JP5402357B2 - Method for producing high-Si cold-rolled steel sheet with excellent chemical conversion properties - Google Patents
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本発明は、リン酸塩処理等の化成処理を施したのち塗装をして使用される自動車用高Ｓｉ冷延鋼板の製造方法に関する。特にＳｉの強化能を利用した引張強度５９０ＭＰａ以上で、ＴＳ×Ｅｌが１８０００ＭＰａ・％以上で加工性に優れた高Ｓｉ高強度冷延鋼板の製造に好適である。 The present invention relates to a method for producing a high-Si cold-rolled steel sheet for automobiles that is used after being subjected to chemical conversion treatment such as phosphate treatment. In particular, it is suitable for production of a high-Si high-strength cold-rolled steel sheet having a tensile strength of 590 MPa or more utilizing the strengthening ability of Si and TS × El of 18000 MPa ·% or more and excellent workability.
近年自動車の軽量化の観点から、引張強度５９０ＭＰａ以上の高い強度を有する冷延鋼板の需要が高まっている。自動車用冷延鋼板は塗装を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。冷延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ひとつである。 In recent years, from the viewpoint of reducing the weight of automobiles, there is an increasing demand for cold-rolled steel sheets having a high tensile strength of 590 MPa or more. Cold-rolled steel sheets for automobiles are used after being coated, and a chemical conversion treatment called a phosphate treatment is performed as a pretreatment for the coating. The chemical conversion treatment of cold-rolled steel sheet is one of the important treatments for ensuring the corrosion resistance after painting.
冷延鋼板の強度を高めるためには、Ｓｉの添加が有効である。しかし、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、鋼板最表面にＳｉ酸化物（ＳｉＯ２）の薄膜を形成する。それ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ミクロな領域（スケ）ができ、化成処理性が低下する。 In order to increase the strength of the cold rolled steel sheet, addition of Si is effective. However, during continuous annealing, Si is oxidized even in a reducing N 2 + H 2 gas atmosphere in which Fe oxidation does not occur (reducing Fe oxide), and a thin film of Si oxide (SiO 2 ) is formed on the outermost surface of the steel sheet. Form. Since this inhibits the formation reaction of the chemical conversion film during the chemical conversion treatment, a micro region (scaling) where the chemical conversion film is not generated is formed, and the chemical conversion treatment performance is lowered.
高Ｓｉ冷延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には、酸化性雰囲気中で鋼板温度を３５０〜６５０℃に到達せしめて鋼板表面に酸化膜を形成させ、しかる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。 As a conventional technique for improving the chemical conversion processability of a high-Si cold-rolled steel sheet, Patent Document 1 discloses that an oxide film is formed on the steel sheet surface by causing the steel sheet temperature to reach 350 to 650 ° C. in an oxidizing atmosphere, and then reduced. A method of heating to a recrystallization temperature and cooling in an acidic atmosphere is described.
また、特許文献２には、質量％で、Ｓｉを０．１％以上、及び／又は、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。 Patent Document 2 discloses a cold-rolled steel sheet containing, by mass%, Si of 0.1% or more and / or Mn of 1.0% or more in an iron oxidizing atmosphere at a steel plate temperature of 400 ° C. or more. A method is described in which an oxide film is formed on the surface of the steel sheet, and then the oxide film on the surface of the steel sheet is reduced in an iron reducing atmosphere.
さらに、特許文献３には、Ｓｉを０．１ｗｔ％以上３．０ｗｔ％以下含有する高強度冷延鋼板表層の結晶粒界及び／又は結晶粒内に、化成処理性等の改良に有効な酸化物を有することを特徴とする高強度冷延鋼板が、特許文献４には、鋼板表面と直交する方向の断面を電子顕微鏡にて倍率５００００倍以上で観察したときに、鋼板表面長さ１０μｍに占めるＳｉ含有酸化物の割合が、任意に選択される５箇所の平均で８０％以下となるようにするリン酸塩処理性に優れた鋼板が、特許文献５には、ｍａｓｓ％で、Ｃ：０．１％超、Ｓｉ：０．４％以上を含み、Ｓｉ含有量（ｍａｓｓ％）／Ｍｎ含有量（ｍａｓｓ％）が０．４以上であり、引張強さが７００ＭＰａ以上であって、鋼板表面におけるＳｉを主成分とするＳｉ基酸化物の表面被覆率が２０面積％以下で、かつ前記Ｓｉ基酸化物の被覆領域において当該領域内に内接される最大円の直径が５μｍ以下とされた化成処理性に優れる高強度冷延鋼板が、特許文献６には、質量％で、Ｃ：０．０１〜０．３％、Ｓｉ：０．２〜３．０％、Ｍｎ：０．１〜３．０％、Ａｌ：０．０１〜２．０％を含有し、引張強度が５００ＭＰａ以上の高張力鋼板において、該鋼板表面の結晶粒の平均粒径が０．５μｍ以下であり、かつ該鋼板表面の幅１０μｍ以上の観察領域を断面ＴＥＭ観察用に薄片加工し、該薄片試料を１０ｎｍ以下の酸化物が観察できる条件でＴＥＭ観察により測定した、酸化シリコンおよびマンガンシリケートの１種または２種をこれらの合計量で７０質量％以上含有する酸化物種が、上記断面からみた粒界領域表面に対して３０％以下存在し、該鋼板表面からの深さで０．１〜１．０μｍの範囲内に存在する上記酸化物種の粒径が０．１μｍ以下であることを特徴とする化成処理性に優れた高張力鋼板が、記載されている。 Further, Patent Document 3 discloses an oxidation effective for improving chemical conversion treatment properties, etc. in the crystal grain boundaries and / or crystal grains of the surface layer of a high strength cold-rolled steel sheet containing 0.1 wt% or more and 3.0 wt% or less of Si. A high-strength cold-rolled steel sheet characterized by having an article has a steel sheet surface length of 10 μm in Patent Document 4 when a cross section in a direction orthogonal to the steel sheet surface is observed with an electron microscope at a magnification of 50000 times or more. A steel sheet excellent in phosphatability in which the ratio of the Si-containing oxide to occupy is 80% or less on an average of five arbitrarily selected points is disclosed in Patent Document 5 as mass%, C: More than 0.1%, Si: 0.4% or more, Si content (mass%) / Mn content (mass%) is 0.4 or more, tensile strength is 700 MPa or more, Surface coverage of Si-based oxide containing Si as the main component on the surface Patent Document 6 discloses a high-strength cold-rolled steel sheet that is 20 area% or less and that has excellent chemical conversion treatment properties in which the diameter of the maximum circle inscribed in the Si-based oxide coating region is 5 μm or less. Is, by mass%, C: 0.01 to 0.3%, Si: 0.2 to 3.0%, Mn: 0.1 to 3.0%, Al: 0.01 to 2.0% In a high-tensile steel plate containing a tensile strength of 500 MPa or more, an observation region having an average grain size of 0.5 μm or less on the surface of the steel plate and a width of 10 μm or more on the surface of the steel plate is sliced for TEM observation. An oxide species containing one or two types of silicon oxide and manganese silicate in a total amount of 70% by mass or more measured by TEM observation under conditions where the oxide can be observed below 10 nm. 3 with respect to the surface of the grain boundary region as seen from the cross section. Excellent in chemical conversion treatment, characterized by being 0% or less and having a particle size of 0.1 μm or less in the range of 0.1 to 1.0 μm in depth from the steel sheet surface. High tensile steel plates are described.
特許文献１の製造方法では、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、酸化膜が厚くなりすぎて、あと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はく離を生じ、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。 In the manufacturing method of Patent Document 1, 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 oxidation does not occur sufficiently, or the oxide film becomes too thick, and in a subsequent reducing atmosphere. In some cases, an oxide film remains or peels during annealing, and surface properties may deteriorate. In the examples, a technique for oxidizing in the air is described. However, in the oxidation in the air, a thick oxide is formed and subsequent reduction is difficult, or a reducing atmosphere with a high hydrogen concentration is required. There is a problem.
特許文献２の製造方法は、４００℃以上で空気比０．９３以上１．１０以下の直火バーナを用いて鋼板表面のＦｅを酸化したのち、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、化成処理性を低下させるＳｉＯ２の最表面での酸化を抑制し、最表面にＦｅの還元層を形成させる方法である。特許文献２には、直火バーナでの加熱温度が具体的に記されていないが、Ｓｉを多く（０．６％以上）含有する場合には、Ｆｅより酸化しやすい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。 The manufacturing method of Patent Document 2 is an N 2 + H 2 gas atmosphere in which Fe on the steel sheet surface is oxidized using a direct fire burner having an air ratio of 0.93 or more and 1.10 or less at 400 ° C. or higher, and then Fe oxide is reduced. Is a method of suppressing oxidation at the outermost surface of SiO 2 that lowers the chemical conversion processability by annealing and forming a reduced layer of Fe on the outermost surface. Patent Document 2 does not specifically describe the heating temperature in an open flame burner, but when it contains a large amount of Si (0.6% or more), the amount of oxidation of Si that is easier to oxidize than Fe is large. Therefore, oxidation of Fe is suppressed, or oxidation of Fe itself is too little. As a result, formation of the surface Fe reduction layer after reduction was insufficient, and SiO 2 was present on the steel plate surface after reduction, and there was a case where the conversion film was scaled.
特許文献３の鋼板は、Ｓｉ酸化物を鋼板の内部に形成させ、表面のＳｉ酸化物を無くすことにより、化成処理性を改善する鋼板である。製造方法は、鋼板を冷間圧延する前段階の熱間圧延時に、高温（実施例では６２０℃以上が良好）で巻き取り、その熱を利用しＳｉ酸化物を鋼板の内部に形成させるものであるが、巻き取られたコイルは外側の冷却速度は速く、内側の冷却速度は遅いため、鋼板長手方向の温度ムラが大きく、コイル全長で均一な表面品質を得るのが難しいという問題があった。 The steel plate of patent document 3 is a steel plate which improves chemical conversion property by forming Si oxide in the inside of a steel plate, and eliminating Si oxide on the surface. The manufacturing method involves winding at a high temperature (in the embodiment, good at 620 ° C. or higher) at the time of hot rolling before the cold rolling of the steel sheet, and using that heat to form Si oxide inside the steel sheet. However, the wound coil has a fast outer cooling rate and a slow inner cooling rate, which causes large temperature unevenness in the longitudinal direction of the steel sheet, and it is difficult to obtain uniform surface quality over the entire length of the coil. .
特許文献４、５、６は、規定の仕方は異なるが、表面を覆うＳｉ酸化物量の上限を規定した鋼板である。製造方法としては、連続焼鈍の昇温中または均熱中に還元性であるＮ２＋Ｈ２ガス雰囲気の露点（あるいは水蒸気水素分圧比）をある範囲に制御し、Ｓｉを鋼板内部に酸化させるものである。その露点範囲は特許文献４では−２５℃以上、特許文献５では−２０℃から０℃と記載されている。特許文献６では予熱、昇温、再結晶化のそれぞれの工程で水蒸気水素分圧比の範囲を規制する方法を採っている。これらの方法では、一般的には露点が−２５℃以下になるＮ２＋Ｈ２ガス雰囲気の露点を、水蒸気や空気を導入すること等により高めに制御する必要があり、操業制御性の観点から問題があり、その結果、良好な化成処理性が安定して得られなかった。また、露点を高く（あるいは水蒸気水素分圧比を高く）することは、雰囲気の酸化性を高めるため、炉壁や炉内のロールの劣化を速めたり、ピックアップと呼ばれるスケール疵を鋼板表面に発生させる場合があった。 Patent Documents 4, 5, and 6 are steel plates that define the upper limit of the amount of Si oxide covering the surface, although the way of defining is different. As a manufacturing method, the dew point (or steam hydrogen partial pressure ratio) of the reducing N 2 + H 2 gas atmosphere is controlled within a certain range during temperature rise or soaking of continuous annealing, and Si is oxidized inside the steel sheet. is there. The dew point range is described in Patent Document 4 as -25 ° C or higher, and in Patent Document 5 as -20 ° C to 0 ° C. Patent Document 6 adopts a method of regulating the range of the steam hydrogen partial pressure ratio in each step of preheating, temperature elevation, and recrystallization. In these methods, it is generally necessary to control the dew point of the N 2 + H 2 gas atmosphere at which the dew point is −25 ° C. or lower by introducing water vapor or air, etc., from the viewpoint of operation controllability. There was a problem, and as a result, good chemical conversion treatment was not stably obtained. In addition, increasing the dew point (or increasing the steam hydrogen partial pressure ratio) increases the oxidization of the atmosphere, so that the deterioration of the furnace wall and the rolls in the furnace is accelerated, and scale soot called pickup is generated on the steel sheet surface. There was a case.
本発明は、前記課題を解決した、均熱炉の還元性雰囲気の露点あるいは水蒸気水素分圧比を制御することなく、かつ、Ｓｉを０．６％以上含有しても、良好な化成処理性を有する高Ｓｉ冷延鋼板の製造方法を提供することを目的とする。 The present invention solves the above-mentioned problems, without controlling the dew point of the reducing atmosphere of the soaking furnace or the steam hydrogen partial pressure ratio, and even if Si is contained in an amount of 0.6% or more, good chemical conversion treatment performance is achieved. It aims at providing the manufacturing method of the high Si cold-rolled steel plate which has.
上記課題を解決する本発明の手段は、下記の通りである。 Means of the present invention for solving the above problems are as follows.
（１）Ｃ：０．０５〜０．３質量％、
Ｓｉ：０．５６〜３質量％、
Ｍｎ：１．０〜３．０質量％、
Ｐ：０．１質量％以下、
Ｓ：０．０５質量％以下、
Ａｌ：０．０１〜１質量％、
Ｎ：０．０１質量％以下、
を含有し、残部がＦｅおよび不可避的不純物からなる成分組成を有する冷延鋼板を連続焼鈍する際に、昇温時に鋼板温度が少なくとも５５０℃以上で空気比０．９５以上の直火バーナを用いて鋼板を加熱し、鋼板温度が７５０℃以上になるまで昇温し、その後、露点−２５℃以下の、１〜１０体積％Ｈ２＋残部Ｎ２ガス雰囲気の炉で均熱焼鈍することを特徴とする化成処理性に優れた高Ｓｉ冷延鋼板の製造方法。
（２）前記（１）において、空気比０．９５以上の直火バーナを用いた加熱は鋼板温度が８００℃以下で行うことを特徴とする化成処理性に優れた高Ｓｉ冷延鋼板の製造方法。
(1) C : 0.05 to 0.3% by mass,
Si: 0.56-3 mass%,
Mn: 1.0 to 3.0% by mass,
P: 0.1% by mass or less,
S: 0.05 mass% or less,
Al: 0.01-1% by mass,
N: 0.01% by mass or less,
When a cold-rolled steel sheet having a composition composed of Fe and the inevitable impurities is continuously annealed, a direct fire burner having a steel sheet temperature of at least 550 ° C. and an air ratio of 0.95 or more is used at the time of temperature rise steel sheet was heated Te, the temperature was raised to steel temperature ing above 750 ° C., then the dew point of -25 ° C. or less, 1 to 10 vol% H 2 + balance N 2 to soak annealing furnace gas atmosphere producing how high Si cold rolled steel sheet excellent in chemical conversion treatability, wherein.
(2) Production of a high-Si cold-rolled steel sheet excellent in chemical conversion property, characterized in that in (1), heating using a direct fire burner having an air ratio of 0.95 or more is performed at a steel sheet temperature of 800 ° C or lower. Method.
（３）Ｃ：０．０５〜０．３質量％、
Ｓｉ：０．５６〜３質量％、
Ｍｎ：１．０〜３．０質量％、
Ｐ：０．１質量％以下、
Ｓ：０．０５質量％以下、
Ａｌ：０．０１〜１質量％、
Ｎ：０．０１質量％以下、
を含有し、残部がＦｅおよび不可避的不純物からなる成分組成を有する冷延鋼板を連続焼鈍する際に、昇温時に鋼板温度が少なくとも５５０℃以上で空気比０．９５以上の直火バーナを用いて鋼板を加熱し、その後空気比０．８９以下の直火バーナを用いて鋼板を加熱して鋼板温度が７５０℃以上になるまで昇温した後、露点が−２５℃以下の、１〜１０体積％Ｈ２＋残部Ｎ２ガス雰囲気の炉で均熱焼鈍することを特徴とする化成処理性に優れた高Ｓｉ冷延鋼板の製造方法。
（４）前記（３）において、空気比０．９５以上の直火バーナによる鋼板加熱時間は、空気比０．８９以下の直火バーナによる鋼板加熱時間以上であることを特徴とする化成処理性に優れた高Ｓｉ冷延鋼板の製造方法。
（５）前記（３）または（４）において、空気比０．８９以下の直火バーナを用いた加熱は鋼板温度が８００℃以下で行うことを特徴とする化成処理性に優れた高Ｓｉ冷延鋼板の製造方法。
(3) C: 0.05 to 0.3% by mass,
Si: 0.56-3 mass%,
Mn: 1.0 to 3.0% by mass,
P: 0.1% by mass or less,
S: 0.05 mass% or less,
Al: 0.01-1% by mass,
N: 0.01% by mass or less,
When a cold-rolled steel sheet having a composition composed of Fe and the inevitable impurities is continuously annealed, a direct fire burner having a steel sheet temperature of at least 550 ° C. and an air ratio of 0.95 or more is used at the time of temperature rise After heating the steel sheet using a direct fire burner with an air ratio of 0.89 or less until the steel sheet temperature is raised to 750 ° C. or higher, the dew point is −25 ° C. or lower, 1 to 10 vol% H 2 + manufacturing how high Si cold rolled steel sheet excellent in chemical conversion treatability, which comprises soaking annealing furnace balance N 2 gas atmosphere.
(4) In the above (3), the chemical conversion treatment property is characterized in that the heating time of the steel sheet by the direct fire burner having an air ratio of 0.95 or more is equal to or longer than the heating time of the steel sheet by a direct fire burner having an air ratio of 0.89 or less. For producing high-Si cold-rolled steel sheet with excellent resistance.
(5) In the above (3) or (4), heating using a direct fire burner with an air ratio of 0.89 or less is performed at a steel plate temperature of 800 ° C. or less, and high Si cooling excellent in chemical conversion processability A method for producing rolled steel sheets.
（６）前記（１）〜（５）のいずれかにおいて、さらに、鋼板がＣｒ、Ｍｏ、Ｎｉ、Ｃｕの１種または２種以上を各々０．０１〜１質量％含有することを特徴とする化成処理性に優れた高Ｓｉ冷延鋼板の製造方法。 (6) In any one of the above (1) to (5) , the steel sheet further includes 0.01 to 1% by mass of one or more of Cr, Mo, Ni, and Cu, respectively. producing how high Si cold rolled steel sheet excellent in chemical convertibility.
（７）前記（１）〜（６）のいずれかにおいて、さらに、鋼板がＴｉ、Ｎｂ、Ｖの１種又は２種以上を各々０．００１〜０．１質量％含有することを特徴とする化成処理性に優れた高Ｓｉ冷延鋼板の製造方法。 (7) the (1) any crab Oite to (6), further characterized in that the steel sheet is Ti, Nb, respectively one or more of V containing 0.001 to 0.1 wt% producing how high Si cold rolled steel sheet excellent in chemical conversion treatability to.
本発明によれば、直火バーナを用いた鋼板表面でのＦｅの酸化と、その後の還元を利用してＳｉを鋼板内部に酸化させることで、Ｓｉを０．６％以上含有する高Ｓｉ冷延鋼板について、化成処理性を改善するとともに、引張強度５９０ＭＰａ以上で、ＴＳ×Ｅｌが１８０００ＭＰａ・％以上で加工性の優れた高Ｓｉ冷延鋼板を製造することが出来る。また、焼鈍雰囲気の制御（特に露点を高く制御すること）が不要であるので、操業制御性の点で有利であり、また炉壁や炉内のロールの劣化を早めたり、ピックアップと呼ばれるスケール疵を鋼板表面に発生させたりする問題も改善することができる。 According to the present invention, high Si cooling containing 0.6% or more of Si by oxidizing Fe into the steel sheet using oxidation of Fe on the steel sheet surface using a direct fire burner and subsequent reduction. With respect to the rolled steel sheet, it is possible to improve the chemical conversion property, and it is possible to produce a high Si cold-rolled steel sheet having a tensile strength of 590 MPa or more, TS × El of 18000 MPa ·% or more and excellent workability. In addition, control of the annealing atmosphere (especially controlling the dew point to a high level) is unnecessary, which is advantageous in terms of operational controllability, speeds up deterioration of the furnace wall and rolls in the furnace, and scales called pickups. It is also possible to improve the problem of generating slag on the steel sheet surface.
本発明が対象とする鋼板の化学成分の限定理由を説明する。なお、成分に関する「％」表示は特に断らない限り質量％を意味する。 The reason for limiting the chemical components of the steel sheet to which the present invention is applied will be described. In addition, unless otherwise indicated, the "%" display regarding a component means the mass%.
Ｓｉは鋼板の加工性を低下させずに強度を上げる元素であり、０．６％未満では加工性すなわち、ＴＳ×Ｅｌが劣化する。さらに、好ましくは１．１０％を超えて含有させる。ただし３％を超えると鋼板の脆化が著しく、加工性が劣化し、また化成処理性が劣化するため、上限を３％とする。 Si is an element that increases the strength without reducing the workability of the steel sheet, and if it is less than 0.6%, the workability, that is, TS × El is deteriorated. Furthermore, it preferably contains more than 1.10%. However, if it exceeds 3%, the steel sheet becomes extremely brittle, the workability deteriorates, and the chemical conversion property deteriorates, so the upper limit is made 3%.
鋼板の化学成分は、Ｓｉの他に、金属組織をフェライト−マルテンサイト、ＴＲＩＰなどに制御し、所望する材質を得るために、固溶強化能およびマルテンサイト生成能を有するＣ、Ｍｎを、Ｃを０．０５％以上、好ましくは０．１０％以上を含有し、またＭｎを１．０％以上含有する。一方Ｃ、Ｍｎを過度に添加すると、鋼板の加工性が著しく低下することから、Ｃを０．３％以下、Ｍｎを３．０％以下とする。 In addition to Si, the chemical composition of the steel sheet is controlled to have a metal structure of ferrite-martensite, TRIP, etc., and in order to obtain a desired material, C and Mn having solid solution strengthening ability and martensite forming ability are added. Is 0.05% or more, preferably 0.10% or more, and Mn is 1.0% or more. On the other hand, when C and Mn are added excessively, the workability of the steel sheet is remarkably lowered, so C is 0.3% or less and Mn is 3.0% or less.
Ａｌは脱酸材として添加される。０．０１％未満では、その効果が不十分である。一方、１％を超えると、その効果が飽和し、不経済となる。したがって、Ａｌ量は０．０１〜１％とする。 Al is added as a deoxidizing material. If it is less than 0.01%, the effect is insufficient. On the other hand, if it exceeds 1%, the effect is saturated and uneconomical. Therefore, the Al content is 0.01 to 1%.
その他、不可避的不純物としてＰ、Ｓ、Ｎが含有される。Ｐは０．１％以下、好ましくは０．０１５％以下である。Ｓは０．０５％以下、好ましくは０．００３％以下である。Ｎは０．０１％以下である。 In addition, P, S, and N are contained as inevitable impurities. P is 0.1% or less, preferably 0.015% or less. S is 0.05% or less, preferably 0.003% or less. N is 0.01% or less.
また、材質および金属組織の制御のために、Ｃｒ、Ｍｏ、Ｎｉ、Ｃｕの１種または２種以上を各々０．０１〜１％含有してもよい。鋼板の強度を上げるため、Ｔｉ、Ｎｂ、Ｖの１種または２種以上を各々０．００１〜０．１％含有してもよい。素材の強度および塗装焼付け後の強度を上げるため、Ｂを０．０００３〜０．００５％含有させても良い。 Moreover, you may contain 0.01 to 1% of 1 type, or 2 or more types of Cr, Mo, Ni, and Cu, respectively, for control of a material and a metal structure. In order to increase the strength of the steel sheet, one or more of Ti, Nb, and V may be contained in an amount of 0.001 to 0.1%. In order to raise the intensity | strength of a raw material and the baking baking after baking, you may contain 0.0003 to 0.005% of B.
次に製造方法について説明する。 Next, a manufacturing method will be described.
上記成分組成の鋼を熱間圧延し、引き続き酸洗した後、冷間圧延を施し、その後連続焼鈍ラインで連続焼鈍する。連続焼鈍前までの冷延鋼板の製造方法は、特に限定されず、公知の方法を用いることが出来る。 The steel having the above component composition is hot-rolled, subsequently pickled, then cold-rolled, and then continuously annealed in a continuous annealing line. The manufacturing method of the cold rolled steel sheet before continuous annealing is not specifically limited, A well-known method can be used.
連続焼鈍ラインでは、昇温、均熱、冷却の連続する３工程が行われる。一般的な連続焼鈍ラインは、鋼板を加熱昇温する加熱炉、均熱する均熱炉、冷却炉を備える。あるいは加熱炉の前にさらに予熱炉を備える。 In the continuous annealing line, three steps of continuous temperature rise, soaking, and cooling are performed. A general continuous annealing line includes a heating furnace for heating and heating a steel plate, a soaking furnace for soaking, and a cooling furnace. Alternatively, a preheating furnace is further provided before the heating furnace.
昇温時には、空気比を０．９５以上に調整した直火バーナを用いた加熱炉で、鋼板温度５５０℃以上で加熱し、鋼板温度が６５０℃を超えるまで昇温する。これにより、鋼板表面にＦｅ酸化物が形成される。鋼板温度５５０℃超の温度から空気比を０．９５以上に調整した直火バーナを用いて鋼板を加熱しても十分なＦｅ酸化量は得られない。 At the time of temperature rise, it is heated at a steel plate temperature of 550 ° C. or higher in a heating furnace using a direct fire burner adjusted to an air ratio of 0.95 or higher, and the temperature is raised until the steel plate temperature exceeds 650 ° C. Thereby, Fe oxide is formed on the steel plate surface. Even if the steel sheet is heated using a direct flame burner in which the air ratio is adjusted to 0.95 or more from a temperature exceeding 550 ° C., a sufficient amount of Fe oxidation cannot be obtained.
鋼板温度５５０℃未満から空気比を０．９５以上に調整した直火バーナで加熱しても問題はないが、５５０℃未満の温度域では十分なＦｅ酸化量は得られない。Ｆｅ酸化物形成の観点からは、できるだけ高い温度まで到達させた方が良く、好ましくは鋼板温度が７００℃以上、より好ましくは７５０℃以上になるまで昇温する。しかし、過度に酸化させると、次の還元性雰囲気炉でＦｅ酸化物が剥離し、ピックアップの原因となるので、空気比を０．９５以上に調整した直火バーナを用いた加熱は鋼板温度が８００℃以下で行うことが好ましい。 There is no problem even if heating is performed with a direct flame burner in which the air ratio is adjusted to 0.95 or more from a steel plate temperature of less than 550 ° C., but a sufficient amount of Fe oxidation cannot be obtained in a temperature range of less than 550 ° C. From the viewpoint of Fe oxide formation, it is better to reach the highest possible temperature, and the temperature is preferably increased until the steel sheet temperature is 700 ° C. or higher, more preferably 750 ° C. or higher. However, if oxidized excessively, the Fe oxide peels off in the following reducing atmosphere furnace and causes pickup, so heating with a direct-fired burner with an air ratio adjusted to 0.95 or higher causes the steel plate temperature to It is preferable to carry out at 800 degrees C or less.
ここで、直火バーナとは、製鉄所の副生ガスであるコークス炉ガス（ＣＯＧ）等の燃料と空気を混ぜて燃焼させたバーナ火炎を直接鋼板表面に当てて鋼板を加熱するものである。直火バーナは、輻射方式の加熱よりも鋼板の昇温速度が速いため、加熱炉の炉長を短くしたり、ラインスピードを速く出来る利点がある。さらに、直火バーナは空気比を０．９５以上とし、燃料に対する空気の割合を多くすると、未燃の酸素が火炎中に残存し、その酸素で鋼板の酸化を促進することが可能となる。空気比が高い方が酸化性が強くなるため、Ｆｅ酸化物形成の観点からは、空気比はできるだけ高い方が良く、空気比は１．１０以上が好ましい。しかし、過度に酸化させると、次の還元性雰囲気の均熱炉でＦｅ酸化物が剥離し、ピックアップの原因となるので、１．３０以下とすることが好ましい。 Here, the direct fire burner heats the steel sheet by directly applying the burner flame, which is burned by mixing fuel and air, such as coke oven gas (COG), which is a by-product gas of an ironworks, to the surface of the steel sheet. . The direct fire burner has an advantage that the furnace length of the heating furnace can be shortened and the line speed can be increased because the heating rate of the steel sheet is faster than that of the radiation type heating. Further, when the direct fire burner has an air ratio of 0.95 or higher and the ratio of air to fuel is increased, unburned oxygen remains in the flame, and the oxygen can promote oxidation of the steel sheet. The higher the air ratio, the stronger the oxidizability. From the viewpoint of Fe oxide formation, the air ratio should be as high as possible, and the air ratio is preferably 1.10 or more. However, if it is excessively oxidized, the Fe oxide is peeled off in the following soaking furnace in a reducing atmosphere and causes pickup, so that it is preferably 1.30 or less.
直火バーナの燃料は、ＣＯＧ、液化天然ガス（ＬＮＧ）等を使用できる。 COG, liquefied natural gas (LNG), etc. can be used for the fuel of the direct fire burner.
加熱炉の前に予熱炉を備える場合、予熱炉の雰囲気は特に限定されない。通常行われている条件でよい。例えば、直火バーナを備えた加熱炉の高温の燃焼ガスを予熱炉に導入しても良い。また、予熱炉に、空気比０．７〜１．３の直火バーナを用いることも出来る。 When the preheating furnace is provided before the heating furnace, the atmosphere of the preheating furnace is not particularly limited. The usual conditions may be used. For example, you may introduce the high temperature combustion gas of the heating furnace provided with the direct-fired burner into the preheating furnace. In addition, a direct fire burner having an air ratio of 0.7 to 1.3 can be used for the preheating furnace.
直火バーナを備える加熱炉では、Ｆｅの過度の酸化を防止する点から、加熱炉前段は空気比０．９５以上の直火バーナを使用し、加熱炉後段は空気比０．８９以下の直火バーナ使用してもよい。この場合、加熱炉前段で空気比０．９５以上の直火バーナを少なくとも鋼板温度５５０℃以上で使用し、加熱炉出側で鋼板温度を７００℃以上にすれば、十分なＦｅ酸化量を得ることが可能である。Ｆｅ酸化物形成の観点からは、できるだけ高い温度まで到達させた方が良く、好ましくは鋼板温度が７５０℃以上になるまで昇温する。また、前記効果を得るには、空気比０．９５以上の直火バーナによる鋼板加熱時間は、空気比０．８９以下の直火バーナによる鋼板加熱時間以上とすることが好ましい。また加熱炉後段の直火バーナの空気比は燃焼効率の点から０．７以上が好ましい。また、空気比０．８９以下の直火バーナを用いた加熱雰囲気はＦｅ還元性であり、過度に高温まで加熱すると、次の均熱炉に入る前にＦｅ酸化物が還元されてしまい、均熱炉でのＦｅ酸化物の還元によるＳｉの内部酸化の生成が少なくなることから、空気比０．８９以下の直火バーナを用いた加熱は鋼板温度が８００℃以下で行うことが好ましい。 In a heating furnace equipped with a direct-fired burner, from the viewpoint of preventing excessive oxidation of Fe, a direct-fired burner having an air ratio of 0.95 or more is used for the front stage of the heating furnace, and a direct-fired burner having an air ratio of 0.89 or less is used for the latter stage of the heating furnace. A fire burner may be used. In this case, if a direct flame burner with an air ratio of 0.95 or more is used at a steel plate temperature of 550 ° C. or higher at the front stage of the heating furnace and the steel plate temperature is set to 700 ° C. or higher on the heating furnace outlet side, a sufficient amount of Fe oxidation is obtained. It is possible. From the viewpoint of Fe oxide formation, it is better to reach as high a temperature as possible, and the temperature is preferably increased until the steel sheet temperature reaches 750 ° C. or higher. Moreover, in order to acquire the said effect, it is preferable to make the steel plate heating time by the direct-fired burner with an air ratio of 0.95 or more into the steel plate heating time with the direct-fired burner with an air ratio of 0.89 or less. The air ratio of the direct-fired burner at the latter stage of the heating furnace is preferably 0.7 or more from the viewpoint of combustion efficiency. In addition, the heating atmosphere using an open flame burner with an air ratio of 0.89 or less is Fe reducing, and if heated to an excessively high temperature, the Fe oxide is reduced before entering the next soaking furnace, and soaking. Since generation of internal oxidation of Si due to reduction of Fe oxide in the heat furnace is reduced, it is preferable to perform heating using an open flame burner with an air ratio of 0.89 or less at a steel plate temperature of 800 ° C. or less.
直火バーナを用いて鋼板を上記のように加熱昇温した後、ラジアントチューブバーナを備えた均熱炉で均熱焼鈍する。均熱炉に導入する雰囲気ガスは、１〜１０体積％Ｈ２＋残りＮ２である。雰囲気ガスのＨ２％を１〜１０体積％に限定したのは、１体積％未満では
連続的に通板される鋼板表面のＦｅ酸化物を還元するのにＨ２が不足し、１０体積％を超えてもＦｅ酸化物の還元は飽和するため、過分のＨ２が無駄になる。露点が−２５℃超になると炉内のＨ２Ｏの酸素による酸化が著しくなりＳｉの内部酸化が過度に起こるため、露点は−２５℃以下に限定する。これにより、均熱炉内は、Ｆｅの還元性雰囲気となり、加熱炉で生成したＦｅ酸化物の還元が起こる。このとき、還元によりＦｅと分離された酸素が、一部鋼板内部に拡散し、Ｓｉと反応することにより、ＳｉＯ２の内部酸化が起こる。Ｓｉが鋼板内部で酸化し、化成処理反応が起こる鋼板最表面のＳｉ酸化物が減少するため、鋼板最表面の化成処理性は良好となる。
After heating and heating the steel sheet as described above using a direct fire burner, soaking is performed in a soaking furnace equipped with a radiant tube burner. The atmospheric gas introduced into the soaking furnace is 1 to 10% by volume H 2 + the remaining N 2 . The reason for limiting the H 2 % of the atmospheric gas to 1 to 10% by volume is that if it is less than 1% by volume, H 2 is insufficient to reduce the Fe oxide on the surface of the steel plate to be continuously passed, and 10% by volume. Since the reduction of Fe oxide saturates even if the temperature exceeds 1, excess H 2 is wasted. When the dew point exceeds -25 ° C, the oxidation of H 2 O in the furnace by oxygen becomes significant and excessive internal oxidation of Si occurs, so the dew point is limited to -25 ° C or less. Thereby, the inside of the soaking furnace becomes a reducing atmosphere of Fe, and the reduction of the Fe oxide generated in the heating furnace occurs. At this time, oxygen separated from Fe by reduction partially diffuses into the steel plate and reacts with Si, thereby causing internal oxidation of SiO 2 . Since Si is oxidized inside the steel sheet and the Si oxide on the outermost surface of the steel sheet where the chemical conversion reaction occurs is reduced, the chemical conversion property of the outermost surface of the steel sheet is improved.
均熱焼鈍は、材質調整の観点から、鋼板温度が７５０℃から９００℃の範囲内で行われる。均熱時間は２０秒から１８０秒が好ましい。均熱焼鈍後の工程は、品種によって様々であるが、本発明はその工程は特に限定されない。例えば、均熱焼鈍後、ガス、気水、水等により冷却され、必要に応じ、１５０℃から４００℃の焼き戻しを施す。冷却後、あるいは焼き戻し後に、表面性状を調整するために、塩酸や硫酸などを用いた酸洗を行ってもよい。また、化成処理時の化成結晶の生成を促進し、化成処理性を向上させるために、鋼板表面にＮｉ付着量５〜１００ｍｇ／ｍ２のＮｉめっきを施してもいい。 Soaking is performed in the range of 750 ° C. to 900 ° C. from the viewpoint of material adjustment. The soaking time is preferably 20 seconds to 180 seconds. The process after soaking is varied depending on the variety, but the process is not particularly limited in the present invention. For example, after soaking, it is cooled with gas, air, water, etc., and tempered at 150 ° C. to 400 ° C. as necessary. In order to adjust the surface properties after cooling or tempering, pickling using hydrochloric acid or sulfuric acid may be performed. Moreover, in order to promote the production | generation of the chemical crystal at the time of chemical conversion treatment, and to improve chemical conversion treatment property, you may give Ni plating of 5-100 mg / m < 2 > of Ni adhesion to the steel plate surface.
表１に示す化学成分を有する鋼Ａ〜Ｎを公知の方法により熱間圧延、酸洗、冷間圧延して厚さ１．５ｍｍの鋼板を製造した。この鋼板を、直火バーナを備える加熱炉、ラジアントチューブタイプの均熱炉、冷却炉を備える連続焼鈍ラインに通して加熱焼鈍して高強度冷延鋼板を得た。直火バーナは燃料にＣＯＧを使用し、空気比を種々変更した。均熱後の冷却は表２に示すとおり、水、気水またはガスで冷却した。その際、水冷却の場合は水温まで冷却後、一部は表２記載の保持温度まで再加熱し、保持した。気水、ガス冷却の場合は、表２に保持温度が記載されているものはその温度まで冷却し、そのまま表２記載の時間保持し、その後室温まで冷却した。表２に保持温度が記載されていないものは、室温まで冷却を行った。さらに、表２記載の酸で酸洗し、または、そのまま製品とした。 Steels A to N having chemical components shown in Table 1 were hot-rolled, pickled, and cold-rolled by a known method to produce a steel plate having a thickness of 1.5 mm. The steel sheet was heated and annealed through a continuous annealing line equipped with a heating furnace equipped with a direct fire burner, a radiant tube type soaking furnace, and a cooling furnace to obtain a high-strength cold-rolled steel sheet. The direct fire burner used COG as the fuel and changed the air ratio in various ways. Cooling after soaking was performed with water, air or gas as shown in Table 2. At that time, in the case of water cooling, after cooling to the water temperature, a part was reheated to the holding temperature shown in Table 2 and held. In the case of air-water and gas cooling, those whose holding temperatures are listed in Table 2 were cooled to that temperature, held as they were for the time shown in Table 2, and then cooled to room temperature. Those for which the holding temperature is not described in Table 2 were cooled to room temperature. Furthermore, it pickled with the acid of Table 2, or was made into the product as it was.
酸洗条件は下記である。
塩酸酸洗：酸濃度１〜２０％、液温度３０〜９０℃、酸洗時間５〜３０ｓｅｃ
硫酸酸洗：酸濃度１〜２０％、液温度３０〜９０℃、酸洗時間５〜３０ｓｅｃ
The pickling conditions are as follows.
Hydrochloric acid pickling: acid concentration 1-20%, liquid temperature 30-90 ° C, pickling time 5-30 sec
Acid pickling: acid concentration 1-20%, liquid temperature 30-90 ° C, pickling time 5-30 sec
得られた高強度冷延鋼板の機械的特性および化成処理性を評価した。 The mechanical properties and chemical conversion properties of the obtained high strength cold rolled steel sheets were evaluated.
機械的特性はＪＩＳ５号試験片（ＪＩＳＺ２２０１）を圧延方向と直角方向から採取し、ＪＩＳＺ２２４１に準拠して試験した。塗装焼付け処理後の強度として、５％予歪後、１７０℃で２０分間保持した後、再引張における引張強さ（ＴＳＢＨ）を調査し、初期引張強さ（ＴＳ０）と比較し、その差をΔＴＳ（ＴＳＢＨ−ＴＳ０）と定義した。加工性は引張強さ（ＴＳ）×伸び（Ｅｌ）の値で評価した。 For mechanical properties, a JIS No. 5 test piece (JISZ2201) was taken from the direction perpendicular to the rolling direction and tested according to JISZ2241. As strength after paint baking treatment, after 5% pre-strain, after holding at 170 ° C for 20 minutes, the tensile strength in re-tension (TS BH ) was investigated and compared with the initial tensile strength (TS 0 ) The difference was defined as ΔTS (TS BH −TS 0 ). Workability was evaluated by the value of tensile strength (TS) × elongation (El).
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社製の化成処理液（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。
The evaluation method of chemical conversion property is described below.
As the chemical conversion treatment liquid, a chemical conversion treatment liquid (Palbond L3080 (registered trademark)) manufactured by Nippon Parkerizing Co., Ltd. was used, and chemical conversion treatment was performed by the following method.
日本パーカライジング社製の脱脂液ファインクリーナ（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社製の表面調整液プレパレンＺ（登録商標）で３０秒表面調整行い、４３℃の化成処理液（パルボンドＬ３０８０）に１２０秒浸漬した後、水洗し、温風で乾燥した。
化成皮膜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した。○、◎が合格レベルである。
◎：５％以下
○：５％超１０％以下
×：１０％超え
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 seconds with surface conditioning solution Preparen Z (registered trademark) manufactured by Nihon Parkerizing Co., Ltd., a chemical conversion treatment solution at 43 ° C After being immersed in (Palbond L3080) for 120 seconds, it was washed with water and dried with warm air.
The chemical conversion film was randomly observed with a scanning electron microscope (SEM) at a magnification of 500 times, and 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. ○ and ◎ are acceptable levels.
◎: 5% or less ○: Over 5% and 10% or less ×: Over 10%
本実施例に供した鋼、連続焼鈍ラインの製造条件および評価結果を表２に示した。 Table 2 shows the production conditions and evaluation results of the steel and continuous annealing line used in this example.
本発明例では、引張強さ（ＴＳ）５９０ＭＰａ以上、ＴＳ×Ｅｌ：１８０００ＭＰａ・％以上の良好な加工性と、良好な化成処理性が得られ、比較例は加工性、化成処理性のいずれかが劣る。 In the examples of the present invention, good workability with a tensile strength (TS) of 590 MPa or more and TS × El: 18000 MPa ·% or more and good chemical conversion treatment properties are obtained, and the comparative example is either workability or chemical conversion treatment properties. Is inferior.
表１に示す化学成分を有する鋼Ａ〜Ｆを公知の方法により熱間圧延、酸洗、冷間圧延を行い厚さ１．５ｍｍの鋼板を製造した。この鋼板を、予熱炉、直火バーナを備える加熱炉、ラジアントチューブタイプの均熱炉、冷却炉を備える連続焼鈍ラインに通して加熱焼鈍して高強度冷延鋼板を得た。直火バーナは燃料にＣＯＧを使用し、空気比を種々変更した。均熱後の冷却は表３に示すとおり、水、気水またはガスで冷却した。その際、水冷却の場合は水温まで冷却後、一部は表３記載の保持温度まで再加熱し、保持した。気水、ガス冷却の場合は、表３に保持温度が記載されているものはその温度まで冷却し、そのまま表３記載の時間保持し、その後室温まで冷却した。表３に保持温度が記載されていないものは、室温まで冷却を行った。さらに、表３記載の酸で酸洗し、または、そのまま製品とした。 Steels A to F having chemical components shown in Table 1 were hot-rolled, pickled, and cold-rolled by a known method to produce a steel plate having a thickness of 1.5 mm. The steel sheet was heated and annealed through a continuous annealing line equipped with a preheating furnace, a heating furnace equipped with a direct-fired burner, a radiant tube type soaking furnace, and a cooling furnace to obtain a high-strength cold-rolled steel sheet. The direct fire burner used COG as the fuel and changed the air ratio in various ways. Cooling after soaking was performed with water, air or gas as shown in Table 3. At that time, in the case of water cooling, after cooling to the water temperature, a part was reheated to the holding temperature shown in Table 3 and held. In the case of air-water and gas cooling, those whose holding temperatures are listed in Table 3 were cooled to that temperature, held as they were for the time shown in Table 3, and then cooled to room temperature. Those for which the holding temperature is not described in Table 3 were cooled to room temperature. Furthermore, it pickled with the acid of Table 3, or was made into the product as it was.
得られた高強度冷延鋼板の機械的特性と化成処理性を評価した。機械的特性と化成処理性の評価は実施例１に記載した方法で評価した。 The mechanical properties and chemical conversion properties of the obtained high-strength cold-rolled steel sheets were evaluated. The mechanical properties and chemical conversion treatment were evaluated by the method described in Example 1.
本実施例に供した鋼、連続焼鈍ラインの製造条件および評価結果を表３に示した。 Table 3 shows the production conditions and evaluation results of the steel and continuous annealing line used in this example.
本発明例では、引張強さ（ＴＳ）５９０ＭＰａ以上、ＴＳ×Ｅｌ：１８０００ＭＰａ・％以上の良好な加工性と、良好な化成処理性が得られ、比較例は加工性、化成処理性のいずれかが劣る。 In the examples of the present invention, good workability with a tensile strength (TS) of 590 MPa or more and TS × El: 18000 MPa ·% or more and good chemical conversion treatment properties are obtained, and the comparative example is either workability or chemical conversion treatment properties. Is inferior.
表１に示す化学成分を有する鋼Ａ〜Ｎを公知の方法により熱間圧延、酸洗、冷間圧延して厚さ１．５ｍｍの鋼板を製造した。この鋼板を、予熱炉、直火バーナを備える加熱炉、ラジアントチューブタイプの均熱炉、冷却炉を備える連続焼鈍ラインに通して加熱焼鈍して高強度冷延鋼板を得た。直火バーナを備える加熱炉は４ゾーンに分かれ、各ゾーン長は同じである。直火バーナは燃料にＣＯＧを使用し、加熱炉の前段（３ゾーン）と後段（１ゾーン）の空気比を種々変更した。均熱後の冷却は表４に示すとおり、水、気水またはガスで冷却した。その際、水冷却の場合は水温まで冷却後、一部は表４記載の保持温度まで再加熱し、保持した。気水、ガス冷却の場合は、表４に保持温度が記載されているものはその温度まで冷却し、そのまま表４記載の時間保持し、その後室温まで冷却した。表４に保持温度が記載されていないものは、室温まで冷却を行った。さらに、表４記載の酸で酸洗し、または、そのまま製品とした。 Steels A to N having chemical components shown in Table 1 were hot-rolled, pickled, and cold-rolled by a known method to produce a steel plate having a thickness of 1.5 mm. The steel sheet was heated and annealed through a continuous annealing line equipped with a preheating furnace, a heating furnace equipped with a direct-fired burner, a radiant tube type soaking furnace, and a cooling furnace to obtain a high-strength cold-rolled steel sheet. A heating furnace equipped with an open flame burner is divided into four zones, and each zone has the same length. The direct fire burner used COG as the fuel, and variously changed the air ratio between the front stage (3 zones) and the rear stage (1 zone) of the heating furnace. Cooling after soaking was performed with water, air or gas as shown in Table 4. At that time, in the case of water cooling, after cooling to the water temperature, a part was reheated to the holding temperature shown in Table 4 and held. In the case of air-water and gas cooling, those whose holding temperatures are listed in Table 4 were cooled to that temperature, held as they were for the time shown in Table 4, and then cooled to room temperature. Those in which the holding temperature is not described in Table 4 were cooled to room temperature. Furthermore, it pickled with the acid of Table 4, or was made into the product as it was.
得られた高強度冷延鋼板の機械的特性と化成処理性を評価した。機械的特性と化成処理性の評価は実施例１に記載した方法で行った。 The mechanical properties and chemical conversion properties of the obtained high-strength cold-rolled steel sheets were evaluated. Evaluation of mechanical properties and chemical conversion treatment was performed by the method described in Example 1.
本実施例に供した鋼、連続焼鈍ラインの製造条件および評価結果を表４に示した。 Table 4 shows the manufacturing conditions and evaluation results of the steel and continuous annealing line used in this example.
本発明例では、引張強さ（ＴＳ）５９０ＭＰａ以上、ＴＳ×Ｅｌ：１８０００ＭＰａ・％以上の良好な加工性と、良好な化成処理性が得られ、比較例は、加工性、化成処理性のいずれかが劣る。 In the examples of the present invention, good workability with a tensile strength (TS) of 590 MPa or more, TS × El: 18000 MPa ·% or more, and good chemical conversion treatment properties are obtained. But inferior.
本発明は、良好な化成処理性を有する高Ｓｉ含有の高強度冷延鋼板の製造方法として利用することができる。 INDUSTRIAL APPLICABILITY The present invention can be used as a method for producing a high-strength cold-rolled steel sheet having high Si content that has good chemical conversion properties.
Claims (7)
Ｓｉ：０．５６〜３質量％、
Ｍｎ：１．０〜３．０質量％、
Ｐ：０．１質量％以下、
Ｓ：０．０５質量％以下、
Ａｌ：０．０１〜１質量％、
Ｎ：０．０１質量％以下
を含有し、残部がＦｅおよび不可避的不純物からなる成分組成を有する冷延鋼板を連続焼鈍する際に、昇温時に鋼板温度が少なくとも５５０℃以上で空気比０．９５以上の直火バーナを用いて鋼板を加熱し、鋼板温度が７５０℃以上になるまで昇温し、その後、露点−２５℃以下の、１〜１０体積％Ｈ２＋残部Ｎ２ガス雰囲気の炉で均熱焼鈍することを特徴とする化成処理性に優れた高Ｓｉ冷延鋼板の製造方法。 C: 0.05-0.3 mass%,
Si: 0.56-3 mass%,
Mn: 1.0 to 3.0% by mass,
P: 0.1% by mass or less,
S: 0.05 mass% or less,
Al: 0.01-1% by mass,
N: When continuously annealing a cold-rolled steel sheet having a composition of 0.01% by mass or less and the balance being composed of Fe and inevitable impurities, the temperature of the steel sheet is at least 550 ° C. and the air ratio is 0. A steel plate is heated using a 95 or more direct-fired burner, the temperature is raised until the steel plate temperature reaches 750 ° C. or higher, and then 1-10 vol% H 2 + balance N 2 gas atmosphere with a dew point of −25 ° C. or lower. A method for producing a high-Si cold-rolled steel sheet excellent in chemical conversion treatment, characterized by soaking in a furnace.
Ｓｉ：０．５６〜３質量％、
Ｍｎ：１．０〜３．０質量％、
Ｐ：０．１質量％以下、
Ｓ：０．０５質量％以下、
Ａｌ：０．０１〜１質量％、
Ｎ：０．０１質量％以下
を含有し、残部がＦｅおよび不可避的不純物からなる成分組成を有する冷延鋼板を連続焼鈍する際に、昇温時に鋼板温度が少なくとも５５０℃以上で空気比０．９５以上の直火バーナを用いて鋼板を加熱し、その後空気比０．８９以下の直火バーナを用いて鋼板を加熱して鋼板温度が７５０℃以上になるまで昇温した後、露点が−２５℃以下の、１〜１０体積％Ｈ２＋残部Ｎ２ガス雰囲気の炉で均熱焼鈍することを特徴とする化成処理性に優れた高Ｓｉ冷延鋼板の製造方法。 C: 0.05-0.3 mass%,
Si: 0.56-3 mass%,
Mn: 1.0 to 3.0% by mass,
P: 0.1% by mass or less,
S: 0.05 mass% or less,
Al: 0.01-1% by mass,
N: When continuously annealing a cold-rolled steel sheet having a composition of 0.01% by mass or less and the balance being composed of Fe and inevitable impurities, the temperature of the steel sheet is at least 550 ° C. and the air ratio is 0. The steel plate is heated using a direct fire burner of 95 or higher, and then heated using a direct fire burner having an air ratio of 0.89 or lower until the steel plate temperature reaches 750 ° C. or higher. A method for producing a high-Si cold-rolled steel sheet excellent in chemical conversion property, characterized by soaking in a furnace of 1 to 10% by volume H 2 + balance N 2 gas atmosphere at 25 ° C. or lower.
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