JP3887308B2 - High strength and high ductility hot dip galvanized steel sheet and its manufacturing method - Google Patents

Description

【０１１４】
これらのＡc1とＡc3変態温度から計算される焼鈍温度に１０％Ｈ₂−Ｎ₂雰囲気で昇温・保定した後、０．１〜１０℃／秒の冷却速度で６００〜７１０℃まで冷却し、その後、１〜１０℃／秒の冷速でめっき浴温度まで冷却し、浴組成を種々に変化させた４６０℃の溶融亜鉛めっき浴に３秒間侵漬することで、めっきを行った。この際のめっき付着量は、片面４０ｇ／ｍ²とした。
【０１１５】
この後、一部の鋼板については、めっき浴温度〜６００℃の温度範囲で保持を行った後、３５０℃までの温度域を０．１〜１００℃／秒の冷却速度で冷却後、室温まで冷却した。製造条件の詳細を表２〜５に示す。
【０１１６】
【表２】

【０１１７】
【表３】

【０１１８】
【表４】

【０１１９】
【表５】

【０１２０】
めっき表面外観におけるドロス巻き込みの状況の目視観察及び不めっき部面積の測定により、めっき性を評価した。作製しためっき層中濃度測定は、アミン系インヒビターを入れた５％塩酸でめっき層を溶かした後、ＩＣＰ発光分析法を用いて行った。
【０１２１】
めっき密着性は、パウダリングを調査し、その剥離幅が３ｍｍを超えた場合を不合格とした。
【０１２２】
これらめっきを施した鋼板から、ＪＩＳ５号試験片を採取し、ゲージ長さ５０ｍｍ、引張り試験速度１０ｍｍ／分で、常温引張り試験を行った。
【０１２３】
穴拡げ性は、直径１０ｍｍの円形穴を、クリアランスが１２％となる条件にて打ち抜き、かえりがダイ側となるようにし、６０°円錐ポンチにて成形し、穴拡げ率λ（％）により評価した。
【０１２４】
残留オーステナイト体積率Ｖγの測定は、めっき層／鋼板界面より板厚の７／１６内層を化学研磨後、Ｍｏ管球を用いたＸ線回折で、フェライトの（２００）の回折強度Ｉα（２００）、フェライトの（２１１）の回折強度Ｉα（２１１）とオーステナイトの（２２０）の回折強度Ｉγ（２２０）及び（３１１）の回折強度Ｉγ（３１１）の強度比より求めた。
Ｖγ（体積％）
＝０．２５
×｛Ｉγ（２２０）／（１．３５×Ｉα（２００）＋Ｉγ（２２０））
＋Ｉγ（２２０）／（０．６９×Ｉα（２１１）＋Ｉγ（２２０））
＋Ｉγ（３１１）／（１．５×Ｉα（２００）＋Ｉγ（３１１））
＋Ｉγ（３１１）／（０．６９×Ｉα（２１１）＋Ｉγ（３１１））｝
【０１２５】
内部酸化物の体積率と分布については、研磨を行った後、ＳＥＭ及びＥＰＭＡを用いて観察することで、測定を行った。
【０１２６】
表６〜９に機械特性、めっき特性等を示す。表６〜９に示すように、鋼板成分が所定の範囲を満たすものは、不めっきもなく良好なめっき性が得られている。
【０１２７】
【表６】

【０１２８】
【表７】

【０１２９】
【表８】

【０１３０】
【表９】

【０１３１】
鋼板の成分組成が所定の範囲であったとしても、製造条件及び鋼板組織が所定の要件を満たさないものは、高強度、高延性及びめっき密着性に劣り、さらには、残留オーステナイト分率が低くなり、強度−延性バランス（ＴＳ×Ｅｌ．）も２１０００（ＭＰａ・％）未満となり、強度−延性バランスに劣る。
【０１３２】
製造条件が本発明の要件を満たすものであっても、成分組成の範囲が所定の要件を満たさないものは、本発明の効果を得ることができない。
【０１３３】
【発明の効果】
本発明により、良好なめっき性が得られ、強度−延性バランス（ＴＳ×Ｅｌ．）も２１０００（ＭＰａ・％）を超える強度９８０ＭＰａ超の高強度高延性溶融亜鉛めっき鋼板が得られた。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a high-strength, high-ductility hot-dip galvanized steel sheet excellent in workability suitable for automobiles, building materials, home appliances, and the like, and a method for producing the same.
[0002]
[Prior art]
Lightweight parts of automobile cross members and side members are being studied in order to respond to recent trends in lighter fuel consumption, and in terms of materials, the strength and collision safety can be ensured even if they are made thinner. Therefore, increasing the strength of steel sheets is being promoted.
[0003]
However, since the formability of the material deteriorates as the strength increases, it is necessary to manufacture a steel sheet that satisfies both formability and high strength in order to realize the weight reduction of the member.
[0004]
As an index representing formability, elongation (El.) At the time of a tensile test is used, and this high value is used as one of moldability indices. Further, as the strength, the tensile strength (TS) which is the maximum stress in the tensile test is used as the value, and the product (TS × El.) Of these steel plates exceeds 21000 (MPa ·%). Is known as a high strength and high ductility steel sheet.
[0005]
As steel plates having these characteristics, there are steel plates containing retained austenite as disclosed in Patent Document 1 and Patent Document 2.
[0006]
These steel sheets containing retained austenite have only C, Si and Mn as their constituent elements, and in the case of cold-rolled steel sheets, after annealing in a two-phase region, bainite in a temperature range of about 300 to 450 ° C. Steel sheets containing residual austenite in the metal by heat treatment characterized by transformation, and these steel sheets are disclosed in Patent Document 3 and Patent Document 4 in order to form a structure containing residual austenite. , Si or Al must be contained.
[0007]
Since these steel sheets have obtained excellent ductility by transforming retained austenite contained in the metal structure into martensite by stress-induced transformation at the time of press forming, Patent Document 5 and Patent Document As disclosed in FIG. 6, many studies have been conducted so far focusing on improving the stability and volume ratio of retained austenite.
[0008]
[Patent Document 1]
Japanese Patent Laid-Open No. 1-2230715
[Patent Document 2]
JP-A-2-217425
[Patent Document 3]
JP-A-5-171344
[Patent Document 4]
JP-A-5-195143
[Patent Document 5]
JP-A-10-130776
[Patent Document 6]
Japanese Patent Laid-Open No. 4-9859
[Patent Document 7]
JP-A-3-28359
[Patent Document 8]
Japanese Patent Laid-Open No. 3-64437
[0009]
[Problems to be solved by the invention]
In addition, reflecting the high performance of automobile steel plates, the plating of automobile parts is progressing for the purpose of improving corrosion resistance and appearance, but at present, except for specific parts installed in the car, there are many A galvanized steel sheet is used for the member.
[0010]
However, since these steel plates contain a large amount of Si, the surface of the steel plate is likely to be oxidized, causing slight unplating during hot dip galvanizing, and problems such as poor plating adhesion in the processed part after alloying. is there.
[0011]
As means for solving these problems, for example, in Patent Document 7 and Patent Document 8, 0.002 to 2.0 g / mm on the steel plate surface.²Plating properties are improved by performing single or composite plating of Ni, Cu, Co, and Fe. However, in this method, a new plating facility is provided in front of the hot dip galvanizing line, or electric There was a problem that a plating process had to be performed in the plating line, resulting in a significant cost increase.
[0012]
The present invention solves the above-mentioned problems, and provides a high-strength galvannealed steel sheet excellent in plating adhesion, a high-strength galvanized steel sheet excellent in plating adhesion, and a method for producing the same. Objective.
[0013]
[Means for Solving the Problems]
As a result of various investigations, the present inventors have confirmed that, with respect to plating properties, by adding Ni or Cu alone or in combination to steel, the hot dip galvanizing wettability of high-strength steel plates can be secured, and alloys It has been found that alloying in chemical plating is promoted. This effect is exhibited when the content of these elements in the steel is 0.001% or more.
[0014]
Further, in the steel, ferrite is contained as a main phase in a volume fraction of 50% or more, residual austenite is contained in an amount of 3 to less than 50%, and the remaining structure is martensite and bainite, thereby obtaining a strength-ductility balance. It has been found that excellent high strength and high ductility steel sheets can be produced.
[0015]
  Furthermore, while adding one or two of Ti and Nb to the steel, the maximum heating temperature in the annealing process after hot rolling is set to a cooling rate of Ac1 + 30 (° C.) or higher and 1 (° C./second) or higher. so620After cooling to a temperature range of ˜800 (° C.), followed by cooling at a cooling rate of 1 to 100 (° C./second) from a Zn plating bath temperature to a Zn plating bath temperature + 100 (° C.), 350 to Zn plating In the temperature range of bath temperature + 100 (° C.), hold for 1-3000 seconds including the immersion time of the plating bath, then immerse in a Zn plating bath, and then cool to room temperature, or plating bath temperature˜100 It has been found that by holding in a temperature range of ° C., it is possible to produce a high-strength and high-ductility steel sheet having an average particle diameter of ferrite as a main phase of 5 μm or less and an excellent balance between strength and ductility.
[0016]
The present invention has been completed based on the above findings, and the gist thereof is as follows.
[0017]
      [1] By mass%
      C: 0.0001 to 0.3%,
      Si: 0.1 to 4%,
      Al: 0.001 to 4%,
      Mn: 0.001 to 3%,
      P: 0.0001 to 0.3%,
      S: 0.01% or less, 0.001 to 4% in total of one or two of Ni and Cu, and further 0.001 to 1 in total of one or two of Ti and Nb 1% content, the balance iron and inevitable impurities, the microstructure has a volume fraction and contains 50% or more of ferrite as the main phase,ResidualIt contains less than 3 to 50% austenite, and the remaining structure is bainite or martensite and bainite.The average particle size of the ferrite having a volume ratio of 80% or more is 5 μm or less.On the surface of the steel plate
      Al: 0.001 to 0.5%,
      A high-strength, high-ductility hot-dip galvanized steel sheet comprising Fe: 5 to 20%, the balance having a hot-dip galvanized layer composed of Zn and inevitable impurities, and having a tensile strength of over 980 MPa.
[0018]
      [2] By mass%
      C: 0.0001 to 0.3%,
      Si: 0.1 to 4%,
      Al: 0.001 to 4%,
      Mn: 0.001 to 3%,
      P: 0.0001 to 0.3%,
      S: 0.01% or less, 0.001 to 4% in total of one or two of Ni and Cu, and further 0.001 to 1 in total of one or two of Ti and Nb 1% content, the balance iron and inevitable impurities, the microstructure has a volume fraction and contains 50% or more of ferrite as the main phase,ResidualIt contains less than 3 to 50% austenite, and the remaining structure is bainite or martensite and bainite.The average particle size of the ferrite having a volume ratio of 80% or more is 5 μm or less.On the surface of the steel plate
      Al: 0.001 to 0.5%,
      Fe: A high-strength, high-ductility hot-dip galvanized steel sheet having a hot-dip galvanized layer containing less than 5%, the balance being Zn and inevitable impurities, and having a tensile strength of over 980 MPa.
[0019]
[3] Furthermore, in steel, in mass%,
Mo: 0.001 to 4%,
Cr: 0.001 to 4%,
Co: 0.001 to 4%
The high strength and high ductility hot dip galvanized steel sheet according to [1] or [2], characterized by containing one or more of the following.
[0020]
[4] The ratio of the Cu content (mass%) in the plating layer to the Cu content (mass%) in steel is a, the Ni content (mass%) in the plating layer and the Ni content ( Mass ratio) is b
0.0001 ≦ a + b ≦ 0.2
The high strength and high ductility hot dip galvanized steel sheet according to any one of [1] to [3], wherein:
[0021]
[5] Furthermore, in steel, in mass%,
V: 0.001 to 1% is contained. The high strength and high ductility hot dip galvanized steel sheet according to any one of [1] to [4].
[0022]
[6] Furthermore, in steel, in mass%,
B: The high strength and high ductility hot dip galvanized steel sheet according to any one of [1] to [5], which contains 0.0001 to 0.1%.
[0023]
[7] Further, the steel contains 0.001 to 1% in total of one or more of Mg, Zr, Ca, Y, Hf, and La—Ce in elemental mass. The high strength and high ductility hot dip galvanized steel sheet according to any one of [1] to [6].
[0024]
      [8] In the vertical cross section of the plated steel plate,layer/ From the steel plate interface, MgO, CaO, ZrO₂, CeO₂, La₂O_Three, HfO₂TiO₂, Y₂O_Three, SiO₂, MnO and Al₂O_ThreeIn the steel sheet in the range up to the maximum depth where one or more internal oxides exist,Is an internal oxideMgO, CaO, ZrO₂, CeO₂, La₂O_Three, HfO₂TiO₂, Y₂O_Three, SiO₂, MnO and Al₂O_ThreeThe high strength hot-dip galvanized steel sheet according to any one of [1] to [7], wherein 1 type or 2 types or more are included in an area ratio of 1% or more.
[0025]
      [9] In the vertical cross section of the plated steel plate,layer/ In steel plates from the steel plate interface to 10 μm,Is an internal oxideMgO, CaO, ZrO₂, CeO₂, La₂O_Three, HfO₂TiO₂, Y₂O_Three, SiO₂, MnO and Al₂O_ThreeThe high-strength and high-ductility hot-dip galvanized steel sheet according to any one of [1] to [8], wherein the total of one or more of the above is contained in an area ratio of 0.1% or more.
[0027]
      [10The cast slab composed of the component composition according to any one of [1] to [7] is heated as it is or after being cooled again, and the hot-rolled steel sheet wound after hot rolling is pickled and then cold-rolled After that, in the oxidation zone in the plating line, oxidation is performed in an atmosphere having a combustion air ratio of 0.9 to 1.5, and thereafter, in the reduction zone, the common logarithm log (PH of water pressure and hydrogen partial pressure)₂O / PH₂) In a reducing atmosphere satisfying the following formula (1), after annealing at Ac1 + 30 (° C) or higher and Ac3-10 (° C) or lower, at a cooling rate of 0.1 ° C / second or higher.620After cooling to a temperature range of ˜800 ° C., and subsequently cooling at a cooling rate of 1 to 100 ° C./second from a Zn plating bath temperature to a Zn plating bath temperature +100 (° C.), 350 to Zn plating bath temperature +100 ( C.) in a temperature range of 1 to 3000 seconds including the immersion time of the subsequent plating bath, and then immersed in a Zn plating bath and then cooled to room temperature and has a high strength having a tensile strength of over 980 MPa. A method for producing a high-strength, high-ductility hot-dip galvanized steel sheet, comprising producing a high-ductility hot-dip galvanized steel sheet.
    −0.8 ≧ log (PH₂O / PH₂(1)
[0028]
      [11After being immersed in the Zn plating bath, it is held for 1 to 300 seconds in a temperature range of bath temperature to Zn plating bath temperature + 100 (° C.), and cooled to room temperature.10] The manufacturing method of the high intensity | strength high ductility hot-dip galvanized steel plate of description.
      [12]  The method for producing a high strength and high ductility hot dip galvanized steel sheet according to [10] or [11], wherein the casting slab is heated at a heating temperature of 1100 to 1250 ° C. and a finishing temperature of 850 ° C. or higher..
[0029]
DETAILED DESCRIPTION OF THE INVENTION
Details of the present invention will be described below.
[0030]
  The steel sheet of the present invention is a steel sheet manufactured by controlling the component composition and manufacturing conditions of the steel sheet within a certain range, and contains 50% or more of ferrite as a main phase in volume fraction.ResidualAustenite is contained in an amount of less than 3 to 50%, and the remaining structure is a steel plate having a tensile strength of over 980 MPa obtained by hot dip galvanizing on a steel plate made of bainite or martensite and bainite, and has strength and excellent ductility. And it has the corrosion resistance, It is characterized by the above-mentioned.
[0031]
The ductility of the high-strength hot-dip galvanized steel sheet according to the present invention depends on the volume fraction of retained austenite contained in the product. Residual austenite contained in the metal structure stably exists in a state where it is not subjected to stress, but when deformed, it transforms into martensite, and excellent ductility is obtained by transformation-induced plasticity.
[0032]
However, since the effect hardly appears when the volume fraction is less than 3%, the lower limit is set to 3% or more. On the other hand, when the volume fraction of retained austenite is 50% or more, if extremely remarkable molding is performed, a large amount of martensite is present after molding, which may cause problems in secondary workability and impact characteristics. Therefore, in the present invention, the upper limit value is set to less than 50%.
[0033]
Moreover, even if carbides, alloy carbides, nitrides and oxides are contained as phases other than the main phase ferrite, second phase retained austenite, bainite and martensite, it does not depart from the present invention.
[0034]
Furthermore, when the average particle diameter of the volume ratio of 80% or more of ferrite as the main phase is set to 5 μm or less, the strength-ductility balance is further improved. However, this effect becomes remarkable because the average particle size is 3 μm or less, and the average particle size is preferably 3 μm or less. On the other hand, the lower limit of the average particle diameter is not particularly defined, and the effects of the present invention can be obtained. Furthermore, it is effective for improving toughness and hole expansibility.
[0035]
  In addition, the above microstructure, ferrite, bainite,ResidualAustenite, martensite, oxidationMaterialThe remaining structure is identified, the presence position is observed, and the average particle diameter (average equivalent circle diameter) and the space factor are measured using the Nital reagent and the reagent disclosed in Japanese Patent Application Laid-Open No. 59-219473 in the cross section in the rolling direction of the steel sheet. Alternatively, it can be quantified by observing a cross section perpendicular to the rolling direction and observing the optical microscope, scanning electron microscope, and transmission electron microscope at 500 to 20000 times.
[0036]
  Also platinglayer/ Near the steel plate interfaceinternalOxide morphology and identification were performed using a scanning microscope, transmission electron microscope and EPMA.
[0037]
  The present inventors, in mass%, C: 0.0001 to 0.3%, Si: 0.1 to 4%, Al: 0.001 to 4%, Mn: 0.001 to 3%, P: 0.0001-0.3%, S: 0.01% or less, Ni: 0.01-4%, Cu: 0.01-4%, Ti: 0.001-1%, Nb: 0.001- The cast slab containing 1% and the balance Fe and inevitable impurities, as cast, or once again cooled and then heated again, the hot-rolled steel sheet wound up after hot rolling, cold-rolled after pickling, Using an annealing furnace having an oxidation zone and a reduction zone, the oxidation zone is oxidized in an atmosphere having a combustion air ratio of 0.9 to 1.2, and then the moisture pressure and hydrogen partial pressure are reduced in the reduction zone. Common logarithm log (PH₂O / PH₂) In the range of −0.8 or less, annealing is performed at Ac1 + 100 (° C.) or more and 1000 ° C. or less, and at a cooling rate of 0.1 to 50 ° C./second.620After cooling to a temperature range of ˜800 ° C., and subsequently cooling at a cooling rate of 1 to 100 ° C./second from a Zn plating bath temperature to a Zn plating bath temperature +100 (° C.), 350 to Zn plating bath temperature +100 ( C.) in a temperature range of 1 to 3000 seconds including the subsequent plating bath immersion time, and then immersed in a Zn plating bath and then cooled to room temperature.
[0038]
Furthermore, about some samples, after immersing in Zn plating bath on the same conditions, after alloying processing by hold | maintaining for 5 to 60 seconds at Zn plating bath temperature -550 degreeC, the temperature range to 350 degreeC is carried out. The solution was cooled at a cooling rate of 0.5 to 100 ° C./second, and then cooled to room temperature.
[0039]
Said test was done and the external appearance was evaluated in five steps based on the defect occurrence rate of the plating surface. As a result, it was found that by setting the steel plate component in the above range, scores 5 to 4 with almost no appearance defects were obtained.
[0040]
The grades 1 to 5 were determined by visually judging the occurrence of non-plating on the appearance of plating. The evaluation index is as follows.
[0041]
Score 5: Almost no plating. (Area ratio is 0.1% or less)
Score 4: Unplated is negligible. (Area ratio is over 0.1% and 3% or less)
Score 3: Less plating. (Area ratio is more than 3% and less than 5%)
Score 2: Many unplated. (Area ratio is more than 5% and less than 50%)
Score 1: Not plated. (Over 50% in area ratio)
There are no particular restrictions on the plating adhesion amount, but from the viewpoint of corrosion resistance, the adhesion amount on one side is 5 g / mm.²The above is desirable. For the purpose of improving paintability, corrosion resistance 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 However, the present invention does not depart from the present invention.
[0042]
The reason why the Al content in the plating layer is within the range of 0.001 to 0.5% is that if it is less than 0.001%, dross generation is remarkable and a good appearance cannot be obtained, exceeding 0.5% When Al is added, the alloying reaction is remarkably suppressed, and it becomes difficult to form an alloyed hot-dip galvanized layer.
[0043]
Furthermore, by performing the alloying treatment, Fe is taken into the plating layer, and a high-strength and high-ductility hot-dip galvanized steel sheet excellent in paintability and spot weldability can be obtained. If the amount of Fe in the plating layer exceeds 20% by mass, the adhesion of the plating itself is impaired, and the plating layer breaks and falls off during processing and adheres to the mold, thereby causing defects during molding.
[0044]
On the other hand, in order to improve spot weldability, it is desirable that the Fe content be 5% or more. Therefore, when alloying is performed, the range of the amount of Fe in the plating layer is 5 to 20% by mass.
[0045]
Further, when the alloying treatment is not performed, even if the amount of Fe in the plating layer is less than 5% by mass, the corrosion resistance, ductility and workability, which are the effects excluding spot welding obtained by alloying, are good.
[0046]
Next, the reason for limiting the component composition of the steel sheet in the present invention will be described.
[0047]
C: An austenite stabilizing element, which moves from ferrite to austenite during two-phase heating and bainite transformation temperature range, and stabilizes austenite by concentrating in austenite. As a result, austenite is stabilized even at room temperature, and excellent ductility is ensured by transformation-induced plasticity.
[0048]
  When C is less than 0.0001% by mass, the volume fraction is 3% or more.ResidualSince it is difficult to ensure austenite, the lower limit was set to 0.0001% by mass.
[0049]
On the other hand, if C exceeds 0.3 mass%, welding becomes difficult, so the upper limit was made 0.3 mass%.
[0050]
Si: In addition to Si being a strengthening element, Si does not dissolve in cementite, so it delays cementite precipitation and delays the decomposition of austenite into ferrite and cementite. During this time, it becomes possible to concentrate C into austenite, and austenite can exist even at room temperature.
[0051]
However, in order to obtain a steel sheet having a strength-ductility balance having a strength of over 980 MPa, addition of 0.1% by mass or more is necessary. On the other hand, if it exceeds 4%, the weldability deteriorates, so the upper limit was made 4% by mass.
[0052]
Mn: Mn is an element necessary for ensuring the strength, and if it is less than 0.001% by mass, the reinforcing effect is not exhibited, so the lower limit was made 0.001% by mass. On the other hand, if it exceeds 3% by mass, the ductility is adversely affected, so 3% by mass was made the upper limit.
[0053]
Al: In addition to being used as a deoxidizer, Al does not dissolve in cementite, so it delays cementite precipitation and delays the decomposition of austenite into ferrite and cementite. During this time, it becomes possible to concentrate C into austenite, and austenite can exist even at room temperature.
[0054]
However, if it is less than 0.001% by mass, the effect is not exhibited. On the other hand, if it exceeds 4% by mass, weldability deteriorates, so the upper limit was made 4% by mass.
[0055]
Since it is economically disadvantageous to make P: P less than 0.0001% by mass, this value is set as the lower limit. On the other hand, addition of more than 0.3% by mass adversely affects weldability and manufacturability during production and hot rolling. Therefore, the upper limit value was set to 0.3% by mass.
[0056]
S: S adversely affects weldability and manufacturability during production and hot rolling. For this reason, the upper limit was set to 0.01% by mass.
[0057]
In addition to being strengthening elements, Ni and Cu change the oxide form of Al and Si, causing improvement in wettability and promotion of alloying. Since this effect is less effective when one or two elements in the element group are added in a total amount of less than 0.001% by mass, the lower limit is set to 0.001% by mass. On the other hand, if it exceeds 4%, the ductility is adversely affected, so the upper limit was made 4% by mass.
[0058]
Since Ti and Nb form fine carbides, nitrides, or carbonitrides, they are extremely effective for strengthening steel sheets, and in addition to making the main phase ferrite grains finer, greatly contributing to improved toughness Bring. Since this effect is small when one or two types are added in a total amount of less than 0.001% by mass, the lower limit is set to 0.001% by mass.
[0059]
On the other hand, addition of a large amount prevents deterioration of ductility and concentration of C in retained austenite, so the upper limit of addition was set to 1% by mass in one or two types in total. Furthermore, the addition of these elements into steel suppresses softening of the welded portion when performing welding such as spot welding, arc welding, laser welding, etc., and is therefore excellent in weldability.
[0060]
Furthermore, the steel plate which this invention makes object can contain the 1 type (s) or 2 or more types of Mo, Cr, Co for the purpose of the further improvement of intensity | strength.
[0061]
Mo: Mo is important for securing retained austenite because it delays cementite precipitation and pearlite transformation. However, if it is less than 0.001% by mass, the effect is not exhibited. On the other hand, if it exceeds 4% by mass, the ductility is adversely affected, so the upper limit was made 4% by mass.
[0062]
Cr: Cr is a strengthening element. However, since the effect is not exhibited as it is less than 0.001 mass%, the lower limit was set to 0.001 mass%. On the other hand, addition exceeding 4% by mass has an adverse effect on ductility, so the upper limit was made 4% by mass.
[0063]
Co: Co is a strengthening element. However, since the effect is not exhibited as it is less than 0.001 mass%, the lower limit was set to 0.001 mass%. On the other hand, the addition exceeding 4% by mass adversely affects the ductility and increases the cost, which is economically disadvantageous. Therefore, the upper limit is set to 4% by mass.
[0064]
Further, the ratio of the Cu content (mass%) in the plating layer and the Cu content (mass%) in the steel is a (= Cu content in the plating layer / Cu content in the steel), Ni content (mass in the plating layer). %) And the Ni content (mass%) in the steel is b (= Ni content in the plating layer / Ni content in the steel), these satisfy 0.0001 ≦ a + b ≦ 0.2. Further, an excellent plating appearance can be obtained.
[0065]
When a + b is less than 0.0001, the effect of the present invention is not exhibited, and excessive addition to the alloy exceeding 0.2 is not economically preferable, so that the above range is preferably satisfied.
[0066]
The above relationship between a and b is an expression newly found by the inventors through experiments.
[0067]
Furthermore, the steel plate targeted by the present invention can contain V, which is a strong carbide forming element, for the purpose of further improving the strength. V forms extremely fine carbides, nitrides, or carbonitrides, so is extremely effective for strengthening steel sheets, and can be added in an amount of 0.001% by mass or more as necessary. On the other hand, addition of a large amount hinders deterioration of ductility and concentration of C in retained austenite, so the upper limit of addition was set to 1% by mass.
[0068]
B can also be added as needed. B is effective for strengthening grain boundaries and strengthening steel by adding 0.0001% by mass or more, but when the addition amount exceeds 0.1% by mass, the effect is not only saturated, Since the steel sheet strength is increased more than necessary and the workability is lowered, the upper limit was made 0.1 mass%.
[0069]
Addition of Mg, Zr, Ca, Y, Hf, and La—Ce changes the oxide form of Al and Si, and improves wettability and promotes alloying. This effect is exhibited by containing one or more elements in the element group in a total amount of 0.001% by mass or more.
[0070]
The addition of less than 0.001% by mass has little effect, so the lower limit was made 0.001% by mass. Excessive addition causes an increase in cost and deterioration of castability, so the upper limit was made 1 mass%.
[0071]
  Furthermore, in the vertical section of the plated steel plate,layer/ In the steel plate in the range from the steel plate interface to 10 μm,Is an internal oxideMgO, CaO, ZrO₂, CeO₂, La₂O_Three, HfO₂TiO₂, Y₂O_Three, SiO₂, MnO and Al₂O_ThreeWhen the total of one kind or two kinds or more is 0.1% or more by area ratio, MnO, Al₂O_Three, SiO₂By changing the form from external oxidation to internal oxidation, further improvement in wettability and promotion of alloying can be obtained.
[0072]
  Also,Is an internal oxideMgO, CaO, ZrO₂, CeO₂, La₂O_Three, HfO₂TiO₂And Y₂O_ThreeIs ferrite,ResidualFormed not only in the grain boundaries of each phase of austenite and bainite, but also in the grains of these phases,MnO, Al ₂ O _Three , SiO ₂ ofSince the internal oxide is uniformly dispersed, it contributes to improvement of toughness, ductility and hole expandability.
[0073]
  On the other hand, in order to promote alloying, theseinternalThe total oxide is preferably 50% or less in terms of area ratio, but when the alloying treatment is not performed, these oxidesinternalEven if the total area ratio of one kind or two or more kinds of oxides is 50% or more, the corrosion resistance, ductility and workability which are the effects excluding spot welding obtained by alloying are good.
[0074]
  Also,Is an internal oxideMgO, CaO, ZrO₂, CeO₂, La₂O_Three, HfO₂TiO₂And Y₂O_ThreeDue to the presence ofMnO, Al ₂ O _Three , SiO ₂ ofSince the internal oxide is uniformly dispersed, it contributes to improvement of hole expansibility.
[0075]
  Also, in the vertical cross section of the plated steel plate,layer/ From the steel plate interfaceIs an internal oxideMgO, CaO, ZrO₂, CeO₂, La₂O_Three, HfO₂TiO₂, Y₂O_Three, SiO₂, MnO and Al₂O_ThreeDuring the steel sheet structure in the range up to the maximum depth where these exist, theseinternalWhen the total of 1 type or 2 types or more of oxides is contained in an area ratio of 1% or more, further improvement of wettability and promotion of alloying can be obtained.
[0076]
Since this effect becomes apparent when the area ratio is 1% or more, this range is preferable. More preferably, the area ratio is 5% or more.
[0077]
  Meanwhile, theseinternalWhen the area ratio of the oxide exceeds 50%, element diffusion between the plating layer and the steel sheet is inhibited, and alloying is delayed. Therefore, in order to promote alloying, the area ratio of the internal oxide is preferably 50% or less.
[0078]
However, when the alloying treatment is not performed, even if the area ratio of the internal oxide is 50% or more, the corrosion resistance, ductility and workability, which are the effects excluding spot welding obtained by alloying, are good. .
[0079]
  Also,Is an internal oxideMgO, CaO, ZrO₂, CeO₂, La₂O_Three, HfO₂TiO₂And Y₂O_ThreeBySiO ₂ , MnO or Al ₂ O _Three ofSince the internal oxide is uniformly dispersed, it contributes to improvement of hole expansibility.
[0080]
Note that identification / observation and area ratio measurement of the oxides present in the steel sheet as described above can be performed using EPMA, FE-SEM, or the like. In the present invention, 50 fields or more were measured at 2000 to 20000 times, and the area ratio was determined by image analysis.
[0081]
In addition, for identification of oxides, extraction replica samples were prepared and TEM, EPMA, and EBSP were used.
[0082]
Also, here, MnO, Al₂O_Three, SiO₂May be a complex oxide containing other atoms or a lot of defects, but it was determined by finding the closest one from elemental analysis and structural identification.
[0083]
The area ratio measurement can be obtained by performing surface analysis of each component using EPMA, FE-SEM, or the like. In this case, although it is difficult to identify an individual accurate structure, it can be determined from the form and the composition thereof together with the result of the structural analysis described above.
[0084]
A method for producing a steel sheet having the above structure and characteristics will be described. A cast slab having a component composition that satisfies the above-described component composition is cast as it is, or once heated after being cooled, the hot-rolled steel sheet wound after hot rolling is pickled and cold-rolled, and then hot-dip galvanized. Plating is performed on the line.
[0085]
In order to perform hot dip galvanizing on a high-strength steel sheet according to the method of the present invention, first, an iron oxide film is formed in an oxidation zone in a plating line. In the iron oxide film, since diffusion of Si and Al is difficult, formation of oxides of Si and Al is suppressed.
[0086]
At this time, if the thickness of the iron oxide film is less than several tens of mm, the effect of suppressing the diffusion of Si and Al is poor, and the formation of oxides of Si and Al is difficult to suppress. For this reason, the iron oxide film thickness is preferably several tens of mm or more.
[0087]
However, the combustion air ratio in the oxidation zone when forming the oxide film needs to be 0.9 or more in order to generate an iron oxide film sufficient to suppress the formation of oxides of Si and Al. If it is less, a sufficient iron oxide film cannot be formed.
[0088]
On the other hand, if the combustion air ratio exceeds 1.5, the formed oxide film becomes thick, and it takes an extremely long time for the subsequent reduction of the iron oxide film in the reduction zone, which is uneconomical. Moreover, when an oxide remains between a plating layer and a steel plate, plating adhesion will be inhibited. Therefore, the combustion air ratio in the oxidation zone is set to 0.9 to 1.5, and more preferably 0.9 to 1.2.
[0089]
Next, the water pressure (PH₂O) and hydrogen partial pressure (PH₂) Ratio within the range of the following formula (2).
−0.8 ≧ log (PH₂O / PH₂(1)
[0090]
Where log is a common logarithm and log (PH₂O / PH₂) Is set to −0.8 or less, if it exceeds −0.8, the iron oxide film formed in the oxidation zone cannot be reduced, and an oxide remains between the plating layer and the steel sheet. It is because it will inhibit.
[0091]
In the continuous annealing of the cold-rolled steel sheet, heating is performed to Ac1 + 30 (° C.) or more in order to set the volume ratio of ferrite as the main phase to 50% or more. If the heating temperature at this time is lower than Ac1 + 30 (° C.), the ferrite volume fraction cannot be made 50% or more, and the ductility is inferior.
[0092]
At the same time, when the heating temperature is set to Ac1 + 30 (° C.) or more and Ac3-10 (° C.) or less, the ferrite particle size can be reduced, and further increase in strength, ductility and hole expandability are caused.
[0093]
This effect is exhibited when the heating temperature is set to Ac1 + 30 (° C) or higher and Ac3-10 (° C) or lower. However, this effect becomes remarkable because the heating temperature is Ac3-50 (° C.) or lower, and heating at Ac3-50 (° C.) or lower is desirable.
[0094]
  If the holding time of annealing is too short, there is a high possibility that undissolved carbide remains,ResidualSince the austenite volume fraction decreases, the holding time for annealing is preferably 10 seconds or more. On the other hand, if the holding time is too long, there is a high possibility that the crystal grains become coarse and the strength, ductility and hole expansibility are lowered.
[0095]
  After that, as the primary cooling, at a cooling rate of 0.1 ° C./second or more620After cooling to a temperature range of ˜800 ° C., followed by cooling to a plating bath temperature to a plating bath temperature + 100 (° C.) at a cooling rate of 1 to 100 ° C./second as secondary cooling, 350 to a plating bath temperature Hold in the temperature range of +100 (° C.) for 1 to 3000 seconds including the immersion time of the plating bath.
[0096]
This maintains the bainite transformation without transforming the austenite generated by heating in the two-phase region to pearlite, and passes the temperature region of 350 to Zn plating bath temperature +100 (° C.) over 1 to 3000 seconds. This is because the structure is obtained as ferrite (+ bainite) + residual austenite to obtain predetermined characteristics.
[0097]
  After annealing,620If the primary cooling rate to ˜800 ° C. is less than 0.1 ° C./second, the ferrite grains become coarse, which is not preferable. Therefore, the lower limit was set to 0.1 ° C./second. The upper limit is not particularly defined, but excessively increasing the cooling rate causes excessive capital investment. Therefore, the upper limit is desirably 100 ° C./second or less. However, even if this value is exceeded, the effects shown in the present invention are exhibited.
[0098]
In addition, when the secondary cooling rate from the plating bath temperature to the plating bath temperature +100 (° C.) is less than 1 ° C./second, austenite is transformed into pearlite during cooling, so that residual austenite does not remain and is not desirable. . On the other hand, when the secondary cooling rate is faster than 100 ° C./sec, the cooling end point temperature in the plate width direction varies, and it becomes impossible to produce a uniform steel plate.
[0099]
The reason why the holding temperature before plating bath immersion is set to 350 to Zn plating bath temperature + 100 (° C.) is that bainite transformation occurs in this temperature range, and residual austenite remains at room temperature. When the temperature is lower than 350 ° C., the austenite generated by heating in the two-phase region causes martensitic transformation and no residual austenite remains, so the lower limit temperature was set to 350 ° C.
[0100]
On the other hand, if the holding temperature is higher than the Zn plating bath temperature +100 (° C.), the austenite generated by heating in the two-phase region is transformed into pearlite, or cementite is precipitated from the austenite, so the austenite is bainite. Therefore, the upper limit temperature was set to Zn plating bath temperature +100 (° C.).
[0101]
If the holding time including the Zn plating bath immersion time is less than 1 second, it is not preferable because the time for immersing the steel sheet in the plating bath is not sufficient, and if it exceeds 3000 seconds, the equipment becomes too large and uneconomical. Therefore, the holding time is set to 1 to 3000 seconds.
[0102]
In the alloying treatment that is selectively performed after immersion in the plating bath, the holding temperature is set to the bath temperature to the Zn plating bath temperature +100 (° C.). If the temperature is higher than this temperature, the austenite is transformed into pearlite, or Since cementite is precipitated from austenite, austenite is decomposed into bainite, so the upper limit temperature was set to Zn plating bath temperature +100 (° C.). If the holding temperature is lower than the bath temperature, it takes a long time for alloying, so the lower limit temperature was taken as the bath temperature.
[0103]
The high strength and high ductility hot dip galvanized steel sheet described in the present invention can be obtained without holding in the temperature range of bath temperature to plating bath temperature +100 (° C.) after bath immersion.
[0104]
The cooling rate from the temperature of the Zn plating bath or from the holding temperature after immersion of the Zn plating to room temperature is not particularly specified, but the cooling rate in this temperature range exceeds 100 ° C./sec. However, there is no problem in terms of the material, but excessively increasing the cooling rate leads to high manufacturing costs, so the upper limit is preferably set to 100 ° C./second.
[0105]
On the other hand, the lower limit can provide the effect of the present invention without any particular limitation. However, if the temperature is less than 0.5 ° C./second, the equipment becomes too large and uneconomical. It is desirable to make it more than seconds.
[0106]
  In order to control oxides and improve wettability and alloying, it is desirable to control temperature and processing history from the hot rolling stage. First, the heating temperature of the slab is set to 1100 to 1250 ° C., the finishing temperature is set to 850 ° C. or more, and the deskeRingThere is a high pressure deskRingIt is desirable to remove the oxidized phase formed by hot rolling as much as possible by performing strong pickling.
[0107]
In addition, the material of the high-strength and high-ductility hot-dip galvanized steel sheet of the present invention is generally manufactured through refining, steelmaking, casting, hot rolling, and cold rolling processes, which are ordinary iron making processes, but part of them. Or even if it manufactures omitting all, as long as the conditions concerning this invention are satisfied, the effect of this invention can be acquired.
[0108]
Further, in order to further improve the plating adhesion, the present invention does not depart from the present invention even if the steel sheet is plated with Ni, Cu, Co, or Fe alone or plurally before annealing.
[0109]
Furthermore, the effect of the present invention can be obtained even when annealing is performed to remove oxides on the surface of the steel sheet, and then immersed in a plating bath to perform plating.
[0110]
【Example】
Hereinafter, the present invention will be described in more detail by way of examples.
[0111]
Example 1
The slab whose component composition is listed in Table 1 was hot rolled, pickled, and cold rolled to a thickness of 1 mm. Thereafter, the Ac1 and Ac3 transformation temperatures were determined by calculation according to the following formulas depending on the components (mass%) of each steel.
[0112]
  Ac1 = 723-10.7 × Mn (%) + 29.1 × Si (%),
  Ac3 = 910−203 × C (%) ^1/2 + 44.7 × Si (%) + 31.5 ×
        Mo (%)-30 × Mn (%)-11 × Cr (%) + 400 × Al (%)
[0113]
[Table 1]

[0114]
The annealing temperature calculated from these Ac1 and Ac3 transformation temperatures is 10% H.₂-N₂After the temperature is raised and maintained in the atmosphere, it is cooled to 600 to 710 ° C. at a cooling rate of 0.1 to 10 ° C./second, and then cooled to the plating bath temperature at a cooling rate of 1 to 10 ° C./second, and the bath composition Plating was carried out by immersing in a hot-dip galvanizing bath at 460 ° C. with various changes in the temperature for 3 seconds. In this case, the plating adhesion amount is 40 g / m on one side²It was.
[0115]
Then, about some steel plates, after hold | maintaining in the temperature range of plating bath temperature -600 degreeC, the temperature range to 350 degreeC is cooled by the cooling rate of 0.1-100 degrees C / sec. Cooled down. Details of the production conditions are shown in Tables 2-5.
[0116]
[Table 2]

[0117]
[Table 3]

[0118]
[Table 4]

[0119]
[Table 5]

[0120]
The plating property was evaluated by visual observation of the state of dross entrainment on the plating surface appearance and measurement of the area of the non-plated part. The concentration in the prepared plating layer was measured using ICP emission analysis after dissolving the plating layer with 5% hydrochloric acid containing an amine-based inhibitor.
[0121]
For plating adhesion, powdering was investigated and the case where the peel width exceeded 3 mm was rejected.
[0122]
JIS No. 5 test specimens were collected from these plated steel plates and subjected to a room temperature tensile test at a gauge length of 50 mm and a tensile test speed of 10 mm / min.
[0123]
Hole expandability is evaluated by punching a circular hole with a diameter of 10 mm under the condition that the clearance is 12%, forming the burr on the die side, forming with a 60 ° conical punch, and evaluating the hole expansion ratio λ (%). did.
[0124]
The residual austenite volume fraction Vγ is measured by X-ray diffraction using a Mo tube after chemically polishing the 7/16 inner layer of the plate thickness from the plating layer / steel plate interface, and the diffraction intensity Iα (200) of ferrite (200). The diffraction intensity Iα (211) of ferrite (211) and the diffraction intensity Iγ (220) of austenite (220) and the diffraction intensity Iγ (311) of (311) were obtained from the intensity ratio.
Vγ (volume%)
= 0.25
× {Iγ (220) / (1.35 × Iα (200) + Iγ (220))
+ Iγ (220) / (0.69 × Iα (211) + Iγ (220))
+ Iγ (311) / (1.5 × Iα (200) + Iγ (311))
+ Iγ (311) / (0.69 × Iα (211) + Iγ (311))}
[0125]
  internalThe volume ratio and distribution of the oxide were measured by observing with SEM and EPMA after polishing.
[0126]
Tables 6 to 9 show mechanical characteristics, plating characteristics, and the like. As shown in Tables 6 to 9, when the steel plate component satisfies the predetermined range, good plating properties are obtained without any non-plating.
[0127]
[Table 6]

[0128]
[Table 7]

[0129]
[Table 8]

[0130]
[Table 9]

[0131]
Even if the component composition of the steel sheet is within a predetermined range, the manufacturing conditions and the steel sheet structure that do not satisfy the predetermined requirements are inferior in high strength, high ductility and plating adhesion, and further, the retained austenite fraction is low. Therefore, the strength-ductility balance (TS × El.) Is also less than 21000 (MPa ·%), which is inferior to the strength-ductility balance.
[0132]
Even if the manufacturing conditions satisfy the requirements of the present invention, the effects of the present invention cannot be obtained if the component composition range does not satisfy the predetermined requirements.
[0133]
【The invention's effect】
According to the present invention, good plating properties were obtained, and a high-strength, high-ductility hot-dip galvanized steel sheet having a strength exceeding 980 MPa that exceeded the strength-ductility balance (TS × El.) Of 21000 (MPa ·%) was obtained.

Claims (12)

% By mass
C: 0.0001 to 0.3%,
Si: 0.1 to 4%,
Al: 0.001 to 4%,
Mn: 0.001 to 3%,
P: 0.0001 to 0.3%,
S: 0.01% or less, 0.001 to 4% in total of one or two of Ni and Cu, and further 0.001 to 1 in total of one or two of Ti and Nb Containing 1%, balance iron and inevitable impurities, microstructure is volume fraction, containing 50% or more of ferrite as the main phase, containing less than 3-50% residual austenite, and remaining structure is bainite or, Ri name from martensite and bainite, the average particle diameter on a volume ratio of 80% or more of the ferrite, the surface of the der Ru steel below 5 [mu] m, in mass%,
Al: 0.001 to 0.5%,
A high-strength, high-ductility hot-dip galvanized steel sheet comprising Fe: 5 to 20%, the balance having a hot-dip galvanized layer composed of Zn and inevitable impurities, and having a tensile strength of over 980 MPa. % By mass
C: 0.0001 to 0.3%,
Si: 0.1 to 4%,
Al: 0.001 to 4%,
Mn: 0.001 to 3%,
P: 0.0001 to 0.3%,
S: 0.01% or less, 0.001 to 4% in total of one or two of Ni and Cu, and further 0.001 to 1 in total of one or two of Ti and Nb Containing 1%, balance iron and inevitable impurities, microstructure is volume fraction, containing 50% or more of ferrite as the main phase, containing less than 3-50% residual austenite, and remaining structure is bainite or, Ri name from martensite and bainite, the average particle diameter on a volume ratio of 80% or more of the ferrite, the surface of the der Ru steel below 5 [mu] m, in mass%,
Al: 0.001 to 0.5%,
Fe: A high-strength, high-ductility hot-dip galvanized steel sheet having a hot-dip galvanized layer containing less than 5%, the balance being Zn and inevitable impurities, and having a tensile strength of over 980 MPa. Furthermore, in steel,
Mo: 0.001 to 4%,
Cr: 0.001 to 4%,
Co: 0.001 to 4%
The high-strength, high-ductility hot-dip galvanized steel sheet according to claim 1, comprising one or more of the following. The ratio of the Cu content (mass%) in the plating layer to the Cu content (mass%) in steel is a, the Ni content (mass%) in the plating layer and the Ni content (mass%) in the steel. If the ratio of is b,
0.0001 ≦ a + b ≦ 0.2
The high strength and high ductility hot dip galvanized steel sheet according to any one of claims 1 to 3, wherein: Furthermore, in steel,
V: 0.001-1% is contained, The high intensity | strength high ductility hot-dip galvanized steel plate of any one of Claims 1-4 characterized by the above-mentioned. Furthermore, in steel,
B: 0.0001-0.1% is contained, The high intensity | strength high ductility hot dip galvanized steel plate of any one of Claims 1-5 characterized by the above-mentioned.   Further, the steel is characterized by containing 0.001 to 1% in total of one or more of Mg, Zr, Ca, Y, Hf, and La—Ce element groups in mass%. The high strength and high ductility hot dip galvanized steel sheet according to any one of claims 1 to 6. In the vertical cross section of the plated steel sheet, MgO, CaO, ZrO ₂ , CeO ₂ , La ₂ O ₃ , HfO ₂ , TiO ₂ , Y ₂ O ₃ , SiO ₂ , MnO, and Al ₂ from the plated layer / steel sheet interface. In the steel sheet in the range up to the maximum depth where one or more internal oxides of O ₃ are present, internal oxides MgO, CaO, ZrO ₂ , CeO ₂ , La ₂ O ₃ , HfO ₂ , TiO 8. One or more of ₂ , Y ₂ O ₃ , SiO ₂ , MnO, and Al ₂ O ₃ are contained in an area ratio of 1% or more. The high-strength hot-dip galvanized steel sheet described in 1. In the vertical cross section of the plated steel sheet, the internal oxides MgO, CaO, ZrO ₂ , CeO ₂ , La ₂ O ₃ , HfO ₂ , TiO ₂ , Y ₂ O are present in the steel sheet from the plated layer / steel interface to 10 μm. _3, SiO _2, MnO, and, wherein one or the sum of two or more of Al ₂ O _3, to any one of claims 1-8, characterized in that it comprises an area ratio of 0.1% or more High strength high ductility hot dip galvanized steel sheet. The cast slab having the component composition according to any one of claims 1 to 7 is cast as it is or after being cooled again, and then heated again, and the hot-rolled steel sheet wound up after hot rolling is pickled and then cold-rolled. Then, in the oxidation zone in the plating line, it was oxidized in an atmosphere with a combustion air ratio of 0.9 to 1.5, and then in the reduction zone, the logarithm logarithm of water pressure and hydrogen partial pressure (PH ₂ O / PH ₂ ) After annealing at Ac1 + 30 (° C) or higher and Ac3-10 (° C) or lower in a reducing atmosphere satisfying the following formula (1), the temperature is 620 to 800 ° C at a cooling rate of 0.1 ° C / second or higher. Then, after cooling to a Zn plating bath temperature to a Zn plating bath temperature +100 (° C.) at a cooling rate of 1 to 100 ° C./second, a temperature range of 350 to a Zn plating bath temperature +100 (° C.) 1 to 300 including the immersion time of the subsequent plating bath High strength and high ductility hot dip galvanized steel characterized by producing a high strength and high ductility hot dip galvanized steel sheet having a tensile strength of over 980 MPa after being held for 2 seconds and then immersed in a Zn plating bath and then cooled to room temperature. Manufacturing method of plated steel sheet.
−0.8 ≧ log (PH ₂ O / PH ₂ ) (1) 11. The high strength according to claim 10 , wherein after being immersed in the Zn plating bath, holding is performed for 1 to 300 seconds in a temperature range of bath temperature to Zn plating bath temperature + 100 (° C.) and cooling to room temperature. A method for producing a high ductility hot-dip galvanized steel sheet. The method for producing a high-strength, high-ductility hot-dip galvanized steel sheet according to claim 10 or 11, wherein hot rolling is performed at a heating temperature of the cast slab of 1100 to 1250 ° C and a finishing temperature of 850 ° C or higher.