JP4025718B2 - Extremely low carbon steel sheet excellent in surface properties, workability and formability, and method for producing the same - Google Patents
Extremely low carbon steel sheet excellent in surface properties, workability and formability, and method for producing the same Download PDFInfo
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- 229910001209 Low-carbon steel Inorganic materials 0.000 title claims description 29
- 238000004519 manufacturing process Methods 0.000 title claims description 20
- 229910000831 Steel Inorganic materials 0.000 claims description 145
- 239000010959 steel Substances 0.000 claims description 145
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 41
- 229910052760 oxygen Inorganic materials 0.000 claims description 41
- 239000001301 oxygen Substances 0.000 claims description 41
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical group [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 26
- 229910052799 carbon Inorganic materials 0.000 claims description 19
- 229910052802 copper Inorganic materials 0.000 claims description 19
- 229910052758 niobium Inorganic materials 0.000 claims description 18
- 238000000034 method Methods 0.000 claims description 15
- 229910052742 iron Inorganic materials 0.000 claims description 13
- OKTJSMMVPCPJKN-UHFFFAOYSA-N Carbon Chemical compound [C] OKTJSMMVPCPJKN-UHFFFAOYSA-N 0.000 claims description 11
- 238000005266 casting Methods 0.000 claims description 11
- 229910052748 manganese Inorganic materials 0.000 claims description 10
- 229910052710 silicon Inorganic materials 0.000 claims description 10
- 238000003756 stirring Methods 0.000 claims description 8
- 238000009849 vacuum degassing Methods 0.000 claims description 6
- 239000012535 impurity Substances 0.000 claims description 4
- 230000005499 meniscus Effects 0.000 claims description 4
- 238000005261 decarburization Methods 0.000 claims description 3
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 20
- 230000007547 defect Effects 0.000 description 15
- 238000007711 solidification Methods 0.000 description 12
- 230000008023 solidification Effects 0.000 description 12
- 239000010960 cold rolled steel Substances 0.000 description 10
- 239000007789 gas Substances 0.000 description 5
- 238000005054 agglomeration Methods 0.000 description 4
- 230000002776 aggregation Effects 0.000 description 4
- 238000005097 cold rolling Methods 0.000 description 4
- 238000009749 continuous casting Methods 0.000 description 4
- 239000006185 dispersion Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000007670 refining Methods 0.000 description 4
- 229910045601 alloy Inorganic materials 0.000 description 3
- 239000000956 alloy Substances 0.000 description 3
- 238000004581 coalescence Methods 0.000 description 3
- 238000007796 conventional method Methods 0.000 description 3
- 238000005098 hot rolling Methods 0.000 description 3
- 238000007689 inspection Methods 0.000 description 3
- 239000000463 material Substances 0.000 description 3
- 230000000007 visual effect Effects 0.000 description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 2
- GWEVSGVZZGPLCZ-UHFFFAOYSA-N Titan oxide Chemical compound O=[Ti]=O GWEVSGVZZGPLCZ-UHFFFAOYSA-N 0.000 description 2
- 230000000052 comparative effect Effects 0.000 description 2
- 238000005336 cracking Methods 0.000 description 2
- 230000004907 flux Effects 0.000 description 2
- 230000008018 melting Effects 0.000 description 2
- 238000002844 melting Methods 0.000 description 2
- 239000002245 particle Substances 0.000 description 2
- 239000002244 precipitate Substances 0.000 description 2
- 238000010992 reflux Methods 0.000 description 2
- ATJFFYVFTNAWJD-UHFFFAOYSA-N Tin Chemical compound [Sn] ATJFFYVFTNAWJD-UHFFFAOYSA-N 0.000 description 1
- 239000002253 acid Substances 0.000 description 1
- 239000000654 additive Substances 0.000 description 1
- 230000000996 additive effect Effects 0.000 description 1
- 238000000137 annealing Methods 0.000 description 1
- 239000010953 base metal Substances 0.000 description 1
- 238000004140 cleaning Methods 0.000 description 1
- 230000007423 decrease Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000009826 distribution Methods 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- 238000009830 intercalation Methods 0.000 description 1
- 230000002687 intercalation Effects 0.000 description 1
- 230000000116 mitigating effect Effects 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- 229910052759 nickel Inorganic materials 0.000 description 1
- 230000003287 optical effect Effects 0.000 description 1
- 239000000843 powder Substances 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000001953 recrystallisation Methods 0.000 description 1
- 239000011819 refractory material Substances 0.000 description 1
- 238000005096 rolling process Methods 0.000 description 1
- 238000005070 sampling Methods 0.000 description 1
- 229910052814 silicon oxide Inorganic materials 0.000 description 1
- 239000007784 solid electrolyte Substances 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 238000001179 sorption measurement Methods 0.000 description 1
- 238000009628 steelmaking Methods 0.000 description 1
- 239000000126 substance Substances 0.000 description 1
Classifications
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B22/00—Use of inorganic materials as active ingredients for mortars, concrete or artificial stone, e.g. accelerators, shrinkage compensating agents
- C04B22/0093—Aluminates
-
- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B28/00—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements
- C04B28/02—Compositions of mortars, concrete or artificial stone, containing inorganic binders or the reaction product of an inorganic and an organic binder, e.g. polycarboxylate cements containing hydraulic cements other than calcium sulfates
Description
本発明は、表面性状性、加工性および成形性に優れた極低炭素鋼板およびその製造方法に関するものである。 The present invention relates to an ultra-low carbon steel sheet excellent in surface properties, workability and formability, and a method for producing the same.
転炉や真空処理容器で精錬された溶鋼中には、多量の溶存酸素が含まれており、この過剰酸素は酸素との親和力が強い強脱酸元素であるＡｌにより脱酸されるのが一般的である。しかし、Ａｌは脱酸によりアルミナ系介在物を生成し、これが凝集合体して粗大なアルミナクラスターとなる。このアルミナクラスターは鋼板製造時に表面疵発生の原因となり、薄鋼板の品質を大きく劣化させる。特に、炭素濃度が低く、精錬後の溶存酸素濃度が高い薄鋼板用素材である極低炭素溶鋼では、アルミナクラスターの量が非常に多く、表面疵の発生率が極めて高いため、アルミナ系介在物の低減対策は大きな課題となっている。 The molten steel smelted in the converter or vacuum processing vessel contains a large amount of dissolved oxygen, and this excess oxygen is generally deoxidized by Al, which is a strong deoxidizing element with a strong affinity for oxygen. Is. However, Al produces alumina inclusions by deoxidation, which aggregate and coalesce into coarse alumina clusters. This alumina cluster causes surface flaws during the production of the steel sheet and greatly deteriorates the quality of the thin steel sheet. In particular, ultra-low carbon molten steel, which is a material for thin steel sheets with a low carbon concentration and a high dissolved oxygen concentration after refining, has a very high amount of alumina clusters and a very high rate of surface flaws. Measures to reduce this are a major issue.
これに対して、従来は（特許文献１）の介在物吸着用フラックスを溶鋼表面に添加してアルミナ系介在物を除去する方法、或いは（特許文献２）の注入流を利用してＣａＯフラックスを溶鋼中に添加し、これによりアルミナ系介在物を吸着除去する方法が提案、実施されてきた。一方、アルミナ系介在物を除去するのではなく、生成させない方法として、（特許文献３）にあるように溶鋼をＭｇで脱酸し、Ａｌでは殆ど脱酸しない薄鋼板用溶鋼の溶製方法も開示されている。
しかしながら、上述の特許文献１や特許文献２に記載されている様な、アルミナ系介在物を除去する方法では、極低炭素溶鋼中に多量に生成したアルミナ系介在物を表面疵が発生しない程度まで低減することは非常に難しい。
また、特許文献３に記載されている様な、アルミナ系介在物を全く生成しないＭｇ脱酸では、Ｍｇの蒸気圧が高く、溶鋼への歩留まりが非常に低いため、極低炭素鋼のように溶存酸素濃度が高い溶鋼をＭｇだけで脱酸するには多量のＭｇを必要とし、製造コストを考えると実用的なプロセスとは言えない。
これらの問題を鑑み、本発明は溶鋼中で殆ど介在物を生成させることなく、凝固時に酸化物を微細分散させることにより、確実に表面疵を防止した上で、加工性と成形性にも優れた極低炭素鋼板とその製造方法を提示することを目的とする。
However, in the method for removing alumina inclusions as described in Patent Document 1 and Patent Document 2 described above, surface flaws are not generated in the alumina inclusions produced in a large amount in the ultra-low carbon molten steel. It is very difficult to reduce to
In addition, Mg deoxidation that does not produce any alumina inclusions as described in Patent Document 3 has a high vapor pressure of Mg and a very low yield to molten steel, so that it is like an ultra-low carbon steel. In order to deoxidize molten steel having a high dissolved oxygen concentration with only Mg, a large amount of Mg is required.
In view of these problems, the present invention is excellent in workability and formability while reliably preventing surface flaws by finely dispersing oxides during solidification without generating inclusions in the molten steel. An object of the present invention is to present a very low carbon steel sheet and a method for producing the same.
上記課題を解決するために、本発明は以下の構成を要旨とする。
（１）溶鋼の炭素濃度を０．００５質量％以下まで脱炭した後、該溶鋼にＣｕとＮｂを添加し、溶鋼中にＣｕを０．０１〜３．０質量％、Ｎｂを
−０．０１５≦｛Ｎｂ−（９３／１２）×Ｃ−（９３／１４）×Ｎ｝≦０．２
となるように含有させ、溶鋼中の溶存酸素濃度が０．０１質量％以上、０．０６質量％以下である溶鋼を鋳造することを特徴とする極低炭素鋼鋳片の製造方法。
（２）溶鋼の炭素濃度を０．００５質量％以下まで脱炭した後、該溶鋼にＣｕとＮｂを添加し、溶鋼中にＣｕを０．０１〜３．０質量％、Ｎｂを
−０．０１５≦｛Ｎｂ−（９３／１２）×Ｃ−（９３／１４）×Ｎ｝≦０．２
となるように含有させ、さらに酸可溶Ａｌ濃度が０．００５質量％以下となるようにＡｌを添加して、および／または、Ｔｉ濃度が０．０１質量％以下となるようにＴｉを添加して、溶鋼中の溶存酸素濃度を０．０１質量％以上、０．０６質量％以下に調整した溶鋼を鋳造することを特徴とする極低炭素鋼鋳片の製造方法。
（３）Ｎｉを０．５×Ｃｕ濃度以下となるように含有させることを特徴とする請求項１または２に記載の極低炭素鋼鋳片の製造方法。
（４）Ｓｉを０．００５質量％以上、０．０３質量％以下、Ｍｎを０．０８質量％以上、０．３質量％以下となるように含有させることを特徴とする（１）〜（３）のいずれかに記載の極低炭素鋼鋳片の製造方法。
（５）溶鋼の脱炭に際し、真空脱ガス処理により行うことを特徴とする（１）〜（４）のいずれかに記載の極低炭素鋼鋳片の製造方法。
（６）溶鋼を鋳造するに際し、電磁攪拌を行いながら鋳造することを特徴とする（１）〜（５）のいずれかに記載の極低炭素鋼鋳片の製造方法。
（７）溶鋼を鋳造するに際し、電磁攪拌を行って、メニスカス位置における溶鋼を４０ｃｍ／ｓ以上、１００ｃｍ／ｓ以下の平均流速で旋回させながら鋳造することを特徴とする（１）〜（６）のいずれかに記載の極低炭素鋼鋳片の製造方法。
（８）（１）、（５）〜（７）のいずれかに記載の方法により製造された鋼板であって、
Ｃ：０．００５質量％以下、Ｃｕ：０．０１〜３．０質量％、さらにＮｂを
−０．０１５≦｛Ｎｂ−（９３／１２）×Ｃ−（９３／１４）×Ｎ｝≦０．２
を満足するように含有し、残部が鉄および不可避的不純物である鋼であって、その鋼中には直径０．５μｍから３０μｍの微細酸化物が１０００個／ｃｍ２以上、１００００００個／ｃｍ２以下分散しており、該微細酸化物の個数割合で４０％以上が少なくともＳｉ、Ｍｎ、Ｆｅを含んでいることを特徴とする極低炭素鋼板。
（９）（２）、（５）〜（７）のいずれかに記載の方法により製造された鋼板であって、
Ｃ：０．００５質量％以下、酸可溶Ａｌ濃度が０．００５質量％以下および／またはＴｉ濃度が０．０１質量％以下、Ｃｕ：０．０１〜３．０質量％、さらにＮｂを
−０．０１５≦｛Ｎｂ−（９３／１２）×Ｃ−（９３／１４）×Ｎ｝≦０．２
を満足するように含有し、残部が鉄および不可避的不純物である鋼であって、その鋼中には直径０．５μｍから３０μｍの微細酸化物が１０００個／ｃｍ２以上、１００００００個／ｃｍ２以下分散しており、該酸化物の個数割合で４０％以上が少なくともＳｉ、Ｍｎ、Ｆｅを含んでいることを特徴とする極低炭素鋼板。
（１０）Ｎｉ：０．５×Ｃｕ質量％以下を含有する鋼であることを特徴とする（８）または（９）に記載の極低炭素鋼板。
（１１）Ｓｉ：０．００５質量％以上、０．０３質量％以下、Ｍｎ：０．０８質量％以上、０．３質量％以下を含有する鋼であることを特徴とする（８）〜（１０）のいずれかに記載の極低炭素鋼板。
（１２）前記の鋼中に存在する酸化物の個数割合で４０％以上が少なくともＳｉ酸化物、Ｍｎ酸化物、Ｆｅ酸化物の含有率で、２０質量％以上であることを特徴とする（８）〜（１１）のいずれかに記載の極低炭素鋼板。
In order to solve the above-described problems, the present invention has the following configuration.
( 1 ) After decarburizing the molten steel to a carbon concentration of 0.005 mass% or less, Cu and Nb are added to the molten steel, and the molten steel contains 0.01 to 3.0 mass% of Cu and Nb of -0. 015 ≦ {Nb− (93/12) × C− (93/14) × N} ≦ 0.2
And it is contained so that the dissolved oxygen concentration in the soluble steel 0.01 mass% or more, the production method of ultra-low carbon steel slab characterized by casting molten steel is 0.06 wt% or less.
(2) After decarburizing the molten steel to a carbon concentration of 0.005% by mass or less, Cu and Nb are added to the molten steel, and 0.01 to 3.0% by mass of Cu and Nb of −0. 015 ≦ {Nb− (93/12) × C− (93/14) × N} ≦ 0.2
In addition , Al is added so that the acid-soluble Al concentration is 0.005% by mass or less, and / or Ti is added so that the Ti concentration is 0.01% by mass or less. And the manufacturing method of the ultra-low carbon steel slab characterized by casting the molten steel which adjusted the dissolved oxygen concentration in molten steel to 0.01 mass% or more and 0.06 mass% or less.
(3) The method of producing ultra low carbon steel cast slab according to claim 1 or 2 N i, characterized in that it is contained to be equal to or less than 0.5 × Cu concentration.
( 4 ) Si is contained so as to be 0.005% by mass or more and 0.03% by mass or less, and Mn is contained by 0.08% by mass or more and 0.3% by mass or less (1) to ( 3) The method for producing an ultra-low carbon steel slab according to any one of 3).
( 5 ) The method for producing an ultra-low carbon steel slab according to any one of (1) to ( 4) , wherein the decarburization of the molten steel is performed by vacuum degassing.
( 6 ) The method for producing an ultra low carbon steel slab according to any one of (1) to ( 5 ), wherein molten steel is cast while performing electromagnetic stirring.
( 7 ) When casting molten steel, electromagnetic stirring is performed, and the molten steel at the meniscus position is cast while turning at an average flow velocity of 40 cm / s or more and 100 cm / s or less (1) to ( 6 ). The manufacturing method of the ultra-low carbon steel slab in any one of.
( 8 ) (1) It is the steel plate manufactured by the method in any one of (5)-(7),
C: 0.005 mass% or less, Cu: 0.01-3.0 mass%, and Nb −0.015 ≦ {Nb− (93/12) × C− (93/14) × N} ≦ 0 .2
In which the balance is iron and unavoidable impurities, and the steel contains fine oxides having a diameter of 0.5 μm to 30 μm of 1000 / cm 2 or more and 1000000 / cm 2. An ultra-low carbon steel sheet which is dispersed below , and 40% or more of the fine oxides contain at least Si, Mn and Fe .
( 9 ) (2) A steel plate manufactured by the method according to any one of (5) to (7),
C: 0.005 mass% or less, acid-soluble Al concentration is 0.005 mass% or less and / or Ti concentration is 0.01 mass% or less, Cu: 0.01 to 3.0 mass%, and Nb − 0.015 ≦ {Nb− (93/12) × C− (93/14) × N} ≦ 0.2
In which the balance is iron and unavoidable impurities, and the steel contains fine oxides having a diameter of 0.5 μm to 30 μm of 1000 / cm 2 or more and 1000000 / cm 2. An ultra-low carbon steel sheet that is dispersed below and 40% or more of the oxides contain at least Si, Mn, and Fe .
( 10 ) The ultra-low carbon steel sheet according to ( 8) or (9), wherein the steel contains Ni: 0.5 × Cu mass% or less.
( 11 ) Si: 0.005% by mass or more and 0.03% by mass or less, Mn: 0.08% by mass or more, 0.3% by mass or less steel containing (8) to (8) 10) The ultra-low carbon steel sheet according to any one of 10) .
( 12 ) The number ratio of oxides present in the steel is 40% or more, and the content of at least Si oxide, Mn oxide and Fe oxide is 20% by mass or more (8 ) To (11) .
本発明によると、溶鋼中に殆ど介在物を生成させることなく、凝固時に酸化物を微細に析出させることができるため、確実に表面疵を防止でき、且つ鋼板中のＣを固定すると共に、熱延鋼板の集合組織をも制御できるため加工性、成形性にも優れた薄鋼板を製造することが可能となる。 According to the present invention, the oxide can be finely precipitated at the time of solidification without generating almost any inclusions in the molten steel, so that surface flaws can be reliably prevented and C in the steel sheet can be fixed, Since the texture of the rolled steel sheet can also be controlled, it is possible to manufacture a thin steel sheet having excellent workability and formability.
以下に本発明を詳細に説明する。
本発明の製造法では、転炉や電気炉等の製鋼炉で精錬して、或いはさらに真空脱ガス処理等を行って、炭素濃度を０．００５質量％以下とした溶鋼にＣｕとＮｂを添加し、且つ溶存酸素濃度を０．０１〜０．０６質量％になるように調整する。
この溶製法の基本思想は、鋳造時に酸素と反応してＣＯガスを発生させない程度まで炭素濃度を低減し、且つＡｌを殆ど添加せず、溶存酸素を多量に残すことにより、溶鋼中に殆ど介在物を生成させず、且つ脱酸力の極めて弱いＮｂとＣｕを添加してＣ、Ｎの固定と集合組織制御を行うことで、薄板用鋼板としての材質をも確保することにある。
The present invention is described in detail below.
In the production method of the present invention, Cu and Nb are added to molten steel that has been refined in a steelmaking furnace such as a converter or an electric furnace, or further subjected to vacuum degassing treatment to a carbon concentration of 0.005 mass% or less. And the dissolved oxygen concentration is adjusted to 0.01 to 0.06 mass%.
The basic idea of this melting method is to reduce the carbon concentration to such an extent that it does not generate CO gas by reacting with oxygen during casting. Almost no intercalation is present in molten steel by adding little Al and leaving a large amount of dissolved oxygen. It is to secure the material for the steel sheet for the thin plate by adding Nb and Cu which have no deoxidizing power and performing C and N fixation and texture control.
転炉や真空処理容器で脱炭処理された溶鋼中には、多量の溶存酸素が含まれており、この溶存酸素は通常Ａｌの添加により殆ど脱酸される（（１）式の反応）ため、多量のアルミナ系介在物を生成する。
２Ａｌ＋３Ｏ＝Ａｌ２Ｏ３ （１）
このアルミナ系介在物は脱酸直後からお互いに凝集合体し、粗大なアルミナ系介在物となり、鋼板製造時に表面欠陥発生の原因となる。しかし、脱炭処理後の溶鋼中にＡｌを全く添加しないか、或いは添加する場合でも少量を添加し、殆ど脱酸しなければ、多量の溶存酸素が溶鋼中に含まれているが、介在物は殆ど生成せず、非常に清浄性の高い溶鋼が得られる。通常、このような溶存酸素の高い溶鋼を鋳造すると、凝固時にＣＯガスが発生し、激しい突沸現象が生じると共に、鋳片内に多量の気泡が捕捉されるため、鋳造性が悪化するだけでなく、鋳片品質も大きく低下する。そこで、本発明では、Ａｌを全く添加しない、あるいは殆ど添加せずに溶存酸素を残す代わりに、Ｃ濃度を極力低下させることにより、凝固時のＣＯガス発生を抑制することに着目した。その結果、実験的検討からＣ濃度を０．００５質量％以下にすれば、凝固時のＣＯガス発生速度は極めて低下することが判明した。
The molten steel decarburized in a converter or vacuum processing vessel contains a large amount of dissolved oxygen, and this dissolved oxygen is usually almost deoxidized by the addition of Al (reaction (1)). A large amount of alumina inclusions are produced.
2Al + 3O = Al 2 O 3 (1)
The alumina inclusions aggregate and coalesce with each other immediately after deoxidation to form coarse alumina inclusions, which cause surface defects during steel plate production. However, if Al is not added at all in the molten steel after decarburization treatment or if a small amount is added and almost no deoxidization is performed, a large amount of dissolved oxygen is contained in the molten steel. Is hardly produced, and a very clean steel can be obtained. Normally, when casting such molten steel with high dissolved oxygen, CO gas is generated during solidification, and a severe bumping phenomenon occurs, and a large amount of bubbles are trapped in the slab, which not only deteriorates the castability. The slab quality is also greatly reduced. Therefore, in the present invention, attention was focused on suppressing CO gas generation during solidification by reducing the C concentration as much as possible instead of leaving Al with little or no addition of Al. As a result, it has been found from experimental studies that the CO gas generation rate during solidification is extremely reduced when the C concentration is 0.005 mass% or less.
薄板用鋼板においては加工性を高めるために、Ｃ濃度を極力低下させるとともに、鋼中に固溶したＣとＮを他元素の添加により固定することが重要である。通常、ＡｌやＴｉ等が鋼中のＣとＮを固定する元素として使用されるが、これらの元素をＣやＮを固定するに十分な量を添加すると溶鋼を強く脱酸してしまう。
そこで、本発明ではＮやＣを十分に固定できる程度の量を添加しても、殆ど溶鋼を脱酸しないような、脱酸力が極めて弱い元素としてＮｂを添加することを見出した。しかし、Ｎｂ添加だけでは、得られる鋼板の全伸びは大幅に改善されるものの、ランクフォード値（ｒ値と記載する）は通常Ａｌ脱酸のＴｉ添加極低炭素鋼に比べて若干低めの値となる。
そこで、本発明者らは鋼板においてｒ値向上に適した板面方位｛１１１｝の集合組織を発達させ易い添加元素について詳細に検討したところ、酸素濃度が高い本発明の鋼板ではＣｕ添加が最も有効であることを見いだした。
したがって、本発明では、鋼板の加工性、すなわち全伸びとｒ値の両方を高めるために、ＮｂとＣｕの両方を添加する必要がある。
In the steel sheet for thin plate, in order to improve workability, it is important to reduce the C concentration as much as possible and fix C and N dissolved in the steel by adding other elements. Usually, Al, Ti or the like is used as an element for fixing C and N in the steel, but if these elements are added in an amount sufficient to fix C or N, the molten steel is strongly deoxidized.
Therefore, in the present invention, it has been found that Nb is added as an element having a very weak deoxidizing power so as to hardly deoxidize molten steel even if an amount sufficient to fix N or C is added. However, although the total elongation of the resulting steel sheet is greatly improved by adding Nb alone, the Rankford value (described as r value) is slightly lower than that of Ti-added ultra-low carbon steel that is usually Al deoxidized. It becomes.
Therefore, the present inventors have studied in detail the additive elements that are easy to develop a texture of the plate surface orientation {111} suitable for improving the r value in the steel sheet, and Cu addition is the most in the steel sheet of the present invention having a high oxygen concentration. I found it effective.
Therefore, in the present invention, it is necessary to add both Nb and Cu in order to improve the workability of the steel sheet, that is, both the total elongation and the r value.
上記の様にＣ濃度を０．００５質量％以下まで脱炭しても、溶鋼中の溶存酸素濃度が高過ぎると、凝固時のＣＯガス発生を抑制することはできないため、この場合溶存酸素濃度もある程度低くする必要がある。
これら過剰な溶存酸素分だけであれば、ＡｌやＴｉ等で脱酸することは可能であるが、実験的な検討から溶存酸素濃度で０．０１質量％よりも低下させるまで脱酸すると、アルミナやチタニア等の介在物が多くなり過ぎ、浮上除去されずに溶鋼中に残留してしまう。
また、ＮｂとＣｕを添加した際に、溶存酸素濃度が本発明の範囲であれば、ＡｌやＴｉ等を全く添加しなくても良い。
反対に、溶存酸素濃度が０．０６質量％を超えると、Ｃ濃度を０．００５質量％以下に下げても鋳片内にＣＯ気泡が捕捉されてしまうため、圧延後に気泡系の欠陥が発生する。
よって、溶鋼中の溶存酸素濃度は０．０１質量％以上、０．０６質量％以下にする必要がある。なお、溶鋼中の溶存酸素濃度は固体電解質を用いた酸素センサーにより、Ｃ濃度については溶鋼サンプリング法により分析することができる。
Even if the carbon concentration is decarburized to 0.005 mass% or less as described above, if the dissolved oxygen concentration in the molten steel is too high, CO gas generation during solidification cannot be suppressed. Needs to be lowered to some extent.
If it is only these excessive dissolved oxygen components, it is possible to deoxidize with Al, Ti, etc., but if it is deoxidized from an experimental study until the dissolved oxygen concentration is reduced to less than 0.01% by mass, alumina will be removed. And too much inclusions such as titania remain in the molten steel without being lifted and removed.
Further, when Nb and Cu are added, if the dissolved oxygen concentration is within the range of the present invention, it is not necessary to add Al or Ti at all.
On the other hand, if the dissolved oxygen concentration exceeds 0.06% by mass, CO bubbles are trapped in the slab even if the C concentration is lowered to 0.005% by mass or less, resulting in bubble-type defects after rolling. To do.
Therefore, the dissolved oxygen concentration in the molten steel needs to be 0.01% by mass or more and 0.06% by mass or less. The dissolved oxygen concentration in the molten steel can be analyzed by an oxygen sensor using a solid electrolyte, and the C concentration can be analyzed by a molten steel sampling method.
次に、溶鋼に添加されたＮｂの好ましい溶鋼中の濃度について説明する。Ｎｂは、Ｃ、Ｎを析出物として固定することにより鋼板の加工性を向上させる働きをする。しかし、必要以上に添加すると固溶Ｎｂとして鋼中に存在し、再結晶温度を上昇させるため、これに対応した焼鈍温度で処理しないと、熱間加工組織が存在し易くなり延性を低下させる。
従って、溶鋼へのＮｂの好ましい添加範囲は、各元素の化学当量を用いて記述される次式の中辺を指標として用いると適切に表すことができる。すなわち、次式の中辺の値が−０．０１５未満、および０．２を超えると延性が低下し易くなる。以上の理由から、
−０．０１５≦｛Ｎｂ−（９３／１２）×Ｃ−（９３／１４）×Ｎ｝≦０．２
の関係を満たすことが好ましい。
また、この範囲のＮｂ添加量であれば、Ｎｂと平衡する酸素濃度は０．０１質量％以上であり、Ｎｂを添加しても溶存酸素を０．０１質量％以上確保できる。
Next, the preferable concentration of Nb added to the molten steel in the molten steel will be described. Nb functions to improve the workability of the steel sheet by fixing C and N as precipitates. However, if it is added more than necessary, it exists in the steel as solid solution Nb and raises the recrystallization temperature. Therefore, if it is not treated at an annealing temperature corresponding to this, a hot-worked structure tends to exist and ductility is lowered.
Therefore, the preferable addition range of Nb to the molten steel can be appropriately expressed by using the middle side of the following formula described using the chemical equivalent of each element as an index. That is, when the value of the middle side of the following formula is less than −0.015 and exceeds 0.2, the ductility tends to be lowered. For the above reasons,
−0.015 ≦ {Nb− (93/12) × C− (93/14) × N} ≦ 0.2
It is preferable to satisfy the relationship.
Further, if the amount of Nb added is within this range, the oxygen concentration in equilibrium with Nb is 0.01% by mass or more, and even if Nb is added, dissolved oxygen can be secured at 0.01% by mass or more.
次に、溶鋼に添加されたＣｕの好ましい溶鋼中の濃度について説明する。Ｃｕは鋼板において高ｒ値が得られ易い｛１１１｝方位の集合組織を発達させる効果を有しており、最低でも０．０１質量％以上添加しないとその効果が現れにくいので、添加量は０．０１質量％以上とすることが好ましい。一方、Ｃｕ添加量が３．０質量％を超えると、Ｃｕ脆化に起因して熱延後の鋼板表面性状が悪化し易いため、上限値を３．０質量％とすることが好ましい。 Next, the preferable density | concentration in the molten steel of Cu added to molten steel is demonstrated. Cu has the effect of developing a texture of {111} orientation in which a high r value is easily obtained in a steel sheet. Since the effect is difficult to appear unless it is added at least 0.01% by mass, the addition amount is 0. It is preferable to set it to 0.01 mass% or more. On the other hand, if the Cu addition amount exceeds 3.0% by mass, the steel sheet surface properties after hot rolling are likely to deteriorate due to Cu embrittlement, so the upper limit is preferably set to 3.0% by mass.
ＮｉはＣｕによる熱延表面性状の悪化を緩和する効果があり、質量ベースでＣｕの半分超を目安に添加するのが一般的である。本発明の酸素濃度が高い鋼板では、溶鋼中の溶存酸素濃度が０．０１質量％以上の場合、熱延板のスケール・地鉄界面が平滑化され、スケール剥離性が向上することにより、Ｃｕ脆化が抑制されることを見いだしている。このため、本発明では、Ｎｉを添加しない状態でも、熱延板の表面性状は良好となり本発明の特徴を最大限に引き出せるが、必要な場合にはＣｕの半分以下の量でＮｉを添加しても良い。元々熱延板の表面性状が良い本鋼板において、従来のＣｕ添加鋼並にＮｉを添加しても、コスト上昇を招くのみであり、Ｎｉの上限値はＣｕ濃度の１／２以下とすることが好ましい。 Ni has the effect of mitigating the deterioration of hot rolled surface properties due to Cu, and it is common to add more than half of Cu on a mass basis. In the steel sheet having a high oxygen concentration of the present invention, when the dissolved oxygen concentration in the molten steel is 0.01% by mass or more, the scale-base metal interface of the hot-rolled sheet is smoothed, and the scale peelability is improved. It has been found that embrittlement is suppressed. For this reason, in the present invention, even when Ni is not added, the surface properties of the hot-rolled sheet are good and the characteristics of the present invention can be maximized. However, if necessary, Ni is added in an amount less than half of Cu. May be. In the present steel sheet having a good surface property of the hot-rolled sheet, even if Ni is added to the conventional Cu-added steel, the cost is only increased, and the upper limit value of Ni should be 1/2 or less of the Cu concentration. Is preferred.
最近では、連続鋳造機内に鋳型内電磁攪拌装置、あるいは電磁コイルが装備されるようになっており、これらを用いることで、ＣＯ気泡を鋳片に捕捉させることなく、鋳造できることを知見した。本発明者らは凝固時に電磁攪拌を行う際の、鋳型内メニスカスにおける溶鋼流速を４０〜１００ｃｍ／ｓ程度確保すれば、溶存酸素濃度を０．０６質量％程度にしてもＣＯ気泡を鋳片に殆ど捕捉させることなく、鋳造できるためより好ましいことを知見している。なお、電磁攪拌による溶鋼の旋回流速が４０ｃｍ／ｓ未満では十分なＣＯ気泡の洗浄効果が得られにくく、旋回流速が１００ｃｍ／ｓ超ではＣＯ気泡は洗浄されるが、溶鋼表面にあるモールドパウダーを巻き込み、表面欠陥が発生し易くなる。 Recently, an in-mold electromagnetic stirrer or an electromagnetic coil has been installed in a continuous casting machine, and it has been found that casting can be performed without trapping CO bubbles in a slab. When the present inventors secure a flow rate of molten steel at the meniscus in the mold of about 40 to 100 cm / s when performing electromagnetic stirring during solidification, the CO bubbles are formed in the slab even if the dissolved oxygen concentration is about 0.06% by mass. It has been found that it is more preferable because it can be cast with almost no capture. In addition, if the swirling flow velocity of the molten steel by electromagnetic stirring is less than 40 cm / s, it is difficult to obtain a sufficient CO bubble cleaning effect. If the swirling flow velocity exceeds 100 cm / s, the CO bubbles are washed, but the mold powder on the molten steel surface is removed. Entrainment and surface defects are likely to occur.
次に、本発明の鋼板について説明する。なお、上記方法で製造した鋳片を熱間圧延して得られる熱延鋼板、さらに冷間圧延して得られる冷延鋼板等の、鋳片を加工して得られる鋼板を、本発明では鋼板と定義する。
溶鋼中のＣ濃度を非常に低くすると、溶存酸素は鋳造中にＦｅ酸化物系介在物として析出する。このＦｅ酸化物系介在物は溶鋼中で生成するのではなく、凝固時に析出するため、凝集合体することなく、鋳片内に微細に分散する。なお、Ｆｅ酸化物系介在物とは純粋なＦｅ酸化物だけでなく、Ｓｉ酸化物やＭｎ酸化物等と複合化した酸化物も含む。従って、本発明の様な極低炭素鋼の鋼板においては、少なくとも酸化物としてＳｉ、Ｍｎ、Ｆｅが含まれている。言い換えれば、Ｓｉ、Ｍｎ、Ｆｅの各酸化物の１種以上が含まれている。
Next, the steel plate of the present invention will be described. In the present invention, a steel plate obtained by processing a slab, such as a hot-rolled steel plate obtained by hot rolling a slab produced by the above method, and a cold-rolled steel plate obtained by cold rolling, is a steel plate in the present invention. It is defined as
When the C concentration in the molten steel is very low, dissolved oxygen precipitates as Fe oxide inclusions during casting. The Fe oxide inclusions are not formed in the molten steel, but are precipitated during solidification, so that they are finely dispersed in the slab without agglomeration and coalescence. The Fe oxide inclusions include not only pure Fe oxides but also oxides complexed with Si oxides, Mn oxides, and the like. Therefore, the ultra-low carbon steel plate as in the present invention contains at least Si, Mn, and Fe as oxides. In other words, one or more oxides of Si, Mn, and Fe are included.
また、本発明の鋼板中にある介在物分散状態を評価したところ、直径０．５μｍから３０μｍの微細酸化物が鋼板中に１０００個／ｃｍ２以上１００００００個／ｃｍ２以下分散しており、この様に介在物が微細に分散していることで、表面欠陥の防止を達成できる。
尚、上記微細酸化物の直径を０．５μｍから３０μｍとしたのは、本発明の鋼板における介在物の大きさがほぼ０．５μｍから３０μｍの範囲にほぼ収まっているためであり、３０μｍ程度の大きさの介在物であれば表面欠陥を十分に防止できる。
また、介在物分散状態として１０００個／ｃｍ２以上１００００００個／ｃｍ２以下としたのは、本発明における鋼板の介在物がこの個数密度の範囲内にある場合、表面欠陥が発生しないためである。
ここで、介在物の分散状態は、鋼板の研磨面を１００倍と１０００倍の光学顕微鏡で観察し、単位面積内の介在物粒径分布を評価した。この介在物の粒径、すなわち直径とは長径と短径を測定し、（長径×短径）０．５とした。
Moreover, when the inclusion dispersion state in the steel sheet of the present invention was evaluated, fine oxides having a diameter of 0.5 μm to 30 μm were dispersed in the steel sheet at 1000 / cm 2 or more and 1000000 / cm 2 or less. Thus, the inclusion of fine inclusions can prevent the surface defects.
The reason why the diameter of the fine oxide is set to 0.5 μm to 30 μm is because the size of the inclusions in the steel sheet of the present invention is substantially within the range of about 0.5 μm to 30 μm, which is about 30 μm. If the inclusion has a size, surface defects can be sufficiently prevented.
The inclusion dispersion state is set to 1000 / cm 2 or more and 1000000 / cm 2 or less because the surface defects do not occur when the inclusions of the steel sheet in the present invention are within the number density range. .
Here, regarding the dispersion state of inclusions, the polished surface of the steel sheet was observed with an optical microscope of 100 times and 1000 times, and the inclusion particle size distribution within a unit area was evaluated. The particle size of the inclusion, that is, the diameter was measured by measuring the major axis and the minor axis, and was set to 0.5 (major axis × minor axis).
また、鋼板中に存在する酸化物の個数割合で４０％以上が少なくともＳｉ、Ｍｎ、Ｆｅを含んでいれば、殆どの介在物が凝固時に生成し、凝集合体する時間が短いので、微細に分散でき、表面欠陥が発生しにくいため好ましい。
ここで、少なくともＳｉ、Ｍｎ、Ｆｅを含むとは、Ｓｉ、Ｍｎ、Ｆｅの１種以上という意味であり、以降も同様の意味で用いている。
In addition, if more than 40% of the oxides present in the steel sheet contain at least Si, Mn, and Fe, most of the inclusions are formed during solidification, and the time for agglomeration and coalescence is short. This is preferable because surface defects are less likely to occur.
Here, containing at least Si, Mn, and Fe means one or more of Si, Mn, and Fe, and the same meaning is used hereinafter.
また、鋼板中に存在する酸化物の個数割合で４０％以上が少なくともＳｉ酸化物、Ｍｎ酸化物、Ｆｅ酸化物の含有率で２０質量％以上、より好ましくは５０質量％以上であれば、酸化物は殆ど凝固完了に近い時期に生成し、凝集合体する時間が非常に短いので、介在物が微細分散し、表面欠陥が発生し難いため、より好ましい。
このような酸化物分散状態および組成を有する鋼板では、表面欠陥は発生しない。
Further, if the number ratio of oxides present in the steel sheet is 40% or more, the content of at least Si oxide, Mn oxide, and Fe oxide is 20% by mass or more, more preferably 50% by mass or more. Since the product is formed almost at the completion of solidification and the time for agglomeration and coalescence is very short, inclusions are finely dispersed and surface defects are less likely to occur, which is more preferable.
In a steel sheet having such an oxide dispersion state and composition, no surface defects are generated.
以上の結果から、本発明により溶鋼中で殆ど介在物を生成させることなく、凝固時にＦｅＯ系の酸化物を析出させ微細に分散させることができるため、鋼板製造時に介在物は表面疵発生の原因とならず、さらに鋼板中のＮｂとＣｕにより加工性が大きく改善されるため、薄板用鋼板の品質と材質を大きく向上できる。 From the above results, according to the present invention, it is possible to precipitate and finely disperse FeO-based oxides during solidification without generating inclusions in the molten steel. Furthermore, since the workability is greatly improved by Nb and Cu in the steel plate, the quality and material of the steel plate for thin plate can be greatly improved.
薄板用鋼板は、自動車用外板等の加工が厳しい用途に用いられるため、加工性を付加する必要がある。薄板用鋼板の加工性を高めるためには、Ｃ濃度を極力低下させ、その上で鋼中に固溶したＣとＮを他元素の添加により固定することが重要である。Ｃ濃度に関しては、加工性の観点から０．０１質量％以下、好ましくは０．００５質量％以下にするのが良い。しかし、凝固時のＣＯ気泡発生防止の条件はＣ濃度０．００５質量％以下であるので、本発明では加工性の条件から決まるＣ濃度は十分に満足されている。なお、Ｃ濃度の下限値は特に規定するものではない。 Since the steel sheet for thin plates is used for applications in which processing of an outer plate for automobiles and the like is severe, it is necessary to add workability. In order to improve the workability of the steel sheet for thin plates, it is important to reduce the C concentration as much as possible and fix C and N dissolved in the steel by adding other elements. The C concentration is 0.01% by mass or less, preferably 0.005% by mass or less from the viewpoint of workability. However, since the condition for preventing the generation of CO bubbles during solidification is a C concentration of 0.005% by mass or less, the present invention sufficiently satisfies the C concentration determined from the workability conditions. The lower limit value of the C concentration is not particularly specified.
また、鋼板中のその他の成分の作用について言及する。
鋼板中のＳｉ濃度は、０．００５質量％以上、０．０３質量％以下であることが好ましい。Ｓｉ濃度は０．００５質量％未満では板の強度が不足し易いため、またＳｉ濃度が０．０３質量％超では板の加工性が低下するためである。
また、Ｓｉ濃度が０．０３質量％以下であれば平衡酸素濃度も０．０２質量％超となり、溶存酸素濃度を０．０２質量％以上確保することは可能である。
鋼板中のＭｎ濃度が０．０８質量％未満になると熱間圧延時にへげ疵が発生し易くなり、またＭｎ濃度は０．３質量％を超えると板の加工性が低下する。このため、鋼板中のＭｎ濃度は０．０８質量％以上、０．３質量％以下であることが好ましい。
また、ＭｎはＳｉに比べても非常に脱酸力が弱いため、Ｍｎ濃度を０．３質量％にしても平衡酸素濃度は０．１質量％超であり、溶鋼中に０．０２質量％から０．０６質量％の溶存酸素を確保できる。
Reference is also made to the action of other components in the steel sheet.
The Si concentration in the steel sheet is preferably 0.005% by mass or more and 0.03% by mass or less. This is because if the Si concentration is less than 0.005 mass%, the strength of the plate tends to be insufficient, and if the Si concentration exceeds 0.03 mass%, the workability of the plate decreases.
Further, if the Si concentration is 0.03% by mass or less, the equilibrium oxygen concentration also exceeds 0.02% by mass, and it is possible to ensure the dissolved oxygen concentration to be 0.02% by mass or more.
If the Mn concentration in the steel sheet is less than 0.08% by mass, cracks are likely to occur during hot rolling, and if the Mn concentration exceeds 0.3% by mass, the workability of the plate is lowered. For this reason, it is preferable that Mn density | concentration in a steel plate is 0.08 mass% or more and 0.3 mass% or less.
Further, since Mn has a very weak deoxidizing power compared with Si, even if the Mn concentration is 0.3% by mass, the equilibrium oxygen concentration is over 0.1% by mass, and 0.02% by mass in the molten steel. From 0.06 mass%, dissolved oxygen can be secured.
本発明では、凝集合体し易いアルミナ系介在物を生成させないように、溶鋼中にＡｌを殆ど添加しない。実験的検討では、鋼板の酸可溶Ａｌ濃度が０．００５質量％を超えると鋼板中のアルミナ系介在物が増加することから、その上限値は０．００５質量％とした。
ここで、酸可溶Ａｌとは、酸に溶解するＡｌ量であり、通常は溶存Ａｌ濃度（Ａｌ２Ｏ３になっていないＡｌの濃度）に対応する。
また、耐火物等から不可避的に侵入するアルミナ系介在物については問題とならない。これは、少量のアルミナ系介在物であれば、溶鋼中の溶存酸素が高いため、溶鋼とアルミナ系介在物の界面エネルギーは低下しており、凝集合体が殆ど生じないためである。
In the present invention, Al is hardly added to the molten steel so as not to generate alumina inclusions that easily aggregate and coalesce. In the experimental examination, when the acid-soluble Al concentration of the steel sheet exceeds 0.005 mass%, alumina inclusions in the steel sheet increase, so the upper limit was set to 0.005 mass%.
Here, the acid-soluble Al is the amount of Al dissolved in the acid, and usually corresponds to the dissolved Al concentration (the concentration of Al that is not Al 2 O 3 ).
Further, there is no problem with alumina inclusions that inevitably enter from refractories. This is because, if a small amount of alumina inclusions are present, the dissolved oxygen in the molten steel is high, so that the interfacial energy between the molten steel and the alumina inclusions is lowered, and almost no agglomeration occurs.
さらに、鋼中のＴｉはＣとＮをＴｉＮやＴｉＣとして固定するため、加工性を向上させる上で有効であるが、Ｔｉの添加量も多くなると、例えばＴｉ濃度が０．０１質量％超になると平衡酸素濃度が０．０１質量％未満になるため、十分な溶存酸素濃度を確保できない。よって、加工性をさらに高める必要からＴｉを添加する場合には、０．０１質量％以下の範囲で添加しても良い。
以下に、実施例及び比較例を挙げて、本発明について説明する。
Furthermore, Ti in steel fixes C and N as TiN and TiC, which is effective in improving workability. However, when the amount of Ti added is increased, for example, the Ti concentration exceeds 0.01% by mass. Then, since the equilibrium oxygen concentration is less than 0.01% by mass, a sufficient dissolved oxygen concentration cannot be ensured. Therefore, when adding Ti in order to further improve workability, it may be added in a range of 0.01% by mass or less.
Hereinafter, the present invention will be described with reference to examples and comparative examples.
転炉での精錬と環流式真空脱ガス装置での処理により、Ｃ濃度を０．００１８質量％とした溶鋼３００ｔを溶製した。この溶鋼に合金を添加し、０．０１質量％Ｓｉ、０．１５質量％Ｍｎ、０．０１５質量％Ｎｂ、０．０８質量％Ｃｕ、０．００１５質量％Ｎ、０．０４５質量％溶存酸素、０．００１質量％以下酸可溶Ａｌとした。この溶鋼を連続鋳造法で厚み２５０ｍｍ、幅１８００ｍｍのスラブに鋳造した。鋳造した鋳片は８５００ｍｍ長さに切断し、１コイル単位とした。このようにして得られたスラブは、常法により熱間圧延、冷間圧延し、最終的には０．７ｍｍ厚みで幅１８００ｍｍコイルの冷延鋼板とした。品質については、冷間圧延後の検査ラインで目視観察を行い、１コイル当たりに発生する表面欠陥の発生個数を評価した。その結果、表面欠陥は発生せず、さらにＣｕ脆化による割れ発生も見られなかった。また、冷延鋼板内の介在物を調査したところ、直径０．５μｍから３０μｍの微細酸化物が鋼板内に３３０００個／ｃｍ２分散しており、その７０％はＳｉ酸化物、Ｍｎ酸化物、Ｆｅ酸化物を合計で６０質量％以上含有していた。さらに、得られた冷延鋼板の加工性を評価し、全伸び５５％、ｒ値２．３の高加工性鋼板であった。 300 t of molten steel with a C concentration of 0.0018% by mass was produced by refining in a converter and treatment in a reflux-type vacuum degassing apparatus. An alloy is added to this molten steel, and 0.01% by mass Si, 0.15% by mass Mn, 0.015% by mass Nb, 0.08% by mass Cu, 0.0015% by mass N, 0.045% by mass dissolved oxygen 0.001% by mass or less of acid-soluble Al. This molten steel was cast into a slab having a thickness of 250 mm and a width of 1800 mm by a continuous casting method. The cast slab was cut to a length of 8500 mm to make one coil unit. The slab thus obtained was hot-rolled and cold-rolled by a conventional method, and finally formed into a cold-rolled steel sheet having a thickness of 0.7 mm and a coil width of 1800 mm. Regarding quality, visual observation was performed on the inspection line after cold rolling, and the number of surface defects generated per coil was evaluated. As a result, no surface defects occurred, and no cracking due to Cu embrittlement was observed. Further, when the inclusions in the cold-rolled steel sheet were investigated, fine oxides having a diameter of 0.5 μm to 30 μm were dispersed in the steel sheet at 33000 / cm 2 , 70% of which were Si oxide, Mn oxide, The total amount of Fe oxide was 60% by mass or more. Furthermore, the workability of the obtained cold-rolled steel sheet was evaluated, and it was a highly workable steel sheet having a total elongation of 55% and an r value of 2.3.
転炉での精錬と環流式真空脱ガス装置での処理によりＣ濃度を０．００１５質量％とした溶鋼３００ｔを溶製した。この溶鋼に合金を添加し、０．０１質量％Ｓｉ、０．１５質量％Ｍｎ、０．０１５質量％Ｎｂ、２．０質量％Ｃｕ、０．５質量％Ｎｉ、０．００１８質量％Ｎ、０．００５質量％Ｔｉ、０．０１５質量％溶存酸素、０．００１質量％酸可溶Ａｌとした。この溶鋼を鋳型内電磁攪拌装置を有する連続鋳造機を用いて、メニスカスにおける溶鋼を平均流速４５ｃｍ／ｓで電磁攪拌しながら、厚み２５０ｍｍ、幅１８００ｍｍのスラブに鋳造した。鋳造した鋳片は８５００ｍｍ長さに切断し、１コイル単位とした。このようにして得られたスラブは、常法により熱間圧延、冷間圧延し、最終的には０．７ｍｍ厚みで幅１８００ｍｍコイルの冷延鋼板とした。鋳片品質については、冷間圧延後の検査ラインで目視観察を行い、１コイル当たりに発生する表面欠陥の発生個数を評価した。その結果、表面欠陥およびＣｕ脆化による割れも発生しなかった。また、冷延鋼板内の介在物を調査したところ、直径０．５μｍから３０μｍの微細酸化物が鋼板内に２２０００個／ｃｍ２分散しており、その５０％はＳｉ酸化物、Ｍｎ酸化物、Ｆｅ酸化物を合計で４０質量％以上含有する球状酸化物であった。さらに、得られた冷延鋼板の加工性を評価し、全伸び５４％、ｒ値２．２の高加工性鋼板であった。 300 t of molten steel having a C concentration of 0.0015% by mass was produced by refining in a converter and treatment in a reflux vacuum degassing apparatus. An alloy is added to this molten steel, and 0.01 mass% Si, 0.15 mass% Mn, 0.015 mass% Nb, 2.0 mass% Cu, 0.5 mass% Ni, 0.0018 mass% N, 0.005 mass% Ti, 0.015 mass% dissolved oxygen, and 0.001 mass% acid-soluble Al were used. The molten steel was cast into a slab having a thickness of 250 mm and a width of 1800 mm while electromagnetically stirring the molten steel in the meniscus at an average flow rate of 45 cm / s using a continuous casting machine having an in-mold electromagnetic stirring device. The cast slab was cut to a length of 8500 mm to make one coil unit. The slab thus obtained was hot-rolled and cold-rolled by a conventional method, and finally formed into a cold-rolled steel sheet having a thickness of 0.7 mm and a coil width of 1800 mm. Regarding the slab quality, visual observation was performed on the inspection line after cold rolling, and the number of surface defects generated per coil was evaluated. As a result, neither surface defects nor cracking due to Cu embrittlement occurred. Further, when the inclusions in the cold-rolled steel sheet were investigated, fine oxides having a diameter of 0.5 μm to 30 μm were dispersed in the steel sheet at 22,000 / cm 2 , 50% of which were Si oxide, Mn oxide, It was a spherical oxide containing a total of 40 mass% or more of Fe oxide. Furthermore, the workability of the obtained cold-rolled steel sheet was evaluated, and it was a highly workable steel sheet having a total elongation of 54% and an r value of 2.2.
[比較例１]
転炉での精錬と環流式真空脱ガス装置での処理により炭素濃度を０．００１５質量％とした取鍋内溶鋼に合金を添加すると共に、Ａｌで脱酸し、０．０１質量％Ｓｉ、０．１５質量Ｍｎ、０．０２質量％Ｔｉ、０．３質量％Ｃｕ、０．００２質量％Ｎ、０．０４質量％Ａｌ、０．０００２質量％溶存酸素濃度とした。この溶鋼を連続鋳造法で厚み２５０ｍｍ、幅１８００ｍｍのスラブに鋳造した。鋳造した鋳片は８５００ｍｍ長さに切断し、１コイル単位とした。このようにして得られたスラブは、常法により熱間圧延、冷間圧延し、最終的には０．７ｍｍ厚みで幅１８００ｍｍコイルの冷延鋼板とした。鋳片品質については、冷間圧延後の検査ラインで目視観察を行い、１コイル当たりに発生する表面欠陥の発生個数を評価した。その結果、スラブ平均で５個／コイルの表面欠陥が発生すると共に、Ｃｕ脆化による割れも発生した。また、冷延鋼板内の介在物調査したところ、直径０．５μｍから３０μｍの微細酸化物が鋼板内に２００個／ｃｍ２しかなく、３０μｍを超える大型介在物も多数見られた。鋼板中の介在物の９５％はアルミナ系介在物であった。さらに、得られた冷延鋼板の加工性を評価したところ、全伸び４０％、ｒ値１．４で高加工性鋼板は得られなかった。
[Comparative Example 1]
An alloy is added to the molten steel in the ladle with a carbon concentration of 0.0015 mass% by refining in a converter and treatment in a reflux vacuum degassing apparatus, and deoxidized with Al, 0.01 mass% Si, It was set as 0.15 mass Mn, 0.02 mass% Ti, 0.3 mass% Cu, 0.002 mass% N, 0.04 mass% Al, 0.0002 mass% dissolved oxygen concentration. This molten steel was cast into a slab having a thickness of 250 mm and a width of 1800 mm by a continuous casting method. The cast slab was cut to a length of 8500 mm to make one coil unit. The slab thus obtained was hot-rolled and cold-rolled by a conventional method, and finally formed into a cold-rolled steel sheet having a thickness of 0.7 mm and a coil width of 1800 mm. Regarding the slab quality, visual observation was performed on the inspection line after cold rolling, and the number of surface defects generated per coil was evaluated. As a result, a surface defect of 5 pieces / coil on the average of slabs occurred, and cracks due to Cu embrittlement also occurred. Further, when the inclusions in the cold-rolled steel sheet were investigated, there were only 200 / cm 2 of fine oxides having a diameter of 0.5 μm to 30 μm in the steel sheet, and many large inclusions exceeding 30 μm were also seen. 95% of the inclusions in the steel plate were alumina inclusions. Furthermore, when the workability of the obtained cold rolled steel sheet was evaluated, a high workability steel sheet was not obtained with a total elongation of 40% and an r value of 1.4.
Claims (12)
−０．０１５≦｛Ｎｂ−（９３／１２）×Ｃ−（９３／１４）×Ｎ｝≦０．２
となるように含有させ、溶鋼中の溶存酸素濃度が０．０１質量％以上、０．０６質量％以下である溶鋼を鋳造することを特徴とする極低炭素鋼鋳片の製造方法。 After decarburizing the molten steel to a carbon concentration of 0.005% by mass or less, Cu and Nb are added to the molten steel, and the molten steel contains 0.01 to 3.0% by mass of Cu and Nb of −0.015 ≦ { Nb− (93/12) × C− (93/14) × N} ≦ 0.2
And it is contained so that the dissolved oxygen concentration in the soluble steel 0.01 mass% or more, the production method of ultra-low carbon steel slab characterized by casting molten steel is 0.06 wt% or less.
−０．０１５≦｛Ｎｂ−（９３／１２）×Ｃ−（９３／１４）×Ｎ｝≦０．２
となるように含有させ、さらに酸可溶Ａｌ濃度が０．００５質量％以下となるようにＡｌを添加して、および／または、Ｔｉ濃度が０．０１質量％以下となるようにＴｉを添加して、溶鋼中の溶存酸素濃度を０．０１質量％以上、０．０６質量％以下に調整した溶鋼を鋳造することを特徴とする極低炭素鋼鋳片の製造方法。 After decarburizing the molten steel to a carbon concentration of 0.005% by mass or less, Cu and Nb are added to the molten steel, and the molten steel contains 0.01 to 3.0% by mass of Cu and Nb of −0.015 ≦ { Nb− (93/12) × C− (93/14) × N} ≦ 0.2
In addition , Al is added so that the acid-soluble Al concentration is 0.005% by mass or less, and / or Ti is added so that the Ti concentration is 0.01% by mass or less. And the manufacturing method of the ultra-low carbon steel slab characterized by casting the molten steel which adjusted the dissolved oxygen concentration in molten steel to 0.01 mass% or more and 0.06 mass% or less.
Ｃ：０．００５質量％以下、Ｃｕ：０．０１〜３．０質量％、さらにＮｂを
−０．０１５≦｛Ｎｂ−（９３／１２）×Ｃ−（９３／１４）×Ｎ｝≦０．２
を満足するように含有し、残部が鉄および不可避的不純物である鋼であって、その鋼中には直径０．５μｍから３０μｍの微細酸化物が１０００個／ｃｍ２以上、１００００００個／ｃｍ２以下分散しており、該微細酸化物の個数割合で４０％以上が少なくともＳｉ、Ｍｎ、Ｆｅを含んでいることを特徴とする極低炭素鋼板。 A steel plate produced by the method according to claim 1, 5 to 7,
C: 0.005 mass% or less, Cu: 0.01-3.0 mass%, and Nb −0.015 ≦ {Nb− (93/12) × C− (93/14) × N} ≦ 0 .2
In which the balance is iron and unavoidable impurities, and the steel contains fine oxides having a diameter of 0.5 μm to 30 μm of 1000 / cm 2 or more and 1000000 / cm 2. An ultra-low carbon steel sheet which is dispersed below , and 40% or more of the fine oxides contain at least Si, Mn and Fe .
Ｃ：０．００５質量％以下、酸可溶Ａｌ濃度が０．００５質量％以下および／またはＴｉ濃度が０．０１質量％以下、Ｃｕ：０．０１〜３．０質量％、さらにＮｂを
−０．０１５≦｛Ｎｂ−（９３／１２）×Ｃ−（９３／１４）×Ｎ｝≦０．２
を満足するように含有し、残部が鉄および不可避的不純物である鋼であって、その鋼中には直径０．５μｍから３０μｍの微細酸化物が１０００個／ｃｍ２以上、１００００００個／ｃｍ２以下分散しており、該酸化物の個数割合で４０％以上が少なくともＳｉ、Ｍｎ、Ｆｅを含んでいることを特徴とする極低炭素鋼板。 A steel plate produced by the method according to claim 2, 5 to 7,
C: 0.005 mass% or less, acid-soluble Al concentration is 0.005 mass% or less and / or Ti concentration is 0.01 mass% or less, Cu: 0.01 to 3.0 mass%, and Nb − 0.015 ≦ {Nb− (93/12) × C− (93/14) × N} ≦ 0.2
In which the balance is iron and unavoidable impurities, and the steel contains fine oxides having a diameter of 0.5 μm to 30 μm of 1000 / cm 2 or more and 1000000 / cm 2. An ultra-low carbon steel sheet that is dispersed below and 40% or more of the oxides contain at least Si, Mn, and Fe .
At least Si oxide is more than 40% of the number of oxides present in the steel, Mn oxides, at a content of Fe oxide, claim, characterized in that at least 20 wt% 8-11 The ultra-low carbon steel sheet according to any one of the above.
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