JP4840567B2 - Manufacturing method of high strength steel sheet - Google Patents

Description

The present invention, automobile bodies, reinforcements, wheels, undercarriage components, optimal to other manufacturing any mechanical structural parts, the tensile strength is a method of manufacturing a more high-strength thin steel plate 590 MPa.

  In order to protect the global environment and improve the safety of passengers, thinning and high strength are being investigated for automotive steel sheets. There are solid solution strengthening, precipitation strengthening, transformation strengthening, etc. to increase the strength of the steel sheet. Of these, precipitation strengthening is a method that is advantageous in reducing manufacturing costs in that high strength is achieved with a small amount of additive elements. It is. Further, since precipitation strengthened steel can provide high yield strength, precipitation strengthening can be said to be an effective strengthening method in this respect.

The precipitation strengthening method is a method of obtaining strength by mainly adding elements such as Ti, Nb, and V into steel and generating carbonitrides of these elements. As a technique for manufacturing such a component requiring high strength as described above using such a precipitation strengthening method, for example, those disclosed in Patent Documents 1, 2, 3, and 4 have been proposed. However, when the above elements are added to the steel, particularly when the tensile strength of the product is 590 MPa class or more, in the continuous casting process, lateral cracks (lateral cracks) occur on the surface of the slab corner and the long side. This is likely to occur, causing the surface quality of the product to deteriorate and the yield to decrease. Moreover, in order to reduce the said defect, the drastic reduction of a continuous casting speed is required, and the fall of production efficiency is unavoidable.
JP 59-1632 A JP 59-229464 A Japanese Patent Laid-Open No. 2-77522 JP 2000-212687 A

The present invention was made in view of such circumstances, and an object thereof is to provide a method for manufacturing a precipitation strengthening type high strength thin steel plate which can achieve both excellent continuous castability and high strength.

  As a result of intensive studies to solve the above problems, the present inventors have found that surface cracks (lateral cracks) in the continuous casting process are caused by the carbonitrides of Ti, Nb, and V, which are precipitation strengthening elements. It has been found that such surface cracks can be controlled by making the nitrogen extremely low, thereby making it possible to remarkably improve the continuous castability without reducing the product strength. Further, as a result of studying various chemical properties, surface properties, and chemical composition for improving continuous castability and manufacturing methods necessary for high-strength steel sheets for automobiles, the present invention has been completed.

This invention is completed based on such knowledge, and provides the following (1)- (8) .
(1) By mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01 % Or less, N: 0.0019% or less, Sol. A steel containing Al: 0.01 to 0.1%, Ti: 0.03 to 0.09%, the balance being Fe and inevitable impurities is continuously cast into a slab, and this slab is directly or A method for producing a high-strength thin steel sheet, which is once cooled and heated, hot-rolled at 830 ° C or higher, cooled at an average cooling rate of 20 ° C / sec or higher, and then wound at 500 to 620 ° C.
(2) By mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01 % Or less, N: 0.0019% or less, Sol. A steel containing Al: 0.01 to 0.1%, Nb: 0.03 to 0.09%, the balance being Fe and inevitable impurities is continuously cast into a slab, and this slab is directly or A method for producing a high-strength thin steel sheet, which is once cooled and heated, hot-rolled at 830 ° C or higher, cooled at an average cooling rate of 20 ° C / sec or higher, and then wound at 500 to 620 ° C.
(3) By mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01 % Or less, N: 0.0019% or less, Sol. Al: 0.01 to 0.1%, and Ti and Nb satisfy the range of Ti: 0.01% or more, Nb: 0.01% or more, and Ti + Nb: 0.03 to 0.15% In this case, the steel containing the balance of Fe and inevitable impurities is continuously cast into a slab. The slab is directly or once cooled and heated, and then hot-rolled at 830 ° C. or higher, and an average cooling rate of 20 ° C. After cooling at / sec or more, the manufacturing method of the high strength thin steel plate characterized by winding at 500-620 degreeC.
(4) The method for producing a high-strength thin steel sheet according to any one of (1) to (3) above, wherein continuous annealing is further performed at 820 ° C. or less, and hot dip galvanizing or alloying hot dip galvanizing is performed.
(5) By mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01 % Or less, N: 0.0019% or less, Sol. A steel containing Al: 0.01 to 0.1%, Ti: 0.03 to 0.09%, the balance being Fe and inevitable impurities is continuously cast into a slab, and this slab is directly or Once cooled and heated, hot-rolled at 830 ° C. or higher, cooled at an average cooling rate of 20 ° C./sec or higher, and then wound at 500 to 620 ° C. to form a hot-rolled steel plate. A method for producing a high-strength thin steel sheet, which is rolled and continuously annealed at 720 to 820 ° C.
(6) By mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01 % Or less, N: 0.0019% or less, Sol. A steel containing Al: 0.01 to 0.1%, Nb: 0.03 to 0.09%, the balance being Fe and inevitable impurities is continuously cast into a slab, and this slab is directly or Once cooled and heated, hot-rolled at 830 ° C. or higher, cooled at an average cooling rate of 20 ° C./sec or higher, and then wound at 500 to 620 ° C. to form a hot-rolled steel plate. A method for producing a high-strength thin steel sheet, which is rolled and continuously annealed at 720 to 820 ° C.
(7) By mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01 % Or less, N: 0.0019% or less, Sol. Al: 0.01 to 0.1%, and Ti and Nb satisfy the range of Ti: 0.01% or more, Nb: 0.01% or more, and Ti + Nb: 0.03 to 0.15% In this case, the steel containing the balance of Fe and inevitable impurities is continuously cast into a slab. The slab is directly or once cooled and heated, and then hot-rolled at 830 ° C. or higher, and an average cooling rate of 20 ° C. Of high strength thin steel sheet characterized by being rolled at 500 to 620 ° C. to be a hot rolled steel sheet, cold-rolled and continuously annealed at 720 to 820 ° C. Production method.
(8) The method for producing a high-strength thin steel sheet according to any one of (1) to (7) above, further containing V: 0.01 to 0.2% by mass%.

According to the present invention, it is possible to obtain a method for producing a high strength thin steel plate having excellent continuous castability and high strength. For this reason, since the yield fall by the surface defect in a continuous casting process and the fall of the production efficiency by the fall of a continuous casting speed can be suppressed, a high strength steel plate can be manufactured at low cost.

  Hereinafter, the present invention will be specifically described by dividing it into chemical components and production methods.

[Chemical composition]
First, the reasons for limiting the chemical components of the steel sheet of the present invention will be described. In the following description, “%” means “% by mass”.
C: 0.04 to 0.09%
C precipitates as Ti, Nb, V and carbides, and greatly contributes to strengthening. If the content is less than 0.04%, Ti, Nb and V carbides are not sufficiently precipitated, and the strength is remarkably lowered. On the other hand, if it exceeds 0.09%, surface cracks (longitudinal cracks) parallel to the drawing direction due to non-uniform solidification occur in the continuous casting process, so the yield and production efficiency are significantly reduced. Therefore, the C content is 0.04 to 0.09%. From the viewpoint of obtaining high joint strength in the spot welded portion, 0.06% or more is desirable.

Si: 0.50% or less Since Si strengthens the ferrite phase in solid solution, it may be added to improve the strength. However, if the content exceeds 0.50%, surface defects called red scale occur in the hot rolling process, and the yield decreases. Therefore, the Si content is 0.50% or less. From the viewpoint of obtaining good chemical conversion properties, 0.15% or less is desirable.

Mn: 1.20 to 1.80%
Mn is an important element for stably achieving a high precipitation strengthening amount. If the content is less than 1.20%, the precipitate becomes coarse and sufficient strength cannot be obtained. On the other hand, if it exceeds 1.80%, the structure of steel becomes a needle-like ferrite structure or a bainite structure after hot rolling, and sufficient elongation cannot be obtained. Therefore, the Mn content is 1.20 to 1.80%. From the viewpoint of obtaining good plating adhesion as a plating original plate, 1.60% or less is desirable.

P: 0.050% or less Since P strengthens the ferrite phase by solid solution strengthening, P may be added to improve the strength. However, if the content exceeds 0.050%, the spot welding strength decreases. Therefore, the P content is 0.050% or less.

S: 0.01% or less S is contained as an impurity in the steel sheet. However, if the content exceeds 0.01%, the weldability is significantly reduced. Therefore, the S content is set to 0.01% or less. From the viewpoint of obtaining good stretch flangeability, 0.005% or less is desirable.

N: 0.0019% or less N is contained as an impurity in the steel sheet. N is harmful because it promotes the formation of surface cracks in the continuous casting process, and when its content exceeds 0.0019%, its influence becomes extremely significant. Therefore, the N content is 0.0019% or less. From the viewpoint of enhancing the effect of suppressing the formation of surface cracks, 0.0015% or less is desirable.
The present invention is characterized by significantly reducing the yield and production efficiency by suppressing surface cracks in the continuous casting process due to the formation of Ti, Nb, and V carbonitrides by significantly reducing N in this way. There is.
Means for reducing N are not particularly limited, and various steelmaking techniques, for example, promotion of denitrification in converter blowing, nitrogen pickup suppression technique from the atmosphere, vacuum degassing method, etc., or By using it alone, N may be reduced to the above range.

Sol. Al: 0.01 to 0.1%
Al is added for deoxidation in the steelmaking process. Sol. If the Al content is less than 0.01%, the effect of deoxidation is not sufficient, and if it exceeds 0.1%, the effect is saturated, and weldability and plating properties are deteriorated. Therefore, Sol. Al content shall be 0.01 to 0.1%.

Ti and Nb are added singly or in combination for precipitation strengthening. Further, V may be further added as a selective component for precipitation strengthening.
Ti: 0.03 to 0.09%
Ti precipitates as carbonitride and increases the strength. When added alone, if the content is less than 0.03%, this effect is not sufficient. On the other hand, if it exceeds 0.09%, the occurrence of surface cracks in continuous casting becomes significant, and the yield and production efficiency decrease. Therefore, when adding Ti alone, the content is made 0.03 to 0.09%.

Nb: 0.03 to 0.09%
Nb precipitates as carbonitride and increases the strength. When added alone, if the content is less than 0.03%, this effect is not sufficient. On the other hand, if it exceeds 0.09%, the occurrence of surface cracks in continuous casting becomes significant, and the yield and production efficiency decrease. Therefore, when adding Nb independently, the content shall be 0.03-0.09%. From the viewpoint of improving production efficiency in the hot rolling process and the cold rolling process, 0.05% or less is desirable.

Ti and Nb are Ti: 0.01% or more, Nb: 0.01% or more, and Ti + Nb: 0.03-0.15%
By adding Ti and Nb in combination, the strength and continuous castability can be improved with a better balance than when they are added alone. This is because conditions such as the temperature at which surface cracks are likely to occur in continuous casting due to degradation of crack resistance characteristics are different for Ti and Nb, so this deterioration at each specific temperature is greatly mitigated when combined addition, This is considered to be because the generation of surface cracks is mitigated by averaging. When the content of each of Ti and Nb is less than 0.01%, the effect of composite addition cannot be obtained. Furthermore, if the content of Ti + Nb is less than 0.03%, the strength is insufficient. On the other hand, if it exceeds 0.15%, the occurrence of surface cracks in continuous casting becomes remarkable, and the yield and production efficiency decrease. Therefore, when Ti and Nb are added together, the contents of Ti and Nb are Ti: 0.01% or more, Nb: 0.01% or more, and Ti + Nb: 0.03 to 0.15%. .

V: 0.01 to 0.2%
V is added in combination with Ti and Nb, and has the effect of refining precipitates and improving strength, and is added as necessary. If the content is less than 0.01%, this effect is not sufficient, and if it exceeds 0.2%, surface cracks occur in continuous casting, and the yield and production efficiency decrease. Therefore, when adding V, the content is made 0.01 to 0.2%.

  The balance consists of Fe and inevitable impurity elements. Such inevitable impurity elements are allowed within a range that does not deteriorate the high strength and excellent continuous castability that are the object of the present invention. For example, Cu: 0.1% or less, Ni: 0.1% or less, Sn: 0.01% or less, Mo: 0.01% or less, Cr: 0.1% or less, Sb: 0.01% or less, O: 0.003% or less, Zr: 0.01% or less it can.

[Production method]
Next, the manufacturing method of the present invention will be described.
-Continuous casting of steel having the above chemical composition and composition In the present invention, the slab is cast by a continuous casting method. This is because the continuous casting method is a premise from the problem of the present invention and has a higher production efficiency than the mold casting method. The continuous casting machine is preferably a vertical bending die. This is because the vertical bending die is excellent in the balance between equipment cost and surface quality, and exhibits a remarkable effect of suppressing surface cracks. The drawing speed of continuous casting is desirably 2.0 m / min or more. This is because the effect of suppressing surface cracks of the present invention becomes more remarkable at 2.0 m / min or more. Further, the surface temperature of the slab in the bending band and the straightening band in continuous casting is desirably 600 ° C. or lower or 850 ° C. or higher. This is because when the slab is bent and deformed at a temperature exceeding 600 ° C. and less than 850 ° C., surface cracks (lateral cracks) are likely to occur.

-After continuous casting, the slab is directly or once cooled and heated, hot-rolled at 830 ° C or higher, cooled at an average cooling rate of 20 ° C / sec or higher, and then wound at 500 to 620 ° C. The rolling start temperature in the case of direct rolling is preferably 1000 ° C. or higher, and the heating temperature in the case of once cooling and heating is preferably 1150 ° C. or higher. This is because when the rolling start temperature is less than 1000 ° C., the rolling load becomes high and the production efficiency of hot rolling slightly decreases. Moreover, it is for heating at 1150 degreeC or more to accelerate | stimulate solutionization of a carbonitride production | generation element, and to improve a reinforcement capability further. The reason why the slab after continuous casting is hot-rolled at 830 ° C. or higher is that when it is hot-rolled below 830 ° C., the structure becomes non-uniform and the elongation deteriorates. Moreover, the average cooling rate after hot rolling is 20 ° C./sec or more because if it is less than 20 ° C./sec, coarse Ti, Nb, and V carbonitrides that do not contribute to strengthening when heated to a high temperature. This is because the strength is remarkably lowered due to precipitation. The coiling temperature is set to 500 to 620 ° C., when the coiling temperature is less than 500 ° C., the bainite structure is generated and the elongation is lowered. On the other hand, when the coiling temperature exceeds 620 ° C., coarse Ti that does not contribute to strengthening, This is because Nb and V carbonitrides precipitate, so that the strength is remarkably lowered. Here, after the hot rolling, continuous annealing may be performed at 820 ° C. or less, and hot dip galvanizing or alloying hot dip galvanizing may be performed. Annealing is performed in order to reduce the surface oxide film and improve the plating property. The reason why the annealing temperature is set to 820 ° C. or lower is that when the temperature exceeds 820 ° C., the precipitates of Ti, Nb, and V become coarse and the strength decreases.

-In addition to the said process as needed, it cold-rolls and performs continuous annealing at 720-820 degreeC Cold rolling may be a conventional method. Annealing is performed for the purpose of removing cold rolling strain by recrystallization to improve workability, or reducing the surface oxide film to improve surface treatment properties such as plating and chemical conversion treatment. The continuous annealing is performed because the production efficiency can be increased as compared with the batch annealing and the softening of the steel sheet due to the coarsening of the precipitates can be suppressed. The reason for setting the continuous annealing temperature to 720 to 820 ° C. is that if the annealing temperature is less than 720 ° C., the effect of annealing is not sufficient, and if it exceeds 820 ° C., the precipitates of Ti, Nb and V become coarse and the strength decreases. is there. In the continuous annealing step, hot dip galvanizing or alloying hot dip galvanizing may be performed simultaneously.

  The hot-rolled steel sheet or cold-rolled steel sheet manufactured as described above may be subjected to a skin pass for shape correction and surface roughness adjustment. Furthermore, various surface treatments such as electrogalvanization and organic lubricating coating may be performed.

  Examples of the present invention will be specifically described below.

Example 1
Steel numbers 1 to 22 having the chemical components and compositions shown in Table 1 were continuously cast into slabs. The casting speed was 2.0 to 2.5 m / min. The slab surface temperature of the bending band was 860 to 950 ° C., and the slab surface temperature of the correction band was 850 to 910 ° C. After cooling to 700 ° C. or lower once, it was heated to 1150 to 1250 ° C. and hot rolled. The final rolling temperature was 830 to 850 ° C., and the finished plate thickness was 1.6 to 3.2 mm. Immediately after hot rolling, it was cooled at an average cooling rate of 25 to 80 ° C./second and wound up at 520 to 600 ° C. Further, steel numbers 10 and 11 were annealed at 800 ° C. after cold rolling at a rolling rate of 50%.

  Table 2 shows the evaluation results of mechanical properties and surface defects. For mechanical properties, a JIS No. 5 tensile test piece was taken at right angles to the rolling direction and tested in accordance with JIS Z2241. For surface defects, the surface of the product plate was visually evaluated, and for defective materials, the defect classification (see Japan Iron and Steel Institute hot-rolled steel sheet manual (2000), P44) was noted.

  As is apparent from Table 2, steel numbers 2 to 11 as examples of the present invention have both high strength of 590 MPa class or higher and high elongation of 25% or more in mechanical properties. In addition, despite the high speed casting of 2.0 m / min or higher, a good surface free from surface defects due to surface cracks in the slab was obtained. On the other hand, in the steel numbers 12-22 which are comparative examples, either characteristic was inferior. Steel No. 12 had a high C, and slab solidification cracking occurred, which caused surface defects due to nicks. Since Steel No. 13 had high Si, a surface defect called red scale occurred in the hot rolling process. Steel No. 14 had a low Mn, so the precipitates became coarse and the strength was low. Steel No. 15 had a high Mn and a bainite structure, so the elongation was low. Steel Nos. 16, 17, and 18 had high N, so surface cracks occurred in the slab during the continuous casting process, resulting in product surface defects. Steel No. 19 had a high Nb, so that a surface crack occurred in the slab during the continuous casting process, resulting in a surface defect of the product. Since Steel No. 20 had high Ti, surface cracks occurred in the slab during the continuous casting process, resulting in product surface defects. Steel No. 21 had a high Nb + Ti, so that a surface crack occurred in the slab during the continuous casting process, resulting in a product surface defect. Since Steel No. 22 had a high V, surface cracks occurred in the slab during the continuous casting process, resulting in product surface defects. Steel Nos. 2 and 9 in the inventive examples were slightly higher than N in excess of 0.0015%, and a slight baldness was generated on the surface of the product. It was.

(Example 2)
Hot-rolled steel sheets and cold-rolled steel sheets were manufactured under the manufacturing conditions shown in Table 3. The steel numbers are as shown in Table 1. The plate thickness of the hot-rolled steel plate is 1.6 to 3.2 mm, and the plate thickness of the cold-rolled steel plate is 1.2 to 2.0 mm. Reference symbol L was hot-rolled, pickled, and annealed and hot-dip galvanized in a continuous hot-dip galvanizing facility (hereinafter referred to as “CGL”). Cold rolling was performed after removing the scale by pickling. Reference symbols Y and Z were pickled and cold-rolled, and then annealed and hot-dip galvanized with CGL.

  Table 4 shows the evaluation results of mechanical properties and surface defects. For mechanical properties, a JIS No. 5 tensile test piece was taken at right angles to the rolling direction and tested in accordance with JIS Z2241. For surface defects, the surface of the product plate was visually evaluated, and for defective materials, the defect classification published by the Japan Iron and Steel Institute Hot Rolled Steel Sheet Manual (2000), P44) was noted.

  The results are shown in Table 4. Since the coil | winding temperature was low for the code | symbol C, the deposit coarsened and elongation fell. Since the finishing temperature of the hot rolling was low for the code D, the structure became non-uniform and the elongation decreased. Code F had a low average cooling rate after hot rolling, so the precipitates became coarse and the strength decreased. Since the winding temperature of the code | symbol I was high, the precipitate coarsened and the intensity | strength fell. Since the finishing temperature of the hot rolling of M is low, the structure becomes non-uniform and the elongation decreases. Since the winding temperature of the code N is high, the precipitate is coarsened and the strength is lowered. The symbol R had a low average cooling rate after hot rolling, resulting in coarse precipitates and a decrease in strength. Since S has a low annealing temperature, it was not sufficiently recrystallized and the elongation was significantly reduced. Since the annealing temperature of the code T is high, the precipitates are coarsened and the strength is remarkably reduced. On the other hand, in other examples, the mechanical properties were both high strength of 590 MPa class or higher and high elongation of 25% or more. In addition, despite the high speed casting of 2.0 m / min or higher, a good surface free from surface defects due to surface cracks in the slab was obtained. Note that among the manufacturing conditions within the scope of the present invention, the symbols V, W, and X are minute on the surface of the product because the slab surface temperature of either the bending band or the straightening band is higher than 600 ° C. and lower than 850 ° C. Although baldness occurred, it was at a level where there was no practical problem.

  The present invention realizes excellent surface properties, high efficiency, and low cost, which has been difficult to achieve with high strength in the past, and is used for automobile bodies, reinforcing materials, wheels, undercarriage parts, and other machines. Applicable to structural parts. In particular, increasing the strength of steel sheets for automobiles is the most effective means for improving the fuel efficiency and safety of automobiles, so there are great social expectations for high-efficiency, low-cost, high-strength steel sheets. The invention is considered to be extremely useful in industry.

Claims (8)

In mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01% or less, N: 0.0019% or less, Sol. A steel containing Al: 0.01 to 0.1%, Ti: 0.03 to 0.09%, the balance being Fe and inevitable impurities is continuously cast into a slab, and this slab is directly or A method for producing a high-strength thin steel sheet, which is once cooled and heated, hot-rolled at 830 ° C or higher, cooled at an average cooling rate of 20 ° C / sec or higher, and then wound at 500 to 620 ° C. In mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01% or less, N: 0.0019% or less, Sol. A steel containing Al: 0.01 to 0.1%, Nb: 0.03 to 0.09%, the balance being Fe and inevitable impurities is continuously cast into a slab, and this slab is directly or A method for producing a high-strength thin steel sheet, which is once cooled and heated, hot-rolled at 830 ° C or higher, cooled at an average cooling rate of 20 ° C / sec or higher, and then wound at 500 to 620 ° C. In mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01% or less, N: 0.0019% or less, Sol. Al: 0.01 to 0.1%, and Ti and Nb satisfy the range of Ti: 0.01% or more, Nb: 0.01% or more, and Ti + Nb: 0.03 to 0.15% In this case, the steel containing the balance of Fe and inevitable impurities is continuously cast into a slab. The slab is directly or once cooled and heated, and then hot-rolled at 830 ° C. or higher, and an average cooling rate of 20 ° C. After cooling at / sec or more, the manufacturing method of the high strength thin steel plate characterized by winding at 500-620 degreeC. The method for producing a high-strength thin steel sheet according to any one of claims 1 to 3, further comprising performing continuous annealing at 820 ° C or less and performing hot dip galvanizing or alloying hot dip galvanizing. In mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01% or less, N: 0.0019% or less, Sol. A steel containing Al: 0.01 to 0.1%, Ti: 0.03 to 0.09%, the balance being Fe and inevitable impurities is continuously cast into a slab, and this slab is directly or Once cooled and heated, hot-rolled at 830 ° C. or higher, cooled at an average cooling rate of 20 ° C./sec or higher, and then wound at 500 to 620 ° C. to form a hot-rolled steel plate. A method for producing a high-strength thin steel sheet, which is rolled and continuously annealed at 720 to 820 ° C. In mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01% or less, N: 0.0019% or less, Sol. A steel containing Al: 0.01 to 0.1%, Nb: 0.03 to 0.09%, the balance being Fe and inevitable impurities is continuously cast into a slab, and this slab is directly or Once cooled and heated, hot-rolled at 830 ° C. or higher, cooled at an average cooling rate of 20 ° C./sec or higher, and then wound at 500 to 620 ° C. to form a hot-rolled steel plate. A method for producing a high-strength thin steel sheet, which is rolled and continuously annealed at 720 to 820 ° C. In mass%, C: 0.04 to 0.09%, Si: 0.50% or less, Mn: 1.20 to 1.80%, P: 0.050% or less, S: 0.01% or less, N: 0.0019% or less, Sol. Al: 0.01 to 0.1%, and Ti and Nb satisfy the range of Ti: 0.01% or more, Nb: 0.01% or more, and Ti + Nb: 0.03 to 0.15% In this case, the steel containing the balance of Fe and inevitable impurities is continuously cast into a slab. The slab is directly or once cooled and heated, and then hot-rolled at 830 ° C. or higher, and an average cooling rate of 20 ° C. Of high strength thin steel sheet characterized by being rolled at 500 to 620 ° C. to be a hot rolled steel sheet, cold-rolled and continuously annealed at 720 to 820 ° C. Production method. The method for producing a high-strength thin steel sheet according to any one of claims 1 to 7, further comprising V: 0.01 to 0.2% in terms of mass%.