C
o: A ring sample having a wall thickness of 100 mm obtained by centrifugal casting (140 G) a molten metal containing 5.2%, Nb: 0 to 7.2%, and N: 0.04% was subjected to a 1050 ° C normalizing treatment and a 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 having a diameter of 190 × 15 and a test material having a diameter of 50 × 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 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 composite roll manufactured by centrifugal casting according to the present invention does not necessarily need to contain the above-mentioned Ni.

[0035]

【Example】

(Example 1) A molten metal having the chemical composition shown in Table 1 (material of the present invention: B
To E, Q, and comparative materials: A, F to P) were cast by centrifugal casting, ring samples having a thickness of 100 mm were prototyped, and Shore hardness, hot wear, and thermal shock tests were performed.

[0036]

[Table 1]

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

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

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.

[0040]

[Table 2]

Further, since the comparative materials F to P do not fall outside the scope of the present invention, the F material has a low C content and thus has insufficient hardness, and the wear resistance of the outer layer decreases due to segregation of carbide. ,
For the G material, the wear resistance of the outer layer is reduced due to segregation of carbides, for the H material, the crack resistance is reduced, and for the I material, the hardness is insufficient. In addition, the crack resistance of the J material is reduced due to the excessive amount of C, the crack resistance is reduced due to the excessive amount of Si, and the crack resistance of the L material is reduced due to the excessive amount of Mn. The M material has an excessive amount of Cr, so that the abrasion resistance and crack resistance are reduced. The N material has an excessive amount of Mo, which reduces the crack resistance, and the O material has an insufficient amount of V. Wear resistance and crack resistance are reduced,
Since the material has an excessive amount of V, the crack resistance is reduced.

A composite roll having an outer layer and an inner layer having the composition shown in Table 3 and having 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, 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 the heat treatment, inspections such as ultrasonic flaw detection were performed, and the results are shown in Table 4.

The composite rolls A and B of the material of the present invention were sound rolls having no defect in the outer layer, the boundary portion and the inner layer, but the composite roll C of the comparative example having a large N content had a boundary portion between the outer layer and the inner layer. Showed a UT defect.

[0044]

[Table 3]

[0045]

[Table 4]

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

(Example 2) An outer layer, an intermediate layer and an inner layer having the compositions shown in Table 5 were used.
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 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. Table 6 shows the results of inspections such as ultrasonic flaw detection after the heat treatment.

[0048]

[Table 5]

[0049]

[Table 6]

The composite rolls D and E of the material of the present invention were sound rolls having no defects in the outer layer, the boundary portion, the intermediate layer, and the inner layer, whereas the composite roll F of the comparative example having a large N content contained the outer layer and the intermediate layer. UT defects were found at the boundary between the intermediate layer and the intermediate layer and the inner layer.

As a result of using the composite rolls D and E 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.

[0052]

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 a composite roll according to a second embodiment.

FIG. 6 is a diagram showing rolling results of a composite roll manufactured in Example 2 in an actual mill compared with those of a conventional roll.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) C22C 38/00 302 B22D 19/16 C22C 38/18

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%, N: 0.08% or less, Co: 10.0% or less, Cu: 2.0% or less, W: 1.0% or less, Ti: 2.0% or less, Zr: 2.0% or less, B ： 0.1%
It contains one or more selected from the following and satisfies the following formulas (1) and (2): V + 1.8Nb ≦ 7.5 C−6.0 (%) (1) 0.2 ≦ Nb /V≦0.8 (2) A composite roll made by centrifugal casting, comprising the balance of 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,
N: 0.08% or less, Co: 10.0% or less, Cu: 2.0%
Hereafter, W: 1.0% or less, Ti: 2.0% or less, Zr: 2.0
% Or less, B: one or two selected from 0.1% or less
V + 1.8Nb ≦ 7.5 C−6.0 (%) (1) 0.2 ≦ Nb / V ≦ 0.8 (2) The balance of Fe and A composite roll made of centrifugal casting, comprising an unavoidable impurity. 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.