JP2003342676A - Cemented-carbide-made composite roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a highly safe composite roll which is made by the metallic joining of an outer layer comprising a cemented carbide to an inner layer comprising an iron alloy and in which the residual tensile stress at the joining boundary is relaxed and the breaking of a roll during rolling is prevented. <P>SOLUTION: In the cemented-carbide-made composite roll fabricated by the metallic joining of an outer layer comprising a WC cemented carbide to an inner layer comprising an iron alloy, the outer periphery of the inner layer joined to the outer layer substantially consists of a metal structure mainly comprising martensite. The inner layer is an iron alloy containing 0.1-2.0 wt.% C, 4.0 wt.% or less Ni, 4.0 wt.% or less Cr, and 3.0 wt.% of less Mo. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a rolling roll used for rolling a metal material such as a steel material such as a thin strip material, a plate material, a wire material and a bar material, and an inner layer made of a material having particularly excellent toughness, The present invention relates to a cemented carbide rolling composite roll provided with an outer layer made of cemented carbide on the outer circumference of the inner layer.

[0002]

2. Description of the Related Art In order to meet the demand for higher quality of rolled materials such as improved dimensional accuracy, and improved productivity by reducing the number of man-hours required to change rolls, tungsten carbide (WC) -based alloys excellent in wear resistance and surface roughness are used. Hard alloys are applied to rolling rolls such as wire rods, steel bars, flat steels, and strip steels. As is well known, the WC-based cemented carbide is a sintered alloy in which WC is bonded with a metal element such as Co, Ni or Cr.

Cemented carbide is more expensive than other roll materials and has excellent wear resistance, but it has poor toughness due to its high hardness. Therefore, when cemented carbide is used as a rolling roll, a structure in which a hollow sleeve made of cemented carbide is fitted to a metal shaft material having excellent toughness is generally adopted. In the case of such a structure, if the inner surface of the cemented carbide sleeve has a rough surface, excessive tensile stress is locally generated during fitting, and the sleeve is easily cracked beyond the fracture strength of the cemented carbide sleeve. There is a problem.

Therefore, in recent years, a composite roll in which an outer layer made of a cemented carbide and an inner layer made of an iron-based alloy having excellent toughness are metal-bonded has been disclosed in, for example, Japanese Patent Laid-Open Nos. 10-5823 and 10-23.
No. 5824 is disclosed.

Although the conventional composite roll has excellent performance, the coefficient of thermal expansion of the cemented carbide and the iron-based alloy is about 6 × 10 ⁻⁶ / ° C. and 12 × 10 ⁻⁶ / ° C., respectively, which is about twice as high. Since they are different from each other, a large tensile stress is generated in the joint boundary portion between the outer layer and the inner layer during cooling after the metal joining. If rolling is performed in this state, the stress due to rolling acts on the joint boundary portion, and if this combined stress exceeds the joint strength at the boundary, the roll may be destroyed.

In order to relieve this tensile stress, for example, Japanese Patent Laid-Open No. 10-5824 discloses an iron-based alloy of 20 as an inner layer.
Bainite transformation at 0-600 ° C, or 200-85
It is disclosed that materials that undergo pearlite and bainite transformation at 0 ° C. are preferred.

[0007]

However, the residual stress is the volume ratio between the cemented carbide as the outer layer and the iron-based alloy as the inner layer, the shape of the inner layer, that is, the hollow shape with a hole in the center, or There is a problem in that the relaxation of the tensile stress due to the transformation of the inner layer as described above is still insufficient, depending on the difference in the structure such as whether or not the hole is solid.

Therefore, the present invention relaxes the tensile residual stress at the joining boundary and prevents roll breakage during rolling in a composite roll in which an outer layer made of a cemented carbide and an inner layer made of an iron-based alloy are metal-joined. The purpose is to provide a highly safe roll.

[0009]

That is, a cemented carbide composite roll of the present invention comprises an outer layer made of a WC-based cemented carbide,
In a cemented carbide composite roll in which an inner layer made of an iron-based alloy is metal-bonded, the outer peripheral portion of the inner layer bonded to the outer layer is substantially composed of a metal structure mainly composed of martensite.

In the present invention, the chemical composition of the inner layer is C: 0.1 to 2.0% by weight, Ni: 4.0% or less, C:
It is an iron-based alloy containing r: 4.0% or less and Mo: 3.0% or less. Also, the inner layer is B = 270 ×
C (wt%) + 90 × Mn (wt%) + 37 × Ni (wt%) + 70 ×
B value shown in Cr (wt%) + 83 × Mo (wt%) is 300wt%
It is characterized by satisfying the above. Furthermore, the compressive residual stress in the circumferential direction of the central portion of the outer layer of the roll in the rotational axis direction is 100 to 500 MPa at room temperature.

[0011]

In a composite roll in which an outer layer made of a WC-based cemented carbide and an inner layer made of an iron-based alloy are metal-bonded, a transformation mainly composed of martensite is generated on the outer peripheral portion of the inner layer bonded to the outer layer. By so doing, it is possible to relax the tensile residual stress at the joint boundary portion between the outer layer and the inner layer, obtain sufficient joint strength, and prevent cracking during rolling.

In order to generate martensite on the outer peripheral portion of the inner layer, the inner layer must contain the alloys shown below in a weight ratio. The amount of C in the inner layer is an important factor in iron-based materials. C is the most basic component because it determines the matrix structure of the iron-based material depending on its content. When C is less than 0.1%, the inner layer mainly undergoes pearlite transformation, excessive tensile residual stress is generated at the boundary joint between the outer layer and the inner layer, and delamination at the boundary joint between the outer layer and the inner layer is likely to occur. Also 2.
If it exceeds 0%, a large amount of austenite remains, which makes it difficult to control transformation and difficult to control residual stress.

Ni is an austenite stabilizing element and is an important element for improving hardenability. However, if it exceeds 4.0%, the amount of retained austenite increases and the matrix structure becomes unstable, so it is preferably 4.0% or less.

Cr is an important element that affects mechanical properties because it combines with C to form a carbide to improve hardness. Further, since it is an element that stabilizes austenite, it is an important element in controlling transformation. Cr
If it exceeds 4.0%, the amount of retained austenite increases, the mechanical properties deteriorate, and it becomes difficult to control the transformation.

Mo is an important element for controlling hardness, that is, mechanical strength, because it forms a carbide by combining with C. However, if the addition amount is too large, the toughness is reduced. Therefore, Mo is 3.0% or less.

[0016] Mn has a deoxidizing effect and has an effect of enhancing quench hardening. However, if it exceeds 2.0%, the toughness deteriorates, so 2.0% or less is desirable.

Further, as a result of earnest research on the contribution of each component to the martensitic transformation, B = 270 × C (wt%) + 90 × Mn (wt%) from the relationship based on the bainite start temperature.
+37 x Ni (wt%) +70 x Cr (wt%) +83 x Mo (wt
It has been found that martensitic transformation can be stably obtained in the outer peripheral portion of the inner layer when the B value represented by the formula (%) is 300 wt% or more.

[0018]

Embodiment 1 Next, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic cross-sectional view for explaining the HIP method used to manufacture a composite roll for rolling. The right half of FIG. 1 is omitted because it is symmetrical. In FIG. 1, inner diameter φ150 mm, length 1000
A solid inner layer 1 made of an iron-based alloy having the composition shown in Example 1 of Table 1 was placed in the center of the HIP can 2 of mm. Further, a cemented carbide powder composed of WC: 50% and Co: 50% by weight was molded by CIP and then sintered to prepare an intermediate layer material 4 having a thickness of 2 mm. Then, the intermediate layer material 4 was arranged on the outer periphery of the inner layer 1 as an intermediate layer.

Then, the outer surface of the intermediate layer material 4 and the HIP can 2
The void formed between the inner surface and the inner surface was filled with the cemented carbide powder 3 composed of WC: 85%, Co: 12%, and Ni: 3% by weight as a roll outer layer.

Next, the HIP can 2 was welded and hermetically sealed, deaerated by a vacuum pump, and then HIP processed by a HIP device. Here, 5 is a heater and 6 is a HIP furnace. After cooling, the HIP can 2 was removed by machining.
Thus, a composite roll having an outer layer of the cemented carbide of the present invention was obtained. In the composite roll of the present invention, it was confirmed by color check that there was no crack on the end face of the roll, and by ultrasonic flaw detection that the outer layer, the intermediate layer and the inner layer were joined properly. Further, a sample of the outer peripheral portion of the inner layer joined to the outer layer, that is, the inner layer in the vicinity of the joint boundary portion between the outer layer and the inner layer was sampled, and the hardness was measured. Furthermore, when the structure of this sample was confirmed, it was composed of a metal structure mainly composed of martensite.

Further, the compressive residual stress in the circumferential direction at the central portion of the outer layer of the roll in the rotational axis direction was measured by the fracture method using a strain gauge. Table 2 shows the hardness of the outer peripheral portion of the inner layer and the compressive residual stress value in the circumferential direction of the outer layer in the central portion in the rotational axis direction.

(Embodiment 2) FIG. 2 shows a schematic cross-sectional view for explaining the HIP method used for manufacturing a composite roll for rolling. In FIG. 2, the right half part is omitted because it is symmetrical. In Fig. 2, inner diameter φ300mm, length 1500m
A hollow cylindrical inner layer 1 made of an iron-based alloy having the composition shown in Example 2 of Table 1 is disposed in the center of the HIP can 2 of m.
In the space formed between the outer surface of the HIP can 2 and the inner surface of the HIP can 2,
WC: 8 by weight ratio pre-pressed as outer layer of roll
A cemented carbide material 3 consisting of 0% and Co: 20% was inserted.

A clearance of about 5 mm is formed between the inner surface of the cemented carbide material 3 and the outer surface of the inner layer 1, and the clearance is made of a cemented carbide of WC: 30% and Co: 70% by weight. Powder 4 for the intermediate layer was filled.

Next, the HIP can 2 was welded and hermetically sealed, deaerated by a vacuum pump, and then HIP processed by a HIP device. After cooling, the HIP can 2 was removed by machining. Thus, a composite roll having an outer layer of the cemented carbide of the present invention was obtained. When the same inspection as in Example 1 was performed, it was confirmed that the outer layer and the inner layer were joined to each other with the intermediate layer interposed therebetween, and that the outer peripheral portion of the inner layer joined to the outer layer was composed of a metal structure mainly composed of martensite. did it. Table 2 shows the hardness of the outer peripheral portion of the inner layer and the compressive residual stress value of the outer layer.

(Example 3) A hollow cylindrical inner layer made of an iron-based alloy having the composition shown in Example 3 of Table 1 was used in the same manner as in Example 2 except that the intermediate layer was not applied. Thus, a composite roll in which the inner layer and the outer layer of the cemented carbide were directly bonded was manufactured. When the same inspection as in Example 1 was carried out, it was confirmed that the outer layer and the inner layer were joined together soundly, and that the outer peripheral portion of the inner layer joined with the outer layer was composed of a metallic structure mainly composed of martensite. Table 2 shows the hardness of the outer peripheral portion of the inner layer and the compressive residual stress value of the outer layer.

Comparative Example 1 In the same manner as in Example 1, a composite roll was manufactured using a hollow cylindrical inner layer made of an iron-based alloy having the composition shown in Comparative Example 1 in Table 1. After roll production
When the same inspection as in Example 1 was conducted, cracks were found at the joints of the outer layer, the intermediate layer and the inner layer over the entire circumference. Also,
When inspected by ultrasonic flaw detection, cracks developed on the entire surface of the roll. Further, when a sample of the outer peripheral portion of the inner layer joined to the outer layer was sampled and the structure was confirmed, it was found to be composed of a metal structure mainly composed of bainite. Table 2 shows the hardness of the outer peripheral portion of the inner layer and the compressive residual stress value of the outer layer.

Comparative Example 2 In the same manner as in Example 2, a composite sleeve roll was manufactured using a hollow cylindrical inner layer made of an iron-based alloy having the composition shown in Comparative Example 2 in Table 1. After the roll was manufactured, the same inspection as in Example 1 was carried out. As a result, the outer layer and the inner layer were bonded to each other with the intermediate layer interposed therebetween, and no crack was observed on the entire surface of the roll. Further, when a sample of the outer peripheral portion of the inner layer joined to the outer layer was sampled and the structure was confirmed, it was found to be composed of a metal structure mainly composed of bainite. However, the compressive residual stress in the circumferential direction at the central portion of the outer layer in the rotational axis direction was as high as 559 MPa.

When this sleeve roll was fixed to the shaft by shrinkage fitting and used for actual rolling, cracks occurred at the joint between the outer layer and the inner layer after rolling. It is thought that this is because the stress, such as the rolling load acting during rolling, acted as a result of the tensile residual stress acting on the joint between the outer layer and the inner layer, and the stress above the joint strength at the boundary. To be

Comparative Example 3 In the same manner as in Example 3, a composite roll was manufactured using a hollow cylindrical inner layer made of an iron-based alloy having the composition shown in Comparative Example 3 in Table 1. After roll production
When the same inspection as in Example 1 was conducted, cracks were found at the joint between the outer layer and the inner layer over the entire circumference. In addition, cracks had spread all over the roll. Further, when a sample of the outer peripheral portion of the inner layer joined to the outer layer was sampled and the structure was confirmed, it was found to be composed of a metal structure mainly composed of bainite.

[0030] Table 1                   Inner layer content (% by weight)             C      Mn      Cr    Ni      Mo    B value Example 1 0.49 0.53 1.62 3.05 0.53 532 Example 2 1.12 0.37 0.54 1.00 0.51 452 Example 3 0.27 0.68 1.18 2.24 0.29 324 Comparative Example 1 0.19 0.76 0.66 1.58 0.20 241 Comparative Example 2 0.30 0.43 0.99 2.14 0.15 281 Comparative Example 3 0.37 0.49 1.02-0.19 231         -: Not detected

[0031]

From the above results, according to the present invention, the outer layer of the cemented carbide and the outer layer of the iron-based alloy are joined to each other to generate a transformation mainly containing martensite in the outer peripheral portion of the inner layer of the ferrous alloy. It is possible to relax tensile residual stress at the joint boundary with the inner layer. In addition, the B value of the inner layer is 300 wt%
By the above, it was found that the tensile residual stress at the joint boundary portion between the outer layer and the inner layer can be reliably relaxed.

[0033]

According to the composite roll of the present invention, the outer layer made of cemented carbide and the inner layer made of iron-based alloy are metal-bonded to each other.
It is possible to obtain a highly safe roll that relieves the tensile residual stress at the joint boundary portion and prevents roll breakage during rolling.

[Brief description of drawings]

FIG. 1 HIP used to manufacture a composite roll for rolling
The schematic sectional drawing explaining a method is shown.

FIG. 2 H used to manufacture another composite roll for rolling
The schematic sectional drawing explaining IP method is shown.

[Explanation of symbols]

1 inner layer, 2 HIP can, 3 cemented carbide powder (cemented carbide material), 4 intermediate layer material (intermediate layer powder), 5
Heater, 6 HIP furnace

Claims (4)

[Claims] 1. In a cemented carbide composite roll in which an outer layer made of a WC-based cemented carbide and an inner layer made of an iron-based alloy are metal-bonded, the outer peripheral portion of the inner layer bonded to the outer layer substantially forms martensite. A cemented carbide composite roll characterized by comprising a metallic structure as a main component. 2. The chemical composition of the inner layer is C: in a weight ratio.
The iron-based alloy containing 0.1 to 2.0%, Ni: 4.0% or less, Cr: 4.0% or less, and Mo: 3.0% or less. Cemented carbide composite roll. 3. The inner layer is B = 270 × C (wt%) + 9
0 x Mn (wt%) + 37 x Ni (wt%) + 70 x Cr (wt%) +
The cemented carbide composite roll according to claim 1 or 2, wherein a B value represented by 83 x Mo (wt%) satisfies 300 wt% or more. 4. The compressive residual stress in the circumferential direction at the central portion of the outer layer of the roll in the rotation axis direction is 100 to 50 at room temperature.
It is 0 MPa, The composite roll made from a cemented carbide in any one of Claims 1-3 characterized by the above-mentioned.