JP5853884B2 - Hot-dip galvanized steel sheet and manufacturing method thereof - Google Patents
Hot-dip galvanized steel sheet and manufacturing method thereof Download PDFInfo
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- 229910001335 Galvanized steel Inorganic materials 0.000 title claims description 30
- 239000008397 galvanized steel Substances 0.000 title claims description 30
- 238000004519 manufacturing process Methods 0.000 title claims description 13
- 229910001566 austenite Inorganic materials 0.000 claims description 53
- 229910000734 martensite Inorganic materials 0.000 claims description 33
- 229910000831 Steel Inorganic materials 0.000 claims description 31
- 239000010959 steel Substances 0.000 claims description 31
- 230000009466 transformation Effects 0.000 claims description 30
- 230000000717 retained effect Effects 0.000 claims description 27
- 238000001816 cooling Methods 0.000 claims description 24
- 229910000859 α-Fe Inorganic materials 0.000 claims description 22
- 238000005096 rolling process Methods 0.000 claims description 20
- 238000005246 galvanizing Methods 0.000 claims description 15
- 238000000137 annealing Methods 0.000 claims description 11
- 238000005098 hot rolling Methods 0.000 claims description 11
- 238000005097 cold rolling Methods 0.000 claims description 8
- 229910052799 carbon Inorganic materials 0.000 claims description 7
- 229910052750 molybdenum Inorganic materials 0.000 claims description 7
- 229910052804 chromium Inorganic materials 0.000 claims description 6
- 229910052802 copper Inorganic materials 0.000 claims description 6
- 229910052748 manganese Inorganic materials 0.000 claims description 6
- 229910052759 nickel Inorganic materials 0.000 claims description 6
- 229910052758 niobium Inorganic materials 0.000 claims description 6
- 229910052720 vanadium Inorganic materials 0.000 claims description 6
- 239000010960 cold rolled steel Substances 0.000 claims description 5
- 239000012535 impurity Substances 0.000 claims description 5
- 238000002844 melting Methods 0.000 claims description 4
- 230000008018 melting Effects 0.000 claims description 4
- HCHKCACWOHOZIP-UHFFFAOYSA-N Zinc Chemical compound [Zn] HCHKCACWOHOZIP-UHFFFAOYSA-N 0.000 claims description 2
- 229910052718 tin Inorganic materials 0.000 claims description 2
- 229910052725 zinc Inorganic materials 0.000 claims description 2
- 239000011701 zinc Substances 0.000 claims description 2
- 230000000694 effects Effects 0.000 description 14
- 229910001563 bainite Inorganic materials 0.000 description 12
- 238000000034 method Methods 0.000 description 12
- 238000007747 plating Methods 0.000 description 11
- 238000005275 alloying Methods 0.000 description 8
- 230000007423 decrease Effects 0.000 description 8
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 8
- 230000015572 biosynthetic process Effects 0.000 description 7
- 239000000203 mixture Substances 0.000 description 6
- 238000000354 decomposition reaction Methods 0.000 description 5
- 238000010438 heat treatment Methods 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 229910001562 pearlite Inorganic materials 0.000 description 4
- 238000005728 strengthening Methods 0.000 description 4
- 238000000576 coating method Methods 0.000 description 3
- 230000007547 defect Effects 0.000 description 3
- 230000003111 delayed effect Effects 0.000 description 3
- 229910052742 iron Inorganic materials 0.000 description 3
- 239000006104 solid solution Substances 0.000 description 3
- 238000004804 winding Methods 0.000 description 3
- 229910000794 TRIP steel Inorganic materials 0.000 description 2
- 229910045601 alloy Inorganic materials 0.000 description 2
- 239000000956 alloy Substances 0.000 description 2
- 230000003749 cleanliness Effects 0.000 description 2
- 239000011248 coating agent Substances 0.000 description 2
- 230000006866 deterioration Effects 0.000 description 2
- 239000000446 fuel Substances 0.000 description 2
- 150000001247 metal acetylides Chemical class 0.000 description 2
- 238000005498 polishing Methods 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 229920006395 saturated elastomer Polymers 0.000 description 2
- 238000005204 segregation Methods 0.000 description 2
- 230000000087 stabilizing effect Effects 0.000 description 2
- 230000003746 surface roughness Effects 0.000 description 2
- 238000009864 tensile test Methods 0.000 description 2
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 description 1
- UCKMPCXJQFINFW-UHFFFAOYSA-N Sulphide Chemical compound [S-2] UCKMPCXJQFINFW-UHFFFAOYSA-N 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 238000005452 bending Methods 0.000 description 1
- 239000005539 carbonized material Substances 0.000 description 1
- 238000005266 casting Methods 0.000 description 1
- 238000009749 continuous casting Methods 0.000 description 1
- 238000012937 correction Methods 0.000 description 1
- 230000002349 favourable effect Effects 0.000 description 1
- 238000007654 immersion Methods 0.000 description 1
- 238000005461 lubrication Methods 0.000 description 1
- 238000000465 moulding Methods 0.000 description 1
- 238000005554 pickling Methods 0.000 description 1
- 229910001568 polygonal ferrite Inorganic materials 0.000 description 1
- 238000001556 precipitation Methods 0.000 description 1
- 238000003825 pressing Methods 0.000 description 1
- 238000003303 reheating Methods 0.000 description 1
- 238000011160 research Methods 0.000 description 1
- 239000011347 resin Substances 0.000 description 1
- 229920005989 resin Polymers 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
Landscapes
- Coating With Molten Metal (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Description
本発明は、自動車用鋼板としての用途に好適な加工性に優れる高強度溶融亜鉛めっき鋼板およびその製造方法に関する。 The present invention relates to a high-strength hot-dip galvanized steel sheet excellent in workability suitable for use as a steel sheet for automobiles and a method for producing the same.
近年、地球環境の保全の見地から自動車の燃費向上が重要な課題となっている。このため、車体材料の高強度化により薄肉化を図り、車体そのものの軽量化により燃費向上を図る動きが活発になってきている。自動車部品のようにプレス加工や曲げ加工により成型される鋼板では、高強度を保ちつつ加工に耐えうる成形性が要求されている。特に、実際のプレス成形においてはネッキングが無く加工できることが強く求められており、均一伸び(以下、UEL)が重要である。UELの向上には、残留オーステナイトによる変態誘起塑性(Transformation Induced Plasticity、以下、TRIP)効果の活用が有効であることが知られており、例えば特許文献1では、TRIP鋼に関する技術が開示されている。このような、いわゆる低合金TRIP鋼は、通常、焼鈍、冷却後の過時効帯での保持によりベイナイト変態させて、オーステナイト中に炭素(以下、C)を濃化させ、オーステナイトを安定化することで残留オーステナイトを生成させる方法で製造される。しかしながら、溶融亜鉛めっき鋼板においては、めっき浴浸漬あるいは合金化熱処理によってオーステナイトの分解が起きるため、加工性(延性)が著しく低下するという問題がある。これに対し、特許文献2ではMoを添加することでオーステナイトの分解を抑制し、加工性(延性)を向上させる技術が開示されている。しかし、MoやCr等のオーステナイト安定化元素はオーステナイトの分解抑制に有効である一方、ベイナイト変態の進行を著しく妨げるために、めっき処理前時点で安定なオーステナイトの量が減少するという問題がある。一般的に両者はトレードオフの関係にあり、ベイナイト変態を妨げずにオーステナイトの分解を抑制する技術はない。 In recent years, improving the fuel efficiency of automobiles has become an important issue from the viewpoint of conservation of the global environment. For this reason, efforts are being made to reduce the thickness by increasing the strength of the vehicle body material and to improve the fuel efficiency by reducing the weight of the vehicle body itself. Steel sheets that are formed by pressing or bending like automobile parts are required to have formability that can withstand processing while maintaining high strength. In particular, in actual press molding, there is a strong demand for processing without necking, and uniform elongation (hereinafter referred to as UEL) is important. For improving UEL, it is known that the use of transformation induced plasticity (hereinafter referred to as TRIP) effect due to retained austenite is effective. For example, Patent Document 1 discloses a technique related to TRIP steel. . Such a so-called low-alloy TRIP steel is usually bainite transformed by annealing and holding in an overaged zone after cooling, and carbon (hereinafter referred to as C) is concentrated in austenite to stabilize austenite. And produced by a method of generating retained austenite. However, in the hot dip galvanized steel sheet, there is a problem that workability (ductility) is remarkably lowered because austenite is decomposed by immersion in the plating bath or heat treatment by alloying. On the other hand, Patent Document 2 discloses a technique that suppresses the decomposition of austenite and improves workability (ductility) by adding Mo. However, while austenite stabilizing elements such as Mo and Cr are effective in suppressing the decomposition of austenite, there is a problem that the amount of stable austenite decreases at the time before plating because it significantly hinders the progress of bainite transformation. In general, the two are in a trade-off relationship, and there is no technique for suppressing the decomposition of austenite without hindering the bainite transformation.
本発明は、上記した従来技術が抱える問題を有利に解決し、自動車部品用素材として好適な、引張強度TS:980MPa以上、TS×UEL:15000MPa・%以上である加工性に優れた高強度溶融亜鉛めっき鋼板およびその製造方法を提供することを目的とする。 The present invention advantageously solves the problems of the prior art described above, and is suitable as a material for automobile parts. High strength melting excellent in workability of tensile strength TS: 980 MPa or more, TS × UEL: 15000 MPa ·% or more It aims at providing a galvanized steel plate and its manufacturing method.
本発明者らは、上記した課題を達成し、加工性に優れる高強度溶融亜鉛めっき鋼板を製造するため、鋼板の成分組成およびミクロ組織の観点から鋭意研究を重ねた結果、所定量のSn添加が上記課題の解決に極めて有効であることを突き止めた。すなわち、Snその他特定の成分組成を有する鋼において、ミクロ組織として、ベイニティックフェライト、マルテンサイトと焼戻しマルテンサイトならびに残留オーステナイトの面積率を所定の範囲に制御することが重要であることがわかった。また、製造方法の一実施形態として、Snその他特定の成分組成を有する鋼に仕上げ圧延温度をAr3変態点以上で熱間圧延を施した後、冷却し、400〜700℃で巻取り冷間圧延を施し製造した冷延鋼板に、Ac3変態点−50℃〜1000℃で10s以上保持した後、5℃/s以上の平均冷却速度で冷却停止温度150〜550℃まで冷却し、350〜550℃で10〜1500s保持し、その後溶融亜鉛めっき処理を行うことによって、TSが980MPa以上、TS×UELが15000MPa・%以上である加工性に優れた高強度溶融亜鉛めっき鋼板が得られることを見出した。 In order to achieve the above-mentioned problems and to produce a high-strength hot-dip galvanized steel sheet having excellent workability, the present inventors have conducted extensive research from the viewpoint of the component composition and microstructure of the steel sheet. As a result, a predetermined amount of Sn is added. Has been found to be extremely effective in solving the above problems. That is, it was found that it is important to control the area ratio of bainitic ferrite, martensite and tempered martensite, and retained austenite within a predetermined range as a microstructure in steel having Sn and other specific component compositions. . As one embodiment of the manufacturing method, steel having Sn or other specific component composition is hot-rolled at a finish rolling temperature of Ar3 transformation point or higher, cooled, and then cold-rolled at 400 to 700 ° C. The cold-rolled steel sheet produced by applying the above-mentioned temperature is maintained at Ac3 transformation point −50 ° C. to 1000 ° C. for 10 s or more, then cooled to a cooling stop temperature of 150 to 550 ° C. at an average cooling rate of 5 ° C./s or more, and 350 to 550 ° C. It was found that a high-strength hot-dip galvanized steel sheet excellent in workability with TS of 980 MPa or more and TS × UEL of 15000 MPa ·% or more is obtained by holding for 10 to 1500 seconds at .
本発明は、このような知見に基づきなされたもので、以下の発明を提供する。
(1)質量%で、C:0.15〜0.40%、Si:0.5〜3.0%、Al:0.010〜3.000%、Mn:1.5〜4.0%、P:0.100%以下、S:0.020%以下、Sn:0.01〜0.50%を含み、残部がFeおよび不可避的不純物からなる成分組成を有し、かつ面積率3〜68%のベイニティックフェライトと、面積率の合計が10〜65%のマルテンサイトおよび焼戻しマルテンサイトと、面積率5%以上の残留オーステナイトとを含むミクロ組織を有する加工性に優れた高強度溶融亜鉛めっき鋼板。
(2)さらに、質量%で、Cr:0.005〜0.200%、Mo:0.005〜0.200%、V:0.005〜0.200%、Ni:0.005〜0.200%、Cu:0.005〜0.200%から選ばれる少なくとも一種の元素を含有し、かつその合計が0.200%以下である(1)に記載の加工性に優れた高強度溶融亜鉛めっき鋼板。
(3)さらに、質量%で、Ti:0.005〜0.200%、Nb:0.005〜0.200%から選ばれる少なくとも1種の元素を含有する(1)または(2)に記載の加工性に優れた高強度溶融亜鉛めっき鋼板。
(4)さらに、質量%で、B:0.0003〜0.0050%を含有する(1)〜(3)のいずれかに記載の加工性に優れた高強度溶融亜鉛めっき鋼板。
(5)さらに、質量%で、Ca:0.001〜0.005%、REM:0.001〜0.005%から選ばれる少なくとも一種の元素を含有する(1)〜(4)のいずれかに記載の加工性に優れた高強度溶融亜鉛めっき鋼板。
(6)(1)〜(5)のいずれかに記載の成分を有するスラブに、仕上げ圧延温度をAr3変態点以上で熱間圧延終了後、冷却し、400〜700℃の温度で巻き取る熱延工程を施し熱延板とした後、冷間圧延を施し製造した冷延鋼板に連続焼鈍を施すに際し、Ac3変態点−50℃〜1000℃まで加熱し10s以上保持した後、5℃/s以上の平均冷却速度で冷却停止温度150〜550℃まで冷却した後、350〜550℃の温度で10〜1500s保持した後、溶融亜鉛めっきを施すことを特徴とする加工性に優れた高強度溶融亜鉛めっき鋼板の製造方法。
(7)(6)に記載の高強度溶融亜鉛めっき鋼板の製造方法において、溶融亜鉛めっき後、さらに亜鉛めっきの合金化処理を施すことを特徴とする加工性に優れた高強度溶融亜鉛めっき鋼板の製造方法。
The present invention has been made based on such findings, and provides the following inventions.
(1) By mass%, C: 0.15 to 0.40%, Si: 0.5 to 3.0%, Al: 0.010 to 3.000%, Mn: 1.5 to 4.0% , P: 0.100% or less, S: 0.020% or less, Sn: 0.01 to 0.50%, with the balance being composed of Fe and inevitable impurities, and an area ratio of 3 High-strength melt with excellent workability having a microstructure containing 68% bainitic ferrite, martensite and tempered martensite with a total area ratio of 10 to 65%, and retained austenite with an area ratio of 5% or more Galvanized steel sheet.
(2) Further, in terms of mass%, Cr: 0.005 to 0.200%, Mo: 0.005 to 0.200%, V: 0.005 to 0.200%, Ni: 0.005 to 0.00. 200%, Cu: at least one element selected from 0.005 to 0.200%, and the total thereof is 0.200% or less, the high-strength molten zinc having excellent workability as described in (1) Plated steel sheet.
(3) Further described in (1) or (2) containing at least one element selected from Ti: 0.005 to 0.200% and Nb: 0.005 to 0.200% by mass%. High-strength hot-dip galvanized steel sheet with excellent workability.
(4) The high-strength hot-dip galvanized steel sheet excellent in workability according to any one of (1) to (3), further containing, by mass%, B: 0.0003 to 0.0050%.
(5) In addition, any one of (1) to (4) containing at least one element selected from Ca: 0.001 to 0.005% and REM: 0.001 to 0.005% by mass% High-strength hot-dip galvanized steel sheet with excellent workability as described in 1.
(6) The heat which winds at the temperature of 400-700 degreeC after the hot rolling completion | finish in the slab which has a component in any one of (1)-(5) after finishing rolling temperature at Ar3 transformation point or more. After performing a rolling step to obtain a hot-rolled sheet, the cold-rolled steel sheet produced by performing cold rolling is heated to Ac3 transformation point −50 ° C. to 1000 ° C. and held for 10 s or more, and then 5 ° C./s. After cooling to a cooling stop temperature of 150 to 550 ° C. at the above average cooling rate, holding at a temperature of 350 to 550 ° C. for 10 to 1500 s, and then applying hot dip galvanization, high strength melting with excellent workability Manufacturing method of galvanized steel sheet.
(7) In the method for producing a high-strength hot-dip galvanized steel sheet according to (6), a high-strength hot-dip galvanized steel sheet excellent in workability characterized by further subjecting it to an alloying treatment of galvanizing after hot-dip galvanizing Manufacturing method.
なお、本発明において、加工性に優れた高強度溶融亜鉛めっき鋼板とは、引張強度TSが980MPa以上、TS×UEL:15000MPa・%以上の溶融亜鉛めっき鋼板をいう。また、本発明の高強度溶融亜鉛めっき鋼板は、溶融亜鉛めっき処理後合金化処理を施さないめっき鋼板(以下、GIと称することもある)、合金化処理を施すめっき鋼板(以下、GAと称することもある)のいずれも含むものである。 In the present invention, the high-strength hot-dip galvanized steel sheet excellent in workability refers to a hot-dip galvanized steel sheet having a tensile strength TS of 980 MPa or more and TS × UEL: 15000 MPa ·% or more. The high-strength hot-dip galvanized steel sheet of the present invention includes a plated steel sheet (hereinafter sometimes referred to as GI) that is not subjected to alloying after the hot-dip galvanizing process, and a plated steel sheet (hereinafter referred to as GA) that is subjected to the alloying process. In some cases).
本発明によれば、自動車部品用素材として好適な、TS:980MPa以上、TS×UEL:15000MPa・%以上である加工性に優れた高強度溶融亜鉛めっき鋼板を得ることができる。 According to the present invention, it is possible to obtain a high-strength hot-dip galvanized steel sheet excellent in workability, which is suitable as a material for automobile parts, TS: 980 MPa or more and TS × UEL: 15000 MPa ·% or more.
以下に、本発明の詳細を説明する。なお、成分元素の含有量を表す「%」は、特に断らない限り「質量%」を意味する。 Details of the present invention will be described below. Note that “%” representing the content of component elements means “% by mass” unless otherwise specified.
1)成分組成
C:0.15〜0.40%
Cは、マルテンサイトや焼戻しマルテンサイトなどの低温変態相を生成させてTSを上昇させるために必要な元素である。また、オーステナイトを安定させて残留オーステナイトを生成させ、鋼の加工性を向上させるのに有効な元素である。C量が0.15%未満では、残留オーステナイトの生成が不十分になり高加工性を得ることが難しい。一方、スポット溶接性の観点からはC量は低いことが好ましく、上限を0.40%とする。したがって、C量は0.15〜0.40%、好ましくは0.17〜0.35%とする。
1) Component composition C: 0.15 to 0.40%
C is an element necessary for increasing TS by generating a low-temperature transformation phase such as martensite and tempered martensite. Further, it is an element effective for stabilizing austenite to generate retained austenite and improving the workability of steel. If the C content is less than 0.15%, the production of retained austenite becomes insufficient and it is difficult to obtain high workability. On the other hand, from the viewpoint of spot weldability, the C content is preferably low, and the upper limit is made 0.40%. Therefore, the C content is 0.15 to 0.40%, preferably 0.17 to 0.35%.
Si:0.5〜3.0%
Siは、鋼を固溶強化してTSを上昇させたり、炭化物の生成を抑制して残留オーステナイトを生成させ鋼の加工性を向上させるのに有効な元素である。こうした効果を得るには、Si量を0.5%以上とする必要がある。一方、3.0%を超えると、脆性が顕著になり、また表面性状や溶接性の劣化を招く。したがって、Si量は0.5〜3.0%、好ましくは0.5〜2.5%、より好ましくは0.8〜2.0%とする。
Si: 0.5 to 3.0%
Si is an element effective for improving the workability of steel by solid-solution strengthening steel to increase TS, or suppressing the formation of carbides to generate retained austenite. In order to obtain such an effect, the Si amount needs to be 0.5% or more. On the other hand, when it exceeds 3.0%, brittleness becomes remarkable, and surface properties and weldability are deteriorated. Therefore, the Si amount is 0.5 to 3.0%, preferably 0.5 to 2.5%, more preferably 0.8 to 2.0%.
Al:0.010〜3.000%
AlはSiと同様、鋼を固溶強化してTSを上昇させたり、炭化物の生成を抑制して残留オーステナイトを生成させ鋼の加工性を向上させるのに有効な元素である。また、脱酸材としても有効である。こうした効果を得るには、Al量を0.010%以上とする必要がある。一方、3.000%を超えると、オーステナイト化が困難になり、焼鈍後に所望の組織が得られない。したがって、Al量は0.010〜3.000%、好ましくは0.010〜2.000%、より好ましくは0.010〜1.000%とする。
Al: 0.010 to 3.000%
Al, like Si, is an element effective for improving the workability of steel by solid-solution strengthening steel to raise TS and suppressing the formation of carbides to produce retained austenite. It is also effective as a deoxidizer. In order to obtain such an effect, the Al amount needs to be 0.010% or more. On the other hand, if it exceeds 3.000%, austenitization becomes difficult, and a desired structure cannot be obtained after annealing. Therefore, the amount of Al is made 0.010 to 3.000%, preferably 0.010 to 2.000%, more preferably 0.010 to 1.000%.
Mn:1.5〜4.0%
Mnは、鋼を固溶強化してTSを上昇させたり、マルテンサイトや焼戻しマルテンサイトなどの低温変態相の生成を促進させてTSを上昇させる元素である。こうした効果を得るには、Mn量を1.5%以上にする必要がある。一方、Mn量が4.0%を超えると、介在物の増加が顕著になり、鋼の清浄度や加工性低下の原因となる。したがって、Mn量は1.5〜4.0%、好ましくは1.8〜3.5%とする。
Mn: 1.5-4.0%
Mn is an element that raises TS by solid-solution strengthening steel and raises TS, or promotes the generation of low-temperature transformation phases such as martensite and tempered martensite. In order to acquire such an effect, it is necessary to make Mn amount 1.5% or more. On the other hand, when the amount of Mn exceeds 4.0%, the increase of inclusions becomes remarkable, which causes the cleanliness of steel and the deterioration of workability. Therefore, the amount of Mn is 1.5 to 4.0%, preferably 1.8 to 3.5%.
Sn:0.01〜0.50%
Snは、オーステナイトを安定化し、またその分解を抑制し、残留オーステナイトを得てUELを上昇させる元素である。こうした効果を得るには、Sn量を0.01%以上とする必要がある。一方、Sn量が0.50%を超えると、脆性が顕著になる。したがって、Sn量は0.01〜0.50%、好ましくは0.02〜0.25%とする。
Sn: 0.01 to 0.50%
Sn is an element that stabilizes austenite, suppresses its decomposition, and obtains retained austenite to raise UEL. In order to obtain such an effect, the Sn amount needs to be 0.01% or more. On the other hand, when the Sn content exceeds 0.50%, brittleness becomes remarkable. Therefore, the Sn content is 0.01 to 0.50%, preferably 0.02 to 0.25%.
P:0.100%以下
Pは、粒界偏析により鋼を劣化させ、溶接性を劣化させるため、その量は極力低減することが望ましい。したがって、P量は0.100%以下とする。
P: 0.100% or less P degrades steel by grain boundary segregation and degrades weldability. Therefore, the amount is desirably reduced as much as possible. Therefore, the P content is 0.100% or less.
S:0.020%以下
Sは、MnSなどの介在物として存在して、溶接性を劣化させるため、その量は極力低減することが好ましい。したがって、S量は0.020%以下とする。
S: 0.020% or less S is present as inclusions such as MnS, and deteriorates weldability. Therefore, the amount is preferably reduced as much as possible. Therefore, the S amount is 0.020% or less.
残部はFeおよび不可避的不純物であるが、必要に応じて以下の元素の1種以上を適宜含有させることができる。 The balance is Fe and inevitable impurities, but one or more of the following elements can be appropriately contained as necessary.
Cr:0.005〜0.200%、Mo:0.005〜0.200%、V:0.005〜0.200%、Ni:0.005〜0.200%、Cu:0.005〜0.200%から選ばれる少なくとも1種を含有し、かつその合計が0.200%以下
Cr、Mo、V、Ni、Cuはマルテンサイトなどの低温変態相を生成させるため、高強度化に有効な元素である。こうした効果を得るには、Cr、Mo、V、Ni、Cuから選ばれる少なくとも1種の元素の各々の含有量を0.005%以上にすることが好ましい。一方、これらの元素の添加量が多くなるとベイナイト変態の遅延が顕著になり、残留オーステナイトの量が減少して加工性が低下するため、その合計の上限を0.200%とする。したがって、Cr、Mo、V、Ni、Cuから選ばれる少なくとも1種の元素の各々の含有量は0.005〜0.200%、かつ合計で0.200%以下が好ましい。より好ましくは、合計で0.100%以下とする。
Cr: 0.005 to 0.200%, Mo: 0.005 to 0.200%, V: 0.005 to 0.200%, Ni: 0.005 to 0.200%, Cu: 0.005 Contains at least one selected from 0.200%, and the total is 0.200% or less. Cr, Mo, V, Ni, and Cu generate low-temperature transformation phases such as martensite, and are effective in increasing strength. Element. In order to obtain such an effect, the content of each of at least one element selected from Cr, Mo, V, Ni, and Cu is preferably 0.005% or more. On the other hand, when the addition amount of these elements increases, the delay of the bainite transformation becomes remarkable, and the amount of retained austenite decreases and the workability decreases, so the upper limit of the total is made 0.200%. Therefore, the content of each of at least one element selected from Cr, Mo, V, Ni, and Cu is preferably 0.005 to 0.200% and a total of 0.200% or less. More preferably, the total content is 0.100% or less.
Ti:0.005〜0.200%、Nb:0.005〜0.200%から選ばれる少なくとも1種
TiおよびNbは、炭窒化物を形成し、鋼を析出強化により高強度化するのに有効な元素である。こうした効果を得るには、TiおよびNbの各々の含有量を0.005%以上にすることが好ましい。一方、TiおよびNbの各々の含有量が0.200%を超えると、高強度化の効果は飽和し、UELが低下する。したがって、含有量は0.005〜0.200%が好ましい。
At least one type of Ti and Nb selected from Ti: 0.005 to 0.200% and Nb: 0.005 to 0.200% forms carbonitrides and increases the strength of the steel by precipitation strengthening. It is an effective element. In order to obtain such an effect, the content of each of Ti and Nb is preferably 0.005% or more. On the other hand, when the content of each of Ti and Nb exceeds 0.200%, the effect of increasing the strength is saturated and the UEL decreases. Therefore, the content is preferably 0.005 to 0.200%.
B:0.0003〜0.0050%
Bはオーステナイト粒界からのフェライト生成を抑制し低温変態相を生成させて鋼の強度を上昇させるのに有効である。こうした効果を得るには、Bの含有量を0.0003%以上にすることが好ましい。一方、0.0050%を超えると、その効果は飽和しコストアップを招く。したがって、含有量は0.0003〜0.0050%が好ましい。
B: 0.0003 to 0.0050%
B is effective in suppressing the formation of ferrite from the austenite grain boundaries and generating a low-temperature transformation phase to increase the strength of the steel. In order to obtain such an effect, the B content is preferably 0.0003% or more. On the other hand, if it exceeds 0.0050%, the effect is saturated and the cost is increased. Therefore, the content is preferably 0.0003 to 0.0050%.
Ca:0.001〜0.005%、REM:0.001〜0.005%から選ばれる少なくとも1種
Ca、REMは、いずれも硫化物の形態制御により加工性を改善させるのに有効な元素である。こうした効果を得るには、Ca、REMから選ばれる少なくとも1種の元素の各々の含有量を0.001%以上にすることが好ましい。一方、0.005%を超えると、鋼の清浄度に悪影響を及ぼし特性が低下するおそれがある。したがって、含有量は0.001%〜0.005%が好ましい。
At least one type of Ca and REM selected from Ca: 0.001 to 0.005% and REM: 0.001 to 0.005% are both effective elements for improving workability by controlling the form of sulfide. It is. In order to obtain such an effect, the content of each of at least one element selected from Ca and REM is preferably 0.001% or more. On the other hand, if it exceeds 0.005%, the cleanliness of the steel is adversely affected and the properties may be deteriorated. Therefore, the content is preferably 0.001% to 0.005%.
Nは、不可避的不純物として、0.006%以下で含有しても問題はない。 Even if N is contained as an inevitable impurity in an amount of 0.006% or less, there is no problem.
2)ミクロ組織
ベイニティックフェライト:3〜68%
ベイナイト変態によって生成するベイニティックフェライトはオーステナイトへCを濃化させ、残留オーステナイトを得るのに有効である。かかる効果を発現させるためには、ベイニティックフェライトを面積率で3%以上とする必要がある。一方、ベイニティックフェライト自体の強度はあまり高くないため、その面積率が68%を超えるとTSで980MPa以上を得ることが困難になる。したがって、ベイニティックフェライトの面積率は3〜68%とする。
2) Microstructure bainitic ferrite: 3 to 68%
Bainitic ferrite produced by the bainite transformation is effective in concentrating C into austenite and obtaining retained austenite. In order to express such an effect, it is necessary to make bainitic ferrite 3% or more in area ratio. On the other hand, since the strength of bainitic ferrite itself is not so high, when the area ratio exceeds 68%, it becomes difficult to obtain 980 MPa or more in TS. Therefore, the area ratio of bainitic ferrite is set to 3 to 68%.
マルテンサイトおよび焼戻しマルテンサイトの合計:10〜65%
マルテンサイトおよび焼戻しマルテンサイトはTSを上昇させるのに有効である。また、350〜550℃の温度で10〜1500s保持する前の冷却停止時に生成するマルテンサイト(焼鈍後の焼戻しマルテンサイト)はベイナイト変態の起点となってベイナイト変態を促進させ、ベイニティックフェライトを生成することによりオーステナイトにCを濃化させることで残留オーステナイトを生成させてUELを上昇させるのに有効である。かかる効果を発現するためにはマルテンサイトおよび焼戻しマルテンサイトの面積率が合計で10%以上とする必要がある。一方、その面積率が65%を超えると、残留オーステナイトの生成量の低下が顕著になり、UELが低下する。したがって、マルテンサイトおよび焼戻しマルテンサイトの面積率は合計で10〜65%とする。
Total of martensite and tempered martensite: 10-65%
Martensite and tempered martensite are effective in raising TS. In addition, martensite (tempered martensite after annealing) generated when cooling is stopped at a temperature of 350 to 550 ° C. for 10 to 1500 seconds is the starting point of bainite transformation and promotes bainite transformation. It is effective in increasing the UEL by generating residual austenite by concentrating C in the austenite. In order to exhibit such an effect, the area ratio of martensite and tempered martensite needs to be 10% or more in total. On the other hand, when the area ratio exceeds 65%, the decrease in the amount of retained austenite generated becomes significant, and the UEL decreases. Therefore, the total area ratio of martensite and tempered martensite is 10 to 65%.
残留オーステナイト:5%以上
残留オーステナイトはUELの上昇に有効であり、かかる効果を十分に発現するためには残留オーステナイトを面積率で5%以上とする必要がある。上限は特に規定しないが、本発明の範囲内で製造する場合は、安定化されて残存し得るオーステナイトはおよそ20%以下程度である。したがって、残留オーステナイトは面積率で5%以上、好ましくは8%以上とする。
Residual austenite: 5% or more Residual austenite is effective in increasing UEL, and in order to sufficiently exhibit such an effect, it is necessary that the retained austenite be 5% or more in terms of area ratio. The upper limit is not particularly defined, but when manufactured within the scope of the present invention, the austenite that can remain stabilized is about 20% or less. Accordingly, the retained austenite is 5% or more in area ratio, preferably 8% or more.
また本発明においては、ベイニティックフェライト、マルテンサイト、焼戻しマルテンサイト、残留オーステナイトが上記の条件を満足する限り、その他の相(例えば、ポリゴナルフェライト、パーライト)を含んでも良い。しかしながら、TSおよびUELの観点からは、その他の相は合計で20%以下とすることが好ましい。
ここで、ベイニティックフェライト、マルテンサイト、焼戻しマルテンサイトの面積率とは、観察面積に占める各相の面積の割合のことで、ベイニティックフェライト、マルテンサイト、焼戻しマルテンサイトの面積率は、鋼板の板厚断面を研磨後、3%ナイタールで腐食し、板厚1/4の位置をSEM(走査型電子顕微鏡)で1500倍の倍率で3視野撮影し、得られた画像データからMedia Cybernetics社製のImage−Proを用いて各相の面積率を求め、3視野の平均面積率を各相の面積率とした。前記画像データにおいて、ベイニティックフェライトは、SEMの2次電子像で黒色を呈し、その形態から他の相と区別できる。マルテンサイトおよび残留オーステナイトはともにSEMの2次電子像で白色を呈するが、下記方法にて残留オーステナイトの面積率を求められることから白色組織全体の面積率から残留オーステナイトの面積率を減ずることでマルテンサイトの面積率が求められる。焼戻しマルテンサイトは、マルテンサイト内部のラス組織に沿った明らかな炭化物生成が見られる白色を呈する組織であり、他の相と区別できる。また、残留オーステナイトの割合は、鋼板を板厚1/4の位置まで研磨した後、化学研磨によりさらに0.1mm研磨した面について、X線回折装置でMoのKα線を用いて、fcc鉄の(200)、(220)、(311)面とbcc鉄の(200)、(211)、(220)面の積分強度を測定し、bcc鉄各面からの積分反射強度に占めるfcc鉄各面からの積分反射強度の強度比を求め、これを残留オーステナイトの面積率とした。
In the present invention, bainitic ferrite, martensite, tempered martensite, and retained austenite may contain other phases (for example, polygonal ferrite and pearlite) as long as the above conditions are satisfied. However, from the viewpoint of TS and UEL, the total of other phases is preferably 20% or less.
Here, the area ratio of bainitic ferrite, martensite, and tempered martensite is the ratio of the area of each phase in the observed area, and the area ratio of bainitic ferrite, martensite, and tempered martensite is After polishing the plate thickness section of the steel plate, it was corroded with 3% nital, and the position of the plate thickness 1/4 was photographed with three fields of view at a magnification of 1500 times with SEM (scanning electron microscope), and from the obtained image data, Media Cybernetics The area ratio of each phase was determined using Image-Pro manufactured by the company, and the average area ratio of the three fields of view was defined as the area ratio of each phase. In the image data, bainitic ferrite exhibits a black color in the secondary electron image of the SEM and can be distinguished from other phases from its form. Both martensite and retained austenite are white in the secondary electron image of SEM. However, the area ratio of retained austenite can be obtained by the following method, so the area ratio of retained austenite is reduced from the area ratio of the entire white structure. The site area ratio is required. Tempered martensite is a white-colored structure in which clear carbide formation along the lath structure inside martensite is observed, and can be distinguished from other phases. The ratio of retained austenite is determined by using the Kα ray of Mo with an X-ray diffractometer on the surface polished by 0.1 mm by chemical polishing after the steel plate is polished to a thickness of 1/4. Measure the integrated intensity of the (200), (220), (311) planes and the (200), (211), (220) planes of bcc iron, and each surface of fcc iron in the integrated reflection intensity from each surface of bcc iron The intensity ratio of the integrated reflection intensity from was obtained, and this was defined as the area ratio of retained austenite.
3)製造条件
本発明の高強度溶融亜鉛めっき鋼板は、上記の成分組成を有するスラブに、仕上げ圧延温度をAr3変態点以上で熱間圧延終了後、冷却し、400〜700℃の温度で巻き取る熱延工程を施し熱延板とした後、さらに冷間圧延を施し製造した冷延鋼板に連続焼鈍を施すに際し、Ac3変態点−50℃〜1000℃まで加熱し10s以上保持した後、5℃/s以上の平均冷却速度で冷却停止温度150〜550℃まで冷却した後、350〜550℃で10〜1500s保持した後に溶融亜鉛めっき処理を施すことによって製造できる。
以下、詳しく説明する。
3) Manufacturing conditions The high-strength hot-dip galvanized steel sheet of the present invention is cooled and wound at a temperature of 400 to 700 ° C. on the slab having the above component composition after finishing the hot rolling at a finish rolling temperature not lower than the Ar3 transformation point. After performing the hot rolling process to obtain a hot rolled sheet, the cold rolled steel sheet produced by further cold rolling is subjected to continuous annealing, heated to an Ac3 transformation point of −50 ° C. to 1000 ° C. and held for 10 s or more. After cooling to a cooling stop temperature of 150 to 550 ° C. at an average cooling rate of at least ° C./s, it can be produced by performing hot dip galvanizing treatment after holding at 350 to 550 ° C. for 10 to 1500 seconds.
This will be described in detail below.
仕上げ圧延温度をAr3変態点以上で熱間圧延
Ar3変態点未満で熱間圧延を行うと、フェライト生成域のためオーステナイトとフェライトが混粒した不均一組織になりやすく、冷間圧延性やUELの低下を招く。したがって、仕上げ圧延温度をAr3変態点以上で熱間圧延を行うことが好ましい。なお、Ar3変態点は以下の式より求めた。
Ar3(℃)=868−396×(%C)+25×(%Si)−68×(%Mn)
式中、%C、%Si、%Mnはそれぞれの元素の含有量(質量%)を示す。
When hot rolling is performed at a finish rolling temperature higher than the Ar3 transformation point and less than the hot rolling Ar3 transformation point, it tends to be a heterogeneous structure in which austenite and ferrite are mixed because of the ferrite formation region. Incurs a decline. Therefore, it is preferable to perform hot rolling at a finish rolling temperature of Ar3 transformation point or higher. The Ar3 transformation point was determined from the following formula.
Ar3 (° C.) = 868-396 × (% C) + 25 × (% Si) −68 × (% Mn)
In the formula,% C,% Si, and% Mn indicate the content (mass%) of each element.
400〜700℃の温度で巻き取る熱延工程
巻取り温度が700℃を超えると、鋼板表面が過度に酸化し、表面粗度の上昇や欠陥の原因となる。一方、巻取り温度が400℃未満では熱延板形状の悪化が顕著になる。したがって、巻取り温度は400℃〜700℃が好ましく、より好ましくは560〜670℃である。
When the coiling temperature at a temperature of 400 to 700 ° C. is higher than 700 ° C., the surface of the steel sheet is excessively oxidized, resulting in an increase in surface roughness and defects. On the other hand, when the coiling temperature is less than 400 ° C., the deterioration of the hot-rolled plate shape becomes remarkable. Therefore, the coiling temperature is preferably 400 ° C to 700 ° C, more preferably 560 to 670 ° C.
冷間圧延
冷間圧延条件としては、冷間圧下率を5%以上とすることが好ましい。また、冷間圧延時の圧延負荷を低減するために、巻き取り後の熱延板に、熱延板焼鈍を施してもよい。
As a cold rolling cold rolling condition, it is preferable that the cold rolling reduction is 5% or more. Moreover, in order to reduce the rolling load at the time of cold rolling, you may give hot-rolled sheet annealing to the hot-rolled sheet after winding.
Ac3変態点−50℃〜1000℃まで加熱し10s以上保持する
Ac3変態点−50℃未満では、オーステナイトの生成が不十分となり、最終的に得られる残留オーステナイト量が低下して、加工性が低下する。上限は、製造性の観点から1000℃以下とすることが好ましい。なお、Ac3変態点は次の式により求めた。
Ac3(℃)=910−203×√(%C)+44.7×(%Si)−30×(%Mn)+200×(%Al)
式中、%C、%Si、%Mn、%Alはそれぞれの元素の含有量(質量%)を示す。
保持時間が10s未満では、オーステナイトの生成が不十分なり、最終的に得られる残留オーステナイト量が低下し、加工性が低下する。したがって、保持時間は10s以上とする。上限は特に規定しないが、製造性の観点から1000s以下程度とすることが好ましい。
Ac3 transformation point −50 ° C. to 1000 ° C. Heated to 10 ° C. or more, and Ac3 transformation point−less than −50 ° C., austenite formation is insufficient, the amount of retained austenite finally obtained is lowered, and workability is lowered. To do. The upper limit is preferably 1000 ° C. or less from the viewpoint of productivity. The Ac3 transformation point was determined by the following formula.
Ac3 (° C.) = 910−203 × √ (% C) + 44.7 × (% Si) −30 × (% Mn) + 200 × (% Al)
In the formula,% C,% Si,% Mn, and% Al indicate the content (mass%) of each element.
When the holding time is less than 10 s, austenite is not sufficiently generated, the amount of retained austenite finally obtained is lowered, and workability is lowered. Accordingly, the holding time is 10 s or longer. The upper limit is not particularly specified, but is preferably about 1000 s or less from the viewpoint of manufacturability.
5℃/s以上の平均冷却速度
平均冷却速度が5℃/s未満では、冷却中にフェライトやパーライトが過度に生成しTSが低下する。したがって、平均冷却速度は5℃/s以上とする。
When the average cooling rate of 5 ° C./s or more is less than 5 ° C./s, ferrite and pearlite are excessively generated during cooling and TS is lowered. Therefore, the average cooling rate is 5 ° C./s or more.
150〜550℃の冷却停止温度
冷却停止温度が150℃未満では、焼戻しマルテンサイトが過度に生成して、最終的に得られる残留オーステナイト量が減少し、加工性が低下する。一方、冷却停止温度が550℃を超えるとベイナイト変態が遅延するためにベイニティックフェライトの生成量が減少してオーステナイトへのC濃化が不足し、またフェライトやパーライトが生成しやすくなるために、最終的に得られる残留オーステナイト量が低下し、加工性が低下する。したがって、冷却停止温度は150〜550℃、好ましくは200〜500℃とする。
Cooling stop temperature of 150 to 550 ° C. If the cooling stop temperature is less than 150 ° C., tempered martensite is excessively generated, the amount of retained austenite finally obtained is reduced, and workability is lowered. On the other hand, when the cooling stop temperature exceeds 550 ° C., the bainite transformation is delayed, so the amount of bainitic ferrite is reduced, C concentration in austenite is insufficient, and ferrite and pearlite are easily generated. The amount of retained austenite finally obtained is lowered, and the workability is lowered. Therefore, the cooling stop temperature is 150 to 550 ° C, preferably 200 to 500 ° C.
350〜550℃の保持温度で10〜1500s保持する
保持温度が350℃未満では、ベイナイト変態が遅延することに加えて下部ベイナイトが生成するためにオーステナイトへのC濃化量が低下して十分な残留オーステナイトが得られず、加工性が低下する。一方、550℃を超えるとベイナイト変態が遅延するためにベイニティックフェライトの生成量が減少してオーステナイトへのC濃化が不足し、また、フェライトやパーライトが生成しやすくなるために、最終的に得られる残留オーステナイト量が減少し、加工性が低下する。したがって、温度は350〜550℃、好ましくは370〜500℃とする。また、所望の保持温度とするために、前記冷却停止温度から、必要に応じて再加熱してもよい。
保持時間が10s未満では、ベイナイト変態が十分起こらず、ベイニティックフェライトの生成量が減少して残留オーステナイトが十分に得られなくなるため、加工性が低下する。一方、保持時間が1500sを超えるとオーステナイトの分解が顕著になり、加工性が低下する。したがって、保持時間を10〜1500sとする。
If the holding temperature of holding for 10 to 1500 s at a holding temperature of 350 to 550 ° C. is less than 350 ° C., the bainite transformation is delayed and the lower bainite is generated, so the amount of C enrichment to austenite is reduced and sufficient. Residual austenite cannot be obtained and workability is reduced. On the other hand, when the temperature exceeds 550 ° C., the bainite transformation is delayed, so the amount of bainitic ferrite produced is reduced, C concentration in austenite is insufficient, and ferrite and pearlite are easily produced. Thus, the amount of retained austenite obtained is reduced, and the workability is lowered. Therefore, the temperature is 350 to 550 ° C, preferably 370 to 500 ° C. Further, in order to obtain a desired holding temperature, reheating may be performed as necessary from the cooling stop temperature.
If the holding time is less than 10 s, bainite transformation does not occur sufficiently, the amount of bainitic ferrite produced decreases, and sufficient retained austenite cannot be obtained, so that workability is lowered. On the other hand, when the holding time exceeds 1500 s, the decomposition of austenite becomes remarkable and the workability deteriorates. Therefore, the holding time is 10 to 1500 s.
溶融亜鉛めっき処理
上記焼鈍を施した後、溶融亜鉛めっき、さらに必要に応じて合金化処理を施す。めっき処理は、上記により得られた鋼板を440℃以上500℃以下の亜鉛めっき浴中に浸漬し、その後、ガスワイピングなどによってめっき付着量を調整して行うことが好ましい。めっき付着量としては、20〜60g/m2の範囲であることが好ましい。さらに、亜鉛めっきを合金化する際は460℃以上580℃以下の温度域に1秒以上40秒以下保持して合金化することが好ましい。亜鉛めっき浴としては、Al量が0.08〜0.28質量%である亜鉛めっき浴を用いることが好ましい。
Hot-dip galvanizing treatment After the above-mentioned annealing, hot-dip galvanizing and further alloying treatment as necessary. The plating treatment is preferably performed by immersing the steel plate obtained as described above in a galvanizing bath at 440 ° C. or higher and 500 ° C. or lower, and then adjusting the plating adhesion amount by gas wiping or the like. The plating adhesion amount is preferably in the range of 20 to 60 g / m 2 . Furthermore, when alloying galvanizing, it is preferable to alloy by maintaining in a temperature range of 460 ° C. or more and 580 ° C. or less for 1 second or more and 40 seconds or less. As the galvanizing bath, it is preferable to use a galvanizing bath having an Al content of 0.08 to 0.28 mass%.
溶融亜鉛めっき処理、あるいはさらに、合金化処理を施した後の鋼板には、形状矯正や表面粗度の調整などを目的に調質圧延を行うことができる。また、樹脂や油脂コーティングなどの各種塗装処理を施すこともできる。 The steel sheet after being subjected to hot dip galvanizing treatment or further alloying treatment can be subjected to temper rolling for the purpose of shape correction, adjustment of surface roughness, and the like. Moreover, various coating processes, such as resin and oil-fat coating, can also be given.
その他の製造方法の条件は、特に限定しないが、以下の条件で行うのが好ましい。 The conditions for other production methods are not particularly limited, but the following conditions are preferable.
スラブは、マクロ偏析を防止するため、連続鋳造法で製造するのが好ましいが、造塊法、薄スラブ鋳造法により製造することもできる。スラブを熱間圧延するには、スラブをいったん室温まで冷却し、その後再加熱して熱間圧延を行ってもよいし、スラブを室温まで冷却せずに加熱炉に装入して熱間圧延を行うこともできる。あるいはわずかの保熱を行った後に直ちに熱間圧延する省エネルギープロセスも適用できる。スラブを加熱する場合は、炭化物を溶解させたり、圧延荷重の増大を防止するため、1100℃以上に加熱することが好ましい。また、スケールロスの増大を防止するため、スラブの加熱温度は1300℃以下とすることが好ましい。 The slab is preferably produced by a continuous casting method in order to prevent macro segregation, but can also be produced by an ingot-making method or a thin slab casting method. To hot-roll the slab, the slab may be cooled to room temperature and then re-heated for hot rolling, or the slab may be charged in a heating furnace without being cooled to room temperature. Can also be done. Alternatively, an energy saving process in which hot rolling is performed immediately after performing a slight heat retention can also be applied. When heating a slab, it is preferable to heat to 1100 degreeC or more in order to dissolve a carbide | carbonized_material and to prevent the increase in rolling load. In order to prevent an increase in scale loss, the heating temperature of the slab is preferably 1300 ° C. or lower.
スラブを熱間圧延する時は、スラブの加熱温度を低くしても圧延時のトラブルを防止する観点から、粗圧延後の粗バーを加熱することもできる。また、粗バー同士を接合し、仕上げ圧延を連続的に行う、いわゆる連続圧延プロセスを適用できる。また、圧延荷重の低減や形状・材質の均一化のために、仕上げ圧延の全パスあるいは一部のパスで摩擦係数が0.10〜0.25となる潤滑圧延を行うことが好ましい。 When hot rolling a slab, the rough bar after rough rolling can be heated from the viewpoint of preventing troubles during rolling even if the heating temperature of the slab is lowered. Moreover, what is called a continuous rolling process which joins rough bars and performs finish rolling continuously can be applied. Further, in order to reduce the rolling load and make the shape and material uniform, it is preferable to perform lubrication rolling in which the friction coefficient is 0.10 to 0.25 in all passes or a part of the finish rolling.
巻取り後の鋼板は、スケールを酸洗などにより除去した後、上記の条件で冷間圧延、焼鈍、溶融亜鉛めっきが施される。 The steel sheet after winding is subjected to cold rolling, annealing, and hot dip galvanizing under the above conditions after removing the scale by pickling.
表1に示す成分組成の鋼を真空溶解炉により溶製し、圧延して鋼スラブとした(表1中、Nは不可避的不純物である)。これらの鋼スラブを1200℃に加熱後粗圧延、仕上げ圧延して巻取り、板厚2.3mmの熱延板とした。次いで、1.4mmまで冷間圧延して冷延鋼板を製造し、焼鈍に供した。表2、3に示す焼鈍条件で焼鈍を行った後、溶融亜鉛めっき処理を行い、鋼板No.1〜28を作製した。溶融亜鉛めっき鋼板(GI)は、460℃のめっき浴中に浸漬し、付着量35〜45g/m2のめっきを形成させた後、平均冷却速度10℃/秒で室温まで冷却することで作製した。また、合金化溶融亜鉛めっき鋼板(GA)は、めっき形成後550℃で合金化処理を行い、平均冷却速度10℃/秒で室温まで冷却することで作製した。そして、得られた溶融亜鉛めっき鋼板について、圧延方向と直角方向にJIS5号引張試験片を採取し、歪速度10−3/秒で引張試験を行った。なお、各鋼板のミクロ組織については、前述の方法により、面積率を求めた。 Steel having the composition shown in Table 1 was melted in a vacuum melting furnace and rolled into a steel slab (in Table 1, N is an unavoidable impurity). These steel slabs were heated to 1200 ° C., followed by rough rolling, finish rolling and winding to obtain hot rolled sheets having a sheet thickness of 2.3 mm. Subsequently, it cold-rolled to 1.4 mm, manufactured the cold-rolled steel plate, and used for the annealing. After annealing under the annealing conditions shown in Tables 2 and 3, hot dip galvanizing treatment was performed, and steel plate No. 1-28 were produced. A hot dip galvanized steel sheet (GI) is immersed in a plating bath at 460 ° C., formed with a coating amount of 35 to 45 g / m 2 , and then cooled to room temperature at an average cooling rate of 10 ° C./second. did. Moreover, the alloyed hot-dip galvanized steel sheet (GA) was produced by performing alloying treatment at 550 ° C. after plating formation and cooling to room temperature at an average cooling rate of 10 ° C./second. And about the obtained hot-dip galvanized steel plate, a JIS No. 5 tensile test piece was extracted in a direction perpendicular to the rolling direction, and a tensile test was performed at a strain rate of 10 −3 / sec. In addition, about the microstructure of each steel plate, the area ratio was calculated | required by the above-mentioned method.
また、めっき性は外観を目視判定して不めっき・欠陥の有無について評価した。 In addition, the plating property was evaluated by visually judging the appearance and the presence or absence of non-plating / defects.
結果を表4、5に示す。 The results are shown in Tables 4 and 5.
本発明例ではTSが980MPa以上、TS×UELが15000MPa・%以上となり、加工性を有することが確認された。また、本発明例では、不めっき・欠陥は無く、めっき性が良好である。 In the example of the present invention, TS was 980 MPa or more, TS × UEL was 15000 MPa ·% or more, and it was confirmed that the material had processability. Moreover, in the example of this invention, there is no non-plating and a defect and plating property is favorable.
本発明によれば、TS:980MPa以上、TS×UEL:15000MPa・%以上である加工性に優れた高強度溶融亜鉛めっき鋼板を得ることができる。本発明の高強度溶融亜鉛めっき鋼板を自動車用部品用途に使用すると、自動車の軽量化に寄与し、自動車車体の高性能化に大きく寄与することができる。 According to the present invention, it is possible to obtain a high-strength hot-dip galvanized steel sheet having excellent workability that is TS: 980 MPa or more and TS × UEL: 15000 MPa ·% or more. When the high-strength hot-dip galvanized steel sheet of the present invention is used for automotive parts, it contributes to reducing the weight of an automobile and greatly contributes to improving the performance of an automobile body.
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