KR20060015048A - Carbide Composite Rolls for Sheet Rolling - Google Patents

Abstract

An inner layer made of steel or iron material and a cemented carbide outer layer bonded to the outer circumference, wherein R = σ _c (1-ν) / Eα (where σ _c : four-point flexural strength at room temperature, ν: Poisson's ratio at room temperature, E: Young's modulus at room temperature, α: Average thermal expansion coefficient R from room temperature to 800 ° C.).

Cemented carbide, sheet rolling, composite roll, thermal crack resistance, thermal shock coefficient, thermal expansion coefficient, Poisson's ratio, Young's modulus, flexural strength

Description

Carbide Composite Roll for Sheet Rolling {CEMENTED CARBIDE COMPOSITE ROLLS FOR STRIP ROLLING}

1 (A) is a cross-sectional view showing a roll body portion of the cemented carbide composite roll according to the first embodiment of the present invention,

1B is a cross-sectional view showing a roll body part of a cemented carbide composite roll according to a second embodiment of the present invention,

1 (C) is a cross-sectional view showing a roll body part of a cemented carbide composite roll according to a third embodiment of the present invention,

1: (D) is sectional drawing which shows the roll main-body part of the cemented carbide composite roll which concerns on the 4th Example of this invention.

The present invention is composed of an inner layer made of a steel or iron-based material having excellent toughness and an outer layer made of a hard cemented carbide, and a rolled composite roll suitable for sheet rolling, and such a composite roll. It relates to a method of evaluating the thermal crack resistance of.

In order to improve the surface quality of the rolled plate and to improve the wear resistance of the roll, grain-based cast iron rolls or high-speed steel rolls have been conventionally used for hot rolling, and chrome or semi-high for cold rolling. Semi-high-speed forged steel rolls have been widely used. In recent years, rolls of cemented carbide have been developed which are significantly superior in wear resistance as compared to high speed steel rolls. The cemented carbide is a small bond obtained by combining tungsten carbide (WC) with metal elements such as Co, Ni, Fe, and the like, and may contain carbides such as Ti, Ta, and Nb in addition to WC.

For example, Japanese Patent Application No. 58-39906 fits a WC-Co-Ni-Cr cemented carbide sleeve with a heat shrinkage of about 0.1 / 1000 to a shaft material of a steel product having excellent toughness, so that the side of the sleeve is fixed. Disclosed is a small sleeve roll for wire rod rolling mechanically fixed to a shaft material by a ring, a spacer ring, or the like. Carbide sleeve rolls of this kind are relatively short in length with an outer diameter of about 100-500 mm and a length of about 10-300 mm.

Japanese Patent Application Laid-Open No. 10-5823 is composed of an inner layer sleeve made of a steel-based material of a solvent, a cemented outer layer sleeve made of cemented carbide bonded to the outer circumference thereof, and a shaft material fixed by shrink fitting in the inner layer sleeve, The cemented carbide comprises 60 to 90% by weight of at least one of the hard particles of carbides, nitrides and carbonitrides of group IVa to VIa elements of the periodic table, and is substantially Fe, Ni, Co, Cr, Mo and The composite sleeve which is a sintered compact of the mixed powder which consists of at least 1 sort (s) of metal powder among W, and is provided with the compressive residual stress of the circumferential direction of 100 MPa or more to the surface of an outer layer sleeve is disclosed.                         

Japanese Patent Application Laid-Open No. Hei 10-5824 is obtained by diffusing and bonding an outer layer of a cemented carbide to the outer circumference of a shaft material made of a steel material of a solvent, wherein the cemented carbide is a hard particle of carbides, nitrides, and carbonitrides of elements IVa to VIa of the periodic table. 60-90 weight% of remainders are sintered compacts of the mixed powder which consists of at least 1 sort (s) of metal powder of Fe, Ni, Co, Cr, Mo, and W as remainder, and has a circumferential direction of 100 MPa or more on the surface of the said outer layer The composite roll provided with the compressive residual stress of is disclosed.

Japanese Laid-Open Patent Publication No. 2002-301506 is composed of a cemented carbide outer layer comprising tungsten carbide particles metal-bonded to the intermediate layer, consisting of an inner layer made of iron-based material and a cemented carbide containing tungsten carbide particles. The composite roll whose content of the tungsten carbide particle in the said intermediate | middle layer is smaller than content of the tungsten carbide particle in the said outer layer is disclosed.

These cemented carbide rolls have remarkably superior abrasion resistance and spattering resistance compared to conventional casting rolls and forging rolls. Especially, the composite rolls of Unexamined-Japanese-Patent No. 10-5823 and 10-5824 have the advantage that the fixing member in the prefabricated carbide roll of Unexamined-Japanese-Patent No. 58-39906 is unnecessary. Moreover, since a roll main body part consists of a cemented carbide outer layer over the whole length, it is suitable for rolling a wide board | plate material.

During sheet rolling, there is a possibility that a so-called stoppage accident in which the mill stops with the rolled material being held in, or a so-called squeeze accident in which the rolled material is sandwiched between the rolls may occur. When such a rolling accident occurs, a large mechanical and thermal load is applied to the roll surface, and deep cracks are likely to occur on the outer surface of the roll. The crack may be advanced inside the roll outer layer by thermal and mechanical cyclic loading by subsequent rolling, and the roll may be broken. An important characteristic of the roll is that such an accident does not occur.

The cemented carbide roll has a higher carbide ratio such as WC, so that the steel sheet has less seizure, less heat flows from the roll surface, and a smaller thermal expansion rate. This is small. However, since the cemented carbide roll is hard, thermal cracking is likely to occur, and cracks generated once are very easily developed, and in the worst case, the roll is broken or the outer layer is peeled off.

In addition, there was no suitable parameter for evaluating whether or not thermal cracking was likely to occur in the cemented carbide rolls. For example, the mechanical strength of a cemented carbide roll does not directly indicate the occurrence of thermal cracking, and even a cemented carbide roll having a high mechanical strength may cause cracking due to thermal shock. Thus, the thermal crack resistance of the cemented carbide rolls could not be accurately evaluated.

Accordingly, an object of the present invention is to provide a cemented carbide composite roll for sheet rolling that is not only excellent in wear resistance and fracture resistance, but also hardly causes an accident such as thermal cracking or breakage.

Still another object of the present invention is to provide a method for accurately and simply evaluating the thermal crack resistance of a cemented carbide composite roll for sheet rolling.

The thermal shock coefficient R [= σ _c (1-ν) / was obtained by performing a temperature-cooled cooling test on the cemented carbide composite roll in consideration of the occurrence of cracks due to thermal shock when the strength of the material was insufficient compared to the thermal stress generated. It was found that when Eα] is 400 or more, generation of thermal shock cracks can be effectively prevented. The present invention has been completed based on this finding.

That is, the cemented carbide composite roll for rolling according to the present invention includes an inner layer made of a steel-based or iron-based material and a cemented carbide outer layer bonded to the outer circumference of the inner layer. R = σ _c (1-ν) / Eα (where σ _c : 4-point bending strength at room temperature, ν: Poisson's ratio at room temperature, E: at room temperature Is the Young's modulus, α: the average thermal expansion coefficient from room temperature to 800 ° C.).

A preferable example of the cemented carbide composite roll of the present invention is a sleeve roll in which a cemented carbide outer layer is joined to the outer periphery of a hollow cylindrical inner layer made of a steel-based or iron-based material. In this sleeve roll, it is preferable that the ratio of the cross-sectional area of the said inner layer with respect to the cross-sectional area of the whole roll in the cross section perpendicular | vertical to a roll axis is 0.5 or more.

It is preferable that the compressive residual stress of the surface inner direction is given to the outer layer surface. It is preferable that at least one intermediate layer is formed between the outer layer and the inner layer. It is preferable that the said intermediate layer consists of cermet.

The method of the present invention for evaluating the thermal cracking resistance of the cemented carbide composite roll for roll rolling comprising an inner layer made of steel or iron material and a cemented carbide outer layer bonded to the outer periphery of the inner layer, the ambient temperature of the outer layer Measuring the four-point flexural strength σ _c , Poisson's ratio ν at room temperature, Young's modulus E at room temperature, and the average coefficient of thermal expansion α from room temperature to 800 ° C., R = σ _c : (1-ν) / Eα Calculating a thermal shock coefficient R expressed by a formula; and determining that the thermal shock coefficient R has sufficient thermal crack resistance when the thermal shock coefficient R is 400 or more.

DESCRIPTION OF PREFERRED EMBODIMENTS

The cemented carbide composite rolls of the present invention are also good in solid composite rolls or in prefabricated composite rolls in which a composite sleeve roll is fitted by shrink fitting a shaft material. 1 (A) -1 (D) show the main-body part of the various cemented carbide composite rolls of this invention. FIG. 1A shows a solid composite roll in which an inner layer (shaft material) 1 made of steel or iron material and a cemented carbide outer layer 2 are joined. 1B shows a solid cemented carbide composite roll in which the inner layer 1 and the cemented carbide outer layer 2 are joined through an intermediate layer 3. Fig. 1C shows a hollow cemented carbide composite sleeve roll in which a hollow inner layer 1 and a cemented carbide outer layer 2 are joined. FIG. 1D shows a hollow cemented carbide composite sleeve roll in which a hollow inner layer 1 and a cemented carbide outer layer 2 are joined through an intermediate layer 3. In each figure, (4) represents a joining interface.

In either embodiment, the thermal shock coefficient R [= σ _c (1-ν) / Eα] of the outer layer 2 is 400 or more. The thermal shock coefficient R is the four-point flexural strength σ _c (MPa) at room temperature measured for the test piece of cemented carbide cut out from the outer layer 2, the average coefficient of thermal expansion α (° C.- ¹ ) from room temperature to 800 ° C., at room temperature. Was obtained from Poisson's ratio ν and Young's modulus E (MPa) at room temperature.

The large thermal shock coefficient R of the cemented carbide outer layer 2 means that the crack resistance (thermal crack resistance) against the sudden temperature change is large. It is preferable that it is 500 or more, and, as for thermal shock coefficient R, it is more preferable that it is 600 or more.

In order to reduce thermal stress, it is preferable to apply compressive residual stress to the outer layer surface of the cemented carbide composite roll in advance. The compressive residual stress in the plane inward direction on the outer layer surface prevents the generated thermal crack from advancing. It is preferable that compressive residual stress is 100-500 Mpa.

The compressive residual stress on the surface of a cemented carbide composite roll (particularly a composite sleeve roll) is caused by the difference in deformation between the outer layer and the inner layer, the value of which is the inner layer relative to the cross-sectional area of the whole roll in the vertical section with respect to the roll axis. It becomes large according to ratio of cross-sectional area (inner / outer layer cross-sectional ratio). Therefore, in order to give a big compressive residual stress to a roll surface, it is preferable to make inner layer / outer layer cross-sectional ratio more than a predetermined value. As a result of various studies, it was found that when the inner / outer layer cross-sectional ratio is 0.5 or more, a sufficiently large compressive residual stress can be applied to the roll surface. As for an inner layer / outer layer cross-sectional ratio, 0.55 or more are more preferable, and 0.6 or more are the most preferable.

Since the joint strength of an outer layer and an inner layer can be improved by interposing at least one intermediate | middle layer which consists of cermets or metals, such as a cemented carbide, and metal between an outer layer made from a cemented carbide and an inner layer made of a steel or iron material. Among these, it is more preferable that the intermediate | middle layer adjacent to the outer layer of a cemented carbide alloy is a cermet type material, such as a cemented carbide of 30 mass% or more. In order to fully raise the bonding strength of an outer layer and an inner layer, it is preferable that the thickness (intermediate thickness in the case of two or more layers) of an intermediate | middle layer shall be 1 mm or more.

In the method for producing a composite roll of the present invention, the cemented carbide outer layer is metallurgical (diffused) on an inner layer made of steel or iron material by vacuum sintering, pressure sintering or hot-isostatic pressing (HIP). By bonding).

In order to evaluate the thermal crack resistance of the obtained composite roll, (1) the four-point flexural strength σ _c at room temperature of the outer layer, Poisson's ratio ν at room temperature, Young's modulus E at room temperature, and average thermal expansion coefficient from room temperature to 800 ° C. α is measured, (2) the thermal shock coefficient R expressed by the formula of R = σ _c (1-ν) / Eα is calculated, and (3) whether the thermal shock coefficient R is 400 or more, and R is 400 In the case of abnormality, it is determined to have sufficient thermal crack resistance.

The present invention will be described in more detail according to the following examples, but the present invention is not limited to these examples.

Example  One

80 mass% of WC powder having an average particle diameter of 5 μm and 20 mass% of Co powder having an average particle diameter of 1 μm were wet mixed with a ball mill for 20 hours, followed by drying to form a raw material powder of a cemented carbide for an outer layer. .

Using the raw material powder of the cemented carbide for outer layer, a hollow sleeve (outer layer) made of a semi-sintered cemented carbide having an outer diameter of 700 mm, an inner diameter of 655 mm, and a length of 2000 mm was produced. On the outer circumferential surface of the hollow cylindrical SCM440 steel inner layer having an outer diameter of 650 mm, an inner diameter of 500 mm and a length of 2000 mm, a suspension in which the raw material powder of the cermet for the intermediate layer was dispersed in alcohol was applied with a brush, followed by drying to form an intermediate layer. The inner layer was placed in the center of a HIP can having an inner diameter of 700 mm and a length of 2000 mm, and the hollow plastic sintered sleeve was placed therein.

A steel lid was welded to the can for HIP, degassed at 700 ° C, and sealed. After confirming that there was no leakage in the HP can, HIP treatment was performed at 1300 degreeC and 1000 atmospheres. After cooling, the can for HT was removed by machining, and the ultrasonic flaw inspection confirmed that the bonding of the outer layer, the intermediate layer, and the inner layer was abnormal. In this way, in the cross section perpendicular | vertical to an axis line, the composite sleeve made for the cemented carbide for plate rolling whose ratio of the cross-sectional area of the inner layer with respect to the cross-sectional area of the whole sleeve roll was 0.75.

About the test piece cut out from the outer layer of this composite sleeve, the four-point bending strength σ _c at room temperature, the average coefficient of thermal expansion α from room temperature to 800 ° C., Poisson's ratio ν at room temperature, and Young's modulus E at room temperature were measured by JIS R 1601. The thermal shock coefficient R [σ _c (1-ν) / Eα] was calculated from the measured data. Moreover, a strain gauge was attached to the axial direction center part of an outer layer, and the compressive residual stress of the surface direction in the outer layer surface was measured by the breaking method. Moreover, the test piece containing an inner layer, an intermediate | middle layer, and an outer layer was cut out in the radial direction of a composite sleeve, and transverse strength was measured by JISR1601. The results are shown in Table 1.

Example  2

80 mass% of WC powder having an average particle diameter of 10 μm and 20 mass% of Co powder having an average particle diameter of 1 μm were wet-mixed with a ball mill for 10 hours, and then dried to form a raw material powder of a cemented carbide for outer layer.

A hollow cylindrical forged steel inner layer having an outer diameter of 650 mm, an inner diameter of 500 mm, and a length of 2000 mm was provided in a can for steel HIP having an inner diameter of 710 mm and a length of 2000 mm, and a steel pipe having an inner diameter of 510 mm and a thickness of 2 mm was arranged around the inner layer as a partition.

The raw material powder of the cemented carbide for outer layer was filled between the inner surface and the partition of the HIP can. Moreover, the cermet powder for intermediate | middle layer formation was filled between a partition and an inner layer. Subsequently, a partition was taken out, the steel lid was welded to the can for HIP, and it degassed at 700 degreeC, and then the can for HIP was sealed. After confirming that there was no leakage in the HIP can, HIP treatment was performed at 1300 degreeC and 1000 atmospheres. After cooling, the HIP cans were removed by machining. In this manner, a cemented carbide composite sleeve having an inner layer / outer layer cross-sectional ratio of 0.75 was obtained.

About this composite sleeve, the four-point flexural strength σ _c at room temperature, the average coefficient of thermal expansion α from room temperature to 800 ° C., Poisson's ratio ν at room temperature, and Young's modulus E at room temperature were measured. And thermal shock coefficient R [= σ _c (1-ν) / Eα] were calculated from the obtained data. Moreover, the compressive residual stress in the surface direction on the outer layer surface, and the tensile strength strength of the test piece including an inner layer, an intermediate layer, and an outer layer were measured. The results are shown in Table 1.

Example  3

70 mass% of WC powder with an average particle diameter of 5 micrometers and 30 mass% of Co powder with an average particle diameter of 1 micrometer were wet-mixed with an attritor for 5 hours, and it dried and formed the raw material powder of the cemented carbide for outer layers. Using the raw material powder of the cemented carbide for outer layer, a hollow sleeve (outer layer) molded article having an outer diameter of 300 mm, an inner diameter of 200 mm, and a length of 1000 mm was produced. This hollow sleeve was sheathed on the inner layer which consists of solid SCM440 steel materials whose outer diameter is 180 mm and length 1000 mm.

The obtained composite was vacuum sintered at 1350 ° C. Ultrasonic flaw inspection was performed about the obtained composite roll, and it confirmed that there was no abnormality in joining of an outer layer and an inner layer. Thus, in the cross section perpendicular | vertical to the roll axis | shaft, the cemented carbide composite roll whose cross-sectional area ratio of the inner layer with respect to the cross-sectional area of the whole roll was 0.8 was obtained.

About this composite sleeve, the four-point flexural strength σ _c at room temperature, the average coefficient of thermal expansion α from room temperature to 800 ° C., Poisson's ratio ν at room temperature, and Young's modulus E at room temperature were measured. was calculated for the thermal shock coefficient _{R [σ c (1-ν} ) / Eα] from the obtained data. In addition, the tensile strength of the plane in the outer layer surface, and the tensile strength of the test piece including the inner layer and the outer layer were measured. The results are shown in Table 1.

TABLE 1

Note: (1) Four-point flexural strength at room temperature.

(2) Average coefficient of thermal expansion from room temperature to 800 ° C.

(3) Poisson's ratio at room temperature

(4) Young's modulus at room temperature.

(5) Thermal shock coefficient [= σ _c (1-ν) / Eα].

(6) In-plane compressive residual stress at the outer layer surface.

(7) The tensile strength of the test piece cut out in the radial direction of the composite sleeve to include the inner layer (middle layer) and the outer layer.

As is apparent from Table 1, all of the cemented carbide composite rolls of Examples 1 to 3 had a thermal shock coefficient R of 400 or more, and had sufficient tensile strength.

Each cemented carbide composite sleeve of Examples 1 and 2 was shrink-fitted to the shaft material of chromium molybdenum steel, and machined to a predetermined size to produce a cemented carbide composite roll. Using each of the cemented carbide composite rolls of Examples 1 to 2, the steel sheet (thickness 2 mm, width 800 mm) was rolled on a hot thin plate rolling finish stand. As a result of observing the roll surface after rolling, it was confirmed that the roll surface was very flat and that the abrasion resistance and the fracture resistance were very good. Moreover, the crack surface hardly generate | occur | produced on the roll surface, and the growth of a crack was also suppressed.

Since the cemented carbide composite roll for plate rolling of the present invention has a cemented carbide outer layer having a thermal shock coefficient R of 400 or more, it is not only excellent in wear resistance and fracture resistance, but also the occurrence of cracking due to thermal shock is suppressed. In addition, by providing a compressive residual stress to the outer layer, the occurrence and progress of the initial crack are suppressed.

Claims (6)

A cemented carbide composite roll for plate rolling comprising an inner layer made of a steel or iron-based material and a cemented carbide outer layer bonded to the outer circumference of the inner layer, In the outer layer, the formula R = σ _c (1-ν) / Eα (where σ _c : four-point bending strength at room temperature, ν: Poisson's ratio at room temperature, E: Young's modulus at room temperature, (alpha): The thermal shock coefficient R expressed by the average thermal expansion coefficient from normal temperature to 800 degreeC) is 400 or more, The cemented carbide composite roll for plate rolling characterized by the above-mentioned. The method of claim 1, The composite roll has a structure of a sleeve roll in which a cemented carbide outer layer is bonded to an outer circumference of the inner layer, which is a hollow cylinder made of steel or iron material, In the cross section perpendicular | vertical to the axis line of the said roll, the ratio of the cross-sectional area of the said inner layer with respect to the cross-sectional area of the whole roll is 0.5 or more, The cemented carbide composite roll for plate rolling characterized by the above-mentioned. The method according to claim 1 or 2, A cemented carbide composite roll for plate rolling, characterized in that the outer layer surface has a compressive residual stress in a plane inward direction. The method according to any one of claims 1 to 3, A cemented carbide composite roll for plate rolling, comprising at least one intermediate layer between the outer layer and the inner layer. The method of claim 4, wherein The cemented carbide composite roll for plate rolling, characterized in that the intermediate layer is made of cermet. In the method of evaluating the thermal cracking resistance (heat cracking resistance) of the cemented carbide composite roll for sheet rolling comprising an inner layer made of steel or iron material and the cemented carbide outer layer bonded to the outer periphery of the inner layer, Measuring the four-point flexural strength σ _c at room temperature of the outer layer, Poisson's ratio ν at room temperature, Young's modulus E at room temperature, and an average coefficient of thermal expansion α from room temperature to 800 ° C., Calculating a thermal shock coefficient R expressed by the formula R = σ _c : (1-ν) / Eα, and Determining that the thermal shock coefficient R has sufficient thermal crack resistance when the thermal shock coefficient R is 400 or more; Method comprising a.

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