JP3783408B2 - Assembling roll for hot plate rolling with excellent accident resistance, wear resistance, and rough skin resistance - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an assembly for hot rolling, in which a composite sleeve in which an outer layer made of a sintered alloy of high-speed powder is formed on the outer periphery of a hollow cylindrical inner layer made of cast steel, forged steel or graphite cast steel is shrink-fitted to a shaft. More particularly, the present invention relates to an assembly roll for hot plate rolling suitable as an operation roll for a continuous hot sheet finishing mill because it has excellent accident resistance, wear resistance, and rough skin resistance.
[0002]
[Prior art]
In hot plate rolling rolls, the demand for wear resistance and rough skin resistance is increasing in order to reduce roll costs and improve the quality of rolled plates, and continuous casting with an outer layer made of high-speed alloy material. Application of a built-up roll (W088 / 07594), a centrifugal casting roll whose outer layer is made of a high-speed alloy material, and the like are progressing, but the current situation is that the demand has not been sufficiently met.
[0003]
As a further wear-resistant and rough skin-resistant material, a high-speed sintered alloy by hot isostatic pressing (HIP) method has attracted 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 shaft of the roll, and a predetermined high-speed alloy powder is filled in the annular space between the shaft and the metal capsule. The entire roll needs to be charged into a HIP furnace and subjected to HIP treatment. In order to charge the entire roll into the HIP furnace, a large roll such as for hot plate rolling needs to use a corresponding large HIP furnace, so the energy cost and the atmospheric cost are extremely high. It was.
[0004]
Therefore, as proposed in Japanese Patent Laid-Open No. 56-69304, a shaft material having a length corresponding to the body of the roll is used, and the metal powder is subjected to HIP treatment around the shaft, and after HIP treatment, There is a method of attaching support portions at both ends of the shaft member by welding or the like. According to this method, the size of the furnace when performing the HIP treatment only needs to be large enough to accommodate the body of the roll, so that an HIP furnace that is large enough to accommodate the entire roll is not required. There is.
[0005]
However, in the above method, the inner layer material needs to have a solid cylindrical shape. The solid cylindrical inner layer is heavier than the hollow cylindrical inner layer and may be limited 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 member by the HIP method is assembled by shrink fitting on a roll shaft member. It is valid.
[0006]
On the other hand, in the recent hot plate rolling method, a large load is applied to the work roll and the maximum contact pressure of the work roll is also increasing, and accidents in rolling operations such as narrowing and biting are inevitable. ing. Due to these accidents during rolling operations, there may be a drawing crack accompanied by thermal cracking or seizure in the roll surface layer.
[0007]
Usually, when a crack occurs, it is used for the next rolling after completely removing the crack by grinding or the like. When used for rolling with a crack left, the crack often develops due to an external force due to rolling. This crack shows a tendency to develop almost in parallel with the surface of the roll after proceeding to the oblique deep part mainly in the circumferential direction opposite to the rotation direction of the roll due to repeated load during rolling. When the crack reaches the critical dimension in this progressing process, it leads to spalling where the roll surface layer part is largely peeled off.
[0008]
[Problems to be solved by the invention]
Therefore, conventionally, in order to suppress the progress of cracks that are the starting point of spalling, a method of constantly applying a roll circumferential and axial compressive stress to the outer layer has been adopted. However, although it is an extremely rare phenomenon, as a phenomenon different from the above-mentioned spalling due to the rolling load, the crack has progressed even in the state where the developed crack remains inside and the rolling load is not applied. It may peel off (called delayed fracture), leaving a safety issue.
[0009]
When the sleeve roll is shrink-fitted to the roll shaft material, it is necessary to set an appropriate shrinkage rate in order to prevent the sleeve roll and the roll shaft material from slipping or breaking the sleeve roll during rolling.
However, when shrink fitting is performed, the stress applied for the purpose described above changes.
[0010]
The present invention has been made in view of such circumstances, and by applying an appropriate residual stress after shrink-fitting, the development of cracks in the outer layer at the time of narrowing or the like is suppressed, and no rolling load is applied. The purpose of the present invention is to provide an assembling roll for hot plate rolling that is superior in accident resistance and safety, which suppresses the development of cracks that cause delayed fracture that occurs in a state, and that is excellent in wear resistance and rough skin resistance. To do.
[0011]
[Means for Solving the Problems]
As a result of diligent research, the inventor of the present invention uses a material having an elongation in the inner layer of the roll, and a hot sleeve formed by shrink-fitting a composite sleeve having an outer layer made of a sintered alloy of high-speed powder on the outer periphery of the inner layer. In the roll-type rolls, the compressive stress in the roll circumferential direction in the outer layer is kept within the specified range, and at the same time, the stress in the roll radial direction in the outer layer can be reduced to a certain value or less so that accident resistance and safety can be significantly improved. I found.
[0012]
That is, the assembly roll for hot plate rolling of the present invention is a heat formed by shrink-fitting 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 to a shaft material. It is an assembly-type roll for hot rolling, and the outer layer is obtained by sintering a high-speed alloy powder by hot isostatic pressing, and the stress in the roll circumferential direction in the outer layer after shrink fitting is −600 to − 200 MPa, the stress in the roll radial direction 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.
[0013]
DETAILED DESCRIPTION OF THE INVENTION
In the manufacturing process of the 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 the outer layer and the inner layer when performing HIP sintering. For example, when heat treatment is performed, the inner layer transformed at a higher temperature than the outer layer is elastically deformed by being tightened by the untransformed outer layer when undergoing transformation expansion, but the higher the temperature at which the inner layer undergoes transformation expansion, the higher the ratio of plastic deformation Becomes higher. At the time 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 that has not been transformed this time undergoes transformation expansion. In the process of transformation expansion of the outer layer, the dimensions of the outer layer in the axial, circumferential, and radial directions tend to be relatively larger than the inner layer. The load on 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 pulled in the radial direction.
[0014]
In the outer layer, we want to keep the circumferential and axial compressive stresses high in order to make the thermal cracks during rolling biting shallow, but the higher the circumferential and axial compressive stresses, the higher the tensile stress in the radial direction. Since the risk of outer layer peeling increases, the radial tensile stress must be kept as small as possible.
[0015]
When the compressive stress in the roll circumferential direction in the outer layer is less than 200 MPa, thermal cracks are likely to enter deeply, and when the compressive stress in the outer layer exceeds 600 MPa, it is easy to peel off. Therefore, the stress in the roll circumferential direction in the outer layer is preferable. A more preferable stress in the roll circumferential direction is −400 to −250 MPa. Further, if the stress in the roll radial direction in the outer layer exceeds +100 MPa, it is not preferable because cracks are likely to develop even in a state where no rolling load is applied, and peeling easily occurs.
[0016]
In the present invention, the outer layer is made of a high-speed alloy material excellent in wear resistance and rough skin 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 forged steel ring body equivalent to SCM440 having an elongation of 1% or more was used as the inner layer, and a composite sleeve having an outer layer formed by sintering and diffusion bonding high-speed alloy powder by the HIP method on the outer periphery thereof was formed. Then, this composite sleeve was fitted to a roll shaft material made of forged steel by shrink fitting to manufacture 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.
[0018]
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, surface low and medium frequency quenching was performed at 1080 ° C., and then tempering was performed twice at 500 to 550 ° C. Next, as a result of measuring the stress in the outer layer of this roll by the Sachs method, the stress in the roll circumferential direction in the outer layer was measured at -250 MPa on the outer layer surface, and at maximum -300 MPa in the outer layer. In consideration of the fact that the compressive stress in the radial direction due to shrink fitting is taken into account in the assembled state by shrink fitting, the stress in the roll radial direction in the outer layer was +70 MPa at the maximum. This stress distribution is shown in FIG.
Also, as shown in FIG. 2, heavy turning was performed with a parting tool having an acute angle of 90 degrees in 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 to examine the degree of peeling tendency in the outer layer, and it has been empirically found that a composite roll having a residual stress distribution that does not peel by this test has excellent peeling resistance even in an actual rolling mill. It has been confirmed. On the other hand, as a comparative example, a roll having the same size and a radial stress of 130 MPa causes peeling when the tool tip reaches 3 mm before the boundary layer as shown in FIG. It was.
[0019]
From these results, since the roll of the present invention has a predetermined circumferential compressive stress applied to the outer layer, the thermal crack is suppressed shallow, and the outer layer has a predetermined radial tensile stress and a predetermined Since the circumferential stress is applied, the crack growth rate is suppressed. As a result, it is difficult to cause separation even when the rolling load is applied, and it can be sufficiently expected that the safety is remarkably improved with respect to separation when no load is applied.
[0020]
As a result of using the roll of the present invention as an operating roll of an actual continuous hot sheet finishing mill, the surface roughness resistance is 2.3 times and the wear resistance is 2.7 times as compared with the melted high speed roll. Obtained.
[0021]
【The invention's effect】
In the prefabricated roll for hot rolling of the present invention, a predetermined circumferential compressive stress is applied to the outer layer made of a high-speed sintered alloy, so that thermal cracks that develop into spalling are suppressed shallowly, and cracks are prevented. The amount of roll grinding to be eliminated decreases. In addition, since a predetermined radial tensile stress and a predetermined circumferential stress that are not excessive are applied to the outer layer, the crack growth rate is suppressed. As a result, it is possible to provide a roll that hardly peels even when a rolling load is applied and that has significantly improved safety against peeling when no load is applied.
[Brief description of the drawings]
BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a stress distribution diagram related to a rolling assembly type roll according to Example 1 of the present invention.
FIG. 2 is a conceptual diagram showing a method for examining the presence or absence of peeling from a tool tip corner according to the present invention.

Claims (1)

  An assembly roll for hot rolling, in which 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 is shrink-fitted to a shaft material, the outer layer being a high-speed roll The alloy powder is sintered by hot isostatic pressing, the stress in the roll circumferential direction in the outer layer after shrink fitting is -600 to -200 MPa, the stress in the roll radial direction in the outer layer is +100 MPa or less, An assembly type roll for hot plate rolling excellent in accident resistance, wear resistance, and rough skin resistance, characterized in that the elongation of the inner layer is 1% or more.

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