JP5915412B2 - High strength hot-rolled steel sheet excellent in bendability and manufacturing method thereof - Google Patents

Description

  The present invention relates to a high-strength hot-rolled steel sheet having high tensile strength (TS): 980 MPa or more and excellent workability (particularly bendability) useful for the use of automobile members and a method for producing the same.

In recent years, from the viewpoint of global environmental conservation, the automobile industry as a whole has been directed to improving automobile fuel efficiency in order to reduce CO ₂ emissions. The most effective way to improve the fuel efficiency of automobiles is to reduce the weight of automobile bodies by reducing the thickness of the parts used. In addition, in order to ensure the safety of passengers in the event of a collision, it is also required to strengthen the automobile body and improve the collision safety of the automobile body. From such a viewpoint, a high-strength hot-rolled steel sheet capable of achieving both weight reduction and safety is used as a material for automobile members, and the amount of use is increasing year by year.

  On the other hand, since many automobile parts made of steel plates are formed by press working or the like, steel sheets for automobile parts are required to have excellent workability in addition to high strength. In particular, ultra-high strength steel sheets with a tensile strength of 980 MPa or more are often used for members that improve impact resistance performance, such as pillars and members, but these members have complex shapes, so when manufacturing parts, Severe bending is applied to the steel plate. Therefore, there is a case where excellent bending workability is required particularly for a steel sheet for automobile parts having a tensile strength of 980 MPa or more.

However, in general, as steel materials increase in strength, ductility decreases and workability deteriorates. For this reason, a steel sheet with a tensile strength of 980 MPa or more has various problems when it is formed into a desired part shape. For example, if a steel sheet having a tensile strength of 980 MPa or more is subjected to press working, cracks and necking at the bent portion become prominent, making it difficult to form the part.
For the above reasons, it is essential to develop a high-strength steel sheet having excellent bending workability when applying the high-strength steel sheet to automobile parts and the like.

Various techniques for increasing the strength and formability of steel sheets have been proposed so far.
For example, Patent Document 1 proposes a technique in which a steel plate composition is a mass%, contains C: 0.05 to 0.20%, Nb: 0.1 to 1.0%, and has a solid solution C content of 0.03% or less. ing. And according to the technique proposed in Patent Document 1, by limiting the amount of dissolved C in the component system containing Nb and C, the matrix is a soft ferrite phase and the matrix is a hard second phase. It is said that a certain NbC-dispersed steel sheet structure is obtained, and a wear-resistant steel sheet having excellent bending workability is obtained.

  Moreover, in patent document 2, steel plate composition is the mass%, C: 0.02-0.2%, Si: 0.01-1.0%, Mn: 0.1-2.0%, P: 0.2% or less, sol.Al:0.001-0.5%, Ti: 0.1% or less, Nb: 0.1% or less, V: 0.5% or less, Mo: 0.5% or less, and Ti + Nb: 0.1% or less, steel sheet structure as ferrite main phase structure, and steel sheet surface A technique for defining the average grain size of ferrite at a depth of 1/4 of the plate thickness and the rate of increase of the average grain size at 700 ° C. has been proposed. And according to the technique proposed by patent document 2, it is supposed that the steel plate excellent in workability will be obtained.

In Patent Document 3, by mass%, C: 0.0001% or more, 0.25% or less, Si: 0.001% or more, 2.5% or less, Mn: 0.01% or more, 2.5% or less, P: 0.2% or less, S: 0.03% or less , Al: 0.01% or more, 2.0% or less, N: 0.01% or less, O: Hot rolling of steel pieces containing 0.01% or less, the total rolling reduction from Ar ₃ transformation temperature to (Ar ₃ +100) ° C Is controlled to be 25% or more, and at least one pass in the above temperature range is rolled so that the friction coefficient is 0.2 or less, and the hot rolling is finished at an Ar ₃ transformation temperature to (Ar ₃ +100) ° C. A technique for manufacturing a ferritic thin steel sheet by cooling and winding under predetermined conditions has been proposed. According to the technique proposed in Patent Document 3, when a steel slab having the above composition is hot-rolled, the rolling reduction and friction coefficient between Ar ₃ transformation temperature and (Ar ₃ +100) ° C. are defined, and Ar ₃ It is said that a ferritic thin steel sheet having excellent shape freezing properties when processed mainly for bending is obtained by completing the rolling in the temperature range from the transformation temperature to (Ar ₃ +100) ° C.

In Patent Document 4, in mass%, C: 0.05-0.2%, Si: 0.001-3.0%, Mn: 0.5-3.0%, P: 0.001-0.2%, Al: 0.001-3%, V: Over 0.1% In the final rolling by the tandem rolling mill after rough rolling, steel ingots and steel slabs with a component composition containing up to 1.0% are processed at the Ar ₃ point or higher in the rolling stand one stage before the final rolling. A technology for producing a hot-rolled steel sheet by rolling and then cooling to a temperature below (Ar ₃ point-50 ° C) at an average cooling rate of 50 ° C / second or more and then applying a reduction of 20% or less in the final stand. Proposed. According to the technique proposed in Patent Document 4, fine ferrite can be obtained stably and reliably, and the carbonitride containing V in the ferrite grains is refined, and is excellent in ductility, hole expansibility and fatigue resistance. It is said that a hot-rolled steel sheet is obtained.

JP 2007-262429 A JP 2008-189978 A JP 2003-055739 A JP 2004-143518 A

  However, although the technique proposed in Patent Document 1 substantially strengthens the steel sheet by dispersing NbC, it is difficult to obtain a steel sheet having a tensile strength of 980 MPa or more with the technique using NbC. is there. The amount of particle dispersion strengthening obtained by dispersing precipitates increases with an increase in the carbonized body volume fraction, but NbC increases the carbonized body volume fraction because its solubility product in steel is small and the atomic density is large. It is because it cannot be done. In addition, in the technique proposed in Patent Document 2, Ti and V are added as precipitation strengthening elements to steel, but the contents of Ti and V forming carbides are small, or appropriate addition is not made. After all, the tensile strength of the steel sheet does not reach 980 MPa.

The techniques proposed in Patent Document 3 and Patent Document 4 require finish rolling at a low temperature in the vicinity of the Ar ₃ point, but with steel sheets having a tensile strength of 980 MPa or more, the rolling load becomes significant as the rolling temperature decreases. Therefore, manufacturing becomes difficult. Furthermore, in the case of the technique proposed in Patent Document 3, it is essential to add a large amount of C, Si and Mn when the tensile strength of the steel sheet is set to 980 MPa or more as shown in the Examples. A steel plate containing a large amount of these elements is inferior in bending workability. The technique proposed in Patent Document 4 also has a problem inferior in bending workability because it contains a large amount of V that lowers workability.

As described above, in the prior art, a steel sheet having a tensile strength of 980 MPa or more and good bending workability could not be obtained.
This invention is made | formed in view of this situation, Comprising: It aims at providing the high strength steel plate which has the tensile strength of 980 MPa or more and was excellent also in the bendability.

In order to solve the above-mentioned problems, the present inventors paid attention to a ferrite single-structure steel sheet having good workability, and intensively studied various factors affecting the strengthening and workability of the steel sheet, particularly bendability.
In order to increase the strength of a ferritic single-structure steel sheet, it is extremely effective to disperse a large amount of fine carbides in the originally soft ferrite phase. Therefore, the present inventors first examined means for precipitating a large amount of fine carbides in the ferrite phase. As a result, in order to obtain fine carbides, it was found that lowering the temperature of the Ar ₃ point of the steel sheet is effective.

Carbides that contribute to the strengthening of steel sheets are precipitated during the cooling process after hot rolling at the time of steel sheet production, but carbides that precipitate in the high temperature range tend to coarsen, while fine carbides that precipitate in the low temperature range are fine. Carbide is obtained. The carbide precipitates almost simultaneously with the austenite → ferrite transformation of the steel in the cooling process after the hot rolling is completed. For the above reasons, by reducing the temperature of the Ar ₃ transformation point of steel, carbide precipitates in a low temperature region, and fine carbide can be obtained.

On the other hand, as a means for developing a texture for improving the bending workability of a steel sheet, it is known as an effective means that the finish rolling temperature of hot rolling is in the vicinity of the Ar ₃ transformation point when manufacturing the steel sheet. Therefore, by lowering the Ar ₃ transformation point of the steel and setting the hot rolling finish rolling temperature in the vicinity of the Ar ₃ transformation point, a hot-rolled steel sheet having high strength and excellent bending workability can be obtained. Presumed to be.

However, when a steel having a low Ar ₃ transformation point is hot-rolled at a finish rolling temperature in the vicinity of the Ar ₃ transformation point, the problem of productivity (rollability) arises. This is because the rolling load increases remarkably as the finish rolling temperature is lowered, and rolling becomes difficult. Such a problem becomes apparent particularly when a high-strength steel sheet of 980 MPa or more is manufactured.
Therefore, the present inventors have sought a means for developing a texture effective for improving the bending workability of a steel sheet even when the finish rolling temperature is significantly higher than the Ar ₃ transformation point.

As a result, in order to develop the texture, it has been found that it is also effective to suppress austenite recrystallization during hot rolling. Further, the inventors have conceived that TiN is dispersed in a steel sheet as a means for suppressing recrystallization of austenite. And as a result of further investigation, the steel composition was adjusted to a composition that lowers the Ar ₃ transformation point and disperses TiN in the steel sheet, and further the hot rolling finish rolling temperature from the Ar ₃ transformation point. In addition, it was found that by setting the temperature to 100 ° C. or higher, a fine rolled carbide precipitates and a hot rolled steel sheet with a developed texture effective for improving the bending workability of the steel sheet can be obtained.

  Further, by developing the texture, a hot-rolled steel sheet having excellent bending workability can be obtained, but the present inventors have studied means for further improving the bending workability of the steel sheet. As a result, it has been found that it is important to reduce as much as possible the solid solution elements that lower the workability after developing the specific texture described above.

  Here, examples of elements remaining in a solid solution state in the steel sheet include Si and Mn. As a result of investigations by the present inventors, V, which is a constituent element of carbide, is not formed of carbide and is not solid. It became clear that it remained as a dissolved state. Therefore, in order to give fine bending workability to a steel sheet while precipitating fine carbides to increase the strength of the steel sheet, it is important to avoid using V as much as possible and to obtain more carbide with Ti. The present inventors have found that there is.

The present invention has been completed based on the above findings, and the gist thereof is as follows.
[1] By mass%, C: 0.06% to 0.1%, Si: 0.05%, Mn: 0.1% to 1.2%, P: 0.03% or less, S: 0.005% or less, Al: 0.08% or less, N : 0.0035% or more and 0.0090% or less, Ti: 0.14% or more and 0.25% or less, V: 0.01% or more and 0.15% or less, with the balance consisting of Fe and inevitable impurities, and the ferrite phase area ratio of 95% or more The average grain size of the ferrite phase is 5 μm or less, the average grain size of the carbide in the ferrite phase grains is 6 nm or less, and the [001] <110> orientation X of the plate surface at the center of the plate thickness The line random intensity ratio is 7.5 or more, the average X-ray random intensity ratio of the [111] <112> to [111] <110> orientation groups is 3.0 or less, contains TiN as a precipitate, and the average particle diameter of the TiN Has a structure with a precipitation amount of 0.01% or more by mass% and a tensile strength of 980 MPa or more. Rolled steel sheet.

[2] A high-strength hot-rolled steel sheet excellent in bendability according to [1], further including Nb: 0.01% to 0.05% by mass% in addition to the composition.

[3] In the above [1] or [2], in addition to the above composition, any one of Mo: 0.5% or less, W: 0.1% or less, Zr: 0.5% or less, Hf: 0.5% or less A high-strength hot-rolled steel sheet excellent in bendability characterized by containing one or more kinds.

[4] In any one of the above [1] to [3], in addition to the above composition, B: 0.0002% or more and 0.0030% or less is further contained by mass%, and high strength excellent in bendability Hot rolled steel sheet.

[5] In any one of the above [1] to [4], in addition to the above composition, Se, Te, Po, As, Bi, Ge, Pb, Ga, In, Tl, Zn, Cd in addition to the composition. Hg, Ag, Au, Pd, Pt, Co, Rh, Ir, Ru, Os, Tc, Re, Ta, Be, Sr, REM, Ni, Cr, Sb, Cu, Sn, Mg, Ca A high-strength hot-rolled steel sheet excellent in bendability characterized by containing a total of 0.2% or less of seeds or more.

[6] A high-strength hot-rolled steel sheet excellent in bendability according to any one of [1] to [5], wherein the steel sheet surface has a plating layer.

[7] The high-strength hot-rolled steel sheet having excellent bendability according to [6], wherein the plated layer is a galvanized layer.

[8] The high-strength hot-rolled steel sheet having excellent bendability according to [6], wherein the plated layer is an alloyed galvanized layer.

[9] A steel material is heated, subjected to hot rolling consisting of rough rolling and finish rolling, and after finishing rolling is cooled, wound, and made into a hot-rolled steel sheet. : 0.06% to 0.1%, Si: 0.05% or less, Mn: 0.1% to 1.2%, P: 0.03% or less, S: 0.005% or less, Al: 0.08% or less, N: 0.0035% to 0.0090%, Ti: 0.14% or more and 0.25% or less, V: 0.01% or more and 0.15% or less, with the balance being Fe and inevitable impurities, heating temperature of the heating is 1150 ° C or more and 1350 ° C or less, and the finish rolling In the above, the cumulative rolling reduction in the temperature range of (Ar ₃ transformation point + 100 ° C) to (Ar ₃ transformation point + 300 ° C) is 30% or more, the finish rolling temperature is (Ar ₃ transformation point + 100 ° C) or more, and the cooling Within 2 seconds after finishing rolling, the average cooling rate of the cooling is set to 40 ° C./s or more, and the winding temperature of the winding is set to 550 A method for producing a high-strength hot-rolled steel sheet excellent in bendability, characterized by having a temperature of ℃ to 700 ℃.

[10] A method for producing a high-strength hot-rolled steel sheet excellent in bendability according to [9], further comprising Nb: 0.01% or more and 0.05% or less by mass% in addition to the composition.

[11] In the above [9] or [10], in addition to the above composition, any one of the following by mass: Mo: 0.5% or less, W: 0.1% or less, Zr: 0.5% or less, Hf: 0.5% or less The manufacturing method of the high strength hot-rolled steel plate excellent in the bendability characterized by containing 1 or more types.

[12] In any one of the above [9] to [11], in addition to the above composition, B: 0.0002% or more and 0.0030% or less in addition to the composition, B: 0.0002% or more and 0.0030% or less A method for producing a hot-rolled steel sheet.

[13] In any one of the above [9] to [12], in addition to the composition, Se, Te, Po, As, Bi, Ge, Pb, Ga, In, Tl, Zn, Cd in addition to the composition. Hg, Ag, Au, Pd, Pt, Co, Rh, Ir, Ru, Os, Tc, Re, Ta, Be, Sr, REM, Ni, Cr, Sb, Cu, Sn, Mg, Ca A method for producing a high-strength hot-rolled steel sheet excellent in bendability, characterized by containing at least 0.2% in total of seeds.

[14] The method for producing a high-strength hot-rolled steel sheet excellent in bendability according to any one of [9] to [13], wherein a plating layer is formed on the surface of the hot-rolled steel sheet.

[15] The method for producing a high-strength hot-rolled steel sheet having excellent bendability according to [14], wherein the plated layer is a galvanized layer.

[16] The method for producing a high-strength hot-rolled steel sheet having excellent bendability, wherein the plating layer is an alloyed galvanized layer in [14].

  According to the present invention, a high-strength steel sheet having a tensile strength of 980 MPa or more and excellent in bendability is obtained, suitable for use as a structural member of an automobile, and can be reduced in weight and molded into an automobile member. The effect is remarkable. Further, since a high strength hot rolled steel sheet having a bending workability and a tensile strength of 980 MPa or more can be obtained, further application development of the high strength hot rolled steel sheet becomes possible, and an industrially remarkable effect is achieved.

Hereinafter, the present invention will be described in detail.
First, the reason for limiting the structure of the hot-rolled steel sheet of the present invention will be described.
The hot rolled steel sheet of the present invention has a ferrite phase area ratio of 95% or more, an average crystal grain size of the ferrite phase of 5 μm or less, an average grain size of carbides in the ferrite phase crystal grains of 6 nm or less, The [001] <110> orientation X-ray random intensity ratio of the plate surface at the thickness center is 7.5 or more, and the average X-ray random intensity ratio of [111] <112> to [111] <110> orientation groups is 3.0 or less. And has a structure containing TiN as a precipitate, an average particle diameter of TiN of 5 μm or less, and a precipitation amount of 0.01% or more by mass%.

Area ratio of ferrite phase: 95% or more The matrix metal structure of the hot-rolled steel sheet is preferably a ferrite single-phase structure excellent in workability. If a second phase structure such as a bainite phase, martensite phase, or cementite is mixed in the steel sheet structure, stress concentration occurs at the interface between the ferrite phase and the second phase structure having different hardnesses during bending of the steel sheet, causing cracks. And lowers the bendability of the steel sheet. Therefore, in the present invention, it is preferable that the metal structure of the hot-rolled steel sheet is a ferrite single phase structure, but sufficient bending workability can be obtained if the ferrite area ratio is 95% or more even if it is not completely a ferrite single phase. Therefore, the area ratio of the ferrite phase is 95% or more. Preferably it is 98% or more.

  In the hot-rolled steel sheet of the present invention, examples of the structure other than the ferrite phase that can be contained in the steel sheet include pearlite, bainite, and martensite. When these structures are present in a large amount in the steel sheet, the steel sheet properties (bending workability, etc.) are deteriorated. Therefore, it is preferable to reduce these structures as much as possible, but it is acceptable if the total area ratio with respect to the entire metal structure of the steel sheet is 5% or less. Preferably it is 2% or less.

Average crystal grain size of ferrite phase: 5 μm or less When the average crystal grain size of the ferrite phase exceeds 5 μm, a mixed grain structure in which individual ferrite grains have different sizes tends to be formed. Such a mixed grain structure causes uneven stress loading at each grain boundary during bending of the steel sheet, leading to voids and a factor in reducing the bending workability of the steel sheet. Further, as the crystal grain size of the ferrite phase increases, the amount of grain refinement strengthening also decreases, so that it becomes difficult to obtain a tensile strength of 980 MPa or more. Therefore, the average crystal grain size of the ferrite phase is 5 μm or less. Preferably, it is 4 μm or less. The standard deviation of the average crystal grain size of the ferrite phase is preferably 2 μm or less.

Carbides in ferrite phase crystal grains In the hot-rolled steel sheet of the present invention, it is essential to finely precipitate carbides in ferrite phase crystal grains in order to ensure strength. In the present invention, carbides finely precipitated in the ferrite phase grains include mainly composite carbides of Ti and V, and Ti carbide, V carbide, or even Nb, W, Mo, Hf, Zr in the carbide. Also included.

Average particle diameter of carbide in ferrite crystal grains: 6 nm or less As described above, in the hot rolled steel sheet of the present invention, strengthening is mainly achieved by finely dispersing composite carbide of Ti and V, but the carbide is fine. As the number of particles increases, the number of particles that inhibit dislocation movement increases, and the amount of strengthening obtained by dispersing carbide increases. In order to obtain a hot-rolled steel sheet having a desired tensile strength (980 MPa or more), it is necessary to finely disperse carbides of at least 6 nm or less. Preferably it is 5 nm or less.

[001] <110> orientation X-ray random intensity ratio of the plate thickness center plate: 7.5 or more Average X-ray random of [111] <112> to [111] <110> orientation group of the plate thickness center plate surface Strength ratio: 3.0 or less It has been clarified that when a specific texture is developed, reduction of the plate thickness at the most severe part during bending of the steel sheet can be suppressed, and problems such as necking and cracking can be avoided. The X-ray random intensity ratio of the [001] <110> orientation of the plate surface at the center of the plate thickness is 7.5 or more, and the average of the [111] <112> to [111] <110> orientation groups of the plate surface at the center of the plate thickness If the X-ray random intensity ratio is 3.0 or less, the above effect can be obtained because the plate surface direction preferentially contracts in the bending process, not the plate thickness direction.

Precipitation amount of TiN: 0.01% or more by mass% As described above, austenite recrystallization during hot rolling is necessary to develop a texture ([001] <110> texture) effective in improving the bending workability of steel sheets. It is effective to suppress this.
TiN has the effect of suppressing recrystallization of austenite during hot rolling, and realizes non-recrystallized austenite at high temperatures (temperature range of Ar ₃ transformation point + 100 ° C. or higher).

Therefore, by precipitating TiN in the steel before finish rolling, the recrystallization of austenite is suppressed even when the finish rolling temperature is raised, and the structure after austenite → ferrite transformation is suppressed in the cooling process following finish rolling. [001] It becomes possible to develop <110> texture. And since a desired texture can be developed without lowering the finish rolling temperature to the vicinity of the Ar ₃ transformation point, a hot-rolled steel sheet having high strength and excellent bending workability without excessively increasing the rolling load is obtained. can get.

  In order to obtain such an effect, at least the precipitation amount of TiN ((mass of TiN contained in steel plate) / (mass of steel plate) × 100) needs to be 0.01% or more. Preferably it is 0.012% or more. However, TiN tends to be a starting point of voids during bending of the steel sheet, and thus excessive precipitation causes a decrease in the bending workability of the steel sheet. Therefore, the amount of TiN deposited is preferably suppressed to 0.023% or less.

Average particle diameter of TiN: 5 μm or less As mentioned above, TiN tends to be the starting point of voids, but if the average particle diameter is 5 μm or less, stress concentration at the TiN-matrix interface is reduced and the bendability of the steel sheet is remarkable. Does not have any adverse effects. For the above reasons, the average particle diameter of TiN contained in the steel sheet is 5 μm or less.

  Next, the reason for limiting the component composition of the hot-rolled steel sheet of the present invention will be described. In addition,% showing the following component composition shall mean the mass% (mass%) unless there is particular notice.

C: 0.06% to 0.1%
C is combined with Ti, V, or Nb, Mo, W, Zr, and Hf and finely dispersed in the steel sheet as a carbide. That is, C is an element that forms fine carbides and remarkably strengthens the ferrite structure, and is an essential element for strengthening the hot-rolled steel sheet. In order to obtain a high-strength steel sheet having a tensile strength of 980 MPa or more, the C content needs to be at least 0.06%. On the other hand, if the C content exceeds 0.1%, it is difficult to form a solution of the steel material in the steel of the present invention. As a result, coarse Ti-based carbides are precipitated and the amount of Ti finely precipitated is reduced, so that the strength is lowered. Furthermore, when the C content exceeds 0.1%, a large amount of cementite is precipitated, and the bendability of the steel sheet is significantly deteriorated. This is because the microvoids are easily generated at the interface between the cementite and the matrix (ferrite), which causes cracks in the bent portion. Therefore, the C content is 0.06% or more and 0.1% or less. Preferably they are 0.07% or more and 0.09% or less.

Si: 0.05% or less
Si is actively contained in conventional high-strength steel sheets as an effective element for improving the steel sheet strength without reducing ductility (elongation). However, Si is easy to concentrate on the steel sheet surface, and forms firelite (Fe ₂ SiO ₄ ) on the steel sheet surface. Since this firelite is formed in a wedge shape on the surface of the steel sheet, it becomes a starting point of cracking when the steel sheet is bent. That is, Si is an element that significantly reduces the bending workability of the steel sheet, and in the present invention, it is desirable to reduce the Si content as much as possible. However, since 0.05% is acceptable, the upper limit of Si content is 0.05%. Preferably it is 0.03% or less. Note that the Si content may be reduced to the impurity level.

Mn: 0.1% or more and 1.2% or less
Mn has the effect of lowering the austenite → ferrite transformation temperature (Ar ₃ transformation point). Since carbides become finer as the austenite → ferrite transformation temperature decreases, Mn is an effective element for increasing the strength of steel sheets. In order to obtain such an effect, the Mn content needs to be 0.1% or more. On the other hand, most of Mn remains in a solid solution state in the steel, and the solid solution element lowers the ductility. Further, in the case of a steel sheet having a tensile strength of 980 MPa or more, a decrease in bendability due to a solid solution element becomes obvious, so the Mn content needs to be 1.2% or less. For these reasons, the Mn content is set to 0.1% or more and 1.2% or less. Preferably they are 0.3% or more and 1.1% or less.

P: 0.03% or less
P is a harmful element that segregates at the grain boundary and becomes the starting point of grain boundary cracking during processing and degrades the bendability of the steel sheet, and therefore it is preferable to reduce it as much as possible. Therefore, in the present invention, the P content is set to 0.03% or less in order to avoid the above problems. Preferably it is 0.02% or less. The P content may be reduced to the impurity level.

S: 0.005% or less
S exists as an inclusion such as MnS in steel. This inclusion extends during hot rolling, and the extended inclusion becomes a starting point of cracking during bending, thereby reducing the bendability of the steel sheet. Therefore, in the present invention, it is preferable to reduce the S content as much as possible, and it is 0.005% or less. Preferably it is 0.003% or less. The S content may be reduced to the impurity level.

Al: 0.08% or less
Al is an element that acts as a deoxidizer. In order to acquire such an effect, it is desirable to contain 0.02% or more. On the other hand, Al forms an oxide or the like and becomes a starting point of voids during bending of the steel sheet. Further, in the steel of the present invention, a large amount of TiN is positively precipitated for the purpose of enhancing the bending workability of the steel sheet, so inclusions other than TiN must be reduced as much as possible. When the Al content is excessive, Al combines with N to form AlN, and the amount of TiN deposited decreases. In particular, if the Al content exceeds 0.08%, an adverse effect on the bendability of the steel sheet becomes obvious, so the Al content is set to 0.08% or less. Preferably it is 0.06% or less.

N: 0.0035% or more and 0.0090% or less
N is an element that combines with Ti at the stage of steelmaking and continuous casting to form TiN and has an effect of suppressing austenite recrystallization during hot rolling.
As a result of studies by the present inventors, it has been clarified that the ferrite structure transformed from non-recrystallized austenite develops a texture that improves the bendability of the steel sheet. Therefore, N is an element effective in improving the bendability of the steel sheet, and in the present invention, it is necessary to contain N at least 0.0035% or more.

  On the other hand, if the N content is excessively high, TiN is precipitated excessively, resulting in a decrease in the amount of carbides (Ti and V composite carbides and Ti carbides) contributing to strengthening, and the tensile strength of the steel sheet is reduced. 980MPa is not reached. Furthermore, TiN has the effect of enhancing the bending workability of the steel sheet, but can also be a starting point for void generation during bending of the steel sheet. And when N content exceeds 0.0090%, these problems cannot be disregarded and the bad influence on the bendability of a steel plate becomes obvious. For these reasons, the N content is set to be 0.0035% or more and 0.0090% or less. Preferably it is 0.0050% or more and 0.0080% or less.

Ti: 0.14% to 0.25%
Ti is an element that contributes to increasing the strength of steel sheets by forming carbides with C. Ti is an element that forms TiN, which is essential for improving the bending workability of the steel sheet. In order to improve the bending workability of the steel sheet while ensuring the desired hot-rolled steel sheet strength (tensile strength: 980 MPa or more), the Ti content needs to be 0.14% or more. On the other hand, when the Ti content exceeds 0.25%, when manufacturing a hot-rolled steel sheet, coarse Ti carbide cannot be dissolved by heating the steel material (slab) before hot rolling, and finally obtained ( Coarse Ti carbide remains on the hot-rolled steel sheet after winding. If coarse Ti carbide remains in this way, not only the effect of increasing the strength is saturated, but the coarse Ti carbide becomes a starting point of voids during bending of the steel sheet, and the bendability of the steel sheet decreases. Therefore, the Ti content is 0.14% or more and 0.25% or less. Preferably they are 0.15% or more and 0.23% or less.

V: 0.01% or more and 0.15% or less
V, like Ti, is an element that forms a carbide with C and contributes to increasing the strength of the steel sheet. V is effective for increasing the strength of the steel sheet because it combines with Ti to form a fine composite carbide. In order to ensure the desired steel plate strength (tensile strength: 980 MPa or more), the V content needs to be 0.01% or more. On the other hand, V has a low carbide forming ability, and as a result of investigations by the present inventors, it has been found that V has a larger amount remaining in steel as a solid solution state without forming carbide than Ti. As a result of further investigation by the inventors, not only C, Si, and Mn, which are generally known as solid solution elements, but also V may be a cause of lowering the bending workability of the steel sheet. It was revealed.

  In the present invention, when the V content exceeds 0.15%, the V solid solution amount is remarkably increased, which lowers the ductility of the steel sheet and adversely affects the bendability. Therefore, the V content is 0.01% or more and 0.15% or less. Preferably they are 0.05% or more and 0.13% or less.

  The above is the basic composition in the present invention. In addition to the basic composition described above, the following elements may be further contained.

Nb: 0.01% or more and 0.05% or less
Nb has an effect of inhibiting recrystallization of austenite grains before austenite → ferrite transformation in a hot rolling process when producing a hot-rolled steel sheet. Since the structure transformed from non-recrystallized austenite develops a texture that improves bendability, Nb has the effect of improving the bendability of the steel sheet. In order to obtain such an effect, the Nb content is preferably set to 0.01% or more. On the other hand, when the Nb content exceeds 0.05%, the above effect is saturated. For the above reasons, the Nb content is preferably 0.01% or more and 0.05% or less.

One or more of Mo: 0.5% or less, W: 0.1% or less, Zr: 0.5% or less, Hf: 0.5% or less
Mo, W, Zr and Hf are elements that form carbides and contribute to increasing the strength of the steel sheet. Furthermore, since these elements have the effect of lowering the austenite → ferrite transformation temperature (Ar ₃ transformation point), they can be said to be extremely effective elements from the viewpoint of increasing the strength of the steel sheet. On the other hand, when the content of these elements is excessive, the ferrite transformation is significantly delayed in the cooling process after the finish rolling at the time of hot-rolled steel sheet production, and a ferrite single-phase structure cannot be obtained substantially. For the above reasons, the contents of Mo, Zr, and Hf are each preferably 0.5% or less, and the W content is preferably 0.1% or less. Further, when two or more of these elements are contained, it is desirable that the total amount does not exceed 0.5%.

B: 0.0002% to 0.0030%
B is an element that easily segregates at the grain boundaries, and has an effect of reducing the driving force of austenite recrystallization during hot rolling and suppressing the recrystallization of austenite grains. Furthermore, since it has an effect of lowering the austenite → ferrite transformation point (Ar ₃ transformation point), it can be expected to increase the strength by making the carbide finer. In order to obtain these effects, the B content is preferably 0.0002% or more. On the other hand, when the B content exceeds 0.0030%, the above effects tend to be saturated. Therefore, the B content is preferably 0.0002% or more and 0.0030% or less.

Se, Te, Po, As, Bi, Ge, Pb, Ga, In, Tl, Zn, Cd, Hg, Ag, Au, Pd, Pt, Co, Rh, Ir, Ru, Os, Tc, Re, Ta, One or more of Be, Sr, REM, Ni, Cr, Sb, Cu, Sn, Mg, and Ca: 0.2% or less in total These elements are 0.2% in total from the viewpoint of bendability of the steel sheet Is acceptable. Preferably, the total content is 0.09% or less.
Components other than the above are Fe and inevitable impurities.

  A plating layer may be formed on the surface of the hot-rolled steel sheet of the present invention. The type of the plating layer is not particularly limited, and any of an electroplating layer and an electroless plating layer can be applied. Further, the alloy component of the plating layer is not particularly limited, and a hot dip galvanized layer, an alloyed hot dip galvanized layer, and the like can be cited as suitable examples. is there. By forming a plating layer on the surface, the corrosion resistance of the hot-rolled steel sheet is improved, and it becomes possible to apply it to automobile parts used in severe corrosive environments.

Next, the manufacturing method of the hot rolled steel sheet of the present invention will be described.
In the present invention, the steel material (steel slab) having the above composition is heated, subjected to hot rolling consisting of rough rolling and finish rolling, cooled after completion of finish rolling, and wound into a hot-rolled steel sheet. At this time, the heating temperature of the heating is 1150 ° C. or more and 1350 ° C. or less, and the cumulative rolling reduction in the temperature range of (Ar ₃ transformation point + 100 ° C.) or more (Ar ₃ transformation point + 300 ° C.) in the finish rolling is 30 %, The finishing rolling temperature is set to (Ar ₃ transformation point + 100 ° C.) or more, the cooling is started within 2 seconds after finishing rolling, the cooling average cooling rate is set to 40 ° C./s or more, and the winding step The immediately preceding winding temperature is 550 ° C. or more and 700 ° C. or less.

  In the present invention, the method for melting steel is not particularly limited, and a known melting method such as a converter or an electric furnace can be employed. Further, secondary refining may be performed in a vacuum degassing furnace. Thereafter, the slab (steel material) is preferably formed by a continuous casting method from the viewpoint of productivity and quality, but the slab may be formed by a known casting method such as an ingot-bundling rolling method or a thin slab continuous casting method. .

  In addition, when it is set as a slab (steel material) by a continuous casting method, TiN precipitates mainly at the time of continuous casting. To suppress the TiN contained in the finally obtained hot-rolled steel sheet (hot-rolled steel sheet after winding) to a desired average particle size (5 μm or less), the casting speed during continuous casting is set to 1.0 m / min or more. Thus, it is desirable to suppress TiN particle growth.

Heating temperature of steel material: 1150 ° C or higher and 1350 ° C or lower The steel material obtained as described above is subjected to rough rolling and finish rolling. In the present invention, the steel material is heated prior to rough rolling to be substantially homogeneous. The austenite phase needs to be dissolved and coarse carbides need to be dissolved. When the heating temperature of the steel material is below 1150 ° C, coarse carbides do not dissolve, so the amount of carbides finely dispersed in the cooling and winding process after hot rolling is reduced, resulting in the final hot rolling. The strength of the steel sheet is significantly reduced. On the other hand, when the heating temperature exceeds 1350 ° C., the scale bites and deteriorates the surface properties of the steel sheet.

For the above reasons, the heating temperature of the steel material is set to 1150 ° C or higher and 1350 ° C or lower. Preferably they are 1150 degreeC or more and 1320 degrees C or less. However, when hot rolling the steel material, if the steel material after casting is in the temperature range of 1150 ° C or higher and 1350 ° C or lower, or if the carbide of the steel material is dissolved, the steel material is heated. Direct rolling may be performed without any problem. The rough rolling conditions are not particularly limited.
In the present invention, subsequent to rough rolling, finish rolling is performed under the following conditions.

Cumulative rolling reduction in a temperature range of (Ar ₃ transformation point + 100 ° C) or more and (Ar ₃ transformation point + 300 ° C) or less: 30% or more As described above, in the present invention, the steel sheet structure is X in the [001] <110> orientation. Bending workability of steel sheet is improved by forming a texture with a random wire strength ratio of 7.5 or more and an average X-ray random strength ratio of [111] <112> to [111] <110> orientation groups of 3.0 or less. I am trying. In order to form such a texture, it is important to accumulate strain energy in the state where austenite grains are not recrystallized during finish rolling.

  Generally, in order to suppress recrystallization of austenite grains, finish rolling at a lower temperature is considered important. Therefore, it is presumed that a steel sheet excellent in bending workability can be obtained by increasing the cumulative rolling reduction in the low temperature region during finish rolling. However, rolling at a low temperature increases the rolling load and makes it difficult to produce hot-rolled steel sheets.

In order to cope with such a problem, in the present invention, the austenite recrystallization temperature is increased by optimizing the steel composition and dispersing an appropriate amount of TiN. That is, in the present invention, austenite grains are recrystallized even when finish rolling is performed at a temperature range significantly higher than the Ar ₃ transformation point, specifically, at a temperature range of (Ar ₃ transformation point + 100 ° C.) or higher. Strain energy can be accumulated in a state where it is not. Further, by performing finish rolling in a temperature range of (Ar ₃ transformation point + 100 ° C.) or higher, it is possible to reduce the rolling load and ensure the rollability.

Therefore, in the present invention, a desired texture is formed while securing the rollability by defining the cumulative rolling reduction in a temperature range of (Ar ₃ transformation point + 100 ° C.) or higher to a predetermined value or higher. However, in the temperature range exceeding (Ar ₃ transformation point + 300 ° C), the driving force for recrystallization of austenite grains is larger than the pinning force of TiN, so the austenite grains recrystallize and the desired texture is obtained. Disappear. For the above reasons, in the present invention, the cumulative rolling reduction in the temperature range of (Ar ₃ transformation point + 100 ° C.) or more and (Ar ₃ transformation point + 300 ° C.) or less is defined.

If the cumulative rolling reduction in the temperature range of (Ar ₃ transformation point + 100 ° C) to (Ar ₃ transformation point + 300 ° C) is less than 30%, the strain energy accumulated in the state where austenite grains do not recrystallize is insufficient. Thus, the desired texture described above cannot be obtained. Therefore, in the present invention, the cumulative rolling reduction in the above temperature range is set to 30% or more. Preferably it is 35% or more. However, if the cumulative rolling reduction in the above temperature range becomes excessively high, there is a concern that the rolling load is significantly increased due to the work hardening of austenite and the rollability is lowered.

Finishing rolling temperature: (Ar ₃ transformation point + 100 ° C.) or more When rolled in the vicinity of austenite → ferrite transformation temperature (Ar ₃ transformation point), the rolling load of the steel of the present invention is remarkably increased, making it difficult or impossible to produce. Further, when hot rolling is performed in the vicinity of the Ar ₃ transformation point, ferrite transformation starts, and a structure partially including processed ferrite is obtained. When such a processed ferrite is included, the bendability may be significantly reduced, and it is difficult to stably manufacture a steel sheet having good bendability. Accordingly, the finish rolling temperature is (Ar ₃ transformation point + 100 ° C.) or higher. It is preferably (Ar ₃ transformation point + 150 ° C.) or higher. However, if the finish rolling temperature becomes excessively high, the scale formed on the steel sheet surface will bite, and the bendability may be lowered because it becomes the starting point of cracking during bending, so (Ar ₃ transformation point +250) ° C or less It is preferable that

Time until start of forced cooling after finish rolling: within 2 seconds In high-temperature steel sheets immediately after finish rolling, carbides are generated by strain-induced precipitation because the strain energy accumulated in the austenite phase is large. Since this carbide precipitates at a high temperature and is easy to coarsen, it is difficult to obtain a fine precipitate when strain-induced precipitation occurs. Therefore, in the present invention, it is necessary to start forced cooling immediately after the end of hot rolling for the purpose of suppressing strain-induced precipitation, and cooling is started within at least 2 seconds after the end of finish rolling. Preferably it is within 1.5 seconds.

Average cooling rate: 40 ° C./s or more As described above, the longer the time during which the steel sheet after the finish rolling is maintained at a high temperature, the more easily the coarsening of the carbide by strain-induced precipitation proceeds. Further, in the present invention, the austenite → ferrite transformation is suppressed by containing a predetermined amount of Mn in the steel sheet, but if the cooling rate is low, the ferrite transformation starts at a high temperature, and the carbide tends to become coarse. Therefore, it is necessary to rapidly cool after finish rolling, and to avoid the above problem, it is necessary to cool at an average cooling rate of 40 ° C./s or more. Preferably, it is 50 ° C./s or more. However, if the cooling rate after finishing rolling is excessively increased, there is a concern that it is difficult to control the coiling temperature and it is difficult to obtain a stable strength.

Winding temperature: 550 ° C. or higher and 700 ° C. or lower If the winding temperature is lower than 550 ° C., a sufficient amount of carbide cannot be obtained, and the steel sheet strength decreases. On the other hand, when the coiling temperature exceeds 700 ° C., the precipitated carbide is coarsened, so that the steel sheet strength is lowered. Accordingly, the coiling temperature range is 550 ° C. or higher and 700 ° C. or lower. Preferably they are 570 degreeC or more and 670 degrees C or less.

  Note that the hot-rolled steel sheet after being rolled by hot rolling does not change its properties even if the scale is attached to the surface or the scale is removed by pickling. The above-described excellent characteristics are exhibited in any state. In the present invention, the hot-rolled steel sheet after winding may be plated to form a plating layer on the surface of the hot-rolled steel sheet.

  The hot-rolled steel sheet of the present invention has little material fluctuation even when heat treatment up to 740 ° C. is performed for a short time. Therefore, for the purpose of imparting corrosion resistance to the steel sheet, the hot-rolled steel sheet of the present invention can be plated, and a plating layer can be provided on the surface thereof. Since it can be manufactured even at a heating temperature of 740 ° C. or lower in the plating process, the effect of the present invention described above is not impaired even if the hot-rolled steel sheet of the present invention is plated. The type of the plating layer is not particularly limited, and any of an electroplating layer and an electroless plating layer can be applied. Further, the alloy component of the plating layer is not particularly limited, and a hot dip galvanized layer, an alloyed hot dip galvanized layer, and the like can be cited as suitable examples. is there.

  The plating method is not particularly limited, and any conventionally known method can be applied. For example, after passing through a continuous plating line with an annealing temperature of 740 ° C. or lower, a method of immersing and pulling up the steel plate in a plating bath can be used. Further, after the plating treatment, the steel plate surface may be heated in a furnace such as a gas furnace to perform the alloying treatment.

A steel material having a chemical composition shown in Table 1 and having a thickness of 250 mm was hot-rolled under the hot rolling conditions shown in Table 2 to obtain a hot-rolled steel sheet having a thickness of 1.4 to 3.2 mm. In addition, the average cooling rate described in Table 2 is an average cooling rate in the plate surface portion from the finish rolling temperature to the winding temperature. The Ar3 transformation point shown in Table 2 is obtained by heating the various steels shown in Table 1 at 1250 ° C for 10 minutes using a thermal expansion measuring device, then cooling them to 900 ° C at a cooling rate of 20 ° C / s. This is a value obtained by setting the transformation start temperature as the Ar ₃ transformation point when cooling is performed at a cooling rate of 40 ° C./s after applying a strain of 30 s ⁻¹ and a rolling reduction rate of 25% three times.

In addition, a part of the obtained hot-rolled steel sheet is passed through a hot dip galvanizing line with an annealing temperature of 720 ° C, and then immersed in a 460 ° C plating bath (plating composition: Zn-0.13 mass% Al). And a hot-dip galvanized material (GI material). Some steel plates were passed through a hot dip galvanizing line, immersed in a plating bath, and then alloyed at 520 ° C. to obtain an alloyed hot dip galvanized material (GA material). The plating adhesion amount was 45 g / m ² per side for both GI and GA materials.

  Samples are taken from the hot-rolled steel sheet (hot-rolled steel sheet, GI material, GA material) obtained as described above, and subjected to structure observation, tensile test, and bending test. The area ratio of the ferrite phase and the type of structure other than the ferrite phase And area ratio, average crystal grain size of ferrite phase, X-ray random strength ratio of texture, average particle size and content of TiN, average particle size of carbide, yield strength, tensile strength, elongation, critical bending radius, etc. Asked. The test method was as follows.

(I) Microstructure observation The area ratio of the ferrite phase was evaluated by the following method. About the central part of the plate thickness with a cross section parallel to the rolling direction, the corrosion appearance structure by 5% nital was magnified 400 times with a scanning optical microscope and photographed for 10 fields of view. The ferrite phase is a structure having a form in which corrosion marks and cementite are not observed in the grains. Further, the area ratio and particle size were determined using polygonal ferrite, bainitic ferrite, acicular ferrite and granular ferrite as ferrite. The area ratio of the ferrite phase was obtained by separating the ferrite phase from the ferrite phase other than the ferrite phase such as bainite and martensite by image analysis, and obtaining the area ratio of the ferrite phase with respect to the observation field. At this time, the grain boundary observed as a linear form was counted as a part of the ferrite phase.

  The average crystal grain size of the ferrite phase was obtained by enlarging the above 400 times, drawing 10 horizontal lines and 10 vertical lines for each of the three representative photographs, and determining the final grain size according to ASTM E 112-10. Table 3 shows the average values of the three sheets. In addition, the standard deviation of the ferrite grain described in Table 3 is a standard deviation with respect to the grain size obtained by each line.

The obtained hot-rolled steel sheet was thinned to the center of the sheet thickness by grinding or the like. Next, in order to remove the distortion of the processed surface generated by grinding or the like, a sample was prepared by reducing the thickness by at least 0.3 mm or more by chemical polishing or electrolytic polishing. Using these samples, the texture was measured by X-ray diffraction.
[001] <110> orientation X-ray random intensity ratio is the X-ray random intensity ratio at φ1 = 0 ° and Φ = 0 ° in the φ2 = 45 ° section of the three-dimensional texture measured by X-ray diffractometer Is obtained. The average X-ray random intensity ratio of the {111} <112> to [111] <110> orientation groups is φ1 = 30 °, φ = 55 ° and φ1 = 90 ° in the φ2 = 45 ° cross section of the three-dimensional texture. = 55 °, φ1 = 60 °, and Φ = 55 °.

  The average particle diameter of TiN was obtained by preparing a sample from the center of the thickness of the hot-rolled steel sheet by the replica method, observing with a transmission electron microscope (magnification: 65000 times), and calculating the average particle diameter of 100 or more points. . The composition of each precipitate was identified by EDX attached to TEM.

The precipitation amount (% by mass) of TiN was determined by the following method using a sample similar to the sample used when determining the average particle diameter of TiN.
For each sample, the nitride was extracted by dissolving the matrix in a 10% Br methanol-dissolved extract, and the mass fraction of N as a nitride contained therein was determined. Since nitrides contain both TiN and AlN, the amount of N precipitation as AlN was determined, and the amount of N precipitation as TiN was determined by subtracting from the total amount of nitride. TiN deposition amount ((TiN mass contained in sample) / (sample mass) × 100) was calculated with a TiN stoichiometric ratio of 1: 1.

  The average particle size of the carbides in the ferrite phase grains was measured using a transmission electron microscope (magnification: 135000 times) by preparing a sample from the center of the thickness of the obtained hot rolled steel sheet using a thin film method. It calculated | required by the average of the particle size of the carbide | carbonized_material more than a point. In calculating the carbide particle size, coarse cementite or nitride having a particle size of 1.0 μm or more was not included.

(Ii) Tensile test JIS No. 5 tensile test piece was produced from the obtained hot-rolled steel sheet in the direction perpendicular to the rolling direction, the tensile test was conducted 5 times in accordance with the provisions of JIS Z 2241 (2011), and the average yield strength ( YS), tensile strength (TS), and total elongation (EL) were determined. The crosshead speed in the tensile test was 10 mm / min.

(Iii) Bending test (bendability evaluation)
From the obtained hot-rolled steel sheet, a strip-shaped test piece (100 W × 35 L mm) was collected by shearing so that the longitudinal direction was perpendicular to the rolling direction. At this time, the shear plane and the fracture surface were in the same direction on the end face of the test piece. Using the test piece collected as described above, the bending test by the V-block method in accordance with JIS Z 2248 is performed three times, and the outside of the curved part of the sample after the test is observed with the naked eye, and there are no defects such as tears and wrinkles. Things were accepted. Tests were conducted using metal fittings with various inner radiuses, and the minimum inner radius R (mm) of the accepted metal fittings was divided by the thickness t (mm) of the hot-rolled steel sheet, as shown in the following formula. The value (R / t) was taken as the critical bending radius.
(Limit bending radius) = (Minimum inner radius R of the accepted metal fittings) / (Steel plate thickness t)

A smaller limit bending radius indicates a better result. The evaluation when the critical bending radius was 2.0 or less was evaluated as “good”, and the evaluation when the critical bending radius was over 2.0 was evaluated as “poor”.
The results obtained as described above are shown in Table 3.

  Each of the inventive examples is a hot-rolled steel sheet having a tensile strength of TS: 980 MPa or more, excellent bendability, and having both strength and workability. On the other hand, in a comparative example that is out of the scope of the present invention, a predetermined high strength is not ensured or good bendability is not obtained.

Claims (16)

% By mass
C: 0.06% or more and 0.1% or less, Si: 0.05% or less,
Mn: 0.1% or more and 1.2% or less, P: 0.03% or less,
S: 0.005% or less, Al: 0.08% or less,
N: 0.0035% to 0.0090%, Ti: 0.14% to 0.25%,
V: 0.01% or more and 0.15% or less, with the balance consisting of Fe and inevitable impurities, the area ratio of the ferrite phase is 95% or more, the average crystal grain size of the ferrite phase is 5 μm or less, The average particle diameter of the carbide in the crystal grains is 6 nm or less, the X-ray random intensity ratio in the [001] <110> orientation on the plate surface at the center of the plate thickness is 7.5 or more, and [111] <112> to [111] The average X-ray random intensity ratio of the <110> orientation group is 3.0 or less, contains TiN as a precipitate, the average particle diameter of TiN is 5 μm or less, and the precipitation amount is 0.01% or more by mass%. A high-strength hot-rolled steel sheet with excellent bendability, characterized by having a structure of   The high-strength hot-rolled steel sheet with excellent bendability according to claim 1, further comprising Nb: 0.01% or more and 0.05% or less by mass% in addition to the composition.   In addition to the composition, the composition further contains at least one of Mo: 0.5% or less, W: 0.1% or less, Zr: 0.5% or less, Hf: 0.5% or less in terms of mass%. A high-strength hot-rolled steel sheet having excellent bendability as described in 1 or 2.   The high-strength hot-rolled steel sheet having excellent bendability according to any one of claims 1 to 3, further comprising B: 0.0002% to 0.0030% by mass% in addition to the composition. In addition to the above composition, in addition to mass, Se : 0.0002% or less , Te : 0.0009% or less , Po : 0.0003% or less , As : 0.0003% or less , Bi : 0.0002% or less , Ge : 0.0003% or less , Pb : 0.0001 %: Ga : 0.0003% or less , In : 0.0008% or less , Tl : 0.0002% or less , Zn : 0.0003% or less , Cd : 0.0001% or less , Hg : 0.0002% or less , Ag : 0.0001% or less , Au : 0.0003% or less , Pd : 0.0003% or less , Pt : 0.0001% or less , Co : 0.002% or less , Rh : 0.0003% or less , Ir : 0.0002% or less , Ru : 0.0009% or less , Os : 0.0002% or less , Tc : 0.0002% or less , Re : 0.0005% or less , Ta : 0.0002% or less , Be : 0.0003% or less , Sr : 0.0003% or less , REM : 0.01% or less , Ni : 0.02% or less , Cr : 0.03% or less , Sb : 0.01% or less , Cu : 0.09 % Or less , Sn : 0.0002% or less , Mg : 0.002% or less , Ca : 0.002% or less , and a total of 0.1433 % or less. A high-strength hot-rolled steel sheet with excellent bendability as described in Crab.   The high-strength hot-rolled steel sheet having excellent bendability according to any one of claims 1 to 5, wherein the steel sheet surface has a plating layer.   The high-strength hot-rolled steel sheet with excellent bendability according to claim 6, wherein the plated layer is a galvanized layer.   The high-strength hot-rolled steel sheet with excellent bendability according to claim 6, wherein the plated layer is an alloyed galvanized layer. The steel material is heated, subjected to hot rolling consisting of rough rolling and finish rolling, and after finishing rolling, cooled, wound, and hot rolled steel sheet,
The steel material in mass%,
C: 0.06% or more and 0.1% or less, Si: 0.05% or less,
Mn: 0.1% or more and 1.2% or less, P: 0.03% or less,
S: 0.005% or less, Al: 0.08% or less,
N: 0.0035% to 0.0090%, Ti: 0.14% to 0.25%,
V: Contains 0.01% or more and 0.15% or less, with the balance being composed of Fe and inevitable impurities,
The heating temperature of the heating is 1150 ° C. or more and 1350 ° C. or less, and in the finish rolling, the cumulative rolling reduction in the temperature range of (Ar ₃ transformation point + 100 ° C.) or more (Ar ₃ transformation point + 300 ° C.) is 30% or more, The finish rolling temperature is set to (Ar ₃ transformation point + 100 ° C.) or more, the cooling is started within 2 seconds after finishing rolling, the cooling average cooling rate is set to 40 ° C./s or more, and the winding temperature of the winding The method for producing a high-strength hot-rolled steel sheet having excellent bendability according to claim 1, wherein the temperature is set to 550 ° C. or higher and 700 ° C. or lower.   The method for producing a high-strength hot-rolled steel sheet having excellent bendability according to claim 9, further comprising Nb: 0.01% or more and 0.05% or less by mass% in addition to the composition.   In addition to the composition, the composition further contains at least one of Mo: 0.5% or less, W: 0.1% or less, Zr: 0.5% or less, Hf: 0.5% or less in terms of mass%. A method for producing a high-strength hot-rolled steel sheet having excellent bendability according to 9 or 10.   The production of a high-strength hot-rolled steel sheet having excellent bendability according to any one of claims 9 to 11, further comprising B: 0.0002% or more and 0.0030% or less by mass% in addition to the composition. Method. In addition to the above composition, in addition to mass, Se : 0.0002% or less , Te : 0.0009% or less , Po : 0.0003% or less , As : 0.0003% or less , Bi : 0.0002% or less , Ge : 0.0003% or less , Pb : 0.0001 %: Ga : 0.0003% or less , In : 0.0008% or less , Tl : 0.0002% or less , Zn : 0.0003% or less , Cd : 0.0001% or less , Hg : 0.0002% or less , Ag : 0.0001% or less , Au : 0.0003% or less , Pd : 0.0003% or less , Pt : 0.0001% or less , Co : 0.002% or less , Rh : 0.0003% or less , Ir : 0.0002% or less , Ru : 0.0009% or less , Os : 0.0002% or less , Tc : 0.0002% or less , Re : 0.0005% or less , Ta : 0.0002% or less , Be : 0.0003% or less , Sr : 0.0003% or less , REM : 0.01% or less , Ni : 0.02% or less , Cr : 0.03% or less , Sb : 0.01% or less , Cu : 0.09 % Or less , Sn : 0.0002% or less , Mg : 0.002% or less , Ca : 0.002% or less , and a total of 0.1433 % or less. A method for producing a high-strength hot-rolled steel sheet having excellent bendability as described above.   The method for producing a high-strength hot-rolled steel sheet with excellent bendability according to any one of claims 9 to 13, wherein a plating layer is formed on the surface of the hot-rolled steel sheet.   The method for producing a high-strength hot-rolled steel sheet with excellent bendability according to claim 14, wherein the plating layer is a galvanization layer.   The method for producing a high-strength hot-rolled steel sheet with excellent bendability according to claim 14, wherein the plated layer is an alloyed galvanized layer.