JP2006124773A - Hot rolled steel strip and its production method - Google Patents
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本発明は、熱延鋼帯およびその製造方法に関する。特に、本発明は、ホイール・ディスクなどの厳しい成形に供され、かつ美麗な表面外観が要望される用途に好適な熱延鋼帯とその製造方法に関するものである。 The present invention relates to a hot-rolled steel strip and a method for producing the same. In particular, the present invention relates to a hot-rolled steel strip suitable for applications that are subjected to severe molding of wheel disks and the like and require a beautiful surface appearance, and a method for producing the same.
熱間圧延によって製造されるいわゆる熱延鋼板は、比較的安価な構造材料として、自動車をはじめとする各種の産業機器に広く使用されている。特に伸びフランジ加工などの厳しい加工に供され、大量に生産される自動車の足廻り部品などへの適用が近年増加しつつある。 A so-called hot-rolled steel sheet manufactured by hot rolling is widely used as a relatively inexpensive structural material in various industrial equipment including automobiles. In recent years, application to automobile undercarriage parts that are subjected to severe processing such as stretch flange processing and produced in large quantities has been increasing in recent years.
伸びフランジ加工性や張り出し加工性を向上させるには、例えば特許文献1にあるようにSi添加が有効であることが知られている。しかしながら高Si含有鋼は熱間圧延でのスケール剥離性が低下するため、酸洗後の平均表面粗さRaで2.0μm以上を有するような、島状スケール疵と呼ばれるスケールの押し込み疵を生じ、表面外観上問題があった。美麗な表面を確保するには酸洗後の表面全体を、平均表面粗さRaで1.5μm以下、さらに好ましくは1.0μm以下とするのが好ましい。 In order to improve stretch flange workability and overhang workability, it is known that Si addition is effective as disclosed in Patent Document 1, for example. However, since the high Si content steel has reduced scale peelability in hot rolling, it has a scale indentation wrinkle called an island-shaped scale wrinkle having an average surface roughness Ra of 2.0 μm or more after pickling, There was a problem with the surface appearance. In order to ensure a beautiful surface, the entire surface after pickling is preferably 1.5 μm or less, more preferably 1.0 μm or less in terms of average surface roughness Ra.
島状スケール疵を防止するための技術としてデスケーリング圧力を例えば5.0〜30.0kgf/cm2という高圧にする技術が、例えば特許文献2に開示されている。しかしながら高圧デスケーリングは非常に高価な設備で、その維持も大変で、コスト的に不利であった。またさらに高い衝突圧を広範囲に得るのは困難で、コイル状にして提供し得る短辺が200mm以上で長辺が100m以上のような広範囲において均一美麗な表面を得ることは困難であった。熱延鋼板は通常コイル状に巻き取って供給され、成形直前に切り板にされるため、コイルの中で一部でも表面不良があると、切り板採取時や成形後に抜き取りが必要で、大きな手間となっていた。 For example, Patent Document 2 discloses a technique for increasing the descaling pressure to, for example, a high pressure of 5.0 to 30.0 kgf / cm 2 as a technique for preventing island-like scale defects. However, high-pressure descaling is a very expensive facility, and its maintenance is difficult, and it is disadvantageous in cost. In addition, it is difficult to obtain a higher impact pressure in a wide range, and it is difficult to obtain a uniform and beautiful surface in a wide range such as a short side of 200 mm or more and a long side of 100 m or more that can be provided in a coil shape. Hot-rolled steel sheets are usually supplied in the form of a coil and cut into a cut plate just before forming. If there is a surface defect even in a part of the coil, it is necessary to extract it at the time of cutting or after forming the cut plate. It was a hassle.
高圧デスケーリングを使用しない方法としては例えば特許文献3の技術が開示されているが、Siを含む鋼の島状スケール疵抑制にはその効果は不十分であった。
本発明の課題は、前述したような従来技術の問題点を解決し、高い加工性と広い範囲で良好な表面性状を有する熱延鋼帯とその製造方法を提供することにある。特に、加工性の点からSiを添加し、(5xP+Al)/Si≦0.728 を満足する鋼は島状スケール疵を抑制することが著しく困難であるため、本発明は、(5xP+Al)/Si≦0.728を満足する成分を有する鋼を対象とするものである。 An object of the present invention is to solve the problems of the prior art as described above, and to provide a hot-rolled steel strip having high workability and a good surface property over a wide range, and a method for producing the same. In particular, steel added with Si from the point of workability and satisfying (5xP + Al) /Si≦0.728 is extremely difficult to suppress island scale flaws. Therefore, the present invention provides (5xP + Al) It is intended for steel having a component satisfying /Si≦0.728.
本発明者らは鋭意実験の結果、下記構成により、従来製造ができなかった、広範囲に表面が美麗なSi含有熱延鋼板を得ることが可能になり、発明を完成するに至ったのである。その熱延鋼帯はコイル状にして大量に提供でき、切り板採取時やプレス工程での表面不良部の抜き取り等が不要である。 As a result of diligent experiments, the present inventors have been able to obtain a Si-containing hot-rolled steel sheet having a beautiful surface in a wide range, which could not be produced in the past, and completed the invention. The hot-rolled steel strip can be provided in a large amount in the form of a coil, and it is not necessary to extract a defective surface or the like at the time of cutting a plate or in a pressing process.
ここに、本発明は下記の通りである。
(1) 質量%で、C:0.02〜0.25%、Si:0.04〜2.5%、Mn:0.3〜2.3%、P:0.050%以下、S:0.02%以下、Al:0.005〜0.50%およびN:0.02%以下を含有し、残部が鉄および不純物からなり、かつ鋼中のP、AlおよびSiの含有量が下記(I)式を満足する化学組成を有し、引張強さ(MPa)と穴拡げ率(%)の積が40000(MPa・%)以上であり、表面および裏面において島状スケール疵を有しない、短辺が200mm以上で長辺が100m以上の熱延鋼帯。
Here, the present invention is as follows.
(1) By mass%, C: 0.02 to 0.25%, Si: 0.04 to 2.5%, Mn: 0.3 to 2.3%, P: 0.050% or less, S: 0.02% or less, Al: 0.005 to 0.50%, and N: 0.02 %, The balance is iron and impurities, and the P, Al and Si contents in the steel satisfy the following formula (I), and have tensile strength (MPa) and hole expansion A hot-rolled steel strip with a product of rate (%) of 40000 (MPa ·%) or more, no island-like scale ridges on the front and back surfaces, a short side of 200 mm or more and a long side of 100 m or more.
(5xP+Al)/Si≦0.728 (I)
ここで、式中のP、AlおよびSiは鋼板中の各元素の含有量(質量%)である。
(2) 前記化学組成が、質量%で、さらにTi:0.3%以下、Nb:0.3%以下およびV:0.5%以下からなる群から選ばれた1種または2種以上を含有することを特徴とする(1) に記載の熱延鋼帯。
(5xP + Al) /Si≦0.728 (I)
Here, P, Al, and Si in the formula are the contents (mass%) of each element in the steel sheet.
(2) The chemical composition further includes one or more selected from the group consisting of Ti: 0.3% or less, Nb: 0.3% or less, and V: 0.5% or less in terms of mass%. The hot-rolled steel strip described in (1).
(3) 前記化学組成が、質量%で、さらにMo:1.0%以下、Cr:1.0%以下、Cu:1.0%以下、Ni:1.0%以下およびB:0.01%以下からなる群から選ばれた1種または2種以上を含有することを特徴とする(1) または(2) に記載の熱延鋼帯。 (3) The chemical composition is 1% selected from the group consisting of Mo: 1.0% or less, Cr: 1.0% or less, Cu: 1.0% or less, Ni: 1.0% or less, and B: 0.01% or less. The hot rolled steel strip according to (1) or (2), wherein the hot rolled steel strip contains seeds or two or more kinds.
(4) 前記化学組成が、質量%で、さらにCa:0.01%以下を含有することを特徴とする(1) ないし(3) のいずれかに記載の熱延鋼帯。
(5) 下記(A)〜(C)の工程を備えることを特徴とする熱延鋼帯の製造方法:
(A)(1) 〜(4) のいずれかに記載の化学組成を有する鋼塊または鋼片に、圧延完了時の表面温度をFeO とFe2SiO4との共晶点以上とした粗熱間圧延を施して粗バーとする工程;
(B)前記粗バーにデスケーリングを施した後に仕上げ熱間圧延を開始して圧延完了時の表面温度を800℃以上とした仕上げ熱間圧延を前記(A)の工程の後420秒以内に終了する工程;および
(C)前記仕上げ熱間圧延の後、平均冷却速度10℃/s以上で700℃以下まで冷却して巻取る工程。
(4) The hot-rolled steel strip according to any one of (1) to (3), wherein the chemical composition further includes, by mass%, Ca: 0.01% or less.
(5) A method for producing a hot-rolled steel strip comprising the following steps (A) to (C):
(A) Coarse heat with a steel ingot or steel slab having the chemical composition described in any one of (1) to (4) having a surface temperature at the completion of rolling equal to or higher than the eutectic point of FeO and Fe 2 SiO 4 A process of forming a rough bar by hot rolling;
(B) After the descaling of the rough bar, the finish hot rolling is started and the finish hot rolling at a surface temperature of 800 ° C. or higher is completed within 420 seconds after the step (A). And (C) a step of cooling and winding up to 700 ° C. or less at an average cooling rate of 10 ° C./s or more after the finish hot rolling.
(6) 下記(a)〜(e)の工程を備えることを特徴とする熱延鋼帯の製造方法:
(a)(1) ないし(4) のいずれかに記載の化学組成を有する鋼塊または鋼片に粗熱間圧延を施して粗バーとする工程;
(b)粗熱間圧延終了後に前記粗バーの表面温度をFeO とFe2SiO4との共晶点以上に加熱する工程;
(c)前記(b)の工程の後、前記粗バーにデスケーリングを施した後に仕上げ熱間圧延を開始して圧延完了時の表面温度を800℃以上とした仕上げ熱間圧延を前記(b)の工程の後420秒以内に終了する工程;および
(d)前記仕上げ熱間圧延の後、平均冷却速度10℃/s以上で700℃以下まで冷却して巻取る工程。
(6) A method for producing a hot-rolled steel strip comprising the following steps (a) to (e):
(A) A step of subjecting a steel ingot or steel slab having the chemical composition according to any one of (1) to (4) to rough hot rolling to obtain a rough bar;
(B) a step of heating the surface temperature of the coarse bar to a temperature equal to or higher than the eutectic point of FeO and Fe 2 SiO 4 after completion of the rough hot rolling;
(C) After the step (b), after the descaling is performed on the rough bar, the finish hot rolling is started, and the finish hot rolling is performed at a surface temperature of 800 ° C. or higher when the rolling is completed (b) And (d) a step of cooling to 700 ° C. or lower at an average cooling rate of 10 ° C./s or higher after the finish hot rolling.
(7) 前記FeO とFe2SiO4との共晶点が下記(II)式により与えられる温度であることを特徴とする(5) または(6) に記載の熱延鋼帯の製造方法。
(FeO とFe2SiO4との共晶点)=168.15x((5xP+Al)/Si)2-245.12x(5xP+Al)/Si+1170
(II)
ここで、式中のP、AlおよびSiは鋼板中の各元素の含有量(質量%)でありFeO とFe2SiO4との共晶点の単位は℃である。
(7) The method for producing a hot-rolled steel strip according to (5) or (6), wherein the eutectic point of FeO and Fe 2 SiO 4 is a temperature given by the following formula (II):
(Eutectic point of FeO and Fe 2 SiO 4 ) = 168.15x ((5xP + Al) / Si) 2 -245.12x (5xP + Al) / Si + 1170
(II)
Here, P, Al and Si in the formula are the contents (mass%) of each element in the steel sheet, and the unit of eutectic point of FeO and Fe 2 SiO 4 is ° C.
(8) 前記粗熱間圧延に先立って、前記鋼塊または鋼片を加熱炉にて1050℃以上とし、次いで加熱炉から抽出し、その後120秒以内にデスケーリングを施してから粗熱間圧延を行うことを特徴とする(5) 〜(7) のいずれかに記載の熱延鋼帯の製造方法。 (8) Prior to the rough hot rolling, the steel ingot or steel slab is heated to 1050 ° C. or higher in a heating furnace, then extracted from the heating furnace, and then descaling within 120 seconds, followed by rough hot rolling. The method for producing a hot-rolled steel strip according to any one of (5) to (7), wherein:
(9) 前記加熱炉での加熱において、前記鋼塊または鋼片が1200℃以上となる時間を75分未満とすることを特徴とする(8) に記載の熱延鋼帯の製造方法。 (9) The method for producing a hot-rolled steel strip according to (8), wherein in the heating in the heating furnace, the time for the steel ingot or the steel slab to be 1200 ° C. or higher is less than 75 minutes.
本発明に係る熱延鋼板は、ホイール・ディスクなど厳しいバーリング成形等がなされ、かつ美麗な表面が要求される用途に最適で、かかる効果を有する本発明の意義は極めて著しい。 The hot-rolled steel sheet according to the present invention is optimal for applications that require strict burring forming such as wheels and disks and requires a beautiful surface, and the significance of the present invention having such effects is extremely remarkable.
次に、本発明の発明特定事項とその作用について詳細に説明する。なお、本明細書において鋼の化学組成を示す「%」は特にことわりがない限り、「質量%」である。
(A)鋼塊または鋼片の化学組成
C:Cは高強度化に必要な元素である。その含有量が0.02%未満ではその効果が小さく、0.25%を超えて含有すると溶接性が低下するため、その含有量は0.02〜0.25%と定めた。好ましい範囲は0.02〜0.18%である。
Next, the invention specific matter and the operation of the present invention will be described in detail. In this specification, “%” indicating the chemical composition of steel is “% by mass” unless otherwise specified.
(A) Chemical composition of steel ingot or steel slab C: C is an element necessary for high strength. If the content is less than 0.02%, the effect is small. If the content exceeds 0.25%, the weldability deteriorates, so the content was determined to be 0.02 to 0.25%. A preferred range is 0.02 to 0.18%.
Si:Siは高強度化と伸びフランジ性を両立させるために必要な元素である。0.04%未満ではその効果が小さく、2.5%を超えて含有すると靭性が低下する。したがってその含有量は0.04〜2.5%と定めた。好ましい範囲は0.15〜1.7%であり、最も好ましいのは0.4〜1.5%である。 Si: Si is an element necessary for achieving both high strength and stretch flangeability. If the content is less than 0.04%, the effect is small, and if the content exceeds 2.5%, the toughness decreases. Accordingly, the content is determined to be 0.04 to 2.5%. A preferred range is 0.15 to 1.7%, and most preferred is 0.4 to 1.5%.
Mn:Mnは高強度化に有効であるとともに、SをMnSとして固定し、熱間脆性を抑制する働きがある。0.3%未満ではその効果が小さく、2.3%を超えて含有すると溶接性が低下するため、その含有量は0.3〜2.3%と定めた。好ましくは0.8〜2.3%である。 Mn: Mn is effective for increasing the strength and also has a function of fixing S as MnS and suppressing hot brittleness. If the content is less than 0.3%, the effect is small, and if the content exceeds 2.3%, the weldability deteriorates, so the content was determined to be 0.3-2.3%. Preferably it is 0.8 to 2.3%.
P:Pは靱性を劣化させる好ましくない元素である。したがってPの含有量を0.050%以下と定めた。ただしPにはスケールの剥離性を向上させる働きがあるので、含有量は0.005〜0.03%が好ましく、0.01〜0.03%がさらに好ましい。 P: P is an undesirable element that deteriorates toughness. Therefore, the content of P is set to 0.050% or less. However, since P has a function of improving the peelability of the scale, the content is preferably 0.005 to 0.03%, and more preferably 0.01 to 0.03%.
S:SはMnS量を増加させ伸びフランジ性を低下させる好ましくない元素である。したがってその含有量は0.02%以下と定めた。好ましくは0.008%以下、さらに好ましくは0.004%以下である。 S: S is an undesirable element that increases the amount of MnS and lowers stretch flangeability. Therefore, the content is determined to be 0.02% or less. Preferably it is 0.008% or less, More preferably, it is 0.004% or less.
Al:Alは脱酸に用いられるとともに、スケールの剥離性を向上させる重要な元素である。その効果は0.005%未満では不十分で、また0.50%を超えて含有してもその効果が飽和し、コスト的に不利になる。したがって0.005〜0.50%と定めた。好ましくは0.03〜0.50%、さらに好ましくは0.06〜0.50%、最も好ましいのは、0.10〜0.50%である。 Al: Al is an important element that is used for deoxidation and improves the peelability of the scale. The effect is insufficient if it is less than 0.005%, and even if it exceeds 0.50%, the effect is saturated, which is disadvantageous in terms of cost. Therefore, it was determined to be 0.005 to 0.50%. Preferably it is 0.03-0.50%, More preferably, it is 0.06-0.50%, Most preferably, it is 0.10-0.50%.
N:Nは不純物元素である。含有量が高すぎると高温延性が低下し、表面疵の問題が発生する。上限0.02%までは許容される。
Ti、Nb、V:これらは任意添加成分であり、1種または2種以上含有させることができ、析出強化により鋼板の高強度化に寄与させることができる。この効果を得るにはいずれも0.003%以上含有させることが好ましい。添加量が多すぎても効果が飽和するので、各元素の含有量は、Ti:0.3%以下、Nb:0.3%以下、V:0.5%以下と定めた。
N: N is an impurity element. If the content is too high, the high temperature ductility is lowered and the problem of surface flaws occurs. An upper limit of 0.02% is allowed.
Ti, Nb, V: These are optional added components, which can be contained alone or in combination of two or more, and can contribute to increasing the strength of the steel sheet by precipitation strengthening. In order to acquire this effect, it is preferable to contain 0.003% or more of all. Since the effect is saturated even if the addition amount is too large, the content of each element is determined to be Ti: 0.3% or less, Nb: 0.3% or less, and V: 0.5% or less.
Mo、Cr、Cu、Ni、B:これらは任意添加成分であり、1種または2種以上含有させることができ、固溶強化、変態強化を通じて高強度化に寄与する。この効果を確実に得るには、それぞれ0.005%以上含有させることが好ましい。しかしながら過度に添加すると化成処理性の劣化や靭性の劣化や加工性の劣化をもたらすので、その含有量はMo:1.0%以下、Cr:1.0%以下、Cu:1.0%以下、Ni:1.0%以下、B:0.01%以下と定めた。 Mo, Cr, Cu, Ni, B: These are optional added components, which can be used alone or in combination of two or more, and contribute to high strength through solid solution strengthening and transformation strengthening. In order to ensure this effect, it is preferable to contain 0.005% or more of each. However, excessive addition causes deterioration of chemical conversion property, deterioration of toughness and workability, so the content is Mo: 1.0% or less, Cr: 1.0% or less, Cu: 1.0% or less, Ni: 1.0% or less , B: determined to be 0.01% or less.
Ca:Caも任意添加成分であり、硫化物系介在物を球状化させる働きがあり、穴拡げ性等局部延性の必要な加工性を向上させる働きがある。この効果を確実に得るには、含有量を0.0001%以上とすることが好ましい。しかしながら0.01%を超えて含有させてもその効果は飽和するのでその含有量を0.01%以下と定めた。 Ca: Ca is also an optional additive, has a function of spheroidizing sulfide inclusions, and a function of improving workability required for local ductility such as hole expandability. In order to reliably obtain this effect, the content is preferably 0.0001% or more. However, even if the content exceeds 0.01%, the effect is saturated, so the content was determined to be 0.01% or less.
本発明においては、さらに下記式(I) を満足する化学組成とするが、これは本発明の対象がSiを添加することで加工性を確保する高Si含有鋼を対象としており、本発明の課題の一つがそのような高Si含有鋼のスケール剥離性を改善することにあるためである。 In the present invention, the chemical composition further satisfies the following formula (I), but this is the object of the present invention is a high Si content steel that secures workability by adding Si. This is because one of the problems is to improve the scale peelability of such a high Si content steel.
(5xP+Al)/Si≦0.728 (I)
上記式(I)を満足しない場合には、スケール剥離性の問題が深刻にならない代わり、加工性も十分でない。
(5xP + Al) /Si≦0.728 (I)
When the above formula (I) is not satisfied, the problem of scale peelability does not become serious, and the workability is not sufficient.
残部Feおよび不純物である。不純物としては、0.01%以下のSn等が例示される。
本発明によれば、表裏面に島状スケール疵のみられない熱延鋼板が得られるが、このときの「島状スケール疵」とは、すでに述べたようにデスケール処理で剥離されなかった残留スケールに由来する押し込み疵であり、目視により容易に判別できるものであり酸洗後の表面粗さRa で云えば2.0μm以上のものを指す。したがって本発明に係わる熱延鋼板は斯かる部位を有しないものであり、酸洗後の平均表面粗さRaで云えば1.5μm以下、より好ましくは1.0μm 以下である。
The balance is Fe and impurities. Examples of impurities include 0.01% or less of Sn.
According to the present invention, a hot-rolled steel sheet that does not have island-shaped scales on the front and back surfaces can be obtained. This is an indentation flaw derived from the above, which can be easily discerned by visual observation and indicates a surface roughness Ra after pickling of 2.0 μm or more. Therefore, the hot-rolled steel sheet according to the present invention does not have such a portion, and the average surface roughness Ra after pickling is 1.5 μm or less, more preferably 1.0 μm or less.
次に、本発明にかかる熱延鋼板の製造方法について説明するが、それは実用上から好ましい製造例を示すもので、本発明にかかる熱間圧延鋼板がそれにより製造されたものにのみ制限されるという趣旨ではない。 Next, although the manufacturing method of the hot-rolled steel sheet concerning this invention is demonstrated, it shows a manufacturing example preferable from a practical use, and the hot-rolled steel sheet concerning this invention is restrict | limited only to what was manufactured by it. That's not to say.
本発明において、このような化学組成の鋼は、例えば転炉、電気炉等により溶製される。鋼種も、リムド鋼、キャップド鋼、セミキルド鋼またはキルド鋼のいずれでもよい。さらに、素材である鋼塊または鋼片としては、造塊−分塊圧延により得られる鋼片あるいは連続鋳造により得られる鋳片のいずれを用いてもよい。 In the present invention, the steel having such a chemical composition is produced by, for example, a converter, an electric furnace or the like. The steel type may also be any of rimmed steel, capped steel, semi-killed steel or killed steel. Furthermore, as a steel ingot or steel slab as a raw material, either a steel slab obtained by ingot-splitting rolling or a slab obtained by continuous casting may be used.
(B)熱間圧延条件
Si含有鋼の島状スケール疵を抑制するには、粗熱間圧延後から仕上げ熱間圧延前のデスケーリングが重要である。その製造方法は、Si含有鋼にて粗熱間圧延後にスケールが剥離しやすい高温でデスケーリングを行い、その後短時間に仕上げ熱間圧延を完了することを基本とする。この時のデスケーリングは低衝突圧で可能であり、したがって安定して広範囲に良好な表面を得ることができる。衝突圧は9.8kPa(0.1 kgf/cm2)〜490kPa(5kgf/cm2)が好ましく、9.8kPa(0.1 kgf/cm2)〜196kPa(2kgf/cm2)がさらに好ましい。
(B) Hot rolling conditions In order to suppress island-like scale flaws in Si-containing steel, descaling after rough hot rolling and before finish hot rolling is important. The manufacturing method is basically based on performing descaling at a high temperature at which the scale is easily peeled after rough hot rolling with Si-containing steel, and then finishing hot rolling in a short time. Descaling at this time is possible with a low collision pressure, and therefore a good surface can be stably obtained over a wide range. The collision pressure is preferably 9.8 kPa (0.1 kgf / cm 2 ) to 490 kPa (5 kgf / cm 2 ), and more preferably 9.8 kPa (0.1 kgf / cm 2 ) to 196 kPa (2 kgf / cm 2 ).
本発明にかかるSi含有鋼で上記条件が最適な理由は以下のように考えられる。
Si含有鋼の特徴としてスケールの生成速度が遅いことが挙げられる。スケールが薄すぎるとデスケーリングでスケールの剥離が起こりにくくなるため、効率良く剥離させるには、粗熱間圧延終了温度を高くするか、粗熱間圧延完了後高温に再加熱してデスケーリングを行う必要がある。
The reason why the above conditions are optimal in the Si-containing steel according to the present invention is considered as follows.
A characteristic of Si-containing steel is that the generation rate of scale is slow. If the scale is too thin, it becomes difficult for the scale to exfoliate due to descaling.For efficient exfoliation, increase the end temperature of rough hot rolling or reheat to high temperature after completion of rough hot rolling to perform descaling. There is a need to do.
ここに、本発明者らの知見によれば、これは粗バーの表面に生成するFe2SiO4が溶融化する温度、換言すれば、粗バーの表面に生成するFeOとFe2SiO4との共晶点以上に粗バーの温度を高めれば、Fe2SiO4の強い酸化抑制効果を消失できるために、高Si含有鋼からなる粗バーであっても酸化スケールを十分に生成できることが分かった。 Here, according to the findings of the present inventors, this is the temperature at which Fe 2 SiO 4 to generate on the surface of the coarse bar is melted, in other words, the FeO and Fe 2 SiO 4 to produce a surface roughness bar It can be seen that if the temperature of the coarse bar is raised above the eutectic point, the strong oxidation inhibition effect of Fe 2 SiO 4 can be lost, so that even a coarse bar made of steel with high Si content can sufficiently generate oxide scale. It was.
さらに粗バーの鋼界面のスケールが溶融に近い状態のため、スケールの剥離も容易である。これらによってデスケーリングし易くすることができるために、その後に高衝突圧のデスケーリングを行わなくても確実にデスケーリングを行うことができ、スケール疵を生じない。 Furthermore, since the scale at the steel interface of the coarse bar is close to melting, peeling of the scale is easy. Since the descaling can be facilitated by these, the descaling can be surely performed without performing the descaling of the high collision pressure after that, and scale flaws are not generated.
酸化スケールを十分に生成させるためには、上記高温の粗バーの状態から1秒以上経てからデスケーリングするのが好ましい。
本発明者らの上記新しい技術思想に基づく実験の結果、上記デスケーリングが向上するための好ましい温度は、168.15x((5xP+Al)/Si)2-245.12x(5xP+Al)/Si+1170(℃)以上であった。
In order to sufficiently generate the oxide scale, it is preferable to perform descaling after one second or more from the state of the high-temperature coarse bar.
As a result of experiments based on the new technical idea of the present inventors, a preferable temperature for improving the descaling is 168.15x ((5xP + Al) / Si) 2 -245.12x (5xP + Al) / Si + It was 1170 (° C) or higher.
デスケーリング後さらに厚いスケールが生成するとスケール押し込み疵による表面不良が発生するが、Si含有鋼では長辺で100mの広い範囲を製造するのに必要なほどの時間を要しても問題となるほどの厚いスケールは生成しないのである。しかしながら、あまり長い時間を要すると問題となるほどにスケールが厚くなるため、粗バーが上記温度以上の状態から、つまり、例えばそのような状態での粗熱間圧延終了後、あるいは粗バーヒータによるそのような状態への加熱後、420秒以内にデスケーリングと仕上げ熱間圧延を完了する、つまり終了する必要がある。好ましくは300秒以内、さらに好ましくは180秒以内である。 If a thicker scale is generated after descaling, surface defects due to scale indentation will occur, but with Si-containing steel, even if it takes as much time as necessary to produce a wide area of 100 m on the long side, it will be a problem. Thick scale does not generate. However, since the scale becomes thick enough to cause a problem if it takes too long time, the rough bar is in a state above the above temperature, that is, after the end of the rough hot rolling in such a state, for example, or with a rough bar heater. After heating to the desired state, descaling and finish hot rolling must be completed within 420 seconds, that is, finished. Preferably it is within 300 seconds, more preferably within 180 seconds.
粗バーのデスケーリングは、共晶点以上で行うのがスケールの剥離の点より好ましい。
なお、仕上げ熱間圧延は5スタンド以上で各パス間10秒以内の熱間圧延機が並ぶ仕上圧延機で熱間圧延されるのが通常である。また粗バーの鋼界面のスケールを上記溶融状態にするには、粗熱間圧延完了温度を高くするか、または粗バーヒータで加熱する方法、粗バーをコイル状に巻き取って炉に入れる方法や粗バーを保温カバーにて高温の状態で保持する方法等が考えられる。
The descaling of the coarse bar is preferably performed at or above the eutectic point from the viewpoint of scale peeling.
In addition, the finish hot rolling is usually hot-rolled by a finishing mill with 5 or more stands and a hot rolling mill within 10 seconds between each pass. In order to bring the scale of the steel interface of the coarse bar into the above molten state, a method for increasing the temperature of the coarse hot rolling or heating with a coarse bar heater, a method of winding the coarse bar into a coil and putting it in a furnace, A method of holding the coarse bar at a high temperature with a heat insulating cover can be considered.
さらに本発明の好適態様によれば、仕上げ熱間圧延前に前後の粗バー同士を接合して連続仕上げ熱間圧延を実施するのも安定的に通板するのに有効である。
また上記以外、加熱炉で発生するスケールについては、加熱温度を1050℃以上に加熱後、加熱炉抽出後120秒以内で、かつ粗圧延開始前に1回以上実施することが除去しやすい条件である。前述の理由により、高温加熱にてスケール厚みを厚くし、さらに120秒以内の高温のままでデスケーリングを実施することで、加熱炉で発生するスケールに対しては効果的にデスケーリングを実施できる。加熱温度は、好ましくは1150℃以上、さらに好ましくは1200℃以上、最も好ましくは1230℃以上である。またデスケーリングまでの時間は、90秒以内が好ましく、60秒以内がさらに好ましい。
Furthermore, according to the preferred embodiment of the present invention, it is effective to join the rough bars before and after and perform continuous finish hot rolling before finish hot rolling in order to pass the plate stably.
In addition to the above, the scale generated in the heating furnace is a condition that is easy to remove after heating at a temperature of 1050 ° C or higher, within 120 seconds after extraction of the heating furnace, and at least once before the start of rough rolling. is there. For the above-mentioned reasons, by increasing the scale thickness by high-temperature heating and further performing descaling while maintaining the high temperature within 120 seconds, it is possible to effectively scale the scale generated in the heating furnace. . The heating temperature is preferably 1150 ° C or higher, more preferably 1200 ° C or higher, and most preferably 1230 ° C or higher. The time until descaling is preferably within 90 seconds, and more preferably within 60 seconds.
また加熱時間は特に規定する必要はないが、省力や厚いスケールの取れ残りを防止する観点より1200℃以上の在炉時間を75分間未満とするのが良い。
その他の条件としては加工性の観点より、仕上温度は800℃以上、巻取温度は700℃以下、巻取りまでの平均冷却速度は10℃/s以上であるのが好ましい。仕上温度が800℃未満では組織がバンド状になり伸びフランジ性が低下し、また冷却速度が10℃/s未満であったり、巻取温度が700℃を超えたりすると炭化物や組織の粗大化が起こり、局部延性が低下し伸びフランジ性が低下することがある。
The heating time is not particularly specified, but the in-furnace time of 1200 ° C. or more is preferably less than 75 minutes from the viewpoint of saving labor and preventing the removal of a thick scale.
As other conditions, from the viewpoint of workability, it is preferable that the finishing temperature is 800 ° C. or higher, the winding temperature is 700 ° C. or lower, and the average cooling rate until winding is 10 ° C./s or higher. If the finishing temperature is less than 800 ° C, the structure becomes band-like and stretch flangeability decreases, and if the cooling rate is less than 10 ° C / s, or if the coiling temperature exceeds 700 ° C, carbides and the structure become coarse. Occurs, the local ductility is lowered, and the stretch flangeability may be lowered.
なお、仕上圧延完了後から巻取りまでの冷却途中で1秒以上の空冷を実施するのもフェライト生成が促進され伸び向上に有効である。
製造された熱延鋼板については、通常はスキンパス圧延による形状矯正や酸洗によるスケールの除去が行われ、表面には防錆油が塗布される。
In addition, air cooling for 1 second or more during the cooling from the completion of finish rolling to winding is effective for improving the elongation because ferrite formation is promoted.
The manufactured hot-rolled steel sheet is usually subjected to shape correction by skin pass rolling or scale removal by pickling, and rust preventive oil is applied to the surface.
このように本発明によって製造された鋼板は良好な加工性と良好な表面性状を有する。特に表面性状に関しては、表面および裏面において島状スケール疵を有しない、短辺が200mm以上で長辺が100m以上の加工性と表面性状に優れた熱延鋼帯が製造できる。かかる熱延鋼帯を需要者が使用するに当たり良好な表面の好ましい範囲は、短辺では400mm以上、さらに好ましくは700mm以上、長辺は400m以上、さらに好ましくは600m以上である。換言すれば、本発明によればそのような範囲において島状スケール疵の見られない表面性状の優れた熱延鋼帯が提供できるのである。 Thus, the steel plate manufactured by the present invention has good workability and good surface properties. In particular, with regard to the surface properties, a hot-rolled steel strip having no island-like scale ridges on the front and back surfaces and having excellent workability and surface properties with a short side of 200 mm or more and a long side of 100 m or more can be produced. When a customer uses such a hot-rolled steel strip, the preferable range of the surface is 400 mm or more on the short side, more preferably 700 mm or more, and the long side is 400 m or more, more preferably 600 m or more. In other words, according to the present invention, it is possible to provide a hot-rolled steel strip having an excellent surface property in which no island-like scale defects are observed in such a range.
次に、実施例によって本発明の作用効果についてさらに具体的に説明する。 Next, the effects of the present invention will be described more specifically with reference to examples.
第1表に示す化学組成の鋼を転炉にて溶製後、連続鋳造にてスラブとした。そのスラブに粗熱間圧延を施して板厚36mmの粗バーとし、次いで、仕上げ熱間圧延を施して板厚3.6mmとし、板厚3.6mm、幅1230mm、長さ600mの熱延鋼帯を製造した。 Steel having the chemical composition shown in Table 1 was melted in a converter and then made into a slab by continuous casting. The hot slab is subjected to rough hot rolling to form a rough bar with a thickness of 36 mm, then finish hot rolling to a thickness of 3.6 mm, and a hot rolled steel strip having a thickness of 3.6 mm, a width of 1230 mm, and a length of 600 m. Manufactured.
第2表には熱間圧延条件を示す。なおスラブを加熱炉から抽出後30秒後にデスケーリングを実施した。また粗バーを加熱する場合は、高周波誘導加熱である粗バーヒータにて行った。 Table 2 shows the hot rolling conditions. Note that descaling was performed 30 seconds after the slab was extracted from the heating furnace. Moreover, when heating a rough bar, it performed with the rough bar heater which is high frequency induction heating.
粗熱間圧延完了後の粗バーは粗バーヒータ設備を通過後デスケーリングされて仕上げ熱間圧延に供される。なお、粗熱間圧延終了後から粗バーヒータ通板までの間にデスケーリングは実施していない。 The rough bar after completion of the rough hot rolling is descaled after passing through the rough bar heater equipment, and is subjected to finish hot rolling. Note that descaling is not performed between the end of rough hot rolling and the passage of the rough bar heater.
第2表に示す粗圧延終了後から粗バーヒータ通板完了までの時間と粗バーヒータ通板完了から仕上げ圧延終了までの時間は、いずれも圧延鋼板の先端、つまりトップの位置で決める。粗熱間圧延終了後から粗バーヒータ設備通板完了までの時間が圧延トップとボトムで50秒の差があった。温度は板幅中央位置を測定し、第2表には圧延ボトム位置の温度を示す。粗バーヒータで加熱をしない場合には、粗バーヒータ設備通過完了の温度でボトム部はトップ部より60℃低かった。 The time from the end of rough rolling shown in Table 2 to the completion of rough bar heater passing plate and the time from the completion of rough bar heater passing plate to the end of finish rolling are both determined by the tip of the rolled steel plate, that is, the top position. There was a difference of 50 seconds between the rolling top and the bottom from the completion of rough hot rolling to the completion of rough bar heater installation. The temperature is measured at the center position of the sheet width, and Table 2 shows the temperature at the rolling bottom position. When heating was not performed with the coarse bar heater, the bottom portion was 60 ° C. lower than the top portion at the temperature at which the passage through the coarse bar heater facility was completed.
得られた熱延鋼板について、スキンパスでの平坦矯正および酸洗でのスケール除去を行った後、コイルを巻き戻しながら表裏面検査を行った。また圧延直角方向にJIS5号引張試験片を採取して引張試験、さらに伸びフランジ性を評価するために穴広げ試験も実施した。これらの結果は第3表に示す。 The obtained hot-rolled steel sheet was subjected to flattening with a skin pass and scale removal by pickling, and then the front and back surfaces were inspected while rewinding the coil. In addition, a JIS No. 5 tensile test piece was taken in the direction perpendicular to the rolling, and a tensile test was conducted, and further a hole expansion test was conducted to evaluate stretch flangeability. These results are shown in Table 3.
なお、表裏面検査は、60〜90℃で5〜20%の塩酸水溶液に浸漬する条件での酸洗処理を行ってから行った。幅中央1000mm範囲で全長の600m長さで島状スケール疵のなかったものを◎、幅中央1000mmの範囲で島状スケール疵が1箇所以上あるが400m以上の長さで島状スケール疵のないコイルの製造が可能であったものを○、島状スケール疵が1箇所以上あるが、スリットにて200mm幅で100m以上の長さの島状スケール疵のないコイルを製造できたものを△、スリットで幅切断を実施しても200mm幅で100m以上の長さの島状スケール疵のないコイルを製造できなかったものを×で表し、表裏面検査結果として第3表に合わせて示す。なお△以上(△、○、◎)を合格とした。また島状スケール部の平均粗さRaを測定すると2.0μm以上あり、島状スケール疵のない部分のRaを測定すると1.0μm以下であった。 In addition, the front and back inspection was performed after performing the pickling process on the conditions immersed in 5-20% hydrochloric acid aqueous solution at 60-90 degreeC. The length of the center is 1000mm and the length is 600m, and there is no island scale 疵. The range of the width center is 1000mm and there is one or more island scale 疵, but the length is 400m or more and there is no island scale 島. The one that was able to manufacture the coil was ◯, and there were one or more island-shaped scale ridges, but the one that was able to produce a coil without an island-shaped scale moth with a width of 200 mm and a length of 100 m or more was △, Even if the width was cut with a slit, a coil having a width of 200 mm and a length of 100 m or more without an island-like scale was not indicated by x, and the results of front and back inspection are shown in Table 3. In addition, more than (triangle | delta) ((triangle | delta), (circle), (double-circle)) was set as the pass. Further, when the average roughness Ra of the island-shaped scale portion was measured, it was 2.0 μm or more, and when the Ra of the portion having no island-shaped scale defects was measured, it was 1.0 μm or less.
本発明鋼である試験番号1〜4、15〜32は50%以上の良好な穴広げ性を示し、また本発明範囲を満たす良好な表面性状を示した。粗圧延終了温度と粗バーヒータ加熱温度の両方とも低かった試験番号5、6、9、10、11、粗圧延終了または粗バーヒータ加熱後から仕上げ圧延完了までの時間が長かった試験番号7、8は表面が不良であった。仕上げ温度が低かった試験番号12、熱間圧延後の冷却速度が低かったり巻取温度が高かったりした試験番号13、14は穴拡げ性に劣っていた。 Test Nos. 1 to 4 and 15 to 32, which are steels of the present invention, showed good hole expansion properties of 50% or more, and also exhibited good surface properties satisfying the scope of the present invention. Test Nos. 5, 6, 9, 10, 11 in which both the rough rolling end temperature and the coarse bar heater heating temperature were low, and test Nos. 7 and 8 in which the time from the end of the rough rolling or the heating of the coarse bar heater to the completion of the finish rolling was long The surface was bad. Test No. 12 where the finishing temperature was low and Test Nos. 13 and 14 where the cooling rate after hot rolling was low or the coiling temperature was high were inferior in hole expansibility.
Pが本発明範囲を外れた試験番号33は表面は良好であったが、穴広げ性に劣った。Siが本発明範囲を外れた試験番号34は穴広げ性に劣っていた。Cの高い試験番号35は穴広げ性に劣っていた。 Test No. 33 in which P was out of the scope of the present invention had a good surface, but was inferior in hole expansibility. Test No. 34 in which Si was out of the scope of the present invention was inferior in hole expansibility. Test number 35 with a high C was inferior in hole expansibility.
Claims (9)
(5xP+Al)/Si≦0.728 (I)
ここで、式中のP、AlおよびSiは鋼板中の各元素の含有量(質量%)である。 In mass%, C: 0.02 to 0.25%, Si: 0.04 to 2.5%, Mn: 0.3 to 2.3%, P: 0.050% or less, S: 0.02% or less, Al: 0.005 to 0.50%, and N: 0.02% or less It has a chemical composition in which the balance is composed of iron and impurities, and the contents of P, Al, and Si in the steel satisfy the following formula (I): tensile strength (MPa) and hole expansion rate (% ) Product of 40000 (MPa ·%) or more, no island-scale scales on the front and back surfaces, hot-rolled steel strip with a short side of 200 mm or more and a long side of 100 m or more.
(5xP + Al) /Si≦0.728 (I)
Here, P, Al, and Si in the formula are the contents (mass%) of each element in the steel sheet.
(A)請求項1〜4のいずれかに記載の化学組成を有する鋼塊または鋼片に、圧延完了時の表面温度をFeO とFe2SiO4との共晶点以上とした粗熱間圧延を施して粗バーとする工程;
(B)前記粗バーにデスケーリングを施した後に仕上げ熱間圧延を開始して圧延完了時の表面温度を800℃以上とした仕上げ熱間圧延を前記(A)の工程の後420秒以内に終了する工程;および
(C)前記仕上げ熱間圧延の後、平均冷却速度10℃/s以上で700℃以下まで冷却して巻取る工程。 A method for producing a hot-rolled steel strip comprising the following steps (A) to (C):
(A) Rough hot rolling with the steel ingot or steel slab having the chemical composition according to any one of claims 1 to 4 having a surface temperature at the completion of rolling equal to or higher than the eutectic point of FeO and Fe 2 SiO 4 Giving a rough bar by applying;
(B) After the descaling of the rough bar, the finish hot rolling is started and the finish hot rolling at a surface temperature of 800 ° C. or higher is completed within 420 seconds after the step (A). And (C) a step of cooling and winding up to 700 ° C. or less at an average cooling rate of 10 ° C./s or more after the finish hot rolling.
(a)請求項1ないし4のいずれかに記載の化学組成を有する鋼塊または鋼片に粗熱間圧延を施して粗バーとする工程;
(b)粗熱間圧延終了後に前記粗バーの表面温度をFeO とFe2SiO4との共晶点以上に加熱する工程;
(c)前記(b)の工程の後、前記粗バーにデスケーリングを施した後に仕上げ熱間圧延を開始して圧延完了時の表面温度を800℃以上とした仕上げ熱間圧延を前記(b)の工程の後420秒以内に終了する工程;および
(d)前記仕上げ熱間圧延の後、平均冷却速度10℃/s以上で700℃以下まで冷却して巻取る工程。 A method for producing a hot-rolled steel strip comprising the following steps (a) to (e):
(A) a step of subjecting the steel ingot or steel slab having the chemical composition according to any one of claims 1 to 4 to rough hot rolling to form a rough bar;
(B) a step of heating the surface temperature of the coarse bar to a temperature equal to or higher than the eutectic point of FeO and Fe 2 SiO 4 after completion of the rough hot rolling;
(C) After the step (b), after the descaling is performed on the rough bar, the finish hot rolling is started, and the finish hot rolling is performed at a surface temperature of 800 ° C. or higher when the rolling is completed (b) And (d) a step of cooling to 700 ° C. or lower at an average cooling rate of 10 ° C./s or higher after the finish hot rolling.
(FeO とFe2SiO4との共晶点)=168.15x((5xP+Al)/Si)2-245.12x(5xP+Al)/Si+1170
(II)
ここで、式中のP、AlおよびSiは鋼板中の各元素の含有量(質量%)でありFeOとFe2SiO4との共晶点の単位は℃である。 The method for producing a hot-rolled steel strip according to claim 5 or 6, wherein the eutectic point of the FeO and Fe 2 SiO 4 is a temperature given by the following formula (II).
(Eutectic point of FeO and Fe 2 SiO 4 ) = 168.15x ((5xP + Al) / Si) 2 -245.12x (5xP + Al) / Si + 1170
(II)
Here, P, Al, and Si in the formula are the contents (mass%) of each element in the steel sheet, and the unit of eutectic point of FeO and Fe 2 SiO 4 is ° C.
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