JP2004243341A - Composite roll for rolling made of cemented carbide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite roll for rolling made of a cemented carbide in which the outer layer of the roll is formed of the cemented carbide excellent in wear resistance, and at the same time, which is provided with the intermediate layer with high strength made of the cemented carbide with the low WC content, and which has high reliability in strength. <P>SOLUTION: The composite roll for rolling made of the cemented carbide has the following characteristics. The outer layer made of the cemented carbide is joined to the outer periphery of the inner layer made of a steel-based or an iron-based material via the intermediate layer. The intermediate layer is made of the cemented carbide formed by using WC raw material powder with the average particle size of ≤ 3 μm. The content of the WC particles of the intermediate layer is ≤ 70 % at the weight ratio. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a composite roll for rolling in which an outer layer made of a high-hardness cemented carbide is formed on the outer periphery of an inner layer made of a steel or iron-based material having excellent toughness. In particular, the present invention relates to a roll for plate rolling that requires high bonding strength.
[0002]
[Prior art]
In rolling, materials with high hardness tend to be used in order to improve skin quality and abrasion resistance.In applications requiring the highest abrasion resistance, powdered metal-based materials and hard particles are contained. Cermet type rolls are also used. Among them, cemented carbide rolls are often used mainly in finishing stands because of their excellent wear resistance and crack resistance.
[0003]
For example, Patent Literature 1 describes a roll for rolling a wire made of a WC cemented carbide of WC-Co-Ni-Cr. This roll for wire rod rolling is a small-sized sleeve roll obtained by sintering a cemented carbide alone, and is fitted to a steel roll shaft having excellent toughness at a shrink fitting rate of about 0.1 / 1000. The rolls are mechanically assembled by pressing and fixing the side surfaces of the rolls with a fixing ring, a spacer ring, or the like. The dimensions of this type of cemented carbide sleeve roll are relatively short with an outer diameter of 100 to 500 mm and a length in the direction of the rotation axis of about 10 to 300 mm.
[0004]
In the case of a roll in which a cemented carbide sleeve is fitted to a roll shaft as described above, many components such as a fixing ring, a spacer ring, a disc spring, and a nut are required, and the assembly structure is complicated, and high assembly accuracy is required. Therefore, there is a problem that man-hours and costs related to assembly are required. In addition, there is a problem that the portion occupied by the cemented carbide, that is, the portion usable for rolling is less than half of the length of the roll body, which is not efficient.
[0005]
Further, since the cemented carbide has a high thermal conductivity, the temperature of the cemented carbide tends to rise during rolling use, and the heat is easily transmitted to the steel roll shaft, and the roll shaft expands significantly. Therefore, since the thermal expansion coefficient of the cemented carbide is smaller than that of steel, a tensile stress is applied to the cemented carbide sleeve in the radial direction and the axial direction. In the case where the interference at the time of shrink fitting is large, if the tensile stress in the radial direction becomes too high, there is a possibility that a crack may be caused from the inner surface of the cemented carbide sleeve. On the other hand, when the interference at the time of shrink fitting is so small that there is a concern about such cracking, the cemented carbide sleeve may slip during rolling.
[0006]
In order to overcome the drawbacks of the assembling type super hard roll, for example, Patent Literature 2 proposes a composite roll in which a super hard alloy and a steel material are metallically joined. This means that at least one or two or more of hard particles of carbides, nitrides and carbonitrides of elements IVa to VIa of the periodic table are added to the outer periphery of the sleeve forming the inner layer made of steel at 60 to 90% by weight. And a cemented carbide outer layer formed by sintering a mixed powder consisting essentially of at least one or two or more metal powders of Fe, Ni, Co, Cr, Mo and W and simultaneously diffusion-bonding the mixed powder. A composite sleeve in which a circumferential compressive residual stress of 100 MPa or more is applied to the outer layer surface is fitted and fixed to a roll shaft. Patent Document 3 also proposes a composite roll having a solid structure in which a cemented carbide and a steel solid shaft are metallically joined.
[0007]
This kind of cemented carbide composite roll eliminates the need for fixing rings, disc springs, nuts, etc. in conventional assembling cemented carbide rolls, and can be used for rolling because the entire surface of the roll body length is composed of an outer layer. Has the advantage that it can be expanded.
[0008]
[Patent Document 1]
JP-B-58-39906 [Patent Document 2]
JP-A-10-8212 [Patent Document 3]
JP 10-8213 A
[Problems to be solved by the invention]
Since cemented carbide composite rolls have a structure that is composited with an inner layer with high toughness, shrink-fitting and keying can be used for fastening to the roll shaft. It can be applied to
[0010]
However, shrink-fit stress due to shrink-fitting to the shaft material and repetitive stress due to rolling load act on the roll, and due to roll strength design, the joint layer at the boundary between the outer layer of cemented carbide and the inner layer of steel-based material etc. Strength most affects roll breakage. In particular, when compressive residual stress is applied to the roll surface to prevent breakage from the roll surface, the residual stress of the tensile component acts in the roll radial direction at the boundary between the outer layer and the inner layer, The risk of the roll breaking from the boundary increases.
[0011]
In order to prevent such roll breakage, it is necessary to increase the bonding strength at the boundary. When a cemented carbide and an iron-based or steel-based material are directly joined, carbon diffuses and moves from the cemented carbide layer to the iron or steel layer due to the difference in carbon activity, and the carbon in the cemented carbide layer near the boundary becomes depleted. , Η phase is formed, and the material strength is reduced.
[0012]
As a method for preventing such η phase, it is effective to interpose an intermediate layer made of a cemented carbide formed of relatively fine WC particles between the cemented carbide layer and iron or steel-based material. More preferably, it is effective to interpose an intermediate layer made of a cemented carbide having a WC particle content of 70% or less. An object of the present invention is to provide a cemented carbide rolling composite roll having a high-strength intermediate layer made of a cemented carbide having a low WC content and having high strength and reliability.
[0013]
[Means for Solving the Problems]
The cemented carbide rolling composite roll of the present invention has an outer layer made of a cemented carbide joined to an outer periphery of an inner layer made of a steel or iron material via an intermediate layer, and the intermediate layer has an average particle size. It is characterized by being made of a cemented carbide formed using WC raw material powder of 3 μm or less.
[0014]
Further, in the composite roll for cemented carbide rolling according to the present invention, the content of the WC particles in the intermediate layer is 70% or less by weight. Further, the thickness of the intermediate layer is 1 mm or more. Further, a compressive residual stress is provided as a residual stress in a direction parallel to the roll surface on the outer layer surface at the center in the roll axis direction.
[0015]
[Action]
At the boundary between the outer layer of the cemented carbide and the inner layer of the iron-based or steel-based material, a cemented carbide having a relatively low content of WC particles as an ordinary cemented carbide is used as an intermediate layer in order to increase the bonding strength. Is effective. The strength of the intermediate layer also depends on the particle size of the WC particles, and by using fine WC particles, the strength of the intermediate layer can be increased and roll breakage from this portion can be prevented. .
[0016]
Further, in the composite roll of the present invention, in order to secure sufficient intermediate layer strength, the content of WC particles in the intermediate layer is preferably set to 70% by weight or less. Further, it is desirable that the thickness of the intermediate layer be 1 mm or more. Two or more intermediate layers may be interposed between the outer layer and the inner layer.
[0017]
In addition, by applying compressive residual stress to the surface of the outer layer (roll body) at the center in the axial direction of the roll in parallel with the roll surface, the accident resistance is sufficiently improved, and the boundary between the outer layer and the inner layer is provided. It is desirable because it is difficult to peel from the surface. This compressive stress is desirably 100 to 500 MPa in consideration of the strength of the boundary portion and the inner layer.
[0018]
As a method for producing the composite roll of the present invention, an outer layer made of a cemented carbide is joined by vacuum sintering, pressure sintering or hot isostatic pressing (HIP) using an inner layer made of a steel or iron material. Let it. The configuration of the roll may be a solid composite roll, or may be a composite sleeve roll assembled by shrink fitting a shaft material such as steel.
[0019]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example 1)
First, WC raw material powder having an average particle size of 10 μm and one type of Co raw material powder having an average particle size of 1 μm were prepared as the cemented carbide raw material powder for forming the outer layer. Co raw material powder was mixed at a ratio of 20%, wet-mixed in a ball mill for 20 hours, and then dried to obtain a cemented carbide raw material powder for forming an outer layer.
[0020]
Also, as the cemented carbide material powder for forming the intermediate layer disposed between the outer layer and the inner layer, two types of WC material powder having an average particle diameter of 3 μm and 5 μm and Co powder having an average particle diameter of 1 μm were prepared. It is blended at a ratio of 50% by weight of WC raw material powder and 50% of Co raw material powder by weight, and is separately blended at a ratio of 75% of WC raw material powder and 25% of Co raw material powder. , A cemented carbide raw material powder for forming an intermediate layer.
[0021]
A hollow sleeve made of a cemented carbide temporary sintered body having an outer diameter of 300 mm, an inner diameter of 240 mm, and a length of 500 mm was prepared using the above-mentioned raw material powder of the hard alloy for forming the outer layer.
[0022]
A hollow cylindrical SCM440 having an outer diameter of 220 mm, an inner diameter of 160 mm, and a length of 500 mm was disposed as an inner layer in the center of a HIP can having an inner diameter of 310 mm and a length of 550 mm. Then, the hollow sleeve made of the cemented carbide was inserted around the inner layer.
[0023]
Next, the above-mentioned cemented carbide raw material powder for forming the intermediate layer was filled in the gap formed between the outer surface of the inner layer and the inner surface of the outer layer of the hollow sleeve. Thereafter, the HIP can was welded and sealed with a steel lid, and then deaerated by a vacuum pump at 700 ° C. After confirming that no leak occurred in the HIP can, HIP treatment was performed at 1350 ° C. and 1400 atm. After cooling, the HIP can was processed and removed, and the ultrasonic inspection was used to confirm that the bonding between the outer layer, the intermediate layer, and the inner layer was sound.
[0024]
In this way, a plurality of rolls having the same specifications were manufactured for each type of WC raw material powder used to form the intermediate layer, each of which had a different average particle size.
[0025]
Further, the strength of the boundary joint was measured. The strength of the boundary joint is measured by cutting out a bending test piece of the boundary joint including the inner layer, the intermediate layer, and the outer layer in the roll diameter direction, and performing a bending test in accordance with JIS R1601 to measure the bending strength (MPa). Was measured. Further, a strain gauge was attached to the center portion of the outer layer in the roll axis direction, and the residual stress (MPa) in the roll circumferential direction in the outer layer was measured by a breaking method. Table 1 shows the results. In Table 1, the WC particle size represents the average particle size (μm) of the WC raw material powder used for the intermediate layer, the WC content represents the content (% by weight) of the WC particles in the intermediate layer, and the minus sign of the residual stress represents compression. .
[0026]
Table 1
No WC grain size WC content Bending strength Residual stress Rolling condition 1 350 1653-205 Good 2 5 50 1140-233 Cracking at boundary 3 5 75 721-241 Cracking at boundary
From Table 1, No. 2 and No. When the roll No. 3 was subjected to rolling, cracks occurred at the boundary. No. With the roll No. 1 (Example of the present invention), no crack was generated at the boundary portion, and good results could be obtained.
[0028]
(Example 2)
In a HIP can composed of steel having an outer diameter of 730 mm and a length of 2300 mm, forged steel serving as a hollow cylindrical inner layer having an outer diameter of 480 mm, an inner diameter of 300 mm, and a length of 2500 mm is installed, and an inner diameter of 490 mm and a thickness of 2 mm is formed around the inner layer. A steel pipe serving as a partition was arranged.
[0029]
A WC raw material powder having an average particle size of 10 μm and a Co raw material powder having an average particle size of 1 μm are prepared, blended at a ratio of 85% WC raw material powder and 15% Co raw material powder, wet-mixed with a ball mill for 20 hours, and then dried. Then, a cemented carbide raw material powder for forming an outer layer was prepared, and this was filled in a gap between the inner surface of the HIP can and the outer surface of the steel pipe.
[0030]
Further, a gap between the inner surface of the steel pipe and the outer surface of the inner layer was filled with a mixed powder of 30% of WC powder having an average particle size of 3 μm and 70% of Co powder having an average particle size of 1 μm to become an intermediate layer. After filling, the steel pipe of the partition was pulled out, and then the HIP can was welded and sealed with a steel lid, and deaerated by a vacuum pump at 700 ° C. After confirming that no leak occurred in the HIP can, HIP treatment was performed at 1300 ° C. and 1400 atm. After cooling, the HIP can was processed and removed to produce a cemented carbide alloy sleeve roll. After machining the inner diameter of the composite sleeve roll, the composite sleeve roll was shrink-fitted to a chromium molybdenum steel shaft material to complete the cold rollable assembling roll of the present invention.
[0031]
In the same manner as in Example 1, a bending test piece at the boundary joint including the inner layer, the intermediate layer, and the outer layer was cut out in the roll diameter direction, and a bending test in accordance with JIS R1601 was performed to measure the bending strength (MPa). Further, the residual stress (MPa) in the circumferential direction of the roll was measured. As a result, the bending strength was 1780 (MPa) and the residual stress was -320 (MPa), and sufficient characteristic values could be obtained.
[0032]
【The invention's effect】
According to the cemented carbide rolling composite roll of the present invention, the outer layer of the roll is excellent in abrasion resistance and has a high-strength intermediate layer made of a cemented carbide having a low WC content, and has a high reliability in terms of strength. And a roll for cemented carbide rolling with a high hardness can be obtained.

Claims (4)

An outer layer made of a cemented carbide is joined to an outer periphery of an inner layer made of a steel-based or iron-based material via an intermediate layer. A composite roll for cemented carbide rolling, comprising an alloy. 2. The composite roll for cemented carbide rolling according to claim 1, wherein the content of WC particles in the intermediate layer is 70% or less by weight. 3. The composite roll for cemented carbide rolling according to claim 1, wherein the thickness of the intermediate layer is 1 mm or more. 4. The cemented carbide rolling according to claim 1, wherein a compressive residual stress is given as a residual stress in a direction parallel to the roll surface on the outer layer surface at a central portion in the roll axis direction. 5. Composite roll.