JP4340989B2 - Cemented carbide composite roll - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is used for rolling steel materials such as strips, plates, wires, rods, and the like, and an outer layer material made of tungsten carbide (WC) cemented carbide is metal on the outer periphery of an inner layer material made of a material having excellent toughness. The present invention relates to a cemented cemented carbide composite roll.
[0002]
[Prior art]
In order to meet the demands for high quality rolling materials such as improved dimensional accuracy, reduced surface wrinkles, and improved surface gloss, WC cemented carbides with excellent wear resistance, rough skin resistance, etc. are used for wire rods, steel bars, It is applied to rolling rolls such as flat steel. As is well known, the WC cemented carbide is a sintered alloy in which WC is bonded with a metal element such as Co, Ni, and Fe, and often contains carbides such as Ti, Ta, and Nb in addition to WC.
[0003]
For example, Japanese Examined Patent Publication No. 58-39906 describes a wire-rolling roll made of a WC-Co-Ni-Cr WC cemented carbide. This wire rolling roll is a small sleeve roll obtained by sintering a cemented carbide single body, and is fitted to a steel roll shaft material with excellent toughness at a shrinkage fit of about 0.1 / 1000. The roll side is pressed and fixed by a fixing ring, a spacer ring or the like, and mechanically assembled. The size of this kind of cemented carbide sleeve roll is relatively short with an outer diameter of 100 to 500 mm and a length in the rotation axis direction of about 10 to 300 mm.
[0004]
[Problems to be solved by the invention]
In the case of a roll in which a sleeve made of a cemented carbide alloy as described above is fitted to a roll shaft material, a large number of members such as a fixing ring and a spacer ring are required, the assembly structure is complicated, and high assembly accuracy is required. There is a problem that man-hours and costs for assembly are required. Moreover, there is a problem that the portion occupied by the cemented carbide, that is, the portion that can be used for rolling is less than half of the length of the roll body, which is not efficient.
[0005]
Furthermore, since the cemented carbide has a high thermal conductivity, the temperature of the cemented carbide is likely to rise during rolling, the heat is easily transferred to the steel roll shaft material, and the roll shaft material expands greatly. Therefore, since the thermal expansion coefficient of cemented carbide is smaller than that of steel, tensile stress is applied to the cemented carbide sleeve in the radial and axial directions. When the tightening allowance at the time of shrink fitting is large, if the tensile stress in the radial direction becomes too high, there is a risk of causing cracks from the inner surface of the cemented carbide sleeve. On the other hand, if the tightening allowance 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 addition, the cemented carbide alone has a problem that large and long sleeve rolls cannot be manufactured because large deformation is likely to occur in the formed body due to the influence of its own weight during sintering.
[0007]
To solve these problems, for example, a cemented carbide composite roll disclosed in Japanese Patent Application No. 8-158658 has been proposed. 60% to 90% by weight of at least one or more of carbides, nitrides, and carbonitrides of IVa to VIa group elements in the periodic table are formed on the outer periphery of the sleeve forming the inner layer material made of steel. And a cemented carbide outer layer material obtained by sintering and simultaneously bonding a mixed powder composed of at least one or more metal powders of Fe, Ni, Co, Cr, Mo and W. A composite sleeve having a circumferential residual compressive stress of 100 MPa or more on the surface of the outer layer material is fitted and fixed to the roll shaft material.
[0008]
Since such a composite roll made of cemented carbide has a high toughness of the inner layer material, the entire length of the sleeve can be fixed to the roll shaft material by shrink fitting, resulting in a simple structure. Moreover, since the entire surface of the roll body length is constituted by the outer layer material, the portion that can be used for rolling can be enlarged. Therefore, the frequency of roll replacement is reduced, and the rolling stop time can be shortened.
[0009]
Also, compressive residual stress can be applied to the surface of the outer layer material by metal-bonding the inner layer material and the outer layer material having different thermal expansion coefficients. As a result, it is possible to suppress the progress of heat cracks that occur during rolling compared to a cemented carbide single roll, and to reduce the amount of roll rework. Further, even when a large crack of, for example, about 1 mm is generated during rolling, the progress of the crack into the interior can be prevented by the compressive residual stress.
[0010]
The composite roll made of cemented carbide in which the outer layer material of cemented carbide is metal-bonded to the outer periphery of the inner layer material in this way has many advantages. However, when compressive residual stress is applied to the outer layer material, the radius is roughly proportional to that. Since directional tensile residual stress is generated, it is necessary to further improve the bonding reliability between the inner layer material and the outer layer material of the cemented carbide, and it is an object of the present invention to respond to this.
[0011]
[Means for Solving the Problems]
The cemented carbide composite roll of the present invention is a cemented carbide composite roll in which an outer layer material made of tungsten carbide (WC) -based cemented carbide is metal-bonded to the outer periphery of an inner layer material made of a material having excellent toughness. Boundary member including inner layer material, metal layer and outer layer material in a bending test in accordance with JIS R1601, in which a material and an outer layer material are joined by a HIP process through a metal layer whose main component is a carbide non-forming element The bending strength of the bending test piece is 600 MPa or more.
[0012]
In the cemented carbide composite roll of the present invention, it is desirable that the metal layer contains a carbide non-forming element as a main component, and particularly contains Co or Ni in an amount of 50% by weight or more. The metal layer preferably has a thickness of 10 to 1000 μm. However, even if it exceeds 1000 μm, there is no problem as long as the predetermined bending strength of the present invention is satisfied.
[0013]
Moreover, in the bending test based on JIS R1601, the bending strength of the bending test piece including the boundary joint portion is 600 MPa or more. More preferably, it is 800 MPa or more.
[0014]
Moreover, it is preferable to provide unevenness on the joint surface of the inner layer material or the outer layer material, and the unevenness preferably has a height of 10 μm or more and a pitch of 10 μm or more.
[0015]
[Action]
C diffusion occurs from the outer layer material to the inner layer material when the outer layer material of the cemented carbide and the inner layer material such as steel containing carbon (C) are metallicly joined. As a result, the WC of the cemented carbide near the joint between the outer layer material and the inner layer material is changed to double carbide (W, Co) ₆ C. This double carbide is fragile compared to WC and causes a reduction in the strength of the boundary joint. Therefore, by providing a metal layer made of a non-carbide element such as Co and Ni at the boundary junction, the diffusion of C can be suppressed, and Co and Ni are elements included in the outer layer material of the cemented carbide. Therefore, the affinity with the outer layer material is good and the bonding strength can be increased. The effect is sufficient when the thickness of the metal layer is 10 to 1000 μm. However, it is difficult to make the thickness of the metal layer uniform over the entire boundary junction, and in some boundary junctions, the thickness may be less than 10 μm. Moreover, it is not this limitation when the predetermined bending strength of this invention can be obtained even if it exceeds 1000 micrometers.
[0016]
The surface of the inner layer material or outer layer material is provided with irregularities by applying a spiral screw process or the like in advance, thereby increasing the surface area of the joint portion and improving the strength of the boundary joint portion. Propagation has the effect of preventing or slowing propagation because cracks diverge along the irregularities. The unevenness may be formed by performing groove processing in the circumferential direction or the rotation axis direction. If the unevenness is too fine, the effect is not sufficient. Therefore, the height (depth) of the unevenness is preferably 10 μm or more, and the pitch between adjacent recesses or protrusions is preferably 10 μm or more.
[0017]
With the above configuration, it is possible to withstand the residual stress in the radial direction of the boundary joint that occurs when surface compressive stress is applied to the cemented carbide composite roll, and it is safe against peeling from the boundary joint during rolling. The rate can be increased.
[0018]
In the composite roll made of cemented carbide according to the present invention, the outer layer material made of WC-based cemented carbide has a content of WC particles of 60 to 95% by weight and an average particle size of WC particles of 1 to 10 μm, depending on the rolling application. Set as appropriate within the range. If the length of the outer layer material in the roll axial direction (length of the roll body) is 250 mm or more, it is desirable because the portion that can be used for rolling can be expanded. The inner layer material is preferably a steel material or cast iron material having excellent toughness.
[0019]
DETAILED DESCRIPTION OF THE INVENTION
(Example 1)
A hollow cylindrical SNCM439 steel inner layer material having an outer diameter of 300 mm, an inner diameter of 180 mm, and a length of 700 mm was prepared. The outer peripheral surface of the inner layer material was spirally threaded with a lathe to provide irregularities having a height of about 1 mm and a pitch of about 1 mm. Moreover, in order to form a metal layer, Ni plating was given to the uneven surface provided in the inner layer material.
[0020]
In addition, WC powder having an average particle diameter of 6 μm, 1 μm Co powder, 1 μm Ni powder, and 1 μm Cr powder were prepared, and the ratio of WC 85%, Co 9.3%, Ni 4.7%, and Cr 1% by weight%. Were mixed in a ball mill for 20 hours, followed by drying to prepare a mixed powder to be a cemented carbide material.
[0021]
Next, after filling the outer periphery of the steel inner layer material with a mixed powder as a cemented carbide material, canning, deaeration treatment and sealing, it is isothermal at 1320 ° C., 100 MPa for 2 hours. Pressure (HIP) treatment was performed. Then, after cooling and taking out from the HIP furnace, the capsule for HIP processing was removed by machining, and finish processing was performed to a predetermined dimension to obtain a cemented carbide composite roll of the present invention.
[0022]
When this cemented carbide composite roll was inspected by ultrasonic flaw detection, it was confirmed that the reflection from the boundary joint was almost constant and there was no welding failure. In addition, when a ring-shaped test piece was cut out from the end of the roll of the present invention and subjected to an organization investigation, a metal layer mainly composed of Ni having a thickness of about 100 μm was formed at the boundary joint corresponding to the uneven surface of the inner layer material. The double carbide (W, Co) ₆ C in the metal layer was less than 1 area%.
[0023]
Moreover, in order to measure the intensity | strength of a boundary junction part, the bending test based on JISR1601 was done. When the bending test piece of the boundary joint portion including the inner layer material, the metal layer, and the outer layer material was cut out and tested in the roll diameter direction, the bending strength was 840 MPa on average.
[0024]
(Comparative Example 1)
As Comparative Example 1, a cemented carbide composite roll was produced in the same manner as in Example 1 except that the outer peripheral surface of the inner layer material was smooth and Ni plating for forming a metal layer was not performed on the inner layer material. When a ring-shaped test piece was cut out from the end of the roll of Comparative Example 1 and the tissue was mirror-polished, a carbide different in color from the WC contained in the outer layer material in the vicinity of the boundary joint and having grown to several tens of μm was confirmed. It was. When corroded by Mr. Murakami's solution, it turned black and turned out to be a double carbide with a different composition. Moreover, when a bending test piece of the boundary joint portion including the inner layer material and the outer layer material was cut out in the roll diameter direction and subjected to a bending test in accordance with JIS R1601, the bending strength was as low as 310 MPa on average. there were.
[0025]
(Example 2)
The composite roll made of cemented carbide of the present invention obtained by the same method as in Example 1 was shrink-fitted and fixed on the outer periphery of a roll shaft made of steel to produce a roll for hot wire rolling intermediate stand. This type of roll conventionally used is, for example, an assembly-type roll in which two sleeves made of cemented carbide are shrink-fitted on a roll shaft, and the rollable portion is about 200 to 250 mm. On the other hand, in the roll of the present invention, the part that can be rolled was enlarged to 500 mm. As a result, the frequency of roll change has been halved. In addition, since the strength of the boundary joint is high, it can withstand the rolling stress and thermal stress generated during rolling in addition to the residual stress and shrinkage stress in the radial direction caused by the shrinkage difference between the outer layer material and the inner layer material. I was able to.
[0026]
【The invention's effect】
ADVANTAGE OF THE INVENTION According to this invention, the joining reliability of an inner-layer material and the outer-layer material of a cemented carbide can be improved, and also it can expand application also to severe rolling applications.

Claims (3)

In a cemented carbide composite roll in which an outer layer material made of tungsten carbide (WC) cemented carbide is metal-bonded to the outer periphery of an inner layer material made of a material having excellent toughness, the inner layer material and the outer layer material are made of carbide-free elements. In the bending test according to JIS R1601, the bending strength of the bending test piece of the boundary joint portion including the inner layer material, the metal layer, and the outer layer material is 600 MPa. A composite roll made of cemented carbide characterized by the above. 2. The cemented carbide composite roll according to claim 1 , wherein the metal layer contains 50% by weight or more of Co or Ni. The composite layer made of cemented carbide according to claim 1 or 2 , wherein the metal layer has a thickness of 10 to 1000 µm.