JP3578435B2 - Hot-rolled steel sheet for structural use excellent in press formability and surface properties and method for producing the same - Google Patents
Hot-rolled steel sheet for structural use excellent in press formability and surface properties and method for producing the same Download PDFInfo
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Description
【0001】
【発明の属する技術分野】
本発明は、プレス成形性と表面性状に優れた引張強さ490N/mm2 以上の構造用熱延鋼板とその製造方法に関するものである。
【0002】
【従来の技術】
自動車用や産業機械用のギヤー部品、チェーン部品、フレーム部品等の素材として使用される鋼材は、JISG4051に規定される機械構造用炭素鋼やJISG4102〜4106に規定されるSCR420,SCM420等の構造用合金鋼が使用されている。これらの鋼材は、所定の形状に打ち抜かれたり、あるいはプレス成形された後、浸炭焼き入れ・焼戻し等の熱処理によって材質を改善し、一部はショットピーニング等を施して塗装後製品化される。これらの鋼材には成形加工前は軟質で加工性に優れ、熱処理後においては強度、耐衝撃性、耐摩耗性等に優れていることが要求される。
【0003】
一方、機械構造用炭素鋼やSCR420,SCM420等の構造用合金鋼を熱間圧延ままの高強度レベルで使用する場合、焼鈍等の軟化処理を施すことで加工性を改善していた。さらに、構造用合金鋼は、製造過程の熱間圧延中に生成した酸化スケールに起因したスケール疵による鋼板や製品の表面品質劣化、厚く生成した酸化スケールの過大な剥離による生産歩留の低下などが問題となっていた。
【0004】
【発明が解決しようとする課題】
本発明は、これまで熱延ままでは比較的軽度な成形加工部品に限られていた高強度の構造用熱延鋼板のプレス成形性を向上させ、プレス成形加工の際に懸念されていた成形加工中に発生する割れやクラックに起因した生産性の低下を改善するとともに、構造用鋼板のスケール疵を防止し表面性状を改善することを課題とする。
【0005】
【課題を解決するための手段】
本発明は、前記の目的を達成するために重量%で、C:0.10〜0.50%、Si:0.35%以下、Mn:0.60〜1.00%、P:0.03%以下、S:0.006%以下、Cu:0.30%以下、Ni:0.25%以下、Cr:0.90〜1.50%、Mo:0.10〜0.50%、酸可溶性Al:0.05%以下、Ca:0.003%以上、Ca/S:0.60〜1.70、残部が実質的にFeからなり、金属組織がフェライトとパ−ライトの均質な混合組織からなる構造用熱延鋼板を提供する。この熱延鋼板は、鋼スラブを1150〜1300℃に加熱後、全圧下率50%以上、最終圧下率10%以上の熱間圧延を施し、仕上温度をAr3 変態点〜Ar3 +50℃、巻取温度を400〜600℃、熱延仕上げから巻取りまでの平均冷却速度を30〜60℃/秒に制御して製造され通常の方法で調質圧延及び酸洗が施される。
【0006】
【発明の実施の形態】
本発明では、Ca,Ca/Sを規制して鋼板中の介在物の形態制御し、熱間圧延条件の制御により板厚中央部に縞状(バンド)組織のないフェライトとパーライトの均質な混合組織によってプレス成形性や靱性を向上させている。また、鋼材の製造過程で問題となる熱延中に発生するスケール疵を防止し、鋼板の表面性状を向上させるためにCuとNi添加量を規制してスケール肌を改善している。
【0007】
以下、本発明における構造用熱延鋼板の成分と含有量の限定理由について説明する。
C:0.10〜0.50%
Cは鋼の性質を決定する上で重要な元素であり、添加量とともに強度・硬度が増大し 耐摩耗性等が向上するが、加工性・靱性等が低下するので上限を0.50%とし、下限は強度の面から0.10%とした。
Si:0.35%以下
Siは脱酸剤と焼入れ促進元素として添加するが、厳しい加工を要求される鋼材においては、0.35%を超えて含有させると鋼は硬質となり脆化を惹起する恐れがあり、また、多量のSi添加は鋼板表面のスケール肌等に悪影響を及ぼすため、Si含有量の上限を0.35%以下とした。
【0008】
Mn:0.60〜1.00%
Mnの添加量とともに強度は増加するが、プレス加工性の劣化原因となるMn系介在物の増加と縞状(バンド)組織の顕在化のため材質の異方性が強くなる。 高強度化とプレス加工性の面からMn含有量は0.60〜1.00%とした。
P:0.03%以下
PやSは鋼材の靭性を低下させるだけでなく、鋼の結晶粒界に偏析して粒界脆化を惹起させるため極力低い方が好ましいが0.03%までは許容できる。
S:0.006%以下
S含有量はPと同様に低いほど好ましいが、0.006%以下であれば硫化物系介在物は少なくなり加工性は改善される。
【0009】
Cu:0.30%以下
Cuの添加とともに熱延中に生成する酸化スケールと鋼板表面の境界に濃化してスケール剥離性が向上する。しかし、0.20%以上添加すると溶融金属脆化により鋼板表面に微細なクラックが発生しやすくなる。このようなことから、 望ましいCuの添加範囲は0.10〜0.15%である。
Ni:0.25%以下
Cuを0.20%以上添加する場合に問題となる溶融金属脆化により、鋼板表面に発生する微細なクラックを抑制するためCuとほぼ同量の添加を必要とする。しかし、Cuの添加が0.20%未満のときには溶融金属脆化は問題ないためNiを添加する必要はない。
【0010】
Cr:0.90〜1.50%
Crは鋼の焼入れ特性の向上と機械的性質を改善する添加元素であるが、Cr添加量を増加することによって強度、靱性等が向上するが1.50%を超えると耐力は逆に低下するためCr含有量を0.90〜1.50%とした。
Mo:0.10〜0.50%
Cr添加鋼、Cr−Ni含有鋼などにMoを複合添加するとさらに機械的性質が改善され、焼入れ性や焼戻し軟化抵抗を増加する。Mo添加量が多くなるとより機械的性質は向上するが製造コストが高価となるのでMoの添加量を0.10〜0.50%とした。
【0011】
酸可溶性Al:0.05%以下
Alは脱酸、窒素の固定、結晶粒度調整のために添加する。本発明ではオーステナイト結晶粒の成長を抑制することにより成形時の加工性を向上させるために酸可溶性Al含有量を0.05%以下とした。
【0012】
Ca:0.003%以上
Caは脱酸、脱硫に効果を発揮する元素であり、脱酸された鋼の硫化物系非金属介在物の形態と分布を調整し加工性を改善する。この効果を得るためには0. 003%以上の添加量を必要とする。
Ca/S:0.60〜1.70
Ca/Sと硫化物系介在物の関係を示した図1より、Ca/Sの比が0.60以上であれば、硫化物系の介在物が少ない鋼材が得られるので加工性は良好となる。衝撃値による異方性とCa/Sとの関係を示した図2より、Ca/Sの比が0.60以上であれば衝撃値による異方性の値が0.5以上となり異方性の小さい靱性の高い鋼材が得られる。しかし、Ca/Sが1.70を超えると酸化物系の複合介在物が増加していき加工性が劣化するので上限を1.70とした。
【0013】
前記成分の鋼を転炉で溶製した後、脱ガスを経て連続鋳造にて鋳片とし、加熱炉へ装入後熱間圧延により帯鋼を得る。強度レベルの高い構造用熱延鋼板の製造においては、熱間圧延条件と仕上圧延後の冷却を制御して良好な加工性を有する高強度の鋼材が得られる。
【0014】
加熱温度 1150〜1300℃ :
1150℃以下では粗圧延時のスラブ割れやスケール剥離性の低下による表面品質低下が問題となる。1300℃以上では高温脆性、スケールの多量剥離による品質低下やスケールロスによる歩留低下等が問題となる。
全圧下率50%以上,最終圧下率10%以上 :
全圧下率を50%以上,最終圧下率を10%以上として炭化物を分散させた組織を得ることでプレス加工性や靱性を改善する。全圧下率が50%及び最終圧下率が10%に満たないと均一な炭化物の分散した組織が得られにくい。また、 熱延の圧下率が小さいと再結晶が遅延しフェライトとパーライトの縞状(バン ド)組織となりやすいため加工性、靱性等の改善は期待できない。
【0015】
仕上温度 Ar3 変態点〜Ar3 +50℃:
仕上圧延をAr3 変態点〜Ar3 +50℃の低温温度域で終了することで微細なフェライト結晶粒が得られ強度や靱性等の機械的性質が向上する。仕上温度がAr3 変態点に達しないと変形抵抗が増大し、熱間圧延工程での通板性に支障を来す。また、オーステナイトとフェライトの2相域圧延となるため加工フェライトが生成し易くなるため、圧延後の鋼板表層には粗大化した結晶粒が生成し加工性が劣化する。他方、仕上温度がAr3 +50℃を超えると、熱延組織が粗大化し加工性が劣化すると共に圧延後の冷却過程での冷却歪みが増大して鋼板の形状が劣化する。また、冷却ムラが発生し易くなるため機械的性質のコイル内の安定性が損なわれる。
【0016】
巻取温度400〜600℃で熱延仕上〜巻取までの平均冷却速度30〜60℃/秒:
熱延後の鋼帯は、加工性や靱性に影響を及ぼす縞状(バンド)組織の生成を防止し微細なフェライトとパーライトの整粒組織を得るために400〜600℃の温度域で巻取られる。400℃未満では、強度上昇が著しくなり加工性が損なわれ、逆に600℃を超える巻取温度では490N/mm2 以上の強度が得られない。一方、巻取までの平均冷却速度も前記所望組織を得るために必要であり、30℃/秒未満では所望組織は得られず縞状(バンド)組織の割合が増加し、490N/mm2 以上の強度と良好な加工性を得ることができない。平均冷却速度が大きくなると鋼板は硬質となり、良好な加工性が得られなくなるため上限を60℃/秒とした。
【0017】
【実施例】
表1に示した成分をもつ1〜5の鋼を溶製したスラブを粗圧延で厚さ30mmとした後、板厚4.5mmの熱延鋼板を製造した。いずれの鋼種も仕上温度を850℃とし、巻取温度を500〜600℃、平均冷却速度を30〜50℃/秒とした。熱延板からサンプルを切り出して硬度測定、引張り試験、孔拡げ試験を行った。また、鋼板の表面性状は目視観察により鋼板のスケール疵の状況を判断した。引張試験は、JIS5号試験片を用い、平行部の標点間距離を50mmとして行った。孔拡げ試験は、150mm角の鋼板の中央部にクリアランス10%にて10mm(do)の穴を打抜いた後、その穴部について、球頭のポンチにて押し上げる方法で行い、穴周辺に亀裂が発生した時点での穴径(d)を測定して、次式で定義される穴拡げ率(λ)を求めた。
λ=(d−do)/do×100
表2に示すとおり、本発明例1〜3は引張強さ490N/mm2 以上の強度を有し、かつ比較例に比べて、ランクフォード値、孔拡げ率が向上して加工性が優れており、鋼板表面のスケール疵も軽微で表面性状が優れていることがわかる。また、本発明例4は、Cuを添加した本発明例1〜3に比べスケール疵の程度は大きいがランクフォード値、孔拡げ率が向上して加工性が優れていることがわかる。比較例5はS添加量が本発明範囲より多く、Ca添加による介在物制御を行っていないためランクフォード値や穴拡げ率が低く、スケール疵の程度も大きくなっていた。
【0018】
【表1】
【0019】
【表2】
【0020】
表3には表1に示した材料の曲げと突き曲げ試験にて加工性の評価を行った結果である。比較例5は密着あるいは0.5tR,1.0tR曲げのいずれの試験でも割れが発生しているに対し、 Ca,Ca/Sを規制して鋼板中の介在物の形態制御した本発明例1〜4は、いずれの曲げ試験条件においても割れが発生しておらず加工性に優れていることがわかる。
【0021】
【表3】
【0022】
【発明の効果】
本発明では、Ca,Ca/Sを規制して鋼板中の介在物の形態制御し、熱間圧延条件の制御により板厚中央部に縞状(バンド)組織のないフェライトとパーライトの均質な混合組織を得てプレス成形性や靱性を得ることができる。また、鋼板の表面性状を向上させるためにCuとNi添加量を規制して酸化スケール剥離性を改善しているので製造過程で問題となるスケール疵が防止できる。
これまで熱延ままでは比較的軽度な成形加工部品に限られていた構造用熱延鋼板のプレス成形加工性を向上させた高強度で高靱性の材料が提供できるので、成形加工中に発生する割れやクラックに起因した生産性の低下を改善できる。
【図面の簡単な説明】
【図1】(Ca/S)と硫化物系介在物量との関係を示す図である。
【図2】(Ca/S)と衝撃異方性との関係を示す図である。[0001]
TECHNICAL FIELD OF THE INVENTION
TECHNICAL FIELD The present invention relates to a hot-rolled steel sheet for structural use having a tensile strength of 490 N / mm 2 or more, which is excellent in press formability and surface properties, and a method for producing the same.
[0002]
[Prior art]
Steel materials used as materials for gear parts, chain parts, frame parts, etc. for automobiles and industrial machines are carbon steel for mechanical structures specified in JIS G4051 and structural materials such as SCR420 and SCM420 specified in JISG4102-4106. Alloy steel is used. These steel materials are stamped into a predetermined shape or press-molded, and after heat treatment such as carburizing quenching and tempering, the materials are improved, and some of them are subjected to shot peening or the like, and then painted to be commercialized. These steel materials are required to be soft and excellent in workability before forming, and to be excellent in strength, impact resistance, wear resistance and the like after heat treatment.
[0003]
On the other hand, when carbon steel for mechanical structure or structural alloy steel such as SCR420 and SCM420 is used at a high strength level as hot rolled, workability is improved by performing softening treatment such as annealing. In addition, structural alloy steels suffer from deterioration in the surface quality of steel sheets and products due to scale flaws caused by oxide scale generated during hot rolling in the manufacturing process, and reduced production yield due to excessive peeling of thick oxide scale. Was a problem.
[0004]
[Problems to be solved by the invention]
The present invention improves the press-formability of high-strength hot-rolled steel sheets for structural use, which was previously limited to relatively light-formed parts when hot-rolled as it is, and has been a concern at the time of press-forming. An object of the present invention is to improve the productivity by lowering the productivity caused by cracks and cracks generated therein and to prevent scale flaws of the structural steel sheet to improve the surface properties.
[0005]
[Means for Solving the Problems]
According to the present invention, in order to achieve the above object, C: 0.10 to 0.50%, Si: 0.35% or less, Mn: 0.60 to 1.00%, P: 0. 03% or less, S: 0.006% or less, Cu: 0.30% or less, Ni: 0.25% or less, Cr: 0.90 to 1.50%, Mo: 0.10 to 0.50%, Acid-soluble Al: 0.05% or less, Ca: 0.003% or more, Ca / S: 0.60 to 1.70, the balance substantially consisting of Fe, and the metal structure is homogeneous between ferrite and pearlite. Provided is a structural hot-rolled steel sheet having a mixed structure. This hot-rolled steel sheet is subjected to hot rolling at a total draft of 50% or more and a final draft of 10% or more after heating the steel slab to 1150 to 1300 ° C, and the finishing temperature is changed from Ar 3 transformation point to Ar 3 + 50 ° C. It is manufactured by controlling the winding temperature to 400 to 600 ° C. and the average cooling rate from hot-rolling finishing to winding to 30 to 60 ° C./second, and is subjected to temper rolling and pickling by ordinary methods.
[0006]
BEST MODE FOR CARRYING OUT THE INVENTION
In the present invention, the morphology of inclusions in a steel sheet is controlled by regulating Ca, Ca / S, and the uniform mixing of ferrite and pearlite without a banded (band) structure at the center of the sheet thickness is controlled by controlling the hot rolling conditions. The press formability and toughness are improved by the structure. Further, in order to prevent scale flaws generated during hot rolling, which is a problem in the production process of steel materials, and to improve the surface properties of the steel sheet, the amounts of Cu and Ni added are regulated to improve the scale surface.
[0007]
Hereinafter, the reasons for limiting the components and contents of the hot rolled steel sheet for a structure in the present invention will be described.
C: 0.10 to 0.50%
C is an important element in determining the properties of steel. Strength and hardness increase with the addition amount, and wear resistance and the like improve. However, workability and toughness decrease, so the upper limit is set to 0.50%. The lower limit was set to 0.10% from the viewpoint of strength.
Si: 0.35% or less Si is added as a deoxidizing agent and a quenching promoting element. However, in a steel material required to be severely processed, if the content exceeds 0.35%, the steel becomes hard and causes embrittlement. There is a possibility that the addition of a large amount of Si may adversely affect the scale surface on the surface of the steel sheet. Therefore, the upper limit of the Si content is set to 0.35% or less.
[0008]
Mn: 0.60-1.00%
Although the strength increases with the addition amount of Mn, the anisotropy of the material becomes strong due to the increase of Mn-based inclusions which cause the deterioration of press workability and the manifestation of a striped (band) structure. From the viewpoint of high strength and press workability, the Mn content was set to 0.60 to 1.00%.
P: 0.03% or less P and S not only lower the toughness of the steel material but also segregate at the crystal grain boundaries of the steel to cause grain boundary embrittlement. acceptable.
S: 0.006% or less S content is preferably as low as P, but if it is 0.006% or less, sulfide-based inclusions are reduced and workability is improved.
[0009]
Cu: 0.30% or less Addition of Cu concentrates at the boundary between the oxide scale generated during hot rolling and the steel sheet surface, and improves the scale releasability. However, when added in an amount of 0.20% or more, fine cracks are likely to be generated on the surface of the steel sheet due to embrittlement of molten metal. For this reason, a desirable addition range of Cu is 0.10 to 0.15%.
Ni: 0.25% or less Addition of approximately the same amount as Cu is required to suppress fine cracks generated on the steel sheet surface due to molten metal embrittlement which is a problem when adding 0.20% or more of Cu. . However, when the addition of Cu is less than 0.20%, there is no problem of molten metal embrittlement, so there is no need to add Ni.
[0010]
Cr: 0.90 to 1.50%
Cr is an additive element that improves the quenching properties and mechanical properties of steel, but the strength and toughness are improved by increasing the amount of added Cr, but when the content exceeds 1.50%, the proof stress decreases. Therefore, the Cr content is set to 0.90 to 1.50%.
Mo: 0.10 to 0.50%
When Mo is added to Cr-added steel or Cr-Ni-containing steel in combination, the mechanical properties are further improved, and the hardenability and the temper softening resistance are increased. When the amount of Mo added increases, the mechanical properties are further improved, but the production cost becomes expensive. Therefore, the amount of Mo added is set to 0.10 to 0.50%.
[0011]
Acid-soluble Al: 0.05% or less Al is added for deoxidation, fixation of nitrogen, and adjustment of crystal grain size. In the present invention, the content of the acid-soluble Al is set to 0.05% or less in order to improve the workability at the time of forming by suppressing the growth of austenite crystal grains.
[0012]
Ca: 0.003% or more Ca is an element that exerts an effect on deoxidation and desulfurization, and adjusts the form and distribution of sulfide-based nonmetallic inclusions in the deoxidized steel to improve workability. In order to obtain this effect, a value of 0. It requires an addition amount of 003% or more.
Ca / S: 0.60 to 1.70
According to FIG. 1 showing the relationship between Ca / S and sulfide-based inclusions, if the Ca / S ratio is 0.60 or more, a steel material having a small amount of sulfide-based inclusions is obtained, so that the workability is good. Become. From FIG. 2 showing the relationship between the anisotropy due to the impact value and Ca / S, if the ratio of Ca / S is 0.60 or more, the value of the anisotropy due to the impact value becomes 0.5 or more, A steel material having a small toughness and a high toughness can be obtained. However, if Ca / S exceeds 1.70, the number of oxide-based composite inclusions increases and the workability deteriorates, so the upper limit was set to 1.70.
[0013]
After smelting the steel of the above component in a converter, it is degassed, continuously cast into slabs, charged into a heating furnace and hot rolled to obtain a strip. In the production of a structural hot-rolled steel sheet having a high strength level, a high-strength steel material having good workability can be obtained by controlling hot rolling conditions and cooling after finish rolling.
[0014]
Heating temperature 1150-1300 ° C:
If the temperature is 1150 ° C. or less, there is a problem that slab cracks occur during rough rolling and surface quality is reduced due to reduced scale releasability. If the temperature is 1300 ° C. or higher, problems such as high-temperature brittleness, quality deterioration due to large scale peeling, yield reduction due to scale loss, and the like become problems.
Total reduction 50% or more, Final reduction 10% or more:
Press workability and toughness are improved by obtaining a structure in which carbides are dispersed with a total reduction ratio of 50% or more and a final reduction ratio of 10% or more. If the total draft is less than 50% and the final draft is less than 10%, it is difficult to obtain a uniform carbide-dispersed structure. On the other hand, if the rolling reduction of the hot rolling is small, recrystallization is delayed and a banded structure of ferrite and pearlite tends to be formed, so that improvement in workability and toughness cannot be expected.
[0015]
Finishing temperature Ar 3 transformation point to Ar 3 + 50 ° C .:
Mechanical properties such as the finish rolling Ar 3 transformation point to Ar 3 + By ending with 50 low temperature range of ℃ fine ferrite grains are obtained strength and toughness is improved. If the finishing temperature does not reach the Ar 3 transformation point, the deformation resistance increases, which impairs the sheet passing property in the hot rolling process. Further, since the two-phase rolling of austenite and ferrite is performed, processed ferrite is easily generated, so that coarse crystal grains are generated on the surface layer of the steel sheet after rolling, thereby deteriorating the workability. On the other hand, when the finishing temperature exceeds Ar 3 + 50 ° C., the hot-rolled structure becomes coarse and workability is deteriorated, and the cooling strain in the cooling process after rolling is increased to deteriorate the shape of the steel sheet. In addition, since cooling unevenness easily occurs, the stability of the mechanical properties in the coil is impaired.
[0016]
Average cooling rate from hot rolling finish to winding at a winding temperature of 400 to 600 °
The steel strip after hot rolling is wound in a temperature range of 400 to 600 ° C. in order to prevent the formation of a striped (band) structure that affects workability and toughness and to obtain a fine grained structure of ferrite and pearlite. Can be If the temperature is lower than 400 ° C., the strength rises remarkably, and the workability is impaired. Conversely, if the winding temperature exceeds 600 ° C., the strength of 490 N / mm 2 or more cannot be obtained. On the other hand, the average cooling rate until winding is also necessary to obtain the desired structure. If the temperature is lower than 30 ° C./sec, the desired structure cannot be obtained, and the ratio of banded (band) structure increases, and 490 N / mm 2 or more And good workability cannot be obtained. When the average cooling rate increases, the steel sheet becomes harder and good workability cannot be obtained, so the upper limit was set to 60 ° C./sec.
[0017]
【Example】
A slab obtained by melting
λ = (d−do) / do × 100
As shown in Table 2, Examples 1 to 3 of the present invention have a tensile strength of 490 N / mm2 or more, and have improved Rankford values and hole expansion ratios and are excellent in workability as compared with Comparative Examples. It can also be seen that the scale flaws on the surface of the steel sheet were slight and the surface properties were excellent. In addition, it can be seen that Inventive Example 4 has a larger scale flaw than Inventive Examples 1 to 3 to which Cu is added, but has an improved Rankford value and hole expansion ratio, and is excellent in workability. In Comparative Example 5, the amount of S added was larger than the range of the present invention, and the inclusion control was not performed by adding Ca, so that the Rankford value and the hole expansion ratio were low, and the degree of scale flaws was large.
[0018]
[Table 1]
[0019]
[Table 2]
[0020]
Table 3 shows the results of evaluating the workability of the materials shown in Table 1 by bending and butt bending tests. Comparative Example 5 shows cracks in both the adhesion test and the 0.5tR and 1.0tR bending tests, but the present invention example 1 in which the form of inclusions in the steel sheet was controlled by regulating Ca and Ca / S. Nos. 4 to 4 show that no cracking occurred under any of the bending test conditions and the workability was excellent.
[0021]
[Table 3]
[0022]
【The invention's effect】
In the present invention, the morphology of inclusions in a steel sheet is controlled by regulating Ca and Ca / S, and the uniform mixing of ferrite and pearlite without a banded (band) structure in the center of the sheet thickness is controlled by controlling the hot rolling conditions. By obtaining a structure, press formability and toughness can be obtained. In addition, since the addition of Cu and Ni is regulated in order to improve the surface properties of the steel sheet and the oxide scale releasability is improved, scale flaws, which are problematic in the production process, can be prevented.
Until now, hot-rolled as-is was limited to relatively light-formed parts. High-strength, high-toughness materials with improved press-formability of hot-rolled steel sheets for structural use can be provided. It is possible to improve the decrease in productivity due to cracks and cracks.
[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between (Ca / S) and the amount of sulfide-based inclusions.
FIG. 2 is a diagram showing a relationship between (Ca / S) and impact anisotropy.
Claims (2)
C:0.10〜0.50%、
Si:0.35%以下、
Mn:0.60〜1.00%、
P:0.03%以下、
S:0.006%以下
Cu:0.30%以下、
Ni:0.25%以下、
Cr:0.90〜1.50%、
Mo:0.10〜0.50%、
酸可溶性Al:0.05%以下、
Ca:0.003%以上、
Ca/S:0.60〜1.70、
残部が実質的にFeからなり、金属組織がフェライトとパ−ライトの均質な混合組織からなるプレス成形性と表面性状に優れた構造用熱延鋼板。In weight percent,
C: 0.10 to 0.50%,
Si: 0.35% or less,
Mn: 0.60-1.00%,
P: 0.03% or less,
S: 0.006% or less Cu: 0.30% or less,
Ni: 0.25% or less,
Cr: 0.90 to 1.50%,
Mo: 0.10 to 0.50%,
Acid-soluble Al: 0.05% or less,
Ca: 0.003% or more,
Ca / S: 0.60 to 1.70,
A hot-rolled steel sheet for structural use excellent in press formability and surface properties, the balance being substantially composed of Fe, and the metal structure being a homogeneous mixed structure of ferrite and pearlite.
C:0.10〜0.50%、
Si:0.35%以下、
Mn:0.60〜1.00%、
P:0.03%以下、
S:0.006%以下
Cu:0.30%以下、
Ni:0.25%以下、
Cr:0.90〜1.50%、
Mo:0.10〜0.50%、
酸可溶性Al:0.05%以下、
Ca:0.003%以上、
Ca/S:0.60〜1.70、
残部が実質的にFeからなる鋼スラブを、
1150〜1300℃に加熱後、全圧下率50%以上、最終圧下率10%以上の熱間圧延を施し、仕上温度をAr3 変態点〜Ar3 +50℃、巻取温度を400〜600℃、熱延仕上げから巻取りまでの平均冷却速度を30〜60℃/秒とするプレス成形性と表面性状に優れた構造用熱延鋼板の製造方法。In weight percent,
C: 0.10 to 0.50%,
Si: 0.35% or less,
Mn: 0.60-1.00%,
P: 0.03% or less,
S: 0.006% or less Cu: 0.30% or less,
Ni: 0.25% or less,
Cr: 0.90 to 1.50%,
Mo: 0.10 to 0.50%,
Acid-soluble Al: 0.05% or less,
Ca: 0.003% or more,
Ca / S: 0.60 to 1.70,
A steel slab whose balance is substantially made of Fe,
After heating to 1150 to 1300 ° C, hot rolling is performed at a total draft of 50% or more and a final draft of 10% or more, the finishing temperature is Ar 3 transformation point to Ar 3 + 50 ° C, and the winding temperature is 400 to 600 ° C. A method for producing a hot-rolled steel sheet for structural use having excellent press formability and surface properties in which the average cooling rate from hot-rolling finishing to winding is 30 to 60 ° C / sec.
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JP07467797A JP3578435B2 (en) | 1997-03-12 | 1997-03-12 | Hot-rolled steel sheet for structural use excellent in press formability and surface properties and method for producing the same |
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