JPH05255807A - High strength cold rolled steel sheet and calvanized high strength cold rolled steel sheet excellent in formability and their manufacture - Google Patents

Abstract

PURPOSE:To manufacture a high strength cold rolled steel sheet excellent in press formability at low cost by incorporating specified content of C, Si, Mn, P, S, Al, N, B, Ti and Nb. CONSTITUTION:The compsn. of a steel sheet consists of, by weight, 0.0003 to 0.01% C, <=0.03% Si, >0.5 to 3.5% Mn, 0.01 to 0.12% P, 0.0005 to 0.015% S, 0.005 to 0.1% Al, 0.0003 to 0.006% N, 0.0001 to <0.0005% B, 0.003 to 0.1% Ti and >0.01 to 0.1% Nb, and the balance substantial Fe. By the addition of small amounts of Si and P, its yield strength is increased, and its work hardening rate in a low distortion area is reduced. By the addition of Mn, its yield strength is hardly increased, its tensile strength is increased and its work hardening rate in a low strain area in increased. Ti and Nb improve its workability and surface treating properties.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a cold rolled steel sheet having high strength and excellent formability, and a method for producing the same.

[0002]

2. Description of the Related Art With the recent progress in vacuum degassing of molten steel, it has become easier to produce ultra-low carbon steel, and the demand for ultra-low carbon steel sheet having good workability is increasing more and more.
Among them, for example, the ultra-low carbon steel sheet containing the composite addition of Ti and Nb disclosed in JP-A-59-31827 and JP-A-59-38337 has extremely good workability, Since it has both paint bake hardening (BH) properties and excellent hot-dip galvanizing properties, it is becoming an important position. On the other hand, many attempts have heretofore been made to increase the strength while ensuring the workability.
In particular, when the tensile strength related to the present invention is 35 to 50 Kgf / mm ² , P, Si and the like are added to steel and the strength is increased by utilizing these solid solution strengthening mechanism. For example,
JP-A-59-31827 and JP-A-59-3
In Japanese Patent No. 8337, Si and P are mainly added to an ultra-low carbon steel plate to which Ti and Nb are added, and the tensile strength is 45 kg.
Disclosed is a method for manufacturing a high-strength cold-rolled steel sheet up to f / mm ² grade. Japanese Patent Publication No. 57-57945 is a typical prior art relating to a method for producing a high-strength cold-rolled steel sheet by adding P to a Ti-added ultra-low carbon steel. Furthermore, Japanese Patent Publication Sho 61-276
Japanese Patent No. 931 discloses a method for manufacturing a bake hardenable steel sheet for ultra deep drawing using an ultra low carbon steel to which Ti and Nb are added in combination. In the above publication, the strength is enhanced by adding Si or P.

As described above, P has been conventionally used as a strengthening element,
Next, Si is frequently used. This is because it has been considered that P and Si have a very high solid solution strengthening ability and can be added with a small amount to increase the strength, the ductility and the deep drawability do not decrease so much, and the addition cost does not increase so much. However, in reality, if an attempt is made to increase the strength only with these elements, not only the strength but also the yield strength will increase significantly at the same time. is there. Further, in the case of hot dip galvanizing, Si causes a plating failure, and P and Si significantly reduce the alloying rate, so that there is a problem that productivity is lowered.

On the other hand, it is also known to utilize Mn or Cr as a solid solution strengthening element. JP-A-63-19014
No. 1 and JP-A-64-62440 disclose Mn.
Was added to the Ti-containing ultra-low carbon steel sheet, and
Japanese Patent Publication No. 42742 and Japanese Patent Publication No. 57-57945 described above disclose a technique of adding Mn and Cr to a Ti-added ultra-low carbon steel, but (i) addition of Mn and Cr is mainly added. The elements P and Si have only a supplementary role, and therefore the obtained cold rolled steel sheet also has a high yield strength for its strength, and (ii) for the purpose other than (i) above, for example, (a) processing (B) B to improve the curing rate
Impart H-characteristics, (c) improve secondary workability,
(D) It is not positively added for the purpose of improving the galvanizability of hot-dip galvanizing. Further, Japanese Patent Laid-Open No. 2-111841 discloses a well-workable cold-rolled steel sheet having bake hardenability obtained by adding 1.5% or more and less than 3.5% Mn to an ultra-low carbon steel containing Ti and hot dip galvanizing. A steel sheet is disclosed. By adding a large amount of Mn, the purpose is to improve the operation stability of hot rolling and the homogeneity of the metal structure due to the reduction of the Ar ₃ transformation point. Further, addition of 0.2 to 1.0% of Cr or V is disclosed for the purpose of further improving ductility. However, there is no description from the viewpoint that the addition of a large amount of Mn or Cr improves the mechanical properties, particularly the balance between strength and ductility. Further, the amount of Nb added is set to 0.01% or less in order to suppress an increase in the recrystallization temperature, but in actuality, addition of 0.01% or more is essential from the viewpoint of workability and hot dip galvanizing characteristics. , 0.01% or more does not significantly increase the recrystallization temperature.

[0005]

Steel sheets used for automobile panels and the like are strictly required to have good surface formability such that spring back and surface distortion do not occur after pressing. By the way, it is well known that the lower the yield strength is, the more preferable the surface shape property is. However, increasing the strength of a steel sheet generally involves a marked increase in the yield strength as described in the prior art. Therefore, it is necessary to suppress the increase in yield strength as much as possible and achieve the increase in strength. Further, the steel sheet after press forming is required to have dent resistance. The dent resistance property means resistance to permanent dent deformation of a steel plate when a stone or the like hits the assembled vehicle. When the plate thickness is constant, the dent resistance property becomes better as the deformation stress after press working and paint baking is higher.
Therefore, considering steel sheets having the same yield strength, the higher the work hardening ability in the low strain region and the higher the paint bake hardening ability, the higher the dent resistance property.

From the above, a desirable high-strength steel sheet used for an automobile panel or the like is a steel sheet which does not have a very high yield strength, is significantly work-hardened, and preferably has a paint bake hardenability. Needless to say, it is also necessary to have excellent workability such as average r value (deep drawing property) and elongation (protrusion property), and it is also necessary to be substantially non-aging at room temperature. The present invention satisfies these needs, and has a tensile strength of 35 to 50 Kgf / mm ² and a yield strength of 15 to 28 Kgf / m 2.
m ^2, WH amount which is an index of work hardenability in a low strain region (2%
(Deformation stress-yield strength) is 4 Kgf / mm ² or more, BH property of ² Kgf / mm ² or more can be imparted if necessary, and the average r value and elongation are good, and secondary work brittleness hardly occurs, It is another object of the present invention to provide a high-strength cold-rolled steel sheet having good hot-dip galvanizing properties as needed. The high-strength cold-rolled steel sheet according to the present invention is used by press forming automobiles, household electric appliances, buildings and the like. Further, it includes both a cold-rolled steel sheet in a narrow sense that is not surface-treated and a cold-rolled steel sheet that has been subjected to surface treatment such as Zn plating or alloyed Zn plating for rust prevention. Since the steel sheet according to the present invention is a steel sheet having both strength and workability, it is possible to reduce the plate thickness in comparison with conventional steel sheets in use.
That is, the weight can be reduced. Therefore, it can contribute to global environment conservation.

[0007]

[Means for Solving the Problems] In order to achieve the above-mentioned objectives, the inventors of the present invention conducted extensive research and obtained new findings as described below. That is, Si, P, Mn, and Cr, which are typical solid solution strengthening elements, are added to the ultra-low carbon steel to which Ti and Nb are added, and tensile properties after cold rolling, annealing, and temper rolling, especially, The yield strength and work hardening phenomenon were investigated in detail. As a result, Si and P, which have been frequently used as solid solution strengthening elements in the past, (a) first increase the yield strength remarkably by adding a trace amount, and (b) as a result, the work hardening rate in the low strain region is remarkably reduced. It turned out to do. On the other hand, Mn, which has not been used as a solid solution strengthening element in the past,
When Cr is added, (a) the yield strength is hardly increased and the tensile strength is increased, and (c) as a result, the work hardening rate in the low strain region is increased rather by these additions, which is a very important new factor. I got the knowledge.

As a result of investigating these mechanisms, (a) the yield strength is determined by the difference in atomic radius between the Fe element and the added X element, and increases as the difference in atomic radius increases, (b) The work-hardening rate is closely related to the slip behavior of dislocations, and if the stacking fault energy is lowered by the addition of the X element, it becomes difficult to cross-slip dislocations, and as a result, the dislocation density increases and the work-hardening rate increases. It was constructed.
According to this, Si and P have significantly smaller atomic radii than Fe, and therefore the difference in atomic radii becomes large, so that the yield strength increases remarkably, and Mn and Cr have very close atomic radii to those of Fe, so that the yield strength changes almost. You can understand that you did not let me. On the other hand, although the influence on the stacking fault energy related to the work hardening rate is not always clear, from the detailed observation result of the dislocation structure after the initial work hardening by the electron microscope, Si and P are almost within the investigated addition amount range. For the first time, it was revealed that Mn and Cr tend to lower the stacking fault energy without affecting it.

Due to the above mechanism, it is considered that when Mn and Cr are added, the yield strength hardly changes, the work hardening rate increases, and the tensile strength increases. Such characteristic behavior means that the addition of Mn and Cr is preferable to the conventional addition of Si and P in order to achieve the above-mentioned object of the present invention. Therefore, in the present invention, Mn, Cr
The active use of is the basic solution to the prior art.
However, since the desired strength may not be obtained and the manufacturing cost may be increased only by adding Mn and Cr, it is also considered to use P in combination. Furthermore, the present inventors have obtained new knowledge that the BH property is also improved by positively adding Mn and Cr. This is because these elements have an attractive interaction with C, and therefore stabilize the solid solution C in the matrix equilibrating with TiC or NbC, and the solubility product of these becomes large, and the solid solution during reannealing is increased during annealing. Therefore, it is considered that the amount of residual solid solution C has increased. Therefore, Mn, C
The addition of r can also be utilized as a new means for imparting BH property. Further, solid solution C that contributes to BH property is also effective as B as a means for preventing secondary work embrittlement, which is known as a drawback of ultra-low carbon steel.

The use of an ultra-low carbon steel in which Ti and Nb are added together as the base steel has a relation with the object of the present invention to produce a high-strength cold-rolled steel sheet having excellent workability and surface treatment characteristics. To do. In other words, the characteristics such as workability and surface treatability are superior to the case where Ti or Nb is added alone, and the production characteristics of being able to prevent a remarkable increase in the recrystallization temperature are well balanced, and the characteristics are comprehensively superior. is there.

Further, the present inventors have suppressed the addition amounts of Si and P, which are often used as strengthening elements in conventional steel,
The present invention steel utilizing Mn and Cr has the following new advantages, especially in the production of galvannealed steel sheet by the continuous hot dip galvanizing process of the Zenzimer system. That is, since Si and P suppress the alloying reaction of Zn and Fe, when producing a steel sheet containing a large amount of these elements, the line speed had to be reduced and the productivity had to be reduced. Further, the addition of Si deteriorates the adhesion of the plating and causes various problems during press molding.
On the other hand, it was found that the addition of Mn and Cr did not have such an adverse effect. This point was also utilized as a solution to the problems of the conventional method.

The present invention is constructed on the basis of such an idea and new knowledge, and the gist thereof is as follows. (1)% by weight, C: 0.0003 to 0.01%, S
i: 0.03% or less, Mn: more than 0.5 to 3.5%, P:
0.01-0.12%, S: 0.0005-0.015
%, Al: 0.005-0.1%, N: 0.0003-
0.0060%, B: 0.0001 to less than 0.0005%, Ti: 0.003 to 0.1% and Nb:
A high-strength cold-rolled steel sheet and a hot-dip galvanized high-strength cold-rolled steel sheet containing both of more than 0.01% and 0.1% and having the balance Fe and unavoidable impurities and being excellent in formability. (2)% by weight, C: 0.0003 to 0.01%, S
i: 0.03% or less, Mn: more than 0.5 to 3.5%, C
r: 0.01 to 3.0%, P: 0.01 to 0.12%,
S: 0.0005 to 0.015%, Al: 0.005 to
0.1%, N: 0.0003 to 0.0060%, Ti: 0.003 to 0.1% and Nb: 0.01
A high-strength cold-rolled steel sheet and a hot-dip galvanized high-strength cold-rolled steel sheet, which contain both super-0.1% and are excellent in formability, consisting of the balance Fe and inevitable impurities. (3) The high-strength cold-rolled steel sheet and the hot-dip galvanized high-strength cold-rolled steel sheet having excellent formability according to claim (2), which contains B: 0.0001 to 0.0020%. (4) A slab composed of the chemical components according to claims (1) to (3) is hot-rolled at a temperature of (Ar ₃ -100) ° C or higher, and wound at a temperature of room temperature to 750 ° C. 60
A method for producing a high-strength cold-rolled steel sheet having excellent formability, which comprises performing cold rolling at a rolling ratio of at least 100% and setting an annealing temperature in continuous annealing to 700 to 900 ° C. (5) A slab consisting of the chemical components according to claims (1) to (3) is hot-rolled at a temperature of (Ar ₃ -100) ° C or higher, and wound at a temperature of room temperature to 750 ° C. 60
Cold rolling at a rolling ratio of at least 100% and an annealing temperature of 700 to
A method for producing a hot-dip galvanized high-strength cold-rolled steel sheet excellent in formability, which comprises performing in-line annealing type hot dip galvanizing at 900 ° C.

[0013]

The reason why the steel composition and manufacturing conditions are limited as described above in the present invention will be further described. C: C is an extremely important element that determines the material properties of the product. The present invention is premised on a vacuum degassed ultra low carbon steel, but if C is less than 0.0003%, the grain boundary strength decreases, secondary work embrittlement occurs, and the manufacturing cost significantly increases. Therefore, the lower limit is made 0.0003%. On the other hand, if the C content exceeds 0.01%, the strength increases, but the formability remarkably decreases, so the upper limit is made 0.01%. Si: When Si is added in excess of 0.03%, the yield strength increases, the chemical conversion processability decreases, the adhesiveness of hot dip galvanizing decreases, and the productivity decreases due to the delay of the alloying reaction. The problem occurs. Therefore, the upper limit is 0.03
%. The lower limit is the lower the better, and is not specified.

Mn: Mn is an effective solid solution strengthening element that does not significantly increase the yield strength and increases the strength, and also has the effect of imparting bake hardenability and improving the chemical conversion treatment property and hot dip galvanizing property. Therefore, it is positively added in the present invention. With the addition of 0.5% or less, the above-mentioned effects do not remarkably appear, so the lower limit is made over 0.5%. On the other hand, if it exceeds 3.5%, the low temperature transformation product after annealing increases, the yield strength remarkably increases, and the ductility decreases. Furthermore, since the average r value also decreases, the upper limit is set to 3.
5%. Cr: Cr, like Mn, is also an effective element that increases the strength without substantially increasing the yield strength and imparts the bake hardenability, so that it can also be used positively in the present invention. However, if the addition amount is less than 0.01%, the effect does not appear, so the lower limit value is made 0.01%. On the other hand, if it exceeds 3%, the pickling property of the hot-rolled sheet deteriorates or the chemical conversion treatment property of the product sheet deteriorates, so the upper limit is made 3%.

Similar to Si, P: P is known as an element for increasing the strength at a low cost, and its addition amount changes depending on the target strength level, but the tensile strength is 35 to 50 Kgf as in the present invention. In order to achieve the value of / mm ² , the addition amount should be 0.
It is set to 01% or more. However, if the addition amount exceeds 0.12%, the yield strength increases excessively and causes a surface shape defect during pressing. Furthermore, the alloying reaction becomes extremely slow during continuous hot dip galvanizing, which lowers productivity. In addition, secondary processing embrittlement also occurs. Therefore, the upper limit is 0.12%
And S: It is preferable that the amount of S is low, but if it is less than 0.0005%, the manufacturing cost increases, so this is made the lower limit. On the other hand, if it exceeds 0.015%, a large amount of MnS is precipitated and the workability deteriorates, so this is made the upper limit.

Al: Al is used for adjusting the deoxidation, but 0.
If it is less than 005%, the yield of addition of Ti and Nb decreases. On the other hand, if it exceeds 0.1%, the cost increases. Ti: Ti has a role of securing workability and non-aging property of the ultra-low carbon steel by fixing N, or part or all of C and S. If Ti is less than 0.003%, the effect of addition does not appear, so this is made the lower limit. On the other hand, if it exceeds 0.1%, the alloy cost will be significantly increased, so the upper limit is made 0.10%. Nb: Nb has a role of securing workability and non-aging property of the ultra low carbon steel sheet by fixing a part or all of C as NbC. When the amount of Nb is 0.01% or less,
Since the effect of addition does not appear, this is the lower limit. On the other hand, if the amount of Nb exceeds 0.10%, the alloy cost will increase significantly, the recrystallization temperature will increase, and the workability will decrease, so the upper limit is made 0.10%.

N: N is preferably low. However, 0.
If it is less than 0003%, a significant cost increase will occur. On the other hand, if the amount is too large, it becomes necessary to add a large amount of Ti or Al or the workability deteriorates, so 0.0060% is made the upper limit. B: When N is fixed in advance, B segregates at the grain boundaries and is effective in preventing secondary work embrittlement.
Add 0001 to less than 0.0005%. 0.0001
%, The effect is insufficient, and 0.0005%
If it becomes above, the yield point will rise and it will cause deterioration of workability. However, when Cr is contained, solid solution C is easily secured, so that addition of B is not essential for secondary workability. However, when aiming to further improve the secondary workability, B
Is added, the yield point does not increase significantly even if 0.0005% or more is added, so the upper limit is 0.0
020%.

Next, the reasons for limiting the manufacturing conditions will be described. The finishing temperature for hot rolling needs to be Ar ₃ −100 ° C. or higher from the viewpoint of ensuring workability of the product sheet.
The winding temperature is from room temperature to 750 ° C. The present invention is characterized in that the product material thereof is not so much affected by the hot rolling winding temperature. This is an extremely low carbon steel in which N is fixed as TiN, as well as Mn and C.
It is considered that this is also due to the fact that the composition of the hot-rolled sheet is remarkably fine and uniform due to the considerable addition of r. The upper limit of the coiling temperature of 750 ° C. is determined from the viewpoint of preventing a decrease in yield due to material deterioration at both ends of the coil.

Cold rolling may be performed under ordinary conditions, and the rolling reduction is set to 60% or more for the purpose of ensuring deep drawability after annealing. Continuous melting Z with continuous annealing or in-line annealing
The annealing temperature of the n-plating equipment is 700 ° C to 900 ° C. If the annealing temperature is lower than 700 ° C, recrystallization is insufficient. Further, the workability and the BH property are improved as the annealing temperature rises, but if it exceeds 900 ° C, the temperature is too high and the plate breakage and the flatness of the plate deteriorate. Thus, according to the present invention, the tensile strength is 35 to 50 Kgf / mm ² , the yield strength is 15 to 28 Kgf / mm ² ,
If the WH amount (2% deformation stress-yield strength), which is an index of work hardening ability in the low strain region, is 4 Kgf / mm ² or more, ² Kgf /
Manufacture of high-strength cold-rolled steel sheets that can impart BH properties of mm ² or more, have good average r value and elongation, are unlikely to cause secondary work embrittlement, and have good hot-dip galvanizing properties as required. To be done. Next, the present invention will be described with reference to examples.

[0020]

【Example】

Example 1 Steels having the compositions shown in Table 1 were melted and hot-rolled at a slab heating temperature of 1200 ° C., a finishing temperature of 900 ° C. and a winding temperature of 650 ° C. to obtain 3.8 _mm thick steel plates.
After pickling, cold rolling with a reduction rate of 80% is applied to make a cold-rolled sheet of 0.76 mm, then heating rate 15 ° C / sec, soaking 830 ° C.
Continuous annealing was performed at a cooling rate of 20 ° C./sec for 50 seconds. Further, temper rolling was carried out at a rolling reduction of 0.5%, and JIS No. 5 tensile test pieces were sampled and subjected to a tensile test. The results of the tensile test are summarized in Table 2.

[0021]

[Table 1]

[0022]

[Table 2]

Here, the WH amount which is important in the present invention is the work hardening amount when a tensile strain of 2% is applied in the rolling direction, and is the amount obtained by subtracting the yield stress (YP) from the 2% deformation stress. is there. The BH content is 2% prestrained material at 170 ° C x 2
It is the amount of increase in stress (value obtained by subtracting 2% deformation stress from the falling yield stress at the time of re-pulling test) when the tensile test is carried out again after the heat treatment equivalent to coating baking for 0 minutes. Also, 2
Subsequent embrittlement transition temperature is 50 mm from the temper-rolled steel plate.
The ductile-brittle transition temperature when a blank of mm is punched and then cup-formed with a punch having a diameter of 33 mm and subjected to a drop weight test at various temperatures.

As is clear from Table 2, the steel of the present invention has a lower yield strength, a better surface shape, and a higher WH and BH content than the high-strength steel having the same level of tensile test as conventional steels. Because of its high price, it is a suitable material for outer and inner panel of automobiles, for example. That is, it can be expected that the steel of the present invention has a lower yield strength and a better surface shape after pressing than the conventional steel even with the same strength. On the other hand, as shown in FIG. 1, the steel of the present invention has the same yield strength (WH) as compared with the conventional steel.
+ BH) amount is high, so dent resistance characteristics (σ _d = YP + WH
+ BH) is also improved at the same time. Further, as shown in Table 2, the steels of the present invention contain less P and Si than the conventional steels, and M
Since a large amount of n and Cr are added, the amount of BH is also high and the resistance to 2
It is also excellent in subsequent processing brittleness. Here, the steel 2-4 is T
When the product sheet was artificially aged at 100 ° C. for 1 hour because the amounts of i and Nb were too small, the yield point elongation (YP-E1) was 1.3%. This causes stretcher strain during pressing.

Example 2 1-1, 1-2, 1-of Table 1
Steel having the composition shown in 3, 2-1, 2-2, 2-3 is melted, and the slab heating temperature is 1150 ° C. and the finishing temperature is 910.
Hot rolling under conditions of ℃ and winding temperature of 600 ℃ 4.0
The steel plate has a thickness of mm. After pickling, cold rolling with a reduction rate of 80% is applied to make a cold-rolled sheet of 0.8 mm, and then a heating rate of 15 ° C /
After heating up to a maximum heating temperature of 820 ° C in seconds, about 10 ° C /
Cooling in seconds, conventional hot dip galvanizing at 460 ° C. (Al concentration in the melt is 0.11%), and heating to 520
After alloying at 20 ° C. for 20 seconds, it was cooled to room temperature at about 10 ° C./second. The obtained galvannealed steel sheet was measured for mechanical properties, plating adhesion, and Fe concentration in the plating film. These results are also summarized in Table 3.

[0026]

[Table 3]

Here, the plating adhesion was determined by performing a 180 ° C. contact bending, peeling the zinc coating after adhering a cellophane tape to the bent portion and then peeling it off to determine the amount of peeled plating adhered to the tape. The evaluation was made into the following 5 grades. 1 ... Large peeling, 2 ... During peeling, 3 ... Small peeling, 4 ... Small peeling,
5 ... No peeling at all The Fe concentration in the plating layer was determined by X-ray diffraction.

As is clear from Table 3, the steel of the present invention has a low YP, a high WH and BH content, and a high dent resistance and corresponding σ _d as compared with the conventional steel. This is the point confirmed also in Example 1. Further, the steel of the present invention has better plating adhesion than the conventional steel, and the Fe concentration in the alloy layer is also an amount corresponding to that of the δ _l phase considered to be a desirable phase. This is considered to be because in the present invention, Si that deteriorates the plating adhesion and P and Si that control the alloying reaction are reduced as much as possible, and Mn and Cr are added to increase the strength.

[0029]

As is apparent from the above description, according to the present invention, a high-strength cold-rolled steel sheet excellent in press formability, which has never been obtained, can be obtained by a low-cost manufacturing method. Further, the steel of the present invention has good hot-dip galvanizing properties and can also exhibit a rust preventive function. As a result, when the steel of the present invention is used for the body and frame of automobiles, the thickness of the plate can be reduced, that is, the weight of the vehicle body can be reduced. Therefore, the present invention can greatly contribute to the conservation of the global environment, which has been a hot topic recently. .. Thus, the industrial significance of the present invention is extremely great.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship with a yield σ _d (index of a dent characteristic).

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI technical display location C23C 2/06 2/40

Claims (5)

[Claims] 1. C: 0.0003 to 0.01 by weight.
%, Si: 0.03% or less, Mn: over 0.5 to 3.5
%, P: 0.01 to 0.12%, S: 0.00055
0.015%, Al: 0.005-0.1%, N: 0.
0003 to 0.0060%, B: 0.0001 to 0.0
Less than 005%, further containing both Ti: 0.003 to 0.1% and Nb: more than 0.01 to 0.1%, the balance F
A high-strength cold-rolled steel sheet and a hot-dip galvanized high-strength cold-rolled steel sheet, which are excellent in formability and composed of e and unavoidable impurities. 2. C: 0.0003 to 0.01 by weight.
%, Si: 0.03% or less, Mn: over 0.5 to 3.5
%, Cr: 0.01 to 3.0%, P: 0.01 to 0.1
2%, S: 0.0005 to 0.015%, Al: 0.0
05-0.1%, N: 0.0003-0.0060%,
Furthermore, Ti: 0.003 to 0.1% and Nb: 0.0
A high-strength cold-rolled steel sheet and a hot-dip galvanized high-strength cold-rolled steel sheet containing both of more than 1 and 0.1% and having the balance of Fe and unavoidable impurities and excellent in formability. 3. A high-strength cold-rolled steel sheet having excellent formability and a hot-dip galvanized high-strength cold-rolled steel sheet according to claim 2, which contains B: 0.0001 to 0.0020%. 4. A slab made of the chemical composition according to any one of claims 1 to 3 is hot-rolled at a temperature of (Ar ₃ -100) ° C. or higher and wound at a temperature of room temperature to 750 ° C. A method for producing a high-strength cold-rolled steel sheet having excellent formability, which comprises: taking, cold rolling at a rolling rate of 60% or more, and setting an annealing temperature in continuous annealing to 700 to 900 ° C. 5. A slab made of the chemical composition according to any one of claims 1 to 3 is hot-rolled at a temperature of (Ar ₃ -100) ° C. or higher and wound at a temperature of room temperature to 750 ° C. Of hot-dip galvanized high-strength cold-rolled steel sheet having excellent formability, which is characterized by performing in-line hot-dip galvanizing at an annealing temperature of 700 to 900 ° C. by performing cold rolling at a rolling rate of 60% or more. Production method.