JP3528716B2 - High-strength cold-rolled steel sheet, high-strength galvanized steel sheet excellent in surface properties and press formability, and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel plate required for automobile outer panel panels or members such as hoods, doors, fenders, and side panels, and vehicle structural members such as reinforcements. The present invention relates to a high-strength cold-rolled steel sheet, a high-strength zinc-based plated steel sheet and a method for producing the same, which have excellent formability in composite forming and excellent surface properties even after press forming.

[0002]

2. Description of the Related Art In response to needs for high strength and light weight of automobiles, plated steel sheets applied to automobile exterior members, members, reinforcement structural members and the like are
There is a demand for strength, moldability, and particularly good surface properties. The r value is as important as the elongation for formability. In recent years, there has been a great demand for improving the formability of high-strength steel sheets, and a high r-value is required. To obtain a high r-value, T is based on ultra-low carbon steel with a C concentration of about 30 ppm or less.
It is effective to add carbonitride-forming elements such as i and Nb, and in general, Interstitial Free steel (hereinafter abbreviated as IF steel)
Is widely used as. Furthermore, based on this steel, high-strength steel sheets to which solid solution strengthening elements such as Mn, P, and Si have been added have been developed. However, the steel solid-solution strengthened based on IF steel is Mn, P, Si when zinc-based plating treatment is performed.
As a result, the surface of the zinc-based plating is inferior in quality, and the quality of the outer panel of an automobile is not stable. Further, since the solid solution strengthening element is expensive, there is a problem that the cost of the steel sheet increases. Further, it is difficult to secure both a high r-value and resistance to surface roughening during press molding. That is, high temperature annealing is indispensable for improving the r value, but in IF steel having a high crystal grain growth property, crystal grains become coarse and rough skin is likely to occur when high temperature annealing is performed in order to obtain a high r value.

In order to reduce solid solution elements such as Mn, P, and Si, a technique has been disclosed in which C is added as a very low carbon steel, which is slightly higher than 30 to 100 ppm, and precipitation strengthening is performed with TiC (Japanese Patent Laid-Open No. Hei 10 (1999) -135242). 1
0-46289, JP-A-5-195080). Although TiC contributes to precipitation hardening, the size of the precipitate is large because it is generated at a high temperature of A ₃ or higher, and the effect on refining the structure of hot-rolled sheet, refining of cold-rolled sheet structure, and precipitation strengthening is small. . Also, Ti, N
When b is added in combination, C precipitates as TiC during cooling at a high temperature, so NbC fine precipitates do not form. Therefore, it was not possible to manufacture a steel sheet having excellent surface properties and press formability due to the effect of fine precipitation of NbC peculiar to the addition of Nb alone. Further, if Ti is contained in the steel, streaky plating unevenness is generated on the surface of the steel sheet, so it cannot be said that it is suitable for an automobile outer panel.

[0004]

SUMMARY OF THE INVENTION The object of the present invention is to achieve high moldability and durability required for automobile structural members such as hoods, doors, fenders, side panels, and other automobile outer panel panels or members, and reinforcements. Excellent skin roughness,
An object of the present invention is to provide a high-strength cold-rolled steel sheet, a zinc-based plated steel sheet, and a method for producing the same, which are free from surface defects after pressing the original plate and the press at low cost.

[0005]

DISCLOSURE OF THE INVENTION The inventors of the present invention have found that excellent strength and moldability required for molding composite molded parts such as automobile outer panel materials or members such as fenders and side panels, and automobile structural members such as reinforcements. And earnestly researched in order to obtain a high-strength zinc-based plating base plate, a zinc-based plated steel plate, and a method of manufacturing the same. As a result, by controlling C to a limited range of 0.0040 to 0.010% that does not exist in the prior art, and by adding Nb so that the balance with C is optimal, NbC is finely precipitated,
It has been found that due to the effect of these fine precipitates, the crystal grains of the hot-rolled sheet are made finer, so that the r value of the product after cold-rolling and annealing is remarkably improved. According to the more optimal manufacturing method,
Since the crystal grain size after annealing is 10 μm or less and the high r value of 1.5 or more required for press molding of the composite molded part can be obtained, it is possible to obtain a molding resistance which is conventionally impossible in the press molding of the composite molded part. Both rough skin and excellent moldability were achieved.

At the same time, Mn, P is controlled by controlling the precipitation of NbC.
It has been found that since the strength can be increased without adding a large amount of Mn, the deterioration of the plating surface property due to the addition of Mn, P can be suppressed, and a steel sheet having excellent surface properties as an automobile outer plate or a structural member can be manufactured. By controlling the upper limit of Ti to 0.019% or less and Ti ≤ 48S / 32 + 48N / 14,
It has been found that a good surface quality can be obtained without the occurrence of streaky surface defects that occur during the galvannealing treatment. Furthermore, in order to enhance the strength of the steel sheet while maintaining good surface properties, an appropriate range of balance of Mn, P and Si was found.

The present invention has been made as a result of further studies based on the above findings, and the characteristic constitution is as follows.

(1) In% by weight, C: 0.0040 to 0.010% Si: 0.05% or less Mn: 1.0 to 2.5% P: 0.02 to 0.1% S: 0.02% or less sol.Al: 0.01 to 0.1% N: 0.0100% The following Nb: 0.036 to 0.14%, 12Nb / 93C is contained in the range of 1.1 to less than 2.5, the balance substantially consists of Fe and unavoidable impurities, and the average crystal grain size is 10 μm or less. A high-strength cold-rolled steel sheet having excellent surface properties and press formability (first invention).

(2) wt%, Ti: 0.019% or less and
A high-strength cold-rolled steel sheet excellent in surface properties and press formability according to the above (1), characterized by containing Ti satisfying a relationship of Ti ≦ 48S / 32 + 48N / 14 (second invention).

(3) A high-strength cold-rolled steel sheet excellent in surface properties and press formability according to the above (1) or (2), characterized by containing 0.0015% or less of B: 0.0015% by weight (No. 1). 3 invention).

(4) A high-strength zinc-based steel excellent in surface properties and press formability, characterized in that it has a zinc-based plating film on the surface of the cold-rolled steel sheet according to any one of (1) to (3) above. Plated steel sheet.

(5) Directly or 1100-1250 ° C. after continuous casting of the steel having the composition as described in any of (1) to (3) above.
After reheating to 10 to 40%,
After hot rolling at a finishing temperature of Ar _{3 to} 920 ℃, cooling rate is 15 ℃ / sec.
The surface characterized by being cooled to 700 ° C. or less by the above, cold-rolled at a cold rolling ratio of 50% or more, continuously annealed at 780 ° C. to Ac ₃ , and subjected to temper rolling with a rolling reduction of 0.4 to 1.0%. A method for producing a high-strength cold-rolled steel sheet excellent in properties and press formability (fifth invention).

(6) Directly or 1100-1250 ° C. after continuous casting of the steel having the composition as described in any of (1) to (3) above.
After reheating to 10 to 40%,
After hot rolling at a finishing temperature of Ar _{3 to} 920 ℃, cooling rate is 15 ℃ / sec.
After cooling to 700 ° C or less, cold rolling at a cold rolling ratio of 50% or more, continuous annealing at 780 ° C to Ac ₃ and temper rolling at a rolling reduction of 0.4 to 1.0%, and then zinc-based plating. Or a zinc-based plating followed by temper rolling with a rolling reduction of 0.4 to 1.0%, which is a method for producing a high-strength zinc-based plated steel sheet having excellent surface properties and press formability (the sixth invention). ).

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The reasons for limiting the composition of the additive element, the metal structure and mechanical properties, and the manufacturing method of the present invention will be described. In addition,% shows weight%. (1) Component composition, metal structure and mechanical properties C: 0.0040 to 0.010% C combines with Nb to form NbC fine carbide which is a feature of the present invention. Optimizing the C concentration is essential for precipitating fine NbC at an appropriate volume ratio, and controlling the C concentration is one of the most important constituent features of the present invention. The finely precipitated NbC has the effect of making the crystal grain size of the hot rolled sheet finer and improving the r value after cold rolling annealing. Further, since NbC can be precipitated extremely finely, a large effect of precipitation strengthening can be obtained, and the strength can be enhanced without adding a large amount of solid solution elements such as Mn, P and Si. Therefore, color unevenness on the plated surface due to the solid solution element is reduced, and the surface quality is improved. When the C concentration is less than 0.0040%, the volume ratio of NbC precipitates is not sufficient to obtain the effect of the present invention, and when it exceeds 0.010%, the effect of suppressing grain growth of the cold rolled annealed plate by NbC becomes too large, and the r value Deteriorate. Further, NbC is excessively generated and the elongation deteriorates, so the content is made 0.0040 to 0.010%. Further, C is preferably 0.0050% or more to improve the surface properties, and 0.0080% or less to improve the moldability. Further, in order to further improve the moldability, it is preferably 0.0074% or less.

Si: 0.05% or less Si can be added at a low cost because it can be strengthened at a low cost, but if it is added in excess of 0.05%, the surface concentration of Si during annealing deteriorates and the plating property deteriorates. Therefore, Si must be 0.05% or less.

Mn: 1.0 to 2.5% Mn is added for strengthening by solid solution strengthening. 1.
If it is less than 0%, the effect of solid solution strengthening is not sufficient. When Mn is 2.5% or more, the surface properties and elongation of the steel sheet are significantly deteriorated.
It should be 1.0-2.5%.

P: 0.02 to 0.1% P is added for strengthening by solid solution strengthening. Addition of 0.02% or more is indispensable in order to achieve both surface properties and high strength. On the other hand, if the P concentration exceeds 0.1%, slab cracking may occur due to slab center segregation. P is
It should be 0.02 to 0.1%. Further, if the P concentration exceeds 0.08%, it takes a long time for alloying the zinc-based plating layer to alloy it, so it is preferably 0.08% or less.

S: 0.02% or less S exists as an impurity in the steel, but it must be removed to 0.02% or less because it markedly deteriorates the appearance of the plate surface.

Sol.Al: 0.01 to 0.1% Al is added as a deoxidizing material. If the concentration of solid solution Al is less than 0.01%, deoxidation is not sufficient, and if it exceeds 0.1%, the steel sheet is strengthened by solid solution strengthening of Al and ductility deteriorates.

N: 0.0100% or less N forms a solid solution in the steel sheet structure, and if contained in excess, it causes surface defects such as stretcher strain marks. Therefore, N must be 0.0100% or less.

Nb: 0.036 to 0.14% and 1.1 <12Nb / 93C <
2.5 Nb is added in order to combine with C to form fine precipitates of NbC essential to the present invention, thereby making the structure fine and improving surface properties and mechanical properties. Nb among the carbide-forming elements
It is the most suitable element in that an extremely fine precipitate can be obtained because it precipitates just below the A ₃ point. On the other hand, since the precipitate of Ti, which is the same carbide-forming element, precipitates at a high temperature of A ₃ point or higher, the precipitate becomes too coarse to obtain the effect of the present invention. Therefore, proper addition of Nb is an essential constituent feature of the present invention. If it is less than 0.036%, the precipitation amount of NbC is insufficient, and the effect of precipitate formation cannot be obtained.
The volume ratio becomes too high and the strength remarkably increases, deteriorating the moldability. Further, in order to enhance the effect of NbC precipitation due to the addition of Nb, it is desirable to exceed 0.08%.

When 12Nb / 93C is 1.1 or less, solid solution C remains in a non-equilibrium state, surface defects such as stretcher strain are likely to occur, and it is suitable for deep drawing (11
1) Since it has an effect of preventing the formation of a texture having a surface in the plate surface direction, the value is 1.1 or more. On the other hand, when 2.5 or more, Nb is Fe
Since it is excessively contained in the alloy, not only the ductility is deteriorated but also the hot workability is deteriorated and the yield is lowered. In order to further enhance the effect of NbC fine precipitation, 12N
It is desirable that b / 93C is over 1.5. Further, in order to enhance the effect, it is preferably 1.7 or more.

Ti: 0.019% or less and Ti ≦ 48S / 32 + 48N / 14 In the present invention, when further refining the crystal grains is promoted, Ti is set to 0.
It can be added so as to satisfy 019% or less and Ti ≦ 48S / 32 + 48N / 14. Ti has the effect of precipitating impurities N and S as TiN and TiS to render them harmless, and at the same time, to refine the crystal grain size by these precipitates. This effect appears at 0.005% or more. However, when Ti is added in excess of 48S / 32 + 48N / 14, not only the above effect is saturated, but also TiC is precipitated and C is reduced, so that the effect of NbC precipitation is reduced.
Also, if Ti is added in excess of 0.019%, color unevenness will occur on the plating surface and the surface properties will deteriorate, so it is necessary to make it 0.019% or less.

B: 0.0015% or less B may be added to prevent secondary work embrittlement. However, if it is added in excess of 0.0015%, the r-value and the elongation will be significantly deteriorated. Therefore, when it is added, it should be 0.0015% or less.

Next, the metal structure will be described. Average crystal grain size: 10 μm or less The crystal grain size is very important for improving the surface quality after molding such as pressing for the purpose of improvement in the present invention. If it exceeds 10 μm, the surface quality after molding will deteriorate, so it is necessary to set the crystal grain size to 10 μm or less.

Next, the method for manufacturing the steel sheet of the present invention will be described. After continuously casting the steel having the component composition described in the first invention to the third invention, hot rolling is performed directly or after reheating to 1100-1250 ° C. This is because if the temperature is less than 1150 ° C, the rolling load is high and the work efficiency becomes poor, and if the temperature exceeds 1250 ° C, the surface properties of the product deteriorate. The total of the final two-stage rolling reduction is 10% to 40%,
After hot rolling at a finishing temperature of Ar _{3 to} 920 ° C. In order to bring out the characteristics of the steel of the present invention, it is important to control the rolling reduction here.
If it is less than 10%, the hot rolled structure becomes coarse and the effect of improving the r value cannot be obtained. On the other hand, if it exceeds 40%, unrecrystallized austenite will be formed after hot rolling, resulting in a non-uniform hot-rolled structure.
Value and surface quality deteriorate. When the finishing temperature is less than Ar ₃ , the surface layer becomes ferrite and the hot rolled structure becomes coarse, so that the r value decreases. On the other hand, if the temperature exceeds 920 ° C., the growth of austenite grains during cooling is fast, it becomes difficult to make the hot rolled structure finer, and the r value cannot be improved.

Cooling rate after hot rolling is 700 ° C at 15 ° C / sec or more
Must be cooled to If the temperature is less than 15 ° C / sec, grain growth occurs during cooling, the hot rolled structure becomes coarse, and 1.5
The above r value cannot be obtained. This effect becomes remarkable above 700 ° C, so it is important to cool to below this temperature.

The cold rolling reduction rate must be 50% or more. The rolling ratio of cold rolling is appropriately controlled depending on the steel composition, but with the steel of the present invention, an r value of 1.5 or more cannot be obtained at less than 50%.

Next, after cold rolling, continuous annealing is performed. In order to satisfy both the r value of 1.5 or more and the grain size of 10 μm or less, continuous annealing is performed at 780 ° C. to Ac ₃ . 1.5 if the annealing temperature is less than 780 ℃
Can not be obtained above r value, not only can not be obtained equiaxed grains following 10μm by austenitizing exceeds Ac _3, since r value becomes less than 1.5, and 780 ° C. to Ac _3.
Further, in the steel of the present invention, by setting the annealing temperature to 860 ° C. or higher, the r value can be further improved with the crystal grain size of 10 μm, so the annealing temperature is preferably 860 ° C. or higher. The reason for continuous annealing is that the heating rate is 20 ° C./sec or more, and if the heating rate is less than 20 ° C./sec, a texture advantageous for deep drawing is not formed and the r value is less than 1.5.

Temper rolling with a rolling reduction of 0.4 to 1.0% is performed on the annealed sheet. Control of temper rolling rate is important in the invention, and if it is less than 0.4%, the effect of N aging may not be sufficiently suppressed, and if it exceeds 1.0%, the yield point of the present invention steel increases significantly, forming Deteriorates sex.

The cold-rolled steel sheet produced in this manner has excellent surface properties and press formability. Further, this steel sheet is suitable as a material steel plate for plating, particularly as a material steel plate for zinc-based plating, since a zinc-based plated steel sheet having excellent surface properties and press formability can be obtained after zinc-based plating.

In the case of producing a zinc-based plated steel sheet using the cold-rolled steel sheet as a raw material, the plating may be either electroplating or hot dipping. Annealing may be performed using a continuous plating line including an annealing step, and then plating may be performed. in this case,
The temper rolling step may be omitted, and the temper rolling may be performed after plating or after the alloying treatment.

When alloying the plating layer, it is desirable to use an induction heating type alloying furnace in order to shorten the alloying time.

[0034]

EXAMPLES Example 1 Steels Nos. 1 to 20 shown in Table 1 were continuously cast, reheated at 1150 to 1190 ° C., and then hot rolled to a plate thickness of 2.8 mm. Hot rolling finish temperature is 880-910
It was ℃. At that time, the total of the final two-stage rolling reductions was set to 15%. Then, after cooling at an average cooling rate of 20 ° C / sec, the film was wound at 640 ° C. Cold rolling to 0.70 mm (cold rolling rate
75%), using a hot dip galvanizing line equipped with continuous annealing equipment, holding at 865 ° C for about 90 seconds, then hot dip galvanizing, alloying treatment of the plating layer, and then temper rolling with a rolling reduction of 0.7% to obtain a test material. Obtained.

[0035]

[Table 1]

The mechanical properties, average crystal grain size, surface properties, and resistance to roughening of the test material obtained above were investigated. The r-value measurement was performed after pickling with hydrochloric acid to remove the influence of the plating layer, and the average r-value from the r-value measurement results in three directions: mean-r = (r ₀ + 2 *
r ₄₅ + r ₉₀ ) / 4 was calculated. Here, r ₀ : r value in a direction parallel to the rolling direction, r ₄₅ : r value in the rolling direction and 45 ° direction, r ₉₀ :
It is the r value in the direction perpendicular to the rolling direction.

The particle size was measured by the cutting method (JIS G0552).
The surface quality is A (excellent) to D by visually observing the plating properties of the steel sheet.
It was evaluated in 4 grades of (poor). Roughness resistance is measured by measuring the centerline average roughness Ra of the crown of the ball head punch with a radius of 100 mm and projecting 30 mm, and Ra: 1 μm or less is good (symbol: ○), Ra: Roughness is over 1 μm. Poorness (symbol: ×)
Was judged as. The survey results are shown in Table 2.

[0038]

[Table 2]

Steel plates having a grain size of 10 μm or less within the composition range of the present invention are all high in strength, have an r value of 1.5 or more, and have a rough skin resistance evaluation of ∘, and have excellent press formability and rough skin resistance. It is also excellent and is most suitable for automobile outer panels or automobile structural members.

On the other hand, steel Nos. 10 and 11 having an average crystal grain size of more than 10 μm have poor surface roughening resistance. It is considered that, because C was less than 0.0040%, the effect of NbC precipitation became insufficient, and the crystal grain growth was not suppressed during annealing. Further, Steel No. 11 has a high 12Nb / 93C outside the range of the present invention, so the elongation and r value are not good.

In Steel 12, since 12Nb / 93C in Table 1 is 1.1 or less, solid solution C remains and the r value is poor. Also, since the C concentration is high, the amount of NbC is too large and the elongation is low. Steel 13 has a low Mn concentration and therefore has a low elongation. In addition, streaky plating surface defects caused by Mn are generated, so that the surface quality is not good. Steel 14 does not have sufficient strength because the P concentration is too low. Further, in Steel 15, the P concentration was too high, so the elongation was low, and when the plating film was alloyed, poor alloying occurred and the surface properties became poor. steel
In 16 and 19, the r-value is not good because 12Nb / 93C is 1.1 or less.
Steels 17 and 20 have poor elongation and r-value because 12Nb / 93C is 2.5 or more. Steel 18 had too high a Ti concentration, so that streaky surface defects were generated on the plated surface, and this also deteriorated the surface roughening resistance.

(Example 2) Slabs of steel Nos. 1 to 5 having the composition within the scope of the present invention shown in Table 1 were reheated and then hot rolled to a plate thickness of 2.8 mm. Then average cooling rate 20 ℃ / sec
After cooling with, it was wound up at 640 ° C. Furthermore, cold rolling to 0.70 mm (cold rolling rate 75%), using a hot dip galvanizing line equipped with continuous annealing equipment, heating to a specified annealing temperature at a heating rate of about 20 ° C / sec to anneal the molten zinc. A test material was obtained by plating, alloying the plated layer, and then temper rolling with a rolling reduction of 1.0%. Table 3 shows the heating temperature, hot rolling reduction, finishing temperature, and annealing temperature of the reheated slab.

The test materials obtained above were examined for mechanical properties, average crystal grain size, surface properties, and resistance to roughening in the same manner as in Example 1. The survey results are also shown in Table 3.

[0044]

[Table 3]

Symbol A of the invention example satisfying the sixth invention range,
E, F, G all have good characteristics. On the other hand, the sixth
The symbols B, C, D and H of the comparative examples which are out of the scope of the invention are inferior in any of the characteristics. For example, the symbol B indicates that the heating temperature is too high,
Color-uneven surface defects occurred on the plated surface. Also sign
In C and D, the r value was deteriorated in the hot rolling process because the rolling ratio of the final two stages was out of the range of the present invention. In the symbol H, the r-value and elongation deteriorated because the annealing temperature was too low.

The present example is an example of a hot-dip galvanized steel sheet which has been subjected to post-annealing plating and temper rolling. A cold-rolled steel sheet which has been subjected to temper rolling after annealing and electrogalvanizing which has been further electroplated. With respect to the steel plate, the same result as that of the above-mentioned embodiment can be obtained.

[0047]

As described above, according to the present invention, r
With a value of 1.5 or more, it has excellent moldability and resistance to rough skin,
It is possible to obtain a high-strength cold-rolled steel sheet or a high-strength zinc-based plated steel sheet having no surface defects after pressing the original plate and at a low manufacturing cost. INDUSTRIAL APPLICABILITY The steel sheet of the present invention is suitable as a steel sheet used for automobile structural members such as hoods, doors, fenders, side panels, and other automobile exterior panel panels or members, and reinforcements.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C22C 38/12 C22C 38/12 38/14 38/14 (72) Inventor Seiji Nakamura 1-2 1-2 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Masahiko Sekiguchi 1-2-2 Marunouchi, Chiyoda-ku, Tokyo Japan Steel Pipe Co., Ltd. (72) Inventor Akira Miyamoto 1-2-1 Marunouchi, Chiyoda-ku, Tokyo Nippon Steel Pipe Co., Ltd. (72) Inventor Toshiaki Urabe, 1-2-1, Marunouchi, Chiyoda-ku, Tokyo Nihonkokan Co., Ltd. (56) Reference JP-A-11-209845 (JP, A) JP-A-11-302782 (JP, A) JP-A-6-158176 (JP, A) JP-A-2-163318 (JP, A) JP-A-2-163346 (JP, A) JP-A-5-86420 (JP, A) JP-A-7 -70650 (JP, A) JP-A-3 170618 (JP, A) JP flat 8-170147 (JP, A) JP flat 8-209249 (JP, A) (58 ) investigated the field (Int.Cl. ^7, DB name) C22C 38/00 B21B 3 / 00 C21D 9/46

Claims (6)

(57) [Claims] 1. By weight%, C: 0.0040 to 0.010% Si: 0.05% or less Mn: 1.0 to 2.5% P: 0.02 to 0.1% S: 0.02% or less sol.Al: 0.01 to 0.1% N: 0.0100% or less Nb: 0.036 to 0.14%, 12Nb / 93C is contained in the range of 1.1 to less than 2.5, the balance is substantially Fe and inevitable impurities, and the average crystal grain size is 10 μm or less. High strength cold rolled steel sheet with excellent properties and press formability. 2. In% by weight, Ti: 0.019% or less and Ti
The high-strength cold-rolled steel sheet having excellent surface properties and press formability according to claim 1, comprising Ti satisfying a relation of ≤48S / 32 + 48N / 14. 3. A high-strength cold-rolled steel sheet having excellent surface properties and press formability according to claim 1 or 2, which further contains B: 0.0015% or less by weight. 4. A high-strength zinc-based plated steel sheet having excellent surface properties and press formability, which has a zinc-based plating film on the surface of the cold-rolled steel sheet according to claim 1. 5. A steel having the composition of any one of claims 1 to 3 is cast directly or after being reheated to 1100 to 1250 ° C., and the total reduction ratio of the final two stages is 10 to 40%. Finishing temperature is A
After hot rolling at r ₃ ~920 ℃, 700 ℃ at a cooling rate of 15 ° C. / sec or higher
After cooling to below, cold rolling at a cold rolling rate of 50% or more, then 780
A method for producing a high-strength cold-rolled steel sheet having excellent surface properties and press formability, which comprises continuously annealing at ℃ to Ac ₃ and temper rolling at a rolling reduction of 0.4 to 1.0%. 6. The steel having the composition of any one of claims 1 to 3 is cast directly or after being reheated to 1100 to 1250 ° C., and the total reduction ratio of the final two stages is 10 to 40%. Finishing temperature is A
After hot rolling at r ₃ ~920 ℃, 700 ℃ at a cooling rate of 15 ° C. / sec or higher
After cooling to below, cold rolling at a cold rolling rate of 50% or more, then 780
Continuous annealing at ℃ ~ Ac ₃ and then temper rolling with a rolling reduction of 0.4 to 1.0% and then zinc-based plating, or after performing zinc-based plating, temper rolling with a rolling reduction of 0.4 to 1.0% A method for producing a high-strength zinc-based plated steel sheet excellent in surface properties and press formability, which is characterized by the above.