JP2003342668A - Composite roll made of cemented carbide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite roll made of a cemented carbide in which the outer layer consisting of the cemented carbide and the inner layer consisting of an iron based alloy are fixed by metal connecting, the tensile residual stress at a connecting boundary part is mitigated, and the deterioration of a connecting strength at the connecting boundary part between an outer layer and an inner layer due to the formation of oxides is prevented, so that high connection reliability is ensured. <P>SOLUTION: In the composite roll made of the cemented carbide in which the outer layer consisting of a WC based cemented carbide and the inner layer consisting of the iron based alloy are fixed by metal connecting, an oxygen quantity in the outer layer is ≤0.05 wt.% and also the inner layer contains ≥0.6 wt.% Cr. <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, in order to cause transformation of such an iron-based alloy at a relatively low temperature, it is necessary to add a large amount of Cr, Mn, Si and the like. These elements are also oxide-forming elements, and if oxides are generated at the bonding boundary between the outer layer and the inner layer, the bonding strength at the bonding boundary deteriorates and the roll may break from the bonding boundary during rolling. There is a problem that there is.

In view of the above, the present invention provides 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-bonded to each other, while relaxing the tensile residual stress at the joint boundary portion, and at the same time, forming an outer layer and an inner layer by oxide formation. It is an object of the present invention to provide a cemented carbide composite roll having high joint reliability and preventing deterioration of the joint strength at the joint boundary part with and.

[0009]

Means for Solving the Problems In examining the above problems, the present inventor can prevent the decrease in the bonding strength at the bonding boundary by suppressing the amount of oxygen in the outer layer made of cemented carbide. In addition, the present invention has been completed based on the finding that the tensile residual stress at the joint boundary can be relaxed by containing an appropriate amount of Cr, which is a bainite forming element, in the inner layer made of an iron-based alloy. That is, the present invention is a cemented carbide alloy 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, and the amount of oxygen in the outer layer is 0.05 wt% or less, and The inner layer is made of Cr.
It is characterized by containing 6 wt% or more.

Further, the present invention is characterized in that an intermediate layer is provided between the outer layer and the inner layer, and the amount of oxygen in the intermediate layer is 0.05 wt% or less. Further, in a bending test according to JIS R1601, a bending strength of a bending test piece including a joint boundary portion between an outer layer and an inner layer is 600 MPa or more.

[0011]

When the outer layer of the cemented carbide and the inner layer of the iron-based alloy are joined by sintered metal, oxygen in the outer layer diffuses into the inner layer at the joining interface. Then, it reacts particularly with Cr, which is an oxide-forming element contained in the inner layer, to easily form a Cr-based oxide in the vicinity of the bonding boundary.

If this Cr-based oxide is formed by being arranged along the bonding boundary, the bonding strength is reduced. Therefore,
In order to maintain sufficient bonding strength, it is necessary to suppress the amount of oxygen in the outer layer below a certain level and control the formation of Cr-based oxide in the inner layer. Further, Si and Mn in the inner layer are also oxide forming elements similarly to Cr, and are likely to deteriorate the bonding strength at the bonding boundary.

The roll of the present invention has an oxygen content of 0.
By suppressing the amount to be 05 wt% or less, and more preferably 0.02 wt% or less, it is possible to prevent the formation of oxides arranged in the vicinity of the bonding boundary.

The roll of the present invention may have an intermediate layer made of cemented carbide between the outer layer and the inner layer. Also in that case, similarly to the above, by suppressing the amount of oxygen in the intermediate layer to 0.05 wt% or less, more preferably 0.02 wt% or less, it is possible to prevent the formation of oxides arranged near the junction boundary portion.

Cemented carbide is produced by mixing WC powder, which is hard particles, and powder such as Co, Ni and Cr, which is a binder, and sintering the mixture. Usually, commercially available cemented carbide powder contains much oxygen. Contains. This oxygen reacts with the carbon (C) of WC and can be discharged as CO gas. Therefore, by controlling the sintering conditions such as the sintering temperature and the atmosphere in the sintering furnace, the amount of oxygen in the cemented carbide can be controlled. Can be adjusted over the entire roll.

Further, in order to reduce the tensile residual stress at the joint boundary portion between the outer layer and the inner layer, transformation such as bainite transformation or martensite transformation must occur at a certain low temperature. Therefore, in order to cause bainite transformation or martensite transformation in the cooling process after sintering, it is necessary to add at least 0.6 wt% or more of Cr, which is a bainite forming element, to the inner layer. On the other hand, if the amount of Cr in the inner layer is too large, the balance of C in WC in the outer layer changes, and WC changes to a relatively brittle double carbide (W, Co) ₃ C.
% Or less is desirable. For the same reason, the inner layer is Si,
0.5 to 2.0 in total of one or more of Mn and Ni
It is desirable to contain wt%.

The bonding strength between the outer layer and the inner layer in the composite roll of the present invention is measured by a bending test in accordance with JIS R1601 by cutting a bending test piece including a bonding boundary portion between the outer layer and the inner layer from the roll. Evaluate by. The composite roll of the present invention has a bending strength of 60 according to this evaluation method.
It is preferably 0 MPa 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. In FIG. 1, the right half portion is omitted because it is symmetrical. 1, inner diameter φ350 mm, length 90
A hollow cylindrical 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 a 0 mm HIP can 2.
In addition, a cemented carbide powder composed of WC: 50% and Co: 50% by weight is molded by CIP, and then sintered in a vacuum furnace to reduce oxygen, and an intermediate thickness of 2 mm is obtained. Layer material 4 was prepared. 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 having a weight ratio of WC: 80% and Co: 20% as an outer layer of the roll. The cemented carbide powder 3 was used after being granulated in advance and pre-sintered in a vacuum furnace to reduce oxygen.

Then, the HIP can 2 was welded and sealed, deaerated by a vacuum pump, and then HIP processed. Here, 5 is a heater and 6 is a HIP furnace. After cooling
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. With the composite roll of the present invention, it was confirmed by ultrasonic flaw detection that the outer layer, the intermediate layer, and the inner layer were joined together soundly.
Furthermore, it was confirmed from the microstructure observation that oxides arranged along the boundary were not formed near the boundary junction between the intermediate layer and the inner layer.

Taking samples from the outer and middle layers,
The amount of oxygen contained in them was measured. The results are shown in Table 2. Further, a bending test piece including a boundary joint portion between an outer layer and an inner layer with an intermediate layer interposed was cut out from the central portion of the roll, and JI
The bending strength was measured by a bending test according to SR1601. The results are shown in Table 3.

Example 2 A hollow cylindrical inner layer made of an iron-based alloy having the composition shown in Example 2 of Table 1 was used in the same manner as in Example 1 except that the intermediate layer was not applied. hand,
A composite roll was produced in which the inner layer and the cemented carbide outer layer were directly joined. When the same inspection as in Example 1 was conducted, the outer layer and the inner layer were joined to each other soundly, and formation of oxides arranged along the boundary near the joint boundary was not recognized. Table 2 shows the amount of oxygen in the outer layer, and Table 3 shows the measurement results of the bending strength at the joint boundary.

(Embodiment 3) 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 φ200mm, length 2000m
A solid inner layer 1 made of an iron-based alloy having the composition shown in Example 3 of Table 1 was placed in the center of the HIP can 2 of m, and was formed between the outer surface of the inner layer 1 and the inner surface of the HIP can 2. A cemented carbide material 3 having a weight ratio of WC: 80% and Co: 20% was inserted into the void as an outer layer of the roll. In addition, cemented carbide material 3
Are those which have been previously molded using a press and have been sintered using an atmosphere furnace to reduce oxygen.

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 with WC: 50% and Co: 50% by weight. Powder 4 for the intermediate layer was filled. The powder 4 for the intermediate layer was used after being granulated in advance with a spray dryer and pre-sintered in an atmosphere furnace to reduce oxygen.

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 carried out, the outer layer and the inner layer were soundly joined with the intermediate layer sandwiched therebetween, and formation of oxides arranged along the boundary in the vicinity of the joined boundary was not recognized. Table 2 shows the amounts of oxygen in the outer layer and the intermediate layer, and Table 3 shows the measurement results of the bending strength at the joint boundary.

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. However, the composition of the intermediate layer material 4 forming the intermediate layer and the cemented carbide powder 3 forming the roll outer layer are the same as those in Example 1, respectively,
Those that had not been granulated in advance and pre-sintered to reduce oxygen were used.

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 cracks were observed on the entire surface of the roll. However, the bending strength of the joint boundary portion between the outer layer and the inner layer was as low as 400 MPa. As a result of the structure observation, it was found that a large amount of Cr-based oxides arranged along the boundary were formed near the bonding boundary portion, and this oxide was the cause of deteriorating the bonding strength.

(Comparative Example 2) 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 2 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. As a result of the structural examination, the Cr content in the inner layer was 0.
Since it was as small as 47 wt%, it was found that the base was not austenite, but became a base that induces stress cracking of bainite and martensite.

Comparative Example 3 A composite roll was manufactured in the same manner as in Example 3 except that the solid inner layer having the composition shown in Comparative Example 3 in Table 1 was used. After the roll was manufactured, the same inspection as in Example 1 was performed, and it was found that cracks were generated at the joints of the outer layer, the intermediate layer and the inner layer over the entire circumference. In addition, when an inspection was performed by ultrasonic flaw detection, cracks developed on the entire surface of the roll. As a result of the structure investigation, since the Cr content in the inner layer is too large, a large amount of Cr-based oxide is generated, and the Cr-based oxides are arranged along the joint boundary portion, and the relatively brittle Cr-based carbide is also present in the joint boundary portion. Was being generated. It was found that these were the causes of the deterioration of the bonding strength at the bonding boundary.

Table 1 Inner Layer Component Content (wt%) C Si Mn Ni Cr Example 1 0.39 0.24 0.63 1.64 0.68 Example 2 0.51 0.29 0.68 1 0.08 0.83 Example 3 0.31 0.24 0.39 3.25 1.81 Comparative Example 1 0.39 0.24 0.63 1.64 0.68 Comparative Example 2 0.19 0.19 0.69 0.45 0.47 Comparative Example 3 0.31 0.24 0.39 2.60 2.59

[0031]

[0032]

From the above results, according to the present invention, by suppressing the oxygen content in the outer layer and the intermediate layer made of cemented carbide,
Since it is possible to prevent the formation of oxides that are arranged in the vicinity of the bonding boundary portion that causes the deterioration of the bonding strength between the outer layer and the inner layer, it is possible to obtain a composite roll having a high bonding strength between the outer layer and the inner layer. Further, by setting the Cr content of the inner layer to a predetermined amount or more, the tensile residual stress at the joint boundary portion between the outer layer and the inner layer can be relaxed, and cracking of the roll can be prevented.

[0034]

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 cemented carbide composite roll having a high joining reliability in which the tensile residual stress at the joining boundary portion is relaxed and the joining strength at the joining boundary portion between the outer layer and the inner layer is prevented from being deteriorated due to the formation of oxide.

[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 (3)

[Claims] 1. A cemented carbide alloy 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, and the oxygen content in the outer layer is 0.05 wt% or less, and the inner layer is Is a cemented carbide composite roll characterized by containing Cr in an amount of 0.6 wt% or more. 2. The cemented carbide composite roll according to claim 1, wherein an intermediate layer is provided between the outer layer and the inner layer, and the oxygen content in the intermediate layer is 0.05 wt% or less. 3. A bending test according to JIS R1601, wherein a bending strength of a bending test piece including a joint boundary portion between an outer layer and an inner layer is 600 MPa or more. The composite roll made of cemented carbide as described in.