Technical field
[0001]
The present invention coated steel sheet, a manufacturing method and a galvannealed steel sheet hot-dip galvanized steel sheet. The present invention is particularly, as automotive body, suitable for press molding, to excellent uniformity ductility and local ductility and high strength galvanized steel sheet and high strength galvannealed steel sheet processes for their preparation.
BACKGROUND
[0002]
　Today industrial art is highly specialization, the material used in the art, are specialized and and higher performance is required. With respect to steel sheets for automobiles, to improve fuel economy of by body weight reduction, high strength is required. The strength, refers to both yield strength and tensile strength.
[0003]
　When applied to high-strength steel sheet to a vehicle body of an automobile, while lighter body by reducing the plate thickness of the steel sheet, it is possible to impart the desired strength to the body. However, in the press-molding to form the body of an automobile, the thinner the thickness of the steel sheet to be used, cracks and wrinkles are likely to occur. Therefore, the thin steel sheet for automobiles is required also excellent uniformity ductility and local ductility.
[0004]
　In order to improve the collision safety performance of motor vehicles, it is necessary to automotive steel sheets have excellent shock absorption. From the viewpoint of impact absorption properties, automotive steel sheet, the strength is added to the higher, it is necessary to have excellent local ductility in order to suppress the cracking during impact load load.
[0005]
　Thus, the automobile steel sheet, (1) high strength for weight reduction and crashworthiness improvement of the vehicle body, (2) highly uniform ductility for improvement of formability, and improvement of (3) moldability and high local ductility is required for the improvement of collision safety.
[0006]
　However, the improvement of uniform ductility and local ductility of the steel sheet, the strength of a steel sheet, a contradictory elements, it is difficult to satisfy these properties at the same time. Although the corrosion resistance is required for automotive steel sheets, to maintain the corrosion resistance is more difficult to achieve both high ductility and high strength.
[0007]
　Previously, as a method for improving the ductility of high-strength cold-rolled steel sheet, technologies to contain residual austenite in the metal structure has been proposed. Steel sheet containing retained austenite transformation induced plasticity austenite during processing caused by the transformation into martensite: the (Transformation Induced Plasticity TRIP), showing a large elongation.
[0008]
　Patent Documents 1 and 2, a steel sheet containing Si and Mn, ferrite - and heated to two-phase region or austenite single phase region of austenite and annealed to cool, the austempering treatment for holding at 350 ~ 500 ° C. method for producing a high strength cold rolled steel sheet to stabilize the austenite performed is disclosed. These techniques, in cold-rolled steel sheet, can be balanced well improve the strength and ductility.
[0009]
　However, in the production of hot-dip galvanized steel sheets and galvannealed steel sheets, in a typical continuous galvanizing, constraints holding temperature and holding time, can not be sufficiently performing austempering. Furthermore, since the austenite is decomposed easily at the plating step and the alloying step, it is difficult to ensure the retained austenite requirements.
[0010]
　Patent Document 3, by containing Si and Mn more than a certain percentage with respect to C, to suppress the transformation of austenite during alloying treatment, high strength alloyed retained austenite to form a metal structure that mixed in the ferrite method for manufacturing a galvanized steel sheet is disclosed. However, for the deterioration of the local ductility of interest in steel sheet containing retained austenite in the metal structure, not any consideration it is made.
[0011]
　Patent Document 4, in the average ferrite grain diameter is less 10μm and tempered martensite was dispersed retained austenite and the low-temperature transformation product phase, ductility, stretch flangeability, and the high tension having excellent fatigue resistance hot-dip galvanized steel sheet is disclosed. Tempered martensite is effective in improving the stretch flange formability and fatigue properties, when comminuted tempered martensite, these characteristics are further improved.
[0012]
　However, in order to obtain a metal structure comprising a tempered martensite and residual austenite, the primary heat treatment for producing martensite, tempered martensite, further require secondary heat treatment for obtaining a residual austenite since the, productivity is greatly reduced. Further, in the manufacturing method described in Patent Document 4, the secondary heat treatment Ac 1 for performing points or more at high temperature, tempered martensite is excessively softened, it is difficult to obtain a high strength.
[0013]
　As described above, the strength (yield strength and tensile strength), the ductility (uniform ductility and local ductility) is the opposite element, to produce a sufficiently elevated steel both are difficult in the prior art is there.
CITATION
Patent Document
[0014]
Patent Document 1: JP 61-157625 Patent Publication
Patent Document 2: JP 61-217529 Patent Publication
Patent Document 3: JP-A 11-279691 JP
Patent Document 4: JP 2001-192768 JP
Summary of the Invention
Problems that the Invention is to Solve
[0015]
　The present invention has been made in view of the above technical background, excellent uniformity ductility and local ductility, further, the yield strength and tensile strength is high, the plated steel sheet having excellent formability and impact absorption properties, a method of manufacturing a galvanized steel sheet and, and to provide a method for manufacturing a galvannealed steel sheet.
Means for Solving the Problems
[0016]
　The present inventors have found that in hot-dip galvanized steel sheets and galvannealed steel sheet, while ensuring the tensile strength and yield strength were intensively studied a method for improving the uniformity ductility and local ductility. As a result, it is leading to obtain findings the following (A) ~ (E).
[0017]
　(A) low carbon galvanized steel sheet containing Si and Mn, or a low carbon galvannealed steel sheet containing Si and Mn, when produced in a continuous galvanizing line, uniform ductility and local ductility is reduced and, further, the yield strength may be lowered. This is because the continuous galvanizing line, austempering is insufficient, presumably because metal structure including the C concentration is low residual austenite and hard martensite is formed.
[0018]
　(B) However, if the reheating treatment to hot-dip galvanized steel sheets and galvannealed steel sheet having a metallic structure including a such C concentration is low residual austenite and hard martensite subjected, galvanized steel sheet and improved uniformity ductility and local ductility of the galvannealed steel sheet, further, also improved yield strength.
[0019]
　The reason for this is not clear, (a) C enrichment occurs to austenite during reheating, the stability of the austenite is increased, and (b) is tempered is hard martensite, a soft tempered martensite change it to, it is presumed to be due to.
[0020]
　(C) before performing the reheating process, if subjected to temper rolling the galvanized steel sheet and the galvannealed steel sheet, uniform ductility and local ductility hot-dip galvanized steel sheet or galvannealed steel sheet is further improved, also to further improve the yield strength.
[0021]
　The reason for this is not clear, by (a) temper rolling, dislocations austenite is introduced, followed with concentration of C into austenite during reheat treatment is promoted Mn also thickened, the stability of the austenite is further be improved, by rolling (b) refining a portion of the austenite is transformed into martensite, the metal structure after reheating treatment, the tempered martensite is increased, and, after reheating treatment (c) martensitic transformation which may occur during cooling is suppressed, in the metal structure after reheating treatment, it is estimated that hard martensite be less, due to.
[0022]
　(D) refining characteristics improving effect by rolling, in the metal structure of the hot-dip galvanized steel sheets and galvannealed steel sheet is temper rolling increases as austenite is small.
[0023]
　The reason for this is not clear, (a) processing strain in austenite is concentrated, the more austenite is small, the dislocation amount to be introduced into austenite is increased, and, (b) Thus, the austenite during reheating C enrichment and Mn enriched is promoted to the stability of the austenite is estimated to be attributable to, be further enhanced.
[0024]
　(E) temper rolling, the metal structure of the hot-dip galvanized steel sheets and galvannealed steel sheet is produced by reheating process is performed, in addition to the residual austenite and tempered martensite, the inclusion of polygonal ferrite without local ductility hot-dip galvanized steel sheets and galvannealed steel sheet is impaired, uniform ductility is further improved.
[0025]
　The reason for this is not clear, to rise (a) Mn concentration in the residual austenite, the stability of the austenite is increased, (b) Normal, Mn in austenite prevents concentration of C into austenite, but temper by performing the rolling reheating heat treatment, C enrichment to austenite is promoted, C concentration in the retained austenite is secured, it is estimated that in particular due to.
[0026]
　The present inventors, based on the findings of the above (A) ~ (E), facilities after galvanized steel plate (steel plate), or galvanized, further alloyed after perform temper rolling, by reheating process is performed, high residual austenite of C concentration and Mn concentration, tempered martensite, and has a metal structure including polygonal ferrite, uniform ductility and local ductility good, further, that it is possible to produce a yield strength and high tensile hot-dip galvanized steel sheets and galvannealed steel sheet strength, and further findings.
[0027]
　The present invention has been completed based on the above findings, its gist the following. In the present invention, "steel" is intended to include "steel strip".
[0028]
　(1) chemical composition, in
mass%,
C: 0.03% ~
0.70%, Si: 0.25% ~ 2.50%, Mn: 1.00% ~
5.00%, P: 0 .100% or
less, S: 0.010% or
less, Sol. Al: 0.001%
~ 2.500%, N: 0.020% or less
Ti:
0% ~ 0.300%,
Nb: 0% ~ 0.300%, V: 0% ~
0.300%, Cr :
0%
~ 2.000%,
Mo: 0% ~ 2.000%, B: 0% ~
0.0200%, Cu: 0% ~ 2.000%, Ni: 0% ~
2.000%, Ca :
0% ~ 0.0100%,
Mg: 0% ~ 0.0100%, REM: 0% ~ 0.1000%, and
Bi: 0% ~ 0.0500%,
wherein the balance being iron and impurities ,
　metal structure, 5.0 vol% of residual austenite, comprises 5.0 volume% of tempered martensite,
　C amount of said residual austenite is characterized in that at least 0.85 wt% plating steel sheet.
[0029]
　(2) the metal structure further comprises 2.0 volume% of polygonal ferrite,
　plating Mn amount of the retained austenite is described in the characterized by satisfying the following formula (1) (1) steel sheet.
[Mn] gamma / [Mn] ave ≧ 1.10 · · ·
(1) [Mn] gamma : Mn amount of retained austenite (mass%)
[Mn] ave : Mn amount of the chemical composition of the steel sheet (wt%)
[0030]
　(3) the chemical composition further contains, by
mass%,
Ti: 0.001% ~ 0.300%, Nb: 0.001% ~ 0.300%,
and, V: 0.001% ~ 0.300 plated steel sheet according to (1) or (2), characterized in that it contains one or more kinds% selected from the group consisting of.
[0031]
　(4) the chemical composition further contains, by
mass%,
Cr: 0.001% ~ 2.000%, Mo: 0.001% ~ 2.000%,
and, B: 0.0001% ~ 0.0200 plated steel sheet according to any one of% the characterized in that it contains one or more selected from the group consisting of (1) to (3).
[0032]
　(5) the chemical composition further contains, by
mass%, Cu: 0.001% to 2.000%,
and, Ni: 1 kind or two kinds selected from the group consisting of 0.001% to 2.000% plated steel sheet according to any one of the characterized in that it contains (1) to (4).
[0033]
　(6) The chemical composition further contains, by
mass%,
Ca: 0.0001% ~ 0.0100%, Mg: 0.0001% ~ 0.0100%,
and, REM: 0.0001% ~ 0.1000 plated steel sheet according to any one of% the characterized in that it contains one or more selected from the group consisting of (1) to (5).
[0034]
　(7) the chemical composition further contains, by
mass%, Bi: plated steel sheet according to any one of the characterized in that it contains between 0.0001% 0.0500% (1) to (6).
[0035]
　(8) The coated steel sheet, plated steel sheet according to any one of the, which is a galvanized steel sheet comprising a galvanized layer (1) to (7).
[0036]
　(9) The coated steel sheet, plated steel sheet according to any one of above, wherein the galvanized layer is a galvannealed steel sheet that has been alloyed (1) to (7).
[0037]
　(10) chemical composition, in
mass%,
C: 0.03% ~
0.70%, Si: 0.25% ~ 2.50%, Mn: 1.00% ~
5.00%, P: 0 .100% or
less, S: 0.010% or
less, Sol. Al: 0.001%
~ 2.500%, N: 0.020% or less
Ti:
0% ~ 0.300%,
Nb: 0% ~ 0.300%, V: 0% ~
0.300%, Cr :
0%
~ 2.000%,
Mo: 0% ~ 2.000%, B: 0% ~
0.0200%, Cu: 0% ~ 2.000%, Ni: 0% ~
2.000%, Ca :
0% ~ 0.0100%,
Mg: 0% ~ 0.0100%, REM: 0% ~ 0.1000%, and
Bi: 0% ~ 0.0500%,
wherein the balance being iron and impurities the steel sheet, Ac 1 and performing annealing by heating to point greater than
　after the step of performing the annealing, the average cooling rate in a temperature range of 650 ° C. ~ 500 ° C. as less than 2 ° C. / sec or higher 100 ° C. / sec , cooled to 500 ° C. or less, and performing a first cooling,
　after the first step of performing cooling, the first A step of performing hot-dip galvanizing to the cooling in the step of performing a cooling steel sheet,
　after the step of subjecting the hot-dip galvanizing, the steel sheet to the molten zinc plated, plating in the step of subjecting the hot-dip galvanized the average cooling rate in the temperature range from temperature to 300 ° C. as above 2 ° C. / sec, cooled to 300 ° C. or less, and performing a second cooling,
　after the step of performing the second cooling, the second of the cooled steel sheet in the process for cooling, and performing temper rolling or elongation 0.10%,
　after the step of performing the temper rolling, the steel sheet of the temper rolling is performed was heated to 200 ° C. ~ 600 ° C. temperature range of, and performing heat treatment for holding at least one second from the temperature,
　method for producing a galvanized steel sheet, characterized in that it comprises a.
[0038]
　(11) in the step of performing the annealing, the steel sheet Ac 3 perform annealing by heating to point greater than
　after the step of performing the annealing, the annealed steel sheet, the heating temperature (heating temperature - method for manufacturing a galvanized steel sheet according to, characterized in that cooling the average cooling rate in the temperature range up to 50 ° C.) as the following 7 ° C. / sec (10).
[0039]
　(12) chemical composition, in
mass%,
C: 0.03% ~
0.70%, Si: 0.25% ~ 2.50%, Mn: 1.00% ~
5.00%, P: 0 .100% or
less, S: 0.010% or
less, Sol. Al: 0.001%
~ 2.500%, N: 0.020% or less
Ti:
0% ~ 0.300%,
Nb: 0% ~ 0.300%, V: 0% ~
0.300%, Cr :
0%
~ 2.000%,
Mo: 0% ~ 2.000%, B: 0% ~
0.0200%, Cu: 0% ~ 2.000%, Ni: 0% ~
2.000%, Ca :
0% ~ 0.0100%,
Mg: 0% ~ 0.0100%, REM: 0% ~ 0.1000%, and
Bi: 0% ~ 0.0500%,
wherein the balance being iron and impurities the steel sheet, Ac 1 and performing annealing by heating to point greater than
　after the step of performing the annealing, the average cooling rate in a temperature range of 650 ° C. ~ 500 ° C. as less than 2 ° C. / sec or higher 100 ° C. / sec , cooled to 500 ° C. or less, and performing a first cooling,
　after the first step of performing cooling, the first A step of performing molten zinc plating steel plate cooled by the step of performing cooling,
　after the step of subjecting the hot-dip galvanizing, the steel sheet to the molten zinc plated, alloyed with an alloying treatment temperature and performing,
　after the step of performing the alloying treatment, the steel sheet of the alloying treatment is performed, the average cooling rate in a temperature range of up to 300 ° C. from the alloying treatment temperature of 2 ° C. / sec or more, 300 ° C. and cooled to below, and performing a second cooling,
　after said second step for cooling, to the second steel sheet which has been cooled in the process for cooling, elongation 0.10% or more and performing temper rolling,
　after the step of performing the temper rolling, heating the steel sheet to the temper rolling is performed in the temperature range of 200 ° C. ~ 600 ° C., held for more than one second at that temperature a step of performing heat treatment
　to further comprising a Method for manufacturing a galvannealed steel sheet.
[0040]
　(13) in the step of performing the annealing, the steel sheet Ac 3 perform annealing by heating to point greater than
　after the step of performing the annealing, the annealed steel sheet, the heating temperature (heating temperature - method for manufacturing a galvannealed steel sheet according to, characterized in that cooling the average cooling rate in the temperature range up to 50 ° C.) as the following 7 ° C. / sec (12).
Effect of the invention
[0041]
　According to the present invention, excellent uniformity ductility and local ductility, further, the yield strength and tensile strength is high, and provides the produced hot-dip galvanized steel sheets and galvannealed steel sheet excellent in formability and shock absorption can.
BRIEF DESCRIPTION OF THE DRAWINGS
[0042]
[1] Figure 1 is a diagram for explaining a method of manufacturing a galvanized steel sheet.
FIG. 2 is a diagram for explaining a method of manufacturing a galvannealed steel sheet.
DESCRIPTION OF THE INVENTION
[0043]
　Plated steel sheet of the present invention,
　the chemical composition, in
mass%,
C: 0.03% ~ 0.70%,
Si: 0.25% ~ 2.50%, Mn: 1.00% ~ 5.00% ,
P: 0.100 Pasento
less, S: 0.010 Pasento
below, Sol. Al: 0.001%
~ 2.500%, N: 0.020% or less
Ti:
0% ~ 0.300%,
Nb: 0% ~ 0.300%, V: 0% ~
0.300%, Cr :
0%
~ 2.000%,
Mo: 0% ~ 2.000%, B: 0% ~
0.0200%, Cu: 0% ~ 2.000%, Ni: 0% ~
2.000%, Ca :
0% ~ 0.0100%,
Mg: 0% ~ 0.0100%, REM: 0% ~ 0.1000%, and
Bi: 0% ~ 0.0500%,
wherein the balance being iron and impurities ,
　metal structure, 5.0 vol% of residual austenite, comprises 5.0 volume% of tempered martensite,
　C amount of said residual austenite is characterized in that at least 0.85% by weight.
[0044]
　Plated steel sheet of the present invention is characterized in that a galvanized steel sheet comprising a galvanized layer.
[0045]
　Plated steel sheet of the present invention is characterized in that galvanized layer is a galvannealed steel sheet which has been alloyed.
[0046]
　Method for manufacturing a galvanized steel sheet of the present invention, the chemical composition, in
mass%,
C: 0.03% ~ 0.70%, Si:
0.25% ~ 2.50%, Mn: 1.00%
5.00 Pasento ～, P: 0.100 Pasento
less, S: 0.010 Pasento
below, Sol. Al: 0.001%
~ 2.500%, N: 0.020% or less
Ti:
0% ~ 0.300%,
Nb: 0% ~ 0.300%, V: 0% ~
0.300%, Cr :
0%
~ 2.000%,
Mo: 0% ~ 2.000%, B: 0% ~
0.0200%, Cu: 0% ~ 2.000%, Ni: 0% ~
2.000%, Ca :
0% ~ 0.0100%,
Mg: 0% ~ 0.0100%, REM: 0% ~ 0.1000%, and
Bi: 0% ~ 0.0500%,
wherein the balance being iron and impurities the steel sheet, Ac 1 and performing annealing by heating to point greater than
　after the step of performing the annealing, the average cooling rate in a temperature range of 650 ° C. ~ 500 ° C. as less than 2 ° C. / sec or higher 100 ° C. / sec , cooled to 500 ° C. or less, and performing a first cooling,
　after the first step of performing cooling, the first A step of performing hot-dip galvanizing to the cooling in the step of performing a cooling steel sheet,
　after the step of subjecting the hot-dip galvanizing, the steel sheet to the molten zinc plated, plating in the step of subjecting the hot-dip galvanized the average cooling rate in the temperature range from temperature to 300 ° C. as above 2 ° C. / sec, cooled to 300 ° C. or less, and performing a second cooling,
　after the step of performing the second cooling, the second of the cooled steel sheet in the process for cooling, and performing temper rolling or elongation 0.10%,
　after the step of performing the temper rolling, the steel sheet of the temper rolling is performed was heated to 200 ° C. ~ 600 ° C. temperature range of, and performing heat treatment for holding at least one second from the temperature,
　characterized in that it comprises a.
[0047]
　Method for manufacturing a galvannealed steel sheet of the present invention, the chemical composition, in
mass%,
C: 0.03% ~ 0.70%, Si: 0.25% ~
2.50%, Mn: 1. Pasento
～ 5.00 00 Pasento, P: 0.100 Pasento
less, S: 0.010 Pasento
below, Sol. Al: 0.001%
~ 2.500%, N: 0.020% or less
Ti:
0% ~ 0.300%,
Nb: 0% ~ 0.300%, V: 0% ~
0.300%, Cr :
0%
~ 2.000%,
Mo: 0% ~ 2.000%, B: 0% ~
0.0200%, Cu: 0% ~ 2.000%, Ni: 0% ~
2.000%, Ca :
0% ~ 0.0100%,
Mg: 0% ~ 0.0100%, REM: 0% ~ 0.1000%, and
Bi: 0% ~ 0.0500%,
wherein the balance being iron and impurities the steel sheet, Ac 1 and performing annealing by heating to point greater than
　after the step of performing the annealing, the average cooling rate in a temperature range of 650 ° C. ~ 500 ° C. as less than 2 ° C. / sec or higher 100 ° C. / sec , cooled to 500 ° C. or less, and performing a first cooling,
　after the first step of performing cooling, the first A step of performing molten zinc plating steel plate cooled by the step of performing cooling,
　after the step of subjecting the hot-dip galvanizing, the steel sheet to the molten zinc plated, alloyed with an alloying treatment temperature and performing,
　after the step of performing the alloying treatment, the steel sheet of the alloying treatment is performed, the average cooling rate in a temperature range of up to 300 ° C. from the alloying treatment temperature of 2 ° C. / sec or more, 300 ° C. and cooled to below, and performing a second cooling,
　after said second step for cooling, to the second steel sheet which has been cooled in the process for cooling, elongation 0.10% or more and performing temper rolling,
　after the step of performing the temper rolling, heating the steel sheet to the temper rolling is performed in the temperature range of 200 ° C. ~ 600 ° C., held for more than one second at that temperature a step of performing heat treatment
　to further comprising a .
[0048]
　Hereinafter, galvanized steel sheet of the present embodiment, the galvannealed steel sheet, and a method for their preparation will be described. In the following description, unless otherwise specified, it refers to the finally obtained steel sheet by a manufacturing method according to the present embodiment as a "hot-dip galvanized steel sheet" or "galvannealed steel sheet", or "steel sheet", manufactured in the middle of a steel plate is referred to as "steel plate".
[0049]
　(A) Chemical composition
　First, galvanized steel sheet according to the present embodiment, the galvannealed steel sheet, and the reason for limiting the chemical composition of the base steel sheet used in these production methods will be described. Hereinafter,% of the chemical composition means mass%.
[0050]
　[C: 0.03% ~ 0.70%]
　C is an element effective for obtaining a residual austenite. The C content is less than 0.03%, since not obtained metal structure containing retained austenite and tempered martensite to be described later, the C content is 0.03% or more. Preferably C content of 0.10% or more, more preferably 0.13% or more, further preferably 0.16% or more.
[0051]
　On the other hand, when the C content exceeds 0.70%, the weldability of the steel sheet is remarkably reduced, the C content is set to 0.70%. Preferably C content is 0.30% or less, more preferably 0.26% or less, more preferably not more than 0.24%.
[0052]
　[Si: 0.25% ~
　2.50%] Si suppresses the precipitation of cementite, and is an element that an activity of accelerating the formation of residual austenite. Further, Si is to prevent the tempered martensite is excessively softened, is also the element an action of maintaining the strength. The Si content is less than 0.25%, the effect is not exhibited sufficiently, Si content is 0.25% or more, preferably Si content of 0.60 percent, more preferably 1.00% ultra, more preferably 1.45 percent.
[0053]
　On the other hand, when the Si content exceeds 2.50%, the plating of the steel sheet is remarkably reduced, since the weldability of the steel sheet is lowered, Si content is at most 2.50%. Preferably the Si content 2.30% or less, more preferably 2.10% or less, more preferably not more than 1.90%.
[0054]
　[Mn: 1.00% ~ 5.00%] Mn
　has an effect of improving the hardenability of steel, is an effective element for obtaining a metal structure including a residual austenite and tempered martensite described later . The Mn content is less than 1.00%, these effects are not sufficiently exhibited, Mn content is 1.00% or more. Preferably the Mn content is 1.50%, more preferably above 2.00% greater, more preferably 2.50 percent. On the other hand, when the Mn content exceeds 5.00%, the weldability of the steel sheet is degraded, the Mn content is not more than 5.00%. Preferably the Mn content 4.00% or less, more preferably 3.50% or less, more preferably not more than 3.00%.
[0055]
　[P: 0.100% or less]
　P is an impurity element, since thereby embrittle steel segregates on grain boundaries, it is preferred elements as small. When the P content exceeds 0.100%, the embrittlement of the steel sheet becomes remarkable, P content is 0.100% or less. Preferably P content is less than 0.020% or, more preferably less than 0.015%, more preferably less than 0.010%. The lower limit of the P content including 0%, when reducing the P content to less than 0.0001%, the manufacturing cost is greatly increased, practically steel, the P content has 0.0001% substantially which is the lower limit.
[0056]
　[S: 0.010% or less]
　S is an impurity element, to form a sulfide inclusions in the steel, so degrades the local ductility of the steel sheet, it is preferred elements as small. When S content exceeds 0.010%, the deterioration of the local ductility of the steel sheet becomes remarkable, the S content is 0.010% or less. Preferably 0.005% or less is S content, more preferably not more than 0.0012%. The lower limit of the S content including 0%, when reducing the S content to less than 0.0001%, the manufacturing cost is greatly increased, practically steel, the S content is 0.0001% substantially which is the lower limit.
[0057]
　[Sol. Al: 0.001% ~
　2.500%] Al is an element for deoxidizing the molten steel. sol. The Al content is less than 0.001%, its effect is not exhibited sufficiently, sol. Al content is 0.001% or more. Preferably sol. Al content is 0.015% or more, more preferably 0.025% or more, further preferably 0.045% or more. Further, Al is, like Si, without the effect of promoting the formation of retained austenite is an effective element to obtain a metal structure comprising a retained austenite and tempered martensite to be described later. From this point of view, sol. Al content is preferably 0.050% or more. More preferably sol. Al content 0.055% or more, more preferably 0.060% or more.
[0058]
　On the other hand, sol. When Al content is 2.500% greater, excessive amounts of alumina (Al 2 O 3 ) is generated, the surface flaws of the alumina due easily occurs, sol. Al content is at most 2.500%. In addition, sol. When Al content is 0.080% or more, the transformation point is increased to increase Ac 3 because annealing in the temperature range of points exceeding difficult, sol. Al content is preferably less than 0.080%. More preferably sol. Al content is 0.075% or less, more preferably 0.070% or less, particularly preferably less than 0.065%.
[0059]
　N: 0.020% or less
　N is an impurity element, in the continuous casting of steel, because it forms a nitride which causes cracking of the slab, the smaller is the preferred element. When N content exceeds 0.020%, the concern of the slab cracking is increased, the N content is set to 0.020% or less. Preferably the N content is 0.010% or less, more preferably less than 0.008% or, more preferably not more than 0.005%. The lower limit of the N content including 0%, when reducing the N content to less than 0.0001%, the manufacturing cost is greatly increased, practically steel, the N content is 0.0001% substantially which is the lower limit.
[0060]
　Furthermore, in order to improve the characteristics, in addition to the above elements, it may be contain elements described below.
[0061]
　[Ti:
　0% ~ 0.300%]
　[Nb: 0% ~ 0.300%] [V: 0% ~
　0.300%] Ti, Nb and,, V is the metal structure is miniaturized, the intensity and an element which contributes to the improvement of ductility. However, when the content of these elements exceeds 0.300%, the these effects are saturated, and so the manufacturing cost is increased, Ti, Nb, and less 0.300% Both the content of V to.
[0062]
　Ti, Nb, and, if V is excessive, the recrystallization temperature rises during annealing, the metal structure after annealing becomes uneven, there is a possibility that local ductility is impaired. Therefore, Ti content is preferably less than 0.080% or less, and more preferably not more than 0.035% Nb content is preferably less than 0.050%, more preferably at 0.030% or less , V content is preferably 0.200% or less, more preferably less than 0.100%.
[0063]
　Ti, Nb, and, the lower limit of the V content including 0%, in order to ensure the effect, Ti, Nb, and the content of V are both preferably not less than 0.001%. Ti content is more preferably 0.005% or more, more preferably 0.010% or more, Nb content is more preferably 0.005% or more, further preferably 0.010% or more, particularly preferably is 0.015% or more, V content is more preferably 0.010% or more, further preferably 0.020% or more. As described above, in order to obtain the effects described above is, Ti: 0.001% ~ 0.300%, Nb: 0.001% ~ 0.300%, and, V: 0.001% ~ 0.300 preferably contains one or more selected from the group consisting of%.
[0064]
　[Cr:
　0% ~
　2.000%] [Mo: 0% ~ 2.000%] [B: 0% ~
　0.0200%] Cr, Mo and,, B is to increase the hardenability of steel is an element effectively acting to obtain a metal structure comprising a retained austenite and tempered martensite to be described later.
[0065]
　However, the Cr content and Mo content exceeds 2.000%, and, B content exceeds 0.0200%, the effect is saturated and the production cost is increased. Therefore, Cr content and Mo content are both not more than 2.000%, B content is at most 0.0200%. Preferably, Cr content 1.000% or less, Mo content 0.500% is less, B content is 0.0030% or less.
[0066]
　Cr, Mo and the lower limit of the B content, including any of the elements even 0%, in order to ensure the effect, Cr content and Mo content is preferably not less than 0.001% B content is preferably 0.0001% or more. More preferably, Cr content 0.100% or more, Mo content 0.050% or more, B content is 0.0010% or more. As described above, in order to obtain the effects described above is, Cr: 0.001% ~ 2.000%, Mo: 0.001% ~ 2.000%, and, B: 0.0001% ~ 0.0200 preferably contains one or more selected from the group consisting of%.
[0067]
　[Cu:
　0% ~ 2.000%] [Ni: 0% ~
　2.000%] Cu and Ni is an element contributing to the improvement of yield strength and tensile strength. However, when the Cu content and Ni content exceeds 2.000%, the effect is saturated, so the production cost is increased, the Cu content and Ni content are both at most 2.000%. Preferably, none of the Cu content and Ni content is less than 0.800%.
[0068]
　The lower limit of the Cu content and Ni content including 0%, in order to ensure the effect, none of the Cu content and Ni content is preferably 0.001% or more. More preferably, the content of each element is 0.010% or more. As described above, in order to obtain the effects described above are, Cu: 0.001% to 2.000%, and, Ni: 1 kind or two kinds selected from the group consisting of 0.001% to 2.000% preferably contains a.
[0069]
　[Ca:
　0% ~
　0.0100%] [Mg: 0% ~ 0.0100%] [REM: 0% ~
　0.1000%] Ca, Mg and,, REM is to adjust the shape of the inclusions an element which contributes to the improvement of local elongation.
[0070]
　However, Ca content and Mg content exceeds 0.0100% and, REM content exceeds 0.1000%, the effect is saturated and the production cost is increased. Therefore, none of the Ca content and the Mg content is 0.0100% or less, REM content is at most 0.1000%. Preferably, Ca content and the Mg content is less 0.0020%, REM content is 0.0100% or less.
[0071]
　Ca, Mg, and, including 0% none lower limit of the content of REM, in order to ensure the effect, Ca, Mg, and any content of REM is not less than 0.0001% preferable. More preferably, the content of each element is also 0.0005% or more. As described above, in order to obtain the effects described above are, Ca: 0.0001% ~ 0.0100%, Mg: 0.0001% ~ 0.0100%, and REM: 0.0001% ~ 0.1000% preferably contains one or more selected from the group consisting of.
[0072]
　Here, the REM, Sc, Y, and is a generic name for a total of 17 lanthanoid elements. Lanthanoid, for industrial it is added in the form of misch metal. In the present invention, REM content refers to the total amount of these elements.
[0073]
　[Bi: 0% ~
　0.0500%] Bi is to refine the solidified structure, an element which contributes to the improvement of local elongation. However, when the Bi content exceeds 0.0500%, the effect is saturated, so the production cost is increased, the Bi content is not more than 0.0500%. Preferably Bi content is 0.0100% or less, more preferably 0.0050% or less. The lower limit of the Bi content including 0%, in order to ensure the effect, the Bi content is preferably 0.0001% or more. More preferably Bi content of 0.0003% or more. As described above, in order to obtain the effects described above are, Bi: preferably contains between 0.0001% 0.0500%.
[0074]
　Galvanized steel sheet according to the present embodiment, the galvannealed steel sheet, and the balance of the chemical composition of the base steel sheet used in these production methods are iron and impurities. Impurities, in producing the steel industrially, steel raw materials such as ores or scrap, or an element which is mixed with various factors in the manufacturing process. These elements are contained it is acceptable within a range that does not inhibit the characteristics of the present invention.
[0075]
　(B) metal structure
　will now be described metal structure of hot-dip galvanized steel sheets and galvannealed steel sheet according to the present embodiment. Metal structure of hot-dip galvanized steel sheets and galvannealed steel sheet according to the present embodiment, while maintaining the yield strength and tensile strength, in order to improve the uniformity ductility and local ductility, by volume%, the residual austenite 5. 0% ultra-containing, and 5.0% ultra containing tempered martensite, Furthermore, C = amount in the residual austenite is characterized in that at least 0.85% by weight. And, preferably, further a polygonal ferrite 2.0% ultra-containing, Mn content in the retained austenite and satisfies the following formula (1). Note that the C content in the retained austenite, which means the C concentration in the austenite phase in, the Mn content in the residual austenite, means a Mn concentration in the austenite phase.
[0076]
　[Mn] gamma / [Mn] ave ≧ 1.10 · · ·
　(1) [Mn] gamma : Mn amount of retained austenite
　(mass%) [Mn] ave : Mn amount of the chemical composition of the steel sheet (wt%)
[0077]
　Hereinafter, the organization requirements will be described sequentially.
[0078]
　: Residual austenite 5.0 vol percent]
　To improve the uniform ductility, the volume fraction of retained austenite is set to 5.0 percent. Preferably the volume fraction of retained austenite is 6.0%, and more preferably 8.0 percent, more preferably 10.0 percent.
[0079]
　However, the residual austenite is present in excess, because local ductility is deteriorated, the volume fraction of retained austenite is preferably less than 30.0%. More preferably an less than 20.0% volume fraction of retained austenite, more preferably less than 15.0%.
[0080]
　: Tempered martensite 5.0 vol percent]
　while maintaining the yield strength and tensile strength, in order to improve the local ductility, the volume ratio of the tempered martensite is 5.0 percent. Preferably tempering volume fraction of martensite 16.0 percent, and more preferably a volume ratio 30.0% of tempered martensite, more preferably 40.0 percent, and particularly preferably is 50.0 percent .
[0081]
　However, when tempered martensite is present in excess, because uniform ductility is deteriorated, the volume ratio of the tempered martensite is preferably 70.0% or less. More preferably the volume ratio of the tempered martensite is less than 60.0%.
[0082]
　: Polygonal ferrite 2.0 vol percent]
　in order to further the uniform ductility improvement, the volume ratio of polygonal ferrite is preferably 2.0 percent. More preferably 6.0 percent volume ratio of polygonal ferrite, more preferably 8.0 percent, and particularly preferably 13.0 percent.
[0083]
　However, when the polygonal ferrite is present in excess, and decreases the yield strength and tensile strength, further, since reduced local ductility, the volume ratio of polygonal ferrite is preferably less than 35.0%. More preferably less than 30.0% volume fraction of polygonal ferrite, more preferably less than 25.0%, particularly preferably less than 20.0%.
[0084]
　: [C content in the residual austenite less than 0.85 wt%
　in residual austenite of the metal structure of the hot-dip galvanized steel sheets and galvannealed steel sheet of the present embodiment, the residual austenite stabilizes, uniform ductility and local ductility to improve, C content in the retained austenite is set to 0.85 mass% or more.
[0085]
　In order to uniformly ductile further improvement, C content in the retained austenite is preferably not less than 0.87 wt%, more preferably not less than 0.89 mass%. On the other hand, when the C content in the retained austenite is too large, since uniform ductility is not obtained TRIP effect is deteriorated, the amount of C in the retained austenite is preferably less than 1.50 wt%. More preferably the amount of C in the retained austenite is less than 1.20 wt%, more preferably less than 1.10 wt%.
[0086]
　[Mn content in the residual austenite: formula
　(1)] [Mn] gamma / [Mn] ave ≧ 1.10 · · ·
　(1) [Mn] gamma : Mn amount of retained austenite
　(mass%) [Mn ] ave : Mn amount of the chemical composition of the steel sheet (mass%)
　the formula (1) is, [Mn] gamma [Mn] and ave an expression that defines the relationship between. In retained austenite galvanized steel sheet and the galvannealed steel sheet of the present embodiment, it is preferred that Mn is requirement concentrated. Mn also, like C, and residual austenite stabilizes, functions effectively to improve the uniformity ductility and local ductility.
[0087]
　To take advantage thereof the full capabilities, [Mn] gamma / [Mn] ave preferably set to 1.10 or more, more preferably 1.15 or more. [Mn] gamma / [Mn] ave limit is not particularly limited, but substantially 2.00. From the viewpoint of productivity, [Mn] gamma / [Mn] ave is preferably 1.35 or less, more preferably 1.25 or less.
[0088]
　[Martensite]
　In hot-dip galvanized steel sheet and the galvannealed steel sheet of the present embodiment, while maintaining the yield strength, in order to further improve the local ductility, the amount of martensite as much as possible to suppress. Here, the martensite refers tempered not even martensite, i.e. that fresh martensite. The volume fraction of martensite is less than 5.0% is preferred. More preferably at a volume fraction of martensite is less than 2.0%, more preferably less than 1.0%.
[0089]
　[Remaining structure]
　metal structure of the remaining structure is a low temperature transformation structure, such as acicular ferrite and bainite may contain perlite, may contain precipitates, such as cementite. Remaining structure is, low temperature transformation products, pearlite, and, since it is not required to contain the precipitate, the low-temperature transformation product, perlite, and the lower limit of each of the volume fraction of the precipitates is 0 vol%.
[0090]
　Low temperature transformation products, pearlite, and the upper limit of each of the volume fraction of the precipitates is not particularly limited. However, the low-temperature transformation product, pearlite, and, when the precipitates are present in excess, because the yield strength and tensile strength decreases, the low-temperature transformation product, perlite, and the sum of the volume fraction of the precipitates is 40.0% the following are preferred. More preferably the sum of the volume fraction of these tissues 20.0% or less, more preferably not more than 10.0%.
[0091]
　When pearlite are present in excess, the yield strength and tensile strength decreases, further, since uniform ductility decreases, the volume ratio of pearlite is less than 10.0% is preferable. More preferably less than the volume ratio of pearlite is 5.0% or less, more preferably less than 3.0%.
[0092]
　Metal structure of hot-dip galvanized steel sheets and galvannealed steel sheet according to the present embodiment is measured as follows. Any test specimen was sampled from the position, polished parallel longitudinal section in the rolling direction, from the boundary between the steel sheet and the plated layer which is the base material, 1/4 depth of thickness of the steel sheet as a base material for the steel sheet in position, to observe the metal structure by using a scanning electron microscope (SEM), the image processing to measure the area ratio of each organization. Area ratio was equal to the volume fraction, the measured area ratio and volume fraction.
[0093]
　Tempered martensite, in that the iron carbide present in the internal structure is extended in a plurality of directions can be distinguished from bainite. Polygonal ferrite, that take the form of bulk, and dislocation density in low point, can be distinguished from acicular ferrite.
[0094]
　The volume fraction of retained austenite, and, C content in the retained austenite, the test pieces were taken from an arbitrary position of the steel sheet 1 from the boundary of the steel sheet and the plated layer as a base material for the plate thickness of the steel sheet which is a base material / 4 was chemically polished rolling surface to a depth position, using X-ray diffraction apparatus (XRD), determined by measuring the X-ray diffraction intensity and the diffraction peak position.
[0095]
　Mn content in the residual austenite ([Mn] gamma ) is measured as follows. In any of the test pieces were taken from the position, 1/4 depth position of the plate thickness of the steel sheet which is a base material from the boundary between the steel sheet and the plated layer which is the base material of the steel plate, the electron backscatter pattern analyzer (EBSP ) using SEM provided with an observation of the metal structure, to check the residual austenite grains.
[0096]
　Subsequently, measuring the Mn concentration of the residual austenite grains by SEM with an electron beam microanalyzer (EPMA). Was measured by EMPA against 10 or more residual austenite grains, the average value of the obtained amount of Mn [Mn] gamma and.
[0097]
　In the measurement by EPMA, for irradiating an electron beam on the residual austenite grains with a small beam diameter than the particle size of the residual austenite, it is preferable to use a SEM equipped with a field emission electron microprobe (FE-EPMA) .
[0098]
　Galvanized layer, and a galvannealed layer is a plating layer formed by normal plating conditions, and may be alloyed plating layer. However, when the Fe concentration in the galvannealed layer is less than 7 mass%, the weldability and sliding resistance may become insufficient, Fe concentration of galvannealed layer is 7 mass% or more It is preferred.
[0099]
　The upper limit of the Fe concentration in the galvannealed layer, from the viewpoint of powdering resistance, preferably 20 wt% or less, more preferably 15 wt% or less. Fe content of the plating layer can be adjusted by controlling the processing conditions in the alloying treatment after hot-dip galvanizing.
[0100]
　(C) mechanical properties
　Mechanical properties of hot-dip galvanized steel sheets and galvannealed steel sheet according to the present embodiment is not particularly limited to a specific mechanical properties.
[0101]
　However, defining a uniform elongation in the direction perpendicular to the rolling direction and UEl (Uniform Elongation). The total elongation direction (TEL perpendicular to the rolling direction 0 defines the value converted to the total elongation of the plate thickness 1.2mm corresponding based) the following equation (2) and TEL (Total Elongation). Further, the direction of local elongation perpendicular to the rolling direction to be converted in the plate thickness 1.2mm corresponding defined lel (Local Elongation) according to the following equation (3). In hot-dip galvanized steel sheets and galvannealed steel sheet according to the present embodiment, from the viewpoint of press formability, the value of TS × UEL is 10000 MPa ·% or more, and the value of TS × lel is 5000 MPa ·% or more it is preferable that.
[0102]
　The value of TS × UEL, since increases in the case where both the tensile strength and the uniform elongation is excellent, is used as an index for evaluating the uniform ductility. The value of TS × lel, since increases in the case where both the tensile strength and local elongation are good, is used as an index for evaluating the local ductility.
[0103]
　TS × value of UEl is 11000 mPa% or more, the value of TS × lel is not less than 6000 MPa%, more preferably. TS × value of UEl is 12000 MPa% or more, the value of TS × lel is not less than 7000 MPa%, more preferably.
　= TEL TEL 0 × (1.2 / t
　0 ) 0.2 · · · (2) lel = TEL-UEL · · · (3)
[0104]
　Here, TEL in the formula (2) 0 is the measured value of total elongation as measured using a JIS5 No. Tensile test pieces, t 0 is the thickness of JIS5 No. Tensile test piece was subjected to measurement. Further, TEL and LEl, respectively, extend all corresponds to the case of thickness 1.2 mm, and a converted value of local elongation. UEl is a measured value of uniform elongation was measured using a JIS5 No. tensile specimens.
[0105]
　In order to improve the shock absorption of the steel sheet, the tensile strength of the steel sheet (TS) is more than 780MPa is preferable. More preferably the tensile strength of the steel sheet (TS) is more than 980 MPa, more preferably at least 1180 MPa. Yield ratio of the steel sheet (YR) is preferably 0.59 or more. More preferably the yield ratio of the steel sheet (YR) is 0.66 or more, further preferably 0.72 or more.
[0106]
　Is local ductility is higher cracking during shock load load suppression, since the absorbed energy increases, in terms of crack suppression, the value of TS × lel the above ·% 5500MPa are preferred. More preferably the value of TS × lel is 6500 mPa ·% or more.
[0107]
　(D) manufacturing method
　Next, a method for manufacturing a preparation and galvannealed steel sheet hot-dip galvanized steel sheet of the present embodiment.
[0108]
　Method for manufacturing a galvanized steel sheet according to the present embodiment, a steel sheet having a chemical composition described above, Ac 1 and performing annealing by heating to point greater than after the step of performing the annealing, 650 ° C. ~ 500 as less than 2 ° C. / sec or higher 100 ° C. / sec average cooling rate in a temperature range of ° C., cooled to 500 ° C. or less, and performing a first cooling, after the step of performing the first cooling, the second a step of performing hot-dip galvanizing the cooled steel sheet in the step of performing a first cooling, after the step of subjecting the hot-dip galvanizing, the steel sheet to the molten zinc plated, subjecting said hot-dip galvanizing process the average cooling rate 2 ° C. / sec or more in a temperature range of up to 300 ° C. from the plating temperature in the cooled to 300 ° C. or less, and performing a second cooling, after the step of performing the second cooling, the the second of cooling To the cooled steel sheet in the step of performing, and performing temper rolling elongation 0.10% or more, after the step of performing the temper rolling, 200 ° C. The steel sheet of the temper rolling is performed was heated to a temperature range of ~ 600 ° C., and a step of performing heat treatment for holding at least one second from the temperature, the.
[0109]
　Among them, the preferred methods of the method for manufacturing hot-dip galvanized steel sheet according to the present embodiment, as shown in FIG. 1, a base steel sheet having a chemical composition described above, Ac 3 performs annealing by heating to point than a step, after the step of performing the annealing, the annealed steel sheet, the average cooling rate in the temperature range from the heating temperature to (the heating temperature -50 ° C.) was cooled as 7 ° C. / sec or less, and further, the average cooling rate in a temperature range of 650 ° C. ~ 500 ° C. as less than 2 ° C. / sec or higher 100 ° C. / sec, cooled to 500 ° C. or less, and performing a first cooling step of performing the first cooling after the the step of performing hot-dip galvanizing to a first of the cooled steel sheet in the process for cooling, after the step of subjecting the hot-dip galvanizing, the steel sheet to the molten zinc plated, the molten zinc the step of applying a plating The average cooling rate in a temperature range from definitive plating temperature to 300 ° C. as above 2 ° C. / sec, cooled to 300 ° C. or less, and performing a second cooling, after the step of performing the second cooling, the the steel plate cooled by the step of performing a second cooling, and performing temper rolling 0.10% or more elongation, after the step of performing the temper rolling, the temper rolling is performed material steel sheet is heated to a temperature range of 200 ° C. ~ 600 ° C., and a step of performing heat treatment for holding at least one second from the temperature, the.
[0110]
　Method for manufacturing a galvannealed steel sheet of the present embodiment, a steel sheet having a chemical composition described above, Ac 1 and performing annealing by heating to point greater than after the step of performing the annealing, is the annealing and the base steel sheet, the average cooling rate in a temperature range of 650 ° C. ~ 500 ° C. as less than 2 ° C. / sec or higher 100 ° C. / sec, cooled to 500 ° C. or less, and performing a first cooling, the first after the step of performing cooling, the a step of performing hot-dip galvanizing to a first of the cooled steel sheet in the process for cooling, after the step of subjecting the hot-dip galvanized, steel sheet, wherein the molten zinc plated to, in the temperature range of the step of performing an alloying treatment in an alloying treatment temperature, after the step of performing the alloying treatment, the steel sheet of the alloying process is performed, up to 300 ° C. from the alloying treatment temperature the average cooling rate 2 ° C. / second or more As above, it cooled to 300 ° C. or less, and performing a second cooling, after the step of performing the second cooling, the base steel sheet which is cooled in a second step of performing cooling, elongation 0. and performing more than 10% of temper rolling, after the step of performing the temper rolling, heating the steel sheet to the temper rolling is performed in the temperature range of 200 ℃ ~ 600 ℃, 1 sec at that temperature and a step of performing heat treatment of holding more.
[0111]
　Among them, preferred method of the production method of the galvannealed steel sheet of the present embodiment, as shown in FIG. 2, a steel sheet having a chemical composition described above, Ac 3 annealed by heating to point than and performing, after the step of performing the annealing, said annealed steel sheet, cooling the average cooling rate in the temperature range from the heating temperature to (heating temperature -50 ° C.) as 7 ° C. / sec or less, and further, the average cooling rate in a temperature range of 650 ° C. ~ 500 ° C. as less than 2 ° C. / sec or higher 100 ° C. / sec, cooled to 500 ° C. or less, and performing a first cooling step of performing the first cooling after the step of performing hot-dip galvanizing the cooled steel sheet in the step of performing the first cooling, after the step of subjecting the hot-dip galvanizing, the steel sheet to the molten zinc plated, alloying treatment Engineering to perform the alloying treatment at a temperature And extent, after the step of performing the alloying treatment, the steel sheet of the alloying treatment is performed, the average cooling rate in a temperature range of up to 300 ° C. from the alloying treatment temperature of more than 2 ° C. / sec, 300 ℃ cooled to below, and performing a second cooling, after said second step for cooling, to the second steel sheet which has been cooled in the process for cooling, elongation 0.10% or more after the step of performing and performing temper rolling, the temper rolling, heating the steel sheet to the temper rolling is performed in the temperature range of 200 ° C. ~ 600 ° C., held for more than one second at that temperature heat treatment and a step of performing.
[0112]
　Method for producing a steel plate subjected to the manufacturing method and a manufacturing method of the galvannealed steel sheet hot-dip galvanized steel sheet of the present embodiment is not limited to a particular production method. For example, manufactured in cast slabs having the chemical composition described above is heated to a temperature range below 1250 ° C., after heating, finish rolling temperature is Ar 3 perform hot rolling at and at 850 ° C. greater than points. Then, wound below coiling temperature 500 ° C. or higher 700 ° C., subjected to cold rolling at a reduction rate of less than 40% to 70% to produce a steel sheet.
[0113]
　Casting of the slab is not limited to the particular casting, although continuous casting method is preferred, may be a steel piece cast steel ingot by other casting methods with slabbing like. In the continuous casting process, in order to suppress the occurrence of surface defects due to inclusions, in the mold, it is preferable to flow the molten steel with an electromagnetic stirrer and the like. Billet hot state after the ingot or slabbing the high temperature after continuous casting is once cooled, reheated, it may be subjected to hot rolling.
[0114]
　Further, the steel strip hot state after the ingot or slabbing the high temperature after continuous casting may be directly subjected to hot rolling without being reheated, hot after performing auxiliary heating it may be subjected to rolling. Incidentally, the steel ingot and slab subjected to hot rolling are collectively referred to as "slab".
[0115]
　To prevent coarsening of the austenite, the temperature of the slab subjected to hot rolling, preferably less than 1250 ° C.. More preferably the temperature of the slab is 1200 ° C. or less. The lower limit of the temperature of the slab subjected to hot rolling is not particularly limited, a hot rolling Ar 3 is preferably a temperature that can be completed in more points.
[0116]
　Conditions of the hot rolling is not particularly limited, when the completion temperature of the hot rolling is too low, the hot-rolled steel sheet metal structure, coarse low-temperature transformation tissue enlargement exhibition in the rolling direction is generated, a uniform ductility and local ductility since there is a possibility of inhibiting completion temperature of the hot rolling is Ar 3 and 850 ° C. greater is preferably at least points. More preferably hot rolling completion temperature is Ar 3 and 880 ° C. greater or more points, more preferably Ar 3 is and 900 ° C. greater or more points. The upper limit of the completion temperature of the hot rolling is not particularly limited, in terms of grain refinement of the metal structure of the hot-rolled steel sheet is preferably 1000 ° C. or less.
[0117]
　In the case where hot rolling consisting of rough rolling and finish rolling, to complete the finish rolling within the above temperature range, between the rough rolling and finish rolling, may be heated roughly rolled material. At this time, the rear end of the rough rolling material, by heating the rough rolled material such that the temperature higher than the tip of the rough rolled material, the temperature variations of the entire length of the rough rolled material at the start of the finish rolling 140 ° C. or less it is preferable to suppress the. The temperature suppression, uniformity of characteristics in a coil wound hot rolled steel sheet is improved.
[0118]
　Heating the rough rolled material may be performed using a known method. For example, between the roughing mill and the finishing mill, the solenoid induction heating unit provided on the basis of the temperature distribution and the like in the longitudinal direction of the rough rolled material on the upstream side of the induction heating apparatus, by the solenoid type induction heating device heating temperature Yutakaryou may be controlled.
[0119]
　Conditions up winding starts after the end of hot rolling is not particularly limited, a hot-rolled steel sheet in order to enhance the cold rollability of the hot rolled steel sheet by softening, when starting the coiling temperature (winding it is preferred to temperature) of the 600 ° C. or higher. Coiling temperature, more preferably at least 640 ° C., and even more preferably 680 ° C.. When the coiling temperature is too high, because it may pickling of hot-rolled steel sheet is impaired, the coiling temperature is preferably 750 ° C. or less, and more preferably less than 720 ° C.. After winding, it is preferable to cool the temperature range from the winding temperature to (coiling temperature -50 ° C.) at an average cooling rate 15 ° C. / time greater. Thus, the productivity is increased, in the annealing step described below, dissolution of the carbide is accelerated.
[0120]
　The hot-rolled steel sheets and cold-rolled cold-rolled steel sheet according to a conventional method. Before cold rolling may be performed descaling by pickling or the like. To promote recrystallization and uniform metal structure after cold rolling and annealing, in order to further improve the local ductility, the reduction ratio of cold rolling is preferably 40% or more. When rolling reduction is too high, the rolling load is increased, because it may rolling it becomes difficult, the rolling reduction is preferably less than 70%, more preferably less than 60%.
[0121]
　Next, processes for conditions in the manufacturing method and a manufacturing method of the galvannealed steel sheet hot-dip galvanized steel sheet of the present embodiment.
[0122]
　[Step for annealing]
　(heating temperature: Ac 1 point greater)
　in the step of annealing the steel sheet, steel sheet is heated. Heating temperature, in order to generate the austenite during heating, Ac 1 and point greater. Ac 1 The point is the temperature at which austenite begins to generate the metal structure upon heating the steel sheet. To improve the local ductility of galvanized steel sheet and galvannealed steel sheet by homogenizing the metal structure, a steel sheet, Ac 3 it is preferable to anneal by heating to point greater. Ac 3 points, upon heating the steel sheet, the temperature at which ferrite disappears with metal structure.
[0123]
　The temperature range steel sheet, i.e., by heating to the austenite region, carbide dissolves in the metal structure of the hot-dip galvanized steel sheets and galvannealed steel sheet, C amount of retained austenite and residual austenite is increased to.
[0124]
　The upper limit of the heating temperature is not particularly limited, the heating temperature is too high, austenite becomes coarse, so local ductility is impaired, the heating temperature (Ac 3 preferably points +100) ° C. or less, (Ac 3 point +50) ° C. more preferably equal to or less than. Regardless of the heating temperature, holding time at the heating temperature is not particularly limited, for homogenizing the metal structure in the coil, the holding time is preferably 10 seconds or more, the retention time in the suppression of the coarsening of austenite It is preferably within 240 seconds.
[0125]
　First step for cooling]
　(average cooling in the temperature range from the heating temperature to (heating temperature -50 ° C.) Speed: 7 ° C. / sec)
　the steel sheet, Ac 3 when annealed by heating to point than , in the step of performing a first cooling, it is preferable that the average cooling rate 7 ° C. / sec or less in the temperature range from the heating temperature to (heating temperature -50 ° C.). This cooling, in the metal structure of the hot-dip galvanized steel sheets and galvannealed steel sheets, with Mn content in the retained austenite is increased, and generation of polygonal ferrite, uniformly ductility and local ductility is improved.
[0126]
　Average the cooling rate exceeds 7 ° C. / sec in the temperature range from the heating temperature to (heating temperature -50 ° C.), with Mn content in the residual austenite is lowered, polygonal ferrite amount is reduced, uniform ductility and local ductility is impaired. Therefore, the average cooling rate in the temperature range is preferably not more than 7 ° C. / sec. More preferably an average cooling rate of 5 ° C. / sec or less in the above temperature range. Does not specify the lower limit of the average cooling rate is particularly in view of productivity, more 1 ° C. / sec is preferable.
[0127]
　Also, the wider temperature range of cooling below the average cooling rate of 7 ° C. / sec, with Mn content in the residual austenite increases, polygonal ferrite amount increases. Therefore, it is preferable to cool the steel sheet below the average cooling rate of 7 ° C. / sec in a temperature range from the heating temperature to (heating temperature -100 ° C.), a temperature range from the heating temperature to (heating temperature -150 ° C.) it is more preferable to cool the steel sheet below the average cooling rate of 7 ° C. / sec in.
[0128]
　(Average cooling rate in a temperature range of 650 ℃ ~ 500 ℃: less than 2 ° C. / sec or higher 100 ° C. / sec)
　in the step of performing a first cooling, 2 ° C. The average cooling rate in a temperature range of 650 ℃ ~ 500 ℃ / and 100 ° C. / less than a second or more seconds, without isothermal holding in the middle, the steel sheet is cooled to 500 ° C. or less.
[0129]
　Average the cooling rate is less than 2 ° C. / sec in a temperature range of 650 ° C. ~ 500 ° C., polygonal ferrite and pearlite is excessively generated, the yield strength and tensile strength decreases. Therefore, the average cooling rate in the temperature range is set to 2 ° C. / sec or more. Preferably the average cooling rate in the temperature range 3 ° C. / sec or more, more preferably 4 ° C. / sec or more, further preferably 5 ° C. / sec or more.
[0130]
　On the other hand, if the average cooling rate in a temperature range of 650 ° C. ~ 500 ° C. is at 100 ° C. / sec or more, the shape of the steel sheet is impaired, the average cooling rate in the temperature range should be less than 100 ° C. / sec. Preferably the average cooling rate is 50 ° C. / sec or less in the above temperature range, more preferably 30 ° C. / sec or less, more preferably from 20 ° C. / sec.
[0131]
　(Cooling stop temperature 500 ° C. or less)
　the steel sheet was cooled at the required average cooling rate, subsequently, cooled to 500 ° C. or less. While cooling conditions are not particularly limited at 500 ° C. or less of the temperature range, the temperature range of 460 ° C. or higher 500 ° C. or less, it is preferable to keep the steel sheet 4 seconds to 45 seconds. More preferably retain 10 seconds to 35 seconds. This retention, in the metal structure formed in the step of performing a second cooling to be described later, is the amount of C is adjusted moderately in the volume fraction and residual austenite retained austenite improves the uniform ductility and local ductility, further , yield strength is also increased.
[0132]
　[Galvanized step of performing]
　after the step of performing the first cooling, the steel sheet is subjected to galvanizing. Between the step of performing steps a galvanized performing a first cooling for steel sheet may be performed at least one of cooling and heating as required.
[0133]
　The bath temperature and bath composition of the hot-dip galvanizing, well generic and not particularly limited. Coating weight is also not particularly limited, and may be within the normal range. For example, per side 20 g / m of steel sheet 2 ~ 80 g / m 2 adhesion amount is preferable. Plating temperature is not particularly limited, but is usually, 460 ℃ ~ 470 ℃.
[0134]
　[Step perform alloying]
　in the production of galvannealed steel sheet, after the step of performing hot-dip galvanizing, the steel sheet to hot dip plated, for galvanizing is alloyed and heated to the required temperature (alloying treatment temperature), the alloying process.
[0135]
　Alloying treatment is preferably carried out in such conditions Fe concentration in the plating layer is 7 wt% or more. For example, in the alloying treatment temperature is 470 ° C.-560 ° C., and, it is preferable to perform alloying treatment under the condition of alloying treatment time 5 seconds to 60 seconds.
[0136]
　Second step for cooling]
　(average cooling in the temperature range from the plating temperature or alloying temperature to 300 ° C. Speed: 2 ° C. / sec or more)
　(cooling stop temperature: 300 ° C. or less)
　step of performing galvanizing after, or in the cooling after the step of performing alloying treatment, the temperature range from the plating temperature to 300 ° C., or an average cooling rate in a temperature range of up to 300 ° C. from alloying treatment temperature 2 ° C. / sec or higher as it is cooled to 300 ° C. or less.
[0137]
　If the average cooling rate in the step of performing a second cooling is less than 2 ° C. / sec, pearlite is excessively generated, the yield strength and tensile strength decreases, and the amount of retained austenite decreases, uniform ductility is impaired. Therefore, the average cooling rate in the temperature range is set to 2 ° C. / sec or more. Preferably the average cooling rate in the temperature range 3 ° C. / sec or more, more preferably 5 ° C. / sec greater, more preferably from 10 ° C. / sec greater.
[0138]
　The upper limit of the average cooling rate in the step of performing a second cooling is not particularly limited, from the viewpoint of economy, preferably 500 ° C. / sec or less. Further, in order to perform temper rolling below efficiently, the cooling stop temperature is preferably room temperature.
[0139]
　Steel sheet after the step of performing a second cooling comprises a residual austenite of less 35.0% 5.0% or more by volume, and the metal C content in the retained austenite is less than 0.85 wt% to have a tissue is preferred. Thus, in the step of performing a heat treatment described later, is promoted C enriched and Mn enrichment of retained austenite improves the uniform ductility and local ductility, yield strength also increases.
[0140]
　The volume fraction of retained austenite is more preferably not more than 30.0% to 10.0%, more preferably less 25.0% to 15.0%. C content of retained austenite is more preferably less than 0.80 wt%, more preferably less than 0.75 wt%, particularly preferably less than 0.70 wt%. C of a lower limit of the residual austenite is not particularly limited, about 0.50 wt% is a substantial lower limit.
[0141]
　[Tempering step for rolling]
　(elongation: 0.10% or more)
　after the step of performing a second cooling, the steel sheet is subjected to temper rolling of 0.10% or more elongation. From this temper rolling, in the heat treatment step described below, C enrichment and Mn enrichment of the austenite is promoted, in the metal structure of the hot-dip galvanized steel sheets and galvannealed steel sheet, C content and Mn in residual austenite increased amount, improves uniform ductility and local ductility, yield strength also increases.
[0142]
　When the elongation ratio is less than 0.10%, since the effect in the step of performing a subsequent heat treatment is not obtained, the elongation is 0.10% or more. Preferably 0.30% or more elongation, more preferably 0.50% or more. There are no particular restrictions limit the elongation, the elongation is too high, since increases rolling load, the elongation preferably below 2.00%. More preferably less than 1.50% elongation, more preferably less than 1.00%.
[0143]
　Temperature is not particularly limited to perform temper rolling, in order to efficiently impart working strain in austenite temperature at which the temper rolling is cold preferably, tempering start temperature of rolling is preferably room temperature. Further, temper rolling is preferably performed in skin pass rolling.
[0144]
　[Step of performing a heat treatment]
　(heating temperature: 200 ° C. ~ 600 ° C.)
　(retention time: 1 second or more)
　after the step of performing a temper rolling, heating the steel sheet to a temperature range of 200 ° C. ~ 600 ° C., the temperature in holding more than 1 second.
[0145]
　If the heat treatment temperature (maximum heating temperature) is lower than 200 ° C., C enriched and Mn enrichment of the austenite becomes insufficient, uniform ductility is impaired. Further, if the heat treatment temperature (maximum heating temperature) is lower than 200 ° C., hard martensite is left, the yield strength with local ductility is impaired is reduced. Therefore, the heat treatment temperature is set to 200 ° C. or higher. Preferably the heat treatment temperature is 240 ° C. or higher, more preferably 260 ° C. or higher, further preferably 280 ° C. or higher.
[0146]
　On the other hand, when the heat treatment temperature exceeds 600 ° C., and the amount of residual austenite becomes insufficient, uniform ductility is impaired, and tempered martensite is excessively softened, the yield strength and tensile strength decreases. Further, when the heat treatment temperature exceeds 600 ° C., hard fresh martensite is generated, together with local ductility is impaired, yield strength is reduced. Therefore, the heat treatment temperature is set to 600 ° C. or less. Preferably the heat treatment temperature is 550 ° C. or less, more preferably 500 ° C. or less, still more preferably 450 ° C. or less.
[0147]
　When the heat treatment time (retention time at the maximum heating temperature) is less than one second, C enriched and Mn enrichment of the austenite becomes insufficient, uniform ductility is impaired. Further, the heat treatment time is less than one second, hard martensite is remained, with local ductility is impaired, yield strength is reduced. Therefore, the heat treatment time shall not be less than one second. Preferably the heat treatment time 5 seconds, more preferably above 10 seconds, more than more preferably from 15 seconds greater.
[0148]
　On the other hand, when the heat treatment time is too long, the amount of retained austenite is reduced, uniform ductility is impaired, also tempered martensite is excessively softened, the yield strength and tensile strength decreases. Further, the heat treatment time is too long, hard fresh martensite is generated, together with local ductility is impaired, yield strength is reduced. Therefore, the upper limit of the heat treatment time is preferably less 5760 minutes. Heat treatment time and more preferably less 2880 minutes, more preferably not more than 1440 minutes.
[0149]
　Heat treatment time is preferably adjusted appropriately in accordance with the heat treatment temperature. For example, if the heat treatment temperature is 200 ° C. or higher 300 ° C. or less, the heat treatment time is preferably 3 minutes greater, more preferably 10 minutes than, greater more preferably 20 minutes.
[0150]
　If the heat treatment temperature is below 600 ° C. 400 ° C. or higher, the heat treatment time is preferably 20 minutes or less, more preferably less than 6 minutes, more preferably less than 3 minutes. From the viewpoint of productivity, the heat treatment temperature is 400 ° C. greater, and the heat treatment time is preferably 20 minutes or less.
[0151]
　After the step of performing a heat treatment, for flat correct steel sheet may be subjected to temper rolling the material steel plate, or may be subjected to coating with a coating oil or lubricating action on steel plate.
[0152]
　Thickness of the hot-dip galvanized steel sheets and galvannealed steel sheet according to the present embodiment is not limited to a specific thickness, in the manufacturing method of the galvanized steel sheet and the galvannealed steel sheet of the present embodiment, the plate it is suitable for the production of steel plate having a thickness 0.8 mm ~ 2.3 mm.
Example
[0153]
　Next, a description will be given of an embodiment of the present invention, conditions in examples are an example of conditions adopted for confirming the workability and effects of the present invention, the present invention is, in this single condition example the present invention is not limited. The present invention does not depart from the gist of the present invention, as long as they achieve the object of the present invention, it is capable of adopting various conditions.
[0154]
(Example 1)
　using a vacuum melting furnace, and casting the molten steel having the chemical compositions shown in Table 1, were prepared steels A ~ S. Table Ac in 1 1 point and Ac 3 point was determined from the thermal expansion changes upon heating the cold-rolled steel sheet of the steel A ~ S at 2 ° C. / sec. After holding the steel A ~ was heated S in the 1200 ° C. 60 minutes for hot rolling under the conditions shown in Table 2.
[0155]
　Specifically, Ar 3 in points above temperature range, by performing rolling 10 passes to the steel A ~ S, to obtain a hot rolled steel plate having a thickness of 2.5 mm ~ 3.0 mm. After hot rolling, with water spray, hot-rolled steel sheet is cooled to 550 ° C. ~ 680 ° C., charged with cooling end temperature as coiling temperature, the hot-rolled steel sheet to an electric oven which is maintained in this coiling temperature to, and held for 60 minutes. Thereafter, the hot-rolled steel sheet and the furnace cooled to room temperature at a cooling rate of 20 ° C. / time, to simulate the slow cooling after coiling.
[0156]
　The hot-rolled steel sheet after annealing and pickling as a base material for cold rolling, subjected to cold rolling at a reduction ratio from 47 to 52%, cold rolled steel plate having a thickness of 1.2 mm ~ 1.6 mm (steel sheet ) was obtained. Using galvanized simulator, after heating the steel sheet to 650 ° C. at a heating rate of 10 ° C. / sec, at a heating rate of 2 ° C. / sec, heated to the temperature shown in Table 2, 30-90 ByoHitoshinetsu did.
[0157]
　Then, the cooling conditions shown in Table 2 was cooled steel sheet to 460 ° C., the steel sheet is immersed in molten zinc plating bath was maintained at 460 ° C., was galvanized to the base steel sheet. Some steel sheet, after hot-dip galvanizing, and heated to 520 ° C., subjected to alloying treatment.
[0158]
　Plating temperature (meaning plating bath temperature), or, from the alloying temperature, the cooling conditions shown in Table 2 were subjected to secondary cooling (second cooling) to the steel sheet. The secondary cooled steel sheet, was subjected to skin pass rolling elongation 0.50%, heat-treated in the heat treatment conditions shown in Table 2, hot-dip galvanized steel sheet or galvannealed steel sheet (hereinafter, molten zinc the plated steel sheet and galvannealed steel sheet are collectively referred to as "coated steel sheet".) was obtained.
[0159]
　If the stop temperature of the secondary cooling and 100 ° C. performs skin pass rolling without cooling to room temperature after stopping the secondary cooling, subsequently, without cooling to room temperature, the heat treatment in the heat treatment conditions shown in Table 2 went. For some steel sheet were omitted skin pass rolling or heat treatment.
[0160]
　The "plate thickness after rolling" of hot rolling conditions described in Table 2 shows the thickness of the resulting hot rolled steel sheets. The "residence time in the temperature range of 500 ~ 460 ° C." annealing conditions listed in Table 2, in the step of performing the first cooling means the residence time in the temperature range 500 ~ 460 ° C.. Relates "presence of alloying treatment" of annealing conditions listed in Table 2, the symbol "yes" indicates that the alloying treatment is performed after galvanizing, symbol "NO", after galvanizing indicating that the alloying process is not performed. The annealing conditions listed in Table 2, "secondary cooling rate", the case of performing alloying treatment, means an average cooling rate in a temperature range of up to 300 ° C. from alloying temperature, alloying treatment If you did not, it refers to the average cooling rate in a temperature range from the plating temperature to 300 ° C.. In Table 2, notation as "RT" indicates room temperature. Table 2 relates to "the presence or absence of temper rolling", the symbol "Yes" indicates that the temper rolling in the step of performing a temper rolling was carried out, the symbol "NO" is that the temper rolling was not performed show. In column labeled "heat treatment conditions" in Table 2, "-" notation and indicates that the heat treatment was not performed.
[0161]
[Table 1]

[0162]
[Table 2]

[0163]
　From plated steel sheet and the secondary cooling after the end of the steel sheet, the XRD measurement test specimen was sampled from the boundary between the steel sheet and the plated layer to 1/4 depth position of the plate thickness of the steel sheet, the rolling surface of the test piece and chemical polishing. Subjected to X-ray diffraction analysis on this rolling surface, the volume fraction of retained austenite, and was measured C content in the retained austenite.
[0164]
　More specifically, the incident Mo-K [alpha line to the test piece, alpha-phase (200), (211) integrated intensity of the diffraction peak, and, gamma phase (200), (220), (311) diffraction peak the integrated intensity was measured to determine the volume fraction of retained austenite.
[0165]
　Further, the incident Fe-K [alpha line, gamma phase (200), (220), (311) from the position of the diffraction peaks, the austenite lattice constant (a gamma seeking), C content in the retained austenite (C gamma ) and, a gamma (Å) = 3.578 + 0.033 × C gamma was calculated using a relational expression of (mass%).
[0166]
　Further, the SEM observation specimen from plated steel sheet was taken, after polishing the parallel longitudinal section in the rolling direction of the test piece subjected to nital corrosion and repeller corrosion to the longitudinal section, the boundary between the steel sheet and the plated layer It was observed metallographic at 1/4 depth position of the plate thickness of the steel sheet. The image processing, tempered martensite, polygonal ferrite, fresh martensite, and was measured volume fraction of the remaining structure.
[0167]
　The volume ratio of fresh martensite, the sum of the volume fraction of the retained austenite and fresh martensite measured by repeller corrosion was determined by subtracting the volume fraction of retained austenite which is measured by the XRD measurement.
[0168]
　Yield stress (YS), tensile strength (TS), and, uniform elongation (UEL) along the direction perpendicular to the rolling direction from the coated steel sheet were taken JIS5 No. Tensile test specimen, subjected to tensile test to the test piece Te was determined.
[0169]
　The speed of pulling, to 1mm / min until it reaches the yield point, was the and later 10mm / min. Yield ratio (YR) was determined by dividing the YS in the TS. Total elongation (TEL) and local elongation (lel) performs a tensile JIS5 No. tensile test pieces taken along a direction perpendicular tested in the rolling direction, the measured value of total elongation (TEL 0 ) and the measured value of the uniform elongation (UEL) using, based on the above formula (2) and (3) to determine the conversion value corresponding to the case of thickness 1.2 mm.
[0170]
　The value of YR is not less 0.59 or more, the value of TS × UEL is at 10000 MPa ·% or more, and the value of TS × lel is equal 5000 MPa ·% or more were judged to be good characteristics. The value of TS × UEL is at 12000 MPa ·% or more, and the value of TS × lel is equal 6000 MPa ·% or more were judged to be particularly good properties.
[0171]
　Table 3 shows the results of observation of the secondary cooling after the end of the metal structure, observation of metallic structure of the plated steel sheet, and the results of evaluation of the mechanical properties of the plated steel sheet.
[0172]
　In column labeled "secondary cooling after the end of the metal structure" in Table 3, the symbol "-" indicates that that has not been observed metallographic. "Residual austenite in the amount of C (mass%)" in Table 3 in the title column, the symbol "-" indicates that no measured the amount of C in the retained austenite. In Table 3, column labeled "TEl" indicates the total elongation in terms of thickness 1.2mm equivalent, column labeled "UEl" indicates the uniform elongation was labeled "LEl" column indicates the local elongation in terms of thickness 1.2mm equivalent.
[0173]
　In the remarks column in Table 3, "○" is attached sample was present invention example, "×" was given samples are comparative examples. In Table 1 to Table 3, numerical values ​​or symbols underlined means that are outside the scope of the present invention.
[0174]
[table 3]

[0175]
　Invention Examples marked with ○ mark in remarks (Test No. A1 ~ A3, A9, A11, A13, A14, A19, A21, A23, A26, A28 ~ A37, and, A40 ~ A45), both, TS × UEl is 10,000 or more, TS × lel it is 5,000 or more, showed a good uniformity ductility and local ductility. Further, YR showed 0.59 higher than the value. Especially for test No. A11, A21, A26, A28, A30, A31, A34, tempered martensite of 16% or more, and the polygonal ferrite 2.0% ultra-containing, TS × UEL is 12000 or more, and TS × LEl is at least 6,000, showed a particularly good uniform ductility and local ductility.
[0176]
　On the other hand, test results for steel chemical composition or process conditions are out of the range of the present invention (test × mark remarks numbers A4 ~ A8, A10, A12, A15 ~ A18, A20, A22, A24, A25, A27 , A38, and A39) are yield ratio, uniform ductility, and any or all of the local ductility was poor.
[0177]
　Specifically, the steel C having a chemical composition within the scope of the present invention, E, was used N, Test No. A15 was not performed skin pass rolling, A24, and, in A38, TS × UEL and TS × lel it was low. Steel A, test using a C (Test No. A10, and, A20), since which was not subjected to the heat treatment, the values ​​of YR and TS × lel In test No. A10 is low, the test numbers A20 in YR, TS × UEL, and , the value of TS × LEl was low.
[0178]
　Steel A, C, E, studies using N (Test No. A4, A16, A25, A39), since the heat treatment temperature was too low, test No. A4 in YR and TS × value of LEl low, Test No. A16, A25, the A39 YR, TS × UEL, and the value of TS × lel was low. Moreover, steel A, C, test using F (Test No. A5, A17, and A27) in order the heat treatment temperature was too high, YR, TS × UEL, and had lower TS × lel.
[0179]
　Although using steel A having a chemical composition within the scope of the present invention, in Test No. A6 soaking temperature was too low in the annealing process, it was lower TS × UEL.
　In tests using steel A (Test No. A7), since the average cooling rate in a temperature range of 650 ~ 500 ° C. In the first cooling step is too low, had low YR and TS × lel.
　Steel A, test using a C (Test No. A8, and, A18) in, since the average cooling rate in the temperature range of the alloying treatment temperature ~ 300 ° C. (secondary cooling rate) is too low in the second cooling step, the test in No. A8 YR and TS × value of lel is low, the value of TS × UEL and TS × lel in test No. A18 is low.
[0180]
　In Test No. A12 using steel B, since the Si content in the steel was small, YR, the TS × UEL and TS × lel lower. In Test No. A22 with steel D, since Mn content in the steel was small, it was low YR and TS × lel.
[0181]
(Example 2)
　conducted an experiment in the same manner as in Example 1, the steels A ~ S shown in Table 1, were produced plated steel sheet under the conditions shown in Table 4. The results are shown in Table 5. Incidentally, the same as in Example 1 for measurement procedure.
[0182]
　Also, the Mn content in the residual austenite, the EBSP measurement specimen from plated steel sheet was taken, after electrolytic polishing the parallel longitudinal section in the rolling direction, from the boundary between the steel sheet and the plating layer of the plate thickness of the steel sheet 1 / 4 to observe the metal structure in the depth position, by image processing, it was confirmed the distribution of the residual austenite. Subsequently, using a SEM equipped with a FE-EPMA, to observe the metal structure of the same field, it performs EMPA measured for 10 or more residual austenite grains was measured Mn content in the residual austenite. The average value of the obtained amount of Mn determined, the average value, Mn content in the retained austenite ([Mn] gamma was). The Mn content of the steel sheet of the base material [Mn] ave as, [Mn] gamma / [Mn] ave was calculated.
[0183]
　The value of YR is not less 0.59 or more, the value of TS × UEL is at 10000 MPa ·% or more, and the value of TS × lel is equal 5000 MPa ·% or more were judged to be good characteristics. The value of TS × UEL is 12000 MPa ·% or more, and the value of TS × lel is equal 6000 MPa ·% or more were judged to be particularly good properties.
　Further, described in Table 4 and Table 5 are the same as Table 2 and Table 3, respectively. Also, "[Mn] gamma / [Mn] ave in" and the title column, the symbol "-" indicates that no measured the Mn content in the residual austenite.
[0184]
[Table 4]

[0185]
[table 5]

[0186]
　Invention Examples marked with ○ mark in remarks (Test No. B1, B2, B5, B6, B11, B13, B14, B18, B21 ~ B23, B25 ~ B35, and, B38 ~ B42), both, TS × UEl is 10,000 or more, TS × lel it is 5,000 or more, showed a good uniformity ductility and local ductility. Further, YR showed 0.59 higher than the value.
[0187]
　In particular, test numbers B1, B5, B6, B11, B18, B23, B26, B27, B29, B30, B32 ~ B35, B38, and, B39, the heating temperature is Ac 3 are points greater, and the first cooling since the average cooling rate in the temperature range from the heating temperature (heating temperature -50 ° C.) in step was 7 ° C. / sec or less, further polygonal volume ratio of ferrite is less than 2.0%, [Mn] gamma / [Mn ] Ave was 1.10 or more. As a result, the samples of these test numbers, TS × UEL is 12000 or more, and TS × lel is not less 6000 or more, it showed a particularly good uniform ductility and local ductility.
[0188]
　On the other hand, test results for steel chemical composition or process conditions are out of the range of the present invention (test × mark remarks number B3, B4, B7 ~ B10, B12, B15 ~ B17, B19, B20, B24, B36 and B37 is yield ratio, uniform ductility, and any or all of the local ductility was poor.
[0189]
　Specifically, the steel C having a chemical composition within the scope of the present invention, E, was used N, Test No. B7, B19 was not performed skin pass rolling, and, in B36, C content in the retained austenite and [Mn] gamma / [Mn] ave is low, had low TS × UEL and TS × lel. For Steel C of the test number using B12 is not subjected to heat treatment, tempered martensite volume fraction, C content in the retained austenite and [Mn] gamma / [Mn] ave is low, YR, TS × UEL, and, TS × LEl was low.
[0190]
　Steel C, E, was used N, Test No. B8 heat treatment temperature was too low, B20 having a chemical composition within the scope of the present invention, and, in B37, tempered martensite volume fraction, C content in the retained austenite and [Mn] gamma / [Mn] ave is low, YR, TS × UEL, and had lower TS × lel. Steel C, test using F (Test No. B9, and, B24) in order the heat treatment temperature was too high, low C content of retained austenite volume fraction and residual austenite, YR, TS × UEL, and, TS × LEl was low.
[0191]
　Although using steel C having the chemical compositions within the scope of the present invention, in Test No. B16 soaking temperature was too low in the annealing process, a low residual austenite volume fraction and tempered martensite volume fraction, TS × UEL is low It was.
　Steel A, test using a C (Test No. B3, and, B15) in, since the average cooling rate in a temperature range of 650 ~ 500 ° C. In the first cooling step is too low, the test No. B3, the residual austenite volume fraction, tempered martensite volume fraction and [Mn] gamma / [Mn] ave is low, had low YR and TS × lel. In Test No. B15, residual austenite volume fraction and [Mn] gamma / [Mn] ave is low, YR, TS × UEL, and had lower TS × lel.
　Although using steel C having a chemical composition within the scope of the present invention, the average in the cooling rate (secondary cooling rate) of test numbers were too low B10 in the temperature range of the alloying treatment temperature ~ 300 ° C. In the second cooling step a low C content of retained austenite volume fraction and residual austenite was less TS × UEL and TS × lel.
[0192]
　In Test Number B4 was using steel B, since the Si content in the steel was small, residual austenite volume fraction and residual austenite in the amount of C is low, YR, the TS × UEL and TS × lel lower. In Test No. B17 with steel D, since Mn content in the steel was small, residual austenite volume fraction and [Mn] gamma / [Mn] ave is low, it had low YR and TS × lel.
Industrial Applicability
[0193]
　As described above, according to the present invention, excellent uniformity ductility and local ductility, further, the yield strength and tensile strength is high, and hot-dip galvanized steel sheet and a galvannealed steel sheet excellent in formability and shock absorption it can be manufactured provided. Hot-dip galvanized steel sheet and a galvannealed steel sheet produced by the present invention are the optimum to automotive body structural components such as members or pillars, the present invention has high industrial applicability .

The scope of the claims
[Requested item 1]
　Chemical composition, in
mass%,
C:
0.03% ~ 0.70%, Si: 0.25% ~ 2.50%, Mn:
1.00% ~ 5.00%, P: 0.100%
less, S: 0.010 Pasento
below, Sol. Al: 0.001%
~ 2.500%, N: 0.020% or less
Ti:
0% ~ 0.300%,
Nb: 0% ~ 0.300%, V: 0% ~
0.300%, Cr :
0%
~ 2.000%,
Mo: 0% ~ 2.000%, B: 0% ~
0.0200%, Cu: 0% ~ 2.000%, Ni: 0% ~
2.000%, Ca :
0% ~ 0.0100%,
Mg: 0% ~ 0.0100%, REM: 0% ~ 0.1000%, and
Bi: 0% ~ 0.0500%,
wherein the balance being iron and impurities ,
　metal structure, 5.0 vol% of residual austenite, comprises 5.0 volume% of tempered martensite,
　C amount of said residual austenite is characterized in that at least 0.85 wt% plating steel sheet.
[Requested item 2]
　Wherein the metal structure further comprises 2.0 volume% of polygonal ferrite,
　plated steel sheet according to claim 1, Mn content of said residual austenite is characterized by satisfying the following formula (1).
[Mn] gamma / [Mn] ave ≧ 1.10 · · ·
(1) [Mn] gamma : Mn amount of retained austenite (mass%)
[Mn] ave : Mn amount of the chemical composition of the steel sheet (wt%)
[Requested item 3]
　The chemical composition further contains, by
mass%,
Ti: 0.001% to 0.300%, Nb: 0.001% to 0.300%,
and, V: made of 0.001% to 0.300% plated steel sheet according to claim 1 or 2, characterized in that it contains one or more kinds selected from the group.
[Requested item 4]
　The chemical composition further contains, by
mass%,
Cr: 0.001% - 2.000%, Mo: 0.001% - 2.000%,
and, B: consisting of 0.0001% - 0.0200% plated steel sheet according to any one of claims 1 to 3, characterized in that it contains one or more kinds selected from the group.
[Requested item 5]
　The chemical composition further contains, by
mass%, Cu: 0.001% to 2.000%,
and, Ni: containing one or two elements selected from the group consisting of 0.001% to 2.000% plated steel sheet according to any one of claims 1 to 4, wherein the.
[Requested item 6]
　The chemical composition further contains, by
mass%,
Ca: 0.0001% - 0.0100%, Mg: 0.0001% - 0.0100%, and
REM: the group consisting of 0.0001% - 0.1000% plated steel sheet according to any one of claims 1 to 5, characterized in that it contains one or more selected from.
[Requested item 7]
　The chemical composition further contains, by
mass%, Bi: plated steel sheet according to any one of claims 1 to 6, characterized in that it contains between 0.0001% 0.0500%.
[Requested item 8]
　The plated steel sheet, plated steel sheet according to any one of claims 1 to 7, characterized in that the galvanized steel sheet comprising a galvanized layer.
[Requested item 9]
　The plated steel sheet, plated steel sheet according to any one of claims 1 to 7, wherein the galvanized layer is a galvannealed steel sheet which has been alloyed.
[Requested item 10]
　Chemical composition, in
mass%,
C:
0.03% ~ 0.70%, Si: 0.25% ~ 2.50%, Mn:
1.00% ~ 5.00%, P: 0.100%
less, S: 0.010 Pasento
below, Sol. Al: 0.001%
~ 2.500%, N: 0.020% or less
Ti:
0% ~ 0.300%,
Nb: 0% ~ 0.300%, V: 0% ~
0.300%, Cr :
0%
~ 2.000%,
Mo: 0% ~ 2.000%, B: 0% ~
0.0200%, Cu: 0% ~ 2.000%, Ni: 0% ~
2.000%, Ca :
0% ~ 0.0100%,
Mg: 0% ~ 0.0100%, REM: 0% ~ 0.1000%, and
Bi: 0% ~ 0.0500%,
wherein the balance being iron and impurities the steel sheet, Ac 1 and performing annealing by heating to point greater than
　after the step of performing the annealing, the average cooling rate in a temperature range of 650 ° C. ~ 500 ° C. as less than 2 ° C. / sec or higher 100 ° C. / sec , cooled to 500 ° C. or less, and performing a first cooling,
　after the first step of performing cooling, the first A step of performing hot-dip galvanizing to the cooling in the step of performing a cooling steel sheet,
　after the step of subjecting the hot-dip galvanizing, the steel sheet to the molten zinc plated, plating in the step of subjecting the hot-dip galvanized the average cooling rate in the temperature range from temperature to 300 ° C. as above 2 ° C. / sec, cooled to 300 ° C. or less, and performing a second cooling,
　after the step of performing the second cooling, the second of the cooled steel sheet in the process for cooling, and performing temper rolling or elongation 0.10%,
　after the step of performing the temper rolling, the steel sheet of the temper rolling is performed was heated to 200 ° C. ~ 600 ° C. temperature range of, and performing heat treatment for holding at least one second from the temperature,
　method for producing a galvanized steel sheet, characterized in that it comprises a.
[Requested item 11]
　Wherein in the step of performing annealing, the steel sheet of the Ac 3 perform annealing by heating to point greater than
　after the step of performing the annealing, the annealed steel sheet, the heating temperature (heating temperature -50 ° C.) method for manufacturing a galvanized steel sheet according to claim 10, characterized in that cooling the average cooling rate of less 7 ° C. / sec in the temperature range up.
[Requested item 12]
　Chemical composition, in
mass%,
C:
0.03% ~ 0.70%, Si: 0.25% ~ 2.50%, Mn:
1.00% ~ 5.00%, P: 0.100%
less, S: 0.010 Pasento
below, Sol. Al: 0.001%
~ 2.500%, N: 0.020% or less
Ti:
0% ~ 0.300%,
Nb: 0% ~ 0.300%, V: 0% ~
0.300%, Cr :
0%
~ 2.000%,
Mo: 0% ~ 2.000%, B: 0% ~
0.0200%, Cu: 0% ~ 2.000%, Ni: 0% ~
2.000%, Ca :
0% ~ 0.0100%,
Mg: 0% ~ 0.0100%, REM: 0% ~ 0.1000%, and
Bi: 0% ~ 0.0500%,
wherein the balance being iron and impurities the steel sheet, Ac 1 and performing annealing by heating to point greater than
　after the step of performing the annealing, the average cooling rate in a temperature range of 650 ° C. ~ 500 ° C. as less than 2 ° C. / sec or higher 100 ° C. / sec , cooled to 500 ° C. or less, and performing a first cooling,
　after the first step of performing cooling, the first Step of performing hot-dip galvanizing the cooled steel sheet in the process for cooling,
　after the step of subjecting the hot-dip galvanizing, the steel sheet to the molten zinc plated performs alloying with alloying treatment temperature a step,
　after the step of performing the alloying treatment, the steel sheet of the alloying treatment is performed, the average cooling rate in a temperature range of up to 300 ° C. from the alloying treatment temperature of more than 2 ° C. / sec, 300 ℃ cooled to below, and performing a second cooling,
　after said second step for cooling, to the second steel sheet which has been cooled in the process for cooling, elongation 0.10% or more and performing temper rolling,
　after the step of performing the temper rolling, heating the steel sheet to the temper rolling is performed in the temperature range of 200 ° C. ~ 600 ° C., held for more than one second at that temperature heat treatment a step of performing
　, characterized in that it comprises a Method for producing a gold galvannealed steel sheet.
[Requested item 13]
　Wherein in the step of performing annealing, the steel sheet of the Ac 3 perform annealing by heating to point greater than
　after the step of performing the annealing, the annealed steel sheet, the heating temperature (heating temperature -50 ° C.) method for manufacturing a galvannealed steel sheet according to claim 12, characterized in that cooling the average cooling rate of less 7 ° C. / sec in the temperature range up.