JP6515292B2 - Method of manufacturing high strength steel plate - Google Patents
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Description
本発明は、自動車用部材の使途に有用な、表面品質に優れた高強度鋼板に関する。 The present invention relates to a high-strength steel sheet excellent in surface quality, which is useful for automotive members.
近年、ＣＯ2排出量低減（燃費向上）と衝突安全性に対するニーズを背景に、自動車ボディの軽量化と高強度化が進められている。自動車ボディの軽量化には、使用部品の薄肉化が最も有効である。すなわち、自動車ボディの強度を維持しつつその軽量化を図るためには、自動車部品用素材となる鋼板の高強度化により鋼板を薄肉化することが有効である。 BACKGROUND ART In recent years, weight reduction and high strength of an automobile body have been promoted on the background of needs for CO 2 emission reduction (improvement of fuel consumption) and collision safety. In order to reduce the weight of the automobile body, it is most effective to reduce the thickness of parts used. That is, in order to reduce the weight of the vehicle body while maintaining the strength of the vehicle body, it is effective to reduce the thickness of the steel plate by increasing the strength of the steel plate serving as a material for an automobile part.
鋼板を高強度化するためには、製鋼工程において、Nb、V、Ti等の合金元素を単独、あるいは複合して添加される。しかし、これらの元素を添加すると、熱間の延性が低下し、連続鋳造工程において、スラブの表面に「横割れ」あるいはコーナー部に「カギ割れ」と称する表面割れの発生を助長させることになる。 In order to increase the strength of the steel sheet, alloying elements such as Nb, V and Ti are added singly or in combination in the steel making process. However, the addition of these elements reduces the hot ductility and promotes the generation of surface cracks called "lateral cracks" in the surface of the slab or in the corners in the continuous casting process. .
スラブの表面割れを残存させたまま、熱間圧延工程において、幅プレス後、粗圧延、仕上圧延を行った場合、熱延鋼板のエッジ部にエッジヘゲが発生する。 When rough rolling and finish rolling are performed after the width press in the hot rolling process with the surface cracks of the slab remaining, edge bales are generated at the edge portion of the hot rolled steel sheet.
このようなエッジヘゲが発生した場合には、当初予定していた幅以上の耳切りを行わざるを得ず、せっかく製造した鋼板が製品とならない場合が多く発生している。 In the case where such edge wrinkling occurs, it is compelled to carry out the trimming beyond the width originally planned, and in many cases the steel plate produced so much does not become a product.
これを防ぐために、予め広い幅で熱延鋼板を製造し、最終製品にするまでに耳切りを行ったり、熱間圧延前にスラブの表面検査を実施して、検出した割れをグラインダーで研削して除去する等の処置をせねばならず、製造工程を追加したり、製造歩留を大きく低下させざるを得ないという課題があった。 In order to prevent this, hot-rolled steel plates are manufactured in wide width beforehand, cut off before finalization, surface inspection of slabs before hot rolling, and grinding detected cracks with a grinder There is a problem that it is necessary to take measures such as removal, and to add a manufacturing process or to greatly reduce the manufacturing yield.
上記に対して、連続鋳造工程におけるスラブの横割れやカギ割れは、スラブの表面温度が鋼の脆化温度域（約700℃〜850℃）のときにスラブを曲げ部や矯正部で曲げ加工することにより発生することが知られている。そのため、スラブの割れ防止手段として、連続鋳造時の二次冷却条件を調整することによって、曲げ部及び矯正部のスラブ表面温度を脆化温度域から外す方法が多数提案されている。なお、ここで、曲げ部とは平板状のスラブを円弧状に曲げ加工する部位で、矯正部とは円弧状のスラブを平板状に曲げ加工する部位である。 In contrast to the above, lateral cracking or key cracking of the slab in the continuous casting process causes the slab to be bent at a bending portion or a straightening portion when the surface temperature of the slab is in the steel embrittlement temperature range (about 700 ° C. to 850 ° C.) It is known to occur by doing. Therefore, as a means for preventing the cracking of the slab, many methods have been proposed to remove the slab surface temperature of the bent portion and the straightening portion from the embrittlement temperature range by adjusting the secondary cooling condition during continuous casting. Here, the bent portion is a portion where a flat slab is bent into an arc shape, and the correction portion is a portion where an arc slab is bent into a flat shape.
例えば、特許文献１には、曲げ部におけるスラブ表面温度を脆化温度域以下の700℃以下とする方法が開示されている。また、特許文献２には、矯正部におけるスラブ上面温度を脆化温度域以上の900℃以上とするとともに、下面を上面よりも150℃以上高くする方法が開示されている。更に、特許文献３には、矯正部区間内を無注水として、スラブ表面温度を上昇させる方法が開示されている。 For example, Patent Document 1 discloses a method of setting the slab surface temperature at a bending portion to 700 ° C. or less, which is below the embrittlement temperature range. Moreover, while making the slab upper surface temperature in a correction part into 900 degreeC or more more than an embrittlement temperature range by patent document 2, the method of making a lower surface 150 degreeC or more higher than an upper surface is disclosed. Furthermore, Patent Document 3 discloses a method of raising the slab surface temperature without supplying water in the correction section.
また、特許文献４の方法は、連続鋳造時の二次冷却において、スラブ表面を一旦Ar3変態点以下まで冷却した後、復熱させて相変態させることによりスラブ表層の組織を微細化し、割れ感受性を低減する方法が開示されている
特許文献５には、湾曲型または垂直曲げ型の鋼のスラブ連続鋳造設備において、二次冷却帯の曲げ部または矯正部の入り側、もしくは曲げ部及び矯正部の双方の入り側に、スラブのコーナー部を加熱するため加熱装置を設置する方法が開示されている。
Further, in the method of Patent Document 4, in the secondary cooling at the time of continuous casting, after the slab surface is once cooled to the Ar 3 transformation point or less, the structure of the surface layer of the slab is refined by reheating and phase transformation, and cracking sensitivity Patent Document 5 discloses a method for reducing the amount of bending in the bending or straightening section of a secondary cooling zone, or a bending section and a straightening section in a steel slab continuous casting facility of curved or vertical bending type. A method of installing a heating device to heat the corners of the slab on both entry sides of the
特許文献６には、Nb、Vなどの合金元素が添加された鋼にTiを少量添加すること、及びNの含有量を制限することにより、スラブのコーナー部、端部の熱間延性が向上し、エッジヘゲの発生を防ぐ方法が開示されている。 In Patent Document 6, by adding a small amount of Ti to a steel to which an alloy element such as Nb or V is added, and limiting the content of N, the hot ductility of the corner portion and the end portion of the slab is improved. And methods of preventing the occurrence of edge baldness are disclosed.
しかしながら、特許文献1、2では、スラブの長片表面よりコーナー部の表面温度が低いため、スラブ幅方向の全部位が脆化温度域を完全に回避することは難しく、Nbなどが添加された割れ感受性の強い高強度鋼の鋳造においては効果が不十分である。 However, in Patent Documents 1 and 2, since the surface temperature of the corner portion is lower than the surface of the long piece of slab, it is difficult to completely avoid the embrittlement temperature range in all parts in the width direction of the slab, and Nb or the like is added. The effect is insufficient in the casting of high strength steels with high cracking sensitivity.
特許文献3の方法は、矯正部区間内で脆化温度域を回避することを目的としているが、矯正部区間内を無注水とするだけでは、スラブ全体が脆化温度域を完全に回避することは不十分である。コーナー部も含めて脆化温度域を高温側に回避するためには、矯正部までの二次冷却を大幅に緩冷却化する必要がある。その場合、凝固シェルの強度が低下して内部割れが発生するという問題がある。 Although the method of Patent Document 3 aims to avoid the embrittlement temperature range in the correction section section, the entire slab completely avoids the embrittlement temperature area only by supplying no water in the correction section section. That is insufficient. In order to avoid the embrittlement temperature range to the high temperature side including the corner portion, it is necessary to significantly slow down the secondary cooling to the correction portion. In that case, there is a problem that the strength of the solidified shell is reduced to cause internal cracking.
特許文献4の方法で開示されている温度条件を達成させるためには、二次冷却の初期に非常に大きな温度降下が必要であるので、一般的な連続鋳造機では、二次冷却能力が不足し鋳造速度を低下させる必要がある。その結果、生産性が低下するという問題がある。 In order to achieve the temperature conditions disclosed by the method of Patent Document 4, a very large temperature drop is necessary at the beginning of secondary cooling, so a general continuous casting machine lacks a secondary cooling capacity. It is necessary to reduce the casting speed. As a result, there is a problem that productivity falls.
特許文献５に開示されている様に、連続鋳造設備の二次冷却帯において、バーナー式加熱装置や、誘導加熱装置を設置することは、高温多湿で非常に設備の稼働環境が悪いところに設置することになり、十分なパフォーマンスを得られにくい。また、多大な設備費を要するという問題がある。 As disclosed in Patent Document 5, in the secondary cooling zone of a continuous casting facility, installing a burner-type heating device or an induction heating device is installed in a place where the operating environment of the facility is extremely poor due to high temperature and humidity. It will be difficult to get enough performance. In addition, there is a problem that a large equipment cost is required.
特許文献６については、本発明者の研究により、Tiを少量添加するだけでは、スラブコーナー部の割れに起因するエッジヘゲの発生を完全に抑止するには不十分であることがわかった。また、N含有量を制限するには溶製工程において、多量のArガスを用いる必要が生じる等の課題がある。 With regard to Patent Document 6, according to the study of the present inventor, it has been found that the addition of a small amount of Ti is not sufficient to completely suppress the generation of the edge bark due to the cracking of the slab corner. In addition, in order to limit the N content, there are problems such as the necessity of using a large amount of Ar gas in the melting step.
本発明は、かかる事情に鑑みてなされたものであって、熱間圧延の過程においてエッジヘゲが発生し難い表面品質に優れた高強度鋼板を提供することを目的とする。 The present invention has been made in view of such circumstances, and it is an object of the present invention to provide a high-strength steel sheet excellent in surface quality in which edge burrs are not easily generated in the process of hot rolling.
上記課題を解決すべく、鋭意研究・検討を行った。その結果、Nb、Tiが添加された鋼において、Nbの含有量とTiの含有量を、Nの含有量に応じて調整することにより、すなわち、下記式（1）を満たす範囲で添加することにより、スラブの割れに起因する高強度鋼板のエッジヘゲ発生を抑止可能であることを見出した。
（Ti−48/14×N）/Nb≧0.22 … （1）
ただし、式中［Ti］はTi含有量（質量％）を、［N］はN含有量（質量％）を、［Nb］はNb含有量（質量％）を示す。
In order to solve the above-mentioned problems, we conducted intensive studies and studies. As a result, in a steel to which Nb and Ti have been added, the Nb content and the Ti content are adjusted according to the N content, that is, in a range satisfying the following formula (1) It has been found that it is possible to suppress the generation of edge wrinkling of high strength steel plate due to the cracking of the slab.
(Ti-48 / 14 × N) /Nb≧0.22 (1)
However, in the formula, [Ti] indicates the Ti content (% by mass), [N] indicates the N content (% by mass), and [Nb] indicates the Nb content (% by mass).
本発明は以上の知見に基づいてなされたものであり、以下を要旨とするものである。
［１］成分組成は、質量％で、C: 0.05〜0.15％、Si：0.01〜0.90％、Mn：1.0〜3.5％、P：0.040％以下、S：0.010％以下、sol.Al:0.01〜0.08％、Nb：0.01〜0.10％、Ti：0.010〜0.050％、N：0.005％以下を含有し、残部はFeおよび不可避的不純物からなり、かつ、下記関係式(1)を満たすことを特徴とする高強度鋼板。
（Ti−48/14×N）/Nb≧0.22 ・・・・・・(1)
ただし、式中［Ti］はTi含有量（質量％）を、［N］はN含有量（質量％）を、［Nb］はNb含有量（質量％）を示す。
［２］熱延鋼板であることを特徴とする上記［１］に記載の高強度鋼板。
［３］冷延鋼板用またはめっき鋼板用の熱延鋼板であることを特徴とする上記［２］に記載の高強度鋼板。
The present invention has been made based on the above findings, and the gist of the present invention is as follows.
[1] Component composition is, in mass%, C: 0.05 to 0.15%, Si: 0.01 to 0.90%, Mn: 1.0 to 3.5%, P: 0.040% or less, S: 0.010% or less, sol. Al: 0.01 to 0.01% 0.08%, Nb: 0.01 to 0.10%, Ti: 0.010 to 0.050%, N: 0.005% or less, the balance being composed of Fe and unavoidable impurities, and satisfying the following relational expression (1). High strength steel plate.
(Ti-48 / 14 × N) /Nb≧0.22 (1)
However, in the formula, [Ti] indicates the Ti content (% by mass), [N] indicates the N content (% by mass), and [Nb] indicates the Nb content (% by mass).
[2] The high-strength steel sheet as described in the above [1], which is a heat-rolled steel sheet.
[3] The high-strength steel sheet according to [2], which is a hot-rolled steel sheet for cold-rolled steel sheet or plated steel sheet.
なお、本発明において、高強度鋼板とは、引張強さ（TS）が590MPa以上の鋼板である。また、本発明の高強度鋼板は、熱延鋼板、冷延鋼板用またはめっき鋼板用（溶融亜鉛めっき鋼板、合金化亜鉛めっき鋼板、電気めっき鋼板等）の素材となる熱延鋼板、さらに、この熱延鋼板を素材とする冷延鋼板、めっき鋼板のいずれも対象とするものである。 In the present invention, a high strength steel plate is a steel plate having a tensile strength (TS) of 590 MPa or more. The high strength steel plate of the present invention is a hot rolled steel plate, a hot rolled steel plate for cold rolled steel plates or plated steel plates (hot-dip galvanized steel plate, alloyed galvanized steel plate, electroplated steel plate, etc.) Both cold-rolled steel plates and plated steel plates, which are made of heat-rolled steel plates, are covered.
本発明によれば、引張強さ：590MPa以上を有し、表面品質に優れた高強度鋼板が得られる。
熱間延性が向上し、エッジヘゲが発生することを防ぐことができる。特に、割れ感受性の高いNbが所定量以上含有された高強度鋼板であっても、エッジヘゲを発生させることなく高い生産性で製造することが可能となる。
本発明の高強度鋼板は引張強さ：590MPa以上を有し、かつ表面品質に優れるため、自動車の構造部材等の使途に好適に用いることができ、自動車部品の軽量化やその信頼性を向上させる等、その効果は著しい。
According to the present invention, a high strength steel plate having a tensile strength of 590 MPa or more and excellent in surface quality can be obtained.
Hot ductility can be improved to prevent the generation of edge wrinkling. In particular, even a high-strength steel sheet containing Nb having a high degree of cracking sensitivity and having a predetermined amount or more can be manufactured with high productivity without generating edge wrinkling.
The high strength steel plate of the present invention has a tensile strength of 590 MPa or more and is excellent in surface quality, so it can be suitably used as a structural member of an automobile, etc., and the weight reduction of automobile parts and its reliability are improved. The effect is remarkable.
高強度鋼板を製造する際には、スラブの横割れやカギ割れに起因するエッジ欠陥が多発し、熱間圧延の過程においてエッジヘゲが発生し、大きな問題となっていた。これに対して、本発明者は、高強度鋼板に使用されているNb、Tiの熱間圧延に及ぼす影響を調査し、以下の知見を得た。Nbは強度向上のために添加される。一方で、Nb添加により熱間延性が低下する。これはNb窒化物がγ粒界に析出するためである。これに対して、Tiを添加することにより、Tiが窒化物を生成し、γ粒界に析出するNb窒化物の生成量を低減させ、熱間延性を向上させる。その結果、スラブの横割れやカギ割れが抑制されてエッジヘゲの発生を防止することができる。そして、N含有量、Nb含有量、Ti含有量を適正に制御することがスラブの横割れやカギ割れを抑制してエッジヘゲの発生を防止する。以上を知見し、本発明を完成するに至った。 When manufacturing a high strength steel plate, edge defects caused by lateral cracks or key cracks of the slab frequently occur, and edge bales are generated in the process of hot rolling, which is a serious problem. On the other hand, the present inventor investigated the influence exerted on the hot rolling of Nb and Ti used in high strength steel plate, and obtained the following findings. Nb is added to improve the strength. On the other hand, hot ductility is reduced by the addition of Nb. This is because Nb nitride precipitates at γ grain boundaries. On the other hand, when Ti is added, Ti forms nitrides, reduces the formation amount of Nb nitrides precipitated in the γ grain boundaries, and improves the hot ductility. As a result, lateral cracking and key cracking of the slab can be suppressed to prevent the generation of edge hair. Then, by appropriately controlling the N content, the Nb content, and the Ti content, it is possible to suppress lateral cracking and key cracking of the slab and to prevent the generation of edge hair. Having found the above, the present invention has been completed.
以上により、本発明では、熱間延性が向上し、幅プレスあるいは幅圧下圧延を行ってもエッジヘゲが発生せず、スラブのコーナー部、端部を除去する必要がない。また、スラブの割れの有無を検査したり、割れがあった場合、研削して除去する必要がなくなる。これにより連続鋳造設備から熱間圧延設備までスラブを冷却することなく、直送して圧延する所謂ホットチャージ圧延が可能となるため、加熱炉でスラブを昇熱するためのエネルギーを大幅に削減することが出来る。また、熱延鋼板のエッジヘゲが発生する可能性のある端部の耳切りが不要となるため、鋼板の大幅な歩留向上が可能となる。 As described above, according to the present invention, the hot ductility is improved, and no edge burrs are generated even when the width press or the width reduction rolling is performed, and it is not necessary to remove the corner portion and the end portion of the slab. In addition, it is not necessary to inspect the presence or absence of cracks in the slab or to grind and remove the cracks if any. As a result, so-called hot charge rolling can be performed by direct feeding and rolling without cooling the slab from the continuous casting facility to the hot rolling facility, so that the energy for heating the slab in the heating furnace can be significantly reduced. Can do. In addition, since it is not necessary to cut off the end portion of the heat-rolled steel sheet which may cause edge hair formation, it is possible to significantly improve the yield of the steel sheet.
以下、本発明について詳細に説明する。なお、以下の％は、特に断らない限り質量％を意味するものとする。 Hereinafter, the present invention will be described in detail. The following% means% by mass unless otherwise specified.
C:0.05〜0.15％
Cは鋼の強度上昇のために重要な元素である。しかし、0.05％未満では鋼板は十分な強度が得られない。一方、0.15％を超えるとスポット溶接性が劣化する。したがって、Cの含有量は0.05〜0.15％とする。好ましくは、0.06〜0.09％である。
C: 0.05 to 0.15%
C is an important element for increasing the strength of steel. However, if it is less than 0.05%, the steel plate can not obtain sufficient strength. On the other hand, if it exceeds 0.15%, spot weldability deteriorates. Therefore, the content of C is set to 0.05 to 0.15%. Preferably, it is 0.06 to 0.09%.
Si：0.01〜0.90％
Siは強度上昇及び伸び特性向上などを目的として含有する。鋼板の延性をさほど低下させることなく強度を確保するために有効な元素である。Ｓｉ量が0.01％未満の場合、高強度かつ高加工性の鋼板が製造できない。一方、0.90％を超えると、製品の赤スケールによる表面外観の劣化や、化成処理性の低下が顕著となる。したがって、Siの含有量は0.01〜0.90％とする。好ましくは0.01〜0.25％である。さらに好ましくは0.02〜0.10％である。
Si: 0.01 to 0.90%
Si is contained for the purpose of strength increase and elongation property improvement. It is an element effective to secure the strength without significantly reducing the ductility of the steel sheet. When the amount of Si is less than 0.01%, a steel plate having high strength and high workability can not be manufactured. On the other hand, when it exceeds 0.90%, the deterioration of the surface appearance due to the red scale of the product and the deterioration of the chemical conversion treatment property become remarkable. Therefore, the content of Si is 0.01 to 0.90%. Preferably it is 0.01 to 0.25%. More preferably, it is 0.02 to 0.10%.
Mn：1.0〜3.5％
Mnは鋼の強度上昇のために重要な元素である。しかし、1.0％未満では、強化に寄与する炭化物が高温で生成するため、強度が低下し、引張強度590MPa以上を確保するのが困難である。一方、3.5％を超えると、低温変態相主体の組織となるため、伸びが低下する。したがって、Mnの含有量は1.0〜3.5％とする。好ましくは1.5〜2.0％である。
Mn: 1.0 to 3.5%
Mn is an important element for increasing the strength of steel. However, if it is less than 1.0%, a carbide contributing to strengthening is formed at a high temperature, so the strength decreases and it is difficult to secure a tensile strength of 590 MPa or more. On the other hand, if it exceeds 3.5%, the structure is mainly formed by the low temperature transformation phase, so the elongation is reduced. Therefore, the content of Mn is set to 1.0 to 3.5%. Preferably it is 1.5 to 2.0%.
P：0.040以下
Ｐは強度上昇などを目的として含有することができる。この効果を得るためには0.010％以上含有することが好ましい。しかしながら、0.040％を超えて含有すると溶接性が低下する。また、延性が劣化する。したがって、Ｐの含有量は0.040％以下とする。好ましくは0.022％以下である。
P: 0.040 or less P can be contained for the purpose of increasing the strength and the like. In order to acquire this effect, it is preferable to contain 0.010% or more. However, if the content exceeds 0.040%, the weldability is reduced. In addition, the ductility is degraded. Therefore, the content of P is 0.040% or less. Preferably it is 0.022% or less.
S：0.010％以下
Sは不純物元素として鋼中に含有され、その含有量が0.010％を超えると製品の加工性や溶接性が劣化する。したがって、Sの含有量は0.010％以下とする。好ましくは0.005％以下である。
S: 0.010% or less
S is contained in the steel as an impurity element, and when its content exceeds 0.010%, the workability and weldability of the product deteriorate. Therefore, the content of S is made 0.010% or less. Preferably it is 0.005% or less.
sol.Al:0.01〜0.08％
Alは脱酸のために添加される。しかし、その含有量がsol.Alとして0.01％未満ではこの効果が十分でない。一方、0.08％を超えると、延性低下および脆化温度域を拡大し、連続鋳造時の割れ感受性を助長し、エッジヘゲが発生しやすくなる。よって、sol.Alの含有量は0.01〜0.08％とする。好ましくは0.01〜0.06％である。さらに好ましくは0.02〜0.05％である。
sol.Al: 0.01 to 0.08%
Al is added for deoxidation. However, if the content is less than 0.01% as sol. Al, this effect is not sufficient. On the other hand, if it exceeds 0.08%, the ductility reduction and embrittlement temperature range is expanded, the crack sensitivity in continuous casting is promoted, and edge hair is easily generated. Therefore, the content of sol.Al is 0.01 to 0.08%. Preferably it is 0.01 to 0.06%. More preferably, it is 0.02 to 0.05%.
Nb：0.01〜0.10％
Nbは主に熱間圧延工程で炭窒化物を形成させ、強度を上昇させる。このような効果を得るためには、0.01％以上添加する。一方、Nbは添加すると、その量の増大に伴い熱間延性が低下する。また、Nbを過度に添加すると、熱延板が硬化し、熱間圧延、冷間圧延での圧延荷重が増大する。また、加工性が低下する。このため、Nbの含有量は0.10％以下とする。好ましくは0.03〜0.06％である。さらに好ましくは0.04〜0.05％である。
Nb: 0.01 to 0.10%
Nb mainly forms carbonitrides in the hot rolling process to increase the strength. In order to obtain such an effect, 0.01% or more is added. On the other hand, when Nb is added, the hot ductility decreases with the increase of the amount. Also, if Nb is added excessively, the hot-rolled sheet hardens, and the rolling load in hot rolling and cold rolling increases. Also, the processability is reduced. Therefore, the content of Nb is 0.10% or less. Preferably it is 0.03 to 0.06%. More preferably, it is 0.04 to 0.05%.
Ti：0.010〜0.050％
上述したNb添加による熱間延性低下に対し、Tiを添加することにより、Tiが窒化物を生成し、γ粒界に析出するNb窒化物の生成量を低減させ、熱間延性を向上させる。その結果、エッジヘゲの発生を防止する。しかし、Tiが0.010％未満では、熱間延性向上の効果が十分ではない。一方、0.050％を超えると、TiCの析出により熱間延性が低下する。したがって、Tiの含有量は0.010〜0.050％とする。好ましくは0.015〜0.030である。
Ti: 0.010 to 0.050%
With respect to the reduction in hot ductility due to the addition of Nb described above, by adding Ti, Ti forms nitrides, reduces the amount of Nb nitrides precipitated in the γ grain boundaries, and improves the hot ductility. As a result, the generation of edge hair is prevented. However, if Ti is less than 0.010%, the effect of hot ductility improvement is not sufficient. On the other hand, if it exceeds 0.050%, the hot ductility decreases due to the precipitation of TiC. Therefore, the content of Ti is set to 0.010 to 0.050%. Preferably it is 0.015 to 0.030.
N：0.005％以下
Nは製鋼工程で溶鋼の攪拌のための窒素バブリングなどにより不純物として鋼中に含有される。通常、その含有量が0.003％を超えると、γ粒界に析出するNbとの窒化物の量が増大することにより、脆化温度域が拡大し、連続鋳造時の割れ感受性を助長し、エッジヘゲが発生しやすくなる。しかし、本発明では、Tiを後述するNbとの比率で添加することにより、NをTiの窒化物として固定して、γ粒界に析出するNb窒化物の量を抑制できるため、熱間延性の低下を防ぐことが可能となる。そのため、本発明ではNの含有量を0.005％まで許容する。0.003％以下に低下させるには、製鋼工程での溶鋼の攪拌には窒素を使用せずArによりバブリングするなどの方法を取る必要があるが、本発明では上記理由により、Nの含有量を0.005％まで緩和できる。以上より、Nの含有量は0.005％以下とする。好ましくは0.004％以下である。本発明では、多量のArを使用する必要がなくなり、経済的に優位である。
N: 0.005% or less
N is contained in the steel as an impurity by nitrogen bubbling or the like for stirring the molten steel in the steel making process. Usually, when the content exceeds 0.003%, the amount of nitrides with Nb precipitated in the γ grain boundaries increases, the embrittlement temperature range is expanded, and the susceptibility to cracking during continuous casting is promoted, so that edge wrinkling occurs. Is more likely to occur. However, in the present invention, by adding Ti in a ratio to Nb described later, N can be fixed as a nitride of Ti, and the amount of Nb nitride precipitated in the γ grain boundary can be suppressed, so Can be prevented. Therefore, in the present invention, the content of N is allowed to 0.005%. In order to reduce the content to 0.003% or less, it is necessary to use a method such as bubbling with Ar instead of nitrogen for stirring the molten steel in the steel making process, but in the present invention, the content of N is 0.005 for the above reason. It can be reduced to%. From the above, the content of N is made 0.005% or less. Preferably it is 0.004% or less. In the present invention, it is not necessary to use a large amount of Ar, which is economically advantageous.
本発明において、上記以外の残部は、Feおよび不可避的不純物である。不可避的不純物としては、Cr、Cu、Ni、Sn、Sb、O、Zr等が挙げられ、本発明の効果を奏さない範囲であれば、Cr：0.10％以下、Cu：0.10％以下、Ni：0.10％以下、Sn：0.01％以下、Sb：0.01％以下、O：0.003％以下、Zr：0.01％以下まで許容できる。 In the present invention, the remainder other than the above is Fe and unavoidable impurities. As the unavoidable impurities, Cr, Cu, Ni, Sn, Sb, O, Zr, etc. may be mentioned, and if the effect of the present invention is not exhibited, Cr: 0.10% or less, Cu: 0.10% or less, Ni: 0.10% or less, Sn: 0.01% or less, Sb: 0.01% or less, O: 0.003% or less, and Zr: 0.01% or less.
さらに、本発明では、上記Nb、Ti、Nの限定に加え、Ti、Nb、Nの含有量が、下記関係式(1)を満たすこととする。
（Ti−48/14×N）/Nb≧0.22 ・・・・・・(1)
ただし、式中［Ti］はTi含有量（質量％）を示し、［N］はN含有量（質量％）を示し、［Nb］はNb含有量（質量％）を示す。
Furthermore, in the present invention, in addition to the limitations of Nb, Ti, and N, the contents of Ti, Nb, and N satisfy the following relational expression (1).
(Ti-48 / 14 × N) /Nb≧0.22 (1)
However, in the formula, [Ti] indicates the Ti content (mass%), [N] indicates the N content (mass%), and [Nb] indicates the Nb content (mass%).
上述したように、Nbは強度向上のために添加される。一方で、Nb添加によりNb窒化物がγ粒界に析出し熱間延性が低下する。これに対して、Tiを添加することにより、Tiが窒化物を生成し、γ粒界に析出するNb窒化物の生成量を低減させ、熱間延性を向上させる。その結果、スラブの横割れやカギ割れが抑制されてエッジヘゲの発生を防止することができる。
計算上、Tiは、含有するNが全てTi窒化物（TiN）として生成され消費されるとして、NとTiの原子量比倍（48/14）の量を含有すれば良い。しかし、実際は、含有したTiが全てTi窒化物の生成に使用されるとは限らず、また成分分析上のバラツキもあるので、Tiは、ある程度余裕をみて含有する必要がある。また、そのTi余裕量（Ti-48/14×N）は、Nb含有量に応じて変化すると推定される。
以上より、検討した結果、Ti余裕量とNb含有量の比、すなわち（Ti-48/14×N）／Nb指数が、エッジヘゲの発生状況を整理するのに有効であるとの知見を得た。そして、さらに検討を進め、上記知見に基づき、実績を調査したところ、（Ti-48/14×N）/Nbとエッジヘゲ発生状況には相関があることがわかった。
As mentioned above, Nb is added to improve the strength. On the other hand, due to the addition of Nb, Nb nitride precipitates at γ grain boundaries, and the hot ductility is reduced. On the other hand, when Ti is added, Ti forms nitrides, reduces the formation amount of Nb nitrides precipitated in the γ grain boundaries, and improves the hot ductility. As a result, lateral cracking and key cracking of the slab can be suppressed to prevent the generation of edge hair.
In terms of calculation, Ti may be contained in an amount of atomic weight ratio multiple of N and Ti (48/14), assuming that all the contained N is generated and consumed as Ti nitride (TiN). However, in practice, not all of the contained Ti is used for the formation of Ti nitride, and there is also variation in component analysis, so Ti needs to be contained with some margin. Also, it is estimated that the Ti margin (Ti-48 / 14 × N) changes according to the Nb content.
From the above, as a result of investigation, it was found that the ratio of Ti margin and Nb content, that is, (Ti-48 / 14 × N) / Nb index, was effective for organizing the generation state of edge hair . Then, further investigations were conducted, and the results were investigated based on the above findings, and it was found that (Ti-48 / 14 × N) / Nb and the state of edge hair generation are correlated.
Nb、Ti添加高強度鋼板の成分実績と、エッジヘゲの発生状況を綿密に調べた。得られた結果を図１に示す。エッジヘゲの発生の有無は目視にて確認した。鋼板幅端部から50mm以内の範囲に、長さ10mm以上のヘゲが鋼板幅両端部のいずれかに存在していれば、エッジヘゲあり、ヘゲが発生していなければエッジヘゲ発生なしと判定し、エッジヘゲありのコイル数とエッジヘゲ発生率を求めた。 The component results of Nb and Ti-added high-strength steel sheet and the occurrence of edge bales were examined in detail. The obtained result is shown in FIG. The presence or absence of the occurrence of edge hair was visually confirmed. If there is a bark with a length of 10 mm or more in any of the both ends of the steel sheet width within 50 mm from the width end of the steel sheet, there is an edge bark, and if there is no bark, it is judged that there is no edge bark generation The number of coils with edge bales and the incidence of edge bales were determined.
図１より、Ti、N、Nbが（Ti-48/14×N）／Nb≧0.22を満たす場合、エッジヘゲの発生を抑えることが可能であることを見出した。この値が大きいほどNb窒化物よりTi窒化物が析出しやくなると考えられる。0.22以上であれば、Tiを添加することにより、γ粒界でのNbの窒化物の析出を抑制し、粒界脆化を抑止して熱間延性が大きく向上する。好ましくは（Ti-48/14×N）／Nb≧0.28である。 From FIG. 1, it was found that when Ti, N and Nb satisfy (Ti-48 / 14 × N) /Nb≧0.22, it is possible to suppress the generation of edge hair. It is believed that the larger this value is, the more easily Ti nitride precipitates than Nb nitride. If it is 0.22 or more, by adding Ti, precipitation of Nb nitride at γ grain boundaries is suppressed, grain boundary embrittlement is suppressed, and hot ductility is greatly improved. Preferably, (Ti-48 / 14 × N) /Nb≧0.28.
次に、本発明の高強度鋼板の製造方法の一実施形態について説明する。
本発明の高強度鋼板は、上述の成分組成を有するスラブを好ましくは湾曲型または垂直曲げ型のスラブ連続鋳造設備で鋳造し、スラブのコーナー部あるいは端部を除去することなく、1100〜1300℃で加熱保持してから熱間圧延を開始し、熱間圧延の粗圧延に先立って、幅圧下量（両幅の合計圧下量）50mm以上400mm以下の幅プレスあるいは幅圧下圧延を行い、仕上げ圧延温度を800〜950℃、巻取り温度を450〜700℃として、熱間圧延することで製造される。
Next, an embodiment of a method of manufacturing a high strength steel plate of the present invention will be described.
The high-strength steel plate of the present invention is preferably a slab of the above-described composition cast in a curved or vertical bending slab continuous casting facility, and without removing the corners or ends of the slab, 1100 to 1300 ° C. The hot rolling is started after holding by heating, and prior to the rough rolling of hot rolling, width reduction (total reduction of both widths) of 50 mm or more and 400 mm or less of width press or width reduction rolling is performed to finish rolling. They are manufactured by hot rolling at a temperature of 800 to 950 ° C. and a winding temperature of 450 to 700 ° C.
本発明において、鋼の溶製方法は特に限定されず、転炉、電気炉等、公知の溶製方法を採用することができる。また、真空脱ガス炉にて2次精錬を行ってもよい。その後、生産性や品質上の問題から連続鋳造法によりスラブとする。 In the present invention, the method of melting steel is not particularly limited, and a known melting method such as a converter or an electric furnace can be adopted. Further, secondary refining may be performed in a vacuum degassing furnace. Then, it is made into a slab by the continuous casting method from the problem on productivity and quality.
連続鋳造設備：湾曲型または垂直曲げ型
鋼の連続鋳造設備には、垂直型連続鋳造設備、垂直曲げ型連続鋳造設備、湾曲型連続鋳造設備、水平型連続鋳造設備の４種類の型式が存在するが、本発明では、これらのうち湾曲型連続鋳造設備または垂直曲げ型のスラブ連続鋳造設備を用いるのが好ましい。垂直型連続鋳造設備および水平型連続鋳造設備は、曲げ部および矯正部が存在せず、曲げおよび矯正による引張応力がスラブに作用しないため、本発明の鋼を適用しなくてもエッジヘゲは発生しにくく表面特性の向上には有利である。しかし、設備コストおよび生産性の観点から、湾曲型連続鋳造設備または垂直曲げ型連続鋳造設備に劣り、工業的に高強度鋼板を製造するには湾曲型連続鋳造設備または垂直曲げ型のスラブ連続鋳造設備の方が適している。なお、湾曲型連続鋳造設備と垂直曲げ型連続鋳造設備を比較すると、垂直部を有する垂直曲げ型の方が、曲げ部の曲率が小さく、スラブに作用する引張応力が大きいため、割れが発生しやすい。
Continuous casting equipment: There are four types of continuous casting equipment for curved or vertical bending steel: vertical continuous casting equipment, vertical bending continuous casting equipment, curved continuous casting equipment, and horizontal continuous casting equipment. In the present invention, among these, it is preferable to use a curved continuous casting facility or a vertical bending slab continuous casting facility. In vertical type continuous casting equipment and horizontal type continuous casting equipment, since the bending portion and the correction portion do not exist and tensile stress due to bending and correction does not act on the slab, edge burrs are generated even without applying the steel of the present invention. It is advantageous for improving the surface characteristics. However, from the viewpoint of equipment cost and productivity, it is inferior to curved continuous casting equipment or vertical bending continuous casting equipment, and for manufacturing high strength steel plate industrially, curved continuous casting equipment or vertical bending slab continuous casting Equipment is better. In addition, when the bending type continuous casting equipment and the vertical bending type continuous casting equipment are compared, the curvature of the bending portion is smaller and the tensile stress acting on the slab is larger in the case of the vertical bending type having the vertical portion, and therefore the crack occurs. Cheap.
スラブ加熱温度：1100〜1300℃
加熱段階に存在している析出物は最終的に得られる鋼板内では粗大な析出物として存在するため、強度に寄与しない。そのため、鋳造時に析出したTi、Nb析出物を再溶解させる必要がある。1100℃以上の加熱によりTi、Nb析出物が再溶解し、強度への寄与が認められる。また、スラブ表層の気泡、偏析など欠陥をスケールオフし、鋼板表面の亀裂、凹凸を減少し、平滑な鋼板表面を達成する観点からも1100℃以上に加熱するのが好ましい。一方、1300℃を超えて加熱すると、酸化重量の増加に伴うスケールロスの増大につながる。また、表層からの脱炭、オーステナイト粒の粗大化を引き起こし、特性にばらつきが生じたりプレス後の表面不良を発生させる。以上より、スラブ加熱温度は1100℃以上1300℃以下の範囲とすることが好ましい。但し、スラブに熱間圧延を施すに際し、鋳造後のスラブが1200℃以上の温度域にある場合、或いはスラブの炭化物が溶解している場合には、スラブを加熱することなく直送圧延してもよい。
Slab heating temperature: 1100-1300 ° C
The precipitates present in the heating stage do not contribute to the strength because they are present as coarse precipitates in the finally obtained steel sheet. Therefore, it is necessary to re-dissolve Ti and Nb precipitates deposited at the time of casting. By heating at 1100 ° C. or more, Ti and Nb precipitates are redissolved, and a contribution to strength is observed. Further, from the viewpoint of scaling off defects such as bubbles and segregation on the surface layer of the slab, reducing cracks and irregularities on the surface of the steel plate, and achieving a smooth steel surface, heating to 1100 ° C. or more is preferable. On the other hand, heating above 1300 ° C. leads to an increase in scale loss with an increase in the oxidation weight. In addition, decarburization from the surface layer and coarsening of austenite grains are caused to cause variations in characteristics and to cause surface defects after pressing. As mentioned above, it is preferable to make slab heating temperature into the range of 1100 degreeC or more and 1300 degrees C or less. However, when the slab is subjected to hot rolling, if the slab after casting is in the temperature range of 1200 ° C. or more, or if the carbides of the slab are melted, the direct delivery rolling is also performed without heating the slab. Good.
幅プレスあるいは幅圧下圧延：幅圧下量（両幅の合計圧下量）50mm以上400mm以下
幅プレスあるいは幅圧下圧延は、寸法の精度向上や圧延形状の向上のために50mm以上行うのが好ましい。50mm未満では、粗圧延機、仕上圧延機に入る際の形状に問題が生じて、通板ができなくなる場合があり、このような事象が発生した場合には莫大な損害が生じる。幅プレスあるいは幅圧下圧延によりスラブ幅を調整する方法は、設備能力の点から限界があり、現状での幅調整代は高々400mm程度である。したがって、熱間圧延の粗圧延に先立って行う幅プレスあるいは幅圧下圧延は、幅圧下量（両幅の合計圧下量）50mm以上400mmｍｍ以下が好ましい。
Width press or width reduction rolling: Width reduction amount (total reduction amount of both widths) 50 mm or more and 400 mm or less Width press or width reduction rolling is preferably performed 50 mm or more in order to improve the dimensional accuracy and the rolling shape. If it is less than 50 mm, problems may occur in the shape of the rough rolling mill and the finishing rolling mill, which may make it impossible to pass the plate. If such an event occurs, a great deal of damage may occur. The method of adjusting the slab width by width press or width rolling is limited in terms of equipment capacity, and the width adjustment allowance at present is at most about 400 mm. Therefore, as for the width press or width reduction rolling performed prior to the rough rolling of hot rolling, the width reduction amount (total reduction amount of both widths) is preferably 50 mm or more and 400 mm or less.
粗圧延条件については特に限定されない。 The rough rolling conditions are not particularly limited.
仕上げ圧延温度：800〜950℃
仕上げ圧延温度を800℃以上とすることで、均一な熱延母相組織を得ることができる。仕上げ圧延温度が800℃を下回ると、鋼板の組織が不均一となり、成形時の材料の均一な変形を阻害し、要求される優れた成形性を有することが困難となる。一方、仕上げ圧延温度が950℃を超えると、酸化物生成量が急激に増大し、地鉄と酸化物の界面が荒れ、酸洗、冷間圧延後の表面品質が劣化する。このように、冷間圧延後の表面品質が低下すると、最終製品が溶融亜鉛めっき鋼板の場合は、めっきと鋼板の界面の鋼板側内部へ進展している亀裂と凹部の存在が顕著となり、プレス成形時に割れ易くなる。また、結晶粒径が過度に粗大となり、成形時にプレス品表面荒れを生じる場合がある。よって、仕上げ圧延温度は800〜950℃とすることが好ましい。
Finish rolling temperature: 800 to 950 ° C
By setting the finish rolling temperature to 800 ° C. or more, it is possible to obtain a uniform hot-rolled matrix structure. When the finish rolling temperature is less than 800 ° C., the structure of the steel sheet becomes nonuniform, which prevents uniform deformation of the material during forming, making it difficult to have the required excellent formability. On the other hand, when the finish rolling temperature exceeds 950 ° C., the amount of oxide formation sharply increases, the interface between the base iron and the oxide becomes rough, and the surface quality after pickling and cold rolling deteriorates. As described above, when the surface quality after cold rolling decreases, when the final product is a hot-dip galvanized steel sheet, the presence of cracks and recesses extending to the inside of the steel sheet at the interface between the plating and the steel sheet becomes remarkable. It becomes easy to break at the time of molding. In addition, the crystal grain size may be excessively coarsened to cause roughening of the surface of a pressed product during molding. Therefore, the finish rolling temperature is preferably 800 to 950 ° C.
巻取り温度：450〜700℃
巻取り温度が700℃を超えると粗大粒が生成し、鋼板組織が不均一となり、延性が低下する。また、表層からの脱炭、スケールの成長が著しく表面品質が劣化する。一方、巻取り温度が450℃未満では、熱延板強度の上昇により熱間圧延によって生じた加工組織が残留し、冷間圧延負荷が増大する、このため、巻取り温度は450〜700℃とすることが好ましい。
Winding temperature: 450-700 ° C
When the coiling temperature exceeds 700 ° C., coarse grains are formed, the steel sheet structure becomes uneven, and the ductility decreases. In addition, decarburization from the surface layer and growth of scale significantly degrade the surface quality. On the other hand, if the coiling temperature is less than 450 ° C., the working structure generated by the hot rolling remains due to the increase of the hot-rolled sheet strength and the cold rolling load increases. Therefore, the coiling temperature is 450 to 700 ° C. It is preferable to do.
以上により、本発明の高強度鋼板（熱延鋼板）が製造される。この熱延鋼板を素材として冷延鋼板を製造する場合は、上記により得られた熱延鋼板に対して、必要に応じて酸洗、次いで冷間圧延を行い、次いで焼鈍処理を施すことで製造することができる。また、この熱延鋼板を素材としてめっき鋼板を製造する場合は、上記により得られた冷延鋼板に対して、溶融亜鉛めっき処理や、溶融亜鉛めっき処理後さらに合金化処理を施したり、電気亜鉛めっき処理や電気Ni-亜鉛めっき処理等を施すことで製造することができる。 By the above, the high strength steel plate (hot rolled steel plate) of the present invention is manufactured. When manufacturing a cold rolled steel sheet by using this hot rolled steel sheet as a material, the hot rolled steel sheet obtained above is subjected to pickling and then cold rolling if necessary, and then subjected to an annealing treatment. can do. Moreover, when producing a plated steel sheet by using this hot rolled steel sheet as a raw material, the cold rolled steel sheet obtained above may be subjected to hot dip galvanization treatment, further galvanization treatment after hot dip galvanization treatment, or electro zinc It can be manufactured by applying a plating treatment or an electric Ni-zinc plating treatment.
酸洗の条件は特に限定されない。冷間圧延は所望の板厚を得るため施す必要がある。冷間圧延率に制約はないが、加工性を確保するために30％以上が好ましい。 The conditions for pickling are not particularly limited. Cold rolling needs to be applied to obtain a desired plate thickness. The cold rolling rate is not limited, but is preferably 30% or more in order to ensure processability.
連続焼鈍および連続溶融亜鉛めっき時の均熱温度は、再結晶化の促進と鋼板表層の組織の粗大化を抑制するため、Ａｃ１点以上900℃以下が好ましい。また、焼鈍温度での滞留時間が短すぎるとミクロ組織が十分に焼鈍されずに冷間圧延による加工組織が存在した不均一な組織となり延性が低下する。一方、滞留時間が長すぎると製造時間の増加を招き製造コスト上好ましくない。このため、上記温度域での滞留時間は30〜1200秒が好ましい。特に好ましい滞留時間は30〜120秒の範囲である。 The soaking temperature at the time of continuous annealing and continuous hot-dip galvanizing is preferably at least Ac 1 and at most 900 ° C. in order to suppress the promotion of recrystallization and the coarsening of the structure of the steel sheet surface layer. In addition, when the residence time at the annealing temperature is too short, the microstructure is not sufficiently annealed, the structure is uneven due to cold rolling, and the ductility is lowered. On the other hand, if the residence time is too long, the production time increases, which is not preferable in terms of production cost. Therefore, the residence time in the above temperature range is preferably 30 to 1200 seconds. Particularly preferred residence times are in the range of 30 to 120 seconds.
加熱後の冷却は、特に限定しない。例えば、ガスジェット冷却設備を用いて、焼鈍温度から100℃/s未満の平均冷却速度で450℃以下の冷却停止温度まで冷却することが好ましい。焼鈍温度からの冷却中に適量のフェライト、ベイナイト、マルテンサイトを析出させ、強度と延性のバランスを制御することが可能となる。冷却停止温度が450℃超えの場合、ミクロ組織中にフェライト・パーライトが多量に生成し、ベイナイト・マルテンサイト生成量が少なくなるため、強度が急激に低下し、590MPa以上の引張強度を得ることができない。平均冷却速度が100℃/s以上の場合、冷却中に十分な量のフェライトの析出が生じないため優れた延性を得ることができない。 Cooling after heating is not particularly limited. For example, it is preferable to cool to a cooling stop temperature of 450 ° C. or less at an average cooling rate from an annealing temperature to less than 100 ° C./s using a gas jet cooling facility. It is possible to precipitate appropriate amounts of ferrite, bainite and martensite during cooling from the annealing temperature, and to control the balance between strength and ductility. When the cooling stop temperature exceeds 450 ° C., a large amount of ferrite and pearlite is formed in the microstructure and the amount of bainite and martensite formation decreases, so the strength rapidly decreases and a tensile strength of 590 MPa or more can be obtained. Can not. When the average cooling rate is 100 ° C./s or more, since sufficient precipitation of ferrite does not occur during cooling, excellent ductility can not be obtained.
次いで、必要に応じて酸洗、再酸洗を行う。
酸洗、再酸洗を施すことで、鋼板表面のＳｉ酸化物、Ｓｉ−Ｍｎ酸化物を除去し、化成処理性を向上させる。再酸洗では、酸洗で用いる酸洗液とは異なり、かつ、非酸化性の酸を酸洗液として用いることが好ましい。
酸洗は常法にて行うことができ、条件は特に限定されない。例えば、硝酸、塩酸、弗酸、硫酸およびそれらを2種以上混合した酸のいずれかを用いることができる。
Next, if necessary, pickling and re-pickling are performed.
By carrying out pickling and re-pickling, the Si oxide and the Si-Mn oxide on the surface of the steel sheet are removed to improve the chemical conversion treatability. In re-acid washing, it is preferable to use a non-oxidizing acid as the pickling solution, unlike the pickling solution used in the pickling.
Pickling can be performed by a conventional method, and the conditions are not particularly limited. For example, any of nitric acid, hydrochloric acid, hydrofluoric acid, sulfuric acid and acids in which two or more of them are mixed can be used.
引張強さ（TS）が590MPa級、980MPa級の冷延鋼板を製造するに当り、表1に記載の成分組成にて、垂直曲げ型連続鋳造機で鋳造した220〜260mm板厚、900〜1700mm幅のスラブを用いた。No.1〜10が590MPa級、No.11〜20が980MPa級である。 220 to 260 mm plate thickness, 900 to 1700 mm cast by a vertical bending type continuous casting machine with the component composition described in Table 1 when producing a cold rolled steel sheet having a tensile strength (TS) of 590 MPa class and 980 MPa class A slab of width was used. Nos. 1 to 10 are 590 MPa grade, and Nos. 11 to 20 are 980 MPa grade.
上記スラブに対して、スラブ加熱温度を1100℃以上とし、50〜300mmの幅プレスを行い、次いで、仕上げ圧延温度を800〜950℃、巻取り温度を450〜700℃として熱間圧延を行った。次いで、酸洗工程にて鋼板の表面検査を実施し、特に鋼板幅端部から50mm以内の範囲におけるヘゲの発生の有無を目視にて確認した。長さ10mm以上のヘゲが存在していれば、エッジヘゲあり、ヘゲが発生していなければ、エッジヘゲ発生なしと判定した。 The slab heating temperature was set to 1100 ° C. or higher, 50 to 300 mm wide pressing was performed, and then the hot rolling was performed with a finishing rolling temperature of 800 to 950 ° C. and a winding temperature of 450 to 700 ° C. . Subsequently, the surface inspection of the steel plate was carried out in the pickling step, and in particular, the presence or absence of the occurrence of the hair in the range within 50 mm from the width end of the steel plate was visually confirmed. It was judged that the edge was not generated if an edge was present if a ridge having a length of 10 mm or more was present, and no edge was generated.
また、上記により得られた鋼板に対して、引張特性を測定した。圧延方向に対して90°方向（C方向）を引張方向とするJIS5号引張試験片（JIS Z 2201）を採取し、JIS Z 2241の規定に準拠した引張試験を行い、引張強さ（TS）を測定した。590MPa級（No.1〜10）ではすべての試験片が590〜680MPaの範囲内、980MPa級（No.11〜20）ではすべての試験片が980〜1090MPaの範囲内であった。 Moreover, the tensile property was measured with respect to the steel plate obtained by the above. A JIS No. 5 tensile test specimen (JIS Z 2201) having a tensile direction of 90 ° (C direction) with respect to the rolling direction is collected, and a tensile test is carried out in accordance with the provisions of JIS Z 2241 to obtain a tensile strength (TS). Was measured. In the 590 MPa grade (No. 1 to 10), all the test pieces were in the range of 590 to 680 MPa, and in the 980 MPa grade (No. 11 to 20), all the test pieces were in the range of 980 to 1090 MPa.
表1より、Ti、Nb、Nが、(Ti-48/14×N)/Nb≧0.22の範囲外である比較例のNo.1〜5、11〜15の場合は、エッジヘゲが発生した。これに対して、Ti、Nb、Nが、(Ti-48/14×N)/Nb≧0.22の範囲内である本発明例のNo.6〜10、16〜20の場合は、エッジヘゲの発生がなく、表面品質に優れた高強度鋼板が得られていた。 From Table 1, in the case of Nos. 1 to 5 and 11 to 15 of the comparative example in which Ti, Nb, and N are out of the range of (Ti-48 / 14 × N) /Nb0.20.22, edge bales occurred. On the other hand, in the case of Nos. 6 to 10 and 16 to 20 of the inventive example in which Ti, Nb, and N are in the range of (Ti-48 / 14 × N) /Nb0.20.22, the generation of edge baldness And a high strength steel plate excellent in surface quality was obtained.
Claims (3)
0.36≧（Ti−48/14×N）/Nb≧0.22 ・・・・・・(1)
ただし、式中［Ti］はTi含有量（質量％）を、［N］はN含有量（質量％）を、［Nb］はNb含有量（質量％）を示す。 The chemical composition, in mass%, C: 0.0 70 ~0.15% , Si: 0.01~0.90%, Mn:. 1 5 ~ 2.0%, P: 0.040% or less, S: 0.010% or less, sol. Al: 0.0 2 ~0.0 5%, Nb: 0.0 37 ~0.10%, Ti: 0.021~0.0 30%, N: containing 0.0029 to 0.005%, the balance being Fe and unavoidable impurities, and the following relational expression (1) A slab with a component composition to be filled is cast in a curved or vertical bending type slab continuous casting facility, heated at 1100-1300 ° C. without removing the corners or ends of the slab, and then hot rolling is started. Then, prior to rough rolling in hot rolling, width reduction or width reduction rolling of 50 mm to 400 mm width reduction amount (total reduction amount of both widths) is performed, and the finish rolling temperature is 800 to 950 ° C., and the winding temperature is It hot-rolls as 450-700 degreeC, The manufacturing method of the high strength steel plate characterized by the above-mentioned.
0.36 ≧ (Ti-48 / 14 × N) /Nb≧0.22 (1)
However, in the formula, [Ti] indicates the Ti content (% by mass), [N] indicates the N content (% by mass), and [Nb] indicates the Nb content (% by mass).
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