Work roll for rolling, manufacturing method for work roll for rolling, temper rolling method for metallic band, and manufacturing method for metallic band

Abstract

To provide a work roll for rolling that can correct a shape of a metallic band by applying proper expansion, in temper rolling, although the metallic band is a high-strength metallic band whose tensile strength is above 1310 MPa.SOLUTION: The work roll for rolling comprises a trunk part having a ceramic whose young's modulus is above 350 GPa on a surface part thereof and a chromium plated layer formed on an outer peripheral surface of the trunk part, where a thickness of the chromium plated layer is 5 μm or more and 30 μm or less, arithmetic average roughness Ra of the outer peripheral surface of the chromium plated layer is 4.0 μm or more and 6.0 μm or less, and skewness Rsk is -0.4 or more and 0.1 or less.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a rolling work roll, a method for manufacturing a rolling work roll, a method for temper rolling a metal strip, and a method for manufacturing a metal strip. [Background technology]

[0002] In recent years, the need for lighter automobiles due to environmental regulations has increased, and the demand for high-strength steel sheets is growing. High-strength steel sheets are manufactured by heat treating cold-rolled steel sheets using continuous annealing equipment or continuous hot-dip galvanizing equipment to appropriately control the microstructure of the steel sheets. The heat-treated steel sheets are then subjected to temper rolling to give them an elongation of 2.0% or less, which flattens the shape of the steel sheets and gives the steel sheets an appropriate roughness on their surfaces.

[0003] However, since high-strength steel sheets having a tensile strength exceeding 980 MPa after a heat treatment process have a high yield stress, the rolling load becomes too large in a normal temper rolling machine, which can cause a problem that the elongation required for shape correction cannot be ensured. In response to this problem, Patent Document 1 discloses a temper rolling method for a steel strip, in which temper rolling is performed with an elongation of 0.1% or more on a steel strip having a yield strength of 340 MPa or more using a rolling work roll having an average surface roughness Ra of 3.0 to 10.0 μm.

[0004] Patent Document 2 discloses a temper rolling machine using a rolling work roll having a Young's modulus of 500 GPa or more at the surface layer and a Vickers hardness of 1050 HV or more. According to Patent Document 2, by using the rolling work roll, it is possible to impart an elongation rate that can correct the shape even to a high-strength steel strip having a tensile strength of 980 MPa or more.

[0005] Patent Document 3 discloses a temper rolling method for temper rolling a metal strip having a 0.2% proof stress exceeding 350 MPa using a dull work roll having a roll diameter of 1000 mm or more and 1400 mm or less and a Young's modulus of the roll surface layer of 450 GPa or more. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2008-173684 A [Patent Document 2] JP 2017-119303 A [Patent Document 3] JP 2011-189404 A Summary of the Invention [Problem to be solved by the invention]

[0007] In the method described in Patent Document 1, the arithmetic mean roughness Ra of the rolling work roll is set in the range of 3.0 to 10.0 μm, and the steel strip is temper rolled. However, when temper rolling a steel strip having a tensile strength of 1180 MPa or more, the rolling load becomes large, and there is a problem that the elongation required for shape correction may not be ensured for a steel sheet having a tensile strength of 1310 MPa or more.

[0008] In Patent Document 2, the Young's modulus of the surface layer of the rolling work roll is set to 500 GPa or more, and a high-strength steel sheet having a tensile strength of 980 MPa or more is temper rolled. However, even in this case, there is a problem that the elongation required for shape correction may not be ensured for a steel sheet having a tensile strength of 1310 MPa or more.

[0009] In Patent Document 3, a dull work roll having a Young's modulus of 450 GPa or more is used as a work roll for temper rolling. However, even in this case, there is a problem that the elongation required for shape correction may not be ensured for a steel sheet having a tensile strength of 1310 MPa or more.

[0010] The present invention has been made to solve the above problems, and an object of the present invention is to provide a rolling work roll capable of imparting an appropriate elongation to a high-strength metal strip having a tensile strength of 1310 MPa or more in temper rolling to correct the shape of the metal strip. Another object of the present invention is to provide a method for manufacturing a rolling work roll, a method for temper rolling a metal strip using the rolling work roll, and a method for manufacturing a metal strip the shape of which has been flattened by temper rolling. [Means for solving the problem]

[0011] The means for solving the above problems are as follows. [1] A work roll for rolling, comprising: a barrel portion having a ceramic having a Young's modulus of 350 GPa or more in a surface layer portion; and a chrome plating layer formed on an outer peripheral surface of the barrel portion, wherein the thickness of the chrome plating layer is 5 μm or more and 30 μm or less, the arithmetic mean roughness Ra of the outer peripheral surface of the chrome plating layer is 4.0 μm or more and 6.0 μm or less, and the skewness Rsk is -0.4 or more and 0.1 or less. [2] A method for manufacturing a work roll for rolling, comprising: a dulling step of performing shot-dulling on an outer peripheral surface of a barrel portion having a ceramic surface layer with a Young's modulus of 350 GPa or more; and a plating layer forming step of forming a chrome plating layer on the outer peripheral surface of the barrel portion that has been shot-dulled, wherein in the dulling step, dulling conditions are set according to a thickness of the chrome plating layer so that the arithmetic mean roughness Ra of the outer peripheral surface after the chrome plating layer is formed in the plating layer forming step is 4.0 μm or more and 6.0 μm or less, and the skewness Rsk is -0.4 or more and 0.1 or less. [3] The method for manufacturing a rolling work roll according to [2], wherein the average particle size of the shot particles used in the shotdulling is 250 μm or more and 710 μm or less. [4] The method for manufacturing a rolling work roll according to [2] or [3], wherein the shot dulling is performed using an air blast type dulling device and the projection pressure of the shot particles is set to 0.3 MPa or more and 0.7 MPa or less. [5] A method for temper rolling a metal strip, comprising temper rolling the metal strip using the rolling work roll according to [1]. [6] A method for temper rolling a metal strip, comprising temper rolling the metal strip using a rolling work roll manufactured by the method for manufacturing a rolling work roll according to any one of [2] to [4]. [7] A method for producing a metal strip, comprising the steps of: producing a metal strip having a tensile strength of 1,310 MPa or more by using the method for temper rolling a metal strip according to [5]. [8] A method for producing a metal strip, comprising the steps of: producing a metal strip having a tensile strength of 1,310 MPa or more by using the method for temper rolling a metal strip according to [6]. Effect of the Invention

[0012] By using the rolling work roll according to the present invention, it is possible to provide a suitable elongation by temper rolling and correct the shape of a high-strength metal strip, even if the metal strip has a tensile strength of 1310 MPa or more. Moreover, by temper rolling with the rolling work roll, it is possible to produce a metal strip with a flattened shape, even if the metal strip has a high strength of tensile strength of 1310 MPa or more. [Brief description of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic diagram showing an example of a temper rolling mill equipped with a rolling work roll according to this embodiment. [Diagram 2] FIG. 2 is a schematic diagram showing an example of an installation of a temper rolling mill provided in a metal strip production line. [Diagram 3] FIG. 3 is a schematic diagram of a rolling work roll 12a before a chrome plating layer is formed. [Figure 4] FIG. 4 is a schematic diagram of a rolling work roll on which a chrome plating layer is formed. [Diagram 5] FIG. 5 is a schematic cross-sectional view of the outer circumferential surface of the chrome plating layer. [Figure 6] FIG. 6 is a schematic cross-sectional view showing a state in which the convex portion on the outer peripheral surface of the chrome plating layer is pressed into the surface of the metal strip. [Figure 7] FIG. 7 is a schematic cross-sectional view of the outer circumferential surface of the chrome plating layer. [Figure 8]FIG. 8 is a schematic cross-sectional view showing a state in which the irregularities on the outer peripheral surface of the chrome plating layer are pressed into the surface of the metal strip. [Figure 9] FIG. 9 is a schematic diagram of a shot blasting machine, which is an example of a shot blasting machine for performing shot blasting. [Figure 10] FIG. 10 is a schematic diagram showing the state of projections and recesses formed on the surface of the workpiece by shot particles. [Figure 11] FIG. 11 is a graph showing an example of the effect of the shot particle size and air pressure, which are the processing conditions of shot blasting, on the arithmetic mean roughness Ra and the skewness Rsk. [Figure 12] FIG. 12 is a graph showing the relationship between the thickness of a chrome plating layer and the surface roughness of the outer circumferential surface of the plating layer. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] The present invention will be specifically described below through the embodiments of the present invention. The following embodiments are preferred examples of the present invention, and the present invention is not limited to these embodiments.

[0015] The rolling work roll according to this embodiment is used as a work roll of a temper rolling mill. FIG. 1 is a schematic diagram showing an example of a temper rolling mill 10 (hereinafter, may be referred to as "rolling mill 10") equipped with the rolling work roll according to this embodiment. FIG. 1(a) is a schematic side view of the rolling mill 10, and FIG. 1(b) is a schematic front view of the rolling mill 10. The rolling mill 10 is used to temper roll a high-strength metal strip having a tensile strength of 1310 MPa or more as the metal strip.

[0016] The rolling mill 10 has as its main components a pair of rolling work rolls (hereinafter, sometimes referred to as "work rolls") 12a, 12b, backup rolls 14a, 14b, and a housing 16. The work rolls 12a, 12b are rolls that come into direct contact with a metal strip 100, which is a material to be rolled, and apply a reduction pressure. The backup rolls 14a, 14b are provided to support the pair of work rolls 12a, 12b from above and below and to suppress deflection of the work rolls. One end of the pair of work rolls 12a, 12b is connected to a driving motor via a coupling or a reducer, and the work rolls 12a, 12b are rotated by the driving motor. However, depending on the rolling mill, the backup rolls 14a, 14b may be rotated by the driving motor to rotate the work rolls 12a, 12b. A load detector (load cell) 20 is provided between the housing 16 of the rolling mill 10 and the bearing housings 18 of the backup rolls 14a, 14b. The load detector 20 detects the rolling load of the rolling mill 10. A reduction device 21 is provided above the housing 16. The reduction device 21 adjusts the roll gap, which is the gap between the work rolls 12a, 12b, by vertically displacing the bearing housings 18. In the rolling mill 10, the pair of work rolls 12a, 12b that directly contact and reduce the metal strip 100 are rolling work rolls according to this embodiment.

[0017] The rolling mill 10 shown in Fig. 1 is provided in a production line for a metal strip 100. Fig. 2 is a schematic diagram showing an example of an installation of a temper rolling mill provided in a production line for the metal strip 100. The rolling mill 10 is provided, for example, downstream of a continuous annealing line for the metal strip 100, and performs temper rolling on the metal strip 100 that has been heat-treated through a heating zone, a soaking zone, and a cooling zone. An entry bridle roll 22, an entry tensiometer 24, an exit tensiometer 26, and an exit bridle roll 28 are provided before and after the rolling mill 10.

[0018] When temper rolling the metal strip 100 using the rolling mill 10, the heat-treated metal strip 100 is rolled at a predetermined elongation rate. The elongation rate (also called elongation rate) means the elongation rate of the metal strip 100 before and after rolling, and is defined as the increase rate of the length of the metal strip 100 before and after temper rolling. The elongation rate is measured by the difference in peripheral speed between the entry bridle roll 22 and the exit bridle roll 28. Under conditions where the elongation rate is small, it may be the same as the reduction rate, which is the rate of change in the plate thickness. In this case, temper rolling may be performed using the reduction rate as an index instead of the elongation rate.

[0019] When a conventional rolling work roll is installed in the rolling mill 10 shown in Figures 1 and 2 to perform temper rolling on a metal strip having a tensile strength of 1310 MPa or more, the rolling load required to impart an appropriate elongation to the metal strip exceeds the equipment specifications of the rolling mill 10. For this reason, when a conventional rolling work roll is used, there are cases where the elongation required for shape correction of the metal strip cannot be ensured. In contrast, when the rolling work rolls 12a, 12b according to the present embodiment are installed, the increase in the rolling load in the rolling mill 10 is suppressed, so that an appropriate elongation can be imparted even to a metal strip having a tensile strength of 1310 MPa or more.

[0020] Next, a rolling work roll and its manufacturing method according to this embodiment will be described. Fig. 3 is a schematic diagram of the rolling work roll 12a before the chrome plating layer 34 is formed. Fig. 3(a) is a side view, and Fig. 3(b) is a cross-sectional view taken along line AA in Fig. 3(a). Since the rolling work roll 12a and the rolling work roll 12b are the same work roll, the following description will be given using the rolling work roll 12a.

[0021] Before forming the chrome plating layer 34, the rolling work roll 12a has a structure in which a body 32 is fixed to a shaft portion 30. The body 32 is made of ceramics having a Young's modulus of 350 GPa or more. The ceramics are sintered bodies mainly composed of inorganic compound materials, for example, cemented carbide containing 70 to 86% by mass of tungsten carbide (WC) and the remainder being cobalt (Co). This forms the body 32 whose surface layer has a Young's modulus of 350 GPa or more. The shaft portion 30 is made of forged steel or cast steel containing chromium and some vanadium as its component composition.

[0022] Next, shot-dulling is performed on the outer peripheral surface 32a of the body, the surface of which has a Young's modulus of 350 GPa or more. This process is the dulling step. As a result, microscopic irregularities are imparted to the outer peripheral surface 32a of the body. Shot-dulling is a processing method in which metal or ceramic particles are sprayed toward and collided with the surface of the workpiece to form microscopic irregularities on the surface of the workpiece.

[0023] The metal or ceramic particles collided with the workpiece in shot peening are called shot particles. There are spherical and polygonal shot particles, and either type of shot particle can be used. Spherical particles are often produced by gas atomization, and the surface tension of the molten metal gives them a shape close to a sphere. When spherical particles are used as shot particles, residual stress is formed on the surface of the workpiece. This residual stress becomes compressive residual stress, and is sometimes called shot peening.

[0024] On the other hand, polygonal shot particles are manufactured by a water atomization method or a pulverization method. When polygonal particles are used as the shot particles, microscopic irregularities are formed on the surface of the workpiece while removing a part of the surface of the workpiece. As the polygonal shot particles, cut wires obtained by cutting metal wire into small pieces or sand such as silica sand extracted from minerals (sometimes called sandblasting) may be used (sometimes called sandblasting). In the shotdulling process in the manufacturing method for a rolling work roll according to this embodiment, any of the above shot particles may be used.

[0025] The average particle size of the shot particles used in shotdulling is preferably 250 μm or more and 710 μm or less. If the average particle size of the shot particles is less than 250 μm, it is difficult to impart a sufficient arithmetic mean roughness Ra to the surface of the rolling work roll, which is not preferable. If the average particle size of the shot particles exceeds 710 μm, the arithmetic mean roughness Ra imparted to the surface of the rolling work roll becomes too large, which is not preferable. In addition, shot particles with a large particle size repeatedly collide with the surface of the rolling work roll, which may crush the protrusions and reduce the skewness Rsk to less than -0.4, which is not preferable.

[0026] The shot particles used in the shotdulling process are preferably hard shot particles such as zirconia, alumina, black silicon carbide, diamond, etc., and the Vickers hardness of these particles is preferably 1800 HV or more. In order to impart relatively large irregularities to the outer peripheral surface 32a of the body, the shot particles are collided with the outer peripheral surface 32a of the body at a relatively high speed, so that from the viewpoint of durability, it is preferable to use hard shot particles.

[0027] On the other hand, in addition to shot dipping, there are other methods for forming microscopic irregularities on the outer peripheral surface 32a of the body, such as electric discharge machining, laser machining, and electron beam machining. However, in methods such as electric discharge machining, laser machining, and electron beam machining, which form irregularities by partially melting the surface of the workpiece, the outer peripheral surface 32a of the body is thermally affected, and microscopic cracks due to the thermal effect are generated on the outer peripheral surface 32a of the ceramic body. For this reason, shot dipping, which is less affected by heat, is used in this embodiment.

[0028] FIG. 4 is a schematic diagram of a rolling work roll 12a on which a chrome plating layer 34 is formed. FIG. 4(a) is a side view, and FIG. 4(b) is a BB cross-sectional view of FIG. 4(a). In the manufacture of the rolling work roll 12a according to this embodiment, the chrome plating layer 34 is formed on the outer peripheral surface 32a of the barrel portion that has been subjected to shotdulling. In this case, the shotdulling processing is performed under processing conditions set according to the thickness of the chrome plating layer 34 so that the arithmetic mean roughness Ra of the outer peripheral surface 34a of the chrome plating layer is 4.0 μm or more and 6.0 μm or less, and the skewness Rsk is −0.4 or more and 0.1 or less. A specific method for setting the shotdulling processing conditions will be described later.

[0029] The chrome plating layer 34 formed on the outer peripheral surface 32a of the shotdulled body is a hard chrome plating layer. The hard chrome plating layer is applied mainly for the purpose of ensuring wear resistance. The hard chrome plating layer can be formed by immersing the body 32 in a plating bath whose main component is chromic anhydride (chromium trioxide (CrO3)) with a trace amount of sulfuric acid added as a catalyst. This process is the plating layer formation step. The hardness of the hard chrome plating layer is 750HV or more and 1000HV or less.

[0030] The chrome plating layer 34 is formed on the outer peripheral surface 32a of the barrel portion because a film having a lower hardness than the barrel portion 32 is formed, which prevents the ceramic having a high hardness from contacting the backup roll, thereby reducing damage to the backup roll that contacts the rolling work roll. In addition, the use of hard chrome plating can suppress wear of the rolling work roll 12a that directly contacts the metal strip. From this viewpoint, in this embodiment, the thickness of the chrome plating layer 34 formed on the outer peripheral surface 32a of the barrel portion is preferably 5 μm or more. On the other hand, if the thickness of the chrome plating layer 23 is thicker than 30 μm, the microscopic unevenness of the outer peripheral surface 32a of the barrel portion provided by shotdulling will change due to the formation of the chrome plating layer 34, making it difficult to obtain the target arithmetic mean roughness Ra and skewness Rsk. For this reason, the thickness of the chrome plating layer 23 is preferably 30 μm or less. From the above viewpoint, the thickness of the chrome plating layer 23 is more preferably 5 μm or more and 10 μm or less.

[0031] In this embodiment, the conditions of shot dipping are set so that the arithmetic mean roughness Ra of the outer peripheral surface of the chrome plating layer formed on the outer peripheral surface of the rolling work roll 12a is 4.0 μm or more and 6.0 μm or less, and the skewness Rsk is -0.4 or more and 0.1 or less. As a result, the surface roughness of the rolling work roll 12a becomes arithmetic mean roughness Ra of 4.0 μm or more and 6.0 μm or less, and skewness Rsk of -0.4 or more and 0.1 or less.

[0032] The arithmetic mean roughness Ra and skewness Rsk are line roughness values ​​defined in JIS B 0601:2013. The arithmetic mean roughness Ra is an index that represents the average height of the roughness curve in the reference length. The skewness Rsk is defined by the following formula (1).

[0033]

number

[0034] Skewness Rsk is known as a parameter closely related to the friction and wear phenomenon of the contacting sliding surface. Skewness Rsk is an index that indicates the symmetry of the convex and concave portions of an uneven surface, and is zero if the statistical distribution of the convex and concave portions is normal, and Rsk is large on a surface that is mainly made up of convex portions, and small on a surface that is mainly made up of concave portions. It is preferable to calculate the arithmetic mean roughness Ra and skewness Rsk from the line roughness measured in the axial direction of the roll barrel.

[0035] As described above, the rolling work roll 12a according to this embodiment uses ceramics with a Young's modulus of 350 GPa or more for the trunk portion 32. As a result, even if the rolling work roll 12a receives a large contact pressure from the metal strip 100 during temper rolling, flattening deformation of the rolling work roll 12a is suppressed, and therefore, even when temper rolling is performed on a high-strength metal strip 100, an excessively large rolling load is suppressed.

[0036] In addition, by subjecting the outer peripheral surface 32a of the body portion to shot dipping, the arithmetic mean roughness Ra of the outer peripheral surface 34a of the chrome plating layer is set to 4.0 μm or more and 6.0 μm or less, and the skewness Rsk is set to -0.4 or more and 0.1 or less. In this way, by appropriately controlling the form of the microscopic irregularities on the surface of the rolling work roll 12a, it becomes possible to perform temper rolling while suppressing an increase in the rolling load, even for high-strength metal strips having a tensile strength of 1310 MPa or more.

[0037] Next, the surface roughness of the rolling work roll 12a will be described, first in terms of the arithmetic mean roughness Ra. The outer peripheral surface 34a of the chrome plating layer of the rolling work roll 12a according to this embodiment has a surface roughness of arithmetic mean roughness Ra of 4.0 μm or more and 6.0 μm or less. This promotes the pressing of the protrusions formed on the outer peripheral surface 34a of the chrome plating layer into the surface of the metal strip 100 during temper rolling, and the pressing of the protrusions provides an effect of elongating the metal strip 100 as a whole (elongation effect).

[0038] FIG. 5 is a schematic cross-sectional view of the outer peripheral surface 34a of the chrome plating layer. FIG. 5(a) shows a rolling work roll with Ra≧4.0 μm, and FIG. 5(b) shows a rolling work roll with Ra<4.0 μm. As shown in FIGS. 5(a) and 5(b), the larger the arithmetic mean roughness Ra, the greater the height of the convex portions formed on the outer peripheral surface. Note that the schematic cross-sectional views shown in FIGS. 5 to 8 are depicted with a larger magnification in the vertical direction than in the horizontal direction to make it easier to understand the shape of the concaves and convexes. For this reason, they are depicted as having a larger inclination than the inclination of the actual concaves and convexes.

[0039] Fig. 6 is a schematic cross-sectional view showing a state in which the protrusions on the outer peripheral surface 34a of the chrome plating layer are pressed into the surface of a metal strip 100. Fig. 6(a) shows the state of the metal strip 100 when a rolling work roll with Ra ≧ 4.0 μm is used, and Fig. 6(b) shows the state of the metal strip 100 when a rolling work roll with Ra < 4.0 μm is used.

[0040] As shown in FIG. 6(a), when the arithmetic mean roughness Ra is 4.0 μm or more, even if the convex portions on the outer peripheral surface are pressed into the surface of the metal band 100, there is no interference between adjacent plastic deformation regions (plastically strained portions). This suppresses an increase in resistance to the pressing of the convex portions, and therefore suppresses an increase in the rolling load. In contrast, when the arithmetic mean roughness Ra is less than 4.0 μm, the intervals between the convex portions formed on the outer peripheral surface become smaller, and the area of ​​the plastic deformation regions (plastically strained portions) formed near the surface layer of the metal band 100 becomes larger. This significantly increases the resistance to the pressing of the convex portions, and therefore the increase in the rolling load becomes significant.

[0041] Thus, in the rolling work roll 12a according to this embodiment, the calculated average roughness Ra is set to 4.0 μm or more to suppress an increase in the rolling load. However, if the arithmetic average roughness Ra becomes too large, wear of the protruding parts of the outer peripheral surface becomes more likely to progress, and it becomes difficult to perform shot dulling on the outer peripheral surface 32a of the body portion to increase the arithmetic average roughness Ra of the outer peripheral surface 34a of the chrome plating layer. For this reason, the arithmetic average roughness Ra imparted to the outer peripheral surface 34a of the chrome plating layer needs to be 4.0 μm or more and 6.0 μm or less.

[0042] Next, the skewness Rsk will be described. The outer peripheral surface 34a of the chrome plating layer of the rolling work roll 12a according to this embodiment has a surface roughness with a skewness Rsk of -0.4 or more and 0.1 or less. This promotes the pressing of the protrusions formed on the outer peripheral surface into the surface of the metal strip 100 during temper rolling, and promotes the elongation effect of the metal strip 100 due to the pressing of the protrusions.

[0043] Fig. 7 is a schematic cross-sectional view of the outer peripheral surface 34a of the chrome plating layer. Fig. 7(a) shows a rolling work roll with a skewness Rsk of -0.4 or more, and Fig. 7(b) shows a rolling work roll with a skewness Rsk of less than -0.4. When the skewness Rsk is -0.4 or more, the convex portions on the surface have sharp tips and a curled (cirque) shape with a long bottom length of the valley. On the other hand, when the skewness Rsk is less than -0.4, the convex portions on the outer peripheral surface have small sharp tips and a plateau shape with a long top length of the convex portions.

[0044] Fig. 8 is a schematic cross-sectional view showing a state in which the irregularities on the outer peripheral surface 34a of the chrome plating layer are pressed into the surface of a metal strip 100. Fig. 8(a) shows the state of the metal strip 100 when a rolling work roll with a skewness Rsk of -0.4 or more is used, and Fig. 8(b) shows the state of the metal strip 100 when a rolling work roll with a skewness Rsk of less than -0.4 is used.

[0045] When the skewness Rsk is -0.4 or more, the convex parts on the outer peripheral surface are easily pressed into the surface of the metal band 100, there is no interference between adjacent plastic deformation regions, and resistance to the pressing of the convex parts is suppressed, so that an increase in the rolling load is suppressed. In contrast, when the skewness Rsk is less than -0.4, the contact area between the convex parts on the outer peripheral surface and the surface of the metal band 100 becomes large, so that interference between adjacent plastic deformation regions is likely to occur. As a result, resistance to the pressing of the convex parts increases significantly, so that the increase in the rolling load becomes noticeable.

[0046] Thus, in the rolling work roll 12a according to this embodiment, the skewness Rsk is set to -0.4 or more to suppress an increase in the rolling load. However, if the skewness Rsk becomes too large, the wear of the protruding parts of the surface becomes more likely to progress. In addition, if the skewness Rsk is made large, there is a risk that microscopic cracks will occur on the outer peripheral surface 32a of the body part in the dulling step. For this reason, the skewness Rsk imparted to the outer peripheral surface 34a of the chrome plating layer must be -0.4 or more and 0.1 or less, and is preferably -0.2 or more and 0.1 or less. The skewness Rsk imparted to the outer peripheral surface 34a of the chrome plating layer is more preferably 0.0 or more and 0.1 or less. This makes it possible to further suppress an increase in the rolling load.

[0047] If a granular precipitation-type chrome plating method is applied as the dulling method, in which the chrome plating layer 34 is precipitated in granular form on the outer peripheral surface 32a of the body, the convex portions on the surface are formed in a spherical shape, and the skewness Rsk imparted to the outer peripheral surface 34a of the chrome plating layer is less than -0.4. As described above, when the skewness Rsk is less than -0.4, the resistance to the pressing of the convex portions increases, and the increase in the rolling load becomes large. For this reason, the granular precipitation-type chrome plating method is excluded as a dulling method for the rolling work roll 12a according to this embodiment.

[0048] Next, shot blasting, which is a method for dulling a work roll for rolling in this embodiment, will be described. Fig. 9 is a schematic diagram of a shot blasting device 40, which is an example of a shot blasting device for performing shot blasting. The shot blasting device 40 is an air blasting device, and is composed of an air blast nozzle 42 and a projection chamber 44. The air blast nozzle 42 is connected to a shot particle supplying section 48 that supplies shot particles 46 to the air blast nozzle 42. The air blast nozzle 42 is also connected to a compressed air supply system 50 that supplies compressed air from a compressor (not shown).

[0049] The air blast nozzle 42 has an internal shape set so as to accelerate the compressed air supplied from the compressed air supply system 50. The shot particles 46 are accelerated by the compressed air accelerated inside the air blast nozzle 42 and sprayed onto the workpiece. The projection chamber 44 is configured to house the rolling work roll therein and is configured so that the shot particles 46 that are sprayed onto the rolling work roll and scattered do not fly out. The pressure of the compressed air supplied to the air blast nozzle 42 is called the projection pressure or air pressure.

[0050] The air blast type shot blasting machine 40 has a circulation system that collects the shot particles 46 projected in the projection chamber 44 at the bottom of the projection chamber 44 and reuses the shot particles 46. For example, the shot particle supply unit 48 is configured as a cyclone, and is configured to remove shot particles 46 that have been crushed and become small, and supply only shot particles 46 of a certain size or larger to the air blast nozzle 42. On the other hand, the shot particles 46 that have been crushed and become small are separated by the cyclone and collected by a dust collector 52.

[0051] In shot blasting, the microscopic irregularities formed on the surface of the workpiece vary depending on the particle size (average particle size, particle size distribution), material (hardness, Young's modulus) and shape (spherical, polygonal) of the shot particles 46. This is because the particle size, material and shape of the shot particles 46 affect the impact force when they impact the surface of the workpiece and the deformation state of the surface of the workpiece when they impact. In addition, the microscopic irregularities formed on the surface of the workpiece vary depending on the impact speed (projection speed) of the shot particles 46, the projection density (weight or number of shot particles 46 projected per unit area of ​​the workpiece) and the projection time (time for projecting the shot particles 46 onto the workpiece). The impact speed, projection density and projection time affect the impact force when the shot particles 46 impact the surface of the workpiece and the amount of work required to form the irregularities, thereby affecting the deformation state of the surface of the workpiece.

[0052] In shot blasting, which imparts microscopic irregularities to the surface of the rolling work roll 12a, the arithmetic mean roughness Ra of the surface of the rolling work roll can be increased by increasing the momentum imparted to the shot particles 46. In order to increase the momentum imparted to the shot particles 46, shot particles 46 with a large average particle size can be selected and the projection speed of the shot particles 46 can be increased. This increases the impact force of the shot particles 46 colliding with the work roll surface, forming relatively large irregularities. On the other hand, in order to increase the skewness Rsk of the rolling work roll, shot particles 46 with a relatively small average particle size can be selected.

[0053] FIG. 10 is a schematic diagram showing the state of the unevenness formed on the surface of the workpiece by the shot particles 46. FIG. 10(a) shows the case where the particle size of the shot particles 46 is small, and FIG. 10(b) shows the case where the particle size of the shot particles 46 is large. As shown in FIG. 10(a), when the particle size of the shot particles 46 is small, many localized recesses are formed, and an uneven shape with a pointed top is formed. Therefore, the skewness Rsk of the surface of the workpiece becomes large. On the other hand, as shown in FIG. 10(b), when the particle size of the shot particles 46 is large, even if a pointed protrusion is formed on the surface of the workpiece, the top of the protrusion is crushed by the shot particles 46 that collide with later, and the pointed protrusion is unlikely to remain. Therefore, the skewness Rsk of the surface of the workpiece becomes small.

[0054] For the above reasons, in the manufacturing method of the rolling work roll according to the present embodiment, shot particles 46 having an average particle size of 710 μm or less are used as the shot particles 46 to be projected onto the outer peripheral surface 32a of the barrel portion. On the other hand, if the average particle size of the shot particles 46 is too small, the arithmetic mean roughness Ra of the outer peripheral surface 34a after the chrome plating layer 34 is formed may be less than 4.0 μm. For this reason, it is preferable to use shot particles 46 having an average particle size of 250 μm or more and 710 μm or less as the shot particles 46 to be projected onto the outer peripheral surface 32a of the barrel portion. It is more preferable to use shot particles 46 having an average particle size of 250 μm or more and 400 μm or less as the shot particles 46 to be projected onto the outer peripheral surface 32a of the barrel portion. The particle size of the shot particles 46 may be expressed by the number, and in this case, it is preferable to use shot particles 46 having a number size of #24 or more and #60 or less.

[0055] In addition, in order to make the arithmetic mean roughness Ra of the outer peripheral surface 23a after the chrome plating layer 23 is formed 4.0 μm or more, it is preferable to control the projection speed of the shot particles 46 to 200 m / s or more. In order to project the shot particles at a high speed such as a projection speed of 200 m / s or more, it is preferable to use an air blast type shot blasting machine. In this case, the air pressure (projection pressure) for projecting the shot particles should be 0.3 MPa or more. On the other hand, if the air pressure is higher than 0.7 MPa, there is a risk that the projection chamber 44 will be destroyed by erosion. Therefore, the air pressure for projecting the shot particles 46 is preferably 0.3 MPa or more and 0.7 MPa or less.

[0056] FIG. 11 is a graph showing an example of the influence of the particle size of the shot particles 46 and the air pressure, which are processing conditions of the shot shaping process, on the arithmetic mean roughness Ra and the skewness Rsk. As shown in FIG. 11, when the particle size of the shot particles 46 becomes smaller, the arithmetic mean roughness Ra of the microscopic irregularities formed on the outer peripheral surface 32a of the body becomes smaller and the skewness Rsk increases. Also, when the air pressure for projecting the shot particles 46 becomes larger, the arithmetic mean roughness Ra of the microscopic irregularities formed on the outer peripheral surface 32a of the body becomes larger and the skewness Rsk increases. In this way, by controlling the processing conditions of the shot shaping process, the arithmetic mean roughness Ra and the skewness Rsk formed on the outer peripheral surface 32a of the body can be controlled to an appropriate range (the area shown in gray in FIG. 11).

[0057] In this embodiment, the processing conditions for shot densification are set so that the arithmetic mean roughness Ra of the outer peripheral surface 34a of the chrome plating layer after the formation of the chrome plating layer 34 is 4.0 μm or more and 6.0 μm or less, and the skewness Rsk is -0.4 or more and 0.1 or less. Furthermore, it is preferable to set the processing conditions for the shot densification according to the thickness of the chrome plating layer 34. Here, "according to the thickness of the chrome plating layer 34" means that when the shot densification is performed on the outer peripheral surface 32a of the trunk part, the processing conditions are set according to the thickness of the chrome plating layer 34 that is preset according to the manufacturing specifications.

[0058] The thicker the chrome plating layer 34, the less likely the microscopic irregularities formed on the outer peripheral surface 32a of the trunk portion will remain on the outer peripheral surface 34a of the chrome plating layer, and the lower the arithmetic mean roughness Ra and skewness Rsk. The processing conditions for shot dipping on the outer peripheral surface 32a of the trunk portion are set taking into consideration the reduction in arithmetic mean roughness Ra and skewness Rsk corresponding to this thickness.

[0059] Specifically, the reduction amounts ΔRa and ΔRsk of the arithmetic mean roughness Ra and skewness Rsk due to the chrome plating layer 34 are specified in advance according to the thickness of the chrome plating layer 23. Then, at the stage of performing shot blasting on the outer peripheral surface 32a of the trunk portion, the processing conditions may be set so that the arithmetic mean roughness Ra and skewness Rsk obtained by adding the reduction amounts ΔRa and ΔRsk corresponding to the preset thickness of the chrome plating layer 34 to the target arithmetic mean roughness Ra and skewness Rsk are obtained.

[0060] Fig. 12 is a graph showing the relationship between the thickness of the chrome plating layer 34 and the surface roughness of the outer circumferential surface of the plating layer. Fig. 12(a) is a graph showing the relationship between the thickness of the chrome plating layer 34 and the arithmetic mean roughness Ra, and Fig. 12(b) is a graph showing the relationship between the thickness of the chrome plating layer 34 and the skewness Rsk.

[0061] As shown in FIG. 12(a), even if the arithmetic mean roughness Ra of the workpiece before chrome plating is 5.0 μm, when the thickness of the chrome plating layer 34 is 30 μm or more, the arithmetic mean roughness Ra after chrome plating is small. On the other hand, the change in skewness Rsk due to chrome plating behaves differently depending on whether the skewness Rsk on the outer peripheral surface 32a of the trunk is positive or negative. As shown in FIG. 12(b), when the skewness Rsk on the outer peripheral surface 32a of the trunk is positive, when the thickness of the chrome plating layer 34 is 30 μm or more, the skewness Rsk after chrome plating decreases. On the other hand, when the skewness Rsk on the outer peripheral surface 32a of the trunk is negative, when the thickness of the chrome plating layer 34 is 30 μm or more, the skewness Rsk after chrome plating increases.

[0062] In this way, since the arithmetic mean roughness Ra and skewness Rsk change depending on the thickness of the chrome plating layer, if the changes with respect to the thickness are specified in advance, it is possible to set processing conditions such that the arithmetic mean roughness Ra of the outer peripheral surface 34a of the chrome plating layer is 4.0 μm or more and 6.0 μm or less, and the skewness Rsk is -0.4 or more and 0.1 or less.

[0063] By incorporating the rolling work roll 12a according to this embodiment into the rolling mill 10, the rolling mill becomes suitable for temper rolling of a high-strength metal strip 100. In this case, the diameter of the rolling work roll 2 is preferably 300 mm or more and 800 mm or less, similar to the work rolls of a normal temper rolling mill. If the diameter of the rolling work roll 12a is less than 300 mm, the deflection of the rolling work roll increases when the rolling load is high, which may cause the shape of the metal strip 100 to become distorted, which is not preferable. In addition, if the diameter of the rolling work roll 12a is greater than 800 mm, the rolling load increases, which is not preferable because the effect of using the rolling work roll 12a of this embodiment is reduced.

[0064] In this embodiment, one or more rolling mills 10 incorporating the rolling work rolls 12a according to this embodiment are used to perform temper rolling to impart an elongation of 0.1% or more and 0.6% or less to the metal strip. This suppresses an increase in the rolling load during temper rolling, so that even when a rolling mill with normal equipment specifications is used, an elongation of 0.1% or more required for shape correction of the metal strip 100 can be ensured. However, it is preferable that the elongation imparted to a high-strength metal strip is 0.6% or less. If the elongation imparted is greater than 0.6%, excessive strain is imparted to the metal strip 100, which is undesirable because it may cause the elongation (ductility) of the metal strip product to decrease due to work hardening. In addition, if the elongation imparted is greater than 0.6%, the frictional force at the contact interface between the unevenness imparted to the surface of the rolling work rolls 12a and the metal strip 100 increases, which may increase the rolling load during temper rolling, which is undesirable. In addition, a rolling mill with normal equipment specifications means a rolling mill capable of applying a rolling load of 5 kN / mm or more and 15 kN / mm or less.

[0065] By performing temper rolling using the rolling mill 10 incorporating the rolling work roll 12a according to this embodiment, even if a metal strip having a tensile strength of 1310 MPa or more has a disturbed shape (flatness) due to rapid cooling such as water quenching in the continuous annealing process, the shape can be flattened, and a metal strip with good flatness can be produced. EXAMPLES

[0066] <Example 1> Next, Example 1 will be described in which temper rolling was performed on a metal strip having a tensile strength of 1310 MPa class, a thickness of 2.1 mm, and a width of 1200 mm. The arithmetic mean roughness Ra of the metal strip before temper rolling was 0.3 μm. In Example 1, a rolling work roll was used in which the outer peripheral surface of a ceramic body part made of 79 mass% tungsten carbide and the remainder made of a metal binder, or a body part made of forged steel, was shot-dulled, and a chrome plating layer was formed on the outer peripheral surface. The diameter of the body part was 530 mm, the Young's modulus of the ceramic was 390 GPa, and the Young's modulus of the forged steel was 250 GPa. The diameter of the body part was 530 mm, and the thickness of the body part was 20 mm.

[0067] In Example 1, the outer peripheral surface of the body was subjected to shotdulling using a sandblasting method, which is a type of air blasting method. As the processing conditions for the shotdulling, the particle size of the shot particles and the air pressure for projecting the shot particles were changed to perform the shotdulling, and the values ​​of the arithmetic mean roughness Ra and skewness Rsk of the microscopic irregularities formed on the outer peripheral surface of the body were confirmed. Furthermore, after the shotdulling, the outer peripheral surface of the body was chrome plated, and the arithmetic mean roughness Ra and skewness Rsk formed on the outer peripheral surface of the chrome plating layer were confirmed. The types of shot particles used in the examples are shown in Table 1 below.

[0068] [Table 1]

[0069] Among the rolling work rolls manufactured in this manner, the work rolls having a surface roughness of 4.0 μm or more and 6.0 μm or less on the outer peripheral surface of the chrome plating layer with arithmetic mean roughness Ra and -0.4 or more and 0.1 or less on the outer peripheral surface of the chrome plating layer were designated as examples of the invention, while the work rolls having a surface roughness outside the range of 4.0 μm or more and 6.0 μm or less and / or outside the range of -0.4 or more and 0.1 or less on the outer peripheral surface of the chrome plating layer were designated as comparative examples.

[0070] The rolling work rolls of the invention and comparative examples were loaded into a four-high rolling mill to perform temper rolling of a metal strip with a tensile strength of 1310 MPa (yield strength 1160 MPa). The temper rolling mill used had a backup roll diameter of 1400 mm. The temper rolling conditions were constant load control so that the rolling load was constant at 11000 kN, and the elongation rate (elongation rate) given to the steel sheet at that time was measured. In other words, the higher the elongation rate, the higher the effect of reducing the rolling load. The front tension and rear tension given during temper rolling were both controlled to be constant at 100 kN. The surface roughness of the rolling rolls and the results of temper rolling are shown in Table 2 below.

[0071] [Table 2]

[0072] From Table 2, it can be seen that by specifying in advance the difference between the surface roughness after dulling and the surface roughness after chrome plating in accordance with the thickness of the chrome plating layer, it is possible to determine the processing conditions for shot dulling that will result in the appropriate arithmetic mean roughness Ra and skewness Rsk after chrome plating.

[0073] In addition, as shown in Table 2, in Nos. 1 to 5, in which the Young's modulus of the body was 350 GPa or more, the arithmetic mean roughness Ra after chrome plating was 4.0 μm or more and 6.0 μm or less, and the skewness Rsk was -0.4 or more and 0.1 or less, the elongation rate of temper rolling was 0.1% or more. In particular, in Nos. 1 to 4, the elongation rate of temper rolling was 0.2%, which was a more preferable result than No. 5. On the other hand, in No. 6, in which forged steel with a Young's modulus of 250 GPa was used for the body, the elongation rate of temper rolling was 0%, and the appropriate elongation rate could not be imparted to the metal strip. Similarly, in Nos. 7 to 12, in which the arithmetic mean roughness Ra after chrome plating did not satisfy the range of 4.0 μm or more and 6.0 μm or less, or the skewness Rsk did not satisfy the range of -0.4 or more and 0.1 or less, the elongation rate of temper rolling was 0%, and the appropriate elongation rate could not be imparted to the metal strip. From these results, it was confirmed that by performing temper rolling using the rolling work roll according to this embodiment, it is possible to impart an appropriate elongation rate and correct the shape of a metal strip, even if the metal strip has a high strength of tensile strength of 1310 MPa class.

[0074] <Example 2> As Example 2, an example of temper rolling of a metal strip with a tensile strength of 1310 MPa (yield strength 1160 MPa) will be described. The metal strip to be rolled had a thickness of 1.2 mm and a width of 1050 mm. In Example 2, a rolling work roll was used in which the outer peripheral surface of a ceramic body made of 79 mass% tungsten carbide and the remainder a metal binder was shot-dulled and a chrome plating layer was formed on the outer peripheral surface. The Young's modulus of the ceramic was 390 GPa and the diameter of the body was 530 mm.

[0075] In Example 2, a shot blasting device shown in FIG. 9 was used to perform shot blasting on the barrel before the formation of the chrome plating layer. Zirconia alumina (a composite material of alumina and zirconia) particles were used as the shot particles. The shot blasting was performed by changing the particle size of the shot particles and the air pressure for projecting the shot particles, and the values ​​of the arithmetic mean roughness Ra and skewness Rsk of the microscopic irregularities formed on the outer peripheral surface of the barrel were adjusted. Furthermore, after the shot blasting, a chrome plating layer having a thickness of 10 μm was formed on the outer peripheral surface of the barrel. The arithmetic mean roughness Ra and skewness Rsk of the outer peripheral surface of the chrome plating layer were measured.

[0076] Among the rolling work rolls manufactured in this manner, the work rolls having a surface roughness of 4.0 μm or more and 6.0 μm or less on the outer peripheral surface of the chrome plating layer with arithmetic mean roughness Ra and -0.4 or more and 0.1 or less on the outer peripheral surface of the chrome plating layer were designated as examples of the invention, while the work rolls having a surface roughness outside the range of 4.0 μm or more and 6.0 μm or less and / or outside the range of -0.4 or more and 0.1 or less on the outer peripheral surface of the chrome plating layer were designated as comparative examples.

[0077] In Example 2, temper rolling was performed so that the rolling load per unit width of the metal strip was constant at 6.3 kN / mm. In Example 2, cases where the elongation of the metal strip after temper rolling was 0.2% or more and 0.6% or less was ensured were marked with "◎", and cases where the elongation of the metal strip after temper rolling was 0.1% or more and less than 0.2% were marked with "◯". On the other hand, cases where the elongation of the metal strip after temper rolling was not 0.1% or more and 0.6% or less were marked with "X". The surface roughness of the outer peripheral surface of the chrome plating layer of the rolling work roll and the results of temper rolling are shown in Table 3 below.

[0078] [Table 3]

[0079] As shown in Table 3, in the inventive examples Nos. 20 to 26, the elongation of the metal strip was ensured to be 0.1% or more and 0.6% or less, and it was confirmed that the shape of the metal strip could be corrected by temper rolling. On the other hand, in the comparative examples Nos. 27 and 28, the elongation of the metal strip could not be ensured to be 0.1% or more and 0.6% or less with the same rolling load.

[0080] In the inventive examples Nos. 20 to 22, the elongation of the metal strip was ensured to be 0.2% or more and 0.6% or less, and a larger elongation was imparted to the metal strip than Nos. 23 to 26 when the same rolling load was applied. From these results, it was confirmed that it is preferable to impart a surface roughness of arithmetic mean roughness Ra of 4.0 μm to 6.0 μm and skewness Rsk of 0.00 to 0.10 to the outer peripheral surface of the chrome plating layer of the rolling work roll. It was also confirmed that by using the rolling work roll imparted with this surface roughness, it is possible to impart a more appropriate elongation and correct the shape of the metal strip, even if the metal strip has a high tensile strength of 1310 MPa or more. [Explanation of symbols]

[0081] 10. Rolling Mill 12a Work Roll 12b work roll 14a Backup Role 14b Backup role 16 Housing 18 Bearing box 20 Load detector 21 Rolling device 22 Inlet bridle roll 24 Inlet tension meter 26 Outlet tension meter 28 Exit bridle roll 30 Shaft 32 Torso 32a Outer periphery of the body 34 Chromium plating layer 34a Outer surface of chrome plating layer 40 Shot blasting equipment 42 Air Blast Nozzle 44 Projection room 46 shot particles 48 Shot particle supply section 50 Compressed Air Supply System 52 Dust collector

Claims

1. A body portion having a ceramic with a Young's modulus of 350 GPa or more in a surface layer portion; A chrome plating layer formed on the outer peripheral surface of the body portion; having The thickness of the chrome plating layer is 5 μm or more and 30 μm or less, The arithmetic mean roughness Ra of the outer peripheral surface of the chromium plating layer is 4.0 μm or more and 6.0 μm or less, and the skewness Rsk is −0.4 or more and 0.1 or less.

2. a dulling step of performing shot dulling on an outer peripheral surface of a body portion having a ceramic with a Young's modulus of 350 GPa or more in a surface layer portion; a plating layer forming step of forming a chrome plating layer on the outer peripheral surface of the shot-dulled body portion; Including, In the dulling step, dulling conditions are set according to a thickness of the chrome plating layer so that an arithmetic mean roughness Ra of the outer peripheral surface after the chrome plating layer is formed in the plating layer forming step is 4.0 μm or more and 6.0 μm or less, and a skewness Rsk is −0.4 or more and 0.1 or less.

3. 3. The method for producing a rolling work roll according to claim 2, wherein the average particle size of the shot particles used in the shotdulling is 250 μm or more and 710 μm or less.

4. 4. The method for producing a rolling work roll according to claim 2, wherein the shot dulling is performed using an air blast type dulling device, and the blasting pressure of the shot particles is set to 0.3 MPa or more and 0.7 MPa or less.

5. A method for temper rolling a metal strip, comprising temper rolling the metal strip using the rolling work roll according to claim 1.

6. 4. A method for temper rolling a metal strip, comprising temper rolling the metal strip using a rolling work roll manufactured by the method for manufacturing a rolling work roll according to claim 2 or 3.

7. A method for temper rolling a metal strip, comprising temper rolling the metal strip using a work roll manufactured by the method for manufacturing a work roll for rolling according to claim 4.

8. A method for producing a metal strip, comprising the step of producing a metal strip having a tensile strength of 1310 MPa or more by using the method for temper rolling a metal strip according to claim 5.

9. A method for producing a metal strip, comprising the step of producing a metal strip having a tensile strength of 1310 MPa or more by using the method for temper rolling a metal strip according to claim 6.

10. A method for producing a metal strip, comprising the step of producing a metal strip having a tensile strength of 1310 MPa or more by using the method for temper rolling a metal strip according to claim 7.

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