EP3895818B1 - Work roll for rolling, rolling machine equipped with same, and rolling method - Google Patents
Work roll for rolling, rolling machine equipped with same, and rolling method Download PDFInfo
- Publication number
- EP3895818B1 EP3895818B1 EP19895432.3A EP19895432A EP3895818B1 EP 3895818 B1 EP3895818 B1 EP 3895818B1 EP 19895432 A EP19895432 A EP 19895432A EP 3895818 B1 EP3895818 B1 EP 3895818B1
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- European Patent Office
- Prior art keywords
- rolling
- roll
- case
- skin pass
- surface roughness
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- 238000005096 rolling process Methods 0.000 title claims description 167
- 238000000034 method Methods 0.000 title claims description 45
- 239000011651 chromium Substances 0.000 claims description 57
- 229910052804 chromium Inorganic materials 0.000 claims description 42
- 238000007747 plating Methods 0.000 claims description 42
- VYZAMTAEIAYCRO-UHFFFAOYSA-N Chromium Chemical compound [Cr] VYZAMTAEIAYCRO-UHFFFAOYSA-N 0.000 claims description 37
- 230000002093 peripheral effect Effects 0.000 claims description 4
- 230000001376 precipitating effect Effects 0.000 claims description 3
- 229910000831 Steel Inorganic materials 0.000 description 59
- 239000010959 steel Substances 0.000 description 59
- 230000003746 surface roughness Effects 0.000 description 44
- 230000008569 process Effects 0.000 description 29
- 239000010410 layer Substances 0.000 description 25
- 230000000052 comparative effect Effects 0.000 description 20
- 230000000694 effects Effects 0.000 description 16
- 239000011247 coating layer Substances 0.000 description 15
- 238000002474 experimental method Methods 0.000 description 13
- 238000005299 abrasion Methods 0.000 description 8
- 239000010941 cobalt Substances 0.000 description 7
- 229910017052 cobalt Inorganic materials 0.000 description 7
- GUTLYIVDDKVIGB-UHFFFAOYSA-N cobalt atom Chemical compound [Co] GUTLYIVDDKVIGB-UHFFFAOYSA-N 0.000 description 7
- 230000003247 decreasing effect Effects 0.000 description 7
- 238000012545 processing Methods 0.000 description 7
- UONOETXJSWQNOL-UHFFFAOYSA-N tungsten carbide Chemical compound [W+]#[C-] UONOETXJSWQNOL-UHFFFAOYSA-N 0.000 description 7
- 238000012937 correction Methods 0.000 description 6
- 239000000463 material Substances 0.000 description 6
- 230000035882 stress Effects 0.000 description 6
- 238000000137 annealing Methods 0.000 description 5
- 238000007373 indentation Methods 0.000 description 5
- 238000005498 polishing Methods 0.000 description 4
- 230000009467 reduction Effects 0.000 description 4
- QAOWNCQODCNURD-UHFFFAOYSA-N Sulfuric acid Chemical compound OS(O)(=O)=O QAOWNCQODCNURD-UHFFFAOYSA-N 0.000 description 3
- 230000008859 change Effects 0.000 description 3
- 238000000926 separation method Methods 0.000 description 3
- KRVSOGSZCMJSLX-UHFFFAOYSA-L chromic acid Substances O[Cr](O)(=O)=O KRVSOGSZCMJSLX-UHFFFAOYSA-L 0.000 description 2
- 239000010960 cold rolled steel Substances 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- AWJWCTOOIBYHON-UHFFFAOYSA-N furo[3,4-b]pyrazine-5,7-dione Chemical compound C1=CN=C2C(=O)OC(=O)C2=N1 AWJWCTOOIBYHON-UHFFFAOYSA-N 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
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- 238000012360 testing method Methods 0.000 description 2
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- LDXJRKWFNNFDSA-UHFFFAOYSA-N 2-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)-1-[4-[2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidin-5-yl]piperazin-1-yl]ethanone Chemical compound C1CN(CC2=NNN=C21)CC(=O)N3CCN(CC3)C4=CN=C(N=C4)NCC5=CC(=CC=C5)OC(F)(F)F LDXJRKWFNNFDSA-UHFFFAOYSA-N 0.000 description 1
- IHCCLXNEEPMSIO-UHFFFAOYSA-N 2-[4-[2-(2,3-dihydro-1H-inden-2-ylamino)pyrimidin-5-yl]piperidin-1-yl]-1-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethanone Chemical compound C1C(CC2=CC=CC=C12)NC1=NC=C(C=N1)C1CCN(CC1)CC(=O)N1CC2=C(CC1)NN=N2 IHCCLXNEEPMSIO-UHFFFAOYSA-N 0.000 description 1
- YLZOPXRUQYQQID-UHFFFAOYSA-N 3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)-1-[4-[2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidin-5-yl]piperazin-1-yl]propan-1-one Chemical compound N1N=NC=2CN(CCC=21)CCC(=O)N1CCN(CC1)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F YLZOPXRUQYQQID-UHFFFAOYSA-N 0.000 description 1
- NIPNSKYNPDTRPC-UHFFFAOYSA-N N-[2-oxo-2-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)ethyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 NIPNSKYNPDTRPC-UHFFFAOYSA-N 0.000 description 1
- AFCARXCZXQIEQB-UHFFFAOYSA-N N-[3-oxo-3-(2,4,6,7-tetrahydrotriazolo[4,5-c]pyridin-5-yl)propyl]-2-[[3-(trifluoromethoxy)phenyl]methylamino]pyrimidine-5-carboxamide Chemical compound O=C(CCNC(=O)C=1C=NC(=NC=1)NCC1=CC(=CC=C1)OC(F)(F)F)N1CC2=C(CC1)NN=N2 AFCARXCZXQIEQB-UHFFFAOYSA-N 0.000 description 1
- 238000005422 blasting Methods 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 238000005097 cold rolling Methods 0.000 description 1
- 238000010924 continuous production Methods 0.000 description 1
- 239000013078 crystal Substances 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009713 electroplating Methods 0.000 description 1
- 238000005246 galvanizing Methods 0.000 description 1
- 238000011835 investigation Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000003672 processing method Methods 0.000 description 1
- 239000000523 sample Substances 0.000 description 1
- 238000005488 sandblasting Methods 0.000 description 1
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Images
Classifications
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B27/00—Rolls, roll alloys or roll fabrication; Lubricating, cooling or heating rolls while in use
- B21B27/02—Shape or construction of rolls
- B21B27/03—Sleeved rolls
- B21B27/032—Rolls for sheets or strips
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/60—Electroplating characterised by the structure or texture of the layers
- C25D5/605—Surface topography of the layers, e.g. rough, dendritic or nodular layers
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/60—Electroplating characterised by the structure or texture of the layers
- C25D5/615—Microstructure of the layers, e.g. mixed structure
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D5/00—Electroplating characterised by the process; Pretreatment or after-treatment of workpieces
- C25D5/60—Electroplating characterised by the structure or texture of the layers
- C25D5/625—Discontinuous layers, e.g. microcracked layers
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D7/00—Electroplating characterised by the article coated
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B1/00—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations
- B21B1/22—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length
- B21B2001/228—Metal-rolling methods or mills for making semi-finished products of solid or profiled cross-section; Sequence of operations in milling trains; Layout of rolling-mill plant, e.g. grouping of stands; Succession of passes or of sectional pass alternations for rolling plates, strips, bands or sheets of indefinite length skin pass rolling or temper rolling
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B2265/00—Forming parameters
- B21B2265/18—Elongation
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B2267/00—Roll parameters
- B21B2267/10—Roughness of roll surface
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B2267/00—Roll parameters
- B21B2267/28—Elastic moduli of rolls
-
- C—CHEMISTRY; METALLURGY
- C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
- C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
- C25D3/00—Electroplating: Baths therefor
- C25D3/02—Electroplating: Baths therefor from solutions
- C25D3/04—Electroplating: Baths therefor from solutions of chromium
Definitions
- the present invention relates to a rolling work roll for rolling a high-strength steel strip and a rolling mill having the roll, and a rolling method.
- a skin pass rolling mill with which soft reduction is performed on a steel strip with a rolling reduction ratio of, for example, 1% or less, is known.
- a steel strip is homogeneously elongated by the skin pass rolling mill so that the shape of the steel strip is corrected to obtain predetermined flatness.
- the properties of the steel strip such as mechanical properties, such as yield point elongation, tensile strength, and elongation, and surface roughness, are improved by performing skin pass rolling.
- mechanical properties such as yield point elongation, tensile strength, and elongation, and surface roughness
- a hard steel strip typified by a high-tensile-strength steel strip.
- a significantly high rolling load is necessary to achieve an elongation ratio required for shape correction.
- Patent Literature 1 discloses a method in which skin pass rolling is performed by using a work roll having a surface average roughness Ra of 3.0 ⁇ m to 10.0 ⁇ m.
- Patent Literature 2 which forms the basis for the preamble of claim 1, discloses a method utilizing a cemented carbide which consists of tungsten carbide (WC) and cobalt (Co) and whose surface layer has a Young's modulus of 500 GPa or higher as a roll material.
- Patent Literature 3 discloses a method in which skin pass rolling is performed by using a roll whose surface layer has a Young's modulus of 450 GPa or higher and whose surface roughness Ra is 1 ⁇ m or more and 10 ⁇ m or less.
- the surface of a rolling work roll has a predetermined arithmetic average roughness which is obtained by performing dull texturing process.
- dull texturing process for example, a shot blasting processing method or a discharge dull texturing process is used as described in Patent Literature 1.
- a problem such as a decrease in surface roughness due to abrasion or crack growth with an increase in rolling distance.
- there is a problem in that it is necessary, for example, to repair or replace a rolling work roll due to the above problem occurring in the rolling work roll, which makes it difficult to stably perform a rolling operation.
- An object of the present invention is to provide a rolling work roll with which it is possible to stably perform a rolling operation when skin pass rolling is performed on a high-strength steel strip and a rolling mill having the roll, and a rolling method.
- the present invention has the features to solve the problems as described in the appended claims.
- Fig. 1 is a schematic diagram illustrating a preferable embodiment of a rolling mill 10 having rolling work rolls according to the present invention.
- the rolling mill 10 in Fig. 1 is used for performing skin pass rolling on a wide steel strip having a tensile strength of, for example, 980 MPa or higher.
- the skin pass rolling mill 10 has a pair of rolling work rolls 2 and back-up rolls 3, each of which supports a corresponding one of the rolling work rolls 2.
- a payoff reel 5 is arranged upstream of the skin pass rolling mill 10, and a tension reel 6 is arranged downstream of the skin pass rolling mill 10.
- bridle rolls may be arranged upstream or downstream of the skin pass rolling mill 10 to apply tension to the steel strip 1.
- the rolling work roll 2 has a structure in which a roll barrel 2x made of a cemented carbide is fixed to, for example, a shaft.
- the roll barrel 2x is made of a cemented carbide which has a Young's modulus of 450 GPa or higher and which contains, for example, by mass%, 86% tungsten carbide (WC) and a balance of cobalt (Co).
- Young's modulus is 450 GPa or higher, it is possible to prevent an increase in the contact arc length in a roll bite between the rolling work rolls 2 and the steel strip 1 due to the flattening deformation of the rolling work rolls 2 and to thereby prevent an excessive increase in rolling load acting on the rolling work rolls 2, even when skin pass rolling is performed on a high-strength steel sheet.
- a recess and projection layer 2y containing granular Cr is formed in the part corresponding to the roll barrel surface of the roll barrel 2x.
- the recessed and projected shape including the surface morphology is formed by performing chromium plating and thereby precipitating granular chromium so that an arithmetic average roughness (hereinafter, referred to as "surface roughness") Ra of 2.0 ⁇ m to 10.0 ⁇ m is obtained.
- surface roughness arithmetic average roughness
- the surface roughness Ra of the rolling work rolls 2 be 3.0 ⁇ m or more to realize the elongation effect.
- the surface roughness Ra of the recess and projection layer 2y be more than 4.0 ⁇ m.
- the surface roughness Ra of the recess and projection layer 2y not be more than 10.0 ⁇ m from the viewpoint of not only extreme difficulty in stably forming large surface roughness on the rolling work rolls 2 in industrial processes but also roll service life. Therefore, it is preferable that the surface roughness Ra of the work rolls be 10.0 ⁇ m or less.
- This recess and projection layer 2y is formed of granular Cr, which is precipitated by performing a chromium plating treatment.
- a chromium plating treatment which is performed to improve the adhesiveness between the surface of the roll barrel 2x and a chromium coating layer
- the polished surface is subjected to, for example, a sand blasting treatment so as to have a surface roughness Ra of 0.8 ⁇ m.
- the surface of the roll barrel 2x is subjected to a washing treatment followed by a chromium plating treatment.
- the chromium plating treatment is performed, for example, under the conditions of a low plating bath temperature of 50°C or lower and a high current density of 60 A/dm 2 or more. With this, it is possible to increase the diameter of Cr crystal grains which are precipitated on the surface of the roll barrel 2x. That is, in the case of an industrially used hard chromium coating layer, the morphology and hardness of Cr precipitated vary depending on electroplating conditions (plating bath temperature, current density, and plating time).
- the treatment is performed under the conditions of a plating bath temperature of about 50°C to 60°C and a current density of about 40 A/dm 2 to 60 A/dm 2 to obtain a flat and smooth surface.
- a plating bath temperature of about 50°C to 60°C and a current density of about 40 A/dm 2 to 60 A/dm 2
- plating is performed under the conditions of a low plating bath temperature of 50°C or lower and a high current density of 60 A/dm 2 or more to precipitate granular Cr.
- Fig. 2 is an enlarged surface photograph illustrating an example of the recess and projection layer of the rolling work roll in the skin pass rolling mill in Fig. 1 .
- chromium plating was performed in a plating solution containing chromic acid (CrO 3 ) and sulfuric acid (H 2 SO 4 ) under the conditions of a plating bath temperature of 37°C, a current density of 120 A/dm 2 , and a plating time of 150 min.
- a granular recess and projection layer 2y was formed on the surface of the roll barrel 2x through the precipitation of Cr.
- the surface roughness Ra was determined by using a contact-type roughness meter, the surface roughness Ra was 3.9 ⁇ m.
- no crack or the like occurred in the recess and projection layer 2y.
- the surface roughness Ra of the recess and projection layer 2y is controlled by controlling plating time.
- Fig. 3 is a graph illustrating the variation in surface roughness Ra after the plating when only a plating time is varied under the plating conditions for Fig. 2 . Since there is an increase in surface roughness Ra with an increase in plating time, it is possible to achieve desired surface roughness Ra by controlling the plating conditions.
- the average grain diameter of Cr precipitated on the roll surface by performing chromium plating be 50 ⁇ m or more. This is for the purpose of effectively realizing an elongation effect due to the indentation of the recessed and projected shape onto the steel sheet surface.
- a rolling experiment was performed to clarify the effect of decreasing a rolling load due to rolling work rolls 2 having the recess and projection layer 2y described above.
- a high-tensile-strength steel sheet having a thickness of 0.215 mm, a width of 20 mm, a length of 200 mm, and a yield stress of 1500 MPa was used as a sample material.
- a 4-high rolling mill having work rolls having a diameter of ⁇ 70 mm was used as a skin pass rolling mill 10 to perform cut-sheet rolling without tension under a dry condition without a lubricant. This was a 1/7-scale model experiment for a roll diameter and a sheet thickness used in practical rolling performed on a high-tensile-strength steel sheet for an automobile.
- the roll barrel 2x was made of 2%-Cr steel having a Young's modulus of 206 GPa, and the surface thereof was subjected to grindstone polishing to obtain a surface roughness Ra of 0.2 ⁇ m.
- the roll barrel 2x was made of 2%-Cr steel, and the surface thereof was subjected to discharge dull texturing process to obtain a surface roughness Ra of 3.0 ⁇ m.
- conventional example 2 No.
- the roll barrel 2x was made of a cemented carbide containing, by mass%, 86% tungsten carbide (WC) and a balance of cobalt and having a Young's modulus of 503 GPa. The surface thereof was subjected to grindstone polishing to obtain a surface roughness Ra of 0.2 ⁇ m.
- the roll barrel 2x was made of the same cemented carbide as in the case of conventional example 2 (No. 3), and the surface thereof was subjected to chromium plating for dull texturing process to form the recess and projection layer 2y having a surface roughness Ra of 2.5 ⁇ m.
- Fig. 4 is a graph illustrating the variation in load per unit width with respect to an elongation ratio in the case of conventional examples 1 and 2, comparative example 1, and example 1.
- the load per unit width of conventional example 1 (No. 2) in which the surface roughness is large, is lower than that of comparative example 1, which indicates that the elongation effect due to the indentation of the projected portions of the surface of the rolling work rolls onto the surface of the steel sheet was realized.
- elongation ratio denotes the ratio of a change in the length in the longitudinal direction of a steel strip before and after rolling to the original length.
- the elongation ratio is 0.2% or more, since it is possible to sufficiently correct the shape of a steel strip, even if it is a high-strength cold-rolled steel strip, it is possible to achieve generally good flatness on the front and back surface sides of the steel strip.
- the elongation ratio applied to a steel strip be 0.5% or less to control the rolling load acting on the work rolls and the skin pass rolling mill 10 to be within the load capacity of the skin pass rolling mill.
- the roll barrel 2x was made of a cemented carbide (having a Young's modulus of 503 GPa) containing, by mass%, 86% tungsten carbide (WC) and a balance of cobalt, and the surface thereof was subjected to direct discharge dull texturing process to obtain a surface roughness Ra of 3.0 ⁇ m.
- Fig. 5 is an enlarged surface photograph illustrating the surface of the recess and projection layer in the case where the roll barrel 2x made of a cemented carbide was subjected to dull texturing process by performing direct discharge processing as in the case of comparative example 2.
- a crack CK occurred on the surface due to the impact when discharge processing was performed.
- a crack CK occurs in the case where a material such as a cemented carbide which contains mainly ceramics that is a brittle material is subjected to discharge processing.
- the roll barrel 2x was made of a cemented carbide (having a Young's modulus of 503 GPa) containing, by mass%, 86% tungsten carbide (WC) and a balance of cobalt, and the surface thereof was subjected to chromium plating to form the recess and projection layer 2y having a surface roughness Ra of 3.0 ⁇ m.
- the roll barrel 2x was made of 2%-Cr steel having a Young's modulus of 206 GPa, and the surface thereof was subjected to discharge dull texturing process to obtain a surface roughness Ra of 4.5 ⁇ m.
- the roll barrel 2x was made of a cemented carbide (having a Young's modulus of 450 GPa) containing, by mass%, 80% tungsten carbide (WC) and a balance of cobalt, and the surface thereof was subjected to discharge dull texturing process to obtain a surface roughness Ra of 4.5 ⁇ m without performing chromium plating.
- the roll barrel 2x was made of a cemented carbide (having a Young's modulus of 450 GPa) containing, by mass%, 80% tungsten carbide (WC) and a balance of cobalt, and the surface thereof was subjected to chromium plating to form the recess and projection layer 2y having a surface roughness of 4.5 ⁇ m.
- the average grain diameter of Cr precipitated was 60 ⁇ m.
- a hard chromium coating layer having a thickness of 1 ⁇ m was further formed on the roll surface under alternate plating conditions.
- the reason why the additional hard chromium coating layer was formed under alternate plating conditions is as follows. In the case where a recessed and projected shape is formed by precipitating granular Cr on the surface of the roll under the plating conditions of a low plating bath temperature of 50°C or lower and a high current density of 60 A/dm 2 , the Vickers hardness of the chromium coating layer is about 700 to 900.
- the Vickers hardness of the hard chromium coating layer is about 900 to 1100.
- the reason why a hard chromium coating layer was further formed under alternate plating conditions after granular Cr had been precipitated on the roll surface by using the same method as that in the case of example 3 is because, since a significantly hard coating layer is formed on the outermost surface of the rolling work roll, there is a further improvement in abrasion resistance.
- the thickness of the additional hard chromium coating layer is set to be 1 ⁇ m as described above is because, in the case where the thickness is equal to or more than that, since there is a decrease in the height difference in the recessed and projected shape formed by grains in the early stage, there is a decreased elongation effect when skin pass rolling is performed. That is, by forming an additional thin hard chromium coating layer on the granular chromium precipitated in the early stage of the plating process, it is possible to increase the hardness of the surface of the coating layer without changing the roughness pattern formed of granular chromium. Here, for such a reason, it is preferable that the thickness of the additional hard chromium coating layer be 0.5 ⁇ m to 10 ⁇ m.
- Fig. 6 is a graph illustrating the variation in surface roughness with respect to a rolling distance when a rolling experiment is performed by using the rolling work rolls given in Table 3.
- Fig. 6 it is clarified that, in the case of comparative example 3 where 2%-Cr steel roll was subjected to discharge dull texturing process, there is a significant decrease in roughness with an increase in rolling distance.
- comparative example 4 where a cemented carbide was subjected to direct discharge dull texturing process to obtain high roughness, since the hardness of the cemented carbide is significantly high, the best roll roughness retainability with respect to the rolling distance was achieved.
- fracturing occurred in the roll surface after a rolling distance of 1.67 km, it was difficult to further continue rolling. This is because, as described above, in the case where a cemented carbide is subjected to direct discharge processing, a crack occurs and grows due to stress applied when rolling is performed, which makes it difficult to use such a roll in practical rolling.
- the recess and projection layer 2y which is formed on the outer peripheral surface of the roll barrel 2x, which has a surface roughness Ra of 2.0 ⁇ m to 10.0 ⁇ m, and which is formed of granular chromium, since it is possible to inhibit a decrease in surface roughness Ra due to abrasion and a deterioration in work roll properties due to, for example, the occurrence of a crack, even when there is an increase in rolling distance, it is possible to stably perform skin pass rolling.
- the shape (flatness) of the steel strip is likely to be deteriorated due to thermal stress generated when quenching is performed and due to transformation stress generated when transformation occurs in a metallographic structure. It is not possible to eliminate such a shape defect of a steel strip even if shape correction of the steel strip is tried when cold rolling is performed before annealing is performed. Therefore, it is necessary to perform shape correction by performing skin pass rolling on the steel strip after annealing has been performed.
- a high-tensile-strength steel sheet having a tensile strength of 980 MPa or higher is used as a raw material for automobile parts, which are obtained by performing press forming on the steel sheet.
- the surface of the steel sheet is subjected to dull texturing process (recessed and projected processing).
- the dull texturing process of the surface of the steel strip 1 the surface condition of the steel strip is controlled by printing the recessed and projected shape of the rolling work rolls 2 of the skin pass rolling mill 10 onto the surface of the steel sheet, where the recessed and projected shape of the rolling work rolls are ordinarily prepared by performing dull texturing process in advance.
- the elongation ratio is controlled by applying tension to the steel strip and by setting a work roll gap when skin pass rolling is performed.
- a tension and a rolling load higher than conventional ones are necessary.
- the roll barrel 2x is made of a cemented carbide having a Young's modulus of 450 GPa or higher. With this, even when rolling is performed on a high-tensile-strength steel sheet having a tensile strength of 980 MPa or higher, it is possible to achieve the desired load per unit width without increasing roll diameter.
- the recess and projection layer 2y is formed of granular chromium, which is precipitated by performing a chromium plating. With this, it is possible not only to form the recess and projection layer 2y without a crack but also to achieve a Vickers hardness with which the abrasion is less likely to occur in the surface, even when rolling is repeated.
- the recess and projection layer 2y is formed of granular chromium, since the projected portion of the granular chromium has a spherical shape, there is a decreased local stress concentration during rolling, which results in an increase in abrasion resistance compared with the case of an ordinary chromium coating layer. As a result, since there is a decrease in the frequency of the repair and replacement of the work rolls, it is possible to stably operate a rolling process.
- a technique of the present invention is applied to a stand-alone skin pass rolling mill illustrated in Fig. 4
- the technique of the present invention may be applied to rolling mills which are installed as in-line rolling mills in continuous process lines such as a continuous annealing line (CAL) and a continuous galvanizing line (CGL).
- CAL continuous annealing line
- CGL continuous galvanizing line
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- Engineering & Computer Science (AREA)
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Description
- The present invention relates to a rolling work roll for rolling a high-strength steel strip and a rolling mill having the roll, and a rolling method.
- Conventionally, a skin pass rolling mill, with which soft reduction is performed on a steel strip with a rolling reduction ratio of, for example, 1% or less, is known. A steel strip is homogeneously elongated by the skin pass rolling mill so that the shape of the steel strip is corrected to obtain predetermined flatness. Moreover, the properties of the steel strip, such as mechanical properties, such as yield point elongation, tensile strength, and elongation, and surface roughness, are improved by performing skin pass rolling. Nowadays, due to a trend toward a high value-added steel strip, there is an increasing demand for a hard steel strip typified by a high-tensile-strength steel strip. Particularly in the case of a high-tensile-strength steel sheet having a tensile strength of a 980 MPa or higher, a significantly high rolling load is necessary to achieve an elongation ratio required for shape correction.
- Therefore, various kinds of skin pass rolling methods for a high-tensile-strength steel sheet have been proposed to date (for example, refer to
Patent Literature 1 to Patent Literature 3).Patent Literature 1 discloses a method in which skin pass rolling is performed by using a work roll having a surface average roughness Ra of 3.0 µm to 10.0 µm.Patent Literature 2, which forms the basis for the preamble ofclaim 1, discloses a method utilizing a cemented carbide which consists of tungsten carbide (WC) and cobalt (Co) and whose surface layer has a Young's modulus of 500 GPa or higher as a roll material.Patent Literature 3 discloses a method in which skin pass rolling is performed by using a roll whose surface layer has a Young's modulus of 450 GPa or higher and whose surface roughness Ra is 1 µm or more and 10 µm or less. -
- PTL 1:
Japanese Unexamined Patent Application Publication No. 2008-173684 - PTL 2:
Japanese Unexamined Patent Application Publication No. 2017-119303 - PTL 3:
Japanese Unexamined Patent Application Publication No. 2011-189404 - In the case of
Patent Literature 1 toPatent Literature 3 described above, the surface of a rolling work roll has a predetermined arithmetic average roughness which is obtained by performing dull texturing process. Usually, it is considered that, when dull texturing process is performed, for example, a shot blasting processing method or a discharge dull texturing process is used as described inPatent Literature 1. However, in the case of such a method, there is a risk of a problem such as a decrease in surface roughness due to abrasion or crack growth with an increase in rolling distance. In such a case, there is a problem in that it is necessary, for example, to repair or replace a rolling work roll due to the above problem occurring in the rolling work roll, which makes it difficult to stably perform a rolling operation. - An object of the present invention is to provide a rolling work roll with which it is possible to stably perform a rolling operation when skin pass rolling is performed on a high-strength steel strip and a rolling mill having the roll, and a rolling method.
- The present invention has the features to solve the problems as described in the appended claims. Advantageous Effects of Invention
- By using the rolling work roll and a rolling mill having the roll, and the rolling method according to the present invention described above, since a recess and projection layer which is formed on the outer peripheral surface of the roll barrel, which has an arithmetic average roughness of 2.0 µm to 10.0 µm, and which contains granular chromium is used, it is possible to inhibit problems occurring in a work roll such as a decrease in surface roughness due to abrasion and crack growth, even when there is an increase in rolling distance, which makes it possible to stably perform a rolling operation.
-
- [
Fig. 1] Fig. 1 is a schematic diagram illustrating a preferable embodiment of a rollingmill 10 having rollingwork rolls 2 according to the present invention. - [
Fig. 2] Fig. 2 is an enlarged surface photograph illustrating an example of a recess andprojection layer 2y of therolling work roll 2 in the skin pass rolling mill inFig. 1 . - [
Fig. 3] Fig. 3 is a graph illustrating an example of the variation in surface roughness with respect to a plating time. - [
Fig. 4] Fig. 4 is a graph illustrating an example of the variation in rolling load with respect to an elongation ratio in the case of conventional examples 1 and 2, comparative example 1, and example 1 in Table 1. - [
Fig. 5] Fig. 5 is an enlarged surface photograph illustrating the surface of a cemented carbide which has been subjected to conventional discharge dull texturing process. - [
Fig. 6] Fig. 6 is a graph illustrating the variation in surface roughness of the rolls with respect to a rolling distance of the work rolls when a rolling experiment is performed by using the rolling work rolls given in Table 3. Description of Embodiments - Hereafter, the embodiments of the present invention will be described.
Fig. 1 is a schematic diagram illustrating a preferable embodiment of a rollingmill 10 having rolling work rolls according to the present invention. The rollingmill 10 inFig. 1 is used for performing skin pass rolling on a wide steel strip having a tensile strength of, for example, 980 MPa or higher. The skinpass rolling mill 10 has a pair ofrolling work rolls 2 and back-uprolls 3, each of which supports a corresponding one of therolling work rolls 2. Apayoff reel 5 is arranged upstream of the skinpass rolling mill 10, and atension reel 6 is arranged downstream of the skinpass rolling mill 10. Thereby, while asteel strip 1 is subjected to tension by using thepayoff reel 5 and thetension reel 6, thesteel strip 1 is subjected to rolling reduction by using therolling work rolls 2 so that thesteel strip 1 is subjected to a predetermined elongation ratio of, for example, 0.2% to 1.0%. However, bridle rolls may be arranged upstream or downstream of the skinpass rolling mill 10 to apply tension to thesteel strip 1. - The
rolling work roll 2 has a structure in which aroll barrel 2x made of a cemented carbide is fixed to, for example, a shaft. Theroll barrel 2x is made of a cemented carbide which has a Young's modulus of 450 GPa or higher and which contains, for example, by mass%, 86% tungsten carbide (WC) and a balance of cobalt (Co). In the case where Young's modulus is 450 GPa or higher, it is possible to prevent an increase in the contact arc length in a roll bite between therolling work rolls 2 and thesteel strip 1 due to the flattening deformation of therolling work rolls 2 and to thereby prevent an excessive increase in rolling load acting on therolling work rolls 2, even when skin pass rolling is performed on a high-strength steel sheet. - In the part corresponding to the roll barrel surface of the
roll barrel 2x, a recess andprojection layer 2y containing granular Cr is formed. In the recess andprojection layer 2y, the recessed and projected shape including the surface morphology is formed by performing chromium plating and thereby precipitating granular chromium so that an arithmetic average roughness (hereinafter, referred to as "surface roughness") Ra of 2.0 µm to 10.0 µm is obtained. Here, it is preferable that the recess andprojection layer 2y be formed at least on the roll barrel surface of theroll barrel 2x, but the recess andprojection layer 2y may be formed throughout the outer peripheral surface of theroll barrel 2x. - Incidentally, in the case where skin pass rolling is performed with a rolling reduction ratio of 1.0% or less by using
rolling work rolls 2 having high surface roughness Ra, there is a decrease in rolling load. This is considered to be because, since the rough recessed and projected shape of therolling work rolls 2 is printed onto the surface of the steel strip, there is a marked phenomenon (elongation effect), in which the portions of the steel strip that are pushed out by the indentation of the projected parts of the work roll contribute to elongation. - In the case where the surface roughness Ra is less than 2.0 µm, when plastic deformation is induced by indenting the recessed and projected shape of the rolling work rolls 2 onto the surface of the steel sheet, since the adjacent recessed portions and projected portions interfere with each other, there is an insufficient elongation effect. In particular, it is preferable that the surface roughness Ra of the rolling work rolls 2 be 3.0 µm or more to realize the elongation effect. Here, under a skin pass rolling condition in which a low elongation ratio of about 0.2% is applied, in the case where the surface roughness Ra of the work rolls is more than 4.0 µm, the distance between adjacent projected portions is so large that there is almost no plastic deformation interference. Therefore, to effectively realize the elongation effect and to thereby decrease the rolling load, it is preferable that the surface roughness Ra of the recess and
projection layer 2y be more than 4.0 µm. - On the other hand, it is preferable that the surface roughness Ra of the recess and
projection layer 2y not be more than 10.0 µm from the viewpoint of not only extreme difficulty in stably forming large surface roughness on the rolling work rolls 2 in industrial processes but also roll service life. Therefore, it is preferable that the surface roughness Ra of the work rolls be 10.0 µm or less. - This recess and
projection layer 2y is formed of granular Cr, which is precipitated by performing a chromium plating treatment. First, as a pretreatment for a chromium plating treatment which is performed to improve the adhesiveness between the surface of theroll barrel 2x and a chromium coating layer, after the surface of theroll barrel 2x is polished so that the surface roughness Ra thereof is, for example, 0.2 µm, the polished surface is subjected to, for example, a sand blasting treatment so as to have a surface roughness Ra of 0.8 µm. Subsequently, the surface of theroll barrel 2x is subjected to a washing treatment followed by a chromium plating treatment. - The chromium plating treatment is performed, for example, under the conditions of a low plating bath temperature of 50°C or lower and a high current density of 60 A/dm2 or more. With this, it is possible to increase the diameter of Cr crystal grains which are precipitated on the surface of the
roll barrel 2x. That is, in the case of an industrially used hard chromium coating layer, the morphology and hardness of Cr precipitated vary depending on electroplating conditions (plating bath temperature, current density, and plating time). Generally, in the case of bright plating, which is widely used, the treatment is performed under the conditions of a plating bath temperature of about 50°C to 60°C and a current density of about 40 A/dm2 to 60 A/dm2 to obtain a flat and smooth surface. On the other hand, in the case of the recess andprojection layer 2y described above, since it is necessary that a recessed and projected shape be formed to obtain the predetermined surface roughness Ra, plating is performed under the conditions of a low plating bath temperature of 50°C or lower and a high current density of 60 A/dm2 or more to precipitate granular Cr. -
Fig. 2 is an enlarged surface photograph illustrating an example of the recess and projection layer of the rolling work roll in the skin pass rolling mill inFig. 1 . In the case of the recess andprojection layer 2y inFig. 2 , chromium plating was performed in a plating solution containing chromic acid (CrO3) and sulfuric acid (H2SO4) under the conditions of a plating bath temperature of 37°C, a current density of 120 A/dm2, and a plating time of 150 min. Thereby, a granular recess andprojection layer 2y was formed on the surface of theroll barrel 2x through the precipitation of Cr. At this time, when the surface roughness Ra was determined by using a contact-type roughness meter, the surface roughness Ra was 3.9 µm. In addition, no crack or the like occurred in the recess andprojection layer 2y. - The surface roughness Ra of the recess and
projection layer 2y is controlled by controlling plating time.Fig. 3 is a graph illustrating the variation in surface roughness Ra after the plating when only a plating time is varied under the plating conditions forFig. 2 . Since there is an increase in surface roughness Ra with an increase in plating time, it is possible to achieve desired surface roughness Ra by controlling the plating conditions. Here, it is preferable that the average grain diameter of Cr precipitated on the roll surface by performing chromium plating be 50 µm or more. This is for the purpose of effectively realizing an elongation effect due to the indentation of the recessed and projected shape onto the steel sheet surface. By increasing the average grain diameter of Cr, since it is possible to increase the distance between adjacent recessed portions and projected portions, it is possible to inhibit interference between the adjacent recessed portions and projected portions when plastic deformation is induced by the indentation of the recessed and projected shape onto the surface of the steel sheet. - A rolling experiment was performed to clarify the effect of decreasing a rolling load due to rolling work rolls 2 having the recess and
projection layer 2y described above. Here, in the experiment, a high-tensile-strength steel sheet having a thickness of 0.215 mm, a width of 20 mm, a length of 200 mm, and a yield stress of 1500 MPa was used as a sample material. In addition, a 4-high rolling mill having work rolls having a diameter of φ70 mm was used as a skinpass rolling mill 10 to perform cut-sheet rolling without tension under a dry condition without a lubricant. This was a 1/7-scale model experiment for a roll diameter and a sheet thickness used in practical rolling performed on a high-tensile-strength steel sheet for an automobile. - By performing rolling with various roll gaps by using 4 kinds of work rolls given in Table 1 as work rolls, an investigation was conducted regarding the relationship between the rolling load and the elongation ratio, which was derived from a change in the length of the steel sheet before and after rolling.
[Table 1] No. Roll Barrel Material Roll Barrel Young's Modulus (GPa) Dull Texturing Process Arithmetic Average Roughness Ra (µm) Note 1 2%-Cr Steel 206 Bright Polishing 0.2 Comparative Example 1 2 2%-Cr Steel 206 Discharge Dull Texturing Process 3.0 Conventional Example 1 3 Cemented carbide (86% WC) 503 Bright Polishing 0.2 Conventional Example 2 4 Cemented carbide (86% WC) 503 Cr Plating for Dull Texturing Process 2.5 Example 1 - In Table 1, in the case of comparative example 1 (No. 1), the
roll barrel 2x was made of 2%-Cr steel having a Young's modulus of 206 GPa, and the surface thereof was subjected to grindstone polishing to obtain a surface roughness Ra of 0.2 µm. In the case of conventional example 1 (No. 2), theroll barrel 2x was made of 2%-Cr steel, and the surface thereof was subjected to discharge dull texturing process to obtain a surface roughness Ra of 3.0 µm. In the case of conventional example 2 (No. 3), theroll barrel 2x was made of a cemented carbide containing, by mass%, 86% tungsten carbide (WC) and a balance of cobalt and having a Young's modulus of 503 GPa. The surface thereof was subjected to grindstone polishing to obtain a surface roughness Ra of 0.2 µm. In the case of example 1 (No. 4), theroll barrel 2x was made of the same cemented carbide as in the case of conventional example 2 (No. 3), and the surface thereof was subjected to chromium plating for dull texturing process to form the recess andprojection layer 2y having a surface roughness Ra of 2.5 µm. -
Fig. 4 is a graph illustrating the variation in load per unit width with respect to an elongation ratio in the case of conventional examples 1 and 2, comparative example 1, and example 1. As illustrated inFig. 4 , on the basis of a comparison between comparative example 1 (No. 1) and conventional example 1 (No. 2), whose work rolls are both made of 2%-Cr steel, in terms of load per unit width for the same elongation ratio, the load per unit width of conventional example 1 (No. 2), in which the surface roughness is large, is lower than that of comparative example 1, which indicates that the elongation effect due to the indentation of the projected portions of the surface of the rolling work rolls onto the surface of the steel sheet was realized. - On the other hand, in the case of conventional example 2 (No. 3) where the
roll barrel 2x was made of a cemented carbide, the load per unit width was lower than that for the same elongation in the case of conventional example 1 (No. 2), which indicates that the effect of inhibiting flattening deformation due to an increase in the Young's modulus of the rolls was realized. In the case of example 1 (No. 4), the load per unit width was lower than that in the case of conventional example 2 (No. 3) as a result of the realization of not only the elongation effect due to the indentation of the projected portions of the surface of the rolling work rolls but also the effect of inhibiting flattening deformation of the rolls, which indicates that the effect of decreasing the rolling load was large. - Incidentally, skin pass rolling is usually performed with an elongation ratio of about 0.2% to 1.0%, and there is an improvement in the flatness of a steel strip with an increase in elongation ratio within such a range of the elongation ratio. Here, the term " elongation ratio " denotes the ratio of a change in the length in the longitudinal direction of a steel strip before and after rolling to the original length. In the case where the elongation ratio is 0.2% or more, since it is possible to sufficiently correct the shape of a steel strip, even if it is a high-strength cold-rolled steel strip, it is possible to achieve generally good flatness on the front and back surface sides of the steel strip. In addition, it is preferable that the elongation ratio applied to a steel strip be 0.5% or less to control the rolling load acting on the work rolls and the skin
pass rolling mill 10 to be within the load capacity of the skin pass rolling mill. - To evaluate the soundness of a roll surface when continuous operation is performed, a rolling contact test in which two rolling work rolls were pressed against each other with a constant surface pressure while rotating was performed in the case of comparative example 2 and example 2 described below. In the case of comparative example 2, the
roll barrel 2x was made of a cemented carbide (having a Young's modulus of 503 GPa) containing, by mass%, 86% tungsten carbide (WC) and a balance of cobalt, and the surface thereof was subjected to direct discharge dull texturing process to obtain a surface roughness Ra of 3.0 µm. -
Fig. 5 is an enlarged surface photograph illustrating the surface of the recess and projection layer in the case where theroll barrel 2x made of a cemented carbide was subjected to dull texturing process by performing direct discharge processing as in the case of comparative example 2. As illustrated inFig. 5 , a crack CK occurred on the surface due to the impact when discharge processing was performed. Here, it is known that a crack CK occurs in the case where a material such as a cemented carbide which contains mainly ceramics that is a brittle material is subjected to discharge processing. - On the other hand, in the case of example 2, the
roll barrel 2x was made of a cemented carbide (having a Young's modulus of 503 GPa) containing, by mass%, 86% tungsten carbide (WC) and a balance of cobalt, and the surface thereof was subjected to chromium plating to form the recess andprojection layer 2y having a surface roughness Ra of 3.0 µm. - As a continuous operation experiment, by using a 4-high rolling mill having work rolls having a diameter of φ70 mm and a barrel length of 40 mm, the work rolls were rotated at a velocity of 50 mpm while the work rolls were pressed against each other with a load of 1.8 tons. The pressure between the work rolls has a maximum value in an elastic contact region between the work rolls which are pressed against each other, and the maximum pressure in this experiment was set to be 1011 MPa. This value is at the comparable level of the surface pressure applied to the work rolls of a skin pass rolling mill used in a continuous annealing line in practical use or the like. In the experiment, the rolling contact test was performed for various durations, and the surface of the work roll was observed after each time by using a microscope to check whether or not, for example, cracking, fracturing, or separation occurred in the surface of the work roll. The experimental results are summarized in Table 2.
[Table 2] No. 0 min (Initial Stage) 30 min 60 min 120 min 240 min 300 min Note 1 Crack Observed Crack Observed Crack Observed Crack Observed Crack Observed Separation Occurred Comparative Example 2 2 Sound Sound Sound Sound Sound Sound Example 2 - In Table 2, in the case of comparative example 2 where the predetermined surface roughness Ra was obtained by performing discharge dull texturing process, it was clarified that a crack occurred on the surface of the work roll at the initial stage (refer to
Fig. 5 ). In the case where rolling is performed by using a rolling work roll having such a crack, the crack grows with an increase in rolling contact time due to stress applied to the rolling work roll during rolling. As a result, after a rolling contact time of 300 min, fracturing and separation occurred in the roll surface. On the other hand, in the case where the rolling work roll which had been subjected to chromium plating for dull texturing process was used, for example, no cracking or fracturing was observed (as denoted by the term "sound" in Table 2), which indicates that it is possible to stably use such a roll. - In addition, to evaluate roll roughness retainability when continuous operation is performed, a rolling experiment was performed by using 4 kinds of rolling work rolls, as in comparative example 3, comparative example 4, example 3, and example 4 given in Table 3 below.
[Table 3] No. Roll Barrel Material Roll Barrel Young's Modulus (GPa) Dull Texturing Process Arithmetic Surface Roughness Ra (µm) Note 1 2%-Cr Steel 206 Discharge Dull Texturing Process 4.5 Comparative Example 3 2 Cemented carbide (80% Co) 450 Discharge Dull Texturing Process 4.5 Comparative Example 4 3 Cemented carbide (80% WC) 450 Cr Plating for Dull Texturing Process 4.5 Example 3 4 Cemented carbide (80% WC) 450 Cr Plating for Dull Texturing Process + Hard Cr Plating 4.5 Example 4 - In the case of comparative example 3, the
roll barrel 2x was made of 2%-Cr steel having a Young's modulus of 206 GPa, and the surface thereof was subjected to discharge dull texturing process to obtain a surface roughness Ra of 4.5 µm. In the case of comparative example 4, theroll barrel 2x was made of a cemented carbide (having a Young's modulus of 450 GPa) containing, by mass%, 80% tungsten carbide (WC) and a balance of cobalt, and the surface thereof was subjected to discharge dull texturing process to obtain a surface roughness Ra of 4.5 µm without performing chromium plating. - On the other hand, in the case of example 3, the
roll barrel 2x was made of a cemented carbide (having a Young's modulus of 450 GPa) containing, by mass%, 80% tungsten carbide (WC) and a balance of cobalt, and the surface thereof was subjected to chromium plating to form the recess andprojection layer 2y having a surface roughness of 4.5 µm. At this time, the average grain diameter of Cr precipitated was 60 µm. - In the case of example 4, after granular Cr was precipitated on the roll surface by using the same method as that in the case of example 3 described above, a hard chromium coating layer having a thickness of 1 µm was further formed on the roll surface under alternate plating conditions. Here, the reason why the additional hard chromium coating layer was formed under alternate plating conditions is as follows. In the case where a recessed and projected shape is formed by precipitating granular Cr on the surface of the roll under the plating conditions of a low plating bath temperature of 50°C or lower and a high current density of 60 A/dm2, the Vickers hardness of the chromium coating layer is about 700 to 900. On the other hand, in the case where an ordinary hard chromium coating layer is formed under the conditions of a plating bath temperature of about 50°C to 60°C and a current density of about 40 A/dm2 to 60 A/dm2, the Vickers hardness of the hard chromium coating layer is about 900 to 1100. Here, the reason why a hard chromium coating layer was further formed under alternate plating conditions after granular Cr had been precipitated on the roll surface by using the same method as that in the case of example 3 is because, since a significantly hard coating layer is formed on the outermost surface of the rolling work roll, there is a further improvement in abrasion resistance.
- The reason why the thickness of the additional hard chromium coating layer is set to be 1 µm as described above is because, in the case where the thickness is equal to or more than that, since there is a decrease in the height difference in the recessed and projected shape formed by grains in the early stage, there is a decreased elongation effect when skin pass rolling is performed. That is, by forming an additional thin hard chromium coating layer on the granular chromium precipitated in the early stage of the plating process, it is possible to increase the hardness of the surface of the coating layer without changing the roughness pattern formed of granular chromium. Here, for such a reason, it is preferable that the thickness of the additional hard chromium coating layer be 0.5 µm to 10 µm.
- Then, by using the 4 kinds of rolling work rolls having a roll diameter of φ70 mm and barrel length of 40 mm given in Table 3 as rolling work rolls of a 4-high rolling mill, a continuous coil rolling experiment was performed with tension being applied. A high-tensile-strength steel sheet having a thickness of 0.215 mm, a width of 20 mm, and a yield stress of 1500 MPa was used as a material to be rolled. Coil rolling was performed with a tension of 100 MPa being applied to the inlet and exit sides of the mill, under a dry condition without a lubricant, and with a rolling load per unit width of 0.2 ton/mm. At this time, the variation in the surface roughness of each of the rolls with respect to a rolling distance was determined.
-
Fig. 6 is a graph illustrating the variation in surface roughness with respect to a rolling distance when a rolling experiment is performed by using the rolling work rolls given in Table 3. As illustrated inFig. 6 , it is clarified that, in the case of comparative example 3 where 2%-Cr steel roll was subjected to discharge dull texturing process, there is a significant decrease in roughness with an increase in rolling distance. In the case of comparative example 4 where a cemented carbide was subjected to direct discharge dull texturing process to obtain high roughness, since the hardness of the cemented carbide is significantly high, the best roll roughness retainability with respect to the rolling distance was achieved. However, since fracturing occurred in the roll surface after a rolling distance of 1.67 km, it was difficult to further continue rolling. This is because, as described above, in the case where a cemented carbide is subjected to direct discharge processing, a crack occurs and grows due to stress applied when rolling is performed, which makes it difficult to use such a roll in practical rolling. - On the other hand, it is clarified that, in the case of example 3 and example 4 of the present invention, although there is a decrease in roughness due to early-stage abrasion, the roll roughness retainability with respect to the rolling distance thereafter was far better than that in the case of comparative example 3. In particular, it is clarified that, in the case of example 4 where a thin hard chromium coating layer is formed on the surface, excellent roll roughness retainability was achieved.
- According to the embodiments described above, by using the recess and
projection layer 2y which is formed on the outer peripheral surface of theroll barrel 2x, which has a surface roughness Ra of 2.0 µm to 10.0 µm, and which is formed of granular chromium, since it is possible to inhibit a decrease in surface roughness Ra due to abrasion and a deterioration in work roll properties due to, for example, the occurrence of a crack, even when there is an increase in rolling distance, it is possible to stably perform skin pass rolling. In particular, it is possible to decrease a rolling load by only changing the raw material of the rollingwork roll 2 used for the skinpass rolling mill 10 and a method for processing the surface thereof without causing any change in equipment such as a roll radius, which has a significant effect on the industry. - In particular, in the case of the kind of a high-tensile-strength steel sheet that is manufactured by using a continuous annealing method in which quenching and tempering are performed, the shape (flatness) of the steel strip is likely to be deteriorated due to thermal stress generated when quenching is performed and due to transformation stress generated when transformation occurs in a metallographic structure. It is not possible to eliminate such a shape defect of a steel strip even if shape correction of the steel strip is tried when cold rolling is performed before annealing is performed. Therefore, it is necessary to perform shape correction by performing skin pass rolling on the steel strip after annealing has been performed.
- In addition, a high-tensile-strength steel sheet having a tensile strength of 980 MPa or higher is used as a raw material for automobile parts, which are obtained by performing press forming on the steel sheet. To increase oil retainability when press forming is performed, it is necessary that the surface of the steel sheet is subjected to dull texturing process (recessed and projected processing). In the dull texturing process of the surface of the
steel strip 1, the surface condition of the steel strip is controlled by printing the recessed and projected shape of the rolling work rolls 2 of the skinpass rolling mill 10 onto the surface of the steel sheet, where the recessed and projected shape of the rolling work rolls are ordinarily prepared by performing dull texturing process in advance. - The elongation ratio is controlled by applying tension to the steel strip and by setting a work roll gap when skin pass rolling is performed. To achieve a larger elongation ratio, a tension and a rolling load higher than conventional ones are necessary. In particular, in the case where skin pass rolling is performed on a high-tensile-strength steel strip having a tensile strength of higher than 980 MPa, since the deformation resistance of the steel strip is significantly high, further larger rolling load is necessary.
- Since an often-used ordinary skin pass rolling mill is not designed under the assumption that skin pass rolling is performed on such a high-tensile-strength steel strip, the rolling load exceeds the load capacity of the skin pass rolling mill when skin pass rolling is performed on a high-tensile-strength steel strip. Here, it is considered that rolling load is decreased by changing the structure of a skin pass rolling mill from a 4-high type to a 6-high type or the like and thereby decreasing a work roll diameter. However there is a problem in that, since this requires extensive equipment modification, there is an increase in cost.
- As described above, particularly in the case of a high-tensile-strength steel strip where shape correction is required, there may be a problem of an increase in rolling load to the extent that the capacity of an existing skin pass rolling mill is exceeded. Therefore, it is a fact that shape correction is performed by using a leveler or the like in subsequent processes now, which results in a problem of an increase in manufacturing costs due to additional processes and of a protracted delivery period.
- Therefore, processing is performed on the surfaces of the rolling work rolls 2 to achieve a surface roughness Ra of 2.0 µm to 10.0 µm so that it is possible to realize the desired rolling effect while decreasing the rolling load. In addition, the
roll barrel 2x is made of a cemented carbide having a Young's modulus of 450 GPa or higher. With this, even when rolling is performed on a high-tensile-strength steel sheet having a tensile strength of 980 MPa or higher, it is possible to achieve the desired load per unit width without increasing roll diameter. - On the other hand, when discharge dull texturing process is performed to achieve a surface roughness Ra of 2.0 µm to 10.0 µm as described above, since there is a decrease in the surface roughness Ra of the rolling work rolls due to abrasion with an increase in rolling distance, there may be a case where the effect of maintaining low rolling load is not realized.
- Therefore, the recess and
projection layer 2y is formed of granular chromium, which is precipitated by performing a chromium plating. With this, it is possible not only to form the recess andprojection layer 2y without a crack but also to achieve a Vickers hardness with which the abrasion is less likely to occur in the surface, even when rolling is repeated. In addition, in the case where the recess andprojection layer 2y is formed of granular chromium, since the projected portion of the granular chromium has a spherical shape, there is a decreased local stress concentration during rolling, which results in an increase in abrasion resistance compared with the case of an ordinary chromium coating layer. As a result, since there is a decrease in the frequency of the repair and replacement of the work rolls, it is possible to stably operate a rolling process. - In addition, by using at least one rolling
mill 10 described above to perform skin pass rolling with an elongation ratio of 0.2% or more, since it is possible to sufficiently perform shape correction on a steel sheet, even when it is a high-strength cold-rolled steel strip, it is generally possible to achieve good flatness on the front and back surface sides of the steel strip. - The embodiments of the present invention are not limited to the embodiments described above, and it is possible to make various changes to the embodiments within the scope as defined by the appended claims. In addition, although an example in which a technique of the present invention is applied to a stand-alone skin pass rolling mill illustrated in
Fig. 4 has been described, the technique of the present invention may be applied to rolling mills which are installed as in-line rolling mills in continuous process lines such as a continuous annealing line (CAL) and a continuous galvanizing line (CGL). -
- 1
- steel strip
- 2
- rolling work roll
- 2x
- roll barrel
- 2y
- recess and projection layer
- 3
- back-up roll
- 5
- payoff reel
- 6
- tension reel
- 10
- skin pass rolling mill
- CK
- crack
- Ra
- arithmetic average roughness (surface roughness)
Claims (4)
- A rolling work roll (2) comprising:a roll barrel (2x) made of a cemented carbide having a Young's modulus of 450 GPa or higher; anda recess and projection layer (2y) which is formed on an outer peripheral surface of the roll barrel (2x), characterized in that the recess and projection layer (2y) has an arithmetic average roughness of 2.0 µm to 10.0 µm, and which contains granular chromium.
- The rolling work roll (2) according to Claim 1, wherein the recess and projection layer (2y) is formed by performing chromium plating and thereby precipitating granular chromium.
- A skin pass rolling mill (10) having at least one rolling stand and comprising the rolling work roll (2) according to Claim 1 or 2.
- A rolling method comprising performing skin pass rolling with an elongation ratio of 0.2% or more by using at least one stand of the rolling mill (10) according to Claim 3.
Applications Claiming Priority (2)
Application Number | Priority Date | Filing Date | Title |
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JP2018232080 | 2018-12-12 | ||
PCT/JP2019/041848 WO2020121657A1 (en) | 2018-12-12 | 2019-10-25 | Work roll for rolling, rolling machine equipped with same, and rolling method |
Publications (3)
Publication Number | Publication Date |
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EP3895818A1 EP3895818A1 (en) | 2021-10-20 |
EP3895818A4 EP3895818A4 (en) | 2022-01-26 |
EP3895818B1 true EP3895818B1 (en) | 2023-03-08 |
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Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
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EP19895432.3A Active EP3895818B1 (en) | 2018-12-12 | 2019-10-25 | Work roll for rolling, rolling machine equipped with same, and rolling method |
Country Status (5)
Country | Link |
---|---|
EP (1) | EP3895818B1 (en) |
JP (1) | JP6680426B1 (en) |
CN (1) | CN113195123B (en) |
MX (1) | MX2021007044A (en) |
WO (1) | WO2020121657A1 (en) |
Families Citing this family (1)
Publication number | Priority date | Publication date | Assignee | Title |
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JP7338604B2 (en) * | 2020-10-27 | 2023-09-05 | Jfeスチール株式会社 | Manufacturing method of cold-rolled steel sheet |
Family Cites Families (22)
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JPS52107243A (en) * | 1976-03-05 | 1977-09-08 | Yoshinobu Kobayashi | Surface treating process for cemented carbide |
JPS61129205A (en) * | 1984-11-29 | 1986-06-17 | Sumitomo Metal Ind Ltd | Wear-resistant rolling roll |
JPH0765227B2 (en) * | 1987-11-04 | 1995-07-12 | 住友金属工業株式会社 | Method for manufacturing chrome plating roll |
JPH0688051B2 (en) * | 1988-04-08 | 1994-11-09 | 住友金属工業株式会社 | Chrome-plated roll for cold rolling |
JPH07122157B2 (en) * | 1990-09-11 | 1995-12-25 | 株式会社サトーセン | Roll surface treatment method |
JP3296886B2 (en) * | 1993-06-21 | 2002-07-02 | 日新製鋼株式会社 | Continuous cold rolling equipment |
JP3209705B2 (en) * | 1997-03-25 | 2001-09-17 | 川崎製鉄株式会社 | Composite roll for cold rolling |
JP3438695B2 (en) * | 2000-02-29 | 2003-08-18 | Jfeスチール株式会社 | Manufacturing method of chrome plating roll |
JP4358524B2 (en) * | 2002-01-18 | 2009-11-04 | 新日本製鐵株式会社 | Cold rolling, conveying, cooling chrome plating roll, manufacturing method thereof, and manufacturing method of steel sheet |
JP4096628B2 (en) * | 2002-05-29 | 2008-06-04 | Jfeスチール株式会社 | Cold rolling machine for metal sheet and cold rolling method using the same |
US7296517B2 (en) * | 2003-11-11 | 2007-11-20 | Fujifilm Corporation | Roll for metal rolling, and support for lithographic printing plate |
JP4379115B2 (en) * | 2003-12-26 | 2009-12-09 | Jfeスチール株式会社 | Dull roll for cold rolling metal sheet and method for producing the same |
CN2829927Y (en) * | 2005-05-25 | 2006-10-25 | 上海通乐冶金设备工程有限公司 | Frosting roller for cold rolling banding steel |
JP5045264B2 (en) | 2006-06-23 | 2012-10-10 | Jfeスチール株式会社 | Method for temper rolling of steel strip and method for producing high-tensile cold-rolled steel sheet |
JP5488080B2 (en) * | 2010-03-17 | 2014-05-14 | 新日鐵住金株式会社 | Temper rolling mill and temper rolling method with excellent roughness transfer efficiency |
CN102381878B (en) * | 2010-08-31 | 2013-12-25 | 宝山钢铁股份有限公司 | Manufacturing method of flat roller with self-texturing feature |
CN202052762U (en) * | 2011-03-30 | 2011-11-30 | 芜湖恒达薄板有限公司 | Working roll for cold-rolling strip steel |
CN103056173A (en) * | 2011-10-21 | 2013-04-24 | 襄阳博亚精工装备股份有限公司 | Turning roll with spongy chromium plating technique to achieve roll face texturing and manufacturing method thereof |
CN105127203A (en) * | 2015-10-10 | 2015-12-09 | 上海通乐冶金设备工程有限公司 | Shot blasting texturing chromeplate work roll for cold rolling temper mill and production process of work roll |
JP2017100149A (en) * | 2015-11-30 | 2017-06-08 | Jfeスチール株式会社 | Hard metal work roll and method for utilization thereof |
JP6428731B2 (en) * | 2015-12-28 | 2018-11-28 | Jfeスチール株式会社 | Temper rolling mill and temper rolling method |
CN207043019U (en) * | 2017-06-30 | 2018-02-27 | 河源正信硬质合金有限公司 | Hard alloy roll |
-
2019
- 2019-10-25 EP EP19895432.3A patent/EP3895818B1/en active Active
- 2019-10-25 JP JP2019571566A patent/JP6680426B1/en active Active
- 2019-10-25 MX MX2021007044A patent/MX2021007044A/en unknown
- 2019-10-25 CN CN201980082402.1A patent/CN113195123B/en active Active
- 2019-10-25 WO PCT/JP2019/041848 patent/WO2020121657A1/en unknown
Also Published As
Publication number | Publication date |
---|---|
JPWO2020121657A1 (en) | 2021-02-15 |
WO2020121657A1 (en) | 2020-06-18 |
EP3895818A4 (en) | 2022-01-26 |
CN113195123A (en) | 2021-07-30 |
CN113195123B (en) | 2023-05-23 |
MX2021007044A (en) | 2021-08-11 |
EP3895818A1 (en) | 2021-10-20 |
JP6680426B1 (en) | 2020-04-15 |
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