JP2001355043A - High strength hot dip galvannealed steel sheet and high strength steel sheet excellent in hole expandability and ductility and their production method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To produce a high strength hot dip galvannealed steel sheet excellent in hole expandability and ductility at a low cost. SOLUTION: This high strength hot dip galvannealed steel sheet having strength of >=490 MPa and a hole expanding ratio of >=80% and excellent in ductility has a steel composition containing 0.02 to 0.10% C, 0.1 to 1.0% Si, 0.8 to 2.5% Mn, 0.001 to 0.025% P, <=0.010% S, 0.003 to 0.1% Al and <=0.008% N, in which the relations of C-(12/48)×Ti*-(12/93)×Nb<=0.09 and -340×C+76×Si-2×Mn+939×Ti+1334×Nb+5470×N>=70 are satisfied, and further, crystal grains with a crystal grain size of <=20 μm occupy >=80% and has a bainitic ferritic structure.

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention
High strength alloyed hot-dip galvanized steel sheet and high strength
Regarding steel sheets and their manufacturing methods, more specifically,
Excellent ductility with strength of 490MPa or more and hole expansion ratio of 80% or more
High strength galvannealed steel sheet and high strength steel sheet
And a method for producing them. [0002] In recent years, in order to reduce the weight of automobiles,
There is a demand for higher strength steel sheets for vehicles. Moreover, this self
Depending on the application of the steel sheet for vehicles, not only strength but also corrosion resistance
Required. There has been research on increasing the strength of steel sheets.
For example, solid solution strengthening elements and precipitation strengthening elements
Addition, or use the tissue as bainite or dual phase.
It is commonly used to strengthen a tissue by doing so. one
On the other hand, to improve the corrosion resistance of steel sheets,
It is known to provide However, the various
Applying the Organizational Strengthening Act can lead to various issues, including:
There is. That is, Si is generally used as a solid solution strengthening element.
However, when a large amount of Si is added, it is called firelite.
Produces a reddish scale that reduces appearance and paintability
There is a problem. In addition, Si-added steel is
It is difficult to form an oxide layer in the pre-oxidation step during the heat treatment. That
Therefore, the subsequent alloying treatment becomes difficult, and the plating adhesion
Deteriorates. Further, the hot-rolled steel sheet is subjected to cold rolling after pickling.
If hot dip galvanizing is performed without performing
It will drop to the edge. This is a hot rolled steel sheet that has been pickled.
The surface of the crystal grain is etched with the grain boundary preferentially etched
Grain boundary is etched because of
Plating on the hot-rolled steel sheet
Also has a hole that expands like a steel plate for a suspension arm.
In steel plates to be worked, Zn embrittlement occurs due to punching of holes
Layer is missing together with the crystal grains, causing a notch effect
In addition, the hole expanding property is extremely reduced. On the other hand, as a precipitation strengthening element,
Ti, Nb, etc., which are oxide forming elements, are used.
Sexually, it is a level that is considered to be general-purpose steel, and has excellent elongation
There is a problem that a rung property cannot be obtained. In addition, Ti,
Nb-added steel has coarse carbides during galvannealing.
, Softening easily occurs. [0006] Therefore, the deterioration of the hole spreadability and plating adhesion is considered.
Prevent galvanizing steel sheet or steel sheet
Various proposals have been made to increase the strength. example
For example, in Patent No. 2553413, the circle equivalent radius is 0.1 μm or more.
To limit the microstructure ratio of cementite to 0.1% or less
High-strength galvannealed steel with excellent hole spreading properties
A board has been proposed. [0007] Further, Japanese Patent Application Laid-Open No. 4-346645 discloses Cu
0.5 to 2.0% (in the present specification, there is no particular limitation)
As long as “%” means “% by mass”)
To ensure the hole-expanding properties of the high-strength hot-dip galvanized steel sheet.
And has been proposed. Japanese Patent Application Laid-Open No. 5-263145 discloses a Cu-added
Alloying hot-dip galvanizing by adding Mn to steel
Heat treatment process such as a short time process (for example,
Minutes), the precipitation is insufficient because the heat treatment time is too short
Promotes the precipitation of Cu and increases the height of the galvannealed steel sheet.
Strengthening has been proposed. Further, Japanese Patent No. 2820819 discloses that Si, Mn, etc.
Add special elements mainly V and Nb together with strengthening elements
High strength thin steel with excellent stretch flangeability
A board has been proposed. [0010] Also, Japanese Patent Application Laid-Open No. Hei 5-311244 discloses
Quenched to below the Ms point in the
Is to generate martensite in all of
Generating tempered martensite in part or all
High strength hot rolled sheet with excellent stretch flange formability
It has been proposed to manufacture gold galvanized steel sheets.
You. [0011] Japanese Patent No. 2792434 discloses a molten zinc coating.
Limits the dew point and air-fuel ratio of
Optimum maximum temperature in pre-oxidation furnace depending on Si content
Control to apply hot-dip galvanizing to high Si steel.
It has been proposed. Japanese Patent Application Laid-Open No. 6-293910 discloses a
Consisting of a two-phase structure of ferrite and bainite
Disclosure of manufacturing method for high-strength hot-rolled steel sheet with excellent spreadability and ductility
Have been. Japanese Patent Application Laid-Open No. 7-48648 discloses a bay bay.
Nitic ferrite structure and a circle equivalent diameter of 0.5 μm or more
Baini containing coarse cementite and 0.1% or less in space factor
And / or tick ferrite structures
780 N / mm ^Two Has the above tensile strength
Corrosion resistance and overhang, that is, balance between strength and ductility.
-Strength hot-rolled steel sheet with excellent burring properties and its manufacturing method
The law is disclosed. Japanese Patent Application Laid-Open No. 7-11382 discloses an
686 N / mm with a ferrite structure ^Two More than high
High strength hot rolled with high strength and excellent stretch flangeability
A steel sheet and a method for manufacturing the same are disclosed. Further, Japanese Patent Application Laid-Open No. Hei 6-172924 discloses
Tensile strength 500N / mm ^Two Stretch flange even with high strength
A high-strength hot-rolled steel sheet excellent in workability is disclosed. [0016] However, these conventional methods
All of the inventions have the problems listed below. Special
The invention proposed by U.S. Pat.
There is no element to fix and cementite under heat treatment conditions
Suppress generation. Therefore, to take advantage of organizational transformation
Large variations in the organization and stable performance
Is difficult. In addition, high strength with the addition of strengthening elements such as Si and Mn
Measures for plating processability, which is a problem with high-grade steel sheets, have been fully developed.
It is not shown, and good plating properties cannot be obtained. [0017] Japanese Patent Application Laid-Open No. 4-346645 proposes
In the present invention, the use of expensive Cu increases the cost. Ma
In addition, in order to ensure plating properties, Ni
Plating is also performed, resulting in higher costs and economic realization.
Practical use is difficult. Japanese Patent Application Laid-Open No. 5-263145 has proposed
In the invention, the cost increases due to the use of Cu, which is also economical.
It is difficult to put it to practical use. No. 2820819.
In the invention described above, there is a problem when various strengthening elements are added.
Good, without taking measures against plating processability
High plating properties cannot be obtained. Japanese Patent Application Laid-Open No. Hei 5-311244 proposes
In the invention, the organizational variation is large due to the use of the structural transformation.
It is difficult to obtain excellent performance stably. Patent No.
In the invention proposed by No. 2792434, the alloyed molten zinc
Layer of Zn embrittled by punching hole in plated steel sheet
Is lost due to the notch effect
For hot-rolled steel sheet and cold-rolled steel sheet
No countermeasures were taken against the extreme decline
Therefore, the workability of the steel sheet is not sufficiently considered. Japanese Patent Application Laid-Open No. 6-293910 proposes
In the invention, the hard second phase is formed by a composite
Is easy to be the starting point of cracking in
The characteristics are not stable due to the variation of the fraction. Japanese Patent Application Laid-Open No. 7-48648 proposes
In the invention, as described in the embodiment, Ti
It is necessary to add a large amount of about 0.1 to 0.15%,
This causes poor appearance of the steel sheet surface. In addition, corrosion resistance
It is also necessary to add a large amount of Cu, P and Ni to secure
Yes, costly. Japanese Patent Application Laid-Open No. 7-11382 proposes
In the invention, as described in the embodiment, Ti
It is necessary to add a large amount of about 0.1 to 0.25%,
Causes poor appearance of the steel sheet surface and increases costs
No. Further, Japanese Patent Application Laid-Open No. 6-172924 discloses
In the proposed invention, as described in the embodiment,
Then, melt the steel melted by vacuum melting at 550-250 ° C (mainly 40
(° C) in the laboratory.
But in actual production, such low winding temperature
Water cooling becomes very unstable and the winding temperature rises sharply in the coil.
The current cooling technology can change the winding temperature as intended.
Control is impossible and cannot be implemented in practice.
No. As described above, in the conventional technology, the hole expanding property and
High-strength steel sheet or high-strength alloyed molten steel with excellent ductility
It is not possible to manufacture lead-coated steel sheets stably at low cost.
I didn't come. Here, the object of the present invention is to provide
High-strength steel sheet or high-strength alloyed molten zinc with excellent ductility
The objective is to produce stable steel sheets at low cost. Yo
More specifically, the strength should be 490MPa or more, and the hole expansion rate should be 80% or more.
And high strength alloyed molten steel with excellent ductility
Providing low-cost and stable manufacturing technology for lead-coated steel sheets
Is to provide. Means for Solving the Problems The present inventors have achieved the above object.
As a result of repeated experiments and researches to achieve
New findings (1) to (4) listed in (1) are obtained. (1) In order to obtain good hole expanding properties and ductility
Is not enough to define the range of various elements.
Control the content of each element by correlating
In addition, control the temperature conditions of hot rolling in consideration of actual production
By doing, the structure of the obtained steel sheet, 20μm or less
It is effective to make the crystal grains occupy 80% or more.
You. (2) Plating is performed using the above steel sheet as a base material.
By specifying the plating conditions at the time of
Plating property can be secured. That is, alloyed molten zinc
Line, there is an annealing process before the hot-dip plating process,
Heating → soaking → cooling → plating (immersion) → alloying (heating)
Follow the process, of which the heating step
Control the atmosphere (dew point and temperature) of the pre-oxidation furnace
Rolling controls the amount of scale generated on the steel sheet surface.
Is controlled. Scaling of the surface of the steel sheet formed in this pre-oxidation furnace
ル becomes a reduced iron layer in the uniform atmosphere, which is a reducing atmosphere. Si addition
Oxidized scale is difficult to form on steel sheet, so
Concentration of Si, the wettability of plating decreases, and alloying is delayed
I do. Therefore, the atmosphere (dew point and temperature) of the pre-oxidation furnace was changed.
By controlling the amount of oxide scale,
Control the concentration, which can reduce the delay of alloying
You. (3) Alloyed molten zinc with excellent hole expanding
For steel sheets, the steel sheet table at the interface between the plating layer and the steel sheet
The grain boundaries between the individual crystals on the plane are less than 2.0 μm in width.
It is stitched. (4) To control the crystal grain boundaries,
Strengthening leads to selective oxidation of grain boundaries,
No. However, galvannealing of Si-added steel
Pre-oxidation must be carried out in order to
The dew point of the pre-oxidation furnace should be 30 ° C or less
It is effective to set the fuel ratio to 0.8 to 1.25. The present inventors have made these new findings (1)
As a result of further study based on ~ (4), we changed to low C steel
Balance of Si, Ti, Nb, etc.
By specifying, the hole expansion ratio is 80% or more with strength of 490MPa or more
High-strength steel sheet with high ductility and high-strength alloyed melt
Stable and low cost of galvanized steel sheet even in the actual manufacturing process
The present inventors have found that the present invention can be manufactured by the present invention, and have completed the present invention. In the present invention, C: 0.02 to 0.10%, Si: 0.1 to 0.1%
1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025%,
S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.008%
Hereinafter, if necessary, Ti: 0.003 to 0.1% and Nb: 0.00
One or two of 3 to 0.1%, balance Fe and unacceptable
It has a steel composition consisting of inevitable impurities,
It is characterized by satisfying both the relations of the expression (2).
Excellent ductility with a temperature of 490MPa or more and a hole expansion rate of 80% or more
High strength alloyed hot-dip galvanized steel sheet. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 ・ ・ ・ ・ ・ ・ ・ (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) , Ti ^* = Ti− (48/14) × N− (4
8/32) × S. The high-strength alloyed molten zinc according to the present invention
For plated steel sheets, Cr: 0.005 to 0.10%, Mo: 0.
005 to 0.10%, V: 0.005 to 0.10% and B: 0.0001 to
One or more selected from the group consisting of 0.0100%
May be contained. The high-strength alloy according to the present invention
Hot-dip galvanized steel sheet has a crystal grain size of 20μm or less.
Accounts for 80% or more of the area ratio, bainitic ferrite structure
Is exemplified. The high-strength alloy according to the present invention described above.
Hot-dip galvanized steel sheet is located at the interface between the coating layer and the steel sheet.
Grain boundaries between individual crystals on the steel sheet surface
It is illustrated that underetching has been performed. From another viewpoint, the present invention relates to a method for producing C: 0.02 to 0.
10%, Si: 0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001
0.025%, S: 0.010% or less, Al: 0.003 to 0.1
%, N: 0.008% or less, Ti: 0.003 to 0.1 as required
% And Nb: one or two of 0.003 to 0.1%,
It has a steel composition consisting of the balance Fe and unavoidable impurities.
A steel slab that satisfies both the relations (1) and (2)
Hot-rolled at a finish rolling temperature of 880-970 ° C
After that, at a cooling rate of 35-55 ° C / sec in a temperature range of 600-700 ° C
Cool, then 5 to 40 ° C / sec in the temperature range of 400 to 600 ° C
After cooling at the cooling speed of the above, winding, pickling, and then melting
By performing galvanization, crystal grains with a grain size of 20 μm or less can be formed.
Crystal grains occupy 80% or more of area ratio, bainitic ferrite
Of the steel sheet surface at the interface between the plating and the steel sheet
The grain boundaries between each crystal are etched less than 2.0 μm wide
Specializing in the production of galvannealed steel sheets
With strength of 490MPa or more and hole expansion ratio of 80% or more
Of high-strength galvannealed steel sheet with excellent ductility
Manufacturing method. The high strength alloyed molten zinc according to the present invention
In the production method of galvanized steel sheet, hot-dip galvanizing
However, heating in the pre-oxidation furnace of the continuous galvanizing equipment,
Set the air-fuel ratio to 0.8 to 1.25 in an atmosphere with a dew point of 30 ° C or less.
The maximum temperature of the steel sheet reached in the pre-oxidation furnace
It is desirable that the process be performed so as to satisfy the following formula (3).
No. 700 + 100 × ln [Si] ≦ T ≦ 830 + 50 × ln [Si] (3) In the equation (3), the symbol T represents the maximum value in the pre-oxidation furnace.
Indicates the ultimate steel sheet temperature (° C), and the symbol [Si] indicates the S
i Indicates the content (%). These high-strength alloyed melts according to the present invention
In the method of manufacturing a galvanized steel sheet, the billet further includes Cr:
0.005 to 0.10%, Mo: 0.005 to 0.10%, V: 0.005 to 0.
10% and B: selected from the group consisting of 0.0001-0.0100%
One or more of these may be contained. From another point of view, the present invention relates to a method for preparing C: 0.02 to 0.
10%, Si: 0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001
0.025%, S: 0.010% or less, Al: 0.003 to 1.0
%, N: 0.008% or less, Cr: 0.005 to 0.
10%, Mo: 0.005 to 0.10%, V: 0.005 to 0.10% and
B: one or more selected from the group consisting of 0.0001 to 0.0100%
Is a steel set consisting of two or more, the balance being Fe and unavoidable impurities
And the relationship of the following equations (1) and (2)
490MPa strength and wide hole characterized by satisfying
This is a high-strength steel sheet with a ductility of 80% or more and excellent ductility. C- (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) ^* = Ti-(48/14) x N-(48/32) x S
You. Further, the present invention relates to a method for producing C: 0.02 to 0.10%, Si:
0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
8% or less, Cr: 0.005 to 0.10%, Mo: 0, if necessary.
005 to 0.10%, V: 0.005 to 0.10% and B: 0.0001 to
One or more selected from the group consisting of 0.0100%,
It has a steel composition consisting of the balance Fe and unavoidable impurities.
Equation (1) and the following equation (2) are both satisfied.
In particular, crystal grains with a crystal grain size of 20 μm or less occupy an area ratio of 80% or more.
, Granular bainitic ferrite or mulberry
It is made of one or more of sea polygonal ferrites.
Characterized by strength of 490MPa or more and hole expansion rate of 80% or less
It is a high-strength steel sheet which is superior and has excellent ductility. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) ^* = Ti-(48/14) x N-(48/32) x S
You. In the present invention, C: 0.02 to 0.10%, Si:
0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
Steel composition of 8% or less, with the balance being Fe and unavoidable impurities
Satisfies both the relations of the following equations (1) and (2).
In addition, the area ratio of crystal grains with a crystal grain size of 20 μm or less
Over 80%, granular bainitic ferrite
Or one or more of Kvasy polygonal ferrites
Of the steel sheet surface at the interface between the plating layer and the steel sheet
Grain boundaries between individual crystals are etched under 2.0 μm in width
Characterized by strength of 490MPa or more and holes
Alloyed molten zinc with an expansion ratio of 80% or more and excellent ductility
It is a steel plate. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) ^* = Ti-(48/14) x N-(48/32) x S
You. In the present invention, C: 0.02 to 0.10%, Si:
0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
8% or less, Cr: 0.005 to 0.10%, Mo: 0.005 to
0.10%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100
% Or more selected from the group consisting of
And has a steel composition consisting of unavoidable impurities, the following (1)
Equation and the relationship of the following equation (2).
Crystal grains with a crystal grain size of 20 μm or less occupy an area ratio of 80% or more.
Rannular bainitic ferrite or kvasipo
Made of at least one of the rigorous ferrites, plating
Between individual crystals on the steel sheet surface at the interface between the layer and the steel sheet
Make sure that the grain boundaries are etched to a width of 2.0 μm or less.
Characteristic, with strength of 490MPa or more and hole expansion rate of 80% or more
It is a galvannealed steel sheet with excellent ductility. C- (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) ^* = Ti-(48/14) x N-(48/32) x S
You. According to the present invention, the strength is 490 MPa or more.
And a steel sheet with excellent ductility with a hole expansion ratio of 80% or more
In alloyed hot-dip galvanized steel sheets, Ti:
0.003 to 0.1% and Nb: one of 0.003 to 0.1%
Or containing two types. Further, the present invention relates to a method for producing C: 0.02-0.10%, Si:
0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
8% or less, if necessary, Ti: 0.003 to 0.1% and Nb:
One or two of 0.003 to 0.1%, with the balance being Fe and
It has a steel composition consisting of unavoidable impurities.
And slabs satisfying both of the following equations (2): 880-97
After hot rolling at a finish rolling temperature of 0 ° C, 600-700
At a cooling rate of 35-55 ° C / sec.
Then, at a cooling rate of 5 to 40 ° C / sec in a temperature range of 400 to 600 ° C
By cooling and winding, crystals with a crystal grain size of 20 μm or less
Granules occupy 80% or more of the area, granular bainitic
Ferrite or kvasy polygonal ferrite
Characterized by a strength of at least 490MPa
High-strength steel with excellent ductility with a hole expansion ratio of 80% or more
This is a method for manufacturing a plate. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) ^* = Ti-(48/14) x N-(48/32) x S
You. In the present invention, C: 0.02 to 0.10%, Si:
0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
Steel composition of 8% or less, with the balance being Fe and unavoidable impurities
Satisfies both the relations of the following equations (1) and (2).
Hot rolling at 880-970 ° C finishing rolling temperature
After cooling, cool at a temperature of 600-700 ° C at 35-55 ° C / sec.
Cooling at a cooling rate, and then
After cooling at a cooling rate of 40 ° C / second, winding and pickling
The heating in the pre-oxidation furnace with the continuous galvanizing equipment,
In an atmosphere with a dew point of 30 ° C or less, set the air-fuel ratio to 0.8 to 1.25,
In addition, the maximum reached steel sheet temperature in the pre-oxidation furnace satisfies the following equation (3).
By performing hot dip galvanizing, the crystal grain size is 20μm
The following crystal grains occupy an area ratio of 80% or more.
Nitic ferrite or Kvasy polygonal ferrule
Strength, comprising at least one of the following:
Excellent ductility with 490MPa or more and hole expansion ratio of 80% or more
A method for producing a galvannealed steel sheet. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) 700 + 100 × ln [Si] ≦ T ≦ 830 + 50 × ln [Si] ・ ・ ・ ・ ・ ・ ・ (3) However, Ti ^* = Ti-(48/14) x N-(48/32) x S
You. The high-strength steel sheet or
In the production method of galvannealed steel sheet,
Further, Cr: 0.005 to 0.10%, Mo: 0.005 to 0.10%,
V: 0.005 to 0.10% and B: 0.0001 to 0.0100%
One or more selected from the group
desirable. From another viewpoint, the present invention relates to a method for producing C: 0.02 to 0.
10%, Si: 0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001
0.025%, S: 0.010% or less, Al: 0.003 to 0.1
%, N: 0.008% or less, balance Fe and unavoidable impurities
It has a steel composition consisting of the following formulas (1) and (2).
While satisfying both the requirements, a crystal grain size of 20 μm or less
The crystal grains occupy an area ratio of 80% or more.
Cuprite or kvasy polygonal ferrite
Strength of 490MPa or less, characterized by comprising at least one of the following:
High strength with excellent ductility with top and hole expansion ratio of 80% or more
It is a galvannealed steel sheet. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) ^* = Ti-(48/14) x N-(48/32) x S
You. Further, the present invention relates to a method for producing C: 0.02 to 0.10%, Si:
0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.00
8% or less, Cr: 0.005 to 0.10%, Mo: 0.005 to
0.10%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100
% Or more selected from the group consisting of
And has a steel composition consisting of unavoidable impurities, the following (1)
Equation and the relationship of the following equation (2).
Crystal grains with a crystal grain size of 20 μm or less occupy an area ratio of 80% or more.
Rannular bainitic ferrite or kvasipo
Specially composed of at least one of
With strength of 490MPa or more and hole expansion ratio of 80% or more
High strength alloyed hot-dip galvanized steel sheet with excellent ductility
You. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) ^* = Ti-(48/14) x N-(48/32) x S
You. Further, the present invention relates to a method for producing C: 0.02 to 0.10%, Si:
0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.00
Steel composition of 8% or less, with the balance being Fe and unavoidable impurities
Satisfies both the relations of the following equations (1) and (2).
In addition, the area ratio of crystal grains with a crystal grain size of 20 μm or less
Over 80%, granular bainitic ferrite
Or one or more of Kvasy polygonal ferrites
Of the steel sheet surface at the interface between the plating layer and the steel sheet
Grain boundaries between individual crystals are etched under 2.0 μm in width
Characterized by strength of 490MPa or more and holes
High-strength alloying melt with an expansion ratio of 80% or more and excellent ductility
It is a galvanized steel sheet. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) ^* = Ti-(48/14) x N-(48/32) x S
You. Further, the present invention relates to a method for producing C: 0.02 to 0.10%, Si:
0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.00
8% or less, Cr: 0.005 to 0.10%, Mo: 0.005 to
0.10%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100
% Or more selected from the group consisting of
And has a steel composition consisting of unavoidable impurities, the following (1)
Equation and the relationship of the following equation (2).
Crystal grains with a crystal grain size of 20 μm or less occupy an area ratio of 80% or more.
Rannular bainitic ferrite or kvasipo
Made of at least one of the rigorous ferrites, plating
Between individual crystals on the steel sheet surface at the interface between the layer and the steel sheet
Make sure that the grain boundaries are etched to a width of 2.0 μm or less.
Characteristic, with strength of 490MPa or more and hole expansion rate of 80% or more
High strength alloyed hot-dip galvanized steel sheet with excellent ductility
is there. C- (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) ^* = Ti-(48/14) x N-(48/32) x S
You. Further, according to the present invention, the strength is 490M.
High in ductility with Pa or more and hole expansion ratio of 80% or more
The strength alloyed hot-dip galvanized steel sheet has an additional Ti: 0.003
~ 0.1% and Nb: one of 0.003 to 0.1% or
It is desirable to contain two types. Further, the present invention relates to a method for producing C: 0.02 to 0.10%, Si:
0.1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.00
Steel composition of 8% or less, with the balance being Fe and unavoidable impurities
Satisfies both the relations of the following equations (1) and (2).
Hot rolling at 880-970 ° C finishing rolling temperature
After cooling, cool at a temperature of 600-700 ° C at 35-55 ° C / sec.
Cooling at a cooling rate, and then
After cooling at a cooling rate of 40 ° C / second, winding and pickling
From the hot dip galvanizing, the crystal grain size 20μm
The following crystal grains occupy an area ratio of 80% or more.
Nitic ferrite or Kvasy polygonal ferrule
Composed of one or more of the
Grain boundaries between individual crystals on the steel plate surface are 2.0 μm wide
The following hot-dip galvannealed steel sheet
Manufactured, characterized by strength of 490MPa or more and wide hole
High-strength alloyed molten metal with excellent ductility
This is a method for manufacturing a lead-plated steel sheet. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) ^* = Ti-(48/14) x N-(48/32) x S
You. According to the present invention, the strength is 490 MPa or more.
High-strength alloy with 80% or more hole expansion ratio and excellent ductility
In the method for producing a hot-dip galvanized steel sheet,
Pieces of Ti: 0.003-0.1% and Nb: 0.003-0.1%
It is desirable to contain one or two of them. According to the present invention, the strength is 490 MPa or more.
High-strength alloy with 80% or more hole expansion ratio and excellent ductility
In the production method of hot-dip galvanized steel sheet,
The plating is performed in the pre-oxidation furnace of the continuous hot-dip galvanizing equipment.
Heat the air-fuel ratio to 0.8 to 1.25 in an atmosphere with a dew point of 30 ° C or less.
And reached the maximum in the pre-oxidation furnace
The test should be performed so that the steel sheet temperature satisfies the following formula (3).
Is desirable. 700 + 100 × ln [Si] ≦ T ≦ 830 + 50 × ln [Si] (3) where T is the highest reached steel sheet temperature in the pre-oxidation furnace (° C.).
[Si] indicates the Si content (% by mass) of the base steel sheet.
You. Further, according to the present invention, the strength 49
Excellent ductility with 0MPa or more and hole expansion ratio of 80% or more
In the method of manufacturing high-strength galvannealed steel sheets,
However, Cr: 0.005 to 0.10%, Mo: 0.005 to 0.10
%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100%
One or more selected from the group consisting of
Is desirable. (First Embodiment) Hereinafter, the present invention will be described.
Strength alloyed hot-dip galvanized steel sheet and its production
Embodiments of the manufacturing method will be described in detail with reference to the accompanying drawings.
explain. First, the high-strength alloyed molten alloy according to the present invention
Limit composition of billet used in manufacturing method of lead-plated steel sheet
The reason for this is explained. (C: 0.02 to 0.10%) To obtain high hole expansion properties, use a steel plate group.
It is effective to use bainitic ferrite
You. When C content exceeds 0.10%, many carbides are formed
As a result, hole expandability and ductility deteriorate. On the other hand, when the C content is
If it is less than 0.02%, sufficient strength cannot be obtained. So
Here, in the present invention, the structure of the steel sheet is
C content should be 0.02% or more and 0.10% or less to make
limit. (Si: 0.1 to 1.0%) Si is useful for strengthening steel.
Is effective and has little adverse effect on ductility
Therefore, it is a component that you want to add in large quantities in terms of mechanical properties
However, if added excessively, the plating properties are significantly impaired. That is, the Si content is less than 0.1%
If a steel sheet with excellent mechanical properties such as strength cannot be obtained,
In the atmosphere of the pre-oxidation furnace,
Oxide scale is formed, and this oxide scale is
Reduced iron layer generated by reduction in the alloy significantly accelerates the alloying reaction
Exceeds the appropriate range for the degree of alloying,
Peeling of the plating film such as waddling is caused. Sa
Furthermore, in the reduction step after the pre-oxidation step,
Scale (transport roll) adheres to the
It also causes the generation of flaws and the like. On the other hand, if the Si content exceeds 1.0%,
You have to heat it up to form a layer
Temperature during pre-oxidation too high, exceeding the recrystallization temperature
Steel sheet softens, and improvement of mechanical properties cannot be expected
You. Therefore, in the present invention, the Si content is 0.1% or less.
The upper limit is 1.0% or less. (Mn: 0.8-2.5%) Mn is inferior to C, Si, etc.
Is an effective strengthening element. And Mn has
Has the effect of suppressing excessive generation of
You. In order to exert these effects, Mn should be 0.8% or more
It is necessary to add. But Mn over 2.5%
Even if is added, the effect of enhancing the strengthening ability is saturated,
Plating property deteriorates. Therefore, in the present invention, the Mn content is
Limited to 0.8% or more and 2.5% or less. (P: 0.001 to 0.025%) P is steel reinforcement
Is an effective component and wants to be added in large quantities, but contains P
If the amount exceeds 0.025%, the layer is easily embrittled and the plating layer
Deteriorates the powdering properties of On the other hand, when the P content is 0.00
Reduction to less than 1% involves a corresponding increase in costs. There
In the present invention, the P content is 0.001% or more and 0.025% or less.
Limited. (S: 0.010% or less) S exceeds 0.010%
When it is contained, it forms an A-based inclusion with Mn and forms a stretch flange.
Since it is an impurity element that lowers the
Is desirable. Therefore, in the present invention, the S content is 0.010
% Or less. (Al: 0.003 to 0.1%) Al is used as a deoxidizing component.
In addition, addition is indispensable for the purification of steel. This
For this, at least 0.003% of Al is added. On the other hand, Al
If the content exceeds 0.1%, the cleaning effect of steel saturates,
It only comes at a cost. Therefore, in the present invention, Al
The content is limited to not less than 0.003% and not more than 0.1%. (N: 0.008% or less) N is a stretch flange
It is an impurity that degrades the properties. Therefore, in the present invention, N
The content is limited to 0.008% or less. (Ti: 0.003 to 0.1% and Nb: 0.003 to 0.1%)
One or two of 0.1%) Ti and Nb
Also, in the present invention, an optional additive element that is added as needed
Therefore, by containing the amount in the above range,
Fix solid solution carbon and solid solution nitrogen which deteriorate processability,
Improves hole-expandability and gives a significant increase in strength
Is a preferable element. Further, at least one of Ti and Nb is
By adding an appropriate amount, in an actual production line
It is difficult to control the cooling temperature.
Improve hole-expandability without using complicated cooling patterns
Efficient low temperature phase bainitic ferrite
can get. On the other hand, when the content of each of Ti and Nb is 0.1
%, The effect saturates. Therefore, the present invention
Then, Ti: 0.003-0.1% and Nb: 0.003-0.1%
Contain one or two of them and limit
Is desirable. (Cr: 0.005 to 0.10%, Mo: 0.005 to 0.10%)
%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100%
One or more selected from the group consisting of
In the present invention, all of them have high strength,
As an optional additive element to improve
It is. That is, the contents of Cr, Mo, V and B are within the above range.
Below the lower limit of the enclosure, the required high strength and excellent hole expansion
And elongation is difficult to obtain, while exceeding the upper limit,
In addition to higher costs, the effect of improving characteristics is saturated.
You. Therefore, at least one of Cr, Mo, V and B
When seeds are added, Cr: 0.005% or more and 0.10% or less,
Mo: 0.005% or more and 0.10% or less, V: 0.005% or more and 0.10%
Below, B: 0.0001% or more and 0.0100% or less
desirable. (Equation (1)) In the present invention, C, Ti, N, S and
And content of Nb are defined by the following formula (1).
Limited to. That is, C- (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) However, in equation (1), Ti ^* = Ti- (48/14)
× N− (48/32) × S. The reason is as follows.
This is for preventing the generation of mentite. Preferably steel
C in one or two of Ti or Nb as carbide
Good ductility and good ductility
Controlling the bainitic ferrite single phase structure
it can. (Equation (2)) In the present invention, C, Si, M
The content of each of n, Ti, Nb and N is calculated by the following equation (2).
Limit to specified relationship. That is, −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) The reason for this is that a good hole-expanding property is ensured.
It is not enough to specify the range of various elements
It is necessary to control each element
By satisfying expression (2), the target of 80% or more
This is because the hole expanding property can be satisfied. Incidentally, both Ti and Nb are used in the present invention.
Is an optional additive element and may not contain Ti or Nb.
However, in this case, in equations (1) and (2), Ti =
0, Nb = 0. Other than the above, Fe and unavoidable impurities
You. The high-strength galvannealed steel sheet according to the present invention
In the manufacturing method, to a slab having such a composition, hot rolling,
Cooling, winding, pickling and galvannealing
U. Hereinafter, these steps will be described. (Hot Rolling) In the present invention, the above steel composition is
Hot rolling at a finishing rolling temperature of 880-970 ° C
I do. In addition, from melting of billet to heating before hot rolling
In the steps, well-known and commonly used steps may be followed. For example steel
The heating temperature of the piece can be, for example, 1200 to 1290 ° C.
You. The structure after the completion of the hot rolling is referred to as bainity.
The austenitic phase must be
It is necessary to aim for coarsening. To do so, it must be at least 880 ° C
Finish rolling must be performed in a temperature range of 970 ° C. or lower. Finish
Fine austenite grains when upper rolling temperature is lower than 880 ° C
Cementite is generated and bainitic ferrite
The texture cannot be obtained, and the hole-expanding property decreases. on the other hand,
If the finish rolling temperature exceeds 970 ° C, the oxide scale will be excessive.
And surface scratches increase. Therefore, in the present invention
Means that the finishing temperature of hot rolling is limited to 880 ° C to 970 ° C
I do. (Cooling) After the hot rolling is completed,
First cooling at a cooling rate of 35 to 55 ° C / sec in a temperature range of 0 ° C
Do. After the hot rolling, the cooling rate of the first cooling is
If the temperature is less than 35 ° C / sec, the austen
The ferrite phase generated from the
Since it does not have a light structure, the hole-expanding property is reduced. one
On the other hand, when the cooling rate of the first cooling exceeds 55 ° C./sec,
The controllability of the next intermediate holding temperature deteriorates and the characteristic value varies.
Becomes larger. Therefore, in the present invention, the finish
The cooling rate of the subsequent first cooling is 35 ° C / sec or more and 55 ° C / sec or less.
Limited to. Also, an appropriate amount of bainitic ferrite set
In order to produce a weave, a temperature between 600 ° C and 700 ° C
Area holding or air cooling is effective. Temperature below 600 ° C
Growth of bainitic ferrite structure
Undesirably, on the other hand, when held in a temperature range above 700 ° C,
Of bainitic ferrite to increase the growth of
Weaving will not be obtained. Therefore, just after finishing rolling,
After cooling, keep the temperature in the range of 600 ° C to 700 ° C.
You. Thereafter, in order to suppress the growth of crystal grains,
A second cooling rate of 5 to 40 ° C / sec in a temperature range of 400 to 600 ° C
Cooling is performed. That is, the cooling rate of the second cooling
Is less than 5 ° C./sec.
Excellent elongation fl
No resilience can be obtained. On the other hand, the cooling rate of this second cooling
Exceeds 40 ° C./sec.
The controllability of the winding temperature is reduced, and the characteristic value varies.
growing. Therefore, in the present invention, the cooling of the second cooling is performed.
The cooling speed is limited to 5 ° C / sec or more and 40 ° C / sec or less. (Winding) When the winding temperature exceeds 600 ° C.,
Mentite phase is formed, and the hole-expanding property is reduced. Meanwhile, winding
When the extraction temperature falls below 400 ° C, a martensitic phase is formed,
Shape controllability of the steel sheet deteriorates. The winding temperature is 600 ℃
Exceeds, the selective oxidation of the grain boundaries on the steel sheet surface is promoted
As a result, a notch effect is created during
You. In addition, drilling of plated steel sheets
Of the grains embrittled by Zn in the blanking process
Extremely wide hole after alloyed hot-dip galvanizing
Performance deteriorates. Therefore, in the present invention, bainitic
To obtain a ferrite structure, the winding temperature should be 400 ° C or higher and 60 ° C.
Limit to 0 ° C or less. (Pickling) After cooling, galvannealed alloying
Pickling is performed as a pretreatment of the treatment. Pickling is well known and used
It may be performed according to conditions. (Alloying hot-dip galvanizing) After pickling, the alloy
Perform hot-dip galvanizing. In the present invention, the composition of the steel sheet is
It is difficult to secure good plating properties only by
Yes, properly control plating conditions as well as steel sheet composition
There is a need. That is, an alloyed hot-dip galvanizing line
Has an annealing process before the hot-dip plating process.
Heating → soaking → cooling → plating (immersion) → alloying
Heat) process. Of these, the furnace in the heating process
Oxidation furnace, which controls its atmosphere and temperature
Control the scale production on the steel sheet surface
be able to. Furthermore, the steel sheet formed in this pre-oxidation furnace
Surface scale is reduced by reducing atmosphere
It becomes an iron layer. In the case of Si-added steel, it is difficult to form oxide scale.
As a result, the silicon concentrates on the steel sheet surface and the wettability of the plating
And alloying is delayed. So, formed
In order to optimize the amount of oxidation scale,
It is effective to control the atmosphere (dew point and temperature). This alloyed hot-dip galvanizing is a continuous hot-dip galvanizing.
Heating in pre-oxidizing furnace of galvanizing equipment, dew point is 30 ℃ or less
In an atmosphere with an air-fuel ratio of 0.8 to 1.25
In the pre-oxidation furnace, the maximum temperature reached in the pre-oxidation furnace
It is desirable to be carried out in a convenient manner. 700 + 100 × ln [Si] ≦ T ≦ 830 + 50 × ln [Si] (3) In the equation (3), the symbol T represents the maximum value in the pre-oxidation furnace.
Indicates the ultimate steel sheet temperature (° C), and the symbol [Si] indicates the S
i Indicates the content (% by mass). That is, the air-fuel ratio when processing in the pre-oxidation furnace
Is preferably 0.8 to 1.25, more preferably 0.9 to 1.2.
And If the air-fuel ratio is less than 0.8, the oxidation potential
Steel plate temperature (means the highest reached steel plate temperature.
Required for proper alloying
No oxidized scale is formed. On the other hand, the air-fuel ratio exceeds 1.25
If so, the combustion gas does not stabilize, so
Plating defects may occur due to adhesion, or the temperature in the pre-oxidation furnace
The cloth becomes uneven and a uniform oxide scale is produced on the steel plate surface.
If the alloying treatment is performed without any
appear. Therefore, in the present invention, in the atmosphere of the pre-oxidation furnace,
It is desirable to limit the air-fuel ratio to 0.8 to 1.25. The dew point of the atmospheric gas in the pre-oxidation furnace is:
Higher is advantageous for generating oxide scale.
However, when the dew point exceeds 30 ° C, the formation of oxide scale is accelerated.
The effect is small and the oxide scale is difficult to reduce.
Is not preferred. Therefore, in the present invention, the pre-oxidation
It is desirable that the dew point of the atmospheric gas in the furnace be 30 ° C or less.
From the same point of view, it should be -40 ° C or more and 0 ° C or less
Is more desirable. Furthermore, the steel sheet temperature in the pre-oxidation furnace was
The limitation, as in equation (3), is the scale production during pre-oxidation.
The diffusion rate of Fe into the plating layer from the base metal
Is different depending on the Si content. That is, when the steel sheet temperature is 700 + 100 × ln [S
i] (° C), the line speed during pre-oxidation
Required to achieve an appropriate degree of alloying without lowering
It is difficult to obtain the amount of steel while the steel plate temperature is 830+
If it is higher than 50 × ln [Si] (° C), the amount of oxide scale is large.
Too much, the reduced Fe layer generated at the time of soaking increases,
In order to proceed, the alloying degree exceeds 14% and powdering etc.
Plating peeling during construction increases. In addition, the pre-oxidation furnace
Scale adheres to hearth roll as the amount of kale increases
However, it also causes the occurrence of a pressing flaw. Therefore, in the present invention,
Limit the steel sheet temperature in the pre-oxidation furnace as shown in the above equation (3).
Is desirable. The heating method at the time of pre-oxidation is such that a steel sheet is sandwiched.
To release the combustion flame of the burner from the side,
Non-oxidizing furnace system in which the furnace is rapidly heated by radiant heat, or
An open fire burner that directly applies the burner's combustion frame to a steel plate
Method, but the stability of the furnace atmosphere is maintained.
A non-oxidizing furnace system using radiant heat from above is preferred. Thus, crystal grains having a crystal grain size of 20 μm or less are obtained.
Account for more than 80%,
Of the individual crystals on the steel sheet surface at the plating and steel sheet interface
If the grain boundaries between the layers are etched to a width of 2.0 μm or less,
A metallized hot-dip galvanized steel sheet is manufactured. That is, good workability, especially hole expanding property,
Strength alloyed hot-dip galvanized steel sheet with excellent ductility
Manufactured with various component systems and various conditions to obtain
Comprehensive investigation of the quality and structure of the damaged steel sheets
As a result, the structure is bainitic ferrite structure,
Group whose crystal structure is less than 20μm and 80% or more
Weaving allows for extremely high strength steel,
Excellent workability (hole spreading and ductility)
Turned out to be. For this purpose, a cementite structure is formed.
Is disadvantageous when the crystal grains are coarse, and disadvantageous when the crystal grains are coarse.
It is not desirable. Therefore, in the present invention, the texture
80% or more of crystal grains with a particle size of 20 μm or less
It is desirable to limit to a ferrite structure. In addition, the steel at the interface between the plating layer and the steel sheet
The grain boundaries between individual crystals on the plate surface are less than 2.0 μm wide.
Is used to ensure the adhesion of the plating.
It is effective. That is, the interface between the plating layer and the steel sheet
Grain boundaries between individual crystals on the steel sheet surface are 2.0 μ wide
If it is etched larger than m
Of Zn embrittled grains by punching
The notch effect allows the electrode after galvannealing
The hole-expanding property at the end deteriorates. On the other hand, the grain boundaries are 2.0 μm wide
Or less, preferably 1.5 μm or less in width
If the recesses provide an anchoring effect during plating,
Improves the adhesion between the plate and the plating phase. However, in the Si-added steel, the oxygen potential
Raise the char to strengthen the pre-oxidation conditions and increase the oxidation scale
If not formed, it will be difficult to form galvannealed alloys.
You. Therefore, in the present invention, the winding temperature during hot rolling is set to 4
Set the temperature to 00 to 600 ° C and expose the pre-oxidation furnace during the plating process.
Temperature is 30 ° C or less, and the air-fuel ratio is 0.8 to 1.25.
The above purpose is achieved by suppressing the selective oxidation of grain boundaries.
Can be reliably achieved. The etching specified in the present invention is
After hot-dip galvanizing, add hydrochloric acid solution with inhibitor
Suppresses etching of the steel sheet surface and dissolves only the plating film
Can be confirmed by observing the steel sheet surface after SEM
You. Thus, the production method according to the present invention
As a result, the galvannealed steel sheet according to the present invention is provided.
Provided. The galvannealed steel according to the present invention
Plates are as follows: C: 0.02 to 0.10%, Si: 0.1 to 1.0%, Mn: 0.8
~ 2.5%, P: 0.001 ~ 0.025%, S: 0.010% or less,
Al: 0.003 to 0.1%, N: 0.008% or less, Ti: 0.003 to
0.1% and Nb: one or two of 0.003 to 0.1%
Species, if necessary, Cr: 0.005 to 0.10%, Mo: 0.
005 to 0.10%, V: 0.005 to 0.10% and B: 0.0001 to
One or more selected from the group consisting of 0.0100%,
It has a steel composition consisting of the balance Fe and unavoidable impurities.
It is necessary to satisfy both the relations of Equation (1) and Equation (2) below.
Characterized by strength of 490MPa or more and hole expansion rate of 80% or more
High-strength galvannealed steel sheet with excellent ductility
It is. The high-strength alloyed molten zinc according to the present invention
80% or more of the crystal grains with a grain size of 20 μm or less
Occupied by bainitic ferrite structure.
FIG. 1 shows a high strength alloyed molten zinc plating according to the present invention.
In the picture of the metal structure observed by the electron microscope
is there. FIG. 1 shows that the high-strength alloyed molten zinc according to the present invention
Plated steel sheet is bainitic ferrite with angular grain boundaries.
You can see that it is composed of The high-strength alloying solution according to the present invention
Hot-dip galvanized steel sheet is used at the interface between the coating layer and the steel sheet.
Grain boundaries between individual crystals on steel plate surface are 2.0 μm or less in width
Has been etched. As described above, according to the present invention, after plating,
Conventionally used for Si-containing steels that are difficult to alloy.
Operating conditions using large continuous galvanizing equipment
Hot dip galvanizing and subsequent alloying without changing width
Processing can be performed reliably and at low cost. (Second Embodiment) Next, the present invention will be described.
The accompanying drawings show an embodiment of a high-strength steel sheet and a manufacturing method thereof.
This will be described in detail with reference to planes. First, a method for producing a high-strength steel sheet according to the present invention.
The reasons for limiting the composition of billets used in the
You. (C: 0.02 to 0.10%) To obtain high hole expansion properties, use a steel plate group.
Woven into granular bainitic ferrite or mulberry
Be at least one of sea polygonal ferrite
Is valid. If the C content exceeds 0.10%,
Oxides are formed and the hole expanding property and ductility deteriorate. on the other hand,
If the C content is less than 0.02%, sufficient strength cannot be obtained.
It becomes. Therefore, in the present invention, the structure of the steel sheet is
-Bainitic ferrite or Kvasy polygonal
In order to make one or more of the ferrites, the C content is
Limited to 0.02% or more and 0.10% or less. (Si: 0.1 to 1.0%) Si is useful for strengthening steel.
Is effective and has little adverse effect on ductility
Therefore, it is a component that you want to add in large quantities in terms of mechanical properties
However, when added in excess, the appearance and red scale formation
There is a drawback that paintability is significantly impaired. Furthermore,
Significantly inhibits plating. That is, the Si content is less than 0.1%
If a steel sheet with excellent mechanical properties such as strength cannot be obtained,
Not only when plating, but in the atmosphere of the pre-oxidation furnace, the steel sheet surface
A very thick oxide scale is formed on the
Is reduced in a reduction furnace to form a reduced iron layer that forms an alloying reaction.
Exceeding the appropriate range of alloying degree to significantly promote
At the time of construction, peeling of the plating film such as powdering may occur.
Is done. Further, in the reduction step after the pre-oxidation step,
Scale adheres to the hearth roll (transport roll),
It may also be a cause of the occurrence of press flaws on the surface. On the other hand, when the Si content exceeds 1.0%,
And paintability are significantly impaired. During plating, an oxide layer is formed.
High temperature in order to
Temperature rises too high and the steel sheet softens beyond the recrystallization temperature
As a result, improvement in mechanical properties cannot be expected. Therefore, in the present invention, the Si content is 0.1% or less.
The upper limit is 1.0% or less. (Mn: 0.8-2.5%) Mn is inferior to C, Si, etc.
Is an effective strengthening element. And Mn has
Has the effect of suppressing excessive generation of
You. In order to exert these effects, Mn should be 0.8% or more
It is necessary to add. But Mn over 2.5%
Even if is added, the effect of enhancing the strengthening ability is saturated,
Plating property deteriorates. Therefore, in the present invention, the Mn content is
Limited to 0.8% or more and 2.5% or less. (P: 0.001 to 0.025%) P is steel reinforcement
Is an effective component and wants to be added in large quantities, but contains P
If the amount exceeds 0.025%, the layer is easily embrittled and the plating layer
Deteriorates the powdering properties of On the other hand, when the P content is 0.00
Reduction to less than 1% involves a corresponding increase in costs. There
In the present invention, the P content is 0.001% or more and 0.025% or less.
Limited. (S: 0.010% or less) S exceeds 0.010%
When it is contained, it forms an A-based inclusion with Mn and forms a stretch flange.
Since it is an impurity element that lowers the
Is desirable. Therefore, in the present invention, the S content is 0.010
% Or less. (Al: 0.003 to 1.0%) Al is used as a deoxidizing component.
In addition, addition is indispensable for the purification of steel. This
For this, at least 0.003% of Al is added. On the other hand, Al
If the content exceeds 1.0%, the cleaning effect of steel saturates,
It only comes at a cost. Therefore, in the present invention, Al
The content is limited to not less than 0.003% and not more than 1.0%. (N: 0.008% or less) N is a stretch flange
It is an impurity that degrades the properties. Therefore, in the present invention, N
The content is limited to 0.008% or less. (Ti: 0.003 to 0.1% and Nb: 0.003 to 0.1%)
One or two of 0.1%) Ti and Nb
Also, in the present invention, an optional additive element that is added as needed
Therefore, by containing the amount in the above range,
Fix solid solution carbon and solid solution nitrogen which deteriorate processability,
Improves hole-expandability and gives a significant increase in strength
Is a preferable element. Furthermore, the most important point of the present invention is that Ti
Cooling temperature in actual production by adding required trace amount of N and Nb
Complicated cooling such as winding in a relatively low temperature region where
Effective in improving hole-expandability without taking
Nuclear bainitic ferrite or kvasy poly
Gonal ferrite is obtained. On the other hand, when the content of each of Ti and Nb is 0.1
%, The effect saturates. Therefore, the present invention
Then, Ti: 0.003-0.1% and Nb: 0.003-0.1%
Contain one or two of them and limit
Is desirable. (Cr: 0.005 to 0.10%, Mo: 0.005 to 0.10
%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100%
One or more selected from the group consisting of
In the present invention, all of them have high strength,
As an optional additive element to improve
It is. That is, the contents of Cr, Mo, V and B are within the above range.
Below the lower limit of the enclosure, the required high strength and excellent hole expansion
And elongation is difficult to obtain, while exceeding the upper limit,
In addition to higher costs, the effect of improving characteristics is saturated.
You. Therefore, at least one of Cr, Mo, V and B
When seeds are added, Cr: 0.005% or more and 0.10% or less,
Mo: 0.005% or more and 0.10% or less, V: 0.005% or more and 0.10%
Below, B: 0.0001% or more and 0.0100% or less
desirable. (Equation (1)) In the present invention, C, Ti, N, S and
And content of Nb are defined by the following formula (1).
Limited to. That is, C- (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) However, in equation (1), Ti ^* = Ti- (48/14)
× N− (48/32) × S. [0133] The reason for this is that there is a problem that the hole expansion property is reduced.
This is for preventing the generation of mentite. Preferably steel
C in one or two of Ti or Nb as carbide
Good ductility and good ductility
Granular bainitic ferrite or kvasy
Polygonal ferrite structure can be controlled. (Equation (2)) In the present invention, C, Si, M
The content of each of n, Ti, Nb and N is calculated by the following equation (2).
Limit to specified relationship. That is, −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) The reason for this is that a good hole-expanding property is ensured.
It is not enough to specify the range of various elements
It is necessary to control each element
By satisfying expression (2), the target of 80% or more
This is because the hole expanding property can be satisfied. Incidentally, both Ti and Nb are used in the present invention.
Is an optional additive element and may not contain Ti or Nb.
However, in this case, in equations (1) and (2), Ti =
0, Nb = 0. Other than the above, Fe and unavoidable impurities
You. In the method of manufacturing a high-strength steel sheet according to the present invention,
Hot rolling, cooling, winding, pickling
And galvannealing. Below, these steps
Will be described. (Hot Rolling) In the present invention, the above steel composition is
Hot rolling at a finishing rolling temperature of 880-970 ° C
I do. In addition, from melting of billet to heating before hot rolling
In the steps, well-known and commonly used steps may be followed. For example steel
The heating temperature of the piece can be, for example, 1200 to 1290 ° C.
You. The structure after the completion of the hot rolling was granulated.
-Bainitic ferrite or Kvasy polygonal
To obtain ferrite, the austenite phase must be coarse.
It is necessary to plan. For this purpose, the temperature must be between 880 ° C and 970 ° C.
It is necessary to perform finish rolling in the lower temperature range. Finish rolling temperature
When the temperature falls below 880 ° C, austenite grains become fine and
Mentite is formed and granular bainitic
Light or kvasy polygonal ferrite cannot be obtained.
And the hole spreadability decreases. On the other hand, the finish rolling temperature is 97
Exceeding 0 ° C causes excessive formation of oxide scale, causing
The number of scratches increases. Therefore, in the present invention, the finish of hot rolling
The temperature is limited to between 880 ° C and 970 ° C. (Cooling) After the completion of hot rolling, 600 to 70
First cooling at a cooling rate of 35 to 55 ° C / sec in a temperature range of 0 ° C
Do. After the completion of hot rolling, the cooling rate of the first cooling is
If the temperature is less than 35 ° C / sec, the austen
The ferrite phase generated from the
Tick ferrite or Kvasy polygonal ferrai
広 げ 穴 た め 、 、 穴 穴 穴. On the other hand,
When the cooling rate of cooling of 1 exceeds 55 ° C / sec, the next intermediate
The controllability of the holding temperature deteriorates, and the dispersion of the characteristic values increases.
You. Therefore, in the present invention, the first roll immediately after the finish rolling is completed.
Limit the cooling rate to between 35 ° C / sec and 55 ° C / sec.
You. Also, an appropriate amount of granular bainitic
Produces ferrite or kvasy polygonal ferrite
To maintain the temperature range between 600 ° C and 700 ° C.
Holding or air cooling is effective. Holds at temperatures below 600 ° C
Even granular bainitic ferrite or
Vasily polygonal ferrite growth is not expected, while 70%
When maintained at a temperature above 0 ° C, crystal grain growth becomes active.
For granular bainitic ferrite or
Kvasy polygonal ferrite cannot be obtained. There
And after the first cooling immediately after the end of finish rolling, 600 ° C or more
Keep in a temperature range of 700 ° C or less. Thereafter, in order to suppress the growth of crystal grains,
A second cooling rate of 5 to 40 ° C / sec in a temperature range of 400 to 600 ° C
Cooling is performed. That is, the cooling rate of the second cooling
Is less than 5 ° C./sec.
Labanitic Ferrite or Kvasy Polygona
Excellent stretch flangeability because it does not become
I can't get it. On the other hand, the cooling rate of the second cooling is 40 ° C. /
Over a second, the winding following this second cooling
Controllability of the temperature of the
You. Therefore, in the present invention, the cooling rate of the second cooling is
Is limited to 5 ° C./sec or more and 40 ° C./sec or less. (Winding) If the winding temperature exceeds 600 ° C.,
Mentite phase is formed, and the hole-expanding property is reduced. Meanwhile, winding
When the extraction temperature falls below 400 ° C, a martensitic phase is formed,
Shape controllability of the steel sheet deteriorates. The winding temperature is 600 ℃
Exceeds, the selective oxidation of the grain boundaries on the steel sheet surface is promoted
As a result, a notch effect is created during
You. In addition, drilling of plated steel sheets
Of the grains embrittled by Zn in the blanking process
Extremely wide hole after alloyed hot-dip galvanizing
Performance deteriorates. Therefore, in the present invention, granulave
Inititic ferrite or kvasy polygonal
Winding temperature should be more than 400 ℃ to 600 ℃ to get light texture
Limited to the following. (Pickling) After cooling, pickling is performed. Pickling is
What is necessary is just to carry out on well-known and common conditions. (Alloyed hot dip galvanizing) After pickling, alloyed hot dip galvanizing
In the present invention, the composition of the steel sheet should be controlled.
It is difficult to secure good plating properties with
It is necessary to properly control the plating conditions as well as the composition of the plate.
You. That is, an alloyed hot-dip galvanizing line
Has an annealing process before the hot-dip plating process.
Heating → soaking → cooling → plating (immersion) → alloying
Heat) process. Of these, the furnace in the heating process
Oxidation furnace, which controls its atmosphere and temperature
Control the scale production on the steel sheet surface
be able to. Furthermore, the steel sheet formed in this pre-oxidation furnace
Surface scale is reduced by reducing atmosphere
It becomes an iron layer. Oxide scale is difficult to form with Si-added steel
As a result, the silicon concentrates on the steel sheet surface and the wettability of the plating
And alloying is delayed. So, formed
In order to optimize the amount of oxidation scale,
It is effective to control the atmosphere (dew point and temperature). The galvannealing is performed by continuous hot-dip galvanizing.
Heating in pre-oxidizing furnace of galvanizing equipment, dew point is 30 ℃ or less
In an atmosphere with an air-fuel ratio of 0.8 to 1.25
In the pre-oxidation furnace, the maximum temperature reached in the pre-oxidation furnace
It is desirable to be carried out in a convenient manner. 700 + 100 × ln [Si] ≦ T ≦ 830 + 50 × ln [Si] (3) In the equation (3), the symbol T represents the maximum value in the pre-oxidation furnace.
Indicates the ultimate steel sheet temperature (° C), and the symbol [Si] indicates the S
i Indicates the content (% by mass). That is, the air-fuel ratio at the time of treatment in the pre-oxidation furnace
Is preferably 0.8 to 1.25, more preferably 0.9 to 1.2.
And If the air-fuel ratio is less than 0.8, the oxidation potential
Steel plate temperature (means the highest reached steel plate temperature.
Required for proper alloying
No oxidized scale is formed. On the other hand, the air-fuel ratio exceeds 1.25
If so, the combustion gas does not stabilize, so
Plating defects may occur due to adhesion, or the temperature in the pre-oxidation furnace
The cloth becomes uneven and a uniform oxide scale is produced on the steel plate surface.
If the alloying treatment is performed without any
appear. Therefore, in the present invention, in the atmosphere of the pre-oxidation furnace,
It is desirable to limit the air-fuel ratio to 0.8 to 1.25. The dew point of the atmospheric gas in the pre-oxidation furnace is
Higher is advantageous for generating oxide scale.
However, when the dew point exceeds 30 ° C, the formation of oxide scale is accelerated.
The effect is small and the oxide scale is difficult to reduce.
Is not preferred. Therefore, in the present invention, the pre-oxidation
It is desirable that the dew point of the atmospheric gas in the furnace be 30 ° C or less.
From the same point of view, it should be -40 ° C or more and 0 ° C or less
Is more desirable. Furthermore, the steel sheet temperature in the pre-oxidation furnace was
The limitation, as in equation (3), is the scale production during pre-oxidation.
The diffusion rate of Fe into the plating layer from the base metal
Is different depending on the Si content. That is, when the steel sheet temperature is 700 + 100 × ln [S
i] (° C), the line speed during pre-oxidation
Required to achieve an appropriate degree of alloying without lowering
It is difficult to obtain the amount of steel while the steel plate temperature is 830+
If it is higher than 50 × ln [Si] (° C), the amount of oxide scale is large.
Too much, the reduced Fe layer generated at the time of soaking increases,
In order to proceed, the alloying degree exceeds 14% and powdering etc.
Plating peeling during construction increases. In addition, the pre-oxidation furnace
Scale adheres to hearth roll as the amount of kale increases
However, it also causes the occurrence of a pressing flaw. Therefore, in the present invention,
Limit the steel sheet temperature in the pre-oxidation furnace as shown in the above equation (3).
Is desirable. The heating method during pre-oxidation is such that a steel sheet is sandwiched.
To release the combustion flame of the burner from the side,
Non-oxidizing furnace system in which the furnace is rapidly heated by radiant heat, or
An open fire burner that directly applies the burner's combustion frame to a steel plate
Method, but the stability of the furnace atmosphere is maintained.
A non-oxidizing furnace system using radiant heat from above is preferred. Thus, crystal grains having a crystal grain size of 20 μm or less are obtained.
Account for more than 80%,
Of the individual crystals on the steel sheet surface at the plating and steel sheet interface
If the grain boundaries between the layers are etched to a width of 2.0 μm or less,
A metallized hot-dip galvanized steel sheet is manufactured. That is, good workability, especially hole expanding property,
To obtain a high-strength steel sheet with excellent ductility
Of steel sheets produced under various conditions and various conditions
A comprehensive survey of quality and organization revealed that the organization
Labanitic Ferrite and Kvasy Polygona
At least one of the ferrites
A structure with 80% or more of crystal grains of 20μm or less
Due to the high strength of steel,
It is clear that the workability (hole spreading and ductility) can be reliably obtained.
Revealed. For this purpose, a cementite structure is formed.
Is disadvantageous when the crystal grains are coarse, and disadvantageous when the crystal grains are coarse.
It is not desirable. Therefore, in the present invention, the texture
80% or more of crystal grains with a particle size of 20μm or less, granular
Bainitic ferrite and kvasy polygonal
It is desirable to limit to at least one of the ferrites. In addition, the steel at the interface between the plating layer and the steel sheet
The grain boundaries between individual crystals on the plate surface are less than 2.0 μm wide.
Is used to ensure the adhesion of the plating.
It is effective. That is, the interface between the plating layer and the steel sheet
Grain boundaries between individual crystals on the steel sheet surface are 2.0 μ wide
If it is etched larger than m
Of Zn embrittled grains by punching
The notch effect allows the electrode after galvannealing
The hole-expanding property at the end deteriorates. On the other hand, the grain boundaries are 2.0 μm wide
Or less, preferably 1.5 μm or less in width
If the recesses provide an anchoring effect during plating,
Improves the adhesion between the plate and the plating phase. However, in Si-added steel, oxygen potential
Raise the char to strengthen the pre-oxidation conditions and increase the oxidation scale
If not formed, it will be difficult to form galvannealed alloys.
You. Therefore, in the present invention, the winding temperature during hot rolling is set to 4
Set the temperature to 00 to 600 ° C and expose the pre-oxidation furnace during the plating process.
Temperature is 30 ° C or less, and the air-fuel ratio is 0.8 to 1.25.
The above purpose is achieved by suppressing the selective oxidation of grain boundaries.
Can be reliably achieved. Note that the etching specified in the present invention is
After hot-dip galvanizing, add hydrochloric acid solution with inhibitor
Suppresses etching of the steel sheet surface and dissolves only the plating film
Can be confirmed by observing the steel sheet surface after SEM
You. As described above, the production method according to the present invention
Accordingly, a high-strength steel sheet according to the present invention is provided. this
The high-strength steel sheet according to the present invention has C: 0.02 to 0.10%, Si:
0.1-1.0%, Mn: 0.8-2.5%, P: 0.001-0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
8% or less, Ti: 0.003 to 0.1% and Nb: 0.003 to 0.1
% Or one of two percent, optionally Cr:
0.005 to 0.10%, Mo: 0.005 to 0.10%, V: 0.005 to 0.
10% and B: selected from the group consisting of 0.0001-0.0100%
One or two or more, the balance Fe and unavoidable impurities
It has the following steel composition and has the relationship between the following equations (1) and (2).
Strength of 490MPa or more, characterized by satisfying both parties
High-strength steel with excellent ductility with a hole expansion ratio of 80% or more
It is a sheet or a high strength galvannealed steel sheet. The high-strength steel sheet according to the present invention has
80% or more of crystal grains with a diameter of 20μm or less
Inititic ferrite or kvasy polygonal
It consists of one or more of the lights. Figure 1 shows this
The structure of the high-strength steel sheet according to the present invention was observed with an electron microscope.
It is a photograph of a damaged metal structure. From FIG. 1, it can be seen that the high
High-strength steel sheets are made of granular bainite with angular grain boundaries.
Cuprite or kvasy polygonal ferrite
It can be seen that it is composed of at least one of the following. The structure of the high-strength hot-rolled steel sheet of the present embodiment
Will be described. This organization is a granular bainiti
Cuprite or kvasy polygonal ferrite
One or more of the following. Granular Bainitic Fe
One of light or kvasy polygonal ferrite
More than one species is most preferred, but substantially granular
Inititic ferrite or kvasy polygonal
At least one of the lights may be used. That is, manufacturing
Above, the inevitable organization, other organizations, cementer
And may also produce graphite, polygonal ferrite, etc.
But granular bainitic ferrite or mulberry
To the extent that the characteristics of sea polygonal ferrite are not impaired
Specifically, at least granular bainiti
Other than kuferrite and quasi polygonal ferrite
10% or less, preferably about several% or less
Up to the range is acceptable. Next, a set of high-strength hot-rolled steel sheets according to the present embodiment is described.
The weaving observation method and its characteristics will be described. Spawn tissue
For example, an etching process such as nital etching
Work. And optically, so that individual crystal grains can be seen
Microscope (x500x) or SEM (500x to 3000x)
Observe by etc. Granular bainitic ferrite
Or Kvasy polygonal ferrite
Individual grain boundaries of polygons
It is characterized by the presence of fine irregularities on the sides. On the other hand, usually
In the ferrite structure of the above, each side of the grain boundary is almost straight
Has become. The steel bainite photo book-1 (Publisher
Japan Iron and Steel Association, date of issue June 29, 1992, 4 pages, table
According to 1), granular bainitic ferrite
(Granular bainitic α) is characterized by Granular bainiti
c ferritic intermediate stage structure; dislocate
d substructure but fairly recovered like “lath-les
s ". On the other hand, Quasi-polygonal ferrite (Quasi-poly
gonal α) is characterized by irregular changeful shape, for
med at lower temperature crossing over γ-grain b
oundary; mostly recovered. This sentence
The composition is slightly different from that of the present invention,
Many are listed, and all of these organizations are
Similar to the structure of the high-strength steel sheet of the embodiment, the present invention
Is the intended organization. The high-strength alloyed molten alloy according to the present invention
Lead-plated steel sheet is a steel sheet at the interface between the plating layer and the steel sheet.
The grain boundaries between individual crystals on the surface are less than 2.0 μm wide.
Has been ching. Thus, according to the present invention, after plating,
Conventionally used for Si-containing steels that are difficult to alloy.
Operating conditions using large continuous galvanizing equipment
Hot dip galvanizing and subsequent alloying without changing width
Processing can be performed reliably and at low cost. EXAMPLES (Example 1) Component compositions shown in Tables 1 and 2
Of steels A to 1Q having the following properties: Of these, steel A
~ 1E, 1O and 1P are steels satisfying the scope of the present invention.
Yes, steels 1F to 1N, 1Q do not satisfy the scope of the present invention
Comparative steel. The steels A to 1Q are shown in Tables 3 and 4.
Hot rolling, cooling, winding, pickling and alloying
Perform hot-dip galvanizing, alloyed hot-dip galvanized sheet with a thickness of 2.6 mm
A plated steel sheet was manufactured. [Table 1] [Table 2] [Table 3] [Table 4] The conditions for the galvannealing were as follows:
Using a non-oxidizing furnace as the air-fuel ratio: 0.95, dew point: 0 ° C
Was. On the other hand, the processing conditions in the reduction furnace are as listed below.
did. Atmosphere: N _Two 75% by volume + H _Two 25% by volume (dew point = -40 ° C) Steel plate temperature: 790 to 900 ° C Processing time: 120 seconds The plating bath should be the following bath temperature and bath composition.
After drying, the basis weight is 40 to 55 g / m per side ^Two Adjust to become
Was. The temperature of the material penetrating into the plating bath was 470 ° C. Bath temperature: 460 ° C. Bath composition: Al = 0.11 to 0.14% (the balance is zinc) In the alloying treatment after plating, the degree of alloying was adjusted.
For this purpose, the temperature of the steel sheet was changed in the range of 500 to 630 ° C. In order to investigate the mechanical properties of these steel sheets,
A tensile test and a hole expansion test were performed, and the results are shown in Table 5.
did. In addition, in the table, the stretch flangeability
Was evaluated. [Table 5] The hole expansion ratio (λ) refers to the Japan Iron and Steel Federation.
Based on the standard JFS T1001 hole expansion test method,
A 10mm diameter circular hole is punched into a lead-plated steel
Press a 60 ° conical punch to expand the hole,
It means the enlargement rate of the hole at the time of the crack, λ (%)
= {(Db-di) / di} × 100. However
The symbol di is the initial hole diameter (mm), and the symbol db is
The hole diameter (mm) is indicated respectively. The tensile test was carried out using a JIS No. 5 test piece.
went. Furthermore, the evaluation of the degree of alloying is performed by visual observation and
It was carried out by a Udling test. That is, by visual observation
Is to visually observe the appearance of the test piece after alloying
Judge whether the process is evenly performed up to the surface.
In the powdering test, a powdering test is performed to
Calculate the ring amount and judge whether the level is practically acceptable
did. In addition, the powdering test was performed alloying treatment
A test piece (disc) cut from the steel sheet
After cylindrical drawing, tape is applied to the outer wall of the processed test piece.
Peel off after processing by peeling after sticking
The test film before processing is completely removed from the test piece
Peeling from the difference between the weight of the test piece and the weight of the test piece after tape peeling
Amount (this is called the amount of powdering;
(The amount of powdering per specimen)
By, went. If the amount of powdering is less than 20mg / piece
There was no practical problem and the powdering property was good. [0181] In the items of the degree of alloying evaluation in Table 5, the circles indicate
If the amount of dulling is 20mg / piece or less, * mark is powdering
Is more than 20 mg / piece. [Cylinder drawing processing conditions] Blank diameter: 90mmφ Punch diameter: 50mmφ (shoulder diameter = 5mm) Die diameter: 54mmφ (shoulder diameter = 5mm) Wrinkle suppressing pressure: 1.0 ton lubrication: Use of rust-preventive oil Width of the crystal grain boundary
10% salt with 3% inhibitor
After removing only the plating film with an acid solution, 10
Observation was performed at a magnification of 00, and the maximum width was measured. As shown in Tables 1, 3 and 5, the present invention
According to Test Examples 1 to 31, which are clear examples, strength of 490 MPa or more and
The ductility and plating adhesion are 80% or more.
Excellent high strength galvannealed steel sheet
You can see that Because of this, these high-strength alloyed melts
Galvanized steel sheets are used for automotive steel sheets, especially suspension
Steel that is processed with hole expansion, such as steel plates for arm
It can be suitably used for a plate. On the other hand, as shown in Tables 2, 4 and 5,
In the test No. 32, which is a comparative example, the C content was within the scope of the present invention.
Lower than the lower limit, the crystal grain size becomes coarse and the strength is low.
And the mechanical properties became poor. Test No. 33 indicates that the C content was within the range of the present invention.
Exceeding the upper limit, formula (1) cannot be satisfied, so hole-expanding properties, etc.
The workability was poor. Test number 34 indicates that the Si content
Because it exceeds the upper limit of the scope of the invention, it has high strength and holes
Spreadability decreased. Test No. 35 shows that the Mn content falls within the range of the present invention.
Since the value was below the lower limit, the strength was poor. Test number 36
Since the Mn content exceeds the upper limit of the range of the present invention, the strength
And the hole-expanding property decreased. Also, plating adhesion
Sex was also unpleasant. Test No. 37 has a Ti content, and Test No. 38 has an Nb content.
Since the content exceeds the upper limit of the range of the present invention,
High strength, low elongation and widening
I dropped it. [0187] Test No. 39 and Test No. 40
Does not satisfy Equation (2), so the desired bainitic
A cellulite structure was not obtained, and the hole-expanding property was reduced. Examination number
No. 41 shows that the maximum temperature in the pre-oxidation furnace during the plating process is
Since formula (3) is not satisfied, alloying becomes difficult and plating
Adhesion was poor. [0188] Test No. 42 was performed in the pre-oxidation furnace during the plating process.
Since the maximum temperature at which the temperature does not satisfy equation (3), the degree of alloying
Was excessive, and plating peeling occurred frequently during processing. Further
In Test No. 43, the Si content was below the lower limit of the range of the present invention.
Because of turning, the strength was reduced. Also, in the pre-oxidation furnace,
The very thick oxide scale formed in the furnace is reduced in the reduction furnace.
And the reduced iron layer significantly accelerated the alloying reaction.
Poor powdering properties during construction, resulting in low evaluation of alloying degree
I dropped it. (Example 2) Steels A, F, N, and
Continuous hot-dip galvanized steel sheet consisting of 1A
After performing hot dip galvanizing in the plating equipment,
This was performed to obtain an alloyed hot-dip galvanized steel sheet. In a non-oxidizing furnace
The steel sheet temperature was 750 ° C. Processing conditions and reduction furnace
And plating conditions were the same as in Example 1, and
Then, the steel plate temperature was fixed at 560 ° C. Made of these steel sheets
Table 6 summarizes the fabrication conditions. [Table 6] [0191] These alloyed hot-dip galvanized steel
The air-fuel ratio during pre-oxidation and the degree of alloying
The influence of the dew point of the atmospheric gas was investigated. In the investigation of the degree of alloying
In addition to examining the alloying state by visual observation,
The degree of alloying of the coating was determined. The degree of alloying (alloy layer
Content of Fe in the plating solution)
By measuring the concentrations of Fe, Zn and Al
I did. In addition, abnormalities such as the occurrence of defects in the plating film
The presence or absence was also visually observed. Table 7 shows the evaluation results of steel sheets.
Are shown together. [Table 7] The circle in the column of evaluation in Table 7 indicates the degree of alloying.
Is 7 to 11% (particularly a preferable range with a thicker thickness),
Indicates that the alloying degree is 6% or more and less than 7% or 11% or more and 14% or less
Below, the cross mark indicates that the degree of alloying is less than 6% or more than 14%.
And 6 to 14% was regarded as an appropriate degree of alloying. As shown in Tables 6 and 7, in the examples of the present invention,
With certain test numbers 1, 7, 8, 10, 13, 16, 18
Temperature of 490MPa or more and hole expansion rate of 80% or more.
High-strength alloyed hot-dip zinc alloy with excellent adhesion and plating adhesion
It can be seen that a steel plate was obtained. Because of this, these
High-strength galvannealed steel sheets are
With hole expansion like steel plate for suspension arm
It can be suitably used for a steel plate to be processed. On the other hand, in test number 2, the winding temperature
Below the lower limit of the light range
Cellulite structure cannot be obtained.
Also fell. In test number 4, the finishing temperature of hot rolling was
Scale exceeds the upper limit of the bright range.
Occurred. In test number 5, the holding temperature after the first cooling was
From finish rolling to intermediate temperature to fall below the scope of the invention
Cooling rate is too high, hole expansion and elongation are not enough
It also fell. Test No. 11 shows that the holding temperature after the first cooling was
The desired bainitic features to exceed the scope of the invention
The light structure was not obtained, and the hole expanding property was reduced. Exam number
15, the finishing temperature of the hot rolling is below the lower limit of the range of the present invention
And the cooling rate of the first cooling is too low.
Both spreadability and elongation decreased. Test No. 17 indicates that the winding temperature is within the range of the present invention.
Desired bainitic ferrite set to exceed upper limit
Weaving was not obtained, and the hole-expanding property was reduced. Test number 9 and
Test No. 12 had a dew point of 30 ° C as shown in Table 6.
The alloying progresses too much and the degree of alloying
And the plating adhesion was degraded. Test No. 7 had a dew point of 30 ° C.
The evaluation of the degree of gold was △. To make this rating positive,
It is desirable to keep the dew point below 0 ° C. Test number 3
And Test No. 6, as shown in Table 6, the air-fuel ratio was 0.8 or less.
The alloying treatment was insufficient due to being full. In test number 14, the air-fuel ratio is larger than 1.25
Plating loss due to soot adhesion due to incomplete combustion
Occurs, and the alloying degree exceeds the
It was good. Further, in test numbers 1, 7, 11, 15, and 16,
Is the case where the air-fuel ratio is the lower limit and the upper limit, respectively.
Although the appearance of the plating film was good, the degree of alloying
Was evaluated as △. To mark the degree of alloying as ○
Therefore, it is preferable to set the air-fuel ratio to 0.9 to 1.2.
You can see that. (Example 3) Component compositions shown in Tables 8 and 9
A to 1Q having the following formulas were melted. Among them, steel A to 1E,
1O and 1P both have the composition defined in the present invention.
Satisfactory steel. Steels 1F to 1N and 1Q
Is a comparative steel that does not satisfy the composition specified in the present invention.
Of these, steels A to 1E, 10 and 1P are listed in Table 10.
Conditions shown (conditions that satisfy the conditions specified in the present invention)
Hot rolling, cooling, winding and pickling,
A hot-rolled steel sheet having a thickness of 2.6 mm was manufactured. And the obtained heat
For each of the rolled steel sheets, the area of crystal grains of 20 μm or less
Modulus, microstructure, yield point, strength, elongation, hole widening
Was measured. Table 11 summarizes the measurement results. [Table 8] [Table 9] [Table 10] [Table 11] As shown in Tables 8, 10, and 11, the present invention
Test number 1-31 that satisfies the light range, strength 490Mpa
High strength with excellent ductility with a hole expansion ratio of 80% or more
It can be seen that a hot-rolled steel sheet was obtained. Therefore, these
High-strength hot-rolled steel sheets are used for automotive steel sheets, especially suspension
A steel plate that is processed with hole expansion like a steel plate for an arm
Can be suitably used. On the other hand, as shown in Tables 9, 10 and 11,
In the test No. 32, which is a comparative example, the C content was regulated by the present invention.
Below the lower limit of the specified range, the crystal grain size becomes coarse.
The strength decreased, and the mechanical properties became poor. [0209] Test No. 33 shows that the C content was
Since the value exceeds the upper limit of the specified range, Expression (1) is defined in the present invention.
Out of the specified range.
It became good. Test No. 34 indicates that the Si content was
Exceeds the upper limit of the specified range, so strength and hole expanding
Were both uncomfortable. In test number 35, the Mn content
Below the lower limit of the range specified in
Was. Test No. 36 indicates that the Mn content was
Because the value exceeds the upper limit of the specified range, strength and hole
Both spreadability became unpleasant. Test number 37 and
38 was too high for Ti content and Nb content
Strength, elongation and hole-expandability
Was. [0212] Test numbers 39 and 40 were both
Since the formula (1) or (2) is not satisfied, the required organization
And the hole-expanding properties were unsatisfactory. In addition, test number 41
Is below the lower limit of the range specified in the present invention Si content
The strength was poor. (Example 4) Component sets shown in Tables 12 and 13
Of 43 types of steels A to 1Q having different composition
~ 1E, 1O and 1P are steels satisfying the scope of the present invention.
Yes, steels 1F to 1N and 1Q do not satisfy the scope of the present invention
Comparative steel. The steels A to 1Q were prepared according to the conditions shown in Tables 14 and 15.
Hot rolling, cooling, winding, pickling and alloying
2.6mm thick alloyed hot dip galvanized with lead plating
A steel plate was manufactured. [Table 12] [Table 13] [Table 14] [Table 15] The conditions for the galvannealing were as follows:
Using a non-oxidizing furnace as the air-fuel ratio: 0.95, dew point: 0 ° C
Was. On the other hand, the processing conditions in the reduction furnace are as listed below.
did. Atmosphere: N _Two 75% by volume + H _Two 25% by volume
(Dew point = -40 ° C) Steel sheet temperature: 790 to 900 ° C Processing time: 120 seconds The plating bath should have the following bath temperature and composition.
After drying, the basis weight is 40 to 55 g / m per side ^Two Adjust to become
Was. The temperature of the material penetrating into the plating bath was 470 ° C. Bath temperature: 460 ° C. Bath composition: Al = 0.11 to 0.14% (the balance is zinc) In the alloying treatment after plating, the degree of alloying was adjusted.
For this purpose, the temperature of the steel sheet was changed in the range of 500 to 630 ° C. In order to investigate the mechanical properties of these steel sheets,
A tensile test and a hole expansion test were performed, and the results are shown in Table 16.
did. In addition, in the table, the stretch flangeability
Was evaluated. [Table 16] [0224] The hole expansion ratio (λ) refers to the Japan Iron and Steel Federation.
Based on the standard JFS T1001 hole expansion test method,
A 10mm diameter circular hole is punched into a lead-plated steel
Press a 60 ° conical punch to expand the hole,
It means the enlargement rate of the hole at the time of the crack, λ (%)
= {(Db-di) / di} × 100. However
The symbol di is the initial hole diameter (mm), and the symbol db is
The hole diameter (mm) is indicated respectively. Further, the tensile test was performed using a JIS No. 5 test piece.
went. Furthermore, the evaluation of the degree of alloying is performed by visual observation and
It was carried out by a Udling test. That is, by visual observation
Is to visually observe the appearance of the test piece after alloying
Judge whether the process is evenly performed up to the surface.
In the powdering test, a powdering test is performed to
Calculate the ring amount and judge whether the level is practically acceptable
did. In addition, the powdering test was performed alloying treatment
A test piece (disc) cut from the steel sheet
Perform cylindrical drawing, and tape on the outer wall of the test specimen after processing.
Peels off after processing,
Completely removed from the test piece
From the difference between the weight of the test piece and the weight of the test piece after tape removal
Peeling amount (This is called the "powdering amount.
(The amount of powdering per test piece)
By doing that. Powdering amount 20mg / piece or more
There is no problem under practical use, and the powdering property is good.
Was. In the items of the evaluation of the degree of alloying in Table 16,
○ indicates that the powdering amount is 20 mg / piece or less.
And * indicates the case where powdering exceeds 20 mg / unit.
You. [Cylinder drawing processing conditions] Blank diameter: 90mm Punch diameter: 50mm (shoulder diameter = 5mm) Die diameter: 54mm (shoulder diameter = 5mm) Wrinkle suppressing pressure: 1.0 ton Lubrication: Use of anti-rust oil: Steel plate surface at plating and steel plate interface Width of the crystal grain boundary
10% salt with 3% inhibitor
After removing only the plating film with an acid solution,
Observation was made at 1000 times higher, and the maximum width was measured. As shown in Tables 12, 14 and 16, the present invention
According to Test Examples 1 to 31, which are clear examples, strength of 490 MPa or more and
The ductility and plating adhesion are 80% or more.
Excellent high strength galvannealed steel sheet
You can see that Because of this, these high-strength alloyed melts
Galvanized steel sheets are used for automotive steel sheets, especially suspension
Steel that is processed with hole expansion, such as steel plates for arm
It can be suitably used for a plate. On the other hand, as shown in Tables 13, 15 and 16,
In the test No. 32, which is a comparative example, the C content was regulated by the present invention.
Below the lower limit of the specified range, the crystal grain size becomes coarse.
The strength decreased, and the mechanical properties became poor. Test No. 33 indicates that the C content was within the range of the present invention.
Exceeding the upper limit, formula (1) cannot be satisfied, so hole-expanding properties, etc.
The workability was poor. Test number 34 indicates that the Si content
Because it exceeds the upper limit of the scope of the invention, it has high strength and holes
Spreadability decreased. Test No. 35 shows that the Mn content falls within the range of the present invention.
Since the value was below the lower limit, the strength was poor. Test number 36
Since the Mn content exceeds the upper limit of the range of the present invention, the strength
And the hole-expanding property decreased. Also, plating adhesion
Sex was also unpleasant. Test No. 37 has a Ti content, and Test No. 38 has an Nb content.
Since the content exceeds the upper limit of the range of the present invention,
High strength, low elongation and widening
I dropped it. Test No. 39 and Test No. 40
Does not satisfy Equation (2), so the desired bainitic
A cellulite structure was not obtained, and the hole-expanding property was reduced. Examination number
No. 41 shows that the maximum temperature in the pre-oxidation furnace during the plating process is
(3) Not satisfying the formula, alloying becomes difficult, and plating
Adhesion was poor. [0233] Test No. 42 is for the inside of the pre-oxidation furnace during plating.
Since the maximum temperature at which the temperature does not satisfy equation (3), the degree of alloying
Was excessive, and plating peeling occurred frequently during processing. Further
In Test No. 43, the Si content was below the lower limit of the range of the present invention.
Because of turning, the strength was reduced. Also, in the pre-oxidation furnace,
The very thick oxide scale formed in the furnace is reduced in the reduction furnace.
And the reduced iron layer significantly accelerated the alloying reaction.
Poor powdering properties during construction, resulting in low evaluation of alloying degree
I dropped it. (Example 5) In Table 12, steels A, F, N,
Continuous hot-dip galvanized steel sheet consisting of 1A
After performing hot dip galvanizing in the plating equipment,
This was performed to obtain an alloyed hot-dip galvanized steel sheet. In a non-oxidizing furnace
The steel sheet temperature was 750 ° C. Processing conditions and reduction furnace
And plating conditions were the same as in Example 2, and
Then, the steel sheet temperature was set to 560 ° C. Manufacturing conditions for these steel sheets
The results are summarized in Table 17. [Table 17] The alloyed hot-dip galvanized steel
The air-fuel ratio during pre-oxidation and the degree of alloying
The influence of the dew point of the atmospheric gas was investigated. In the investigation of the degree of alloying
In addition to examining the alloying state by visual observation,
The degree of alloying of the coating was determined. The degree of alloying (alloy layer
Content of Fe in the plating solution)
By measuring the concentrations of Fe, Zn and Al
I did. In addition, abnormalities such as the occurrence of defects in the plating film
The presence or absence was also visually observed. Table 18 shows the evaluation results of steel sheets.
Are shown together. [Table 18] In Table 18, the circles in the column of evaluation indicate the degree of alloying.
Is 7 to 11% (particularly a preferable range with a thicker thickness),
Indicates that the alloying degree is 6% or more and less than 7% or 11% or more and 14% or less
Below, the cross mark indicates that the degree of alloying is less than 6% or more than 14%.
And 6 to 14% was regarded as an appropriate degree of alloying. As shown in Tables 17 and 18, in the present invention examples
With certain test numbers 1, 7, 8, 10, 13, 16, 18
Temperature of 490MPa or more and hole expansion rate of 80% or more.
High-strength alloyed hot-dip zinc alloy with excellent adhesion and plating adhesion
It can be seen that a steel plate was obtained. Because of this, these
High-strength galvannealed steel sheets are
With hole expansion like steel plate for suspension arm
It can be suitably used for a steel plate to be processed. On the other hand, in test number 2, the winding temperature
Below the lower limit of the light range
Cellulite structure cannot be obtained.
Also fell. Test No. 4 shows that the finishing temperature of hot rolling was
Scale exceeds the upper limit of the bright range.
Occurred. In test number 5, the holding temperature after the first cooling was
From finish rolling to intermediate temperature to fall below the scope of the invention
Cooling rate is too high, hole expansion and elongation are not enough
It also fell. Test No. 11 shows that the holding temperature after the first cooling was
The desired bainitic features to exceed the scope of the invention
The light structure was not obtained, and the hole expanding property was reduced. Exam number
15, the finishing temperature of the hot rolling is below the lower limit of the range of the present invention
And the cooling rate of the first cooling is too low.
Both spreadability and elongation decreased. Test No. 17 indicates that the winding temperature was within the range of the present invention.
Desired bainitic ferrite set to exceed upper limit
Weaving was not obtained, and the hole-expanding property was reduced. Test number 9 and
Test No. 12 had a dew point of 30 as shown in Table 17.
Over ℃, alloying progresses too much and the degree of alloying is appropriate
Exceeding the range, the plating adhesion deteriorated. Test No. 7 had a dew point of 30 ° C.
The evaluation of the degree of gold was △. To make this rating positive,
It is desirable to keep the dew point below 0 ° C. Test number 3
And Test No. 6, as shown in Table 17, the air-fuel ratio was 0.8
Therefore, the alloying treatment was insufficient. In test number 14, the air-fuel ratio is larger than 1.25
Plating loss due to soot adhesion due to incomplete combustion
Occurs, and the alloying degree exceeds the
It was good. Furthermore, Test Nos. 1, 7, 11, 15 and 16
In the case where the air-fuel ratio is the lower limit and the upper limit, respectively,
Although the appearance of the plating film was good, the degree of alloying
Was evaluated as △. To mark the degree of alloying as ○
Therefore, it is preferable to set the air-fuel ratio to 0.9 to 1.2.
You can see that. As described in detail above, according to the present invention,
And high strength steel with excellent hole spreadability and ductility
To produce low-alloy hot-dip galvanized steel sheets at low cost
Was completed. More specifically, strength 490MPa or more, hole expansion rate
High strength steel sheet with high ductility of 80% or more and high strength
To provide an alloyed hot-dip galvanized steel sheet and a method for producing the same.
I was able to. The significance of the present invention having such effects is extremely high.
Remarkable.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a photograph of a metal structure obtained by observing the structure of steel according to the present invention with an electron microscope.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) C22C 38/38 C22C 38/38 C23C 2/02 C23C 2/02 2/06 2/06 2/40 2 / 40 (72) Inventor Yoshihiro Kawanishi 3 Oaza Hikari, Kashima City, Ibaraki Prefecture Sumitomo Metal Industries Kashima Works, Ltd. (72) Inventor Hiroyuki Kashiwagi 3 Oaza Hikari Kashima City, Ibaraki Prefecture Sumitomo Metal Industries Kashima Works F-term ( 4K027 AA02 AA05 AA23 AB44 AC12 4K037 EA01 EA02 EA05 EA11 EA15 EA16 EA19 EA23 EA25 EA27 EA31 EA32 EB05 EB08 EB09 FA03 FC04 FD02 FD03 FD04 FD08 FE06 GA05 HA02 JA07

Claims (1)

[Claims 1] In mass%, C: 0.02 to 0.10%, Si: 0.1
~ 1.0%, Mn: 0.8 ~ 2.5%, P: 0.001 ~ 0.025%,
S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.008%
Hereinafter, a steel composition consisting of the balance Fe and unavoidable impurities, characterized by satisfying both the relationship of the following formula (1) and the following formula (2), strength 490MPa or more and hole expansion ratio 80
% High-strength alloyed hot-dip galvanized steel sheet with excellent ductility. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 2. C: 0.02 to 0.10%, Si: 0.1% by mass
~ 1.0%, Mn: 0.8 ~ 2.5%, P: 0.001 ~ 0.025%,
S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.008%
Hereinafter, Cr: 0.005 to 0.10%, Mo: 0.005 to 0.10%
%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100%, having a steel composition consisting of one or more selected from the group consisting of the balance Fe and unavoidable impurities. A high-strength galvannealed steel sheet having a strength of 490 MPa or more and a hole expansion rate of 80% or more and excellent ductility, characterized by satisfying both of the relations of formula (2). C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 3. A mass%, C: 0.02 to 0.10%, Si: 0.1%
~ 1.0%, Mn: 0.8 ~ 2.5%, P: 0.001 ~ 0.025%,
S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.008%
Hereinafter, a steel composition comprising the balance of Fe and unavoidable impurities, satisfying both the following expressions (1) and (2), and having an area ratio of 80%
A high-strength galvannealed steel sheet having a strength of 490 MPa or more and a hole expansion rate of 80% or more and having excellent ductility, characterized by comprising a bainitic ferrite structure. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 4. A mass%, C: 0.02 to 0.10%, Si: 0.1
~ 1.0%, Mn: 0.8 ~ 2.5%, P: 0.001 ~ 0.025%,
S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.008%
Hereinafter, Cr: 0.005 to 0.10%, Mo: 0.005 to 0.10%
%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100%, having a steel composition consisting of one or more selected from the group consisting of the balance Fe and unavoidable impurities. (2) While satisfying both the relations of the formula, the crystal grains having a crystal grain size of 20 μm or less occupy an area ratio of 80% or more and are composed of bainitic ferrite structure. The strength is 490 MPa or more and the hole expansion rate is 80%. This is a high-strength galvannealed steel sheet having excellent ductility. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 5. A mass%, C: 0.02 to 0.10%, Si: 0.1%
~ 1.0%, Mn: 0.8 ~ 2.5%, P: 0.001 ~ 0.025%,
S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.008%
Hereinafter, a steel composition comprising the balance of Fe and unavoidable impurities, satisfying both the following expressions (1) and (2), and having an area ratio of 80%
Occupying the above, comprising a bainitic ferrite structure, characterized in that the grain boundaries between individual crystals on the steel sheet surface at the interface between the plating layer and the steel sheet are etched 2.0 μm or less in width, strength not less than 490MPa and High-strength alloyed hot-dip galvanized steel sheet with 80% or more hole expansion ratio and excellent ductility. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 6. In mass%, C: 0.02 to 0.10%, Si: 0.1
~ 1.0%, Mn: 0.8 ~ 2.5%, P: 0.001 ~ 0.025%,
S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.008%
Hereinafter, Cr: 0.005 to 0.10%, Mo: 0.005 to 0.10%
%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100%, having a steel composition consisting of one or more selected from the group consisting of the balance Fe and unavoidable impurities. In addition to satisfying both of the relations of the formula (2), the crystal grains having a grain size of 20 μm or less occupy an area ratio of 80% or more and have a bainitic ferrite structure. Grain boundaries between
Characterized by being etched to 2.0 μm or less,
High-strength galvannealed steel sheet with strength of 490MPa or more and hole expansion ratio of 80% or more and excellent ductility. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 7. Ti: 0.003 to 0.1% by mass%
And Nb: one or two of 0.003 to 0.1%, according to any one of claims 1 to 6, having a strength of 490 MPa or more and a hole expansion ratio of 80% or more and ductility. High strength alloyed hot-dip galvanized steel sheet. 8. A mass%, C: 0.02 to 0.10%, Si: 0.1
~ 1.0%, Mn: 0.8 ~ 2.5%, P: 0.001 ~ 0.025%,
S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.008%
Hereinafter, hot rolling is performed at a finish rolling temperature of 880 to 970 ° C. on a steel slab having a steel composition including the balance of Fe and unavoidable impurities and satisfying both of the following expressions (1) and (2). After that, it is cooled at a cooling rate of 35-55 ° C / sec to a temperature range of 600-700 ° C and then 5-40 ° C to a temperature range of 400-600 ° C.
After cooling at a cooling rate of / sec, winding, pickling,
By performing hot-dip galvanizing, the crystal grains with a crystal grain size of 20 μm or less occupy an area ratio of 80% or more and have a bainitic ferrite structure. The grain boundaries between the plating and the individual crystals on the steel sheet surface at the steel sheet interface are formed. Manufacture of high-strength galvannealed steel sheet with a strength of 490 MPa or more and a hole expansion rate of 80% or more and excellent ductility, characterized by manufacturing an alloyed hot-dip galvanized steel sheet with a width of 2.0 μm or less etched. Method. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 9. The steel slab according to claim 1, wherein the steel slab is composed of Ti:
9. The strength of 490 MPa according to claim 8, which contains one or two of 003 to 0.1% and Nb: 0.003 to 0.1%.
A method for producing a high-strength alloyed hot-dip galvanized steel sheet having a ductility of 80% or more and excellent ductility. 10. The hot-dip galvanizing may be performed by heating in a pre-oxidation furnace of a continuous hot-dip galvanizing facility, and having a dew point of 30%.
The air-fuel ratio is set to 0.8 to 1.25 in an atmosphere of not more than ℃, and the highest attained steel sheet temperature in the pre-oxidation furnace is as follows.
The method for producing a high-strength galvannealed steel sheet according to claim 8 or 9, wherein the method is performed so as to satisfy the expression (3). 700 + 100 × ln [Si] ≦ T ≦ 830 + 50 × ln [Si] (3) where T is the highest reached steel sheet temperature in the pre-oxidation furnace (° C)
And [Si] indicates the Si content (% by mass) of the base steel sheet. 11. The steel slab further comprises, in mass%, Cr:
0.005 to 0.10%, Mo: 0.005 to 0.10%, V: 0.005 to 0.
10. The composition according to claim 8, which contains one or more selected from the group consisting of 10% and B: 0.0001 to 0.0100%.
0. The method for producing a high-strength galvannealed steel sheet according to any one of items 0 to 0. 12. In mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
It has a steel composition of 8% or less, with the balance being Fe and unavoidable impurities, and satisfies both the following expressions (1) and (2), with a strength of 490 MPa or more and a hole expansion ratio of 80%. This is a high-strength steel sheet with excellent ductility. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 13. A mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
8% or less, Cr: 0.005 to 0.10%, Mo: 0.005 to
0.10%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100
% Or more selected from the group consisting of
And has a steel composition consisting of unavoidable impurities, the following (1)
A high-strength steel sheet excellent in ductility, having a strength of 490 MPa or more and a hole expansion ratio of 80% or more, which satisfies both the formula and the relationship of the following formula (2). C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 14. In mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
It has a steel composition of 8% or less, the balance being Fe and unavoidable impurities, and satisfies both the following expressions (1) and (2), and has an area ratio of crystal grains having a crystal grain size of 20 μm or less.
High-strength steel sheet occupying 80% or more and consisting of at least one of granular bainitic ferrite and kvasy polygonal ferrite, having a strength of 490MPa or more and a hole expansion ratio of 80% or more and excellent ductility. . C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 15. In mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
8% or less, Cr: 0.005 to 0.10%, Mo: 0.005 to
0.10%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100
% Or more selected from the group consisting of
And has a steel composition consisting of unavoidable impurities, the following (1)
Equation and the relationship of the following equation (2).
A crystal grain with a grain size of 20 μm or less occupies an area ratio of 80% or more, and is made of at least one of granular bainitic ferrite and kvasy polygonal ferrite, with a strength of 490 MPa or more and a hole expansion rate of 80% or more. High strength steel sheet with excellent ductility. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 16. In mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
It has a steel composition of 8% or less, the balance being Fe and unavoidable impurities, and satisfies both the following expressions (1) and (2), and has an area ratio of crystal grains having a crystal grain size of 20 μm or less.
Occupies 80% or more, and is composed of one or more of granular bainitic ferrite and kvasy polygonal ferrite, and the grain boundary between individual crystals on the steel sheet surface at the interface between the plating layer and the steel sheet is 2.0 μm or less in width. An alloyed hot-dip galvanized steel sheet with excellent ductility, having a strength of 490 MPa or more and a hole expansion rate of 80% or more, characterized by being etched. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 17. In mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
8% or less, Cr: 0.005 to 0.10%, Mo: 0.005 to
0.10%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100
% Or more selected from the group consisting of
And has a steel composition consisting of unavoidable impurities, the following (1)
Equation and the relationship of the following equation (2).
A crystal grain having a crystal grain size of 20 μm or less occupies an area ratio of 80% or more, and is composed of one or more of granular bainitic ferrite and kvasy polygonal ferrite, and individual crystals on the steel sheet surface at the interface between the plating layer and the steel sheet. An alloyed hot-dip galvanized steel sheet having a strength of 490 MPa or more, a hole expansion rate of 80% or more, and excellent ductility, characterized in that the grain boundaries between them are etched at a width of 2.0 μm or less. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 18. Further, in mass%, Ti: 0.003 to 0.1
% And Nb: at least 490 MPa and a hole expansion ratio of 80% or more according to any one of claims 12 to 17, containing one or two of 0.003 to 0.1%. Steel sheet with excellent ductility or galvannealed steel sheet. 19. In mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
A steel slab having a steel composition of 8% or less, with the balance being Fe and unavoidable impurities, and satisfying both of the following equations (1) and (2) is hot-rolled at a finish rolling temperature of 880-970 ° C After rolling, it is cooled to a temperature range of 600-700 ° C at a cooling rate of 35-55 ° C / sec, and then cooled to a temperature range of 400-600 ° C.
By winding at a cooling rate of 40 ° C / sec, the crystal grains with a crystal grain size of 20 μm or less occupy an area ratio of 80% or more, and from one or more of granular bainitic ferrite or kvasy polygonal ferrite. A method for producing a high-strength steel sheet having a strength of 490 MPa or more and a hole expansion ratio of 80% or more and having excellent ductility. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 20. The steel slab further comprises:
20. The strength of claim 19, comprising one or two of 0.003 to 0.1% and Nb: 0.003 to 0.1%.
A method for producing a high-strength steel sheet having excellent ductility with a pressure of 0 MPa or more and a hole expansion ratio of 80% or more. 21. In mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 1.0%, N: 0.00
A steel slab having a steel composition of 8% or less, with the balance being Fe and unavoidable impurities, and satisfying both of the following equations (1) and (2) is hot-rolled at a finish rolling temperature of 880-970 ° C After rolling, it is cooled to a temperature range of 600-700 ° C at a cooling rate of 35-55 ° C / sec, and then cooled to a temperature range of 400-600 ° C.
After cooling at a cooling rate of 40 ° C./second, winding and pickling, heating in a pre-oxidation furnace with continuous galvanizing equipment,
In an atmosphere with a dew point of 30 ° C or less, set the air-fuel ratio to 0.8 to 1.25,
And the maximum attained steel sheet temperature in the pre-oxidation furnace is hot-dip galvanized to satisfy the following formula (3), and the crystal grain size is 20μm
The following crystal grains occupy an area ratio of 80% or more, and are composed of at least one of granular bainitic ferrite and kvasy polygonal ferrite.
A method for producing an alloyed hot-dip galvanized steel sheet with excellent ductility of 490 MPa or more and hole expansion rate of 80% or more. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) 700 + 100 × ln [Si] ≦ T ≦ 830 + 50 × ln [Si] (3) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 22. The steel slab further comprises Cr:
0.005 to 0.10%, Mo: 0.005 to 0.10%, V: 0.005 to 0.
22. The high-strength steel sheet or alloyed molten zinc according to any one of claims 19 to 21, containing one or more selected from the group consisting of 10% and B: 0.0001 to 0.0100%. Manufacturing method of plated steel sheet. 23. In mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.00
It has a steel composition of 8% or less, the balance being Fe and unavoidable impurities, and satisfies both the following expressions (1) and (2), and the area ratio of crystal grains having a crystal grain size of 20 μm or less is
A high-strength alloy with a strength of 490 MPa or more and a hole expansion ratio of 80% or more and excellent ductility, occupying at least 80% and comprising at least one of granular bainitic ferrite and kvasy polygonal ferrite. Galvanized steel sheet. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 24. In mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.00
8% or less, Cr: 0.005 to 0.10%, Mo: 0.005 to
0.10%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100
% Or more selected from the group consisting of
And has a steel composition consisting of unavoidable impurities, the following (1)
Equation and the relationship of the following equation (2).
A crystal grain having a crystal grain size of 20 μm or less occupies an area ratio of 80% or more, and is made of at least one of granular bainitic ferrite and kvasy polygonal ferrite. A strength of 490 MPa or more and a hole expansion rate of 80%. This is a high-strength galvannealed steel sheet having excellent ductility. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 25% by mass, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.00
It has a steel composition of 8% or less, the balance being Fe and unavoidable impurities, and satisfies both the following expressions (1) and (2), and has an area ratio of crystal grains having a crystal grain size of 20 μm or less.
Occupies 80% or more, and is composed of one or more of granular bainitic ferrite and kvasy polygonal ferrite, and the grain boundary between individual crystals on the steel sheet surface at the interface between the plating layer and the steel sheet is 2.0 μm or less in width. A high-strength galvannealed steel sheet having excellent ductility, having a strength of 490 MPa or more and a hole expansion rate of 80% or more, characterized by being etched. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 26. In mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.00
8% or less, Cr: 0.005 to 0.10%, Mo: 0.005 to
0.10%, V: 0.005 to 0.10% and B: 0.0001 to 0.0100
% Or more selected from the group consisting of
And has a steel composition consisting of unavoidable impurities, the following (1)
Equation and the relationship of the following equation (2).
A crystal grain having a crystal grain size of 20 μm or less occupies an area ratio of 80% or more, and is composed of one or more of granular bainitic ferrite and kvasy polygonal ferrite, and individual crystals on the steel sheet surface at the interface between the plating layer and the steel sheet. A high-strength galvannealed steel sheet having a strength of 490 MPa or more and a hole expansion rate of 80% or more and excellent ductility, characterized in that the grain boundaries between the two are etched by a width of 2.0 μm or less. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 27. Further, in mass%, Ti: 0.003 to 0.1
27% and Nb: one or two of 0.003 to 0.1%, having a strength of 490 MPa or more and a hole expansion ratio of 80% or more according to any one of claims 23 to 26. High strength galvannealed steel sheet with excellent ductility. 28. In mass%, C: 0.02 to 0.10%, Si: 0.
1 to 1.0%, Mn: 0.8 to 2.5%, P: 0.001 to 0.025
%, S: 0.010% or less, Al: 0.003 to 0.1%, N: 0.00
A steel slab having a steel composition of 8% or less, with the balance being Fe and unavoidable impurities, and satisfying both of the following equations (1) and (2) is hot-rolled at a finish rolling temperature of 880-970 ° C After rolling, it is cooled to a temperature range of 600-700 ° C at a cooling rate of 35-55 ° C / sec, and then cooled to a temperature range of 400-600 ° C.
After cooling at a cooling rate of 40 ° C./second, winding, pickling, and hot-dip galvanizing, the crystal grain size is 20 μm.
The following crystal grains occupy an area ratio of 80% or more, and are composed of one or more of granular bainitic ferrite and kvasy polygonal ferrite. 2.0 μm width
A method for producing a high-strength galvannealed steel sheet having a strength of 490 MPa or more and a hole expansion ratio of 80% or more and excellent ductility, characterized by producing an alloyed galvanized steel sheet etched below. C− (12/48) × Ti ^* − (12/93) × Nb ≦ 0.09 (1) −340 × C + 76 × Si−2 × Mn + 939 × Ti + 1334 × Nb + 5470 × N ≧ 70 (2) where Ti ^* = Ti− (48/14) × N− (48/32) × S. 29. The steel slab further comprises Ti:
29. The strength of claim 28, comprising one or two of 0.003 to 0.1% and Nb: 0.003 to 0.1%.
A method for producing a high-strength alloyed hot-dip galvanized steel sheet having excellent ductility of 0 MPa or more and a hole expansion rate of 80% or more. 30. The hot-dip galvanizing method further comprises heating in a pre-oxidizing furnace of a continuous hot-dip galvanizing facility, and having a dew point of 30%.
The air-fuel ratio is set to 0.8 to 1.25 in an atmosphere of not more than ℃, and the highest attained steel sheet temperature in the pre-oxidation furnace is as follows.
30. The method for producing a high-strength galvannealed steel sheet according to claim 28 or 29, wherein the method is performed so as to satisfy the expression (3). 700 + 100 × ln [Si] ≦ T ≦ 830 + 50 × ln [Si] (3) where T is the highest reached steel sheet temperature in the pre-oxidation furnace (° C)
And [Si] indicates the Si content (% by mass) of the base steel sheet. 31. The steel slab further comprises Cr:
0.005 to 0.10%, Mo: 0.005 to 0.10%, V: 0.005 to 0.
31. The high-strength galvannealed steel sheet according to any one of claims 28 to 30, comprising one or more selected from the group consisting of 10% and B: 0.0001 to 0.0100%. Manufacturing method.