JPS6274051A - Thin cold rolled high tensile steel sheet having baking hardenability and its production - Google Patents

Abstract

PURPOSE:To produce a thin steel sheet which has high baking hardenability and is free from deterioration with age by subjecting a steel contg. C and Mn at specified ratios to hot rolling and cold rolling then annealing the steel at a specified soaking temp. then subjecting the steel sheet to quick cooling and slow cooling under specific conditions. CONSTITUTION:The steel contg. 0.08-0.20wt% C and 1.5-3.5% Mn is subjected to hot rolling and cold rolling to a required thickness. The steel structure is composed of uniform bainite contg. <=5% ferrite or bainite structure partly contg. martensite. The cold rolled sheet is annealed within a range of holding temp. Ac3 point - Ac3+100 deg.C. The steel sheet is then quickly cooled at a cooling rate of >=20 deg.C/sec down to a 200-400 deg.C range and in succession thereof, the steel sheet is slowly cooled at a rate of <=0.5 deg.C/sec. The thin cold rolled high tensile steel sheet having >=15kgf/mm<2> baking hardenability, good workability and high strength of about >=80kgf/mm<2> is obtd. by the above- mentioned method.

Description

【発明の詳細な説明】 産業上の利用分野 この発明は自動車の単体など、成形加工の用途に供され
る高張力冷延薄鋼板およびその製造方法に関し、特に成
形７Ｊ１］工後の塗装工程において焼付は処理を受けた
際に降伏点が大きく増加するという、所謂焼付は硬化性
が著しく大きい高張力薄鋼板およびその製造方法に関す
るものである。DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a high-strength cold-rolled thin steel sheet used for forming processing such as a single unit of an automobile, and a method for manufacturing the same, particularly in the painting process after forming 7J1]. The so-called seizure, in which the yield point greatly increases when subjected to a treatment, relates to a high tensile strength thin steel sheet with extremely high hardenability and a method for manufacturing the same.

従来の技術 自動車の単体外装板等には従来から単体軽量化のために
高張力薄鋼板か広く使用されている。このような自動車
用の高張力薄鋼板としては、プレス加工で代表される成
形加工が施されることから、比較的軟質で成形加工性が
良いことが必要で轟ると同時に、自動車車体外装板等に
要求される充分な強度を有することが必要でおり、そこ
で最近では成形時には比較的軟質で市って成形後の塗装
焼付は工程で時効硬化により強度が上昇する特性を有す
る鋼板、すなわち焼付は硬化性が大きい鋼板が使用され
るようになっている。Conventional Technology High tensile strength thin steel plates have been widely used for the exterior panels of automobiles in order to reduce the weight of the unit. High-strength thin steel sheets for automobiles are required to be relatively soft and have good formability, as they undergo forming processes such as press working. Therefore, recently, steel sheets that are relatively soft during forming and whose strength increases through age hardening during the painting process after forming have been developed. Steel plates with high hardenability are now being used.

焼付は硬化性の指標となる焼付は硬化量は、一般に次の
ようにして測定される。すなわち、先ずプレス成形に相
当する２％程度の予ひずみを与えておき、その後焼付は
処理に相当するｔ７０℃ｘ２０分間の熱処理を行なう。Seizure is an index of hardenability. The amount of seize and hardening is generally measured as follows. That is, first, a prestrain of about 2%, which corresponds to press forming, is applied, and then heat treatment is performed at t70° C. for 20 minutes, which corresponds to baking treatment.

そして２％予ひずみ時の変形応力と熱処理後の降伏応力
との差を算出し、その値を焼付は硬化量とする。Then, the difference between the deformation stress at 2% pre-strain and the yield stress after heat treatment is calculated, and this value is taken as the amount of hardening by baking.

ところで従来の焼付は硬化性を有する鋼板としては種々
のものがあるが、最近では特に高い焼付は硬化性を有す
る高強度高延性鋼板とじＣ，例えば特公昭５５−４８５
７５号公報に記載されているように窒素（Ｎ＞量を高め
た高Ｎ鋼の焼入れ焼もどし、荊か知られ−Ｃｄ５つ、ま
た例えばＩ−日不金属学会報」１９　（１９８０）　Ｐ
４３９おるいは′ニー日本金属学会報」１つ（１９８０
）　Ｐｌｏ、［鉄と鋼ｊ　ＶＯＩ　６８　（１９８２）
　Ｎｏ、９．　Ｐ１３４８に記載されているような２相
粗鐵鋼板（ＤｕａｌＰｈａＳｅ鋼板）などが知られてい
る。By the way, there are various types of steel plates that have conventional baking properties, but recently, particularly high baking properties have been developed using hardenable high-strength, high-ductility steel plates such as Toji C, such as Japanese Patent Publication No. 55-485.
As described in Publication No. 75, quenching and tempering of high N steel with an increased amount of nitrogen (N>5), as well as e.g.
439 or 'Ni Bulletin of the Japan Institute of Metals' (1980)
) Plo, [Tetsu to Hagane j VOI 68 (1982)
No, 9. A dual-phase coarse steel plate (DualPhaSe steel plate) as described in P1348 is known.

発明が解決すべき問題点 従来の一般的な焼付は硬化性を有する鋼板では、焼付は
硬化■は５．、ｆ、、／’−程度に過ぎない。将に高い
焼付は硬化性を杓する前述の特公昭５５−１．８５７５
号公報記載の鋼板でも１２豹ｆ／−以下であり、またそ
の公報記載の高Ｎ鋼では＼吊の調整か容易ではなり、−
月貿のばらつきが大きいという問題かおり、ざらに引張
り強さくＴＳ＞が６０Ｋｇｆ／ｍｍ２以下に過ぎなかっ
た。一方従来の２相組織鋼板でも焼付（′ｊ硬化量は１
０Ｋｓｆ／−以下であった。また従来の鋼板においては
、焼付は硬化性をさらに高めようとすれば、湯温時効に
よる材質劣化の問題も避は得なかった。Problems to be Solved by the Invention In conventional general steel plates that have hardening properties, baking hardens ■5. , f, , /'-. The above-mentioned Japanese Patent Publication No. 55-1.8575, which generally has a high degree of hardening, has poor hardenability.
Even with the steel plate described in the publication, it is less than 12 f/-, and with the high N steel described in that publication, it is not easy to adjust the suspension.
Due to the problem of large monthly fluctuations, the tensile strength was only 60Kgf/mm2 or less. On the other hand, even with conventional dual-phase steel sheets, baking ('j hardening amount is 1
It was 0Ksf/- or less. Furthermore, in conventional steel sheets, if baking attempts to further enhance hardenability, the problem of material deterioration due to aging at hot water temperatures is unavoidable.

この発明は以上の事情を背景としてなされたもので、従
来よりも一層高い焼付は硬化性、具体的には１５に９ｆ
／ｍｍ以上の高い焼付は硬化量を示し、しかも湯温での
時効劣化がほとんどなく、かつ良加工性を有する高張力
冷延薄鋼板を提供することを目的とするものである。This invention was made against the background of the above-mentioned circumstances.
The object of the present invention is to provide a high-tensile cold-rolled thin steel sheet that has a high degree of hardening of /mm or more, has almost no aging deterioration at hot water temperatures, and has good workability.

問題点を解決するための手段 上述の目的を達成するべく本発明者等か種々実験・検討
を重ねた結果、主として冷間圧延後の焼鈍サイクルを制
御することにより、鋼板組織を従来の冷延薄鋼板では用
いられていなかったベイナイト主体の組織とすることに
よって、従来の薄鋼板では達成し得なかった焼付は硬化
１１５Ｋｓｆ／−以上の著しく高い焼付は硬化性を有し
かつ良好な加工性でしかも湯温での時効劣化の少ない薄
鋼板が得られることを見出し、この発明をなすに至った
のである。Means for Solving the Problems In order to achieve the above-mentioned object, the present inventors have conducted various experiments and studies, and found that the structure of the steel sheet can be improved by controlling the annealing cycle after cold rolling. By adopting a bainite-based structure that has not been used in thin steel sheets, it has hardenability that could not be achieved with conventional thin steel sheets. In addition, they discovered that a thin steel sheet with less aging deterioration at hot water temperatures could be obtained, leading to the creation of this invention.

具体的には、不願の第１発明の焼付は硬化性高張力冷延
薄鋼板は、重量％でＣを０．０８〜０．２０％、〜１ｎ
を１．５〜３，５％含有しかつ残部が「ｅおよび不可避
的不純物よりなり、しかも鋼組織か、フェライト量５％
以下の均一なベイナイトもしくは一部マルテンサイトを
含むべ・イナイトで偶成されていることを特徴とするも
ので市る。Specifically, the baking-hardenable high-tensile cold-rolled thin steel sheet of the first invention contains 0.08 to 0.20% C by weight and 1n.
It contains 1.5 to 3.5% of
It is characterized by being composed of the following uniform bainite or bainite containing some martensite.

また第２発明の・焼付は硬化性高張力冷延薄鋼板は、重
ｆｆ１％でＣ０．０８〜０．２０％、Ｍｎ１．５〜３．
５％のほか、１＼ｂ　０．０１〜０．１０％、ｌｉｏ、
０１〜ｏ、ｉｏ％、８５〜３０ｐｐｍのうらの１千重ま
たは２種以上を含有し、残部がＦｅｎよび不可避的不純
物よりなり、しかも鋼組織か、前記同様にフェライト量
５％以下の均一なベイナイトもしくは〜部マルテンサイ
１〜を含むベイナイトで偶成されていることを特徴とす
るものである。The baking-hardening high tensile strength cold-rolled thin steel sheet of the second invention has a weight of 1% C, 0.08 to 0.20% C, and 1.5 to 3 Mn.
In addition to 5%, 1\b 0.01-0.10%, lio,
01-0, io%, 85-30 ppm of 1,000 F or more, the remainder consists of Fen and unavoidable impurities, and is a steel structure or has a uniform ferrite content of 5% or less as described above. It is characterized by being made of bainite or bainite containing 1 to 1 part martensitic acid.

ざらに第３発明は、焼付Ｇ′ｊ硬化訃高張力冷延鋼板を
製造する方法を提供づるもので市って、重量％でＣを０
．０８〜０．２０％、Ｍｎを１．５〜３．５％含有する
鋼を常法によって熱間圧延および冷間圧延して所用の板
厚とした後に速決焼鈍を施すに必たり、焼鈍均熱温度を
８０３点以上、Ａｃ３点＋１００°Ｃ以下とし、かつ焼
鈍後の冷却過程における４００℃以下２００℃以上の温
度域内までを２０°Ｃ／　ＳｅＣ以上の冷却速度で急冷
し、引続いて０．５°Ｃ／　ＳｅＣ以上の冷却速度で徐
冷することを特徴とするものである。The third invention provides a method for manufacturing a baked G'j hardened high tensile strength cold rolled steel sheet, and the third invention provides a method for producing a high tensile strength cold rolled steel sheet with a C content of 0% by weight.
．． When steel containing 08 to 0.20% Mn and 1.5 to 3.5% Mn is hot-rolled and cold-rolled to the required thickness by a conventional method and then subjected to rapid annealing, annealing equalization is necessary. The thermal temperature is set to 803 points or higher and Ac3 point +100°C or lower, and the temperature range of 400°C or lower to 200°C or higher in the cooling process after annealing is rapidly cooled at a cooling rate of 20°C/SeC or higher, followed by 0. It is characterized by gradual cooling at a cooling rate of .5°C/SeC or higher.

作　　　用 先ずこの発明における鋼成分限定理由について説明する
。Function First, the reason for limiting the steel composition in this invention will be explained.

Ｃは０．０８％未満ではγ→αの変態速度が大きく、連
続焼鈍でフェライト量を５％以下とすることが困難であ
り、フェライト量５％以下のベイナイト主体の組織を冑
て極めて大きい焼付は硬化性を得るというこの発明の目
的が連成できなくなる。If C is less than 0.08%, the transformation rate of γ → α is high, and it is difficult to reduce the amount of ferrite to 5% or less by continuous annealing. The purpose of this invention, which is to obtain curability, cannot be achieved.

一方Ｃが０．２０％を越えればこの発明で主として対象
としている自動車用鋼板においてスポット溶接が困難と
なり、スポット溶接強度が低下する問題がある。したが
ってＣ量は０．０８〜０．２０％の範囲内とした。On the other hand, if C exceeds 0.20%, it becomes difficult to spot weld steel sheets for automobiles, which is the main object of this invention, and there is a problem that spot welding strength decreases. Therefore, the amount of C was set within the range of 0.08 to 0.20%.

Ｍｎはフェライト変態を抑制してベイナイトを出現し易
くする元素でおってこの発明の鋼板で必須の元素であり
、Ｍｎ１．５％未満では、＊めて高い焼付は硬化性か得
られない。このようにＭｎ１．５％未満で極めて高い焼
付は硬化性が得られない理由は木だ明らかではないが、
おそらくはＭｎとＣとの相互作用によるものと思われる
。一方Ｍｎが３．５％を越えてもそれ以上焼付は硬化性
は大きくならず、特に添加のメリットはない。したがっ
てＭｒＮ＆１．５〜３．５％の範囲内とした。Mn is an element that suppresses ferrite transformation and facilitates the appearance of bainite, and is an essential element in the steel sheet of the present invention.If Mn is less than 1.5%, only high hardening properties can be obtained. Although it is not clear why wood cannot be hardened with extremely high Mn of less than 1.5%,
This is probably due to the interaction between Mn and C. On the other hand, even if Mn exceeds 3.5%, the baking hardenability will not increase any further, and there is no particular advantage to adding Mn. Therefore, MrN was set within the range of 1.5 to 3.5%.

この発明の鋼板における塁本的な必須成分は上述のＣお
よびＭｎであるが、特に第２発明においては、Ｃ，Ｍｎ
のほか、Ｎ　ｂ−Ｔ　！　％　Ｂの１種または２種以上
を含有するものとする。その作用、添加量限定理由は次
の通りである。The basic essential components in the steel plate of this invention are the above-mentioned C and Mn, but especially in the second invention, C, Mn
In addition to Nb-T! %B shall be contained. The effect and reason for limiting the amount added are as follows.

Ｎｂは加工性を保ちつつ高強度化するために有効な元素
である。その効果は０．０１％以上の添加で顕著となる
がｏ、ｉｏ％ではぼ飽和するから、Ｎｂを添加する場合
の添加量は０．０１〜ｏ、ｉｏ％の範囲内とした。また
Ｔ１もその作用と添加量、限定理由はＮｂと同様である
。Nb is an effective element for increasing strength while maintaining workability. The effect becomes remarkable when the amount of Nb added is 0.01% or more, but it is nearly saturated at 0.01% or more, so the amount of Nb added is within the range of 0.01 to 0.0000%. Further, the action, addition amount, and reason for limitation of T1 are the same as those of Nb.

Ｂは極微旦でフェライト変態を抑制するに有効であるが
、５ｐｐｍ未満の添加ではその効果がなく、またその効
果は３０ｐｐｍ程度で飽和する。したがって８を添加す
る場合の添加量は５〜３０ｐｐｍの範囲内とした。Although B is effective in suppressing ferrite transformation in very small amounts, it has no effect when added at less than 5 ppm, and its effect is saturated at about 30 ppm. Therefore, when adding 8, the amount added was within the range of 5 to 30 ppm.

なあ＼ｂ、Ｔｉ、１３はそれらのうち２種または３種を
複合添加しても特に支障はなく、したがっていずれか１
種または２種以上を添加することとした。Hey\b, Ti, 13, there is no particular problem even if two or three of them are added in combination, so any one of them can be added.
We decided to add one or more seeds.

ざらにこの発明の鋼板においては、前述のように鋼成分
を限定するのみならず、鋼組織をベイナイト主体とした
ものと規定したことが極めて重要である。すなわち、フ
ェライト量が５％以下のベイナイト主体の組織とするこ
とが極めて大きい焼付は硬化性を得るために必要である
。このような事実は本発明者等の次のような実験により
見出されたものである。Roughly speaking, in the steel plate of the present invention, it is extremely important not only to limit the steel composition as described above, but also to define the steel structure to be mainly bainite. That is, extremely large baking is required to obtain a bainite-based structure with a ferrite content of 5% or less in order to obtain hardenability. This fact was discovered through the following experiments conducted by the inventors.

Ｃ０．１１％、Ｍｎ３．０％、Ｎｂ０．０４％を含有し
、残部がＦｅおよび不可避的不純物よりなる鋼を、常法
にしたがって熱間圧延、酸洗、冷間圧延し、続いて連続
焼鈍に相当する種々の条件下での熱処理を行なっ−Ｃ種
々の量のフェライト相分率（残部はベイナイト）の鋼板
を冑、それぞれ焼付は硬化量を調べたところ、フェライ
ト相分率と焼付は硬化量との間には第１図に示すような
関係が市ることが判明した。A steel containing 0.11% C, 3.0% Mn, and 0.04% Nb, with the balance consisting of Fe and unavoidable impurities, was hot rolled, pickled, and cold rolled in accordance with conventional methods, and then continuously annealed. Heat treatment was carried out under various conditions corresponding to -C. Steel plates with various amounts of ferrite phase fraction (the remainder is bainite) were examined to determine the amount of hardening in each case. It was found that there is a relationship between the amount and the amount shown in Figure 1.

第１図から明らかなように、フェライト相分率５％以下
で残部かベイナイト相であれば１５Ｋｓｆ／ｍｒ＃以上
の著りく大きい焼付は硬化量が得られる。このようにベ
イナイト相主体の組織の場合に穫めて大きな焼付は硬化
量が得られる理由は未だ明確ではないが、フェライト相
と比較してベイナイト相ははるかに多量の固溶Ｃを含有
し、また転位密度も大でおり、そのためひずみ時効後の
変形１６カもフェライト相より大きいと考えられ、この
ことからベイナイト相主体の組織ではフェライト相主体
の組織よりもひずみ時効後の変形応力が高くなること、
したがって焼付は硬化量が大きくなるものと推定される
。As is clear from FIG. 1, if the ferrite phase fraction is 5% or less and the remainder is bainite phase, a significant hardening amount of 15Ksf/mr# or more can be obtained. The reason why a larger amount of hardening is obtained in the case of a structure mainly composed of bainite phase is still not clear, but compared to the ferrite phase, the bainite phase contains a much larger amount of solid solution C, In addition, the dislocation density is large, and therefore the deformation force after strain aging is thought to be larger than that of the ferrite phase.This means that the deformation stress after strain aging is higher in a structure mainly composed of bainite phase than in a structure mainly composed of ferrite phase. thing,
Therefore, it is estimated that the amount of hardening increases with baking.

なお５％以下のフェライト相に対する残部はその全てが
均一なベイナイト相であることが最も望ましいが、一部
マルチンサイ相を含有しているべイナイト相でも実用上
は支障ない。但し後者の場合マルテンサイト相は３０％
以下が望ましい。It is most desirable that the remainder of the 5% or less ferrite phase be entirely a homogeneous bainite phase, but a bainite phase partially containing a martini phase does not pose any practical problem. However, in the latter case, the martensite phase is 30%
The following are desirable.

上述のようなベイナイト相生体の組織を得るためには、
熱間圧延および冷間圧延後の連続焼鈍条件、とくにその
冷却条件が重要である。そこで次に連続焼鈍条件につい
てその限定理由を説明する。In order to obtain the tissue of the bainite phase organism as described above,
Continuous annealing conditions after hot rolling and cold rolling, especially cooling conditions, are important. Therefore, the reasons for limiting the continuous annealing conditions will be explained next.

先ず焼鈍温度（加熱昇温後の均熱温度）はＡｃ３点以上
の温度が必要である。これは連続焼鈍後の冷却過程で急
冷を開始する前の鋼組織を均一なオーステナイト組織と
しておくために必要である。First, the annealing temperature (soaking temperature after heating and raising the temperature) needs to be at least Ac3 point. This is necessary in order to maintain the steel structure as a uniform austenite structure before starting rapid cooling in the cooling process after continuous annealing.

しかしながら８０３点＋１００　℃を越えればオーステ
ナイト組織が粗大となるため、冷却後に得られる組織も
粗大となり、材質的に望ましくなくなる。However, if the temperature exceeds 803 points +100° C., the austenite structure becomes coarse, and the structure obtained after cooling also becomes coarse, making the material undesirable.

したがって焼鈍温度はＡｃ３点以上、Ａｃ３点＋１００
°Ｃ以下とした。Therefore, the annealing temperature is 3 points Ac or higher, 3 points Ac + 100
below °C.

このようにオーステナイト化した後ハ、おる程度以上の
急冷によりフェライト変態を抑制してベイナイト変態を
促進するこが必要であり、そのたメニハ４００〜２００
′Ｃの範囲内の温度まで２０℃／Ｓｅｃ以上の冷却速度
で急冷することが必要である。第２図に、冷却速度と各
種材質との関係を小り。この実験は、Ｃ０．１３％、Ｍ
ｎ２．８％を含有し残部がＦｅおよび不可避的不純物よ
りなる１１４につい−Ｃ１常法にしたがって熱間圧延−
酸洗−冷間圧延して板厚１．０ｎｉｎとした後、８７０
°Ｃて１８０秒均熱均熱その温度から３００°Ｃまでの
冷却速度を種々変化させ、引続いて、０．５°Ｃ／　ｓ
ｅｃの冷却速度で徐冷した場合について、焼付は硬化量
、伸び、引張り強さを調べ、３００°Ｃまでの冷却速度
と各ｖｆ質との関係を第２図に示したものである。第２
図から明らかなように、３００℃までの冷却速度か２０
°Ｃ／　ＳｅＣ禾満ては焼付は硬化量が小さく、引張り
強さも低いことが判る。After turning into austenite in this way, it is necessary to suppress ferrite transformation and promote bainite transformation by rapid cooling to a temperature higher than 400 to 200.
It is necessary to perform rapid cooling to a temperature within the range of 'C at a cooling rate of 20°C/Sec or more. Figure 2 shows the relationship between cooling rate and various materials. This experiment consisted of C0.13%, M
Regarding 114 containing 2.8% n and the remainder consisting of Fe and unavoidable impurities - C1 hot rolling according to the usual method -
After pickling and cold rolling to a plate thickness of 1.0 nin, 870
°C for 180 seconds Soaking The cooling rate from that temperature to 300 °C was varied, followed by 0.5 °C/s.
For the case of slow cooling at a cooling rate of EC, the amount of hardening, elongation, and tensile strength were investigated, and the relationship between the cooling rate up to 300°C and each VF quality is shown in Figure 2. Second
As is clear from the figure, the cooling rate up to 300°C is 20°C.
It can be seen that the hardening amount is small and the tensile strength is low when baking at °C/SeC.

これは、２０　℃／　Ｓｅｃ未）菌では充分にベイナイ
ト変態が促進されなかったためで市る。したかつ−ＣＡ
ｃ３点心Ａｃ３点＋１００°Ｃに力１」熱均熱した後に
は２０℃／ＳｅＣ以上の冷却速度で急冷することが必要
で市る。This is due to the fact that bainite transformation was not sufficiently promoted in the bacteria (20°C/Sec). Shikatsu-CA
After soaking the c3 dim sum Ac3 point at +100°C for 1 hour, it is necessary to rapidly cool it at a cooling rate of 20°C/SeC or higher.

またこのような２０℃／　Ｓｅｃ以上の急冷は、４００
〜２００℃の温度域内で停止させる必要かおる。急冷停
止温度が４００°Ｃより高ければベイナイト変態が充分
に促進されず、そのため焼付は硬化性か低下し、また急
冷停止温度が高過ぎる場合、その後の徐冷でパーライト
変態が生じて低温変態相の焼もどしにより強度が低下す
る。一方急冷停止温度が低過ぎればマルテンサイトが過
剰となるとともに自己焼もどし効果が期待できず、特に
延性の劣化を招き、このような傾向は急冷停止温度が２
００℃より低い場合に顕著となる。したがって２０℃／
ｓｅｃ以上の冷却速度での急冷は４００℃以下２００℃
以上の温度域内の温度までとし、その後は徐冷する必要
がおる。In addition, such rapid cooling of 20℃/Sec or more
It is necessary to stop the process within a temperature range of ~200°C. If the quenching stop temperature is higher than 400°C, the bainite transformation will not be promoted sufficiently, resulting in a decrease in hardenability of baking, and if the quenching stop temperature is too high, pearlite transformation will occur during subsequent slow cooling, resulting in a low-temperature transformation phase. Strength decreases due to tempering. On the other hand, if the quenching stop temperature is too low, there will be excess martensite and the self-tempering effect cannot be expected, leading to deterioration of ductility in particular.
This becomes noticeable when the temperature is lower than 00°C. Therefore 20℃/
Rapid cooling at a cooling rate of sec or more is 200℃ below 400℃
It is necessary to bring the temperature to within the above temperature range, and then slowly cool it.

急冷停止後の徐冷は０．５°Ｃ／　ｓｅｃ以下の冷却速
度とする必要が必る。０．５°Ｃ／　Ｓｅｃを越える冷
却速度となれば伸びの劣化が著しく、成形加工性を損う
からである。The slow cooling after stopping the rapid cooling must be performed at a cooling rate of 0.5°C/sec or less. This is because if the cooling rate exceeds 0.5°C/Sec, the elongation deteriorates significantly and moldability is impaired.

なおＡｃ３点〜Ａｃ３点＋１００°Ｃに均熱した後の冷
却速度２０°Ｃ／　ｓｅｃ以上の急冷時の冷却速度の上
限は特に定めないが、冷却速度か高過ぎればマルテンサ
イトの生成量が多くなってしまう。マルテンサイトの過
剰な生成を抑えてベイナイト主体の組織とするためには
、成分にも依存するが概ねｉ　ｏ　ｏ　’ｃ／ＳａＣ程
度以下の冷却速度とすることが好ましい。There is no particular upper limit to the cooling rate during rapid cooling of 20°C/sec or more after soaking from Ac3 point to Ac3 point + 100°C, but if the cooling rate is too high, a large amount of martensite will be produced. turn into. In order to suppress excessive production of martensite and obtain a structure consisting mainly of bainite, it is preferable to set the cooling rate to about io o'c/SaC or less, although it depends on the components.

以上のように連続焼鈍条件を適切に設定することによっ
て、フェライト量５％以下の均一なベイナイトまたは一
部マルテンサイトを含むベイナイト主体の組織を有する
、１５Ｋｓｆ、／ｒｍ以上の焼付は硬化量でしかも引張
り強さも高くかつ良加工性の高張力冷延鋼板を得ること
ができる。By appropriately setting the continuous annealing conditions as described above, baking of 15Ksf/rm or more with a uniform bainite structure with a ferrite content of 5% or less or a bainite-based structure containing some martensite can be achieved with a hardening amount. A high tensile strength cold rolled steel sheet with high tensile strength and good workability can be obtained.

実施例 第１表のＡ〜Ｈに示す各種成分組成の鋼を溶製し、常法
にしたがって仕上圧延温度８００〜９００°Ｃで熱間圧
延し、４５０〜６００　℃て巻取った後、酸洗し、ざら
に冷間圧延を施して板厚１．００　ｍｍの冷延鋼板とし
た。次いで第２表中に示す種々の条件で連続焼鈍し、焼
鈍−冷却後の材質を調査した。またフェライト分率（Ｖ
ｆ　）を調べるとともに、スポット溶接継手強度も調べ
た。その結果を第２表に示す。なお第１表中において「
−次冷却速度」は均熱温度から一次冷却停止温度までの
平均冷却速度、「二次冷却速度」は−次冷却速度停止温
度から湯温近１カまでの平均冷却速度を表わす。Examples Steels having various compositions shown in Table 1, A to H, were melted, hot rolled at a finish rolling temperature of 800 to 900°C according to a conventional method, and coiled at 450 to 600°C. The sample was washed and roughly cold-rolled to obtain a cold-rolled steel plate with a thickness of 1.00 mm. Next, continuous annealing was performed under various conditions shown in Table 2, and the material properties after annealing and cooling were investigated. Also, the ferrite fraction (V
f), and the spot weld joint strength was also investigated. The results are shown in Table 2. In Table 1, “
``Secondary cooling rate'' represents the average cooling rate from the soaking temperature to the primary cooling stop temperature, and ``secondary cooling rate'' represents the average cooling rate from the -second cooling rate stop temperature to one point near the hot water temperature.

第２表において、成分組成がこの発明の範囲内の鋼Ａ（
ＡＣ３点温度約８３０℃）に対し連続焼鈍をＡｃ３点未
満の均熱温度で施したＮ０１３の場合および３００℃ま
での冷却速度か５°Ｃ／　Ｓｅｃと低かったＮｏ、　４
の場合は、いずれもフェライト分率が８０％、８５？６
と高く、充分な焼付は硬化量が１ｑられなかった。In Table 2, steel A (
In the case of N013, which was subjected to continuous annealing at a soaking temperature below AC3 points (AC3 point temperature of approximately 830°C), and the cooling rate to 300°C was as low as 5°C/Sec, No. 4
In both cases, the ferrite fraction is 80%, 85?6
The amount of hardening could not be reduced by 1q due to sufficient baking.

また同じ鋼Ａに対し急冷後の２次冷却速度が３℃／　Ｓ
ｅｃと高かったＮｏ、　２の場合は、伸びが充分ではな
く、加工性に劣ることが判明した。−力成分組成がこの
発明の範囲内のＩＢ（ＡＣ３点約８２０℃）について、
連続焼鈍を＾Ｃ３点＋１００°Ｃを越える均熱温度で施
したＮ０１６の場合は伸びが低く、加工性が劣ることが
判明した。ざらに鋼中のＣＭが０．２５％と高い鋼Ｅの
場合（Ｎｏ、９＞、製造条件はこの発明の範囲内でもス
ポット溶接強度か不足することが判明した。またＭｎ童
が１．００％と低い鋼Ｆの場合（Ｎｏ、１０）およびＣ
倣が０．０５％と低い鋼Ｇ（Ｎｏ、１２）には、いずれ
もフェライト分率が高く、充分な焼付は硬化量が得られ
ず、また強度も低かった。そしてこの発明の成分範囲内
の８１３について急冷佇止温曳（Ｔ２）か４００°Ｃよ
り８１い場合（Ｎ０．１１＞にも、）１ライｌ−分率が
高く、光分な焼付は硬化量が得られなかった。Also, for the same steel A, the secondary cooling rate after quenching was 3℃/S
In the case of No. 2, which had a high ec, it was found that the elongation was not sufficient and the workability was poor. -For IB (AC 3 points approximately 820°C) whose force component composition is within the scope of this invention,
It was found that N016, which was subjected to continuous annealing at a soaking temperature exceeding ^C3 point +100°C, had low elongation and poor workability. In the case of steel E, which has a high CM content of 0.25% (No. 9), it was found that the spot welding strength was insufficient even though the manufacturing conditions were within the scope of this invention. Also, the Mn temperature was 1.00%. In the case of steel F as low as % (No, 10) and C
Steel G (No. 12) with a low profile of 0.05% all had a high ferrite fraction, could not be hardened sufficiently by baking, and had low strength. For 813 within the composition range of this invention, when the quenching temperature (T2) is lower than 400°C (also at N0.11), the 1 lye l-fraction is high and the light baking is hardened. I couldn't get the quantity.

これに対し、成分組成がこの発明条１′４を満たし、か
つＶ７条件もＪの発ｌ３１−１を渦だ万場合（Ｎ０．１
、Ｎｏ。On the other hand, if the component composition satisfies this invention article 1'4, and the V7 condition is also a vortex for the emission 131-1 of J (N0.1
, No.

５、ト！ｏ、　７、陥、８、Ｎｏ、　１３　＞に（よ、
いずれも則組械がフェライト量５％以■の・＼ゴナイト
士体の粗織となり、こわらの場合いずれも１！’Ａｆ／
−以上の光分な焼付は硬化量が１ｑられ、かつ伸びも充
分て加工性が良好−（゛あり、しかも強度的にも引張強
さ８０Ｖ／−以上の高強度が冑られた。またスポラ１〜
溶接における強度不足も生じなかった。5. To! o, 7, fall, 8, No, 13 >ni(yo,
In both cases, the regular structure is a coarse weave of gonite body with a ferrite content of 5% or more, and in the case of stiffness, it is 1! 'Af/
- With the above light baking, the hardening amount was 1q, and the elongation was sufficient, resulting in good workability. 1~
There was no lack of strength in welding.

発明の効宋 以上の説明で明らかなように、この発明によれば、焼付
は硬化量が１５Ｋｇｆ／−一以上と、慢めて大きい焼付
は硬化性を有し、しかも良加工ｉ生で８０’ｐｆ　、／
”　ｔｗ？以上の高強度を有する高張力冷延薄銅板か得
られ、したがって自ａｎのドアインパクトビームなと、
成形加工後に塗装焼付けか行なわれる用途であってしか
も高強度が要求される部平、４１：適用して■益なもの
である。Effects of the Invention Song As is clear from the above explanation, according to this invention, the hardening amount of the baking is 15 kgf/-1 or more, and the baking has a large hardening property, and moreover, the hardening amount is 80 kgf/-1 or more with good machining. 'pf, /
We can obtain high-tensile cold-rolled thin copper sheets with a high strength of over 20%, and therefore our own door impact beams.
41: It is advantageous to apply it to applications where painting is baked after molding and high strength is required.

【図面の簡単な説明】[Brief explanation of drawings]

第１図はフェライト相分率（残部ベイナイト）と焼付は
硬化量との関係を示す相関図、第２図は連続焼鈍におけ
る均熱後の３ＱＯ°Ｃまでの冷却速度と材質（ｆｉ付は
硬化量、伸び、引張強ざ）との関係を示す相関図で市る
。Figure 1 is a correlation diagram showing the relationship between the ferrite phase fraction (remaining bainite) and hardening amount. Figure 2 is a correlation diagram showing the relationship between the ferrite phase fraction (remaining bainite) and the amount of hardening. A correlation diagram showing the relationship between the weight, elongation and tensile strength.

Claims (3)

【特許請求の範囲】[Claims] （１）重量％でＣ　０．０８〜０．２０％、Ｍｎ　１．
５〜３．５％を含有し、残部がＦｅおよび不可避的不純
物からなる成分組成を有し、かつ鋼組織が、フェライト
量５％以下の均一なベイナイトもしくは一部マルテンサ
イトを含むベイナイトで構成され、焼付け硬化量が１５
Ｋｇｆ／ｍｍ＾２以上である焼付け硬化性高張力冷延薄
鋼板。(1) C 0.08-0.20% by weight, Mn 1.
5 to 3.5%, with the remainder consisting of Fe and unavoidable impurities, and the steel structure is composed of uniform bainite with a ferrite content of 5% or less or bainite partially containing martensite. , baking hardening amount is 15
A bake-hardenable high tensile strength cold-rolled thin steel sheet having a tensile strength of Kgf/mm^2 or more. （２）重量％でＣ　０．０８〜０．２０％、Ｍｎ　１．
５〜３．５％を含有し、かつＮｂ　０．０１〜０．１０
％、Ｔｉ　０．０１〜０．１０％、Ｂ　５〜３０ｐｐｍ
のうちから選ばれた１種以上を含有し、残部がＦｅおよ
び不可避的不純物よりなる成分組成を有し、かつ鋼組織
が、フェライト量５％以下の均一なベイナイトもしくは
一部マルテンサイトを含むベイナイトで構成され、焼付
け硬化量が１５Ｋｇｆ／ｍｍ＾２以上である焼付け硬化
性高張力冷延薄鋼板。(2) C 0.08-0.20% by weight, Mn 1.
Contains 5-3.5% and Nb 0.01-0.10
%, Ti 0.01-0.10%, B 5-30ppm
Bainite containing one or more selected from the following, with the balance consisting of Fe and unavoidable impurities, and whose steel structure is a uniform bainite with a ferrite content of 5% or less or a part of martensite. A bake-hardenable high-tensile cold-rolled thin steel sheet having a bake-hardening amount of 15 Kgf/mm^2 or more. （３）重量％でＣ　０．０８〜０．２０％、Ｍｎ　１．
５〜３．５％を含有する鋼に熱間圧延および冷間圧延を
施して所要の板厚とした後、連続焼鈍するにあたり、焼
鈍均熱温度をＡｃ＿３点以上、Ａｃ＿３点＋１００℃以
下の範囲内とし、かつ焼鈍後の冷却過程において２００
℃以上４００℃以下の温度域内の温度までを２０℃／ｓ
ｅｃ以上の冷却速度で急冷し、引続きその温度から０．
５℃／ｓｅｃ以下の冷却速度で徐冷することを特徴とす
る焼付け硬化性高張力冷延鋼板の製造方法。(3) C 0.08-0.20% by weight, Mn 1.
After hot-rolling and cold-rolling the steel containing 5 to 3.5% to the required thickness, when continuously annealing, the annealing soaking temperature is in the range of Ac_3 points or more and Ac_3 points + 100 ° C or less. 200% in the cooling process after annealing.
20℃/s for temperatures within the temperature range of ℃ to 400℃
Rapid cooling is performed at a cooling rate of EC or higher, and then the temperature is reduced to 0.
A method for producing a bake-hardenable high-tensile cold-rolled steel sheet, comprising slow cooling at a cooling rate of 5° C./sec or less.