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 arithmetic average roughness Ra of the outer peripheral surface of the chromium plated layer is 4.0 μm or more and 10.0 μm or less, and skewness Rsk is -0.4 or more and 0.5 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 the outer peripheral surface of the barrel portion, wherein the outer peripheral surface of the chrome plating layer has an arithmetic mean roughness Ra of 4.0 μm or more and 10.0 μm or less, and a skewness Rsk of -0.4 or more and 0.5 or less. [2] The work roll for rolling according to [1], wherein the roll diameter is 150 mm or more and less than 1000 mm, and the thickness of the chrome plating layer is 50 μm or more and 0.15% or less of the roll diameter. [3] A method for manufacturing a rolling work roll, comprising: a plating layer forming step of forming a chrome plating layer on the outer peripheral surface of a body portion having a ceramic having a Young's modulus of 350 GPa or more in a surface layer portion; and a dulling step of dulling the outer peripheral surface of the chrome plating layer, wherein the dulling step imparts a surface roughness of arithmetic mean roughness Ra of 4.0 μm or more and 10.0 μm or less, and a skewness Rsk of −0.4 or more and 0.5 or less to the outer peripheral surface of the chrome plating layer. [4] The method for manufacturing a rolling work roll according to [3], wherein in the dulling step, the outer peripheral surface of the chrome plating layer is dulled by electric discharge machining. [5] In the dulling step, the product of the pulse current and the pulse time is 500 A·μs or more and 12000 A·μs or less, and the number of discharges per unit area of ​​the outer peripheral surface of the chrome plating layer is 30 times / mm 2 More than 800 times / mm 2The method for manufacturing a rolling work roll according to [4], wherein electric discharge machining is performed under the following electric discharge machining conditions. [6] A method for temper rolling a metal strip, comprising temper rolling the metal strip using the rolling work roll according to [1] or [2]. [7] 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 [3] to [5]. [8] A method for manufacturing a metal strip, comprising the steps of: manufacturing 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] or [7]. 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 an electric discharge machining facility 40 for dulling the outer peripheral surface of a chrome plating layer. [Figure 10] FIG. 10 is a schematic diagram showing a pulse current in electric discharge machining. [Figure 11] FIG. 11 is a graph showing an example of the influence of the product of the pulse current P and the pulse time t1 and the number of discharges N, which are electric discharge machining conditions, on the arithmetic mean roughness Ra and the skewness Rsk. 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] 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). The rolling work roll 12a according to this embodiment has a chrome plating layer 34 formed on the outer peripheral surface 32a of the body part, the surface layer of which has a Young's modulus of 350 GPa or more. The chrome plating layer 34 is a hard chrome plating layer. The hard chrome plating layer is provided mainly for the purpose of ensuring wear resistance.

[0023] The hard chrome plating layer can be formed by immersing the trunk 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 750 HV or more and 1000 HV or less. The surface roughness of the outer peripheral surface 34a of the chrome plating layer on which the hard chrome plating is formed is an arithmetic mean roughness Ra of 0.2 μm or more and 0.5 μm or less. Before forming the chrome plating layer 34, it is preferable to pre-treat the outer peripheral surface 32a of the trunk by etching so that the arithmetic mean roughness Ra is 0.5 μm or more and 3.0 μm or less. This improves the adhesion between the trunk 32 and the chrome plating layer 34.

[0024] Furthermore, after forming a chrome plating layer 34 on the outer peripheral surface 32a of the body, a dulling process is performed on the outer peripheral surface 34a of the chrome plating layer. The dulling process may be performed using a known means applied to impart roughness to the rolling work roll 12a. For example, the dulling process may be performed using shot dulling, electric discharge machining, electron beam machining, laser machining, or the like. In the shot dulling process, shot particles are projected onto the processing surface to impart irregularities to the surface. In the electric discharge machining, an electrode is used to generate an electric discharge between the processing surface and the surface to impart irregularities to the surface. In the electron beam machining, an electron beam is irradiated onto the processing surface in a reduced pressure atmosphere in a chamber to impart irregularities to the surface. In the laser machining process, a laser beam is irradiated onto the processing surface to melt a part of the surface to impart irregularities. This process is the dulling process step.

[0025] The rolling work roll 12a of this embodiment is manufactured by imparting a surface roughness of arithmetic mean roughness Ra of 4.0 μm or more and 10.0 μm or less and a skewness Rsk of −0.4 or more and 0.5 or less to the outer peripheral surface 34a of the chrome plating layer by dulling. The arithmetic mean roughness Ra and the skewness Rsk are line roughnesses defined in JIS B 0601:2013. The arithmetic mean roughness Ra is an index representing the average height of a roughness curve in a reference length. The skewness Rsk is defined by the following formula (1).

[0026]

number

[0027] 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.

[0028] 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.

[0029] Furthermore, when the outer peripheral surface of a ceramic having a Young's modulus of 350 GPa or more is dulled, cracks and fissures occur on the ceramic surface, and the durability of the rolling work roll 12a is reduced. In contrast, in the rolling work roll 12a according to this embodiment, a chrome plating layer 34 is formed on the outer peripheral surface 32a of the barrel, and the outer peripheral surface 34a of the chrome plating layer is dulled, thereby suppressing the occurrence of cracks on the ceramic surface. It is preferable to form a hard chrome plating having a hardness of 700 HV or more as the chrome plating layer 34. This improves the wear resistance of the rolling work roll 12a, and also improves the durability of the dull texture (irregularities on the surface of the rolling roll) imparted to the outer peripheral surface 34a of the chrome plating layer.

[0030] Furthermore, the outer peripheral surface 34a of the chrome plating layer of the rolling work roll 12a according to this embodiment is subjected to dulling to impart a surface roughness of arithmetic mean roughness Ra of 4.0 μm to 10.0 μm and skewness Rsk of -0.4 to 0.5. By appropriately controlling the form of microscopic irregularities on the surface of the rolling work roll 12a in this manner, 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.

[0031] 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 10.0 μm or less. This promotes 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).

[0032] 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 FIG. 5(a) and (b), the higher the arithmetic mean roughness Ra, the higher the height of the convex portion formed on the outer peripheral surface. In order to make it easier to understand the shape of the concaves and convexes, the cross-sectional views shown in FIG. 5 to FIG. 8 are drawn with a larger magnification in the vertical direction than in the horizontal direction. For this reason, these drawings are drawn to have a larger inclination than the inclination of the actual concaves and convexes.

[0033] 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.

[0034] 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.

[0035] In this way, 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, the wear of the protruding parts of the outer peripheral surface becomes more likely to progress, and dulling processing to increase the arithmetic average roughness Ra becomes difficult. 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 10.0 μm or less, and preferably 6.0 μm or more and 10.0 μm or less.

[0036] 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 0.5 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.

[0037] 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.

[0038] 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.

[0039] 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.

[0040] 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, wear of the protruding parts of the surface becomes more likely to progress. 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 0.5 or less, and is preferably -0.2 or more and 0.4 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 0.4 or less. This makes it possible to further suppress an increase in the rolling load.

[0041] 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.

[0042] Next, a method for dulling the outer peripheral surface 34a of the chrome plating layer using electric discharge machining will be described. As a method for dulling, electric discharge machining is preferably used. By controlling the machining conditions such as the pulse current, pulse time, and the number of discharges per unit area of ​​the surface, the arithmetic mean roughness Ra and skewness Rsk of the outer peripheral surface 34a of the chrome plating layer can be easily controlled within a target range.

[0043] 9 is a schematic diagram of an electric discharge machining equipment 40 that performs dull machining on the outer peripheral surface 34a of the chrome plating layer. The electric discharge machining equipment 40 includes a roll support section 42 and an electric discharge machining section 44. The roll support section 42 has a roll chuck 46, a roll rotation motor 48, and a tailstock 50. The roll chuck 46 supports the rolling work roll 12a from one axial end side. The roll rotation motor 48 drives the rolling work roll 12a to rotate at a predetermined rotation speed. The tailstock 50 supports the rolling work roll 12a from the other axial end side.

[0044] The electric discharge machining unit 44 has an electrode 52, an electrode position control unit 54, a power supply unit 56 that supplies current to the electrode 52, and a control unit 58 that controls the current waveform from the power supply unit 56. The electric discharge machining unit 44 further has an oil tank 62 that immerses the discharge region generated between the rolling work roll 12a and the electrode 52 in electric discharge machining oil 60. The electric discharge machining oil 60 is, for example, Metalwork EDF-K2 manufactured by ENEOS Corporation or Daphne Marg Plus ED3 manufactured by Idemitsu Kosan Co., Ltd.

[0045] The electrode 52 may be made of copper alloy or graphite formed into a plate or rod shape. The electrode 52 may be provided with a hole for passing electric discharge oil 60 therethrough, and the electric discharge oil 60 may be supplied from the tip of the electrode 52 to prevent electric discharge debris from accumulating between the rolling work roll 12a and the electrode 52. The electrode 52 may be arranged to face the surface of the rolling work roll 12a, and one or more electrodes may be arranged in the axial or circumferential direction of the rolling work roll 12a. The electrode position control unit 54 has a servo feed mechanism that supports the electrode 52 and maintains the distance (gap) between the rolling work roll 12a and the tip of the electrode 52 at a set condition. When machining the body of the rolling work roll 12a, the electric discharge machining equipment 40 may use either a method of moving the electrode 52 to perform electric discharge machining, or a method of fixing the electrode 52 and moving the rolling work roll 12a in the axial direction to perform electric discharge machining.

[0046] FIG. 10 is a schematic diagram showing a pulse current in electric discharge machining. FIG. 10(a) is a schematic diagram of the pulse current during machining time T, and FIG. 10(b) is an enlarged schematic diagram showing a part of the pulse current. The control device 58 controls the current supplied from the power supply device 56 to the electrode 52 to generate an arc discharge between the rolling work roll 12a and the electrode 52 (gap), thereby imparting unevenness to the surface of the rolling work roll 12a. The control device 58 controls the pulse current value P supplied to the electrode 52, and the time (pulse time) t1 during which the pulse current P is supplied and the time (pulse stop time) t2 during which the pulse current is not supplied within the time t of one cycle so as to satisfy preset conditions.

[0047] In the electric discharge machining conditions for dulling the rolling work roll 12a according to the present embodiment, it is preferable to control the product of the pulse current P and the pulse time t1 to be 500 A·μs or more and 12000 A·μs or less. If the product of the pulse current P and the pulse time t1 is less than 500 A·μs, the height of the unevenness of the outer peripheral surface 34a of the chrome plating layer generated by the arc discharge becomes small. This is not preferable because it may not be possible to ensure an arithmetic mean roughness Ra of 4.0 μm or more on the outer peripheral surface 34a of the chrome plating layer. On the other hand, if the product of the pulse current P and the pulse time t1 exceeds 12000 A·μs, the arithmetic mean roughness Ra of the outer peripheral surface 23a of the chrome plating layer 23 may exceed 10.0 μm. Furthermore, if the product of the pulse current P and the pulse time t1 exceeds 12000 A·μs, the heat generation amount of the rolling work roll 12a increases, which may cause abnormalities in the arc discharge, which is not preferable. In the electric discharge machining conditions for dulling the rolling work roll 12a, it is more preferable to control the product of the pulse current P and the pulse time t1 to be 2000 A·μs or more and 10000 A·μs or less.

[0048] In the electric discharge machining conditions for dulling the rolling work roll 12a, it is further preferable to control the pulse current P to be 15 A or more and 150 A or less, and the pulse time t1 to be 20 μs or more and 300 μs or less. If the pulse current P exceeds 150 A or the pulse time t1 exceeds 300 μs, the amount of heat generated by the rolling work roll 12a increases, which is not preferable because it may cause abnormal arc discharge. On the other hand, if the pulse current P is less than 15 A or the pulse time t1 is less than 20 μs, the height of the unevenness of the outer peripheral surface 34a of the chrome plating layer generated by the arc discharge becomes small, which is not preferable because the specified unevenness may not be obtained.

[0049] Further, under the electric discharge machining conditions of the rolling work roll 12a, the number of arc discharges per unit area of ​​the outer peripheral surface 34a of the chrome plating layer is set to 30 times / mm 2 More than 800 times / mm 2 It is preferable to control the number of discharges to the outer peripheral surface 34a of the chrome plating layer to be 30 times / mm 2 If the number of discharges to the outer peripheral surface 34a of the chrome plating layer is less than 800 times / mm, the number of arc discharges decreases, and a recess is formed on a part of the outer peripheral surface. As a result, the outer peripheral surface 34a of the chrome plating layer has a plateau shape with long protrusions, and the skewness Rsk of the outer peripheral surface tends to be less than -0.4. Furthermore, the recesses and protrusions formed on the outer peripheral surface 34a of the chrome plating layer tend to be non-uniform, which is undesirable as it may deteriorate the surface appearance of the metal strip 100 after the temper rolling. On the other hand, if the number of discharges to the outer peripheral surface 34a of the chrome plating layer is 800 times / mm, 2 If the number of arc discharges exceeds 40 times / mm, the number of arc discharges becomes too large, the chrome plating layer formed becomes thin, and the durability of the work roll 12a for rolling may decrease, which is not preferable. 2 More than 700 times / mm 2 It is more preferable to control the frequency to be less than 100 times / mm 2 More than 400 times / mm 2 It is more preferable to control the temperature so that the temperature is equal to or lower than the above.

[0050] The number of discharges to the outer peripheral surface 34a of the chrome plating layer can be controlled by the control device 58 setting the processing time T, which is the total time for performing the electric discharge processing of the rolling work roll 12a. 2 ), the number of electrodes 52 M, and the time t (s) of one cycle are used to calculate the number of discharges N (times / mm 2 ) can be calculated using the following formula (2).

[0051] N = M × T / (t × Q) (2)

[0052] Fig. 11 is a graph showing an example of the influence of the product of the pulse current P and the pulse time t1 and the number of discharges N, which are electric discharge machining conditions, on the arithmetic mean roughness Ra and the skewness Rsk. As shown in Fig. 11, by controlling the product of the pulse current P and the pulse time t1 in the electric discharge machining and the number of discharges N, the arithmetic mean roughness Ra and skewness Rsk formed on the outer peripheral surface 34a of the chrome plating layer can be controlled to appropriate values ​​(the area shown in gray in Fig. 11).

[0053] The roll diameter of the rolling work roll 12a is preferably 150 mm or more and less than 1000 mm, and the thickness of the chrome plating layer 34 formed on the outer peripheral surface 32a of the body part is preferably 50 μm or more and 0.15% or less of the roll diameter. The roll diameter of the rolling work roll 12a is the diameter of the outer peripheral surface of the body part 32 plus the thickness of the chrome plating layer 34.

[0054] When the roll diameter of the rolling work roll 12a is less than 150 mm, the thickness of the chrome plating layer 34 becomes relatively large relative to the roll diameter. As a result, the effect of suppressing flattening deformation obtained by using ceramics having a Young's modulus of 350 GPa or more for the barrel 32 relatively decreases, and the advantage of using ceramics having a Young's modulus of 350 GPa or more for the barrel 32 may be reduced, which is not preferable. When the roll diameter of the rolling work roll 12a is 1000 mm or more, the contact arc length when temper rolling is performed on the high-strength metal strip 100 becomes large. As a result, even if the roll flattening is reduced by using ceramics having a Young's modulus of 350 GPa or more for the barrel 32, the rolling load may increase and the required elongation may not be imparted to the metal strip 100, which is not preferable.

[0055] Furthermore, if the thickness of the chrome plating layer 34 is less than 50 μm, the chrome plating layer in the recesses on the surface becomes thin when the outer peripheral surface 34a of the chrome plating layer is dulled, which is not preferable. If the chrome plating layer becomes thin, the durability (life) of the rolling work roll may be shortened when it is continuously used as a rolling work roll. Furthermore, if the thickness of the chrome plating layer 34 exceeds 0.15% of the roll diameter, the adhesion between the body portion 32 and the chrome plating layer 34 may decrease, which is not preferable. In particular, in the rolling work roll 12a according to this embodiment, ceramic is used for the body portion 32, so it is preferable to ensure sufficient adhesion between the body portion 32 and the chrome plating layer 34.

[0056] For example, when a work roll having a diameter of 530 mm is used for temper rolling of a high-strength metal strip having a tensile strength of 1180 MPa or more, a rolling load of about 6.5 kN / mm is applied per unit width. If the thickness of the chrome plating layer 34 exceeds 0.15% of the roll diameter, the position where the internal shear stress is maximum is not inside the trunk portion 32 but at the interface between the trunk portion 32 and the chrome plating layer 34 or inside the chrome plating layer 34. Therefore, if the shear stress acting between the trunk portion 32 and the chrome plating layer 34 becomes larger than the adhesive strength between the trunk portion 32 and the chrome plating layer 34, peeling of the chrome plating layer 34 may occur.

[0057] 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. Then, one or more such rolling mills 10 are used to perform temper rolling that imparts an elongation of 0.1% or more and 0.6% or less to the metal strip 100. This suppresses an increase in the rolling load in temper rolling, so that even when a rolling mill with normal equipment specifications is used, it becomes possible to ensure an elongation of 0.1% or more required for shape correction of the metal strip 100. 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 may reduce the elongation (ductility) of the metal strip product due to work hardening, and this is not preferable. Moreover, if the elongation is made greater than 0.6%, the frictional force at the contact interface between the unevenness imparted to the surface of the rolling work roll 12a and the metal strip 100 increases, which is undesirable since it may increase the rolling load in temper rolling. Note that the rolling mill with normal equipment specifications means a rolling mill capable of imparting a rolling load of 5 kN / mm or more and 15 kN / mm or less.

[0058] 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

[0059] <Example 1> Next, Example 1 will be described, in which temper rolling was performed on a metal strip having a thickness of 2.0 mm and a tensile strength of 1470 MPa class. In Example 1, a ceramic having a Young's modulus of 350 GPa was used for the barrel portion, and a rolling work roll was used in which a chrome plating layer was formed on the outer peripheral surface of the barrel portion, and then the outer peripheral surface of the chrome plating layer was subjected to electric discharge machining to have a dull finish.

[0060] The body was made of ceramics consisting of 70% by mass of tungsten carbide (WC) and the remainder of cobalt (Co). The chrome plating layer was formed by immersing the body in a plating bath whose main component was chromic anhydride (chromium trioxide CrO3) with a trace amount of sulfuric acid added as a catalyst, and was adjusted so that the thickness was 200 μm under all conditions. Before forming the chrome plating layer, the arithmetic mean roughness Ra of the body was adjusted to be 0.2 μm to 0.5 μm.

[0061] The electrodes used in the electric discharge machining were made of copper alloy and were formed into a plate shape. The electric discharge machining conditions were controlled by changing the pulse current P within the range of 25 A to 150 A and changing the pulse time t1 so that the product of the pulse current P and the pulse time t1 was 400 A·μs to 20,000 A·μs. In addition, the electric discharge machining conditions for the rolling work rolls were set to a value of 30 times / mm2 for the number of times that arc discharges occurred per unit area on the outer peripheral surface of the chrome plating layer (number of discharges). 2 More than 800 / mm 2 As a result, the outer peripheral surface of the chrome plating layer was given a surface roughness having an arithmetic mean roughness Ra of 4.0 μm or more and 9.6 μm or less and a skewness Rsk of −0.65 or more and 0.40 or less.

[0062] Among the rolling work rolls thus manufactured, those having a surface roughness of arithmetic mean roughness Ra of 4.0 μm or more and 10.0 μm or less on the outer peripheral surface of the chrome plating layer and a skewness Rsk of -0.4 or more and 0.5 or less were taken as examples of the invention, while those having a surface roughness of arithmetic mean roughness Ra of the outer peripheral surface of the chrome plating layer outside the range of 4.0 μm or more and 10.0 μm or less and / or a skewness Rsk outside the range of -0.4 or more and 0.5 or less were taken as comparative examples.

[0063] Using the rolling work rolls of the invention and comparative examples, temper rolling was carried out on a metal strip having a tensile strength of 1470 MPa (yield strength 1300 MPa). In Example 1, temper rolling was carried out so that the rolling load per unit width of the metal strip was constant at 6.57 kN / mm. Then, a case where the elongation rate of the metal strip by temper rolling was ensured to be 0.1% or more and 0.6% or less was marked as "good", and a case where the elongation rate of the metal strip by temper rolling was not ensured to be 0.1% or more and 0.6% or less was marked as "poor". The surface roughness of the rolling work rolls and the results of temper rolling are shown in Table 1 below.

[0064] [Table 1]

[0065] As shown in Table 1, it was confirmed that the elongation of the metal strip of 0.1% to 0.6% was ensured and the shape of the metal strip could be corrected in the invention examples Nos. 1, 2, 6, and 7. On the other hand, in the comparative examples Nos. 3 to 5, the elongation of the metal strip of 0.1% to 0.6% could not be ensured with the same rolling load.

[0066] From the results of Example 1, it was confirmed that by using the rolling work roll according to this embodiment, it is possible to provide an appropriate elongation rate and correct the shape of a high-strength metal strip, even if the metal strip has a tensile strength of 1310 MPa or more. It was also confirmed that by performing 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 tensile strength of 1310 MPa or more.

[0067] <Example 2> Example 2 describes an example in which temper rolling was performed on a metal strip with a tensile strength of 1470 MPa class. In Example 2, as in Example 1, ceramics consisting of 70% by mass of tungsten carbide (WC) and the remainder of cobalt (Co) were used for the barrel of the rolling work roll. The Young's modulus of the surface layer of the barrel was 350 GPa. In Example 2, a chrome plating layer was formed on the outer peripheral surface of the barrel with a different thickness, and the processing conditions of the electric discharge processing, which is a dull processing, were changed to impart a predetermined arithmetic mean roughness Ra and skewness Rsk to the outer peripheral surface of the chrome plating layer.

[0068] The chrome plating layer formed on the outer periphery of the body is hard chrome plating, which is performed by immersing the body in a plating bath whose main component is chromic anhydride (chromium trioxide: CrO3) with a small amount of sulfuric acid added as a catalyst. The chrome plating conditions were adjusted by changing the current and plating time so that the thickness of the chrome plating layer would be between 100μm and 200μm.

[0069] The electrodes used in the electric discharge machining were made of copper alloy or graphite and were formed into a plate shape. The electric discharge machining conditions were as follows: pulse current P was changed within the range of 20 A to 120 A, and pulse time t1 was changed within the range of 10 μs to 170 μs. This controlled the product of pulse current P and pulse time t1 to be within the range of 300 A·μs to 17,000 A·μs. In addition, pulse stop time t2 was changed within the range of 20 μs to 1,500 μs. The number of times arc discharges were generated per unit area on the outer peripheral surface of the chrome plating layer (number of discharges) was increased to 20 times / mm by changing the machining time T within the range of 10 min to 150 min. 2 More than 150 times / mm 2 The arithmetic mean roughness Ra and skewness Rsk of the rolling work roll formed by electric discharge machining are shown in Table 2 below, and the electric discharge machining conditions are shown in Table 3 below.

[0070] [Table 2]

[0071] [Table 3]

[0072] As shown in Tables 2 and 3, it is understood that the arithmetic mean roughness Ra and skewness Rsk of the rolling work roll can be controlled by changing the electric discharge machining conditions such as the electrode, pulse current, pulse time, and number of electric discharges. Of the rolling work rolls manufactured in this manner, the rolling work rolls having a surface roughness of arithmetic mean roughness Ra of 4.0 μm or more and 10.0 μm or less on the outer peripheral surface of the chrome plating layer and a skewness Rsk of -0.4 or more and 0.5 or less were used as the inventive examples. On the other hand, the rolling work rolls having a surface roughness of arithmetic mean roughness Ra of the outer peripheral surface of the chrome plating layer outside the range of 4.0 μm or more and 10.0 μm or less and / or a skewness Rsk outside the range of -0.4 or more and 0.5 or less were used as the comparative examples.

[0073] Using the rolling work rolls of the invention and the comparative example, temper rolling of a metal strip having a tensile strength of 1470 MPa class was carried out. The temper rolling was carried out so that the rolling load per unit width of the metal strip was constant at 6.57 kN / mm. In Example 2 as well, the case where the elongation rate of the metal strip by temper rolling was ensured to be 0.1% or more and 0.6% or less was marked as "good", and the case where the elongation rate of the metal strip by temper rolling was not ensured to be 0.1% or more and 0.6% or less was marked as "poor". The evaluation results are also shown in Table 2 above.

[0074] As shown in Table 2, in the inventive examples Nos. 10 to 14 and 18, the necessary elongation was imparted to the metal strip. On the other hand, in the comparative examples Nos. 15 to 17, the elongation of the metal strip could not be sufficiently ensured for the same rolling load. From these results, it was confirmed that by using the rolling work roll according to this embodiment, even a high-strength metal strip having a tensile strength of 1310 MPa or more can be imparted with an appropriate elongation and the shape of the metal strip can be corrected. Furthermore, it was confirmed that by adjusting the electric discharge machining conditions, it is possible to manufacture a rolling work roll having a surface roughness in which the arithmetic mean roughness Ra on the outer peripheral surface of the chrome plating layer is 4.0 μm or more and 10.0 μm or less, and the skewness Rsk is -0.4 or more and 0.5 or less.

[0075] <Example 3> As Example 3, an example of temper rolling of a metal strip having a tensile strength of 1470 MPa (yield strength 1300 MPa) and a thickness of 1.2 mm and a width of 1140 mm will be described. In Example 3, as in Examples 1 and 2, ceramics consisting of 70% by mass of tungsten carbide (WC) and the remainder of cobalt (Co) were used for the barrel of the rolling work roll. The Young's modulus of the surface layer of the barrel was 350 GPa. In Example 3, a chrome plating layer having a thickness of 200 μm was formed on the outer peripheral surface of the barrel, and then the outer peripheral surface of the chrome plating layer was subjected to electric discharge machining to produce a rolling work roll that was dulled. The barrel of the rolling work roll used in Example 3 had a diameter of 450 mm.

[0076] The electrode used for the electric discharge machining was graphite formed into a plate shape. The electric discharge machining conditions were controlled so that the product of the pulse current P and pulse time t1 was within the range of 300 A·μs to 17,000 A·μs by varying the pulse current P within the range of 20 A to 120 A and the pulse time t1 within the range of 10 μs to 170 μs. In addition, the pulse stop time t2 was varied within the range of 20 μs to 1,500 μs. The number of times arc discharges were generated per unit area on the outer peripheral surface of the chrome plating layer (number of discharges) was controlled to 20 times / mm by varying the machining time T within the range of 10 min to 150 min. 2More than 150 times / mm 2 The thickness was controlled to be within the following range. As a result, the outer peripheral surface of the chrome plating layer was given a surface roughness having an arithmetic mean roughness Ra of 3.0 μm or more and 9.5 μm or less and a skewness Rsk of −0.50 or more and 0.40 or less.

[0077] Among the rolling work rolls manufactured in this manner, the work rolls having a surface roughness of 4.0 μm or more and 10.0 μm or less on the outer peripheral surface of the chrome plating layer with arithmetic mean roughness Ra and -0.4 or more and 0.5 or less with skewness Rsk were designated as examples of the invention. On the other hand, the rolling work rolls having a surface roughness outside the range of 4.0 μm or more and 10.0 μm or less on the outer peripheral surface of the chrome plating layer with skewness Rsk outside the range of -0.4 or more and 0.5 or less were designated as comparative examples. Using the rolling work rolls of the examples and comparative examples, temper rolling of a metal strip with a tensile strength of 1470 MPa class was carried out.

[0078] In Example 3, temper rolling was performed so that the rolling load per unit width of the metal strip was constant at 6.57 kN / mm. In Example 3, cases where the elongation rate 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 rate 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 rate of the metal strip after temper rolling was not 0.1% or more and 0.6% or less were not ensured were marked with "X". The surface roughness of the rolling work rolls and the results of temper rolling are shown in Table 4 below.

[0079] [Table 4]

[0080] As shown in Table 4, in the inventive examples Nos. 20 to 31, 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. 32 and 33, 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.

[0081] In the inventive examples Nos. 20 to 26, 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. 27 to 31 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 6.0 μm to 10.0 μm and skewness Rsk of 0.00 to 0.40 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, a more appropriate elongation can be imparted to the metal strip, even if the metal strip has a high strength with a tensile strength of 1310 MPa or more, and the shape of the metal strip can be corrected. [Explanation of symbols]

[0082] 10. Rolling Mill 12a Work Roll 12b work roll 14a Backup Roll 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 Electrical discharge machining equipment 42 Roll support part 44 Electric discharge machining department 46 Roll chuck 48 Roll rotation motor 50 Tailstock 52 electrodes 54 Electrode position control unit 56 Power supply 58 Control device 60 Electric discharge machining oil 62 Oil tank

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 arithmetic mean roughness Ra of the outer peripheral surface of the chromium plating layer is 4.0 μm or more and 10.0 μm or less, and the skewness Rsk is −0.4 or more and 0.5 or less.

2. The roll diameter is 150 mm or more and less than 1000 mm, 2. The rolling work roll according to claim 1, wherein the thickness of the chromium plating layer is 50 μm or more and 0.15% or less of the roll diameter.

3. a plating layer forming step of forming a chrome plating layer on an outer peripheral surface of the body portion having a ceramic with a Young's modulus of 350 GPa or more in a surface layer portion; A dulling step of dulling the outer peripheral surface of the chrome plating layer; Including, In the dulling step, the outer peripheral surface of the chrome plating layer is given a surface roughness having an arithmetic mean roughness Ra of 4.0 μm or more and 10.0 μm or less and a skewness Rsk of −0.4 or more and 0.5 or less.

4. The method for producing a rolling work roll according to claim 3 , wherein in the dulling step, the outer peripheral surface of the chrome plating layer is dulled by electric discharge machining.

5. In the dulling step, the product of the pulse current and the pulse time is 500 A·μs or more and 12000 A·μs or less, and the number of discharges per unit area of ​​the outer peripheral surface of the chrome plating layer is 30 times / mm ２ More than 800 times / mm ２ 5. The method for producing a rolling work roll according to claim 4, wherein electric discharge machining is performed under the following electric discharge machining conditions:

6. A method for temper rolling a metal strip, comprising temper rolling the metal strip using the rolling work roll according to claim 1 or 2.

7. 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 claims 3 to 5.

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 6.

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 7.

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