JP5651964B2 - Alloyed hot-dip galvanized steel sheet excellent in ductility, hole expansibility and corrosion resistance, and method for producing the same - Google Patents

Description

The present invention relates to an alloyed hot-dip galvanized steel sheet having excellent ductility, hole expansibility and corrosion resistance, and a method for producing the same.

  In order to achieve both weight reduction and safety of automobile bodies, parts, etc., the strength of steel plates as materials is being increased. In general, when the strength of a steel plate is increased, ductility, hole expansibility and the like are lowered, and formability is impaired. Therefore, in order to use a high-strength steel sheet as a member for automobiles, balances such as strength, ductility and hole expansibility are necessary. On the other hand, when it is intended for use as a member for automobiles, from the viewpoint of ensuring corrosion resistance and weldability, an alloyed hot-dip galvanized steel sheet is preferred, and a high-strength hot-dip alloyed hot-dip galvanized steel sheet excellent in workability and corrosion resistance Is desired.

  In response to the demand for ductility, so-called TRIP steel sheets utilizing transformation-induced plasticity of retained austenite have been proposed so far (for example, Patent Documents 1 and 2). These concentrate C in austenite and stabilize austenite by adding carbide precipitation inhibiting elements such as Si and Al. On the other hand, an alloyed hot-dip galvanized steel sheet can be made by alloying iron and zinc by performing reheating treatment after applying hot-dip zinc to the surface of the steel sheet.

  However, when trying to make an alloyed hot-dip galvanized steel sheet in TRIP steel, a part of austenite is easily decomposed into carbides and the amount of retained austenite is reduced, so that the strength-ductility balance is lowered. In addition, since a large amount of carbide which is an embrittlement phase precipitates, there is a problem such as a decrease in hole expansibility.

  Further, when the decrease in the amount of retained austenite due to precipitation of carbide is compensated for by an increase in the amount of C, a decrease in weldability becomes a problem.

Japanese Patent Laid-Open No. 61-217529 Japanese Patent Laid-Open No. 5-59429

  In order to ensure strength and ductility, the present invention uses TRIP steel in which a certain amount or more of residual γ is dispersed in a steel sheet, and alloyed hot dip galvanizing is applied to the upper surface of the steel sheet in order to improve corrosion resistance. The present invention provides a high-strength steel plate excellent in corrosion resistance excellent in ductility and hole expansibility, and a method for producing the same.

  The inventors have optimized the components and production conditions of TRIP steel and controlled the structure to produce a steel sheet that is excellent in ductility, that is, total elongation, uniform elongation, and hole expandability, and excellent in corrosion resistance. succeeded in. The gist of the present invention is as follows.

(1) In mass%,
C: 0.10 to 0.50%,
Mn: 1.0-3.0%
Si: 0.005 to 2.5%,
Al: 0.005 to 2.5%,
Containing
P: 0.05% or less,
S: 0.02% or less,
N: 0.006% or less, consisting of Fe and unavoidable impurities, the sum of Si and Al is Si + Al ≧ 0.8%, the microstructure is ferrite with an area ratio of 10 to 75%, 2 to 30 % Of retained austenite, the balance is bainite, the amount of C in the retained austenite is 0.8 to 1.0%, the product of tensile strength and total elongation is 19000 MPa ·% or more, Ductility and hole characterized in that the product of uniform elongation is 14000 MPa ·% or more, the product of tensile strength, uniform elongation and hole expansibility: TS × u−EL × λ is 550 GPa ·% ·% or more Alloyed hot-dip galvanized steel sheet with excellent spreadability and corrosion resistance.

(2) Furthermore, in mass%,
Cr: 0.01 to 0.8%
Mo: 0.01 to 0.3%,
Ni: 0.01 to 5%,
Cu: 0.01 to 5%
The alloyed hot-dip galvanized steel sheet having excellent ductility, hole expansibility and corrosion resistance as described in (1) above, comprising one or more of the above.

(3) Furthermore, in mass%,
Nb: 0.001 to 0.10%
Ti: 0.001 to 0.10%
V: 0.001 to 0.10%
W: 0.001% to 0.10%
An alloyed hot-dip galvanized steel sheet excellent in ductility, hole expansibility and corrosion resistance as described in (1) or (2) above, comprising one or more of the above.

(4) Furthermore, in mass%,
B: Alloyed hot dip galvanizing excellent in ductility, hole expansibility and corrosion resistance as described in any one of (1) to (3) above, containing 0.0003 to 0.003% or less steel sheet.

(5) Furthermore, in mass%,
Ca: 0.0005 to 0.05%,
REM: 0.0005 to 0.05%
Mg: 0.0005 to 0.05%
Zr: 0.0005 to 0.05%
The alloyed hot-dip galvanized steel sheet having excellent ductility, hole expansibility and corrosion resistance according to any one of the above (1) to (4), comprising one or two of the following.

(6) The alloy having excellent ductility, hole expansibility and corrosion resistance according to any one of the above (1) to (5), wherein the ferrite has an average crystal grain size of 10 μm or less in a microstructure Hot-dip galvanized steel sheet.

(7) In the microstructure, martensite or tempered martensite is equal to or less than 25% (1) to (6) excellent alloy ductility and hole expansion and corrosion resistance according to any one of Hot-dip galvanized steel sheet.

(8) Tensile strength of the steel sheet is characterized in that the on 900MPa or more (1) ductility and hole expansion and excellent galvannealed steel sheet in corrosion resistance according to any one of (1) to (7).

(9) A method for producing a galvannealed steel sheet having the composition described in any one of (1) to (5), wherein the composition is any one of (1) to (4) After melting and casting steel having hot rolling and cold rolling, the steel is held in the temperature range of Ac1 to Ac3 ° C for 10 to 300 seconds and then cooled at 3 to 200 ° C / s. In the temperature range of 300 to 550 ° C., hold for 214 to 362 s, hot dip galvanize, then alloy at 470 to 600 ° C., and the amount of C in the austenite after the hot dip galvanization A method for producing an alloyed hot-dip galvanized steel sheet excellent in ductility, hole expansibility and corrosion resistance, characterized by being controlled to 0.8 to 1.0%.

(10) In the manufacturing method of the alloyed hot-dip galvanized steel sheet according to (9), the finishing temperature of the hot rolling is 1000 to 850 ° C, and 10 to 100 ° C / s up to a temperature range of 600 ° C or less after finishing. A method for producing an galvannealed steel sheet excellent in ductility, hole expansibility and corrosion resistance, characterized by cooling at an average cooling rate and winding up at 600 ° C. or less.

(11) In the method for producing an alloyed hot-dip galvanized steel sheet having excellent ductility and corrosion resistance as described in (9) or (10), the reduction ratio of the cold rolling is 40 to 85%. And a method for producing an alloyed hot-dip galvanized steel sheet having excellent hole expandability and corrosion resistance.

  ADVANTAGE OF THE INVENTION According to this invention, the high strength steel plate excellent in formability, such as ductility and hole expansion, and corrosion resistance can be provided. If this steel plate is used, industrial contributions are particularly remarkable, such as making it possible to achieve both weight reduction and safety of automobiles and secure corrosion resistance.

Effect of C content in residual γ on weight density of cementite Effect of C content in residual γ on balance of strength, ductility and hole expansibility

  As a result of intensive studies, the present inventors have limited the amount of C in the retained austenite to 0.8 to 1.0%, thereby achieving high strength with excellent moldability such as ductility and hole expansibility and corrosion resistance. The inventors have found that a steel plate can be produced and have completed the present invention. The reason will be described below.

  TRIP steel concentrates C in austenite by ferrite and bainite transformation in the annealing process, and austenite exists stably even at room temperature. However, in order to make an alloyed hot-dip galvanized steel sheet, which is a steel sheet having high corrosion resistance and spot weldability, it is necessary to perform an alloying treatment through a plating bath after annealing. The alloying treatment is a process of holding at a temperature of 480 ° C. or higher. However, when cementite is precipitated from austenite during the alloying treatment, the amount of C in the austenite is lowered, and the balance between strength and ductility is reduced. Moreover, it becomes a starting point of a crack at the time of a hole expansion test, and a moldability deteriorates.

  Therefore, the present inventors investigated a method for reducing the amount of cementite deposited. As a result of adjusting the annealing temperature and heating time and adjusting the structural fraction in the steel, the amount of C in the retained austenite is adjusted to 0.8 to 1.0%, so that the precipitation of cementite as shown in FIG. The amount was reduced, and it was found that the balance of strength, ductility and hole expandability was excellent as shown in FIG.

  The lower limit of the amount of C in the retained austenite is set to 0.8% because if less than 0.8%, austenite is unstable, the TRIP effect is small, and the ductility improvement is small. On the other hand, the upper limit of the amount of C in the retained austenite is set to 1.0%. When the upper limit is exceeded, a large amount of carbide is generated from austenite, which becomes the starting point of cracking during the hole expansion test, and the strength, ductility and hole This is because the balance of spreadability is reduced. The reason why carbide tends to precipitate when the amount of C in the retained austenite exceeds 1.0% is not clear, but generally the higher the amount of C in the austenite, the greater the driving force for precipitation of cementite. It is thought to be caused by

  Next, the components of the steel sheet of the present invention will be described.

  C is an extremely important element for increasing the strength of the steel and securing retained austenite. In order to obtain a sufficient amount of retained austenite, a C amount of 0.10% or more is required. On the other hand, when C is contained excessively, weldability is impaired, so the upper limit of the C content is set to 0.50%.

  Mn is an element that stabilizes austenite and improves hardenability. In order to ensure sufficient hardenability, it is necessary to add 1.0% or more of Mn. On the other hand, if Mn is added excessively, ductility is impaired, so the upper limit of the amount of Mn is made 3.0%.

  Si and Al are deoxidizers, and 0.005% or more of each is preferably added. In addition, it is an element that stabilizes ferrite during annealing, and suppresses precipitation of cementite during bainite transformation, thereby increasing the C concentration of austenite and contributing to securing retained austenite. The effect of suppressing the precipitation of cementite was obtained when the total sum of Si and Al was 0.8 or more, and thus was limited to Si + Al ≧ 0.8%. The higher the Si and Al, the greater the effect. However, excessive addition of Si or Al causes deterioration of the surface properties, paintability, weldability, etc., so the upper limit is set to 2.5%.

  P is an impurity, and if contained excessively, ductility and weldability are impaired. Therefore, the upper limit of the P content is 0.05%.

  S is an impurity, and if contained excessively, MnS stretched by hot rolling is generated, which causes deterioration of formability such as ductility and hole expansibility. Therefore, the upper limit of the S amount is 0.02%.

  N is an impurity. When it exceeds 0.006%, ductility is deteriorated. Therefore, the upper limit of the N amount is set to 0.006%.

  Furthermore, you may add 1 type, or 2 or more types of Cr, Mo, Ni, Cu. Cr, Mo, Ni, and Cu are elements that improve the strength of the steel sheet. In order to obtain this effect, addition of 0.01% or more is necessary. However, when these elements are added excessively, the strength increases and ductility may be impaired. Therefore, it is preferable to set the upper limit to Mo: 0.3%, Cr: 0.8%, Ni: 5%, and Cu: 5%, respectively.

  Nb, Ti, V, and W are elements that generate fine carbides, nitrides, or carbonitrides, and are effective in securing strength. Therefore, it is possible to add one or more as necessary. is there. To achieve this, an addition of 0.010% is necessary. Therefore, the lower limit was made 0.010%. On the other hand, excessive addition increases the strength too much and lowers the ductility, so the upper limit was made 0.10%.

  B can delay the transformation and increase the strength of the steel. If the amount to be added is small, the hardenability is weak and the required strength cannot be obtained to promote ferrite formation at high temperatures. Therefore, the lower limit of B is set to 0.0003%. On the other hand, if it is added in a large amount, the hardenability becomes too strong and the ferrite and bainite transformation is slowed down, so that the concentration of C into the retained austenite phase is delayed. Therefore, the upper limit was made 0.003%.

  The steel can further contain one or more of Ca, Mg, Zr, and REM (rare earth elements) alone or in total from 0.0005% to 0.05%. Ca, Mg, Zr, and REM improve the local ductility and hole expansibility by controlling the shapes of sulfides and oxides. For this purpose, it is necessary to add one or more of these elements alone or in total of 0.0005% or more. However, excessive addition deteriorates workability, so the upper limit was made 0.05%.

  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 ferrite, retained austenite, martensite, and the balance is bainite.

  Ferrite is a structure with excellent ductility, but if it is too much, the strength decreases. The strength level may be a target level of development, but by setting the strength level to 10 to 75%, an excellent balance between strength and ductility can be obtained.

  Residual austenite is a structure that increases ductility, particularly uniform elongation, by transformation-induced plasticity, and an area ratio of 2% or more is required. Moreover, since it transforms into martensite by processing, it contributes to the improvement of strength. The higher the area of retained austenite, the better. However, in order to ensure retained austenite with an area ratio of more than 30%, it is necessary to increase the amount of C and Si, which impairs weldability and surface properties. Therefore, the upper limit of the area ratio of retained austenite is set to 30% or less.

  Furthermore, it may contain 25% or less of martensite or tempered martensite. These structures are hard structures and are effective in securing strength. However, in the present invention, in order to ensure ductility, the upper limit is 25% in area ratio.

  A method for identifying the tissue will be described below.

  The microstructure is observed with an optical microscope using a sample that has undergone nital corrosion. The area ratio of the ferrite is obtained by analyzing the structure photograph. Moreover, it is confirmed by an optical microscope that pearlite is not observed, and the remainder of ferrite, retained austenite, and martensite is defined as bainite.

  Martensite is difficult to distinguish from retained austenite with an optical microscope. For this reason, first, a structure subjected to repeller corrosion is observed with an optical microscope, and the total area ratio of residual austenite and martensite is obtained by image analysis. Next, the area ratio of retained austenite is measured by an X-ray diffraction method. Then, the area ratio of residual austenite measured by X-ray diffraction is subtracted from the total area ratio of residual austenite and martensite measured by an optical microscope.

  The average crystal grain size of ferrite is preferably 10 μm or less. When the thickness is 10 μm or less, the structure becomes fine, so that the strength is increased. However, since the structure is made uniform, the strain is uniformly introduced, and the ductility and hole expansion are improved.

  The crystal grain size of ferrite can be determined by taking a structure photograph with an optical microscope or a scanning electron microscope, and by a cutting method or image processing.

Next, the tensile properties of the steel sheet of the present invention will be described.
The tensile strength is preferably 900 MPa or more. This is because when a steel plate is used as a material for automobile members or pillars, the plate thickness is reduced by increasing the strength, thereby contributing to weight reduction. In order to perform press molding, drawing is mainly important. Therefore, rather than good the higher the product of strength and ductility, TS × t-EL ≧ 19000MPa %, it is necessary to make the TS × u-EL ≧ 14000MPa% . In addition to drawing, members that require hole expansion need to have ductility and hole expandability, so the product of tensile strength, uniform elongation, and hole expandability must be 550 GPa · %% or more. It is.

  Next, the manufacturing method of the steel plate of this invention is demonstrated.

  The steel sheet of the present invention is produced by hot rolling a steel piece obtained by melting and casting steel in a conventional manner, and subjecting the hot-rolled steel sheet to pickling, cold rolling, and annealing. Hot rolling is performed with a normal continuous hot rolling line, and annealing after cold rolling is performed with a continuous annealing line. Further, skin pass rolling may be performed on the cold-rolled steel sheet.

  The molten steel may be one produced by a normal blast furnace method or one using a large amount of scrap as in the electric furnace method. The slab may be manufactured by a normal continuous casting process or may be manufactured by thin slab casting.

  The steel slab is heated and hot rolled. The heating temperature of the steel slab is not particularly specified, but is preferably set to 1000 ° C. or higher in order to reduce the deformation resistance. In order to dissolve the carbide, it is more preferable to set the heating temperature to 1050 ° C. or higher. The upper limit of the heating temperature of the steel slab is preferably 1250 ° C. or lower in order to suppress the coarsening of the particle size.

  If the finishing temperature of the hot rolling is too high, scale formation is promoted, and the surface quality and corrosion resistance of the product are adversely affected. Therefore, the finishing temperature of hot rolling is set to 1000 ° C. or less. On the other hand, when the finishing temperature of hot rolling is less than 850 ° C., (α + γ) two-phase region rolling occurs, and the shape of the plate may be deteriorated.

  After finishing rolling, it is cooled, wound and coiled. Although the cooling rate is not specified, it is preferably 10 ° C./s or more in order to suppress layered pearlite. Furthermore, in order to refine the particle size, the cooling rate is preferably 30 ° C./s or more. The upper limit of the cooling rate is preferably 100 ° C./s or less in order to accurately control the coiling temperature.

  The coiling temperature after cooling is preferably 600 ° C. or lower. This is because when the coiling temperature exceeds 600 ° C., a ferrite-pearlite coarse and non-uniform structure is formed in the hot-rolled structure, and the average grain diameter of the ferrite of the cold-rolled steel sheet is over 10 μm.

  In cold rolling, the reduction ratio is set to 40% or more in order to refine the microstructure after annealing. On the other hand, if the rolling reduction of cold rolling exceeds 85%, the load increases due to work hardening, and the productivity is impaired. Therefore, the rolling reduction of cold rolling is 40 to 85%.

  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.

  The purpose of annealing heating is to recrystallize the work structure formed by cold rolling and to concentrate austenite stabilizing elements such as C into austenite. In the present invention, the heating temperature for annealing is a temperature at which ferrite and austenite coexist. When the annealing heating temperature is less than Ac1, the amount of austenite obtained at the annealing temperature is small, and sufficient residual austenite cannot be left in the steel sheet. Moreover, since the higher temperature of annealing leads to coarsening of crystal grains, the upper limit of the annealing temperature was set to Ac3.

  The holding time for annealing is not particularly specified, but it is preferable to hold for 10 s or more in order to sufficiently dissolve the carbide and to secure the C amount of austenite. On the other hand, if the annealing holding time exceeds 300 s, the productivity decreases. Therefore, the heating temperature for annealing is preferably 10 to 300 s.

  Cooling after annealing is important for promoting the transformation from the austenite phase to the ferrite phase and concentrating C in the untransformed austenite phase to stabilize the austenite. When this cooling rate is less than 3 ° C./sec, pearlite is generated. On the other hand, when the cooling rate exceeds 200 ° C./sec, the ferrite transformation cannot sufficiently proceed, so the cooling rate after annealing is set to 3 to 200 ° C./sec.

  Cooling temperature shall be 300-550 degreeC. This is because martensite is likely to be generated at a temperature lower than 300 ° C., and it is difficult to cause the bainite transformation to proceed at a temperature higher than 550 ° C., and cementite is likely to be generated during the bainite transformation.

  The cold-rolled steel sheet produced as described above is immersed in a hot dip zinc plating bath for plating. The bath temperature is 450-475 ° C. If the temperature is lower than 450 ° C, the viscosity of the molten zinc is high, which is not suitable for wiping by wiping, and tends to cause bottom dross. This is because problems such as an increase in production and an increase in the amount of zinc vapor occur.

It is important to limit the amount of C in the austenite to 0.8 to 1.0% by these processes from annealing to plating bath immersion. Therefore, in the temperature range of 300 to 550 ° C. after cooling, it is necessary to limit the holding time including the galvanizing process to 214 to 362 s. In the temperature range, bainite transformation proceeds and C is concentrated in austenite. If it is less than 214 s, the C concentration in the austenite becomes 0.8% or less, and a large amount of martensite is transformed during cooling after the alloying treatment, so that the retained austenite fraction of the present invention cannot be achieved. On the other hand, when it exceeds 362 s, C in the austenite exceeds 1.0%, and a large amount of cementite is precipitated during the subsequent alloying treatment, so that ductility and hole expandability are greatly deteriorated. Therefore, as described in the examples of Table 2, in the temperature range of 300 to 550 ° C. after cooling, it is necessary to limit the holding time including the galvanizing treatment to 214 to 362 s. In the said temperature range, bainite transformation advances and C concentrates in austenite. When the retention time is less than the lower limit, the C concentration in the austenite is 0.8% or less, and a large amount of martensite is transformed during cooling after the alloying treatment, so that the retained austenite fraction of the present invention cannot be achieved. On the other hand, when the upper limit value of the holding time is exceeded, C in the austenite exceeds 1.0%, and a large amount of cementite is precipitated during the subsequent alloying treatment, so that ductility and hole expandability are greatly deteriorated. Due to this limitation, the amount of C in the residual γ can be made 0.8 to 1.0%, and carbides are less likely to precipitate by the subsequent alloying treatment.

  Subsequently, an alloying treatment is performed at a temperature of 470 to 600 ° C. When the alloying treatment temperature is less than 470 degrees, alloying does not proceed, or the progress of alloying is insufficient and an alloyed hot-dip galvanized layer cannot be formed, and the surface of the steel sheet is inferior in workability. This is because it is covered with the η phase and the ζ phase. In addition, when the processing temperature is higher than 600 ° C, alloying progresses too much and the plating adhesion during processing decreases, and austenite before alloying during alloying includes bainite and pearlite containing carbides. This is because the material is transformed to a tensile strength characteristic.

  By manufacturing a steel plate as described above, a high-strength galvannealed steel plate of 900 MPa or more excellent in formability and corrosion resistance can be obtained.

  Cold-rolled steel sheets were manufactured under the conditions shown in Table 2 using steel pieces having the components shown in Table 1. The area ratio of ferrite, retained austenite, and martensite in the obtained steel sheet was measured by observation with an optical microscope and by X-ray diffraction. When pearlite was observed, the area ratio of bainite and the area ratio of pearlite were obtained with an optical microscope. The ferrite crystal grain size was determined by image processing using an optical micrograph or, if the grain size was 3 μm or less, using a scanning electron micrograph. The precipitation amount of carbide was obtained by collecting an extraction residue by electrolytic extraction, and determining the amount of the extraction residue by fluorescent X-ray diffraction. For the extraction of the precipitate by electrolysis, a 10% acetylacetone-1% tetramethylammonium chloride-methanol electrolyte was used.

  Table 3 shows the microstructure.

  The tensile properties of the steel sheet were evaluated by conducting a tensile test according to JIS Z 2241.

Ac1 and Ac3 were determined by the following formulas. (Reference: “Steel Materials Science” by WCLeslie, translated by Koyasu Naruyasu, Maruzen p273)
Ac1 = 723-10.7 × Mn% -16.9 × Ni% + 29.1 × Si% + 16.9 × Cr% + 6.38 × W%
Ac3 = 910-203 × √ (C%) － 15.2 × Ni% + 44.7 × Si% + 104 × V% + 31.5 × Mo% + 13.1 × W% −30 × Mn% −11 × Cr% + 20 × Cu% + 700P% + 400 × Al%

  The test results will be described below.

  Steel types A to P are steels whose chemical components are within the scope of the present invention. On the other hand, steel type Q has a small amount of C, and as shown in treatment number 45, stable retained austenite cannot be secured and the tensile properties are poor. In steel type R, the total amount of Si + Al is small, and carbides are generated during the plating bath to alloying treatment, and as shown in treatment number 44, retained austenite cannot be secured and the tensile properties are poor. Steel type S has a small amount of Mn and poor hardenability, so that pearlite is generated during cooling from annealing, and retained austenite cannot be secured as shown in treatment number 20, resulting in poor tensile properties.

Process Nos. 3, 4, 18-20, 23, 29, and 31 were used as reference examples because the total structure value exceeded 100% due to errors in microstructural measurement.
In the case of the treatment numbers 18 to 29, the chemical components are within the scope of the present invention, but since the C amount in the austenite is less than 0.8, the TRIP effect cannot be obtained sufficiently, and the balance between strength and ductility is low .

  Although the chemical components of the treatment numbers 30 to 42 are within the scope of the present invention, the amount of C in the austenite exceeds 1%, and a large amount of cementite is precipitated, resulting in strength, ductility, and hole expandability. The balance is low.

  For the comparative steels as described above, those with treatment numbers 1 to 17 have the appropriate chemical composition of the test steel, and various conditions such as cooling of the slab, hot rolling, annealing, plating, and residual γ Since the amount of C was within the range of the present invention, moderate retained austenite can be secured, and the amount of cementite precipitated is small. As a result, an alloyed hot-dip galvanized high-strength steel sheet having an excellent balance of strength, ductility and hole expandability could be produced.

  ADVANTAGE OF THE INVENTION According to this invention, the high strength steel plate excellent in formability, such as ductility and hole expansion, and corrosion resistance can be provided. If this steel plate is used, industrial contributions are particularly remarkable, such as making it possible to achieve both weight reduction and safety of automobiles and secure corrosion resistance.

Claims (11)

% By mass
C: 0.10 to 0.50%,
Mn: 1.0-3.0%
Si: 0.005 to 2.5%,
Al: 0.005 to 2.5%,
Containing
P: 0.05% or less,
S: 0.02% or less,
N: 0.006% or less, balance Fe and inevitable impurities, the sum of Si and Al is Si + Al ≧ 0.8%, and the microstructure is ferrite with an area ratio of 10 to 75%, 2 to 30 % Of retained austenite, the balance is bainite, the amount of C in the retained austenite is 0.8 to 1.0%, the product of tensile strength and total elongation is 19000 MPa ·% or more, Ductility and hole characterized in that the product of uniform elongation is 14000 MPa ·% or more, the product of tensile strength, uniform elongation and hole expansibility: TS × u−EL × λ is 550 GPa ·% ·% or more Alloyed hot-dip galvanized steel sheet with excellent spreadability and corrosion resistance. Furthermore, in mass%,
Cr: 0.01 to 0.8%
Mo: 0.01 to 0.3%,
Ni: 0.01 to 5%,
Cu: 0.01 to 5%
The alloyed hot-dip galvanized steel sheet having excellent ductility, hole expansibility and corrosion resistance according to claim 1, comprising one or more of the following. Furthermore, in mass%,
Nb: 0.001 to 0.10%
Ti: 0.001 to 0.10%
V: 0.001 to 0.10%
W: 0.001% to 0.10%
The alloyed hot-dip galvanized steel sheet having excellent ductility, hole expansibility and corrosion resistance according to claim 1 or 2, characterized by containing at least one of the following. Furthermore, in mass%,
The alloyed hot-dip galvanized steel sheet having excellent ductility, hole expansibility and corrosion resistance according to any one of claims 1 to 3, wherein B: 0.0003 to 0.003% or less is contained. Furthermore, in mass%,
Ca: 0.0005 to 0.05%,
REM: 0.0005 to 0.05%
Mg: 0.0005 to 0.05%
Zr: 0.0005 to 0.05%
The alloyed hot-dip galvanized steel sheet having excellent ductility, hole expansibility and corrosion resistance according to any one of claims 1 to 4, wherein the alloyed hot-dip galvanized steel sheet is excellent.   The alloyed hot-dip galvanized steel sheet having excellent ductility, hole expansibility and corrosion resistance according to any one of claims 1 to 5, wherein the average crystal grain size of ferrite is 10 µm or less in a microstructure.   The alloyed hot-dip galvanized steel sheet having excellent ductility, hole expansibility and corrosion resistance according to any one of claims 1 to 6, characterized in that in the microstructure, martensite or tempered martensite is 25% or less. .   The alloyed hot-dip galvanized steel sheet excellent in ductility, hole expansibility and corrosion resistance according to any one of claims 1 to 7, wherein the steel sheet has a tensile strength of 900 MPa or more. It is a manufacturing method of the alloying hot-dip galvanized steel plate of the composition described in any one of Claims 1-5 , Comprising: Steel which has a composition of any one of Claims 1-4 is melted. After casting, hot rolling and cold rolling, holding in the temperature range of Ac1 to Ac3 ° C for 10 to 300 s, cooling at 3 to 200 ° C / s, and a temperature of 300 to 550 ° C In the region, 214 to 362 s is held, hot dip galvanized, alloyed at 470 to 600 ° C., and the amount of C in the austenite after the hot dip galvanized is 0.8 to 1.0. A method for producing a galvannealed steel sheet excellent in ductility, hole expansibility and corrosion resistance, characterized by being controlled to%.   The manufacturing method of the galvannealed steel sheet according to claim 9, wherein a finishing temperature of the hot rolling is 1000 to 850 ° C, and an average cooling rate of 10 to 100 ° C / s to a temperature range of 600 ° C or less after finishing. A method for producing an alloyed hot-dip galvanized steel sheet excellent in ductility, hole expansibility and corrosion resistance, characterized by cooling at 600 ° C. and winding at 600 ° C. or lower.   In the manufacturing method of the galvannealed steel plate excellent in the ductility and corrosion resistance of Claim 9 or 10, The reduction rate of the said cold rolling shall be 40 to 85%, and the ductility and hole expansibility characterized by the above-mentioned A method for producing a galvannealed steel sheet having excellent corrosion resistance.

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