JP2013204141A - High-strength steel sheet excellent in surface quality and manufacturing method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high-strength steel sheet that is hard to generate edge scabs and is excellent in surface quality, and to provide a manufacturing method thereof.SOLUTION: A high-strength steel sheet contains, by mass%, C of 0.07-0.14%, Si of 0.01-0.9%, Mn of 1.0-2.5%, P of 0.05% or less, S of 0.01% or less, sol. Al of 0.01-0.06%, and Cr of 0.7% or less, and it also contains either or both of Nb of 0.01-0.1% and V of 0.02-0.2%, satisfying formula 2×[Nb]+[V]≥0.05 (where [Nb] and [V] represent mass% of Nb and V respectively). Furthermore, the high-strength steel sheet contains Ti of 0.010-0.020% and N of 0.003% or less, and the remainder is formed of Fe and inevitable impurities.

Description

  The present invention relates to a high-strength steel plate excellent in surface quality and a method for producing the same. The high-strength steel sheet of the present invention is a hot-rolled steel sheet, a cold-rolled steel sheet, or a hot-rolled steel sheet that is a material for a surface-treated steel sheet, and a cold-rolled steel sheet and a zinc-based plated steel sheet that are made from this hot-rolled steel sheet. To do.

  Steel sheets for automobiles are required to have high strength in order to satisfy the conflicting characteristics of improving fuel efficiency and protecting passengers by reducing weight. High-strength steel plates require alloy elements such as Nb and V, and these alloy elements are added in the molten steel production process. The addition of these alloy elements promotes the occurrence of surface cracks called “lateral cracks” on the surface or corner of the slab slab in the continuous casting process. Moreover, hot ductility falls by single addition or combined addition of Nb and V. This is because Nb and V carbonitrides precipitate at the γ grain boundaries and cause “grain boundary embrittlement”. For this reason, during continuous casting, internal cracks due to bulging may occur on the short sides of the continuous casting slab.

  On the other hand, in the method of manufacturing a hot-rolled steel sheet, a slab is manufactured with a specific width larger than the order width, and this slab is subjected to width press or width reduction rolling before the hot rolling rough rolling to obtain a desired width. After making the slab width, hot rolling including rough rolling and finish rolling has been performed to produce a hot-rolled steel sheet having an order width. The method of adjusting the slab width by the width press or width rolling is preferable from the viewpoint of improving the productivity of continuous casting because the width during casting (slab width) can be increased. Furthermore, performing the width press or the width reduction rolling prior to the rough rolling leads to the improvement of the dimensional accuracy and the rolling shape, which is preferable from the viewpoint of improving the hot rolling productivity. Therefore, recently, in order to increase the continuous casting capacity, this method is actively applied even to a size having a large order quantity.

  However, in steel to which alloy elements such as Nb and V are added, surface cracks called “lateral cracks” exist on the surface or corner of the slab slab, or internal cracks due to bulging occur on the short sides of the continuous cast slab. The edge of the hot-rolled steel sheet may be generated by performing hot rolling, or by performing a width press prior to the hot rolling rough rolling, because it has occurred or the hot ductility has decreased. There is a risk of generating edge shaving in the part.

  When such edge shading occurs, it is necessary to cut the ears beyond the originally planned width, and there are many cases where the manufactured steel sheet does not become a product. In order to prevent this, it has been necessary to produce a hot rolled steel sheet with a wide width, assuming an edge shaving occurrence site, and to carry out ear-knitting before making the final product.

  In view of such a problem, Patent Document 1 discloses a method of width-cutting a continuous cast slab from the both side ends of the continuous cast slab toward the center of the width at least ½ of the slab thickness. . In this case, it is not necessary to listen, and the product width as originally planned can be manufactured, but the loss due to the width cutting in the slab stage is large.

On the other hand, Patent Documents 2 to 4 propose a continuous casting method and a method for improving continuous casting equipment. Specifically, Patent Document 2 discloses a method of increasing the slab surface temperature with no injection water in the correction section, and Patent Document 3 discloses that the slab surface is once cooled to an Ar ₃ transformation point or less in secondary cooling. Then, a method of refining the phase of the slab by reheating and refining the structure of the slab to reduce the susceptibility to cracking, Patent Document 4 discloses that a secondary slab in a curved or vertical bending slab has a secondary structure. A method is disclosed in which a heating device for heating the corner portion of the slab is installed on the bent side of the cooling zone or the entrance side of the correction portion, or on the entrance side of both the bent portion and the correction portion.

JP 2006-255731 A Japanese Patent Laid-Open No. 2003-62648 JP 9-225607 A JP 2007-160341 A

  As described above, high-strength steel sheets that are expected to increase in demand for automotive applications in the future have alloy elements such as Nb and V added to them, causing transverse cracks and internal cracks, Since the rolling property is reduced, there is a risk of generating edge lashes at the edge part of the hot-rolled steel sheet during hot rolling or width pressing, and the yield is inevitably deteriorated in order to remove that part. It was. Moreover, in order to prevent such a thing, although the continuous casting method and the improvement method of a continuous casting installation are proposed, it cannot be said that it is still enough.

  This invention is made | formed in view of this situation, Comprising: It aims at providing the high strength steel plate excellent in the surface quality which is hard to generate | occur | produce edge shaving in the process of hot rolling, and its manufacturing method.

  As a result of intensive studies and examinations to solve the above problems, the present inventors have added a small amount of Ti to steel to which alloy elements such as Nb and V are added, and restricting the N content, The hot ductility of the corners and ends of the slab is improved, edge sag does not occur even if width pressing or width rolling is performed, and a high-strength steel sheet that does not require removal of the corners and ends of the slab is obtained. I found out.

  This invention was made | formed based on the said knowledge, and provides the following (1)-(6).

  (1) By mass%, C: 0.07 to 0.14%, Si: 0.01 to 0.9%, Mn: 1.0 to 2.5%, P: 0.05% or less, S: 0.01% or less, sol.Al: 0.01-0.06%, Cr: 0.7% or less, Nb: 0.01-0.1%, V: 0.02-0.2 % Or both of them so as to satisfy 2 × [Nb] + [V] ≧ 0.05 (where [Nb] and [V] represent mass% of Nb and V, respectively) Furthermore, Ti: 0.010-0.020%, N: 0.003% or less is further contained, and the remainder consists of Fe and an unavoidable impurity, The high strength steel plate excellent in the surface quality characterized by the above-mentioned.

  (2) A high-strength steel sheet having excellent surface quality as described in (1) above, which is a hot-rolled steel sheet.

  (3) The high-strength steel sheet having excellent surface quality as described in (2) above, which is a hot-rolled steel sheet for cold-rolled steel sheets or zinc-based plated steel sheets.

  (4) A slab having the composition described in (1) above is cast by a curved or vertical bending slab continuous casting equipment and heated at 1150 to 1300 ° C. without removing the corner or end of the slab. The hot rolling is started after the holding, and prior to the rough rolling of the hot rolling, the width reduction amount (total reduction amount of both widths) of 100 mm or more and 400 mm or less is performed, and the finish rolling temperature is set. A method for producing a high-strength steel sheet having excellent surface quality, characterized by hot rolling at 850 to 950 ° C and a coiling temperature of 450 to 650 ° C.

(5) After hot rolling, pickling and cold rolling are further performed, then Ac is heated to _one point or more and 900 ° C. or less, cooled after the heating, and temper-rolled. The manufacturing method of the high strength steel plate excellent in the surface quality as described in 4).

(6) After hot rolling, further pickling and cold rolling are performed, then Ac is heated to ₁ point or higher and 900 ° C. or lower, hot dip galvanizing treatment is performed in the cooling process after the heating, and temper rolling The manufacturing method of the high strength steel plate excellent in the surface quality as described in said (4) characterized by performing.

  According to the present invention, the hot ductility of the corner and end of the slab is improved by adding a small amount of Ti to the steel to which alloying elements such as Nb and V are added, and limiting the N content. Thus, it is possible to prevent the occurrence of edge shaving. In particular, even a slab for high-strength steel sheets containing a predetermined amount or more of Nb and V, which are highly susceptible to cracking, can be manufactured with high productivity without generating edge lashes. In recent years, there has been a great demand for high-strength steel sheets from the viewpoint of improving the global environment by improving the fuel efficiency of automobiles, and the present invention is extremely effective industrially.

  When manufacturing hot-rolled steel sheets with high strength, cold-rolled steel sheets or surface-treated steel sheets, edge defects due to internal cracks in the continuous cast slab and surface cracks in the corners frequently occur. Edge shavings occurred in the product, which was a big problem. As a result of investigating the influence of Nb, V, and Ti used on high-strength steel sheets on hot rolling, the inventors of the present invention promoted the generation of edge baldness, and a small amount of Ti caused hot ductility. The present invention has found that it is effective to appropriately control the contents of C, N, Nb, Ti, and V to suppress internal cracks in the slab and surface cracks in the corners. It came to complete.

  Hereinafter, the present invention will be described in detail by dividing it into steel component compositions and production methods.

(1) Component composition of steel The component composition of the high-strength steel sheet according to the present invention is mass%, C: 0.07 to 0.14%, Si: 0.01 to 0.9%, Mn: 1.0. -2.5%, P: 0.05% or less, S: 0.01% or less, sol.Al: 0.01-0.06%, Cr: 0.7% or less, Nb: 0. One or both of 01 to 0.1%, V: 0.02 to 0.2%, 2 × [Nb] + [V] ≧ 0.05 (where [Nb] and [V] are And Nb and V, respectively, are included so as to satisfy the above requirements. Further, Ti: 0.010 to 0.020%, N: 0.003% or less is contained, the balance being Fe and inevitable It is an impurity.

C: 0.07 to 0.14%
C is an important element for increasing the strength of steel. However, if it is less than 0.07%, the steel sheet cannot obtain sufficient strength. On the other hand, if it exceeds 0.14%, spot weldability deteriorates. Therefore, the C content is 0.07 to 0.14%.
By the way, the occurrence of edge shaving is greatly influenced by the solidification behavior when casting with a continuous casting machine. In steel, molten iron undergoes phase transformation to δ iron or γ iron depending on the carbon component. δ iron begins to change to γ iron as the temperature falls, and eventually transforms to α iron. When changing from δ iron to γ iron, the interstitial distance decreases and contracts, and when γ iron changes to α iron, it expands. Further, even when the phase is not transformed, the steel shrinks if the temperature of the steel is lowered. Therefore, the shrinkage of steel at a high temperature is highly dependent on the C concentration. When the C concentration is in the range of 0.09% to 0.17%, the phase transformation of δ iron to γ iron occurs at a high temperature. When the C concentration is 0.09%, the solidified structure is δ iron, but the transformation to γ iron starts immediately after solidification. At the peritectic point with a C concentration of 0.17%, the solidified structure starts with γ iron. The shrinkage during continuous casting is the largest at C = 0.09%, and there is a high possibility of edge scabs. When C is less than 0.07% and exceeds 0.14%, the shrinkage is relatively small. The possibility of occurrence of edge shading is reduced. Therefore, in the range of 0.07 to 0.14%, there is a high possibility that edge shading will occur, so composition control that suppresses edge shaving is necessary.

Si: 0.01-0.9%
Si is contained for the purpose of increasing strength and improving elongation characteristics. However, if it is less than 0.01%, sufficient characteristics cannot be obtained. On the other hand, if it exceeds 0.9%, the deterioration of the surface appearance due to the red scale of the product and the deterioration of the chemical conversion treatment property become remarkable. Therefore, the Si content is set to 0.01 to 0.9%.

Mn: 1.0 to 2.5%
Mn is an important element for increasing the strength of steel. However, if it is less than 1.0%, carbides that contribute to strengthening at high temperatures are generated at high temperatures, so the strength decreases. On the other hand, if it exceeds 2.5%, the structure is mainly composed of a low-temperature transformation phase, so that the elongation is lowered. Therefore, the Mn content is set to 1.0 to 2.5%.

P: 0.05% or less P may be added for the purpose of increasing the strength. However, if the content exceeds 0.05%, the weldability is significantly lowered. Therefore, the P content is 0.05% or less.

S: 0.01% or less S is contained as an impurity in steel, and if the content exceeds 0.01%, the workability and weldability of the product are significantly deteriorated. Therefore, the S content is limited to 0.01% or less.

sol. Al: 0.01 to 0.06%
Al is added for deoxidation. However, its content is sol. If the content is less than 0.01% as Al, this effect is not sufficient. On the other hand, if it exceeds 0.06%, the effect is saturated and uneconomical. It promotes cracking susceptibility at the time, and edge scab is likely to occur. Therefore, sol. The Al content is set to 0.01 to 0.06%.

Cr: 0.7% or less Cr is an element effective for quenching strengthening of steel, and is an element necessary for producing a low yield ratio steel sheet. In order to obtain this effect, it is necessary to contain 0.1% or more, but if the content exceeds 0.7%, this effect is saturated, the surface quality is remarkably deteriorated, and there is a concern that the corrosion resistance is reduced. is there. On the other hand, Cr is an unnecessary element when producing a high yield ratio steel sheet, and when it is contained in an amount of 0.1% or more, it becomes difficult to obtain a high yield strength. It is necessary to make the Cr content less than 0.1%. Therefore, considering both the low yield ratio steel sheet and the high yield ratio steel sheet, the Cr content is set to 0.7% or less.

Nb: 0.01 to 0.1%, V: 0.02 to 0.2%, or both, and 2 × [Nb] + [V] ≧ 0.05
Nb and V are mainly added in order to form carbonitrides in the hot rolling process and increase the strength. On the other hand, when Nb and V are added singly or in combination, hot ductility decreases as the amount increases. In particular, the influence of Nb is large. Furthermore, when Nb and V are added excessively, the hot-rolled sheet is cured, and the load in hot rolling and cold rolling increases. In addition, the ductility of the ferrite deteriorates and the workability decreases. For this reason, the Nb content is 0.1% or less and the V content is 0.2% or less. As described above, hot ductility is decreased by adding Nb and V alone or in combination. However, when Nb is less than 0.01% and V is less than 0.02%, the decrease in hot ductility is small, and the present invention is applied. do not have to. In addition, in the case of 2 × [Nb] + [V] ≧ 0.05 (where [Nb] and [V] indicate mass% of Nb and V, respectively), the possibility of occurrence of edge shaving increases. It is meaningful to apply the invention. Therefore, in the present invention, either or both of Nb: 0.01 to 0.1% and V: 0.02 to 0.2% satisfy 2 × [Nb] + [V] ≧ 0.05. Contained. Note that the influence on the decrease in hot ductility is that Nb is greater than V, and twice the Nb content and the V content are equivalent.

Ti: 0.010 to 0.020%
In contrast to the above-described decrease in hot ductility due to the addition of Nb and V alone or in combination, the addition of a small amount of Ti improves the hot ductility and prevents the occurrence of edge lashes. However, if Ti is less than 0.010%, the effect of improving hot ductility is not sufficient, and if it exceeds 0.020%, the increase in strength due to an increase in the amount of Ti added becomes large, and hot ductility occurs due to precipitation of TiC. Decreases. Therefore, the content of Ti is set to 0.010 to 0.020%.

N: 0.003% or less N is contained in steel as an impurity by nitrogen bubbling or the like for stirring the molten steel in the steelmaking process. In the case of 2 × [Nb] + [V] ≧ 0.05 (where [Nb] and [V] represent mass% of Nb and V, respectively), the content exceeds 0.003% Further, the ductility lowering and embrittlement temperature range is expanded, the cracking susceptibility during continuous casting is promoted, and edge sag is likely to occur. This is because when the nitrogen content is high, Nb and V carbonitrides precipitate at the austenite grain boundaries and lower the ductility. Therefore, the N content is limited to 0.003% or less. In order to reduce the N content, a method such as bubbling with Ar without using nitrogen may be used for stirring the molten steel in the steel making process. In addition, it is thought that the addition of a small amount of Ti described above has the effect of substantially reducing N because Ti is fixed as TiN.
As described above, the shrinkage during continuous casting is the largest at C = 0.09%, and the possibility of occurrence of edge baldness is increased. Therefore, when C is in the range of 0.08 to 0.11%, the N content is desirably limited to 0.0025% or less.

Balance: Fe and inevitable impurities The balance of the above components is Fe and inevitable impurities. That is, elements other than those described above may be contained within a range that does not deteriorate the workability of the product, which is the object of the present invention, as long as they are inevitable impurity elements. For example, Cu: 0.1% or less, Ni: 0.1% or less, Sn: 0.01% or less, Sb: 0.01% or less, O: 0.003% or less, Zr: 0.01% or less, etc. It is.

(2) Manufacturing condition Next, one Embodiment of the manufacturing condition for manufacturing the steel plate of this invention is described.
In producing a high-strength steel sheet having the above component composition, a slab having the above component composition is cast by a slab continuous casting equipment of a curved type or a vertical bending type, and without removing a corner portion or an end portion of the slab. Hot rolling is started after heating and holding at ˜1300 ° C., and prior to rough rolling of hot rolling, width reduction (total reduction of both widths) of 100 mm or more and 400 mm or less is performed. The hot rolling is preferably performed at a finish rolling temperature of 850 to 950 ° C. and a winding temperature of 450 to 650 ° C.

Continuous casting equipment: Curved type or vertical bending type There are four types of continuous casting equipment for steel: vertical type continuous casting equipment, vertical bending type continuous casting equipment, curved type continuous casting equipment, and horizontal type continuous casting equipment. However, in the present invention, a curved or vertical bending type slab continuous casting facility is the object. In vertical continuous casting equipment and horizontal continuous casting equipment, there is no bending part and straightening part, and tensile stress due to bending and straightening does not act on the slab. Although it is difficult to improve the surface characteristics, it is inferior to the curved or vertical bending type continuous casting equipment from the viewpoint of equipment cost and productivity, and is not suitable for industrially producing high-strength steel sheets. In addition, when the curved type and the vertical bending type are compared, the vertical bending type having the vertical part is more likely to be cracked because the curvature of the bending part is smaller and the tensile stress acting on the slab is larger.

Slab heating temperature: 1150-1300 ° C
It is necessary to redissolve the Ti, Nb, and V precipitates precipitated during casting, and the precipitates present in the heating stage are present as coarse precipitates in the finally obtained steel sheet, and thus do not contribute to strength. . Contribution to strength is recognized by heating above 1150 ° C, but heating above 1300 ° C causes decarburization from the surface layer and coarsening of austenite grains, resulting in variations in properties and surface defects after pressing Let Moreover, it is preferable to heat to 1150 degreeC or more also from a viewpoint which scales off defects, such as a bubble of a slab surface layer, and segregation, reduces the crack and unevenness | corrugation of a steel plate surface, and achieves the smooth steel plate surface. As mentioned above, it is preferable that slab heating temperature shall be the range of 1150 degreeC or more and 1300 degrees C or less.

Width press or width reduction rolling: width reduction amount (total reduction amount of both widths) 100 mm or more and 400 mm or less The width pressing or width reduction rolling is performed 100 mm or more for improving the dimensional accuracy and rolling shape. If it is less than 100 mm, there is a problem in the shape when entering the roughing mill and the finishing mill, and there is a case where the sheet cannot be passed. If such an event occurs, enormous damage occurs. The method of adjusting the slab width by width pressing or width rolling is limited in terms of equipment capacity, and the current width adjustment allowance is about 400 mm at most. Accordingly, the width pressing or width rolling performed prior to the rough rolling of the hot rolling has a width reduction amount (total reduction amount of both widths) of 100 mm to 400 mm.

Finish rolling temperature: 850-950 ° C
The press formability is improved by setting the finish rolling temperature to 850 ° C. or higher. When the finish rolling temperature is less than 850 ° C., it is remarkable after the hot rolling, especially in the edge portion in the width direction, etc., but the unrecrystallized austenite and recrystallization having the crystal grain size stretched by the partial hot rolling Austenite may be mixed. A grain-sized recrystallized austenite forms a grain-sized structure, and in the region where originally expanded grains exist, a ferrite phase and a low-temperature transformation phase exist in the vicinity of the prior austenite grain boundary, and a band-like structure is formed. Will be formed. Thus, when it becomes a non-uniform | heterogenous structure | tissue, the uniform deformation | transformation of the material at the time of shaping | molding will be inhibited, and it will become difficult to have the outstanding moldability requested | required. On the other hand, when the finish rolling temperature exceeds 950 ° C., the amount of oxide generated increases rapidly, the base metal-oxide interface becomes rough, and the surface quality after pickling and cold rolling deteriorates. Thus, when the surface quality after cold rolling deteriorates, in the hot dip galvanized steel sheet, which is the final product, the presence of cracks and recesses that progress to the inside of the steel sheet side at the plating-steel sheet interface becomes noticeable. It becomes easy to break. Further, the crystal grain size becomes excessively large, and the surface of the pressed product may be roughened during molding. Therefore, the finish rolling temperature is preferably 850 to 950 ° C.

Winding temperature: 450-650 ° C
When the coiling temperature exceeds 650 ° C., decarburization from the surface layer and scale growth are remarkably deteriorated in surface quality. Also inside the steel sheet, Si, Mn-based oxides are formed in the grain boundaries and in the grains, microcracks after pickling, iron powder peels off after cold rolling, and becomes a concave part, so that the surface of the cold rolled material becomes Roughness and formability deteriorate. Further, when the coiling temperature is less than 450 ° C, the cold rolling load increases due to the increase in hot-rolled sheet strength. For this reason, the coiling temperature is preferably set to 450 to 650 ° C.

When pickling and cold rolling after hot rolling as described above, pickling and cold rolling may be performed according to a conventional method. The cold rolling rate is preferably 30% or more in order to promote recrystallization of ferrite.
After hot rolling in this way, the continuous annealing and the continuous hot dip galvanizing soaking temperature are set to Ac ₁ point or higher and 900 ° C. or lower in order to suppress the recrystallization of ferrite and the coarsening of the structure of the steel sheet surface layer. .

  Examples of the present invention will be described below.

Using a slab having the components shown in Table 1, hot rolling, pickling, cold rolling, continuous annealing, or continuous hot dip galvanizing treatment was performed under the conditions shown in Table 2. In Steel A, B, C, D, E, F, G, H, Q, R, S, and T, three types of steel, hot rolled steel sheet, cold rolled steel sheet, and galvannealed steel sheet (GA) are used. , J, K, and L produce two types of cold-rolled steel sheets and galvannealed steel sheets (GA), and steels M, N, O, and P produce one kind of galvannealed steel sheets (GA). did. The slab used was cast using a vertical bending type continuous casting machine that has a relatively small bending portion curvature and a large tensile stress acting on the slab, and is relatively easy to crack. Hot-rolled steel sheet is 2.8 mm thick, cold-rolled steel sheet is 1.4 mm thick, galvannealed steel sheet is 1.4 mm thick, and zinc coating weight (per one side) is 45 g / m ² (double-sided plating) ) Was manufactured. The galvanizing bath temperature was 460 ° C., and the alloying of the plating was performed at 550 ° C. Each steel plate thus obtained was subjected to the material test shown below to investigate the material characteristics. The obtained results are shown in Table 3 (hot rolled steel plate), Table 4 (cold rolled steel plate), and Table 5 (alloyed hot dip galvanized steel plate).

  For mechanical properties, a tensile test based on JISZ2241 (1998) was conducted using a JISZ2201 (1998) No. 5 tensile test specimen taken so that the tensile direction was perpendicular to the rolling direction. Strength: MPa), TS (tensile strength: MPa), EL (total elongation:%) were measured. The surface quality was judged by the presence or absence of edge shaving by passing the obtained hot-rolled steel sheet, cold-rolled steel sheet, and galvannealed steel sheet through a finishing line and observing the state of the steel sheet surface. It was judged that there was edge shave if there was a shave at a position from the width end of the steel plate to 50 mm, and if there was no shave, if there was no shave.

as a result,
-Edge shading occurred in A, C, E, G, I, K, M, O, Q, and S, where Ti is outside the scope of the present invention.
-B, F, J, L, N, P, R, and T in which Ti is within the scope of the present invention were good without edge sag.
・ Although Ti was added in an appropriate amount, D and H with a high N amount were edge-heavy.

  The high-strength steel sheet of the present invention is suitable as an automotive part, but can also be suitably used in other fields where strict dimensional accuracy and workability are required, such as the construction field and the home appliance field.

Claims (6)

  In mass%, C: 0.07 to 0.14%, Si: 0.01 to 0.9%, Mn: 1.0 to 2.5%, P: 0.05% or less, S: 0.01 %, Sol.Al: 0.01-0.06%, Cr: 0.7% or less, Nb: 0.01-0.1%, V: 0.02-0.2% Either or both of them are contained so as to satisfy 2 × [Nb] + [V] ≧ 0.05 (where [Nb] and [V] represent mass% of Nb and V, respectively), Furthermore, Ti: 0.010-0.020%, N: 0.003% or less, The remainder consists of Fe and an unavoidable impurity, The high strength steel plate excellent in the surface quality characterized by the above-mentioned.   The high-strength steel sheet having excellent surface quality according to claim 1, which is a hot-rolled steel sheet.   The high-strength steel sheet with excellent surface quality according to claim 2, which is a hot-rolled steel sheet for cold-rolled steel sheets or galvanized steel sheets.   A slab having the component composition according to claim 1 is cast by a slab continuous casting equipment of a curved type or a vertical bending type, and is heated and held at 1150 to 1300 ° C. without removing a corner portion or an end portion of the slab. The hot rolling is started, and prior to the rough rolling of the hot rolling, the width reduction (total reduction amount of both widths) of 100 mm or more and 400 mm or less is performed, and the finish rolling temperature is 850 to 950 ° C. A method for producing a high-strength steel sheet having excellent surface quality, characterized by hot rolling at a coiling temperature of 450 to 650 ° C. 5. The steel sheet according to claim 4, wherein after hot rolling, pickling and cold rolling are further performed, followed by heating to an Ac point of _{1 to} 900 ° C., cooling after the heating, and temper rolling. Of high strength steel sheet with excellent surface quality. After hot rolling, further pickling and cold rolling are performed, and then heating is performed to Ac ₁ point or higher and 900 ° C. or lower, hot dip galvanizing treatment is performed in the cooling process after the heating, and temper rolling is performed. The manufacturing method of the high strength steel plate excellent in the surface quality of Claim 4 characterized by the above-mentioned.