JP3293001B2 - Method of manufacturing high strength galvannealed hot-rolled steel sheet with excellent stretch flangeability - Google Patents

Description

【発明の詳細な説明】DETAILED DESCRIPTION OF THE INVENTION

【０００１】[0001]

【産業上の利用分野】本発明は自動車を始めとする機械
構造部材や一般加工用に使用される伸びフランジ性の優
れた高強度合金化溶融亜鉛めっき熱延鋼板の製造方法に
関するものである。BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a hot-rolled steel sheet of high strength alloyed hot-dip galvanized steel sheet having excellent stretch flangeability and used for mechanical structural members such as automobiles and general processing.

【０００２】[0002]

【従来の技術】近年、省エネルギーや燃費軽減のために
板厚を減少して高強度化するという強い要求がある。こ
の要求に対して、いわゆるＤｕａｌ Ｐｈａｓｅ鋼等が
開発されてきたが、伸びフランジ加工の厳しい部材では
これらの高強度熱延鋼板でも割れが生じるため、適用部
材が限定されているのが現状であり、高強度−良加工性
の鋼板が求められている。2. Description of the Related Art In recent years, there has been a strong demand for reducing the thickness and increasing the strength to save energy and reduce fuel consumption. In response to this requirement, so-called Dual Phase steel and the like have been developed. However, in the case of members with strict stretch flange processing, cracks occur even in these high-strength hot-rolled steel sheets, and at present the applicable members are limited. There is a demand for a steel plate having high strength and good workability.

【０００３】このような状況を打破すべく、伸びフラン
ジ性に優れた熱延鋼板の製造方法が特公平２−４８６０
８号公報、特公平開昭５１−４４５０８号公報に開示さ
れている。しかし、特公平２−４８６０８号公報に開示
されているような高強度化のためにＳｉを添加する方法
では、Ｓｉスケールの発生による不めっきの問題があ
る。In order to overcome such a situation, a method for producing a hot-rolled steel sheet having excellent stretch flangeability is disclosed in Japanese Examined Patent Publication No. 2-4860.
No. 8, JP-B-51-44508. However, the method of adding Si for increasing the strength as disclosed in Japanese Patent Publication No. 2-48608 has a problem of non-plating due to generation of Si scale.

【０００４】また、特開昭５１−４４５０８号公報に開
示されている方法は、Ｃｒ添加を必要とするため経済的
に不利であり、本発明のように引張強度５４０ＭＰａ以
上の高強度鋼板を意図したものではない。また、これら
の特許公報では合金化溶融亜鉛めっきを施されたものに
ついての開示はない。溶融亜鉛めっきは連続式溶融亜鉛
めっきラインで施されるが、ライン中で再加熱されるた
め、目的とする品質を得るためには多大な困難が伴う。
例えば再加熱のために結晶粒が粗大化すると、熱延まま
の材質に比較して強度が低下する。Further, the method disclosed in Japanese Patent Application Laid-Open No. 51-44508 is economically disadvantageous because it requires the addition of Cr, and is intended for a high-strength steel sheet having a tensile strength of 540 MPa or more as in the present invention. It was not done. Further, in these patent publications, there is no disclosure about those subjected to galvannealing. Hot-dip galvanizing is performed in a continuous hot-dip galvanizing line, but since it is reheated in the line, it is very difficult to obtain the desired quality.
For example, when the crystal grains are coarsened due to reheating, the strength is reduced as compared with a hot rolled material.

【０００５】この強度低下を補って目的の強度を得るた
めには鋼中の合金量を増やすことが必要となるが、この
合金量の増加によってめっき密着性の低下や不めっきと
いった問題が生じる。そこで、溶融亜鉛めっきを施した
良加工性高強度鋼板を製造する試みとして特開昭６２−
１３３０５９号公報にはＮｂ，Ｔｉ，Ｖを添加した鋼成
分系にて引張強度４４０ＭＰａ以上の高強度溶融亜鉛め
っき鋼板が提示されているが、伸びフランジ性について
は何ら検討されていない。It is necessary to increase the amount of alloy in steel in order to compensate for this decrease in strength and obtain the desired strength. However, the increase in the amount of alloy causes problems such as a decrease in plating adhesion and non-plating. Therefore, as an attempt to produce a hot-dip galvanized high-strength high-strength steel sheet, Japanese Patent Laid-Open No.
Japanese Patent No. 133059 discloses a high-strength hot-dip galvanized steel sheet having a tensile strength of 440 MPa or more in a steel component system to which Nb, Ti, and V are added, but no consideration is given to stretch flangeability.

【０００６】[0006]

【発明が解決しようとする課題】伸びフランジ性を向上
させるには炭化物などの第２相のない極低炭素系をベー
スにするのが有効である。そこで、本発明者らは極低炭
素系熱延鋼板の伸びフランジ性を向上させるべく、鋭意
検討を重ねた結果、第２相の影響のない極低炭素系では
伸びフランジ性と各方向のｒ値とは強い相関があること
を見出した。すなわち、伸びフランジ性を評価する穴拡
げ試験では割れが板厚を貫通する時点をもって試験終了
とするが、このときの割れが生じる方向はｒ値の低い方
向で生じる。In order to improve the stretch flangeability, it is effective to use a very low carbon system having no second phase such as carbide. Thus, the present inventors have conducted intensive studies to improve the stretch flangeability of the ultra-low carbon hot rolled steel sheet. As a result, in the ultra-low carbon steel not affected by the second phase, the stretch flangeability and the r in each direction were improved. It was found that there was a strong correlation with the value. That is, in the hole expansion test for evaluating the stretch flangeability, the test is terminated when the crack penetrates the sheet thickness, but the direction in which the crack occurs at this time occurs in the direction of lower r value.

【０００７】このｒ値の最小値を向上させるには各方向
の特性値の差を小さくすること、つまり面内異方性を低
減することが有効である。そのためには熱延鋼板の集合
組織をランダム化すること、すなわちγ粒の動的再結晶
を促進させることが重要である。しかし、Ｃｕ添加鋼は
強い集合組織を形成しやすく、面内異方性が大きい。そ
のため、ｒ値の最小値も小さく、穴拡げ性も向上しにく
かった。In order to improve the minimum value of the r value, it is effective to reduce the difference between the characteristic values in each direction, that is, to reduce the in-plane anisotropy. For that purpose, it is important to randomize the texture of the hot-rolled steel sheet, that is, to promote dynamic recrystallization of γ grains. However, Cu-added steel tends to form a strong texture and has large in-plane anisotropy. For this reason, the minimum value of the r value was small, and the hole expandability was not easily improved.

【０００８】そこで、本発明者らは熱間圧延ラインで、
以下の事項をベースにして、厳密に製造条件を定めるこ
とにより、面内異方性を低減し、ｒ値の最小値を向上さ
せ、伸びフランジ性を向上させることを図った。 （１）粗圧延でγ粒を微細にすることによりγ粒の動的
再結晶を生じやすくする。Therefore, the present inventors have used a hot rolling line,
By strictly determining the manufacturing conditions based on the following items, the in-plane anisotropy was reduced, the minimum value of the r value was improved, and the stretch flangeability was improved. (1) Fine refining of the γ grains by rough rolling facilitates dynamic recrystallization of the γ grains.

【０００９】（２）仕上圧延後段で大圧下で圧延し、か
つ高仕上温度で圧延を終了することによりγ粒の動的再
結晶を促進する。さらに圧延終了後の空冷によっても促
進を行う。 （３）γ粒を未再結晶にさせる傾向が強いＮｂ，Ｔｉを
添加しない。 次に本発明者らはＣｕの析出強化に及ぼすプレスキンパ
スの影響を調査した。(2) The dynamic recrystallization of γ grains is promoted by rolling under high pressure at the stage after the finish rolling and finishing the rolling at a high finishing temperature. Further, it is promoted by air cooling after the end of rolling. (3) Nb and Ti, which tend to cause γ grains to be unrecrystallized, are not added. Next, the present inventors investigated the influence of the presskin pass on the precipitation strengthening of Cu.

【００１０】表１に示す供試鋼を用いて熱延を行った。
この熱延板に、スキンパスを伸び率０、１、２％と変化
させて行ってから、Ｃｕの析出処理を６００℃−３ｍｉ
ｎで行い、引張強度の変化を調査した。図１にこの実験
手順を示す。また図２にはスキンパス率と引張強度の関
係を示す。このように、熱延後スキンパスを施すことに
より同条件の熱処理の場合と比較して、引張強度が向上
することがわかる。これはスキンパスにより導入された
転位がＣｕの析出サイトとなるためと推定される。この
熱延後のスキンパスの効果を利用することにより、同一
Ｃｕ量でもより高強度の鋼板を得ることができる。[0010] Hot rolling was performed using the test steels shown in Table 1.
After performing skin pass on this hot-rolled sheet while changing the elongation to 0, 1, and 2%, a Cu precipitation treatment was performed at 600 ° C.-3 mi.
n, and the change in tensile strength was investigated. FIG. 1 shows the experimental procedure. FIG. 2 shows the relationship between the skin pass ratio and the tensile strength. Thus, it can be seen that applying a skin pass after hot rolling improves the tensile strength as compared with the case of heat treatment under the same conditions. This is presumably because dislocations introduced by the skin pass become Cu precipitation sites. By utilizing the effect of the skin pass after hot rolling, a steel sheet having higher strength can be obtained even with the same amount of Cu.

【００１１】[0011]

【表１】 [Table 1]

【００１２】さらに本発明は連続溶融亜鉛めっきライン
で通板する際、還元雰囲気中の温度を規定し、Ｃｕの析
出強化を利用して穴拡げ性を落とさずに高強度化し、加
えて耐食性およびスポット溶接性の優れた合金化溶融亜
鉛めっきをすることを可能としたものである。前記のよ
うに本発明はかかる問題点に鑑み、外観性状・経済性を
損ねることなく、伸びフランジ性の優れた高強度合金化
溶融亜鉛めっき熱延鋼板の製造方法を提供することを目
的とするものである。Further, the present invention regulates the temperature in a reducing atmosphere when passing through a continuous hot-dip galvanizing line, increases the strength without reducing the hole expanding property by utilizing the precipitation strengthening of Cu, and further increases the corrosion resistance and This makes it possible to perform galvannealing with excellent spot weldability. As described above, the present invention has been made in view of the above problems, and it is an object of the present invention to provide a method of manufacturing a high-strength alloyed hot-dip galvanized steel sheet having excellent stretch flangeability without impairing appearance properties and economy. Things.

【００１３】[0013]

【課題を解決するための手段】本発明の要旨とするとこ
ろは以下の通りである。 （１）ｍａｓｓ％で、Ｃ：０．０１％以下、Ｓｉ：０．
３％以下、Ｍｎ：０．１〜２％、Ａｌ：０．１％以下、
Ｓ：０．０１％以下、Ｐ：０．１％以下を含み、かつＣ
ｕ：０．８〜２．０％を含有し、残部Ｆｅおよび不可避
的不純物よりなる鋼をスラブとした後、直ちにあるいは
１０００〜１２００℃に加熱し、熱間圧延を行う当り、
粗圧延では全圧下率を７０％以上で圧延を行い、仕上圧
延では圧下を有効歪［εｅｆｆ＝最終パス圧下率（％）
＋１／２（最終前１段目パス圧下率（％））＋１／４
（最終前２段目パス圧下率（％））］を３０％以上とす
る圧延を行い、（Ａｒ₃点＋２０℃）〜９５０℃の仕上
温度で圧延を終了し、圧延後１秒以上空冷し、続いて平
均冷却速度１０℃／ｓｅｃ以上で冷却し、７５０℃以下
で巻取って熱延鋼帯とし、得られた熱延鋼帯に伸び率１
〜５％のスキンパスを行ってから、連続溶融亜鉛めっき
ラインにおいて還元雰囲気下に５５０〜６８０℃の温度
で通板し、冷却後、溶融亜鉛めっき槽に浸漬して溶融亜
鉛めっきを施した後、再び加熱し、５００〜６００℃で
合金化することを特徴とする伸びフランジ性の優れた引
張強度が５４０ＭＰａ以上の高強度合金化溶融亜鉛めっ
き熱延鋼板の製造方法。 （２）ｍａｓｓ％で、Ｃ：０．０１％以下、Ｓｉ：０．
３％以下、Ｍｎ：０．１〜２％、Ａｌ：０．１％以下、
Ｓ：０．０１％以下、Ｐ：０．１％以下を含み、かつＣ
ｕ：０．８〜２．０％、Ｎｉ：０．３〜１．０％を含有
し、残部Ｆｅおよび不可避的不純物よりなる鋼をスラブ
とした後、直ちにあるいは１０００〜１２５０℃に加熱
して熱間圧延を行うに当り、粗圧延では全圧下率を７０
％以上で圧延を行い、仕上圧延では圧下を有効歪［εｅ
ｆｆ＝最終パス圧下率（％）＋１／２（最終前１段目パ
ス圧下率（％））＋１／４（最終前２段目パス圧下率
（％））］を３０％以上とする圧延を行い、（Ａｒ₃点
＋２０℃）〜９５０℃の仕上温度で圧延を終了し、圧延
後１秒以上空冷し、続いて平均冷却速度１０℃／ｓｅｃ
以上で冷却し、７５０℃以下で巻取って熱延鋼帯とし、
得られた熱延鋼帯に伸び率１〜５％のスキンパスを行っ
てから、連続溶融亜鉛めっきラインにおいて還元雰囲気
下に５５０〜６８０℃の温度で通板し、冷却後、溶融亜
鉛めっき槽に浸漬して溶融亜鉛めっきを施した後、再び
加熱し、５００〜６００℃で合金化することを特徴とす
る伸びフランジ性の優れた引張強度が５４０ＭＰａ以上
の高強度合金化溶融亜鉛めっき熱延鋼板の製造方法。The gist of the present invention is as follows. (1) Mass%, C: 0.01% or less, Si: 0.
3% or less, Mn: 0.1 to 2%, Al: 0.1% or less,
S: 0.01% or less, P: 0.1% or less, and C
u: a steel containing 0.8 to 2.0%, the balance consisting of Fe and unavoidable impurities is made into a slab, and then immediately or after heating to 1000 to 1200 ° C. to perform hot rolling.
In rough rolling, rolling is performed at a total draft of 70% or more, and in finish rolling, the rolling is reduced by an effective strain [εeff = final rolling reduction (%)].
+1/2 (first stage pass rolling reduction (%) before final) + ／
(2nd pass reduction before final stage (%))] is rolled to 30% or more, rolling is completed at a finishing temperature of (Ar ₃ points + 20 ° C.) to 950 ° C., and air-cooled for 1 second or more after rolling. Subsequently, it is cooled at an average cooling rate of 10 ° C./sec or more, and is wound at 750 ° C. or less to form a hot-rolled steel strip.
After performing a skin pass of 〜5%, the sheet is passed through a continuous hot-dip galvanizing line at a temperature of 550 to 680 ° C. under a reducing atmosphere, cooled, immersed in a hot-dip galvanizing tank, and subjected to hot-dip galvanizing. A method for producing a hot-rolled high-strength galvannealed steel sheet having excellent stretch flangeability and a tensile strength of 540 MPa or more, characterized by heating again and alloying at 500 to 600 ° C. (2) Mass%, C: 0.01% or less, Si: 0.
3% or less, Mn: 0.1 to 2%, Al: 0.1% or less,
S: 0.01% or less, P: 0.1% or less, and C
The steel containing u: 0.8 to 2.0% and Ni: 0.3 to 1.0%, and the balance consisting of Fe and unavoidable impurities is made into a slab, and then immediately or heated to 1000 to 1250 ° C. When performing hot rolling, the total rolling reduction is 70 in rough rolling.
%, And in finish rolling, the reduction is reduced by the effective strain [εe
ff = rolling in which final rolling reduction (%) + 1/2 (first-pass rolling reduction (%) before final) + ／ (second-pass rolling reduction (%) before final)] is 30% or more. Rolling is completed at a finishing temperature of (Ar ₃ points + 20 ° C.) to 950 ° C., and air-cooled for 1 second or more after rolling, and subsequently, an average cooling rate of 10 ° C./sec.
Cooled as above, rolled up at 750 ° C or less to form a hot-rolled steel strip,
After performing a skin pass with an elongation percentage of 1 to 5% on the obtained hot-rolled steel strip, the strip is passed through a continuous hot-dip galvanizing line at a temperature of 550 to 680 ° C under a reducing atmosphere, cooled, and then put into a hot-dip galvanizing tank. After being immersed and subjected to hot-dip galvanizing, it is heated again and alloyed at 500 to 600 ° C. A high-strength alloyed hot-dip galvanized steel sheet having excellent stretch flangeability and a tensile strength of 540 MPa or more. Manufacturing method.

【００１４】[0014]

【作用】次に本発明の各構成要件の限定理由について詳
述する。Ｃは０．０１％以下とする。これを超えると炭
化物が生成し、伸びフランジ性が低下する。Ｍｎは強度
を付与する元素であり、０．１〜２％の範囲で添加す
る。下限値未満では目標強度が得られず、２％を超える
添加では製造上、Ｃのピックアップがあり、Ｃの上限値
を満足できない。Next, the reasons for limiting the constituent elements of the present invention will be described in detail. C is set to 0.01% or less. If it exceeds this, carbides will be generated and the stretch flangeability will be reduced. Mn is an element that imparts strength and is added in the range of 0.1 to 2%. If the amount is less than the lower limit, the target strength cannot be obtained, and if the amount exceeds 2%, C is picked up in production, and the upper limit of C cannot be satisfied.

【００１５】ＳｉはＳｉスケールの原因となるとともに
めっき不良を生じるので０．３％以下とする。Ａｌは脱
酸剤として必要であるが、０．１％を超えるとアルミナ
系介在物が増加し、鋼の伸びフランジ性を損ねる。Ｓは
圧延方向に伸びたＡ系介在物を増加させ、そこを起点に
して割れが伝播するので、穴拡げ性が低下する。そこで
上限値を０．０１％とする。Since Si causes Si scale and causes plating failure, the content of Si is set to 0.3% or less. Al is necessary as a deoxidizing agent, but if it exceeds 0.1%, alumina-based inclusions increase and the stretch flangeability of steel is impaired. S increases the amount of the A-based inclusions extending in the rolling direction, and cracks propagate from the A-based inclusions, so that hole expandability decreases. Therefore, the upper limit is set to 0.01%.

【００１６】Ｐは耐食性を付与する元素である。しか
し、０．１％を超えると延性が落ち、伸びフランジ性が
低下する。Ｃｕは本発明では重要な元素である。すなわ
ち、本発明に従い、巻取およびその後の徐冷中にＣｕを
析出させることにより所定の強度を得ることができる。
Ｃｕが０．８％未満では効果がなく、２．０％超える添
加では効果が飽和するとともにＣｕヘゲと呼ばれる表面
欠陥が熱延中に生じることがある。P is an element imparting corrosion resistance. However, if it exceeds 0.1%, the ductility decreases, and the stretch flangeability decreases. Cu is an important element in the present invention. That is, according to the present invention, a predetermined strength can be obtained by precipitating Cu during winding and subsequent slow cooling.
If Cu is less than 0.8%, there is no effect, and if it exceeds 2.0%, the effect is saturated and a surface defect called Cu scab may occur during hot rolling.

【００１７】このＣｕヘゲを防止するにはＮｉ添加が望
ましいが、０．３％未満では効果がなく、１．０％を超
えると効果が飽和するばかりでなく経済性を損ねる。続
いて熱延条件について述べる。前記したような鋼は通常
転炉で溶製され、連続鋳造にてスラブとされる。転炉溶
製後、種々の二次精錬がなされることもある。In order to prevent this Cu scab, it is desirable to add Ni. However, if it is less than 0.3%, there is no effect, and if it exceeds 1.0%, not only the effect is saturated but also the economic efficiency is impaired. Next, the hot rolling conditions will be described. The steel as described above is usually melted in a converter and is made into a slab by continuous casting. After melting the converter, various secondary refining may be performed.

【００１８】このスラブは冷片、温片あるいは熱片のま
ま加熱炉に挿入される。この時の加熱温度は１０００〜
１２００℃とする。下限は現状の連続熱延設備で生産性
を落とさずに操業できる範囲とした。上限値は１２００
℃とする。これを超えるとＣｕヘゲが発生して表面性状
が劣化する。さらにＮｉを前述の範囲で添加した場合に
は加熱温度の上限値を１２５０℃とする。上限値はＮｉ
添加により向上するが、これを超えるとやはりＣｕヘゲ
を生じるのを避けがたい。下限値は同様に現状の設備で
とりうる値とした。This slab is inserted into a heating furnace as a cold piece, a hot piece or a hot piece. The heating temperature at this time is 1000-
1200 ° C. The lower limit is set within the range that can be operated with the current continuous hot rolling equipment without reducing the productivity. The upper limit is 1200
° C. If it exceeds this, Cu scab occurs and the surface properties deteriorate. Further, when Ni is added in the above range, the upper limit of the heating temperature is set to 1250 ° C. The upper limit is Ni
Although it is improved by the addition, it is still unavoidable to produce Cu scabbing if it exceeds this. Similarly, the lower limit was set to a value that can be taken by existing facilities.

【００１９】熱間圧延工程での圧下率は本発明では重要
な条件である。粗圧延での全圧下率は７０％以上とす
る。これ未満ではγ粒が粗大となり、γの動的再結晶が
生じにくくなり、強い集合組織を形成する。その結果、
面内異方性が大きくなり、各方向のｒ値の最小値が低下
し、伸びフランジ性が低下する。仕上圧延では特に仕上
後段での圧下率が有効であるため、εｅｆｆ＝最終パス
圧下率（％）＋１／２（最終前１段目パス圧下率
（％））＋１／４（最終前２段目パス圧下率（％））で
定義される有効歪を３０％以上とする。これ未満ではγ
粒の動的再結晶が生じにくくなり、強い集合組織を形成
する。その結果、面内異方性が大きくなり、各方向のｒ
値の最小値が低下し、伸びフランジ性が低下する。The rolling reduction in the hot rolling step is an important condition in the present invention. The total rolling reduction in the rough rolling is 70% or more. If it is less than this, the γ grains become coarse, dynamic recrystallization of γ becomes difficult to occur, and a strong texture is formed. as a result,
The in-plane anisotropy increases, the minimum value of the r value in each direction decreases, and the stretch flangeability decreases. In the finish rolling, since the rolling reduction in the post-finishing stage is particularly effective, εeff = the final pass rolling reduction (%) + 1/2 (the final pre-stage first stage rolling reduction (%)) + ／ (the final front second stage). The effective strain defined by the pass rolling reduction (%) is 30% or more. Below this, γ
Dynamic recrystallization of the grains is less likely to occur, and a strong texture is formed. As a result, in-plane anisotropy increases, and r in each direction is increased.
The minimum value of the value decreases, and the stretch flangeability decreases.

【００２０】仕上温度も本発明では極めて重要な条件で
ある。すなわち、本発明に従い仕上温度を規定してＣｕ
添加熱延鋼板の集合組織をランダム化することにより、
面内異方性の低減を図るものである。従って、仕上温度
は（Ａｒ₃ 点＋２０℃）〜９５０℃とする。下限値未満
であると強い集合組織が形成され、面内異方性が大きく
なり、各方向のｒ値の最小値が低下し、伸びフランジ性
が低下する。上限値は加熱温度との兼ね合いで実機で製
造可能な値とする。The finishing temperature is also a very important condition in the present invention. That is, according to the present invention, the finishing temperature is specified and Cu
By randomizing the texture of the hot-rolled steel sheet,
It is intended to reduce in-plane anisotropy. Therefore, the finishing temperature is (Ar ₃ points + 20 ° C.) to 950 ° C. If it is less than the lower limit, a strong texture is formed, the in-plane anisotropy increases, the minimum value of the r value in each direction decreases, and the stretch flangeability decreases. The upper limit is set to a value that can be manufactured with an actual machine in consideration of the heating temperature.

【００２１】仕上圧延後は１秒以上空冷する。これ未満
ではγ粒の未再結晶が残りやすく、集合組織が発達し、
伸びフランジ性が低下する。空冷後の平均冷却速度は１
０℃／ｓｅｃ以上とする。これ未満ではα粒が粗大化
し、延性が低下する。巻取温度は７５０℃以下とする。
これを超えるとα粒が粗大化し、延性が低下する。熱延
後のスキンパス条件は本発明では重要である。前述のよ
うにスキンパスにより連続溶融亜鉛めっきラインでのＣ
ｕの析出強化量を向上させることができる。条件は伸び
率１〜５％とする。下限値未満では効果がなく、上限値
を超えると加工硬化が大きく、延性が劣化する。After finish rolling, air cooling is performed for 1 second or more. Below this, unrecrystallized γ grains are likely to remain, and the texture develops,
The stretch flangeability decreases. Average cooling rate after air cooling is 1
0 ° C./sec or more. If it is less than this, α grains become coarse and ductility decreases. The winding temperature is 750 ° C. or less.
If it exceeds this, α grains become coarse and ductility decreases. Skin pass conditions after hot rolling are important in the present invention. As mentioned above, C in the continuous hot-dip galvanizing line by skin pass
The amount of precipitation strengthening of u can be improved. The condition is an elongation of 1 to 5%. If it is less than the lower limit, there is no effect. If it exceeds the upper limit, work hardening is large and ductility is deteriorated.

【００２２】続いて、連続溶融亜鉛めっき条件を詳述す
る。連続溶融亜鉛めっきラインで通板する際の還元雰囲
気中での温度は本発明では重要である。すなわち、本発
明に従った温度条件で通板し、Ｃｕの析出ないしクラス
ター強化により目標とする強度を得るためである。その
温度は５５０〜６８０℃とする。上限値を超えるとＣｕ
が固溶状態となり、目標とする強度が得られない。下限
値未満であると鋼板表面上に酸化皮膜が残り、めっき密
着性が低下する。Next, the conditions for continuous hot-dip galvanizing will be described in detail. The temperature in the reducing atmosphere at the time of passing through the continuous hot-dip galvanizing line is important in the present invention. That is, the steel sheet is passed under the temperature condition according to the present invention, and a target strength is obtained by precipitation of Cu or cluster strengthening. The temperature is 550-680 ° C. If the upper limit is exceeded, Cu
Is in a solid solution state, and the target strength cannot be obtained. If it is less than the lower limit, an oxide film remains on the surface of the steel sheet, and the plating adhesion decreases.

【００２３】なお、巻取温度によりＣｕの析出ないしク
ラスター強化量が異なるので、熱延鋼帯の引張強度は変
化する。そこで、最終製品で目標とする引張強度に達す
るように、連続溶融亜鉛めっきラインでの還元雰囲気温
度を熱延鋼帯の強度により調整する必要がある。特に目
標とする強度よりも熱延鋼帯の強度が低い場合は、連続
溶融亜鉛めっきラインでの還元雰囲気温度は５７０〜６
３０℃とする。The tensile strength of the hot-rolled steel strip changes because the amount of precipitation of Cu or the amount of cluster reinforcement differs depending on the winding temperature. Therefore, it is necessary to adjust the reducing atmosphere temperature in the continuous hot-dip galvanizing line by the strength of the hot-rolled steel strip so as to reach the target tensile strength in the final product. In particular, when the strength of the hot-rolled steel strip is lower than the target strength, the reducing atmosphere temperature in the continuous hot-dip galvanizing line is 570-6.
30 ° C.

【００２４】溶融亜鉛めっき浴に浸漬後の加熱温度は５
００〜６００℃とする。上限値は現状の設備で可能な値
とした。下限値未満では合金化が不十分となる。好まし
くは５２０〜５６０℃とする。The heating temperature after immersion in the hot dip galvanizing bath is 5
The temperature is set to 00 to 600 ° C. The upper limit was set to a value that is possible with existing equipment. If it is less than the lower limit, alloying becomes insufficient. Preferably it is 520-560 ° C.

【００２５】[0025]

【実施例】表２に示す成分を有する鋼を転炉にて出鋼
し、真空脱ガス等の二次精錬を経てスラブとした。表２
の中でＡ〜Ｅの符号で示す鋼は本発明範囲内であり、Ｆ
〜Ｌで示す鋼は本発明外である。Ｆ鋼はＣが上限超、Ｇ
鋼はＳｉが上限超、Ｈ鋼はＰ、Ａｌ、Ｓが上限超であ
る。Ｉ鋼はＣｕが上限超、Ｊ鋼はＮｉが下限未満、Ｋ鋼
はＴｉを、Ｌ鋼はＮｂ、Ｔｉを含む。EXAMPLE Steel having the components shown in Table 2 was tapped in a converter and subjected to secondary refining such as vacuum degassing to form a slab. Table 2
Among the steels indicated by symbols A to E are within the scope of the present invention,
Steels indicated by L are outside the scope of the present invention. For steel F, C exceeds the upper limit, G
For steel, Si exceeds the upper limit, and for H steel, P, Al, and S exceed the upper limit. I steel contains Cu above the upper limit, J steel contains Ni below the lower limit, K steel contains Ti, and L steel contains Nb and Ti.

【００２６】これらの鋼を出発材として、表３、表４
（表３のつづき）に示す熱延条件および溶融亜鉛めっき
条件で合金化溶融亜鉛めっき熱延鋼板を製造した。得ら
れた鋼板の特性値を表４に示す。引張試験はＪＩＳ Ｚ
２２０１に準じた５号試験片を用い、ＪＩＳ Ｚ ２
２４１記載の方法に従って行った。Using these steels as starting materials, Tables 3 and 4
An alloyed hot-dip galvanized hot-rolled steel sheet was manufactured under the hot-rolling conditions and hot-dip galvanizing conditions shown in (continuation of Table 3). Table 4 shows the characteristic values of the obtained steel sheets. JIS Z for tensile test
JIS Z 2 using No. 5 test piece according to 2201
241 was carried out.

【００２７】また、ｒ値は１０％歪をかけた後、圧延方
向、９０°方向、４５°方向を測定した。実施例で示し
た鋼板では圧延方向のｒ値が最小であったので、それを
表４に示した。伸びフランジ性は打ち抜き穴拡げ試験に
おける穴拡げ比で評価した。試験片は２５０mm角の鋼板
に直径２０mmのパンチと板厚の１０％をクリアランス
（片側）を持たせたダイスにより直径ｄ０（＝ダイス
径）の穴を打ち抜いたものを用いた。穴拡げ試験はプレ
ス試験機にて上記の試験片を打ち抜き、穴バリのない
（バリとは反対の）面側から３０°円錐パンチで押し拡
げ（この際押し拡げ部への材料流入がないようにフラン
ジには６０トンのしわ押えをかける）、クラックが板厚
を貫通する時点で止めることとし、この時の穴径（ｄ）
と元の穴径（ｄ０）の比（ｄ／ｄ０）を穴拡げ比とし
た。The r value was measured in the rolling direction, 90 ° direction, and 45 ° direction after applying 10% strain. Since the r value in the rolling direction was the minimum in the steel sheets shown in Examples, it was shown in Table 4. The stretch flangeability was evaluated by the hole expansion ratio in a punching hole expansion test. The test piece used was a 250 mm square steel sheet punched with a 20 mm diameter punch and a die having a thickness of 10% with a clearance (one side) and a hole having a diameter d0 (= die diameter) punched out. In the hole expansion test, the above test piece was punched out with a press tester, and the hole was pressed and expanded with a 30 ° conical punch from the side with no hole burr (opposite to the burr). A 60-ton wrinkle presser is applied to the flange at the time), and the crack is stopped when the crack penetrates the plate thickness, and the hole diameter at this time (d)
And the ratio (d / d0) of the original hole diameter (d0) as the hole expansion ratio.

【００２８】めっき密着性はインパクト試験で評価し
た。その方法は鋼板に半球状のポンチ（径１２．７mm
φ）を落下させ、形成された円状のくぼみにテープを貼
り、剥離後テープに付着しためっき量を目視で判定し
た。全面剥離を生じたものを不良とし、その他は良好と
した。表３、表４においてＮｏ．１〜Ｎｏ．５、Ｎｏ．
１１およびＮｏ．２３、２４は本発明例の鋼であり、本
発明の目的とする強度と良好な穴拡げ比を有するととも
にＳｉスケールおよびＣｕヘゲの発生はなく、めっき密
着性、合金化度も良好であった。The plating adhesion was evaluated by an impact test. The method uses a hemispherical punch (diameter 12.7 mm) on a steel plate.
φ) was dropped, a tape was attached to the formed circular depression, and the amount of plating adhered to the tape after peeling was visually determined. Samples with complete peeling were evaluated as poor, and others were evaluated as good. In Tables 3 and 4, No. 1 to No. 5, no.
11 and No. Reference numerals 23 and 24 denote steels of the examples of the present invention, which have the strength and a good hole expansion ratio aimed at by the present invention, do not generate Si scale and Cu scab, have good plating adhesion and good alloying degree. Was.

【００２９】Ｎｏ．６〜Ｎｏ．１０．Ｎｏ．１２〜Ｎ
ｏ．２２およびＮｏ．２５〜Ｎｏ．２６は比較例鋼であ
る。Ｎｏ．６は加熱温度が高すぎたためＣｕヘゲが生成
し、表面性状が劣化した。Ｎｏ．７は熱間圧延工程での
粗圧延の全圧下率が低すぎたためにγの動的再結晶が不
十分で、熱延鋼板の集合組織が発達し、面内異方性が大
きくなり、これに伴いＬ方向のｒ値が小さくなり、穴拡
げ比が低下した。Ｎｏ．８は熱間仕上圧延での有効歪が
小さすぎたためにγの動的再結晶が不十分で、熱延鋼板
の集合組織が発達し、面内異方性が大きくなり、これに
伴いＬ方向のｒ値が小さくなり、穴拡げ比が低下した。
Ｎｏ．９は熱間圧延工程での空冷時間が短かったために
γの未再結晶が残り、熱延鋼板の集合組織が発達し、面
内異方性が大きくなり、これに伴いＬ方向のｒ値が小さ
くなり、穴拡げ比が低下した。Ｎｏ．１０は熱間圧延工
程での冷却速度が遅すぎたのでフェライト粒が粗大にな
り、延性が低下した。Ｎｏ．１２は熱間圧延工程での巻
取温度が高すぎたのでフェライト粒が粗大になり、延性
が低下した。Ｎｏ．１３はＣが高すぎたので炭化物が生
成し、穴拡げ比が低下した。Ｎｏ．１４はＳｉが高すぎ
たのでＳｉスケールが生成し、表面性状が劣化した。Ｎ
ｏ．１５はＡｌ、Ｓが高すぎたので介在物が生成し、穴
拡げ比が低下した。Ｎｏ．１６はＣｕが高すぎたのでＣ
ｕヘゲが生成し、Ｎｏ．１７はＮｉが低すぎたのでＣｕ
ヘゲが生成し、いずれも表面性状が劣化した。Ｎｏ．１
８はＴｉを添加したためにγの未再結晶集合組織が発達
し、面内異方性が大きくなり、これに伴いＬ方向のｒ値
が小さくなり、穴拡げ比が低下した。Ｎｏ．１９はＮ
ｂ、Ｔｉを添加したためにγの未再結晶集合組織が発達
し、面内異方性が大きくなり、これに伴いＬ方向のｒ値
が小さくなり、穴拡げ比が低下した。Ｎｏ．２０は連続
溶融亜鉛めっきラインでの還元雰囲気中の温度が低すぎ
たので、めっき密着性が低下した。Ｎｏ．２１は連続溶
融亜鉛めっきラインでの還元雰囲気中の温度が高すぎた
のでＣｕが固溶状態となり、Ｃｕの析出ないしクラスタ
ー強化が得られず、目標とする強度が得られなかった。
Ｎｏ．２２は連続溶融亜鉛めっきラインでの合金化温度
が低すぎたので、めっき層中のＦｅ（％）が低下した。
Ｎｏ．２５はスキンパス率が上限超なので、加工硬化が
大きく、延性が低下した。Ｎｏ．２６はスキンパス率が
下限未満なので、Ｃｕの析出強化量が足らず、強度が低
下した。No. 6-No. 10. No. 12-N
o. 22 and No. 25-No. 26 is a comparative example steel. No. In No. 6, Cu heating was generated because the heating temperature was too high, and the surface properties were deteriorated. No. In No. 7, the dynamic reduction of γ was insufficient because the total rolling reduction of the rough rolling in the hot rolling process was too low, the texture of the hot-rolled steel sheet developed, and the in-plane anisotropy increased. As a result, the r value in the L direction decreased, and the hole expansion ratio decreased. No. In No. 8, the dynamic recrystallization of γ was insufficient because the effective strain in the hot finish rolling was too small, the texture of the hot-rolled steel sheet developed, and the in-plane anisotropy increased. Decreased, and the hole expansion ratio decreased.
No. In No. 9, since the air cooling time in the hot rolling step was short, unrecrystallized γ remained, the texture of the hot-rolled steel sheet developed, the in-plane anisotropy increased, and the r-value in the L direction was increased accordingly. It became smaller and the hole expansion ratio decreased. No. In No. 10, since the cooling rate in the hot rolling step was too slow, the ferrite grains became coarse and the ductility was reduced. No. In No. 12, since the winding temperature in the hot rolling step was too high, ferrite grains became coarse and ductility was reduced. No. In No. 13, carbide was generated because C was too high, and the hole expansion ratio was lowered. No. In No. 14, since Si was too high, Si scale was generated and the surface properties were deteriorated. N
o. In No. 15, inclusions were generated because Al and S were too high, and the hole expansion ratio was lowered. No. 16 is C because Cu was too high.
u hege is produced, and no. No. 17 was Cu because Ni was too low.
The scabs were formed, and the surface properties were deteriorated in each case. No. 1
In No. 8, the unrecrystallized texture of γ was developed due to the addition of Ti, and the in-plane anisotropy was increased. As a result, the r value in the L direction was reduced, and the hole expansion ratio was reduced. No. 19 is N
Due to the addition of b and Ti, the unrecrystallized texture of γ developed, the in-plane anisotropy increased, and the r-value in the L direction decreased, and the hole expansion ratio decreased. No. In No. 20, the temperature in the reducing atmosphere in the continuous hot-dip galvanizing line was too low, so that the plating adhesion was reduced. No. In No. 21, Cu was in a solid solution state because the temperature in the reducing atmosphere in the continuous galvanizing line was too high, and no precipitation or cluster strengthening of Cu was obtained, and a target strength was not obtained.
No. In No. 22, the alloying temperature in the continuous galvanizing line was too low, so that Fe (%) in the plating layer decreased.
No. In No. 25, since the skin pass ratio exceeded the upper limit, work hardening was large and ductility was reduced. No. In No. 26, since the skin pass ratio was less than the lower limit, the amount of precipitation strengthening of Cu was insufficient, and the strength was lowered.

【００３０】[0030]

【表２】 [Table 2]

【００３１】[0031]

【表３】 [Table 3]

【００３２】[0032]

【表４】 [Table 4]

【００３３】[0033]

【発明の効果】以上説明したように本発明によれば、伸
びフランジ性に優れ、かつ耐食性に優れた合金化溶融亜
鉛めっき熱延鋼板を外観性状、経済性を損ねることなく
提供できる。これにより厳しい伸びフランジ加工が必要
な部材に本発明鋼板を適用することにより、例えば自動
車等の軽量化が容易となり燃費の向上や省資源などを可
能にしうるものであり工業的価値は極めて高い。As described above, according to the present invention, an alloyed hot-dip galvanized steel sheet having excellent stretch flangeability and excellent corrosion resistance can be provided without impairing the appearance and economy. By applying the steel sheet of the present invention to a member requiring severe stretch flange processing, it is possible to easily reduce the weight of, for example, an automobile or the like, thereby improving fuel efficiency and saving resources, and the industrial value is extremely high.

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

【図１】Ｃｕ析出強化に及ぼすプレスキンパスの影響を
調べるためのＣｕ析出処理の実験手順を示す図である。FIG. 1 is a diagram showing an experimental procedure of a Cu precipitation treatment for examining the influence of a Preskin pass on Cu precipitation strengthening.

【図２】図１の実験より得られたスキンパスの伸び率の
引張強度に及ぼす影響を示す図である。FIG. 2 is a diagram showing the effect of the elongation percentage of the skin path on the tensile strength obtained from the experiment of FIG.

フロントページの続き (51)Int.Cl.⁷ 識別記号 ＦＩ // Ｃ２２Ｃ 38/00 ３０１ Ｃ２２Ｃ 38/00 ３０１Ｗ 38/16 38/16 (72)発明者 伊丹 淳 千葉県君津市君津１番地 新日本製鐵株 式会社 君津製鐵所内 (56)参考文献 特開 平４−365845（ＪＰ，Ａ) 特開 平３−107425（ＪＰ，Ａ) 特開 平５−271782（ＪＰ，Ａ) 特開 平５−345953（ＪＰ，Ａ) (58)調査した分野(Int.Cl.⁷，ＤＢ名) C21D 9/46 C21D 8/02 C23C 2/00 - 2/40 Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI // C22C 38/00 301 C22C 38/00 301W 38/16 38/16 (72) Inventor Jun Itami No. 1 Kimitsu, Kimitsu City, Chiba Prefecture Made in New Japan (56) References JP-A-4-365845 (JP, A) JP-A-3-107425 (JP, A) JP-A-5-271782 (JP, A) JP-A-5 −345953 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C21D 9/46 C21D 8/02 C23C 2/00-2/40

Claims (2)

(57)【特許請求の範囲】(57) [Claims] 【請求項１】 ｍａｓｓ％で、Ｃ：０．０１％以下、Ｓ
ｉ：０．３％以下、Ｍｎ：０．１〜２％、Ａｌ：０．１
％以下、Ｓ：０．０１％以下、Ｐ：０．１％以下を含
み、かつＣｕ：０．８〜２．０％を含有し、残部Ｆｅお
よび不可避的不純物よりなる鋼をスラブとした後、直ち
にあるいは１０００〜１２００℃に加熱して熱間圧延を
行うに当り、粗圧延では全圧下率を７０％以上で圧延を
行い、仕上圧延では圧下を有効歪［εｅｆｆ＝最終パス
圧下率（％）＋１／２（最終前１段目パス圧下率
（％））＋１／４（最終前２段目パス圧下率（％））］
を３０％以上とする圧延を行い、（Ａｒ₃ 点＋２０℃）
〜９５０℃の仕上温度で圧延を終了し、圧延後１秒以上
空冷し、続いて平均冷却速度１０℃／ｓｅｃ以上で冷却
し、７５０℃以下で巻取って熱延鋼帯とし、得られた熱
延鋼帯に伸び率１〜５％のスキンパスを行ってから、連
続溶融亜鉛めっきラインにおいて還元雰囲気下に５５０
〜６８０℃の温度で通板し、冷却後、溶融亜鉛めっき槽
に浸漬して溶融亜鉛めっきを施した後、再び加熱し、５
００〜６００℃で合金化することを特徴とする伸びフラ
ンジ性の優れた引張強度が５４０ＭＰａ以上の高強度合
金化溶融亜鉛めっき熱延鋼板の製造方法。1. Mass%, C: 0.01% or less, S
i: 0.3% or less, Mn: 0.1 to 2%, Al: 0.1
% Or less, S: 0.01% or less, P: 0.1% or less, and Cu: 0.8 to 2.0%. When hot rolling is performed immediately or after heating to 1000 to 1200 ° C., rolling is performed at a total reduction of 70% or more in rough rolling, and the reduction is effective strain [εeff = final pass reduction (%) in finish rolling. ) +1/2 (first-stage pass rolling reduction (%) before last) + ／ (last-second stage rolling reduction (%))]
Is reduced to 30% or more (Ar ₃ points + 20 ° C.)
Rolling was completed at a finishing temperature of ９950 ° C., air-cooled for 1 second or more after rolling, subsequently cooled at an average cooling rate of 10 ° C./sec or more, and wound at 750 ° C. or less to obtain a hot-rolled steel strip. After performing a skin pass with an elongation of 1 to 5% on the hot-rolled steel strip, the continuous hot-dip galvanizing line is set to 550 in a reducing atmosphere.
After passing through a plate at a temperature of ６680 ° C., after cooling, immersion in a hot-dip galvanizing bath to apply hot-dip galvanizing, and heating again,
A method for producing a hot-rolled hot-dip galvanized steel sheet having excellent stretch flangeability and a tensile strength of 540 MPa or more, characterized by alloying at 00 to 600 ° C. 【請求項２】 ｍａｓｓ％で、Ｃ：０．０１％以下、Ｓ
ｉ：０．３％以下、Ｍｎ：０．１〜２％、Ａｌ：０．１
％以下、Ｓ：０．０１％以下、Ｐ：０．１％以下を含
み、かつＣｕ：０．８〜２．０％、Ｎｉ：０．３〜１．
０％を含有し、残部Ｆｅおよび不可避的不純物よりなる
鋼をスラブとした後、直ちにあるいは１０００〜１２５
０℃に加熱して熱間圧延を行うに当り、粗圧延では全圧
下率を７０％以上で圧延を行い、仕上圧延では圧下を有
効歪［εｅｆｆ＝最終パス圧下率（％）＋１／２（最終
前１段目パス圧下率（％））＋１／４（最終前２段目パ
ス圧下率（％））］を３０％以上とする圧延を行い、
（Ａｒ₃ 点＋２０℃）〜９５０℃の仕上温度で圧延を終
了し、圧延後１秒以上空冷し、続いて平均冷却速度１０
℃／ｓｅｃ以上で冷却し、７５０℃以下で巻取って熱延
鋼帯とし、得られた熱延鋼帯に伸び率１〜５％のスキン
パスを行ってから、連続溶融亜鉛めっきラインにおいて
還元雰囲気下に５５０〜６８０℃の温度で通板し、冷却
後、溶融亜鉛めっき槽に浸漬して溶融亜鉛めっきを施し
た後、再び加熱し、５００〜６００℃で合金化すること
を特徴とする伸びフランジ性に優れた引張強度が５４０
ＭＰａ以上の高強度合金化溶融亜鉛めっき熱延鋼板の製
造方法。2. Mass%, C: 0.01% or less, S
i: 0.3% or less, Mn: 0.1 to 2%, Al: 0.1
%, S: 0.01% or less, P: 0.1% or less, Cu: 0.8-2.0%, Ni: 0.3-1.
Steel containing 0% and the balance of Fe and unavoidable impurities is immediately or 1000 to 125
In performing hot rolling by heating to 0 ° C., rolling is performed at a total reduction ratio of 70% or more in rough rolling, and reduction in effective rolling [εeff = final pass reduction ratio (%) + 1/2 ( Rolling is performed so that the final pre-stage first pass reduction (%)) + ／ (the final pre-stage second pass reduction (%)) is 30% or more.
Rolling is completed at a finishing temperature of (Ar ₃ points + 20 ° C.) to 950 ° C., air-cooled for 1 second or more after rolling, and then average cooling rate of 10
After cooling at 750 ° C./sec or more, winding at 750 ° C. or less to form a hot-rolled steel strip, performing a skin pass with an elongation of 1 to 5% on the obtained hot-rolled steel strip, and then reducing in a continuous hot-dip galvanizing line. It is passed through a plate at a temperature of 550 to 680 ° C, cooled, immersed in a hot-dip galvanizing bath, subjected to hot-dip galvanizing, heated again, and alloyed at 500 to 600 ° C. 540 excellent tensile strength with excellent flangeability
A method for producing a hot-rolled hot-rolled steel sheet having a high strength of at least MPa.