JP2013124383A - High-strength steel sheet and manufacturing method therefor - Google Patents
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本発明は、Ｓｉ含有量が多い場合でも、優れた化成処理性及び電着塗装後の耐食性を有する高強度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-strength steel sheet having excellent chemical conversion property and corrosion resistance after electrodeposition coating even when the Si content is large, and a method for producing the same.
近年、自動車の燃費向上および自動車の衝突安全性向上の観点から、車体材料の高強度化によって薄肉化を図り、車体そのものを軽量化しかつ高強度化する要望が高まっている。そのため、高強度鋼板の自動車への適用が促進されている。 In recent years, from the viewpoint of improving the fuel efficiency of automobiles and improving the collision safety of automobiles, there is an increasing demand for reducing the thickness of the vehicle body by increasing the strength of the vehicle body material and reducing the weight of the vehicle body. For this reason, application of high-strength steel sheets to automobiles is being promoted.
一般に自動車用鋼板は塗装して使用されており、その塗装の前処理として、リン酸塩処理と呼ばれる化成処理が施される。鋼板の化成処理は塗装後の耐食性を確保するための重要な処理の一つである。 In general, steel plates for automobiles are used after being coated, and as a pretreatment for the coating, a chemical conversion treatment called a phosphate treatment is performed. The chemical conversion treatment of the steel sheet is one of the important treatments for ensuring the corrosion resistance after painting.
鋼板の強度、延性を高めるためには、Ｓｉの添加が有効である。しかしながら、連続焼鈍の際にＳｉは、Ｆｅの酸化が起こらない（Ｆｅ酸化物を還元する）還元性のＮ２＋Ｈ２ガス雰囲気でも酸化し、鋼板最表層にＳｉ酸化物（ＳｉＯ２）を形成する。一般に連続焼鈍時間は７００℃以上の高温度域で１００ｓ以上と長いため、ＳｉＯ２の形成量が多くなり、このＳｉＯ２が化成処理中の化成皮膜の生成反応を阻害するため、化成皮膜が生成されない微小領域（以降、スケと称することもある）が形成され、化成処理性が低下する。 In order to increase the strength and ductility of the steel plate, addition of Si is effective. However, during continuous annealing, Si is oxidized even in a reducing N 2 + H 2 gas atmosphere in which no oxidation of Fe occurs (which reduces Fe oxide), and Si oxide (SiO 2 ) is formed on the outermost surface of the steel sheet. To do. In general, the continuous annealing time is as long as 100 s or more in a high temperature range of 700 ° C. or higher, so the amount of SiO 2 formed increases, and this SiO 2 inhibits the formation reaction of the chemical film during the chemical conversion treatment, so that a chemical conversion film is formed. A small region (hereinafter sometimes referred to as “ske”) that is not formed is formed, and the chemical conversion processability is lowered.
高Ｓｉ含有鋼板の化成処理性を改善する従来技術として、特許文献１では、２０〜１５００ｍｇ／ｍ２の鉄被覆層を電気めっき法を用いて鋼板上に形成する方法が開示されている。しかしながら、この方法では、電気めっき設備が別途必要となり工程が増加しコストも増大するという問題がある。 As a conventional technique for improving the chemical conversion property of a high Si-containing steel sheet, Patent Document 1 discloses a method of forming an iron coating layer of 20 to 1500 mg / m 2 on a steel sheet using an electroplating method. However, this method has a problem in that an electroplating facility is separately required, and the number of processes increases and the cost also increases.
また、特許文献２では、Ｍｎ／Ｓｉ比率を規定し、特許文献３ではＮｉを添加することによって、各々リン酸塩処理性を向上させている。しかしながら、その効果は鋼板中のＳｉ含有量に依存するものであり、Ｓｉ含有量の高い鋼板については更なる改善が必要であると考えられる。 Moreover, in patent document 2, the Mn / Si ratio is prescribed | regulated, and patent document 3 is improving the phosphate processability by adding Ni, respectively. However, the effect depends on the Si content in the steel sheet, and it is considered that further improvement is necessary for the steel sheet having a high Si content.
更に、特許文献４では、焼鈍時の露点を−２５〜０℃にすることで、鋼板素地表面から深さ１μｍ以内にＳｉ含有酸化物からなる内部酸化層を形成し、鋼板表面長さ１０μｍに占めるＳｉ含有酸化物の割合を８０％以下にする方法が開示されている。しかしながら、特許文献４に記載の方法の場合、露点を制御するエリアが炉内全体を前提としたものであるため、露点の制御が困難であり安定操業が困難である。また、不安定な露点制御のもとで焼鈍を行った場合、鋼板に形成される内部酸化物の分布状態にバラツキが認められ、鋼板の長手方向や幅方向で化成処理性のムラ（全体または一部でスケ）が発生する懸念がある。 Furthermore, in patent document 4, the dew point at the time of annealing is set to −25 to 0 ° C., thereby forming an internal oxide layer made of an Si-containing oxide within a depth of 1 μm from the surface of the steel sheet, and the steel sheet surface length is 10 μm. A method is disclosed in which the proportion of the Si-containing oxide is 80% or less. However, in the case of the method described in Patent Document 4, since the area for controlling the dew point is premised on the entire inside of the furnace, it is difficult to control the dew point, and stable operation is difficult. In addition, when annealing was performed under unstable dew point control, variations were observed in the distribution of internal oxides formed on the steel sheet, and chemical conversion treatment unevenness in the longitudinal direction and width direction of the steel sheet (overall or There is a concern that some scales may occur.
特許文献５では、酸化性雰囲気中で鋼板温度を３５０〜６５０℃に到達させ鋼板表面に酸化膜を形成させ、その後還元性雰囲気中で再結晶温度まで加熱し冷却する方法が記載されている。しかしながらこの方法では、酸化する方法により鋼板表面に形成される酸化皮膜の厚みに差があり、十分に酸化が起こらなかったり、酸化皮膜が厚くなりすぎて、後の還元性雰囲気中での焼鈍において酸化膜の残留または剥離を生じ、表面性状が悪化する場合があった。実施例では、大気中で酸化する技術が記載されているが、大気中での酸化は酸化物が厚く生成してその後の還元が困難である、あるいは高水素濃度の還元雰囲気が必要である、等の問題がある。 Patent Document 5 describes a method in which a steel sheet temperature reaches 350 to 650 ° C. in an oxidizing atmosphere to form an oxide film on the steel sheet surface, and then heated to a recrystallization temperature and cooled in a reducing atmosphere. However, in this method, there is a difference in the thickness of the oxide film formed on the surface of the steel sheet due to the oxidation method, and sufficient oxidation does not occur, or the oxide film becomes too thick, and in subsequent annealing in a reducing atmosphere. Oxide film may remain or peel off, and surface properties may deteriorate. In the examples, a technique for oxidizing in the air is described, but oxidation in the air generates a thick oxide and subsequent reduction is difficult, or a reducing atmosphere with a high hydrogen concentration is required. There are problems such as.
さらに、特許文献６では、質量％でＳｉを０．１％以上、及び／または、Ｍｎを１．０％以上含有する冷延鋼板について、鋼板温度４００℃以上で鉄の酸化雰囲気下で鋼板表面に酸化膜を形成させ、その後、鉄の還元雰囲気下で前記鋼板表面の酸化膜を還元する方法が記載されている。具体的には、４００℃以上で空気比０．９３以上１．１０以下の直火バーナーを用いて鋼板表面のＦｅを酸化した後、Ｆｅ酸化物を還元するＮ２+Ｈ２ガス雰囲気で焼鈍することにより、化成処理性を劣化させるＳｉの最表面での酸化を抑制し、最表面にＦｅの酸化層を形成させる方法である。特許文献６には、直火バーナーの加熱温度が具体的に記載されていないが、Ｓｉを多く（概ね０．６％以上）含有する場合には、Ｆｅよりも酸化しやすいＳｉの酸化量が多くなってＦｅの酸化が抑制されたり、Ｆｅの酸化そのものが少なすぎたりする。その結果、還元後の表面Ｆｅ還元層の形成が不十分であったり、還元後の鋼板表面にＳｉＯ２が存在し、化成皮膜のスケが発生する場合があった。 Further, in Patent Document 6, a cold-rolled steel sheet containing 0.1% or more of Si and / or 1.0% or more of Mn by mass%, the steel sheet surface in an iron oxidizing atmosphere at a steel sheet temperature of 400 ° C. or more. Describes a method in which an oxide film is formed, and then the oxide film on the surface of the steel sheet is reduced in an iron reducing atmosphere. Specifically, after oxidizing Fe on the surface of the steel sheet using a direct fire burner at 400 ° C. or higher and an air ratio of 0.93 or higher and 1.10 or lower, annealing is performed in an N 2 + H 2 gas atmosphere that reduces Fe oxide. This is a method of suppressing oxidation at the outermost surface of Si, which deteriorates the chemical conversion processability, and forming an Fe oxide layer on the outermost surface. Patent Document 6 does not specifically describe the heating temperature of an open flame burner, but when it contains a large amount of Si (approximately 0.6% or more), the amount of oxidation of Si that is easier to oxidize than Fe. As a result, the oxidation of Fe is suppressed, or the oxidation of Fe itself is too little. As a result, formation of the surface Fe reduction layer after reduction was insufficient, or SiO 2 was present on the steel plate surface after reduction, and there was a case where the conversion film was scaled.
本発明は、かかる事情に鑑みてなされたものであって、Ｓｉ含有量が多く、高温（≧７００℃）での連続焼鈍時間が長い（≧１００ｓ）場合でも、優れた化成処理性及び電着塗装後の耐食性を有する高強度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 has been made in view of such circumstances. Even when the Si content is high and the continuous annealing time at a high temperature (≧ 700 ° C.) is long (≧ 100 s), excellent chemical conversion treatment and electrodeposition are possible. It aims at providing the high-strength steel plate which has the corrosion resistance after coating, and its manufacturing method.
従来は、めっき性を改善する目的で積極的に鋼板の内部を酸化させていた。しかし、同時に、耐食性や加工性が劣化する。そこで、本発明者らは、従来の考えにとらわれない新たな方法で課題を解決する方法を検討した。その結果、焼鈍工程の雰囲気と温度を適切に制御することで、鋼板表層部において内部酸化の形成を抑制し、優れた化成処理性及び電着塗装後の耐食性を有する高強度鋼板が得られることを知見した。 Conventionally, the inside of a steel plate has been actively oxidized for the purpose of improving the plating property. However, at the same time, corrosion resistance and workability deteriorate. Therefore, the present inventors have studied a method for solving the problem by a new method not confined to the conventional idea. As a result, by appropriately controlling the atmosphere and temperature of the annealing process, it is possible to obtain a high-strength steel sheet having excellent chemical conversion property and corrosion resistance after electrodeposition coating by suppressing the formation of internal oxidation in the surface layer portion of the steel sheet. I found out.
具体的には、加熱過程では焼鈍炉内温度：６００℃以上Ａ℃以下（Ａ：７００≦Ａ≦１０００）の温度域を昇温速度：８℃／ｓ以上とし、かつ、均熱過程では焼鈍炉内温度：８００℃以上１０００℃以下の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上とし、さらに、冷却過程では７００℃以上の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上となるように制御して焼鈍し、化成処理を行う。加熱過程において焼鈍炉内温度：６００℃以上Ａ℃以下（Ａ：７００≦Ａ≦１０００）の温度域を昇温速度：８℃／ｓ以上とすることで易酸化性元素の選択的表面酸化（以後、表面濃化と呼ぶ）を極力抑制する。さらに、均熱過程において焼鈍炉内温度：８００℃以上１０００℃以下の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上とし、かつ、冷却過程において７００℃以上の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上とすることで、雰囲気中の還元能力が増し、鋼板表面に表面濃化したＳｉ、Ｍｎなどの易酸化性元素の酸化物を還元することができる。なお、雰囲気中の酸素ポテンシャルは非常に低いため、内部酸化は殆ど起こらない。このような処理を行うことによって、雰囲気中の還元能力が増し、表面濃化したＳｉ、Ｍｎなどの易酸化性元素の酸化物を還元することができる。 Specifically, in the heating process, the temperature range in the annealing furnace: 600 ° C. or more and A ° C. or less (A: 700 ≦ A ≦ 1000) is set to a temperature increase rate of 8 ° C./s or more, and in the soaking process, annealing is performed. Furnace temperature: Temperature range of 800 ° C. or higher and 1000 ° C. or lower is set to hydrogen concentration in the atmosphere: 26 vol% or higher. Further, in the cooling process, temperature range of 700 ° C. or higher is set to hydrogen concentration in atmosphere: 26 vol% or higher. Control and anneal and perform chemical conversion treatment. In the heating process, the temperature in the annealing furnace: 600 ° C. or more and A ° C. or less (A: 700 ≦ A ≦ 1000) is set to a temperature rising rate of 8 ° C./s or more, thereby selectively oxidizing the surface of the easily oxidizable element ( (Hereinafter referred to as surface thickening) is suppressed as much as possible. Furthermore, in the soaking process, the temperature in the annealing furnace: 800 ° C. or more and 1000 ° C. or less is set to the hydrogen concentration in the atmosphere: 26 vol% or more, and the cooling process is performed in the temperature range of 700 ° C. or more in the atmosphere: By setting it to 26 vol% or more, the reducing ability in the atmosphere is increased, and oxides of easily oxidizable elements such as Si and Mn concentrated on the surface of the steel sheet can be reduced. Since the oxygen potential in the atmosphere is very low, little internal oxidation occurs. By performing such treatment, the reducing ability in the atmosphere is increased, and oxides of easily oxidizable elements such as Si and Mn that are concentrated on the surface can be reduced.
通常、鋼板の焼鈍雰囲気の水素濃度は２６ｖｏｌ％より低く、５〜１０ｖｏｌ％が一般的であるため、焼鈍炉全体の雰囲気の水素濃度を２６ｖｏｌ％以上とするためには莫大な設備費と操業コストを要するが、本発明では均熱過程の焼鈍炉内温度が８００℃以上１０００℃以下の温度域と、冷却過程の焼鈍炉内温度が７００℃以上の温度域を、雰囲気中の水素濃度：２６ｖｏｌ％以上となるように制御することで所定の特性が得られるため、設備費や操業コストを低減できるという特徴がある。 Usually, the hydrogen concentration in the annealing atmosphere of the steel sheet is lower than 26 vol%, and generally 5 to 10 vol%. Therefore, in order to make the hydrogen concentration in the atmosphere of the entire annealing furnace 26 vol% or more, huge equipment costs and operation costs are required. However, in the present invention, the temperature range of the annealing furnace in the soaking process is 800 ° C. or more and 1000 ° C. or less, and the temperature range of the annealing furnace temperature in the cooling process is 700 ° C. or more, and the hydrogen concentration in the atmosphere is 26 vol. Since a predetermined characteristic can be obtained by controlling to be equal to or greater than%, the facility cost and the operation cost can be reduced.
なお、雰囲気中の酸素ポテンシャルは非常に低いため、内部酸化は殆ど起こらない。そして、このように雰囲気の水素濃度を制御することにより、内部酸化を形成させずに表面濃化物を還元し、スケ、ムラのない化成処理性、及び、電着塗装後の耐食性に優れる高強度鋼板が得られることになる。なお、化成処理性に優れるとは、化成処理後のスケ、ムラのない外観を有することを言う。 Since the oxygen potential in the atmosphere is very low, little internal oxidation occurs. And by controlling the hydrogen concentration in the atmosphere in this way, the surface concentrate can be reduced without forming internal oxidation, and high strength that is excellent in conversion treatment without scum and unevenness, and corrosion resistance after electrodeposition coating A steel plate will be obtained. In addition, having excellent chemical conversion property means having a non-scaling and uneven appearance after chemical conversion treatment.
ここで、上記水素濃度：２６ｖｏｌ％以上にする領域以外の水素濃度は２６ｖｏｌ％より低い濃度でも構わない。通常の水素濃度である５〜１０％でも問題ない。 Here, the hydrogen concentration other than the region where the hydrogen concentration is 26 vol% or more may be lower than 26 vol%. A normal hydrogen concentration of 5 to 10% is not a problem.
そして、以上の方法により得られる高強度鋼板は、鋼板表面から１００μｍ以内の鋼板表層部において、Ｆｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、Ｂ、Ｎｂ、Ｔｉ、Ｃｒ、Ｍｏ、Ｃｕ、Ｎｉの中から選ばれる１種以上の酸化物の形成が抑制され、その形成量は合計で片面あたり０．０５０ｇ／ｍ２以下に抑制される。これにより、化成処理性に優れ、電着塗装後の耐食性が向上することになる。 And the high-strength steel plate obtained by the above method is from among Fe, Si, Mn, Al, P, B, Nb, Ti, Cr, Mo, Cu, Ni in the steel plate surface layer portion within 100 μm from the steel plate surface. The formation of one or more selected oxides is suppressed, and the amount formed is suppressed to 0.050 g / m 2 or less per side in total. Thereby, it is excellent in chemical conversion property and the corrosion resistance after electrodeposition coating improves.
本発明は上記知見に基づくものであり、特徴は以下の通りである。
［１］質量％で、Ｃ：０．０１〜０．１８％、Ｓｉ：０．４〜２．０％、Ｍｎ：１．０〜３．０％、Ａｌ：０．００１〜１．０％、Ｐ：０．００５〜０．０６０％、Ｓ≦０．０１％を含有し、残部がＦｅおよび不可避的不純物からなる鋼板を連続焼鈍する際に、加熱過程では、焼鈍炉内温度：６００℃以上Ａ℃以下の温度域を昇温速度：８℃／ｓ以上とし、かつ、均熱過程では、焼鈍炉内温度：８００℃以上１０００℃以下の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上とし、かつ、冷却過程では、焼鈍炉内温度：７００℃以上の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上とすることを特徴とする高強度鋼板の製造方法。
ただし、Ａ：７００≦Ａ≦１０００である。
［２］前記鋼板は、成分組成として、質量％で、さらに、Ｂ：０．００１〜０．００５％、Ｎｂ：０．００５〜０．０５％、Ｔｉ：０．００５〜０．０５％、Ｃｒ：０．００１〜１．０％、Ｍｏ：０．０５〜１．０％、Ｃｕ：０．０５〜１．０％、Ｎｉ：０．０５〜１．０％の中から選ばれる１種以上の元素を含有することを特徴とする前記［１］に記載の高強度鋼板の製造方法。
［３］前記連続焼鈍を行った後、硫酸を含む水溶液中で電解酸洗を行うことを特徴とする前記［１］または［２］に記載の高強度鋼板の製造方法。
［４］前記［１］〜［３］のいずれかに記載の製造方法により製造され、鋼板表面から１００μｍ以内の鋼板表層部に生成したＦｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、Ｂ、Ｎｂ、Ｔｉ、Ｃｒ、Ｍｏ、Ｃｕ、Ｎｉの中から選ばれる一種以上の酸化物が、片面あたり０．０５０ｇ／ｍ２以下であることを特徴とする高強度鋼板。
The present invention is based on the above findings, and features are as follows.
[1] By mass%, C: 0.01 to 0.18%, Si: 0.4 to 2.0%, Mn: 1.0 to 3.0%, Al: 0.001 to 1.0% , P: 0.005 to 0.060%, S ≦ 0.01%, and when continuously annealing a steel plate made of Fe and inevitable impurities, the temperature in the annealing furnace is 600 ° C. in the heating process. The temperature range of A ° C. or lower is set to a rate of temperature increase of 8 ° C./s or higher, and in the soaking process, the temperature range of the annealing furnace: 800 ° C. or higher to 1000 ° C. or lower is the hydrogen concentration in the atmosphere: 26 vol% or higher. And in the cooling process, the temperature range in annealing furnace: 700 degreeC or more is made into the hydrogen concentration in atmosphere: 26 vol% or more, The manufacturing method of the high strength steel plate characterized by the above-mentioned.
However, A: 700 ≦ A ≦ 1000.
[2] The steel sheet is in mass% as a component composition, and further B: 0.001 to 0.005%, Nb: 0.005 to 0.05%, Ti: 0.005 to 0.05%, One selected from Cr: 0.001-1.0%, Mo: 0.05-1.0%, Cu: 0.05-1.0%, Ni: 0.05-1.0% The method for producing a high-strength steel sheet according to [1] above, comprising the above elements.
[3] The method for producing a high-strength steel sheet according to [1] or [2], wherein after the continuous annealing, electrolytic pickling is performed in an aqueous solution containing sulfuric acid.
[4] Fe, Si, Mn, Al, P, B, Nb, Ti produced by the production method according to any one of [1] to [3] and formed on the steel sheet surface layer within 100 μm from the steel sheet surface. One or more oxides selected from Cr, Mo, Cu, and Ni are 0.050 g / m 2 or less per side, and a high-strength steel sheet.
なお、本発明において、高強度とは、引張強度ＴＳが３４０ＭＰa以上である。また、本発明の高強度鋼板は、冷延鋼板、熱延鋼板のいずれも含むものである。 In the present invention, the high strength means that the tensile strength TS is 340 MPa or more. The high-strength steel sheet of the present invention includes both cold-rolled steel sheets and hot-rolled steel sheets.
本発明によれば、Ｓｉ含有量が多い場合で、高温域（≧７００℃）での連続焼鈍時間が長い（≧１００ｓ）場合でも、優れた化成処理性及び電着塗装後の耐食性を有する高強度鋼板が得られる。 According to the present invention, even when the Si content is large and the continuous annealing time in a high temperature range (≧ 700 ° C.) is long (≧ 100 s), the high chemical conversion treatment property and the corrosion resistance after electrodeposition coating are high. A strength steel plate is obtained.
以下、本発明について具体的に説明する。なお、以下の説明において、鋼成分組成の各元素の含有量の単位はいずれも「質量％」であり、以下、特に断らない限り単に「％」で示す。 Hereinafter, the present invention will be specifically described. In the following description, the unit of the content of each element of the steel component composition is “mass%”, and hereinafter, it is simply indicated by “%” unless otherwise specified.
先ず、本発明で最も重要な要件である、鋼板表層の構造を決定する焼鈍雰囲気条件について説明する。
鋼中に多量のＳｉおよびＭｎが添加された高強度鋼板において、耐食性を満足させるためには、腐食の起点となる可能性がある鋼板表層の内部酸化を極力少なくすることが求められる。
First, the annealing atmosphere conditions that determine the structure of the steel sheet surface layer, which is the most important requirement in the present invention, will be described.
In a high-strength steel sheet in which a large amount of Si and Mn is added to the steel, in order to satisfy the corrosion resistance, it is required to minimize the internal oxidation of the steel sheet surface layer that may be a starting point of corrosion.
ＳｉやＭｎの内部酸化を促進させることにより化成処理性を向上させることは可能ではあるが、これは逆に耐食性の劣化をもたらすことになってしまう。このため、ＳｉやＭｎの内部酸化を促進させる方法以外で、良好な化成処理性を維持しつつ、内部酸化を抑制して耐食性を向上させる必要がある。検討した結果、本発明では、まず、化成処理性を確保するために、連続焼鈍を行う際に、加熱過程において形成されたＳｉ、Ｍｎなどの表面濃化物を比較的高温の均熱過程で還元する。そして、冷却過程初期の酸素ポテンシャルを低下させることで酸化を防止し、鋼板表面の酸化物を減少させ、化成処理性を改善する。さらに、鋼板表層部において、内部酸化も殆ど形成されないため、耐食性が改善されることになる。 Although it is possible to improve the chemical conversion treatment by promoting the internal oxidation of Si or Mn, this leads to deterioration of the corrosion resistance. For this reason, it is necessary to suppress the internal oxidation and improve the corrosion resistance while maintaining good chemical conversion properties other than the method of promoting the internal oxidation of Si and Mn. As a result of investigation, in the present invention, first, in order to ensure chemical conversion, the surface concentrate such as Si and Mn formed in the heating process is reduced in a relatively high temperature soaking process during continuous annealing. To do. And oxidation is prevented by lowering the oxygen potential in the initial stage of the cooling process, and the oxide on the surface of the steel sheet is reduced to improve the chemical conversion processability. Furthermore, since the internal oxidation is hardly formed in the steel plate surface layer portion, the corrosion resistance is improved.
このような効果は、連続式焼鈍設備（以下、単に焼鈍炉と称することもある）において焼鈍を施すに際し、加熱過程では焼鈍炉内温度：６００℃以上Ａ℃以下（Ａ：７００≦Ａ≦１０００）の温度域を昇温速度：８℃／ｓ以上とし、かつ、均熱過程では焼鈍炉内温度：８００℃以上１０００℃以下の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上とし、さらに、冷却過程では焼鈍炉内温度：７００℃以上の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上となるように制御することにより得られる。このように制御することにより、表面濃化を極力抑制し、加熱過程時に抑制しきれず形成した表面濃化物を均熱過程で還元し、鋼板表層の酸化物（表面濃化物）を減少させる。また、焼鈍雰囲気は低酸素ポテンシャルであるため、内部酸化を殆ど形成させることはない。その結果、スケ、ムラのない優れた化成処理性とより高い耐食性が得られることになる。 Such an effect is obtained when annealing is performed in a continuous annealing facility (hereinafter sometimes simply referred to as an annealing furnace), and in the heating process, the temperature in the annealing furnace is 600 ° C. or more and A ° C. or less (A: 700 ≦ A ≦ 1000). ) Is set to a temperature increase rate of 8 ° C./s or more, and in the soaking process, the temperature range of the annealing furnace is set to 800 ° C. or more and 1000 ° C. or less, and the hydrogen concentration in the atmosphere is set to 26 vol% or more. In the cooling process, the temperature in the annealing furnace: 700 ° C. or higher is obtained by controlling the hydrogen concentration in the atmosphere: 26 vol% or higher. By controlling in this way, the surface enrichment is suppressed as much as possible, and the surface concentrate that cannot be suppressed during the heating process is reduced in the soaking process, and the oxide (surface concentrate) on the surface layer of the steel sheet is reduced. Further, since the annealing atmosphere has a low oxygen potential, almost no internal oxidation is formed. As a result, excellent chemical conversion processability and higher corrosion resistance without any scum and unevenness can be obtained.
加熱過程では、焼鈍炉内温度：６００℃以上Ａ℃以下の温度域を昇温速度：８℃／ｓ以上
加熱過程での焼鈍炉内温度の昇温速度を制御する温度域を６００℃以上とした理由は以下の通りである。６００℃を下回る温度域では、耐食性の劣化等が問題になる程度の表面濃化や内部酸化は、起こらない。よって、本発明の効果が発現する温度域である６００℃以上とする。
また、加熱過程での焼鈍炉内温度の昇温速度を制御する温度域をＡ℃以下（Ａ：７００≦Ａ≦１０００）とした理由は以下の通りである。まず、７００℃を下回る温度域では、昇温速度を８℃／ｓ以上に制御する時間が短く、本発明の効果が小さい。このため、Ａは７００以上とする。一方、１０００℃超えの場合、本発明の効果に何ら問題はないが、焼鈍炉内設備（例えば、ロールなど）の劣化、及びコスト増大の観点から、不利となる。したがって、１０００℃以下とする。
昇温速度を８℃／ｓ以上とした理由は以下の通りである。昇温速度が８℃／ｓ以上で表面濃化の抑制効果が認め始められる。昇温速度の上限は特には設けないが、５００℃／ｓ超えでは効果は飽和しコスト的に不利となるため、５００℃／ｓ以下が望ましい。なお、昇温速度を８℃／ｓ以上とするには、ラジアントチューブおよび又はインダクションヒーター等の加熱を適用することができる。
In the heating process, an annealing furnace temperature: 600 ° C. or more and A ° C. or less temperature increase rate: 8 ° C./s or more The temperature range for controlling the annealing furnace temperature increase rate in the heating process is 600 ° C. or more. The reason for this is as follows. In the temperature range below 600 ° C., surface enrichment and internal oxidation that cause deterioration of corrosion resistance and the like do not occur. Therefore, the temperature is set to 600 ° C. or higher, which is a temperature range in which the effect of the present invention is exhibited.
The reason why the temperature range for controlling the temperature increase rate of the annealing furnace temperature in the heating process is set to A ° C. or lower (A: 700 ≦ A ≦ 1000) is as follows. First, in the temperature range below 700 ° C., the time for controlling the temperature rising rate to 8 ° C./s or more is short, and the effect of the present invention is small. For this reason, A is 700 or more. On the other hand, when the temperature exceeds 1000 ° C., there is no problem in the effect of the present invention, but it is disadvantageous from the viewpoint of deterioration of the equipment in the annealing furnace (for example, rolls) and cost increase. Therefore, it shall be 1000 degrees C or less.
The reason why the heating rate is 8 ° C./s or more is as follows. The suppression effect of surface concentration begins to be recognized at a temperature rising rate of 8 ° C./s or more. The upper limit of the heating rate is not particularly set, but if it exceeds 500 ° C./s, the effect is saturated and disadvantageous in terms of cost. In addition, in order to make a temperature increase rate 8 degrees C / s or more, heating, such as a radiant tube and / or an induction heater, can be applied.
均熱過程では、焼鈍炉内温度：８００℃以上１０００℃以下の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上
均熱過程での雰囲気中の水素濃度を制御する温度域を８００℃以上１０００℃以下とした理由は以下の通りである。８００℃を下回る温度域では、雰囲気中の水素濃度：２６ｖｏｌ％以上にまで増加させ還元能力を増加させたとしても、Ｓｉ、Ｍｎなどの表面濃化物を十分に還元することができない。一方、１０００℃以下とした理由は、１０００℃超えの場合、焼鈍炉内設備（例えば、ロールなど）の劣化、及びコスト増大の観点から、不利となる。したがって、１０００℃以下とする。
雰囲気中の水素濃度を２６ｖｏｌ％以上とした理由は以下の通りである。雰囲気中の水素濃度を２６ｖｏｌ％以上に制御することで、鋼板表面の酸素ポテンシャルが低下し、選択的表面酸化（表面濃化）を抑制することが可能となる。水素濃度の上限は特には設けないが、７５ｖｏｌ％を超えると効果が飽和し、コストが増大するため、７５ｖｏｌ％以下が望ましい。
In the soaking process, the temperature in the annealing furnace is in the temperature range of 800 ° C. or more and 1000 ° C. or less. The hydrogen concentration in the atmosphere is 26 vol% or more. The temperature range in which the hydrogen concentration in the atmosphere in the soaking process is controlled is 800 ° C. or more and 1000 ° C. The reason for the following is as follows. In the temperature range below 800 ° C., even if the hydrogen concentration in the atmosphere is increased to 26 vol% or more and the reducing ability is increased, the surface concentrate such as Si and Mn cannot be sufficiently reduced. On the other hand, the reason why the temperature is set to 1000 ° C. or lower is disadvantageous from the viewpoint of deterioration of the equipment in the annealing furnace (for example, a roll) and cost increase when the temperature exceeds 1000 ° C. Therefore, it shall be 1000 degrees C or less.
The reason why the hydrogen concentration in the atmosphere is set to 26 vol% or more is as follows. By controlling the hydrogen concentration in the atmosphere to 26 vol% or more, the oxygen potential on the steel sheet surface is lowered, and selective surface oxidation (surface concentration) can be suppressed. The upper limit of the hydrogen concentration is not particularly set, but if it exceeds 75 vol%, the effect is saturated and the cost increases, so 75 vol% or less is desirable.
冷却過程では、焼鈍炉内温度：７００℃以上の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上
冷却過程での雰囲気中の水素濃度を制御する温度域を７００℃以上とした理由は以下の通りである。７００℃以上の温度域で、Ｓｉ、Ｍｎなどの表面濃化が始まる。この温度域で雰囲気中の水素濃度を２６ｖｏｌ％以上に制御しない場合、表面濃化が起こってしまう。雰囲気中の水素濃度：２６ｖｏｌ％以上に制御すれば、表面濃化を抑制できる。また、冷却過程以降では雰囲気中の水素濃度を増加させても温度が低いので、表面濃化物を還元することができない。したがって、冷却過程での雰囲気中の水素濃度を制御する温度域を７００℃以上とする。
In the cooling process, the temperature range in the annealing furnace: 700 ° C. or higher The hydrogen concentration in the atmosphere: 26 vol% or higher The reason why the temperature range for controlling the hydrogen concentration in the atmosphere in the cooling process is 700 ° C. or higher is as follows. It is. Surface enrichment of Si, Mn, etc. begins in a temperature range of 700 ° C. or higher. If the hydrogen concentration in the atmosphere is not controlled to 26 vol% or more in this temperature range, surface concentration occurs. If the hydrogen concentration in the atmosphere is controlled to 26 vol% or more, surface concentration can be suppressed. Further, after the cooling process, even if the hydrogen concentration in the atmosphere is increased, the temperature is low, so that the surface concentrate cannot be reduced. Therefore, the temperature range for controlling the hydrogen concentration in the atmosphere during the cooling process is set to 700 ° C. or higher.
次いで、本発明の対象とする高強度鋼板の鋼成分組成について説明する。
Ｃ：０．０１〜０．１８％
Ｃが０.０１％未満であると、固溶、析出、変態等による強化の効果が殆ど認められない。一方、０．１８％を超えると伸びが低下し材質が劣化し、さらには溶接性が劣化する。したがって、Ｃ量は０．０１％以上０．１８％以下とする。
Next, the steel component composition of the high-strength steel sheet that is the subject of the present invention will be described.
C: 0.01 to 0.18%
When C is less than 0.01%, the effect of strengthening due to solid solution, precipitation, transformation or the like is hardly recognized. On the other hand, if it exceeds 0.18%, the elongation decreases, the material deteriorates, and further the weldability deteriorates. Therefore, the C content is 0.01% or more and 0.18% or less.
Ｓｉ：０．４〜２．０％
Ｓｉは鋼を強化し伸びを向上させ良好な材質を得るのに有効な元素であり、本発明の目的とする強度を得るためには０．４％以上が必要である。Ｓｉが０．４％未満では本発明の適用範囲とする強度が得られず、化成処理性についても特に問題とならない。一方、２．０％を超えると鋼の強化能や伸び向上効果が飽和してくる。さらに、化成処理性の改善が困難となってくる。したがって、Ｓｉ量は０．４％以上２．０％以下とする。
Si: 0.4-2.0%
Si is an element effective for strengthening steel and improving elongation to obtain a good material, and 0.4% or more is necessary to obtain the intended strength of the present invention. If Si is less than 0.4%, the strength within the scope of the present invention cannot be obtained, and there is no particular problem with chemical conversion treatment. On the other hand, when it exceeds 2.0%, the steel strengthening ability and the effect of improving elongation become saturated. Furthermore, it becomes difficult to improve the chemical conversion processability. Therefore, the Si amount is set to 0.4% or more and 2.0% or less.
Ｍｎ：１．０〜３．０％
Ｍｎは鋼の高強度化に有効な元素である。機械特性や強度を確保するためは１．０％以上含有させることが必要である。一方、３．０％を超えると溶接性や、強度と延性のバランスの確保が困難になる。したがって、Ｍｎ量は１．０％以上３．０％以下とする。
Mn: 1.0-3.0%
Mn is an element effective for increasing the strength of steel. In order to ensure mechanical properties and strength, it is necessary to contain 1.0% or more. On the other hand, if it exceeds 3.0%, it becomes difficult to secure weldability and the balance between strength and ductility. Therefore, the Mn content is 1.0% or more and 3.0% or less.
Ａｌ：０．００１〜１．０％
Ａｌは溶鋼の脱酸を目的に添加される。溶鋼の脱酸の効果は０．００１％以上で得られる。一方、１．０％を超えるとコストアップになる。さらに、Ａｌの表面濃化が多くなり、化成処理性の改善が困難になってくる。したがって、Ａｌ量は０．００１％以上１．０％以下とする。
Al: 0.001 to 1.0%
Al is added for the purpose of deoxidizing molten steel. The effect of deoxidation of molten steel is obtained at 0.001% or more. On the other hand, if it exceeds 1.0%, the cost increases. Furthermore, the surface concentration of Al increases and it becomes difficult to improve chemical conversion properties. Therefore, the Al content is 0.001% or more and 1.0% or less.
Ｐ：０．００５〜０．０６０％以下
Ｐは不可避的に含有される元素のひとつであり、０．００５％未満にするためには、コストの増大が懸念されるため、０．００５％以上とする。一方、Ｐが０．０６０％を超えて含有されると溶接性が劣化する。さらに、化成処理性の劣化が激しくなり、本発明をもってしても化成処理性を向上させることが困難となる。したがって、Ｐ量は０．００５％以上０．０６０％以下とする。
P: 0.005 to 0.060% or less P is one of the elements inevitably contained, and in order to make it less than 0.005%, there is a concern about an increase in cost, so 0.005% or more And On the other hand, if P exceeds 0.060%, weldability deteriorates. Furthermore, the chemical conversion processability is greatly deteriorated, and even with the present invention, it is difficult to improve the chemical conversion processability. Therefore, the P content is 0.005% or more and 0.060% or less.
Ｓ≦０．０１％
Ｓは不可避的に含有される元素のひとつである。下限は規定しないが、多量に含有すると溶接性及び耐食性が劣化するため０．０１％以下とする。
S ≦ 0.01%
S is one of the elements inevitably contained. The lower limit is not specified, but if it is contained in a large amount, the weldability and corrosion resistance deteriorate, so the content is made 0.01% or less.
なお、下記の理由により、Ｂ：０．００１〜０．００５％、Ｎｂ：０．００５〜０．０５％、Ｔｉ：０．００５〜０．０５％、Ｃｒ：０．００１〜１．０％、Ｍｏ：０．０５〜１．０％、Ｃｕ：０．０５〜１．０％、Ｎｉ：０．０５〜１．０％の中から選ばれる１種以上の元素を必要に応じて添加してもよい。
これらの元素を添加する場合における適正添加量の限定理由は以下の通りである。
For the following reasons, B: 0.001 to 0.005%, Nb: 0.005 to 0.05%, Ti: 0.005 to 0.05%, Cr: 0.001 to 1.0% One or more elements selected from Mo: 0.05-1.0%, Cu: 0.05-1.0%, Ni: 0.05-1.0% are added as necessary. May be.
The reason for limiting the appropriate addition amount in the case of adding these elements is as follows.
Ｂ：０．００１〜０．００５％
Ｂは０．００１％未満では焼き入れ促進効果が得られにくい。一方、０．００５％超えでは化成処理性が劣化する。よって、含有する場合、Ｂ量は０．００１％以上０．００５％以下とする。なお、機械的特性を改善する目的で添加する必要がないと判断される場合は添加する必要はない。
B: 0.001 to 0.005%
When B is less than 0.001%, it is difficult to obtain an effect of promoting quenching. On the other hand, if it exceeds 0.005%, chemical conversion processability deteriorates. Therefore, when it contains, B amount shall be 0.001% or more and 0.005% or less. In addition, when it is judged that it is not necessary to add for the purpose of improving a mechanical characteristic, it is not necessary to add.
Ｎｂ：０．００５〜０．０５％
Ｎｂは０．００５％未満では強度調整の効果が得られにくい。一方、０．０５％超えではコストアップを招く。よって、含有する場合、Ｎｂ量は０．００５％以上０．０５％以下とする。
Nb: 0.005 to 0.05%
If Nb is less than 0.005%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 0.05%, the cost increases. Therefore, when it contains, Nb amount shall be 0.005% or more and 0.05% or less.
Ｔｉ：０．００５〜０．０５％
Ｔｉは０．００５％未満では強度調整の効果が得られにくい。一方、０．０５％超えでは化成処理性の劣化を招く。よって、含有する場合、Ｔｉ量は０．００５％以上０．０５％以下とする。
Ti: 0.005 to 0.05%
If Ti is less than 0.005%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 0.05%, chemical conversion processability is deteriorated. Therefore, when it contains, Ti amount shall be 0.005% or more and 0.05% or less.
Ｃｒ：０．００１〜１．０％
Ｃｒは０．００１％未満では焼き入れ促進効果が得られにくい。一方、１．０％超えではＣｒが表面濃化するため、溶接性が劣化する。よって、含有する場合、Ｃｒ量は０．００１％以上１．０％以下とする。
Cr: 0.001 to 1.0%
When Cr is less than 0.001%, it is difficult to obtain an effect of promoting quenching. On the other hand, if it exceeds 1.0%, the surface of Cr is concentrated, so that the weldability is deteriorated. Therefore, when it contains, Cr amount shall be 0.001% or more and 1.0% or less.
Ｍｏ：０．０５〜１．０％
Ｍｏは０．０５％未満では強度調整の効果が得られにくい。一方、１．０％超えではコストアップを招く。よって、含有する場合、Ｍｏ量は０．０５％以上１．０％以下とする。
Mo: 0.05-1.0%
If Mo is less than 0.05%, the effect of adjusting the strength is difficult to obtain. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when contained, the Mo content is 0.05% or more and 1.0% or less.
Ｃｕ：０．０５〜１．０％
Ｃｕは０．０５％未満では残留γ相形成促進効果が得られにくい。一方、１．０％超えではコストアップを招く。よって、含有する場合、Ｃｕ量は０．０５％以上１．０％以下とする。
Cu: 0.05 to 1.0%
If Cu is less than 0.05%, it is difficult to obtain the effect of promoting the formation of the residual γ phase. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when contained, the Cu content is 0.05% or more and 1.0% or less.
Ｎｉ：０．０５〜１．０％
Ｎｉは０．０５％未満では残留γ相形成促進効果が得られにくい。一方、１．０％超えではコストアップを招く。よって、含有する場合、Ｎｉ量は０．０５％以上１．０％以下とする。
Ni: 0.05-1.0%
If Ni is less than 0.05%, the effect of promoting the formation of residual γ phase is difficult to obtain. On the other hand, if it exceeds 1.0%, cost increases. Therefore, when it contains, Ni amount shall be 0.05% or more and 1.0% or less.
上記以外の残部はＦｅおよび不可避的不純物である。 The balance other than the above is Fe and inevitable impurities.
次に、本発明の高強度鋼板の製造方法とその限定理由について説明する。
上記化学成分を有する鋼を熱間圧延した後、冷間圧延し、次いで、連続式焼鈍設備において焼鈍を行った後、化成処理を行う。なお、熱間圧延終了後、冷間圧延を施さずにそのまま連続焼鈍を行う場合もある。この時、本発明においては、加熱過程では、焼鈍炉内温度：６００℃以上Ａ℃以下（Ａ：７００≦Ａ≦１０００）の温度域を昇温速度：８℃／ｓ以上、均熱過程では、焼鈍炉内温度：８００℃以上１０００℃以下の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上、冷却過程では、７００℃以上の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上で行うこととする。これは本発明において、最も重要な要件である。
Next, the manufacturing method of the high strength steel plate of the present invention and the reason for limitation will be described.
The steel having the above chemical components is hot-rolled, cold-rolled, and then annealed in a continuous annealing facility, followed by chemical conversion treatment. In addition, after completion | finish of hot rolling, continuous annealing may be performed as it is, without performing cold rolling. At this time, in the present invention, in the heating process, the temperature range in the annealing furnace: 600 ° C. or more and A ° C. or less (A: 700 ≦ A ≦ 1000) is set at the rate of temperature increase: 8 ° C./s or more, and in the soaking process. In the annealing furnace, the temperature range of 800 ° C. or higher and 1000 ° C. or lower is set to hydrogen concentration in the atmosphere: 26 vol% or higher. In the cooling process, the temperature range of 700 ° C. or higher is set to hydrogen concentration in the atmosphere: 26 vol% or higher. To do. This is the most important requirement in the present invention.
熱間圧延
通常、行われる条件にて行うことができる。
Hot rolling Usually, it can be performed on the conditions performed.
酸洗
熱間圧延後は酸洗処理を行うのが好ましい。酸洗工程で表面に生成した黒皮スケールを除去し、しかる後冷間圧延する。なお、酸洗条件は特に限定しない。
It is preferable to perform a pickling treatment after hot pickling. The black scale formed on the surface in the pickling process is removed, and then cold-rolled. The pickling conditions are not particularly limited.
冷間圧延
４０％以上８０％以下の圧下率で行うことが好ましい。圧下率が４０％未満では再結晶温度が低温化するため、機械特性が劣化しやすい。一方、圧下率が８０％超えでは高強度鋼板であるため、圧延コストがアップするだけでなく、焼鈍時の表面濃化が増加するため、化成処理性が劣化する。
Cold rolling is preferably performed at a rolling reduction of 40% to 80%. If the rolling reduction is less than 40%, the recrystallization temperature is lowered, and the mechanical characteristics are likely to deteriorate. On the other hand, when the rolling reduction exceeds 80%, the steel sheet is a high-strength steel sheet, so that not only the rolling cost is increased, but also the surface concentration during annealing is increased, so that the chemical conversion treatment property is deteriorated.
冷間圧延した鋼板もしくは熱間圧延した鋼板に対して、連続焼鈍した後、好ましくは電解酸洗処理を行う。次いで、化成処理を施す。
焼鈍炉では、前段の加熱帯で鋼板を所定温度まで加熱する加熱工程を行い、後段の均熱帯で所定温度に所定時間保持する均熱工程を行い、次いで、冷却工程を行う。
上述したように、加熱過程では、焼鈍炉内温度：６００℃以上Ａ℃以下（Ａ：７００≦Ａ≦１０００）の温度域を昇温速度：８℃／ｓ以上とし、かつ、均熱過程では、焼鈍炉内温度：８００℃以上１０００℃以下の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上とし、さらに、冷却過程では、７００℃以上の温度域を雰囲気中の水素濃度：２６ｖｏｌ％以上となるように制御して焼鈍を行う。
なお、上記水素濃度を制御する領域以外の焼鈍炉内雰囲気中の水素濃度は特に限定しない。雰囲気中の水素濃度が２６ｖｏｌ％より低くてもよい。通常の操業条件である５〜１０ｖｏｌ％でも良い。
なお、焼鈍炉内の気体成分は、水素ガス以外には窒素ガスと不可避的不純物気体からなる。本発明効果を損するものでなければ他の気体成分を含有してもよい。
上記昇温速度を制御する領域以外の昇温速度は特に限定しないが、１℃／ｓ以下の場合、昇温に時間がかかりすぎてしまい、製造効率が低下する場合がある。１２０℃／ｓを超えると、効果が飽和し、コストアップとなる場合がある。
A cold-rolled steel plate or a hot-rolled steel plate is preferably subjected to an electrolytic pickling treatment after continuous annealing. Next, chemical conversion treatment is performed.
In the annealing furnace, a heating step of heating the steel sheet to a predetermined temperature is performed in the heating zone in the previous stage, a soaking step in which the steel plate is maintained at a predetermined temperature for a predetermined time in a soaking zone in the subsequent stage, and then a cooling step is performed.
As described above, in the heating process, the temperature range in the annealing furnace: 600 ° C. or more and A ° C. or less (A: 700 ≦ A ≦ 1000) is set to a temperature increase rate of 8 ° C./s or more, and in the soaking process, In the annealing furnace, the temperature range of 800 ° C. or more and 1000 ° C. or less is set to a hydrogen concentration in the atmosphere: 26 vol% or more. In the cooling process, the temperature range of 700 ° C. or more is set to a hydrogen concentration in the atmosphere: 26 vol% or more. It anneals by controlling so that it may become.
The hydrogen concentration in the atmosphere in the annealing furnace other than the region where the hydrogen concentration is controlled is not particularly limited. The hydrogen concentration in the atmosphere may be lower than 26 vol%. 5-10 vol% which is a normal operating condition may be sufficient.
In addition, the gaseous component in an annealing furnace consists of nitrogen gas and an unavoidable impurity gas other than hydrogen gas. Other gas components may be included as long as the effects of the present invention are not impaired.
There is no particular limitation on the temperature increase rate other than the region where the temperature increase rate is controlled, but if it is 1 ° C./s or less, it takes too much time to increase the temperature, and the production efficiency may decrease. If it exceeds 120 ° C./s, the effect may be saturated and the cost may be increased.
冷却後、必要に応じて焼入れ、焼き戻しを行っても良い。この条件は特に限定しないが、焼き戻しは１５０〜４００℃の温度で行うのが好ましい。１５０℃未満では伸びが劣化する傾向にあり、４００℃超えでは硬度が低下する傾向にあるためである。 After cooling, quenching and tempering may be performed as necessary. This condition is not particularly limited, but tempering is preferably performed at a temperature of 150 to 400 ° C. This is because the elongation tends to deteriorate when the temperature is lower than 150 ° C., and the hardness tends to decrease when the temperature exceeds 400 ° C.
本発明においては、電解酸洗を実施しなくとも良好な化成処理性は確保可能であるが、焼鈍時に不可避的に発生する微量な表面濃化物を除去し、より良好な化成処理性を確保する目的で、電解酸洗を行うことが好ましい。電解酸洗の条件は特に限定しないが、焼鈍後に形成された不可避的に表面濃化したＳｉやＭｎの酸化物を効率的に除去するため、電流密度が１Ａ／ｄｍ２以上の交番電解とすることが好ましい。交番電解とする理由は、鋼板を陰極に保持したままでは酸洗効果が小さく、逆に鋼板を陽極に保持したままでは電解時に溶出するＦｅが酸洗液中に蓄積し、酸洗液中のＦｅ濃度が増大してしまい、鋼板表面に付着すると乾き汚れ等の問題が発生してしまうためである。さらに、電解酸洗に用いる酸洗液は特に限定しないが、硝酸やフッ化水素酸は設備に対する腐食性が強く取り扱いに注意を要するため、好ましくない。また塩酸は陰極から塩素ガスを発生する可能性があり好ましくない。このため、腐食性や環境を考慮すると硫酸の使用が好ましい。硫酸濃度は５質量％以上２０質量％以下が好ましい。硫酸濃度が５質量％未満では導電率が低くなることから電解時の浴電圧が上昇し、電源負荷が大きくなってしまう場合がある。一方、２０質量％超えの場合は、ドラッグアウトによる損失が大きくコスト的に問題となる場合がある。電解液の温度は４０℃以上７０℃以下が好ましい。連続電解することによる発熱で浴温が上昇することから、４０℃未満に温度を維持することは困難の場合がある。また、電解槽のライニングの耐久性の観点から温度が７０℃を超えることは好ましくない。 In the present invention, good chemical conversion treatment can be ensured without carrying out electrolytic pickling, but a small amount of surface condensate inevitably generated during annealing is removed to ensure better chemical conversion treatment. For the purpose, it is preferable to perform electrolytic pickling. The conditions of the electrolytic pickling are not particularly limited, but in order to efficiently remove the inevitably surface-enriched Si and Mn oxides formed after annealing, an alternating electrolysis with a current density of 1 A / dm 2 or more is used. It is preferable. The reason for alternating electrolysis is that the pickling effect is small when the steel plate is held at the cathode, and conversely, Fe that is eluted during electrolysis accumulates in the pickling solution while the steel plate is held at the anode. This is because if the Fe concentration increases and adheres to the surface of the steel sheet, problems such as dry dirt occur. Furthermore, the pickling solution used for the electrolytic pickling is not particularly limited, but nitric acid and hydrofluoric acid are not preferable because they are highly corrosive to equipment and require careful handling. Hydrochloric acid is not preferred because it may generate chlorine gas from the cathode. For this reason, use of sulfuric acid is preferable in consideration of corrosivity and environment. The sulfuric acid concentration is preferably 5% by mass or more and 20% by mass or less. If the sulfuric acid concentration is less than 5% by mass, the electrical conductivity will be low, so that the bath voltage during electrolysis will rise and the power load may become large. On the other hand, if it exceeds 20% by mass, the loss due to drag-out may be large, which may cause a problem in cost. The temperature of the electrolytic solution is preferably 40 ° C. or higher and 70 ° C. or lower. Since the bath temperature rises due to heat generated by continuous electrolysis, it may be difficult to maintain the temperature below 40 ° C. Moreover, it is not preferable that temperature exceeds 70 degreeC from a durable viewpoint of the lining of an electrolytic cell.
以上により、本発明の高強度鋼板が製造される。そして、以下のように、鋼板表層構造に特徴を有することになる。
鋼板表面から１００μｍ以内の鋼板表層部では、Ｆｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、Ｂ、Ｎｂ、Ｔｉ、Ｃr、Ｍｏ、Ｃu、Ｎｉの中から選ばれる１種以上の酸化物の形成が合計で片面あたり０．０５０ｇ／ｍ２以下に抑制される。
鋼中にＳｉ及び多量のＭｎが添加された高強度鋼板において、耐食性を満足させるためには、腐食の起点になる可能性がある鋼板表層の内部酸化を極力少なくすることが求められる。そこで、本発明では、化成処理性を確保するために焼鈍工程において酸素ポテンシャルを低下させることで易酸化性元素であるＳｉやＭｎ等の地鉄表層部における活量を低下させる。そして、これらの元素の表面濃化を抑制し、結果的に化成処理性を改善する。さらに、鋼板表層部に形成する内部酸化も抑制され、耐食性が改善することになる。このような効果は、下地鋼板表面から１００μｍ以内の鋼板表層部に、Ｆｅ、Ｓｉ、Ｍｎ、Ａｌ、Ｐ、Ｂ、Ｎｂ、Ｔｉ、Ｃｒ、Ｍｏ、Ｃｕ、Ｎｉの中から選ばれる一種以上の酸化物の形成量を合計で０．０５０ｇ／ｍ２以下に抑制することで認められる。酸化物形成量の合計（以下、内部酸化量と称す）が０．０５０ｇ／ｍ２超えでは、耐食性が劣化する。また、内部酸化量を０．０００１ｇ／ｍ２未満に抑制しても、耐食性改善効果は飽和するため、内部酸化量の下限は０．０００１ｇ／ｍ２が好ましい。
As described above, the high-strength steel sheet of the present invention is manufactured. And it has the characteristics in a steel plate surface layer structure as follows.
In the steel plate surface layer portion within 100 μm from the steel plate surface, the formation of one or more oxides selected from Fe, Si, Mn, Al, P, B, Nb, Ti, Cr, Mo, Cu, and Ni is total. It is suppressed to 0.050 g / m 2 or less per one side.
In a high-strength steel sheet in which Si and a large amount of Mn are added to steel, in order to satisfy the corrosion resistance, it is required to minimize the internal oxidation of the steel sheet surface layer that may be a starting point of corrosion. Therefore, in the present invention, in order to ensure chemical conversion, the oxygen potential in the annealing process is lowered to lower the activity in the surface layer portion of the iron base such as Si and Mn which are easily oxidizable elements. And the surface concentration of these elements is suppressed, and as a result, chemical conversion property is improved. Furthermore, the internal oxidation formed in the steel plate surface layer portion is also suppressed, and the corrosion resistance is improved. Such an effect is obtained by applying one or more kinds of oxidation selected from Fe, Si, Mn, Al, P, B, Nb, Ti, Cr, Mo, Cu, and Ni to the steel sheet surface layer portion within 100 μm from the surface of the base steel plate. It is recognized by suppressing the formation amount of the product to 0.050 g / m 2 or less in total. When the total oxide formation amount (hereinafter referred to as internal oxidation amount) exceeds 0.050 g / m 2 , the corrosion resistance deteriorates. Moreover, even if the amount of internal oxidation is suppressed to less than 0.0001 g / m 2 , the corrosion resistance improving effect is saturated, so the lower limit of the amount of internal oxidation is preferably 0.0001 g / m 2 .
以下、本発明を、実施例に基いて具体的に説明する。
表１に示す鋼組成からなる熱延鋼板を酸洗し、黒皮スケールを除去した後、冷間圧延し、厚さ１．０ｍｍの冷延鋼板を得た。なお、一部は冷間圧延を実施せず、黒皮スケール除去後の熱延鋼板（厚さ２．０ｍｍ）ままの物も用意した。
Hereinafter, the present invention will be specifically described based on examples.
The hot-rolled steel sheet having the steel composition shown in Table 1 was pickled, and after removing the black scale, it was cold-rolled to obtain a cold-rolled steel sheet having a thickness of 1.0 mm. In addition, some did not implement cold rolling, but the thing with the hot-rolled steel plate (thickness 2.0mm) after black scale removal was also prepared.
次いで、上記で得た冷延鋼板及び熱延鋼板を、連続式焼鈍設備に装入した。焼鈍設備では、表２に示す通り、加熱過程における焼鈍炉内の６００℃以上の温度域の昇温速度、均熱過程における焼鈍炉内の８００℃以上１０００℃以下の温度域および冷却過程における焼鈍炉内の７００℃以上の温度域の水素濃度を制御して通板して焼鈍したのち、水焼入れ後に３００℃×１４０ｓ間の焼き戻しを行った。加熱炉ではラジアントチューブとインダクションヒーターによる加熱を行って昇温速度を８℃／ｓとした。引き続き、４０℃、５質量％の硫酸水溶液中、表２に示す電流密度条件にて電解酸洗を行い、供試材を得た。電解酸洗は陽極、陰極の順に３秒ずつの交番電解で行った。
なお、上記水素濃度を制御した領域以外の焼鈍炉の水素濃度は１０ｖｏｌ％とした。また、雰囲気の気体成分は窒素ガスと水素ガスおよび不可避的不純物気体とした。
Next, the cold-rolled steel plate and hot-rolled steel plate obtained above were charged into a continuous annealing facility. In the annealing equipment, as shown in Table 2, the heating rate in the temperature range of 600 ° C. or higher in the annealing furnace in the heating process, the temperature range of 800 ° C. or higher and 1000 ° C. or lower in the annealing furnace in the soaking process, and annealing in the cooling process After controlling the hydrogen concentration in the temperature range of 700 ° C. or higher in the furnace and passing through and annealing, tempering between 300 ° C. and 140 s was performed after water quenching. In the heating furnace, heating was performed with a radiant tube and an induction heater, and the rate of temperature increase was 8 ° C./s. Subsequently, electrolytic pickling was performed at 40 ° C. in a 5% by mass sulfuric acid aqueous solution under the current density conditions shown in Table 2 to obtain a test material. The electrolytic pickling was performed by alternating electrolysis for 3 seconds each in the order of the anode and the cathode.
The hydrogen concentration in the annealing furnace other than the region where the hydrogen concentration was controlled was 10 vol%. The gas components in the atmosphere were nitrogen gas, hydrogen gas, and unavoidable impurity gas.
以上により得られた供試材に対してＪＩＳ Ｚ ２２４１ 金属材料引張試験方法 に従い、引張強度（ＴＳ）、伸び（Ｅｌ）を測定した。また、化成処理性、電着塗装後の耐食性及び加工性を調査した。鋼板表層直下の１００μｍまので鋼板表層部に存在する酸化物の量（内部酸化量）を測定した。測定方法および評価基準を下記に示す。 Tensile strength (TS) and elongation (El) were measured for the specimens obtained as described above in accordance with JIS Z 2241 Metal Material Tensile Test Method. In addition, chemical conversion properties, corrosion resistance after electrodeposition coating, and workability were investigated. The amount of oxide (internal oxidation amount) present in the steel sheet surface layer up to 100 μm just below the steel sheet surface layer was measured. The measurement method and evaluation criteria are shown below.
化成処理性
化成処理性の評価方法を以下に記載する。
化成処理液は日本パーカライジング（株）製の化成処理液（パルボンドＬ３０８０（登録商標））を用い、下記方法で化成処理を施した。
日本パーカライジング（株）製の脱脂液ファインクリーナー（登録商標）で脱脂したのち、水洗し、次に日本パーカライジング（株）製の表面調整液プレパレンＺ（登録商標）で３０ｓ表面調整を行い、４３℃の化成処理液（パルボンドＬ３０８０）に１２０ｓ浸漬した後、水洗し、温風乾燥した。
化成処理後の供試材を走査型電子顕微鏡（ＳＥＭ）で倍率５００倍で無作為に５視野を観察し、化成処理皮膜のスケ面積率を画像処理により測定し、スケ面積率によって以下の評価を行った。○が合格レベルである。
○：１０％以下
×：１０％超
電着塗装後の耐食性
上記の方法で得られた化成処理を施した供試材より寸法７０ｍｍ×１５０ｍｍの試験片を切り出し、日本ペイント（株）製のＰＮ−１５０Ｇ（登録商標）でカチオン電着塗装（焼付け条件：１７０℃×２０分、膜厚２５μｍ）を行った。その後、端部と評価しない側の面をＡｌテープでシールし、カッターナイフにて地鉄に達するクロスカット（クロス角度６０°）を入れ、供試材とした。
The chemical conversion property evaluation method of chemical conversion property is described below.
A chemical conversion treatment liquid (Palbond L3080 (registered trademark)) manufactured by Nihon Parkerizing Co., Ltd. was used as the chemical conversion treatment liquid, and the chemical conversion treatment was performed by the following method.
After degreasing with a degreasing liquid Fine Cleaner (registered trademark) manufactured by Nihon Parkerizing Co., Ltd., washing with water, and then adjusting the surface for 30 s with surface conditioning solution preparen Z (registered trademark) manufactured by Nihon Parkerizing Co., Ltd. After being immersed in a chemical conversion treatment solution (Palbond L3080) for 120 s, it was washed with water and dried with warm air.
The sample after the chemical conversion treatment was randomly observed with a scanning electron microscope (SEM) at a magnification of 500 times, the scale area ratio of the chemical conversion film was measured by image processing, and the following evaluation was made based on the scale area ratio. Went. ○ is an acceptable level.
○: 10% or less ×: More than 10% Corrosion resistance after electrodeposition coating A test piece having a size of 70 mm × 150 mm was cut out from the test material subjected to chemical conversion treatment obtained by the above method, and PN made by Nippon Paint Co., Ltd. Cationic electrodeposition coating (baking conditions: 170 ° C. × 20 minutes, film thickness 25 μm) was performed with −150 G (registered trademark). Thereafter, the end surface and the side not evaluated were sealed with Al tape, and a cross cut (cross angle 60 °) reaching the ground iron with a cutter knife was used as a test material.
次に、供試材を５質量％ＮａＣｌ水溶液（５５℃）中に、２４０時間浸漬後に取り出し、水洗、乾燥後にクロスカット部をテープ剥離し、剥離幅を測定し、以下の評価を行った。○が合格レベルである
○：剥離幅が片側２．５ｍｍ未満
×：剥離幅が片側２．５ｍｍ以上
加工性
加工性は、試料から圧延方向に対して９０°方向にＪＩＳ５号引張試験片を採取し、ＪＩＳ Ｚ ２２４１の規定に準拠してクロスヘッド速度１０ｍｍ／ｍｉｎ一定で引張試験を行い、引張り強度（ＴＳ／ＭＰａ）と伸び（Ｅｌ％）を測定し、ＴＳが６５０ＭＰａ未満の場合は、ＴＳ×Ｅｌ≧２２０００のものを良好、ＴＳ×Ｅｌ＜２２０００のものを不良とした。ＴＳが６５０ＭＰａ以上９００ＭＰａの場合は、ＴＳ×Ｅｌ≧２００００のものを良好、ＴＳ×Ｅｌ＜２００００のものを不良とした。ＴＳが９００ＭＰａ以上の場合は、ＴＳ×Ｅｌ≧１８０００のものを良好、ＴＳ×Ｅｌ＜１８０００のものを不良とした。
Next, the test material was taken out after being immersed in a 5% by mass NaCl aqueous solution (55 ° C.) for 240 hours, washed with water and dried, and then the tape was peeled off, the peel width was measured, and the following evaluation was performed. ○ is acceptable level ○: Peeling width is less than 2.5 mm on one side ×: Peeling width is 2.5 mm or more on one side Workability is obtained by taking a JIS No. 5 tensile test piece from the sample in a 90 ° direction with respect to the rolling direction. In accordance with the provisions of JIS Z 2241, a tensile test is performed at a constant crosshead speed of 10 mm / min, tensile strength (TS / MPa) and elongation (El%) are measured, and when TS is less than 650 MPa, TS The case where xE1 ≧ 22000 was good, and the case where TS × El <22000 was bad. When TS was 650 MPa or more and 900 MPa, TS × El ≧ 20000 was judged good, and TS × El <20000 was judged poor. When TS was 900 MPa or more, TS × El ≧ 18000 was judged good, and TS × El <18000 was judged poor.
鋼板表層１００μｍまでの領域における内部酸化量
内部酸化量は、「インパルス炉溶融−赤外線吸収法」により測定した。ただし、素材（すなわち焼鈍を施す前の供試材）に含まれる酸素量を差し引く必要があるので、本発明では、連続焼鈍後の供試材の両面の表層部を１００μｍ以上研磨して鋼中酸素濃度を測定し、その測定値を素材に含まれる酸素量ＯＨとし、また、連続焼鈍後の供試材の板厚方向全体での鋼中酸素濃度を測定して、その測定値を内部酸化後の酸素量ＯＩとした。このようにして得られた供試材の内部酸化後の酸素量ＯＩと、素材に含まれる酸素量ＯＨとを用いて、ＯＩとＯＨの差（＝ＯＩ−ＯＨ）を算出し、さらに片面単位面積（すなわち１ｍ２）当たりの量に換算した値（ｇ／ｍ２）を内部酸化量とした。
The amount of internal oxidation in the region of the steel sheet surface layer of up to 100 μm was measured by “impulse furnace melting-infrared absorption method”. However, since it is necessary to subtract the amount of oxygen contained in the material (ie, the specimen before annealing), in the present invention, the surface layer portions on both sides of the specimen after continuous annealing are polished by 100 μm or more in the steel. Measure the oxygen concentration, set the measured value as the amount of oxygen OH contained in the material, and measure the oxygen concentration in the steel in the entire thickness direction of the specimen after continuous annealing, and measure the measured value internally. The subsequent oxygen amount OI was used. The difference between OI and OH (= OI-OH) was calculated using the oxygen amount OI after the internal oxidation of the test material thus obtained and the oxygen amount OH contained in the material, and further a single-sided unit. area (i.e. 1 m 2) value converted into the amount per (g / m 2) as an internal oxide amount.
以上により得られた結果を製造条件と併せて表２に示す。 The results obtained as described above are shown in Table 2 together with the production conditions.
表２から明らかなように、本発明例は、Ｓｉ、Ｍｎ等の易酸化性元素を多量に含有する高強度鋼板であるにもかかわらず、化成処理性、電着塗装後の耐食性、加工性に優れることがわかる。
一方、比較例では、化成処理性、電着塗装後の耐食性、加工性のいずれか一つ以上が劣る。
As is apparent from Table 2, the present invention example is a high-strength steel sheet containing a large amount of easily oxidizable elements such as Si and Mn, but chemical conversion treatment, corrosion resistance after electrodeposition coating, workability It turns out that it is excellent.
On the other hand, in the comparative example, any one or more of chemical conversion property, corrosion resistance after electrodeposition coating, and workability is inferior.
本発明の高強度鋼板は、化成処理性、電着塗装後の耐食性、加工性に優れ、自動車の車体そのものを軽量化かつ高強度化するための表面処理鋼板として利用することができる。また、自動車以外にも、素材鋼板に防錆性を付与した表面処理鋼板として、家電、建材の分野等、広範な分野で適用できる。 The high-strength steel sheet of the present invention is excellent in chemical conversion treatment, corrosion resistance after electrodeposition coating, and workability, and can be used as a surface-treated steel sheet for reducing the weight and increasing the strength of the automobile body itself. In addition to automobiles, the steel sheet can be applied in a wide range of fields such as home appliances and building materials as a surface-treated steel sheet provided with rust prevention properties.
Claims (4)
加熱過程では、焼鈍炉内温度：６００℃以上Ａ℃以下の温度域を昇温速度：８℃/s以上とし、
かつ、均熱過程では、焼鈍炉内温度：８００℃以上１０００℃以下の温度域を雰囲気中の水素濃度：２６ｖｏｌ%以上とし、
かつ、冷却過程では、焼鈍炉内温度：７００℃以上の温度域を雰囲気中の水素濃度：２６ｖｏｌ%以上とすることを特徴とする高強度鋼板の製造方法。
ただし、Ａ：７００≦Ａ≦１０００である。 In mass%, C: 0.01 to 0.18%, Si: 0.4 to 2.0%, Mn: 1.0 to 3.0%, Al: 0.001 to 1.0%, P: When continuously annealing a steel sheet containing 0.005 to 0.060%, S ≦ 0.01%, the balance being Fe and inevitable impurities,
In the heating process, the temperature range in the annealing furnace: 600 ° C. or more and A ° C. or less is set to a temperature increase rate of 8 ° C./s or more,
In the soaking process, the temperature in the annealing furnace: 800 ° C. or higher and 1000 ° C. or lower is set to the hydrogen concentration in the atmosphere: 26 vol% or higher,
And in the cooling process, the temperature range in an annealing furnace: 700 degreeC or more is made into hydrogen concentration in atmosphere: 26 vol% or more, The manufacturing method of the high strength steel plate characterized by the above-mentioned.
However, A: 700 ≦ A ≦ 1000.
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| WO2017141952A1 (en) * | 2016-02-18 | 2017-08-24 | Ｊｆｅスチール株式会社 | High-strength cold-rolled steel sheet |
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| CN108660384A (en) * | 2017-03-30 | 2018-10-16 | 宝山钢铁股份有限公司 | A kind of low-alloy steel of sulfuric acid corrosion resistant, steel pipe, steel plate and its manufacturing method |
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