JP2010275600A - Hot rolled steel sheet for high strength cold rolled steel sheet, method for producing the same, and method for producing high strength cold rolled steel sheet - Google Patents
Hot rolled steel sheet for high strength cold rolled steel sheet, method for producing the same, and method for producing high strength cold rolled steel sheet Download PDFInfo
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- 229910000831 Steel Inorganic materials 0.000 title claims abstract description 105
- 239000010959 steel Substances 0.000 title claims abstract description 105
- 239000010960 cold rolled steel Substances 0.000 title claims abstract description 59
- 238000004519 manufacturing process Methods 0.000 title claims abstract description 26
- 229910001568 polygonal ferrite Inorganic materials 0.000 claims abstract description 23
- 229910000859 α-Fe Inorganic materials 0.000 claims abstract description 18
- 229910001563 bainite Inorganic materials 0.000 claims abstract description 16
- 238000001816 cooling Methods 0.000 claims description 68
- 238000005096 rolling process Methods 0.000 claims description 26
- 238000005098 hot rolling Methods 0.000 claims description 18
- 238000000137 annealing Methods 0.000 claims description 17
- 239000000203 mixture Substances 0.000 claims description 16
- 238000004804 winding Methods 0.000 claims description 15
- 238000005097 cold rolling Methods 0.000 claims description 12
- 238000007747 plating Methods 0.000 claims description 12
- 239000012535 impurity Substances 0.000 claims description 5
- 238000005554 pickling Methods 0.000 claims description 3
- -1 further Substances 0.000 claims description 2
- 239000000463 material Substances 0.000 abstract description 23
- 239000013078 crystal Substances 0.000 abstract description 7
- 230000006872 improvement Effects 0.000 abstract description 2
- 230000002265 prevention Effects 0.000 abstract 1
- 230000000694 effects Effects 0.000 description 11
- 229910000734 martensite Inorganic materials 0.000 description 8
- 238000000034 method Methods 0.000 description 8
- 229910001562 pearlite Inorganic materials 0.000 description 8
- 238000005728 strengthening Methods 0.000 description 8
- 230000009466 transformation Effects 0.000 description 8
- 229910001566 austenite Inorganic materials 0.000 description 5
- 230000015572 biosynthetic process Effects 0.000 description 5
- 230000001276 controlling effect Effects 0.000 description 5
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 5
- 230000009471 action Effects 0.000 description 3
- 239000002131 composite material Substances 0.000 description 3
- 230000009467 reduction Effects 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
- 238000009864 tensile test Methods 0.000 description 3
- 230000002411 adverse Effects 0.000 description 2
- 238000005275 alloying Methods 0.000 description 2
- 229910001567 cementite Inorganic materials 0.000 description 2
- 229910052804 chromium Inorganic materials 0.000 description 2
- 239000000498 cooling water Substances 0.000 description 2
- 239000006185 dispersion Substances 0.000 description 2
- 238000005246 galvanizing Methods 0.000 description 2
- 229910052748 manganese Inorganic materials 0.000 description 2
- 229910052750 molybdenum Inorganic materials 0.000 description 2
- 238000003825 pressing Methods 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 230000001737 promoting effect Effects 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 150000003568 thioethers Chemical class 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- FYYHWMGAXLPEAU-UHFFFAOYSA-N Magnesium Chemical compound [Mg] FYYHWMGAXLPEAU-UHFFFAOYSA-N 0.000 description 1
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 description 1
- 229910045601 alloy Inorganic materials 0.000 description 1
- 239000000956 alloy Substances 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- XAGFODPZIPBFFR-UHFFFAOYSA-N aluminium Chemical compound [Al] XAGFODPZIPBFFR-UHFFFAOYSA-N 0.000 description 1
- 238000006243 chemical reaction Methods 0.000 description 1
- 239000011362 coarse particle Substances 0.000 description 1
- 239000000470 constituent Substances 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 235000019628 coolness Nutrition 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 238000005336 cracking Methods 0.000 description 1
- 238000005520 cutting process Methods 0.000 description 1
- 230000003111 delayed effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009713 electroplating Methods 0.000 description 1
- 239000012467 final product Substances 0.000 description 1
- 238000000265 homogenisation Methods 0.000 description 1
- 239000004615 ingredient Substances 0.000 description 1
- 229910052742 iron Inorganic materials 0.000 description 1
- KSOKAHYVTMZFBJ-UHFFFAOYSA-N iron;methane Chemical compound C.[Fe].[Fe].[Fe] KSOKAHYVTMZFBJ-UHFFFAOYSA-N 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 239000011777 magnesium Substances 0.000 description 1
- 238000002844 melting Methods 0.000 description 1
- 230000008018 melting Effects 0.000 description 1
- 229910052751 metal Inorganic materials 0.000 description 1
- 239000002184 metal Substances 0.000 description 1
- 150000001247 metal acetylides Chemical class 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000008520 organization Effects 0.000 description 1
- 239000002245 particle Substances 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 230000001105 regulatory effect Effects 0.000 description 1
- 230000000717 retained effect Effects 0.000 description 1
- 239000000243 solution Substances 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
- 230000003746 surface roughness Effects 0.000 description 1
- 239000013077 target material Substances 0.000 description 1
- 229910052718 tin Inorganic materials 0.000 description 1
- 229910052720 vanadium Inorganic materials 0.000 description 1
- 229910052725 zinc Inorganic materials 0.000 description 1
- 239000011701 zinc Substances 0.000 description 1
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
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Abstract
Description
本発明は、プレス加工にて、自動車や電気機器などの部品を製造するのに用いられる冷延鋼板、特に、750MPa以上の引張強さを有する高強度冷延鋼板の素材として用いられる熱延鋼板およびその製造方法に関するものである。なお、本発明にいう鋼板は、鋼帯をも含む意味とする。また、%は特にことわらぬ限り、質量%を意味するものとする。 The present invention relates to a cold-rolled steel sheet used for manufacturing parts such as automobiles and electrical equipment by press working, and in particular, a hot-rolled steel sheet used as a material for a high-strength cold-rolled steel sheet having a tensile strength of 750 MPa or more. And a manufacturing method thereof. In addition, the steel plate said to this invention shall mean also including a steel strip. Further,% means mass% unless otherwise specified.
高強度冷延鋼板は、熱延鋼板を冷間圧延し、必要に応じ、熱処理することで製造される。 A high-strength cold-rolled steel sheet is manufactured by cold-rolling a hot-rolled steel sheet and heat-treating it as necessary.
近年、高強度冷延鋼板は、プレス加工にて、自動車や電気機器などの構造体骨格用部品を製造する用途が拡大し、特に、引張強さ（TS）が750MPa以上の高強度冷延鋼板の需要が高まっている。 In recent years, high-strength cold-rolled steel sheets have been increasingly used in the manufacture of structural framework parts such as automobiles and electrical equipment by pressing, and in particular, high-strength cold-rolled steel sheets with a tensile strength (TS) of 750 MPa or more. Demand is growing.
その高強度冷延鋼板を用いて製造する部品の寸法精度を高めるため、需要家からは、高強度冷延鋼板の材質や板厚精度に高度なものが求められている。しかしながら、鋼板の高強度化に伴い、鋼板長手方向の材質のばらつきや、局所的な板厚変動は、大きくなりがちである。 In order to increase the dimensional accuracy of parts manufactured using the high-strength cold-rolled steel sheet, customers are demanding advanced materials for the material and thickness accuracy of the high-strength cold-rolled steel sheet. However, as the strength of the steel plate increases, the variation in the material in the longitudinal direction of the steel plate and local fluctuations in the plate thickness tend to increase.
冷延鋼板の材質、特に、引張強さ（TS）のばらつきは、プレス成形性のみならず、プレス成形後のスプリングバックにも大きな影響を及ぼす。このため、そのばらつきは小さいことが望まれる。鋼板を製造する側にとっても、鋼板内の材質の均一化は、歩留り向上、素材コスト低減の点で、強く求められる。板厚精度についても、製造時のトラブル防止や歩留り向上の点で、高度なものが強く求められる。 The material of the cold-rolled steel sheet, particularly the variation in tensile strength (TS), has a great influence not only on press formability but also on springback after press forming. For this reason, the variation is desired to be small. Even on the side of manufacturing a steel plate, the homogenization of the material in the steel plate is strongly required in terms of yield improvement and material cost reduction. As for the plate thickness accuracy, advanced ones are strongly demanded from the viewpoint of preventing troubles during production and improving the yield.
冷延鋼板内の材質の均一さを向上する方法については、従来から多くの提案がなされている。しかし、それらのうちの多くは、TSが440MPa未満の鋼板に関するものであり、また、鋼中析出物を制御するものが多い。（特許文献１，２）
一方、冷間圧延における板厚制御は、従来、ロールクラウン、圧下量、張力などを制御することで行われてきたが、高強度冷延鋼板では、これらの制御だけでは十分な板厚精度が得られない場合もあるため、熱間圧延後の冷却を均一にすることで、熱延鋼板の材質のばらつきを抑える方法も提案されている。
Many proposals have been made on methods for improving the uniformity of the material in the cold-rolled steel sheet. However, many of them relate to steel sheets having a TS of less than 440 MPa, and many control precipitates in steel. (Patent Documents 1 and 2)
On the other hand, sheet thickness control in cold rolling has been conventionally performed by controlling the roll crown, reduction amount, tension, etc., but with high-strength cold-rolled steel sheets, sufficient control of the sheet thickness is not possible with these controls alone. Since it may not be obtained, a method for suppressing variation in the material of the hot-rolled steel sheet by making the cooling after hot rolling uniform has also been proposed.
例えば、特許文献３では、熱間圧延における最終パスの圧延を行う圧延機から巻取装置までの間にある冷却帯を、熱間圧延ラインの延びる方向（ライン方向）にみて４つ以上の冷却ゾーンに区分し、冷却水のかけ方を工夫することで、ライン方向と熱延鋼板の幅方向、いずれの方向にみても、鋼板表面の温度変動が50℃以内で、しかも、冷却速度の変動を5℃/秒以内に抑えるようにし、こうして製造された熱延鋼板を冷間圧延することで、板厚変動の小さい冷延鋼板を製造する方法を提案している。 For example, in Patent Document 3, a cooling zone between a rolling mill that performs rolling in the final pass in hot rolling and a winding device is set to four or more coolings when viewed in the direction in which the hot rolling line extends (line direction). By dividing into zones and devising the way to apply cooling water, the temperature fluctuation of the steel sheet surface is within 50 ° C and the cooling speed fluctuation in both the line direction and the width direction of the hot-rolled steel sheet. Has been proposed to produce a cold-rolled steel sheet having a small thickness variation by cold rolling the hot-rolled steel sheet thus produced.
また、特許文献４では、熱間圧延における仕上圧延完了温度と、そこから巻取り温度に至るまでの冷却速度を制御して、熱延鋼板の尾端から少なくとも200m以内の範囲を、所定の組織（ベイナイト主体、パーライト分率15%以下）とすることで、冷間圧延後の板厚変動の小さい高張力冷延鋼板用熱延鋼板を製造することを提案している。 Moreover, in patent document 4, the finish rolling completion temperature in hot rolling and the cooling rate from there to coiling temperature are controlled, and the range within at least 200 m from the tail end of a hot-rolled steel sheet is set to a predetermined structure. It has been proposed to produce hot-rolled steel sheets for high-tensile cold-rolled steel sheets with small fluctuations in sheet thickness after cold rolling by adopting (mainly bainite, pearlite fraction of 15% or less).
しかしながら、いずれの方法も、最終製品である高強度冷延鋼板の材質のばらつきを低減するまでには至っていない。 However, none of the methods has reached the point of reducing variations in the material of the high-strength cold-rolled steel sheet that is the final product.
本発明は、上記のような実情に鑑み、鋼板長手方向の材質のばらつきや、板厚変動の小さい、高強度冷延鋼板を製造することができる、熱延鋼板およびその製造方法を提供することを目的とする。 In view of the above circumstances, the present invention provides a hot-rolled steel sheet and a method for producing the same, which can produce a high-strength cold-rolled steel sheet having a small variation in material in the longitudinal direction of the steel sheet and a small thickness fluctuation. With the goal.
発明者らは、鋭意検討を重ねた結果、高強度冷延鋼板、特に、その強化手段として、主としてフェライト組織に比べて硬質なマルテンサイト組織を用いる、いわゆる組織強化型高強度冷延鋼板の長手方向の材質（特に引張強さ（TS））のばらつきは、素材となる熱延鋼板の組織を制御することで改善できることを見出した。また、組織制御を行うため、適正化した鋼成分をもつ鋼の熱間圧延時の冷却速度を工夫することで、冷間圧延後の板厚変動も改善できることを見出した。 As a result of intensive studies, the inventors of the present invention have used long-stretched high-strength cold-rolled steel sheets, in particular, the longitudinal direction of so-called structure-strengthened high-strength cold-rolled steel sheets that use a hard martensite structure as a strengthening means mainly compared to a ferrite structure. It was found that the variation in the direction material (especially tensile strength (TS)) can be improved by controlling the structure of the hot-rolled steel sheet. Moreover, in order to perform structure | tissue control, it discovered that the plate | board thickness fluctuation | variation after cold rolling can also be improved by devising the cooling rate at the time of hot rolling of the steel with the optimized steel component.
本発明は以下の通りである。
（１）鋼板のミクロ組織として、ベイナイトおよび／若しくはベイニチックフェライトが合計面積分率にして70%以上の組織で、ポリゴナルフェライトが面積分率にして30%以下で、前記ポリゴナルフェライトの平均結晶粒径が10μm以下の組織を有することを特徴とする高強度冷延鋼板用熱延鋼板。
（２）鋼の成分組成は、
質量%で、
C：0.03〜0.1%、
Si：0.01〜1.5%、
Mn：1.5〜3%、
P：0.08%以下、
S：0.010%以下、
Sol.Al：0.01〜1.20%、
Cr：0.1〜1.5%および／またはMo：0.01〜0.15%
を含有し、残部がFeおよび不可避的不純物からなることを特徴とする上記（１）に記載の高強度冷延鋼板用熱延鋼板。
（３）鋼の成分組成として、
さらに、質量%で、
Nb：0.005〜0.05%、
V：0.005〜0.05%、
Ti：0.005〜0.05%、
B：0.0005〜0.003%
のうちの１種以上を含有することを特徴とする上記（２）に記載の高強度冷延鋼板用熱延鋼板。
（４）鋼の成分組成として、
さらに、質量%で、
Cu：0.01〜0.2%、
Ni：0.005〜0.1%、
Sn：0.01〜0.1%、
Ca：0.005〜0.1%
のうちの１種以上を含有する
上記（２）または（３）に記載の高強度冷延鋼板用熱延鋼板。
（５）質量%で、
C：0.03〜0.1%、
Si：0.01〜1.5%、
Mn：1.5〜3%、
P：0.08%以下、
S：0.010%以下、
Sol.Al：0.01〜1.20%、
Cr：0.1〜1.5%および／またはMo：0.01〜0.15%
を含有し、残部がFeおよび不可避的不純物からなり、
（ｉ）式を満たす成分組成を有する鋼片を、
800〜1000℃の仕上圧延完了温度にて熱間圧延後、
仕上圧延完了後1.8秒以内に冷却を開始し、120〜500℃/秒の平均冷却速度で600℃以下の冷却停止温度まで一次冷却し、
必要に応じて1〜10秒の冷却停止を挟んで二次冷却し、
一次冷却完了から巻取りまで600℃以下に保持し、
600℃以下の巻取り温度で巻取る
ことを特徴とする高強度冷延鋼板用熱延鋼板の製造方法。
300≦K≦400 ・・・（ｉ）
ここに、
K＝540-350（[C%]/0.4）-40[Mn%]+30[Sol.Al%]-20[Cr%]-35[V%]-10[Mo%]
を意味するものとする。
式中、M%は元素Mの鋼中含有量を示す。含有しない元素の含有量はゼロとして扱う。
（６）鋼の成分組成として、
さらに、
質量%で、
Nb：0.005〜0.05%、
V：0.005〜0.05%、
Ti：0.005〜0.05%、
B：0.0005〜0.003%
のうちの１種以上を含有する
上記（５）に記載の高強度冷延鋼板用熱延鋼板の製造方法。
（７）鋼の成分組成として、
さらに、
Cu：0.01〜0.2%、
Ni：0.005〜0.1%、
Sn：0.01〜0.1%、
Ca：0.005〜0.1%
のうちの１種以上を含有する
上記（５）または（６）に記載の高強度冷延鋼板用熱延鋼板の製造方法。
（８）上記（５）、（６）または（７）に記載の熱間圧延を施して得られ熱延鋼板に、酸洗、冷間圧延、および焼鈍を施すことを特徴とする高強度冷延鋼板の製造方法。
（９）焼鈍した後にめっき処理を施すことを特徴とする上記（８）に記載の高強度冷延鋼板の製造方法。
The present invention is as follows.
(1) As the microstructure of the steel sheet, bainite and / or bainitic ferrite has a total area fraction of 70% or more, and polygonal ferrite has an area fraction of 30% or less. A hot-rolled steel sheet for high-strength cold-rolled steel sheets characterized by having a structure with an average crystal grain size of 10 µm or less.
(2) The component composition of steel is
% By mass
C: 0.03-0.1%
Si: 0.01 to 1.5%
Mn: 1.5 to 3%
P: 0.08% or less,
S: 0.010% or less,
Sol.Al: 0.01-1.20%,
Cr: 0.1-1.5% and / or Mo: 0.01-0.15%
The hot-rolled steel sheet for high-strength cold-rolled steel sheets as described in (1) above, wherein the balance is Fe and inevitable impurities.
(3) As a component composition of steel,
Furthermore, in mass%,
Nb: 0.005 to 0.05%,
V: 0.005-0.05%
Ti: 0.005-0.05%,
B: 0.0005-0.003%
The hot-rolled steel sheet for high-strength cold-rolled steel sheets as described in (2) above, containing at least one of the above.
(4) As a component composition of steel,
Furthermore, in mass%,
Cu: 0.01 to 0.2%,
Ni: 0.005-0.1%,
Sn: 0.01 to 0.1%
Ca: 0.005 to 0.1%
The hot-rolled steel sheet for high-strength cold-rolled steel sheets according to (2) or (3) above, which contains one or more of the above.
(5) In mass%,
C: 0.03-0.1%
Si: 0.01 to 1.5%
Mn: 1.5 to 3%
P: 0.08% or less,
S: 0.010% or less,
Sol.Al: 0.01-1.20%,
Cr: 0.1-1.5% and / or Mo: 0.01-0.15%
And the balance consists of Fe and inevitable impurities,
A steel slab having a component composition satisfying the formula (i)
After hot rolling at a finish rolling completion temperature of 800-1000 ° C,
Start cooling within 1.8 seconds after completion of finish rolling, and primary cooling to a cooling stop temperature of 600 ° C. or less at an average cooling rate of 120 to 500 ° C./second,
Secondary cooling with 1-10 seconds cooling stop if necessary,
Hold at 600 ° C or lower from completion of primary cooling to winding
A method for producing a hot-rolled steel sheet for high-strength cold-rolled steel sheet, which is wound at a coiling temperature of 600 ° C or lower.
300 ≦ K ≦ 400 (i)
here,
K = 540-350 ([C%] / 0.4) -40 [Mn%] + 30 [Sol.Al%]-20 [Cr%]-35 [V%]-10 [Mo%]
Means.
In the formula, M% represents the content of element M in steel. The content of elements not contained is treated as zero.
(6) As a component composition of steel,
further,
% By mass
Nb: 0.005 to 0.05%,
V: 0.005-0.05%
Ti: 0.005-0.05%,
B: 0.0005-0.003%
The manufacturing method of the hot-rolled steel sheet for high-strength cold-rolled steel sheets as described in said (5) containing 1 or more types of these.
(7) As a component composition of steel,
further,
Cu: 0.01 to 0.2%,
Ni: 0.005-0.1%,
Sn: 0.01 to 0.1%
Ca: 0.005 to 0.1%
The manufacturing method of the hot-rolled steel sheet for high-strength cold-rolled steel sheets as described in said (5) or (6) containing 1 or more types of these.
(8) High-strength cold characterized by subjecting the hot-rolled steel sheet obtained by performing hot rolling as described in (5), (6) or (7) above to pickling, cold rolling, and annealing. A method for producing rolled steel sheets.
(9) The method for producing a high-strength cold-rolled steel sheet as described in (8) above, wherein a plating treatment is performed after annealing.
本発明によれば、鋼板長手方向の材質のばらつきや、板厚変動の小さい、高強度冷延鋼板を製造することができる。 According to the present invention, it is possible to produce a high-strength cold-rolled steel sheet that has a small variation in material in the longitudinal direction of the steel sheet and a small thickness variation.
それにより、製造時のトラブル防止や歩留り向上を図ることができ、プレス加工する際の加工性や作業性の向上、プレス加工後の製品の品質向上も図ることができる。 As a result, it is possible to prevent problems during production and improve yield, improve workability and workability during press working, and improve product quality after press working.
本発明は、主としてフェライト組織に比べて硬質なマルテンサイト組織を活用する、いわゆる組織強化型高強度冷延鋼板を製造するにあたり、素材となる適正範囲の成分組成を有する熱延鋼板の組織を制御することで、高強度冷延鋼板の長手方向の材質のばらつきや、板厚変動を抑えることができる。 The present invention mainly controls the structure of a hot-rolled steel sheet having a component composition in an appropriate range as a material in manufacturing a so-called structure-strengthened high-strength cold-rolled steel sheet that utilizes a hard martensite structure compared to a ferrite structure. By doing so, the dispersion | variation in the material of the longitudinal direction of a high intensity | strength cold-rolled steel plate and board thickness fluctuation | variation can be suppressed.
まず、製品である高強度冷延鋼板の材質として、引張強さ（TS）にして、TS≧750MPaを目標とする。発明者らは、それに加え、加工性の指標として、伸びフランジ性の指標である、穴広げ率（λ）を代表として挙げ、その目標を、λ≧60%として種々検討を重ね、熱延鋼板組織との関連性を追及した。そして、板厚変動の抑制に効果的な組織とその組織の作り込みの方法についても検討を重ね、本発明を完成した。 First, as the material of the high-strength cold-rolled steel sheet that is the product, the target is TS ≧ 750MPa in terms of tensile strength (TS). In addition to the above, the inventors cited the hole expansion ratio (λ), which is an index of stretch flangeability, as a representative index of workability, and repeated various studies with the target being λ ≧ 60%. We pursued the relationship with the organization. Further, the present invention was completed by repeatedly studying the structure effective for suppressing fluctuations in plate thickness and the method of making the structure.
高強度冷延鋼板の材質と熱延鋼板組織の関連性については、実験室での検討にて、TS≧750MPaでλ≧60%を得るには、熱延鋼板組織を、ベイナイト（ベイニチックフェライト+炭化物）またはベイニチックフェライトが合計面積分率にして70%以上で、しかも、ポリゴナルフェライトが面積分率にして30%以下とすることが必要であることを見出した。ポリゴナルフェライトに対しパーライトの面積分率が高くなると、次第にλが低下する傾向があることも見出した。TS≧750MPaを得るには、TSの焼鈍温度依存性など製造安定性の観点からは、ポリゴナルフェライト主体よりもベイナイト主体の組織の方がよいことも見出した。 Regarding the relationship between the material of the high-strength cold-rolled steel sheet and the hot-rolled steel sheet structure, in order to obtain λ ≧ 60% at TS ≧ 750 MPa, labite (bainitic) It has been found that it is necessary that the total area fraction of ferrite + carbide) or bainitic ferrite is 70% or more, and that of polygonal ferrite is 30% or less. It has also been found that λ tends to decrease gradually as the area fraction of pearlite increases relative to polygonal ferrite. In order to obtain TS ≧ 750 MPa, it was also found that a bainite-based structure is better than a polygonal ferrite-based structure from the viewpoint of production stability such as the dependency of TS on the annealing temperature.
冷延鋼板の板厚変動については、熱延鋼板の硬度変動と冷延鋼板の板厚変動との間に明確な相関があり、従来から、熱延鋼板に生じた硬度変動が、冷間圧延時の制御を乱し、板厚変動の原因になるとされている。熱延鋼板に生じる硬度変動は、主として熱間圧延における冷却速度の変動による鋼板中の組織のばらつきに起因するものである。従って、熱間圧延における冷却制御を工夫することで、均一な組織を得られればよいことになるが、実際には、ランナウトテーブル（ROT）にて通常行われるラミナ冷却では、その冷却装置ごとに異なる冷却定常化までの時間の間に通板される鋼板先端部には冷却水が十分にかからない非定常部が生じたり、鋼板先尾端部には張力が作用しないことに起因して形状不良となった部分に水乗りが生じたり、鋼板先端を巻取る際に巻緩み防止を目的としてラッパーロールを押し付けたりすることが、均一冷却阻害要因になっている。 Regarding the thickness variation of cold-rolled steel sheet, there is a clear correlation between the hardness fluctuation of hot-rolled steel sheet and the thickness variation of cold-rolled steel sheet. It is said that the control of the time is disturbed, causing the thickness variation. Hardness fluctuations that occur in hot-rolled steel sheets are mainly caused by variations in the structure in the steel sheets due to fluctuations in the cooling rate in hot rolling. Therefore, by devising cooling control in hot rolling, it is only necessary to obtain a uniform structure, but in actuality, in lamina cooling normally performed on a run-out table (ROT), for each cooling device. Form failure due to unsteady parts where the cooling water is not sufficiently applied to the tip of the steel plate that is passed between different cooling steady-state times, or because no tension acts on the leading end of the steel plate Uniform cooling is hindered by the occurrence of water riding in the formed portion or pressing the wrapper roll for the purpose of preventing winding loosening when winding the steel sheet tip.
発明者らは、上記のような実情に鑑み、目標とする材質を得ることができ、しかも、板厚変動を抑制するのにも好ましい組織を検討した結果、ベイナイトおよび／若しくはベイニチックフェライトが合計面積分率で70%以上の組織であって、ポリゴナルフェライトが面積分率にして30%以下で、そのポリゴナルフェライトの平均結晶粒径を10μm以下とするのがよいことを見出した。 In view of the above circumstances, the inventors have been able to obtain a target material, and as a result of studying a preferable structure for suppressing fluctuations in plate thickness, bainite and / or bainitic ferrite is found. It was found that the total area fraction should be 70% or more, the polygonal ferrite should have an area fraction of 30% or less, and the average crystal grain size of the polygonal ferrite should be 10 μm or less.
つまり、本発明が意図する熱延鋼板のミクロ組織は、以下の通りとなる。 That is, the microstructure of the hot rolled steel sheet intended by the present invention is as follows.
ベイナイトおよび／若しくはベイニチックフェライトが合計面積分率で70%以上
ポリゴナルフェライトが面積分率で30%以下
ポリゴナルフェライトの平均結晶粒径を10μm以下
仕上圧延後の急冷によりベイナイトやベイニチックフェライトといった低温変態相への変態を促進させることで、コイル巻取り後の冷却履歴如何による組織変動を極力抑制することができる。組織の割合およびポリゴナルフェライトの粒径の規定は、組織混在によるコイル内の材質変動が冷間圧延時の板厚制御を大きく乱すことを回避するためで、ベイナイト、ベイニチックフェライトが70％以上であれば残部組織がこれより軟質なポリゴナルフェライト等になっても、ポリゴナルフェライトの平均結晶粒径が10μm以下であれば、制御を乱す程の大きな材質変動には当たらない。
Bainite and / or bainitic ferrite 70% or more in total area fraction Polygonal ferrite 30% or less in area fraction Polygonal ferrite average grain size 10μm or less Bainite and bainitic by rapid cooling after finish rolling By promoting the transformation to a low-temperature transformation phase such as ferrite, it is possible to suppress as much as possible the structural variation due to the cooling history after coil winding. The ratio of the structure and the grain size of polygonal ferrite are specified in order to prevent material fluctuations in the coil due to mixed structure from greatly disturbing the sheet thickness control during cold rolling, and 70% for bainite and bainitic ferrite. As described above, even if the remaining structure becomes a softer polygonal ferrite or the like, if the average crystal grain size of the polygonal ferrite is 10 μm or less, it does not cause a large material fluctuation to disturb control.
しかしながら、この組織比率が規定から外れたり、比率が規定内であっても、粒径が粗大なポリゴナルフェライトが存在すると、材質変動が大きくなり板厚変動の原因となる。なお、ここでいうポリゴナルフェライトとは、アスペクト比（結晶粒径の、長径/短径）がほぼ１であるようなフェライト粒を指す。 However, even if this structural ratio is out of the specified range or the ratio is within the specified range, if polygonal ferrite having a coarse particle size is present, the material variation becomes large, which causes the plate thickness variation. Polygonal ferrite as used herein refers to ferrite grains having an aspect ratio (major axis / minor axis of crystal grain size) of approximately 1.
また、ベイナイト、ベイニチックフェライト、ポリゴナルフェライトの他、残部組織としてはパーライトが存在することが多くなるが、概ね10％程度以内であればこれを許容しても問題ない。 In addition to bainite, bainitic ferrite and polygonal ferrite, pearlite is often present as the remaining structure, but if it is within about 10%, there is no problem even if this is allowed.
上記所望の組織を得るための熱間圧延の条件を検討したところ、鋼片を、800〜1000℃の仕上圧延完了温度にて熱間圧延後、仕上圧延完了後1.8秒以内に120〜500℃/秒の平均冷却速度で600℃以下の冷却停止温度まで一次冷却し、必要に応じて1〜10秒の冷却停止を挟んで二次冷却し、一次冷却完了から巻取りまで600℃以下に保持し、600℃以下の巻取り温度で巻取るのがよいことを見出した。 When the hot rolling conditions for obtaining the desired structure were examined, the steel slab was hot rolled at a finish rolling completion temperature of 800 to 1000 ° C., and 120 to 500 ° C. within 1.8 seconds after the finish rolling was completed. Primary cooling to a cooling stop temperature of 600 ° C or less at an average cooling rate of 1 / second, followed by secondary cooling with a cooling stop of 1 to 10 seconds as necessary, and holding at 600 ° C or less from completion of primary cooling to winding And found that it is preferable to wind at a winding temperature of 600 ° C. or less.
以下、上記各要件を規定した理由について説明する。 The reason why the above requirements are specified will be described below.
仕上圧延完了温度800〜1000℃
800℃未満では、圧延荷重が高くなり過ぎ、圧延機にかかる負荷が高くなるとともに、圧延中の鋼板の蛇行などの原因にもなるほか、未再結晶オーステナイトからのフェライト変態がバンド状組織の形成を促し、局所的なパーライト組織の生成の原因となり、伸びフランジ性の低下と板厚変動をもたらすため、800℃以上とする。また、1000℃を超えると、冷却する際に、次に説明する、必要な冷却速度を得るのが困難になるため、1000℃以下とする。
Finish rolling completion temperature 800 ~ 1000 ℃
Below 800 ° C, the rolling load becomes too high, the load on the rolling mill becomes high, and it also causes the meandering of the steel plate during rolling, and the ferrite transformation from unrecrystallized austenite forms a band-like structure. It causes the formation of local pearlite structure and causes a reduction in stretch flangeability and fluctuations in sheet thickness. Moreover, when it exceeds 1000 degreeC, when it cools, since it becomes difficult to obtain the required cooling rate demonstrated below, it shall be 1000 degrees C or less.
一次冷却：仕上圧延後1.8秒以内に120〜500℃/秒の平均冷却速度で600℃以下の冷却停止温度まで一次冷却
これは、面積分率（合計）で70%以上のベイナイト組織および／若しくはベイニチックフェライトを得るための条件である。120℃/秒を下回ると、ポリゴナルフェライトが生成しやすくなる。このため、120℃/秒以上とする。500℃/秒を超えると、冷却装置の設備仕様が過大となり、通板中の鋼板形状も悪化する場合がある。このため、500℃/秒以下とする。
Primary cooling: Primary cooling to a cooling stop temperature of 600 ° C. or lower at an average cooling rate of 120 to 500 ° C./second within 1.8 seconds after finish rolling. This is an area fraction (total) of 70% or more of bainite structure and / or This is a condition for obtaining bainitic ferrite. When the temperature is lower than 120 ° C / second, polygonal ferrite is likely to be generated. For this reason, it shall be 120 degrees C / sec or more. If it exceeds 500 ° C / second, the equipment specifications of the cooling device will be excessive, and the shape of the steel plate in the plate may deteriorate. For this reason, it shall be 500 degrees C / sec or less.
冷却開始時間：1.8秒以内
成分系にもよるが、即急冷却しないと、ポリゴナルフェライトの変態ノーズに掛かりやすくなる。これは所望とするベイナイトおよび／若しくはベイニチックフェライトの組織を70％以上確保することが難しくなる。また、組織分率は確保できても、高温で生じるポリゴナルフェライトは粒径が大きくなりやすく、平均結晶粒径10μm以下を確保することが困難となるため、即急冷、少なくとも圧延後1.8秒以内に冷却を開始する。
Cooling start time: Within 1.8 seconds Depending on the component system, if it is not cooled immediately, it will be susceptible to the transformation nose of polygonal ferrite. This makes it difficult to secure a desired bainite and / or bainitic ferrite structure of 70% or more. Even if the structure fraction can be secured, polygonal ferrite generated at high temperatures tends to have a large grain size, making it difficult to secure an average crystal grain size of 10 μm or less. Start cooling.
二次冷却：一次冷却完了から巻取りまで600℃以下に保持
ランナウトテーブル（ROT）にて通常行われるラミナ冷却などによった場合に相当するもので、ベイナイト変態促進およびポリゴナルフェライトの粗大化防止のため、必要に応じて行なう。また、一次冷却から二次冷却まで連続できることがもっとも理想的だが、実際には設備の構造或いは制約上、一次冷却装置と二次冷却装置の間に物理的距離が発生してしまう。そのため止むを得ず冷却が為されない時間が生じてしまうことになるが、所望とする組織を得るため、出来るだけこの時間を短縮することが望ましく、その観点から冷却停止時間を1〜10秒とした。
Secondary cooling: Maintained at 600 ° C or lower from completion of primary cooling to winding, equivalent to the case of laminar cooling normally performed on a run-out table (ROT), etc., promoting bainite transformation and preventing polygonal ferrite from coarsening Therefore, it is performed as necessary. In addition, it is ideal to be able to continue from the primary cooling to the secondary cooling, but in reality, a physical distance is generated between the primary cooling device and the secondary cooling device due to the structure or restrictions of the equipment. Therefore, there will be a time when cooling is unavoidable, but in order to obtain the desired tissue, it is desirable to shorten this time as much as possible. From that point of view, the cooling stop time is 1 to 10 seconds. did.
巻取り温度：600℃以下
二次冷却後まで維持された残留オーステナイトをベイナイトに変態させ、また、巻取り後もパーライトの生成やポリゴナルフェライトの粗大化を防止するため、600℃以下に規定する。600℃を超えると、パーライトの比率が増え、冷延鋼板の成形性を低下させるため、600℃以下とする。好ましくは580℃以下とする。
Winding temperature: 600 ° C or less To keep the retained austenite maintained until after secondary cooling to bainite, and to prevent the formation of pearlite and the coarsening of polygonal ferrite after winding, the temperature is regulated to 600 ° C or less. . If it exceeds 600 ° C, the ratio of pearlite increases and the formability of the cold-rolled steel sheet is lowered, so the temperature is set to 600 ° C or less. Preferably, it is set to 580 ° C. or lower.
450℃未満になると、ベイナイトよりも硬質なマルテンサイトが生成し、熱延鋼板が硬質化して圧延機にかかる負荷が増大し、局所的に生成するマルテンサイトにより硬度変動が生じる場合があるため、450℃以上とするのが好ましい場合もある。 When it is less than 450 ° C, martensite harder than bainite is generated, the hot-rolled steel sheet is hardened, the load applied to the rolling mill is increased, and hardness fluctuation may occur due to locally generated martensite. In some cases, it is preferable to set the temperature to 450 ° C. or higher.
以上のような、熱間圧延における最終パスの圧延以降、冷却制御をしやすくする観点から、熱延鋼板の厚みは、2.0〜4.0mmとするのが好ましい。 From the viewpoint of facilitating cooling control after the final pass rolling in the hot rolling as described above, the thickness of the hot-rolled steel sheet is preferably 2.0 to 4.0 mm.
次に、鋼の成分組成について規定する。成分における%表示は、質量%を意味する。
C：0.03〜0.1%
Cは、鋼の組織強化を目的とする焼入れ性を向上させるために重要な元素であり、TS≧750MPaを得るために0.03%以上を必要とする。一方、0.1%を超えるとセメンタイトなどの鉄系炭化物の粗大化が起こりやすくなり、冷延鋼板の成形性が低下したり、あるいは溶接した場合に著しく硬化するなどの弊害があるため0.1%以下とする。
Next, the component composition of steel is specified. % Indication in a component means the mass%.
C: 0.03-0.1%
C is an important element for improving the hardenability for the purpose of strengthening the steel structure, and 0.03% or more is required to obtain TS ≧ 750 MPa. On the other hand, if it exceeds 0.1%, iron carbide such as cementite is likely to become coarse, and the formability of the cold-rolled steel sheet is reduced, or there is an adverse effect such as significant hardening when welded. To do.
Si：0.01〜1.5%
Siは、鋼の固溶強化に有効な元素であり、TS≧750MPa確保のため、積極的に添加することができる。また、フェライト−マルテンサイトの複合組織とする際の二相域焼鈍時のフェライト−オーステナイト二相域分率調整に有用な元素でもある。その効果を発揮するため、また、パーライトの生成を抑制する観点から、0.01%以上とする。一方、過剰な添加は冷延鋼板の表面品質を悪化させ、また、冷延鋼板に鍍金を施す場合には鍍金性の低下を生じるため、1.5%以下とする。
Si: 0.01-1.5%
Si is an effective element for solid solution strengthening of steel, and can be positively added to secure TS ≧ 750 MPa. Further, it is also an element useful for adjusting the ferrite-austenite two-phase region fraction during two-phase annealing when forming a ferrite-martensite composite structure. In order to exert the effect and from the viewpoint of suppressing the formation of pearlite, the content is made 0.01% or more. On the other hand, excessive addition deteriorates the surface quality of the cold-rolled steel sheet, and when the cold-rolled steel sheet is plated, the plating property is lowered.
Mn：1.5〜3%
Mnは、鋼の固溶強化および組織強化に有効な元素であり、TS≧750MPa確保のため、組織の焼入れ性を向上させる観点から1.5%以上とする。焼入れ性が低下すると、組織強化に有効なマルテンサイトが得にくくなるとともに、パーライトの生成が助長される。一方、過剰な添加は、鋼を鋳造する際に、鋼片表面やコーナー部に割れを生じやすくなるとともに、偏析が助長される。この偏析は焼鈍後にも残存すると、冷延鋼板の品質、特に、伸びフランジ性を低下させるため、3%以下とする。
Mn: 1.5 to 3%
Mn is an element effective for solid solution strengthening and structural strengthening of steel, and is made 1.5% or more from the viewpoint of improving the hardenability of the structure in order to secure TS ≧ 750 MPa. When the hardenability is lowered, it becomes difficult to obtain martensite effective for strengthening the structure, and generation of pearlite is promoted. On the other hand, when the steel is cast excessively, cracking tends to occur on the surface of the steel slab and the corner, and segregation is promoted. If this segregation remains even after annealing, the quality of the cold-rolled steel sheet, particularly the stretch flangeability, is lowered.
P：0.08%以下
Pは、鋼の固溶強化に有効な元素であり、また、フェライト−マルテンサイトの複合組織とする際の二相域焼鈍時のフェライト−オーステナイト二相域分率調整に有用な元素でもあるため、積極的に添加することができる。しかしながら、過剰な添加は、冷延鋼板に鍍金を施す場合には鍍金性の低下、特に合金化溶融金属鍍金を施す場合には合金化の遅延を惹き起こすなどの悪影響もあるため、0.08%以下とする。好ましくは0.05%以下とする。
P: 0.08% or less
P is an effective element for solid solution strengthening of steel, and is also an element useful for adjusting the ferrite-austenite two-phase region fraction during two-phase annealing when forming a ferrite-martensite composite structure. Can be positively added. However, excessive addition has a negative effect such as lowering the plating property when plating a cold-rolled steel sheet, particularly causing a delay in alloying when applying an alloyed molten metal plating, so that it is 0.08% or less. And Preferably it is 0.05% or less.
S：0.010%以下
Sは、硫化物を形成して鋼中介在物として存在すると、冷延鋼板の加工性、特に穴広げ性を低下させるため、0.010%以下とする。
S: 0.010% or less
If S forms sulfides and exists as inclusions in the steel, it lowers the workability of the cold-rolled steel sheet, in particular, the hole expandability, so it is made 0.010% or less.
Sol.Al：0.01〜1.20%
Alは、鋼の溶製段階で脱酸剤として用いられることが多い。この脱酸剤としての効果を発揮するためには、鋼中固溶Al（sol.Al）として0.01%以上存在するのがよいため、0.01%以上とする。また、Alは、SiやP同様、炭化物の生成を抑制する作用や、Ac3点を高める作用により、フェライト−マルテンサイトの複合組織とする際の二相域焼鈍時のフェライト−オーステナイト二相域分率調整に有用な元素でもあるため、積極的に添加することができる。しかしながら、過剰な添加は、効果が飽和するほか、不要な介在物の形成、溶接性の低下などをもたらすため、1.20%以下とする。
Sol.Al: 0.01-1.20%
Al is often used as a deoxidizer in the melting stage of steel. In order to exert the effect as the deoxidizer, 0.01% or more should be present as solute Al (sol. Al) in steel, so 0.01% or more. In addition, Al, like Si and P, suppresses the formation of carbides and increases the Ac3 point, thereby providing a ferrite-austenite two-phase region during two-phase annealing when forming a ferrite-martensite composite structure. Since it is also an element useful for adjusting the rate, it can be positively added. However, excessive addition causes saturation of the effect, formation of unnecessary inclusions, deterioration of weldability, and the like, so 1.20% or less.
Cr：0.1〜1.5%および／またはMo：0.01〜0.15%
Cr、Moは、Mn、V同様、焼入れ性を向上する作用があり、組織強化の観点から積極的に添加することができる。その作用を発揮させるため、Cr：0.1%以上、Mo：0.01%以上とする。一方、これらの元素は高価であることと、過剰な添加は、表面品質、特に耐食性や化成処理性を低下させることがあるため、Cr：1.5%以下、Mo：0.15%以下とする。
さらに、冷却中の変態を制御する観点から、鋼成分は下記（ｉ）式を満たすことが必要となる。
300≦K≦400 ・・・（ｉ）
ここに、
K＝540-350（[C%]/0.4）-40[Mn%]+30[Sol.Al%]-20[Cr%]-35[V%]-10[Mo%]
を意味するものとする。
Cr: 0.1-1.5% and / or Mo: 0.01-0.15%
Cr and Mo, like Mn and V, have the effect of improving hardenability, and can be positively added from the viewpoint of strengthening the structure. In order to exert the effect, Cr: 0.1% or more, Mo: 0.01% or more. On the other hand, these elements are expensive, and excessive addition may deteriorate the surface quality, particularly corrosion resistance and chemical conversion treatment, so Cr: 1.5% or less and Mo: 0.15% or less.
Furthermore, from the viewpoint of controlling the transformation during cooling, the steel component needs to satisfy the following formula (i).
300 ≦ K ≦ 400 (i)
here,
K = 540-350 ([C%] / 0.4) -40 [Mn%] + 30 [Sol.Al%]-20 [Cr%]-35 [V%]-10 [Mo%]
Means.
K＜300またはK＞400となる場合には、冷却速度のコントロールをしても熱延鋼板組織をベイナイトおよび／若しくはベイニチックフェライトが合計面積率で70％以上確保することが困難となるとともに、一次冷却後、巻取りまでの間に、変態発熱を生じたりして、巻取り温度（CT）が目標値から外れやすくなる傾向がある。特に、K＞400となる場合には、フェライト平均粒径が粗大（10μm超え）になりやすくなる。
さらに、上記成分に加え、
Nb：0.005〜0.05%、
V：0.005〜0.05%、
Ti：0.005〜0.05%、
B：0.0005〜0.003%
のうちの１種以上をさらに含有する；
これらの元素は、MnやCr、Moに比べると小さいが、焼入れ性を向上する作用があるため、必要に応じて添加することができる。しかしながら、これらの元素は、過剰に添加すると、焼入れ性を向上する作用が飽和するだけでなく、鋼の再結晶を遅延させるため、冷延鋼板の品質を悪化させる場合がある。このため、上記範囲内で含有させるようにしてもよい。
When K <300 or K> 400, it becomes difficult to secure a hot rolled steel sheet structure with 70% or more of the total area ratio of bainite and / or bainitic ferrite even if the cooling rate is controlled. In addition, after the primary cooling and before winding, transformation heat is generated, and the winding temperature (CT) tends to be easily deviated from the target value. In particular, when K> 400, the average ferrite particle diameter tends to be coarse (over 10 μm).
In addition to the above ingredients,
Nb: 0.005 to 0.05%,
V: 0.005-0.05%
Ti: 0.005-0.05%,
B: 0.0005-0.003%
Further containing one or more of
These elements are smaller than Mn, Cr, and Mo, but have the effect of improving the hardenability, and can be added as necessary. However, when these elements are added excessively, not only the effect of improving the hardenability is saturated, but also the recrystallization of the steel is delayed, so that the quality of the cold-rolled steel sheet may be deteriorated. For this reason, you may make it contain within the said range.
あるいはさらに、
Cu：0.01〜0.2%、
Ni：0.005〜0.1%、
Sn：0.01〜0.1%、
Ca：0.005〜0.1%
のうちの１種以上をさらに含有する；
Cu、Niもまた焼入れ性の向上により鋼の強度を向上する作用があり、また、Sn、Caは硫化物や酸化物の形状を制御することで、成形性を向上する作用があり、それらの作用を発揮させる観点から、必要に応じて添加することができる。しかしながら、これらの元素は、過剰に添加すると、それぞれの作用が飽和するだけでなく、いずれも、冷延鋼板の加工性を低下させるため、上記範囲内で含有させるようにしてもよい。
Or in addition,
Cu: 0.01 to 0.2%,
Ni: 0.005-0.1%,
Sn: 0.01 to 0.1%
Ca: 0.005 to 0.1%
Further containing one or more of
Cu and Ni also have the effect of improving the strength of steel by improving hardenability, and Sn and Ca have the effect of improving formability by controlling the shape of sulfides and oxides. From the viewpoint of exerting the action, it can be added as necessary. However, when these elements are added excessively, not only the respective actions are saturated, but any of these elements may be contained within the above range in order to reduce the workability of the cold-rolled steel sheet.
なお、本発明の鋼板は、上記成分以外の残部は、Feおよび不可避的不純物からなる。ただし、本発明の作用に悪影響を及ぼさない範囲であれば、上記以外の成分を含有することも何らこれを妨げるべき事情はない。 In the steel sheet of the present invention, the balance other than the above components is composed of Fe and inevitable impurities. However, if it is in a range that does not adversely affect the action of the present invention, there is no circumstance that should prevent this from occurring even if it contains components other than those described above.
上記のように、成分組成を調整するとともに、熱間圧延条件（仕上温度、冷却条件）を制御することにより、熱延鋼板の組織を所望のミクロ組織とすることができ、所望のミクロ組織を有する熱延鋼板に冷延、焼鈍あるいはさらにめっき処理を施すことにより、材質のばらつきや板厚変動の小さい高強度冷延鋼板を製造することができる。なお、熱延以降の製造工程については、熱延鋼板を酸洗、冷間圧延、焼鈍を行なうが、これらの製造条件は常法に従えばよく、また焼鈍は連続焼鈍に限らず、バッチ焼鈍であっても良い。さらに、焼鈍後にめっき処理を施す場合には、溶融めっき、電気めっきのいずれの方法でもよく、めっき種類は、通常、鋼板に適用される亜鉛、アルミ、マグネシウムやこれらの合金を用いることができる。溶融めっきの場合には、めっきに合金化処理を施す等の処理を施しても良い。さらに、得られた高強度冷延鋼板に、形状矯正、表面粗度等の調整のために、調質圧延を施してもよい。 As described above, by adjusting the component composition and controlling the hot rolling conditions (finishing temperature, cooling conditions), the structure of the hot-rolled steel sheet can be changed to a desired microstructure. By subjecting the hot-rolled steel sheet to cold rolling, annealing, or further plating, a high-strength cold-rolled steel sheet with small variations in material and thickness variation can be manufactured. In addition, for the manufacturing process after hot rolling, the hot-rolled steel sheet is pickled, cold-rolled, and annealed, but these manufacturing conditions may be in accordance with ordinary methods, and annealing is not limited to continuous annealing, but batch annealing. It may be. Furthermore, when the plating treatment is performed after annealing, any method of hot dip plating and electroplating may be used, and as the plating type, zinc, aluminum, magnesium and alloys thereof which are usually applied to steel plates can be used. In the case of hot dip plating, the plating may be subjected to a treatment such as an alloying treatment. Furthermore, the obtained high-strength cold-rolled steel sheet may be subjected to temper rolling in order to adjust shape correction, surface roughness, and the like.
表１に示す成分組成を有する、引張強さ（TS）が780MPa級の高強度鋼を転炉で溶製し、連続鋳造法にて鋼片とし、これらの鋼片を加熱炉から1200℃で抽出し、熱間圧延ラインにて、粗圧延および仕上圧延を行って、2.8mm厚の熱延鋼板を製造した。仕上圧延完了温度は、Ar3変態温度以上の900℃とした。仕上圧延後冷却開始までの時間は、およそ1秒である。 High strength steel with tensile strength (TS) class of 780MPa having the component composition shown in Table 1 is melted in a converter and made into slabs by continuous casting method. The steel sheet was extracted and subjected to rough rolling and finish rolling in a hot rolling line to produce a hot rolled steel sheet having a thickness of 2.8 mm. The finish rolling completion temperature was 900 ° C., which is not lower than the Ar3 transformation temperature. The time from finish rolling to the start of cooling is approximately 1 second.
熱間圧延ラインにおける仕上圧延機の最終圧延機を出た鋼板は、一次冷却として水冷による急速冷却を行ない、次いで、必要に応じて二次冷却（二次冷却を行ったものは、二次冷却の平均冷却速度は25〜50℃/s）を行ない、引き続いて、所定の巻取り温度にて巻取り、熱延鋼板とした。このときの冷却条件を表２に示す。鋼板コイルは各条件２本ずつ製造し、１本は、得られた熱延鋼板を長手方向各位置にて組織観察するために用い、もう１本は、引き続いて酸洗、冷間圧延を経て、焼鈍（焼鈍温度：850〜900℃）および溶融亜鉛めっき処理（合金化溶融亜鉛めっき）し、1.4mm厚の冷延鋼板を製造した。一部のものについては、冷間圧延後、連続焼鈍ラインに通板して焼鈍し、冷延鋼板を製造した。 The steel sheet exiting the final rolling mill of the finish rolling mill in the hot rolling line is subjected to rapid cooling by water cooling as primary cooling, and then secondary cooling as required (secondary cooling is secondary cooling) The average cooling rate was 25 to 50 ° C./s), followed by winding at a predetermined winding temperature to obtain a hot-rolled steel sheet. Table 2 shows the cooling conditions at this time. Two steel sheet coils are manufactured for each condition, one is used for observing the structure of the obtained hot-rolled steel sheet at each position in the longitudinal direction, and the other is subsequently subjected to pickling and cold rolling. Then, annealing (annealing temperature: 850 to 900 ° C.) and hot dip galvanizing treatment (alloyed hot dip galvanizing) were carried out to produce a cold rolled steel sheet having a thickness of 1.4 mm. About some things, after cold rolling, it passed through the continuous annealing line and annealed, and the cold-rolled steel plate was manufactured.
得られた熱延鋼板の組織を観察するため、長手方向先端部（T部：鋼板先端から5m部）、中央部（M部）、尾端部（B部：鋼板尾端から5m部）からサンプルを採取し、鋼板の幅の1/4に相当する位置にて、組織観察用サンプルとした。サンプルは、圧延方向（RD）に平行な断面を1%Nital液で12秒腐食させ、走査型電子顕微鏡（SEM）で板厚の1/4に相当する位置を含めた周囲（板厚の3/8〜5/8に相当する位置）を観察した。各組織の分率は、3000倍で３視野について写真撮影し、これを画像解析して、組織の構成相を同定するとともに、面積分率を算出し、ポリゴナルフェライトの結晶粒径をJIS G 0552に準拠した切断法で測定した。 In order to observe the structure of the obtained hot-rolled steel sheet, from the longitudinal tip (T part: 5m part from the steel sheet tip), central part (M part), tail end (B part: 5m part from the steel plate tail edge) A sample was collected and used as a structure observation sample at a position corresponding to 1/4 of the width of the steel plate. In the sample, the cross section parallel to the rolling direction (RD) was corroded with 1% Nital solution for 12 seconds, and the circumference including the position corresponding to 1/4 of the plate thickness was measured with a scanning electron microscope (SEM). The position corresponding to / 8 to 5/8) was observed. The fraction of each structure was photographed for 3 fields of view at 3000x, and this was analyzed to identify the constituent phases of the tissue, calculate the area fraction, and determine the crystal grain size of polygonal ferrite as JIS G It was measured by a cutting method according to 0552.
冷延鋼板は、コイル長手方向先端部（T部：コイル先端から5m部）、中央部（M部）、尾端部（B部：コイル尾端から5m部）からサンプルを採取し、鋼帯の幅の1/4に相当する位置にて、引張試験、穴広げ試験、および、組織観察用のサンプルとした。 For cold-rolled steel sheets, samples are taken from the coil longitudinal direction tip (T part: 5m part from the coil tip), central part (M part), and tail end part (B part: 5m part from the coil tail end). At a position corresponding to 1/4 of the width, a sample for tensile test, hole expansion test, and structure observation was used.
板厚変動量の最大値は、冷間圧延コイルについて、コイルの全長に渡ってコイル幅中央部で測定した。 The maximum value of the plate thickness fluctuation amount was measured at the central portion of the coil width over the entire length of the cold rolled coil.
引張試験は、JIS5号引張試験片を、圧延方向に対して90°方向に採取し、この試験片をクロスヘッド速度10mm/minで引張り、引張強さ（TS）を測定した。なお、引張強さ（TS）については、T部、M部およびB部の各値から、鋼板内の引張強さ（TS）のばらつきΔTSを、下記（ｉｉ）式を用いて求めた。 In the tensile test, a JIS No. 5 tensile test piece was sampled at a 90 ° direction with respect to the rolling direction, the test piece was pulled at a crosshead speed of 10 mm / min, and the tensile strength (TS) was measured. In addition, about tensile strength (TS), dispersion | variation (DELTA) TS of the tensile strength (TS) in a steel plate was calculated | required using the following (ii) formula from each value of T part, M part, and B part.
ΔTS＝√（（（TST−TSM）×２＋（TSM−TSB）×２）／３） ・・・（ｉｉ）
ここで、TST、TSM、TSBは、それぞれT部、M部、B部の引張強さ（TS）を意味する。
ΔTS = √ (((TST−TSM) × 2 + (TSM−TSB) × 2) / 3) (ii)
Here, TST, TSM, and TSB mean the tensile strength (TS) of the T part, M part, and B part, respectively.
また、穴広げ試験は、日本鉄鋼連盟規格JFST1001-1996に準拠して行ない、穴広げ率（%）で伸びフランジ性を評価した。 The hole expansion test was conducted in accordance with the Japan Iron and Steel Federation standard JFST1001-1996, and the stretch flangeability was evaluated by the hole expansion ratio (%).
表２に示すように、本発明の成分範囲内の鋼で、熱間圧延にて本発明の範囲内の冷却制御を施したＮｏ．３〜１０は、冷間圧延後の材質および板厚変動が改善しているが、本発明の成分範囲外のＮｏ．１１〜１４、本発明の成分範囲であるが、冷却条件が範囲から外れるＮｏ．１、２は改善していない。 As shown in Table 2, the steel in the component range of the present invention was subjected to cooling control within the range of the present invention by hot rolling. Nos. 3 to 10 have improved material and plate thickness fluctuation after cold rolling, but No. 3 out of the component range of the present invention. 11-14, which is the component range of the present invention, but the cooling conditions are out of the range. 1 and 2 have not improved.
本発明の方法で製造した熱延鋼板を用いることにより、加工性の良い高強度冷延鋼板の板厚変動を小さくでき、しかも、製造時のトラブル防止や歩留り向上も図ることができる。 By using the hot-rolled steel sheet produced by the method of the present invention, it is possible to reduce the thickness variation of the high-strength cold-rolled steel sheet having good workability, and to prevent troubles during production and improve the yield.
Claims (9)
質量%で、
C：0.03〜0.1%、
Si：0.01〜1.5%、
Mn：1.5〜3%、
P：0.08%以下、
S：0.010%以下、
Sol.Al：0.01〜1.20%、
Cr：0.1〜1.5%および／またはMo：0.01〜0.15%
を含有し、残部がFeおよび不可避的不純物からなることを特徴とする請求項１に記載の高強度冷延鋼板用熱延鋼板。 The composition of steel is
% By mass
C: 0.03-0.1%
Si: 0.01 to 1.5%
Mn: 1.5 to 3%
P: 0.08% or less,
S: 0.010% or less,
Sol.Al: 0.01-1.20%,
Cr: 0.1-1.5% and / or Mo: 0.01-0.15%
The hot-rolled steel sheet for high-strength cold-rolled steel sheets according to claim 1, wherein the balance is made of Fe and inevitable impurities.
さらに、質量%で、
Nb：0.005〜0.05%、
V：0.005〜0.05%、
Ti：0.005〜0.05%、
B：0.0005〜0.003%
のうちの１種以上を含有することを特徴とする請求項２に記載の高強度冷延鋼板用熱延鋼板。 As component composition of steel,
Furthermore, in mass%,
Nb: 0.005 to 0.05%,
V: 0.005-0.05%
Ti: 0.005-0.05%,
B: 0.0005-0.003%
The hot-rolled steel sheet for high-strength cold-rolled steel sheets according to claim 2, comprising at least one of the above.
さらに、質量%で、
Cu：0.01〜0.2%、
Ni：0.005〜0.1%、
Sn：0.01〜0.1%、
Ca：0.005〜0.1%
のうちの１種以上を含有する
請求項２または請求項３に記載の高強度冷延鋼板用熱延鋼板。 As component composition of steel,
Furthermore, in mass%,
Cu: 0.01 to 0.2%,
Ni: 0.005-0.1%,
Sn: 0.01 to 0.1%
Ca: 0.005 to 0.1%
The hot-rolled steel sheet for high-strength cold-rolled steel sheets according to claim 2 or 3 containing at least one of the above.
C：0.03〜0.1%、
Si：0.01〜1.5%、
Mn：1.5〜3%、
P：0.08%以下、
S：0.010%以下、
Sol.Al：0.01〜1.20%、
Cr：0.1〜1.5%および／またはMo：0.01〜0.15%
を含有し、残部がFeおよび不可避的不純物からなり、
（ｉ）式を満たす成分組成を有する鋼片を、
800〜1000℃の仕上圧延完了温度にて熱間圧延後、
仕上圧延完了後1.8秒以内に冷却を開始し、120〜500℃/秒の平均冷却速度で600℃以下の冷却停止温度まで一次冷却し、
必要に応じて1〜10秒の冷却停止を挟んで二次冷却し、
一次冷却完了から巻取りまで600℃以下に保持し、
600℃以下の巻取り温度で巻取る
ことを特徴とする高強度冷延鋼板用熱延鋼板の製造方法。
300≦K≦400 ・・・（ｉ）
ここに、
K＝540-350（[C%]/0.4）-40[Mn%]+30[Sol.Al%]-20[Cr%]-35[V%]-10[Mo%]
を意味するものとする。
式中、M%は元素Mの鋼中含有量を示す。含有しない元素の含有量はゼロとして扱う。 % By mass
C: 0.03-0.1%
Si: 0.01 to 1.5%
Mn: 1.5 to 3%
P: 0.08% or less,
S: 0.010% or less,
Sol.Al: 0.01-1.20%,
Cr: 0.1-1.5% and / or Mo: 0.01-0.15%
And the balance consists of Fe and inevitable impurities,
A steel slab having a component composition satisfying the formula (i)
After hot rolling at a finish rolling completion temperature of 800-1000 ° C,
Start cooling within 1.8 seconds after completion of finish rolling, and primary cooling to a cooling stop temperature of 600 ° C. or less at an average cooling rate of 120 to 500 ° C./second,
Secondary cooling with 1-10 seconds cooling stop if necessary,
Hold at 600 ° C or lower from completion of primary cooling to winding
A method for producing a hot-rolled steel sheet for high-strength cold-rolled steel sheet, which is wound at a coiling temperature of 600 ° C or lower.
300 ≦ K ≦ 400 (i)
here,
K = 540-350 ([C%] / 0.4) -40 [Mn%] + 30 [Sol.Al%]-20 [Cr%]-35 [V%]-10 [Mo%]
Means.
In the formula, M% represents the content of element M in steel. The content of elements not contained is treated as zero.
さらに、
質量%で、
Nb：0.005〜0.05%、
V：0.005〜0.05%、
Ti：0.005〜0.05%、
B：0.0005〜0.003%
のうちの１種以上を含有する
請求項５に記載の高強度冷延鋼板用熱延鋼板の製造方法。 As component composition of steel,
further,
% By mass
Nb: 0.005 to 0.05%,
V: 0.005-0.05%
Ti: 0.005-0.05%,
B: 0.0005-0.003%
The manufacturing method of the hot-rolled steel sheet for high-strength cold-rolled steel sheets of Claim 5 containing 1 or more types of these.
さらに、
Cu：0.01〜0.2%、
Ni：0.005〜0.1%、
Sn：0.01〜0.1%、
Ca：0.005〜0.1%
のうちの１種以上を含有する
請求項５または請求項６に記載の高強度冷延鋼板用熱延鋼板の製造方法。 As component composition of steel,
further,
Cu: 0.01 to 0.2%,
Ni: 0.005-0.1%,
Sn: 0.01 to 0.1%
Ca: 0.005 to 0.1%
The manufacturing method of the hot-rolled steel sheet for high-strength cold-rolled steel sheets of Claim 5 or Claim 6 containing 1 or more types of these.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2009130120A JP5481941B2 (en) | 2009-05-29 | 2009-05-29 | Hot-rolled steel sheet for high-strength cold-rolled steel sheet, method for producing the same, and method for producing high-strength cold-rolled steel sheet |
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2013031105A1 (en) * | 2011-08-31 | 2013-03-07 | Ｊｆｅスチール株式会社 | Hot-rolled steel sheet for cold-rolled steel sheet, hot-rolled steel sheet for hot-dipped galvanized steel sheet, method for producing hot-rolled steel sheet for cold-rolled steel sheet, and method for producing hot-rolled steel sheet for hot-dipped galvanized steel sheet |
| WO2015093043A1 (en) * | 2013-12-18 | 2015-06-25 | Ｊｆｅスチール株式会社 | High strength hot-dip galvanized steel sheet and manufacturing method therefor |
| WO2016194273A1 (en) * | 2015-05-29 | 2016-12-08 | Ｊｆｅスチール株式会社 | Hot-rolled steel sheet, full hard cold-rolled steel sheet, and method for producing hot-rolled steel sheet |
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| JPH08295985A (en) * | 1995-04-27 | 1996-11-12 | Nisshin Steel Co Ltd | High strength steel sheet for fine blanking |
| JP2005002441A (en) * | 2003-06-13 | 2005-01-06 | Sumitomo Metal Ind Ltd | High strength steel and its production method |
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| JPH08295985A (en) * | 1995-04-27 | 1996-11-12 | Nisshin Steel Co Ltd | High strength steel sheet for fine blanking |
| JP2005002441A (en) * | 2003-06-13 | 2005-01-06 | Sumitomo Metal Ind Ltd | High strength steel and its production method |
Cited By (10)
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| WO2013031105A1 (en) * | 2011-08-31 | 2013-03-07 | Ｊｆｅスチール株式会社 | Hot-rolled steel sheet for cold-rolled steel sheet, hot-rolled steel sheet for hot-dipped galvanized steel sheet, method for producing hot-rolled steel sheet for cold-rolled steel sheet, and method for producing hot-rolled steel sheet for hot-dipped galvanized steel sheet |
| JP2013049901A (en) * | 2011-08-31 | 2013-03-14 | Jfe Steel Corp | Hot-rolled steel sheet for cold-rolled steel sheet and hot-rolled steel sheet for hot-dipped galvanized steel sheet superior in processability and material stability, and method for producing the same |
| US11098392B2 (en) | 2011-08-31 | 2021-08-24 | Jfe Steel Corporation | Hot rolled steel sheet for cold rolled steel sheet, hot rolled steel sheet for galvanized steel sheet, and method for producing the same |
| WO2015093043A1 (en) * | 2013-12-18 | 2015-06-25 | Ｊｆｅスチール株式会社 | High strength hot-dip galvanized steel sheet and manufacturing method therefor |
| JP5858199B2 (en) * | 2013-12-18 | 2016-02-10 | Ｊｆｅスチール株式会社 | High-strength hot-dip galvanized steel sheet and manufacturing method thereof |
| US10590503B2 (en) | 2013-12-18 | 2020-03-17 | Jfe Steel Corporation | High-strength galvanized steel sheet and method for manufacturing the same |
| WO2016194273A1 (en) * | 2015-05-29 | 2016-12-08 | Ｊｆｅスチール株式会社 | Hot-rolled steel sheet, full hard cold-rolled steel sheet, and method for producing hot-rolled steel sheet |
| JP6066023B1 (en) * | 2015-05-29 | 2017-01-25 | Ｊｆｅスチール株式会社 | Hot-rolled steel sheet, full-hard cold-rolled steel sheet, and hot-rolled steel sheet manufacturing method |
| KR20170139149A (en) * | 2015-05-29 | 2017-12-18 | 제이에프이 스틸 가부시키가이샤 | Hot-rolled steel sheet, full hard cold-rolled steel sheet, and method for producing hot-rolled steel sheet |
| KR102044086B1 (en) | 2015-05-29 | 2019-11-12 | 제이에프이 스틸 가부시키가이샤 | Hot-rolled steel sheet, full-hard cold-rolled steel sheet, and method for manufacturing hot-rolled steel sheet |
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