JP2005262321A - Composite roll made of cemented carbide - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a composite roll for hot rolling mills made of cemented carbide which is improved in resistance to crack and resistance to break and also is excellent in resistance to wear and resistance to surface roughening. <P>SOLUTION: This roll is a composite roll made of the cemented carbide in which a composite sleeve having an outer layer made of cemented carbide in which powdery mixture consisting of at least one ore more kinds of hard particles of carbide, nitride and carbonitride of an element of the group IVa-VIa in Periodic Table of 60-90 wt.% and the balance substantially at least more kind of Fe, Ni, Co, Cr, Mo and W is sintered and simultaneously diffused and joined on the outer periphery of a sleeve in which the inner layer consisting of an ingot steel base material is formed and imparting compressive residual stress of ≥100 MPa to the surface of the outer layer in the circumferential direction is fit and fixed to a shaft material. An inclined alloy layer with thickness of 0.01-5 mm is formed by using the powdery mixture of the cemented carbide having the composition of the hard particles and a binder phase is changed so that the coefficient of thermal expansion approaches that of the inner layer rather than the cemented carbide of the outer layer in the joined boundary part between the sleeve with which the inner layer is formed and the outer layer. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cemented carbide composite roll in which a composite sleeve having an outer layer made of cemented carbide is fitted and fixed to a shaft member.

  Conventionally, cemented carbide such as WC-Co has been used as a roll material for a hot rolling mill. Since cemented carbide is more expensive than cast steel and tool steel, which are other roll materials, it can be considered that the cemented carbide is used only in parts that are in direct contact with the material to be rolled during rolling and require wear resistance. In addition, since it is difficult to increase the diameter and length of cemented carbide, it is desirable to make a hollow sleeve and fit the sleeve to a metal shaft. Further, in the case of a cemented carbide single roll, there is almost no compressive residual stress and there is a problem that the crack resistance is inferior.

  Cemented carbide is hard and excellent in wear resistance, and has a problem that it is strong against compressive stress but weak against impact and tensile stress. For this reason, fitting methods such as shrink fitting, cold fitting, press fitting, etc., which have been performed on conventional metal sleeves cannot be applied as they are. That is, the sleeve made of cemented carbide has a large elastic modulus and poor deformability, so if there are slight irregularities on the mating surface, excessive tensile stress is locally generated by the mating, and the cemented carbide alloy sleeve There is a problem that the breaking strength of the sleeve is exceeded and the sleeve is easily broken.

  Therefore, various methods have been proposed for fitting a cemented carbide sleeve to a metal shaft. For example, in JP-A-60-83708, a spacer whose outer peripheral portion is gradually thickened from the inner peripheral portion is heated and expanded, and the shaft material is loaded together with a cemented carbide sleeve and a disk spring. Then, a method is disclosed in which the side surface of the sleeve is pressed and fixed by being sandwiched between fixing members and generating a large lateral pressure on the disk spring by cooling and contraction of the spacer. However, such a fitting method has a problem that the number of members such as spacers and fixing members is large and the assembly structure is complicated. Further, it cannot be said that the prevention of cracking due to tensile stress acting on the surface of the cemented carbide sleeve after shrink fitting is sufficient.

  In addition, as a conventional cemented carbide composite roll, a brazing material is put between the cemented carbide ring and the inner steel ring and brazed with heat, or a cemented carbide is cast on the outer periphery of the steel ring. Some are welded by the wrapping method. However, the former brazing method has a problem that the fatigue strength of the brazing layer at a high temperature is weak, and peeling or the like occurs during rolling. Further, the latter cast-in method has a problem that high wear resistance cannot be obtained due to the limitation of the manufacturing method.

JP 60-83708 A

  The object of the present invention was made in view of such problems. At the same time, the cemented carbide mixed powder for the outer layer material was sintered and diffused on the outer periphery of the sleeve forming the inner layer using a sintering method. Bonding and applying appropriate compressive residual stress to the outer layer surface improves crack resistance and fracture resistance, as well as cemented carbide for hot rolling mills with excellent wear resistance and rough skin resistance. Is to provide a composite roll.

  The composite roll made of cemented carbide according to the present invention has carbide, nitride and carbonitride hard particles of elements IVa to VIa of the periodic table on the outer periphery of a sleeve forming an inner layer made of a molten steel-based material. Sintered mixed powder comprising at least one or more of 60 to 90% by weight and the balance substantially consisting of at least one or more of metal powders of Fe, Ni, Co, Cr, Mo and W In addition, a cemented carbide composite roll having a composite sleeve having a cemented carbide outer layer that has been diffusion-bonded at the same time and imparted with a circumferential compressive residual stress of 100 MPa or more on the outer layer surface is fitted and fixed to a shaft member. A cemented carbide in which the composition of the hard particles and the binder phase is changed so that the thermal expansion coefficient is closer to the inner layer than the cemented carbide of the outer layer at the boundary between the sleeve forming the inner layer and the outer layer. 0.01 using a mixed powder of And forming a gradient alloy layer of 5mm thickness.

In the cemented carbide composite roll of the present invention, the hard particles are at least one selected from the group consisting of WC, TiC, TaC, NbC and VC. The metal powder preferably further contains 0.1 to 3.0% by weight of a Cr—Si compound composed of at least one of Cr ₃ Si, CrSi and CrSi ₂ .

  The composite roll made of cemented carbide according to the present invention has the outer layer diffusion-bonded to the inner layer at the same time as being sintered, so that it can impart an appropriate compressive residual stress to the outer layer surface and is excellent in crack resistance and crack resistance. . For this reason, when using for the roll for hot rolling used under high temperature and a high load, the outstanding performance can be exhibited.

FIG. 1 is a cross-sectional view showing an example of a composite sleeve constituting the cemented carbide composite roll of the present invention. FIG. 2 is a cross-sectional view in the rotation axis direction showing a composite roll in which the composite sleeve of FIG. 1 is shrink-fitted to a shaft material. FIG. 3 is a cross-sectional view taken along the line AA of FIG. The composite sleeve 1 of the present invention includes an outer layer 11 and an inner layer 12. A longitudinal groove 4 for fitting the locking key 5 is provided on the inner surface of the hollow inner layer 12. The composite roll made of cemented carbide according to the present invention comprises a composite sleeve 1 and a shaft member 3, both of which are firmly fixed by shrinkage fitting. At the time of shrink fitting, the key 5 inserted into the longitudinal groove provided on the outer peripheral surface of the shaft member 3 engages with the longitudinal groove 4 provided on the inner peripheral surface of the inner layer 12, and after shrink fitting. The composite sleeve 1 is prevented from rotating with respect to the shaft member 3. In this example, the composite sleeve is shrink-fitted and fixed to the shaft using a key, but may be shrink-fitted and fixed without using the key.
The outer layer 11 of the composite sleeve 1 is composed of 60 to 90% by weight of at least one or more of carbide, nitride and carbonitride hard particles of elements IVa to VIa of the periodic table, and the balance substantially It is formed by sintering a mixed powder with at least one or more metal powders of Fe, Ni, Co, Cr, Mo and W. If desired, the toughness and oxidation resistance can be improved by adding Cr—Si compound powder such as Cr ₃ Si, CrSi, CrSi ₂ to the mixed powder.

  The inner layer 12 of the composite sleeve 1 is a sleeve made of a molten steel-based material such as cast steel, forged steel, graphite cast steel, carbon steel, and alloy carbon steel. By using a tough steel material for the inner layer 12, the brittleness of the cemented carbide forming the outer layer 11 can be compensated. The preferred composition of the inner layer 12 is C: 0.1 to 2.0, Si: 0.2 to 1.2, Ni: 0.1 to 5.0, Cr: 0.1 to 2.0, by weight%. Mo: 0.1-3.0, the balance being substantially Fe. If C exceeds 2.0%, the amount of carbide or graphite becomes excessive, so the tensile strength and toughness required for the inner layer cannot be ensured. Further, when C is less than 0.1%, the required strength cannot be ensured because it is too soft. Examples of such steel materials include SCM steel, SNCM steel, and SNC steel.

  The composite sleeve 1 is formed by diffusion bonding the mixed powder to the outer periphery of the inner layer 12 by a sintering method such as a vacuum sintering method. The composite roll of the present invention is formed by fitting and fixing the composite sleeve 1 to the shaft member 3 by shrink fitting or the like. The shaft member 3 is made of a metal shaft member such as cast steel, forged steel, or cast iron, and is not particularly limited.

  Since the thermal expansion coefficient of the cemented carbide material of the outer layer 11 is about 1/2 to 1/3 of the thermal expansion coefficient of the steel material of the inner layer 12, thermal stress is generated between the two material layers during the temperature lowering process of the sintering. And if this thermal stress exceeds the strength of each material layer, it will break. In order to prevent the composite sleeve 1 from being broken, a steel material that causes a bainite transformation at 200 to 600 ° C. or a pearlite + bainite transformation at 200 to 850 ° C. is preferable as the inner layer 12. By using such an inner layer material, the shrinkage difference between the inner and outer layers is reduced, and the composite sleeve 1 is not destroyed.

  In the composite sleeve 1 of the present invention, a circumferential compressive residual stress of 100 MPa or more is applied to the outer layer surface of the cemented carbide by diffusion bonding. Preferably, a compressive residual stress of 200 MPa or more is applied. When compressive residual stress in the circumferential direction of 100 MPa or more is applied to the outer layer surface of the cemented carbide, the tensile stress acts on the surface due to abnormal rolling, etc., even for tensile stress acting after fitting, and cracks are generated. Even if such a situation is encountered, since it is canceled out by this compressive residual stress, the progress of cracks and cracks is prevented. When the compressive residual stress is less than 100 MPa, this effect cannot be sufficiently obtained.

  As the hard phase of the cemented carbide forming the outer layer, powders of at least one kind or two or more kinds of hard particles of elements IVa to VIa of the periodic table, such as carbide, nitride and carbonitride, are used. Among them, it is preferable to use hard particles such as WC, TiC, TaC, NbC, and VC which are carbides, and WC is particularly preferable. These hard particles serve as a substrate for the outer layer 11 of the composite sleeve 1, and the more the hard particles contribute to wear resistance. When the blending amount of the hard particles is less than 60% by weight, the wear resistance is insufficient and the rough skin resistance is insufficient. Moreover, when it exceeds 90 weight%, fracture toughness will fall. Therefore, the blending amount of the hard particles is 60 to 90% by weight.

  The average particle diameter of hard particles such as WC is preferably 1 to 10 μm. When the average particle size of the hard particles is less than 1 μm, the fracture toughness of the outer layer 11 is significantly reduced. On the other hand, if it exceeds 10 μm, the bending strength is lowered. In order to provide the outer layer 11 with high toughness, high strength, and excellent wear resistance, the average particle size of the hard particles is more preferably 3 to 7 μm. Further, by sufficiently equalizing the hard particles, the rough skin resistance and toughness of the outer layer can be improved.

  As the binder phase of the cemented carbide forming the outer layer, metals such as Fe, Ni, Co, Cr, Mo, and W form a solid solution binder phase and reinforce the outer layer 11 of the composite sleeve 1. These metal powders may be added alone, but are preferably added in combination. If the metal powder is less than 10% by weight, the binder phase is insufficient. On the other hand, if it exceeds 40% by weight, the outer layer 11 is extremely reduced in hardness and wear resistance is deteriorated. Therefore, the blending amount of the metal powder forming the binder phase is 10 to 40% by weight. A more preferable blending amount of the metal powder is 15 to 25% by weight.

A Cr—Si compound powder can be further added to the metal powder. As the Cr—Si compound, Cr ₃ Si, CrSi, CrSi _{2 and the} like are preferable. The Cr—Si compound powder has the effect of improving the fracture toughness and oxidation resistance of the outer layer 11. Since the Cr-Si compound dissolved in the binder phase during the sintering process precipitates at the interface between the hard phase and the binder phase during the cooling process, the interfacial energy between the two phases rises, suppressing the development of cracks generated by the rolling load. And improve the mechanical strength. Furthermore, the adhesion of Cr ₂ O ₃ particles and SiO ₂ particles is formed to suppress the growth of the multi-hard oxide layer. By such an action, the outer layer 11 containing a Cr—Si compound can improve toughness and oxidation resistance.

When the blending amount of the Cr—Si compound powder is less than 0.1% by weight, the above effect cannot be obtained sufficiently, and when it exceeds 3.0% by weight, the M ₆ C phase (W ₃ Co ₃ C) precipitates and the toughness is increased. Decreases. A more preferable blending amount of the Cr—Si compound powder is 0.5 to 1.0% by weight.

  The powder of each component of the said mixture ratio is mixed, for example using a ball mill etc., and after drying, it classifies and produces mixed powder. Next, the outer periphery of the inner layer made of a molten steel material is filled with a mixed powder and sintered by vacuum sintering or the like. The sintering temperature is preferably in the temperature range of the liquid phase appearance temperature of the mixed powder + 100 ° C. to the liquid phase appearance temperature−100 ° C. The liquid phase appearance temperature of the mixed powder is 1250 to 1350 ° C. although it varies somewhat depending on the composition. The sintering time is preferably 1 to 5 hours.

  Also, a cemented carbide with a composition of hard particles and a binder phase changed on the outer peripheral surface of the sleeve forming the inner layer made of a molten steel-based material so that the thermal expansion coefficient approaches the inner layer compared to the cemented carbide of the outer layer. It is preferable to form the gradient alloy layer with a thickness of 0.01 to 5 mm, for example, by applying the mixed powder in a paste form.

Example 1 A WC powder having an average particle size of 5 μm, a Co powder of 1 μm, a Ni powder of 1 μm, a Cr powder of 1 μm, and a CrSi ₂ powder of 1 μm were blended in the proportions (% by weight) shown in Table 1, and ball mill For 20 hours and then dried. Subsequently, sintering was performed for 2 hours at the sintering temperature shown in Table 1, and a cemented carbide test piece was manufactured.

  About each obtained test piece, the crack resistance test, the oxidation test, the bending test, the hardness test, and the fracture toughness test (K1C) were done. These test results are shown in Table 2.

Crack resistance test On the surface of a test piece mirror-polished with diamond grains having an average particle diameter of 3 μm and 1 μm, five indentations were applied with a load of 1.47 kN using a Vickers indenter, and the crack length (mm) extended from the end of the indentation And the value of load (kN) / crack length (mm) was taken as crack resistance (MN / m).

Oxidation Test Each test piece (13.5 mm × 13.5 mm × 4.6 mm) was subjected to an oxidation treatment at 800 ° C. for 1 hour, and an oxidation loss (mg / cm ² · h) was measured. The oxidation weight loss is a value obtained by removing the oxide layer formed by heating and holding, obtaining a weight reduction value of the test piece, and dividing this by the unit area. A smaller oxidation weight loss value indicates better oxidation resistance.

Folding test Each test piece (4 mm × 8 mm × 30 mm) was subjected to a four-point bending test with a fulcrum distance of 25 mm.

Hardness test Each indented test piece was subjected to three indentations with a Vickers indenter with a load of 294 N, and the indentation length was measured.

Fracture toughness test (K1C)
The fracture toughness value K1C was determined by the SEPB method.

  From Table 2, the cemented carbide of the present invention had good crack resistance, oxidation resistance, bending strength, and fracture toughness value (K1C). Moreover, as a result of observing the WC particles in the cemented carbide by SEM, the WC particles did not have a sharp angle in the test piece of the example, but the WC particles grew to have a sharp angle in the test piece of the comparative example. It was.

(Example 2) On the outer periphery of an inner layer made of SNCM steel having an outer diameter of 300 mm and an inner diameter of 200 mm, an WC powder having an average particle diameter of 5 μm, 85 wt%, 1 μm Co powder, 9 wt%, 1 μm Ni powder, 5.5 wt% A mixed powder consisting of 0.5% by weight of 1 μm CrSi ₂ powder was loaded. Next, sintering was performed at a temperature of 1320 ° C. for 1 hour to obtain a composite sleeve having an outer diameter of 330 mm and a length of 500 mm. The composite sleeve was shrink-fitted on a steel shaft having an outer diameter of 200 mm and a length of 1500 mm to obtain a cemented carbide composite roll of the present invention.

  About the obtained composite sleeve, after applying a strain gauge to the outer layer surface of the cemented carbide, the portion is cut into blocks of 40 mm x 40 mm x 40 mm and compressed in the circumferential direction acting on the outer layer surface by the open method Residual stress was measured. As a result, a compressive residual stress of 200 MPa or more was shown, and it was confirmed that the film had sufficient crack resistance.

  Further, when the bonding state of the boundary portion between the outer layer and the inner layer was examined by an ultrasonic method, the outer layer was firmly diffusion bonded to the inner layer, and no bonding failure and cracks were observed at all. The composite roll made of cemented carbide of the present invention is suitable for use in a roll for a hot sheet rolling mill, a roll for a hot strip rolling mill, etc., and when used in these rolling, it has excellent wear resistance and rough skin resistance. It was found to have crack resistance and breakage resistance.

  The composite roll made of cemented carbide according to the present invention has the outer layer diffusion-bonded to the inner layer at the same time as being sintered, so that it can impart an appropriate compressive residual stress to the outer layer surface and is excellent in crack resistance and crack resistance. . For this reason, when using for the roll for hot rolling used under high temperature and a high load, the outstanding performance can be exhibited.

It is a cross-sectional view of the composite sleeve of the present invention. It is sectional drawing of the rotating shaft direction of the composite roll of this invention. It is AA sectional drawing of FIG.

Explanation of symbols

  1 composite sleeve, 11 outer layer, 12 inner layer, 3 shaft material

Claims (3)

On the outer periphery of the sleeve forming the inner layer made of the molten steel material, 60 to at least one or more of carbides, nitrides, and carbonitrides of IVa to VIa elements of the periodic table are used. Made of cemented carbide obtained by sintering a mixed powder consisting of 90% by weight and the balance substantially consisting of at least one or more metal powders of Fe, Ni, Co, Cr, Mo and W and simultaneously diffusion-bonded A cemented carbide composite roll having an outer layer, and a composite sleeve having a circumferential compressive residual stress of 100 MPa or more applied to the outer layer surface, which is fitted and fixed to a shaft material, the sleeve forming the inner layer; Using a cemented carbide mixed powder in which the composition of the hard particles and the binder phase is changed so that the thermal expansion coefficient is closer to that of the inner layer than that of the outer layer of the cemented carbide, the bonding boundary with the outer layer is 0.01 to 5 mm. Form a gradient alloy layer of thickness Cemented carbide composite roll, characterized in that. 2. The cemented carbide composite roll according to claim 1, wherein the hard particles are at least one selected from the group consisting of WC, TiC, TaC, NbC and VC. The metal powder further contains 0.1 to 3.0 wt% of a Cr-Si compound composed of at least one of Cr ₃ Si, CrSi and CrSi ₂ or more. The cemented carbide composite roll described.