JPH10251794A - Hot rolled steel plate for structural purpose, excellent in press formability and surface characteristic, and its production - Google Patents
Hot rolled steel plate for structural purpose, excellent in press formability and surface characteristic, and its productionInfo
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- JPH10251794A JPH10251794A JP7467797A JP7467797A JPH10251794A JP H10251794 A JPH10251794 A JP H10251794A JP 7467797 A JP7467797 A JP 7467797A JP 7467797 A JP7467797 A JP 7467797A JP H10251794 A JPH10251794 A JP H10251794A
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- rolled steel
- hot
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- press formability
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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。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-rolled steel sheet for structural use having excellent press formability and surface properties and a tensile strength of 490 N / mm 2 or more, and a method for producing the same.
【0002】[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SCR42
0,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。2. Description of the Related Art Steel materials used as materials for gear parts, chain parts, frame parts and the like for automobiles and industrial machines include carbon steel for mechanical structures specified in JIS G4051 and SCR42 specified in JIS G4102 to 4106.
0, SCM420 and other structural alloy steels are used.
These steel materials are stamped into a predetermined shape or press-molded, and after heat treatment such as carburizing quenching and tempering, the quality of the materials is improved. These steel materials are soft and have excellent workability before forming, and have strength and strength after heat treatment.
It is required to have excellent impact resistance, wear resistance, and the like.
【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。On the other hand, carbon steel for machine structure, SCR420,
When a structural alloy steel such as SCM420 is used at a high strength level as hot rolled, workability has been 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】[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。SUMMARY OF THE INVENTION The present invention is intended to improve the press-formability of a high-strength hot-rolled steel sheet for a structure, which was previously limited to relatively light-formed parts when hot-rolled as it is, and to provide a press-forming process. It is an object of the present invention to improve the productivity, which is caused by cracks and cracks generated during the forming process, which has been concerned at the time of forming, and to prevent scale flaws of the structural steel sheet to improve the surface properties.
【0005】[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:0.9
0〜1.50%、Mo:0.10〜0.50%、酸可溶
性Al:0.05%以下、Ca:0.003%以上、C
a/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。According to the present invention, in order to achieve the above-mentioned object, C: 0.10 to 0.50% by weight,
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: 0.9
0 to 1.50%, Mo: 0.10 to 0.50%, acid-soluble Al: 0.05% or less, Ca: 0.003% or more, C
a / S: 0.60 to 1.70, the balance being substantially Fe, and providing a structural hot-rolled steel sheet whose metal structure is a homogeneous mixed structure of ferrite and pearlite. This hot-rolled steel sheet is subjected to hot rolling at a total reduction rate of 50% or more and a final reduction rate of 10% or more after heating the steel slab to 1150 to 1300 ° C., and the finishing temperature is changed from the Ar 3 transformation point to Ar 3 + 50 ° C. It is manufactured by controlling the winding temperature at 400 to 600 ° C. and the average cooling rate from hot rolling finishing to winding at 30 to 60 ° C./second, and is subjected to temper rolling and pickling by ordinary methods.
【0006】[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。DESCRIPTION OF THE PREFERRED EMBODIMENTS In the present invention, the form of inclusions in a steel sheet is controlled by regulating Ca and Ca / S, and no striped (band) structure is formed at the center of the sheet thickness by controlling hot rolling conditions. Press formability and toughness are improved by a homogeneous mixed structure of ferrite and pearlite. 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 are regulated to improve the scale surface.
【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。Hereinafter, the reasons for limiting the components and contents of the hot-rolled structural steel sheet according to the present invention will be described. C: 0.10 to 0.50% C is an important element in determining the properties of steel. The strength and hardness increase with the amount of addition, and wear resistance and the like are improved, but workability and toughness are reduced. As it decreases, the upper limit is 0.50%
And the lower limit was 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 worked, 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 adversely affects 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% 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。Mn: 0.60-1.00% Although the strength increases with the amount of Mn added, the increase in Mn-based inclusions and the stripes (bands) which cause the deterioration of press workability.
The anisotropy of the material becomes stronger due to the manifestation of the tissue. From the viewpoint of high strength and press workability, the Mn content is 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, so that it is preferably as low as possible. acceptable. S: 0.006% or less Although the S content is preferably as low as P, it is preferably 0.006% or less.
% Or less, sulfide-based inclusions are reduced and workability is improved.
【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。Cu: 0.30% or less With the addition of Cu, it is concentrated at the boundary between the oxide scale generated during hot rolling and the steel sheet surface, and scale releasability is improved. However, if added in an amount of 0.20% or more, fine cracks are likely to be generated on the steel sheet surface due to the embrittlement of the molten metal. Therefore, the desirable addition range of Cu is 0.10 to 0.10.
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 becomes 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 with the embrittlement of molten metal, so there is no need to add Ni.
【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。Cr: 0.90 to 1.50% Cr is an additive element for improving the quenching properties and mechanical properties of steel, but the strength and toughness are improved by increasing the amount of added Cr. When the content exceeds 1.50%, the proof stress is reduced, so 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 and 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】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。Acid-soluble Al: 0.05% or less Al is added for deoxidizing, fixing nitrogen, and adjusting 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%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、C
a/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。Ca: 0.003% or more Ca is an element exhibiting an effect on deoxidation and desulfurization, and adjusts the form and distribution of sulfide-based nonmetallic inclusions in deoxidized steel to improve workability. . In order to obtain this effect, use 0. 003
% Or more is required. Ca / S: 0.60 to 1.70 From FIG. 1 showing the relationship between Ca / S and sulfide-based inclusions,
When the ratio of a / S is 0.60 or more, a steel material having few sulfide-based inclusions can be obtained, so that the workability is good. From FIG. 2 showing the relationship between the anisotropy by the impact value and Ca / S,
When the Ca / S ratio is 0.60 or more, the anisotropy value according to the impact value becomes 0.5 or more, and a steel material with small anisotropy and 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】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。After melting the steel of the above component in a converter, it is degassed to form a slab by continuous casting, and then 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】加熱温度 1150〜1300℃ :11
50℃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。Heating temperature 1150-1300 ° C .: 11
If the temperature is lower than 50 ° C., there is a problem that the surface quality is deteriorated due to the slab crack during the rough rolling and the 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 setting the total reduction 50% or more and the final reduction 10% or more to obtain a structure in which carbides are dispersed. If the total reduction is less than 50% and the final reduction 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 is easily formed, so that improvement in workability and toughness cannot be expected.
【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Ar
3 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。Finishing temperature Ar 3 transformation point to Ar 3 +50
° C.: finish rolling to improve the mechanical properties such as Ar 3 transformation point to Ar 3 + 50 ° C. of that ends at low temperature region fine ferrite grains are obtained strength and toughness. Finish temperature is Ar
If the transformation point is not reached, the deformation resistance increases, which impairs the threadability in the hot rolling process. Further, since the two-phase zone 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, and the workability is deteriorated. On the other hand, when the finishing temperature is Ar 3 +
If the temperature exceeds 50 ° C., the hot-rolled structure becomes coarse and the 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 mechanical properties in the coil is impaired.
【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/m
m2 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。Average cooling rate from hot rolling finishing to winding at a winding temperature of 400 to 600 ° C. to 30 to 60 ° C./sec: The strip after hot rolling has strips (bands) which affect workability and toughness. It is wound in a temperature range of 400 to 600 ° C. in order to prevent the formation of a structure and obtain a fine-grained structure of fine ferrite and pearlite.
If the temperature is lower than 400 ° C., the strength is remarkably increased and the workability is impaired.
A strength of m 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 it is less than / sec, the desired structure cannot be obtained and the ratio of the banded (band) structure increases, so that a strength of 490 N / mm 2 or more and good workability cannot be obtained. If the average cooling rate is increased, the steel sheet becomes harder and good workability cannot be obtained, so the upper limit was set to 60 ° C./sec.
【0017】[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4.5
mm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。EXAMPLE A slab obtained by melting steels 1 to 5 having the components shown in Table 1 was roughly rolled to a thickness of 30 mm, and a sheet thickness of 4.5.
mm hot rolled steel sheet was manufactured. The finishing temperature was 850 ° C., the winding temperature was 500 to 600 ° C., and the average cooling rate was 30 to 50 ° C./sec. A sample was cut out from the hot rolled sheet, and a hardness measurement, a tensile test, and a hole expansion test were performed. The surface properties of the steel sheet were visually observed to determine the scale flaws of the steel sheet. The tensile test was performed using a JIS No. 5 test piece with the distance between the reference points of the parallel portions being 50 mm. The hole expansion test is performed by punching a hole of 10 mm (do) with a clearance of 10% in the center of a 150 mm square steel plate, and pushing up the hole with a punch of a ball head. Diameter at the time of occurrence (d)
Was measured to determine a hole expansion ratio (λ) defined by the following equation. 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 higher, and the Rankford value and the hole expansion ratio are improved and the workability is excellent as compared with the comparative example, and the scale flaws on the steel sheet surface are small and the surface properties are excellent. Recognize. In addition, it can be seen that Example 4 of the present invention has a larger scale flaw than Examples 1 to 3 of the present invention in which Cu is added, but has 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 the addition of Ca, so that the Rankford value and the hole expansion rate were low, and the degree of scale flaws was large.
【0018】[0018]
【表1】 [Table 1]
【0019】[0019]
【表2】 [Table 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。Table 3 shows the results of evaluating the workability of the materials shown in Table 1 by bending and thrust tests. Comparative Example 5
Cracks occur in both the adhesion and the 0.5tR and 1.0tR bending tests, whereas Ca, Ca / S
Examples 1 to 4 of the present invention in which the shape of inclusions in the steel sheet was controlled by regulating
No. 4 shows that cracking did not occur under any of the bending test conditions and the workability was excellent.
【0021】[0021]
【表3】 [Table 3]
【0022】[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。According to the present invention, the form of inclusions in a steel sheet is controlled by regulating Ca and Ca / S, and by controlling the hot rolling conditions, ferrite having no banded (band) structure in the center of the sheet thickness can be obtained. Press formability and toughness can be obtained by obtaining a homogeneous mixed structure of pearlite. Further, in order to improve the surface properties of the steel sheet, the amounts of Cu and Ni added are regulated to improve the oxide scale releasability, so that scale flaws which are problematic in the production process can be prevented. Until now, hot-rolled parts were limited to relatively light forming parts, so 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 a decrease in productivity caused by cracks and cracks.
【図1】(Ca/S)と硫化物系介在物量との関係を示
す図である。FIG. 1 is a diagram showing the relationship between (Ca / S) and the amount of sulfide-based inclusions.
【図2】(Ca/S)と衝撃異方性との関係を示す図で
ある。FIG. 2 is a diagram showing a relationship between (Ca / S) and impact anisotropy.
Claims (2)
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A
l: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。C. 0.10 to 0.50% by weight,
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 or less
1.50%, Mo: 0.10 to 0.50%, acid soluble A
l: 0.05% or less, Ca: 0.003% or more, Ca /
S: 0.60 to 1.70, the balance being substantially Fe, and a structural hot-rolled steel sheet excellent in press formability and surface properties having a homogeneous microstructure of ferrite and pearlite.
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A
l: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。2. C: 0.10 to 0.50% by weight,
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 or less
1.50%, Mo: 0.10 to 0.50%, acid soluble A
l: 0.05% or less, Ca: 0.003% or more, Ca /
S: 0.60 to 1.70, a steel slab consisting essentially of Fe, with the balance being heated to 1150 to 1300 ° C, subjected to hot rolling at a total draft of 50% or more and a final draft of 10% or more,
Excellent finishing temperature Ar 3 transformation point to Ar 3 + 50 ° C., the coiling temperature 400 to 600 ° C., an average cooling rate from the hot rolling finish to the take-up press formability and surface properties to 30 to 60 ° C. / sec Of hot rolled steel sheets for structural use.
Priority Applications (1)
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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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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 |
Publications (2)
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JPH10251794A true JPH10251794A (en) | 1998-09-22 |
JP3578435B2 JP3578435B2 (en) | 2004-10-20 |
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