JPH11342406A - Assembly type roll for hot sheet rolling superior in resistance against accident, wear, and surface roughing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an assembly type roll for hot sheet rolling, which superior in accident resistance and safety and also superior in resistance against wear and surface roughing, which controls such progress of cracking as to cause delayed crack which occurs when the rolling load is not applied as well as controls the progress of cracking of an outer layer when reducing, by applying a proper residual stress after shrinkage fitting. SOLUTION: This invention relates to an assembly type roll for hot sheet rolling wherein a composite sleeve having the outer layer diffusion-spliced to the outer periphery of a hollow cylindrical inner layer made of a cast steel, a forged steel or a graphitic cast steel, is shrink-fit in the shaft material. Further the outer layer is made of high-speed steel system alloy powder sintered by a hot isotropic pressure press method, and the roll circumferential stress on the outer layer after shrink-fitting is -600 to -200 MPa, and the roll radius directional stress on the outer layer is +100 MPa or lower, and the elongation of the inner layer is 1% or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of shrink-fitting a shaft sleeve with a composite sleeve having an outer layer made of a sintered alloy of high-speed steel powder formed on the outer periphery of a hollow cylindrical inner layer made of cast steel, forged steel or graphite cast steel. The hot rollable assembling roll, which has excellent accident resistance, abrasion resistance, and surface roughness resistance, is suitable as a working roll for a continuous hot strip finishing mill. For expression roles.

[0002]

2. Description of the Related Art In hot plate rolling rolls, requirements for wear resistance and surface roughening resistance are increasing in order to respond to reduction of roll cost and high quality of rolled plate, and the outer layer is made of high-speed alloy. Continuous casting overlaying roll (W
No. 088/07594) and centrifugal casting rolls whose outer layer is made of a high-speed alloy material have been applied, but at present, they have not been able to sufficiently meet the demand.

As a further wear and roughening resistant material, a high-speed sintered alloy by hot isostatic pressing (HIP) has been receiving attention. When manufacturing a roll in which a high-speed sintered alloy is formed in the outer layer, a metal capsule is attached around the roll shaft, and a predetermined high-speed alloy powder is filled in an annular space between the shaft and the metal capsule. It is necessary to charge the entire roll into a HIP furnace and perform HIP processing. In order to load the entire roll into the HIP furnace, it is necessary to use a correspondingly large HIP furnace for a large roll such as for hot strip rolling, so that energy cost and atmosphere cost are extremely high. Was.

Therefore, as proposed in Japanese Patent Application Laid-Open No. 56-69304, a shaft material having a length corresponding to the body of a roll is used, and a metal powder is HIP-processed around the shaft material.
After the processing, there is a method of attaching the support portions at both ends of the shaft member by welding or the like. According to this method, the size of the furnace at the time of the HIP processing only needs to be large enough to accommodate the body of the roll, and therefore, there is an advantage that a HIP furnace large enough to accommodate the entire roll is not required. There is.

However, in the above method, it is necessary to make the inner layer material have a solid cylindrical shape. The solid cylindrical inner layer is heavier than the hollow cylindrical inner layer, and may be restricted by the HIP furnace. Therefore, considering the limitations of the HIP furnace and the manufacturing cost, a composite sleeve in which a high-speed sintered alloy is formed on the outer periphery of a hollow shaft material by the HIP method is shrink-fitted to a roll shaft material and assembled. It is valid.

On the other hand, in the recent hot plate rolling method, a large load acts on the work rolls, and the maximum contact pressure of the work rolls is also increasing, so that accidents in the rolling operation such as narrowing and biting are inevitable. It has become something. Due to these accidents in the rolling operation, draw cracks accompanied by thermal cracks and seizures may occur on the roll surface layer.

Usually, when a crack is generated, the crack is completely removed by grinding or the like, and then used for the next rolling. When used for rolling with a crack remaining, the crack often develops under the external force of the rolling. Due to the repeated load during rolling, the cracks tend to propagate obliquely deeper, mainly in the circumferential direction opposite to the rotation direction of the roll, and then propagate almost parallel to the surface of the roll. When the crack reaches the critical size in the course of this growth, spalling occurs in which the roll surface layer is largely peeled.

[0008]

Therefore, conventionally, in order to suppress the growth of a crack which is a starting point of spalling, a method of always applying a compressive stress in the circumferential direction of the roll and the axial direction to the outer layer has been adopted. However, although it is an extremely rare phenomenon, as a phenomenon different from the above-mentioned spalling caused by the rolling load, even if the rolling crack remains in the state where the rolling load is not applied while the developed crack remains inside, the crack grows Peeling (referred to as delayed fracture) may leave safety issues.

When shrink-fitting a sleeve roll onto a roll shaft, it is necessary to set an appropriate shrinkage rate in order to prevent slippage of the sleeve roll and the roll shaft during rolling, breakage of the sleeve roll, and the like. However, when shrink fitting is performed, the stress applied for the above purpose changes.

The present invention has been made in view of such circumstances, and by applying an appropriate residual stress after shrink fitting, it is possible to suppress the development of cracks in the outer layer at the time of drawing down and to reduce the rolling load. To provide an assembling roll for hot strip rolling that is excellent in accident resistance and safety, while suppressing the growth of cracks that cause delayed fracture that occurs in a state where it is not added, and is excellent in wear resistance and surface roughness resistance. With the goal.

[0011]

Means for Solving the Problems As a result of earnest studies, the present inventor has developed a composite sleeve in which a material is used for the inner layer of the roll and an outer layer made of a sintered alloy of high-speed powder is formed on the outer layer of the inner layer. In a hot rolled assembling roll that is shrink-fitted to a material, the compressive stress in the outer circumferential direction of the roll in the outer layer is set within a predetermined range, and the stress in the radial direction of the roll in the outer layer is reduced to a certain value or less. It has been found that accident and safety can be significantly improved.

That is, the assembly type roll for hot plate rolling of the present invention shrink-fits a shaft member with a composite sleeve having an outer layer diffusion-bonded to the outer periphery of a hollow cylindrical inner layer made of cast steel, forged steel or graphite cast steel. Wherein the outer layer is obtained by sintering a high-speed steel alloy powder by a hot isostatic pressing method, and the stress in the circumferential direction of the roll in the outer layer after shrink fitting is − It is characterized in that the stress in the radial direction of the roll in the outer layer is +100 MPa or less and the elongation of the inner layer is 1% or more. Here, the sign-of stress represents compression, and + represents tension. Further, in the assembling roll for hot plate rolling of the present invention, it is preferable to apply a compressive stress in which the stress in the roll radial direction in the inner layer gradually decreases from the inner surface of the sleeve toward the outer diameter.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION In the manufacturing process of a composite sleeve roll, residual stress is generated by heat treatment such as quenching and tempering, and difference in thermal expansion coefficient and transformation characteristic between an outer layer and an inner layer during HIP sintering. For example, when heat treatment is performed, the inner layer, which is transformed at a higher temperature with respect to the outer layer, undergoes elasto-plastic deformation due to being constricted by the untransformed outer layer during the transformation expansion. Will be higher. When the transformation expansion of the inner layer is completed, the internal stress of the inner layer is small due to plastic deformation, but when the roll is further cooled, the outer layer, which has not been transformed, undergoes transformation expansion. In the process of transformation and expansion of the outer layer, the dimensions of the outer layer in the axial, circumferential, and radial directions tend to be relatively larger than those of the inner layer. The load of the outer layer tries to balance. As a result, the inner layer is pulled in the axial, circumferential, and radial directions by the outer layer, while the outer layer is compressed in the axial and circumferential directions and is pulled in the radial direction.

In the outer layer, it is desirable to keep the circumferential and axial compressive stresses high in order to make the thermal cracks during rolling bite shallow, but the higher the circumferential and axial compressive stresses, the more radial direction Since the tensile stress of the outer layer increases, the risk of the outer layer peeling increases. Therefore, it is necessary to suppress the tensile stress in the radial direction as small as possible.

The outer layer has a compressive stress in the circumferential direction of the roll of 20.
If it is below 0MPa, thermal cracks are likely to enter deeply, and 600M
If it exceeds Pa, it is easy to peel off, so that the stress in the roll circumferential direction in the outer layer is preferably in the range of -600 to -200 MPa. A more preferable roll circumferential stress is −40.
0 to -250 MPa. On the other hand, if the stress in the outer layer in the radial direction of the roll exceeds +100 MPa, cracks easily develop and peeling easily occurs even when no rolling load is applied, which is not preferable.

In the present invention, the outer layer is made of a high-speed alloy material having excellent wear resistance and surface roughening resistance, and the inner layer is made of a tough material having an elongation of 1% or more such as cast steel, forged steel or graphite cast steel.

[0017]

EXAMPLE A ring sleeve made of forged steel corresponding to SCM440 having an elongation of 1% or more was used as an inner layer, and a composite sleeve having an outer layer formed by sintering and diffusion-bonding a high-speed alloy powder by the HIP method on the outer periphery was formed. Then, the composite sleeve was fitted to a forged steel roll shaft by shrink fitting to produce a composite roll having an integrated assembly structure. The specifications of this roll are as follows: body outer diameter φ415 mm × length 900 mm, boundary diameter between outer layer and inner layer φ272 mm, sleeve inner diameter φ132 mm, shrink fit rate 1/1000.

As a result of trying various quenching methods and conditions for this roll, it was found that the residual stress distribution of the present invention can be obtained under the following conditions. That is, low- and medium-frequency quenching is performed at 1080 ° C., and then 2 to 500-550 ° C.
Tempered several times. Next, as a result of measuring the stress in the outer layer of this roll by the sax method, the stress in the circumferential direction of the roll in the outer layer was -250 MPa on the outer layer surface, and a maximum of -3 in the inner layer.
00 MPa was measured. Further, in consideration of the fact that the compressive stress in the radial direction due to shrink fitting is added in the assembling state by shrink fitting, the stress in the roll radial direction in the outer layer is up to +7.
It was 0 MPa. This stress distribution is shown in FIG. Also,
As shown in FIG. 2, heavy turning was performed with a parting-off tool having a 90-degree acute angle at the center of the body of the roll, and the presence or absence of peeling from the tool tip corner was examined. The roll did not peel.
This test was conducted in order to examine the degree of peeling tendency in the outer layer, and empirically that the composite roll having a residual stress distribution that does not peel in this test has excellent peeling resistance even in an actual rolling mill. Has been verified. On the other hand, as a comparative example, a radial stress of 1
In the case of 30 MPa, as shown in FIG. 2, when the tool tip reached 3 mm before the boundary layer, peeling occurred from the tool tip corner as a starting point.

According to these results, the roll of the present invention has a predetermined circumferential compressive stress applied to the outer layer.
Since the thermal crack is suppressed to a shallow level, and a predetermined radial tensile stress and a predetermined circumferential stress that are not excessive are applied to the outer layer, the growth rate of the crack is suppressed. as a result,
Exfoliation hardly occurs even when a rolling load is applied, and furthermore, it can be expected that remarkable improvement in safety against exfoliation when no load is applied can be obtained.

As a result of using the roll of the present invention as a working roll of an actual continuous hot-sheet finishing rolling mill, as compared with a smelted high-speed roll, the surface roughness resistance was 2.3 times and the wear resistance was 2.7 times. The effect was obtained.

[0021]

The assembled roll for hot rolling according to the present invention has a predetermined circumferential compressive stress applied to the outer layer made of a high-speed sintered alloy, so that the thermal crack that develops into spalling is shallow. The amount of roll grinding for suppressing cracks and eliminating cracks is reduced. In addition, since a predetermined radial tensile stress and a predetermined circumferential stress that are not excessive are applied to the outer layer, the growth rate of the crack is suppressed. As a result, it is possible to provide a roll in which peeling hardly occurs even when a rolling load is applied, and further, the safety with respect to peeling under no load is significantly improved.

[Brief description of the drawings]

FIG. 1 is a stress distribution diagram relating to an assembling roll for rolling according to a first embodiment of the present invention.

FIG. 2 is a conceptual diagram showing a method of checking the presence or absence of peeling from a tool tip corner according to the present invention.

Claims (2)

[Claims] 1. A hot roll assembly type roll obtained by shrink-fitting a shaft with a composite sleeve having an outer layer diffusion-bonded to an outer periphery of a hollow cylindrical inner layer made of cast steel, forged steel or graphite cast steel, The outer layer is obtained by sintering a high-speed alloy powder by a hot isostatic pressing method, and the stress in the circumferential direction of the roll in the outer layer after shrink fitting is −600 to −200 MPa,
Assembling roll for hot strip rolling excellent in accident resistance, abrasion resistance and surface roughening resistance, characterized in that stress in the roll radial direction in the outer layer is +100 MPa or less and elongation of the inner layer is 1% or more. . 2. The stress in the roll radial direction in the inner layer is:
2. The assembly type for hot strip rolling according to claim 1, wherein a compressive stress that gradually decreases from the inner surface of the sleeve toward the outer diameter is added. roll.