JP2002226944A - Hot-rolled, high-tensile steel plate having excellent chemical convertibility and corrosion resistance, and its manufacturing method - Google Patents
Hot-rolled, high-tensile steel plate having excellent chemical convertibility and corrosion resistance, and its manufacturing methodInfo
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- JP2002226944A JP2002226944A JP2001026847A JP2001026847A JP2002226944A JP 2002226944 A JP2002226944 A JP 2002226944A JP 2001026847 A JP2001026847 A JP 2001026847A JP 2001026847 A JP2001026847 A JP 2001026847A JP 2002226944 A JP2002226944 A JP 2002226944A
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Abstract
Description
【０００１】[0001]
【発明の属する技術分野】本発明は、プレス加工により
製造される自動車の足回り部品やホイールディスクなど
の使途に供して好適な、引張強度が 590〜980 MPa レベ
ルで、延性、伸びフランジ性などの成形性および表面性
状に優れ、さらには化成処理性および耐食性にも優れる
熱延高張力鋼板およびその製造方法に関するものであ
る。BACKGROUND OF THE INVENTION The present invention relates to an undercarriage part of an automobile manufactured by press working, a wheel disc, and the like, which have a tensile strength of 590 to 980 MPa and a ductility and stretch flangeability. TECHNICAL FIELD The present invention relates to a hot-rolled high-tensile steel sheet which is excellent in formability and surface properties, and is also excellent in chemical conversion property and corrosion resistance, and a method for producing the same.
【０００２】[0002]
【従来の技術】熱延鋼板は、一般に、連続鋳造した鋳片
をそのまま、あるいはその後1200℃以上の温度に加熱し
てから、粗圧延および仕上圧延の２段階の熱間圧延によ
って製造される。特に引張強度が 590〜980 MPa レベル
の高張力鋼板は、強度確保のため、Siを0.5〜2.5 mass
％程度含有する鋼を用いる。この場合、熱間圧延中にSi
の酸化スケールが鋼表面を覆うため、これが製品にSiス
ケール疵を残す原因となる。このため、通常、粗圧延お
よび仕上圧延の圧延前には高圧水を用いたデスケーリン
グが行なわれるが、このデスケーリングが不十分でスケ
ールの取れ残りがあると、圧延時にスケールが噛み込ま
れてスケール疵となる。このスケール疵は、外観を損ね
るだけでなく、たとえ酸洗でスケールを完全に除去した
としても表面に凹凸が残るため、疲労特性など表面の切
り欠き状欠陥に影響を受ける特性値は低下する。2. Description of the Related Art Generally, a hot-rolled steel sheet is manufactured by continuously rolling a cast slab as it is or after heating it to a temperature of 1200 ° C. or higher, and then performing two stages of rough rolling and finish rolling. In particular, for high-strength steel sheets with a tensile strength of 590 to 980 MPa level, 0.5 to 2.5 mass%
% Steel is used. In this case, during hot rolling,
This oxide scale covers the steel surface, which causes Si scale flaws on the product. For this reason, usually, descaling using high-pressure water is performed before rolling in rough rolling and finish rolling, but if this descaling is insufficient and there is a residue of the scale, the scale is caught during rolling. It becomes scale flaw. These scale flaws not only impair the appearance, but also cause unevenness to be left on the surface even if the scale is completely removed by pickling, so that characteristic values such as fatigue characteristics, which are affected by notch-like defects on the surface, are reduced.
【０００３】また、自動車の足回り部品やホイールディ
スクは、耐食性の観点から化成処理が施されるが、表面
に凹凸が残存していると化成処理皮膜の生成が均一でな
くなるため、化成処理後に外観不良が生じたり、化成処
理後の耐食性が低下する。このようなスケール残りや表
面の凹凸は、特にSiを多量に添加した高張力鋼板の製造
時に顕著に現れる。[0003] In addition, the underbody parts of automobiles and wheel discs are subjected to a chemical conversion treatment from the viewpoint of corrosion resistance. However, if the surface has irregularities, the formation of the chemical conversion treatment film becomes non-uniform. Poor appearance occurs or corrosion resistance after chemical conversion treatment is reduced. Such scale residue and surface irregularities are particularly conspicuous when manufacturing a high-tensile steel sheet containing a large amount of Si.
【０００４】そこで、このようなスケール残りに起因し
た障害を軽減するため、例えば特公昭60−1085号公報に
は、Siを0.10〜4.00mass％含有する鋼スラブを熱間圧延
するに際し、鋳片温度が1000℃以上の時に、吐出圧：８
〜25 MPaの高圧水ジェットによるデスケーリングを累積
時間にして0.04秒以上施す技術が開示されている。ま
た、特開平４−238620号公報には、難剥離性スケール鋼
種を熱間圧延するに際し、仕上圧延前に、単位散布面積
当たりの衝突圧が 0.2 MPa以上、0.4 MPa 以下で、かつ
流量が 0.1リットル／(min・mm2)以上、0.2 リットル／
(min・mm2)以下の高水圧スプレーを鋼板表面に噴射する
技術が開示されている。さらに、特開平７−70649 号に
は、仕上ミル入側での温度をSi量に応じて制御し、単位
面積当たりの衝突圧が 5.0〜30.0 kgf/mm2（49〜294 MP
a)の高水圧でデスケーリングを行う技術が開示されてい
る。[0004] In order to reduce such obstacles caused by scale residue, for example, Japanese Patent Publication No. Sho 60-1085 discloses a method of hot rolling a steel slab containing 0.10 to 4.00 mass% of Si. Discharge pressure: 8 when temperature is 1000 ℃ or more
A technique is disclosed in which descaling by a high-pressure water jet of MPa25 MPa is performed for a cumulative time of 0.04 seconds or more. Also, JP-A-4-238620 discloses that, when hot-rolling a hard-to-peel scale steel type, before finish rolling, the collision pressure per unit spray area is 0.2 MPa or more, 0.4 MPa or less, and the flow rate is 0.1 Liter / (min.mm 2 ) or more, 0.2 liter /
There is disclosed a technique for spraying a high-pressure spray of (min · mm 2 ) or less onto a steel sheet surface. Further, Japanese Patent Application Laid-Open No. 7-70649 discloses that the temperature at the entrance of the finishing mill is controlled in accordance with the amount of Si, and the collision pressure per unit area is 5.0 to 30.0 kgf / mm 2 (49 to 294 MPF).
A technique of performing descaling at a high water pressure of a) is disclosed.
【０００５】[0005]
【発明が解決しようとする課題】しかしながら、上記特
公昭60−1085号公報に開示の技術では、1000℃以上とい
う高温の仕上圧延入側温度（ＦＥＴ）を確保する必要が
あるため、加熱炉から高温で鋼片を抽出しなければなら
ず、原単位が悪化したり、スケールロスが増加するとい
う問題があった。加えて、圧下率やデスケーリングの時
間に種々の制約が加わるため、圧延作業が煩雑になると
いう問題もあった。また、上記特開平４−238620号公報
に開示の技術では、大部分のスケールは剥離されるもの
の、高Si鋼で形成される地金に食い込むようなスケール
は除去されずに残る場合があり、スケール疵を完全には
回避することは難しいという問題があった。さらに、上
記特開平７−70649 号公報に開示の技術では、仕上圧延
の入側温度（ＦＥＴ）をSi量に応じて制御する必要があ
るため、圧延作業が煩雑になるだけでなく、この方法に
よって添加可能となるSi量の上限は1.0 mass％程度であ
り、Siをより多く含有する高Si含有鋼には適用できない
という問題があった。However, in the technique disclosed in Japanese Patent Publication No. 60-1085, it is necessary to secure a high finish-rolling inlet temperature (FET) of 1000 ° C. or more, so that a heating furnace is required. The steel slab must be extracted at a high temperature, and there has been a problem that the basic unit deteriorates and the scale loss increases. In addition, since various restrictions are added to the rolling reduction and the time for descaling, there is a problem that the rolling operation becomes complicated. Further, in the technology disclosed in Japanese Patent Application Laid-Open No. 4-238620, although most of the scale is peeled off, the scale that bites into the base metal formed of high Si steel may remain without being removed, There is a problem that it is difficult to completely avoid scale flaws. Further, in the technique disclosed in Japanese Patent Application Laid-Open No. 7-70649, it is necessary to control the entry side temperature (FET) of the finish rolling in accordance with the amount of Si, which not only complicates the rolling operation but also reduces the method. The upper limit of the amount of Si that can be added by this is about 1.0 mass%, and there is a problem that it cannot be applied to a high Si content steel containing more Si.
【０００６】また、これらの従来技術によって、0.5 ma
ss％以上のSiを含有する鋼板を製造した場合、鋼板表面
の平均粗さがせいぜい２μm 程度のものしか得られず、
満足いくほどの疲労特性や化成処理性を得ることかでき
ないという問題もあった。さらに、仕上圧延の入側で高
圧水によるデスケーリングを施す方法は、水の散布角度
や水温の管理が難しく、季節要因による変動が大きいこ
とや、鋼板の幅中央とエッジ付近では高圧水による冷却
速度が異なるため、材料特性のバラツキが生じることも
問題となっていた。[0006] Also, according to these conventional techniques, 0.5 ma
When a steel sheet containing ss% or more of Si is manufactured, the average roughness of the steel sheet surface is at most only about 2 μm,
There was also the problem that satisfactory fatigue properties and chemical conversion properties could not be obtained. In addition, descaling with high-pressure water on the entry side of finish rolling is difficult to control the spray angle and water temperature of the water, and there are large fluctuations due to seasonal factors. Since the speeds are different, there is also a problem that the material characteristics vary.
【０００７】本発明は、上記の実状に鑑み開発されたも
ので、Siを 0.5mass％以上含有する鋼板であっても、ス
ケール疵の発生を効果的に防止すると共に、鋼板の表面
粗さを低減し、ひいては優れた化成処理および耐食性が
得られる熱延高張力鋼板を、その有利な製造方法と共に
提案することを目的とする。[0007] The present invention has been developed in view of the above situation, and even if the steel sheet contains 0.5 mass% or more of Si, it is possible to effectively prevent the occurrence of scale flaws and reduce the surface roughness of the steel sheet. It is an object of the present invention to propose a hot-rolled high-strength steel sheet capable of reducing the temperature and thereby obtaining excellent chemical conversion treatment and corrosion resistance together with its advantageous production method.
【０００８】[0008]
【課題を解決するための手段】さて、発明者らは、上記
の目的を達成すべく鋭意研究を重ねた結果、鋼板の結晶
粒を微細化すれば、特にデスケーリングを施さなくて
も、スケール残りやスケール疵の発生が効果的に抑制さ
れ、その結果、表面性状ひいては化成処理および耐食性
が著しく改善されることの知見を得た。本発明は、上記
の知見に立脚するものである。Means for Solving the Problems The inventors of the present invention have conducted intensive studies in order to achieve the above-mentioned object. As a result, if the crystal grains of the steel sheet are refined, the scale can be reduced without performing descaling. It has been found that the generation of residues and scale flaws is effectively suppressed, and as a result, the surface properties and, consequently, the chemical conversion treatment and the corrosion resistance are significantly improved. The present invention is based on the above findings.
【０００９】すなわち、本発明の要旨構成は次のとおり
である。 １．Ｃ：0.01〜0.20mass％、Si：0.5 〜2.5 mass％、M
n：1.0 〜3.0 mass％、Ｐ：0.05mass％以下、Al：0.01
〜0.1 mass％、Ｓ：0.005 mass％以下およびTi：0.05〜
0.35mass％を、Ti（mass％）とＣ（mass％）とが次式 −1.4 ≧ log（Ti×Ｃ）≧−1.8 を満足する範囲において含有し、残部はFeおよび不可避
的不純物の組成になり、平均結晶粒径が 3.0μm 以下
で、かつ表面粗さが算術平均粗さRaで 1.5μm 以下であ
ることを特徴とする化成処理性および耐食性に優れる熱
延高張力鋼板。That is, the gist of the present invention is as follows. 1. C: 0.01 to 0.20 mass%, Si: 0.5 to 2.5 mass%, M
n: 1.0 to 3.0 mass%, P: 0.05 mass% or less, Al: 0.01
~ 0.1 mass%, S: 0.005 mass% or less and Ti: 0.05 ~
0.35 mass% is contained in a range where Ti (mass%) and C (mass%) satisfy the following expression: -1.4 ≧ log (Ti × C) ≧ −1.8, and the balance is based on the composition of Fe and unavoidable impurities. A hot-rolled high-strength steel sheet having excellent chemical conversion treatment properties and corrosion resistance, characterized by having an average crystal grain size of 3.0 μm or less and a surface roughness of 1.5 μm or less in arithmetic average roughness Ra.
【００１０】２．上記１において、鋼組織が、フェライ
ト、パーライト、ベイナイト、マルテンサイトおよび残
留オーステナイトのうちから選んだ２種類以上の複合組
織であることを特徴とする化成処理性および耐食性に優
れる熱延高張力鋼板。[0010] 2. 2. The hot-rolled high-strength steel sheet according to 1 above, wherein the steel structure is a composite structure of two or more types selected from ferrite, pearlite, bainite, martensite, and retained austenite.
【００１１】３．Ｃ：0.01〜0.20mass％、Si：0.5 〜2.
5 mass％、Mn：1.0 〜3.0 mass％、Ｐ：0.05mass％以
下、Al：0.01〜0.1 mass％、Ｓ：0.005 mass％以下およ
びTi：0.05〜0.35mass％を、Ti（mass％）とＣ（mass
％）とが次式 −1.4 ≧ log（Ti×Ｃ）≧−1.8 を満足する範囲において含有し、残部はFeおよび不可避
的不純物の組成になる鋼スラブを、1150℃以下に加熱
し、粗圧延後、1050℃以下で仕上圧延を開始し、仕上圧
延第１スタンドでの圧延速度を 400 m/min以上、圧下率
を80％以上とし、仕上圧延の最終圧下を表面粗さ(Ra)が
３μm 以下の圧延ロールで行い、（Ａr3＋150 ℃）〜
（Ａr3＋50℃) で仕上圧延を終了し、ついで20℃/s以上
の冷却速度で600 ℃以下まで冷却後、 600〜350 ℃の温
度範囲で巻き取ることを特徴とする化成処理性および耐
食性に優れる熱延高張力鋼板の製造方法。3. C: 0.01 to 0.20 mass%, Si: 0.5 to 2.
5 mass%, Mn: 1.0 to 3.0 mass%, P: 0.05 mass% or less, Al: 0.01 to 0.1 mass%, S: 0.005 mass% or less, and Ti: 0.05 to 0.35 mass%, Ti (mass%) and C (Mass
%) And the following formula −1.4 ≧ log (Ti × C) ≧ −1.8 is contained, and the remainder is heated to 1150 ° C. or lower by heating the steel slab having the composition of Fe and unavoidable impurities. Thereafter, finish rolling is started at 1050 ° C. or less, the rolling speed at the first stand for finishing rolling is 400 m / min or more, the rolling reduction is 80% or more, and the final rolling of the finish rolling is 3 μm in surface roughness (Ra). Performed with the following rolling rolls (Ar 3 + 150 ° C)
(Ar 3 + 50 ° C), finish rolling, then cool at a cooling rate of 20 ° C / s or more to 600 ° C or less, and wind up in a temperature range of 600 to 350 ° C. For producing hot-rolled high-strength steel sheets with excellent heat resistance.
【００１２】[0012]
【発明の実施の形態】以下、本発明を具体的に説明す
る。まず、本発明において鋼の成分組成を上記の範囲に
限定した理由について説明する。 Ｃ：0.01〜0.20mass％ Ｃは、安価な強化成分であり、所望の鋼板強度に応じて
必要量を含有させる。しかしながら、含有量が0.01mass
％に満たないと結晶粒が粗大化し、本発明で目標とする
平均結晶粒径： 3.0μm 以下を達成できなくなり、一方
0.20mass％を超えると加工性が低下するだけでなく、溶
接性も低下するので、Ｃは0.01〜0.20mass％の範囲に限
定した。より好ましくは0.05〜0.15mass％の範囲であ
る。BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below. First, the reason why the composition of steel is limited to the above range in the present invention will be described. C: 0.01 to 0.20 mass% C is an inexpensive strengthening component, and contains a necessary amount according to the desired steel sheet strength. However, the content is 0.01 mass
%, The crystal grains become coarse, and it is impossible to achieve the average grain size of 3.0 μm or less according to the present invention.
If the content exceeds 0.20 mass%, not only does the workability decrease, but also the weldability decreases, so C was limited to the range of 0.01 to 0.20 mass%. More preferably, it is in the range of 0.05 to 0.15 mass%.
【００１３】−1.4 ≧ log（Ti×Ｃ）≧−1.8 但し、このＣは、後述するTiとの関連において、次式の
関係 −1.4 ≧ log（Ti×Ｃ）≧−1.8 を満足しないと、スラブ加熱時におけるオーステナイト
粒径が微細とならず、その後の粗圧延、仕上圧延による
結晶粒の微細化が促進されないため、最終的に3.0 μm
以下の結晶粒径を得ることができず、化成処理性および
耐食性の向上が期待できない。従って、Ｃは、Tiとの関
連で、上掲式を満足する範囲で含有させることが重要で
ある。なお、式中のＣ、Tiはmass％表示した値である。-1.4 ≧ log (Ti × C) ≧ −1.8 However, in relation to Ti described later, this C does not satisfy the relationship of −1.4 ≧ log (Ti × C) ≧ −1.8. The austenite grain size during slab heating does not become fine, and the subsequent coarse rolling and finish rolling do not promote the refinement of crystal grains.
The following crystal grain size cannot be obtained, and improvement in chemical conversion treatment property and corrosion resistance cannot be expected. Therefore, it is important that C is contained in a range satisfying the above formula in relation to Ti. Note that C and Ti in the formulas are values expressed as mass%.
【００１４】Si：0.5 〜2.5 mass％ Siは、固溶強化成分として強度−伸びバランスを改善し
つつ、強度の上昇に有効に寄与する。この効果は、Si量
が 0.5mass％以上で発現するが、過剰な添加は、その効
果が飽和するだけでなく、むしろ延性や表面性状を劣化
を招くので、Siは 0.5〜2.5 mass％の範囲に限定した。
好ましくは 1.0〜2.0 mass％の範囲である。Si: 0.5 to 2.5 mass% Si effectively contributes to an increase in strength while improving strength-elongation balance as a solid solution strengthening component. This effect is manifested when the amount of Si is 0.5 mass% or more, but excessive addition not only saturates the effect but also deteriorates the ductility and surface properties. Limited to.
Preferably it is in the range of 1.0 to 2.0 mass%.
【００１５】Mn：1.0 〜3.0 mass％ Mnは、Ａr3変態点を低下させる作用を通じて結晶粒の微
細化に寄与し、また、第２相のマルテンサイト化および
残留オーステナイト化を進展させる作用を通じて、強度
−延性バランスおよび強度−疲労強度バランスを高める
効果がある。さらに、Mnは有害な固溶ＳをMnＳとして無
害化する作用も有する。これらの効果は1.0 mass％以上
の添加で発現するが、多量の添加は鋼を硬質化し、かえ
って強度−延性バランスを劣化させる。従って、Mn量は
1.0〜3.0 mass％好ましくは1.0〜2.0 mass％の範囲に
限定した。Mn: 1.0 to 3.0 mass% Mn contributes to the refinement of crystal grains through the action of lowering the Ar 3 transformation point, and also through the action of promoting the formation of martensite and retained austenite in the second phase. This has the effect of increasing the strength-ductility balance and the strength-fatigue strength balance. Further, Mn also has a function of detoxifying harmful solid solution S as MnS. These effects are manifested by addition of 1.0 mass% or more, but addition of a large amount hardens the steel and rather deteriorates the strength-ductility balance. Therefore, the amount of Mn is
The range is limited to 1.0 to 3.0 mass%, preferably 1.0 to 2.0 mass%.
【００１６】Ｐ：0.05mass％以下 Ｐは、強化成分として有用であり、所望の鋼板強度に応
じて添加するが、過剰に添加すると粒界に偏析して脆化
の原因となり、また溶接性を低下させる。従って、Ｐは
0.05mass％以下で含有させるものとした。好ましくは
0.001〜0.03mass％である。P: 0.05 mass% or less P is useful as a strengthening component, and is added according to the desired steel sheet strength. However, if added excessively, it segregates at grain boundaries and causes embrittlement, and also deteriorates weldability. Lower. Therefore, P
The content was set to 0.05 mass% or less. Preferably
It is 0.001 to 0.03 mass%.
【００１７】Al：0.01〜0.10mass％ Alは、脱酸等の目的で添加する。この目的のためには0.
01mass％以上の添加が必要であるが、0.10mass％を超え
て添加してもコストアップになるばかりか、表面欠陥の
原因ともなるので、Alは0.01〜0.10mass％好ましくは0.
02〜0.07mass％の範囲で添加することが好ましい。Al: 0.01 to 0.10 mass% Al is added for the purpose of deoxidation and the like. 0 for this purpose.
Addition of at least 01 mass% is necessary, but adding more than 0.10 mass% not only increases the cost, but also causes surface defects, so Al is 0.01 to 0.10 mass%, preferably 0.1 mass%.
It is preferable to add in the range of 02 to 0.07 mass%.
【００１８】Ｓ：0.005 mass％以下 Ｓは、鋼中のMnと反応してＡ系介在物（JIS G 0555に記
載のように加工によって粘性変形したもの（硫化物な
ど））を生成し、伸びフランジ性や疲労強度を低下させ
る有害な元素である。従って、Ｓは 0.005 mass ％以
下、より好ましくは0.002 mass％以下に制限した。S: 0.005 mass% or less S reacts with Mn in steel to form A-based inclusions (viscously deformed by working (such as sulfide) as described in JIS G 0555), and elongation. It is a harmful element that reduces flangeability and fatigue strength. Therefore, S is limited to 0.005 mass% or less, more preferably 0.002 mass% or less.
【００１９】Ti：0.05〜0.35mass％ Tiは、TiＣとして存在して、スラブ加熱段階でのオース
テナイト粒を微細化するのに有効に作用する。このよう
な作用を発揮させるためには、少なくとも0.05mass％の
含有が必要であるが、0.35mass％を超えると、効果が飽
和し含有量に見合う効果が期待できない。従って、Tiは
0.05〜0.35mass％の範囲に限定した。より好ましくは0.
10〜0.25mass％である。Ti: 0.05 to 0.35 mass% Ti is present as TiC and effectively acts to refine the austenite grains in the slab heating stage. In order to exert such an effect, the content must be at least 0.05 mass%. However, if it exceeds 0.35 mass%, the effect is saturated and an effect corresponding to the content cannot be expected. Therefore, Ti
It was limited to the range of 0.05 to 0.35 mass%. More preferably 0.
It is 10 to 0.25 mass%.
【００２０】以上、鋼板の成分組成範囲について説明し
たが、本発明では、鋼の平均結晶粒径および表面粗さを
所定の範囲に制限することが重要である。 (1) 平均結晶粒径≦3.0 μm 化成処理時にはリン酸塩溶液への浸漬時に表面が電解に
より活性化するが、その際、粒界は選択的にエッチング
され、粒界が化成処理皮膜の基となって化成処理性が向
上する。そのためには、結晶粒界が多いほどすなわち結
晶粒径が小さいほど有利である。また、微細粒とするこ
とにより、強度−延性バランス、強度−穴拡げバランス
も良好となる。従って、本発明では、鋼板の全厚にわた
る平均結晶粒径を 3.0μm 以下に制限したのである。Although the composition range of the steel sheet has been described above, it is important in the present invention to limit the average crystal grain size and the surface roughness of the steel to predetermined ranges. (1) Average crystal grain size ≤ 3.0 μm During the chemical conversion treatment, the surface is activated by electrolysis when immersed in a phosphate solution.At this time, the grain boundaries are selectively etched, and the grain boundaries are formed on the base of the chemical conversion coating. As a result, the chemical conversion property is improved. For that purpose, it is advantageous that the number of crystal grain boundaries is large, that is, the crystal grain size is small. Further, by making the particles fine, the balance between strength and ductility and the balance between strength and hole expansion are also improved. Therefore, in the present invention, the average grain size over the entire thickness of the steel sheet is limited to 3.0 μm or less.
【００２１】(2) 表面粗さ(Ra)≦ 1.5μm 以下 表面粗さを算術平均粗さRaで 1.5μm 以下とするのは、
表面粗さが 1.5μm より大きくなると、耐食性や化成処
理性が低下するためである。なお、表面粗さを0.5μm
未満としても格段に化成処理性や耐食性が向上せず、ま
た0.5 μm 未満に管理することは実機において困難な場
合があるため表面粗さ(Ra)は 0.5μm 以上とすることが
好ましい。ここに、かような鋼板表面粗さは、結晶粒径
と仕上圧延機のロール粗度により調整される。よって、
鋼板表面粗度を本発明の範囲内に調整するためには、仕
上圧延機のロール粗度を３μm 以下に管理することが必
要である。なお、この熱延板の表面粗さについては、従
来特に考慮が払われてなく、一般的な表面粗さは２〜５
μm 程度であった。(2) Surface roughness (Ra) ≦ 1.5 μm or less The reason for making the surface roughness 1.5 μm or less in arithmetic average roughness Ra is as follows.
If the surface roughness is larger than 1.5 μm, the corrosion resistance and the chemical conversion property deteriorate. Note that the surface roughness is 0.5 μm
Even if it is less than 10, the chemical conversion property and the corrosion resistance are not remarkably improved, and it may be difficult to control the surface roughness to less than 0.5 μm in actual equipment, so that the surface roughness (Ra) is preferably 0.5 μm or more. Here, the surface roughness of such a steel sheet is adjusted by the crystal grain size and the roll roughness of a finishing mill. Therefore,
In order to adjust the surface roughness of the steel sheet within the range of the present invention, it is necessary to control the roll roughness of the finishing mill to 3 μm or less. The surface roughness of this hot-rolled sheet has not been particularly taken into consideration conventionally, and the general surface roughness is 2 to 5
It was about μm.
【００２２】図１に、鋼板の平均結晶粒径と表面粗さが
化成処理性に及ぼす影響について調べた結果を示す。同
図に示したとおり、平均結晶粒径が 3.0μm 以下で、か
つ表面粗さ(Ra)が 1.5μm 以下の場合に良好な化成処理
性が得られている。FIG. 1 shows the results of examining the effects of the average crystal grain size and the surface roughness of the steel sheet on the chemical conversion property. As shown in the figure, when the average crystal grain size is 3.0 μm or less and the surface roughness (Ra) is 1.5 μm or less, good chemical conversion property is obtained.
【００２３】上記したように、結晶粒を微細化すること
により化成処理性が向上し、ひいては耐食性が向上する
メカニズムについて、その詳細は不明であるが、次のと
おりと考えられる。一般に、結晶粒界には析出物や介在
物などが集積し易いため、錆などの起点となり易い。し
かしながら、結晶粒の微細化により結晶粒界が増加する
と、粒界面積当たりの不純物濃度が低下するため、相対
的に錆の発生が抑制されることが、理由の１つとして考
えられる。また、かような結晶粒の微細化によって、脱
スケール性が大幅に改善される。その理由は、明確に解
明されたわけではないが、次のように考えている。脱ス
ケールは通常、塩酸溶液に浸漬し行われる。その際、結
晶粒界はエッチングされ易いため、結晶粒が微細化され
結晶粒界面積が増加することにより、表面スケールの剥
離を容易にするものと考えられる。As described above, the details of the mechanism by which the chemical conversion treatment property is improved and the corrosion resistance is improved by refining the crystal grains are unknown, but are considered as follows. Generally, precipitates and inclusions tend to accumulate at the crystal grain boundaries, and thus tend to be a starting point of rust and the like. However, if the crystal grain boundaries increase due to the refinement of crystal grains, the impurity concentration per grain boundary area decreases, which is considered to be one reason that the generation of rust is relatively suppressed. In addition, descaling can be greatly improved by making the crystal grains fine. The reason has not been clearly elucidated, but he thinks as follows. The descaling is usually performed by dipping in a hydrochloric acid solution. At this time, since the crystal grain boundaries are easily etched, it is considered that the crystal grains are refined and the crystal grain boundary area increases, thereby facilitating the separation of the surface scale.
【００２４】さらに、本発明では、鋼組織は、フェライ
ト、パーライト、ベイナイト、マルテンサイトおよび残
留オーステナイトのうちから選んだ２種類以上の複合組
織とすることが好ましい。というのは、かような複合組
織は、伸び−穴拡げバランスに優れ、また疲労特性にも
優れており、熱延高張力鋼板として必要な材料特性をバ
ランスよく備えた組織だからである。Further, in the present invention, the steel structure is preferably a composite structure of two or more types selected from ferrite, pearlite, bainite, martensite and retained austenite. This is because such a composite structure is excellent in elongation-hole expansion balance, excellent in fatigue characteristics, and well-balanced in material properties required for a hot-rolled high-tensile steel sheet.
【００２５】次に、本発明の製造条件について説明す
る。 (1) 熱延前における鋼スラブの加熱温度：1150℃以下 熱延前の加熱温度は、粗圧延、仕上圧延後の結晶粒径に
大きな影響を与えるため重要である。本発明では、加熱
時にTiＣを定量析出させ、微細なTiＣにより結晶粒の成
長を抑制することが必要である。図２に、加熱温度およ
びTi, Ｃ量（mass％）と、得られる熱延板の粒径との関
係について調べた結果を示す。なお、Ti, Ｃ量（mass
％）については log（Ti×Ｃ）で示すものとする。ここ
に、同図の実験に供した鋼の組成は、Si：1.4 mass％,
Mn：1.8 mass％, Ｐ：0.02mass％, Ｓ：0.001 mass％お
よびAl：0.05mass％を基本組成として含有し、ＣとTiを
それぞれＣ：0.01〜0.2 mass％, Ti：0.05〜0.35mass％
の範囲で種々に変化させた鋼であり、かかる組成になる
鋼スラブ（厚さ：260 mm）を、スラブ加熱温度：1000〜
1300℃、圧延終了温度：900 ℃、仕上板厚：3.0mm 、巻
取り温度：450 ℃の条件で製造したものである。同図に
示したとおり、平均結晶粒径を 3.0μm 以下とするには
TiとＣ量との関係において、加熱温度を1150℃以下とす
る必要があることが分かる。なお、得られる鋼スラブ
が、上記したような再加熱材ではなく、連続鋳造後直ち
に熱間粗圧延に供されるいわゆる直送圧延材である場合
には、かようなスラブ加熱は必ずしも行う必要はなく、
そのまま熱間粗圧延に供しても良い。Next, the manufacturing conditions of the present invention will be described. (1) Heating temperature of steel slab before hot rolling: 1150 ° C or less The heating temperature before hot rolling is important because it greatly affects the crystal grain size after rough rolling and finish rolling. In the present invention, it is necessary to deposit TiC quantitatively during heating and to suppress the growth of crystal grains by fine TiC. FIG. 2 shows the results of a study on the relationship between the heating temperature and the amounts of Ti and C (mass%) and the particle size of the obtained hot-rolled sheet. The amount of Ti and C (mass
%) Is represented by log (Ti × C). Here, the composition of the steel used for the experiment in the figure is Si: 1.4 mass%,
Mn: 1.8 mass%, P: 0.02 mass%, S: 0.001 mass%, and Al: 0.05 mass% as a basic composition, C and Ti are respectively C: 0.01-0.2 mass%, Ti: 0.05-0.35 mass%.
The steel slab (thickness: 260 mm) having such a composition is heated at a slab heating temperature of 1000 to
It is manufactured under the conditions of 1300 ° C, rolling end temperature: 900 ° C, finished plate thickness: 3.0 mm, and winding temperature: 450 ° C. As shown in the figure, to make the average grain size less than 3.0μm
From the relationship between Ti and C content, it is understood that the heating temperature needs to be 1150 ° C. or less. Incidentally, if the obtained steel slab is not a reheated material as described above, but a so-called direct-rolled material that is subjected to hot rough rolling immediately after continuous casting, such slab heating is not necessarily performed. Not
It may be subjected to hot rough rolling as it is.
【００２６】(2) 仕上圧延開始温度：1050℃以下 粗圧延後、仕上圧延前には、通常、吐出圧：約５〜20 M
Pa程度のデスケーリングが行われる。本発明では特に仕
上圧延前のデスケーリングを高圧水で行なう必要はな
く、上記のような通常の条件たとえば吐出圧：５〜20 M
Pa程度のデスケーリングでよい。ここに、仕上圧延にお
ける圧延開始温度を1050℃以下としたのは、次の理由に
よる。仕上圧延開始温度が1050℃よりも高いと、圧延に
より導入された歪が回復し、粒が成長粗大化して、最終
的に 3.0μm 以下の結晶粒を得ることが困難となり、ま
た厚いスケールが生成し、それが圧延時に鋼板の内部へ
入り込み、かみ込みスケールとなって表面性状を劣化さ
せる。(2) Finish rolling start temperature: 1050 ° C. or less After rough rolling and before finish rolling, the discharge pressure is usually about 5 to 20 M.
Descaling of about Pa is performed. In the present invention, descaling before finish rolling need not be performed with high-pressure water, and the above-mentioned ordinary conditions, for example, discharge pressure: 5 to 20 M
Descaling of about Pa is sufficient. Here, the reason why the rolling start temperature in the finish rolling is set to 1050 ° C. or less is as follows. When the finish rolling start temperature is higher than 1050 ° C, the strain introduced by rolling is recovered, the grains grow and become coarse, it becomes difficult to finally obtain crystal grains of 3.0 μm or less, and a thick scale is formed. However, it enters the inside of the steel sheet at the time of rolling, and becomes a biting scale to deteriorate the surface properties.
【００２７】(3) 仕上圧延第１スタンドにおける圧延速
度≧400 m/min 、圧下率≧80％ 仕上圧延時における圧延速度および圧下率は、フェライ
ト粒径を 3.0μm 以下にする上で重要である。特に仕上
圧延第１スタンドにおける圧延速度が 400 m/minを下回
る遅い圧延速度となると、仕上圧延でのスタンド間（通
常７スタンド）での滞留時間が長くなるため圧延による
導入された結晶粒への歪みが回復し、また粒成長が促進
されるため、圧延中に結晶粒が粗大化し、微細なγ粒を
得ることができなくなる。また、この第１スタンドにお
ける圧下率が80％より小さいと、粒への歪みが小さく、
オーステナイト粒を微細にすることができない。(3) Rolling speed ≧ 400 m / min and rolling reduction ≧ 80% in the first finishing rolling stand The rolling speed and rolling reduction during finish rolling are important for reducing the ferrite grain size to 3.0 μm or less. . In particular, when the rolling speed at the first stand of the finish rolling is a slow rolling speed of less than 400 m / min, the residence time between the stands (usually seven stands) in the finish rolling becomes long, so that the crystal grains introduced by rolling are reduced. Since the strain is recovered and the grain growth is promoted, the crystal grains become coarse during rolling, and it becomes impossible to obtain fine γ grains. When the rolling reduction in the first stand is less than 80%, distortion to grains is small,
Austenite grains cannot be made fine.
【００２８】図３に、仕上圧延第１スタンドにおける圧
延速度および圧下率と熱延板の結晶粒径との関係につい
て調べた結果を示す。ここに、同図の実験に供した鋼の
組成は、Ｃ：0.09mass％，Si：1.4 mass％，Mn：1.8 ma
ss％，Ｐ：0.02mass％，Ｓ：0.001 mass％，Al：0.05ma
ss％およびTi：0.18mass％を含有し、残部は実質的にFe
の組成になる鋼であり、かかる組成の鋼スラブ（厚さ：
260 mm）を、スラブ加熱温度：1050℃、圧延終了温度：
900 ℃、仕上板厚：3.0 mm、巻取り温度：450 ℃の条件
で製造したものである。なお、仕上圧延第１スタンドに
おける圧延速度は 100〜800 m/min 、圧下率は70, 80,
90％とした。同図より明らかなように、仕上圧延第１ス
タンドにおける圧延速度を 400 m/min以上、圧下率を80
％以上とすることによって、平均結晶粒径を 3.0μm 以
下とすることができた。FIG. 3 shows the results of a study on the relationship between the rolling speed and rolling reduction in the first stand for finish rolling and the crystal grain size of the hot-rolled sheet. Here, the composition of the steel used in the experiment shown in the figure is as follows: C: 0.09 mass%, Si: 1.4 mass%, Mn: 1.8 ma
ss%, P: 0.02 mass%, S: 0.001 mass%, Al: 0.05 ma
ss% and Ti: 0.18 mass%, the balance being substantially Fe
Steel slab of such composition (thickness:
260 mm), slab heating temperature: 1050 ° C, rolling end temperature:
Manufactured under the conditions of 900 ° C, finished plate thickness: 3.0 mm, and winding temperature: 450 ° C. In addition, the rolling speed in the first stand for finish rolling is 100 to 800 m / min, and the rolling reduction is 70, 80,
90%. As is clear from the figure, the rolling speed in the first stand for finishing rolling is 400 m / min or more, and the rolling reduction is 80
%, The average grain size could be reduced to 3.0 μm or less.
【００２９】(4) 仕上圧延終了温度：（Ａr3＋150 ℃）
〜（Ａr3＋50℃) 仕上圧延終了温度が（Ａr3＋50℃) 未満では、表層部の
フェライト粒が粗大となり、一方（Ａr3＋150 ℃）を超
えると、鋼板全体の組織が粗大化して、伸びや穴拡げ性
などの加工性が低下するためである。なお、仕上圧延の
最終圧下は、前述したように鋼板の表面粗さ(Ra)を 1.5
μm以下とするため、表面粗さ(Ra)が３μm 以下の圧延
ロールで行う必要がある。(4) Finish rolling end temperature: (Ar 3 + 150 ° C.)
If it is less than ~ (Ar 3 + 50 ℃) finish rolling temperature is (Ar 3 + 50 ℃), ferrite grains of the surface layer portion becomes coarse, when the content is higher than (Ar 3 +150 ℃), the whole steel sheet microstructure is coarsened, This is because workability such as elongation and hole expandability is reduced. The final reduction in finish rolling is, as mentioned above, the surface roughness (Ra) of the steel sheet is 1.5
In order to reduce the surface roughness to not more than μm, it is necessary to use a roll having a surface roughness (Ra) of 3 μm or less.
【００３０】(5) 仕上圧延終了後、巻取りまでの冷却速
度：20℃/s以上 仕上圧延終了後の冷却速度は20℃/s以上とする必要であ
る。というのは、圧延終了後の冷却速度が20℃/sより遅
い場合には、圧延終了時に微細化しているオーステナイ
ト組織が冷却中に粗大化し、変態後得られる製品板の組
織が粗大化して、本発明で所望する 3.0μm 以下の組織
が得られなくなるからである。(5) Cooling rate after finishing rolling until winding: 20 ° C./s or more The cooling rate after finishing rolling must be 20 ° C./s or more. That is, when the cooling rate after the end of rolling is slower than 20 ° C./s, the austenite structure that has been refined at the end of rolling is coarsened during cooling, and the structure of the product sheet obtained after transformation is coarsened. This is because a tissue of 3.0 μm or less desired in the present invention cannot be obtained.
【００３１】(6) 巻取り温度：600 〜350 ℃ 巻取り温度を 600〜350 ℃としたのは、巻取り温度が 6
00℃を超えると粗大なセメンタイトが生成して、強度−
延性バランスが低下し、一方 350℃未満ではコイル全体
での温度制御が困難となり、均一な材料特性を得ること
ができなくなるからである。上記の巻取り後、通常の酸
洗を施して製品とする。(6) Winding temperature: 600 to 350 ° C. The winding temperature is set to 600 to 350 ° C. because the winding temperature is
If the temperature exceeds 00 ° C., coarse cementite is formed,
This is because the ductility balance is reduced, while if it is lower than 350 ° C., it becomes difficult to control the temperature of the entire coil, and it becomes impossible to obtain uniform material properties. After the above winding, a normal pickling is performed to obtain a product.
【００３２】[0032]
【実施例】表１に示す成分組成になる鋼スラブを、表２
に示す種々の条件で処理し、板厚：3.0 mmの熱延鋼板と
した。得られた熱延鋼板を酸洗後、平均結晶粒径、表面
粗さおよび金属組織を調査した。また、これら熱延鋼板
の機械的特性を調査した。さらに、化成処理性および耐
食性についても調査した。これらの結果を表３に示す。EXAMPLE A steel slab having the composition shown in Table 1 was prepared as shown in Table 2.
To give a hot-rolled steel sheet having a thickness of 3.0 mm. After pickling the obtained hot-rolled steel sheet, the average crystal grain size, surface roughness and metal structure were investigated. The mechanical properties of these hot rolled steel sheets were also investigated. Furthermore, the chemical conversion treatment and corrosion resistance were also investigated. Table 3 shows the results.
【００３３】なお、熱延鋼板の結晶粒径は、板厚断面を
（２％硝酸＋エチルアルコール）溶液でエッチング後、
ＥＢＳＤ（Electron Back Scattering Diffraction) で
隣接する結晶粒界が15°以上である大傾角粒界を全板厚
にわたり測定して、平均結晶粒界を求めた。表面粗さ
は、JIS B 0601の規定に準拠し、カットオフ値や測定範
囲は基準値を用いて測定し、算術平均粗さ(Ra)を求め
た。The crystal grain size of the hot-rolled steel sheet was determined by etching the cross-section of the sheet with a (2% nitric acid + ethyl alcohol) solution.
By EBSD (Electron Back Scattering Diffraction), a large angle grain boundary in which adjacent crystal grain boundaries were 15 ° or more was measured over the entire sheet thickness, and an average crystal grain boundary was obtained. The surface roughness conformed to the provisions of JIS B0601, and the cut-off value and the measurement range were measured using reference values to determine the arithmetic average roughness (Ra).
【００３４】また、化成処理性は、70×150 mmの試験片
を切り出し、リン酸塩処理を行って評価した。すなわ
ち、リン酸塩液中に浸漬後の外観、結晶サイズ、Ｐ比を
測定した。ここに、外観とは、化成処理皮膜が均一に形
成されているかどうかの評価で、均一な場合を◎、不均
一な場合を×で表した。また、結晶サイズとは、化成処
理後の表面を1000倍で電子顕微鏡観察して、化成処理被
膜の平均結晶粒径を測定したもので、このサイズが10μ
m 以下であれば化成処理性が良好といえる。さらに、Ｐ
比とは、Ｘ線回折により測定した、Phosphophyllite(＝
Zn2Fe(PO4) 2 ・4H2O）の（１００）面からのピーク強度
（Ｐ）と Hopeite（＝Zn3Fe(PO4)2・4H2O）の（０２
０）面からのピーク強度（Ｈ）を、次式｛Ｐ／（Ｐ＋
Ｈ）｝に代入して求めた値で、この値が0.85以上であれ
ば化成処理性に優れているといえる。そして、本発明で
は、上記した外観、結晶サイズおよびＰ比の全てが良好
な場合に、化成処理性に優れると評価した。The chemical conversion property is a 70 × 150 mm test piece.
Was cut out and subjected to phosphate treatment for evaluation. Sand
The appearance, crystal size, and P ratio after immersion in a phosphate solution
It was measured. Here, the appearance means that the chemical conversion coating is uniformly formed.
In the evaluation of whether or not the
One case was represented by x. The crystal size is defined as
The surface after treatment was observed with an electron microscope at 1000x,
The average crystal grain size of the film was measured.
If m or less, it can be said that the chemical conversion property is good. Furthermore, P
The ratio refers to Phosphophyllite (=
ZnTwoFe (POFour) Two ・ 4HTwoO) Peak intensity from (100) plane
(P) and Hopeite (= ZnThreeFe (POFour)Two・ 4HTwoO) (02
The peak intensity (H) from the 0) plane is calculated by the following equation: ΔP / (P +
H) The value obtained by substituting into｝. If this value is 0.85 or more,
It can be said that, for example, it is excellent in chemical conversion treatment. And in the present invention
Has good appearance, crystal size and P ratio described above
In such cases, the composition was evaluated as having excellent chemical conversion treatment properties.
【００３５】さらに、耐食性は、70×150 mmの試験片を
切り出し、 0.5％NaCl水溶液に８時間浸漬後、大気中に
16時間放置する合計24時間の処理を１サイクルとして、
30サイクル後の腐食による最大侵食深さを測定すること
によって、評価した。最大侵食深さが 0.1mm以下であれ
ば、耐食性に優れるといえる。また、穴拡げ率：λ
（％）は、日本鉄鋼連盟規格(JFS T1001）に従い、次式
のようにして求めた。 λ＝｛（Ｄh −Ｄ0 ）／Ｄ0 ｝× 100 (％) ここで、Ｄ0 ：初期穴径（10mm） Ｄh ：試験により破断した後の穴径（mm）Further, for corrosion resistance, a test piece of 70 × 150 mm was cut out, immersed in a 0.5% NaCl aqueous solution for 8 hours, and then exposed to air.
A total of 24 hours of processing that is left for 16 hours is one cycle,
It was evaluated by measuring the maximum erosion depth due to corrosion after 30 cycles. If the maximum erosion depth is 0.1 mm or less, it can be said that the corrosion resistance is excellent. The hole expansion rate: λ
(%) Was calculated according to the following equation according to the Japan Iron and Steel Federation Standard (JFS T1001). λ = {(D h -D 0 ) / D 0} × 100 (%) wherein, D 0: Initial hole diameter (10mm) D h: hole diameter after fracture by the test (mm)
【００３６】[0036]
【表１】 [Table 1]
【００３７】[0037]
【表２】 [Table 2]
【００３８】[0038]
【表３】 [Table 3]
【００３９】No.2〜６はいずれも、成分組成は本発明の
範囲を満足しているが、製造条件が本発明範囲を逸脱し
た結果、結晶粒径や表面粗さが本発明の適正範囲から外
れ、その結果、化成処理性や耐食性が大幅に劣化してい
る。また No.16〜21はいずれも、成分組成が本発明の適
正範囲を外れているため、製造方法は適正でも結晶粒径
が微細化せず、表面粗さ、化成処理性および耐食性に劣
っている。これに対し、本発明に従い得られた発明例
（No.1および７〜15）はいずれも、TS×El≧18000 (MPa
・％）、TS×λ≧65000 (MPa・％）という優れた特性を
有するだけでなく、化成処理性および耐食性にも優れて
いた。Nos. 2 to 6 all have the component compositions satisfying the range of the present invention, but as a result of the manufacturing conditions deviating from the range of the present invention, the crystal grain size and the surface roughness are within the proper range of the present invention. As a result, the chemical conversion property and the corrosion resistance are significantly degraded. In addition, No. 16 to 21 each had a component composition outside the proper range of the present invention, so that the production method was appropriate but the crystal grain size was not reduced, and the surface roughness was poor in chemical conversion treatment and corrosion resistance. I have. In contrast, the invention examples (Nos. 1 and 7 to 15) obtained according to the present invention all have TS × El ≧ 18000 (MPa
%) And TS × λ ≧ 65000 (MPa ·%), as well as excellent chemical conversion treatment and corrosion resistance.
【００４０】[0040]
【発明の効果】かくして、本発明によれば、Siを 0.5ma
ss％以上含有する高張力鋼においても、従来のように粗
圧延や仕上圧延の前に高圧水を用いてデスケーリングを
施す必要なしに、スケール残りやスケール疵の発生を効
果的に防止して、鋼板の表面性状を著しく改善すること
ができ、ひいては化成処理性および耐食性を格段に向上
させることができる。As described above, according to the present invention, Si is reduced to 0.5 ma.
Even in high-strength steel containing ss% or more, it is possible to effectively prevent the occurrence of scale residue and scale flaws without the need to perform descaling using high-pressure water before rough rolling and finish rolling as in the past. In addition, the surface properties of the steel sheet can be remarkably improved, and consequently, the chemical conversion property and the corrosion resistance can be remarkably improved.
【図面の簡単な説明】[Brief description of the drawings]
【図１】 鋼板の平均結晶粒径と表面粗さが化成処理性
に及ぼす影響を示した図である。FIG. 1 is a view showing the influence of the average crystal grain size and surface roughness of a steel sheet on chemical conversion treatment properties.
【図２】 加熱温度およびTi, Ｃ量が、熱延板の結晶粒
径に及ぼす影響を、加熱温度と log（Ti×Ｃ）との関係
で示した図である。FIG. 2 is a diagram showing the influence of the heating temperature and the amounts of Ti and C on the crystal grain size of a hot-rolled sheet, as a relationship between the heating temperature and log (Ti × C).
【図３】 仕上圧延第１スタンドにおける圧延速度およ
び圧下率が、熱延板の結晶粒径に及ぼす影響を示した図
である。FIG. 3 is a view showing the influence of a rolling speed and a rolling reduction in a first stand of finish rolling on a crystal grain size of a hot-rolled sheet.
───────────────────────────────────────────────────── フロントページの続き (72)発明者 坂田 敬 千葉県千葉市中央区川崎町１番地 川崎製 鉄株式会社技術研究所内 Ｆターム(参考） 4K037 EA01 EA05 EA06 EA15 EA16 EA23 EA25 EA27 EA28 EA31 EB05 EB08 EB09 EB11 FA01 FA02 FB07 FC04 FC07 FD03 FD04 FE01 FE02 FE05 GA02 HA05 JA02 JA03 JA06 JA07 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Takashi Sakata 1-term Kawasaki-cho, Chuo-ku, Chiba-shi, Chiba F-term (reference) 4K037 EA01 EA05 EA06 EA15 EA16 EA23 EA25 EA27 EA28 EA31 EB05 EB08 EB09 EB11 FA01 FA02 FB07 FC04 FC07 FD03 FD04 FE01 FE02 FE05 GA02 HA05 JA02 JA03 JA06 JA07
Claims (3)
的不純物の組成になり、平均結晶粒径が 3.0μm 以下
で、かつ表面粗さが算術平均粗さRaで 1.5μm 以下であ
ることを特徴とする化成処理性および耐食性に優れる熱
延高張力鋼板。1. C: 0.01 to 0.20 mass%, Si: 0.5 to 2.5 mass%, Mn: 1.0 to 3.0 mass%, P: 0.05 mass% or less, Al: 0.01 to 0.1 mass%, S: 0.005 mass% or less And Ti: 0.05 to 0.35 mass% in a range where Ti (mass%) and C (mass%) satisfy the following expression: -1.4 ≧ log (Ti × C) ≧ −1.8, and the remainder is Fe and inevitable Hot-rolled high-strength steel sheet with excellent chemical conversion properties and corrosion resistance, characterized in that it has a composition of chemical impurities, an average crystal grain size of 3.0 μm or less, and a surface roughness of 1.5 μm or less in arithmetic average roughness Ra. .
ト、パーライト、ベイナイト、マルテンサイトおよび残
留オーステナイトのうちから選んだ２種類以上の複合組
織であることを特徴とする化成処理性および耐食性に優
れる熱延高張力鋼板。2. The steel according to claim 1, wherein the steel structure is a composite structure of two or more kinds selected from ferrite, pearlite, bainite, martensite, and retained austenite, and is excellent in chemical conversion treatment property and corrosion resistance. Hot rolled high strength steel sheet.
的不純物の組成になる鋼スラブを、1150℃以下に加熱
し、粗圧延後、1050℃以下で仕上圧延を開始し、仕上圧
延第１スタンドでの圧延速度を 400 m/min以上、圧下率
を80％以上とし、仕上圧延の最終圧下を表面粗さ(Ra)が
３μm 以下の圧延ロールで行い、（Ａr3＋150 ℃）〜
（Ａr3＋50℃) で仕上圧延を終了し、ついで20℃/s以上
の冷却速度で600 ℃以下まで冷却後、 600〜350 ℃の温
度範囲で巻き取ることを特徴とする化成処理性および耐
食性に優れる熱延高張力鋼板の製造方法。3. C: 0.01 to 0.20 mass%, Si: 0.5 to 2.5 mass%, Mn: 1.0 to 3.0 mass%, P: 0.05 mass% or less, Al: 0.01 to 0.1 mass%, S: 0.005 mass% or less And Ti: 0.05 to 0.35 mass% in a range where Ti (mass%) and C (mass%) satisfy the following expression: -1.4 ≧ log (Ti × C) ≧ −1.8, and the remainder is Fe and inevitable The steel slab, which has the composition of chemical impurities, is heated to 1150 ° C or less, and after rough rolling, finish rolling is started at 1050 ° C or less, the rolling speed at the first stand for finishing rolling is 400 m / min or more, and the rolling reduction is 80% or more, and the final rolling of finish rolling is performed with a rolling roll having a surface roughness (Ra) of 3 μm or less, and (Ar 3 + 150 ° C.)
(Ar 3 + 50 ° C), finish rolling, then cool at a cooling rate of 20 ° C / s or more to 600 ° C or less, and wind up in a temperature range of 600 to 350 ° C. For producing hot-rolled high-strength steel sheets with excellent heat resistance.
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| JP2005281785A (en) * | 2004-03-30 | 2005-10-13 | Kobe Steel Ltd | High strength cold rolled steel sheet having excellent adhesion of coating film and workability |
| JP2005290440A (en) * | 2004-03-31 | 2005-10-20 | Kobe Steel Ltd | High strength cold rolled steel sheet having excellent adhesion of coating film and workability |
| JP4698971B2 (en) * | 2004-03-31 | 2011-06-08 | 株式会社神戸製鋼所 | High-strength cold-rolled steel sheet with excellent coating film adhesion and workability |
| JP4520883B2 (en) * | 2005-03-04 | 2010-08-11 | 新日本製鐵株式会社 | Hot-rolled steel sheet with excellent corrosion resistance after electrodeposition coating and method for producing the same |
| JP2006241539A (en) * | 2005-03-04 | 2006-09-14 | Nippon Steel Corp | Hot rolled steel sheet having excellent corrosion resistance after electrodeposition coating and its production method |
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| GB2450066A (en) * | 2006-03-31 | 2008-12-10 | Kobe Steel Ltd | High-strength cold rolled steel sheet excelling in chemical treatability |
| GB2450066B (en) * | 2006-03-31 | 2011-03-30 | Kobe Steel Ltd | High-strength cold rolled steel sheet excellent in chemical conversion treatment property |
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| JP2011051000A (en) * | 2009-09-04 | 2011-03-17 | Jfe Steel Corp | Method of manufacturing high-strength hot-rolled steel strip |
| JP2013119643A (en) * | 2011-12-06 | 2013-06-17 | Nippon Steel & Sumitomo Metal Corp | High-strength hot-rolled steel sheet having excellent corrosion resistance of coating and bending fatigue characteristic, and method for producing the same |
| CN113227416A (en) * | 2019-03-11 | 2021-08-06 | 日本制铁株式会社 | Hot rolled steel plate |
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