JP2005256115A - High strength hot rolled steel sheet having excellent stretch flange formability and fatigue property - Google Patents
High strength hot rolled steel sheet having excellent stretch flange formability and fatigue property Download PDFInfo
- Publication number
- JP2005256115A JP2005256115A JP2004071179A JP2004071179A JP2005256115A JP 2005256115 A JP2005256115 A JP 2005256115A JP 2004071179 A JP2004071179 A JP 2004071179A JP 2004071179 A JP2004071179 A JP 2004071179A JP 2005256115 A JP2005256115 A JP 2005256115A
- Authority
- JP
- Japan
- Prior art keywords
- mass
- less
- inclusions
- steel sheet
- steel
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Pending
Links
Landscapes
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
本発明は、伸びフランジ性と疲労特性に優れた高強度熱延鋼板に関するものである。 The present invention relates to a high-strength hot-rolled steel sheet excellent in stretch flangeability and fatigue characteristics.
自動車部品の内、特に足回り系と呼ばれるフレーム類やアーム類などには、高強度熱延鋼板が広く用いられている。これらの部品には、走行中の振動に対する耐久性の観点から高い疲労特性が要求される。こうした要求に対しては幾つかの鋼板が提案されている。 High-strength hot-rolled steel sheets are widely used for automobile parts, especially frames and arms called suspension systems. These parts are required to have high fatigue characteristics from the viewpoint of durability against vibration during traveling. Several steel plates have been proposed to meet these requirements.
例えば、特許文献１には、フェライト相とマルテンサイト相の複合組織鋼板中に、微細なＣｕを析出または固溶体を分散させた鋼板（一般にＤＰ鋼板と呼称される）が提案されている。 For example, Patent Document 1 proposes a steel plate (generally called a DP steel plate) in which fine Cu is precipitated or a solid solution is dispersed in a ferrite-structure and martensite-phase composite structure steel sheet.
こうしたＤＰ鋼板は、強度と延性のバランスや疲労特性には優れるものの、穴広げ試験で評価される伸びフランジ性には劣ることが知られている。その理由の一つは、ＤＰ鋼板は、軟質なフェライト相と硬質なマルテンサイト相の複合体であるため、穴広げ加工時に両相の境界部が変形に追随できず、破断の起点になり易いからであると考えられる。 Such DP steel sheet is known to be inferior in stretch flangeability evaluated by a hole expansion test, although it is excellent in the balance between strength and ductility and fatigue characteristics. One of the reasons is that DP steel sheet is a composite of a soft ferrite phase and a hard martensite phase, so the boundary between both phases cannot follow deformation during hole expansion processing, and it tends to be the starting point of fracture. It is thought that it is from.
これに対して、伸びフランジ性にも疲労特性にも優れた熱延鋼板の提案がなされている。特許文献２がその一例で、鋼板の組織をベイナイト相主体とし、構成するその他の相との硬度差を小さくし、更に、粗大な炭化物の生成を回避することなどを要旨とする。 On the other hand, a hot-rolled steel sheet having excellent stretch flangeability and fatigue characteristics has been proposed. Patent document 2 is an example, and the gist is to make the structure of the steel sheet the main component of the bainite phase, to reduce the hardness difference from the other phases to be formed, and to avoid the formation of coarse carbides.
特許文献２に開示されているような、鋼板組織をベイナイト相主体とし、粗大な炭化物の生成を抑制した熱延鋼板は、確かに優れた伸びフランジ性を示すものの、Ｃｕを含有したＤＰ鋼板に比べて、その疲労特性は必ずしも優れているとは言えない。また、粗大な炭化物を抑制しただけでは、厳しい穴広げ加工を行った場合に亀裂の発生を抑制できない。 本発明者らの研究によれば、これらの原因は、鋼板中の酸化物を主体とする介在物の存在にあることが分かった。 As disclosed in Patent Document 2, a hot-rolled steel sheet having a steel sheet structure mainly composed of a bainite phase and suppressing the formation of coarse carbides certainly exhibits excellent stretch flangeability, but is a DP steel sheet containing Cu. In comparison, the fatigue characteristics are not necessarily excellent. Moreover, if only coarse carbides are suppressed, generation of cracks cannot be suppressed when severe hole expansion processing is performed. According to the study by the present inventors, it has been found that these causes are the presence of inclusions mainly composed of oxides in the steel sheet.
繰り返し変形を受けると、表層またはその近傍に存在する粗大なクラスター状介在物の周辺に内部欠陥が発生し、亀裂として伝播することによって疲労特性を劣化させると共に、やはり、粗大なクラスター状介在物は、穴広げ加工時の割れ発生の起点となり易いためである。したがって、鋼中の介在物をできる限り微細球状化することが望ましい。 When subjected to repeated deformation, internal defects are generated around the coarse cluster inclusions on or near the surface layer, and the fatigue properties are deteriorated by propagating as cracks. This is because it tends to be a starting point of cracking during the hole expanding process. Therefore, it is desirable to make the inclusions in the steel as fine as possible.
一般に、鋼の脱酸はＡｌを用いて行われるが、Ａｌ脱酸により生成したアルミナ系介在物は、クラスター化し易く、粗大な介在物として鋼中に残留する。これが、上記のように、疲労特性と伸びフランジ性（穴広げ加工性）を低下させていると考えられるが、介在物微細球状化制御の視点にたって伸びフランジ性と疲労特性に優れる熱延鋼板を提案した例は見られない。 Generally, deoxidation of steel is performed using Al, but alumina inclusions generated by Al deoxidation are easily clustered and remain in the steel as coarse inclusions. As described above, this is thought to reduce the fatigue characteristics and stretch flangeability (hole expansion workability), but from the viewpoint of inclusion micro-spheroidization control, the hot rolled steel sheet is excellent in stretch flangeability and fatigue characteristics. The example which proposed is not seen.
このような状況を鑑み、本発明者らは、（ａ）粗大化し易いアルミナ系介在物を生成させないために殆どＡｌ脱酸をすることなく、（ｂ）介在物がクラスター化して粗大にならず、且つ、（ｃ）割れ発生の起点になり難い球状介在物へと改質する脱酸方法、および、（ｄ）疲労特性を劣化させない添加元素の解明を中心に鋭意研究を進め、更に、化学成分や製造方法にも検討を加えて、本発明を完成させた。 In view of such a situation, the present inventors have (a) almost no Al deoxidation in order not to generate alumina inclusions that are easily coarsened, and (b) inclusions are not clustered and coarsened. In addition, (c) deoxidation method for reforming into spherical inclusions that are unlikely to start cracking, and (d) elucidation of additive elements that do not deteriorate fatigue characteristics The present invention was completed by examining the components and the production method.
その要旨は、以下の通りである。 The summary is as follows.
（１）Ｃ：０．０３〜０．１０質量％、Ｓｉ：０．０５〜１．５質量％、Ｍｎ：１．０〜３．０質量％、Ｐ：０．０５質量％以下、Ｓ：０．０１質量％以下、Ｎ：０．０００５〜０．０１質量％、酸可溶Ａｌ：０．００５質量％以下、Ｔｉ：０．００５質量％以上、ＣｅもしくはＬａの１種または２種の合計：０．０００５〜０．０４質量％以上含有し、更に、下記式を満足し、
−０．０５≦｛Ｔｉ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、平均の介在物組成で、Ｃｅ酸化物もしくはＬａ酸化物の１種または２種の合計が１０〜９０質量％、Ｔｉ酸化物が１０〜９０質量％、Ａｌ2Ｏ3が５０質量％以下の範囲の介在物を含むことを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。
(1) C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01% by mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, one or two of Ce or La Total: 0.0005 to 0.04% by mass or more, further satisfying the following formula,
−0.05 ≦ {Ti− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and unavoidable impurities, and the steel has an average inclusion composition, and the total of one or two of Ce oxide or La oxide is 10 to 90% by mass, Ti oxidation A high-strength hot-rolled steel sheet excellent in stretch flangeability and fatigue characteristics, comprising inclusions in a range of 10 to 90% by mass and Al 2 O 3 in a range of 50% by mass or less.
（２）Ｃ：０．０３〜０．１０質量％、Ｓｉ：０．０５〜１．５質量％、Ｍｎ：１．０〜３．０質量％、Ｐ：０．０５質量％以下、Ｓ：０．０１質量％以下、Ｎ：０．０００５〜０．０１質量％、酸可溶Ａｌ：０．００５質量％以下、Ｔｉ：０．００５質量％以上、ＣｅもしくはＬａの１種または２種の合計：０．０００５〜０．０４質量％以上、および、Ｎｂを含有し、更に下記式を満足し、
−０．０５≦｛Ｔｉ＋（４８／９３）×Ｎｂ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、平均の介在物組成で、Ｃｅ酸化物もしくはＬａ酸化物の１種または２種の合計が１０〜９０質量％、Ｔｉ酸化物が１０〜９０質量％、Ａｌ2Ｏ3が５０質量％以下の範囲の介在物を含むことを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。
(2) C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01% by mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, one or two of Ce or La Total: 0.0005 to 0.04% by mass or more, and Nb, further satisfying the following formula,
−0.05 ≦ {Ti + (48/93) × Nb− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and inevitable impurities, and the steel contains an average inclusion composition, and the total of one or two of Ce oxide or La oxide is 10 to 90% by mass, Ti oxidation A high-strength hot-rolled steel sheet excellent in stretch flangeability and fatigue characteristics, comprising inclusions in a range of 10 to 90% by mass and Al 2 O 3 in a range of 50% by mass or less.
（３）Ｃ：０．０３〜０．１０質量％、Ｓｉ：０．０５〜１．５質量％、Ｍｎ：１．０〜３．０質量％、Ｐ：０．０５質量％以下、Ｓ：０．０１質量％以下、Ｎ：０．０００５〜０．０１質量％、酸可溶Ａｌ：０．００５質量％以下、Ｔｉ：０．００５質量％以上、ＣｅもしくはＬａの１種または２種の合計：０．０００５〜０．０４質量％以上含有し、更に、下記式を満足し、
−０．０５≦｛Ｔｉ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、介在物の個数割合で、５０％以上が少なくとも球状、紡錘状の介在物を含むことを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。
(3) C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01% by mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, one or two of Ce or La Total: 0.0005 to 0.04% by mass or more, further satisfying the following formula,
−0.05 ≦ {Ti− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and inevitable impurities, and in the steel, 50% or more of inclusions include at least spherical and spindle-shaped inclusions, and the stretch flangeability and fatigue High-strength hot-rolled steel sheet with excellent characteristics.
（４）Ｃ：０．０３〜０．１０質量％、Ｓｉ：０．０５〜１．５質量％、Ｍｎ：１．０〜３．０質量％、Ｐ：０．０５質量％以下、Ｓ：０．０１質量％以下、Ｎ：０．０００５〜０．０１質量％、酸可溶Ａｌ：０．００５質量％以下、Ｔｉ：０．００５質量％以上、ＣｅもしくはＬａの１種または２種の合計：０．０００５〜０．０４質量％以上、および、Ｎｂを含有し、更に、下記式を満足し、
−０．０５≦｛Ｔｉ＋（４８／９３）×Ｎｂ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、介在物の個数割合で、５０％以上が少なくとも球状、紡錘状の介在物を含むことを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。
(4) C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01% by mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, one or two of Ce or La Total: 0.0005 to 0.04% by mass or more and Nb, further satisfying the following formula,
−0.05 ≦ {Ti + (48/93) × Nb− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and unavoidable impurities, and the steel has a stretch flangeability and fatigue characterized by including at least spherical and spindle-shaped inclusions in the steel in a proportion of the number of inclusions. High-strength hot-rolled steel sheet with excellent characteristics.
（５）Ｃ：０．０３〜０．１０質量％、Ｓｉ：０．０５〜１．５質量％、Ｍｎ：１．０〜３．０質量％、Ｐ：０．０５質量％以下、Ｓ：０．０１質量％以下、Ｎ：０．０００５〜０．０１質量％、酸可溶Ａｌ：０．００５質量％以下、Ｔｉ：０．００５質量％以上、ＣｅもしくはＬａの１種または２種の合計：０．０００５〜０．０４質量％以上含有し、更に、下記式を満足し、
−０．０５≦｛Ｔｉ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、粒径が０．５μｍ以上１０μｍ以下の介在物が１０００個／ｃｍ2以上、１０００００個／ｃｍ2以下存在することを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。
(5) C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01% by mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, one or two of Ce or La Total: 0.0005 to 0.04% by mass or more, further satisfying the following formula,
−0.05 ≦ {Ti− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and inevitable impurities, and in the steel, inclusions having a particle size of 0.5 μm or more and 10 μm or less are present at 1000 / cm 2 or more and 100,000 / cm 2 or less. High-strength hot-rolled steel sheet with excellent stretch flangeability and fatigue properties.
（６）Ｃ：０．０３〜０．１０質量％、Ｓｉ：０．０５〜１．５質量％、Ｍｎ：１．０〜３．０質量％、Ｐ：０．０５質量％以下、Ｓ：０．０１質量％以下、Ｎ：０．０００５〜０．０１質量％、酸可溶Ａｌ：０．００５質量％以下、Ｔｉ：０．００５質量％以上、ＣｅもしくはＬａの１種または２種の合計：０．０００５〜０．０４質量％以上、および、Ｎｂを含有し、更に、下記式を満足し、
−０．０５≦｛Ｔｉ＋（４８／９３）×Ｎｂ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、粒径が０．５μｍ以上１０μｍ以下の介在物が１０００個／ｃｍ2以上、１０００００個／ｃｍ2以下存在することを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。
(6) C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01% by mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, one or two of Ce or La Total: 0.0005 to 0.04% by mass or more and Nb, further satisfying the following formula,
−0.05 ≦ {Ti + (48/93) × Nb− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and inevitable impurities, and in the steel, inclusions having a particle size of 0.5 μm or more and 10 μm or less are present at 1000 / cm 2 or more and 100,000 / cm 2 or less. High-strength hot-rolled steel sheet with excellent stretch flangeability and fatigue properties.
（７）更に、Ｃｕ：０．２〜２．０質量％、Ｎｉ：０．１〜１．０質量％を含有することを特徴とする前記（１）〜（６）のいずれかに記載の伸びフランジ性と疲労特性に優れた高強度熱延鋼板。 (7) Furthermore, Cu: 0.2-2.0 mass%, Ni: 0.1-1.0 mass% is contained, In any one of said (1)-(6) characterized by the above-mentioned. High-strength hot-rolled steel sheet with excellent stretch flangeability and fatigue characteristics.
（８）更に、鋼板中のベイニティック・フェライト相の面積率が８０〜１００％であることを特徴とする前記（１）〜（７）のいずれかに記載の伸びフランジ性と疲労特性に優れた高強度熱延鋼板。 (8) Further, in the stretch flangeability and fatigue characteristics according to any one of (1) to (7), the area ratio of the bainitic ferrite phase in the steel sheet is 80 to 100%. Excellent high-strength hot-rolled steel sheet.
本発明によれば、伸びフランジ性と疲労特性に優れた高強度熱延鋼板を得ることができる。 According to the present invention, a high-strength hot-rolled steel sheet excellent in stretch flangeability and fatigue characteristics can be obtained.
まず、本発明を完成するに至った実験について説明する。 First, the experiment that led to the completion of the present invention will be described.
本発明者らは、Ｃ：０．０５質量％、Ｓｉ：０．０５質量％、Ｍｎ：１．５質量％、Ｐ：０．０２質量％以下、Ｓ：０．００１質量％を含有し残部がＦｅである溶鋼に対して様々な元素を用いて脱酸を行い、更に、ＴｉやＮｂの添加を経て鋼塊を製造した。得られた鋼塊を熱間圧延して、４ｍｍの熱延鋼板とした。これらの鋼板を穴広げ試験および疲労試験に供すると共に、鋼板中の介在物粒径分布、形態および平均組成を調査した。 The present inventors contain C: 0.05% by mass, Si: 0.05% by mass, Mn: 1.5% by mass, P: 0.02% by mass or less, S: 0.001% by mass, and the balance The molten steel in which Fe is Fe was deoxidized using various elements, and a steel ingot was manufactured through addition of Ti and Nb. The obtained steel ingot was hot-rolled to obtain a 4 mm hot-rolled steel sheet. These steel plates were subjected to a hole expansion test and a fatigue test, and the inclusion particle size distribution, morphology and average composition in the steel plates were investigated.
その結果、Ａｌで殆ど脱酸することなく、少なくともＣｅ、Ｌａを添加して脱酸した鋼板が、最も伸びフランジ性と疲労特性に優れること、その理由は、上記脱酸により生成した球状介在物が鋼板中に微細分散するため、繰り返し変形時や穴広げ加工時に、介在物が割れ発生の起点や亀裂伝播の経路となり難いためであることを見いだした。これを基に、熱延条件の検討を行って、本発明を完成させるに至った。 As a result, the steel sheet deoxidized by adding at least Ce and La with almost no deoxidation with Al is the most excellent in stretch flangeability and fatigue characteristics, because the spherical inclusions produced by the above deoxidation It was found that the inclusions are finely dispersed in the steel sheet, so that inclusions are less likely to become crack initiation points and crack propagation paths during repeated deformation and hole expansion. Based on this, the hot rolling conditions were studied and the present invention was completed.
以下に、本発明の限定理由を述べる。まず、化学成分の限定理由について述べる。 The reasons for limiting the present invention will be described below. First, the reasons for limiting chemical components will be described.
Ｃは、鋼板の強度を確保するために必須の元素であり、高強度鋼板を得るためには、少なくとも０．０３質量％が必要である。しかし、過剰に含まれると、ＴｉやＮｂによる炭化物生成や、冷却条件を駆使しても、伸びフランジ特性に好ましくないセメンタイト相の生成が避けられないので０．１０質量％以下とする。 C is an essential element for securing the strength of the steel sheet, and at least 0.03 mass% is necessary to obtain a high-strength steel sheet. However, if it is contained excessively, carbide generation by Ti or Nb and generation of cementite phase unfavorable for stretch flange characteristics cannot be avoided even if cooling conditions are used, so the content is made 0.10% by mass or less.
Ｓｉは、伸びフランジ性を劣化させることなく強度を確保するのに有効な元素であり、少なくとも０．０５質量％が必要であるが、過剰に含まれると、伸びフランジ性に好ましくないポリゴナル・フェライト相を生成しやすくなるので、その上限は１．５質量％とする。 Si is an element effective for securing the strength without deteriorating the stretch flangeability. At least 0.05% by mass is necessary, but if it is excessively contained, it is not preferable for the stretch ferrite property. Since it becomes easy to produce | generate a phase, the upper limit shall be 1.5 mass%.
Ｍｎは、Ｃ、Ｓｉとともに鋼板の高強度化に有効な元素であり、１．０質量％以上は含有させる必要があるが、３．０質量％を超えて含有させると、延性が劣化するので、上限を３．０質量％とする。 Mn is an element effective for increasing the strength of the steel sheet together with C and Si, and it is necessary to contain 1.0% by mass or more, but if it exceeds 3.0% by mass, ductility deteriorates. The upper limit is 3.0% by mass.
Ｐは、固溶強化元素として有効であるが、偏析による加工性の劣化が懸念されるので、０．０５質量％以下にする必要がある。Ｐの下限値は０質量％を含む。 P is effective as a solid solution strengthening element, but since there is a concern about deterioration of workability due to segregation, it is necessary to make it 0.05% by mass or less. The lower limit value of P includes 0% by mass.
Ｓは、ＭｎＳなどの介在物を形成して伸びフランジ性を劣化させる他、Ｃを炭化物とする目的で含有させるＴｉと結合して、その歩留まりを低下させるなどの有害な作用をする。したがって、できるだけ抑制すべきであるが、０．０１質量％以下であれば許容される。Ｓの下限値は０質量％を含む。 S forms an inclusion such as MnS to deteriorate stretch flangeability, and also has a harmful effect such as combining with Ti contained for the purpose of making C a carbide to lower the yield. Therefore, it should be suppressed as much as possible, but is acceptable if it is 0.01% by mass or less. The lower limit value of S includes 0% by mass.
Ｎは、Ｃを炭化物とする目的で含有させるＴｉと結合して、その歩留まりを低下させる。よって、できるだけ抑制すべきであるが、０．０１質量％以下であれば許容される。一方、０．０００５質量％未満とするにはコストがかかるので、０．０００５質量％を下限とする。 N combines with Ti contained for the purpose of converting C into carbide, and lowers the yield. Therefore, it should be suppressed as much as possible, but is acceptable if it is 0.01% by mass or less. On the other hand, since it costs to make it less than 0.0005 mass%, 0.0005 mass% is made the lower limit.
酸可溶Ａｌは、その酸化物がクラスター化して粗大になり易いため、極力抑制することが望ましい。しかしながら、予備的な脱酸材として０．００５質量％までは用いることが許容される。これは、酸可溶Ａｌ濃度が０．００５質量％超になると、介在物中のＡｌ2Ｏ3含有率が５０質量％を超え、介在物のクラスター化が起こるためである。 It is desirable to suppress acid-soluble Al as much as possible because the oxide is likely to cluster and become coarse. However, it is allowed to use up to 0.005% by mass as a preliminary deoxidizer. This is because when the acid-soluble Al concentration exceeds 0.005% by mass, the Al 2 O 3 content in the inclusions exceeds 50% by mass, and inclusions cluster.
クラスター化防止の観点から、酸可溶Ａｌ濃度は低い方がよく、下限値は０質量％を含む。また、酸可溶Ａｌ濃度とは、酸に溶解したＡｌ量を測定したもので、溶存Ａｌは酸に溶解し、Ａｌ2Ｏ3は酸に溶解しないことを利用した分析方法である。 From the viewpoint of preventing clustering, the acid-soluble Al concentration should be low, and the lower limit includes 0% by mass. The acid-soluble Al concentration is an analytical method that measures the amount of Al dissolved in an acid, and utilizes the fact that dissolved Al dissolves in an acid and Al 2 O 3 does not dissolve in an acid.
Ｔｉは、（本発明ではＡｌで殆ど脱酸しないため）脱酸材として、０．００５質量％以上必要である。Ｔｉ濃度が０．００５質量％未満では、介在物中のＴｉ酸化物含有率が１０質量％未満となり、疲労特性や伸びフランジ性に良い介在物組成、形態および粒径に制御できないためである。 Ti is required to be 0.005% by mass or more as a deoxidizing material (since it is hardly deoxidized with Al in the present invention). This is because when the Ti concentration is less than 0.005 mass%, the Ti oxide content in the inclusions is less than 10 mass%, and the inclusion composition, form, and particle size that are good in fatigue characteristics and stretch flangeability cannot be controlled.
また、ＴｉやＮｂは、Ｃ、ＳおよびＮを析出物として固定することによって鋼板の加工性を向上させる働きをする。一方、ＴｉやＮｂが必要以上に添加された場合には、それらは、フリーのＴｉやフリーのＮｂとして鋼中に存在し、再結晶温度を上昇させ熱間加工組織が存在し易くなり延性を損ねる。そして、その最適なＴｉやＮｂの添加量の範囲は、各元素の化学当量を用いて記述される下記不等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。 Ti and Nb serve to improve the workability of the steel sheet by fixing C, S and N as precipitates. On the other hand, when Ti or Nb is added more than necessary, they are present in the steel as free Ti or free Nb, and the recrystallization temperature is increased and a hot-worked structure is likely to be present, resulting in ductility. Hurt. And the range of the optimal addition amount of Ti or Nb can be appropriately expressed by using the middle side of the following inequality described using the chemical equivalent of each element as an index.
ここで、下記不等式の中辺は、Ｃ、ＮやＳと結合して炭化物、窒化物、硫化物となっていないフリーのＴｉ量とＮｂ量の合計を意味しており、ここでは、その合計を、相当Ｔｉ量（Ｎｂは上記のＴｉと同様の性質を有するため、Ｎｂ量はＴｉ量に換算している。）で表している。 Here, the middle side of the following inequality means the total of the free Ti amount and Nb amount that are not combined with C, N, or S to form carbides, nitrides, and sulfides. Is represented by the equivalent Ti amount (Nb amount is converted to Ti amount because Nb has the same properties as Ti).
すなわち、下記中辺の値が−０．０５未満では延性、伸びフランジ性が劣り、また、０．２を超えると、延性が劣化する。以上の理由から、
−０．０５≦｛Ｔｉ＋（４８／９３）×Ｎｂ−（４８／１２）×Ｃ−（４８／１４） ×Ｎ−（４８／３２）×Ｓ｝≦０．２
の関係を満たすように限定する。なお、Ｎｂを添加しない場合は、Ｎｂ量を０とおいた以下の関係を満たすように限定する。
That is, if the value of the following middle side is less than -0.05, the ductility and stretch flangeability are inferior, and if it exceeds 0.2, the ductility deteriorates. For the above reasons,
−0.05 ≦ {Ti + (48/93) × Nb− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
It is limited to satisfy the relationship. In addition, when not adding Nb, it limits so that the following relationship which set Nb amount to 0 may be satisfied.
−０．０５≦｛Ｔｉ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）× Ｓ｝≦０．２
Ｃｅ、Ｌａは、Ｔｉ脱酸により生成したクラスター状のＴｉ酸化物（例えば、Ｔｉ2Ｏ3、Ｔｉ3Ｏ5）を改質し、微細球状で疲労特性や穴広げ性に良好なＣｅ酸化物（例えば、Ｃｅ2Ｏ3、ＣｅＯ2）−Ｌａ酸化物（例えば、Ｌａ2Ｏ3、ＬａＯ2）−Ｔｉ酸化物系介在物、Ｃｅ酸化物−Ｔｉ酸化物系介在物、または、Ｌａ酸化物−Ｔｉ酸化物系介在物にする効果を有している（上記介在物の中にはＡｌ予備脱酸や耐火物溶損の影響によりＡｌ2Ｏ3を一部含有する場合もある。）。
−0.05 ≦ {Ti− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
Ce and La modify a clustered Ti oxide (for example, Ti 2 O 3 , Ti 3 O 5 ) generated by Ti deoxidation, and are fine spheres and have good fatigue characteristics and hole expansion properties. (e.g., Ce 2 O 3, CeO 2 ) -La oxide (e.g., La 2 O 3, LaO 2 ) -Ti oxide inclusions, Ce oxide -Ti oxide inclusions, or, La oxides -Has the effect of making Ti oxide inclusions (the inclusions may contain a part of Al 2 O 3 due to the effects of Al preliminary deoxidation and refractory melting).
このような介在物改質効果を得るためには、ＣｅもしくはＬａの１種または２種の合計濃度を０．０００５質量％以上０．０４質量％以下にする必要がある。ＣｅもしくはＬａの１種または２種の合計濃度が０．０００５質量％未満では、Ｔｉ酸化物を改質できず、０．０４質量％超ではＴｉ酸化物が還元され、殆どＣｅ酸化物やＬａ酸化物になり、制御したい複合介在物となり難い。 In order to obtain such an inclusion modification effect, the total concentration of one or two of Ce or La needs to be 0.0005 mass% or more and 0.04 mass% or less. If the total concentration of one or two of Ce or La is less than 0.0005% by mass, the Ti oxide cannot be modified, and if it exceeds 0.04% by mass, the Ti oxide is reduced, and almost no Ce oxide or La It becomes an oxide and is difficult to become a composite inclusion to be controlled.
また、選択元素として、Ｃｕ、Ｎｉが挙げられる。 Moreover, Cu and Ni are mentioned as a selective element.
Ｃｕは、固溶強化元素または析出強化元素として鋼板の高強度化に利用できるため、上記の元素に加えて、さらに添加することで疲労強度を一層向上させることができるので、好ましい。しかし、０．２質量％以上を添加しないとその効果は少なく、コスト上昇を招くのみであるので、添加する場合には、０．２質量％を下限値とすることが好ましい。一方、２．０質量％を超えて含有させると、熱延後の鋼板表面性状を悪化させるので、２．０質量％を上限とすることが好ましい。 Since Cu can be used as a solid solution strengthening element or a precipitation strengthening element to increase the strength of the steel sheet, it is preferable because it can be further added to the above elements to further improve the fatigue strength. However, if 0.2% by mass or more is not added, the effect is small and only the cost is increased. Therefore, in the case of adding 0.2% by mass, the lower limit is preferably set. On the other hand, if the content exceeds 2.0% by mass, the surface property of the steel sheet after hot rolling is deteriorated, so it is preferable that the upper limit is 2.0% by mass.
Ｎｉは、上記Ｃｕによる熱延表面性状悪化を緩和する効果があり、Ｃｕの半分程度を目安に添加することが望ましい。したがって、その下限値は０．１質量％である。一方、１．０質量％を超えて添加してもその効果は飽和し、コストの上昇につながるだけなので、１．０質量％を上限とすることが好ましい。 Ni has an effect of relieving the deterioration of hot rolled surface properties caused by Cu, and it is desirable to add about half of Cu as a guide. Therefore, the lower limit is 0.1% by mass. On the other hand, even if added over 1.0% by mass, the effect is saturated and only leads to an increase in cost.
次に、鋼板中における介在物の存在条件について述べる。 Next, conditions for inclusions in the steel sheet will be described.
伸びフランジ性と疲労特性に優れた鋼板を得るためは、鋼板中の介在物は、割れ発生の起点や割れ伝播の経路となり難いように、球状で微細に分散していることが重要である。そこで、本発明の鋼板における介在物の平均組成、形態および粒径分布を調査した。 In order to obtain a steel sheet excellent in stretch flangeability and fatigue characteristics, it is important that the inclusions in the steel sheet are spherically and finely dispersed so that it is difficult to become a starting point of crack generation and a path of crack propagation. Therefore, the average composition, form and particle size distribution of inclusions in the steel sheet of the present invention were investigated.
介在物の平均組成は、ランダムに選んだ複数個（例えば、２０個程度）の介在物を組成分析し、平均濃度を算出することにより求めることができる。 The average composition of inclusions can be obtained by analyzing the composition of a plurality of randomly selected inclusions (for example, about 20) and calculating the average concentration.
その結果、介在物の平均組成でＣｅ酸化物もしくはＬａ酸化物の１種または２種の合計が１０〜９０質量％以上、Ｔｉ酸化物が１０〜９０質量％、Ａｌ2Ｏ3が５０質量％以下の範囲となるように組成制御された鋼板では、伸びフランジ性と疲労特性が向上することが判明した。 As a result, with the average composition of inclusions, the total of one or two of Ce oxide or La oxide is 10 to 90% by mass, Ti oxide is 10 to 90% by mass, and Al 2 O 3 is 50% by mass. It has been found that the steel sheet whose composition is controlled to be in the following range improves stretch flangeability and fatigue characteristics.
平均組成で、Ｃｅ酸化物もしくはＬａ酸化物の１種または２種の合計が１０質量％未満では、ＣｅやＬａ添加による介在物改質効果が小さく、反対に、Ｃｅ酸化物もしくはＬａ酸化物の１種または２種の合計が９０質量％超では、過改質となり、何れの場合も、介在物は微細球状化しないため、平均組成でＣｅ酸化物もしくはＬａ酸化物の１種または２種の合計の下限値は１０質量％、上限値は９０質量％とした。 When the total of one or two of Ce oxide or La oxide is less than 10% by mass with an average composition, the inclusion modification effect due to the addition of Ce or La is small. When the total of one or two types exceeds 90% by mass, over-reformation occurs, and in any case, inclusions do not become fine spheroidized, so one or two types of Ce oxide or La oxide are used in the average composition. The total lower limit was 10% by mass, and the upper limit was 90% by mass.
また、平均組成でＴｉ酸化物が９０質量％超では、Ｃｅ酸化物やＬａ酸化物による改質が不十分であり、反対に、Ｔｉ酸化物が１０質量％未満でも介在物の微細化球状化が困難となるため、平均組成でＴｉ酸化物の上限値を９０質量％、下限値を１０質量％とした。 In addition, when the average composition of Ti oxide exceeds 90% by mass, the modification with Ce oxide or La oxide is insufficient, and conversely, even when the Ti oxide is less than 10% by mass, inclusions are refined and spheroidized. Therefore, the upper limit value of the Ti oxide was 90% by mass and the lower limit value was 10% by mass in the average composition.
更に、介在物中にはＡｌ2Ｏ3を含有しないことが微細球状化の点から好ましいが、Ａｌ予備脱酸や耐火物溶損の影響により、介在物中のＡｌ2Ｏ3含有率が高くなることがある。この場合、平均組成で、介在物中には５０質量％以下に限ってＡｌ2Ｏ3が混入してもよく、下限値は０質量％を含む。これは、介在物中のＡｌ2Ｏ3含有率が５０質量％を超えると、ＣｅやＬａによる改質効果が損なわれ、介在物のクラスター化が進行してしまうためである。 Furthermore, it is preferable not to contain Al 2 O 3 in the inclusions from the viewpoint of fine spheroidization, but the content of Al 2 O 3 in the inclusions is high due to the influence of Al preliminary deoxidation and refractory melting. May be. In this case, Al 2 O 3 may be mixed in the inclusions only to 50% by mass or less with an average composition, and the lower limit includes 0% by mass. This is because when the Al 2 O 3 content in the inclusions exceeds 50% by mass, the reforming effect by Ce or La is impaired, and the inclusions are clustered.
なお、本発明において、上記組成の酸化物以外にスラグや耐火物などから混入する不可避的不純物酸化物は許容される。 In the present invention, inevitable impurity oxides mixed from slag, refractory, etc. are allowed in addition to the oxides having the above composition.
介在物の形態は、ランダムに選んだ複数個の介在物を光学顕微鏡で観察することができる。例えば、ランダムに選んだ１００個の介在物を光学顕微鏡の１００倍と１０００倍で観察し、球状、紡錘状、クラスター状とその他に分類し、球状と紡錘状の介在物の個数割合を求めることが推奨される。 Regarding the form of inclusions, a plurality of inclusions selected at random can be observed with an optical microscope. For example, 100 randomly selected inclusions are observed at 100 times and 1000 times of an optical microscope, and are classified into spherical, spindle, cluster and others, and the number ratio of spherical and spindle inclusions is obtained. Is recommended.
その結果、球状と紡錘状の介在物の個数割合が５０％以上の鋼板では、伸びフランジ性と疲労特性が向上することが判明した。球状と紡錘状の介在物の個数割合が５０％未満では、クラスター状の介在物が相対的に増え、伸びフランジ性と疲労特性が低下するため、その下限値を５０％とした。 As a result, it was found that stretch flangeability and fatigue characteristics are improved in a steel sheet in which the number ratio of spherical and spindle inclusions is 50% or more. When the number ratio of spherical and spindle-shaped inclusions is less than 50%, cluster-like inclusions are relatively increased, and the stretch flangeability and fatigue characteristics are deteriorated. Therefore, the lower limit is set to 50%.
介在物の粒径分布は、光学顕微鏡（例えば１００倍と１０００倍）で介在物を観察して、その粒径を測定することができる。ここで粒径とは、円相当直径を意味している。 The particle size distribution of the inclusions can be measured by observing the inclusions with an optical microscope (for example, 100 times and 1000 times). Here, the particle size means the equivalent circle diameter.
介在物の粒径については、伸びフランジ性に有害な１０μｍを超える大型介在物が減少すると、０．５μｍ以上１０μｍ以下の介在物個数が増加し、このサイズの介在物個数が伸びフランジ性と良く対応するため、０．５μｍ以上１０μｍ以下に着目した。 Regarding the particle size of inclusions, if the number of large inclusions exceeding 10 μm, which is harmful to stretch flangeability, decreases, the number of inclusions of 0.5 μm or more and 10 μm or less increases. In order to respond, attention was focused on 0.5 μm or more and 10 μm or less.
その結果、０．５μｍ以上１０μｍ以下の介在物が１０００個／ｃｍ2以上、１０００００個／ｃｍ2以下存在する鋼板では、伸びフランジ性と疲労特性が向上することが判明した。 As a result, it has been found that stretch flangeability and fatigue characteristics are improved in a steel sheet in which inclusions of 0.5 μm or more and 10 μm or less exist at 1000 pieces / cm 2 or more and 100,000 pieces / cm 2 or less.
０．５μｍ以上１０μｍ以下の介在物が１０００個／ｃｍ2未満では、１０μｍを超える伸びフランジ性に有害な大型介在物が鋼板中に観察され、割れ発生の起点となるため、その個数密度の下限値は１０００個／ｃｍ2とした。また、０．５μｍ以上１０μｍ以下の介在物が１０００００個／ｃｍ2超存在する場合には、介在物の個数が多過ぎて伸びフランジ性と疲労特性が低下するため、その上限値は１０００００個／ｃｍ2とした。 When the number of inclusions of 0.5 μm or more and 10 μm or less is less than 1000 / cm 2 , large inclusions that are harmful to stretch flangeability exceeding 10 μm are observed in the steel sheet and become the starting point of cracking. The value was 1000 pieces / cm 2 . Further, when the 10μm following inclusions than 0.5μm is 100,000 / cm 2 ultra present, the flange formability and fatigue properties extends the number is too large inclusions decreases, the upper limit value is 100,000 / cm 2 .
最後に、鋼板の組織について説明する。 Finally, the structure of the steel plate will be described.
優れた伸びフランジ性を得るためにはベイニティック・フェライトを主相とする組織にすることが好ましい。 In order to obtain excellent stretch flangeability, it is preferable to use a structure having bainitic ferrite as the main phase.
鋼板中のベイニティック・フェライト相の面積率は、好ましくは８０％以上、より好ましくは９０％以上、更に、より好ましくは１００％である。また、残部はベイナイト相またはポリゴナル・フェライト相を２０％以下含有することができ、マルテンサイト相が含まれることは極力避けることが望ましい。こうした、鋼板組織制御に加えて、介在物を微細球状化して分散させることにより、同時に優れた疲労特性も得られる。 The area ratio of the bainitic ferrite phase in the steel sheet is preferably 80% or more, more preferably 90% or more, and still more preferably 100%. Further, the balance may contain 20% or less of bainite phase or polygonal ferrite phase, and it is desirable to avoid the martensite phase as much as possible. In addition to such steel sheet structure control, excellent fatigue properties can be obtained at the same time by dispersing the inclusions into fine spheroids.
次に、高強度熱延鋼板を製造するための熱延条件について述べる。 Next, hot rolling conditions for producing a high strength hot rolled steel sheet will be described.
熱延前の加熱温度は、鋼中のＴｉＣやＮｂＣなどを固溶させるため、１１５０℃以上とすることが好ましい。これらを固溶させておくことにより、圧延後の冷却過程でポリゴナル・フェライトの生成が抑制され、伸びフランジ性にとって好ましいベイニティック・フェライト相を主体とする組織が得られる。 The heating temperature before hot rolling is preferably 1150 ° C. or higher in order to dissolve TiC, NbC and the like in the steel. By solid-dissolving them, the formation of polygonal ferrite is suppressed in the cooling process after rolling, and a structure mainly composed of bainitic ferrite phase which is preferable for stretch flangeability can be obtained.
一方、熱延前の加熱温度が１２５０℃を超えると、スラブ表面の酸化が著しくなり、特に、粒界が選択的に酸化されることに起因する楔状の表面欠陥がデスケーリング後に残り、それが圧延後の表面品位を損ねるので、上限を１２５０℃とすることが好ましい。 On the other hand, when the heating temperature before hot rolling exceeds 1250 ° C., oxidation of the slab surface becomes significant, and in particular, wedge-shaped surface defects resulting from selective oxidation of grain boundaries remain after descaling, Since the surface quality after rolling is impaired, the upper limit is preferably set to 1250 ° C.
上記の温度範囲に加熱された後に、圧延を行うが、その工程の中で、仕上圧延完了温度は鋼板の組織制御上重要である。仕上圧延完了温度が、Ａｒ3点＋５０℃未満では、表層部の結晶粒径が粗大となって疲労特性上好ましくない。一方、Ａｒ3点＋１５０℃超では伸びフランジ性にとって好ましくないポリゴナル・フェライト相が生成し易くなるので、上限をＡｒ3点＋１５０℃とすることが好ましい。 Rolling is performed after heating to the above temperature range, and in the process, the finish rolling completion temperature is important for controlling the structure of the steel sheet. If the finish rolling completion temperature is less than Ar 3 point + 50 ° C., the crystal grain size of the surface layer is coarse, which is not preferable in terms of fatigue characteristics. On the other hand, when the Ar 3 point + 150 ° C. is exceeded, a polygonal ferrite phase that is not preferable for stretch flangeability tends to be generated, and therefore the upper limit is preferably Ar 3 point + 150 ° C.
また、仕上圧延後の鋼板の平均の冷却速度を４０℃／秒以上とし、３００〜５００℃の範囲まで冷却することが、ポリゴナル・フェライト相の生成を抑制し、ベイニティック・フェライト相を主体とする組織を得るために重要である。 Moreover, the average cooling rate of the steel sheet after finish rolling is set to 40 ° C./second or more, and cooling to the range of 300 to 500 ° C. suppresses the formation of polygonal ferrite phase, and mainly bainitic ferrite phase. It is important to obtain an organization.
上記の平均の冷却速度が４０℃／秒未満では、ポリゴナル・フェライト相が生成しやすくなり好ましくない。一方、組織制御の上では冷却速度に上限を設ける必要はないが、余りに速い冷却速度は鋼板の冷却を不均一にするおそれがあり、また、そうした冷却を可能にするような設備の製造には多額の費用が必要となり、そのことで、鋼板の価格上昇を招くと考えられる。このような観点から、冷却速度の上限は１００℃／秒とするのが好ましい。 When the average cooling rate is less than 40 ° C./second, a polygonal ferrite phase is easily generated, which is not preferable. On the other hand, there is no need to set an upper limit on the cooling rate in terms of microstructure control, but too high a cooling rate may cause uneven cooling of the steel sheet, and for the production of equipment that enables such cooling. A large amount of money is required, which is thought to increase the price of steel sheets. From such a viewpoint, the upper limit of the cooling rate is preferably set to 100 ° C./second.
また、冷却停止温度が３００℃より低くなると、伸びフランジ性に好ましくないマルテンサイト相が生成するので、下限を３００℃とする。したがって、巻取温度は、伸びフランジ性を極端に悪化させるマルテンサイト相の生成を抑制するため３００℃以上とすることが好ましい。 On the other hand, when the cooling stop temperature is lower than 300 ° C., a martensite phase that is not preferable for stretch flangeability is generated, so the lower limit is set to 300 ° C. Therefore, the winding temperature is preferably set to 300 ° C. or higher in order to suppress the formation of a martensite phase that extremely deteriorates stretch flangeability.
一方、５００℃超ではポリゴナル・フェライト相の生成が抑制できず、また、Ｃｕを含有している鋼では、フェライト相中にＣｕが局材的に析出して、疲労特性向上効果を低下させるおそれがあるので、５００℃以下とすることが好ましい。したがって、５００℃以下で巻取ることにより、その後の冷却過程でＴｉＣやＮｂＣが析出し、フェライト相中の固溶Ｃ量を大幅に減少させ、伸びフランジ性の向上をもたらす。 On the other hand, when the temperature exceeds 500 ° C., the formation of polygonal ferrite phase cannot be suppressed, and in steel containing Cu, Cu may precipitate locally in the ferrite phase and reduce the fatigue property improvement effect. Therefore, the temperature is preferably 500 ° C. or lower. Therefore, by winding at 500 ° C. or less, TiC and NbC are precipitated in the subsequent cooling process, thereby greatly reducing the amount of solid solution C in the ferrite phase and improving stretch flangeability.
以下、本発明の実施例を比較例とともに説明する。 Examples of the present invention will be described below together with comparative examples.
表１に化学成分を示す鋼のスラブを、表２に示す条件にて熱間圧延し、厚さ３．２ｍｍの熱延板を得た。このようにして得られた鋼板の強度、延性、伸びフランジ性、断面組織、疲労限度比、および、介在物の粒径分布、形態、平均組成を調べた。 A steel slab having chemical components shown in Table 1 was hot-rolled under the conditions shown in Table 2 to obtain a hot-rolled sheet having a thickness of 3.2 mm. The strength, ductility, stretch flangeability, cross-sectional structure, fatigue limit ratio, and particle size distribution, form, and average composition of inclusions were examined.
その結果を、鋼と条件の組み合わせ毎に表３に示す。強度と延性は、圧延方向と平行に採取したＪＩＳ５号試験片の引張試験により求めた。 The results are shown in Table 3 for each combination of steel and conditions. The strength and ductility were obtained by a tensile test of a JIS No. 5 specimen taken in parallel with the rolling direction.
伸びフランジ性は、１５０ｍｍ×１５０ｍｍの鋼板の中央に開けた直径１０ｍｍの打ち抜き穴を６０°の円錐パンチで押し広げ、板厚貫通亀裂が生じた時点での穴径Ｄ（ｍｍ）を測定し、穴広げ値λ＝（Ｄ−１０）／１０で求めたλで評価した。 Stretch flangeability is measured by measuring the hole diameter D (mm) at the time when a through-thickness crack is generated by expanding a punched hole with a diameter of 10 mm with a 60 ° conical punch in the center of a 150 mm × 150 mm steel plate. The hole expansion value λ = (D−10) / 10.
また、疲労特性を表す指標として用いた疲労強度比は、ＪＩＳ Ｚ ２２７５に準拠した方法で求めた２×１０6回時間強さ、σWを鋼板の強度（σB）で除した値（σW／σB）で評価した。 Further, the fatigue strength ratio used as an index representing the fatigue characteristics is a value obtained by dividing the 2 × 10 6 times strength obtained by a method based on JIS Z 2275 and σ W by the strength (σ B ) of the steel sheet (σ W / σ B ).
なお、試験片は同規格に規定の１号試験片であり、平行部が２５ｍｍ、曲率半径Ｒが１００ｍｍ、原板（熱延板）の両面を等しく研削した厚さ３．０ｍｍのものを用いた。 Note that the test piece is a No. 1 test piece defined in the same standard, with a parallel part of 25 mm, a radius of curvature R of 100 mm, and a thickness of 3.0 mm obtained by equally grinding both surfaces of the original plate (hot rolled plate). .
更に、介在物は光学顕微鏡による１００倍と１０００倍の観察を行い、ランダムに選んだ１００個の介在物について粒径と形態を測定した。更に、走査型電子顕微鏡の定量分析機能を用いて、ランダムに選んだ２０個の介在物について組成分析を実施した。 Further, the inclusions were observed 100 times and 1000 times with an optical microscope, and the particle size and form of 100 inclusions selected at random were measured. Furthermore, using a quantitative analysis function of a scanning electron microscope, composition analysis was performed on 20 inclusions randomly selected.
表３から明らかなように、本発明の方法を用いれば、鋼板中に球状介在物が微細分散し、その結果、強度、延性、伸びフランジ性および疲労特性に優れた鋼板を得ることができる。 As apparent from Table 3, when the method of the present invention is used, spherical inclusions are finely dispersed in the steel sheet, and as a result, a steel sheet having excellent strength, ductility, stretch flangeability and fatigue characteristics can be obtained.
しかし、比較例では、介在物組成が本発明の所定組成でないため、鋼板中の介在物は粗大化し、そのため強度、延性、伸びフランジ性および疲労特性が低下している。 However, in the comparative example, since the inclusion composition is not the predetermined composition of the present invention, the inclusion in the steel sheet is coarsened, so that the strength, ductility, stretch flangeability and fatigue characteristics are reduced.
前述したように、本発明によれば、伸びフランジ性と疲労特性に優れた高強度熱延鋼板を得ることができる。 As described above, according to the present invention, a high-strength hot-rolled steel sheet excellent in stretch flangeability and fatigue characteristics can be obtained.
したがって、本発明は、鋼板利用産業において、利用可能性の高いものである。 Therefore, the present invention has high applicability in the steel sheet utilization industry.
Claims (8)
−０．０５≦｛Ｔｉ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、平均の介在物組成で、Ｃｅ酸化物もしくはＬａ酸化物の１種または２種の合計が１０〜９０質量％、Ｔｉ酸化物が１０〜９０質量％、Ａｌ2Ｏ3が５０質量％以下の範囲の介在物を含むことを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。 C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01 % By mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, total of one or two of Ce or La: 0 .0005 to 0.04% by mass or more, and further satisfies the following formula:
−0.05 ≦ {Ti− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and unavoidable impurities, and the steel has an average inclusion composition, and the total of one or two of Ce oxide or La oxide is 10 to 90% by mass, Ti oxidation A high-strength hot-rolled steel sheet excellent in stretch flangeability and fatigue characteristics, comprising inclusions in a range of 10 to 90% by mass and Al 2 O 3 in a range of 50% by mass or less.
−０．０５≦｛Ｔｉ＋（４８／９３）×Ｎｂ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、平均の介在物組成で、Ｃｅ酸化物もしくはＬａ酸化物の１種または２種の合計が１０〜９０質量％、Ｔｉ酸化物が１０〜９０質量％、Ａｌ2Ｏ3が５０質量％以下の範囲の介在物を含むことを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。 C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01 % By mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, total of one or two of Ce or La: 0 .0005 to 0.04% by mass or more, and Nb, further satisfying the following formula,
−0.05 ≦ {Ti + (48/93) × Nb− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and unavoidable impurities, and the steel has an average inclusion composition, and the total of one or two of Ce oxide or La oxide is 10 to 90% by mass, Ti oxidation A high-strength hot-rolled steel sheet excellent in stretch flangeability and fatigue characteristics, comprising inclusions in a range of 10 to 90% by mass and Al 2 O 3 in a range of 50% by mass or less.
−０．０５≦｛Ｔｉ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、介在物の個数割合で、５０％以上が少なくとも球状、紡錘状の介在物を含むことを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。 C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01 % By mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, total of one or two of Ce or La: 0 .0005 to 0.04% by mass or more, and further satisfies the following formula:
−0.05 ≦ {Ti− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and inevitable impurities, and in the steel, 50% or more of inclusions include at least spherical and spindle-shaped inclusions, and the stretch flangeability and fatigue High-strength hot-rolled steel sheet with excellent characteristics.
−０．０５≦｛Ｔｉ＋（４８／９３）×Ｎｂ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、介在物の個数割合で、５０％以上が少なくとも球状、紡錘状の介在物を含むことを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。 C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01 % By mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, total of one or two of Ce or La: 0 .0005 to 0.04% by mass or more, and Nb, further satisfying the following formula,
−0.05 ≦ {Ti + (48/93) × Nb− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and inevitable impurities, and in the steel, 50% or more of inclusions include at least spherical and spindle-shaped inclusions, and the stretch flangeability and fatigue High-strength hot-rolled steel sheet with excellent characteristics.
−０．０５≦｛Ｔｉ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、粒径が０．５μｍ以上１０μｍ以下の介在物が１０００個／ｃｍ2以上、１０００００個／ｃｍ2以下存在することを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。 C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01 % By mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, total of one or two of Ce or La: 0 .0005 to 0.04% by mass or more, and further satisfies the following formula:
−0.05 ≦ {Ti− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and inevitable impurities, and in the steel, inclusions having a particle size of 0.5 μm or more and 10 μm or less are present at 1000 / cm 2 or more and 100,000 / cm 2 or less. High-strength hot-rolled steel sheet with excellent stretch flangeability and fatigue properties.
−０．０５≦｛Ｔｉ＋（４８／９３）×Ｎｂ−（４８／１２）×Ｃ−（４８／１４）×Ｎ−（４８／３２）×Ｓ｝≦０．２
残部が鉄および不可避的不純物からなる鋼であり、その鋼中には、粒径が０．５μｍ以上１０μｍ以下の介在物が１０００個／ｃｍ2以上、１０００００個／ｃｍ2以下存在することを特徴とする伸びフランジ性と疲労特性に優れた高強度熱延鋼板。 C: 0.03-0.10 mass%, Si: 0.05-1.5 mass%, Mn: 1.0-3.0 mass%, P: 0.05 mass% or less, S: 0.01 % By mass or less, N: 0.0005 to 0.01% by mass, acid-soluble Al: 0.005% by mass or less, Ti: 0.005% by mass or more, total of one or two of Ce or La: 0 .0005 to 0.04% by mass or more, and Nb, further satisfying the following formula,
−0.05 ≦ {Ti + (48/93) × Nb− (48/12) × C− (48/14) × N− (48/32) × S} ≦ 0.2
The balance is steel composed of iron and inevitable impurities, and in the steel, inclusions having a particle size of 0.5 μm or more and 10 μm or less are present at 1000 / cm 2 or more and 100,000 / cm 2 or less. High-strength hot-rolled steel sheet with excellent stretch flangeability and fatigue properties.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2004071179A JP2005256115A (en) | 2004-03-12 | 2004-03-12 | High strength hot rolled steel sheet having excellent stretch flange formability and fatigue property |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP2004071179A JP2005256115A (en) | 2004-03-12 | 2004-03-12 | High strength hot rolled steel sheet having excellent stretch flange formability and fatigue property |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| JP2005256115A true JP2005256115A (en) | 2005-09-22 |
Family
ID=35082140
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP2004071179A Pending JP2005256115A (en) | 2004-03-12 | 2004-03-12 | High strength hot rolled steel sheet having excellent stretch flange formability and fatigue property |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP2005256115A (en) |
Cited By (16)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007077412A (en) * | 2005-09-09 | 2007-03-29 | Nippon Steel Corp | High strength hot rolled steel sheet with excellent stretch-flange formability and fatigue characteristic |
| JP2007146280A (en) * | 2005-11-07 | 2007-06-14 | Nippon Steel Corp | High-strength steel sheet superior in formability for extension flange and fatigue characteristics |
| JP2007247001A (en) * | 2006-03-16 | 2007-09-27 | Nippon Steel Corp | High-strength steel sheet for die quenching |
| WO2008007477A1 (en) * | 2006-07-14 | 2008-01-17 | Nippon Steel Corporation | High-strength steel sheet excellent in stretch flangeability and fatigue property |
| JP2008274336A (en) * | 2007-04-26 | 2008-11-13 | Nippon Steel Corp | High strength steel sheet having excellent stretch-flange formability and fatigue property, and method for refining molten steel thereof |
| WO2009151140A1 (en) * | 2008-06-13 | 2009-12-17 | 新日本製鐵株式会社 | High-strength steel sheet and process for producing molten steel for high-strength steel sheet |
| CN103924156A (en) * | 2014-05-05 | 2014-07-16 | 台州学院 | Copper hardened steel added with nanoparticles and preparation method of steel |
| KR20170107556A (en) | 2015-02-25 | 2017-09-25 | 신닛테츠스미킨 카부시키카이샤 | Hot-rolled steel sheet |
| WO2018026015A1 (en) | 2016-08-05 | 2018-02-08 | 新日鐵住金株式会社 | Steel sheet and plated steel sheet |
| KR20190014077A (en) | 2016-08-05 | 2019-02-11 | 신닛테츠스미킨 카부시키카이샤 | Steel plate and coated steel plate |
| KR20190015539A (en) | 2016-08-05 | 2019-02-13 | 신닛테츠스미킨 카부시키카이샤 | Steel plate and coated steel plate |
| KR20190016099A (en) | 2016-08-05 | 2019-02-15 | 신닛테츠스미킨 카부시키카이샤 | Steel plate and coated steel plate |
| US10689737B2 (en) | 2015-02-25 | 2020-06-23 | Nippon Steel Corporation | Hot-rolled steel sheet |
| US10913988B2 (en) | 2015-02-20 | 2021-02-09 | Nippon Steel Corporation | Hot-rolled steel sheet |
| US11401571B2 (en) | 2015-02-20 | 2022-08-02 | Nippon Steel Corporation | Hot-rolled steel sheet |
| CN115838903A (en) * | 2022-12-09 | 2023-03-24 | 中国核动力研究设计院 | Nano mixture dispersed high-strength heat-resistant ferrite steel and application thereof |
-
2004
- 2004-03-12 JP JP2004071179A patent/JP2005256115A/en active Pending
Cited By (29)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP4523899B2 (en) * | 2005-09-09 | 2010-08-11 | 新日本製鐵株式会社 | High-strength hot-rolled steel sheet with excellent stretch flangeability and fatigue characteristics |
| JP2007077412A (en) * | 2005-09-09 | 2007-03-29 | Nippon Steel Corp | High strength hot rolled steel sheet with excellent stretch-flange formability and fatigue characteristic |
| JP2007146280A (en) * | 2005-11-07 | 2007-06-14 | Nippon Steel Corp | High-strength steel sheet superior in formability for extension flange and fatigue characteristics |
| JP2007247001A (en) * | 2006-03-16 | 2007-09-27 | Nippon Steel Corp | High-strength steel sheet for die quenching |
| WO2008007477A1 (en) * | 2006-07-14 | 2008-01-17 | Nippon Steel Corporation | High-strength steel sheet excellent in stretch flangeability and fatigue property |
| JP2008274336A (en) * | 2007-04-26 | 2008-11-13 | Nippon Steel Corp | High strength steel sheet having excellent stretch-flange formability and fatigue property, and method for refining molten steel thereof |
| WO2008136516A1 (en) * | 2007-04-26 | 2008-11-13 | Nippon Steel Corporation | High-strength steel sheet excelling in flange extensibility and fatigue performance and method of smelting for molten steel thereof |
| EP2312004A1 (en) * | 2008-06-13 | 2011-04-20 | Nippon Steel Corporation | High-strength steel sheet and process for producing molten steel for high-strength steel sheet |
| KR101239461B1 (en) * | 2008-06-13 | 2013-03-06 | 신닛테츠스미킨 카부시키카이샤 | High-strength steel sheet and process for producing molten steel for high-strength steel sheet |
| EP2312004A4 (en) * | 2008-06-13 | 2014-03-19 | Nippon Steel & Sumitomo Metal Corp | High-strength steel sheet and process for producing molten steel for high-strength steel sheet |
| US9650690B2 (en) | 2008-06-13 | 2017-05-16 | Nippon Steel & Sumitomo Metal Corporation | High-strength steel sheet and method of producing molten steel for high-strength steel sheet |
| WO2009151140A1 (en) * | 2008-06-13 | 2009-12-17 | 新日本製鐵株式会社 | High-strength steel sheet and process for producing molten steel for high-strength steel sheet |
| CN103924156A (en) * | 2014-05-05 | 2014-07-16 | 台州学院 | Copper hardened steel added with nanoparticles and preparation method of steel |
| US11401571B2 (en) | 2015-02-20 | 2022-08-02 | Nippon Steel Corporation | Hot-rolled steel sheet |
| US10913988B2 (en) | 2015-02-20 | 2021-02-09 | Nippon Steel Corporation | Hot-rolled steel sheet |
| US10689737B2 (en) | 2015-02-25 | 2020-06-23 | Nippon Steel Corporation | Hot-rolled steel sheet |
| KR20170107556A (en) | 2015-02-25 | 2017-09-25 | 신닛테츠스미킨 카부시키카이샤 | Hot-rolled steel sheet |
| US10752972B2 (en) | 2015-02-25 | 2020-08-25 | Nippon Steel Corporation | Hot-rolled steel sheet |
| WO2018026015A1 (en) | 2016-08-05 | 2018-02-08 | 新日鐵住金株式会社 | Steel sheet and plated steel sheet |
| KR20190016099A (en) | 2016-08-05 | 2019-02-15 | 신닛테츠스미킨 카부시키카이샤 | Steel plate and coated steel plate |
| KR20190015539A (en) | 2016-08-05 | 2019-02-13 | 신닛테츠스미킨 카부시키카이샤 | Steel plate and coated steel plate |
| US10889879B2 (en) | 2016-08-05 | 2021-01-12 | Nippon Steel Corporation | Steel sheet and plated steel sheet |
| KR20190014077A (en) | 2016-08-05 | 2019-02-11 | 신닛테츠스미킨 카부시키카이샤 | Steel plate and coated steel plate |
| US11230755B2 (en) | 2016-08-05 | 2022-01-25 | Nippon Steel Corporation | Steel sheet and plated steel sheet |
| US11236412B2 (en) | 2016-08-05 | 2022-02-01 | Nippon Steel Corporation | Steel sheet and plated steel sheet |
| KR20190012262A (en) | 2016-08-05 | 2019-02-08 | 신닛테츠스미킨 카부시키카이샤 | Steel plate and coated steel plate |
| US11649531B2 (en) | 2016-08-05 | 2023-05-16 | Nippon Steel Corporation | Steel sheet and plated steel sheet |
| CN115838903A (en) * | 2022-12-09 | 2023-03-24 | 中国核动力研究设计院 | Nano mixture dispersed high-strength heat-resistant ferrite steel and application thereof |
| CN115838903B (en) * | 2022-12-09 | 2023-09-26 | 中国核动力研究设计院 | Nano-mixture-dispersed high-strength heat-resistant ferritic steel and application thereof |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| JP5093422B2 (en) | High strength steel plate and manufacturing method thereof | |
| JP6293997B2 (en) | High-strength steel sheet with excellent stretch flangeability and bending workability, and method for producing molten steel for the steel sheet | |
| JP4431185B2 (en) | High-strength steel sheet with excellent stretch flangeability and fatigue characteristics and method for producing the molten steel | |
| JP5053186B2 (en) | High-strength steel sheet with excellent stretch flangeability and fatigue characteristics and method for producing the molten steel | |
| WO2016148037A1 (en) | Steel sheet for carburization having excellent cold workability and toughness after carburizing heat treatment | |
| JP5158272B2 (en) | High-strength steel sheet with excellent stretch flangeability and bending workability and method for producing the molten steel | |
| JP2005256115A (en) | High strength hot rolled steel sheet having excellent stretch flange formability and fatigue property | |
| KR102386788B1 (en) | Hot rolled steel sheet and its manufacturing method | |
| JP2009024226A (en) | High-strength thin steel sheet superior in stamped-hole expandability, and manufacturing method therefor | |
| JP2013249502A (en) | High-strength cold-rolled steel plate with excellent bendability and method for manufacturing the same | |
| JP6222041B2 (en) | Ultra-thick steel plate with excellent HIC resistance and manufacturing method thereof | |
| WO2008007477A1 (en) | High-strength steel sheet excellent in stretch flangeability and fatigue property | |
| JP5158271B2 (en) | High-strength steel sheet with excellent stretch flangeability and bending workability and method for producing the molten steel | |
| JP5696359B2 (en) | High-strength steel sheet and method for melting the molten steel | |
| JP4901346B2 (en) | High-strength steel sheet with excellent stretch flangeability and fatigue characteristics | |
| JP5205795B2 (en) | High-strength steel sheet with excellent stretch flangeability and fatigue characteristics and method for producing the molten steel | |
| JP2002363694A (en) | Superhigh strength cold rolled steel sheet having excellent bending workability | |
| JP2017066516A (en) | Ferrite-martensite two-phase stainless steel and manufacturing method therefor | |
| JP4291761B2 (en) | High-strength hot-rolled steel sheet with excellent stretch flangeability and fatigue characteristics | |
| WO2015020028A1 (en) | Soft high-carbon steel sheet | |
| JP4268559B2 (en) | High strength steel plate with excellent stretch flangeability | |
| JP2015145521A (en) | High strength cold rolled steel sheet and method for producing the same | |
| JP4719067B2 (en) | High strength steel plate with excellent stretch flangeability and method for producing the same | |
| JP4523899B2 (en) | High-strength hot-rolled steel sheet with excellent stretch flangeability and fatigue characteristics | |
| JP5058892B2 (en) | DP steel sheet with excellent stretch flangeability and method for producing the same |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| A621 | Written request for application examination |
Effective date: 20060905 Free format text: JAPANESE INTERMEDIATE CODE: A621 |
|
| A977 | Report on retrieval |
Free format text: JAPANESE INTERMEDIATE CODE: A971007 Effective date: 20090330 |
|
| A131 | Notification of reasons for refusal |
Free format text: JAPANESE INTERMEDIATE CODE: A131 Effective date: 20090407 |
|
| A02 | Decision of refusal |
Effective date: 20090811 Free format text: JAPANESE INTERMEDIATE CODE: A02 |