CN117295831A - Method for producing cold-rolled steel sheet and method for producing cold-rolled steel sheet - Google Patents
Method for producing cold-rolled steel sheet and method for producing cold-rolled steel sheet Download PDFInfo
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- CN117295831A CN117295831A CN202280033546.XA CN202280033546A CN117295831A CN 117295831 A CN117295831 A CN 117295831A CN 202280033546 A CN202280033546 A CN 202280033546A CN 117295831 A CN117295831 A CN 117295831A
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- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 64
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 48
- 229910000831 Steel Inorganic materials 0.000 claims abstract description 168
- 239000010959 steel Substances 0.000 claims abstract description 168
- 238000001816 cooling Methods 0.000 claims abstract description 64
- 238000000034 method Methods 0.000 claims abstract description 60
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims abstract description 50
- 238000005098 hot rolling Methods 0.000 claims abstract description 25
- 239000000203 mixture Substances 0.000 claims abstract description 18
- 239000000126 substance Substances 0.000 claims abstract description 15
- 230000009467 reduction Effects 0.000 claims description 6
- 238000005097 cold rolling Methods 0.000 abstract description 23
- 230000008569 process Effects 0.000 abstract description 10
- 238000005096 rolling process Methods 0.000 description 39
- 238000010438 heat treatment Methods 0.000 description 27
- 229910001562 pearlite Inorganic materials 0.000 description 18
- 230000009466 transformation Effects 0.000 description 18
- 229910000859 α-Fe Inorganic materials 0.000 description 18
- 238000012360 testing method Methods 0.000 description 17
- 230000005855 radiation Effects 0.000 description 10
- 230000000694 effects Effects 0.000 description 7
- 239000012535 impurity Substances 0.000 description 7
- 238000005728 strengthening Methods 0.000 description 6
- 238000000605 extraction Methods 0.000 description 5
- 238000011084 recovery Methods 0.000 description 5
- 238000001953 recrystallisation Methods 0.000 description 5
- 238000004804 winding Methods 0.000 description 5
- 229910001566 austenite Inorganic materials 0.000 description 4
- 230000000052 comparative effect Effects 0.000 description 4
- 238000005336 cracking Methods 0.000 description 4
- 239000006104 solid solution Substances 0.000 description 4
- 239000002253 acid Substances 0.000 description 3
- 238000009529 body temperature measurement Methods 0.000 description 3
- 238000004364 calculation method Methods 0.000 description 3
- 238000009749 continuous casting Methods 0.000 description 3
- 238000011156 evaluation Methods 0.000 description 3
- 238000007542 hardness measurement Methods 0.000 description 3
- 229910000734 martensite Inorganic materials 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 238000005192 partition Methods 0.000 description 3
- 238000005554 pickling Methods 0.000 description 3
- 238000005406 washing Methods 0.000 description 3
- VEXZGXHMUGYJMC-UHFFFAOYSA-N Hydrochloric acid Chemical compound Cl VEXZGXHMUGYJMC-UHFFFAOYSA-N 0.000 description 2
- 238000000137 annealing Methods 0.000 description 2
- 238000005266 casting Methods 0.000 description 2
- 238000010586 diagram Methods 0.000 description 2
- 230000006872 improvement Effects 0.000 description 2
- 150000004767 nitrides Chemical class 0.000 description 2
- 238000001556 precipitation Methods 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
- 235000013619 trace mineral Nutrition 0.000 description 2
- 239000011573 trace mineral Substances 0.000 description 2
- 238000007545 Vickers hardness test Methods 0.000 description 1
- 238000013459 approach Methods 0.000 description 1
- 230000003749 cleanliness Effects 0.000 description 1
- 230000001771 impaired effect Effects 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 238000000691 measurement method Methods 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 238000002156 mixing Methods 0.000 description 1
- 238000012986 modification Methods 0.000 description 1
- 230000004048 modification Effects 0.000 description 1
- 238000007747 plating Methods 0.000 description 1
- 238000002360 preparation method Methods 0.000 description 1
- 239000002994 raw material Substances 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- 238000002791 soaking Methods 0.000 description 1
- 239000007921 spray Substances 0.000 description 1
- 238000005507 spraying Methods 0.000 description 1
- 238000012546 transfer Methods 0.000 description 1
- 239000002699 waste material Substances 0.000 description 1
- 229910052726 zirconium Inorganic materials 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0247—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment
- C21D8/0263—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the heat treatment following hot rolling
-
- 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
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B3/00—Rolling materials of special alloys so far as the composition of the alloy requires or permits special rolling methods or sequences ; Rolling of aluminium, copper, zinc or other non-ferrous metals
-
- B—PERFORMING OPERATIONS; TRANSPORTING
- B21—MECHANICAL METAL-WORKING WITHOUT ESSENTIALLY REMOVING MATERIAL; PUNCHING METAL
- B21B—ROLLING OF METAL
- B21B45/00—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills
- B21B45/02—Devices for surface or other treatment of work, specially combined with or arranged in, or specially adapted for use in connection with, metal-rolling mills for lubricating, cooling, or cleaning
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0205—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips of ferrous alloys
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/021—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips involving a particular fabrication or treatment of ingot or slab
- C21D8/0215—Rapid solidification; Thin strip casting
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D8/00—Modifying the physical properties by deformation combined with, or followed by, heat treatment
- C21D8/02—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips
- C21D8/0221—Modifying the physical properties by deformation combined with, or followed by, heat treatment during manufacturing of plates or strips characterised by the working steps
- C21D8/0226—Hot rolling
-
- C—CHEMISTRY; METALLURGY
- C21—METALLURGY OF IRON
- C21D—MODIFYING THE PHYSICAL STRUCTURE OF FERROUS METALS; GENERAL DEVICES FOR HEAT TREATMENT OF FERROUS OR NON-FERROUS METALS OR ALLOYS; MAKING METAL MALLEABLE, e.g. BY DECARBURISATION OR TEMPERING
- C21D9/00—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor
- C21D9/46—Heat treatment, e.g. annealing, hardening, quenching or tempering, adapted for particular articles; Furnaces therefor for sheet metals
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/34—Ferrous alloys, e.g. steel alloys containing chromium with more than 1.5% by weight of silicon
-
- C—CHEMISTRY; METALLURGY
- C22—METALLURGY; FERROUS OR NON-FERROUS ALLOYS; TREATMENT OF ALLOYS OR NON-FERROUS METALS
- C22C—ALLOYS
- C22C38/00—Ferrous alloys, e.g. steel alloys
- C22C38/18—Ferrous alloys, e.g. steel alloys containing chromium
- C22C38/40—Ferrous alloys, e.g. steel alloys containing chromium with nickel
- C22C38/58—Ferrous alloys, e.g. steel alloys containing chromium with nickel with more than 1.5% by weight of manganese
Abstract
The present invention can provide a method for manufacturing a cold-rolled steel sheet, which is a method for manufacturing a steel sheet in the middle of manufacturing a high-tension cold-rolled steel sheet, capable of suppressing end cracks of the steel sheet in the subsequent cold-rolling process. The method for manufacturing the cold-rolled steel sheet comprises the following steps: hot rolling a slab having a predetermined chemical composition so that the outlet side temperature of the finishing mill is 800 ℃ or higher and 940 ℃ or lower; within 3.0 seconds after at least a portion of the hot rolled sheet passes through the final stand of the finishing mill and is fed out onto an output table at 100L/min/m 2 Cooling at least a part of the steel sheet for 0.1 seconds or more at the above water density; and coiling the cooled hot-rolled steel sheet at a coiling temperature of 550 ℃ or higher.
Description
Technical Field
The present invention relates to a method for manufacturing a cold-rolled steel sheet in the middle of manufacturing a high-tensile cold-rolled steel sheet having a tensile strength of 980MPa or more, and a method for manufacturing a cold-rolled steel sheet using the steel sheet manufactured by the method.
Background
When a hot-rolled steel sheet is cold-rolled, cracks may occur in the ends in the sheet width direction (hereinafter also referred to as "widthwise ends" or "widthwise ends") and the ends in the direction parallel to the rolling direction (hereinafter also referred to as "longitudinal leading ends" or "longitudinal trailing ends"). These end cracks are liable to occur in the following cases: in the process of manufacturing a high-tensile cold-rolled steel sheet, the steel used contains a large amount of elements such as Mn that can improve hardenability. The end cracks thus generated may cause breakage of the steel sheet by taking the end cracks as a starting point in the cold rolling process and in the subsequent steps such as the annealing step and the plating step. Therefore, in order to reduce the risk of such end cracks, the hot-rolled steel sheet is removed from the portion where the end cracks are likely to occur. However, as a result, the yield is lowered.
On the other hand, in the cooling process of the hot rolled steel sheet after coiling, the cooling rate of the widthwise end portions of the coiled steel sheet is faster than the widthwise central portion (hereinafter also referred to as "widthwise central portion") of the steel sheet. Therefore, in a hot-rolled steel sheet using a steel containing a large amount of an element that can improve hardenability such as Mn, ferrite and/or pearlite transformation is not sufficiently performed at both ends in the width direction of the steel sheet, and both ends in the width direction of the steel sheet have a hard structure containing a large amount of martensite. The same is true for the front end in the longitudinal direction and the rear end in the longitudinal direction of the steel sheet. For the reasons stated above, it is considered that: in a cold rolling process or the like in manufacturing a high-tensile cold-rolled steel sheet, end cracks of the steel sheet are likely to occur.
As a method for suppressing the cracking of the end portion of the steel sheet, for example, patent document 1 describes a cold rolling method for cold rolling a strip-shaped hot-rolled steel sheet wound in a coil shape and cooled, which includes: a developing step of developing the hot-rolled steel sheet from the coil; a heating step of heating both widthwise end portions of the developed hot-rolled steel sheet to a temperature of 400 ℃ or higher and less than the A1 point of the hot-rolled steel sheet material; an acid washing step of washing the hot-rolled steel sheet after the heating step with an acid; and a cold rolling step of cold-rolling the hot-rolled steel sheet after the pickling step.
Prior art literature
Patent literature
Patent document 1: japanese patent laid-open publication No. 2019-141888
Disclosure of Invention
The present invention provides a method for manufacturing a cold-rolled steel sheet, which is a method for manufacturing a steel sheet in the middle of manufacturing a high-tension cold-rolled steel sheet, and which can suppress end cracks of the steel sheet in the subsequent cold-rolling process.
The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention.
That is, a first aspect of the present invention relates to a method for producing a cold-rolled steel sheet, comprising:
will be contained in chemical composition
C:0.15 to 0.25 mass% inclusive,
Si:0.8 to 3.0 mass% inclusive,
Mn:1.8 to 3.0 mass% inclusive,
Ni, cu, cr, mo:1.0 mass% or less (including 0 mass%)
Ti, nb, V:1.0 mass% or less (including 0 mass%), based on the total mass of the composition
B: less than 0.01% (including 0% by mass)
Hot-rolling the slab so that the outlet side temperature of the finishing mill is 800 ℃ to 940 ℃;
within 3.0 seconds after at least a portion of the hot rolled sheet passes through the final stand of the finishing mill and is fed out onto an output table at 100L/min/m 2 Cooling at least a part of the steel sheet for 0.1 seconds or more at the above water density;
and coiling the cooled hot-rolled steel sheet at a coiling temperature of 550 ℃ or higher.
A second aspect of the present invention relates to a method for manufacturing a cold rolled steel sheet, further comprising: the steel sheet manufactured by the method of the first aspect is cold-rolled at a reduction of 30% to 80%.
Drawings
Fig. 1 is a schematic view showing an example of a method for producing a cold-rolled steel sheet according to the present embodiment.
Fig. 2 is a schematic diagram showing the position of a steel sheet test piece for hardness measurement in this example.
Detailed Description
As described above, in the method described in patent document 1, martensite in the microstructure at both widthwise ends of the steel sheet is converted into tempered martensite by heating. As a result, both ends in the width direction of the steel sheet are softened moderately, and end cracks of the steel sheet are suppressed.
However, in order to heat the steel sheet to a temperature of not more than the A1 point and not less than 400 ℃, a device capable of high-temperature heating and a cost for installing the device are required. Further, since the electric power required for the production line of the cold-rolled steel sheet is also increased, the cost is also increased. Therefore, there is a need for a new method capable of suppressing end cracks in a cold rolling process without the equipment cost and running cost of such an additional high temperature heating step.
Accordingly, the present inventors have repeatedly studied various methods for producing a new cold-rolled steel sheet capable of suppressing occurrence of edge cracks in the steel sheet during cold rolling. The present invention has been completed with particular attention paid to the outlet side temperature of the finishing mill during hot rolling and to the water cooling control step after passing through the final stand of the finishing mill.
Specifically, the method for manufacturing a cold-rolled steel sheet according to the present embodiment includes: using a slab satisfying a specified chemical composition, performing hot rolling so that the outlet side temperature of the finishing mill falls within a specified temperature range; then, after passing through the last frame of the finishing mill, water-cooling the steel plate under specified conditions; then, the steel sheet is coiled at a temperature equal to or higher than the predetermined temperature. According to this method, ferrite and/or pearlite transformation can be promoted at both widthwise end portions, the leading end or the trailing end of the hot-rolled steel sheet, and these end portions can be softened moderately. As a result, the produced steel sheet can be suppressed from having end cracks during the subsequent cold rolling. The produced steel sheet is further subjected to cold rolling, optional heat treatment, or the like, whereby a high-Tensile cold-rolled steel sheet, particularly a high-Tensile cold-rolled steel sheet having a Tensile Strength (TS: tensile Strength) of 980MPa or more can be obtained.
That is, according to the present invention, it is possible to provide a method for manufacturing a cold-rolled steel sheet, which is a method for manufacturing a steel sheet in the middle of manufacturing a high-tension cold-rolled steel sheet, capable of suppressing end cracks of the steel sheet in the subsequent cold-rolling process.
Hereinafter, embodiments of the present invention will be described in detail. The scope of the present invention is not limited to the embodiments described herein, and various modifications may be made without departing from the scope of the present invention.
1. Method for producing cold-rolled steel sheet
Fig. 1 is a schematic view showing an example of a method for producing a cold-rolled steel sheet according to the present embodiment. In fig. 1, each symbol represents a rolling mill 1, a heating furnace 2, a hot rolling mill 3, an output table (run-outable) 4, a cooling apparatus 5, a roughing mill 31, a final stand 311 of the rolling mill, a finishing mill 32, and a final stand 321 of the finishing mill. In the method for producing a cold-rolled steel sheet according to the present embodiment, for example, as shown in fig. 1, a slab having a specific chemical composition is first charged into a heating furnace 2 of a rolling mill 1. Thereafter, the slab extracted from the heating furnace 2 is hot rolled by the hot rolling mill 3 while controlling the outlet side temperature of the finishing mill 32 to be within a specific temperature range. Next, the hot rolled steel sheet fed onto the output table 4 is water-cooled by the cooling equipment 5 under specific conditions. Thereafter, the steel sheet is coiled while the coiling temperature is adjusted to a specific temperature or higher.
These steps and steps optionally included will be described in detail below.
(preparation of slab)
First, a slab satisfying a specified chemical composition is prepared. The slabs may be prepared by any known method. As a method for producing a slab, there is a method of producing a slab by melting steel having the chemical composition described below and then continuously casting the steel. If necessary, a cast obtained by ingot casting or continuous casting may be cogged to obtain a slab.
The slab used in the method for producing a cold-rolled steel sheet according to the present embodiment contains C in its chemical composition: 0.15 mass% or more and 0.25 mass% or less, si:0.8 mass% or more and 3.0 mass% or less, mn:2.0 mass% or more and 3.0 mass% or less, ni, cu, cr, mo:1.0 mass% or less (including 0 mass%), ti, nb, V:1.0 mass% or less (including 0 mass%), and B: less than 0.01% (including 0 mass%). In addition, the slab preferably further contains P:0.1 mass% or less (including 0 mass%), S:0.01 mass% or less (including 0 mass%), al:0.10 mass% or less (including 0 mass%), and N:0.01 mass% or less (including 0 mass%).
The chemical composition of the slab will be described in more detail below.
[ C:0.15 mass% or more and 0.25 mass% or less
C is an important element for improving the strength of the steel sheet. By setting the C content to 0.15 mass% or more, the effect of improving the strength can be exerted, and finally, a high-tensile cold-rolled steel sheet having a tensile strength of 980MPa or more can be obtained. When the C content is 0.25 mass% or less, hardenability can be improved, and insufficient promotion of ferrite and/or pearlite transformation can be prevented. Further, it is possible to suppress the decrease in weldability of the steel sheet caused by the excessive C content. The content of C is preferably 0.16 mass% or more, more preferably 0.17 mass% or more, and still more preferably 0.18 mass% or more. On the other hand, the C content is preferably 0.23 mass% or less, more preferably 0.21 mass% or less, and still more preferably 0.19 mass% or less.
[ Si:0.8 mass% or more and 3.0 mass% or less
Si is a solid solution strengthening element that contributes to the strength of the steel sheet. By setting the Si content to 0.8 mass% or more, the effect of improving the strength can be exerted, and finally, a high-tensile cold-rolled steel sheet having a tensile strength of 980MPa or more can be obtained. By setting the Si content to 3.0 mass% or less, it is possible to suppress a significant decrease in weldability of the steel sheet due to an excessive Si content. The Si content is preferably 1.0 mass% or more, more preferably 1.5 mass% or more, and still more preferably 1.8 mass% or more. On the other hand, the Si content is preferably 2.5 mass% or less, more preferably 2.1 mass% or less, and still more preferably 1.9 mass% or less.
[ Mn:1.8 mass% or more and 3.0 mass% or less
Mn is a solid solution strengthening element contributing to the improvement of the strength of a steel sheet, and is an effective element for improving the strength of a steel sheet by improving hardenability. By setting the Mn content to 1.8 mass% or more, the strength can be improved, and finally a high-tensile cold-rolled steel sheet having a tensile strength of 980MPa or more can be obtained. When the Mn content is 3.0 mass% or less, hardenability can be improved, and insufficient promotion of ferrite and/or pearlite transformation can be prevented. The Mn content is preferably 2.0 mass% or more, more preferably 2.3 mass% or more, and still more preferably 2.5 mass% or more. On the other hand, the Mn content is preferably 2.9 mass% or less, more preferably 2.8 mass% or less, and still more preferably 2.7 mass% or less.
[ Ni, cu, cr, mo:1.0 mass% or less (including 0 mass%) ]
Ni, cu, cr or Mo are solid solution strengthening elements contributing to the strength of the steel sheet. These elements are also effective elements for improving the strength of the steel sheet by improving the hardenability. Therefore, 1 or more elements selected from these elements may be included in the chemical composition of the slab. In order to effectively exert the strength-improving effect, the content of 1 or more elements selected from Ni, cu, cr and Mo is preferably 0.05 mass% or more, respectively. On the other hand, in order to improve hardenability, the promotion of ferrite and/or pearlite transformation is prevented from becoming insufficient, and the content of 1 or more elements selected from Ni, cu, cr and Mo is set to 1.0 mass% or less (including 0 mass%). The content of 1 or more elements selected from Ni, cu, cr, and Mo is more preferably 0.1 mass% or more, respectively. On the other hand, the content of 1 or more elements selected from Ni, cu, cr and Mo is preferably 0.5 mass% or less, respectively.
[ Ti, nb, V:1.0 mass% or less (including 0 mass%) ]
Ti, nb, or V is a precipitation strengthening element that contributes to the strength of the steel sheet. Therefore, 1 or more elements selected from these elements may be included in the chemical composition of the slab. In order to effectively exert the precipitation strengthening effect, the content of 1 or more elements selected from Ti, nb, and V is preferably 0.01 mass% or more, respectively. On the other hand, in order to avoid saturation of the strength-improving effect and cost waste, the content of 1 or more elements selected from Ti, nb, and V is set to 1.0 mass% or less, respectively. The content of 1 or more elements selected from Ti, nb, and V is preferably 0.02 mass% or more, respectively. On the other hand, the content of 1 or more elements selected from Ti, nb, and V is more preferably 0.5 mass% or less, respectively.
[ B:0.01 mass% or less (0 mass% or more) ]
B is an effective element for improving the strength of the steel sheet by improving the hardenability. Thus, B may be included in the chemical composition of the slab. In order to effectively exhibit hardenability, the B content is preferably 0.0001 mass% or more. On the other hand, in order to improve hardenability, the promotion of ferrite and/or pearlite transformation is prevented from becoming insufficient, and the B content is set to 0.01 mass% or less, preferably 0.005 mass% or less.
[ P: preferably 0.1 mass% or less (including 0 mass%) ]
P is an impurity element which is inevitably present. P contributes to strength improvement by solid solution strengthening, but segregates to prior austenite grain boundaries, embrittles the grain boundaries, and thus causes end cracks. Therefore, the P content is preferably suppressed to 0.1 mass% or less, more preferably to 0.05 mass% or less.
[ S: preferably 0.01% by mass or less (including 0% by mass) ]
S is an impurity element which is inevitably present. S forms MnS inclusions. The MnS inclusions become the starting points of cracks, resulting in end cracks. Therefore, the S content is preferably suppressed to 0.01 mass% or less, more preferably to 0.005 mass% or less.
[ Al (S-Al): preferably 0.10 mass% or less (including 0 mass%) ]
A1 is added as a deoxidizing material. In order to effectively exert the function as a deoxidizing material, the Al (S-Al) content is preferably 0.001 mass% or more. On the other hand, al may deteriorate the cleanliness of steel. Therefore, the Al (s—al) content is preferably 0.10 mass% or less, more preferably 0.05 mass% or less.
[ N: preferably 0.01% by mass or less (including 0% by mass) ]
N is an impurity element which is inevitably present. N may form coarse nitrides. The coarse nitrides become the starting points of cracks, resulting in end cracks. Therefore, the N content is preferably suppressed to 0.01 mass% or less, more preferably to 0.005 mass% or less.
The slab according to the present embodiment may contain any other known components in addition to the above components, as long as the promotion of ferrite and/or pearlite transformation, the necessary strength, the sufficient workability, and the like are not impaired. Examples of the other known optional components include Zr, hf, ca, mg, REM (rare earth element).
Remainder (remainder)
The remainder being Fe and unavoidable impurities. The unavoidable impurities include trace elements (for example, as, sb, sn, etc.) which are brought in according to the conditions of the raw materials, the manufacturing facilities, etc., and the mixing of these trace elements, etc. is allowed. The smaller the contents of P, S and N, the more preferable the contents. Therefore, these elements can be regarded as unavoidable impurities. However, these elements can exert their effects better in the present invention by limiting the content to a specific range, and thus are specified as described above. Therefore, in the present specification, the concept of "unavoidable impurities" constituting the remainder does not include elements specified in the compositional range thereof.
(soaking treatment of slab)
Thereafter, the prepared slab is charged into a heating furnace as a general step before rolling.
When heating the slab, the temperature of the slab drawn out by the heating furnace is preferably set to 1180 ℃ or higher and 1280 ℃ or lower. When the withdrawal temperature of the slab in the heating furnace is 1280 ℃ or lower, coarsening of the microstructure of the steel sheet can be suppressed. As a result, ferrite and/or pearlite transformation can be prevented from being suppressed, thereby preventing hardening of the end portions. By setting the withdrawal temperature of the slab to 1180 ℃ or higher, it is possible to prevent the hot rolling from being difficult due to an excessive rolling load. In the present specification, the furnace extraction temperature refers to a temperature calculated by a method described in the following examples.
(Hot rolling)
Subsequently, hot rolling is performed using the slab extracted from the heating furnace to obtain a hot-rolled steel sheet. The hot rolling is performed so that the outlet side temperature of the finishing mill is 800 ℃ or higher and 940 ℃ or lower, and other conditions are not particularly limited and may be appropriately set within a range that does not impair the effects of the present embodiment.
Generally, hot rolling includes rough rolling and finish rolling. Hereinafter, each rolling will be described.
The rough rolling may be performed using, for example, a roughing mill 31 shown in fig. 1. The rough rolling is preferably performed so that the temperature of the outlet side of the roughing mill 31 shown in fig. 1, specifically, the temperature of the steel sheet at the outlet side of the last stand 311 of the roughing mill is 1000 ℃ or higher and 1200 ℃ or lower.
By setting the outlet side temperature of the roughing mill to 1200 ℃ or lower, coarsening of the microstructure of the steel sheet can be suppressed. As a result, ferrite and/or pearlite transformation can be prevented from being suppressed, thereby preventing hardening of the end portions. By setting the outlet side temperature of the roughing mill to 1000 ℃ or higher, it is possible to prevent the rolling load from becoming excessive and the hot rolling from becoming difficult. In the present specification, the outlet side temperature of the roughing mill can be measured by the method described in the following examples. The radiation thermometer may be arranged at a position separated from the last stand of the roughing mill by 0.1m to 20 m.
The time from the extraction of the heating furnace to the completion of rough rolling (the time between extraction and rough rolling) is preferably 240 seconds or less. By setting the time from the extraction from the heating furnace to the completion of rough rolling to 240 seconds or less, coarsening of the microstructure of the steel sheet can be suppressed. As a result, ferrite and/or pearlite transformation can be prevented from being suppressed, thereby preventing hardening of the end portions. In the present specification, the time between the drawing and the rough rolling can be measured by the method described in the following examples.
Finish rolling can be performed, for example, using the finishing mill 32 shown in fig. 1. The finish rolling is preferably performed so that the temperature of the outlet side of the finishing mill 32 shown in fig. 1, specifically, the temperature of the steel sheet measured on the outlet side of the last stand 321 of the finishing mill is 800 ℃ or higher and 940 ℃ or lower.
If finish rolling is performed at high temperature, the worked structure formed during hot rolling may recover, recrystallize, and/or grain size. As a result, ferrite and/or pearlite transformation after coiling is suppressed, resulting in hardening of the steel sheet end. Therefore, by setting the outlet side temperature of the finishing mill to 940 ℃ or lower, recovery of austenite, recrystallization, and/or grain growth can be suppressed, thereby suppressing end hardening of the steel sheet. By setting the outlet side temperature of the finishing mill to 800 ℃ or higher, it is possible to prevent the hot rolling from being difficult due to an increase in rolling load.
The outlet side temperature of the finishing mill is preferably 930 ℃ or less, more preferably 920 ℃ or less. On the other hand, the outlet side temperature of the finishing mill is preferably 850 ℃ or higher, more preferably 870 ℃ or higher. In the present specification, the outlet side temperature of the finishing mill can be measured by the method described in the following examples. The radiation thermometer may be disposed at a position separated from the last stand of the finishing mill by 0.im to 10 m.
Further, the time from the passage of the steel sheet through the last stand of the roughing mill to the arrival at the first stand of the finishing mill (time between roughing and finishing) is preferably 50 seconds or less. By setting the time from the last stand passing through the roughing mill to the first stand reaching the finishing mill to 50 seconds or less, recovery of the worked structure formed during hot rolling, recrystallization, and/or grain growth can be suppressed. As a result, ferrite and/or pearlite transformation after coiling can be prevented more reliably. In the present specification, the time between rough rolling and finish rolling can be determined by the method described in the following examples.
The hot rolled steel sheet leaving the last stand of the finishing mill is fed out to an output table 4 as shown in fig. 1, for example. At this time, the plate speed of the hot rolled steel plate on the output table 4 varies depending on the position of the steel plate in the longitudinal direction, and is about 300 m/min to 1000 m/min.
(Cooling control on output stage)
Next, at least a part of the hot rolled steel sheet was fed through the final stand of the finishing mill and then fed out to the output table within 3.0 seconds at 100L/min/m 2 The above water density cools at least a part of the steel sheet for 0.1 seconds or more.
If the steel sheet is maintained at a high temperature during cooling on the output table, the worked structure formed during hot rolling may recover, recrystallize and/or grain size grow. As a result, ferrite and/or pearlite transformation after coiling is suppressed, thereby causing hardening of the steel sheet end. Therefore, by performing cooling control on the output table, recovery of austenite, recrystallization, and/or grain growth can be suppressed, thereby suppressing end hardening of the steel sheet.
The thickness of the hot rolled steel sheet to be cooled is not particularly limited as long as it is a thickness of a hot rolled steel sheet usual in the art, that is, about 1.0mm to 5.0 mm.
In the present specification, "at least a part of a steel sheet" means: the portion of the hot rolled steel sheet that is to be cooled. Specifically, the "at least a portion of the steel sheet" may be any one of the entire surface of the steel sheet, a specific region in the steel sheet, and a specific portion in the steel sheet. From the viewpoint of ease of cooling control, "at least a part of the steel sheet" is preferably the whole steel sheet. Alternatively, in the case where emphasis is placed on a region of the steel sheet where end cracks are likely to occur, it is preferable that "at least a part of the steel sheet" includes 1 or more regions selected from a region near both ends in the width direction of the steel sheet, a region near the front end in the longitudinal direction, and a region near the rear end in the longitudinal direction. In other words, the method for manufacturing a cold-rolled steel sheet according to the present embodiment can be applied more effectively by setting these regions as the portions of the steel sheet to be water-cooled.
In the present specification, "cooling at least a part of a steel sheet within 3.0 seconds after the steel sheet passes through the last stand of the finishing mill and is sent out onto the output table" strictly means the following. The portion of the steel sheet to be cooled is cooled within 3.0 seconds after being directly fed to the output table, based on the time point of the last stand of the finishing mill passing through the hot rolling (i.e., 0 seconds base point). Specifically, for example, in fig. 1, it means: the portion of the steel sheet to be cooled reaches the cooling device 5 and is cooled within 3.0 seconds after the time point of passing through the last stand 321 of the finishing mill. Hereinafter, the time required until the start of cooling is also referred to as "water cooling start time". The sheet speed of the steel sheet varies with the position in the longitudinal direction. Therefore, in the present specification, the water cooling start time is defined as a time calculated by the method described in the following examples, that is, a time calculated from the minimum value of the plate speed.
By setting the water cooling start time to 3.0 seconds or less, it is possible to avoid holding the hot rolled steel sheet at a high temperature on the output table for a long period of time. If the hot rolled steel sheet is maintained at a high temperature for a long period of time, the worked structure formed during the hot rolling of the steel sheet may recover, recrystallize and/or grow grains. As a result, ferrite and/or pearlite transformation after coiling is eventually suppressed, thereby causing hardening of the steel sheet end. The water cooling start time is preferably 2.5 seconds or less, more preferably 2.0 seconds or less, and still more preferably 1.5 seconds or less.
By setting the water density in the cooling process to 100L/min/m 2 or more, it is possible to avoid the steel sheet on the output table from becoming insufficiently cooled. If the cooling of the steel sheet becomes insufficient, the worked structure formed during hot rolling may recover, recrystallize and/or grow. As a result, ferrite and/or pearlite transformation after coiling is suppressed, thereby causing hardening of the steel sheet end.
The water density during cooling is preferably 200L/min/m 2 The above is more preferably 250L/min/m 2 The above. The upper limit of the water density is not particularly limited, but is preferably 3000L/min/m, for example, from the viewpoint of securing the sheet-passing property of the steel sheet 2 The following is given. In the present specification, the water density can be obtained by the following method in the same manner as described in the following examples: the water flow rate (L/min) for cooling in the portion of the steel sheet to be cooled is divided by the length (m) and width (m) of the partition such as the cooling equipment. In the example described later, the water density was calculated when the portion of the steel sheet to be cooled was a position 4/5 of the total length of the steel sheet from the front end in the longitudinal direction of the steel sheet. The water flow rate for cooling may be controlled by adjusting a valve or the like provided in the cooling device.
By setting the total water cooling time (hereinafter, also referred to as "total water cooling time within 3 seconds") to 0.1 seconds or more, specifically, 3 seconds or less after passing through the last stand of the finishing mill, it is possible to avoid insufficient cooling of the steel sheet. If the cooling of the steel sheet becomes insufficient, the worked structure formed during hot rolling may recover, recrystallize and/or grow. As a result, ferrite and/or pearlite transformation after coiling is suppressed, thereby causing hardening of the steel sheet end.
The total water cooling time within 3 seconds is preferably 0.2 seconds or more, more preferably 0.4 seconds or more. The upper limit of the total water cooling time of 3 seconds or less is not particularly limited, but is less than 3 seconds. The total water cooling time of 3 seconds or less also varies with the position of the steel sheet in the longitudinal direction, as in the case of the water cooling start time. Therefore, in the present specification, the total water cooling time of 3 seconds or less is defined as a time calculated by the method described in the following examples, that is, a time calculated from the maximum value of the plate speed.
In the case where the total length of the output stand is 1, the temperature measured at a position 1/4 to 3/4 away from the final stand of the finishing mill (hereinafter, also referred to as "intermediate temperature") is preferably 650 ℃ or higher, more preferably 700 ℃ or higher, and still more preferably 750 ℃ or higher. By setting the intermediate temperature to 650 ℃ or higher, it is possible to prevent the cooling rate from becoming too fast and the winding temperature from being difficult to ensure. In the present specification, the intermediate temperature means: the temperatures measured were the same as those shown in the examples below. Specifically, the intermediate temperature refers to: when the total length of the output stand is 1, the temperature of the central portion in the coil width direction measured by a radiation thermometer provided at a position separated from the last stand of the finishing mill by 1/4 to 3/4.
The cooling may be performed by any known method, and is not particularly limited. For example, water cooling may employ top laminar flow equipment, bottom spray equipment, and the like.
(coiling)
Thereafter, the cooled hot-rolled steel sheet is coiled at a coiling temperature of 550 ℃ or higher.
By setting the coiling temperature to 550 ℃ or higher, it is ensured that the steel sheet is maintained in the temperature range where ferrite and/or pearlite transformation is performed for a sufficient time after coiling. As a result, hardening of the end portion of the steel sheet can be suppressed.
The winding temperature is preferably 600℃or higher, more preferably 630℃or higher. On the other hand, the winding temperature is preferably 750 ℃ or lower, more preferably 700 ℃ or lower. By setting the coiling temperature to 750 ℃ or less, recovery of the worked structure, recrystallization, and/or grain growth formed during hot rolling can be suppressed, and ferrite and/or pearlite transformation after coiling can be prevented from being suppressed. In the present specification, the winding temperature can be measured by the method described in the following examples. The position of the radiation thermometer is configured as follows: when the total length of the output table is 1, the position is separated by 1/5 from the winding machine side.
The coiled hot rolled steel sheet can be naturally cooled to normal temperature.
In the method for producing a steel sheet, the cold-rolled steel sheet according to the present embodiment in a coil form can be obtained through the steps described above and the steps optionally included. The thus obtained cold-rolled steel sheet according to the present embodiment can suppress cracking of the steel sheet end during the subsequent cold rolling. At this time, additional equipment costs and running costs for high-temperature heating are not required. Further, according to the method for manufacturing a cold-rolled steel sheet in the present embodiment, the problem of reduction in yield due to removal of a portion where end cracks are likely to occur in the subsequent cold rolling process can be solved.
2. Method for producing cold-rolled steel sheet
The method for manufacturing a cold-rolled steel sheet according to the present embodiment further includes: the steel sheet manufactured by the method of the above embodiment is cold-rolled. An example of the method for producing a cold-rolled steel sheet according to the present embodiment will be described below.
(acid washing)
The cold-rolled steel sheet produced by the method according to the above embodiment may be subjected to pickling prior to cold rolling. The pickling method is not particularly limited, and any known method can be used. For example, the scale may be removed by impregnation with hydrochloric acid or the like.
(Cold rolling)
The method of cold rolling is not particularly limited, and any known method can be used. For example, cold rolling may be performed at a reduction of 30% to 80% in order to obtain a desired plate thickness. The thickness of the cold-rolled steel sheet is not particularly limited.
In the production of a cold-rolled steel sheet, a cold-rolled steel sheet for producing a high-tensile cold-rolled steel sheet having a Tensile Strength (TS) of 980MPa or more can be obtained through the steps described above and optionally included steps. The cold-rolled steel sheet of the present embodiment thus obtained can suppress end cracks during cold rolling, and thus can reduce the risk of the steel sheet subsequently breaking due to end cracks or the like. Accordingly, by annealing the cold-rolled steel sheet by any method, a high-tensile cold-rolled steel sheet having a Tensile Strength (TS) of 980MPa or more can be suitably produced.
The outline of the present invention is described above, and the method for manufacturing a cold-rolled steel sheet according to the embodiment of the present invention are summarized as follows.
A first aspect of the present invention relates to a method for manufacturing a cold-rolled steel sheet, comprising:
will be contained in chemical composition
C:0.15 to 0.25 mass% inclusive,
Si:0.8 to 3.0 mass% inclusive,
Mn:1.8 to 3.0 mass% inclusive,
Ni, cu, cr, mo:1.0 mass% or less (including 0 mass%)
Ti, nb, V:1.0 mass% or less (including 0 mass%), based on the total mass of the composition
B: less than 0.01% (including 0% by mass)
Hot-rolling the slab so that the outlet side temperature of the finishing mill is 800 ℃ to 940 ℃;
within 3.0 seconds after at least a portion of the hot rolled sheet passes through the final stand of the finishing mill and is fed out onto an output table at 100L/min/m 2 The above water density is obtained by subjecting at least a part of the steel sheet to a treatment for 0.1 secondsCooling;
and coiling the cooled hot-rolled steel sheet at a coiling temperature of 550 ℃ or higher.
In the above method for producing a cold-rolled steel sheet, the slab preferably further comprises
P:0.1 mass% or less (including 0 mass%)
S:0.01 mass% or less (including 0 mass%)
Al:0.10 mass% or less (including 0 mass%), based on the total mass of the composition
N:0.01 mass% or less (including 0 mass%).
A second aspect of the present invention relates to a method for manufacturing a cold rolled steel sheet, further comprising: the steel sheet manufactured by the method of the first aspect is cold-rolled at a reduction of 30% to 80%.
Examples
Hereinafter, the present invention will be further specifically described by way of examples, but the present invention is not limited to the examples.
In this example, a cold-rolled steel sheet was actually produced by the method according to the present embodiment, and the risk of cracking of the end portion of the steel sheet during the subsequent cold rolling was calculated from the hardness of the produced test piece in the vicinity of the end portion of the steel sheet.
[ production of Cold rolled Steel sheet ]
After steel having a chemical composition (target chemical composition) shown in table 1 below was melted in a converter, slabs were produced by continuous casting. The slab produced by continuous casting is directly charged into a heating furnace in a state where the surface temperature is 200 ℃ or more and 900 ℃ or less, and is heated to a high temperature. Thereafter, the slab is drawn out of the heating furnace, and hot rolled by rough rolling and finish rolling. The thickness was finally 2.3mm. The hot rolled steel sheet is directly fed to an output stage, and the steel sheet on the output stage is cooled by a top laminar flow device and/or a bottom spraying device provided in front of the steel sheet. Thereafter, the cooled hot-rolled steel sheet is wound into a coil and cooled, thereby producing a cold-rolled steel sheet. The total length from the last stand of the finishing mill to the output table of the steel plate coiler was 188.3m.
In the above manufacturing method, cold-rolled steel sheets are manufactured under various conditions by changing conditions of hot rolling, cooling, and coiling. The temperature of the heating furnace during hot rolling, the temperature of the outlet side of the roughing mill, the time from the time of drawing the heating furnace to the time of finishing the roughing mill (time between drawing and roughing), the time from the last stand passing through the roughing mill to the first stand reaching the finishing mill (time between roughing and finishing), the temperature of the outlet side of the finishing mill, the time from the last stand passing through the finishing mill to the time of starting water cooling on the outlet stand (water cooling start time), the total water cooling time within 3 seconds after passing through the last stand of the finishing mill (total water cooling time within 3 seconds), the water density during cooling, the temperature of the steel sheet in the vicinity of the middle of the outlet stand (middle temperature), the time from the outlet side passing through the finishing mill to the temperature measured in the vicinity of the middle of the outlet stand (time between finishing-middle temperature measurement), and the coiling temperature are shown in table 2 below. In table 2 below, "-" indicates that the total water cooling time and the water density within 3.0 seconds are 0, because the water cooling start time has elapsed by 3.0 seconds.
In table 2, detailed measurement and calculation methods of each item are as follows.
Furnace extraction temperature: the temperature of the heating furnace is calculated from the temperature of the slab when the heating furnace is charged, the ambient temperature in the heating furnace, and the residence time in the heating furnace, by using heat transfer calculation.
Outlet side temperature of roughing mill: the temperature of the central portion in the coil width direction was measured using a radiation thermometer provided on the exit side of the roughing mill. The thermometer was set at a position 16.6m away from the last stand of the roughing mill.
Time between draw-rough rolling: the time from the withdrawal of the heating furnace to the end of rough rolling of the end in the longitudinal direction of the steel sheet was set as the withdrawal-rough rolling time.
Time between rough rolling and finish rolling: the time from the end of rough rolling of the tail end in the steel plate length direction to the start of finish rolling of the front end in the steel plate length direction was set as the rough rolling time-the time between finish rolling.
Outlet side temperature of finishing mill: the temperature of the central portion in the coil width direction was measured using a radiation thermometer provided on the outlet side of the finishing mill. The thermometer was placed 5.9m away from the last stand of the finishing mill.
Water cooling start time: the plate speed at the outlet side of the finishing mill varies with the position of the steel plate in the longitudinal direction. Therefore, the water cooling start time is defined based on the plate speed at the front end position where the plate speed in the longitudinal direction of the steel plate is the slowest and grains are liable to grow. Specifically, the water cooling start time was obtained as follows: the distance from the last stand of the finishing mill to the position on the output table where water cooling is performed is divided by the minimum value of the plate speed in the length direction of the steel plate.
Total water cooling time within 3 seconds: the total water cooling time of 3 seconds or less is a value obtained by determining a position 4/5 of the total length of the steel sheet from the longitudinal leading end of the steel sheet (in other words, a position 1/5 of the total length of the steel sheet from the longitudinal trailing end). Specifically, the total water cooling time of 3 seconds or less at this position was obtained by dividing the length (m) of the cooling equipment partition actually cooling by the maximum value of the plate speed in the longitudinal direction of the steel plate.
Water density: the water density is a value obtained by determining a position 4/5 away from the front end in the longitudinal direction of the steel sheet over the entire length of the steel sheet (in other words, a position 1/5 away from the rear end in the longitudinal direction of the steel sheet over the entire length of the steel sheet). Specifically, the water flow rate (L/min) for cooling is divided by the length (m) and width (m) of the cooling device partition actually cooling, thereby obtaining the water volume density in that location.
Intermediate temperature: the temperature of the central portion in the web width direction was measured using a radiation thermometer provided near the middle of the output stage. The thermometer was placed 56.1m away from the last stand of the finishing mill.
Time between finish rolling-intermediate temperature measurement: the time between the arrival of the front end in the longitudinal direction of the steel sheet at the radiation thermometer provided on the outlet side of the finishing mill and the arrival at the radiation thermometer provided near the middle of the output table was set as the time between finish rolling and middle temperature measurement.
Coiling temperature: the temperature of the central portion in the web width direction was measured using a radiation thermometer provided near the end of the output stage. The thermometer was set at a position 180.1m away from the last stand of the finishing mill.
In the classification shown in Table 2, the present invention example is a test piece in which the finish rolling outlet side temperature is 800℃or higher and 940℃or lower, and the water cooling start time is 3.0 seconds or less. On the other hand, comparative example 1 was a test piece in which the finish rolling outlet side temperature was higher than 940℃and the water cooling start time was 3.0 seconds or less. Comparative example 2 is a test piece in which the finish rolling outlet side temperature was 940℃or lower and the water cooling start time was more than 3.0 seconds. Comparative example 3 is a test piece in the case where the finish rolling outlet side temperature is higher than 940℃and the water cooling start time is higher than 3.0 seconds.
[ hardness measurement of test piece of Cold rolled Steel sheet ]
The hardness of each test piece of the cold-rolled steel sheet obtained by the above method was measured. Test pieces at both ends in the width direction of the steel sheet were cut out by shearing so as to include a position separated by 30m from the trailing end in the longitudinal direction of the steel sheet. The test piece size was 10mm (direction parallel to the rolling direction) ×20mm (plate width direction) ×2.3mm (plate thickness). Fig. 2 is a schematic diagram showing the position of a steel sheet test piece for hardness measurement. Arrow X indicates the position of the trailing end in the length direction. As shown in fig. 2, the test pieces are specifically cut in such a manner as to include the following positions: a position (indicated by an arrow Z) separated by 1mm from both ends in the width direction of the steel sheet from the position (indicated by a broken line Y) separated by 30m from the trailing end in the length direction of the steel sheet. Using the test piece thus cut, the vickers hardness at the following positions was measured: a position separated by 1mm from both ends in the width direction of the steel sheet, and a position at a quarter of the sheet thickness, among positions separated by 30m from the trailing end in the length direction of the cold-rolled steel sheet. The vickers hardness test was performed under a load of 9.807N, and the maximum value of the measured values at both ends in the width direction was used for evaluation. When the vickers hardness thus obtained was greater than 290HV, it was evaluated that the end portion of the manufactured cold-rolled steel sheet was hardened, and there was a risk of cracking of the end portion of the steel sheet during cold rolling.
The position separated from the trailing end in the longitudinal direction of the steel sheet by 30m is closer to the trailing end than the position where the water density was obtained in the above-described production process (the position separated from the leading end in the longitudinal direction of the steel sheet by 4/5 of the total length of the steel sheet). In the longitudinal direction of the steel sheet, it is assumed that the sheet speed of the steel sheet is higher as it approaches the trailing end, and that end hardening is generally more likely to occur. Therefore, if no end hardening is observed at a position separated by 30m from the trailing end in the longitudinal direction of the steel sheet, it is considered that, of course, no end hardening is observed at a position separated by 4/5 of the total length of the steel sheet from the leading end in the longitudinal direction of the steel sheet. Furthermore, from the result, it can be assumed that: by appropriately adjusting the portion of the steel sheet to be cooled as needed, hardening of the end portion of the steel sheet in the entire length direction from the leading end to the trailing end can be suppressed.
Table 3 below shows the vickers Hardness (HV) measured on the test piece of each steel sheet and the evaluation results thereof.
TABLE 3 Table 3
The end crack risk rate was calculated from the number of test pieces and the hardness evaluation result of the vickers hardness in each classification of table 3. The calculation results are shown in table 4 below.
TABLE 4 Table 4
(consider
As shown in table 4, the vickers hardness of all 6 test pieces of the present invention example was 290HV or less, and thus the end crack risk rate was 0. On the other hand, the end crack risk of the test pieces of comparative examples 1 to 3 was 0.33, 0.5 or 1.0. From these results, it can be seen that: by setting the outlet side temperature of the finishing mill to 940 ℃ or lower and the water cooling start time to 3.0 seconds or lower, recovery of austenite, recrystallization, and/or grain growth can be suppressed, and hardening of the end portion of the steel sheet can be suppressed.
The present application is based on the Japanese patent application No. 2021-079218 filed 5/7 of 2021, the content of which is included in the present application.
The present disclosure of embodiments and examples is to be considered in all respects as illustrative and not restrictive. The scope of the present invention is shown by the claims rather than the description of the embodiments described above, and all changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.
Industrial applicability
According to the present invention, a method for manufacturing a cold-rolled steel sheet can be provided that can suppress end cracks of the steel sheet during cold rolling. The produced cold-rolled steel sheet can be suitably used without causing a problem of reduction in yield when producing a high-tensile cold-rolled steel sheet having a tensile strength of 980MPa or more.
Claims (3)
1. A method for producing a cold-rolled steel sheet, characterized by comprising:
will be contained in chemical composition
C:0.15 to 0.25 mass% inclusive,
Si:0.8 to 3.0 mass% inclusive,
Mn:1.8 to 3.0 mass% inclusive,
Ni, cu, cr, mo:1.0 mass% or less and comprises 0 mass%,
Ti, nb, V:1.0 mass% or less and 0 mass% or less
B:0.01% or less and 0% by mass
Hot-rolling the slab so that the outlet side temperature of the finishing mill is 800 ℃ to 940 ℃;
within 3.0 seconds after at least a portion of the hot rolled sheet passes through the final stand of the finishing mill and is fed out onto an output table at 100L/min/m 2 Cooling at least a part of the steel sheet for 0.1 seconds or more at the above water density;
and coiling the cooled hot-rolled steel sheet at a coiling temperature of 550 ℃ or higher.
2. The method for producing a cold-rolled steel sheet according to claim 1, wherein,
the slab also contains
P:0.1 mass% or less and comprises 0 mass%,
S:0.01 mass% or less and comprises 0 mass%,
Al:0.10 mass% or less and 0 mass% or less
N:0.01 mass% or less and 0 mass% is included.
3. A method for manufacturing a cold-rolled steel sheet, characterized by further comprising:
a steel sheet produced by the method according to claim 1 or 2, which is cold-rolled at a reduction of 30% to 80%.
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2021079218A JP2022172888A (en) | 2021-05-07 | 2021-05-07 | Method for producing steel sheet for cold-rolling and method for producing cold-rolled steel sheet |
| JP2021-079218 | 2021-05-07 | ||
| PCT/JP2022/017334 WO2022234760A1 (en) | 2021-05-07 | 2022-04-08 | Method for producing steel sheet for cold rolling and method for producing cold-rolled steel sheet |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CN117295831A true CN117295831A (en) | 2023-12-26 |
Family
ID=83932177
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|---|---|---|---|
| CN202280033546.XA Pending CN117295831A (en) | 2021-05-07 | 2022-04-08 | Method for producing cold-rolled steel sheet and method for producing cold-rolled steel sheet |
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| Country | Link |
|---|---|
| JP (1) | JP2022172888A (en) |
| KR (1) | KR20240000569A (en) |
| CN (1) | CN117295831A (en) |
| WO (1) | WO2022234760A1 (en) |
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| JP5825205B2 (en) * | 2011-07-06 | 2015-12-02 | 新日鐵住金株式会社 | Cold rolled steel sheet manufacturing method |
| JP6237047B2 (en) * | 2013-09-25 | 2017-11-29 | 新日鐵住金株式会社 | High strength hot rolled steel sheet with excellent fatigue strength and method for producing the same |
| JP6398210B2 (en) * | 2014-02-07 | 2018-10-03 | 新日鐵住金株式会社 | Cold rolled steel sheet manufacturing method |
| MX2018016000A (en) * | 2016-09-21 | 2019-08-14 | Nippon Steel Corp | Steel sheet. |
| JP7008532B2 (en) | 2018-02-21 | 2022-01-25 | 株式会社神戸製鋼所 | Cold rolling method |
| JP7217274B2 (en) * | 2018-06-29 | 2023-02-02 | 東洋鋼鈑株式会社 | HOT-ROLLED STEEL, HIGH-STRENGTH COLD-ROLLED STEEL, AND METHOD FOR MANUFACTURING THEM |
-
2021
- 2021-05-07 JP JP2021079218A patent/JP2022172888A/en active Pending
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2022
- 2022-04-08 KR KR1020237040251A patent/KR20240000569A/en unknown
- 2022-04-08 WO PCT/JP2022/017334 patent/WO2022234760A1/en active Application Filing
- 2022-04-08 CN CN202280033546.XA patent/CN117295831A/en active Pending
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| JP2022172888A (en) | 2022-11-17 |
| KR20240000569A (en) | 2024-01-02 |
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