JP2004244684A - Method for manufacturing composite rolling mill roll made of cemented carbide, and the roll - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method by which a composite roll having characteristics comparable to those of original liquid-phase-sintered cemented carbide even if unsintered powder, compacts or temporarily sintered compacts are used as an external-layer-forming cemented carbide material by carrying out HIP at a temperature not lower than the liquidus temperature of cemented carbide in manufacturing the composite roll made of cemented carbide. <P>SOLUTION: In the method for manufacturing the composite rolling mill roll made of cemented carbide, the external-layer-forming cemented carbide material is disposed in the outer periphery of an inside layer composed of a steel-based or iron-based material and the both are joined together by HIP treatment. A diffusion preventive layer composed of a material having a melting point higher than that of the external-layer-forming cemented carbide material is provided between the inner surface of an HIP can composed of the steel-based material and the outside surface of the external-layer-forming cemented carbide material, and HIP treatment is carried out at a temperature not lower than the liquid-phase-forming temperature of the external-layer-forming cemented carbide material. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method for producing 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, and a roll obtained by the method.
[0002]
[Prior art]
Patent Literature 1 proposes a composite roll in which a cemented carbide 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 Literature 2 also proposes a composite roll having a solid structure in which a cemented carbide and a steel solid shaft are metallically joined.
[0003]
[Patent Document 1]
Japanese Patent Application Laid-Open No. 10-8212 [Patent Document 2]
JP-A-10-8213
[Problems to be solved by the invention]
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.
[0005]
In such a cemented carbide composite roll, it is necessary to join the outer layer of the cemented carbide and the inner layer of the iron or steel, and usually, the cemented carbide material for forming the outer layer (the raw material powder of the cemented carbide, (A body, a pre-sintered body, a sintered body) and an inner layer are sealed in a HIP can made of a steel-based material and joined by applying a high temperature and a high pressure in a HIP furnace.
[0006]
During the HIP treatment, if the temperature is raised to a temperature at which at least a part of the cemented carbide becomes a liquid phase, at the interface where the inner surface of the HIP can and the cemented carbide are in contact, the cemented carbide having a high carbon content is reduced to a carbon content. The carbon diffuses into the lower HIP can. As a result, the carbon content of the HIP can increases and the melting point decreases accordingly. Due to the decrease in the melting point of the HIP can, the HIP can was melted and damaged during the HIP treatment, and pressure was not applied to the enclosed roll, and the bonding between the outer layer and the inner layer was sometimes incomplete.
[0007]
Therefore, conventionally, when joining the inner layer and the outer layer of the cemented carbide by HIP treatment, in order to prevent the HIP can from being melted and damaged, it is necessary to perform solid-state joining at a low temperature without generating a liquid phase of the cemented carbide. I didn't get it.
[0008]
On the other hand, in order for a cemented carbide to exhibit its original characteristics, a sound sintered body is obtained unless so-called liquid phase sintering is performed, in which at least a part of the cemented carbide is sintered at a liquid phase. This leads to unevenness of the structure and insufficient strength.
[0009]
When the cemented carbide composite roll is joined by the HIP process, the HIP joining must be performed at a liquidus temperature or lower of the cemented carbide in order to prevent the HIP can from being melted and damaged as described above. In order to obtain a roll having the properties of an outer layer having a cemented carbide, sintering at a temperature equal to or higher than the liquidus temperature had to be performed before HIP joining.
[0010]
However, when the step of performing the HIP treatment on the sintered cemented carbide material is employed, the outer sleeve for insertion into the HIP can must be processed to a predetermined size in a hardened and hardened state by sintering. The process requires more man-hours and cost compared to the previous powder state, press-formed body, or pre-sintered body processed at about 1000 ° C. or less.
[0011]
Furthermore, a plurality of sleeves made of a cemented carbide material divided into short lengths are manufactured, and a plurality of these sleeves are stacked around the inner layer, and these split sleeves are simultaneously joined in the roll axis direction during HIP joining with the inner layer. In such a case, if HIP bonding is performed at a liquidus temperature or lower after sintering, segregation in which a binder phase such as cobalt is enriched occurs at the junction between the divided sleeves. For this reason, when this portion is used for rolling, the portion where the binder is enriched is greatly worn, and a corresponding linear dent is generated, which is transferred to a rolled material.
[0012]
In view of such a problem, the present invention performs HIP at a liquidus temperature or higher of a cemented carbide at the time of manufacturing a cemented carbide composite roll, thereby forming an unsintered powder as a cemented carbide material for forming an outer layer. It is an object of the present invention to provide a manufacturing method capable of obtaining a composite roll having characteristics similar to those of a cemented carbide that has been subjected to liquid phase sintering even when a press-formed body or a pre-sintered body is used. Furthermore, by adopting such HIP conditions, even if the cemented carbide material for forming the outer layer is a liquid-phase-sintered split sleeve and they are joined in the roll axis direction, the joint between the split sleeves can be formed. It is an object of the present invention to provide a production method in which segregation does not occur.
[0013]
[Means for Solving the Problems]
The present invention is a method for manufacturing a cemented carbide rolling composite roll in which a cemented carbide material for forming an outer layer is disposed on the outer periphery of an inner layer made of a steel-based or iron-based material and both are joined by HIP processing. A diffusion preventing layer made of a material having a melting point higher than that of the hard metal material for forming the outer layer is provided between the inner surface of the HIP can made of a steel material and the outer surface of the hard metal material for forming the outer layer. The HIP process is performed at a temperature higher than the temperature at which the liquid phase of the cemented carbide material is generated.
[0014]
The diffusion prevention layer is made of any of metals of the 4a group, 5a group, and 6a group or alloys thereof. Further, the diffusion prevention layer is made of any one of niobium, a niobium-based alloy, tantalum, a tantalum-based alloy, chromium, a chromium-based alloy, molybdenum, and a molybdenum-based alloy. Further, the diffusion preventing layer is made of an oxide or a nitride.
Further, the invention is characterized in that the diffusion preventing layer is formed of a foil material or a plate-like material. Furthermore, the invention is characterized in that the diffusion preventing layer is formed by surface treatment such as plating, or formed by thermal spraying or coating.
[0016]
[Action]
In order for the outer layer material to have the same properties as the liquid phase sintering process material in the same way as ordinary cemented carbide, in the cemented carbide roll manufactured by the HIP process, it is manufactured by liquid phase sintering in the HIP process. Must be able to do it. Further, by performing the HIP treatment at a temperature equal to or higher than the liquidus temperature, it becomes possible to prevent segregation of the joint when the divided sleeves of the cemented carbide after the sintering are joined.
[0017]
For this purpose, it is essential to prevent the reaction between the cemented carbide and the HIP can made of a steel material at a temperature not lower than the liquid phase generation temperature in the HIP. A diffusion prevention layer made of a material having a higher melting point than the hard metal material for forming the outer layer is provided between the outer surface of the hard metal material and the direct contact therebetween.
[0018]
The diffusion preventing layer is preferably made of a metal belonging to the group 4a, 5a or 6a or an alloy thereof. For example, niobium, a niobium-based alloy, tantalum, a tantalum-based alloy, chromium, a chromium-based alloy, molybdenum, and a molybdenum-based alloy are desirable. Among them, niobium, a niobium-based alloy, tantalum, and a tantalum-based alloy are more preferable. As a specific forming method, it is preferable to arrange a niobium foil material on the inner surface of the HIP can or to perform a chromium plating surface treatment on the inner surface of the HIP can.
[0019]
The diffusion prevention layer may be made of not only the above-described metal material but also an oxide such as Al ₂ O ₃ , ZrO ₂ , Y ₂ O ₃ , or a nitride such as AlN or BN.
[0020]
BEST MODE FOR CARRYING OUT THE INVENTION
(Example 1)
First, a WC raw material powder having an average particle size of 5 μm and a 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. It was blended at a ratio of 20%, wet-mixed for 20 hours with a ball mill, and then dried.
[0021]
Using this mixed powder, a plurality of short hollow sleeves 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 100 mm were produced. This was used as a cemented carbide material for forming an outer layer.
[0022]
In addition, WC raw material powder having an average particle diameter of 3 μm and Co powder having an average particle diameter of 1 μm are prepared as the cemented carbide raw material powder for forming the intermediate layer disposed between the outer layer and the inner layer. 30% and 70% of Co raw material powder were blended, wet-mixed with a ball mill for 20 hours, and then dried to obtain a material for forming an intermediate layer.
[0023]
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 made of a steel material having an inner diameter of 310 mm and a length of 550 mm.
[0024]
In order to prevent the HIP can and the cemented carbide material for forming the outer layer from coming into direct contact with each other, the inner surface of the HIP can is formed from a niobium having a higher melting point than the cemented carbide material for forming the outer layer, as a diffusion prevention layer characterized by the present invention. Was provided.
[0025]
Next, a plurality of hollow sleeves as a cemented carbide material for forming the outer layer were coaxially stacked and inserted around the inner layer.
[0026]
Next, the above-described material for forming an intermediate layer was filled in a 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, that is, at a temperature or higher at which a liquid phase of the hard metal material for forming the outer layer is generated.
[0027]
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. Further, no melting damage of the HIP can was observed.
[0028]
Furthermore, no segregation in which the binder phase such as cobalt was enriched was found at the joint between the hollow sleeves joined in the roll axis direction. Further, 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. The bending strength was 1780 (MPa), and sufficient strength could be obtained.
[0029]
(Example 2)
In Example 1 described above, the same HIP treatment as in Example 1 was performed without providing a foil material made of niobium having a higher melting point than the cemented carbide material for forming the outer layer on the inner surface of the HIP can as a diffusion preventing layer. . As a result, the HIP can was melted and damaged, and the predetermined HIP pressure did not act on the roll, so that the outer layer and the inner layer of the cemented carbide were not joined, and a composite roll could not be obtained.
[0030]
【The invention's effect】
By performing HIP at the liquidus temperature or higher of the cemented carbide at the time of production of the cemented carbide composite roll, unsintered powder, press-formed or pre-sintered material is used as the cemented carbide material for forming the outer layer. However, it is possible to obtain a composite roll having the same characteristics as those of a cemented carbide that has been subjected to liquid phase sintering. Also, by adopting such HIP conditions, even if the cemented carbide material for forming the outer layer is a liquid-phase-sintered split sleeve and they are joined in the roll axis direction, the joint between the split sleeves is No segregation occurs.

Claims (7)

A method for producing a cemented carbide rolling composite roll in which a cemented carbide material for forming an outer layer is disposed on the outer periphery of an inner layer made of a steel-based or iron-based material and both are joined by HIP processing, A diffusion preventing layer made of a material having a higher melting point than the hard metal material for forming the outer layer is provided between the inner surface of the HIP can made of the material and the outer surface of the hard metal material for forming the outer layer. A method for producing a composite roll for hard metal alloy rolling, wherein the HIP treatment is performed at a temperature not lower than the temperature at which the liquid phase is generated. The method for producing a cemented carbide rolling composite roll according to claim 1, wherein the diffusion preventing layer is made of any of metals of the 4a group, 5a group, and 6a group or alloys thereof. The cemented carbide according to claim 1, wherein the diffusion preventing layer is made of any one of niobium, a niobium-based alloy, tantalum, a tantalum-based alloy, chromium, a chromium-based alloy, molybdenum, and a molybdenum-based alloy. A method for producing a composite roll for rolling. The method according to claim 1, wherein the diffusion preventing layer is made of an oxide or a nitride. The method for manufacturing a composite roll for cemented carbide rolling according to any one of claims 1 to 4, wherein the diffusion preventing layer is formed of a foil material or a plate-like material. The method for producing a cemented carbide rolling composite roll according to any one of claims 1 to 4, wherein the diffusion preventing layer is formed by any one of surface treatment, thermal spraying, and coating. A composite roll for cemented carbide rolling, produced by the production method according to claim 1.