JP4538794B2 - Cemented carbide roll for rolling - Google Patents

Description

    The present invention relates to a composite roll for rolling in which an outer layer made of a cemented carbide with high hardness is formed on the outer periphery of an inner layer made of a steel-based material or iron-based material having excellent toughness. The present invention is particularly suitable as a sheet rolling roll that requires a sufficiently high strength of the joint between the outer layer and the inner layer.

  In rolling, rolls made of high-hardness materials are used to improve skin quality and wear resistance. In applications where the most wear resistance is required, powder metal materials and hard particles are included. Cermet rolls are used. Among them, a cemented carbide roll excellent in wear resistance and crack resistance is often used mainly for finishing stands.

  As a cemented carbide roll, a composite roll is known in which an outer layer made of cemented carbide and an inner layer made of iron-based or steel-based material are metal-bonded. In this type of composite roll, it is important to obtain high joint strength at the joint between the outer layer and the inner layer. As means for achieving this, it is effective to provide an intermediate layer between the outer layer and the inner layer as shown in Patent Document 1 and the like.

  Patent Document 1 discloses a cemented carbide composite roll in which an outer layer material made of a cemented carbide containing tungsten carbide particles is metal-bonded to the outer periphery of an inner layer material made of an iron-based material, the inner layer material and the outer layer A cemented carbide composite roll having an intermediate layer made of a cemented carbide containing one or more layers of tungsten carbide particles between the material and the content of tungsten carbide particles in the intermediate layer less than that of the outer layer material is described. Has been. Further, the content of the tungsten carbide particles in the intermediate layer is preferably 50% by mass or less, and the content of the tungsten carbide particles in the outer layer material is preferably 60% by mass or more. It is described that the bending strength of the folding test piece is 800 MPa or more.

  In Patent Document 2, an outer layer made of cemented carbide is joined to the outer periphery of an inner layer made of steel or iron-based material via an intermediate layer, and the intermediate layer is made of WC raw material powder having an average particle size of 3 μm or less. A composite roll for rolling made of cemented carbide made of a cemented carbide formed by use is described. Further, it is described that the content of WC particles in the intermediate layer is 70% or less by weight.

JP 2002-301506 A JP 2004-243341 A

  The bonding strength between the outer layer and the inner layer in the conventional composite roll for rolling made of cemented carbide was sufficient as a roll for wire rod rolling or bar rolling. However, in plate rolling using a 4Hi mill, 6Hi mill, multi-stage rolling mill, etc., high load stress is also applied from the backup roll and the intermediate roll, so that a high repetitive stress acts on the joint, and thus the strength of the joint. May deteriorate and lead to peeling.

  Also, as disclosed in Patent Document 2, a cemented carbide rolling composite with improved joint strength using a WC and Co cemented carbide having a relatively low WC content of 70 wt% or less as an intermediate layer. In rolls, the η phase generated when the outer layer of cemented carbide and the inner layer of iron-based or steel-based material are directly bonded can be prevented, and a relatively high bonding strength can be obtained. However, when the strength is still weak and a strength evaluation such as a tensile test is performed, a fracture occurs at the boundary between the intermediate layer and the inner layer.

  Accordingly, the present invention improves and strengthens the joint boundary between the intermediate layer and the inner layer, and provides a cemented carbide having a joint having a strong joint strength that can be sufficiently used even when a high load stress such as plate rolling is applied. An alloy rolling composite roll is provided.

The composite roll for rolling made of cemented carbide according to the first aspect of the present invention is provided between an outer layer made of a cemented carbide containing tungsten carbide (WC) and cobalt (Co) and an inner layer made of an iron-based or steel-based material. , A cemented carbide rolling composite roll in which at least one intermediate layer is formed, and the inner layer and the intermediate layer, and the intermediate layer and the outer layer are respectively metal-bonded, and the intermediate layer includes tungsten carbide (WC) and nickel ( It is made of a cemented carbide containing Ni).

The composite roll for rolling made of cemented carbide according to the second aspect of the present invention is provided between an outer layer made of a cemented carbide containing tungsten carbide (WC) and cobalt (Co) and an inner layer made of an iron-based or steel-based material. , A composite roll for rolling made of cemented carbide in which at least one intermediate layer is formed, and the inner layer and the intermediate layer, and the intermediate layer and the outer layer are respectively metal-bonded , the intermediate layer comprising tungsten carbide (WC), cobalt ( It is made of a cemented carbide containing Co) and nickel (Ni). In the second aspect of the present invention, the ratio Co / Ni of the content (mass%) of Co and Ni in the intermediate layer is 1.0 or more.

  Moreover, in the composite roll for rolling made of cemented carbide according to the first and second inventions, the content of WC in the intermediate layer is 70% by mass or less.

  By forming the intermediate layer between the outer layer and the inner layer with a cemented carbide containing WC and Ni or a cemented carbide containing WC, Co and Ni, Ni is added particularly as a cemented carbide of the intermediate layer. As a result, compared with the conventional intermediate layer made of WC-Co cemented carbide composed of WC and Co, the structure of the joint boundary between the intermediate layer and the inner layer is made uniform, and the toughness of the joint is increased. To do.

  In particular, the intermediate layer is formed of a cemented carbide containing WC, Co, and Ni, and the ratio Co / Ni of the content (mass%) of Co and Ni in the intermediate layer is set to 1.0 or more. The structure of the joint boundary portion between the intermediate layer and the inner layer becomes a structure mainly composed of martensite, and high joint strength can be obtained.

  Conventionally, the WC-Co cemented carbide of the intermediate layer and the inner layer are joined by sintering at a high temperature, but the elements contained in both materials are diffused at the joining interface to form a joining boundary. At that time, WC in the intermediate layer tends to dissolve in the Co matrix, but the solid solution limit of W in Co is narrow, and W forms an intermetallic compound with Co. Intermetallic compounds are generally brittle and the presence of the phase formed thereby degrades the mechanical properties of the material.

  On the other hand, the solid solubility limit of W in Ni is wide, and it is difficult to form an intermetallic compound as in the case of Co. For this reason, there is little decrease in mechanical properties such as strength. Such an effect of Ni appears even when Ni is added to the Co base. It was confirmed that the effect appeared even when about 5% of Ni was added to the intermediate layer of the WC-Co cemented carbide.

  When the intermediate layer is formed of a cemented carbide containing WC, Co, and Ni, when the Ni content is larger than that of Co, the base structure of the joint boundary between the intermediate layer and the inner layer is an austenite single phase. Therefore, the strength is relatively low. For this reason, in order to obtain sufficient strength, the ratio Co / Ni of the content (mass%) of Co and Ni in the intermediate layer needs to be a certain level or more. The Co / Ni ratio is preferably 1.0 or more, and more preferably 5.0 or more because higher strength can be obtained. In the present invention, addition of Ni is indispensable, and if all are made of Co, an intermetallic compound appears in the boundary diffusion layer, so that high bonding strength cannot be obtained.

  In addition, when the WC content in the intermediate layer is large, the two-phase region of the alloy layer of WC, Co, and Ni is narrow and the carbon amount is reduced due to carbon diffusion into the inner layer made of iron-based or steel-based material. The composition of the junction boundary between the inner layer and the inner layer easily enters the three-phase region of the WC-Co and Ni-η phases, and the η phase is likely to occur. In order to prevent such η phase generation, it is necessary to set the WC content so that the two-phase region of the alloy layer of WC, Co, and Ni becomes wide. For this reason, the WC content in the intermediate layer is desirably 70% by mass or less. However, if the WC content in the intermediate layer is excessively decreased, the strength of the intermediate layer itself is decreased. Therefore, the WC content is desirably 30% by mass or more.

  The composite roll for rolling according to the present invention has a joining portion (an intermediate layer between the outer layer and the inner layer itself, an intermediate layer located at one end of the intermediate layer itself, a joining boundary portion between the inner layer and the intermediate layer located at the opposite end of the intermediate layer itself) It is suitable for a roll for sheet rolling that is required to have a sufficiently high strength in a region including all the joining boundary portions between the layer and the outer layer. Specifically, it has an outer layer, an intermediate layer, and an inner layer, and the joint portion (outer layer). The intermediate layer itself between the inner layer and the inner layer, the boundary between the intermediate layer and the inner layer located at one end of the intermediate layer itself, the region including all the junction boundary between the intermediate layer and the outer layer located at the opposite end of the intermediate layer itself) When a tensile test specimen placed at the center in the axial direction is subjected to a tensile test, a tensile strength of 800 MPa or more can be obtained. Further, in the tensile test, the fracture position of the test piece appears at a position excluding the joining boundary portion (the joining boundary portion between the intermediate layer and the inner layer or the joining boundary portion between the intermediate layer and the outer layer), that is, the inner layer or the intermediate layer in the present invention.

  As a manufacturing method of the composite roll of the present invention, an outer layer made of cemented carbide is joined by vacuum sintering, pressure sintering or hot isostatic pressing (HIP) method using an inner layer made of steel or iron-based material. Let

  FIG. 1 is a schematic sectional view of a roll body portion of a composite roll according to the present invention. It is sectional drawing which makes a right angle with respect to a roll rotating shaft direction. As the structure of the composite roll of the present invention, as shown in FIG. 1A, a composite sleeve roll in which the outer layer 2 is joined to the outer periphery of the inner layer 1 having the hollow portion 4 via the intermediate layer 3, or the structure shown in FIG. Thus, there is a composite roll in which the outer layer 2 is bonded to the outer periphery of the solid inner layer 1 (also referred to as a shaft material or a core material) via the intermediate layer 3. The composite sleeve roll of the present invention shown in FIG. 1A may be assembled by being shrink-fitted to a shaft material such as steel prepared separately. The inner layer in the present invention refers to an inner layer constituting a composite sleeve roll, or a shaft member and a core member constituting a solid composite roll. In addition to forming one intermediate layer as shown in FIG. 1, another intermediate layer having a different composition or thickness may be further formed, that is, two or more intermediate layers may be formed.

  As a method for constructing the intermediate layer, there is a method in which the mixed powder for forming the intermediate layer adjusted to the composition of the present invention is filled in the void formed between the outer layer and the inner layer and then sintered. Further, there is a method in which a molded body obtained by molding a mixed powder for forming an intermediate layer adjusted to the composition of the present invention with a press or CIP is placed between an outer layer and an inner layer and then sintered. Furthermore, a pre-sintered or sintered body obtained by pre-sintering or sintering a compact formed by pressing or CIP the mixed powder for forming the intermediate layer adjusted to the composition of the present invention is disposed between the outer layer and the inner layer. Then, there is a method of sintering.

Example 1
First, as a cemented carbide raw material powder for outer layer formation, 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 are prepared, and each of them is 80% WC raw material powder and 20% Co raw material powder by mass%. The mixture was wet mixed with a ball mill for 20 hours and then dried to obtain a cemented carbide raw material powder for outer layer formation.

  Further, as the cemented carbide raw material powder for forming the intermediate layer disposed between the outer layer and the inner layer, the WC raw material powder having an average particle size of 5 μm, the Co raw material powder having an average particle size of 1 μm, and the Ni raw material powder having an average particle size of 1 μm Was prepared and blended at a mass percentage of 60% WC raw material powder, 35% Co raw material powder, and 5% Ni raw material powder. That is, the Co / Ni content ratio Co / Ni in the intermediate layer was set to 7.

  Five hollow sleeves made of a cemented carbide made of cemented carbide having an outer diameter of 300 mm, an inner diameter of 240 mm, and a length of 200 mm were produced using the above-mentioned cemented carbide raw material powder for outer layer formation. A hollow cylindrical SCM440 having an outer diameter of 235 mm, an inner diameter of 160 mm, and a length of 1000 mm was disposed as an inner layer in the center of the HIP can having an inner diameter of 310 mm and a length of 550 mm. Then, five hollow sleeves made of cemented carbide for forming the outer layer were inserted on the outer periphery of the inner layer so as to be coaxially stacked so that the side surfaces of the adjacent hollow sleeves were in contact with each other.

  Subsequently, the above-mentioned cemented carbide raw material powder for forming the intermediate layer was filled into a gap formed between the outer diameter surface of the inner layer and the inner diameter surface of the hollow sleeve. Thereafter, the HIP can was hermetically sealed with a steel lid, and then deaerated with a vacuum pump at 700 ° C. After confirming that no leak occurred in the HIP can, the HIP treatment was performed at 1250 ° C. and 1000 atm. After cooling, the HIP can was processed and removed.

  In this way, a composite sleeve roll as shown in FIG. This roll was subjected to ultrasonic flaw detection, and it was confirmed that the outer layer, the intermediate layer, and the inner layer were joined properly. Further, it was confirmed by structure observation that no η phase was generated near the junction boundary between the intermediate layer and the inner layer, and that no intermetallic compound of W and Co was formed.

  In addition, a tensile test specimen including an outer layer, an intermediate layer, and an inner layer in the roll diameter direction and having a joint portion positioned at the center in the axial direction was cut out, a tensile test was performed, and a tensile strength was measured.

  FIG. 2 shows a schematic view of a tensile test specimen. The tensile test specimen 5 has an hourglass shape and includes an outer layer 2, an intermediate layer 3, and an inner layer 1. The total length B is 100 mm, the diameter C is 22 mm, the diameter D is 12 mm, the length of the central parallel part A is 36 mm, and the diameter of the test part S is 8 mm. The position of the joint is the center P of the test piece 5. The surface of the test part was subjected to final adjustment after polishing with emery paper (up to 2000 #), followed by buffing using diamond paste and surface adjustment by electrolytic polishing.

  FIG. 3 shows an enlarged schematic cross-sectional view of the vicinity of the joint in the tensile test specimen. In FIG. 3, the joint portion 6 includes all of the intermediate layer 3 itself between the outer layer 2 and the inner layer 1, the joint boundary portion 7 between the intermediate layer 3 and the inner layer 1, and the joint boundary portion 8 between the intermediate layer 3 and the outer layer 2. Consists of areas that contain.

  Then, a tensile test was performed using a tensile tester (servo pulser manufactured by Shimadzu Corporation, model EHF-EA5). As a result, the tensile strength was 1030 MPa, and a sufficient bonding strength could be obtained. Further, the test piece was broken at the site on the inner layer 2 side, and it was confirmed that the joint strength of the joint was higher than that of the inner layer.

(Example 2)
First, as a cemented carbide raw material powder for outer layer formation, a WC raw material powder having an average particle size of 5 μm, a Co raw material powder having an average particle size of 1 μm, an Ni raw material powder having an average particle size of 1 μm, and a Cr raw material powder having an average particle size of 1 μm are prepared. These were blended in the proportions of WC raw material powder 75%, Co raw material powder 16%, Ni raw material powder 8%, Cr raw material powder 1% in mass%, wet mixed in a ball mill for 20 hours, and then dried to form an outer layer. Cemented carbide raw material powder for use.

  Further, as the cemented carbide raw material powder for forming the intermediate layer disposed between the outer layer and the inner layer, the WC raw material powder having an average particle size of 8 μm, the Co raw material powder having an average particle size of 1 μm, and the Ni raw material powder having an average particle size of 1 μm The WC raw material powder was 50%, the Co raw material powder was 45%, and the Ni raw material powder was 5% by mass. That is, the Co / Ni content ratio Co / Ni in the intermediate layer was set to 9.

  The cemented carbide mixed powder for forming the intermediate layer is molded by CIP, then pre-sintered at 1000 ° C. using a vacuum sintering furnace, and a sleeve-shaped intermediate having a thickness of 3 mm and a relative density of 63%. A plurality of layer forming materials were prepared.

  Next, a hollow cylindrical SNCM439 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 the HIP can having an inner diameter of 310 mm and a length of 550 mm. Then, the sleeve-shaped intermediate layer forming material is arranged on the outer periphery of the inner layer so as to be coaxially stacked so that the side surfaces of the adjacent intermediate layer forming materials are in contact with each other.

  Thereafter, the cemented carbide raw material powder for forming the outer layer was filled in the gap formed between the outer surface of the intermediate layer forming material and the inner surface of the HIP can. Thereafter, the HIP can was hermetically sealed with a steel lid, and then deaerated with a vacuum pump at 700 ° C. After confirming that no leak occurred in the HIP can, the HIP treatment was performed at 1300 ° C. and 1000 atm. After cooling, the HIP can was processed and removed.

  In this way, a composite sleeve roll as shown in FIG. This roll was subjected to ultrasonic flaw detection, and it was confirmed that the outer layer, the intermediate layer, and the inner layer were joined properly. Further, it was confirmed by structure observation that no η phase was generated near the junction boundary between the intermediate layer and the inner layer, and that no intermetallic compound of W and Co was formed.

  As in Example 1, as a result of conducting a tensile test, it was confirmed that the tensile strength was 1075 MPa and the test piece was broken at the site on the inner layer side.

(Comparative Example 1)
As a comparative example, a roll was manufactured under exactly the same conditions as in Example 1 except that the composition of the intermediate layer was different. In other words, as the cemented carbide raw material powder for forming the intermediate layer disposed between the outer layer and the inner layer, 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 are prepared, and the WC raw material in mass%. The mixture was 60% powder and 40% Co raw material powder.

  The obtained composite sleeve roll was subjected to ultrasonic flaw detection, and it was confirmed that the outer layer, the intermediate layer, and the inner layer were joined properly. Moreover, it was confirmed by structure observation that no η phase was generated in the vicinity of the boundary between the intermediate layer and the inner layer. However, an intermetallic compound of W and Co was generated.

  As in Example 1, as a result of conducting a tensile test, it was confirmed that the tensile strength was as low as 750 MPa, and the test piece was broken at the joint boundary portion between the intermediate layer and the inner layer.

  According to the composite roll for rolling made of cemented carbide of the present invention, the outer layer of the roll is excellent in wear resistance, suppresses the generation of η phase at the joint boundary between the intermediate layer and the inner layer, and prevents the formation of intermetallic compounds. Further, it is possible to obtain a cemented carbide rolling roll having a high strength joint made of cemented carbide and having high reliability.

  Since the intermediate layer and the inner layer have greatly different material properties such as thermal expansion coefficient and elastic modulus, a large strain is generated at the joint boundary between them, so there is a possibility that the residual stress inside the roll takes a maximum value. high. In hot rolling, it is necessary to apply high compressive residual stress to the surface in order to suppress the occurrence of thermal cracks from the surface. In such a case, the residual stress inside the roll becomes high and the roll breaks from the joint boundary. The risk of doing so increases. In particular, when the rolling stress is high as in plate rolling, the stress load due to rolling is high, and roll breakage is particularly likely to occur. By obtaining a high-strength joint portion according to the present invention, it is easy to ensure safety against fracture from the joint boundary portion in the case of severe rolling stress application such as hot rolling, especially plate rolling. Become.

The schematic sectional drawing of the roll trunk | drum of the composite roll of this invention is shown. The schematic of the test piece for a tensile test is shown. The expanded schematic sectional drawing of the junction part vicinity in the test piece for a tensile test is shown.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Inner layer, 2 Outer layer, 3 Intermediate layer, 4 Hollow part, 5 Test piece for tensile test 6 Joined part, 7 Joining boundary part of intermediate | middle layer and inner layer, 8 Joining boundary part of intermediate | middle layer and outer layer

Claims (4)

At least one intermediate layer is formed between an outer layer made of a cemented carbide containing tungsten carbide (WC) and cobalt (Co) and an inner layer made of an iron-based or steel-based material , and the inner layer and the intermediate layer A composite roll for rolling made of cemented carbide in which an intermediate layer and an outer layer are respectively metal-bonded, wherein the intermediate layer is made of a cemented carbide containing tungsten carbide (WC) and nickel (Ni). Composite roll for rolling made of hard alloy. At least one intermediate layer is formed between an outer layer made of a cemented carbide containing tungsten carbide (WC) and cobalt (Co) and an inner layer made of an iron-based or steel-based material , and the inner layer and the intermediate layer And a composite roll for rolling made of cemented carbide in which the intermediate layer and the outer layer are respectively metal-bonded, and the intermediate layer is made of a cemented carbide containing tungsten carbide (WC), cobalt (Co) and nickel (Ni). A composite roll for rolling made of cemented carbide. The composite roll for rolling of cemented carbide according to claim 2, wherein the ratio Co / Ni of the content (% by mass) of Co and Ni in the intermediate layer is 1.0 or more. The composite roll for rolling according to any one of claims 1 to 3, wherein the content of WC in the intermediate layer is 70 mass% or less.