JP2002322537A - Galvanized steel sheet having excellent ductility and stretch formability, and production method therefor - Google Patents
Galvanized steel sheet having excellent ductility and stretch formability, and production method thereforInfo
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- JP2002322537A JP2002322537A JP2001127216A JP2001127216A JP2002322537A JP 2002322537 A JP2002322537 A JP 2002322537A JP 2001127216 A JP2001127216 A JP 2001127216A JP 2001127216 A JP2001127216 A JP 2001127216A JP 2002322537 A JP2002322537 A JP 2002322537A
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- steel sheet
- hot
- less
- martensite
- phase
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- Heat Treatment Of Sheet Steel (AREA)
Abstract
Description
【０００１】[0001]
【発明が属する技術分野】本発明は、低強度、高延性の
強度−延性バランスおよび張り出し成形性に優れた溶融
亜鉛めっき鋼板（合金化溶融亜鉛めっき鋼板を含む。）
およびその製造方法に関する。[0001] The present invention relates to a hot-dip galvanized steel sheet (including an alloyed hot-dip galvanized steel sheet) excellent in low strength, high ductility balance and ductility.
And its manufacturing method.
【０００２】[0002]
【従来の技術】自動車用鋼板等には、プレス加工性が求
められ、また耐食性も要求される場合がある。このよう
なプレス加工性と優れた耐食性とを兼ね備えた鋼板とし
て、溶融亜鉛めっき鋼板、合金化溶融亜鉛めっき鋼板が
ある。合金化溶融亜鉛めっき鋼板は、冷延鋼板を母材と
して、これに溶融亜鉛めっきを施した後、さらに亜鉛め
っき層と母材鋼板との密着性を向上させるため、５５０
℃前後の温度で加熱して亜鉛めっき層を合金化処理した
ものである。以下、単に溶融亜鉛めっき鋼板という場合
は、合金化溶融亜鉛めっき鋼板をも含むものとする。2. Description of the Related Art In some cases, steel sheets for automobiles are required to have press workability and corrosion resistance. As a steel sheet having such press workability and excellent corrosion resistance, there is a hot-dip galvanized steel sheet and an alloyed hot-dip galvanized steel sheet. The alloyed hot-dip galvanized steel sheet is prepared by using a cold-rolled steel sheet as a base material and subjecting the same to hot-dip galvanizing, and further improving the adhesion between the galvanized layer and the base material steel sheet by 550.
The zinc-plated layer is alloyed by heating at a temperature of about ° C. Hereinafter, when simply referred to as a hot-dip galvanized steel sheet, it also includes an alloyed hot-dip galvanized steel sheet.
【０００３】[0003]
【発明が解決しようとする課題】溶融亜鉛めっき鋼板の
母材鋼板として、高強度化をねらってフェライトの他に
マルテンサイト、ベイナイトを生成させた複合組織鋼板
が用いられる場合がある。例えば、特開昭５８−３９７
７０号公報には、フェライト＋マルテンサイト＋ベイナ
イトからなる３相組織鋼板を、また特開昭５５−１２２
８２１号公報にはフェライト＋マルテンサイトからなる
２相組織鋼板を母材とする溶融亜鉛めっき鋼板が記載さ
れている。これらの複合鋼板は、高強度でありながら降
伏比（ＹＲ）も低く、形状凍結性に優れる。As a base steel sheet of a hot-dip galvanized steel sheet, a composite structure steel sheet in which martensite and bainite are generated in addition to ferrite in order to increase the strength is sometimes used. For example, JP-A-58-397
No. 70 discloses a three phase steel sheet composed of ferrite + martensite + bainite.
No. 821 describes a hot-dip galvanized steel sheet using a two-phase structure steel sheet composed of ferrite and martensite as a base material. These composite steel sheets have a low yield ratio (YR) while having high strength, and are excellent in shape freezing property.
【０００４】しかしながら、これらの複合組織鋼板を母
材とした溶融亜鉛めっき鋼板は、マルテンサイトやベイ
ナイトの量が多く、通常、強度が５００MPa 以上であ
り、多くは６００MPa 以上である。このため、プレス成
形に際して、軟質鋼板用のプレス成形装置を使用するの
に問題があり、高強度鋼板成形用の特別なプレス成形装
置が必要とされる。また、従来のマルテンサイト、ベイ
ナイトを生成させた溶融亜鉛めっき鋼板では、張り出し
成形性が非常に低く、張り出し成形に適さないため、成
形形状が制約されるという問題がある。However, the hot-dip galvanized steel sheet using these composite structure steel sheets as a base material has a large amount of martensite and bainite, and usually has a strength of 500 MPa or more, and often 600 MPa or more. For this reason, there is a problem in using a press forming apparatus for a soft steel sheet in press forming, and a special press forming apparatus for forming a high-strength steel sheet is required. In addition, the conventional hot-dip galvanized steel sheet in which martensite and bainite are formed has a problem that the stretched formability is extremely low and is not suitable for stretch-formed, so that the formed shape is restricted.
【０００５】本発明はかかる問題に鑑みなされたもの
で、マルテンサイトを含む複合組織でありながら、強度
が５００MPa 未満であり、延性に優れ、しかも優れた張
り出し成形性を有する、溶融亜鉛めっき鋼板（合金化溶
融亜鉛めっき鋼板を含む。）およびその製造方法を提供
することを目的とする。The present invention has been made in view of the above problems, and has a composite structure containing martensite, but has a strength of less than 500 MPa, has excellent ductility, and has excellent stretch forming properties. (Including an alloyed hot-dip galvanized steel sheet) and a method for producing the same.
【０００６】[0006]
【課題を解決するための手段】本発明の溶融亜鉛めっき
鋼板は、化学成分が重量％で、Ｃ ：０．０１０〜０．
０６％、Ｓｉ：０．５％以下、Ｍｎ：０．５％以上、
２．０％未満、Ｐ ：０．２０％以下、Ｓ ：０．０１
％以下、Ａｌ：０．００５〜０．１０％、Ｎ ：０．０
０５％以下、Ｃｒ：１．０％以下、かつＭｎ＋１．３Ｃ
ｒ：１．９〜２．３％および残部Ｆｅを本質的成分と
し、組織がフェライトとマルテンサイトを含む第２相と
からなり、組織中の第２相の割合が面積率で２０％以下
であり、かつ第２相に占めるマルテンサイトの割合が５
０％以上であり、しかもマルテンサイト粒子同士の最近
接粒子間距離が平均で５．４μm 以下である冷延鋼板を
母材とし、その表面に溶融亜鉛めっき層あるいは合金化
溶融亜鉛めっき層が形成されたものである。前記冷延鋼
板の母材は、組織中の第２相の割合を面積率で１０％以
下とし、かつ第２相に占めるマルテンサイトの割合を９
０％以上とし、さらにマルテンサイト粒子同士の最近接
粒子間距離を平均で２．７μm 以下することが好まし
い。The hot-dip galvanized steel sheet of the present invention has a chemical composition of C: 0.010-0.
06%, Si: 0.5% or less, Mn: 0.5% or more,
Less than 2.0%, P: 0.20% or less, S: 0.01
% Or less, Al: 0.005 to 0.10%, N: 0.0
05% or less, Cr: 1.0% or less, and Mn + 1.3C
r: 1.9 to 2.3% and the balance Fe as an essential component, and the structure is composed of ferrite and a second phase containing martensite, and the ratio of the second phase in the structure is 20% or less in area ratio. And the proportion of martensite in the second phase is 5
The base material is a cold-rolled steel sheet that is 0% or more and the average distance between the closest particles between martensite particles is 5.4 μm or less, and a hot-dip galvanized layer or an alloyed hot-dip galvanized layer is formed on the surface of the cold-rolled steel sheet. It was done. In the base material of the cold-rolled steel sheet, the ratio of the second phase in the structure is 10% or less in area ratio, and the ratio of martensite in the second phase is 9%.
It is preferable to set it to 0% or more, and further to make the average distance between the closest particles between the martensite particles 2.7 μm or less.
【０００７】また、本発明の溶融亜鉛めっき鋼板の製造
方法は、前記化学成分を有する鋼材を熱間圧延後、５５
０℃以下の温度で巻き取り、その後冷間圧延を施し、こ
れによって得られた冷延鋼板を連続焼鈍めっきラインに
てフェライト＋オーステナイトの２相共存領域に加熱し
て再結晶焼鈍を行った後、焼鈍温度からめっき温度まで
１〜１０℃／ｓの第１冷却速度で冷却して溶融亜鉛めっ
きを施した後、冷却するものである。この場合、第１冷
却速度を１〜３℃／ｓとし、溶融亜鉛めっき後の第２冷
却速度を１０℃／ｓ以上として冷却することによって、
組織中の第２相の割合を１０％以下に低減するとともに
第２相に占めるマルテンサイトの割合を９０％以上に増
大することができる。また、前記第１冷却速度で冷却し
て前記溶融亜鉛めっきを施した後、さらに溶融亜鉛めっ
き層の合金化処理を施し、その後１０℃／ｓ以上の第２
冷却速度で冷却することができる。この場合において
も、第１冷却速度を１〜３℃／ｓとすることは、前記し
たとおり、第２相の割合を低減し、第２相中のマルテン
サイトの割合を増大させる上で有効である。[0007] The method for producing a hot-dip galvanized steel sheet according to the present invention comprises the steps of:
After winding at a temperature of 0 ° C. or lower, cold rolling is performed, and the obtained cold-rolled steel sheet is heated in a continuous annealing plating line to a two-phase coexisting region of ferrite and austenite to perform recrystallization annealing. After cooling from the annealing temperature to the plating temperature at a first cooling rate of 1 to 10 ° C./s to perform hot-dip galvanizing, cooling is performed. In this case, the first cooling rate is set to 1 to 3 ° C./s, and the second cooling rate after hot-dip galvanizing is set to 10 ° C./s or more for cooling.
The proportion of the second phase in the tissue can be reduced to 10% or less, and the proportion of martensite in the second phase can be increased to 90% or more. Further, after cooling at the first cooling rate and performing the hot-dip galvanizing, an alloying treatment is further performed on the hot-dip galvanized layer, and thereafter, the second hot-dip galvanized layer is subjected to a second heat treatment at 10 ° C.
It can be cooled at a cooling rate. Also in this case, setting the first cooling rate to 1 to 3 ° C./s is effective in reducing the ratio of the second phase and increasing the ratio of martensite in the second phase as described above. is there.
【０００８】[0008]
【発明の実施の形態】本発明は、母材冷延鋼板として複
合組織鋼板を用いるものの、強度の高いマルテンサイト
を含む第２相を少なくし、さらに第２相中のマルテンサ
イト量を抑制することで、マルテンサイトを含む複合組
織ながら、５００MPa 以下の低強度化を実現しつつ、１
７０００MPa*％程度以上の優れた強度−延性バランスを
備えるものとし、さらにマルテンサイトを微細に分散さ
せることで、球頭肩半径２５mm（ｒｐ２５）の球頭ポン
チによる張り出し試験によって測定される張り出し高さ
（以下、ｈ（ｒｐ２５）と表示する。）が２１．９mm程
度以上の従来の軟鋼板並の優れた張り出し成形性を兼備
させることに成功したものである。なお、第２相とは、
フェライト以外の相を意味し、マルテンサイトのほか、
ベイナイトおよび／またはパーライトからなる。本発明
の成分系では、ベイナイトとパーライトの区別は付きに
くく、これらは棒状あるいは球状の炭化物（主にセメン
タイト）を含む組織として観察される。DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention uses a composite structure steel sheet as a base material cold-rolled steel sheet, but reduces the second phase containing high-strength martensite, and further suppresses the amount of martensite in the second phase. As a result, while achieving a low strength of 500 MPa or less, despite the composite structure containing martensite,
An overhang height measured by an overhang test using a ball-head punch having a ball-head shoulder radius of 25 mm (rp25) by providing an excellent strength-ductility balance of about 7000 MPa *% or more and further dispersing martensite finely. (Hereinafter referred to as h (rp25).) It has succeeded in having excellent overhang formability comparable to that of a conventional mild steel sheet having about 21.9 mm or more. The second phase is
Means phases other than ferrite, besides martensite,
It consists of bainite and / or perlite. In the component system of the present invention, it is difficult to distinguish between bainite and pearlite, and these are observed as a structure containing rod-like or spherical carbides (mainly cementite).
【０００９】すなわち、本発明の本発明の溶融亜鉛めっ
き鋼板は、化学成分が重量％で、Ｃ ：０．０１０〜
０．０６％、Ｓｉ：０．５％以下、Ｍｎ：０．５％以
上、２．０％未満、Ｐ ：０．２０％以下、Ｓ ：０．
０１％以下、Ａｌ：０．００５〜０．１０％、Ｎ ：
０．００５％以下、Ｃｒ：１．０％以下、かつＭｎ＋
１．３Ｃｒ：１．９〜２．３％および残部Ｆｅを本質的
成分とし、組織がフェライトとマルテンサイトとを含む
第２相からなり、組織中の第２相の割合が面積率で２０
％以下であり、かつ第２相に占めるマルテンサイトの割
合が５０％以上であり、しかもマルテンサイト粒子同士
の最近接粒子間距離が平均で５．４μm 以下である冷延
鋼板を母材とし、その表面に溶融亜鉛めっき層あるいは
合金化溶融亜鉛めっき層が形成されたものである。「Ｍ
ｎ＋１．３Ｃｒ」中の元素記号は各元素の含有量wt％を
示す。That is, in the hot-dip galvanized steel sheet of the present invention, the chemical composition is expressed in terms of% by weight, and C: 0.010 to 10%.
0.06%, Si: 0.5% or less, Mn: 0.5% or more, less than 2.0%, P: 0.20% or less, S: 0.
01% or less, Al: 0.005 to 0.10%, N:
0.005% or less, Cr: 1.0% or less, and Mn +
1.3Cr: 1.9 to 2.3% and the balance Fe as an essential component, the structure is composed of a second phase containing ferrite and martensite, and the ratio of the second phase in the structure is 20 in area ratio.
% Or less, and the proportion of martensite in the second phase is 50% or more, and the distance between the closest particles between the martensite particles is 5.4 μm or less on average. A hot-dip galvanized layer or an alloyed hot-dip galvanized layer is formed on the surface. "M
The element symbol in “n + 1.3Cr” indicates the content wt% of each element.
【００１０】まず、母材冷延鋼板の成分限定理由（単位
はwt％）について説明する。 Ｃ：０．０１０〜０．０６％ プレス加工性を向上させるにはＣ量は少ない程よいが、
０．０１０％未満ではフェライト＋オーステナイトの２
相領域が狭く、オーステナイトからマルテンサイトが生
成しにくくなるため工業的に生産することが困難であ
る。一方０．０６％を超えると強度が高くなり、軟質鋼
板としてのプレス成形性が劣化する。このため、本発明
ではＣ量の下限を０．０１０％、好ましくは０．０１５
％、より好ましくは０．０２０％とし、上限を０．０６
％、好ましくは０．０４％とする。First, the reasons for limiting the components of the cold rolled steel sheet (unit: wt%) will be described. C: 0.010-0.06% To improve the press workability, the smaller the C content, the better.
If less than 0.010%, 2 of ferrite + austenite
Since the phase region is narrow and martensite is hardly generated from austenite, it is difficult to industrially produce it. On the other hand, if it exceeds 0.06%, the strength becomes high, and the press formability as a soft steel sheet is deteriorated. Therefore, in the present invention, the lower limit of the C content is 0.010%, preferably 0.015%.
%, More preferably 0.020%, and the upper limit is 0.06%.
%, Preferably 0.04%.
【００１１】Ｓｉ：０．５％以下 Ｓｉは固溶強化元素として鋼板の強度向上に寄与する
が、その一方で延性を低下させる。また、過多に添加す
ると溶融亜鉛めっき付着性を著しく劣化させる。このた
め、本発明では上限を０．５％、好ましくは０．２％と
する。Si: 0.5% or less Si contributes to the improvement of the strength of the steel sheet as a solid solution strengthening element, but on the other hand, it lowers the ductility. In addition, excessive addition significantly deteriorates the galvanizing adhesion. Therefore, in the present invention, the upper limit is set to 0.5%, preferably 0.2%.
【００１２】Ｍｎ：０．５％以上、２．０％未満 Ｍｎは焼入性向上元素であり、０．５％未満では焼入性
が過少であり、マルテンサイトの生成が困難となる。ま
た、熱間加工性も低下するようになる。一方、２．０％
以上ではめっき密着性が低下し、めっき不良が生じるよ
うになる。このため、Ｍｎ量を０．５％以上、好ましく
は０．８％以上とし、一方２．０％未満、好ましくは
１．８％以下とする。Mn: 0.5% or more and less than 2.0% Mn is an element for improving hardenability, and if it is less than 0.5%, hardenability is too low and formation of martensite becomes difficult. In addition, the hot workability also decreases. On the other hand, 2.0%
Above, the plating adhesion is reduced and plating failure occurs. Therefore, the Mn content is set to 0.5% or more, preferably 0.8% or more, while less than 2.0%, preferably 1.8% or less.
【００１３】Ｐ：０．２０％以下 Ｐは安価な固溶強化元素であり、鋼を強化するには有用
な元素であるが、本発明では延性の向上を重視するた
め、少ないほどよく、０．２０％以下に止める。好まし
くは０．１０％以下とするのがよい。P: 0.20% or less P is an inexpensive solid solution strengthening element and is a useful element for strengthening steel. However, in the present invention, since emphasis is placed on improving ductility, the smaller the better, the better. Keep below 20%. Preferably, it is 0.10% or less.
【００１４】Ｓ：０．０１％以下 ＳはＳ系析出物（主にＭｎＳ）を生成し、延性を劣化さ
せるので、少ない程よく、本発明では０．０１％以下、
好ましくは０．００６％以下に止める。S: 0.01% or less S forms S-based precipitates (mainly MnS) and deteriorates ductility.
Preferably, it is limited to 0.006% or less.
【００１５】Ａｌ：０．００５〜０．１０％ Ａｌは主に脱酸剤として作用し、少なくとも０．００５
％添加する必要がある。しかし、過多に添加すると脱酸
効果が飽和するだけでなく、アルミナ系介在物の生成に
より延性劣化、連鋳ノズル詰まりによる生産性の劣化等
の問題を引き起こすので、上限を０．１０％とする。Al: 0.005 to 0.10% Al mainly acts as a deoxidizing agent and has a content of at least 0.005%.
% Must be added. However, excessive addition not only saturates the deoxidizing effect, but also causes problems such as deterioration of ductility due to formation of alumina-based inclusions and deterioration of productivity due to clogging of a continuous casting nozzle. Therefore, the upper limit is set to 0.10%. .
【００１６】Ｎ：０．００５％以下 Ｎはその含有量が多いほど、Ｎを固定するのに要する窒
化物形成元素添加量が増えて製造コスト高を招き、また
延性を阻害するようになるので、本発明では少ないほど
よく、Ｎ量の上限を０．００５％、好ましくは０．００
３％とする。N: 0.005% or less As the content of N increases, the amount of addition of a nitride-forming element required for fixing N increases, leading to an increase in manufacturing cost and hindering ductility. In the present invention, the smaller the better, the better. The upper limit of the N content is 0.005%, preferably 0.005%.
3%.
【００１７】Ｃｒ：１．０％以下 Ｃｒは焼入性向上元素であり、Ｍｎと同様の作用を有す
る。また、固溶強化能が小さく本発明のような低強度Ｄ
Ｐ鋼に向くため、好ましくは０．３％以上含有させるの
がよいが、１．０％超では Ｃｒ7Ｃ3が生成して延性が
劣化するので、１．０％以下、好ましくは０．７％以下
とするのがよい。Cr: 1.0% or less Cr is a hardenability improving element and has the same effect as Mn. Further, the solid solution strengthening ability is small, and the low strength
Since it is suitable for P steel, it is preferable to contain 0.3% or more. However, if it exceeds 1.0%, Cr 7 C 3 is generated and ductility is deteriorated. It is better to be 7% or less.
【００１８】Ｍｎ＋１．３Ｃｒ：１．９〜２．３％ Ｍｎ＋１．３Ｃｒは焼入性を表す指標であり、この値が
１．９％未満では焼入性が不十分でマルテンサイト量が
不足する。一方、２．３％超ではめっき性を悪化させ、
めっき不良を誘発する。このため、Ｍｎ＋１．３Ｃｒの
下限を１．９％、好ましくは２．１％とし、一方上限を
２．３％、好ましくは２．２％とする。Mn + 1.3Cr: 1.9 to 2.3% Mn + 1.3Cr is an index indicating hardenability. If this value is less than 1.9%, hardenability is insufficient and the amount of martensite is insufficient. . On the other hand, if the content exceeds 2.3%, the plating property deteriorates,
Induces poor plating. For this reason, the lower limit of Mn + 1.3Cr is set to 1.9%, preferably 2.1%, while the upper limit is set to 2.3%, preferably 2.2%.
【００１９】本発明の溶融亜鉛めっき鋼板の母材冷延鋼
板は、以上の基本成分のほか、残部Ｆｅを本質的成分と
し、前記基本成分、残部Ｆｅおよび不可避的不純物から
なる組成をもつほか、前記基本成分の各作用を妨げない
範囲で、他の元素や、材質特性を向上させる元素を添加
することができる。The base material cold-rolled steel sheet of the hot-dip galvanized steel sheet according to the present invention has, in addition to the above basic components, a balance of Fe as an essential component, and a composition comprising the basic component, the balance of Fe and unavoidable impurities. Other elements and elements for improving the material properties can be added as long as the functions of the basic components are not hindered.
【００２０】母材冷延鋼板の組織は、フェライトと第２
相（マルテンサイトのほか、ベイナイトおよび／または
パーライト、）とからなり、組織中の前記第２相の割合
は、面積％で２０％以下、好ましくは１５％以下、より
好ましくは１０％以下とされる。２０％超では、強度が
高くなり、プレス成形性が低下するようになる。また、
第２相に占めるマルテンサイトの割合は５０％以上、好
ましくは８０％以上、より好ましくは８５％以上とされ
る。第２相中にベイナイトあるいはパーライトが５０％
超占めるようになると、フェライトに導入される可動転
位密度が小さくなり降伏強度（降伏比）が上昇するた
め、延性が低下するようになるからである。各組織の量
は顕微鏡観察によって面積率で測定される。なお、先に
述べたとおり、本発明の成分系においては、ベイナイト
とパーライトとは区別し難く、フェライト、マルテンサ
イト以外の相は棒状、球状の炭化物を含む相として観察
される。The microstructure of the base material cold-rolled steel sheet is ferrite and second
Phase (besides martensite, bainite and / or pearlite), and the ratio of the second phase in the structure is 20% or less, preferably 15% or less, more preferably 10% or less in area%. You. If it exceeds 20%, the strength is increased, and the press formability is reduced. Also,
The proportion of martensite in the second phase is at least 50%, preferably at least 80%, more preferably at least 85%. 50% bainite or perlite in phase 2
This is because, when the ferrite is over-occupied, the mobile dislocation density introduced into the ferrite decreases and the yield strength (yield ratio) increases, so that the ductility decreases. The amount of each tissue is measured by area ratio by microscopic observation. As described above, in the component system of the present invention, it is difficult to distinguish between bainite and pearlite, and phases other than ferrite and martensite are observed as phases containing rod-like and spherical carbides.
【００２１】また、本発明では前記マルテンサイトの粒
子同士の最近接粒子距離が平均で５．４μm 以下、好ま
しくは３．０μm 以下、より好ましくは２．７μm 以下
とされる。マルテンサイト粒子同士の最近接粒子間距離
を規定したのは、張り出し成形性向上のポイントとなる
マルテンサイト粒子の微細分散状態を定量的に表現する
ためであり、最近接粒子距離を５．４μm 以下とするこ
とで、良好な張り出し成形性が得られる。本発明者がマ
ルテンサイト粒子の分散状態と張り出し成形性との相関
について実験に基づいて詳細に調査したところ、前記第
２相の割合、および第２相中のマルテンサイト相の割合
に加え、この最近接粒子間距離を導入することで張り出
し成形性とマルテンサイト粒子の微細分散状態との相関
関係を正しく評価できることが見出された。より詳細に
説明すると、第２相および第２相中のマルテンサイト相
の割合が一定であれば、個々のマルテンサイト粒が大き
くなる程、言い換えるとマルテンサイト粒の単位面積あ
たりの個数が減少する程、個々の粒子間の間隔は広が
り、最近接粒子間距離が大きくなる。逆に、マルテンサ
イト相の量が同じであれば、粒子のサイズが小さけれ
ば、単位面積当たりの個数は増加し、個々の粒子間の距
離は近くなり、最近接粒子距離が小さくなる。従って、
第２相中のマルテンサイト相の割合および第２相中のマ
ルテンサイト粒子間の距離、すなわち最近接粒子間距離
の平均値を求めることにより第２相中のマルテンサイト
粒の微細分散状態を表現することとが可能となる。前記
マルテンサイト粒子の最近接粒子間距離は、例えば図１
に示すように、マルテンサイト粒を内接する方形枠を求
め、その枠間距離を測定することで求めることができ
る。かかる測定は、組織観察写真をコンピュータを用い
て画像解析することに容易に実施することができる。In the present invention, the closest particle distance between the martensite particles is 5.4 μm or less on average, preferably 3.0 μm or less, more preferably 2.7 μm or less. The reason for defining the distance between the closest particles between the martensite particles is to quantitatively express the finely dispersed state of the martensite particles, which is a point for improving the stretch formability, and the distance between the closest particles is 5.4 μm or less. By doing so, good overhang formability can be obtained. The present inventor has conducted detailed investigations on the correlation between the dispersion state of the martensite particles and the stretch formability based on experiments, and found that the ratio of the second phase, and the ratio of the martensite phase in the second phase, It was found that the correlation between the overhang formability and the finely dispersed state of the martensite particles can be correctly evaluated by introducing the distance between the closest particles. More specifically, if the ratio of the second phase and the martensite phase in the second phase is constant, the larger the individual martensite grains, the smaller the number of martensite grains per unit area decreases. As the distance between the particles increases, the distance between the nearest particles increases. Conversely, if the amount of the martensite phase is the same, if the size of the particles is small, the number per unit area increases, the distance between the individual particles becomes shorter, and the distance between the nearest particles becomes smaller. Therefore,
The fine dispersion state of the martensite grains in the second phase is expressed by calculating the ratio of the martensite phase in the second phase and the distance between the martensite grains in the second phase, that is, the average value of the distance between the closest grains. It is possible to do. The distance between the closest particles of the martensite particles is, for example, as shown in FIG.
As shown in Fig. 5, a square frame inscribed with martensite grains is obtained, and the distance between the frames is measured. Such measurement can be easily performed by analyzing the tissue observation photograph using a computer.
【００２２】以上の成分、組織とすることで、強度が５
００MPa 未満に低下し、延性が向上して強度−延性バラ
ンス（ＴＳ×Ｅｌ）が１７５００（MPa ・％）以上とす
ることができ、しかも降伏比が低くなって形状凍結性に
優れ、しかも良好な張り出し成形性が得られる。特に、
前記第２相を組織全体の１０％以下とし、かつ第２相中
のマルテンサイトを９０％以上とすることによって、強
度が５００ＭＰａ未満であっても、３９％程度以上の優
れた延性および１７０００MPa*％程度以上の優れた強度
−延性バランスが得られ、しかも降伏比を５０％程度以
下に低減させることができる。さらに、前記マルテンサ
イトの量的条件の下で、マルテンサイト粒子同士の最近
接粒子間距離を２．７μm 以下とすることによって、よ
り優れた張り出し成形性を得ることができる。このた
め、軟質鋼板用のプレス成形装置においても、優れた張
り出し成形性を得ることができる。By making the above components and structures, the strength is 5
It is reduced to less than 00 MPa, ductility is improved, and the strength-ductility balance (TS × El) can be 17500 (MPa ·%) or more. In addition, the yield ratio is low, so that the shape is freezing and excellent. Overhang formability is obtained. In particular,
By making the second phase 10% or less of the whole structure and the martensite in the second phase 90% or more, even if the strength is less than 500 MPa, excellent ductility of about 39% or more and 17000 MPa * are obtained. % Or more, an excellent strength-ductility balance can be obtained, and the yield ratio can be reduced to about 50% or less. Further, by setting the distance between the closest particles of martensite particles to 2.7 μm or less under the above-mentioned martensite quantitative conditions, more excellent stretch formability can be obtained. For this reason, even in a press forming apparatus for a soft steel plate, excellent overhang formability can be obtained.
【００２３】本発明の溶融亜鉛めっき鋼板の母材冷延鋼
板は、前記化学成分を有する鋼を溶製し、その鋼片を加
熱し、熱間圧延した後、特定の温度範囲にて巻き取り、
酸洗後、常法にて冷間圧延されたものである。巻き取り
温度を除き、熱延条件、冷延条件は通常の条件に従えば
よく、例えば、鋼片の加熱温度は１１００〜１２５０℃
程度とすればよく、熱延仕上げ温度はＡr3点以上とすれ
ばよい。また、冷延率は４０％程度以上、好ましくは５
０％程度以上とすればよい。巻き取り温度は製造条件に
おいて重要であり、５５０℃以下とすることが必要であ
る。母材冷延鋼板は、従来、５５０〜７５０℃で巻き取
られていたが、本発明では巻き取り温度を５５０℃以下
にする。これによって、微細な炭化物が生成し、冷間圧
延後の焼鈍時の再結晶過程において、微細なフェライ
ト、オーステナイトの結晶粒が生成し、焼鈍後のマルテ
ンサイト組織もより微細に分散し、マルテンサイト粒子
同士の最近接粒子間距離を前記所定範囲内にすることが
可能となり、その結果、張出し成形性が向上する。巻き
取り温度は低い程、微細な炭化物の析出がより促進さ
れ、マルテンサイト粒の最近接粒子間距離もより一層小
さくなるため、巻き取り温度は好ましくは５４０℃以
下、より好ましくは５００℃以下とするのがよい。The base material cold-rolled steel sheet of the hot-dip galvanized steel sheet of the present invention is obtained by melting a steel having the above-mentioned chemical composition, heating the steel slab, hot rolling, and winding the steel in a specific temperature range. ,
After pickling, it is cold rolled by a conventional method. Except for the winding temperature, the hot rolling conditions and the cold rolling conditions may be in accordance with ordinary conditions. For example, the heating temperature of the steel slab is 1100 to 1250 ° C.
And the hot-rolling finishing temperature may be Ar 3 points or more. The cold rolling rate is about 40% or more, preferably 5%.
It may be about 0% or more. The winding temperature is important in the production conditions and needs to be 550 ° C. or lower. Conventionally, the base material cold rolled steel sheet has been wound at 550 to 750 ° C, but in the present invention, the winding temperature is set to 550 ° C or less. As a result, fine carbides are generated, and fine ferrite and austenite crystal grains are generated in a recrystallization process at the time of annealing after cold rolling, and the martensite structure after annealing is more finely dispersed. The distance between the particles closest to each other can be set within the above-mentioned predetermined range, and as a result, the stretch formability is improved. As the winding temperature is lower, the precipitation of fine carbides is further promoted and the distance between the closest particles of martensite grains is further reduced, so that the winding temperature is preferably 540 ° C or lower, more preferably 500 ° C or lower. Good to do.
【００２４】このようにして得られた冷延鋼板は、連続
焼鈍めっきラインにてフェライト＋オーステナイトの２
相共存領域に加熱して再結晶焼鈍が行われた後、焼鈍温
度からめっき温度まで１〜１０℃／ｓ、好ましくは１〜
３℃／ｓの第１冷却速度で徐冷されて溶融亜鉛めっきが
施された後、冷却されて、溶融亜鉛めっき鋼板とされ
る。溶融亜鉛めっき後の第２冷却は、放冷でもよいが、
好ましくは１０℃／ｓ以上の冷却速度にて冷却するのが
よい。溶融亜鉛めっき層に合金化処理を施す場合には、
前記第１冷却速度にて徐冷して溶融亜鉛めっき処理を施
し、合金化処理を行った後、１０℃／ｓ以上の第２冷却
速度で急冷することが好ましい。The cold-rolled steel sheet thus obtained was subjected to a continuous ferrite + austenite by a continuous annealing plating line.
After the recrystallization annealing is performed by heating the phase coexistence region, from the annealing temperature to the plating temperature, 1 to 10 ° C./s, preferably 1 to 10 ° C./s.
After being gradually cooled at a first cooling rate of 3 ° C./s and subjected to hot-dip galvanizing, it is cooled to obtain a hot-dip galvanized steel sheet. The second cooling after hot-dip galvanizing may be allowed to cool,
Preferably, the cooling is performed at a cooling rate of 10 ° C./s or more. When performing alloying treatment on the hot-dip galvanized layer,
It is preferable that the steel sheet is gradually cooled at the first cooling rate, subjected to a hot-dip galvanizing treatment, alloyed, and then rapidly cooled at a second cooling rate of 10 ° C./s or more.
【００２５】前記冷延鋼板の処理条件をより詳しく説明
する。図２は、前記冷延鋼板の熱処理線図を示してお
り、上記のように、冷延鋼板は連続焼鈍めっきラインに
て再結晶焼鈍された後、溶融亜鉛めっきが施される。再
結晶焼鈍はフェライト＋オーステナイトの２相領域であ
る、７６０〜８４０℃程度で行えばよい。焼鈍温度が７
６０℃未満では熱延鋼板の炭化物がオーステナイトに十
分に溶け込まないため、炭化物が残存し、延性が低下す
る。一方、８４０℃を越えると第２相の面積率を２０％
未満にするのに焼鈍温度からの第１冷却速度（１ＣＲ）
を非常に遅くすることが必要となるため、工業的生産が
困難になる。好ましくは、下限を７８０℃、上限を８２
０℃とするのがよい。焼鈍時間は、連続焼鈍めっきライ
ンの場合、通常、数秒〜十数秒程度である。The processing conditions for the cold rolled steel sheet will be described in more detail. FIG. 2 shows a heat treatment diagram of the cold-rolled steel sheet. As described above, the cold-rolled steel sheet is subjected to recrystallization annealing in a continuous annealing plating line, and then subjected to hot-dip galvanizing. Recrystallization annealing may be performed at about 760 to 840 ° C., which is a two-phase region of ferrite and austenite. Annealing temperature 7
If the temperature is lower than 60 ° C., the carbide of the hot-rolled steel sheet does not sufficiently dissolve into austenite, so that the carbide remains and the ductility decreases. On the other hand, when the temperature exceeds 840 ° C., the area ratio of the second phase is reduced to 20%.
1st cooling rate from annealing temperature (1CR)
Needs to be very slow, which makes industrial production difficult. Preferably, the lower limit is 780 ° C and the upper limit is 82.
The temperature is preferably set to 0 ° C. The annealing time is usually about several seconds to about several tens of seconds in the case of a continuous annealing plating line.
【００２６】再結晶焼鈍後、溶融亜鉛めっき浴に浸漬す
るまでの第１冷却速度（１ＣＲ）は本発明において重要
に条件であり、１℃／ｓ以上、１０℃／ｓ以下とする。
１℃／ｓ未満ではパーライト変態が生じて、フェライト
量、マルテンサイト量が不足し、強度−延性バランスが
低下する。一方、１０℃／ｓ超では、フェライトの生成
に伴うオーステナイト中のＣ濃度の上昇によるベイナイ
ト変態の遅延が期待することができず、第２相の量およ
び第２相中のベイナイト量が増大し、延性が劣化するよ
うになる。このため、１ＣＲを１℃／ｓ以上とし、一方
１０℃／ｓ以下、好ましくは６℃／ｓ以下とする。特
に、フェライト量を増やし、第２相を全組織の１０％以
下にするには、１ＣＲを１℃／ｓ以上、３℃／ｓ以下に
することが望ましい。かかる冷却速度は、通常、焼鈍後
の鋼板の板厚に応じて制御される。前記第１冷却速度
は、従来に比して遅い冷却速度であり、焼鈍後の鋼板に
カバーを被せたり、カバー内に加熱空気を送給するなど
の積極的方策によって、鋼板の板厚に拘わらず、所期の
冷却速度を得ることもできる。After the recrystallization annealing, the first cooling rate (1CR) until immersion in the hot-dip galvanizing bath is an important condition in the present invention, and is set to 1 ° C./s or more and 10 ° C./s or less.
If it is less than 1 ° C./s, pearlite transformation occurs, the amount of ferrite and the amount of martensite become insufficient, and the strength-ductility balance decreases. On the other hand, when the temperature exceeds 10 ° C./s, the delay of bainite transformation due to an increase in the C concentration in austenite due to ferrite formation cannot be expected, and the amount of the second phase and the amount of bainite in the second phase increase. , The ductility deteriorates. For this reason, 1CR is set to 1 ° C./s or more, while it is set to 10 ° C./s or less, preferably 6 ° C./s or less. In particular, in order to increase the amount of ferrite and make the second phase 10% or less of the entire structure, it is desirable that 1CR be 1 ° C / s or more and 3 ° C / s or less. The cooling rate is usually controlled according to the thickness of the steel sheet after annealing. The first cooling rate is a cooling rate that is slower than the conventional cooling rate, and the first cooling rate is not limited by the thickness of the steel sheet by aggressive measures such as covering the annealed steel sheet with a cover or feeding heated air into the cover. Instead, the desired cooling rate can be obtained.
【００２７】溶融亜鉛めっきは、めっき温度が通常４０
０〜４８０℃程度の溶融亜鉛めっき浴に浸漬することに
よって行われる。めっき後、亜鉛めっき層を合金化しな
い場合はそのまま冷却する。この場合、めっき温度から
の冷却となり、冷却過程でパーライト変態が生じ難いた
め、めっき処理後の第２冷却速度（２ａＣＲ）の制限は
特になく、放冷するだけでよい。もっとも、２ａＣＲを
１０℃／ｓ以上で急冷することで、オーステナイトがパ
ーライト、ベイナイトに変態するのを一層抑制すること
ができ、これによって第２相中のマルテンサイト量を一
層増大させることができ、延性をより一層向上させるこ
とができる。特に、第２相中のマルテンサイト量を９０
％以上とするには、２ａＣＲを１０℃／ｓ以上、好まし
くは３０℃／ｓ以上にすることが望ましい。１０℃／ｓ
以上の冷却速度を得るには、強制空冷、冷却ローラによ
る搬送、あるいはミスト冷却を行えばよい。第２冷却速
度の上限は特に制限されないが、実際には冷却設備の冷
却能力により自ずから上限が定まる。In the case of hot-dip galvanizing, the plating temperature is usually 40
It is performed by immersing in a hot-dip galvanizing bath at about 0 to 480 ° C. After the plating, if the galvanized layer is not alloyed, it is cooled as it is. In this case, since the cooling is performed from the plating temperature and the pearlite transformation hardly occurs in the cooling process, there is no particular limitation on the second cooling rate (2aCR) after the plating treatment, and it is only necessary to allow the cooling. However, by rapidly cooling 2aCR at 10 ° C./s or more, the transformation of austenite into pearlite and bainite can be further suppressed, whereby the amount of martensite in the second phase can be further increased, Ductility can be further improved. In particular, the amount of martensite in the second phase is 90
%, It is desirable that 2aCR be 10 ° C./s or more, preferably 30 ° C./s or more. 10 ° C / s
In order to obtain the above cooling rate, forced air cooling, conveyance by a cooling roller, or mist cooling may be performed. Although the upper limit of the second cooling rate is not particularly limited, in practice, the upper limit is naturally determined by the cooling capacity of the cooling equipment.
【００２８】一方、溶融亜鉛めっき後に亜鉛めっき層を
合金化する場合には、めっき後、５００〜７００℃程度
の温度で、通常、数秒〜十数秒程度加熱する合金化処理
を行う。５００℃未満では、合金化に時間がかかるた
め、工業的生産に不適であり、一方７００℃を超えると
過度に合金化が進み、プレス成形時にパウダリング等の
問題が生じるようになる。好ましくは、５５０〜６００
℃程度である。On the other hand, when the galvanized layer is alloyed after the hot-dip galvanizing, an alloying treatment is carried out after the galvanizing by heating at a temperature of about 500 to 700 ° C., usually for about several seconds to about several tens of seconds. If the temperature is lower than 500 ° C., it takes a long time for alloying, which is not suitable for industrial production. On the other hand, if it exceeds 700 ° C., alloying proceeds excessively, and problems such as powdering at the time of press molding arise. Preferably, 550-600
It is about ° C.
【００２９】合金化処理後は、１０℃／ｓ以上、好まし
くは３０℃／ｓ以上の第２冷却速度（２ｂＣＲ）で冷却
する。合金化後の第２冷却速度２ｂＣＲは、１０℃／ｓ
未満の徐冷ではオーステナイトがパーライト、ベイナイ
トに変態し、第２相中のパーライト、ベイナイト量が増
大し、延性が劣化するようになる。母材冷延鋼板の第２
相の量が１０％以下の少量の場合、２ｂＣＲを２５℃／
ｓ以上、好ましくは３０℃／ｓ以上とすることで、第２
相中のマルテンサイト量を９０％以上とすることができ
る。以下、実施例により本発明をさらに説明するが、本
発明はかかる実施例によって限定的に解釈されるもので
はない。After the alloying treatment, cooling is performed at a second cooling rate (2bCR) of 10 ° C./s or more, preferably 30 ° C./s or more. The second cooling rate 2bCR after alloying is 10 ° C / s
When the cooling rate is lower than 10%, austenite is transformed into pearlite and bainite, the amount of pearlite and bainite in the second phase is increased, and ductility is deteriorated. Second base cold-rolled steel sheet
When the amount of the phase is as small as 10% or less, 2 bCR is added at 25 ° C. /
s or more, preferably 30 ° C./s or more,
The amount of martensite in the phase can be 90% or more. Hereinafter, the present invention will be further described with reference to examples, but the present invention is not construed as being limited to such examples.
【００３０】[0030]
【実施例】下記表１に記載した化学成分の鋼を真空誘導
溶解にて溶製し、その鋼片を１１５０℃にて加熱し、仕
上温度を８５０℃として熱間圧延を行い、４８０℃、６
８０℃にて巻取り、酸洗後、冷延率６０％で冷間圧延を
行い、厚さ１．２mmの冷延鋼板を得た。この冷延鋼板を
連続焼鈍めっきラインにて、８００℃×６０秒で再結晶
焼鈍を行い、表２および表３に示すように、８００℃か
ら冷却速度１ＣＲ（℃／ｓ）にて冷却した後、溶融亜鉛
めっき処理（めっき浴温４６０℃、浸漬時間２０秒）を
施し、試料No. ２０〜４１については放冷（２ａＣＲ＝
４℃／ｓ）あるいはミスト冷却（２ａＣＲ＝１０〜３０
℃／ｓ）を行った。一方、試料No. １〜１９，４２，４
３については、前記条件にて溶融亜鉛めっき後、さらに
５５０℃×１５秒にて合金化処理を行い、その後ミスト
冷却（２ｂＣＲ＝３０℃／ｓ）、あるいは放冷（２ｂＣ
Ｒ＝４℃／ｓ）により冷却した。EXAMPLES Steels having the chemical components described in Table 1 below were melted by vacuum induction melting, and the steel slabs were heated at 1150 ° C., hot-rolled at a finishing temperature of 850 ° C., and heated at 480 ° C. 6
After winding at 80 ° C. and pickling, cold rolling was performed at a cold rolling rate of 60% to obtain a cold-rolled steel sheet having a thickness of 1.2 mm. This cold-rolled steel sheet was subjected to recrystallization annealing at 800 ° C. × 60 seconds in a continuous annealing plating line, and was cooled from 800 ° C. at a cooling rate of 1 CR (° C./s) as shown in Tables 2 and 3. And hot-dip galvanizing treatment (plating bath temperature 460 ° C., immersion time 20 seconds), and the samples No. 20 to 41 were allowed to cool (2aCR =
4 ° C / s) or mist cooling (2aCR = 10-30)
° C / s). On the other hand, sample Nos. 1 to 19, 42, 4
For No. 3, after hot-dip galvanizing under the above conditions, an alloying treatment was further performed at 550 ° C. × 15 seconds, and then mist cooling (2 bCR = 30 ° C./s) or cooling (2 bC
(R = 4 ° C./s).
【００３１】得られた試料から組織観察試験片を採取
し、ミクロ組織を以下の要領で観察した。試験片からめ
っき層を除去し、ナイタール腐食後、１０００倍でＳＥ
Ｍ観察した組織を画像解析により第２相（Ｍ＋Ｂあるい
はＭ＋Ｐ、但しＭ：マルテンサイト、Ｂ：ベイナイト、
Ｐ：パーライト）の面積率を測定した。次にレペラ腐食
後、１０００倍で光学顕微鏡観察した組織を画像解析し
てマルテンサイト量を測定し、第２相に占めるマルテン
サイトの割合（Ｍ／第２相）を求めた。また、マルテン
サイト粒子の分散状態（最近接粒子間距離）は、レペラ
ー腐食後の組織写真よりマルテンサイト粒子をトレース
して市販の画像解析ソフト（商品名：画像解析システム
ＬＵＺＥＸ−Ｆ、製造メーカ：ニレコ）を用いて求め
た。画像解析ソフトでは組織写真中の全マルテンサイト
粒子の各々について最近接粒子間距離を測定し、それら
の平均を求めた。また、得られた試料から引張試験片
（ＪＩＳ５号試験片）および張り出し成形性評価用試験
片を採取し、引張試験（ＪＩＳ２２４１に定められた試
験法）によって機械的性質を調べた。また、半径５０mm
の球頭ポンチによる張り出し試験によって張り出し高さ
を測定し、張り出し高さによって張り出し成形性を評価
した。これらの調査結果を表２および表３に併せて示
す。同表中、Ｍ粒子間距離は、マルテンサイト粒子間の
最近接粒子間距離の平均値を意味する。From the obtained sample, a specimen for tissue observation was collected, and the microstructure was observed in the following manner. The plating layer was removed from the test piece, and after nital corrosion, SE was increased by 1000 times.
The M-observed tissue was analyzed by image analysis to obtain a second phase (M + B or M + P, where M: martensite, B: bainite,
P: pearlite). Next, after the repeller corrosion, the structure observed by an optical microscope at a magnification of 1000 was image analyzed to measure the amount of martensite, and the ratio of martensite in the second phase (M / second phase) was determined. In addition, the dispersion state of martensite particles (distance between closest particles) can be determined by tracing martensite particles from a photograph of the structure after repeller corrosion and commercially available image analysis software (trade name: image analysis system LUZEX-F, manufacturer: Nireco). With the image analysis software, the distance between the closest particles was measured for each of all the martensite particles in the structure photograph, and the average thereof was obtained. In addition, a tensile test piece (JIS No. 5 test piece) and a test piece for stretch formability evaluation were collected from the obtained sample, and mechanical properties were examined by a tensile test (a test method defined in JIS2241). In addition, radius 50mm
The overhang height was measured by an overhang test using a ball-head punch, and the overhang height was used to evaluate the overhang formability. The results of these investigations are shown in Tables 2 and 3. In the table, the distance between M particles means the average value of the distance between the closest particles between the martensite particles.
【００３２】[0032]
【表１】 [Table 1]
【００３３】[0033]
【表２】 [Table 2]
【００３４】[0034]
【表３】 [Table 3]
【００３５】表２、表３より、本発明の鋼成分を有する
鋼種Ｂ〜Ｆ、Ｌ〜Ｐ、Ｕを用い、焼鈍後の冷却速度１Ｃ
Ｒを１０℃／ｓ以下で徐冷してめっき処理を行った溶融
亜鉛めっき鋼板の発明例（試料No. ２２，２４，２７，
２９，３１，３７，３９，４１）、合金化処理後の冷却
速度２ｂＣＲを１０℃／ｓ以上とした合金化溶融亜鉛め
っき鋼板の発明例（No. ３，５，１１，１３，１５，４
３）では、いずれも第２相が組織全体の２０％以下に止
まっており、またその内にマルテンサイト量が８０％以
上となり、またマルテンサイト粒子間の最近接粒子間距
離の平均が５．４μm 以下となっている。このため、強
度が５００MPa 未満に低減される一方、強度−延性バラ
ンスが１７０００MPa*％程度以上であり、しかも降伏比
が最大でも５３％である。さらに、張り出し高さ（ｈ
（ｒｐ２５））が２１．９mm以上となっており、優れた
延性を備え、張り出し成形性に優れることがわかる。特
に、試料No. ３７，３９，４１，４３では、第２相面積
率が１０％以下で、しかも第２相中のマルテンサイト量
が９０％であり、第２相量を減らしつつ、第２相中のマ
ルテンサイト量を増やしたので、伸びが３９％以上で、
降伏比が５０％以下となっており、さらにマルテンサイ
ト粒子間の最近接粒子間距離の平均が２．７μm 以下と
なり、より優れた張り出し成形性を有していることがわ
かる。From Tables 2 and 3, it can be seen that steel types BF, LP and U having the steel components of the present invention were used, and the cooling rate after annealing was 1 C.
Invention Examples of Galvanized Steel Sheets (Sample Nos. 22, 24, 27,
29, 31, 37, 39, 41), invention examples of alloyed hot-dip galvanized steel sheet with a cooling rate of 2 bCR after alloying treatment of 10 ° C./s or more (Nos. 3, 5, 11, 13, 15, 15 and 4)
In (3), in all cases, the second phase is less than 20% of the whole structure, the martensite content is 80% or more, and the average distance between closest particles between martensite particles is 5. It is 4 μm or less. Therefore, while the strength is reduced to less than 500 MPa, the strength-ductility balance is about 17000 MPa *% or more, and the yield ratio is 53% at the maximum. In addition, the overhang height (h
(Rp25)) is 21.9 mm or more, which means that it has excellent ductility and excellent stretch formability. In particular, in Sample Nos. 37, 39, 41, and 43, the area ratio of the second phase was 10% or less, and the amount of martensite in the second phase was 90%. Since the amount of martensite in the phase was increased, the growth was 39% or more,
The yield ratio was 50% or less, and the average of the distance between the closest particles between the martensite particles was 2.7 μm or less, indicating that there was more excellent stretch formability.
【００３６】[0036]
【発明の効果】本発明の溶融亜鉛めっき鋼板によれば、
マルテンサイトを含む複合組織であるにもかからわず、
５００MPa 未満と強度が低く、また強度−延性バランス
に優れ、さらに降伏比も低いので、延性に優れ、優れた
張り出し成形性を備える。また、本発明の製造方法によ
れば、特に巻き取り温度を５５０℃以下とし、再結晶焼
鈍後の第１冷却速度を１〜１０℃／ｓとし、また溶融亜
鉛めっき層に合金化処理を施す場合には前記第１冷却速
度にて冷却するほか、合金化処理後の冷却速度を１０℃
／ｓ以上とするので、マルテンサイトを含む第２相を減
らしつつ、その中のマルテンサイト量を増やすことがで
き、さらにマルテンサイトを微細分散させることがで
き、前記張り出し成形性の優れた溶融亜鉛めっき鋼板を
容易に製造することができる。According to the hot-dip galvanized steel sheet of the present invention,
Despite being a composite organization containing martensite,
Since the strength is low at less than 500 MPa, the strength-ductility balance is excellent, and the yield ratio is low, so that it has excellent ductility and excellent stretch formability. According to the production method of the present invention, the winding temperature is set to 550 ° C. or lower, the first cooling rate after recrystallization annealing is set to 1 to 10 ° C./s, and the galvannealed layer is alloyed. In this case, besides cooling at the first cooling rate, the cooling rate after the alloying treatment is 10 ° C.
/ S or more, it is possible to increase the amount of martensite therein while reducing the amount of the second phase containing martensite, furthermore, it is possible to finely disperse martensite, and the above-described molten zinc having excellent stretch forming properties. A plated steel sheet can be easily manufactured.
【図１】マルテンサイト粒の最近接粒子間距離の測定要
領説明図である。BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is an explanatory diagram of a procedure for measuring a distance between closest particles of martensite grains.
【図２】本発明にかかる溶融亜鉛めっき鋼板のの製造過
程を示す熱処理線図である。FIG. 2 is a heat treatment diagram showing a production process of a hot-dip galvanized steel sheet according to the present invention.
───────────────────────────────────────────────────── フロントページの続き (51)Int.Cl.7 識別記号 ＦＩ テーマコート゛(参考） Ｃ２３Ｃ 2/40 Ｃ２３Ｃ 2/40 (72)発明者 槙井 浩一 兵庫県神戸市西区高塚台１丁目５番５号 株式会社神戸製鋼所神戸総合技術研究所内 (72)発明者 新堂 陽介 兵庫県神戸市西区高塚台１丁目５番５号 株式会社神戸製鋼所神戸総合技術研究所内 Ｆターム(参考） 4K027 AA02 AA05 AA23 AB02 AB28 AB42 AB43 AC12 AC72 AC73 AD27 AE12 4K037 EA01 EA05 EA11 EA15 EA18 EA23 EA25 EA27 EB05 EB11 FB00 FE01 FG00 FH01 FK02 FK03 GA05 HA00 JA06 ──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. 7 Identification code FI Theme coat ゛ (Reference) C23C 2/40 C23C 2/40 (72) Inventor Koichi Makii 1-5-5 Takatsukadai, Nishi-ku, Kobe-shi, Hyogo Prefecture No. 5 Kobe Steel, Ltd. Kobe Research Institute (72) Inventor Yosuke Shindo 1-5-5 Takatsukadai, Nishi-ku, Kobe City, Hyogo Prefecture F-term in Kobe Steel Co., Ltd. Kobe Research Institute 4K027 AA02 AA05 AA23 AB02 AB28 AB42 AB43 AC12 AC72 AC73 AD27 AE12 4K037 EA01 EA05 EA11 EA15 EA18 EA23 EA25 EA27 EB05 EB11 FB00 FE01 FG00 FH01 FK02 FK03 GA05 HA00 JA06
Claims (7)
〜０．０６％、Ｓｉ：０．５％以下、Ｍｎ：０．５％以
上、２．０％未満、Ｐ ：０．２０％以下、Ｓ ：０．
０１％以下、Ａｌ：０．００５〜０．１０％、Ｎ ：
０．００５％以下、Ｃｒ：１．０％以下、かつＭｎ＋
１．３Ｃｒ：１．９〜２．３％および残部Ｆｅを本質的
成分とし、組織がフェライトとマルテンサイトを含む第
２相とからなり、組織中の第２相の割合が面積率で２０
％以下であり、かつ第２相に占めるマルテンサイトの割
合が５０％以上であり、しかもマルテンサイト粒子同士
の最近接粒子間距離が平均で５．４μm 以下である冷延
鋼板を母材とし、その表面に溶融亜鉛めっき層が形成さ
れた、延性および張り出し成形性に優れる溶融亜鉛めっ
き鋼板。C. 0.010% by weight of a chemical component.
0.06%, Si: 0.5% or less, Mn: 0.5% or more, less than 2.0%, P: 0.20% or less, S: 0.
01% or less, Al: 0.005 to 0.10%, N:
0.005% or less, Cr: 1.0% or less, and Mn +
1.3Cr: 1.9 to 2.3% and the balance Fe as essential components, and the structure is composed of a ferrite and a second phase containing martensite, and the ratio of the second phase in the structure is 20 in area ratio.
% Or less, and the proportion of martensite in the second phase is 50% or more, and the distance between the closest particles between the martensite particles is 5.4 μm or less on average. Hot-dip galvanized steel sheet with a hot-dip galvanized layer formed on its surface and excellent in ductility and stretch formability.
以下であり、かつ第２相に占めるマルテンサイトの割合
が９０％以上であり、しかもマルテンサイト粒子同士の
最近接粒子間距離が平均で２．７μm 以下である請求項
１に記載した溶融亜鉛めっき鋼板。2. The ratio of the second phase in the tissue is 10% in area ratio.
2. The hot-dip galvanized steel according to claim 1, wherein the ratio of martensite in the second phase is 90% or more, and the distance between closest martensite particles is 2.7 μm or less on average. steel sheet.
母材とし、その表面に合金化溶融亜鉛めっき層が形成さ
れた、延性および張り出し成形性に優れる溶融亜鉛めっ
き鋼板。3. A hot-dip galvanized steel sheet having excellent ductility and stretch formability, wherein the cold-rolled steel sheet according to claim 1 or 2 is used as a base material and an alloyed hot-dip galvanized layer is formed on the surface thereof.
材を熱間圧延後、５５０℃以下の温度で巻き取り、その
後冷間圧延を施し、これによって得られた冷延鋼板を連
続焼鈍めっきラインにてフェライト＋オーステナイトの
２相共存領域に加熱して再結晶焼鈍を行った後、焼鈍温
度からめっき温度まで１〜１０℃／ｓの第１冷却速度で
冷却して溶融亜鉛めっきを施した後、冷却する、延性お
よび張り出し成形性に優れる溶融亜鉛めっき鋼板の製造
方法。4. A steel material having the chemical composition described in claim 1 is hot-rolled, then wound at a temperature of 550 ° C. or lower, and then cold-rolled, and the cold-rolled steel sheet obtained by this is subjected to continuous annealing plating. After heating the two-phase coexistence region of ferrite + austenite in the line to perform recrystallization annealing, the steel sheet was cooled from the annealing temperature to the plating temperature at a first cooling rate of 1 to 10 ° C./s to perform hot-dip galvanizing. A method for producing a galvanized steel sheet having excellent ductility and stretch formability after cooling.
ｓの第１冷却速度で冷却して溶融亜鉛めっきを施した
後、１０℃／ｓ以上の第２冷却速度で冷却する請求項４
に記載した溶融亜鉛めっき鋼板の製造方法。5. An annealing temperature to a plating temperature of 1 to 3 ° C.
5. After cooling at a first cooling rate of s to perform hot-dip galvanizing, cooling at a second cooling rate of 10 ° C./s or more.
2. A method for producing a hot-dip galvanized steel sheet according to item 1.
材を熱間圧延後、５５０℃以下の温度で巻き取り、その
後冷間圧延を施し、これによって得られた冷延鋼板を連
続焼鈍めっきラインにてフェライト＋オーステナイトの
２相共存領域に加熱して再結晶焼鈍を行った後、焼鈍温
度からめっき温度まで１〜１０℃／ｓの第１冷却速度で
冷却して溶融亜鉛めっきを施した後、さらに溶融亜鉛め
っき層の合金化処理を施し、その後１０℃／ｓ以上の第
２冷却速度で冷却する、延性および張り出し成形性に優
れる溶融亜鉛めっき鋼板の製造方法。6. A steel material having the chemical composition described in claim 1 is hot-rolled, then wound at a temperature of 550 ° C. or lower, and then cold-rolled, and the cold-rolled steel sheet obtained by this is subjected to continuous annealing plating. After heating the two-phase coexistence region of ferrite + austenite in the line to perform recrystallization annealing, the steel sheet was cooled from the annealing temperature to the plating temperature at a first cooling rate of 1 to 10 ° C./s to perform hot-dip galvanizing. Thereafter, a method for producing a hot-dip galvanized steel sheet having excellent ductility and stretch formability, wherein the hot-dip galvanized layer is further alloyed and then cooled at a second cooling rate of 10 ° C./s or more.
ｓの第１冷却速度で冷却する請求項６に記載した溶融亜
鉛めっき鋼板の製造方法。7. From an annealing temperature to a plating temperature, 1 to 3 ° C. /
The method for producing a hot-dip galvanized steel sheet according to claim 6, wherein the steel sheet is cooled at a first cooling rate of s.
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Cited By (11)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| JP2007077510A (en) * | 2006-11-16 | 2007-03-29 | Jfe Steel Kk | High-strength high-ductility galvanized steel sheet excellent in aging resistance and its production method |
| WO2007080810A1 (en) * | 2006-01-11 | 2007-07-19 | Jfe Steel Corporation | Hot-dip zinc-coated steel sheets and process for production thereof |
| US7559997B2 (en) | 2002-06-25 | 2009-07-14 | Jfe Steel Corporation | High-strength cold rolled steel sheet and process for producing the same |
| CN102597292A (en) * | 2009-11-09 | 2012-07-18 | 新日本制铁株式会社 | High-strength steel sheet having excellent processability and paint bake hardenability, and method for producing same |
| CN103146998A (en) * | 2013-02-28 | 2013-06-12 | 首钢总公司 | Over-400Mpa galvanized high-strength structural steel and production method thereof |
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| EP2184374A4 (en) * | 2007-07-11 | 2017-01-04 | JFE Steel Corporation | High-strength hot-dip galvanized steel sheet and process for producing the same |
| CN113286910A (en) * | 2019-03-29 | 2021-08-20 | 日本制铁株式会社 | Steel sheet and method for producing same |
| CN113825846A (en) * | 2019-05-07 | 2021-12-21 | 美国钢铁公司 | Method for producing continuously cast hot-rolled high-strength steel sheet product |
| CN114555846A (en) * | 2019-10-31 | 2022-05-27 | 杰富意钢铁株式会社 | Steel sheet, member, and method for producing same |
| CN115181916A (en) * | 2021-04-02 | 2022-10-14 | 宝山钢铁股份有限公司 | 1280 MPa-level low-carbon low-alloy ultrahigh-strength hot-dip galvanized dual-phase steel and rapid heat treatment hot-dip galvanizing manufacturing method |
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2001
- 2001-04-25 JP JP2001127216A patent/JP3907963B2/en not_active Expired - Fee Related
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| US7559997B2 (en) | 2002-06-25 | 2009-07-14 | Jfe Steel Corporation | High-strength cold rolled steel sheet and process for producing the same |
| EP1972698A4 (en) * | 2006-01-11 | 2014-06-18 | Jfe Steel Corp | Hot-dip zinc-coated steel sheets and process for production thereof |
| WO2007080810A1 (en) * | 2006-01-11 | 2007-07-19 | Jfe Steel Corporation | Hot-dip zinc-coated steel sheets and process for production thereof |
| JP2007211338A (en) * | 2006-01-11 | 2007-08-23 | Jfe Steel Kk | Hot dip galvanized steel sheet and its manufacturing method |
| EP1972698A1 (en) * | 2006-01-11 | 2008-09-24 | JFE Steel Corporation | Hot-dip zinc-coated steel sheets and process for production thereof |
| JP2007077510A (en) * | 2006-11-16 | 2007-03-29 | Jfe Steel Kk | High-strength high-ductility galvanized steel sheet excellent in aging resistance and its production method |
| EP2169091A4 (en) * | 2007-07-11 | 2016-11-30 | Jfe Steel Corp | High-strength hot-dip galvanized steel sheet with low yield strength and with less material quality fluctuation and process for producing the same |
| EP2184374A4 (en) * | 2007-07-11 | 2017-01-04 | JFE Steel Corporation | High-strength hot-dip galvanized steel sheet and process for producing the same |
| EP2500445A1 (en) * | 2009-11-09 | 2012-09-19 | Nippon Steel Corporation | High-strength steel sheet having excellent processability and paint bake hardenability, and method for producing of high-strength steel sheet |
| CN102597292A (en) * | 2009-11-09 | 2012-07-18 | 新日本制铁株式会社 | High-strength steel sheet having excellent processability and paint bake hardenability, and method for producing same |
| EP2500445A4 (en) * | 2009-11-09 | 2017-05-17 | Nippon Steel & Sumitomo Metal Corporation | High-strength steel sheet having excellent processability and paint bake hardenability, and method for producing of high-strength steel sheet |
| US8911567B2 (en) | 2009-11-09 | 2014-12-16 | Nippon Steel & Sumitomo Metal Corporation | High-strength steel sheet having excellent processability and paint bake hardenability, and method for producing of high-strength steel sheet |
| CN103146998A (en) * | 2013-02-28 | 2013-06-12 | 首钢总公司 | Over-400Mpa galvanized high-strength structural steel and production method thereof |
| CN113286910A (en) * | 2019-03-29 | 2021-08-20 | 日本制铁株式会社 | Steel sheet and method for producing same |
| CN113825846A (en) * | 2019-05-07 | 2021-12-21 | 美国钢铁公司 | Method for producing continuously cast hot-rolled high-strength steel sheet product |
| CN114555846B (en) * | 2019-10-31 | 2023-11-24 | 杰富意钢铁株式会社 | Steel sheet, component, and method for producing same |
| CN114555846A (en) * | 2019-10-31 | 2022-05-27 | 杰富意钢铁株式会社 | Steel sheet, member, and method for producing same |
| CN115181916A (en) * | 2021-04-02 | 2022-10-14 | 宝山钢铁股份有限公司 | 1280 MPa-level low-carbon low-alloy ultrahigh-strength hot-dip galvanized dual-phase steel and rapid heat treatment hot-dip galvanizing manufacturing method |
| CN115181916B (en) * | 2021-04-02 | 2023-09-12 | 宝山钢铁股份有限公司 | 1280 MPa-level low-carbon low-alloy ultrahigh-strength hot dip galvanized dual-phase steel and rapid heat treatment hot dip galvanizing manufacturing method |
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