JPH07207413A - Cold rolled steel sheet of high-strength composite structure having excellent workability and tensile strength of 45 to 65kgf/mm2 and its production - Google Patents
Cold rolled steel sheet of high-strength composite structure having excellent workability and tensile strength of 45 to 65kgf/mm2 and its productionInfo
- Publication number
- JPH07207413A JPH07207413A JP176194A JP176194A JPH07207413A JP H07207413 A JPH07207413 A JP H07207413A JP 176194 A JP176194 A JP 176194A JP 176194 A JP176194 A JP 176194A JP H07207413 A JPH07207413 A JP H07207413A
- Authority
- JP
- Japan
- Prior art keywords
- less
- steel sheet
- strength
- austenite
- weight
- 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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Links
Classifications
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02P—CLIMATE CHANGE MITIGATION TECHNOLOGIES IN THE PRODUCTION OR PROCESSING OF GOODS
- Y02P10/00—Technologies related to metal processing
- Y02P10/20—Recycling
Landscapes
- Heat Treatment Of Steel (AREA)
- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
【０００１】[0001]
【産業上の利用分野】本発明は自動車、建築、電機など
の産業分野で使用される加工性に優れた高強度複合組織
冷延鋼板およびその製造方法に関するものである。さら
に詳しくは、４５ｋｇｆ／ｍｍ2 以上６５ｋｇｆ／ｍｍ
2 以下の引張強さをもつ加工性に優れた高強度複合組織
冷延鋼板および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 high-strength cold-rolled steel sheet having a high-strength composite structure, which is used in industrial fields such as automobiles, construction, and electric machines and has excellent workability. More specifically, 45 kgf / mm 2 or more 65 kgf / mm
The present invention relates to a high-strength composite cold-rolled steel sheet having a tensile strength of 2 or less and excellent workability, and a method for producing the same.
【０００２】[0002]
【従来の技術】近年、自動車の快適性、安全性に加えて
車体の軽量化に対する要求が大きくなってきている。こ
れは地球規模で考えた省エネルギーおよび環境問題に対
する要求であり、軽量化による車両燃費の向上とＣＯ2
などの有害排気ガスの減少をその目的としている。この
ような目的を達成させるためには車体構造に利用される
材料の強度を向上させその材料厚みを減少させるか、新
たな低比重の材料を用いることなどが必要である。2. Description of the Related Art In recent years, there has been an increasing demand for vehicle body weight reduction in addition to vehicle comfort and safety. This is a request for energy conservation and environmental issues considered globally, improvement of vehicle fuel efficiency by weight reduction and CO 2
Its purpose is to reduce harmful exhaust gas. In order to achieve such an object, it is necessary to improve the strength of the material used for the vehicle body structure and reduce the material thickness, or to use a new low specific gravity material.
【０００３】新たな低比重材料（例えばＡｌ、Ｍｇ等）
を利用する場合、価格、安定供給量の観点から、従来車
体構成材料の中心として利用されてきた鋼板と共存状態
での利用が前提となると考えられる。この場合に最も問
題となるのはスクラップのリサイクルであり、他材料と
混合した鋼板スクラップはその後の利用では多くのエネ
ルギー、コストを費やして再利用される必要がある。従
って地球全体としてのエネルギーミニマム、環境保持を
目指す上では特殊な部位を除いては、単一材料（すなわ
ち鋼材）での軽量化対策が非常に重要となり、鋼材のよ
り一層の高強度化が期待されている。New low specific gravity materials (eg Al, Mg, etc.)
From the viewpoints of price and stable supply, it is premised that the steel sheet is used in the coexistence state with the steel sheet that has been conventionally used as the center of the body material. In this case, the most problematic issue is scrap recycling, and the steel plate scrap mixed with other materials needs to be reused with a large amount of energy and cost for subsequent use. Therefore, in order to maintain the minimum energy and environment of the earth as a whole, excluding special parts, it is very important to take measures to reduce the weight with a single material (that is, steel), and it is expected that the strength of steel will be even higher. Has been done.
【０００４】上記要求に加えて、車体構成部位の一体成
形は、製造工程の簡略化、連続化のために重要な技術的
要請と考えられる。このような近代化されつつある成形
工程で用いられる鋼材の中で、特に薄鋼板を考えると、
良好な成形性を有することがその鋼板の選択基準とな
る。薄鋼板の成形性の良否は、伸び、ランクフォードの
塑性歪比（ｒ値）、加工硬化指数（ｎ値）や降伏強度で
判断され、複雑な部品の一体成形のためには伸びやｎ値
が高いことが一つの必要条件となる。In addition to the above-mentioned requirements, the integral molding of vehicle body constituent parts is considered to be an important technical requirement for simplification and continuation of the manufacturing process. Among the steel materials used in such modernizing forming process, especially considering thin steel plate,
Having good formability is the selection criterion for the steel sheet. The formability of thin steel sheet is judged by elongation, Rankford's plastic strain ratio (r value), work hardening index (n value) and yield strength. For integral molding of complex parts, elongation and n value Is a high requirement.
【０００５】伸びやｎ値の大きな鋼板の例としては、従
来フェライトとマルテンサイト２相組織のＤｕａｌ Ｐ
ｈａｓｅ（ＤＰ）鋼が知られている。ＤＰ鋼は特公昭５
６−１８０５１号公報や特公昭５９−４５７３５号公報
などで示されているように５０〜８０ｋｇｆ／ｍｍ2 で
最大３０〜３５％程度の全伸びを得ることができる。し
かしながら従来比較的低強度（３５〜４５ｋｇｆ／ｍｍ
2 ）の薄鋼板が用いられている様な複雑な加工を要求さ
れる部位への適用では十分な強度−延性バランスとは言
い難い。As an example of a steel sheet having a large elongation and a large n value, a conventional dual-phase structure of ferrite and martensite dual P
Hase (DP) steel is known. DP Steel is Japanese Patent Sho5
As shown in Japanese Patent Publication No. 6-18051 and Japanese Patent Publication No. 59-45735, a maximum total elongation of about 30 to 35% can be obtained at 50 to 80 kgf / mm 2 . However, it has a relatively low strength (35-45 kgf / mm)
It cannot be said that the strength-ductility balance is sufficient when applied to the parts requiring complicated processing such as the thin steel plate used in 2 ).
【０００６】この材質をさらに向上させるための方法と
して最近、フェライト、ベイナイトおよびオーステナイ
トの混合組織（もしくは一部マルテンサイトを含む）を
ミクロ組織として持つ高強度複合組織鋼板が提案されて
いる。この鋼板は室温で残留しているオーステナイトが
成形時にマルテンサイトに変態することによって高い延
性を示す「変態誘起塑性」を利用するものである。変態
誘起塑性を利用した鋼はＴＲＩＰ鋼として知られている
ように、例えばＺａｃｋａｙら（Ｖ．Ｆ．Ｚａｃｋａｙ
ら：Ｔｒａｎｓ．ＡＳＭ ｖｏｌ．６０（１９６７）２
５２）が示すように７０ｋｇｆ／ｍｍ2 以上で最大９０
％程度の高延性が達成されている。しかしながら、この
様なＴＲＩＰ鋼は高価な合金元素を大量に添加する必要
があるなど必ずしもここでの要求に合致しない。この様
な問題を解決したものとして、特開昭６１−１５７６２
５号公報に自動車用鋼板の様な大量生産が前提となる廉
価な用途に合致した薄鋼板の製造方法が示されている。
この先願発明で述べられている技術は、Ｓｉの添加によ
って炭化物の析出を抑制し、低温でのフェライト変態
（ベイナイト変態）を進行させることによって、未変態
オーステナイト中に効果的に炭素を濃化させ、オーステ
ナイトを安定化させるものである。これらの従来技術は
引張強さＴＳ＞６５ｋｇｆ／ｍｍ2 の高強度鋼板に関す
るものが大部分であるが、自動車用の鋼板として利用さ
れる場合には一般にプレス成形法が利用されることか
ら、ポンチ・ダイスの型の摩耗や形状凍結性、プレス機
本体の荷重能力等から積極的に利用されるには到ってい
ないのが現状である。As a method for further improving this material, a high strength composite structure steel sheet having a microstructure of a mixed structure of ferrite, bainite and austenite (or partly containing martensite) has been proposed. This steel sheet utilizes "transformation-induced plasticity" which shows high ductility by transforming austenite remaining at room temperature into martensite during forming. Steels that utilize transformation-induced plasticity are known as TRIP steels, for example, Zackay et al. (VF Zackay).
Et al: Trans. ASM vol. 60 (1967) 2
52) shows that the maximum is 90 at 70 kgf / mm 2 or more.
%, High ductility has been achieved. However, such TRIP steel does not always meet the requirements here, such as the need to add a large amount of expensive alloying elements. As a solution to such a problem, Japanese Unexamined Patent Publication No. 61-15762.
Japanese Unexamined Patent Publication No. 5 discloses a method for manufacturing a thin steel sheet, such as an automobile steel sheet, which is suitable for a low-priced application that is premised on mass production.
The technology described in the invention of this prior application suppresses the precipitation of carbides by adding Si and advances ferrite transformation (bainite transformation) at a low temperature to effectively enrich carbon in untransformed austenite. , Stabilizes austenite. Most of these conventional techniques relate to high-strength steel sheets having a tensile strength TS> 65 kgf / mm 2 , but when they are used as steel sheets for automobiles, press forming methods are generally used. -Currently, it has not been actively used due to wear of die dies, shape freezeability, load capacity of the press body, etc.
【０００７】[0007]
【発明が解決しようとする課題】ＳｉとＭｎの添加によ
り鋼材中のオーステナイトの安定化をはかり、ＴＳが６
５ｋｇｆ／ｍｍ2 以下の低強度のＴＲＩＰ鋼を製造する
方法については報告されているが、例えば特開平１−１
６８８１９号公報ではＳｉを２重量％以上添加した０．
０８重量％Ｃ鋼で残留オーステナイト量を１２％とした
ＴＳ＝６２ｋｇｆ／ｍｍ2 の鋼板が製造されるとしてい
るが、この鋼の炭素量で１２％のオーステナイトを残留
させた場合には残留オーステナイト中のＣ濃度は最高で
も０．６７重量％となり、加工に対する安定性が非常に
低くなり、安定して高加工性を得ることは困難である。
また、特開昭６４−２５９２１号公報ではＳｉとＭｎを
共に１重量％以上含む場合のみ報告されており、ＴＳ≦
６５ｋｇｆ／ｍｍ2 の強度範囲のＴＲＩＰ鋼およびその
製造方法には言及していない。従って、加工安定性に優
れた残留オーステナイトを含み良好な加工性を示す４５
ｋｇｆ／ｍｍ2 以上６５ｋｇｆ／ｍｍ2 以下の強度の鋼
板とその製造方法を規定する合金添加や製造方法につい
ては未だ不明である。The addition of Si and Mn stabilizes the austenite in the steel material, and TS is 6
A method for producing a TRIP steel having a low strength of 5 kgf / mm 2 or less has been reported.
In Japanese Patent No. 68819, the addition of Si in an amount of 2% by weight or more.
Although it is said that a steel sheet of TS = 62 kgf / mm 2 in which the amount of retained austenite is 12% with 08 wt% C steel is produced, when 12% of austenite is retained by the carbon amount of this steel, the residual austenite is The maximum C concentration is 0.67% by weight, and the stability against processing is extremely low, and it is difficult to stably obtain high processability.
Further, JP-A 64-25921 reports only when both Si and Mn are contained in an amount of 1% by weight or more, and TS ≦
No mention is made of TRIP steel in the strength range of 65 kgf / mm 2 and its manufacturing method. Therefore, it contains retained austenite excellent in processing stability and exhibits good processability.
it is still unclear alloying and manufacturing methods for defining the steel sheet and a manufacturing method thereof kgf / mm 2 or more 65 kgf / mm 2 or less intensity.
【０００８】本発明は、合金添加量および組み合わせを
適正に選択し、最適のミクロ組織にコントロールするこ
とによって効率よく引張強さが４５ｋｇｆ／ｍｍ2 以上
６５ｋｇｆ／ｍｍ2 以下の加工性に優れた高強度複合組
織冷延鋼板とその製造方法を提供することを目的として
いる。[0008] The present invention is properly select the amount and combination additive alloys, high efficiency tensile strength by controlling the optimum microstructure and excellent 45 kgf / mm 2 or more 65 kgf / mm 2 or less workability It is an object of the present invention to provide a cold-rolled steel sheet having a high strength composite structure and a manufacturing method thereof.
【０００９】[0009]
【課題を解決するための手段】本発明者らはＣ、Ｓｉ、
Ａｌ、Ｍｎ、Ｃｒを添加した種々の鋼に対して、成分お
よび製造条件が加工性に及ぼす影響について調査した。
その結果、下記の要旨の本発明によって上記の目的が達
成できることを見出した。 （１）重量％で、 Ｃ ：０．０４％以上０．２３％以下 Ｓｉ：２．５％以下 Ａｌ：２．０％以下 Ｍｎ：２．０％以下 Ｃｒ：２．０％以下 の範囲で、 Ｃｅｑ＝％Ｃ＋０．０６３５％Ｓｉ＋０．０２４７％Ｍ
ｎ＋０．０１２３％Ｃｒ で表現される炭素等量Ｃｅｑが０．１１重量％以上０．
２５重量％以下であり、且つＡｌとＳｉの和が０．６重
量％以上で、 Ｍｎｅｑ＝％Ｍｎ＋０．５２％Ｃｒ で表現されるＭｎ等量Ｍｎｅｑが０．６重量％以上、
２．５重量％以下であり、さらに不可避的な不純物を含
む鋼において、最終的なミクロ組織をフェライト、ベイ
ナイト、残留オーステナイトの３相もしくは一部マルテ
ンサイトを含む４相とし、主相であるフェライトの占積
率を６０％以上、マルテンサイトの占積率を３％以下、
オーステナイトの占積率をＣ重量％で除した値が３５以
上１１０以下であることを特徴とする加工性に優れた引
張強さ４５〜６５ｋｇｆ／ｍｍ2 の高強度複合組織冷延
鋼板。The present inventors have found that C, Si,
For various steels to which Al, Mn, and Cr were added, the effects of the components and manufacturing conditions on workability were investigated.
As a result, they have found that the above-mentioned objects can be achieved by the present invention having the following gist. (1) In% by weight, C: 0.04% or more and 0.23% or less Si: 2.5% or less Al: 2.0% or less Mn: 2.0% or less Cr: 2.0% or less , Ceq =% C + 0.0635% Si + 0.0247% M
Carbon equivalent Ceq expressed by n + 0.0123% Cr 2 is 0.11% by weight or more and 0.1.
25 wt% or less, the sum of Al and Si is 0.6 wt% or more, and Mn equivalent Mneq represented by Mneq =% Mn + 0.52% Cr is 0.6 wt% or more,
In steel containing 2.5% by weight or less and inevitable impurities, the final microstructure is ferrite, bainite, retained austenite, or three phases, or some phases containing martensite, and the main phase is ferrite. Occupancy rate of 60% or more, martensite occupancy rate of 3% or less,
A high-strength composite cold-rolled steel sheet having a tensile strength of 45 to 65 kgf / mm 2 and having excellent workability, wherein the value obtained by dividing the space factor of austenite by C weight% is 35 or more and 110 or less.
【００１０】（２）主相であるフェライト粒の冷間圧延
方向の粒径と板厚方向の粒径の比（長径／短径比）が
１．２５以上１．８以下であることを特徴とする前項１
記載の加工性に優れた引張強さ４５〜６５ｋｇｆ／ｍｍ
2 の高強度複合組織冷延鋼板。 （３）重量％で、 Ｃ ：０．０４％以上０．２３％以下 Ｓｉ：２．５％以下 Ａｌ：２．０％以下 Ｍｎ：２．０％以下 Ｃｒ：２．０％以下 の範囲で、 Ｃｅｑ＝％Ｃ＋０．０６３５％Ｓｉ＋０．０２４７％Ｍ
ｎ＋０．０１２３％Ｃｒ で表現される炭素等量Ｃｅｑが０．１１重量％以上０．
２５重量％以下であり、且つＡｌとＳｉの和が０．６重
量％以上で、 Ｍｎｅｑ＝％Ｍｎ＋０．５２％Ｃｒ で表現されるＭｎ等量Ｍｎｅｑが０．６重量％以上、
２．５重量％以下であり、さらに不可避的な不純物を含
む鋼を、鋳造後一旦室温まで冷却するかもしくは冷却す
ることなしに熱延し、３５０℃から７５０℃の範囲で巻
取った後、３５〜８５％の冷延圧下率の冷延を施し、Ａ
ｃ1 以上Ａｃ3 以下の温度に３０秒以上５分以下の時間
加熱し、その後１℃／秒以上１０℃／秒以下の冷却速度
で５５０℃以上７２０℃以下の温度まで冷却し、引き続
いて１０℃／秒以上２００℃／秒以下の冷却速度で２５
０℃以上５００℃以下まで冷却した後、３００℃以上５
００℃以下の温度範囲で１５秒以上１５分以下保持し、
室温まで冷却することを特徴とする加工性に優れた引張
強さ４５〜６５ｋｇｆ／ｍｍ2 の高強度複合組織冷延鋼
板の製造方法。(2) The ratio (major diameter / minor diameter ratio) of the grain size in the cold rolling direction and the grain size in the plate thickness direction of the ferrite grains as the main phase is 1.25 or more and 1.8 or less. And the preceding paragraph 1
Tensile strength of 45 to 65 kgf / mm with excellent workability
2. High strength composite structure cold rolled steel sheet. (3) In% by weight, C: 0.04% or more and 0.23% or less Si: 2.5% or less Al: 2.0% or less Mn: 2.0% or less Cr: 2.0% or less , Ceq =% C + 0.0635% Si + 0.0247% M
Carbon equivalent Ceq expressed by n + 0.0123% Cr 2 is 0.11% by weight or more and 0.1.
25 wt% or less, the sum of Al and Si is 0.6 wt% or more, and Mn equivalent Mneq represented by Mneq =% Mn + 0.52% Cr is 0.6 wt% or more,
Steel containing not more than 2.5% by weight and unavoidable impurities is cooled to room temperature after casting, or hot-rolled without cooling, and wound in the range of 350 ° C to 750 ° C. Cold rolling with a cold rolling reduction of 35 to 85%
It is heated to a temperature of c 1 or more and Ac 3 or less for 30 seconds or more and 5 minutes or less, and then cooled to a temperature of 550 ° C. or more and 720 ° C. or less at a cooling rate of 1 ° C./second or more and 10 ° C./second or less, and then 10 25 at a cooling rate of ℃ / sec or more and 200 ℃ / sec or less
After cooling to 0 ℃ to 500 ℃, 300 ℃ to 5 ℃
Hold for 15 seconds or more and 15 minutes or less in the temperature range of 00 ° C or less,
A method for producing a high-strength composite cold-rolled steel sheet having a tensile strength of 45 to 65 kgf / mm 2 and excellent in workability, which is characterized by cooling to room temperature.
【００１１】[0011]
【作用】以下に発明の各要素についての作用の詳細を述
べる。まず成分範囲規定の理由について述べる。 Ｃ：Ｃは他の高価な合金元素を用いることなくオーステ
ナイトを安定化させ、室温で残留させるために利用する
本発明で最も重要な元素の一つである。熱処理によって
オーステナイトからフェライトへの変態を利用し、オー
ステナイト中の炭素濃度を高めることでオーステナイト
の安定化がはかれるが、平均Ｃ量が０．０４重量％未満
では最終的に得られる残留オーステナイト占積率が高々
２〜３％であり十分なＴＲＩＰ効果が期待できないため
にこれをＣ添加の下限とした。平均Ｃ量が増加するに従
って得られる最大残留オーステナイト占積率は増加する
が、鋼板の焼き入れ性も上昇するためにＣ＞０．２３重
量％では他の合金添加元素をどの様に調整しても６５ｋ
ｇｆ／ｍｍ2 以下の強度を得ることが困難となる。従っ
てこれをＣ添加の上限とした。The operation of each element of the invention will be described in detail below. First, the reason for defining the component range will be described. C: C is one of the most important elements used in the present invention for stabilizing austenite without using other expensive alloying elements and allowing it to remain at room temperature. Utilizing the transformation from austenite to ferrite by heat treatment to stabilize the austenite by increasing the carbon concentration in the austenite, but if the average C content is less than 0.04% by weight, the residual austenite space factor finally obtained Is at most 2 to 3% and a sufficient TRIP effect cannot be expected, so this was made the lower limit of C addition. The maximum retained austenite space factor obtained as the average C content increases, but the hardenability of the steel sheet also increases. Therefore, at C> 0.23% by weight, other alloy additive elements should be adjusted. Also 65k
It becomes difficult to obtain strength of gf / mm 2 or less. Therefore, this was set as the upper limit of C addition.
【００１２】また、鋼板の強度を４５ｋｇｆ／ｍｍ2 以
上、６５ｋｇｆ／ｍｍ2 以下とするためには合金添加元
素量で補正したＣ等量が適正な範囲にあることが必要で
ある。すなわち、合金元素添加量で補正した（１）式 Ｃｅｑ＝％Ｃ＋０．０６３５％Ｓｉ＋０．０２４７％Ｍｎ ＋０．０１２３％Ｃｒ （１） が０．１１重量％以上０．２５重量％以下である時のみ
上記の強度範囲の鋼板が得られることからこれをＣ等量
の上限および下限とした。Further, the strength of the steel sheet 45 kgf / mm 2 or more, in order to 65 kgf / mm 2 or less is necessary that C equal volume corrected by the alloying element content is in the proper range. That is, only when the formula (1) corrected by the addition amount of alloying element Ceq =% C + 0.0635% Si + 0.0247% Mn + 0.0123% Cr (1) is 0.11% by weight or more and 0.25% by weight or less. Since a steel plate in the above strength range was obtained, this was made the upper and lower limits of the C equivalent.
【００１３】Ａｌ、Ｓｉ：ＡｌとＳｉはオーステナイト
を室温でも安定なほど炭素濃化させるために重要な添加
元素である。鋼板をフェライト／オーステナイト２相域
に加熱し、冷却時にフェライト変態を進行させることに
よってオーステナイト中に炭素を濃化させることが本発
明の技術の中心であるが、フェライト変態の進行と共に
（従ってオーステナイト中の炭素濃度の上昇と共に）炭
化物の生成が起こり易くなり、高温ではパーライト、低
温では上部ベイナイトが生成されるようになり、オース
テナイト中の全炭素量を減少させ、結果として残留オー
ステナイト量を減少させることとなる。ＡｌとＳｉはよ
く知られているように炭化物（ここではセメンタイト）
に固溶しないために炭化物の生成を著しく遅らせる働き
がある。これにより炭化物の形で炭素原子を浪費するこ
となく効率よいオーステナイトへの炭素濃化を可能にす
る。この働きのためにはＡｌとＳｉの添加量の合計が
０．６重量％以上であることが不可欠なのでこれをＡｌ
とＳｉの添加量の合計の下限とした。Ｓｉはこのときフ
ェライト中に固溶し、フェライトを強化することから、
不必要に多量の添加は鋼板の強度の不必要な上昇や加工
性・靱性の劣化をもたらす。従ってその添加量を２．５
％以下と限定した。またＡｌの場合にも不必要に多量の
添加がなされた場合には加工性・靱性の劣化をもたらす
ことから添加量の上限を２．０重量％に制限した。Ａｌ
は鋼板の強度をほとんど上昇させないので（１）式のＣ
ｅｑには含まれないが、Ｓｉは鋼板の強度を上げるの
で、他の添加元素との関係で（１）式を満足する量に制
限する必要がある。Al, Si: Al and Si are important additional elements for carbon concentration so that austenite is stable even at room temperature. Although the core of the technique of the present invention is to concentrate carbon in austenite by heating the steel sheet to the ferrite / austenite two-phase region and advancing the ferrite transformation at the time of cooling, as the ferrite transformation progresses (therefore, in the austenite). Carbide formation (with increasing carbon concentration), pearlite is formed at high temperature and upper bainite is formed at low temperature, which reduces the total carbon content in austenite and consequently the retained austenite content. Becomes As is well known, Al and Si are carbides (here, cementite)
Since it does not form a solid solution, it has the function of significantly delaying the formation of carbides. This enables efficient carbon enrichment to austenite without wasting carbon atoms in the form of carbides. In order for this to work, it is essential that the total amount of Al and Si added is at least 0.6% by weight.
And the lower limit of the total amount of Si added. At this time, Si dissolves in ferrite and strengthens ferrite,
Addition of an unnecessarily large amount leads to an unnecessary increase in strength of the steel sheet and deterioration of workability and toughness. Therefore, add 2.5
Limited to less than or equal to%. Further, in the case of Al as well, if an unnecessarily large amount is added, the workability and toughness are deteriorated, so the upper limit of the addition amount is limited to 2.0% by weight. Al
Does not substantially increase the strength of the steel sheet, so C in equation (1)
Although not included in eq, Si increases the strength of the steel sheet, so it is necessary to limit the amount to satisfy the formula (1) in relation to other additive elements.
【００１４】Ｍｎ、Ｃｒ：Ｍｎ、ＣｒもＳｉやＡｌ同様
炭化物の生成を遅らす働きがあることからオーステナイ
トの残留に貢献する添加元素である。これに加えて、Ｍ
ｎ、Ｃｒの添加はオーステナイトのマルテンサイト変態
開始温度を低下させる。オーステナイトを室温で安定に
するためには上述の通り炭化物の析出を抑えてオーステ
ナイト中の炭素濃度を高めることが必要だが、同時にそ
のオーステナイトのマルテンサイト変態開始温度を低下
させることも重要である。もしもマルテンサイト変態温
度が室温よりも高温であれば、オーステナイトの一部は
不可避的にマルテンサイトに変態し、鋼板の強度を上げ
ると共に延性の劣化をもたらす。Ｍｎｅｑ＝％Ｍｎ＋
０．５２％Ｃｒで表現されるＭｎ等量が０．６重量％未
満の場合には残留オーステナイトを確保しつつマルテン
サイトの生成量を３％以下に抑えることができないので
これをＭｎ等量の下限とした。一方Ｍｎ等量が２．５重
量％超の場合には鋼板強度を６５ｋｇｆ／ｍｍ2 以下と
することが困難であるためにこれをＭｎ等量の上限とし
た。ＣｒはＭｎにくらべて強化能力が小さいために本発
明の目的としては利用し易い元素であるが、２．０重量
％を超ええて添加する場合には十分な量のオーステナイ
トを残留させる効果が飽和するばかりでなく経済的にも
不利益が生じ、また主相であるフェライトの生成を抑制
することから、これをＣｒ添加の上限とした。またＭｎ
も２．０重量％を超ええて添加した場合にはフェライト
の生成を不必要に抑制し、鋼板の強度上昇をもたらすこ
とからこれをＭｎ添加の上限とした。Mn, Cr: Mn and Cr are additive elements that contribute to the retention of austenite because they have a function of delaying the formation of carbides like Si and Al. In addition to this, M
The addition of n and Cr lowers the martensitic transformation start temperature of austenite. In order to stabilize austenite at room temperature, it is necessary to suppress the precipitation of carbides and increase the carbon concentration in austenite as described above, but at the same time, it is important to lower the martensitic transformation start temperature of the austenite. If the martensite transformation temperature is higher than room temperature, a portion of austenite inevitably transforms to martensite, which increases the strength of the steel sheet and deteriorates ductility. Mneq =% Mn +
When the Mn equivalent expressed by 0.52% Cr is less than 0.6% by weight, the amount of martensite produced cannot be suppressed to 3% or less while securing the retained austenite. The lower limit was set. On the other hand, when the Mn equivalent is more than 2.5% by weight, it is difficult to reduce the steel plate strength to 65 kgf / mm 2 or less. Cr is an element that is easy to utilize for the purpose of the present invention because it has a smaller strengthening capacity than Mn, but when it is added in an amount exceeding 2.0% by weight, the effect of leaving a sufficient amount of austenite is saturated. Not only this, but also economically disadvantageous, and since it suppresses the formation of ferrite which is the main phase, this was made the upper limit of Cr addition. Also Mn
When it is added in an amount exceeding 2.0% by weight, the formation of ferrite is unnecessarily suppressed and the strength of the steel sheet is increased. Therefore, this was made the upper limit of Mn addition.
【００１５】次に成分以外の各構成要素の作用の詳細に
ついて述べる。 ミクロ組織：本発明の鋼板は強度が４５〜６５ｋｇｆ／
ｍｍ2 の比較的低強度のＴＲＩＰ鋼を対象にしているこ
とから、軟質なフェライトを主相とすることが前提とな
る。最終的なミクロ組織にオーステナイトを残留させる
ためには、フェライト変態だけでは十分なＣ濃化が達成
できないためにベイナイト変態を利用する。従って最終
的なミクロ組織はフェライト＋ベイナイト＋オーステナ
イトの３相の混合組織となることが望ましい。しかしな
がらオーステナイトのマルテンサイト変態温度を室温以
下にすることが困難な場合もあり、その場合には本発明
の強度範囲で加工性を劣化させないためにはマルテンサ
イトの占積率を３％以下に制御することが必要であるの
でこれをマルテンサイト占積率の上限とする。また、軟
質なフェライトの占積率が６０％未満では鋼板の加工性
が著しく劣化するためにこれをフェライト占積率の下限
とした。最終組織に含まれる残留オーステナイト量は鋼
板の加工性を大きく左右するが、同時にオーステナイト
の加工安定性も鋼板の加工性を支配する因子の一つであ
る。オーステナイトの加工安定性はオーステナイトのＭ
ｓ温度で表現でき、Ｍｓが低温なほどオーステナイトは
安定で、加工の後期に有効に働き鋼板の延性を向上させ
る。オーステナイトのＭｓを低下させるためにはＭｎ等
量を上げることも重要であるが、オーステナイト中のＣ
濃度を一定量以上に高めることも重要である。実製造工
程では鋼に含まれるＣの内一部はフェライト中もしくは
粒界での固溶Ｃとして、また一部はセメンタイトの様な
炭化物として、さらには冷却中に生成したマルテンサイ
ト中の固溶Ｃとして浪費されることから、添加したＣ全
てをオーステナイトに濃化させることはできない。しか
しながら、最終的に得られる最大残留オーステナイト量
は鋼板の平均Ｃ濃度の増加と共に増加する。この時必要
以上のオーステナイトを残留させると、オーステナイト
中の平均的なＣ濃度が低くなり、オーステナイトの安定
性を下げる。残留オーステナイト量をＣ量で除した値が
１１０を超ええるとオーステナイトの加工安定性が低下
して鋼板の加工性を著しく劣化させることからこれを
（オーステナイト占積率）／（％Ｃ）の上限とした。実
験によるとオーステナイト中のＣ濃度は無制限に高める
ことはできない。濃化可能な範囲ではオーステナイト中
のＣ濃度は高いほど鋼板の加工性は良好であることが確
認されている。しかしながら上記の指標（オーステナイ
ト占積率）／（％Ｃ）が３５未満になるほど残留オース
テナイト占積率が低下した場合にはフェライト、ベイナ
イト、オーステナイト以外にマルテンサイトやセメンタ
イト等の硬質な生成物の量が増加し、結果として鋼板の
加工性を著しく劣化させることから、これを上記指標の
下限とした。Next, the details of the action of each component other than the components will be described. Microstructure: The steel sheet of the present invention has a strength of 45 to 65 kgf /
Since the target is a relatively low strength TRIP steel of mm 2 , it is premised that soft ferrite is used as the main phase. In order to retain austenite in the final microstructure, bainite transformation is used because sufficient C concentration cannot be achieved by ferrite transformation alone. Therefore, it is desirable that the final microstructure is a mixed structure of three phases of ferrite + bainite + austenite. However, it may be difficult to set the martensite transformation temperature of austenite to room temperature or lower. In that case, in order to prevent deterioration of workability in the strength range of the present invention, the space factor of martensite is controlled to 3% or less. This is the upper limit of the martensite space factor. Further, if the space factor of soft ferrite is less than 60%, the workability of the steel sheet is significantly deteriorated, so this was made the lower limit of the ferrite space factor. The amount of retained austenite contained in the final structure greatly affects the workability of the steel sheet, but at the same time, the workability of austenite is one of the factors that govern the workability of the steel sheet. The processing stability of austenite is M of austenite.
It can be expressed by s temperature, and the lower Ms is, the more stable austenite is, which works effectively in the latter stage of processing and improves the ductility of the steel sheet. Increasing the Mn equivalent is important to reduce the Ms of austenite, but C in austenite
It is also important to increase the concentration above a certain level. In the actual manufacturing process, some of the C contained in steel is dissolved in ferrite or at grain boundaries as solid solution C, and some as carbides such as cementite, and in solid solution in martensite formed during cooling. Since it is wasted as C, all of the added C cannot be concentrated to austenite. However, the maximum residual austenite amount finally obtained increases with an increase in the average C concentration of the steel sheet. At this time, if more austenite than necessary is left, the average C concentration in the austenite becomes low, and the stability of the austenite decreases. If the value obtained by dividing the amount of retained austenite by the amount of C exceeds 110, the workability of austenite is reduced and the workability of the steel sheet is significantly deteriorated. Therefore, this is the upper limit of (austenite space factor) / (% C). And Experiments show that the C concentration in austenite cannot be increased without limit. It has been confirmed that the workability of the steel sheet is better as the C concentration in austenite is higher in the range where the steel can be concentrated. However, if the retained austenite space factor decreases as the above index (austenite space factor) / (% C) becomes less than 35, the amount of hard products such as martensite and cementite in addition to ferrite, bainite, and austenite Is increased and, as a result, the workability of the steel sheet is significantly deteriorated, so this was made the lower limit of the above index.
【００１６】フェライト粒の長径／短径比：本発明の範
囲内の冷延後焼純された鋼板はフェライトを主相とす
る。このフェライト粒の形状は、鋼板の冷間圧延方向の
断面で観察した場合に圧延方向の平均粒径と板厚方向の
平均粒径とによって特徴づけられる。この２つの粒径の
比（フェライトの長径／短径比）は、冷間圧延方向断面
のミクロ組織写真から圧延方向に平行な一定長さの直線
で切断されるフェライト粒界の数ｎＬと板厚方向での同
一長さの直線で切断されるフェライト粒界の数ｎＺとの
比ｎＬ／ｎＺによって近似される。理由は明確ではない
が、この値が１．２５未満の場合および１．８を超える
場合には良好な強度−加工性のバランスが得られなかっ
た。従ってこれらをフェライト粒の長径／短径比の上限
と下限とする。 製造条件：以上の条件の範囲で成分を
調整した鋼を鋳造した後、スラブを室温まで冷却しても
冷却することなしに直接熱延しても本発明の範囲のミク
ロ組織と鋼板の特性が得られた。スラブを冷却すること
なしに熱延する場合には、熱延工程入り側でのスラブ温
度に応じて加熱炉で温度調整を行ってもよい。熱延後の
巻取り温度が３５０℃未満の場合には熱延鋼板の強度が
高くなりすぎ、冷延の負荷を上昇させて生産性を低下さ
せると共に、冷間途中での鋼板幅方向端部の割れ発生の
原因ともなるのでこれを巻取り温度の下限とした。また
巻取り温度が７５０℃を超ええると熱延鋼板中のパーラ
イトにＭｎ等のオーステナイト安定化元素が必要以上に
濃化し、冷延後に行われる焼純工程でのフェライトの生
成を阻害すると同時に、コイルの長手方向の材質バラツ
キの増加をもたらすことから、これを巻取り温度の上限
とした。その後行われる冷延は冷延圧下率が３５％未満
では均一な再結晶フェライト組織が得られず、材質のバ
ラツキや異方性を大きくすることから、これを下限とし
た。また８５％超の冷延圧下率は冷延工程の負荷を必要
以上に上げ、トータルとしてのコスト上昇をもたらすこ
とからこれを上限とした、焼鈍工程ではＡｃ1 以上Ａｃ
3 以下のフェライト＋オーステナイト２相域に加熱する
ことで目的とした組織が得られる。Ａｃ1 未満では残留
オーステナイトは全く得られず、Ａｃ3 超の加熱では冷
却制御によるフェライト占積率コントロールが困難であ
るためこれらを下限、上限とした。２相域加熱後の冷却
は２段階に分かれ、第１段階では徐冷によるフェライト
変態の促進が図られる。しかしながら１℃／秒未満の冷
却速度は実用上達成困難であるのでこれを下限とした。
また１０℃／秒超では安定したフェライト変態促進が不
可能であるためにこれを上限とした。これに引き続き行
われる第２段の冷却はパーライトの生成を回避するため
に高速で行われる必要がある。１０℃／秒未満の冷却速
度では冷却中にパーライト変態が進行し、オーステナイ
トの安定化に必要なＣを浪費して鋼板の加工性を劣化さ
せるためにこれを下限とした。しかしながら２００℃／
秒超の冷却速度は実用上達成困難であることからこれを
上限とした。この冷却が２５０℃未満まで行われると未
変態オーステナイトがマルテンサイト変態して鋼板を硬
質化し、加工性を劣化させるのでこれを冷却終了温度の
下限とした。また冷却停止温度が５００℃を超ええる場
合にはセメンタイトを含むベイナイト変態が進行しパー
ライト生成の場合と同様にＣを浪費するのでこれを上限
とした。この様な温度に冷却した後に、ベイナイト変態
によるオーステナイトのＣ濃化促進を行わせる。ベイナ
イト変態のための温度は冷却停止温度と同一でもまたそ
れ以上でも最終的な鋼板の特性は変わらない。この時ベ
イナイト変態処理を３００℃未満で行うとマルテンサイ
トに近い硬質のベイナイトやマルテンサイトそのものが
生成して鋼板の強度を必要以上に上昇させたると共にベ
イナイトの中にセメンタイト等の炭化物析出が起きてＣ
の浪費をすることからこれを下限とした。また５００℃
を超える場合には上述の通りセメンタイトを含むベイナ
イト変態が進行しパーライト生成の場合と同様にＣを浪
費するのでこれを上限とした。この温度範囲での保持は
等温もしくはこの温度範囲での徐冷で行われる。この保
持時間が１５秒未満の場合にはオーステナイトへのＣの
濃化が十分ではなく結果としてマルテンサイト占積率が
増加し、鋼板の強度を上げて加工性を劣化させることか
らこれを保持時間の下限とした。また保持時間が１５分
超の場合にはＣ濃化したオーステナイトからのセメンタ
イト等の炭化物析出が起こり結果的には残留オーステナ
イト量を減少させ、且つ鋼板の強度を上げて加工性を劣
化させるのでこれを上限とした。The major axis / minor axis ratio of ferrite grains: The steel sheet after cold rolling and refining within the scope of the present invention has ferrite as the main phase. The shape of the ferrite grains is characterized by the average grain size in the rolling direction and the average grain size in the sheet thickness direction when observed in a cross section of the steel sheet in the cold rolling direction. The ratio of the two grain sizes (ratio of major axis / minor axis of ferrite) is calculated from the microstructure photograph of the cross section in the cold rolling direction by the number nL of ferrite grain boundaries cut by a straight line parallel to the rolling direction and the plate. It is approximated by the ratio nL / nZ to the number nZ of ferrite grain boundaries cut along a straight line of the same length in the thickness direction. Although the reason is not clear, when this value is less than 1.25 and when it exceeds 1.8, a good balance between strength and workability cannot be obtained. Therefore, these are set as the upper limit and the lower limit of the ratio of major axis / minor axis of ferrite grains. Manufacturing conditions: After casting a steel whose components are adjusted in the above range, the microstructure and steel sheet properties within the scope of the present invention can be obtained by cooling the slab to room temperature or directly hot rolling without cooling. Was obtained. When hot-rolling the slab without cooling, the temperature may be adjusted in a heating furnace according to the slab temperature on the hot-rolling process entry side. When the coiling temperature after hot rolling is less than 350 ° C., the strength of the hot rolled steel sheet becomes too high, the load of cold rolling is increased and the productivity is lowered, and the steel sheet widthwise end portion in the middle of cold rolling. Since this may cause the occurrence of cracks, the lower limit of the coiling temperature was set. Further, if the coiling temperature exceeds 750 ° C, austenite stabilizing elements such as Mn are excessively concentrated in pearlite in the hot-rolled steel sheet, which hinders the formation of ferrite in the refining step performed after cold rolling. This causes an increase in material variation in the longitudinal direction of the coil, so this was set as the upper limit of the winding temperature. In the cold rolling performed thereafter, if the cold rolling reduction rate is less than 35%, a uniform recrystallized ferrite structure cannot be obtained, and the variation and anisotropy of the material are increased, so this was made the lower limit. The cold rolling reduction rate of 85% is raised more than necessary load of cold rolling steps, and the upper limit it from bringing the cost increase as the total, in the annealing step Ac 1 or Ac
The desired structure can be obtained by heating to the ferrite + austenite 2 phase region of 3 or less. If it is less than Ac 1 , residual austenite is not obtained at all, and if it exceeds Ac 3 , it is difficult to control the ferrite space factor by cooling control. The cooling after heating in the two-phase region is divided into two stages, and in the first stage, the ferrite transformation is promoted by slow cooling. However, it is practically difficult to achieve a cooling rate of less than 1 ° C./sec.
Further, if it exceeds 10 ° C./sec, stable ferrite transformation cannot be promoted, so this is set as the upper limit. Subsequent cooling of the second stage should be done at high speed to avoid the formation of pearlite. At a cooling rate of less than 10 ° C./sec, pearlite transformation progresses during cooling, C required for stabilizing austenite is wasted, and the workability of the steel sheet is deteriorated. However, 200 ° C /
A cooling rate of more than a second is practically difficult to achieve, so this was set as the upper limit. If this cooling is performed to less than 250 ° C., untransformed austenite transforms to martensite to harden the steel sheet and deteriorates workability, so this was made the lower limit of the cooling end temperature. Further, when the cooling stop temperature exceeds 500 ° C., bainite transformation including cementite proceeds and C is wasted as in the case of pearlite formation, so this was made the upper limit. After cooling to such a temperature, the C concentration of austenite is accelerated by the bainite transformation. If the temperature for bainite transformation is the same as or higher than the cooling stop temperature, the properties of the final steel sheet do not change. At this time, if the bainite transformation treatment is performed at less than 300 ° C., hard bainite close to martensite or martensite itself is generated to increase the strength of the steel plate more than necessary, and carbide precipitation such as cementite occurs in the bainite. C
This is the lower limit because it wastes money. Also 500 ° C
If it exceeds, the bainite transformation containing cementite proceeds as described above, and C is wasted as in the case of pearlite formation, so this was made the upper limit. Holding in this temperature range is performed isothermally or by slow cooling in this temperature range. If the holding time is less than 15 seconds, the concentration of C in austenite is not sufficient and, as a result, the martensite space factor increases, which increases the strength of the steel sheet and deteriorates the workability. The lower limit of If the holding time exceeds 15 minutes, precipitation of carbides such as cementite from C-enriched austenite will occur, and as a result, the amount of retained austenite will be reduced, and the strength of the steel sheet will be increased and workability will be deteriorated. Was set as the upper limit.
【００１７】[0017]
【実施例】表１に示す各鋼種に対し、熱間圧延した後、
冷却、巻取（４２０〜７８０℃の範囲）を行った熱間圧
延鋼板を冷延により１．０ｍｍ厚とした後焼鈍が施さ
れ、機械的性質調査、残留オーステナイトの定量が行わ
れた。焼鈍条件は図１に示す通りである。焼鈍温度（Ｔ
ｓ℃）、焼鈍時間（ｔｓ秒）、焼鈍後の徐冷（ＣＲＩ℃
／秒）及び急冷（ＣＲ２℃／秒）、急冷開始温度（Ｔｑ
℃）、急冷停止温度（Ｔｃ℃）、ベイナイト処理温度
（Ｔｂ℃）、ベイナイト処理時間（ｔｂ秒）を種々変化
させた。EXAMPLES After hot rolling each of the steel types shown in Table 1,
The hot-rolled steel sheet that had been cooled and wound (in the range of 420 to 780 ° C.) was cold-rolled to have a thickness of 1.0 mm, then annealed, and mechanical properties were investigated and residual austenite was quantified. The annealing conditions are as shown in FIG. Annealing temperature (T
s ° C), annealing time (ts seconds), slow cooling after annealing (CRI ° C)
/ Sec), rapid cooling (CR2 ° C / sec), rapid cooling start temperature (Tq
C.), the quenching stop temperature (Tc.degree. C.), the bainite treatment temperature (Tb.degree. C.), and the bainite treatment time (tb seconds) were variously changed.
【００１８】焼鈍により得られた鋼板の機械的性質と焼
鈍条件を表２、表３（表２のつづき−１）、表４（表２
のつづき−２）、表５（表２のつづき−３）、表６（表
２のつづき−４）、表７（表２のつづき−５）に示し
た。また同表中Ｖｆ％，Ｖｇ％，Ｖｍ％は鋼板中のフェ
ライト、残留オーステナイト、マルテンサイト占積率、
Ｃｅｑ、Ｍｎｅｑは請求項１に示したＣ等量とＭｎ等
量、ＣＯＬＤ％は冷延圧下率、ＣＴ℃は熱延巻取り温
度、Ａｃ1 及びＡｃ3 は計算Ａｃ1 、Ａｃ3 の（℃温
度）、径比は主相であるフェライト粒径の圧延方向と板
圧方向の比である。また表中には、靱性が特に劣化した
場合にはその欄に×を、従来材と同等の場合には○を示
した。The mechanical properties and annealing conditions of the steel sheets obtained by annealing are shown in Tables 2 and 3 (continued from Table 2-1) and Table 4 (Table 2).
No. 2), Table 5 (No. 3 in Table 2), Table 6 (No. 4 in Table 2), and Table 7 (No. 5 in Table 2). In the table, Vf%, Vg%, and Vm% are ferrite, residual austenite, and martensite space factor in the steel sheet,
Ceq and Mneq are C and Mn equivalents shown in claim 1, COLD% is cold rolling reduction, CT ° C is hot rolling coiling temperature, and Ac 1 and Ac 3 are calculated Ac 1 and Ac 3 (° C. The temperature) and the diameter ratio are the ratios of the ferrite grain size, which is the main phase, in the rolling direction and the plate pressure direction. Further, in the table, when the toughness is particularly deteriorated, x is shown in that column, and when it is equivalent to the conventional material, o is shown.
【００１９】同表より、本発明の条件を満たす鋼板（表
中に本発明鋼と表示）は、４５〜６５ｋｇｆ／ｍｍ2 の
範囲の強度を持ち、優れた破断伸びを有し、強度と破断
伸びの積ＴＳ×Ｅ１が２２００ｋｇｆ／ｍｍ2 ×％以上
の良好な加工性と強度のバランスが達成されていること
が分かる。From the table, a steel sheet satisfying the conditions of the present invention (indicated by the present invention in the table) has a strength in the range of 45 to 65 kgf / mm 2 , has an excellent breaking elongation, and has a strength and a breaking strength. It can be seen that a good balance between workability and strength is achieved with an elongation product TS × E1 of 2200 kgf / mm 2 ×% or more.
【００２０】[0020]
【表１】 [Table 1]
【００２１】[0021]
【表２】 [Table 2]
【００２２】[0022]
【表３】 [Table 3]
【００２３】[0023]
【表４】 [Table 4]
【００２４】[0024]
【表５】 [Table 5]
【００２５】[0025]
【表６】 [Table 6]
【００２６】[0026]
【表７】 [Table 7]
【００２７】[0027]
【発明の効果】以上述べたように、本発明によれば４５
〜６５ｋｇｆ／ｍｍ2 の優れた延性を有する高強度鋼板
の製造が可能となり、自動車の部品に適用することによ
り自動車車体軽量化に大きく貢献することができる。As described above, according to the present invention, 45
It becomes possible to manufacture a high-strength steel sheet having an excellent ductility of up to 65 kgf / mm 2 , and when applied to automobile parts, it can greatly contribute to weight reduction of the automobile body.
【図面の簡単な説明】[Brief description of drawings]
【図１】冷延後の焼鈍熱サイクルの概念図である。FIG. 1 is a conceptual diagram of an annealing heat cycle after cold rolling.
Claims (3)
ｎ＋０．０１２３％Ｃｒ で表現される炭素等量Ｃｅｑが０．１１重量％以上０．
２５重量％以下であり、且つＡｌとＳｉの和が０．６重
量％以上で、 Ｍｎｅｑ＝％Ｍｎ＋０．５２％Ｃｒ で表現されるＭｎ等量Ｍｎｅｑが０．６重量％以上、
２．５重量％以下であり、さらに不可避的な不純物を含
む鋼において、最終的なミクロ組織をフェライト、ベイ
ナイト、残留オーステナイトの３相もしくは一部マルテ
ンサイトを含む４相とし、主相であるフェライトの占積
率を６０％以上、マルテンサイトの占積率を３％以下、
オーステナイトの占積率をＣ重量％で除した値が３５以
上１１０以下であることを特徴とする加工性に優れた引
張強さ４５〜６５ｋｇｆ／ｍｍ2 の高強度複合組織冷延
鋼板。1. C .: 0.04% or more and 0.23% or less Si: 2.5% or less Al: 2.0% or less Mn: 2.0% or less Cr: 2.0% or less In the range, Ceq =% C + 0.0635% Si + 0.0247% M
Carbon equivalent Ceq expressed by n + 0.0123% Cr 2 is 0.11% by weight or more and 0.1.
25 wt% or less, the sum of Al and Si is 0.6 wt% or more, and Mn equivalent Mneq represented by Mneq =% Mn + 0.52% Cr is 0.6 wt% or more,
In steel containing 2.5% by weight or less and inevitable impurities, the final microstructure is ferrite, bainite, retained austenite, or three phases, or some phases containing martensite, and the main phase is ferrite. Occupancy rate of 60% or more, martensite occupancy rate of 3% or less,
A high-strength composite cold-rolled steel sheet having a tensile strength of 45 to 65 kgf / mm 2 and having excellent workability, wherein the value obtained by dividing the space factor of austenite by C weight% is 35 or more and 110 or less.
の粒径と板厚方向の粒径の比（長径／短径比）が１．２
５以上１．８以下であることを特徴とする請求項１記載
の加工性に優れた引張強さ４５〜６５ｋｇｆ／ｍｍ2 の
高強度複合組織冷延鋼板。2. The ratio of the grain size in the cold rolling direction to the grain size in the plate thickness direction of the ferrite grains as the main phase (major axis / minor axis ratio) is 1.2.
It is 5 or more and 1.8 or less, The high-strength compound structure cold rolled steel sheet having a tensile strength of 45 to 65 kgf / mm 2 excellent in workability according to claim 1.
ｎ＋０．０１２３％Ｃｒ で表現される炭素等量Ｃｅｑが０．１１重量％以上０．
２５重量％以下であり、且つＡｌとＳｉの和が０．６重
量％以上で、 Ｍｎｅｑ＝％Ｍｎ＋０．５２％Ｃｒ で表現されるＭｎ等量Ｍｎｅｑが０．６重量％以上、
２．５重量％以下であり、さらに不可避的な不純物を含
む鋼を、鋳造後一旦室温まで冷却するかもしくは冷却す
ることなしに熱延し、３５０℃から７５０℃の範囲で巻
取った後、３５〜８５％の冷延圧下率の冷延を施し、Ａ
ｃ1 以上Ａｃ3 以下の温度に３０秒以上５分以下の時間
加熱し、その後１℃／秒以上１０℃／秒以下の冷却速度
で５５０℃以上７２０℃以下の温度まで冷却し、引き続
いて１０℃／秒以上２００℃／秒以下の冷却速度で２５
０℃以上５００℃以下まで冷却した後、３００℃以上５
００℃以下の温度範囲で１５秒以上１５分以下保持し、
室温まで冷却することを特徴とする加工性に優れた引張
強さ４５〜６５ｋｇｆ／ｍｍ2 の高強度複合組織冷延鋼
板の製造方法。3. By weight%, C: 0.04% or more and 0.23% or less Si: 2.5% or less Al: 2.0% or less Mn: 2.0% or less Cr: 2.0% or less In the range, Ceq =% C + 0.0635% Si + 0.0247% M
Carbon equivalent Ceq expressed by n + 0.0123% Cr 2 is 0.11% by weight or more and 0.1.
25 wt% or less, the sum of Al and Si is 0.6 wt% or more, and Mn equivalent Mneq represented by Mneq =% Mn + 0.52% Cr is 0.6 wt% or more,
Steel containing not more than 2.5% by weight and unavoidable impurities is cooled to room temperature after casting, or hot-rolled without cooling, and wound in the range of 350 ° C to 750 ° C. Cold rolling with a cold rolling reduction of 35 to 85%
It is heated to a temperature of c 1 or more and Ac 3 or less for 30 seconds or more and 5 minutes or less, and then cooled to a temperature of 550 ° C. or more and 720 ° C. or less at a cooling rate of 1 ° C./second or more and 10 ° C./second or less, and then 10 25 at a cooling rate of ℃ / sec or more and 200 ℃ / sec or less
After cooling to 0 ℃ to 500 ℃, 300 ℃ to 5 ℃
Hold for 15 seconds or more and 15 minutes or less in the temperature range of 00 ° C or less,
A method for producing a high-strength composite cold-rolled steel sheet having a tensile strength of 45 to 65 kgf / mm 2 and excellent in workability, which is characterized by cooling to room temperature.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP176194A JP3569307B2 (en) | 1994-01-12 | 1994-01-12 | High strength composite structure cold rolled steel sheet having excellent workability and a tensile strength of 45 to 65 kgf / mm2, and a method for producing the same |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP176194A JP3569307B2 (en) | 1994-01-12 | 1994-01-12 | High strength composite structure cold rolled steel sheet having excellent workability and a tensile strength of 45 to 65 kgf / mm2, and a method for producing the same |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| JPH07207413A true JPH07207413A (en) | 1995-08-08 |
| JP3569307B2 JP3569307B2 (en) | 2004-09-22 |
Family
ID=11510572
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| JP176194A Expired - Lifetime JP3569307B2 (en) | 1994-01-12 | 1994-01-12 | High strength composite structure cold rolled steel sheet having excellent workability and a tensile strength of 45 to 65 kgf / mm2, and a method for producing the same |
Country Status (1)
| Country | Link |
|---|---|
| JP (1) | JP3569307B2 (en) |
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| US11208705B2 (en) | 2017-11-15 | 2021-12-28 | Nippon Steel Corporation | High-strength cold-rolled steel sheet |
| KR20210061382A (en) * | 2018-09-20 | 2021-05-27 | 아르셀러미탈 | Cold rolled and coated steel sheet and its manufacturing method |
| WO2023139752A1 (en) | 2022-01-21 | 2023-07-27 | 日本製鉄株式会社 | Steel sheet |
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