JP3525812B2 - High strength steel plate excellent in impact energy absorption and manufacturing method thereof - Google Patents
High strength steel plate excellent in impact energy absorption and manufacturing method thereofInfo
- Publication number
- JP3525812B2 JP3525812B2 JP18844999A JP18844999A JP3525812B2 JP 3525812 B2 JP3525812 B2 JP 3525812B2 JP 18844999 A JP18844999 A JP 18844999A JP 18844999 A JP18844999 A JP 18844999A JP 3525812 B2 JP3525812 B2 JP 3525812B2
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- steel sheet
- austenite
- rolled
- energy absorption
- 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.)
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Description
【0001】[0001]
【発明の属する技術分野】本発明は、プレス成形などの
塑性加工により製造される構造部材に好適な、衝撃エネ
ルギー吸収性に優れた高強度鋼板およびその製造方法に
関する。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a high-strength steel sheet which is suitable for a structural member manufactured by plastic working such as press forming and has excellent impact energy absorption, and a manufacturing method thereof.
【0002】[0002]
【従来の技術】乗用車の衝突安全性確保に対する社会的
要求は、近年とみに高まっている。そこで、衝突時に搭
乗者空間を確保するために、車体に様々な補強部材を取
り付け、車体の強度アップが図られている。そのため、
車体重量が増加し、燃費が低下する傾向にある。これ
は、昨今の地球温暖化対策と相反する。そのために、高
張力鋼板を用いて、車体の軽量化を図る動きがある。特
に500MPaを超えるような高強度鋼板の適用が検討
されている。一般に鋼板の高強度化に伴い延性が劣化す
るため、高延性の高強度鋼板が望まれている。2. Description of the Related Art The social demand for ensuring collision safety of passenger cars has been increasing in recent years. Therefore, in order to secure a passenger space during a collision, various reinforcing members are attached to the vehicle body to increase the strength of the vehicle body. for that reason,
The vehicle weight tends to increase and the fuel economy tends to decrease. This conflicts with recent measures against global warming. Therefore, there is a movement to reduce the weight of the vehicle body by using a high-tensile steel plate. In particular, application of high-strength steel sheets having a pressure exceeding 500 MPa is being studied. Since ductility generally deteriorates as the strength of steel sheets increases, high-strength steel sheets with high ductility are desired.
【0003】このようなニーズに対し、SiとMnを複
合添加した低炭素鋼板をフェライト+オーステナイト2
相域焼鈍後、350〜550℃まで急冷し、その温度で
階段状の冷却あるいは短時間保持してオーステナイトを
一部ベイナイトに変態させ最終的にフェライト+ベイナ
イト+残留オーステナイト(残留γ)からなる鋼板は、
変形中に残留オーステナイトが歪誘起変態し、大きな伸
びを示すことが知られている。To meet such needs, a low carbon steel sheet in which Si and Mn are added together is ferrite + austenite 2
After the phase region annealing, it is rapidly cooled to 350 to 550 ° C., and at that temperature stepwise cooling or holding for a short time to transform austenite into a part of bainite and finally to form a steel sheet consisting of ferrite + bainite + retained austenite (residual γ). Is
It is known that retained austenite undergoes strain-induced transformation during deformation and exhibits a large elongation.
【0004】例えば特開昭60−43430号公報で
は、0.30〜0.65%のC、0.7〜2.0%のS
iおよび0.5〜2.0%のMnを含有する鋼板を、焼
鈍過程においてフェライト+オーステナイト2相域に加
熱した後、冷却過程の650℃から450℃の間で10
〜50秒の保持を1回以上行ない、最終製品において、
各々体積率10%以上のフェライトと残留オーステナイ
トおよび残部組織がマルテンサイトおよびベイナイトの
一種または二種からなる鋼板の製造方法が開示されてい
る。For example, in JP-A-60-43430, C of 0.30 to 0.65% and S of 0.7 to 2.0% are used.
After heating a steel sheet containing i and 0.5 to 2.0% of Mn to the ferrite + austenite two-phase region in the annealing process, the temperature of 650 ° C. to 450 ° C. in the cooling process was 10 ° C.
Hold for 50 seconds or more once, and in the final product,
Disclosed is a method for manufacturing a steel sheet in which ferrite having a volume ratio of 10% or more, retained austenite, and the residual structure of one or two of martensite and bainite are disclosed.
【0005】また、特開昭61−157625号公報で
は、0.12〜0.55%のC、0.4〜1.8%のS
iおよび0.2〜2.5%のMnを必須元素として含有
し、更に各々0.5%以下のCu、Cr、Ti、Nb、
V、Mo、0.1%以下のP、3%以下のNiの内、1
種または2種以上含有する鋼板を素材とし、更に上記特
開昭60−43430号公報と同様に、フェライト+オ
ーステナイト2相域に加熱した後、冷却途中の500℃
〜350℃の間の温度で30秒から30分の範囲で保持
する製造方法が開示されている。In Japanese Patent Laid-Open No. 61-157625, 0.12 to 0.55% C and 0.4 to 1.8% S are used.
i and 0.2 to 2.5% of Mn as essential elements, and 0.5% or less of Cu, Cr, Ti and Nb, respectively.
V, Mo, P less than 0.1%, Ni less than 3%, 1
As a raw material, a steel sheet containing two or more kinds of steel is used, and after heating to a ferrite + austenite two-phase region in the same manner as in JP-A-60-43430, 500 ° C. during cooling.
A manufacturing method is disclosed in which the temperature is kept between ˜350 ° C. for 30 seconds to 30 minutes.
【0006】更に、上記のような混合組織を有する鋼板
の欠点である穴拡げのごとき伸びフランジ加工性の不足
を解消するために、Siの一部をAlに置換した残留オ
ーステナイト鋼板の製造方法が特開平5−70886号
公報に開示されている。Further, in order to solve the shortage of stretch flange workability such as hole expansion, which is a drawback of steel sheets having a mixed structure as described above, a method for producing a retained austenitic steel sheet in which a part of Si is replaced by Al is proposed. It is disclosed in JP-A-5-70886.
【0007】[0007]
【発明が解決しようとする課題】以上のような高強度か
つ延性の優れた鋼板が開発されても、衝突安全性の向
上、軽量化のニーズはますます高くなっており、さらに
高強度の鋼板が要望されている。しかしながら、上述の
ような高強度かつ延性の優れた鋼板であっても、強度の
上昇に伴って成形時のスプリングバックによる形状不良
が増大するため、実際に使用できる強度には上限があ
る。さらに、高強度化に伴うC量の増加のため、溶接性
が劣化する恐れもある。[Problems to be Solved by the Invention] Even with the development of steel sheets with high strength and excellent ductility as described above, there is an ever-increasing need for improved collision safety and weight reduction. Is required. However, even in the case of a steel sheet having high strength and excellent ductility as described above, there is an upper limit to the strength that can be actually used because the defective shape due to springback during forming increases as the strength increases. Further, the weldability may be deteriorated due to the increase in the amount of C accompanying the increase in strength.
【0008】そこで、本発明は、高強度化をはかると同
時に本発明の目的である衝突時の衝撃吸収エネルギーが
高い鋼板を提供しようとするものである。Therefore, the present invention is intended to provide a steel sheet which has a high strength and at the same time has a high impact absorption energy at the time of collision, which is the object of the present invention.
【0009】[0009]
【課題を解決するための手段】本発明の要旨は、下記の
(1)、(2)および(3)の衝撃エネルギー吸収性に
優れた高強度冷延鋼板ならびに(4)のその製造方法に
ある。The gist of the present invention resides in the following (1), (2) and (3) high strength cold rolled steel sheet excellent in impact energy absorption and a method for producing the same (4 ). is there.
【0010】(1)質量%で,C:0.05〜0.22
5%、Si:2.0%以下、Al:0.01〜0.06
0%、Mn:0.5〜4.0%、Ni:0〜5.0%、
P:0.1%以下、S:0.1%以下、N:0.01%
以下、残部はFeおよび不可避的不純物からなり、かつ
1.5−3.0×C≦Si+Al≦3.5−5.0×
C、およびMn+(Ni/3)≧1.0(%)、を満足
する化学組成を有し、さらに鋼板の焼付硬化量が50M
Pa以上である冷延鋼板(ここで式中の元素記号は、鋼
中におけるそれぞれの元素の質量%で表示した含有量を
表す)。(1) C: 0.05 to 0.22 in mass%
5 %, Si: 2.0% or less, Al: 0.01 to 0.06
0 %, Mn: 0.5 to 4.0%, Ni: 0 to 5.0%,
P: 0.1% or less, S: 0.1% or less, N: 0.01%
Hereinafter, the balance consists of Fe and unavoidable impurities, and 1.5-3.0 × C ≦ Si + Al ≦ 3.5-5.0 ×
It has a chemical composition satisfying C and Mn + (Ni / 3) ≧ 1.0 (%), and the bake hardening amount of the steel sheet is 50M.
A cold-rolled steel sheet having Pa or more (here, the symbol of the elements in the formula represents the content of each element in the steel expressed in mass%).
【0011】(2)質量%で,C:0.05〜0.22
5%、Si:2.0%以下、Al:0.01〜0.06
0%、Mn:0.5〜4.0%、Ni:0〜5.0%、
P:0.1%以下、S:0.1%以下、N:0.01%
以下、さらにTi:0.005〜0.10%(但し、
(48/14)N+(48/32)S+0.01以下の
場合を除く)、Nb:0.005〜0.10%、V:
0.005〜0.10%の1種以上を、合計で0.00
5〜0.10%含有し、残部はFeおよび不可避的不純
物からなり、かつ1.5−3.0×C≦Si+Al≦
3.5−5.0×C、およびMn+(Ni/3)≧1.
0(%)、を満足する化学組成を有し、さらに鋼板の焼
付硬化量が50MPa以上である冷延鋼板。(2) C: 0.05 to 0.22 in mass%
5 %, Si: 2.0% or less, Al: 0.01 to 0.06
0 %, Mn: 0.5 to 4.0%, Ni: 0 to 5.0%,
P: 0.1% or less, S: 0.1% or less, N: 0.01%
Hereinafter, Ti: 0.005 to 0.10% (however,
(48/14) N + (48/32) S + except 0.01 or less), Nb: 0.005 to 0.10%, V:
0.005 to 0.10% of one or more, 0.00 in total
5 to 0.10%, the balance consisting of Fe and unavoidable impurities, and 1.5-3.0 × C ≦ Si + Al ≦
3.5-5.0 × C, and Mn + (Ni / 3) ≧ 1.
A cold-rolled steel sheet having a chemical composition satisfying 0 (%) and having a bake hardening amount of 50 MPa or more.
【0012】(3)鋼板組織が5%以上の残留オーステ
ナイトおよび5〜15%のベイナイトを含む上記(1)
または(2)に記載する冷延鋼板。(3) The steel sheet structure contains 5% or more of retained austenite and 5 to 15% of bainite.
Alternatively, the cold rolled steel sheet according to (2).
【0013】[0013]
【0014】(4)上記(1)または(2)に記載する
化学組成を有する鋼片を、Ac3点以上に加熱保持して
から熱間圧延し、300〜720℃の温度範囲で巻き取
り、酸洗、冷間圧延を行った後に、連続焼鈍工程におい
て、Ac1点以上、Ac3点以下の温度域に加熱して再結
晶させ、次いで冷却速度10℃/s以下で700℃まで
徐冷し、引き続く冷却途中の550〜350℃の温度域
で30秒以上の保持、または100℃/分以下の冷却速
度での徐冷を行う方法。(4) A steel slab having the chemical composition described in (1) or (2) above is heated and held at an Ac 3 point or more, hot rolled, and wound in a temperature range of 300 to 720 ° C. , After pickling and cold rolling, in a continuous annealing step, heating to a temperature range of Ac 1 point or more and Ac 3 point or less to recrystallize, and then to 700 ° C. at a cooling rate of 10 ° C./s or less.
A method of performing slow cooling, holding in the temperature range of 550 to 350 ° C. for 30 seconds or more during the subsequent cooling, or performing slow cooling at a cooling rate of 100 ° C./min or less.
【0015】ここで、「焼付硬化量」は、下記に示した
方法で測定した値である。「残留オーステナイト量」、
「ベイナイト量」は「発明の実施の形態」の中で示した
方法で測定した値である。Here, the "bake-hardening amount" is a value measured by the method shown below. "Amount of retained austenite",
The “amount of bainite” is a value measured by the method described in “Embodiment of the Invention”.
【0016】本発明者らは、様々な組成、組織バランス
を持った残留オーステナイトを有する鋼板を実験室的規
模で作製し、自動車の衝突における構造部材(以下、部
材と記す)の変形を模擬した試験を行い、衝撃吸収エネ
ルギーを調査した。以下にその実験内容を説明する。The present inventors produced steel sheets having retained austenite having various compositions and structure balances on a laboratory scale, and simulated deformation of structural members (hereinafter referred to as members) in the collision of automobiles. A test was conducted to investigate the impact absorbed energy. The details of the experiment will be described below.
【0017】表1の鋼Aおよび鋼Bの組成を有する厚さ
25mmの鋼片を、実験室において熱間圧延、酸洗、冷
間圧延、焼鈍、調質圧延を行った後、引張試験及び部材
の軸圧壊試験を行った。熱間圧延は、鋼片を1200℃
に30分加熱した後に900℃から800℃の温度範囲
で行い、板厚5mmとした。熱間圧延後、水スプレー冷
却により、600℃まで冷却し、30分保持し、20℃
/時で炉冷することによって実機製造におけるコイル巻
き取りを模擬した。熱延板は、酸洗にてスケールを除去
した後、冷間圧延により板厚1.2mmとした。この冷
延板を、820℃で30秒間均熱後、700℃まで3℃
/秒で徐冷し、その後は過時効温度まで50℃/秒で冷
却し、その温度で保持し、さらに10℃/秒で室温まで
冷却した。過時効温度は250〜600℃、保持時間は
15〜300秒までの範囲で、種々の組み合わせ条件で
試験した。焼鈍後は、伸び率1%で調質圧延を行った。
調質圧延後に引張試験を行った。Steel pieces having a composition of steel A and steel B shown in Table 1 and having a thickness of 25 mm were hot-rolled, pickled, cold-rolled, annealed and temper-rolled in a laboratory, and then subjected to a tensile test and A shaft crush test of the member was performed. Hot rolling the billet at 1200 ℃
After heating for 30 minutes, it was performed in the temperature range of 900 ° C. to 800 ° C. to have a plate thickness of 5 mm. After hot rolling, cool to 600 ° C with water spray cooling, hold for 30 minutes, 20 ° C
The coil winding in the actual manufacturing was simulated by cooling the furnace at 1 / hour. The hot-rolled sheet was pickled to remove the scale and then cold-rolled to a sheet thickness of 1.2 mm. This cold-rolled sheet was soaked at 820 ° C for 30 seconds and then cooled to 700 ° C at 3 ° C.
The sample was gradually cooled at a heating rate of 1 / sec, then cooled to the overaging temperature at 50 ° C./sec, held at that temperature, and further cooled to room temperature at 10 ° C./sec. The overaging temperature was 250 to 600 ° C., the holding time was 15 to 300 seconds, and various combinations of conditions were tested. After annealing, temper rolling was performed at an elongation of 1%.
A tensile test was performed after temper rolling.
【0018】更に焼付硬化量(BH量)を測定するため
に、JIS G 3135に準じて、2%の引張予歪み
を付与し、170℃で20分の塗装焼付相当の熱処理を
行なった後にも引張試験を行った。「焼付硬化量」は、
ひずみ時効降伏荷重から予ひずみ荷重を差し引いた値を
予ひずみ前の試験片平行部断面積で除した値とした。Further, in order to measure the bake-hardening amount (BH amount), a tensile prestrain of 2% was applied according to JIS G 3135, and after heat treatment equivalent to coating baking for 20 minutes at 170 ° C. was performed. A tensile test was conducted. "Bake-hardening amount" is
The value obtained by subtracting the prestrain load from the strain aging yield load was divided by the cross-sectional area of the parallel part of the test piece before prestrain.
【0019】衝撃吸収エネルギーの測定は、次のように
行った。図1に示す軸圧壊試験の供試体は、上記のよう
に製造した鋼板をプレス成形でハット形状にし、同一材
料の鋼板を20mmピッチでスポット溶接した。ハット
壁部の塑性歪みは約2%であった。この供試体を塗装焼
付に相当する170℃、20分の熱処理を行った後、軸
圧壊試験を行った。軸圧壊試験は、350kgの錘体を
高さ3mから落下させて、荷重−変位曲線から100m
mを潰すのに要したエネルギーを算出した。組成Aにつ
いては、引張強さが580〜620MPaのもの、組成
Bについては680〜720MPaのものを抽出し、焼
付硬化量と衝撃吸収エネルギーの関係を調べた。図2に
示すように焼付硬化量が大きいほど衝撃吸収エネルギー
が大きく好ましいことを示している。特に、焼付硬化量
が50MPa以上では、衝撃吸収エネルギーの上昇が著
しい。例えば、組成Aの焼付硬化量50MPaの鋼板
は、組成Bの焼付硬化量が20MPaの鋼板と同等の衝
撃吸収エネルギーを示している。後者は前者より引張強
さが100MPa高いので、焼付硬化は単純な強度上昇
効果以上の作用を持っていると考えられる。The impact absorption energy was measured as follows. In the test piece for the axial crush test shown in FIG. 1, the steel plate manufactured as described above was formed into a hat shape by press forming, and steel plates of the same material were spot welded at a pitch of 20 mm. The plastic strain of the hat wall was about 2%. This sample was heat-treated at 170 ° C. for 20 minutes, which corresponds to baking, and then subjected to a shaft crushing test. In the axial crush test, a weight of 350 kg was dropped from a height of 3 m, and 100 m from the load-displacement curve.
The energy required to crush m was calculated. The composition A having a tensile strength of 580 to 620 MPa and the composition B having a tensile strength of 680 to 720 MPa were extracted, and the relationship between the bake hardening amount and the impact absorption energy was examined. As shown in FIG. 2, the larger the bake-hardening amount is, the larger the shock absorption energy is, which is preferable. In particular, when the bake-hardening amount is 50 MPa or more, the impact absorption energy increases remarkably. For example, a steel sheet having a bake hardening amount of 50 MPa of the composition A exhibits the same impact absorption energy as a steel sheet having a bake hardening amount of the composition B of 20 MPa. Since the latter has a tensile strength higher than that of the former by 100 MPa, bake hardening is considered to have more than a simple strength increasing effect.
【0020】したがって、スプリングバックのような引
張強さに支配される成形性と、軸圧壊吸収エネルギーを
両立させるための基本的考え方は、鋼板の引張強さを確
保した上で、高い焼付硬化量を付与することである。Therefore, the basic idea for achieving both the formability governed by tensile strength such as springback and the axial crush absorption energy is to secure the tensile strength of the steel sheet and then to obtain a high bake hardening amount. Is to give.
【0021】次に組成Aのグループについて金属組織と
引張試験特性との関係を図3に示すが、次の重要な知見
を得た。Next, the relationship between the metal structure and the tensile test characteristics of the group of composition A is shown in FIG. 3, and the following important findings were obtained.
【0022】ベイナイト量(面積率)が多いほど、焼
付硬化量が上昇する。The larger the amount of bainite (area ratio), the higher the amount of bake hardening.
【0023】一方、引張強度(TS)と伸び値(E
L)との積(強度−延性バランス)は、ベイナイト量が
5〜15%の範囲で優れ、ベイナイト量が5%未満ある
いは15%を超えると減少する。On the other hand, tensile strength (TS) and elongation value (E
The product (strength-ductility balance) with L) is excellent when the bainite amount is in the range of 5 to 15%, and decreases when the bainite amount is less than 5% or exceeds 15%.
【0024】したがって、ベイナイト量を5〜15%
に調整すると、焼付硬化量が大きく、即ち衝撃吸収エネ
ルギーが大きく、かつ強度−延性バランスも良好であ
る。Therefore, the amount of bainite is 5 to 15%.
When adjusted to 1, the bake hardening amount is large, that is, the impact absorption energy is large, and the strength-ductility balance is good.
【0025】[0025]
【発明の実施の形態】以下に、本発明鋼板およびその製
造方法について具体的に説明する。BEST MODE FOR CARRYING OUT THE INVENTION The steel sheet of the present invention and the method for producing the same will be described below in detail.
【0026】C: 最も強力なオーステナイト安定化元
素であり、本発明の必須元素の一つである。室温におい
てオーステナイトを安定化するためには、オーステナイ
ト中に1%以上のCが含有されることが必要である。全
C量が0.05%以上の場合には、熱間圧延または焼鈍
のヒートサイクルを最適化すれば、Cを残留オーステナ
イト中に濃縮させることができる。より多量のCを添加
することにより、より高強度鋼板を製造できる。しか
し、0.3%を超えると強度が高くなりすぎるため、ス
プリングバック量が大きいなどの問題により部品への成
形が困難になる。また、溶接性も劣化するため、上限を
0.3%とし、Cの範囲は0.05〜0.3%とした。
好ましくは0.08〜0.23%である。C: The strongest austenite stabilizing element, which is one of the essential elements of the present invention. In order to stabilize austenite at room temperature, 1% or more of C must be contained in austenite. When the total C content is 0.05% or more, C can be concentrated in the retained austenite by optimizing the heat cycle of hot rolling or annealing. A higher strength steel plate can be manufactured by adding a larger amount of C. However, if it exceeds 0.3%, the strength becomes too high, so that it becomes difficult to form a component due to problems such as a large springback amount. Since the weldability also deteriorates, the upper limit was made 0.3% and the range of C was made 0.05 to 0.3%.
It is preferably 0.08 to 0.23%.
【0027】Si: SiはAlと同様にフェライト安
定化元素であり、熱間圧延後の冷却過程あるいは冷延鋼
板の2相域焼鈍において、フェライトの体積率を増加さ
せることにより、平衡するオーステナイト相のC濃度を
高める働きをする。また、ベイナイト変態中に炭化物の
析出を抑制し、オーステナイトにCを濃縮する働きがあ
る。同時にSiはフェライトを強化する作用がある。し
かし、Siの含有量が2.0%を超えると、Si添加鋼
板特有の高Siスケールによる表面品質の劣化が生じる
ので、上限を2.0%とした。また、Alとの関係で含
有量を最適化する。Si: Si, like Al, is a ferrite stabilizing element, and in the cooling process after hot rolling or in the two-phase annealing of a cold rolled steel sheet, the volume ratio of ferrite is increased to equilibrate the austenite phase. Functions to increase the C concentration of. Further, it has a function of suppressing the precipitation of carbide during bainite transformation and concentrating C in austenite. At the same time, Si has a function of strengthening ferrite. However, if the Si content exceeds 2.0%, the surface quality deteriorates due to the high Si scale peculiar to the Si-added steel sheet, so the upper limit was made 2.0%. Further, the content is optimized in relation to Al.
【0028】Al: AlはSiと同様にフェライト安
定化元素で、オーステナイト相のC濃度を高める作用が
あり、Siとの関係で添加量を制限する。溶融亜鉛めっ
き鋼板あるいは合金化溶融亜鉛めっき鋼板を製造する場
合は、めっき濡れ性を阻害しないAlを積極的に添加す
ることが好ましい。また、製鋼時に脱酸剤として使わ
れ、十分な脱酸効果を得るためには、0.01%以上が
必要である。2.0%を超えると鋼板中に介在物が多く
なり延性を損ねるので、これを上限とした。Al: Al, like Si, is a ferrite stabilizing element and has the effect of increasing the C concentration in the austenite phase, and limits the amount added in relation to Si. When producing a hot-dip galvanized steel sheet or an alloyed hot-dip galvanized steel sheet, it is preferable to positively add Al that does not impair the plating wettability. Further, it is used as a deoxidizing agent during steel making, and 0.01% or more is necessary to obtain a sufficient deoxidizing effect. When it exceeds 2.0%, inclusions increase in the steel sheet and the ductility is impaired, so this was made the upper limit.
【0029】Si、Al、Cのバランス: 残留オース
テナイトを十分確保するため、SiとAlは合計で、
「1.5−3.0×C」以上の含有が必要である。しか
し、Si、Alの過剰な添加は残留オーステナイトを安
定化しすぎ、特にC量が高い場合は延性をかえって劣化
させる。そこで、「Si+Al」の上限は、「3.5−
5.0×C」に限定する。また、Alは残留オーステナ
イトを安定化させる効果が大きいので、1.25×Si
(%)以下とすることが好ましい。Balance of Si, Al and C: In order to secure sufficient retained austenite, Si and Al are in total,
It is necessary to contain "1.5-3.0 x C" or more. However, the excessive addition of Si and Al excessively stabilizes the retained austenite, and deteriorates the ductility rather than the ductility especially when the C content is high. Therefore, the upper limit of "Si + Al" is "3.5-
5.0 × C ”. Moreover, since Al has a large effect of stabilizing the retained austenite, 1.25 × Si
(%) Or less is preferable.
【0030】Mn: オーステナイト安定化元素で、本
発明の必須元素の一つであり、その添加量はNiとの関
係で規制される。オーステナイトを安定化し、室温まで
残留させるためには、「Mn+(Ni/3)」が1.0
%以上となるように添加する必要がある。Mnは、鋼中
のSをMnSとして固定し熱間脆性を防止する目的でも
添加されるので、下限を0.5%とした。また、4.0
%を超えると鋼板が硬くなりすぎ高延性が得られないの
で上限を4.0%とした。Mn: An austenite-stabilizing element, which is one of the essential elements of the present invention, and its addition amount is regulated in relation to Ni. In order to stabilize austenite and keep it at room temperature, “Mn + (Ni / 3)” is 1.0
It is necessary to add it so that the content is at least%. Mn is also added for the purpose of fixing S in steel as MnS and preventing hot embrittlement, so the lower limit was made 0.5%. Also, 4.0
%, The steel sheet becomes too hard and high ductility cannot be obtained, so the upper limit was made 4.0%.
【0031】Ni: Mnと同様にオーステナイト安定
化元素として添加してもよい。しかし、Mnと比較して
オーステナイトを安定化する作用が小さく、Mnの3割
程度である。更に、Mnと比べて高価であり、基本的に
はオーステナイトの安定化にはMnを添加すればよい。
しかし、連続溶融亜鉛めっきラインにてめっき鋼板を製
造する場合、鋼板表面にMn酸化物が生成し、めっき濡
れ性が劣化するのを防止する効果がある。Mn含有量と
の合計で規制され、「Mn+(Ni/3)」が1.0%
以上とする必要がある。Ni含有量が、5.0%を超え
ると製品コストが高くなりすぎるためこれを上限とし
た。Ni: Like Mn, it may be added as an austenite stabilizing element. However, the effect of stabilizing austenite is smaller than that of Mn, which is about 30% of Mn. Further, it is more expensive than Mn, and basically Mn may be added to stabilize austenite.
However, when a plated steel sheet is manufactured by a continuous hot-dip galvanizing line, there is an effect of preventing Mn oxide from being generated on the surface of the steel sheet and deteriorating the wettability of the plating. Regulated by the total with Mn content, "Mn + (Ni / 3)" is 1.0%
It is necessary to be above. If the Ni content exceeds 5.0%, the product cost becomes too high, so this was made the upper limit.
【0032】P: Pは低ければ低いほどよい。ただ
し、Pはフェライトを固溶強化する作用を持っており、
その効果を得る場合には添加してもよい。P含有量が
0.1%を超えると、溶接性が劣化するので、0.1%
を上限とする。P: The lower P is, the better. However, P has the effect of strengthening the solid solution of ferrite,
It may be added to obtain the effect. If the P content exceeds 0.1%, the weldability deteriorates, so 0.1%
Is the upper limit.
【0033】S: Sは低い方が好ましい。S含有量が
多いと、MnSの析出量が多くなり、延性を阻害するの
みならず、オーステナイト安定化元素として添加された
Mnを析出物として消費するので、0.1%以下に限定
した。S: S is preferably low. When the S content is high, the amount of MnS precipitated increases, which not only hinders the ductility but also consumes Mn added as an austenite stabilizing element as a precipitate, so the content is limited to 0.1% or less.
【0034】N: Nは現状の製鋼技術で可能な限り低
い方が好ましい。加工性確保のため0.01%を上限と
した。N: N is preferably as low as possible in the current steelmaking technology. The upper limit was 0.01% to ensure workability.
【0035】Ti、Nb、V: いずれも必要に応じて
添加する元素である。これらの元素は炭化物生成元素で
あり、微細な析出物を形成し鋼板を強化する。いずれの
元素も添加する場合は、0.005〜0.10%の範囲
が好ましい。2種以上を複合して添加する場合は、合計
量で.005〜0.10%が好ましい。Ti, Nb, V: All are elements added as necessary. These elements are carbide forming elements and form fine precipitates to strengthen the steel sheet. When any element is added, the range of 0.005 to 0.10% is preferable. When adding two or more compounds in combination, the total amount is. 005 to 0.10% is preferable.
【0036】また、Tiは特に鋼中のNと結合し易く、
AlNの析出に優先してTiNが析出する。AlNの析
出に起因するスラブの割れを防止するとともに、TiN
による熱延板の細粒化効果をうるために、重量比でTi
/N≧3となるよう添加することが好ましい。Further, Ti is particularly easy to bond with N in steel,
TiN is deposited in preference to the deposition of AlN. Prevents slab cracking due to AlN precipitation and
In order to obtain the effect of refining the hot rolled sheet by
It is preferable to add it so that / N ≧ 3.
【0037】焼付硬化量: 既に述べたように、焼付硬
化量が高いほど衝撃吸収エネルギーは向上する。その効
果は50MPa以上で著しく大きい。その理由ははっき
りしないが、次のように推察される。なお本発明で「焼
付硬化量」というのは、「課題を解決するための手段」
の中で規定した引張試験により求めた量である。Bake-hardening amount: As described above, the higher the bake-hardening amount, the higher the impact absorption energy. The effect is remarkably large at 50 MPa or more. The reason for this is not clear, but it is presumed as follows. In the present invention, "bake hardening amount" means "means for solving the problem".
It is the amount obtained by the tensile test specified in the above.
【0038】焼付硬化は、転位が炭素原子によって固着
されるため生じる現象であり、転位が強固に固着される
ほど、可動転位密度が減少し、変形抵抗の歪み速度依存
性は大きくなる。焼付硬化量が高いほど、JIS5号試
験片による引張試験のような準静的な引張試験において
変形抵抗が上昇するのみでなく、歪み速度が大きい衝突
時の変形では、さらに高い変形抵抗を示し、衝撃吸収エ
ネルギーが著しく大きくなるものと推察される。Bake hardening is a phenomenon that occurs because dislocations are fixed by carbon atoms. The stronger the dislocations are fixed, the lower the movable dislocation density and the greater the strain rate dependence of deformation resistance. The higher the bake-hardening amount, the higher the deformation resistance in a quasi-static tensile test such as the tensile test by JIS No. 5 test piece, and also the higher deformation resistance in the deformation at the time of collision with a high strain rate, It is presumed that the impact absorption energy will be significantly increased.
【0039】このような効果を発揮させるためには、少
なくとも50MPa以上の焼付硬化量が必要であり、7
0MPa以上が望ましい。In order to exert such an effect, a bake-hardening amount of at least 50 MPa or more is necessary.
0 MPa or more is desirable.
【0040】残留オーステナイトの体積率: 本発明鋼
の延性は、製品中に含まれる残留オーステナイトの体積
率の増加にともなって向上するため、残留オーステナイ
トの体積率は5%以上が望ましい。これにより、オース
テナイトの歪誘起変態による延性の更なる向上が期待で
きる。また残留オーステナイトの上限は、特に高成形性
を得る場合は、25%以下が望ましい。残部は、主とし
てフェライトまたはフェライト+ベイナイトである。Volume Ratio of Retained Austenite: Since the ductility of the steel of the present invention improves with an increase in the volume ratio of the retained austenite contained in the product, the volume ratio of the retained austenite is preferably 5% or more. Thereby, further improvement of ductility due to strain-induced transformation of austenite can be expected. Further, the upper limit of the retained austenite is preferably 25% or less, particularly when high moldability is obtained. The balance is mainly ferrite or ferrite + bainite.
【0041】なお、残留オーステナイトの体積率は、鋼
板表面に平行な板厚中心面を化学研磨により露出させ、
CoKα線を用いたX線回折により次式で算出される。The volume ratio of retained austenite is determined by exposing the center plane of the plate thickness parallel to the steel plate surface by chemical polishing.
It is calculated by the following formula by X-ray diffraction using CoKα ray.
【0042】残留オーステナイトの体積率(%)={1/(1
+K-1×Iα×Iγ-1)}×100
上記式中、KはSUS304と純鉄の混合粉末からなる
標準試料できめた定数、Iαはフェライトの(211)
面のX線積分強度、Iγは残留オーステナイトの(22
0)面のX線積分強度を表す。Volume ratio of retained austenite (%) = {1 / (1
+ K −1 × I α × I γ −1 )} × 100 In the above formula, K is a constant that can be obtained by a standard sample made of a mixed powder of SUS304 and pure iron, and Iα is (211) of ferrite.
The X-ray integrated intensity of the plane, Iγ, is (22) of the retained austenite.
It represents the X-ray integrated intensity of the 0) plane.
【0043】ベイナイトの面積率: 前述したように、
ベイナイトの面積率の増加にともなって焼付硬化量は増
加するが、強度−延性バランスが低下する。この相反す
る特性を両立させるため、ベイナイトの面積率は5〜1
5%が望ましい。なおベイナイトの面積率は、圧延方向
に垂直な鋼板断面を走査型電子顕微鏡で観察し、ベイナ
イト組織の占める面積を測定して決定した。Area ratio of bainite: As described above,
The bake hardening amount increases with an increase in the area ratio of bainite, but the strength-ductility balance decreases. The area ratio of bainite is 5 to 1 in order to achieve both of these contradictory characteristics.
5% is desirable. The area ratio of bainite was determined by observing a steel plate cross section perpendicular to the rolling direction with a scanning electron microscope and measuring the area occupied by the bainite structure.
【0044】[0044]
【0045】[0045]
【0046】[0046]
【0047】[0047]
【0048】熱延条件: 冷延鋼板の場合、金属組織は
主に連続焼鈍工程で決定されるため、熱延条件に対する
規制は少ないが、次の理由により巻き取り温度を規制す
る。本発明鋼の場合、低温で巻取ると焼きが入り硬くな
るため、その後の酸洗、冷間圧延が困難になる。また、
高温で巻取るとセメンタイトが粗大化し、軟質になり酸
洗、冷間圧延が容易になる反面、焼鈍の均熱時にセメン
タイトが再び固溶するのに時間がかかりすぎ、十分なオ
ーステナイトが残留しなくなる。そのため、300〜7
20℃に限定した。酸洗、冷間圧延に支障のない範囲で
低い温度で巻取るのがよい。好ましくは、550〜65
0℃がよい。 Hot-rolling conditions: In the case of cold-rolled steel sheets, the metal structure is mainly determined in the continuous annealing process, so there are few restrictions on the hot-rolling conditions, but the winding temperature is restricted for the following reasons. In the case of the steel of the present invention, when it is wound at a low temperature, it is hardened and hardened, so that subsequent pickling and cold rolling become difficult. Also,
When wound at high temperature and cementite coarsening, pickling becomes soft, while the cold rolling is facilitated, too much time to cementite during soaking annealing forms a solid solution again, sufficient austenite can not remain . Therefore, 300 to 7
Limited to 20 ° C. It is preferable to wind at a low temperature as long as it does not interfere with pickling and cold rolling. Preferably 550-65
0 ° C is good.
【0049】連続焼鈍条件: まず、「フェライト+オ
ーステナイト」の2相にしてCをオーステナイトに濃縮
するためAc1 点以上、Ac3変態点以下の温度域に加熱
する。加熱温度が低すぎるとセメンタイトが再固溶する
のに時間がかかりすぎ、高すぎるとオーステナイトの体
積率が大きくなりすぎてオーステナイト中のC濃度が低
下する。それ故、800〜850℃の温度範囲で均熱す
ることが望ましい。更に均熱後徐冷してフェライトを成
長させて、オーステナイト中のC濃度を高めるために、
700℃までの冷却速度は10℃/s以下とする。更
に、過時効処理帯に入るまでの温度域では、オーステナ
イトのパーライト変態を抑制するために、冷却速度は逆
に50℃/s以上が望ましい。Continuous Annealing Conditions: First, in order to make C into austenite by forming two phases of "ferrite + austenite", it is heated in a temperature range from Ac 1 point to Ac 3 transformation point. If the heating temperature is too low, it takes too long to re-dissolve cementite, and if it is too high, the volume ratio of austenite becomes too large and the C concentration in austenite decreases . Therefore, it is desirable to carry out soaking in the temperature range of 800 to 850 ° C. In order to further increase the C concentration in austenite by further soaking and then gradually cooling to grow ferrite,
Cooling rate to 700 ° C. is not more than 10 ° C. / s. Further, in the temperature range before entering the overaging treatment zone, the cooling rate is preferably 50 ° C./s or more to suppress the pearlite transformation of austenite.
【0050】過時効処理帯では、550〜350℃の温
度範囲で30秒以上の保持または100℃/分以下の冷
却速度で徐冷し、オーステナイトをベイナイト変態させ
ながら、オーステナイトへのCの濃縮を促進するのがよ
い。550〜350℃の温度範囲で250秒を超える保
持では残留オーステナイトがやや減少するので、250
秒以下が好ましい。550℃超えではベイナイト変態が
生じず、350℃未満では、下部ベイナイトになり、オ
ーステナイトへのCの濃縮が起こりにくい。材料特性面
では、過時効処理帯後の冷却速度はとくに限定する必要
はないが、焼鈍ライン長を短くする観点から強制冷却を
行ってもよい。In the overaging zone, the temperature is maintained at 550 to 350 ° C. for 30 seconds or more or is gradually cooled at a cooling rate of 100 ° C./min or less to transform C into austenite while condensing C into austenite. Good to promote. In the temperature range of 550 to 350 ° C., the retained austenite is slightly reduced when held for more than 250 seconds.
Seconds or less are preferable. If it exceeds 550 ° C, bainite transformation does not occur, and if it is less than 350 ° C, it becomes lower bainite, and C concentration in austenite hardly occurs. In terms of material characteristics, the cooling rate after the overaging zone need not be particularly limited, but forced cooling may be performed from the viewpoint of shortening the annealing line length.
【0051】また、溶融めっき鋼板を製造するために、
連続溶融めっきラインを用いて上記の熱処理を行っても
よい。合金化溶融亜鉛めっきとするために、合金化熱処
理を行っても良い。In order to produce a hot dip plated steel sheet,
You may perform the said heat processing using a continuous hot dip coating line. An alloying heat treatment may be performed in order to achieve galvannealing.
【0052】[0052]
【実施例】(実施例1)表1に化学組成を示す鋼A〜M
の厚さ25mmの鋼片を、実験室において熱間圧延、酸
洗、冷間圧延、焼鈍、調質圧延を行った後、引張試験及
び図1に示す部材の軸圧壊試験を行った。熱間圧延は、
鋼片を1200℃に30分加熱した後に900℃から8
00℃の温度範囲で行い、板厚5mmまで圧延した。熱
間圧延後、水スプレー冷却により、600℃まで冷却
し、30分保持し、20℃/時で炉冷することによって
実機製造におけるコイル巻き取りを模擬した。熱延板
は、酸洗にてスケールを除去した後、冷間圧延により板
厚1.2mmとした。この冷延板を、820℃で30秒
間均熱後、700℃まで3℃/秒で徐冷し、その後は4
00℃まで30℃/秒で冷却し、その温度で150秒間
保持し、さらに10℃/秒で室温まで冷却した。焼鈍後
は、伸び率1%の調質圧延を行った。これらの鋼板の機
械的特性および金属組織を表2に示す。焼付硬化量、残
留オーステナイト(残留γ)量、ベイナイト量は、前記
の方法で求めた。Examples (Example 1) Steels A to M whose chemical compositions are shown in Table 1
The 25 mm thick steel slab was hot-rolled, pickled, cold-rolled, annealed and temper-rolled in the laboratory, and then subjected to a tensile test and an axial crush test of the member shown in FIG. Hot rolling
After heating the billet to 1200 ° C for 30 minutes, the temperature of 900 ° C to 8
The rolling was performed in the temperature range of 00 ° C. and rolled to a plate thickness of 5 mm. After hot rolling, the material was cooled to 600 ° C. by water spray cooling, held for 30 minutes, and furnace cooled at 20 ° C./hour to simulate coil winding in actual machine manufacturing. The hot-rolled sheet was pickled to remove the scale and then cold-rolled to a sheet thickness of 1.2 mm. The cold-rolled sheet was soaked at 820 ° C. for 30 seconds, then gradually cooled to 700 ° C. at 3 ° C./second, and then 4
The mixture was cooled to 00 ° C at 30 ° C / sec, kept at that temperature for 150 seconds, and further cooled to room temperature at 10 ° C / sec. After annealing, temper rolling with an elongation of 1% was performed. Table 2 shows the mechanical properties and metallographic structure of these steel sheets. The bake hardening amount, the amount of retained austenite (residual γ), and the amount of bainite were determined by the above-mentioned method.
【0053】[0053]
【表1】 [Table 1]
【0054】[0054]
【表2】 [Table 2]
【0055】試番3は、Cが0.040%と本発明範囲
より低いため、残留オーステナイトがほとんど存在せ
ず、伸びが劣る。試番5は、Cが0.33%と本発明範
囲より高いため、引張強さが1200MPa以上になっ
ており、プレス成形用途には高強度すぎて適さない。試
番6は、「Si+Al」量が本発明範囲より低いため、
2相域焼鈍中にオーステナイト相中へのCの濃縮が十分
行われないために、残留オーステナイト量が少なく、伸
びが劣る。一方、試番7は「Si+Al」量が本発明で
規定する範囲より高すぎるために、残留オーステナイト
中のC濃度が高くなりすぎ、過剰に安定化されているの
で、残留オーステナイト量が多いにもかかわらず伸びが
低い。試番9は、Mnが0.31%と本発明範囲より低
く、オーステナイトが安定化されないため、室温まで冷
却したときマルテンサイト変態がおき、残留オーステナ
イトは消失してしまうので、伸びが劣る。In sample No. 3, since C is 0.040%, which is lower than the range of the present invention, residual austenite is scarcely present and the elongation is poor. Test No. 5 has a C content of 0.33%, which is higher than the range of the present invention, and therefore has a tensile strength of 1200 MPa or more, which is too high strength and not suitable for press molding applications. In the trial number 6, the amount of “Si + Al” is lower than the range of the present invention,
Since C is not sufficiently concentrated in the austenite phase during the two-phase annealing, the amount of retained austenite is small and the elongation is poor. On the other hand, in the sample No. 7, the amount of “Si + Al” is too higher than the range specified in the present invention, so that the C concentration in the retained austenite becomes too high and is excessively stabilized, so that the amount of retained austenite is large. However, the growth is low. Sample No. 9 has Mn of 0.31%, which is lower than the range of the present invention, and the austenite is not stabilized. Therefore, when cooled to room temperature, martensitic transformation occurs and residual austenite disappears, so that elongation is poor.
【0056】本発明例の試番1、2、4、8、10、1
1、12および13は優れた強度−延性バランス(TS
×EL)を有している。Trial Nos. 1, 2, 4, 8, 10, 1 of the present invention example
1, 12 and 13 have excellent strength-ductility balance (TS
X EL).
【0057】(実施例2)表1に化学組成を示す鋼Aの
厚さ25mmの鋼片を、実験室において熱間圧延、酸
洗、冷間圧延、焼鈍、調質をおこなった後、引張試験お
よび部材の軸圧壊試験をおこなった。熱間圧延は、鋼片
を1200℃に30分間均熱した後に900℃〜800
℃の温度範囲でおこない、板厚5mmとした。熱間圧延
後、水スプレー冷却により、600℃まで冷却し、30
分保持し、20℃/時で炉冷することによって実機製造
におけるコイル巻き取りを模擬した。熱延板は、酸洗に
てスケールを除去した後、冷間圧延により板厚1.2m
mとした。この冷延板を、表3に示す均熱温度で30秒
間均熱後、700℃まで3℃/秒で徐令し、引き続き過
時効開始温度までを30℃/秒で冷却し、その後、過時
効終了温度までを同表の平均冷却速度で冷却し、さらに
10℃/秒で室温まで冷却した。焼鈍後は、伸び率1%
の調質圧延をおこなった。(Example 2) A steel piece having a thickness of 25 mm of steel A having a chemical composition shown in Table 1 was hot-rolled, pickled, cold-rolled, annealed and tempered in a laboratory and then stretched. The test and the axial crush test of the member were performed. Hot rolling is performed by soaking the billet at 1200 ° C for 30 minutes, and then 900 ° C to 800 ° C.
It was carried out in the temperature range of ° C and the plate thickness was set to 5 mm. After hot rolling, cool to 600 ° C with water spray cooling,
The coil winding in the actual production was simulated by holding the temperature for 20 minutes and cooling the furnace at 20 ° C./hour. The hot-rolled sheet has a thickness of 1.2 m by cold rolling after removing the scale by pickling.
m. This cold-rolled sheet was soaked at the soaking temperature shown in Table 3 for 30 seconds, then gradually cooled down to 700 ° C at 3 ° C / second, then cooled to the overaging start temperature at 30 ° C / second, and then overheated. It cooled to the aging completion temperature at the average cooling rate in the same table, and further cooled to room temperature at 10 ° C./sec. After annealing, elongation is 1%
Was temper-rolled.
【0058】なお、表3の試番1,14〜19は、過時
効処理を一定温度でおこなった例である。The trial numbers 1, 14 to 19 in Table 3 are examples in which the overaging treatment is performed at a constant temperature.
【0059】連続焼鈍条件を表3のように変化させた場
合の機械的性質、金属組織および軸圧壊吸収エネルギー
を表4に示す。Table 4 shows the mechanical properties, the metal structure and the axial crush absorption energy when the continuous annealing conditions were changed as shown in Table 3.
【0060】[0060]
【表3】 [Table 3]
【0061】[0061]
【表4】 [Table 4]
【0062】試番14は連続焼鈍の均熱温度が本発明で
規定する範囲より高いので、ほぼオーステナイト単相域
から冷却されるためCの濃縮はおこらず、残留オーステ
ナイトは残らない。焼付硬化量が高いので軸圧壊吸収エ
ネルギーは高いが、伸びが著しく小さく、プレス成形に
耐えない。試番15、22は、過時効時間が短いため残
留オーステナイトが残らず、焼付硬化量も小さいので、
伸び、エネルギー吸収ともに劣る。試番17は過時効時
間が300秒とやや長いため、ベイナイト変態が進行し
残留がやや減少する傾向がある。試番18、19、23
は過時効温度が本発明範囲を外れるため、残留オーステ
ナイトが得られていない。したがい、試番18〜19の
伸びは劣っている。In the sample No. 14, the soaking temperature of continuous annealing is higher than the range specified in the present invention, so that it is cooled from the austenite single phase region, so that C is not concentrated and no residual austenite remains. Since the bake-hardening amount is high, the axial crush absorption energy is high, but the elongation is extremely small and it cannot withstand press forming. Sample Nos. 15 and 22 have a short overaging time, so that residual austenite does not remain and the bake hardening amount is small.
Both elongation and energy absorption are poor. Since the overaging time of Sample No. 17 is 300 seconds, which is slightly long, bainite transformation tends to proceed and the residual amount tends to slightly decrease. Trial No. 18, 19, 23
Since the overaging temperature is outside the range of the present invention, residual austenite is not obtained. Therefore, the growth of trial numbers 18 to 19 is inferior.
【0063】本発明例の試番1、16、20,21は極
めて良好な伸びと吸収エネルギーを兼ね備えている。The trial numbers 1, 16, 20, and 21 of the examples of the present invention have extremely good elongation and absorbed energy.
【0064】[0064]
【0065】[0065]
【0066】[0066]
【0067】[0067]
【0068】[0068]
【発明の効果】本発明によれば、鋼板の強度が必要以上
に高くないので、言い換えれば、成形時のスプリングバ
ック等の不良を発生させることなく、鋼板の焼付硬化量
を規定することにより衝撃吸収エネルギーに優れた鋼板
が得られる。この鋼板を自動車等の構造部材に適用する
ことにより、衝突安全性の向上および軽量化が達成でき
る。According to the present invention, the strength of the steel sheet is not unnecessarily high. In other words, the impact hardening can be achieved by defining the bake hardening amount of the steel sheet without causing defects such as springback during forming. A steel sheet excellent in absorbed energy can be obtained. By applying this steel sheet to structural members such as automobiles, it is possible to improve collision safety and reduce weight.
【図1】衝撃吸収エネルギーを評価するために用いたハ
ット形状の部材の模式図である。FIG. 1 is a schematic view of a hat-shaped member used for evaluating impact absorption energy.
【図2】焼付硬化量と衝撃吸収エネルギーの関係を示す
図である。FIG. 2 is a diagram showing a relationship between a bake-hardening amount and impact absorption energy.
【図3】ベイナイトの面積率と焼付硬化量および強度−
延性バランスとの関係を示す図である。[FIG. 3] Area ratio of bainite and bake hardening amount and strength-
It is a figure which shows the relationship with a ductility balance.
───────────────────────────────────────────────────── フロントページの続き (56)参考文献 特開 平10−158735(JP,A) 特開 平7−252592(JP,A) 特開 平10−130776(JP,A) 特開 平5−179345(JP,A) 特開 平5−70886(JP,A) (58)調査した分野(Int.Cl.7,DB名) C22C 38/00 C21D 9/46 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-10-158735 (JP, A) JP-A-7-252592 (JP, A) JP-A-10-130776 (JP, A) JP-A-5- 179345 (JP, A) JP-A-5-70886 (JP, A) (58) Fields investigated (Int.Cl. 7 , DB name) C22C 38/00 C21D 9/46
Claims (4)
Si:2.0%以下、Al:0.01〜0.060%、
Mn:0.5〜4.0%、Ni:0〜5.0%、P:
0.1%以下、S:0.1%以下、N:0.01%以
下、残部はFeおよび不可避的不純物からなり、かつ
1.5−3.0×C≦Si+Al≦3.5−5.0×
C、およびMn+(Ni/3)≧1.0(%)、を満足
する化学組成を有し、さらに鋼板の焼付硬化量が50M
Pa以上であることを特徴とする衝撃エネルギー吸収性
に優れた高強度冷延鋼板。1. In mass%, C: 0.05 to 0.225 %,
Si: 2.0% or less, Al: 0.01 to 0.060 %,
Mn: 0.5 to 4.0%, Ni: 0 to 5.0%, P:
0.1% or less, S: 0.1% or less, N: 0.01% or less, the balance consisting of Fe and unavoidable impurities, and 1.5-3.0 × C ≦ Si + Al ≦ 3.5-5 0.0 ×
It has a chemical composition satisfying C and Mn + (Ni / 3) ≧ 1.0 (%), and the bake hardening amount of the steel sheet is 50M.
A high-strength cold-rolled steel sheet excellent in impact energy absorption, characterized by having Pa or more.
Si:2.0%以下、Al:0.01〜0.060%、
Mn:0.5〜4.0%、Ni:0〜5.0%、P:
0.1%以下、S:0.1%以下、N:0.01%以
下、さらにTi:0.005〜0.10%(但し、(4
8/14)N+(48/32)S+0.01以下の場合
を除く)、Nb:0.005〜0.10%、V:0.0
05〜0.10%の1種以上を、合計で0.005〜
0.10%含有し、残部はFeおよび不可避的不純物か
らなり、かつ1.5−3.0×C≦Si+Al≦3.5
−5.0×C、およびMn+(Ni/3)≧1.0
(%)、を満足する化学組成を有し、さらに鋼板の焼付
硬化量が50MPa以上であることを特徴とする衝撃エ
ネルギー吸収性に優れた高強度冷延鋼板。2. In mass%, C: 0.05 to 0.225 %,
Si: 2.0% or less, Al: 0.01 to 0.060 %,
Mn: 0.5 to 4.0%, Ni: 0 to 5.0%, P:
0.1% or less, S: 0.1% or less, N: 0.01% or less, and Ti: 0.005 to 0.10% (however, (4
8/14) N + (48/32) S + except 0.01 or less), Nb: 0.005 to 0.10%, V: 0.0
05-0.10% of one or more, 0.005-total
0.10% content, the balance consisting of Fe and unavoidable impurities, and 1.5-3.0 × C ≦ Si + Al ≦ 3.5
−5.0 × C, and Mn + (Ni / 3) ≧ 1.0
(%), A high-strength cold-rolled steel sheet excellent in impact energy absorption, characterized in that the bake hardening amount of the steel sheet is 50 MPa or more.
および5〜15%のベイナイトを含むことを特徴とする
請求項1または2に記載の衝撃エネルギー吸収性に優れ
た高強度冷延鋼板。3. A high-strength cold-rolled steel sheet excellent in impact energy absorption according to claim 1, wherein the steel sheet structure contains 5% or more of retained austenite and 5 to 15% of bainite.
する鋼片を、Ac3点以上に加熱保持してから熱間圧延
し、300〜720℃の温度範囲で巻き取り、酸洗、冷
間圧延を行った後に、連続焼鈍工程において、Ac1点
以上、Ac3点以下の温度域に加熱して再結晶させ、次
いで冷却速度10℃/s以下で700℃まで徐冷し、引
き続く冷却途中の550〜350℃の温度域で30秒以
上の保持、または100℃/分以下の冷却速度での徐冷
を行うことを特徴とする衝撃エネルギー吸収性に優れた
高強度冷延鋼板の製造方法。4. A steel slab having the chemical composition defined in claim 1 or 2 is heated and held at an Ac 3 point or higher, hot-rolled, wound in a temperature range of 300 to 720 ° C., pickled, after the cold rolling, the continuous annealing process, Ac 1 point or more, then heated to a temperature range below Ac 3 point recrystallized, following
Slowly cool to 700 ° C at a cooling rate of 10 ° C / s or less, and then hold for 30 seconds or more in the temperature range of 550 to 350 ° C during the subsequent cooling, or gradually cool at a cooling rate of 100 ° C / min or less. And a method for producing a high-strength cold-rolled steel sheet excellent in impact energy absorption.
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JP3764411B2 (en) | 2002-08-20 | 2006-04-05 | 株式会社神戸製鋼所 | Composite steel sheet with excellent bake hardenability |
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