JP7047517B2 - Cooling method for slabs for high-strength steel sheets, manufacturing method for high-strength hot-rolled steel sheets, manufacturing method for high-strength hot-dip galvanized steel sheets, and manufacturing method for high-strength alloyed hot-dip galvanized steel sheets. - Google Patents

Description

The present invention relates to a method for cooling a slab for a high- strength steel sheet, a method for manufacturing a high- tensile hot-rolled steel sheet, a method for manufacturing a high- strength hot-dip galvanized steel sheet, and a method for manufacturing a high- strength alloyed hot-dip galvanized steel sheet.

As cold-rolled and plated steel sheets applied to vehicle body skeletons are required to have both high tension and elongation, TRIP steel in which retained austenite is dispersed is being applied. It is known that the addition of a large amount of Si makes the slab embrittlement. Generally, when the slab is cooled, stress is generated due to the temperature difference between the surface and the inside of the slab. When this stress is high, cracks occur when the slab is cooled to room temperature, and in the worst case, cracks occur as shown in FIGS. 1 and 2. Alternatively, it opens during hot rolling and the coil during hot rolling breaks. Alternatively, cracks that are extremely small appear as quality defects called hege when reheated by hot rolling. Fine cracks in the slab can be removed by grinding the slab with a grinding machine, but large cracks cannot be removed or may be overlooked, which may result in defects in the product plate. There is a need to. Since the frequency of slab cracking is particularly remarkable in steels containing a large amount of Si, it tends to be a problem in steels containing a large amount of Si. As described in Patent Document 1, measures against cracking of the slab have been conventionally studied.

Japanese Unexamined Patent Publication No. 2007-832743

By the way, while studying measures against cracking of slabs of components containing Si, an attempt was made to confirm the effectiveness of the method described in Patent Document 1, but it was controlled within the range described in Patent Document 1. However, it was found that cracking of steel may not be suppressed.

The present invention has been made in such a background, and the subject of the present invention is not only cracking of the slab during cooling of the slab, but also shaving during hot spreading, etc., even if the slab contains Si. It is to provide a cooling method for a slab for a high- strength steel plate that does not cause quality defects. Another object of the present invention is to provide a method for manufacturing a high- strength hot-rolled steel sheet, a high-tensile hot -dip galvanized steel sheet, and a high- tensile alloyed hot-dip galvanized steel sheet using the cooling method.

In order to solve the above problems, in terms of mass %, C: 0.020 to 0.600%, Si: 0.5 to 3.00%, Mn: 1.00 to 3.00%, P: 0.100. % Or less, S: 0.0001 to 0.0100%, Al: 0.005 to 1.000%, N: 0.0100% or less , and the balance contains Fe and unavoidable impurities . A method for cooling a slab for a high- strength steel plate, characterized in that the average cooling rate of the slab at 500 ° C. or higher and 700 ° C. or lower is 20 ° C./hr or lower.

Further, the slab is further mass%, Ni: 0.01 to 2.00%, Cu: 0.01 to 2.00%, Cr: 0.01 to 2.00%, Mo: 0.01 to 2.00%, Nb: 0.005 to 0.100%, V: 0.005 to 0.100%, W: 0.005 to 0.100%, B: 0.0005 to 0.0100%, REM : 0.0003 to 0.0300%, Ca: 0.0003 to 0.0300%, Ce: 0.0003 to 0.0300%, Mg: 0.0003 to 0.0300%, one or more It is preferable that the composition contains the above.

Further, for the slab for high-strength steel plate having the above component, the slab temperature is secured to exceed 700 ° C. for at least 10 hr or more after the completion of casting, and then the average cooling rate of the slab at 500 ° C. or higher and 700 ° C. or lower is 20 ° C. It is preferably / hr or less.

Further, it is preferable to control the cooling rate of the slab by sandwiching the slab with a plurality of other slabs.

Further, it is preferable that the slabs are sandwiched by the other plurality of slabs at the same time.

Further, when cooling the high-strength steel plate slab, it is preferable to cover it.

Further, using the slab cooled by the cooling method, the slab heating temperature is heated in the range of 1100 to 1300 ° C., and after rough rolling, finish rolling is performed at a finish rolling output side plate temperature of 800 to 1100 ° C. from room temperature. It is preferable to perform winding in a temperature range of 700 ° C. to produce a high- tensile hot-rolled steel sheet.

Further, using the high- strength hot-rolled steel sheet manufactured by the above-mentioned manufacturing method, after pickling the steel sheet and further thinning the sheet thickness, cold rolling with a reduction ratio of 30 to 80% is performed after pickling, and then 700. It is preferable to reheat to a temperature range of about 900 ° C., perform annealing, and then perform temper rolling at a reduction rate of 0.2 to 2.0% to produce a high- strength cold-rolled steel sheet.

Further, using the high- tensile hot-rolled steel sheet manufactured by the above-mentioned manufacturing method, after pickling the steel sheet, and if the plate thickness is to be further reduced, cold rolling with a reduction ratio of 30 to 80% is performed after pickling, and then 700. It is preferable to reheat to a temperature range of about 900 ° C., perform hot-dip galvanizing, and then perform temper rolling at a rolling reduction of 0.2 to 2.0% to produce a high- tensile hot-dip galvanized steel sheet. ..

Further, it is preferable to produce a high- tensile alloyed hot-dip galvanized steel sheet by heating the hot-dip galvanizing to 470 ° C. or higher and 600 ° C. or lower to alloy the hot-dip galvanizing between the hot-dip galvanizing and tempering rolling.

According to the present invention, a method for cooling a slab for a high- strength steel plate, which does not cause not only slab cracking during cooling of the slab but also quality defects such as shavings during hot spreading, even if the slab contains Si. Can be provided. Further, it is possible to provide a method for manufacturing a high- strength hot-rolled steel sheet, a high-tensile hot -dip galvanized steel sheet, and a high- tensile alloyed hot-dip galvanized steel sheet using the cooling method.

It is the figure which showed the crack of a slab. It is a photograph of a slab in which a crack corresponding to the crack shown in the II region of FIG. 1 has occurred. It is a figure which shows the temperature measurement position of a slab. It is a figure which shows the cooling mode of a slab. However, three types of cooling are described: normal cooling, cooling in which the slab to be cooled is sandwiched between two slabs of other components, and cooling in which the slab to be cooled is covered with a cover. It is a figure which shows the cooling history which concerns on the elapsed time and the slab surface temperature. However, it relates to conditions C-1, C-4, conditions C-5, and C-8.

The embodiment for carrying out the invention is shown below. The cooling method of the high- strength steel plate slab 1 of the present embodiment is, in terms of mass %, C: 0.020 to 0.600%, Si: 0.5 to 3.00%, Mn: 1.00 to 3. It contains 00%, P: 0.100% or less, S: 0.0001 to 0.0100%, Al: 0.005 to 1.000%, N: 0.0100% or less , and Fe and unavoidable in the balance. It relates to a continuously cast slab 1 of a high-strength steel plate containing target impurities , and has an average cooling rate of 20 ° C./hr or less at 500 ° C. or higher and 700 ° C. or lower. As a result, even if the slab 1 contains Si, not only the slab 1 is cracked during cooling, but also the slab 1 for high- strength steel plate is cooled so that quality defects such as shavings during hot spreading do not occur. can do.

Here, the flow leading to the present invention will be described. The present inventors, in terms of mass %, C: 0.020 to 0.600%, Si: 0.5 to 3.00%, Mn: 1.00 to 3.00%, P: 0.100%. Hereinafter, a high-strength steel sheet containing S: 0.0001 to 0.0100%, Al: 0.005 to 1.000%, N: 0.0100% or less , and containing Fe and unavoidable impurities in the balance . While examining the cracking of the continuously cast slab 1, it was found that the cause of the slab cracking is the thermal stress generated due to the addition of Si to the steel and the temperature unevenness in the slab 1. Since the steel uses the addition of Si to increase the tension and improve the ductility, the addition of Si is indispensable. In other words, since it is necessary to add Si, we wondered if cracking of the slab 1 could be suppressed by focusing on the reduction of thermal stress caused by the temperature unevenness of the slab 1 (particularly, the temperature difference between the surface and the inside). ..

Therefore, as shown in FIG. 3, a thermocouple is installed in the center of the upper surface of the wide surface of the slab 1, and various cooling conditions and slab cracking, and subsequent cracking during slab cooling or hot rolling, and a surface called hege. The presence or absence of defects was investigated. The temperature at this position is defined as the slab temperature. It is considered that the cracks formed by hot rolling occur when the cracks formed during cooling of the slab are opened by hot rolling heating or rolling, leading to cracks. On the other hand, even if it does not lead to cracks, open cracks may be detected as defects such as hesitation, so this was also evaluated. For some slabs 1, the cooling rate was controlled by sandwiching and cooling with slabs 2 having different components, or by covering the slabs 1 with a cover 3 (see FIG. 4). In addition, the slab temperature was measured by these methods, and the cooling rate and the cooling start temperature were variously changed.

Table 1 shows the chemical composition of the steel used in the study, and Table 2 shows the slab cooling conditions, slab cracking, and the presence or absence of hot-rolled heddle. Further, FIG. 5 shows the elapsed time of each condition and the cooling history related to the slab surface temperature. The elapsed time of 0 hr is the time when the casting is completed.

Condition C-1 was 7 hours after the end of casting, a thermocouple was attached to the slab 1 as described above, a cover 3 was installed, and cooling was started. The average cooling rate at 500 ° C or higher and 700 ° C or lower is 20 ° C / hr or less (10 ° C / hr or lower, 9.0 ° C / hr or lower in the illustrated range), and the holding time above 700 ° C is secured at 10 hr or higher. It was (11 hr) and could be cooled to room temperature without cracking. Then, it was hot rolled and rolled up and cooled to room temperature. Then, after pickling and cold rolling, a continuous annealing facility was passed through at an annealing temperature of 790 ° C. to manufacture a cold rolled steel sheet. Tensile test pieces were collected from the manufactured cold-rolled steel sheet, and a tensile test was carried out. As a result, a tensile strength of 980 MPa or more was secured.

Condition C-4 is that within 6 hours from the end of casting, different steel plate slabs 2 are laid on the bottom, three slabs 1 of steel plate component C are stacked, a thermocouple is attached as described above, and the steel sheet component is further laid. After stacking two slabs 1 of C, different steel plate slabs 2 were stacked on the uppermost stage to start cooling. The holding time over 700 ° C is not secured for 10 hr or more (8 hr), but the average cooling rate between 700 and 500 ° C is 20 ° C / hr or less (10 ° C / hr or less, 8.3 ° C / hr in the illustrated range). ) Was secured. Although the slab 1 cooled to room temperature did not crack, a small burr was observed at the end of the coil after hot rolling. However, since it was a small amount and it was possible to cut and remove the defective part where the baldness was generated, it was not considered as a nonconforming product. After that, pickling-cold rolling was carried out, annealing was performed at 800 ° C. in a continuous annealing facility, then immersed in a hot-dip galvanized bath, and then alloying treatment was performed at 470 ° C. to achieve high- tensile alloying and melting. Manufactured galvanized steel sheets. Tensile test pieces were collected from the manufactured alloyed hot-dip galvanized steel sheet, and a tensile test was carried out. As a result, a tensile strength of 980 MPa or more was secured.

Condition C-5 is that within 5 hours from the start of casting, four different steel plate slabs 2 are stacked, then the slab 1 of the steel plate component C is stacked on the uppermost stage, and then a thermocouple is attached as described above, and the thermocouple is mounted on the slab 1. Cooling was started without stacking another slab. Although the holding time in the temperature range over 700 ° C. could be secured at 10 hr or more (12 hr), the average cooling rate from 700 ° C. to 500 ° C. was 22.2 ° C./hr exceeding 20 ° C./hr. After that, when hot rolling was carried out, cracks were found after heating the slab. In addition, hot rolling could not be performed because multiple cracks were found.

In condition C-8, after the start of casting, the slab 1 of the steel plate component C was placed at the bottom, a thermocouple was installed as described above, and then five slabs 1 of the steel plate component C were stacked and cooled. By placing the slab 1 at the bottom, it was not possible to secure 10 hr or more at over 700 ° C (6 hr), and the average cooling rate between 700 ° C and 500 ° C was 33.3 ° C over 20 ° C / hr. It became / hr. As a result, cracks occurred in the slab 1 cooled to room temperature. In addition, hot rolling could not be performed because multiple cracks were found.

The slab 1 according to the present invention is transshipped depending on various conditions. When transshipment occurs, the cooling rate of the slab 1 may temporarily exceed 20 ° C / hr, for example 120-170 ° C / hr. However, the slab 1 has at least 10 tons or more, its thermal inertia is large, and it seems that the heat shock can be absorbed if the handling time is about transshipment (1 to 2 hours at the longest), and cracks and shavings occur. Does not reach. Although not shown in FIG. 5, in consideration of this in the present invention, the cooling rate is not 20 ° C./hr or less throughout all of 500 ° C. and above and 700 ° C. or less, but the average cooling rate in the temperature range is 20 ° C./hr. It was found that if the following is the case, it does not lead to cracking or swelling.

More specifically, the slab temperature (the surface temperature at the center of the upper surface of the wide surface of the slab 1 ((T: ° C.)) is between 500 ° C. and 700 ° C., and the average cooling rate (V: ° C./hour) of the slab 1 is 20 ° C. It was found that slab cracking can be suppressed by cooling at / hr or less. Further, at least 10 hr or more after the completion of casting, by ensuring the slab temperature at 700 ° C. or higher, the slab 1 is caused by minute cracking. It was found that the temperature can also be suppressed.

Next, the reason for limiting the chemical composition of the high- strength hot-rolled steel sheet, which is the premise of the present invention, will be described. The% of the content is mass%.

The reason for setting C to 0.020 to 0.600% is as follows. C is an element added to increase the tension of the steel sheet. Specifically, it is an element added to secure retained austenite that contributes to high tension and improvement of elongation. If C is less than 0.020%, the required tension cannot be obtained, so the lower limit of the addition amount is 0.020%. On the other hand, if it exceeds 0.600%, the weldability and workability become insufficient. Therefore, it is set to 0.020 to 0.600%.

The reason for setting Si to 0.50 to 3.00% is as follows. Si needs to be added to ensure retained austenite in the annealing process. In addition, it is an essential additive element because it contributes to high tension by strengthening the solid solution. Therefore, it is necessary to add 0.50% or more. Since this effect becomes particularly remarkable at 0.70% or more, it is preferable to add 0.70% or more. On the other hand, addition of more than 3.00% not only saturates the effect, but also causes a strong scale on the hot-rolled sheet. From this, the upper limit is 3.00% or less because the appearance and pickling property are deteriorated. Therefore, it is set to 0.50 to 3.00%.

The reason for setting Mn to 1.00% to 3.00% is as follows. Mn is an element added to increase the strength of the steel sheet. Specifically, it is an element added to control the strength of the steel sheet through transformation control by hot rolling. If it is less than 1.00%, it cannot be sufficiently strengthened, so it is necessary to add 1.00% or more. On the other hand, addition of more than 3.00% is not desirable because the effect is saturated and the economy is poor. Therefore, it is set to 1.00% to 3.00%.

The reason for setting P to 0.100% or less is as follows. P is an element that segregates in the central portion of the thickness of the steel sheet and is also an element that embrittles the welded portion. A lower value is preferable, but the upper limit is preferably 0.100% because of the productivity of de-P and the costly effect. A more preferable upper limit is 0.050%. The effect of the present invention is exhibited without specifying the lower limit, but reducing P to less than 0.001% is further economically disadvantageous, so the lower limit is set to 0.001%.

The reason for setting S to 0.0001 to 0.0100% is as follows. Since S exists as a sulfide and causes slab embrittlement and deteriorates the formability of the product plate, it is preferable to limit the content in the steel sheet. For this reason, it is preferable to set the upper limit to 0.0100%. Reducing S to less than 0.0001% is disadvantageous in terms of productivity and cost of de-S, so it is preferable to set the lower limit to 0.0001%.

The reason for setting Al to 0.005 to 1.000% is as follows. Al is added in an amount of 0.005% or more for tissue control and deoxidation by hot rolling. If it is less than 0.005%, a sufficient deoxidizing effect cannot be obtained, and a large amount of inclusions (oxides) are present in the steel sheet. On the other hand, addition of more than 1.000% is not preferable because it causes slab embrittlement. Therefore, the addition amount needs to be 0.005 to 1.000%.

The reason for setting N to 0.0100% or less is as follows. N is an element that forms a coarse nitride and deteriorates bendability and hole expansion property. If N exceeds 0.0100%, the bendability and hole expansion property are significantly deteriorated, so the upper limit is set to 0.0100%. It should be noted that N is preferably a small amount because it causes blow holes during welding. The lower limit of N does not need to be set in particular, but if it is reduced to less than 0.0001%, the manufacturing cost will increase significantly, so 0.0001% is a substantial lower limit. N is preferably 0.0005% or more from the viewpoint of manufacturing cost.

In addition, other unavoidable elements may be contained in a trace amount. For example, O forms an oxide and exists as an inclusion.

The steel sheet of the present invention further contains one or more of the following elements in the following proportions, if necessary. Ni: 0.01 to 2.00%, Cu: 0.01 to 2.00%, Cr: 0.01 to 2.00%, Mo: 0.01 to 2.00%.

Ni, Cu, Cr and Mo are elements that affect the strength of the steel sheet. These elements bring about higher strength through microstructural control in hot rolling. This effect becomes remarkable when one or more of Ni, Cu, Cr, and Mo are added in an amount of 0.01% or more, respectively, and therefore it is necessary to add 0.01% or more. If the amount of each element exceeds the upper limit of each element, weldability, hot workability and the like deteriorate, so the upper limit of Ni, Cu, Cr and Mo is set to 2.00%.

The steel sheet of the present invention further contains one or more of the following elements in the following proportions, if necessary. Nb: 0.005 to 0.100%, V: 0.005 to 0.100%, W: 0.005 to 0.100%.

Nb, V, and W may be added because they affect the strength of the steel sheet through precipitation strengthening. Since this effect becomes remarkable when 0.005% or more is added, it is desirable to add 0.005% or more. On the other hand, if the addition exceeds 0.100%, the effect is saturated and carbides of Nb, V, and W are precipitated at the hot rolling stage, so that these elements consume C, which is the source of retained austenite. Since the amount of retained austenite is reduced, it is necessary to make it 0.100% or less. The range is preferably 0.005 to 0.090%.

The steel sheet of the present invention further contains B in a proportion of 0.0005 to 0.0100%, if necessary. B may be added because it affects the strength through tissue strengthening in order to control the transformation due to hot rolling. Since this effect becomes remarkable at 0.0005% or more, it is necessary to add 0.0005% or more. On the other hand, addition of more than 0.0100% is not preferable because not only the effect is saturated but also the precipitation of iron-based boride is caused and the quenching effect of B is lost. The desirable range is 0.0005 to 0.0080%, and the more desirable range is 0.0005 to 0.0050%.

The steel sheet of the present invention further contains one or more of the following elements in the following proportions, if necessary. REM: 0.0003 to 0.0300%, Ca: 0.0003 to 0.0300%, Ce: 0.0003 to 0.0300%, Mg: 0.0003 to 0.0300%.

REM, Ca, Ce, and Mg are elements that affect the strength and contribute to the improvement of the material. If the total of one or more of REM, Ca, Ce, and Mg is less than 0.0003%, a sufficient addition effect cannot be obtained, so the lower limit of the total is set to 0.0003%. If the total of one or more of REM, Ca, Ce, and Mg exceeds 0.0300%, castability and hot workability will deteriorate, so the upper limit is 0.0300%. REM is an abbreviation for Rare Earth Metal and refers to an element belonging to the lanthanoid series. In the present invention, REM is often added as a misch metal, and may contain a lanthanoid-series element in a complex in addition to Ce. The effect of the present invention is exhibited even if the steel sheet of the present invention contains elements of the lanthanoid series other than La and Ce as unavoidable impurities, and the effect of the present invention is exhibited even if a metal is added. ..

The microstructure of the product plate is not particularly limited, and the effect of the present invention is exhibited. For example, if the steel sheet has a tensile strength of 590 MPa or more and less than 980 MPa, the microstructure shall be a structure composed of ferrite, bainite, and retained austenite. Is desirable. If it is 980 MPa or more and less than 1180 MPa, it is desirable to have a structure composed of ferrite, bainite, retained austenite and martensite. If it is 1180 MPa or more, it is desirable to have a structure composed of ferrite, bainite, retained austenite and martensite. Furthermore, it is desirable that the martensite is tempered martensite containing carbides inside.

The tensile strength of the product plate is preferably 590 MPa or more. Si is a solid solution strengthening element, and when Si which may cause slab cracking is added, it becomes 590 MPa or more. As described above, this technique is exhibited by applying this technique to the slab 1 which is a material of a steel plate having a tensile strength of 590 MPa or more. Although the effect of the present invention is exhibited without setting an upper limit, the higher the product plate strength, the larger the amount of Si added, and the slab cracking tends to become apparent. From this, the higher the tension steel plate, the greater the effect of applying this technology. Further, the effect is more remarkable at 780 MPa or more, and further at 980 MPa or more.

If the slab 1 is in accordance with the cooling method according to the present invention, high- tensile hot-rolled steel sheets, cold-rolled steel sheets, high- tensile hot-dip galvanized steel sheets, and high- tensile alloying without slab cracking after casting or generation of shavings during hot-rolling. It is possible to manufacture hot-dip galvanized steel sheets. These manufacturing methods are as follows.

First, the slab 1 according to the cooling method of the present invention is used. The following are the same as the manufacturing conditions for ordinary high- strength steel sheets. In hot rolling, the slab heating temperature is heated in the range of 1100 ° C to 1300 ° C, and after rough rolling, finish rolling is performed at a finish rolling output side plate temperature of 800 ° C to 1100 ° C, and the rolling is performed in the temperature range of room temperature to 700 ° C. Roll out. Rapid cooling, plate temperature maintenance / heat retention, and air cooling may be performed between the finishing rolling side and winding. In this way, a high- strength hot-rolled steel sheet is manufactured.

In the case of a high- tensile cold-rolled steel sheet, the high- tensile hot-rolled steel sheet is pickled, and in the case of further thinning, after pickling, cold rolling with a reduction ratio of 30% to 80% is performed, and then 750 ° C. It is reheated to a temperature range of 900 ° C. and tempered and rolled at a reduction rate of 0.2 to 2.0% to obtain a cold-rolled steel sheet. When plating is applied, after the above heat treatment, it is immersed in a hot-dip galvanizing bath, hot-dip galvanized, tempered and rolled at a reduction rate of 0.2% to 2.0%, and high- tensile cold-rolled hot-dip zinc. It shall be a plated steel plate.
In the case of a high- tensile hot-rolled hot-dip galvanized steel sheet, the high- tensile hot-rolled steel sheet is pickled, reheated to a temperature range of 750 ° C to 900 ° C, immersed in a hot-dip galvanized bath, and hot-dip galvanized. High- tensile hot-dip galvanized steel sheet is obtained by temper rolling at a rolling reduction of 0.2% to 2.0%.

In the case of a high- tensile alloyed hot-dip galvanized steel plate, the hot-dip galvanized steel is alloyed by heating to 470 ° C. to 600 ° C. between hot-dip galvanizing and temper rolling in the production of the high- tensile hot-dip galvanized steel plate. A high- tensile alloyed hot-dip galvanized steel plate is used.

According to the present invention, a crack-free slab 1 containing a large amount of Si can be manufactured without cracking, which can contribute to an improvement in yield. Further, since a large amount of Si can be added, it becomes possible to manufacture high- strength steel sheets for automobiles (for example, GA980 / 1180 MPa class TRIP steel) having higher tension .

Although the present invention has been described above with a focus on the embodiments, the present invention is not limited to the above embodiments and can be in various embodiments.

1 slab (cooling target )
2 slab (for cooling control)
3 cover

Claims (11)

By mass%,
C: 0.020 to 0.600%,
Si: 0.5-3.00%,
Mn: 1.00 to 3.00%,
P: 0.100% or less,
S: 0.0001 to 0.0100%,
Al: 0.005 to 1.000%,
N: 0.0100% or less,
For continuously cast slabs for high-strength steel sheets containing Fe and unavoidable impurities in the balance.
A method for cooling a slab for a high-strength steel plate, characterized in that the average cooling rate of the slab at 500 ° C. or higher and 700 ° C. or lower is 20 ° C./hr or lower. The slab is further in mass%
Ni: 0.01-2.00%,
Cu: 0.01-2.00%,
Cr: 0.01-2.00%,
Mo: 0.01-2.00%,
Nb: 0.005 to 0.100%,
V: 0.005 to 0.100%,
W: 0.005 to 0.100%,
B: 0.0005-0.0100%,
REM: 0.0003-0.0300%,
Ca: 0.0003-0.0300%,
Ce: 0.0003-0.0300%,
Mg: 0.0003-0.0300%,
The method for cooling a slab for a high-strength steel plate according to claim 1, wherein the slab for high-strength steel plate contains one or more of the above. The slab for high-strength steel plate having the component according to claim 1 or 2 has a slab temperature of 700 ° C. or higher for at least 10 hr or more after the completion of casting, and then the average of the slab at 500 ° C. or higher and 700 ° C. or lower. The method for cooling a slab for a high-strength steel plate according to claim 1 or 2, wherein the cooling rate is 20 ° C./hr or less. The method for cooling a slab for a high-strength steel plate according to any one of claims 1 to 3, wherein the cooling rate of the slab is controlled by sandwiching the slab between a plurality of other slabs. The method for cooling a slab for a high-strength steel plate according to claim 4, wherein a plurality of the slabs are simultaneously sandwiched by the other plurality of slabs. The method for cooling a slab for a high-strength steel plate according to any one of claims 1 to 5, wherein a cover is applied to cool the slab for the high-strength steel plate. Using the high-strength steel plate slab cooled by the cooling method according to any one of claims 1 to 6, the slab heating temperature is heated in the range of 1100 to 1300 ° C., and after rough rolling, the finish-rolled output side plate temperature is adjusted. A method for manufacturing a high-strength hot-rolled steel sheet, which comprises performing finish rolling at 800 to 1100 ° C. and winding in a temperature range of room temperature to 700 ° C. A high-strength hot-rolled steel sheet manufactured by the manufacturing method according to claim 7 was used, and after pickling, cold rolling with a reduction ratio of 30 to 80% was performed after pickling to further reduce the thickness. After that, it is reheated to a temperature range of 700 to 900 ° C., annealed, and then tempered and rolled at a reduction rate of 0.2 to 2.0% to produce a high-strength cold-rolled steel sheet. Method. A high-tensile hot-rolled steel sheet manufactured by the manufacturing method according to claim 7 is used, pickled, reheated to a temperature range of 700 to 900 ° C., hot-dip galvanized, and then 0.2 to 0.2. A method for manufacturing a high-tensile hot-rolled hot-dip galvanized steel sheet, which comprises performing temper rolling at a rolling reduction of 2.0%. A high-tensile hot-rolled steel sheet manufactured by the manufacturing method according to claim 7 was used, and after pickling, cold rolling with a reduction ratio of 30 to 80% was performed after pickling to further reduce the thickness. After that, it is reheated to a temperature range of 700 to 900 ° C., hot-dip galvanized, and then temper-rolled at a reduction rate of 0.2 to 2.0%. Manufacturing method of galvanized steel sheet. Manufacture of a high-tensile alloyed hot-dip galvanized steel sheet, which comprises heating to 470 ° C. or higher and 600 ° C. or lower to alloy the hot-dip galvanizing between the hot-dip galvanizing of claim 9 or 10 and temper rolling. Method.

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