JP2019167560A - Method for cooling slab for high-strength steel sheet, method for producing high-strength hot-rolled steel sheet, method for producing high-strength hot-dip galvanized steel sheet, and method for producing high-strength alloyed hot-dip galvanized steel sheet - Google Patents

Abstract

To provide a method for cooling a slab for high-strength steel sheet in which, even for a slab containing Si, not only slab cracking during cooling of the slab, but also quality defect such as scab or the like during hot rolling do not occur.SOLUTION: Provided is a method for cooling a slab for high-strength steel sheet, in which, characterized, for a continuously cast slab of a high-tensile steel sheet in which the steel sheet contains, in 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, the average cooling rate for the slab at 500°C to 700°C is set at 20°C/hr or less.SELECTED DRAWING: None

Description

    The present invention relates to a method for cooling a slab for high-strength steel sheets, a method for producing high-strength hot-rolled steel sheets, a method for producing high-strength hot-dip galvanized steel sheets, and a method for producing high-strength galvannealed steel sheets.

  Since cold-rolled and plated steel sheets applied to the body frame are required to have both high strength and elongation, application of TRIP steel in which retained austenite is dispersed has been advanced. It is known that a large amount of Si causes embrittlement of the slab. Generally, when a slab is cooled, stress is generated due to a temperature difference between the slab surface and the inside. When this stress is high, cracks occur when the slab is cooled to room temperature, and worst, cracks occur as shown in FIGS. Or it opens during hot rolling and the coil at the time of hot rolling breaks. Or, a very small crack can appear as a quality defect called “hege” when reheated by hot rolling. Although fine slab cracks can be removed by grinding the slab with a grinder, etc., large cracks cannot be removed or may be missed, which may result in defects in the product plate. There is a need to. The frequency of occurrence of slab cracks is particularly noticeable in steels containing a large amount of Si, and thus tends to be a problem in steels containing a large amount of Si. In addition, as described in Patent Document 1, a countermeasure against cracking of the slab has been conventionally studied.

Japanese Patent Laid-Open No. 2007-837433

  By the way, while examining countermeasures for cracking of the slab of the component containing Si, an attempt was made to confirm the effectiveness of the method described in Patent Document 1, but control was performed within the range described in Patent Document 1. It has also been found that cracking of the steel may not be suppressed.

  The present invention is an invention made in such a background, and the object of the present invention is not only slab cracking during cooling of the slab, but also slabs during hot rolling, even if the slab contains Si. It is providing the cooling method of the slab for high-strength steel plates which the quality defect does not generate | occur | produce. Another object of the present invention is to provide a method for producing a high-strength hot-rolled steel sheet, a high-strength hot-dip galvanized steel sheet, and a high-strength galvannealed steel sheet using the cooling method.

  In order to solve the above problems, the steel sheet is in mass%, C: 0.020 to 0.600%, Si: 0.5 to 3.00%, Mn: 1.00 to 3.00%, P: 0.00. 100% or less, S: 0.0001 to 0.0100%, Al: 0.005 to 1.000%, N: 0.0100% or less For a continuously cast slab of a high-tensile steel plate, 500 ° C to 700 ° C The cooling method of the slab for high-strength steel sheets is characterized in that the average cooling rate of the slab at 20 ° C or less is 20 ° C / hr or less.

  Further, the slab is further in 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: 0.005-0.100%, V: 0.005-0.100%, W: 0.005-0.100%, B: 0.0005-0.0100%, 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 to make it the structure which contains.

  In addition, when the slab of the above component is at least 10 hr or more after the completion of casting, the slab temperature is ensured to be over 700 ° C., and the average cooling rate of the slab at 500 ° C. to 700 ° C. is then set to 20 ° C./hr or less. Is preferred.

  The cooling rate of the slab is preferably controlled by sandwiching the slab with a plurality of other slabs.

  Further, it is preferable that a plurality of the slabs are sandwiched simultaneously by the other plurality of slabs.

  Further, it is preferable to cover the slab for cooling.

  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 the rough rolling, the finish rolling is performed at a finish rolling outlet plate temperature of 800 to 1100 ° C. It is preferable to produce a high-strength hot-rolled steel sheet by scraping in a temperature range of ° C.

  In addition, after using the high-strength hot-rolled steel sheet manufactured by the above-described manufacturing method and pickling it, and further reducing the sheet thickness, the steel sheet is subjected to cold rolling with a reduction rate of 30 to 80% after pickling, and then 700 After reheating to a temperature range of ˜900 ° C. and annealing, temper rolling at a rolling reduction of 0.2 to 2.0% is preferably performed to produce a high-strength cold-rolled steel sheet.

  In addition, after using the high-strength hot-rolled steel sheet manufactured by the above-described manufacturing method and pickling it, and further reducing the sheet thickness, the steel sheet is subjected to cold rolling with a reduction rate of 30 to 80% after pickling, and then 700 It is preferable to produce a high-strength hot-dip galvanized steel sheet by performing re-heating to a temperature range of ˜900 ° C. and hot-dip galvanizing, and then performing temper rolling at a rolling reduction of 0.2 to 2.0%. .

  Moreover, it is preferable to produce a high-strength galvannealed steel sheet by alloying the hot dip galvanizing by heating to 470 ° C. or higher and 600 ° C. or lower between the galvanizing and temper rolling.

  By using the present invention, there is provided a method for cooling a slab for high-strength steel sheets that does not cause quality defects such as slab cracking during hot rolling as well as slab cracking during cooling of the slab even if the slab contains Si. Can be provided. Moreover, the manufacturing method of the high intensity | strength hot-rolled steel plate using the said cooling method, a high-strength hot-dip galvanized steel plate, and a high-strength galvannealed steel plate can be provided.

It is a figure showing the crack of a slab. It is the photograph of the slab in which the crack corresponding to the crack represented by the II area | region of FIG. 1 produced. It is a figure showing the temperature measurement position of a slab. It is a figure showing the cooling aspect of a slab. However, three types are shown: normal cooling, cooling in which a slab to be cooled is sandwiched between two other slabs, and cooling in a state where the slab to be cooled is covered with a cover. It is a figure which shows the cooling history which concerns on elapsed time and slab surface temperature. However, it relates to the conditions C-1, C-4, the conditions C-5, and C-8.

  The form for implementing this invention is shown below. The cooling method of the slab 1 for high-strength steel sheets of this embodiment is that the steel sheet is mass%, C: 0.020 to 0.600%, Si: 0.5 to 3.00%, Mn: 1.00 to 3 Continuous casting of high-strength steel sheet containing 0.000%, P: 0.100% or less, S: 0.0001 to 0.0100%, Al: 0.005 to 1.000%, N: 0.0100% or less The average cooling rate of the slab 1 at 500 ° C. or more and 700 ° C. or less is 20 ° C./hr or less. Thereby, even if it is the slab 1 of the component containing Si, not only the slab cracking during the cooling of the said slab 1 but the cooling method of the slab 1 for high-strength steel plates which does not generate | occur | produce quality defects, such as a baldness at the time of hot rolling, can do.

  Here, the flow that led to the present invention will be described. In the present inventors, the steel sheet is mass%, C: 0.020 to 0.600%, Si: 0.5 to 3.00%, Mn: 1.00 to 3.00%, P: 0.100. %, S: 0.0001 to 0.0100%, Al: 0.005 to 1.000%, N: 0.0100% or less Thus, it has been found that the cause of the slab cracking is the thermal stress generated due to the addition of Si into the steel and the temperature unevenness in the slab 1. Since the steel uses Si addition to increase strength and improve ductility, Si addition is indispensable. That is, since addition of Si is necessary, we considered whether cracking of the slab 1 could be suppressed by paying attention to the reduction of thermal stress due to 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, various cooling conditions and slab cracks, and the surface called cracks and scabs during subsequent slab cooling and hot rolling. The presence or absence of defects was investigated. The temperature at this position is the slab temperature. It is considered that cracks caused by hot rolling are cracks formed during slab cooling, which are opened by hot rolling heating or rolling, resulting in cracks. On the other hand, an open crack may be detected as a defect such as a shave even if it does not lead to cracking, so this was also evaluated. With respect to some slabs 1, the cooling rate was controlled by sandwiching and cooling with slabs 2 of different components or covering the slab 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.

  The chemical composition of the steel used for the study is shown in Table 1, and Table 2 shows the slab cooling conditions, slab cracking, and presence or absence of hot-rolled baldness. Moreover, the cooling history which concerns on the elapsed time of each condition and slab surface temperature is shown in FIG. The elapsed time 0 hr is the end of casting.

  Condition C-1 was 7 hours from the end of casting. A thermocouple was attached to the slab 1 as described above, the cover 3 was installed, and cooling was started. The average cooling rate at 500 ° C. or more and 700 ° C. or less is 20 ° C./hr or less (10 ° C./hr or less, 9.0 ° C./hr or less in the illustrated range), and the holding time at over 700 ° C. is secured for 10 hours or more. (11 hr) and could be cooled to room temperature without cracking. Then, it hot-rolled and scraped off and cooled to room temperature. Then, after pickling and cold rolling, continuous annealing equipment was passed at an annealing temperature of 790 ° C. to produce a cold rolled steel sheet. A tensile test piece was collected from the manufactured cold-rolled steel sheet and subjected to a tensile test, which ensured a tensile strength of 980 MPa or more.

  Condition C-4 is that, within 6 hours from the end of casting, after placing different steel plate slabs 2 at the bottom, three slabs 1 of steel plate components C are stacked, thermocouples are attached as described above, and further steel plate components After two C slabs 1 were stacked, different steel plate slabs 2 were stacked on the top and cooling was started. The holding time exceeding 700 ° C. is not secured for 10 hours or more (8 hours), but the average cooling rate between 700 and 500 ° C. is 20 ° C./hr or less (10 ° C./hr or less in the illustrated range, 8.3 ° C./hr ) Was secured. Although the slab 1 cooled to room temperature did not crack, a small baldness 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 portion where the baldness occurred, no nonconforming product was generated. Then, pickling-cold rolling was performed, and after annealing at 800 ° C. in a continuous annealing facility, it was immersed in a hot dip galvanizing bath, and then alloyed at 470 ° C. to perform high-strength alloying and melting. A galvanized steel sheet was produced. A tensile test piece was taken from the manufactured galvannealed steel sheet and subjected to a tensile test. 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, after four different steel plate slabs 2 are stacked, the slab 1 of steel plate component C is stacked on the top, and then a thermocouple is attached as described above, Cooling started without additional slabs. Although the holding time in the temperature range exceeding 700 ° C. could be secured for 10 hours or more (12 hours), the average cooling rate from 700 ° C. to 500 ° C. was 22.2 ° C./hr, exceeding 20 ° C./hr. Then, when hot rolling was implemented, the crack was found after the slab heating. In addition, since a plurality of cracks were found, hot rolling could not be performed.

  Condition C-8 was that after the slab 1 of the steel plate component C was placed at the bottom after the start of casting, 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 lowest stage, it was not possible to secure 10 hours or more above 700 ° C. (6 hours), and the average cooling rate between 700 ° C. and 500 ° C. was 33.3 ° C. exceeding 20 ° C./hr. / Hr. As a result, cracks occurred in the slab 1 cooled to room temperature. In addition, since a plurality of cracks were found, hot rolling could not be performed.

  Note that the slab 1 according to the present invention undergoes transshipment depending on various conditions. When transshipment occurs, the cooling rate of the slab 1 may temporarily exceed 20 ° C./hr, for example, 120 to 170 ° C./hr. However, the slab 1 has at least 10 tons or more, its thermal inertia is large, and if the handling time is as long as transshipment (longer, 1 to 2 hours), it seems that the heat shock can be absorbed, and the occurrence of cracks and lashes Not reached. Although not shown in FIG. 5, in the present invention, in consideration of this, the cooling rate is not 20 ° C./hr or less through all of 500 ° C. or more and 700 ° C. or less, but is 20 ° C./hr as an average cooling rate in that temperature range. It has been found that cracks and baldness do not occur if the following is true.

  More specifically, the average cooling rate (V: ° C./hour) of the slab 1 between the slab temperature (surface temperature (T: ° C.) at the center of the upper surface of the wide surface of the slab 1 ((T: ° C.)) of 500 ° C. to 700 ° C. is 20 ° C. It has been found that slab cracking can be suppressed by cooling at / hr or less, and at least 10 hours or more after the completion of casting, the slab temperature is kept at 700 ° C. or more to ensure that the slab 1 is cracked. I found out that it can also be suppressed.

  Next, the reasons for limiting the chemical components of the high-strength hot-rolled steel sheet that is the premise of the present invention will be described. In addition,% of content is the mass%.

  The reason why C is set to 0.020 to 0.600% is as follows. C is an element added to increase the strength of the steel sheet. Specifically, it is an element added to ensure retained austenite that contributes to increasing strength and improving elongation. When C is less than 0.020%, the required strength cannot be obtained, so the lower limit addition amount is 0.020%. On the other hand, when it exceeds 0.600%, weldability and workability become insufficient. Therefore, it is set to 0.020 to 0.600%.

  The reason for making Si 0.50 to 3.00% is as follows. Si needs to be added in order to secure retained austenite in the annealing process. In addition, it is an indispensable additive element because it contributes to high strength by solid solution strengthening. For this reason, 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, the addition of more than 3.00% not only saturates the effect but also produces a strong scale on the hot rolled sheet. Therefore, the upper limit is 3.00% or less because the appearance and pickling properties are deteriorated. Therefore, it is set to 0.50 to 3.00%.

  The reason why Mn is set 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 steel sheet strength through transformation control in hot rolling. If it is less than 1.00%, sufficient strengthening cannot be performed, so it is necessary to add 1.00% or more. On the other hand, addition over 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 why P is 0.100% or less is as follows. P is an element that segregates in the central part of the thickness of the steel sheet, and is also an element that embrittles the weld. Although the lower one is preferable, the upper limit is preferably made 0.100% in view of productivity of de-P and cost. A more preferred upper limit is 0.050%. Although the lower limit is not particularly defined, the effect of the present invention is exhibited. However, since it is further economically disadvantageous to reduce P to less than 0.001%, the lower limit is set to 0.001%.

  The reason why S is 0.0001 to 0.0100% is as follows. S is an element that preferably limits the content in the steel sheet because it exists as a sulfide and causes slab embrittlement or deteriorates the formability of the product plate. For this reason, the upper limit is preferably set to 0.0100%. Reducing S to less than 0.0001% is disadvantageous from the standpoint of de-S productivity and cost, so the lower limit is preferably made 0.0001%.

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

  The reason why N is set to 0.0100% or less is as follows. N is an element that forms coarse nitrides and degrades bendability and hole expandability. If N exceeds 0.0100%, the bendability and hole expansibility deteriorate significantly, so the upper limit was made 0.0100%. Note that N is preferable because it causes blowholes during welding. The lower limit of N is not particularly required, but if it is reduced to less than 0.0001%, the manufacturing cost is greatly increased, so 0.0001% is a substantial lower limit. N is preferably 0.0005% or more from the viewpoint of manufacturing cost.

  In addition, it may contain a trace amount of other inevitable elements. 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 ratio as necessary. Ni: 0.01-2.00%, Cu: 0.01-2.00%, Cr: 0.01-2.00%, Mo: 0.01-2.00%.

  Ni, Cu, Cr, and Mo are elements that affect the strength of the steel sheet. These elements bring about high strength through structure control in hot rolling. This effect becomes remarkable when one or more of Ni, Cu, Cr, and Mo are added by 0.01% or more, respectively. 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 2.00%.

  The steel sheet of the present invention further contains one or more of the following elements in the following ratio as 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 significant when 0.005% or more is added, it is desirable to add 0.005% or more. On the other hand, addition of over 0.100% saturates the effect and precipitates Nb, V, and W carbides in the hot-rolled sheet stage, so these elements consume C, which is the source of retained austenite. As a result, the amount of retained austenite is reduced, so it is necessary to make it 0.100% or less. In addition, Preferably, it is 0.005 to 0.090% of range.

  In the steel plate of the present invention, B is further contained in a proportion of 0.0005 to 0.0100% as necessary. B may be added because it affects the strength through strengthening the structure in order to control transformation in 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 over 0.0100% is not preferable because not only the effect is saturated but also the precipitation of iron-based borides is caused, and the effect of B hardenability is lost. A desirable range is 0.0005 to 0.0080%, and a 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 ratio as necessary. REM: 0.0003-0.0300%, Ca: 0.0003-0.0300%, Ce: 0.0003-0.0300%, Mg: 0.0003-0.0300%.

  REM, Ca, Ce, and Mg are elements that influence 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%, the castability and hot workability deteriorate, so the upper limit is made 0.0300%. Note that 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 by misch metal, and may contain a lanthanoid series element in combination with Ce in addition to Ce. Even if the steel sheet of the present invention contains La or a lanthanoid series element other than Ce as an inevitable impurity, the effect of the present invention is exhibited, and even if a metal is added, the effect of the present invention is exhibited. .

  The microstructure of the product plate is not particularly limited, and the effect of the present invention is exhibited. However, if the tensile strength is a steel plate having a tensile strength of 590 MPa or more and less than 980 MPa, the microstructure is 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 make it the structure | tissue which consists of a ferrite, a bainite, a retained austenite, and a martensite. If it is 1180 MPa or more, it is desirable to have a structure composed of ferrite, bainite, retained austenite, and martensite. Furthermore, the martensite is preferably tempered martensite containing carbide inside.

  The product sheet preferably has a tensile strength of 590 MPa or more. Si is a solid solution strengthening element, and when adding Si that may cause slab cracking, it becomes 590 MPa or more. Thus, this effect is exhibited by applying the present technology to the slab 1 that is a material of a steel plate having a tensile strength of 590 MPa or more. Although the upper limit is not particularly defined, the effect of the present invention is exhibited. However, the higher the product plate strength is, the more the Si addition amount tends to increase, and the slab cracking tends to become obvious. For this reason, the higher the strength of the steel plate, the greater the effect of applying this technology. Further, the effect is more remarkable at 780 MPa or more, and further 980 MPa or more.

  If it is the slab 1 according to the cooling method by this invention, the slab crack after casting and the high-strength hot-rolled steel sheet, cold-rolled steel sheet, high-strength hot-dip galvanized steel sheet, and high-strength alloying will not occur at the time of hot rolling. Hot-dip galvanized steel sheet can be manufactured. These manufacturing methods are as follows.

  First, the slab 1 according to the cooling method of the present invention is used. The following is the same as the manufacturing conditions for a normal high-strength steel sheet. In hot rolling, the slab heating temperature is heated in the range of 1100 ° C to 1300 ° C, and after the rough rolling, finish rolling is performed at a finish rolling outlet plate temperature of 800 ° C to 1100 ° C, and rolling is performed in a temperature range from room temperature to 700 ° C. Take. Rapid cooling, holding / holding the plate temperature, and air cooling may be performed from the finish rolling to the scraping. In this way, a high strength hot rolled steel sheet is produced.

In the case of a high-strength cold-rolled steel sheet, after pickling the high-strength hot-rolled steel sheet and further reducing the sheet thickness, the steel sheet is subjected to cold rolling at a reduction rate of 30% to 80% after pickling, and then from 750 ° C to It is reheated to a temperature range of 900 ° C. and subjected to temper rolling at a rolling reduction of 0.2 to 2.0% to obtain a cold rolled steel sheet. When plating is applied, it is immersed in a hot dip galvanizing bath after the above heat treatment, hot dip galvanized, subjected to temper rolling at a rolling reduction of 0.2% to 2.0%, and high strength cold rolled hot dip zinc. A plated steel sheet is used.
In the case of a high-strength hot-rolled hot-dip galvanized steel sheet, the high-strength hot-rolled steel sheet is pickled, reheated to a temperature range of 750 ° C. to 900 ° C., immersed in a hot-dip galvanizing bath, and hot-dip galvanized. Temper rolling at a rolling reduction of 0.2% to 2.0% is performed to obtain a high-strength hot-dip galvanized steel sheet.

  When a high strength alloyed hot dip galvanized steel sheet is used, the hot dip galvanized steel sheet is heated to 470 ° C. to 600 ° C. between the hot dip galvanizing process and the temper rolling process to produce the hot galvanized steel sheet. The high-strength galvannealed steel sheet is used.

  If this invention is used, the slab 1 without a crack containing many Si can be manufactured without a crack, and it can contribute to a yield improvement. In addition, since a large amount of Si can be added, it is possible to manufacture a higher-strength automotive high-strength steel sheet (for example, GA980 / 1180 MPa grade TRIP steel).

  As mentioned above, although this invention was demonstrated centering on embodiment, this invention is not limited to the said embodiment, It can be set as various aspects.

1 Slab (cooling symmetry)
2 Slab (for cooling control)
3 Cover

Claims (11)

The steel plate is 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: For a continuously cast slab of a high-tensile steel plate containing 0.0100% or less,
A method for cooling a slab for high-strength steel sheets, wherein an average cooling rate of the slab at 500 ° C. or more and 700 ° C. or less is 20 ° C./hr or less. The slab is further mass%,
Ni: 0.01 to 2.00%,
Cu: 0.01-2.00%,
Cr: 0.01 to 2.00%
Mo: 0.01-2.00%,
Nb: 0.005 to 0.100%,
V: 0.005-0.100%,
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%,
1 or 2 types or more of these are contained, The cooling method of the slab for high-strength steel plates of Claim 1 characterized by the above-mentioned.   The slab of the component according to claim 1 or 2 is secured at a slab temperature of more than 700 ° C for at least 10 hours or more after completion of casting, and thereafter an average cooling rate of the slab at 500 ° C or more and 700 ° C or less is 20 ° C / The method for cooling a slab for high-strength steel sheets according to claim 1 or 2, characterized in that it is not more than hr.   The method for cooling a slab for high-strength steel sheets according to any one of claims 1 to 3, wherein the cooling rate of the slab is controlled by sandwiching the slab with a plurality of other slabs.   The method for cooling a slab for high-strength steel sheets according to claim 4, wherein a plurality of the slabs are sandwiched simultaneously by the other plurality of slabs.   The method for cooling a slab for high-strength steel sheets according to any one of claims 1 to 5, wherein a cover is applied to cool the slab.   Using the slab cooled by the cooling method according to any one of claims 1 to 6, the slab heating temperature is heated in a range of 1100 to 1300 ° C, and after rough rolling, the finish rolling exit sheet temperature is 800 to 1100 ° C. A method for producing a high-strength hot-rolled steel sheet, comprising performing finish rolling and scraping in a temperature range from room temperature to 700 ° C.   The high-strength hot-rolled steel sheet manufactured by the manufacturing method according to claim 7 is used, and after this pickling, when further reducing the sheet thickness, cold rolling is performed at a reduction rate of 30 to 80% after pickling. Then, after reheating to a temperature range of 700 to 900 ° C. and annealing, temper rolling at a reduction rate of 0.2 to 2.0% is performed, and a high strength cold-rolled steel sheet is manufactured. Method.   A high-strength hot-rolled steel sheet manufactured by the manufacturing method according to claim 7 is used, and after pickling, the steel sheet is reheated to a temperature range of 700 to 900 ° C. and hot dip galvanized, and then 0.2 to A method for producing a high-strength hot-rolled galvanized steel sheet characterized by subjecting temper rolling at a reduction rate of 2.0%.   The high-strength hot-rolled steel sheet manufactured by the manufacturing method according to claim 7 is used, and after this pickling, when further reducing the sheet thickness, cold rolling is performed at a reduction rate of 30 to 80% after pickling. Then, after reheating to a temperature range of 700 to 900 ° C. and performing hot dip galvanization, temper rolling is performed at a reduction rate of 0.2 to 2.0%, and high strength cold rolling and melting is characterized. Manufacturing method of galvanized steel sheet.   A high-strength galvannealed steel sheet is produced by heating the galvanized steel to 470 ° C or higher and 600 ° C or lower between hot dip galvanizing and temper rolling of claim 9 or 10. Method.