JPH06322479A - Good workability hot dip plated high strength steel sheet excellent in fatigue property and local deformability and its production - Google Patents

Abstract

PURPOSE:To obtain a good workability hot dip plated high strength steel sheet excellent in fatigue durability and local deformability by forming a steel sheet having a specified compsn. constituted of C, Mn, Si, V, Ti, Nb and Fe into a specified microstructure. CONSTITUTION:The hot dip plated high strength steel sheet excellent in characteristics has a compsn. contg., by weight, <=0.06% C, 0.2 to 3.0% Mn and <=1.5% Si, furthermore contg. total 0.005 to 0.3% of one or more kinds of alloy elements among <=0.2% V, <=0.2% Ti and <=0.1% Nb and moreover contg., at need, total <=4.0% of one or more kinds of alloy elements among <=2.0% Cu, <=1.0% Mo and <=1.5% Cr or one or two kinds of <=0.01% Ca and <=0.1% rare elements, and the balance Fe with inevitable impurities, and the main phase of the microstructure of the steel sheet finally obtd. is constituted of ferrite or bainite, and, as to iron carbides in grain boundaries, the occupying volume rate is regulated to <=0.1% and the maximum grain size is regulated to <=1mum.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanized high-strength steel sheet which is used for a structure such as an automobile and can contribute to weight reduction of the structure, energy saving, and improvement of safety, and a manufacturing method thereof.

[0002]

2. Description of the Related Art Strengthening of steel is achieved by solid solution strengthening of a ferrite matrix by alloying elements such as Si and Mn, N
Precipitation strengthening of ferrite matrix by fine precipitates of b, Ti, V, etc., structure strengthening using low temperature transformation products such as pearlite, bainite, martensite, fine grain strengthening by refining ferrite grain size, cold working There are processing enhancements, etc., and products that make the most of each characteristic are supplied to the market.

Applying high-strength steel plates to structures such as automobiles,
In order to reduce weight, save energy, improve safety, etc., in addition to increasing the strength of the steel sheet, (1) improvement of various processing performances of the steel sheet (for example, deep drawing formability, overhang formability, burring formability, etc.), (2) Maintaining weldability and heat softening resistance,
Improvement, (3) Durability (for example, fatigue durability and corrosion durability)
Are required to be maintained and improved, and combinations of different properties are required depending on the site of use. For example, when a high-strength steel plate is applied to a road wheel disc for an automobile, a steel plate having high press formability (especially ductility) and excellent fatigue durability is required.

To meet such demands, a ferrite / martensite dual-phase steel sheet (so-called Dual) is used.
Phase: DP steel plate has been proposed (for example, Japanese Patent Publication No. Sho 56-18051 and Japanese Patent Publication No. 59-45735).
Issue). This DP steel sheet is superior in fatigue durability to high strength steel sheets strengthened by various other strengthening mechanisms,
It contributes to making the road wheel disc thinner (lighter) and improving durability. Further, in regions where complicated forming is required, improvement in uniform deformability is required, and for this reason, a high ductility and high strength steel sheet containing retained austenite at room temperature (Japanese Patent Laid-Open No. 63-4017) is proposed. . Further, as a steel sheet having improved local deformability represented by hole expandability which is a problem in undercarriage parts of automobiles, a Si-added high ductility and high strength steel sheet (Japanese Patent Laid-Open No. 61-19733 etc.) is proposed. Welding (spot welding, butt welding, arc welding, etc.), which is important when applied to structures such as automobiles,
As a steel sheet having both heat-resistant softening characteristics and workability, a precipitation strengthening type low alloy high strength steel sheet (HSLA steel sheet) is widely used.

[0005]

However, S which is excellent in the local deformability represented by the hole expanding process as described above.
i addition type high ductility high strength steel plate and precipitation strengthened high strength steel plate excellent in weldability, heat resistance softening property and hole expanding workability are DP
It is inferior in fatigue durability to steel and is not used in parts where fatigue durability is required. On the other hand, the DP steel sheet, which is excellent in fatigue durability, is significantly inferior in hole expanding workability to other high strength steel sheets, and therefore its use site is limited.

[0006] As described above, in a portion positioned as an important safety component in a structure such as an automobile, it is generally possible to improve both fatigue durability and local deformability represented by hole expandability. Despite the demand, at present, a steel sheet satisfying both of them and a manufacturing method thereof have not been presented yet. Therefore, an object of the present invention is to provide a hot-dip galvanized high-strength steel sheet that satisfies both fatigue durability and hole expandability, and a method for producing the same.

[0007]

Means for Solving the Problems The inventors of the present invention have fundamentally investigated the controlling factors of fatigue strength and local deformability through various experimental investigations. As a result, the main phase structure is ferrite or bainite and It was found that a hot-dip galvanized steel sheet in which the amount and size of iron carbide present is controlled can achieve both high fatigue strength and favorable hole expanding workability (local deformability), which have been difficult in the past.

That is, the gist of the present invention is as follows. (1) C: 0.06% by weight or less, Mn: 0.2 to 3.
0% by weight, Si: 1.5% by weight or less, V: 0.2% by weight or less, Ti: 0.2% by weight or less, N
b: 0.005 to 0.3% by weight of one or more alloying elements in total in the range of 0.1% by weight or less, and the balance Fe and inevitable impurities, and finally The main phase of the microstructure of the obtained steel sheet is ferrite or bainite, the occupation ratio of iron carbide in the grain boundary is 0.1% or less, and the maximum particle diameter of this iron carbide is 1
Good workability hot-dip galvanized high-strength steel sheet excellent in fatigue characteristics and local deformability, which is characterized by being less than μm.

(2) Cu: 2.0 wt% or less, Mo:
1% or more of these alloying elements in a total amount of not more than 1.0% by weight and Cr: not more than 1.5% by weight, in total, not more than 4.0% by weight. Good workability hot-dip galvanized high strength steel sheet with excellent fatigue properties and local deformability. (3) Ca: 0.01% by weight or less or rare earth element (REM): 0.1% by weight or less
A high workability hot-dip galvanized steel sheet excellent in fatigue characteristics and local deformability according to the above item 1 or 2, characterized by containing two or more kinds.

(4) The fatigue characteristics and local deformability according to any one of the above items 1, 2 and 3 are excellent in that the total area ratio of martensite and pearlite in the microstructure is less than 4%. Good workability Hot-dip galvanized high strength steel sheet. (5) Good fatigue resistance and local deformability as set forth in any one of the above items 1, 2, 3 and 4, characterized in that λ × σ ^0.8 ≧ 50 and σw / σ ≧ 0.6 are simultaneously satisfied. Workability Hot-dip galvanized high strength steel sheet.

(6) When hot-dip coating a steel sheet, the maximum heating temperature (called ST (° C.)) in the hot-dip plating process is the winding temperature during hot rolling (called CT (° C.)) and V.
Formula (A) defined by the weight ratio V / C of C and C, or CT and the weight ratio of Ti + Nb and C (Ti +
Nb) / C satisfying at least one of the ranges of the formula (B),
3. A method for producing a good workability hot-dip galvanized high-strength steel sheet having excellent fatigue properties and local deformability according to any one of 3, 4, and 5.

[0012]

[Equation 3]

[0013]

[Equation 4]

[0014]

The fatigue strength of a high-strength steel sheet is generally said to increase with the strength of the steel sheet, and has a magnitude about 1/2 of the breaking strength of the steel sheet. However, it has been reported so far that this fatigue strength changes depending on the microstructure of the steel sheet (for example, "Materials" Vol. 38, No. 429).
15 to 21), it is important to optimize the microstructure of the steel sheet. Generally, when the strength of the steel sheet exceeds 50 kgf / mm ² , the ratio of the fatigue strength / steel strength of the steel sheet becomes small, and the effect of increasing the strength on the fatigue strength increase becomes small. The present inventors have added a low alloy high strength steel plate (H
As a result of a detailed investigation of the occurrence of fatigue cracks under repeated stress using SLA steel), fatigue cracks are generated due to lumpy or plate-shaped iron carbide existing at grain boundaries, and these hard grain boundary iron carbides are It was found that they did not contribute to the prevention of crack propagation, and that they hinder the increase in fatigue strength commensurate with the increase in strength of the steel sheet. FIG. 1 shows the experimental results of the above findings. Therefore, reducing coarse grain boundary iron carbide is effective for improving the fatigue strength of the steel sheet as well as optimizing the microstructure of the steel sheet. Further, in order to increase the fatigue strength of the steel sheet, it is more important to lower the carbide space factor at the grain boundary than to lower the iron carbide area ratio (fv) in the steel sheet. The fatigue strength of a steel sheet depends largely on the strength and grain size of the ferrite matrix. Strengthening effectively works to improve the fatigue strength of steel sheets.

Regarding the local deformability of the steel sheet, the hole expanding workability when the matrix of the steel sheet is ferrite or bainite varies depending on the amount and size of iron carbide existing at the grain boundaries. The experimental results are shown in FIG. It was found that the steel sheet in which the grain boundary iron carbide was controlled by selecting the appropriate chemical composition of steel sheet and the manufacturing condition had extremely good hole expanding workability.

As described above, since the local deformability represented by the fatigue strength and the hole expanding workability of the steel sheet is changed by the iron carbide existing in the grain boundary, it is difficult to control the above-mentioned 2 by the control. It has been found that it is possible to combine the two characteristics. The components of the present invention will be described in detail below. Grain boundary iron carbide: When the amount of solute carbon in the steel sheet exceeds the amount of equilibrium solute carbon in ferrite at the final stage of the hot rolling process, excess carbon is when the final microstructure has ferrite as the main phase. In the ferrite grain boundaries or in the grains, and when bainite is the main phase, bainite packets (Sh
During eaf), it precipitates as iron carbide at the interface between bainite and ferrite or in the packet. In addition to this, for example, in the case where a steel strip is manufactured by hot rolling, when the winding process in the final step is performed on the low temperature side of the bainite transformation temperature region (350 ° C. or lower and martensite transformation start temperature Ms or higher), bainite There is a case where iron carbide is included in the ferrite grains. Further, in the case of steel manufactured by heat treatment, iron carbide may be contained in the above grains, packets, and grain boundaries. When the final microstructure of the steel sheet has ferrite or bainite as the main phase, it depends on the amount and size of iron carbide present at grain boundaries (between bainite packets, the interface between bainite and ferrite, and ferrite grain boundaries). The local deformability of the steel plate changes.

When the hole expanding workability, which is a representative of local deformability as a hot rolled steel sheet by thermo-mechanical processing of steels of various components, is investigated, the strength σ (kgf / mm ² ) of the steel sheet and the hole expanding workability (conical punch There is a negative correlation between the final hole diameter and the initial hole diameter ratio λ) obtained in the hole expansion test outside the burr used, and when σ is increased, λ generally decreases. At this time, an ordinary high-strength steel sheet (precipitation-strengthened high-strength steel sheet, etc.) has a value of λ × σ ^0.8 , which represents a balance between strength and hole expanding workability, at most less than 50. When the grain boundary iron carbide of these high-strength steel sheets is investigated, the grain boundary occupancy rate of the iron carbide generally exceeds 0.1%, and the connection of these iron carbide particles at the grain boundaries is remarkable. In order to obtain a good balance between hole expanding workability and steel plate strength, λ
In order to set the value of × σ ^0.8 to 50 or more, it is necessary to limit the iron carbide occupancy rate of grain boundaries to 0.1% or less as shown in FIG. Therefore, in the present invention, the occupation rate of the grain boundary by the iron carbide is specified to be 0.1% or less.

Even if the iron carbide occupancy rate at the grain boundary is 0.1% or less, if the connection of the iron carbide is great, λ × σ ^0.8
It cannot be a steel sheet with good hole expanding workability that satisfies ≧ 50. When the maximum particle size of iron carbide existing at the grain boundary (measurement is performed as the maximum occupied length of iron carbide on the grain boundary appearing on the two-dimensional cut surface) exceeds 1 μm, the value of λ × σ ^0.8 is 5
It does not exceed 0. Therefore, in order to obtain good hole expandability, in the present invention, the iron carbide occupancy rate of grain boundaries is specified to be 0.1% or less, and at the same time, the maximum particle diameter in these iron carbides is 1%.
μm or less.

The fatigue strength σw is defined as the lower limit value of the stress that does not break in the fatigue test under the plane bending cyclic stress load of 10 ⁶ cycles, and the superiority or inferiority of the characteristics is judged by the ratio with the strength σ of the steel sheet. The fatigue strength σw of the steel sheet tends to increase with the strength σ of the steel sheet, but the ratio σw / σ is generally 0.5.
It changes in the range of about 0.6. When the main phase of the final structure of the steel sheet is ferrite or bainite and the iron carbide occupancy rate at the grain boundaries exceeds 0.1%, σw / σ is the same as for ordinary high strength steel sheets (precipitation strengthened high strength steel sheets, etc.) Is from 0.5
A value between 0.6 is taken and sufficient fatigue strength cannot be obtained.
On the other hand, when the iron carbide occupancy rate of the grain boundaries is 0.1% or less and the maximum particle size of these iron carbides does not exceed 1 μm, σw /
The value of σ is 0.6 or more, and DP is considered to show the most stable and high fatigue strength of steel sheets currently used.
It is equal to or higher than the fatigue strength level of steel.
Therefore, in order to increase the fatigue strength of the steel sheet and set the value of σw / σ to be 0.6 or more, the present invention defines the iron carbide occupancy rate at the grain boundary to be 0.1% or less, and the maximum value of those iron carbides. The diameter (maximum length) is defined as 1 μm or less.

From the above, as a steel sheet having excellent hole expanding workability (λ × σ ^0.8 ≧ 50), which is a representative of local deformability, and at the same time having high fatigue strength (σw / σ ≧ 0.6), the main phase Is a ferrite or bainite, and the range of the present invention is a steel sheet in which the iron carbide occupancy of grain boundaries is 0.1% or less and the maximum particle size of these iron carbides is 1 μm or less. Further, in order to further increase the fatigue strength of the steel sheet and satisfy σw / σ ≧ 0.65, it is desirable that the maximum particle size of the iron carbide existing at the grain boundaries be specified to 0.4 μm or less.

C: C serves as a source of iron carbide at grain boundaries, and therefore it is necessary to reduce it as much as possible. When the content of C is too large, the amount of V, Ti, and Nb added for adjusting the amount and size of the grain boundary iron carbide to be within the range of the present invention is increased more than necessary, which is an economical demerit. Not only that, but the ductility is remarkably reduced. Therefore, the upper limit is 0.06% by weight.

V, Ti, Nb: V, Ti, and Nb are effective elements for increasing the strength of the steel sheet by precipitation strengthening, and at the same time, fix C atoms in the steel sheet in the form of alloy carbide to improve workability and fatigue. It has the function of reducing the amount and size of iron carbide at grain boundaries, which is harmful to the properties. Further, these elements prevent coarsening of austenite grains in a region austenitized by various kinds of welding, and suppress softening of a weld heat affected zone. In addition, even in the region where austenite does not occur, the presence of carbonitrides of these elements and solid solution atoms remarkably suppresses the recovery of dislocations, which is effective in suppressing the softening of the weld heat affected zone. For this purpose, 0.2% by weight for V, 0.2% by weight for Ti and 0.
Since the effect is saturated even if added in excess of 1% by weight, these values were made the upper limits of the amounts of Nb, Ti and V added.

V can be increased in hardness in the vicinity of the welded portion by re-precipitating during the rapid cooling after being melted by the heat input of welding. However, a large amount of addition causes an unnecessary increase in hardness in the vicinity of the welded part and promotes embrittlement, so the maximum addition amount is specified as 0.2% by weight. The total amount of one or more of these alloy elements added is 0.005.
If it is less than 10% by weight, the strength is not increased and the amount of iron carbide in the grain boundary and the size are not significantly reduced, so the lower limit of the total amount is set to 0.005% by weight. Further, when the total amount of these elements added exceeds 0.3% by weight, the effects of these elements are saturated,
The total amount is capped at 0.3 because it brings economic disadvantages.
It was set to% by weight.

Mn, Si, Cu, Mo, Cr, Ni: These alloy elements can increase the strength of the steel sheet by forming a solid solution in the ferrite matrix. M
n enhances the hardenability of the steel sheet with solid solution strengthening, but 3.0
If the content exceeds 5% by weight, the performance of the steel sheet deteriorates due to excessive hardening of the welded portion, etc., so the upper limit is made 3.0% by weight. Further, in order to increase the strength of the steel sheet with the addition amount of Mn less than 0.2% by weight, it is necessary to add other alloying elements more than necessary, which causes an economic demerit. Therefore, the lower limit of the amount of Mn added is set to 0.2% by weight.

Si has a function of refining the solid solution of the ferrite matrix and fine-graining the iron carbide at the grain boundaries. However, if the addition amount exceeds 1.5% by weight, the plating will be performed even if the conditions of the hot dip plating process are optimized. Since a defect occurs, the upper limit is 1.5
It was set to% by weight. Cu can significantly increase the strength of the steel sheet by solid solution or precipitation strengthening. However, the effect is saturated when it exceeds 2.0% by weight, so the upper limit is 2.
It was set to 0% by weight. Further, when Cu is added, Ni may be added in order to keep the surface properties of the slab in good condition.

Mo has the same function as Mn, and at the same time,
It serves to fix C atoms in the steel sheet in the form of carbides and reduce the amount of intergranular iron carbides. It is also effective in preventing softening of the weld heat affected zone. However, the addition of a large amount of Mo causes an increase in production cost and further increases the hardenability of the steel sheet more than necessary. Therefore, the upper limit of the addition amount is set to 1.0% by weight.

Cr has the same function as Mo, but its effect is saturated when it exceeds 1.5% by weight, so the upper limit is 1.
It was set to 5% by weight. When one or more of Cu, Mo and Cr are added, if the total amount exceeds 4.0% by weight, the strength of the steel sheet becomes unnecessarily high and the workability of the steel sheet is significantly deteriorated. The upper limit of the total amount added was set to 4.0% by weight.

P, which is generally used as a strengthening element other than these, segregates at the grain boundaries and deteriorates the fatigue strength of the steel sheet, so its content is preferably limited to 0.01% by weight or less. Ca, rare earth element (REM): Ca or rare earth element (REM) has the effect of rendering these inclusions harmless and enhancing formability (particularly local deformability) due to the morphology control effect of sulfide. However, since the addition of a large amount of these elements adversely reduces the cleanliness of the steel sheet, it is specified that Ca is 0.01% by weight or less and rare earth element (REM) is 0.1% by weight or less. Add one or two kinds. Also, in order to reduce such harmful sulfides, S
It is desirable to limit the content of to 0.01 wt% or less.

Hard phase: The local deformability of the steel sheet depends on the uniformity of the structure of the steel sheet, but it is premised on adjusting the iron carbide at grain boundaries to a certain amount or less, which is the object of the present invention. In the case of a high-strength steel sheet, it is necessary to strengthen the ferrite matrix itself by solid solution and precipitation as described above, and as a result, it is recognized that even if ferrite and bainite are mixed, there is no great difference in strength between the two phases. At this time, the microstructure of the steel sheet needs to have ferrite or bainite as the main phase, but the characteristic deterioration is small even when ferrite and bainite are mixed. On the other hand, since the production of martensite and pearlite causes deterioration of local deformability and fatigue strength, the area ratio of these phases needs to be 4% or less, and is preferably adjusted to 1% or less.

Manufacturing conditions in the hot dipping process: C is 0.06
Main additive element when the final product is manufactured through hot-rolling or cold-rolling steel containing one or more of V, Ti, and Nb added in the range of not more than wt% When V is V, as shown in FIG. 3, the maximum heating temperature ST in the hot dip plating step is near 750 ° C., and there is a region showing good hole expanding workability. Also, it has been found that when the main additive is either Ti or Nb, the lower the maximum heating temperature in the hot dip plating step, the better. However, these relationships are related to the weight ratio of the amount of carbide forming elements and C in the steel sheet (either V / C or (Ti + Nb) / C).
Not only depends on the final winding temperature CT of the hot rolling process.
As a result of arranging these relationships, the final steel sheet is within the scope of the present invention only when the maximum heating temperature ST in the hot dip plating step satisfies at least one of the following (A) and (B).

[0031]

[Equation 5]

[0032]

[Equation 6]

[0033]

EXAMPLE Steels having the chemical composition shown in Table 1 were heated from 1000 ° C. to 1
Heating to a range of 300 ° C, Ar ₃ transformation temperature of each steel -30
After hot-rolling is completed at a temperature of ℃ or more, then the hot-rolled steel sheet with a thickness of 2 mm, which is cooled to a predetermined temperature at various cooling rates and wound, is plated in the hot dip plating process, and then subjected to JIS No. 5 tensile test and hole test. Spreading test (punching clearance 15%, as-punched outside burr, using 60-degree conical punch), plane bending fatigue test (double-sided abrasive, double swing with stress ratio R = -1, 25H
The properties were investigated according to z). Table 2 shows a list of characteristic values. In Table 2, CT is the winding temperature (° C), ST is the maximum heating temperature (° C) in the hot dipping process, V ₂ is the total area ratio of martensite and pearlite (%), and f _v is the area ratio of iron carbide. (%), F _s is the occupancy rate of iron carbide in the grain boundary, d is the maximum grain size (μm) of the grain boundary iron carbide, TS is the breaking strength of the steel sheet (kgf / mm ² ), and X is the hole expanding workability. The index is X = λ × σ ^0.8 (λ is the hole expansion ratio = final hole diameter / initial hole diameter), and Y is the index representing the fatigue strength Y = σw / σ (σw is the fatigue strength after repeated 10 ⁶ times kgf / Mm ² , σ is the strength TS of the steel sheet.

From Table 2, the steel sheet of the present invention has very good hole expanding workability such that X ≧ 50, and Y ≧ 0.
It can be seen that it has a high fatigue strength of 60.

[0035]

[Table 1]

[0036]

[Table 2]

[0037]

[Table 3]

* Formula A MIN and Formula A MAX are the upper and lower limit temperatures of ST shown by Formula A * Formula B MAX is the upper limit temperature of ST shown by Formula B * * is the addition of the target component * Formula A, B In the formula column, ○ is within the condition range, × is outside the condition range, * is the addition of the target component * In the d (maximum particle size of grain boundary iron carbide) column? Is not measurable or there is no applicable particle. * 1 in the table is V / C, * 2 is (Ti + Nb) / C * The underline is outside the scope of the present invention.

[0039]

[Table 4]

* A-type MIN and A-type MAX are the upper and lower limit temperatures of ST shown by A-type * B-type MAX is the upper limit temperature of ST shown by B-type * * is the addition of the target component * A-type and B-type In the formula column, ○ is within the condition range, × is outside the condition range, * is the addition of the target component * In the d (maximum particle size of grain boundary iron carbide) column? Is not measurable or there is no applicable particle. * 1 in the table is V / C, * 2 is (Ti + Nb) / C * The underline is outside the scope of the present invention.

[0041]

INDUSTRIAL APPLICABILITY As described above, the present invention is a 50 to 100 kgf / mm ² hot-dip galvanized high-strength steel sheet excellent in local deformability represented by fatigue strength and hole expandability in structures such as automobiles. And the manufacturing method thereof, by using these steel plates, weight reduction of structures such as automobiles,
It can greatly contribute to energy saving and improvement of safety.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between a fatigue strength of a hot-dip plated steel sheet, an occupation rate of iron carbide in a ferrite grain boundary, and a maximum particle diameter of these iron carbides.

FIG. 2 is a diagram showing a relationship between hole expanding workability of a hot-dip plated steel sheet, an occupation rate of iron carbide in a ferrite grain boundary, and a maximum particle diameter of these iron carbides.

FIG. 3 is a diagram showing the effects of the maximum heating temperature and V / C in the hot dip plating step on the hole expanding workability of the hot dip plated steel sheet containing V.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C23C 2/06

Claims (6)

[Claims] 1. C: 0.06 wt% or less, Mn: 0.2
-3.0 wt%, Si: 1.5 wt% or less, V: 0.2 wt% or less, Ti: 0.2 wt% or less,
Nb: 0.005 to 0.3% by weight in total of one or more alloying elements among these in a range of 0.1% by weight or less, and the balance Fe and unavoidable impurities. The main phase of the microstructure of the obtained steel sheet is ferrite or bainite, the occupation ratio of iron carbide in the grain boundaries is 0.1% or less, and the maximum particle diameter of the iron carbide is 1 μm or less. Good workability hot-dip galvanized high strength steel sheet with excellent fatigue properties and local deformability. 2. Cu: 2.0% by weight or less, Mo: 1.0
The fatigue property according to claim 1, wherein one or more alloying elements among them are contained in a total amount of 4.0% by weight or less in the range of less than 1.5% by weight and Cr: 1.5% by weight or less. Good workability hot-dip galvanized steel sheet with excellent local deformability. 3. One or two of Ca: 0.01% by weight or less or a rare earth element (REM): 0.1% by weight or less is contained. Good workability hot-dip galvanized high-strength steel sheet having excellent fatigue properties and local deformability described in 2. 4. The fatigue property and the local deformability according to claim 1, wherein the total area ratio of martensite and pearlite in the microstructure is less than 4%. Good workability Hot-dip galvanized high strength steel sheet. 5. λ × σ ^0.8 ≧ 50 and σw / σ ≧ 0.6
And satisfying at the same time,
Good workability hot-dip galvanized high-strength steel sheet having excellent fatigue properties and local deformability according to any one of 4 above. 6. When hot-dip coating a steel sheet, the maximum heating temperature (called ST (° C.)) in the hot-dip galvanizing step is the coiling temperature during hot rolling (called CT (° C.)) and the addition amounts of V and C. (A) or CT and the weight ratio of Ti + Nb and the amount of C added (Ti + Nb) / C
6. At least one of the ranges of the formula (B) defined by is satisfied.
5. A method for producing a good workability hot-dip galvanized high-strength steel sheet having excellent fatigue properties and local deformability according to any one of 1. [Equation 1] [Equation 2]