JP2013076139A - High-strength hot-dip galvanized steel sheet superior in plating adhesion and formability, and method for manufacturing the same - Google Patents
High-strength hot-dip galvanized steel sheet superior in plating adhesion and formability, and method for manufacturing the same Download PDFInfo
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本発明は、自動車部品などに用いられるめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板とその製造方法に関するものである。 The present invention relates to a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and formability used for automobile parts and the like, and a method for producing the same.
近年、環境問題への対応のため炭酸ガス排出低減や燃費低減を目的に自動車の軽量化が望まれている。また、衝突安全性向上に対する要求はますます高くなっている。自動車の軽量化や衝突安全性向上のためには鋼材の高強度化が有効な手段である。ところが、通常は鋼材を高強度化すると加工性が劣化するため、高強度と加工性を両立する鋼板が必要とされている。 In recent years, in order to cope with environmental problems, it has been desired to reduce the weight of automobiles for the purpose of reducing carbon dioxide emissions and reducing fuel consumption. In addition, there is an increasing demand for improved collision safety. Increasing the strength of steel is an effective means for reducing the weight of automobiles and improving collision safety. However, since the workability usually deteriorates when the strength of the steel material is increased, a steel sheet that achieves both high strength and workability is required.
高延性を有する高強度鋼板として、フェライトとマルテンサイトの２相組織からなるＤｕａl Ｐｈａｓｅ鋼（以下ＤＰ鋼と称す）が開発されており、固溶強化鋼板や析出強化鋼板よりも強度−延性バランスが優れていることに加え、引張強度（ＴＳ）に対する降伏応力（ＹＰ）の割合を示す降伏比（＝ＹＰ/ＴＳ）が低くプレス成形後の形状凍結性に優れるため、使用量が増加してきている。 As a high-strength steel sheet having high ductility, a dual phase steel (hereinafter referred to as DP steel) composed of a two-phase structure of ferrite and martensite has been developed, and has a higher strength-ductility balance than solid solution strengthened steel sheets and precipitation strengthened steel sheets. In addition to being excellent, the yield ratio (= YP / TS) indicating the ratio of the yield stress (YP) to the tensile strength (TS) is low and the shape freezing property after press molding is excellent, so the amount used is increasing. .
また、自動車用高強度鋼板は適用される部品によっては耐食性が必要とされ、そのような場合には溶融亜鉛めっき鋼板が適用されている。また、溶融亜鉛めっきを行った後に合金化処理をした（合金化）溶融亜鉛めっき鋼板も適用されている。 Further, high strength steel sheets for automobiles require corrosion resistance depending on the applied parts, and in such cases, hot dip galvanized steel sheets are applied. In addition, a hot-dip galvanized steel sheet that has been subjected to alloying treatment after being hot-dip galvanized (alloyed) is also applied.
溶融亜鉛めっき鋼板は、通常、ゼンジマー法で製造されるが、焼鈍設備とめっき設備が連続化されており、めっき性を確保するために焼鈍温度からの冷却速度に制約があるため、冷却後にマルテンサイトを確保するためにはＣｒやＭｏなどの合金元素を多量に添加する必要があり、コストが高くなるという問題があった。また、上記ＤＰ鋼においては、延性向上のためにＳｉが添加されるが、Ｓｉ含有量が高いとＳｉが鋼板表面に濃縮し酸化するため、溶融亜鉛めっき時に不めっきが発生し易いという問題があった。 Hot-dip galvanized steel sheets are usually manufactured by the Sendzimer method, but the annealing equipment and plating equipment are continuous, and the cooling rate from the annealing temperature is limited in order to ensure plating properties. In order to secure the site, it is necessary to add a large amount of alloy elements such as Cr and Mo, and there is a problem that the cost becomes high. Further, in the DP steel, Si is added to improve ductility, but if the Si content is high, Si concentrates on the surface of the steel sheet and oxidizes, so that there is a problem that non-plating is likely to occur during hot dip galvanizing. there were.
一方、特許文献１及び２において、Ｓｉ添加高強度鋼板につき、Ｎｉプレめっき後、４３０〜５００℃まで急速加熱し、亜鉛めっき後に４７０〜５５０℃に加熱して合金化処理を行うという合金化溶融亜鉛めっき高強度鋼板の製造方法が記載されている。この方法の場合、原板としてすでに材質を造り込んでいる冷延−焼鈍プロセスで製造した冷延鋼板を使用することが可能であり、最高到達温度が５５０℃程度であることから、原板の加工性をあまり損なわずに合金化溶融亜鉛めっき鋼板を製造することができると考えられる。また、Ｎｉプレめっきなどの処理により、Ｓｉ含有量が高くても不めっきが生じにくい。 On the other hand, in Patent Documents 1 and 2, for Si-added high-strength steel sheet, after Ni pre-plating, it is rapidly heated to 430 to 500 ° C, and after galvanization, it is heated to 470 to 550 ° C to perform alloying melting. A method for producing a galvanized high strength steel sheet is described. In the case of this method, it is possible to use a cold-rolled steel plate manufactured by a cold-rolling-annealing process in which the material has already been made as the original plate, and the maximum reachable temperature is about 550 ° C. It is considered that an alloyed hot-dip galvanized steel sheet can be produced without much damage. In addition, non-plating is less likely to occur even when the Si content is high due to treatment such as Ni pre-plating.
特許文献３にはこのＮiプレめっきの技術を活用して低降伏比型合金化溶融亜鉛めっき鋼板を作製する技術が提案されている。これは、鋼成分、焼鈍条件、合金化溶融亜鉛めっき条件などを制御して、通常の冷延−焼鈍プロセスで製造したＤＰ鋼の冷延鋼板と同等の低降伏比と延性を有する低降伏比型合金化溶融亜鉛めっき鋼板を提供しようとするものである。 Patent Document 3 proposes a technique for producing a low yield ratio galvannealed steel sheet using this Ni pre-plating technique. This is because the steel composition, annealing conditions, alloying hot dip galvanizing conditions, etc. are controlled, and the low yield ratio and ductility are the same as those of DP steel cold-rolled steel sheets manufactured by the normal cold-rolling-annealing process. An object of the present invention is to provide a type alloyed hot-dip galvanized steel sheet.
しかしながら、このようなプロセスで製造した溶融亜鉛めっき鋼板は、延性には優れているものの、穴拡げ性が低いという問題があった。穴拡げ性に優れた鋼板としては、特許文献４に提案されているように、鋼組織をベイナイト単相または析出強化したフェライト単相の組織とすることで組織の均質化を図り、優れた穴拡げ性を有する鋼板が提案されている。しかしこれらの穴拡げ性に優れた鋼板は軟質のフェライト組織を含まないために、延性が低いことに加え、降伏比も高くなるため、張り出し成形性や形状凍結性は劣る。従って、これらの技術を使ってＮｉプレめっき法による溶融亜鉛めっき鋼板の穴拡げ性を改善することは困難である。 However, although the hot dip galvanized steel sheet manufactured by such a process is excellent in ductility, there is a problem that hole expansibility is low. As proposed in Patent Document 4, as a steel plate excellent in hole expansibility, the steel structure is made to be a bainite single phase structure or a precipitation-strengthened ferrite single phase structure so that the structure can be homogenized and excellent holes can be obtained. A steel sheet having expandability has been proposed. However, since these steel plates excellent in hole expansibility do not contain a soft ferrite structure, in addition to low ductility, the yield ratio is also high, so the stretch formability and shape freezeability are poor. Therefore, it is difficult to improve the hole expandability of the hot dip galvanized steel sheet by the Ni pre-plating method using these techniques.
本発明は、上述したような問題点を解決しようとするものであって、焼鈍済みの冷延鋼板を原板としてNiプレめっき法による溶融亜鉛めっき鋼板を製造するに当たり、めっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板とその製造方法を提供するものである。 The present invention is intended to solve the above-mentioned problems, and in producing a hot-dip galvanized steel sheet by Ni pre-plating method using an annealed cold-rolled steel sheet as a base sheet, the plating adhesion and formability are improved. An excellent high-strength hot-dip galvanized steel sheet and a method for producing the same are provided.
本発明者らは、Ｃ、Ｓｉ、Ｍｎ量を変えた種々の鋼について、実験室で溶解、熱延、冷延、焼鈍、合金化溶融亜鉛めっきを行い、所用の強度、延性、穴拡げ性、めっき性を得るための方法を種々検討した。その結果、成分を特定したうえで、冷延-焼鈍後に表面層を０．１μｍ以上研削を行った後にＮｉプレめっきすること、合金化処理温度を５６０℃以下に低温化すること、この手法の温度工程を活用して３種類のマルテンサイトの量を制御すること、により延性やめっき性を劣化させることなく穴拡げ性を向上させることができ、めっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板を製造することができることを見出した。本発明の要旨は、以下のとおりである。
（１）
質量％で、
Ｃ：０．１０〜０．４０％、
Ｓｉ：０．０１〜３．０％、
Ｍｎ：１．７〜３．０％、
Ｐ：０．０４％以下、
Ｓ：０．０１％以下、
Ａｌ：０．００５〜２．０％、
Ｎ：０．００１〜０．０１%、
を含有し、Ｓｉ及びＡｌの含有量が、
Ｓｉ＋Ａｌ＞０．５％
を満足し、残部がＦｅ及び不可避的不純物からなり、
ミクロ組織が、体積分率で主相として次に指定する3種類のマルテンサイト［１］［２］［３］の１種または２種以上とベイナイトを合わせて４０％以上含有し、
マルテンサイト［１］：C濃度（CM1）が0.8質量%未満で、硬さHv1が、
Hv1／（-982.1×CM12＋1676×CM1+189）≦0.60
マルテンサイト［２］:C濃度（CM2）が0.8質量%以上で、硬さHv2が、
Hv2／（-982.1×CM22＋1676×CM2+189）≦0.60
マルテンサイト［３］:C濃度（CM3）が0.8質量%以上で、硬さHv3が、
Hv3／（-982.1×CM32＋1676×CM3+189）≧0.80
残留オーステナイトを０．１〜８％未満含有し、残部組織がフェライトからなる鋼板の表面に、Feを７質量％未満含有し、残部がZn、Alおよび不可避的不純物からなる溶融亜鉛めっき層を有することを特徴とする引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。
（２）
質量％で、
Ｃ：０．１０〜０．４０％、
Ｓｉ：０．０１〜３．０％、
Ｍｎ：１．７〜３．０％、
Ｐ：０．０４％以下、
Ｓ：０．０１％以下、
Ａｌ：０．００５〜２．０％、
Ｎ：０．００１〜０．０１%、
を含有し、Ｓｉ及びＡｌの含有量が、
Ｓｉ＋Ａｌ＞０．５％
を満足し、残部がＦｅ及び不可避的不純物からなり、
ミクロ組織が、体積分率で主相として次に指定する3種類のマルテンサイト［１］［２］［３］の１種または２種以上とベイナイトを合わせて４０％以上含有し、
マルテンサイト［１］：C濃度（CM1）が0.8質量未満で、硬さHv1が、
Hv1／（-982.1×CM12＋1676×CM1+189）≦0.60
マルテンサイト［２］:C濃度（CM2）が0.8質量%以上で、硬さHv2が、
Hv2／（-982.1×CM22＋1676×CM2+189）≦0.60
マルテンサイト［３］:C濃度（CM3）が0.8質量%以上で、硬さHv3が、
Hv3／（-982.1×CM322＋1676×CM3+189）≧0.80
残留オーステナイトを０．１〜８％未満含有し、残部組織がフェライトからなる鋼板の表面に、Ｆｅを７〜１５質量％を含有し、残部がＺｎ、Ａｌおよび不可避的不純物からなる溶融亜鉛めっき層を有することを特徴とする引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。
（３）
３種類のマルテンサイト［１］［２］［３］がそれぞれ、体積分率で
マルテンサイト［１］：１％以上、５０％以下、
マルテンサイト［２］：１％以上、３０％以下、
マルテンサイト［３］：１％以上、１０％以下、
であることを特徴とする（１）または（２）に記載の引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。
（４）
更に、質量％で、
Ｔｉ：０．００５〜０．３％、
Ｎｂ：０．００５〜０．３％、
Ｖ ：０．０１〜０．５％
の1種又は2種以上を含有することを特徴とする上記（１）〜（３）のいずれか１項に記載の引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。
（５）
更に、質量％で、
Ｃｒ：３．０％以下、
Ｍｏ：３．０％以下、
Ｎｉ：５．０％以下、
Ｃｕ：３．０％以下
の1種又は2種以上を含有することを特徴とする上記（１）〜（４）のいずれか１項に記載の引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。
（６）
更に、質量%で、
Ｂ：０．０１％以下
を含有することを特徴とする請求項1〜５のいずれか１項に記載の引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。
（７）
更に、質量%で、
Ｃａ：０．０１％以下、
Ｍｇ：０．０１％以下、
Ｚｒ：０．０５％以下、
ＲＥＭ：０．０５％以下
の１種または２種以上を含有することを特徴とする上記（１）〜（６）のいずれかに記載の引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。
（８）
上記（１）〜（７）のいずれかに記載の鋼板を製造する際、
鋳造スラブを直接または一旦冷却した後１１００℃以上に加熱し、Ar3変態点以上で熱間圧延を完了し、６３０℃以下の温度域にて巻き取り、酸洗、圧下率４０〜７０％の冷延を施し、８００〜９００℃にて焼鈍し、さらに６５０℃以上から４５０℃以下まで２０℃／秒以上で冷却して、３５０〜４５０℃の範囲で１２０秒以上保持し、５０℃以下まで冷却した後、鋼板の表面層を０．１μｍ以上研削除去し、Ｎｉをプレめっきし、２０℃／秒以上の昇温速度で４３０〜４８０℃まで加熱後、溶融亜鉛めっきすることを特徴とする引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板の製造方法。
（９）
上記（１）〜（７）のいずれかに記載の鋼板を製造する際、鋳造スラブを直接または一旦冷却した後１１００℃以上に加熱し、Ar3変態点以上で熱間圧延を完了し、６３０℃以下の温度域にて巻き取り、酸洗、圧下率４０〜７０％の冷延を施し、８００〜９００℃にて焼鈍し、さらに６５０℃以上から４５０℃以下まで２０℃／秒以上で冷却して、３５０〜４５０℃の範囲で１２０秒以上保持し、冷却した後、鋼板の表面層を０．１μｍ以上研削除去し、Ｎｉをプレめっきし、２０℃／秒以上の昇温速度で４３０〜４８０℃まで加熱後、溶融亜鉛めっきし、４７０〜５６０℃で１０〜４０秒の合金化処理を行うことを特徴とする引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板の製造方法。
The present inventors performed melting, hot rolling, cold rolling, annealing, alloying hot dip galvanizing in various laboratories for various steels with different amounts of C, Si, and Mn, and required strength, ductility, and hole expandability. Various methods for obtaining plating properties were studied. As a result, after specifying the components, the surface layer is ground by 0.1 μm or more after cold rolling-annealing and then Ni pre-plating, the alloying temperature is lowered to 560 ° C. or lower, By controlling the amount of three types of martensite using a temperature process, hole expandability can be improved without deteriorating ductility and plating properties, and high strength melting with excellent plating adhesion and formability. It has been found that galvanized steel sheets can be produced. The gist of the present invention is as follows.
(1)
% By mass
C: 0.10 to 0.40%,
Si: 0.01-3.0%,
Mn: 1.7-3.0%,
P: 0.04% or less,
S: 0.01% or less,
Al: 0.005 to 2.0%,
N: 0.001 to 0.01%,
And the content of Si and Al is
Si + Al> 0.5%
And the balance consists of Fe and inevitable impurities,
The microstructure contains 40% or more of bainite in combination with one or more of three types of martensite [1] [2] [3] specified next as the main phase in volume fraction,
Martensite [1]: C concentration (CM1) is less than 0.8% by mass, hardness Hv1 is
Hv1 // (-982.1 × CM1 2 + 1676 × CM1 + 189) ≦ 0.60
Martensite [2]: C concentration (CM2) is 0.8 mass% or more, hardness Hv2 is
Hv2 // (-982.1 × CM2 2 + 1676 × CM2 + 189) ≦ 0.60
Martensite [3]: C concentration (CM3) is 0.8 mass% or more, hardness Hv3 is
Hv3 / (-982.1 × CM3 2 + 1676 × CM3 + 189) ≧ 0.80
A steel sheet containing 0.1 to 8% of retained austenite and the remaining structure being made of ferrite has less than 7% by weight of Fe, and the remainder has a hot-dip galvanized layer made of Zn, Al and inevitable impurities. A high-strength hot-dip galvanized steel sheet with a tensile strength of 980 MPa or more and excellent plating adhesion and formability.
(2)
% By mass
C: 0.10 to 0.40%,
Si: 0.01-3.0%,
Mn: 1.7-3.0%,
P: 0.04% or less,
S: 0.01% or less,
Al: 0.005 to 2.0%,
N: 0.001 to 0.01%,
And the content of Si and Al is
Si + Al> 0.5%
And the balance consists of Fe and inevitable impurities,
The microstructure contains 40% or more of bainite in combination with one or more of three types of martensite [1] [2] [3] specified next as the main phase in volume fraction,
Martensite [1]: C concentration (CM1) is less than 0.8 mass, hardness Hv1 is
Hv1 // (-982.1 × CM1 2 + 1676 × CM1 + 189) ≦ 0.60
Martensite [2]: C concentration (CM2) is 0.8 mass% or more, hardness Hv2 is
Hv2 // (-982.1 × CM2 2 + 1676 × CM2 + 189) ≦ 0.60
Martensite [3]: C concentration (CM3) is 0.8 mass% or more, hardness Hv3 is
Hv3 / (-982.1 × CM3 2 2 + 1676 × CM3 + 189) ≧ 0.80
Hot-dip galvanized layer containing less than 0.1 to 8% of retained austenite, the balance of 7 to 15% by mass of Fe on the surface of the steel plate made of ferrite, and the balance of Zn, Al and inevitable impurities A high-strength hot-dip galvanized steel sheet excellent in plating adhesion and formability having a tensile strength of 980 MPa or more.
(3)
The three types of martensite [1] [2] [3] have a volume fraction of martensite [1]: 1% or more, 50% or less,
Martensite [2]: 1% or more, 30% or less,
Martensite [3]: 1% or more, 10% or less,
A high-strength hot-dip galvanized steel sheet excellent in plating adhesion and formability having a tensile strength of 980 MPa or more as described in (1) or (2).
(4)
Furthermore, in mass%,
Ti: 0.005 to 0.3%,
Nb: 0.005-0.3%
V: 0.01 to 0.5%
High strength hot dip galvanizing with excellent plating adhesion and formability having a tensile strength of 980 MPa or more according to any one of the above (1) to (3), characterized by containing one or more of steel sheet.
(5)
Furthermore, in mass%,
Cr: 3.0% or less,
Mo: 3.0% or less,
Ni: 5.0% or less,
Cu: 3.0% or less of one type or two or more types, (1) to (4) characterized in that the plating adhesion and formability having a tensile strength of 980 MPa or more according to any one of the above (1) to (4) Excellent high-strength hot-dip galvanized steel sheet.
(6)
Furthermore, in mass%,
B: A high-strength hot-dip galvanized steel sheet excellent in plating adhesion and formability having a tensile strength of 980 MPa or more according to any one of claims 1 to 5, characterized by containing 0.01% or less.
(7)
Furthermore, in mass%,
Ca: 0.01% or less,
Mg: 0.01% or less,
Zr: 0.05% or less,
REM: 0.05% or less of one type or two or more types, (1) to (6) characterized in having excellent plating adhesion and formability having a tensile strength of 980 MPa or more High strength hot dip galvanized steel sheet.
(8)
When manufacturing the steel sheet according to any one of (1) to (7) above,
The cast slab is directly or once cooled and then heated to 1100 ° C or higher, and hot rolling is completed at the Ar3 transformation point or higher, wound in a temperature range of 630 ° C or lower, pickled, and cooled at a rolling reduction of 40 to 70%. And then annealed at 800 to 900 ° C., further cooled from 650 ° C. to 450 ° C. at 20 ° C./second or more, held at 350 to 450 ° C. for 120 seconds or more, and cooled to 50 ° C. or less. Then, the surface layer of the steel sheet is ground and removed by 0.1 μm or more, Ni is pre-plated, heated to 430 to 480 ° C. at a temperature rising rate of 20 ° C./second or more, and then hot-dip galvanized. A method for producing a high-strength hot-dip galvanized steel sheet having a strength of 980 MPa or more and excellent plating adhesion and formability.
(9)
When manufacturing the steel sheet according to any one of (1) to (7) above, the cast slab is directly or once cooled and then heated to 1100 ° C or higher, and the hot rolling is completed at the Ar3 transformation point or higher, and 630 ° C. Winding in the following temperature range, pickling, cold rolling with a rolling reduction of 40 to 70%, annealing at 800 to 900 ° C., further cooling from 650 ° C. to 450 ° C. at 20 ° C./s or more. Then, after holding for 120 seconds or more in the range of 350 to 450 ° C. and cooling, the surface layer of the steel plate is ground and removed by 0.1 μm or more, Ni is pre-plated, and 430 to 430 at a temperature rising rate of 20 ° C./second or more. High-strength hot-dip galvanizing with excellent plating adhesion and formability having a tensile strength of 980 MPa or more, characterized by performing hot-dip galvanizing after heating to 480 ° C and performing alloying treatment at 470-560 ° C for 10-40 seconds A method of manufacturing a steel sheet.
本発明によれば、めっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板を得ることができ、産業上の貢献が極めて顕著である。 According to the present invention, a high-strength hot-dip galvanized steel sheet excellent in plating adhesion and formability can be obtained, and the industrial contribution is extremely remarkable.
まず、本発明におけるめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板の成分限定理由について説明する。なお、以下、組成における質量％は単に％と記す。 First, the reasons for limiting the components of the high-strength hot-dip galvanized steel sheet excellent in plating adhesion and formability in the present invention will be described. Hereinafter, mass% in the composition is simply referred to as%.
Ｃ：Ｃは鋼の強度を増加させる元素として添加されるものである。０．１０％未満では９８０ＭＰａ以上の引張強度の確保が困難であり、０．４０％を超える過剰の添加は延性、溶接性、靭性などを著しく劣化させる。従って、Ｃ含有量は０．１０〜０．４０％とした。より好ましい範囲は、０．１０〜０．３０％である。 C: C is added as an element for increasing the strength of steel. If it is less than 0.10%, it is difficult to ensure a tensile strength of 980 MPa or more, and excessive addition exceeding 0.40% significantly deteriorates ductility, weldability, toughness, and the like. Therefore, the C content is set to 0.10 to 0.40%. A more preferable range is 0.10 to 0.30%.
Ｓｉ：Ｓｉは固溶強化により鋼板の強度を増大させるのに有用な元素である。また、Ｓｉはセメンタイトの生成を抑制するため、ベイナイト変態時にオーステナイト中へのＣの濃化を促進させる効果をもち、焼鈍後に残留オーステナイトを生成させるのに必須の元素である。０．０１％未満ではそれらの効果が発現されず、３．０％を超える過剰の添加は熱間圧延で生じるスケールの剥離性や化成処理性を著しく劣化させるため、Ｓｉ含有量は０．０１〜３．０％とした。 Si: Si is an element useful for increasing the strength of a steel sheet by solid solution strengthening. Further, Si suppresses the formation of cementite, and thus has an effect of promoting the concentration of C into austenite during bainite transformation, and is an essential element for generating residual austenite after annealing. If it is less than 0.01%, those effects are not expressed, and excessive addition exceeding 3.0% remarkably deteriorates the peelability and chemical conversion treatment of the scale caused by hot rolling, so the Si content is 0.01 -3.0%.
Ｍｎ：Ｍｎは焼入れ性を高めるために有効な元素である。１．７％未満では焼入れ性を高める効果が十分には発現されず、３．０％を超える過剰の添加は靭性を劣化させる。従って、Ｍｎ含有量は１．７〜３．０％とした。 Mn: Mn is an element effective for improving the hardenability. If it is less than 1.7%, the effect of improving hardenability is not sufficiently exhibited, and excessive addition exceeding 3.0% deteriorates toughness. Therefore, the Mn content is set to 1.7 to 3.0%.
Ｐ：Ｐは、粒界に偏析して粒界強度を低下させ、靱性を劣化させる不純物元素であり、低減させることが望ましい。Ｐの含有量の上限は、現状の精錬技術と製造コストを考慮し、０．０４％に制限した。 P: P is an impurity element that segregates at the grain boundary to lower the grain boundary strength and degrade the toughness, and is desirably reduced. The upper limit of the P content is limited to 0.04% in consideration of the current refining technology and manufacturing costs.
Ｓ：Ｓは、熱間加工性及び靭性を劣化させる不純物元素であり、低減させることが望ましい。Ｓの含有量の上限は、現状の精錬技術と製造コストを考慮し、０．０１％に制限した。 S: S is an impurity element that degrades hot workability and toughness, and is desirably reduced. The upper limit of the S content was limited to 0.01% in consideration of the current refining technology and manufacturing costs.
Ａｌ：Ａｌは脱酸剤として、またＡｌＮを形成し結晶粒粗大化を抑制する効果がある。また、Ｓｉと同様にフェライト安定化元素であり、Ｓｉの代替として使用することもできる。０．００５％未満ではそれらの効果が発現されず、２．０％を超えて過剰添加すると靭性が劣化するため、Ａｌの含有量を０．００５〜２．０％とした。 Al: Al is effective as a deoxidizer and suppresses grain coarsening by forming AlN. Moreover, it is a ferrite stabilizing element like Si, and can be used as a substitute for Si. If it is less than 0.005%, those effects are not manifested, and if over 2.0% is added excessively, the toughness deteriorates, so the Al content was made 0.005 to 2.0%.
Ｎ：Ｎは窒化物を形成し結晶粒粗大化を抑制する効果があるが、０．００１％未満ではその効果が発現されず、０．０１％を超えて添加すると靭性が劣化するため、Ｎ含有量を０．００１〜０．０１％とした。 N: N has the effect of forming nitrides and suppressing crystal grain coarsening, but if less than 0.001%, the effect is not manifested, and if added over 0.01%, the toughness deteriorates. The content was 0.001 to 0.01%.
Ｓｉ＋Ａｌ：ＳｉとＡｌはフェライト安定化とセメンタイト抑制という同じ働きをする元素である。したがって、ＡｌとＳｉの合計添加量が重要となってくる。この合計添加量が、０．５％以下であると、フェライト安定化とセメンタイト抑制の働きが弱くなるため、０．５％より多く添加することとした。過剰の添加は効果が飽和するばかりでなく、スケール形成により、表面性状を著しく劣化させること、めっきの濡れ性を著しく損なうことから、上限は３%以下が望ましい。 Si + Al: Si and Al are elements having the same functions of stabilizing ferrite and suppressing cementite. Therefore, the total addition amount of Al and Si becomes important. If this total addition amount is 0.5% or less, the functions of ferrite stabilization and cementite suppression are weakened, so more than 0.5% is added. The excessive addition not only saturates the effect, but also significantly deteriorates the surface properties and significantly impairs the wettability of the plating due to scale formation. Therefore, the upper limit is preferably 3% or less.
以上が本発明の基本成分であり、通常、上記以外はＦｅ及び不可避的不純物からなるが、所望の強度レベルやその他の必要特性に応じて、Ｃｒ、Ｍｏ、Ｎｉ、Ｃｕ、Ｔｉ、Ｎｂ、Ｖ、Ｂ、Ｃａ、Ｍｇ、Ｚｒ、ＲＥＭの１種又は２種以上を添加しても良い。 The above are the basic components of the present invention, which are usually composed of Fe and unavoidable impurities other than the above, but depending on the desired strength level and other necessary characteristics, Cr, Mo, Ni, Cu, Ti, Nb, V , B, Ca, Mg, Zr, or REM may be added.
Ｔｉ：ＴｉはＴｉＮを形成する元素であり、結晶粒の粗大化の抑制に有効である。靭性を高めるには、０．００５％以上のＴｉを添加することが好ましい。しかし、Ｔｉを過剰に添加するとＴｉＮが粗大化し、靭性が劣化することがある。したがって、Ｔｉの含有量を０．３％以下にすることが好ましい。 Ti: Ti is an element that forms TiN and is effective in suppressing the coarsening of crystal grains. In order to increase toughness, 0.005% or more of Ti is preferably added. However, when Ti is added excessively, TiN becomes coarse and toughness may deteriorate. Therefore, the Ti content is preferably 0.3% or less.
Ｎｂ：Ｎｂは微細な炭窒化物を形成する元素であり、結晶粒の粗大化の抑制に有効である。靭性を高めるには、０．００５％以上のＮｂを添加することが好ましい。しかし、Ｎｂを過剰に添加すると析出物が粗大になり、靭性が劣化することがある。したがって、Ｎｂの含有量を０．３％以下にすることが好ましい。 Nb: Nb is an element that forms fine carbonitrides and is effective in suppressing the coarsening of crystal grains. In order to increase toughness, it is preferable to add 0.005% or more of Nb. However, when Nb is added excessively, the precipitate becomes coarse and the toughness may be deteriorated. Therefore, the Nb content is preferably 0.3% or less.
Ｖ：Ｖは、Ｎｂと同様、微細な炭窒化物を形成する元素である。結晶粒の粗大化を抑制し、靭性を高めるには、０．０１％以上のＶを添加することが好ましい。Ｖ含有量が０．５％を超えると、靭性が劣化することがあるため、Ｖ量の上限は０．５％以下が好ましい。 V: V, like Nb, is an element that forms fine carbonitrides. In order to suppress coarsening of crystal grains and increase toughness, it is preferable to add 0.01% or more of V. If the V content exceeds 0.5%, the toughness may deteriorate, so the upper limit of the V content is preferably 0.5% or less.
Ｃｒ、Ｍｏ、Ｎｉ、Ｃｕ：Ｃｒ、Ｍｏ、Ｎｉ、Ｃｕは、延性及び靭性を向上させる有効な元素である。しかし、Ｃｒ、Ｍｏ、Ｃｕの含有量は、それぞれ、３．０％、Ｎｉの含有量は５．０％を超えると、強度の上昇によって、靭性を損なうことがある。したがって、Ｃｒ量の上限は３．０％以下、Ｍｏ量の上限は３．０％以下、Ｎｉ量の上限は５．０％以下、Ｃｕ量の上限は３．０％以下が好ましい。また、延性及び靭性を向上させるには、Ｃｒ量は０．０５以上、Ｍｏ量は０．０５％以上、Ｎｉ量は０．０５％以上、Ｃｕ量は０．１０％以上が好ましい。 Cr, Mo, Ni, Cu: Cr, Mo, Ni, Cu are effective elements that improve ductility and toughness. However, if the content of Cr, Mo, Cu is 3.0% and the content of Ni exceeds 5.0%, the toughness may be impaired due to the increase in strength. Therefore, the upper limit of the Cr amount is preferably 3.0% or less, the upper limit of the Mo amount is 3.0% or less, the upper limit of the Ni amount is 5.0% or less, and the upper limit of the Cu amount is preferably 3.0% or less. In order to improve ductility and toughness, the Cr content is preferably 0.05 or more, the Mo content is 0.05% or more, the Ni content is 0.05% or more, and the Cu content is preferably 0.10% or more.
Ｂ：Ｂは粒界に偏析し、Ｐ及びＳの粒界偏析を抑制する元素である。また、焼き入れ性を高めるのに有効な元素でもある。しかし、Ｂ量が０．０１％を超えると、粒界に粗大な析出物を生じて、熱間加工性や靭性を損なうことがある。したがって、Ｂの含有量を０．０１％以下とする。なお、粒界の強化によって、延性、靭性及び熱間加工性を向上させたり、焼き入れ性を向上させるためには、０．０００３％以上のＢの添加が好ましい。 B: B is an element that segregates at the grain boundaries and suppresses the grain boundary segregation of P and S. It is also an effective element for enhancing the hardenability. However, if the amount of B exceeds 0.01%, coarse precipitates are produced at the grain boundaries, which may impair hot workability and toughness. Therefore, the B content is 0.01% or less. In order to improve ductility, toughness, hot workability, and improve hardenability by strengthening grain boundaries, 0.0003% or more of B is preferably added.
Ｃａ、Ｍｇ、Ｚｒ、ＲＥＭ：Ｃａ、Ｍｇ、Ｚｒ、ＲＥＭは、硫化物の形態を制御し、Ｓによる熱間加工性や靭性の劣化の抑制に有効な元素である。しかし、過剰に添加しても効果が飽和するため、Ｃａは０．０１％以下、Ｍｇは０．０１％以下、Ｚｒは０．０５％以下、ＲＥＭは０．０５％以下を添加することが好ましい。靭性を向上させるには、Ｃａは０．００１０％以上、Ｍｇは０．０００５％以上、Ｚｒは０．００１０％以上、ＲＥＭは０．００１０％以上を添加することが好ましい。 Ca, Mg, Zr, REM: Ca, Mg, Zr, and REM are elements that control the form of sulfide and are effective in suppressing hot workability and toughness deterioration due to S. However, since the effect is saturated even if it is added excessively, it is possible to add 0.01% or less of Ca, 0.01% or less of Mg, 0.05% or less of Zr, and 0.05% or less of REM. preferable. In order to improve toughness, it is preferable to add 0.0010% or more of Ca, 0.0005% or more of Mg, 0.0010% or more of Zr, and 0.0010% or more of REM.
次に製造条件の限定理由について述べる。
本発明においては、上記の成分からなる鋼を常法で溶製し、鋳造する。得られた鋼片を熱間圧延する。更に、酸洗、冷間圧延及び焼鈍を施した後、Niプレめっきを行い、その後、亜鉛めっきまたは、亜鉛めっき後、合金化処理を行う。
Next, the reasons for limiting the manufacturing conditions will be described.
In the present invention, the steel composed of the above components is melted and cast by a conventional method. The obtained steel slab is hot-rolled. Furthermore, after performing pickling, cold rolling, and annealing, Ni pre-plating is performed, and then galvanization or galvanization is followed by alloying treatment.
熱間圧延においては鋳造スラブを直接または一旦冷却した後１１００℃以上に加熱し、Ar3変態点以上で熱間圧延する。加熱温度が１１００℃未満では材料の均質化が不十分となることから、加熱温度の下限は１１００℃とした。仕上げ圧延温度はオーステナイト＋フェライトの２相域になると鋼板内の不均一性が大きくなり、焼鈍後の成形性が劣化するので仕上げ圧延温度はAr3変態点以上とした。 In hot rolling, the cast slab is directly or once cooled, then heated to 1100 ° C. or higher, and hot rolled at or above the Ar3 transformation point. If the heating temperature is less than 1100 ° C., the material is not sufficiently homogenized, so the lower limit of the heating temperature is 1100 ° C. When the finish rolling temperature is in the two-phase region of austenite + ferrite, the non-uniformity in the steel sheet increases and the formability after annealing deteriorates, so the finish rolling temperature was set to the Ar3 transformation point or higher.
熱間圧延における巻取り温度は６３０℃を超えると、熱延板組織が粗大なフェライト・パーライト組織となり、冷間圧延、焼鈍、亜鉛めっき及び合金化処理後の最終的な鋼板の組織が不均一な組織となり、良好な穴拡げ性が得られないので、巻取り温度の上限は６３０℃にした。より好ましくは、巻取り温度を５２０℃以下とし、ベイナイト単相とするとよい。巻取り温度の下限は特に規定するものではないが、３００℃未満であると熱延板の強度が高くなり冷間圧延に支障をきたす場合があるので、３００℃以上であることが望ましい。 When the coiling temperature in hot rolling exceeds 630 ° C., the hot rolled sheet structure becomes a coarse ferrite / pearlite structure, and the structure of the final steel sheet after cold rolling, annealing, galvanizing and alloying treatment is not uniform. Therefore, the upper limit of the coiling temperature was set to 630 ° C. More preferably, the coiling temperature is set to 520 ° C. or lower to form a bainite single phase. The lower limit of the coiling temperature is not particularly specified, but if it is less than 300 ° C, the strength of the hot-rolled sheet becomes high and may interfere with cold rolling.
冷間圧延は、焼鈍後のミクロ組織を微細化するため、圧下率を４０％以上とする。一方、冷間圧延の圧下率は、７０％を超えると、加工硬化によって負荷が高くなり、生産性を損なう。したがって、冷間圧延の圧下率は、４０〜７０％とする。 In cold rolling, the reduction ratio is set to 40% or more in order to refine the microstructure after annealing. On the other hand, when the rolling reduction of cold rolling exceeds 70%, the load increases due to work hardening, and the productivity is impaired. Therefore, the rolling reduction of cold rolling is 40 to 70%.
冷間圧延後、焼鈍を施す。本発明では、鋼板のミクロ組織を制御するために、焼鈍の加熱温度及び冷却条件が極めて重要である。 After cold rolling, annealing is performed. In the present invention, in order to control the microstructure of the steel sheet, the heating temperature and cooling conditions for annealing are extremely important.
冷間圧延後の焼鈍温度は、熱延時に生成したセメンタイトを十分に溶解し、Ｃが十分に濃化したオーステナイトを確保するために、８００〜９００℃の範囲にした。焼鈍温度が８００℃未満であると必要なオーステナイト量が得られない。焼鈍温度が９００℃を超えるとオーステナイト分率が高くなりすぎ、オーステナイトへのＣの濃化が不十分となる。 The annealing temperature after cold rolling was in the range of 800 to 900 ° C. in order to sufficiently dissolve the cementite produced during hot rolling and to secure austenite in which C was sufficiently concentrated. If the annealing temperature is less than 800 ° C., the necessary austenite amount cannot be obtained. When the annealing temperature exceeds 900 ° C., the austenite fraction becomes too high, and the concentration of C in the austenite becomes insufficient.
焼鈍後は、６５０℃以上の温度から４５０℃以下の温度まで２０℃／秒以上の速度で冷却し、３５０〜４５０℃の範囲で１２０秒以上保持する必要がある。これらの条件のいずれかを逸脱すると、ベイナイト変態が十分に進まず、オーステナイト中へのＣの濃化が不十分となり、冷却後に十分な量の残留オーステナイトを得ることができなくなる。なお、亜鉛めっき及び合金化処理後に十分な強度を確保するためには焼鈍後に十分な量の残留オーステナイトを確保し、合金化処理の冷却過程で一部の残留オーステナイトをマルテンサイトに変態させる必要がある。また、焼鈍時に生成したスケールを除去するために焼鈍後に酸洗を行ってもよい。また、焼鈍後に形状矯正及び降伏点伸びの消失のために調質圧延を行ってもよい。伸び率が０．２％未満ではその効果が十分でなく、伸び率が２％を超えると降伏比が大幅に増大するとともに伸びが劣化する。従って、伸び率を０．２％〜２％とすることが望ましい。
焼鈍（冷却)した後、鋼板の表面層を厚さ０．１μｍ以上研削除去し、その後、Ｎｉをプレめっきする必要がある。鋼板の表面層を０．１μｍ以上研削除去した後にＮｉをプレめっきすることにより、亜鉛めっき後の合金化処理時に、合金化が促進され、合金化処理時の加熱温度を下げることができる。これにより、合金化処理時に残留オーステナイトが分解してセメンタイトが生成することにより穴拡げ性が劣化するのを防ぐことができる。合金化が促進されるメカニズムについては明確ではないが、研削により鋼板表層部に導入される歪の影響により、表面が活性化することが考えられる。鋼板の表面層を研削除去する方法としては、ブラシ研磨、サンドペーパー研磨、機械研磨などの方法を用いればよい。Ｎｉプレめっきの方法は電気めっき、浸漬めっき、スプレーめっきのいずれでもよく、めっき量は０．２〜２ｇ／ｍ２程度が望ましい。鋼板の表面層を研削除去する量が０．１μｍ未満である場合やＮｉプレめっきを行わない場合には、合金化促進効果が得られず、合金化温度を高くせざるを得ないため後術するように穴拡げ性の劣化を防ぐことができない。より合金化促進効果を得るためには鋼板の表面層を研削除去する量を０．５μｍ以上とすることが望ましい。
After annealing, it is necessary to cool at a rate of 20 ° C./second or higher from a temperature of 650 ° C. or higher to a temperature of 450 ° C. or lower and hold it in the range of 350 to 450 ° C. for 120 seconds or longer. If one of these conditions is deviated, the bainite transformation does not proceed sufficiently, the concentration of C in the austenite becomes insufficient, and a sufficient amount of retained austenite cannot be obtained after cooling. In order to secure sufficient strength after galvanizing and alloying treatment, it is necessary to secure a sufficient amount of retained austenite after annealing and transform some retained austenite into martensite during the cooling process of alloying treatment. is there. Moreover, in order to remove the scale produced | generated at the time of annealing, you may perform pickling after annealing. Further, after annealing, temper rolling may be performed for shape correction and loss of yield point elongation. If the elongation is less than 0.2%, the effect is not sufficient. If the elongation exceeds 2%, the yield ratio is greatly increased and the elongation is deteriorated. Therefore, it is desirable that the elongation rate is 0.2% to 2%.
After annealing (cooling), it is necessary to grind and remove the surface layer of the steel sheet with a thickness of 0.1 μm or more, and then to pre-plat Ni. By pre-plating Ni after grinding and removing the surface layer of the steel sheet by 0.1 μm or more, alloying is promoted during the alloying treatment after galvanization, and the heating temperature during the alloying treatment can be lowered. Thereby, it is possible to prevent the hole expandability from deteriorating due to decomposition of residual austenite and generation of cementite during the alloying process. Although the mechanism by which alloying is promoted is not clear, it is conceivable that the surface is activated by the influence of strain introduced into the steel sheet surface layer portion by grinding. As a method for grinding and removing the surface layer of the steel plate, methods such as brush polishing, sandpaper polishing, and mechanical polishing may be used. The Ni pre-plating method may be any of electroplating, immersion plating and spray plating, and the plating amount is preferably about 0.2 to 2 g / m 2 . When the amount of grinding and removing the surface layer of the steel sheet is less than 0.1 μm, or when Ni pre-plating is not performed, the effect of promoting alloying cannot be obtained, and the alloying temperature must be increased, so that the post-operation As such, the deterioration of the hole expandability cannot be prevented. In order to obtain a further alloying promotion effect, it is desirable that the amount of grinding and removing the surface layer of the steel sheet be 0.5 μm or more.
Ｎｉをプレめっきした後、２０℃／秒以上の加熱速度で４３０〜４８０℃まで加熱後、亜鉛めっき浴中で亜鉛めっきを行い、さらに必要に応じて、４７０〜５６０℃で１０〜４０秒の合金化処理を行う。加熱速度が２０℃／秒未満では、鋼板の表面層を研削除去することにより導入された歪が緩和され合金化促進効果が得られなくなる。加熱温度が４３０℃未満ではめっき時に不めっきを生じやすく、４８０℃を超えると鋼板の表面層を研削除去することにより導入された歪が緩和され合金化促進効果が得られなくなる。合金化処理が４７０℃未満では合金化が不十分であり、５６０℃を超えると残留オーステナイトが分解してセメンタイトが生成することにより穴拡げ性が劣化する。合金化時間については、合金化温度とのバランスで決まるが、１０〜４０秒の範囲が適当である。１０秒未満では合金化が進みにくく、４０秒を超えると残留オーステナイトが分解してセメンタイトが生じることにより穴拡げ性が劣化する。 After pre-plating Ni, after heating to 430-480 ° C. at a heating rate of 20 ° C./second or more, galvanizing is performed in a galvanizing bath, and further, if necessary, at 470-560 ° C. for 10-40 seconds. Alloying treatment is performed. When the heating rate is less than 20 ° C./second, the strain introduced by grinding and removing the surface layer of the steel sheet is alleviated and the effect of promoting alloying cannot be obtained. If the heating temperature is less than 430 ° C., non-plating is likely to occur during plating, and if it exceeds 480 ° C., the strain introduced by grinding and removing the surface layer of the steel sheet is alleviated, and the alloying promotion effect cannot be obtained. When the alloying treatment is less than 470 ° C., alloying is insufficient, and when it exceeds 560 ° C., retained austenite is decomposed and cementite is generated, so that the hole expandability is deteriorated. The alloying time is determined by the balance with the alloying temperature, but a range of 10 to 40 seconds is appropriate. If it is less than 10 seconds, alloying is difficult to proceed, and if it exceeds 40 seconds, the retained austenite decomposes and cementite is produced, so that the hole expandability deteriorates.
亜鉛めっき及び合金化処理の後は、最終的な形状矯正及び降伏点伸びの消失のために調質圧延を行うことが望ましい。伸び率が０．２％未満ではその効果が十分でなく、伸び率が１％を超えると降伏比が大幅に増大するとともに伸びが劣化する。従って、伸び率を０．２〜１％とすることが望ましい。 After galvanizing and alloying treatment, it is desirable to perform temper rolling for final shape correction and disappearance of yield point elongation. If the elongation is less than 0.2%, the effect is not sufficient. If the elongation exceeds 1%, the yield ratio is greatly increased and the elongation is deteriorated. Therefore, it is desirable that the elongation rate is 0.2 to 1%.
次にめっき層について説明する。
スポット溶接性や塗装性が望まれる場合には、合金化処理によってこれらの特性を高めることができる。具体的には溶融亜鉛めっき浴に浸漬した後、合金化処理を施すことで、めっき層中にFeが取り込まれ、塗装性やスポット溶接性に優れた高強度溶融亜鉛めっき鋼板を得ることができる。合金化処理後のＦｅ量が７質量％未満ではスポット溶接性が不十分となる。一方、Ｆｅ量が１５質量％を超えるとめっき層自体の密着性を損ない、加工の際めっき層が破壊・脱落し金型に付着することで、成形時の疵の原因となる。したがって、合金化処理を行う場合のめっき層中Fe量の範囲は７％以上、１５％以下とする。
Next, the plating layer will be described.
When spot weldability or paintability is desired, these characteristics can be enhanced by alloying treatment. Specifically, after immersion in a hot dip galvanizing bath, an alloying treatment is performed so that Fe is taken into the plating layer and a high strength hot dip galvanized steel sheet excellent in paintability and spot weldability can be obtained. . If the amount of Fe after alloying is less than 7% by mass, spot weldability is insufficient. On the other hand, if the amount of Fe exceeds 15% by mass, the adhesion of the plating layer itself is impaired, and the plating layer is broken and dropped during processing and adheres to the mold, thereby causing defects during molding. Therefore, the range of Fe content in the plating layer when the alloying process is performed is 7% or more and 15% or less.
また、合金化処理を行わない場合めっき層中のFe量が７質量％未満でも、合金化により得られるスポット溶接を除く効果である耐食性と成形性や穴拡げ性は良好である。 Further, when the alloying treatment is not performed, even if the amount of Fe in the plating layer is less than 7% by mass, the corrosion resistance, the formability and the hole expandability, which are the effects excluding spot welding obtained by alloying, are good.
めっき付着量については、特に制約は設けないが、耐食性の観点から片面付着量で５g/m2 以上であることが望ましい。本発明の溶融亜鉛めっき鋼板上に塗装性、溶接性を改善する目的で上層めっきを施すことや、各種の処理、例えば、クロメート処理、りん酸塩処理、潤滑性向上処理、溶接性向上処理等を施しても、本発明を逸脱するものではない。 The plating adhesion amount is not particularly limited, but is preferably 5 g / m 2 or more in terms of single-sided adhesion from the viewpoint of corrosion resistance. For the purpose of improving the paintability and weldability on the hot dip galvanized steel sheet of the present invention, various treatments such as chromate treatment, phosphate treatment, lubricity improvement treatment, weldability improvement treatment, etc. However, the present invention does not depart from the present invention.
次に、本発明の鋼板のミクロ組織について説明する。
本発明の鋼板のミクロ組織は、穴拡げ性を十分に確保するために以下に定める3種のマルテンサイト［１］［２］［３］とベイナイトを主相とした上で、残組織をフェライトおよび残留オーステナイトとする。なお、各組織の含有率は体積分率で示す。
3種のマルテンサイト［１］［２］［３］の分類方法は、硬度とC濃度である。硬度は、マルテンサイト粒内で3点以上ビッカース硬度を測り、その平均ビッカース硬度Hv1〜Hv3を算出する。本発明において、マルテンサイト粒の濃度とはマルテンサイト粒内にセメンタイトが存在した場合、これも合わせた濃度を示す。従って、マルテンサイト粒のC濃度CM1〜CM3は、正確に分解濃度が得られる条件で、精度が保証される測定方法であればどのような測定方法でも構わないが、例えば、FE-SEM付属のEPMAを用いて、0.5μm以下ピッチでC濃度を注意深く測定することによって得ることができる。以上の値を用いて、以下のように分類する。
マルテンサイト［１］：C濃度（CM1）が0.8質量%未満で、硬さHv1が、
Hv1／（-982.1×CM12＋1676×CM1+189）≦0.60 …式1
マルテンサイト［２］:C濃度（CM2）が0.8質量%以上で、硬さHv2が、
Hv2／（-982.1×CM22＋1676×CM2+189）≦0.60 …式2
マルテンサイト［３］:C濃度（CM3）が0.8質量%以上で、硬さHv3が、
Hv3／（-982.1×CM32＋1676×CM3+189）≧0.80 …式3
Next, the microstructure of the steel sheet of the present invention will be described.
The microstructure of the steel sheet of the present invention is composed of three types of martensite [1] [2] [3] and bainite, which are defined below, in order to ensure sufficient hole expansibility, and the remaining structure is ferrite. And retained austenite. In addition, the content rate of each structure | tissue is shown by a volume fraction.
The classification methods of the three types of martensite [1] [2] [3] are hardness and C concentration. The hardness is determined by measuring Vickers hardness of 3 or more points within the martensite grains, and calculating the average Vickers hardness Hv1 to Hv3. In this invention, the density | concentration of a martensite grain shows the density | concentration combined also when the cementite exists in a martensite grain. Therefore, the C concentration CM1 to CM3 of the martensite grains may be any measuring method as long as accuracy is guaranteed under the condition that the decomposition concentration can be accurately obtained. Using EPMA, it can be obtained by carefully measuring the C concentration with a pitch of 0.5 μm or less. The above values are used to classify as follows.
Martensite [1]: C concentration (CM1) is less than 0.8% by mass, hardness Hv1 is
Hv1 / (-982.1 × CM1 2 + 1676 × CM1 + 189) ≦ 0.60… Formula 1
Martensite [2]: C concentration (CM2) is 0.8 mass% or more, hardness Hv2 is
Hv2 / (-982.1 x CM2 2 +1676 x CM2 + 189) ≤ 0.60 ... Formula 2
Martensite [3]: C concentration (CM3) is 0.8 mass% or more, hardness Hv3 is
Hv3 / (-982.1 × CM3 2 + 1676 × CM3 + 189) ≧ 0.80… Formula 3
これらのマルテンサイト［１］［２］［３］の区別をするために、マルテンサイト中のC量とビッカース硬さの関係式を用いている。式1、2、3の左辺の分母は、C濃度を入れた値がそのC濃度のフレッシュマルテンサイトの硬さを表している。本鋼に含まれているマルテンサイトはその粒内にセメンタイトの析出や、焼戻しによって、フレッシュマルテンサイトの硬さより低くなっている。そこで、分母のフレッシュマルテンサイトであった場合の硬度と、鋼板中のマルテンサイトの硬度との比を取り分類した。 In order to distinguish these martensites [1] [2] [3], a relational expression between the amount of C in martensite and the Vickers hardness is used. In the denominator on the left side of Equations 1, 2, and 3, the value including the C concentration represents the hardness of fresh martensite at the C concentration. The martensite contained in this steel is lower than the hardness of fresh martensite due to precipitation of cementite in the grains and tempering. Therefore, the ratio of the hardness in the case of fresh martensite in the denominator to the hardness of martensite in the steel sheet was classified.
3種のマルテンサイト［１］［２］［３］とベイナイトは、強度を確保した上で、穴拡げ性を確保するために有効であり、同時に残留オーステナイト相の安定性、分率の制御に有用な役割を担う。引張強度が980MPaを超える高強度鋼板では、これらの組織が有効に作用するため、その和を４０％以上とする。更に３種のマルテンサイトは要求される強度レベル、加工性に応じて、１種または２種以上を含むことが必要である。強度と加工性の両立が望まれる場合、２種類以上含むことが望ましい。 The three types of martensite [1] [2] [3] and bainite are effective for securing hole expandability while ensuring strength, and at the same time, controlling the stability and fraction of retained austenite phase. Play a useful role. In a high-strength steel sheet with a tensile strength exceeding 980 MPa, these structures work effectively, so the sum is made 40% or more. Further, the three types of martensite need to contain one or more types depending on the required strength level and workability. When both strength and workability are desired, it is desirable to include two or more types.
さらに、3種のマルテンサイト［１］［２］［３］において、マルテンサイト［１］は、C濃度が低くそれほど硬質でないマルテンサイトもしくは焼戻しマルテンサイトである。この組織は、先に定めた製造方法における、焼鈍後の650℃以上から450℃以下までの冷却により生成したもので、後の350〜450℃の過時効処理および亜鉛めっき浴への浸漬中、もしくは、合金化中に焼戻された相である。この組織は冷却条件により相分率を容易に制御でき、適度な強度が保てる上、穴拡げ性の劣化が少ないため有効であるが、この組織が５０％を超えると延性を劣化させてしまうので、上限を５０％以下とし、高強度材においてこの相の効果を十分に得るためには１％以上あることが望ましい。 Further, in the three types of martensite [1] [2] [3], the martensite [1] is martensite or tempered martensite having a low C concentration and not so hard. This structure is generated by cooling from 650 ° C. to 450 ° C. after annealing in the manufacturing method defined above, and after 350-450 ° C. overaging treatment and dipping in a galvanizing bath, Alternatively, it is a phase tempered during alloying. This structure is effective because it can easily control the phase fraction depending on the cooling conditions and can maintain an appropriate strength, and the deterioration of hole expansibility is small. However, if this structure exceeds 50%, the ductility is deteriorated. The upper limit is 50% or less, and 1% or more is desirable in order to sufficiently obtain the effect of this phase in a high-strength material.
マルテンサイト［２］は、C濃度が高いが、焼戻しによって軟化したマルテンサイトである。この組織は、焼鈍後の350〜450℃での保持においてベイナイト変態が進み、C濃化した残留オーステナイトが、冷却時にマルテンサイトとなり、溶融亜鉛めっき浴への浸漬中、もしくは、合金化中に焼戻されたマルテンサイトである。マルテンサイト［１］と比べて、この組織は強度確保に有効であるが、同相の分率を高めるためには残留オーステナイトの安定性を損ね、延性を劣化させてしまうので、上限を３０％以下とし、高強度材においてこの相の効果を十分に得るためには１％以上あることが望ましい。 Martensite [2] is martensite having a high C concentration but softened by tempering. In this structure, the bainite transformation progresses during holding at 350 to 450 ° C. after annealing, and the C-concentrated retained austenite becomes martensite during cooling and is baked during immersion in a hot dip galvanizing bath or during alloying. Returned martensite. Compared with martensite [1], this structure is more effective in securing strength. However, in order to increase the in-phase fraction, the stability of retained austenite is impaired and ductility is deteriorated, so the upper limit is 30% or less. In order to sufficiently obtain the effect of this phase in a high-strength material, 1% or more is desirable.
マルテンサイト［３］は、C濃度が高く、焼戻しがないマルテンサイト、もしくは、焼戻し量が少ないマルテンサイトである。この組織は、先に定めた製造方法における、溶融亜鉛めっき浴への浸漬中、もしくは、合金化中に残留オーステナイト中にセメンタイトが析出し、セメンタイトを除いた残留オーステナイト中のC濃度が低くなり、最終冷却にてマルテンサイトとなったもの、または、 350〜450℃の範囲で120秒以上保持した後の冷却時に変態したマルテンサイトが溶融亜鉛めっき浴や合金化処理中に若干焼戻されたものである。この組織は、かなり硬く、強度確保には非常に有利であるが、過剰に存在すると穴拡げ性を劣化させるので、上限を１０％以下とし、特に加工性を重視する場合、３％以下が望ましい。高強度材においてこの相の効果を十分に得るためには１％以上あることが望ましい。 Martensite [3] is martensite having a high C concentration and no tempering, or martensite having a small amount of tempering. This structure, in the previously defined manufacturing method, during immersion in the hot dip galvanizing bath, or during alloying, cementite precipitates in the residual austenite, the C concentration in the residual austenite excluding cementite is low, The one that became martensite in the final cooling, or the one that martensite transformed during cooling after holding at 350 to 450 ° C for 120 seconds or more was slightly tempered during hot dip galvanizing bath or alloying treatment It is. This structure is quite hard and is very advantageous for securing the strength. However, if it is excessively present, the hole expandability is deteriorated. Therefore, the upper limit is set to 10% or less. . In order to sufficiently obtain the effect of this phase in a high-strength material, the content is desirably 1% or more.
残留オーステナイトは、変態誘起塑性によって延性、特に一様伸びを高める組織であり、０．１％以上必要であるが、過剰に存在すると穴拡げ性が劣化するので、上限を８%未満とした。 Residual austenite is a structure that enhances ductility, particularly uniform elongation, by transformation-induced plasticity, and is required to be 0.1% or more, but if it is excessive, hole expandability deteriorates, so the upper limit was made less than 8%.
以下、実施例により本発明の効果をさらに具体的に説明する。
表１に示す組成の鋼を鋳造し、１1００℃以上に再加熱した後、Ar3変態点以上で熱間圧延を完了し、冷却後、６3０℃以下の温度域で巻取りを行った。その後、圧下率４０〜７０％の範囲で冷間圧延を行い、表２に示す条件で焼鈍を行った。その後、表２に示す条件で、鋼板表面層の研削、Ｎｉプレめっきを行い、さらに、表２に示す条件で亜鉛めっき及び合金化処理を行い、調質圧延を０．２％の伸び率で行った。板厚は１．４ｍｍとした。なお、焼鈍工程の急冷後、所定の温度で保持する工程は本発明ではベイナイト変態を促進させるための工程であるが、表２中では通例に則して過時効処理と表記している。表２中の過時効処理温度はこの工程中の平均温度を示す。なお、焼鈍温度から急冷開始温度までは２℃／秒で冷却した。
Hereinafter, the effects of the present invention will be described more specifically with reference to examples.
Steel having the composition shown in Table 1 was cast and reheated to 100 ° C. or higher, and then hot rolling was completed at the Ar3 transformation point or higher, and after cooling, winding was performed at a temperature range of 630 ° C. or lower. Then, cold rolling was performed in the range of a rolling reduction of 40 to 70%, and annealing was performed under the conditions shown in Table 2. Thereafter, the steel sheet surface layer was ground and Ni pre-plated under the conditions shown in Table 2, and further galvanized and alloyed under the conditions shown in Table 2, and temper rolling was performed at an elongation of 0.2%. went. The plate thickness was 1.4 mm. In addition, although the process hold | maintained at predetermined temperature after the rapid cooling of an annealing process is a process for accelerating bainite transformation in this invention, in Table 2, it describes with the overaging process according to the usual. The overaging temperature in Table 2 represents the average temperature during this step. In addition, it cooled at 2 degree-C / sec from the annealing temperature to the rapid cooling start temperature.
得られた合金化溶融亜鉛めっき鋼板の機械的特性、穴拡げ性、めっき外観、合金化度、めっき密着性を評価した。機械的特性は引張試験を、ＪＩＳ Ｚ ２２４１に準拠して行って評価した。引張試験の応力−歪曲線より、引張強度（ＴＳ）、全伸び（ＥＬ）を求めた。穴拡げ性は穴拡げ試験を日本鉄鋼連盟規格ＪＦＳ Ｔ １００１に準拠して行い、穴拡げ率（λ）を測定して評価した。加工性の指標として、ＴＳ×ＥＬとＴＳ×λを求め、ＴＳ×ＥＬは１６０００ＭＰａ・％以上、ＴＳ×λは４００００ＭＰａ・％以上を合格とした。めっき外観は目視観察により不めっきの有無を判定した。合金化Ｆｅ％とは、めっき層中のＦｅの質量％を示している。合金化処理を行った合金化溶融亜鉛めっき鋼板では、７〜１５％が合金化がうまく進んだことを示している。合金化処理を行わない溶融亜鉛めっき鋼板では、７％以下でよい。めっき密着性は、２５ｍｍカップ絞り試験を行い、テープテストによる黒化度を測定し、黒化度３０％未満を合格とした。 The obtained alloyed hot-dip galvanized steel sheet was evaluated for mechanical properties, hole expandability, plating appearance, degree of alloying, and plating adhesion. The mechanical properties were evaluated by conducting a tensile test according to JIS Z 2241. Tensile strength (TS) and total elongation (EL) were determined from the stress-strain curve of the tensile test. The hole expansion property was evaluated by performing a hole expansion test in accordance with Japan Iron and Steel Federation standard JFS T 1001, and measuring the hole expansion rate (λ). As indices of workability, TS × EL and TS × λ were obtained, and TS × EL was 16000 MPa ·% or more, and TS × λ was 40000 MPa ·% or more. The appearance of plating was determined by visual observation for the presence or absence of non-plating. The alloying Fe% indicates the mass% of Fe in the plating layer. In the alloyed hot-dip galvanized steel sheet subjected to the alloying treatment, 7 to 15% indicate that the alloying has proceeded well. In a hot dip galvanized steel sheet that is not subjected to alloying treatment, it may be 7% or less. For plating adhesion, a 25 mm cup squeeze test was conducted, the degree of blackening by a tape test was measured, and a degree of blackening of less than 30% was accepted.
表３に引張強度、全伸び、ＴＳ×ＥＬ、ＴＳ×λ、めっき外観（不めっき有無）、合金化Ｆｅ％、めっき密着性の評価結果を示す。評価項目については不合格の場合に下線を付けた。Ｎｏ．１〜１０及び２１〜３０は本発明例であり、いずれの特性も合格となり、目標とする特性の鋼板が得られている。一方、成分または製造方法が本発明の範囲外であるのＮｏ．１１〜２０及び３１〜４０は、いずれかの特性が不合格となっている。 Table 3 shows the evaluation results of tensile strength, total elongation, TS × EL, TS × λ, plating appearance (non-plating presence / absence), alloyed Fe%, and plating adhesion. Evaluation items are underlined if they are rejected. No. 1 to 10 and 21 to 30 are examples of the present invention, and all the properties are acceptable, and a steel plate having the targeted properties is obtained. On the other hand, no. In any of 11 to 20 and 31 to 40, any of the characteristics is rejected.
Claims (9)
Ｃ：０．１０〜０．４０％、
Ｓｉ：０．０１〜３．０％、
Ｍｎ：１．７〜３．０％、
Ｐ：０．０４％以下、
Ｓ：０．０１％以下、
Ａｌ：０．００５〜２．０％、
Ｎ：０．００１〜０．０１%、
を含有し、Ｓｉ及びＡｌの含有量が、
Ｓｉ＋Ａｌ＞０．５％
を満足し、残部がＦｅ及び不可避的不純物からなり、
ミクロ組織が、体積分率で主相として次に指定する3種類のマルテンサイト［１］［２］［３］の１種または２種以上とベイナイトを合わせて４０％以上含有し、
マルテンサイト［１］：C濃度（CM1）が0.8質量%未満で、硬さHv1が、
Hv1／（-982.1×CM12＋1676×CM1+189）≦0.60
マルテンサイト［２］:C濃度（CM2）が0.8質量%以上で、硬さHv2が、
Hv2／（-982.1×CM22＋1676×CM2+189）≦0.60
マルテンサイト［３］:C濃度（CM3）が0.8質量%以上で、硬さHv3が、
Hv3／（-982.1×CM32＋1676×CM3+189）≧0.80
残留オーステナイトを０．１〜８％未満含有し、残部組織がフェライトからなる鋼板の表面に、Feを７質量％未満含有し、残部がZn、Alおよび不可避的不純物からなる溶融亜鉛めっき層を有することを特徴とする引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。 % By mass
C: 0.10 to 0.40%,
Si: 0.01-3.0%,
Mn: 1.7-3.0%,
P: 0.04% or less,
S: 0.01% or less,
Al: 0.005 to 2.0%,
N: 0.001 to 0.01%,
And the content of Si and Al is
Si + Al> 0.5%
And the balance consists of Fe and inevitable impurities,
The microstructure contains 40% or more of bainite in combination with one or more of three types of martensite [1] [2] [3] specified next as the main phase in volume fraction,
Martensite [1]: C concentration (CM1) is less than 0.8% by mass, hardness Hv1 is
Hv1 // (-982.1 × CM1 2 + 1676 × CM1 + 189) ≦ 0.60
Martensite [2]: C concentration (CM2) is 0.8 mass% or more, hardness Hv2 is
Hv2 // (-982.1 × CM2 2 + 1676 × CM2 + 189) ≦ 0.60
Martensite [3]: C concentration (CM3) is 0.8 mass% or more, hardness Hv3 is
Hv3 / (-982.1 × CM3 2 + 1676 × CM3 + 189) ≧ 0.80
A steel sheet containing 0.1 to 8% of retained austenite and the remaining structure being made of ferrite has less than 7% by weight of Fe, and the remainder has a hot-dip galvanized layer made of Zn, Al and inevitable impurities. A high-strength hot-dip galvanized steel sheet with a tensile strength of 980 MPa or more and excellent plating adhesion and formability.
Ｃ：０．１０〜０．４０％、
Ｓｉ：０．０１〜３．０％、
Ｍｎ：１．７〜３．０％、
Ｐ：０．０４％以下、
Ｓ：０．０１％以下、
Ａｌ：０．００５〜２．０％、
Ｎ：０．００１〜０．０１%、
を含有し、Ｓｉ及びＡｌの含有量が、
Ｓｉ＋Ａｌ＞０．５％
を満足し、残部がＦｅ及び不可避的不純物からなり、
ミクロ組織が、体積分率で主相として次に指定する3種類のマルテンサイト［１］［２］［３］の１種または２種以上とベイナイトを合わせて４０％以上含有し、
マルテンサイト［１］：C濃度（CM1）が0.8質量未満で、硬さHv1が、
Hv1／（-982.1×CM12＋1676×CM1+189）≦0.60
マルテンサイト［２］:C濃度（CM2）が0.8質量%以上で、硬さHv2が、
Hv2／（-982.1×CM22＋1676×CM2+189）≦0.60
マルテンサイト［３］:C濃度（CM3）が0.8質量%以上で、硬さHv3が、
Hv3／（-982.1×CM322＋1676×CM3+189）≧0.80
残留オーステナイトを０．１〜８％未満含有し、残部組織がフェライトからなる鋼板の表面に、Ｆｅを７〜１５質量％を含有し、残部がＺｎ、Ａｌおよび不可避的不純物からなる溶融亜鉛めっき層を有することを特徴とする引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。 % By mass
C: 0.10 to 0.40%,
Si: 0.01-3.0%,
Mn: 1.7-3.0%,
P: 0.04% or less,
S: 0.01% or less,
Al: 0.005 to 2.0%,
N: 0.001 to 0.01%,
And the content of Si and Al is
Si + Al> 0.5%
And the balance consists of Fe and inevitable impurities,
The microstructure contains 40% or more of bainite in combination with one or more of three types of martensite [1] [2] [3] specified next as the main phase in volume fraction,
Martensite [1]: C concentration (CM1) is less than 0.8 mass, hardness Hv1 is
Hv1 // (-982.1 × CM1 2 + 1676 × CM1 + 189) ≦ 0.60
Martensite [2]: C concentration (CM2) is 0.8 mass% or more, hardness Hv2 is
Hv2 // (-982.1 × CM2 2 + 1676 × CM2 + 189) ≦ 0.60
Martensite [3]: C concentration (CM3) is 0.8 mass% or more, hardness Hv3 is
Hv3 / (-982.1 × CM3 2 2 + 1676 × CM3 + 189) ≧ 0.80
Hot-dip galvanized layer containing less than 0.1 to 8% of retained austenite, the balance of 7 to 15% by mass of Fe on the surface of the steel plate made of ferrite, and the balance of Zn, Al and inevitable impurities A high-strength hot-dip galvanized steel sheet excellent in plating adhesion and formability having a tensile strength of 980 MPa or more.
マルテンサイト［１］：１％以上、５０％以下、
マルテンサイト［２］：１％以上、３０％以下、
マルテンサイト［３］：１％以上、１０％以下、
であることを特徴とする請求項１または２に記載の引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。 The three types of martensite [1] [2] [3] have a volume fraction of martensite [1]: 1% or more, 50% or less,
Martensite [2]: 1% or more, 30% or less,
Martensite [3]: 1% or more, 10% or less,
The high-strength hot-dip galvanized steel sheet excellent in plating adhesion and formability having a tensile strength of 980 MPa or more according to claim 1 or 2.
Ｔｉ：０．００５〜０．３％、
Ｎｂ：０．００５〜０．３％、
Ｖ ：０．０１〜０．５％
の1種又は2種以上を含有することを特徴とする請求項1〜３のいずれか１項に記載の引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。 Furthermore, in mass%,
Ti: 0.005 to 0.3%,
Nb: 0.005-0.3%
V: 0.01 to 0.5%
A high-strength hot-dip galvanized steel sheet excellent in plating adhesion and formability having a tensile strength of 980 MPa or more according to any one of claims 1 to 3, characterized by containing at least one of the following.
Ｃｒ：３．０％以下、
Ｍｏ：３．０％以下、
Ｎｉ：５．０％以下、
Ｃｕ：３．０％以下
の1種又は2種以上を含有することを特徴とする請求項1〜４のいずれか１項に記載の引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。 Furthermore, in mass%,
Cr: 3.0% or less,
Mo: 3.0% or less,
Ni: 5.0% or less,
Cu: 3.0% or less of one type or two or more types, characterized by high plating adhesion and formability having a tensile strength of 980 MPa or more according to any one of claims 1 to 4 Strength hot dip galvanized steel sheet.
Ｂ：０．０１％以下
を含有することを特徴とする請求項1〜５のいずれか１項に記載の引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。 Furthermore, in mass%,
B: A high-strength hot-dip galvanized steel sheet excellent in plating adhesion and formability having a tensile strength of 980 MPa or more according to any one of claims 1 to 5, characterized by containing 0.01% or less.
Ｃａ：０．０１％以下、
Ｍｇ：０．０１％以下、
Ｚｒ：０．０５％以下、
ＲＥＭ：０．０５％以下
の１種または２種以上を含有することを特徴とする請求項1〜６のいずれかに記載の引張強度980MPa以上有するめっき密着性と成形性に優れた高強度溶融亜鉛めっき鋼板。 Furthermore, in mass%,
Ca: 0.01% or less,
Mg: 0.01% or less,
Zr: 0.05% or less,
REM: 0.05% or less of one type or two or more types, The high strength melt excellent in plating adhesion and formability having a tensile strength of 980 MPa or more according to any one of claims 1 to 6 Galvanized steel sheet.
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