JP2004238687A - High-tension hot-rolled steel sheet and high-tension plated steel sheet which are excellent in bake hardenability and ductility and their production methods - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-tension hot-rolled steel sheet and a high-tension plated steel sheet which are excellent in non-aging property at room temperature whose bake hardenability and ductility can be improved without further decreasing the crystal grain size or increasing the amount of solid solution N. <P>SOLUTION: The high-tension hot-rolled steel sheet has a composition comprising, by mass, 0.05-0.15% C, ≤0.5% Si, 1.2-3.0% Mn, 0.05-1.0% Mo, ≤0.05% P, 0.001-0.1% Al, 0.005-0.02% N and the balance being Fe and unavoidable impurities and has a steel structure comprising, by area, 10-50% low-temperature transformed ferrite phase and the balance substantially being polygonal ferrite phase. The average crystal grain size of the two phases, i.e. the low-temperature transformed ferrite phase and the polygonal ferrite phase, is ≤8 μm. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

【００３８】
【表２】

【００３９】
【表３】

【００４０】
表３から明らかなように、本発明に従い、所定の成分調整をした上で、鋼組織を低温変態フェライト相が面積率で１０〜５０％含有する組織とすることにより、強度−延性バランスが １６０００ ＭＰａ・％以上と、同一強度レベルで見た時の延性に優れ、またＢＨ １００ ＭＰａ以上、ΔＴＳ ９０ ＭＰａ 以上、ΔＥｌ １．５％以下の、焼付硬化性および耐常温時効性に優れた高張力熱延鋼板および高張力めっき鋼板を得ることができた。
【００４１】
【発明の効果】
かくして、本発明によれば、自動車の内板部品等に使用して好適な、焼付硬化性および延性に優れ、また耐常温時効性も良好な高張力熱延鋼板および高張力めっき鋼板を安定して得ることができる。
【図面の簡単な説明】
【図１】製品板の焼付け硬化量（ΔＴＳ）に及ぼす低温変態フェライト相の影響を、鋼板の平均結晶粒径をパラメータとして示した図である。
【図２】本発明に従う冷却曲線を示した模式図である。[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a high-strength hot-rolled steel sheet and a high-strength plated steel sheet suitable for use in structural members and undercarriage members of automobiles, and a method for producing the same, and particularly to an advantageous improvement in bake hardenability and ductility. Is what you do.
The improvement in bake hardenability in the present invention means not only the yield strength after processing and bake coating, but also the improvement in tensile strength. The improvement in ductility means an improvement in elongation when viewed at the same strength level, that is, an improvement in a so-called strength-ductility balance (TS × El).
[0002]
[Prior art]
Patent Document 1 proposes a method of manufacturing a bake hardening type high-tensile hot-rolled steel sheet, which comprises hot rolling a steel containing a large amount of N, and then rapidly cooling the steel to 350 ° C. or lower.
However, the hot-rolled steel sheet manufactured by the above technique has a composite structure mainly composed of ferrite and martensite, and is a technique of imparting bake hardenability by adding N, and has a tensile strength after processing-paint baking treatment. Although the hardness increases, there is a problem that the room temperature aging resistance is deteriorated because there is no consideration for the room temperature aging resistance.
[0003]
Patent Document 2 proposes a hot-rolled steel sheet having improved bake hardenability and normal-temperature aging resistance by controlling the refinement of crystal grains and the amount and existence form of solute N.
However, in order to further improve the bake hardenability using this technique, it is necessary to further refine the crystal grains or further increase the amount of solute N. However, it is actually difficult to further refine the crystal grains. However, since increasing the amount of solute N causes deterioration of ductility due to aging at ordinary temperature, there is a limit to the improvement by this technique.
[0004]
[Patent Document 1]
JP-A-4-74824 [Patent Document 2]
JP 2000-297350 A
[Problems to be solved by the invention]
The present invention relates to the improvement of the technology disclosed in Patent Document 2 described above, and further improves bake hardenability and ductility without necessitating further refinement of crystal grains and further increase in the amount of solute N, and It is an object of the present invention to propose a high-strength hot-rolled steel sheet and a high-strength plated steel sheet which are also excellent in aging resistance at normal temperature, together with their advantageous production methods.
[0006]
[Means for Solving the Problems]
By the way, the present inventors have conducted intensive research to achieve the above object, and as a result, after adjusting the composition of steel to a predetermined range, strictly control the manufacturing process of the steel sheet, the structure of the hot-rolled steel sheet It has been found that by controlling the composition to an appropriate composition, remarkable improvements in bake hardenability and ductility can be achieved without deterioration of the aging resistance at room temperature.
The present invention is based on the above findings.
[0007]
That is, the gist configuration of the present invention is as follows.
1. C: 0.05 to 0.15% by mass%,
Si: 0.5% or less,
Mn: 1.2 to 3.0%,
Mo: 0.05 to 1.0%,
P: 0.05% or less,
Al: 0.001 to 0.1% and N: 0.005 to 0.02%
And the remainder has a composition of Fe and unavoidable impurities, the low-temperature transformed ferrite phase has an area ratio of 10 to 50%, and the balance substantially has a steel structure of a polygonal ferrite phase. A high-tensile hot-rolled steel sheet excellent in bake hardenability and ductility, characterized in that the average crystal grain size of two phases of a low-temperature transformed ferrite phase and a polygonal ferrite phase is 8 μm or less.
[0008]
2. The bake hardenability according to 1 above, wherein the steel sheet further has a composition containing one or two selected from among Cr: 1.0% or less and Ni: 1.0% or less by mass%. High tensile strength hot rolled steel sheet with excellent ductility.
[0009]
3. The printing according to 1 or 2, wherein the steel sheet further has a composition containing one or two selected from Ti: 0.1% or less and Nb: 0.1% or less by mass%. High tension hot rolled steel sheet with excellent curability and ductility.
[0010]
4. In any one of the above items 1 to 3, a high-strength plated steel sheet excellent in bake hardenability and ductility, wherein a plated layer is formed on the surface of the steel sheet.
[0011]
5. C: 0.05 to 0.15% by mass%,
Si: 0.5% or less,
Mn: 1.2 to 3.0%,
Mo: 0.05 to 1.0%,
P: 0.05% or less,
Al: 0.001 to 0.1% and N: 0.005 to 0.02%
Is heated to 1000 to 1300 ° C., and after rough rolling, finish rolling is finished under the conditions of finish rolling exit temperature: (Ar ₃ + 10 ° C.) to (Ar ₃ + 100 ° C.). After that, it is cooled to a temperature range of 750 to 600 ° C. at a speed of 50 ° C./s or more within 1.7 seconds, kept at this temperature range for 3 to 15 seconds, and then cooled at a speed of 20 ° C./s or more, A method for producing a high-tensile hot-rolled steel sheet excellent in bake hardenability and ductility, wherein the steel sheet is wound at a temperature of 500 to 250 ° C.
[0012]
The steel material used in this production method is as described above: C: 0.05 to 0.15%, Si: 0.5% or less, Mn: 1.2 to 3.0%, Mo: 0.05 to 1.0% or less, P: 0.05% or less, Al: 0.001 to 0.1%, and N: 0.005 to 0.02%, with the balance being Fe and inevitable impurities. However, the steel further contains one or two selected from among Cr: 1.0% or less and Ni: 1.0% or less, with the balance being the composition of Fe and unavoidable impurities. And / or further contained in the steel one or two selected from among Ti: 0.1% or less and Nb: 0.1% or less, with the balance being Fe and unavoidable impurities. It may be.
[0013]
6. 5. The method for producing a high-strength plated steel sheet excellent in bake hardenability and ductility according to the above item 5, wherein the surface of the steel sheet is plated after winding.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the present invention will be described specifically.
In the present invention, the reason for limiting the component composition of the steel sheet to the above range will be described. In addition, "%" display about a component shall mean the mass% (mass%) unless there is particular notice.
C: 0.05-0.15%
C is an element that is useful not only for increasing the strength of the steel but also for suppressing the coarsening of crystal grains. However, if the content is less than 0.05%, the effect of adding C is poor. If it exceeds .15%, the weldability deteriorates, so the C content needs to be 0.15% or less, more preferably 0.12% or less.
[0015]
Si: 0.5% or less Si is an element that increases the strength of steel by solid solution strengthening, and its content can be appropriately adjusted according to the required strength. However, if the content exceeds 0.5%, not only does the workability deteriorate, but also the formation of low-temperature transformed ferrite is hindered, so the Si content was limited to 0.5% or less.
[0016]
Mn: 1.2 to 3.0%
Mn is a solid solution strengthening element and is a basic constituent element for obtaining a high strength steel sheet. It also effectively contributes to the formation of low-temperature transformed ferrite. However, when the content is less than 1.2%, the effect of the addition is poor. On the other hand, when the content exceeds 3.0%, not only the workability is deteriorated, but also the weldability is adversely affected. It was limited to the range of 2 to 3.0%.
[0017]
Mo: 0.05 to 1.0%
Mo not only effectively contributes to increasing the strength of steel by solid solution strengthening, but also stabilizes austenite, thereby facilitating the formation of a low-temperature transformed ferrite phase in hot rolling, and cooling after hot rolling. This has the effect of allowing time to start. However, if the content is less than 0.05%, the effect of the addition is poor. On the other hand, if the content exceeds 1.0%, the formation of a low-temperature ferrite phase is hindered, so that the content is limited to 0.05 to 1.0%. I do. Further, it is recommended that the content of Mo be preferably more than 0.1 to 0.5%, more preferably 0.20% or less.
[0018]
P: 0.05% or less P is an element that increases the strength of steel, and its content is appropriately adjusted as necessary. However, if the content exceeds 0.05%, the weldability deteriorates, P may segregate at the grain boundaries, causing the generation of grain boundary cracks, and further inhibits the formation of low-temperature transformed ferrite. The P content was limited to 0.05% or less.
[0019]
Al: 0.001 to 0.1%
Al is an element that is useful as a deoxidizing agent. To deoxidize steel, it is necessary to contain at least 0.001%, but if it exceeds 0.1%, not only the surface properties deteriorate, but also Since it is difficult to secure a fixed amount of dissolved N, Al is contained in the range of 0.001 to 0.1%.
[0020]
N: 0.005 to 0.02%
N is a particularly important element in the present invention, and works effectively to increase the yield strength and tensile strength after the work-paint baking treatment by forming a solid solution in steel. For this purpose, the content of N is required to be not less than 0.005%, but if it exceeds 0.02%, not only the occurrence rate of internal defects is increased, but also slab cracks and the like occur frequently during continuous casting. Become like Therefore, the N content is limited to the range of 0.005 to 0.02%. More preferably, it is in the range of 0.007 to 0.02%.
[0021]
As described above, the essential components have been described. However, in the present invention, other elements described below can be appropriately contained.
One or more of Cr and Ni selected from Cr: 1.0% or less and Ni: 1.0% or less not only effectively contribute to the increase in the strength of steel by solid solution strengthening, but also The effect of stabilizing austenite has an effect of easily forming a low-temperature transformed ferrite phase in hot rolling. To obtain this effect, the contents of Cr and Ni are each preferably set to 0.1% or more. However, in any case, if the content exceeds 1.0%, the formation of the low-temperature transformed ferrite phase is hindered, so that each content is set to 1.0% or less.
[0022]
One or two selected from Ti: 0.1% or less and Nb: 0.1% or less Ti and Nb form carbides and nitrides, respectively, thereby effectively contributing to improvement in strength and toughness. I do. In order to obtain this effect, the contents of Ti and Nb are each preferably set to 0.01% or more. However, when the content exceeds 0.1%, solid solution N is fixed as a nitride, and on the contrary, the bake hardenability is lowered. Therefore, each content is set to 0.1% or less.
As described above, the essential components and the optional components have been described, but the balance other than the above components is Fe and inevitable impurities.
[0023]
In the present invention, it is not sufficient to simply adjust the component composition range to the above range, and it is necessary to also specify the structure and particle size.
Low-temperature transformed ferrite phase area ratio V (α _B ): 10 to 50%
Low-temperature transformation ferrite alpha _B here is ferrite usual meanings: the (polygonal ferrite alpha _P) are distinguished, in ferrite produced in a low temperature range (approximately 500 ° C. or less), the bainitic ferrite or upper bainite Means that. This structure is particularly important in the present invention and is responsible for high bake hardenability.
Bake hardening is a phenomenon in which interstitial solid solution elements (C, N) in steel fix dislocations in the steel, and the strength increases due to an increase in resistance to the movement of the dislocations. In the low-temperature transformation ferrite structure, the effect is promoted because the dislocation density is originally high, and the fixed dislocation acts as a resistance to the movement of the dislocation during plastic deformation, so that it exhibits extremely high bake hardenability. become.
In order to effectively improve bake hardening due to this structure, low-temperature transformed ferrite having an area ratio V (α _B ) of at least 10% is required. However, if it exceeds 50%, the amount of polygonal ferrite is relatively reduced and ductility is deteriorated. Therefore, in the present invention, the amount of the low-temperature transformed ferrite phase is in the range of 10 to 50% in terms of area ratio V (α _B ). Limited.
[0024]
Except for the low-temperature transformation ferrite phase, it substantially consists of a polygonal ferrite phase. As described above, by using polygonal ferrite other than low-temperature transformation ferrite, remarkable improvement in ductility can be achieved.
In addition, as a phase other than the above-mentioned low-temperature transformation ferrite phase and polygonal ferrite phase, a martensite phase or a pearlite phase may be generated, but it becomes difficult to obtain a desired effect when these phases become too large. Therefore, it is preferable that these phases be suppressed to an area ratio of 10% or less.
That is, it is preferable that the total area ratio of the two phases of the low-temperature transformed ferrite phase and the polygonal ferrite phase be 90% or more.
[0025]
The average crystal grain size of the low-temperature transformed ferrite phase and the polygonal ferrite phase is 8 μm or less. The average crystal grain size referred to herein is the two phases of the low-temperature transformed ferrite phase (α _B ) and the polygonal ferrite phase (α _P ). It is important to limit this average crystal grain size to 8 μm or less.
FIG. 1 shows the relationship between the area ratio of the low-temperature transformed ferrite phase and the bake hardening amount (ΔTS) of the product plate for steel type A in Table 1 described below, which has an average crystal grain size of 8 μm or less and 10 to 15 μm. As shown in the figure, when the average crystal grain size is more than 8 μm and 10 to 15 μm, the increase in tensile strength is not expected as in the case where the average crystal grain size is 8 μm or less. .
It should be noted that the grain boundary area as an existing position of solid solution N is increased by making the crystal grains fine, but the solid solution N existing in the grain boundary is stable at room temperature and cannot be diffused. Is suppressed. In this regard, when the average crystal grain size exceeds 8 μm, this effect is significantly reduced.
[0026]
The reason why high bake hardenability is obtained by adopting the above configuration is considered as follows.
Bake hardening occurs because mobile dislocations are fixed by solid solution N due to interaction between mobile dislocations and solid solution N generated during pre-processing. At this time, crystal grains are refined. When the crystal grain boundaries increase, the mobile dislocations are distributed at a high density even if the processing is performed by the same amount of strain. Further, it is considered that the low-temperature transformed ferrite structure contains a large amount of mobile dislocations before the pre-working is performed, and the dislocation density after the pre-working is also high, so that a high bake hardenability is exhibited.
[0027]
Next, the reason why the manufacturing conditions of the present invention are limited as described above will be described.
Steel material heating temperature (slab heating temperature): 1000-1300 ° C
In order to secure the desired solid solution N in the hot rolled sheet, it is necessary to dissolve the nitride at the time of heating before hot rolling. However, if the heating temperature of the steel slab is less than 1000 ° C., it is difficult to leave a desired amount of N in a solid solution state in the hot-rolled sheet, while if it exceeds 1300 ° C., the austenite grains during heating are coarse. It is difficult to reduce the average crystal grain size to 8 μm or less. Therefore, the slab heating temperature was limited to the range of 1000 to 1300 ° C. More preferably, it is in the range of 1100 to 1250 ° C.
The rough rolling using the heated slab as a sheet bar may be performed according to a conventional method.
[0028]
Finish rolling exit side temperature: (Ar ₃ + 10 ° C.) to (Ar ₃ + 100 ° C.)
In finish rolling, in order to arrange the structure of the steel sheet uniformly and finely, it is necessary to control the finish-rolling exit side temperature (referred to as FDT) in a range of (Ar ₃ + 10 ° C.) to (Ar ₃ + 100 ° C.). That is, when the FDT is lower than (Ar ₃ + 10 ° C.), the finish rolling temperature becomes too low, the structure becomes non-uniform, and a partially processed structure remains, and various problems occur during press forming. The danger increases. On the other hand, when the FDT exceeds (Ar ₃ + 100 ° C.), it becomes difficult to refine the crystal grains.
[0029]
Cooling after rolling: After finishing rolling, the steel sheet is cooled to a temperature range of 750 to 600 ° C. within 1.7 seconds at a speed of 50 ° C./s or more, and maintained at this temperature range for 3 to 15 seconds. If the finish rolling is performed to cool the film to the winding temperature at a speed of s or more, and if the cooling is not started within 1.7 seconds, not only the crystal grains become coarse, but also it becomes difficult to form a low-temperature ferrite phase. Since N precipitates and it becomes difficult to secure solid solution N, the cooling start time is set to 1.7 seconds or less after finishing rolling. Here, since the formation of low-temperature ferrite phase is facilitated by stabilizing austenite by the inclusion of Mo, it is necessary to provide cooling with a certain margin of 1.7 seconds or less after finish rolling. Can be.
[0030]
If the cooling rate at that time is less than 50 ° C./s, the crystal grains grow during cooling, making it difficult to make finer, and N precipitates to make it difficult to secure solid solution N. Therefore, the cooling rate is 50 ° C. / S or more.
Then, it is cooled to a temperature range of 750 to 600 ° C., because the transformation of polygonal ferrite is particularly promoted in this temperature range, and a remarkable improvement in ductility can be expected. However, if the holding time in this temperature range is less than 3 seconds, the amount of polygonal ferrite generated is insufficient and the effect cannot be expected. On the other hand, if it exceeds 15 seconds, not only the ferrite grains are coarsened, but also Since the amount becomes too large, it becomes difficult to secure a sufficient amount of low-temperature transformed ferrite thereafter, and the desired amount of bake hardening cannot be obtained. Therefore, the holding time in the temperature range of 750 to 600 ° C. The range was limited to 3 to 15 seconds.
[0031]
The holding process in this temperature range may be a so-called holding process for maintaining a constant temperature, or a so-called slow cooling process for cooling at a rate of less than about 20 ° C./s.
Further, after that, the cooling rate to the winding temperature was set to 20 ° C./s or more because if the cooling rate was less than 20 ° C./s, the growth of polygonal ferrite further increased the predetermined low-temperature transformed ferrite phase fraction. This is because it becomes difficult to secure the information.
[0032]
Winding temperature: 500-250 ° C
After the above-mentioned controlled cooling, winding is performed in a temperature range of 500 to 250 ° C. When the winding temperature is higher than 500 ° C., not only is it difficult to obtain a predetermined amount of a low-temperature transformed ferrite phase, but also a reduction in the crystal grain size is not achieved. If the temperature is lower than 0 ° C., a lower-temperature transformation phase such as martensite becomes dominant, and it is also difficult to obtain a desired low-temperature transformation ferrite phase.
[0033]
FIG. 2 shows a cooling curve according to the invention described above.
As shown in the figure, in the present invention, after quenching to the vicinity of the nose of the polygonal ferrite phase, a predetermined amount of the polygonal ferrite phase was generated by holding the polygonal ferrite phase in the generation temperature range for a certain period of time. Thereafter, the ferrite is cooled to a temperature range where a low-temperature transformed ferrite phase is formed, and is wound in this temperature range to generate a predetermined amount of a low-temperature transformed ferrite phase.
[0034]
The hot-rolled steel sheet obtained as described above is suitable as an original plate for various platings, and can be subjected to various plating treatments as necessary.
Here, examples of the type of plating include electro-galvanizing, hot-dip galvanizing, electro-tin plating, electro-chromium plating, and electro-nickel plating. In the present invention, any plating process can be advantageously applied. it can.
[0035]
【Example】
Molten steel having the component composition shown in Table 1 was melted in a converter and slab was formed by continuous casting, and then hot-rolled under the conditions shown in Table 2 to obtain a hot-rolled steel sheet. Note that a part was subjected to a hot-dip galvanizing treatment after winding.
The obtained hot-rolled steel sheet and plated steel sheet were subjected to a structure test, a tensile test, a bake hardening test, and a normal-temperature aging test.
[0036]
In addition, the steel structure was investigated by the enlarged image of the corrosion appearance structure by nital in the cross section in the direction perpendicular to the rolling direction of the hot-rolled steel sheet.
In the tensile test, a JIS No. 5 tensile test piece was sampled from a direction perpendicular to the rolling direction of the hot-rolled steel sheet, and the test was performed at a strain rate of 10 ⁻³ / s.
In the bake hardening test, as in the tensile test, a JIS No. 5 tensile test piece was sampled from a direction perpendicular to the rolling direction of the hot-rolled steel sheet, subjected to aging treatment after prestraining, and a strain rate of 10 ⁻³ / s It carried out on condition of. The baking conditions were pre-strain: 5% and aging conditions: 170 ° C. × 20 minutes.
The bake hardening amount BH and the increase in the tensile strength ΔTS are respectively expressed by the following formula: BH = (yield stress after aging) − (pre-deformation stress before aging treatment)
ΔTS = (tensile strength after aging)-(tensile strength as hot rolled)
Asked by.
In the room temperature aging test, after performing aging treatment at 50 ° C. for 400 hours, a JIS No. 5 tensile test piece was sampled from a direction perpendicular to the rolling direction, and a tensile test was performed at a strain rate of 10 ⁻³ / s. Then, the elongation El _A was measured, and the difference from the elongation before elongation treatment (elongation as hot rolled) El, ΔEl = El−El _A, was evaluated. If the obtained ΔEl is 2.0% or less, it can be said that normal-temperature aging is not a problem.
Table 3 shows the obtained results.
[0037]
[Table 1]

[0038]
[Table 2]

[0039]
[Table 3]

[0040]
As is clear from Table 3, after the steel composition is adjusted to a predetermined composition according to the present invention, and the steel structure is a structure containing a low-temperature transformed ferrite phase in an area ratio of 10 to 50%, the strength-ductility balance is 16,000. MPa ·% or more, excellent ductility when viewed at the same strength level, and high tensile strength excellent in bake hardenability and normal temperature aging resistance of 100 MPa or more, ΔTS 90 MPa or more, and ΔEl 1.5% or less. A hot rolled steel sheet and a high-strength plated steel sheet were obtained.
[0041]
【The invention's effect】
Thus, according to the present invention, it is possible to stably produce a high-strength hot-rolled steel sheet and a high-strength plated steel sheet which are suitable for use as an inner plate part of an automobile, have excellent baking hardenability and ductility, and also have good aging resistance at ordinary temperature. Can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram showing the effect of a low-temperature transformed ferrite phase on the bake hardening amount (ΔTS) of a product sheet using the average crystal grain size of a steel sheet as a parameter.
FIG. 2 is a schematic diagram showing a cooling curve according to the present invention.

Claims (6)

C: 0.05 to 0.15% by mass%,
Si: 0.5% or less,
Mn: 1.2 to 3.0%,
Mo: 0.05 to 1.0%,
P: 0.05% or less,
Al: 0.001 to 0.1% and N: 0.005 to 0.02%
And the remainder has a composition of Fe and unavoidable impurities, the low-temperature transformed ferrite phase has an area ratio of 10 to 50%, and the balance substantially has a steel structure of a polygonal ferrite phase. A high-tensile hot-rolled steel sheet excellent in bake hardenability and ductility, characterized in that the average crystal grain size of two phases of a low-temperature transformed ferrite phase and a polygonal ferrite phase is 8 μm or less. 2. The bake hardening according to claim 1, wherein the steel sheet further has a composition containing one or two selected from among Cr: 1.0% or less and Ni: 1.0% or less by mass%. High-strength hot-rolled steel sheet with excellent ductility and ductility. 3. The steel sheet according to claim 1, wherein the steel sheet further has a composition containing one or two selected from Ti: 0.1% or less and Nb: 0.1% or less by mass%. High tensile hot rolled steel sheet with excellent bake hardenability and ductility. 4. A high-strength plated steel sheet according to any one of claims 1 to 3, wherein a plated layer is formed on the surface of the steel sheet, and which is excellent in bake hardenability and ductility. C: 0.05 to 0.15% by mass%,
Si: 0.5% or less,
Mn: 1.2 to 3.0%,
Mo: 0.05 to 1.0%,
P: 0.05% or less,
Al: 0.001 to 0.1% and N: 0.005 to 0.02%
Was heated to 1000 to 1300 ° C., and after rough rolling, finish rolling was finished under the conditions of finish rolling exit temperature: (Ar ₃ + 10 ° C.) to (Ar ₃ + 100 ° C.). After that, it is cooled to a temperature range of 750 to 600 ° C. at a speed of 50 ° C./s or more within 1.7 seconds, kept at this temperature range for 3 to 15 seconds, and cooled at a speed of 20 ° C./s or more A method for producing a high-tensile hot-rolled steel sheet having excellent bake hardenability and ductility, wherein the steel sheet is wound at a temperature of 500 to 250 ° C. 6. The method for producing a high-strength plated steel sheet according to claim 5, wherein the surface of the steel sheet is plated after winding.

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