JP6056745B2 - High formability and high strength cold-rolled steel sheet excellent in chemical conversion treatment and production method thereof - Google Patents
High formability and high strength cold-rolled steel sheet excellent in chemical conversion treatment and production method thereof Download PDFInfo
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- 239000000126 substance Substances 0.000 title claims description 51
- 239000010960 cold rolled steel Substances 0.000 title claims description 48
- 238000006243 chemical reaction Methods 0.000 title claims description 47
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- 229910000831 Steel Inorganic materials 0.000 claims description 46
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Description
本発明は、自動車の骨格部材や補強部材等に供して好適な化成処理性に優れた高加工性高強度冷延鋼板およびその製造方法に関するものである。 The present invention relates to a high workability and high strength cold-rolled steel sheet excellent in chemical conversion processability and suitable for use in a skeleton member or a reinforcing member of an automobile, and a method for producing the same.
近年、地球環境保全（大気汚染の防止，温暖化の防止等）の観点から、様々な技術が検討されている。たとえば自動車では、燃費の改善が求められており、その一環として車体の軽量化が重要な課題となっている。一方で、衝突したときに乗員を保護するという観点から、車体の強度を向上させる必要がある。 In recent years, various technologies have been studied from the viewpoint of global environmental conservation (prevention of air pollution, prevention of global warming, etc.). For example, automobiles are required to improve fuel efficiency, and as part of this, weight reduction of the vehicle body is an important issue. On the other hand, it is necessary to improve the strength of the vehicle body from the viewpoint of protecting an occupant when a collision occurs.
そこで、自動車の燃費改善のための軽量化と安全性向上のための高強度化を両立させるために、引張強さ780MPa以上の高強度冷延鋼板が車体の骨格部材や補強部材等に使用されるようになってきている。このような高強度冷延鋼板を使用すれば、高強度であるが故に車体の変形や破壊を抑制して安全性を向上でき、かつ車体を構成する部材の厚みを減少させて軽量化を達成することができる。 Therefore, high-strength cold-rolled steel sheets with a tensile strength of 780 MPa or more are used for the frame members and reinforcement members of the vehicle body in order to achieve both weight reduction for improving fuel economy and high strength for improving safety. It is becoming. If such a high-strength cold-rolled steel sheet is used, it is possible to improve the safety by suppressing the deformation and destruction of the vehicle body because of its high strength, and reduce the thickness of the members that make up the vehicle body, thereby achieving weight reduction. can do.
一方で、自動車の車体の骨格部材や補強部材はプレス加工によって成形されるため、その素材である冷延鋼板には加工性に優れることが要求される。一般に、冷延鋼板の高強度化には、合金元素の添加（固溶強化）、結晶粒の微細化およびマルテンサイト相の生成（変態強化）等が有効であるが、通常、強度が増加するにつれて加工性は劣化する。 On the other hand, since a skeleton member and a reinforcing member of a car body of an automobile are formed by press working, the cold-rolled steel sheet that is the material is required to have excellent workability. In general, the addition of alloying elements (solid solution strengthening), refinement of crystal grains, and the formation of martensite phase (transformation strengthening) are effective in increasing the strength of cold-rolled steel sheets, but usually the strength increases. As the workability deteriorates.
上記した合金元素の中でもSiは、加工性の劣化を抑制しつつ強度を高める作用を有する元素である。このため、Si含有量を増加させることにより、冷延鋼板の高強度化と加工性改善の両立が期待できる。
しかしながら、Siは容易に酸化される元素であることから、Si含有量が多くなり過ぎると、熱間圧延や、通常の冷延鋼板の製造工程で実施される焼鈍においては、還元雰囲気とはいえ、Siは酸化されて冷延鋼板の表層近傍に濃化することになる。その結果、Siを主体とする酸化物が冷延鋼板を被覆することになるので、焼鈍の後で施される化成処理において、化成結晶の生成が阻害され、化成処理性が劣化するという問題があった。
Among the alloy elements described above, Si is an element having an effect of increasing strength while suppressing deterioration of workability. For this reason, by increasing the Si content, it is possible to expect both high strength and improved workability of the cold-rolled steel sheet.
However, since Si is an easily oxidizable element, if the Si content becomes too high, it may be a reducing atmosphere in hot rolling and annealing performed in the normal cold-rolled steel plate manufacturing process. , Si is oxidized and concentrated near the surface layer of the cold-rolled steel sheet. As a result, since the oxide mainly composed of Si covers the cold-rolled steel sheet, in the chemical conversion treatment performed after annealing, there is a problem that the formation of chemical crystals is hindered and the chemical conversion treatment performance deteriorates. there were.
この化成処理性は、強度と加工性を向上した冷延鋼板（以下、高加工性高強度冷延鋼板という）を自動車の車体の骨格部材や補強部材として使用するために要求される重要な特性である。そのため、Si含有量を増加させた高加工性高強度冷延鋼板の化成処理性を改善する技術が種々検討されている。 This chemical conversion property is an important characteristic required for using cold-rolled steel sheets with improved strength and workability (hereinafter referred to as high-workability high-strength cold-rolled steel sheets) as skeleton members and reinforcing members for automobile bodies. It is. Therefore, various techniques for improving the chemical conversion processability of high workability and high strength cold-rolled steel sheets with increased Si content have been studied.
たとえば特許文献１には、高加工性高強度冷延鋼板の表面に生成する酸化物のSi／Mn比を１以下に制御することにより、化成処理性に悪影響を及ぼすSi酸化物の比率を低下させ、これによって、化成処理性を改善する技術が開示されている。
また、特許文献２〜４には、高加工性高強度冷延鋼板の表面に生成する酸化物のSi／Mn比を制御することに加え、酸化物の性状（すなわち寸法、分散密度および被覆率）を制御することによって、化成処理性を改善する技術が開示されている。
これらの技術はいずれも、焼鈍条件を規定することによって、高加工性高強度冷延鋼板の表面に生成する酸化物の組成や性状を制御し、化成処理性を改善しようとするものである。
For example, Patent Document 1 discloses that by controlling the Si / Mn ratio of oxide generated on the surface of a high workability, high strength cold-rolled steel sheet to 1 or less, the ratio of Si oxide that adversely affects chemical conversion treatment is reduced. Thus, a technique for improving the chemical conversion processability is disclosed.
Further, in Patent Documents 2 to 4, in addition to controlling the Si / Mn ratio of the oxide formed on the surface of the high workability high strength cold-rolled steel sheet, the properties of the oxide (that is, dimensions, dispersion density, and coverage) ) Has been disclosed to improve the chemical conversion processability.
All of these techniques are intended to improve the chemical conversion property by controlling the composition and properties of oxides formed on the surface of a high workability and high strength cold-rolled steel sheet by defining the annealing conditions.
さらに、高加工性高強度冷延鋼板の表面に生成する酸化物を除去もしくは破壊する技術も検討されている。
たとえば、特許文献５には、焼鈍した後で高加工性高強度冷延鋼板の鋼板表面を2.0g／m2以上研削し、次いで塩酸で酸洗した後、さらに鋼板表面を0.1〜0.3g／m2研削することによって、化成処理性を改善する技術が開示されている。
特許文献６には、平均粒径30〜300μmの固体粒子を吹き付けることによって、化成処理性を改善する技術が開示されている。
特許文献７には、連続焼鈍後、塩酸や硝酸、弗酸からなる混酸水溶液で鋼板表面を１μm以上除去することによって、化成処理性を改善する技術が開示されている。
Furthermore, a technique for removing or destroying oxides generated on the surface of a high workability and high strength cold-rolled steel sheet has been studied.
For example, Patent Document 5 discloses that after annealing, the steel plate surface of a high workability high strength cold-rolled steel plate is ground at least 2.0 g / m 2 , then pickled with hydrochloric acid, and then the steel plate surface is further 0.1 to 0.3 g / m 2. A technique for improving chemical conversion processability by grinding m 2 is disclosed.
Patent Document 6 discloses a technique for improving chemical conversion treatment properties by spraying solid particles having an average particle size of 30 to 300 μm.
Patent Document 7 discloses a technique for improving chemical conversion treatment by removing the surface of a steel sheet by 1 μm or more with a mixed acid aqueous solution composed of hydrochloric acid, nitric acid, and hydrofluoric acid after continuous annealing.
しかしながら、特許文献１〜４の技術では、表面に生成する酸化物のSi／Mn比を適正な範囲に制御するために、必然的に高加工性高強度冷延鋼板のSi含有量とMn含有量が制約を受ける。そのため、高加工性高強度冷延鋼板の加工性や強度が十分に向上しない。さらに、酸化物の組成や性状は焼鈍条件（たとえば露点，水素濃度等）の影響を受け易いので、化成処理性も十分に向上しない。 However, in the techniques of Patent Documents 1 to 4, in order to control the Si / Mn ratio of the oxide generated on the surface to an appropriate range, the Si content and Mn content of the high workability high strength cold-rolled steel sheet are inevitably required. The amount is constrained. Therefore, the workability and strength of the high workability and high strength cold-rolled steel sheet are not sufficiently improved. Furthermore, since the composition and properties of the oxide are easily affected by annealing conditions (for example, dew point, hydrogen concentration, etc.), chemical conversion properties are not sufficiently improved.
また、特許文献５〜７の技術では、新たな設備が必要となるので、設備費が高くなるだけでなく、生産性と歩留りも低下するため、製造コストの上昇が避けられない。 Further, in the techniques of Patent Documents 5 to 7, since new equipment is required, not only the equipment cost becomes high, but also the productivity and the yield are lowered, so that an increase in manufacturing cost is inevitable.
本発明は、上記の現状に鑑み開発されたもので、高強度、高加工性は言うまでもなく、化成処理性にも優れた高加工性高強度冷延鋼板を、その製造方法と共に提供することを目的とする。
なお、本発明において、「化成処理性に優れた」とは、化成処理薬剤（日本パーカライジング株式会社製パルボンド（登録商標）PB-L3020）を用いて、浴温：43℃、処理時間：120秒の条件で鋼板の表面に化成処理を行った後、その鋼板表面を走査型電子顕微鏡にて500倍で５視野観察し、面積率95％以上の均一な化成結晶が５視野全てにおいて生成していることをいう。
また、「高加工性高強度」とは、強度−伸びバランスＴＳ×ＥＬが18000MPa・％以上となることをいう。
The present invention has been developed in view of the above-described present situation, and it is not limited to high strength and high workability, and provides a high workability high strength cold-rolled steel sheet that is excellent in chemical conversion processability, together with its manufacturing method. Objective.
In the present invention, the "chemical treatment is excellent in resistance" Kasei treatment agent with (Nippon Parkerizing Co., Ltd. Palbond (TM) PB-L3020), bath temperature: 43 ° C., treatment time: 120 After the chemical conversion treatment was performed on the surface of the steel sheet under the condition of seconds, the surface of the steel sheet was observed with a scanning electron microscope at 500 times in 5 fields, and a uniform chemical crystal with an area ratio of 95% or more was generated in all 5 fields. It means that
Further, “high workability and high strength” means that the strength-elongation balance TS × EL is 18000 MPa ·% or more.
さて、発明者らは、Ｃ、SiおよびMnの含有量を種々変化させるともに、種々の合金元素を含有させた溶鋼を溶製し、さらに連続鋳造を経て、熱間圧延、冷間圧延および焼鈍を行って得られた冷延鋼板について、その強度、加工性および化成処理性の綿密な調査を行った。
その結果、Si含有量を適正範囲に制御した上で、適正量のSbを含有させることにより、生産性や歩留りの低下を招くことなく、鋼板の高強度化と加工性の改善を両立でき、さらには化成処理性も向上できるとの知見を得た。
Now, the inventors changed the contents of C, Si and Mn in various ways, melted molten steel containing various alloy elements, and passed through continuous casting, followed by hot rolling, cold rolling and annealing. For the cold-rolled steel sheet obtained by carrying out the above, a thorough investigation was conducted on its strength, workability and chemical conversion treatment.
As a result, by controlling the Si content to an appropriate range, by including an appropriate amount of Sb, it is possible to achieve both high strength of the steel sheet and improvement of workability without causing a decrease in productivity and yield, Furthermore, the knowledge that chemical conversion processability could be improved was acquired.
ここに、適正量のSbを含有させることによって、化成処理性を向上できる理由については必ずしも明らかではないが、発明者らは次のように考えている。
すなわち、Siの酸化は、鋼板表面へH2OあるいはＯ2ガスが化学吸着し、この吸着ガス中のＯ（酸素）原子とSi原子が反応することによって、進行する。Sbは、各種ガスの化学吸着を抑制する性質を有しており、また鋼中では表面に偏析し易い元素である。従って、Sbのこのような特性によって、鋼板表面におけるＯ（酸素）原子とSi原子との反応が阻害され、結果として、Siの酸化が抑制されるためと考えている。
本発明は、上記の知見に立脚するものである。
Here, the reason why the chemical conversion property can be improved by containing an appropriate amount of Sb is not necessarily clear, but the inventors consider as follows.
That is, the oxidation of Si proceeds when H 2 O or O 2 gas is chemically adsorbed on the steel sheet surface and O (oxygen) atoms in the adsorbed gas react with Si atoms. Sb has the property of suppressing chemical adsorption of various gases, and is an element that easily segregates on the surface in steel. Therefore, it is considered that such a characteristic of Sb inhibits the reaction between O (oxygen) atoms and Si atoms on the surface of the steel sheet, and as a result, the oxidation of Si is suppressed.
The present invention is based on the above findings.
すなわち、本発明の要旨構成は次のとおりである。
１．質量％で、
Ｃ：0.05〜0.30％、
Si：0.8〜3.0％、
Mn：1.0〜3.0％、
Ｐ：0.10％以下、
Ｓ：0.01％以下、
Al：0.01〜0.1％、
Ｎ：0.008％以下および
Sb：0.02〜0.10％
を含有し、残部はFeおよび不可避的不純物からなることを特徴とする化成処理性に優れた高加工性高強度冷延鋼板。
ここで、化成処理性に優れたとは、化成処理薬剤（日本パーカライジング株式会社製パルボンド（登録商標）PB-L3020）を用いて、浴温：43℃、処理時間：120秒の条件で上記の高加工性高強度冷延鋼板の化成処理を行った後、その高加工性高強度冷延鋼板の表面を走査型電子顕微鏡にて500倍で５視野観察し、面積率95％以上の均一な化成結晶が５視野全てにおいて生成していることを意味する。
That is, the gist configuration of the present invention is as follows.
1. % By mass
C: 0.05 to 0.30%
Si: 0.8-3.0%
Mn: 1.0-3.0%
P: 0.10% or less,
S: 0.01% or less,
Al: 0.01-0.1%
N: 0.008% or less and
Sb: 0.02 to 0.10%
A high workability high-strength cold-rolled steel sheet excellent in chemical conversion treatment, characterized in that the balance is made of Fe and inevitable impurities.
Here, excellent chemical conversion treatment means that the chemical conversion treatment agent (Nippon Parkerizing Co., Ltd. Palbond (registered trademark) PB-L3020) is used, and the above temperature is high under the conditions of bath temperature: 43 ° C. and treatment time: 120 seconds. After chemical conversion treatment of workable high-strength cold-rolled steel sheet, the surface of the high-workability high-strength cold-rolled steel sheet is observed 500 times with a scanning electron microscope at 5 times, and uniform formation with an area ratio of 95% or more It means that crystals are formed in all 5 fields.
２．前記鋼板が、さらに、質量％で、Cr：0.01〜1.0％、Mo：0.01〜0.2％およびＢ：0.0001〜0.005％のうちから選ばれる１種または２種以上を含有することを特徴とする前記１に記載の化成処理性に優れた高加工性高強度冷延鋼板。 2. The steel sheet further contains one or more selected from Cr: 0.01 to 1.0%, Mo: 0.01 to 0.2% and B: 0.0001 to 0.005% by mass%. The high workability high-strength cold-rolled steel sheet excellent in chemical conversion processability according to 1.
３．前記鋼板が、さらに、質量％で、Ti：0.005〜0.05％、Nb：0.005〜0.05％およびＶ：0.005〜0.05％のうちから選ばれる１種または２種以上を含有することを特徴とする前記１または２に記載の化成処理性に優れた高加工性高強度冷延鋼板。 3. The steel sheet further contains one or more selected from Ti: 0.005 to 0.05%, Nb: 0.005 to 0.05% and V: 0.005 to 0.05% by mass%. A high workability high-strength cold-rolled steel sheet having excellent chemical conversion properties as described in 1 or 2.
４．前記１〜３のいずれかに記載の成分組成からなるスラブを、スラブ加熱後、熱間圧延し、ついで酸洗後、冷間圧延を施したのち、焼鈍し、さらに冷却後、焼戻しを行う一連の工程からなる前記１〜３のいずれかに記載の化成処理性に優れた高加工性高強度冷延鋼板の製造方法において、
上記熱間圧延における仕上げ圧延温度を800〜1000℃、上記冷間圧延における圧下率を20％以上とし、かつ上記焼鈍を、露点：−35℃以下の雰囲気中にて、750〜900℃の温度域で60秒以上保持する条件で行ったのち、30℃／秒以上の平均冷却速度で300℃以下まで冷却した後、焼戻しすることを特徴とする化成処理性に優れた高加工性高強度冷延鋼板の製造方法。
4). A series of slabs comprising the component composition according to any one of the above 1 to 3, after slab heating, hot rolling, then pickling, cold rolling, annealing, further cooling, and tempering In the method for producing a high workability high-strength cold-rolled steel sheet excellent in chemical conversion processability according to any one of 1 to 3 comprising the steps of:
The finish rolling temperature in the hot rolling is 800 to 1000 ° C., the rolling reduction in the cold rolling is 20% or more, and the annealing is performed at a temperature of 750 to 900 ° C. in an atmosphere having a dew point of −35 ° C. or less. High processability and high strength cooling with excellent chemical conversion processability, characterized in that it is carried out under conditions of holding in the zone for 60 seconds or more, and then cooled to 300 ° C or less at an average cooling rate of 30 ° C / second or more and then tempered. A method for producing rolled steel sheets.
本発明によれば、生産性や歩留りを低下させることなく、優れた化成処理性を有する高加工性高強度冷延鋼板を得ることができる。
そして、本発明により得られる高加工性高強度冷延鋼板は、自動車の車体の骨格部材や補強部材として使用するのに好適であり、自動車の軽量化と衝突安全性向上とを両立して、自動車車体の高性能化に大きく貢献する。
ADVANTAGE OF THE INVENTION According to this invention, the high workability high intensity | strength cold-rolled steel plate which has the outstanding chemical conversion property can be obtained, without reducing productivity and a yield.
And the high workability high-strength cold-rolled steel sheet obtained by the present invention is suitable for use as a skeleton member or a reinforcing member of a car body of an automobile, and achieves both reduction in weight of the automobile and improvement in collision safety. Greatly contributes to improving the performance of automobile bodies.
以下、本発明を具体的に説明する。
まず、成分組成を前記の範囲に限定した理由について説明する。なお、各元素の含有量の単位は、特に断りがない限り質量％を意味するものとする。
Ｃ：0.05〜0.30％
Ｃは、鋼板の強度を高める作用を有する重要な元素である。所望する引張強さ（780MPa以上）を得るためには、Ｃ含有量を0.05％以上とする必要がある。好ましくは0.10％超である。一方、Ｃ含有量が0.30％を超えると、溶接性が著しく劣化する。したがって、Ｃ含有量は0.30％以下とする。なお、特に良好な溶接性が求められる場合、Ｃ含有量は0.20％以下とすることが好ましい。より好ましくは0.15％以下である。
Hereinafter, the present invention will be specifically described.
First, the reason why the component composition is limited to the above range will be described. In addition, unless otherwise indicated, the unit of content of each element shall mean the mass%.
C: 0.05-0.30%
C is an important element having an effect of increasing the strength of the steel sheet. In order to obtain a desired tensile strength (780 MPa or more), the C content needs to be 0.05% or more. Preferably it is over 0.10%. On the other hand, when the C content exceeds 0.30%, the weldability is significantly deteriorated. Therefore, the C content is 0.30% or less. When particularly good weldability is required, the C content is preferably 0.20% or less. More preferably, it is 0.15% or less.
Si：0.8〜3.0％
Siは、固溶強化によって強度の向上に寄与する重要な元素であり、加工性の劣化を抑制しつつ、強度を高める作用を有する。所望する引張強さや加工性を得るためには、Si含有量を0.8％以上とする必要がある。一方、Si含有量が3.0％を超えると、強度を向上する効果が飽和するだけでなく、加工性も劣化する。したがって、Si含有量は0.8〜3.0％の範囲とする。好ましくは1.0〜2.0％の範囲である。
Si: 0.8-3.0%
Si is an important element that contributes to improving the strength by solid solution strengthening, and has an effect of increasing the strength while suppressing deterioration of workability. In order to obtain desired tensile strength and workability, the Si content needs to be 0.8% or more. On the other hand, when the Si content exceeds 3.0%, not only the effect of improving the strength is saturated, but also the workability deteriorates. Therefore, the Si content is in the range of 0.8 to 3.0%. Preferably it is 1.0 to 2.0% of range.
Mn：1.0〜3.0％
Mnは、固溶強化によって強度の向上に寄与するとともに、オーステナイト相の焼入れ性を高める元素であり、強度の安定化に有効に寄与する。所望する引張強度を安定して得るためには、Mn含有量を1.0％以上とする必要がある。一方、Mn含有量が3.0％を超えると、加工性が劣化する。したがって、Mn含有量は1.0〜3.0％の範囲とする。好ましくは1.5〜2.5％の範囲である。
Mn: 1.0-3.0%
Mn is an element that contributes to improvement of strength by solid solution strengthening and enhances the hardenability of the austenite phase, and contributes effectively to stabilization of strength. In order to stably obtain the desired tensile strength, the Mn content needs to be 1.0% or more. On the other hand, if the Mn content exceeds 3.0%, the workability deteriorates. Therefore, the Mn content is in the range of 1.0 to 3.0%. Preferably it is 1.5 to 2.5% of range.
Ｐ：0.10％以下
Ｐは、強度を向上する作用を有するので、要求される強度に応じて添加する。しかしながら、Ｐ含有量が0.10％を超えると、溶接性が劣化する。したがって、Ｐ含有量は0.10％以下とする。特に良好な溶接性が求められる場合、Ｐ含有量は0.05％以下とすることが好ましい。
P: 0.10% or less P has an effect of improving the strength, so is added according to the required strength. However, when the P content exceeds 0.10%, the weldability deteriorates. Therefore, the P content is 0.10% or less. When particularly good weldability is required, the P content is preferably 0.05% or less.
Ｓ：0.01％以下
Ｓは、鋼板中に介在物として存在し、加工性、特に伸びフランジ性を劣化させる。このため、Ｓは可能な限り低減する必要がある。ここに、Ｓ含有量が0.01％を超えると、伸びフランジ性に対する悪影響が顕著になる。したがって、Ｓ含有量は0.01％以下とする。特に良好な伸びフランジ性が求められる場合、Ｓ含有量は0.005％以下とすることが好ましい。
S: 0.01% or less S is present as an inclusion in the steel sheet, and deteriorates workability, particularly stretch flangeability. For this reason, S needs to be reduced as much as possible. Here, when S content exceeds 0.01%, the bad influence with respect to stretch flangeability will become remarkable. Therefore, the S content is 0.01% or less. When particularly good stretch flangeability is required, the S content is preferably 0.005% or less.
Al：0.01〜0.1％
Alは、脱酸元素として溶製段階で添加され、溶鋼の清浄度を高める元素である。また、鋼板の組織を微細化する作用も有する。ここに、Al含有量が0.01％未満では、これらの効果が得られない。一方、Al含有量が0.1％を超えると、鋼板の表面性状が劣化する。したがって、Al含有量は0.01〜0.1％の範囲とする。好ましくは0.015％以上である。
Al: 0.01 to 0.1%
Al is an element that is added as a deoxidizing element at the melting stage to increase the cleanliness of molten steel. Moreover, it has the effect | action which refines | miniaturizes the structure of a steel plate. If the Al content is less than 0.01%, these effects cannot be obtained. On the other hand, when the Al content exceeds 0.1%, the surface properties of the steel sheet deteriorate. Therefore, the Al content is in the range of 0.01 to 0.1%. Preferably it is 0.015% or more.
Ｎ：0.008％以下
Ｎは、鋼板に混入する不純物である。Ｎ含有量が0.008％を超えると、強度のバラツキが発生する。したがって、Ｎ含有量は0.008％以下とする。好ましくは0.005％以下である。
N: 0.008% or less N is an impurity mixed in the steel sheet. If the N content exceeds 0.008%, variations in strength occur. Therefore, the N content is 0.008% or less. Preferably it is 0.005% or less.
Sb：0.02〜0.10％
Sbは、本発明において最も重要な添加元素である。ここに、Sbは、鋼板表面に偏析し易く、また外部からのH2OまたはＯ2ガスの化学吸着を抑制するので、鋼板表面における吸着ガス中のＯ（酸素）原子とSi原子との反応を阻害し、Siの酸化を抑制することができる。
Sb含有量が0.02％未満の場合、上記の効果が十分でなく、Siを主体とした酸化物が鋼板表面に形成されるため、化成処理性が低下する。一方、Sb含有量が0.10％を超えると、加工性が劣化する。したがって、Sb含有量は0.02〜0.10％の範囲とする。好ましくは0.02〜0.05％の範囲である。
Sb: 0.02 to 0.10%
Sb is the most important additive element in the present invention. Here, Sb is easily segregated on the steel sheet surface and suppresses chemical adsorption of H 2 O or O 2 gas from the outside, so that the reaction between O (oxygen) atoms and Si atoms in the adsorbed gas on the steel sheet surface Can be inhibited, and oxidation of Si can be suppressed.
When the Sb content is less than 0.02%, the above effect is not sufficient, and an oxide mainly composed of Si is formed on the surface of the steel sheet, so that the chemical conversion treatment performance is lowered. On the other hand, when the Sb content exceeds 0.10%, workability deteriorates. Therefore, the Sb content is in the range of 0.02 to 0.10%. Preferably it is 0.02 to 0.05% of range.
以上、基本成分について説明したが、本発明では、その他にも、以下に述べる成分を必要に応じて適宜含有させることができる。
Cr：0.01〜1.0％、Mo：0.01〜0.2％およびＢ：0.0001〜0.005％のうちから選ばれる１種または２種以上
Cr、MoおよびＢは、オーステナイト相の焼入れ性を高める作用を有する元素であり、必要に応じて添加することができる。このような効果を得るためには、Crは0.01％以上、Moは0.01％以上、Ｂは0.0001％以上をそれぞれ添加することが好ましい。一方、Crは1.0％、Moは0.2％、Ｂは0.005％をそれぞれ超えて添加されると、鋼板の加工性が劣化する。しかも、Cr、MoおよびＢといった高価な元素を多量に使用することによって、鋼板の製造コストも上昇する。したがってCr、MoおよびＢを添加する場合、それぞれCr：0.01〜1.0％、Mo：0.01〜0.2％、Ｂ：0.0001〜0.005％の範囲とすることが好ましい。
The basic components have been described above, but in the present invention, other components described below can be appropriately contained as necessary.
One or more selected from Cr: 0.01 to 1.0%, Mo: 0.01 to 0.2% and B: 0.0001 to 0.005%
Cr, Mo, and B are elements having an action of enhancing the hardenability of the austenite phase, and can be added as necessary. In order to obtain such an effect, it is preferable to add Cr 0.01% or more, Mo 0.01% or more, and B 0.0001% or more. On the other hand, if Cr is added in an amount exceeding 1.0%, Mo is 0.2%, and B exceeds 0.005%, the workability of the steel sheet deteriorates. Moreover, the use of a large amount of expensive elements such as Cr, Mo and B increases the manufacturing cost of the steel sheet. Therefore, when adding Cr, Mo, and B, it is preferable to set it as the range of Cr: 0.01-1.0%, Mo: 0.01-0.2%, B: 0.0001-0.005%, respectively.
Ti：0.005〜0.05％、Nb：0.005〜0.05％およびＶ：0.005〜0.05％のうちから選ばれる１種または２種以上
Ti、NbおよびＶは、鋼板中で炭化物を形成し、析出強化によって鋼板の強度を高める作用を有する。このような効果を得るためには、Ti、NbおよびＶはそれぞれ0.005％以上を添加することが好ましい。一方、Ti、NbおよびＶがそれぞれ0.05％を超えて添加されると、鋼板の加工性が劣化する。しかも、Ti、NbおよびＶといった高価な元素を多量に使用することによって、鋼板の製造コストも上昇する。したがってTi、NbおよびＶを添加する場合、それぞれTi：0.005〜0.05％、Nb：0.005〜0.05％、Ｖ：0.005〜0.05％の範囲とすることが好ましい。
One or more selected from Ti: 0.005-0.05%, Nb: 0.005-0.05% and V: 0.005-0.05%
Ti, Nb, and V have the effect | action which forms the carbide | carbonized_material in a steel plate and raises the intensity | strength of a steel plate by precipitation strengthening. In order to obtain such effects, it is preferable to add 0.005% or more of each of Ti, Nb and V. On the other hand, when Ti, Nb, and V are added in excess of 0.05%, the workability of the steel sheet deteriorates. In addition, by using a large amount of expensive elements such as Ti, Nb and V, the manufacturing cost of the steel sheet also increases. Therefore, when adding Ti, Nb, and V, it is preferable to set it as the range of Ti: 0.005-0.05%, Nb: 0.005-0.05%, and V: 0.005-0.05%, respectively.
本発明の鋼板において、上記以外の成分は、Feおよび不可避的不純物である。なお、不可避的不純物としては、Zn，Co，Sn等が挙げられるが、これらの元素の含有量は、Zn：0.01％以下、Co：0.1％以下、Sn：0.1％以下とすることが好ましい。 In the steel sheet of the present invention, components other than those described above are Fe and inevitable impurities. Inevitable impurities include Zn, Co, Sn, etc. The content of these elements is preferably Zn: 0.01% or less, Co: 0.1% or less, and Sn: 0.1% or less.
次に、本発明の製造方法について説明する。
まず、上記の成分組成を有する溶鋼を、連続鋳造法、造塊・分塊圧延法または薄スラブ鋳造法により、スラブとする。なお、スラブを製造するにあたっては、マクロ偏析を防止するため、連続鋳造法を採用することが好ましい。
Next, the manufacturing method of this invention is demonstrated.
First, the molten steel having the above component composition is made into a slab by a continuous casting method, an ingot-making / slabbing method, or a thin slab casting method. In manufacturing the slab, it is preferable to employ a continuous casting method in order to prevent macro segregation.
スラブ加熱温度：1000〜1300℃
ついで、得られたスラブを一旦室温まで冷却して加熱炉に装入する、あるいは冷却せずに温片のまま加熱炉に装入する等の方法で、スラブを加熱する。スラブ加熱温度が1000℃未満では、スラブの変形抵抗が大きいので、熱間圧延に支障を来たす場合がある。一方、スラブ加熱温度が1300℃を超えると、スケールロスが増加する。したがって、スラブ加熱温度は1000〜1300℃の範囲とすることが好ましい。
Slab heating temperature: 1000-1300 ℃
Next, the slab is heated by such a method that the obtained slab is once cooled to room temperature and charged in a heating furnace, or is charged in a heating furnace without being cooled. When the slab heating temperature is less than 1000 ° C., the deformation resistance of the slab is large, which may hinder hot rolling. On the other hand, when the slab heating temperature exceeds 1300 ° C., the scale loss increases. Therefore, the slab heating temperature is preferably in the range of 1000 to 1300 ° C.
また、スラブを再加熱せず、鋳造後、そのまま熱間圧延を行う直送圧延も適用できる。直送圧延を行う場合も、上記と同じ理由から、スラブの温度は1000〜1300℃の範囲とすることが好ましい。 Further, direct feed rolling in which hot rolling is performed as it is after casting without reheating the slab can be applied. Even when direct rolling is performed, the temperature of the slab is preferably in the range of 1000 to 1300 ° C. for the same reason as described above.
仕上げ圧延温度：800〜1000℃
ついで、上記のように加熱されたスラブに、熱間圧延を施す。この熱間圧延では、必要に応じて粗圧延を行った後、仕上げ圧延を行う。ここに、仕上げ圧延温度が800℃未満では、熱延鋼板の組織が不均一になり、後工程の冷間圧延時やプレス加工時における加工性が劣化する。一方、仕上げ圧延温度が1000℃を超えると、スケールの巻込みに起因する表面疵が発生し易くなる。したがって、仕上げ圧延温度は800〜1000℃の範囲とする。
Finishing rolling temperature: 800 ~ 1000 ℃
Next, hot slab is applied to the slab heated as described above. In this hot rolling, finish rolling is performed after rough rolling as necessary. Here, when the finish rolling temperature is less than 800 ° C., the structure of the hot-rolled steel sheet becomes non-uniform, and workability at the time of cold rolling or press working in the subsequent process deteriorates. On the other hand, when the finish rolling temperature exceeds 1000 ° C., surface flaws due to the winding of the scale are likely to occur. Accordingly, the finish rolling temperature is in the range of 800 to 1000 ° C.
巻取り温度：650℃以下
上記のように熱間圧延を施した熱延鋼板をコイルに巻取る。この巻取り温度が650℃を超えると、巻取りの後でスケールが発生し、酸洗の負荷が増大する。したがって、巻取り温度は650℃以下とすることが好ましい。
Winding temperature: 650 ° C. or less The hot-rolled steel sheet hot-rolled as described above is wound on a coil. When the winding temperature exceeds 650 ° C., scale is generated after winding, and the pickling load increases. Therefore, the winding temperature is preferably 650 ° C. or lower.
冷間圧延の圧下率：20％以上
ついで、得られた熱延鋼板に、酸洗を施してスケールを除去した後、冷間圧延を施す。冷間圧延では、得られる冷延鋼板の表面の平坦度や組織の均一性を確保する観点から、圧下率を20％以上とする必要がある。一方、操業性の観点から、圧下率は80％以下とすることが好ましい。
なお、熱延鋼板のスケールが極めて少ない場合は、酸洗を省略して、冷間圧延を行っても良い。
Cold rolling reduction ratio: 20% or more Next, the obtained hot-rolled steel sheet is pickled to remove scales, and then cold-rolled. In cold rolling, the rolling reduction needs to be 20% or more from the viewpoint of ensuring the flatness of the surface of the obtained cold-rolled steel sheet and the uniformity of the structure. On the other hand, from the viewpoint of operability, the rolling reduction is preferably 80% or less.
When the scale of the hot-rolled steel sheet is very small, pickling may be omitted and cold rolling may be performed.
かくして得られた冷延鋼板に、以下に示す条件で焼鈍を施す。なお、焼鈍は、生産性向上の観点から、連続焼鈍設備を用いることが好ましい。
保持温度：750〜900℃
焼鈍時の保持温度が750℃未満では、十分に再結晶が起こらず、加工性が低下するおそれがある。一方、900℃を超えると、組織が粗大化し、強度と加工性のバランスが崩れる。したがって、焼鈍時の保持温度は750〜900℃の範囲とする。
The cold-rolled steel sheet thus obtained is annealed under the following conditions. In addition, it is preferable to use continuous annealing equipment from a viewpoint of productivity improvement.
Holding temperature: 750-900 ° C
If the holding temperature during annealing is less than 750 ° C., recrystallization does not occur sufficiently, and workability may be reduced. On the other hand, when it exceeds 900 ° C., the structure becomes coarse and the balance between strength and workability is lost. Therefore, the holding temperature at the time of annealing shall be the range of 750-900 degreeC.
保持時間：60秒以上
焼鈍時の保持時間が60秒未満では、再結晶が不均一になる。したがって、焼鈍の保持時間は60秒以上とする。好ましくは120秒以上である。なお、保持時間の上限は600秒程度で十分である。
Holding time: 60 seconds or more If the holding time during annealing is less than 60 seconds, recrystallization becomes non-uniform. Therefore, the annealing holding time is 60 seconds or more. Preferably it is 120 seconds or more. The upper limit of the holding time is about 600 seconds.
露点：−35℃以下
焼鈍時の雰囲気露点が−35℃を超えると、Sbを添加しても、冷延鋼板の表面にSi酸化物が生成し、化成処理および電着塗装を施した高加工性高強度冷延鋼板の耐食性が劣化する場合がある。したがって、焼鈍時の露点は−35℃以下とする必要がある。好ましくは−40℃以下である。
Dew point: -35 ° C or lower When the atmospheric dew point during annealing exceeds -35 ° C, even if Sb is added, Si oxide is generated on the surface of the cold-rolled steel sheet, and high processing is performed by chemical conversion treatment and electrodeposition coating. The corrosion resistance of the high strength cold-rolled steel sheet may deteriorate. Therefore, the dew point during annealing needs to be −35 ° C. or lower. Preferably it is -40 degrees C or less.
冷却条件：30℃／秒以上の平均冷却速度で300℃以下まで冷却
上記の焼鈍が終了した後、得られた冷延鋼板を、30℃／秒以上の平均冷却速度で300℃以下まで冷却する。平均冷却速度が30℃／秒未満では、十分な強度を得るために、合金元素を多量に添加する必要があり、高加工性高強度冷延鋼板の製造コストの上昇を招く。また、冷却停止温度が300℃を超えると、十分な強度が得られなくなる。
Cooling condition: Cool to 300 ° C. or less at an average cooling rate of 30 ° C./second or more After the above annealing is completed, cool the obtained cold-rolled steel sheet to 300 ° C. or less at an average cooling rate of 30 ° C./second or more. . When the average cooling rate is less than 30 ° C./second, it is necessary to add a large amount of alloying elements in order to obtain sufficient strength, which leads to an increase in manufacturing cost of the high workability and high strength cold-rolled steel sheet. Further, when the cooling stop temperature exceeds 300 ° C., sufficient strength cannot be obtained.
焼戻し条件：100〜450℃の温度域に１〜30分保持
さらに、鋼板の加工性を向上させるため、上記の冷却後、再加熱し、焼戻しを行う。焼戻し条件としては、100〜450℃の温度域にて１〜30分保持する焼戻しを行うことが好ましい。
ここに、保持温度が100℃未満では、延性が不十分となり、鋼板の加工性を向上することができない。一方、保持温度が450℃を超えると、強度が不十分となる。また、保持時間が１分未満であると、延性が不十分となり、鋼板の加工性を向上することができない。一方、保持時間が30分を超えると強度が不十分となる。
Tempering conditions: Hold for 1 to 30 minutes in a temperature range of 100 to 450 ° C. Further, in order to improve the workability of the steel sheet, it is reheated and tempered after the above cooling. As tempering conditions, it is preferable to carry out tempering for 1 to 30 minutes in a temperature range of 100 to 450 ° C.
Here, if the holding temperature is less than 100 ° C., the ductility becomes insufficient and the workability of the steel sheet cannot be improved. On the other hand, when the holding temperature exceeds 450 ° C., the strength becomes insufficient. Moreover, when holding time is less than 1 minute, ductility becomes inadequate and the workability of a steel plate cannot be improved. On the other hand, if the holding time exceeds 30 minutes, the strength becomes insufficient.
表１に示す成分のスラブを連続鋳造によって製造し、1250℃に再加熱した後、仕上げ圧延温度：850℃の条件で圧延して厚さ3.0mmの熱延鋼板とし、600℃でコイルに巻き取った。
なお、表１中の鋼種Ａ，Ｂ，Ｄ〜Ｈ、Ｋ〜Ｒは、本発明で規定する成分組成範囲を満足する適合鋼であり、鋼種ＣはSi含有量が、鋼種I、JはSb含有量がそれぞれ、本発明で規定する成分組成範囲を外れる比較鋼である。
A slab having the components shown in Table 1 is manufactured by continuous casting, reheated to 1250 ° C, and then rolled at a finish rolling temperature of 850 ° C to form a hot-rolled steel sheet having a thickness of 3.0 mm. I took it.
Steel types A, B, D to H, and K to R in Table 1 are compatible steels that satisfy the component composition range defined in the present invention, steel type C has a Si content, steel types I and J have Sb. Each content is a comparative steel that deviates from the component composition range defined in the present invention.
ついで、得られた熱延鋼板を酸洗した後、冷間圧延して厚さ1.6mm（圧下率：約46.7％）の冷延鋼板とした。その後、冷延鋼板に、表２に示す条件で焼鈍、ついで冷却を行ったのち、保持温度：150〜400℃、保持時間：１〜20分となる条件で焼戻しを行い、高加工性高強度冷延鋼板を得た。 Next, the obtained hot-rolled steel sheet was pickled and cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1.6 mm (rolling ratio: about 46.7%). Thereafter, the cold-rolled steel sheet was annealed under the conditions shown in Table 2, then cooled, and then tempered under the conditions of holding temperature: 150 to 400 ° C. and holding time: 1 to 20 minutes, and high workability and high strength. A cold-rolled steel sheet was obtained.
そして、得られた高加工性高強度冷延鋼板の機械的性質および化成処理性を調査した。調査結果を表２に示す。なお、調査方法は以下の通りである。
（１）機械的性質
高加工性高強度冷延鋼板の圧延方向に直交する方向を長軸としてＪＩＳ規格５号試験片を採取し、JIS Z 2241（2011年）の規定に準拠して引張試験を行った。得られた引張強さと伸びを、表２にそれぞれＴＳおよびＥＬとして示す。また、加工性を示す指標として、ＴＳ×ＥＬの値を表２に示す。なお、ＴＳ×ＥＬの値が18000MPa・％以上であれば、加工性は良好と言える。
And the mechanical property and chemical conversion property of the obtained high workability high strength cold-rolled steel sheet were investigated. The survey results are shown in Table 2. The survey method is as follows.
(1) Mechanical properties High workability High strength cold-rolled steel sheet JIS standard No. 5 specimen was taken with the direction perpendicular to the rolling direction as the major axis, and tensile test was performed in accordance with the provisions of JIS Z 2241 (2011) Went. The obtained tensile strength and elongation are shown in Table 2 as TS and EL, respectively. Further, as an index indicating workability, Table 2 shows TS × EL values. If the value of TS × EL is 18000 MPa ·% or more, it can be said that the workability is good.
（２）化成処理性
市販の化成処理薬剤（日本パーカライジング株式会社製パルボンド（登録商標）PB-L3020）を用いて、浴温：43℃、処理時間：120秒の条件で高加工性高強度冷延鋼板の化成処理を行った後、その高加工性高強度冷延鋼板の表面を走査型電子顕微鏡にて500倍で５視野観察し、面積率95％以上の均一な化成結晶が５視野全てにおいて生成しているものを良好（○）とし、面積率５％超えの隙間が１視野でも認められるものを不良（×）として評価した。
(2) Chemical conversion treatment property Using a commercially available chemical conversion treatment agent (Palbond (registered trademark) PB-L3020 manufactured by Nihon Parkerizing Co., Ltd. ) , bath temperature: 43 ° C, treatment time: 120 seconds, high workability, high strength cooling After the chemical conversion treatment of the rolled steel sheet, the surface of the high workability, high strength cold-rolled steel sheet is observed at 500 times with a scanning electron microscope at 5 times, and all the 5 fields of uniform chemical crystals with an area ratio of 95% or more are observed. What was produced | generated in (circle) was made into favorable ((circle)), and the thing in which the clearance gap exceeding 5% of area ratio was recognized also by 1 visual field was evaluated as bad (x).
表２から明らかなように、発明例はいずれも、引張強さ（ＴＳ）が780MPa以上であり、またＴＳ×ＥＬの値も18000MPa・％以上と、強度と加工性に優れていることがわかる。また、化成処理性も良好であった。 As is clear from Table 2, all of the inventive examples have excellent strength and workability with a tensile strength (TS) of 780 MPa or more and a TS × EL value of 18000 MPa ·% or more. . Moreover, chemical conversion property was also favorable.
一方、Si含有量が下限に満たない比較例No.３は、ＴＳ×ＥＬの値が18000MPa・％未満となり、加工性に劣っていた。
また、Sbが添加されていない比較例No.17は、Si主体の酸化物が鋼板表面に形成され、化成処理性に劣っていた。
さらに、Sb含有量が上限を超える比較例No.18は、ＴＳ×ＥＬの値が18000MPa・％未満となり、加工性に劣っていた。
On the other hand, Comparative Example No. 3 in which the Si content was less than the lower limit had a TS × EL value of less than 18000 MPa ·% and was inferior in workability.
In Comparative Example No. 17 to which Sb was not added, an oxide mainly composed of Si was formed on the surface of the steel sheet and was inferior in chemical conversion treatment.
Furthermore, Comparative Example No. 18 in which the Sb content exceeded the upper limit had a TS × EL value of less than 18000 MPa ·%, and was inferior in workability.
加えて、焼鈍時における露点が適正範囲外となる比較例No.8は、化成処理性に劣っていた。
また、焼鈍時の保持温度または保持時間が適正範囲外となる比較例No.10及び11は、ＴＳ×ＥＬの値が18000MPa・％未満となり、加工性に劣っていた。
さらに、平均冷却速度または冷却停止温度が適正範囲外となる比較例No.13及び14は、引張強さ（ＴＳ）が780MPaに満たず、またＴＳ×ＥＬの値が18000MPa・％未満となり、加工性に劣っていた。
In addition, Comparative Example No. 8 in which the dew point at the time of annealing was outside the proper range was inferior in chemical conversion treatment.
In Comparative Examples No. 10 and 11 in which the holding temperature or holding time during annealing was outside the appropriate range, the TS × EL value was less than 18000 MPa ·%, and the workability was poor.
Furthermore, in Comparative Examples No. 13 and 14 where the average cooling rate or cooling stop temperature is outside the appropriate range, the tensile strength (TS) is less than 780 MPa, and the value of TS × EL is less than 18000 MPa ·%. It was inferior.
Claims (4)
Ｃ：0.05〜0.30％、
Si：0.8〜3.0％、
Mn：1.0〜3.0％、
Ｐ：0.10％以下、
Ｓ：0.01％以下、
Al：0.01〜0.1％、
Ｎ：0.008％以下および
Sb：0.02〜0.10％
を含有し、残部はFeおよび不可避的不純物からなることを特徴とする化成処理性に優れた高加工性高強度冷延鋼板。
ここで、化成処理性に優れたとは、化成処理薬剤（日本パーカライジング株式会社製パルボンド（登録商標）PB-L3020）を用いて、浴温：43℃、処理時間：120秒の条件で上記の高加工性高強度冷延鋼板の化成処理を行った後、その高加工性高強度冷延鋼板の表面を走査型電子顕微鏡にて500倍で５視野観察し、面積率95％以上の均一な化成結晶が５視野全てにおいて生成していることを意味する。 % By mass
C: 0.05 to 0.30%
Si: 0.8-3.0%
Mn: 1.0-3.0%
P: 0.10% or less,
S: 0.01% or less,
Al: 0.01-0.1%
N: 0.008% or less and
Sb: 0.02 to 0.10%
A high workability high-strength cold-rolled steel sheet excellent in chemical conversion treatment, characterized in that the balance is made of Fe and inevitable impurities.
Here, excellent chemical conversion treatment means that the chemical conversion treatment agent (Nippon Parkerizing Co., Ltd. Palbond (registered trademark) PB-L3020) is used, and the above temperature is high under the conditions of bath temperature: 43 ° C. and treatment time: 120 seconds. After chemical conversion treatment of workable high-strength cold-rolled steel sheet, the surface of the high-workability high-strength cold-rolled steel sheet is observed 500 times with a scanning electron microscope at 5 times, and uniform formation with an area ratio of 95% or more It means that crystals are formed in all 5 fields.
に記載の化成処理性に優れた高加工性高強度冷延鋼板。 The steel sheet further includes one or more selected from Cr: 0.01 to 1.0%, Mo: 0.01 to 0.2%, and B: 0.0001 to 0.005% in mass%. Item 1
High workability and high strength cold-rolled steel sheet with excellent chemical conversion properties as described in 1.
上記熱間圧延における仕上げ圧延温度を800〜1000℃、上記冷間圧延における圧下率を20％以上とし、かつ上記焼鈍を、露点：−35℃以下の雰囲気中にて、750〜900℃の温度域で60秒以上保持する条件で行ったのち、30℃／秒以上の平均冷却速度で300℃以下まで冷却した後、焼戻しすることを特徴とする化成処理性に優れた高加工性高強度冷延鋼板の製造方法。 A slab comprising the component composition according to any one of claims 1 to 3 is slab heated, hot-rolled, then pickled, cold-rolled, annealed, further cooled, and tempered. In the manufacturing method of the high workability high-strength cold-rolled steel sheet excellent in chemical conversion processability in any one of Claims 1-3 which consists of a series of processes,
The finish rolling temperature in the hot rolling is 800 to 1000 ° C., the rolling reduction in the cold rolling is 20% or more, and the annealing is performed at a temperature of 750 to 900 ° C. in an atmosphere having a dew point of −35 ° C. or less. High processability and high strength cooling with excellent chemical conversion processability, characterized in that it is carried out under conditions of holding in the zone for 60 seconds or more, and then cooled to 300 ° C or less at an average cooling rate of 30 ° C / second or more and then tempered. A method for producing rolled steel sheets.
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