JP2018059156A - Steel sheet and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide, for instance, a steel sheet that can combine processability and mechanical characteristics required for an undercarriage member of a vehicle and a structural member of a vehicle body at a high-level, because of having different levels of processability and mechanical characteristics depending on sites in a plane.SOLUTION: A steel sheet 1 has a first region 2 and a second region 3 on a surface of a steel sheet. In a plate thickness direction from a horizontal plane containing the surface of steel sheet, the first region 2 has a first chemical composition over entirety of the plate thickness, and the second region 3 has a second chemical composition different from the first chemical composition from the surface of steel sheet to a predetermined depth, and has the first chemical composition at a depth exceeding the predetermined depth.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a steel plate and a method for manufacturing the steel plate.

  Steel sheets for automobiles are required to have various properties such as reduction in sheet thickness due to increased strength and good workability. A multilayer steel plate (clad plate) is known as a technology that meets such requirements. Since the multilayer steel plate is bonded and rolled by superposing two or more kinds of metal plates, it has the characteristics of each metal plate.

  In recent years, in steel plates for automobiles, in order to further reduce the weight and improve the collision safety, for example, an ultrahigh strength such as a tensile strength of 980 MPa or more has been achieved. Along with this, tailored blanks in which two or more types of steel plates having different properties such as plate thickness, workability, and tensile strength are welded and joined are also used for the purpose of shortening the manufacturing process and reducing the number of dies. It is like that.

  Patent Document 1 discloses an invention in which plasma irradiation is performed on a joint surface when a multilayer steel plate is manufactured by superposing and rolling two or more metal plates.

  In Patent Document 2, a multi-layer steel sheet having excellent strength, ductility, fatigue characteristics, and the like is manufactured by combining and rolling at least two types of steel sheets having different metal structures or mechanical properties and performing a predetermined heat treatment. The invention is disclosed.

  In Patent Document 3, the end of a plated steel sheet having a molten Zn—Al—Mg-based alloy plating layer on both sides and the end of a cold-rolled steel sheet are butt-joined, and the butt joint is melt welded. An invention is disclosed in which a stable weld bead can be obtained even if the heat input energy is large, and a tailored blank that is excellent in drawing workability and perforated corrosion resistance is manufactured at low cost.

  Furthermore, Patent Document 4 has a metal structure having a specific chemical composition and a ferrite single phase, does not generate a humping bead even when high-speed plasma welding is performed, and does not cause deterioration in workability. A high-strength cold-rolled steel sheet for tailored blanks having excellent weldability with a tensile strength of 440 MPa or more is disclosed.

JP 2003-200205 A Japanese Patent No. 5221348 JP 2006-218518 A JP 2010-37595 A

In recent years, steel sheets for forming materials such as automobile undercarriage parts and vehicle body structural members include, for example,
(I) Each part in the surface of the molding material has a different level of workability such that the specific part has stretch flangeability superior to general parts other than this specific part.
(II) Each part in the surface of the molding material is required to have different levels of mechanical properties such that the specific part has a higher tensile strength than the general part.

  The multilayer steel sheets disclosed in Patent Documents 1 and 2 are basically manufactured by superimposing two or more kinds of metal sheets and joining and rolling them over the entire surface. It cannot give a level of workability or mechanical properties.

  In addition, tailored blanks disclosed in Patent Documents 3 and 4 are usually manufactured by butting the edges of two or more types of steel plates having different workability and mechanical properties to each other. It is possible to produce a steel sheet having the workability and mechanical characteristics.

  However, in order to manufacture a tailored blank, it is necessary to blanken two or more types of steel plates with high precision so as to face each other, and to butt and weld both. For this reason, it is difficult to use it as a steel sheet for automobiles, which has a significantly high manufacturing cost and a high demand for low cost.

  As described above, according to the conventional technique, it has not been possible to provide a low-cost steel sheet having different levels (levels) of workability and mechanical properties depending on in-plane parts.

  The object of the present invention is to have a high level of workability and mechanical properties required for, for example, an automobile underbody member and a vehicle body structural member, because it has a different degree of workability and mechanical properties depending on in-plane parts. It is to provide a compatible steel sheet and a manufacturing method thereof.

  As a result of intensive studies in order to solve the above-mentioned problems, the present inventors have obtained knowledge A to D listed below and completed the present invention.

  (A) A material having a different chemical composition from the material to be welded by performing overlay welding by arc welding on the material to be rolled on the entrance side of the preceding rolling stand in the hot rolling process comprising a continuous stand having a plurality of rolling stands. If steel (welding wire) is welded and then finish rolling is completed, a hot-rolled steel sheet in which the level of chemical properties, various workability and mechanical properties varies depending on the in-plane region can be easily produced.

  (B) Since the position, number, amount, shape, and chemical composition of steel (welding wire) to be welded to the material to be rolled can be freely set, for example, a low-strength portion and a high-strength portion on the hot-rolled steel sheet as a base material, Can freely form an ultra-high-strength portion regardless of the position of the base material, and can easily impart different levels of workability and mechanical properties to the hot-rolled steel sheet depending on the in-plane portion of the hot-rolled steel sheet.

  (C) Since steel (welding wire) is welded to the material to be rolled by overlay welding by arc welding, the steel (welding wire) is a difficult-to-roll material made of high alloy steel, high melting point steel, high strength steel or the like. Even if it exists, it can form in the surface of a hot-rolled steel plate easily.

  (D) Although this hot-rolled steel sheet can be manufactured by an existing hot rolling process, the hot-rolled steel sheet is further subjected to ordinary cold rolling, and by performing continuous annealing (CAPL) as necessary, It can also be manufactured as a cold rolled steel sheet.

  The present invention is listed below.

(1) A steel plate having a first region and a second region on the steel plate surface,
In the plate thickness direction from the horizontal plane including the steel plate surface,
The first region has a first chemical composition throughout the thickness of the plate,
The second region has a second chemical composition different from the first chemical composition from the steel sheet surface to a predetermined depth, and the depth exceeding the predetermined depth includes the first chemical composition. A steel sheet having a chemical composition.

  (2) The steel sheet according to item 1, wherein the second region exists along the rolling direction of the steel sheet.

  (3) The steel sheet according to 1 or 2, wherein the second region is one or two or more apart from each other.

  (4) The second region has a chemical composition in which the content of at least one element among the chemical components of the chemical composition of the first region is increased or decreased. The described steel sheet.

  (5) The steel plate according to any one of items 1 to 4, wherein an element constituting the first chemical composition and an element constituting the second chemical composition are different.

  In the present invention, the chemical composition of each of the first region and the second region is exemplified to include C, Si, Mn, P, S, the remaining Fe, and impurities. In this case, the chemical composition of each of the first region and the second region is Al, Ni, Cr, Mo, W, Co, V, Nb, Ti, Cu, Ag, Al, Mo, N. , Ta, Ca, Co, Sn, Zn, Pb, Pd, Sn, Sb, Ru, Pd, Zr, Be, Ga, and Cd.

(6) A method of manufacturing a hot-rolled steel sheet by performing hot rolling using a continuous stand having a plurality of rolling stands on a slab having a first chemical composition,
Finishing rolling is performed after overlay welding a steel having a second chemical composition different from the first chemical composition at a predetermined position on a part of one surface of the material to be rolled on the front stand of the continuous stand. The manufacturing method of a steel plate including a process.

(7) A method of manufacturing a cold-rolled steel sheet by performing cold rolling after performing hot rolling using a continuous stand having a plurality of rolling stands on a slab having a first chemical composition,
A step of performing finish rolling after overlay welding a steel having a second chemical composition different from the first chemical composition at a predetermined position on a part of the surface of the material to be rolled at the front stand of the continuous stand. A method for manufacturing a steel sheet.

  Since the present invention has different levels of workability or mechanical properties depending on in-plane parts, for example, the workability and mechanical properties required for automobile underbody members, vehicle body structural members, etc. are compatible at a high level. Steel sheets can be provided at low cost.

FIG. 1 is an explanatory view schematically showing a configuration of a steel plate according to the present invention.

  The present invention will be described. In the following description, the case where the steel sheet according to the present invention is a molding material of an L-shaped lower arm that is an underbody member of an automobile will be taken as an example. The steel sheet according to the present invention can be used not only for molding materials such as automobile underbody members other than L-shaped lower arms and structural members of vehicle bodies, but also various workability at two or more levels in various industrial fields. And can be widely used for steel sheets that require mechanical properties. The application target of the present invention is not limited to this embodiment, and can be used for various members.

1. Steel plate 1 according to the present invention
FIG. 1 is an explanatory view schematically showing a configuration of a steel plate 1 according to the present invention. A range indicated by a broken line in the surface layer 1a of the steel plate 1 indicates a range cut out from the steel plate 1 as a blank (rolling material) of an L-shaped lower arm. In addition, in FIG. 1, the plate | board thickness of the steel plate 1 is exaggerated and shown.

  The steel plate 1 includes a first region 2 and a second region 3.

(1-1) First region 2
[Chemical composition]
The first chemical composition of the first region 2 contains C, Si, Mn, P, S as essential elements, and B, Nb, Ti, Mo, Cr, as optional elements contained as necessary. It has at least one of V, Co, Sn, and Cu, and has the remainder Fe and impurities.

  The first chemical composition may be a chemical composition of a steel sheet that is normally used as this type of steel sheet, and need not be limited to a specific chemical composition. For example, as essential elements, C: 0.01 to 0.50%, Si: 0.01 to 3.5%, Mn: 0.2 to 3.0%, P: 0.005 to 0.100% , S: 0.0001 to 0.020%, and as optional elements, B: 0.0040% or less, Nb: 0.040% or less, Ti: 0.20% or less, Mo: 3.0% Hereinafter, Cr: 2.0% or less, V: 1.0% or less, Co: 3.0% or less, Sn: 1.0% or less, Cu: 1.0% or less are exemplified.

  Arbitrary elements are appropriately contained depending on the workability and mechanical properties required of the steel sheet 1.

[Machinability or mechanical properties]
The first region 2 has a first chemical composition, thereby having a corresponding first texture and a first degree of workability or mechanical properties. Examples of workability include deep drawability (shrinkable flangeability), overhangability (overhang moldability), stretch flangeability (flange formability), bendability, close contact bendability, shear workability, weldability, and the like. Examples of mechanical properties include tensile strength, yield strength, total elongation, uniform elongation, local elongation, r value, n value, and Erichsen value.

(1-2) Second region 3
[Chemical composition]
The second region 3 has a second chemical composition different from the first chemical composition and a second degree of workability different from the first degree.

  The second chemical composition of the second region 3 contains C, Si, Mn, P, and S as essential elements, and Al, Ni, Cr, Mo, W, and optional elements contained as necessary. Co, V, Nb, Ti, Cu, Ag, Al, Mo, N, Ta, Ca, Co, Sn, Zn, Pb, Pd, Sn, Sb, Ru, Pd, Zr, Be, Ga, Cd With the balance Fe and impurities.

  The second chemical composition may be a chemical composition of a steel sheet normally used as this type of steel sheet, and need not be limited to a specific chemical composition. For example, as essential elements, C: 0.01 to 0.20%, Si: 0.01 to 1.00%, Mn: 0.2 to 3.0%, P: 0.005 to 0.100% , S: 0.0001 to 0.020%, Ni: 6.0% or less, Cr: 2.0% or less, Mo: 2.0% or less, V: 1.0% or less, and as an optional element Nb: 0.04% or less, Ti: 0.20% or less, Cu: 1.0% or less, Co: 3.0% or less, W: 1.0% or less, Ca: 0.010% or less, Examples are Sn: 0.30% or less and Zn: 0.30% or less.

  Arbitrary elements are appropriately contained depending on the properties required for the steel sheet 1.

[Machinability or mechanical properties]
By having the first chemical composition, the second region 3 has a corresponding second texture and a second degree of workability or mechanical properties. Workability is synonymous with the workability of the first region 2, and deep drawability (shrinking flangeability), overhangability (extrusion formability), stretch flangeability (flange formability), bendability, adhesion bendability Examples thereof include shear workability and weldability. Examples of mechanical properties include tensile strength, yield strength, total elongation, uniform elongation, local elongation, r value, n value, and Erichsen value.

[Existing area]
The second region 3 exists in a region 5 from a part 4 of one surface layer 1a to a depth position of, for example, 10 to 600 μm.

  If the second region 3 is present at a depth of less than 10 μm from the portion 4 of the surface layer 1a, the depth of the second region 3 is too shallow, and a desired degree of workability or mechanical properties is provided. You may not be able to. From such a viewpoint, the second region 3 is preferably present at a depth position of 30 μm or more from a part 4 of the surface layer 1a, and is present at a depth position of 50 μm or more from a part 4 of the surface layer 1a. Is more preferable, and it is even more preferable to exist at a depth position of 70 μm or more from a part 4 of the surface layer 1a.

  On the other hand, if the second region 3 is present at a depth of more than 600 μm from a portion 4 of the surface layer 1a, the cost may be significantly increased when the second chemical composition is a high alloy-containing composition. . The second region 3 is preferably present at a depth position of 550 μm or less from a part 4 of the surface layer 1a, more preferably at a depth position of 500 μm or less from a part 4 of the surface layer 1a. More preferably, it is present at a depth position of 4 to 450 μm or less.

  The plate thickness of the steel plate 1 in the portion where only the first region 2 exists is the same as the plate thickness of the steel plate 1 in the portion where the second region 3 exists. That is, the steel plate 1 has a constant plate thickness in the entire region, and therefore the surface of the first region 2 and the surface of the second region 3 are on the same plane.

  The plate thickness of the steel plate 1 is exemplified to be 1.4 to 8.0 mm when the steel plate 1 is a hot-rolled steel plate, and 0.6 to 3.0 mm when the steel plate 1 is a cold-rolled steel plate. It is illustrated that. At this time, the depth of the second region is preferably in the range of 1/300 to 1/5 of the plate thickness.

  The first region 2 and the second region 3 are integrally formed by rolling.

[Shape, number of existence, form of existence]
As shown in FIG. 1, the second region 3 is formed in a circular shape on the surface layer 1 a of the steel plate 1. The second region 3 may be formed in a portion where there is a request to provide a workability and mechanical properties at a level different from the workability and mechanical properties of the first region 2. For this reason, the shape of the second region 3 is not limited to a specific shape, for example, a linear shape, a curved shape, a circular shape, an elliptical shape, an irregular shape, a convex polygon shape, a concave polygon shape, Examples include a spiral shape or a combination of two or more of these.

  As shown in FIG. 1, there are two second regions 3, but the present invention is not limited to this, and one or three or more spaced apart from each other according to the above requirements. Also good.

  Further, the second region 3 may exist continuously or intermittently when present as a linear shape or a curved shape.

[Type of difference in chemical composition between first and second regions 2 and 3]
Although the chemical composition of each of the first region 2 and the second region 3 is different, the type of this difference will be described.

  (A) The second region 3 has a chemical composition in which the content of at least one of the chemical components of the chemical composition of the first region 2 is increased or decreased. For example, the C content of the second region 3 is lower or higher than the C content of the first region 2.

  (B) The second region 3 has a chemical composition that includes a chemical component that is not included in the chemical composition of the first region 2. For example, the second region 3 contains Ti or Nb, but the first region 2 does not contain Ti and Nb.

  (C) The second region 3 has a chemical composition that does not contain at least one chemical component of the chemical composition of the first region 2. For example, the first region 2 contains Cr, but the second region 3 does not contain Cr.

  Thus, the element which comprises a 1st chemical composition differs from the kind of element which comprises a 2nd chemical composition.

[Hot rolled steel sheet and cold rolled steel sheet]
Since the steel sheet 1 can be manufactured by an existing hot rolling process, it is manufactured as a hot rolled steel sheet, but after passing through a normal cold rolling process and a continuous annealing process (cold rolling / CAPL process), It is also manufactured as a cold rolled steel sheet.

(1-3) Third and above regions In the above description, the case where the steel plate 1 has the first region 2 and the second region 3 is taken as an example. However, the present invention is not limited to this case, and the steel sheet 1 has a third region that differs from the second region 3 at least in the chemical composition and the existence region separately from the second region 3. Also good.

  The third region may be the same as or different from the second region 3 except for the chemical composition and the existing region.

  The third region is a steel (welding wire) that is welded by arc welding to a predetermined position on a part of one surface of the material to be rolled in the front stage stand of the continuous stand of the hot rolling process described later. It is provided by adding steel (welding wire) having a chemical composition corresponding to the chemical composition of the three regions.

  Furthermore, the steel plate 1 has at least a chemical composition and presence at least as compared with the second and third regions, as well as at a fourth region where the chemical composition and existence region are different from the second and third regions. You may have the 5th area | region from which an area | region differs. Or you may have the area | region beyond it. In FIG. 1, the third and higher areas are omitted.

  Moreover, you may have a 2nd area | region and 3rd or more area | region not only on the single side | surface of a steel plate but on both surfaces.

  According to the present invention, a multifunctional chemically graded steel sheet can be provided in this way.

2. Manufacturing method of steel plate 1 (2-1) Hot-rolled steel plate The steel plate 1 is basically manufactured by performing hot rolling using a continuous stand having a plurality of rolling stands on a slab having a first chemical composition. Is done.

  The steel plate 1 is formed by depositing steel (welding wire) having a chemical composition different from the first chemical composition at a predetermined position on a part of one surface of the material to be rolled in the front stand of the continuous stand by arc welding. By welding, the steel plate 1 including the first region 2 and the second region 3 is manufactured.

  The second region can be formed along the rolling direction by online work, but when the slab before finishing rolling is temporarily stopped after working offline or after rough rolling, other than the rolling direction. Welding is also possible in the direction (for example, the width direction), and the second region can be formed in this direction.

  The plate thickness of the material to be rolled when steel (welding wire) is overlay welded by arc welding is exemplified to be 10 to 250 mm. When the plate thickness is less than 10 mm, the influence of the welded portion is large, and it becomes difficult to control the structure in the plate thickness direction. Further, there is a high possibility that the plate warps during welding, and hot rolling becomes difficult. If it exceeds 250 mm, the ratio of the component inclination of the surface layer becomes small, so that the effect of improving the characteristics cannot be obtained.

  The finishing temperature of hot rolling is preferably 800 to 1100 ° C. When the finishing temperature is higher than 1100 ° C., the structure becomes coarse and the toughness decreases, so that cracks occur in the hard phase of the surface layer. On the other hand, when the finishing temperature is less than 800 ° C., the difference in deformation resistance during hot rolling due to the components becomes large, so that it is difficult to reduce the thickness accuracy and to make the shape.

  The position where overlay welding by arc welding is performed on the material to be rolled is a hot-rolled steel plate obtained by performing finish rolling on the material to be rolled, or cold rolling is further performed on this hot-rolled steel plate to obtain a cold-rolled steel plate. When this hot-rolled steel sheet or cold-rolled steel sheet is blanked and used as a high-strength blank for an L-shaped lower arm, for example, cracks due to stretch flange molding and wrinkles due to shrink flange molding tend to occur, so these This is the position where it is desired to improve the resistance characteristics (workability) against molding defects.

  The thickness and width of the steel (welding wire) welded to the material to be rolled may be determined as appropriate according to the shape and width of the second region 3 of the steel plate 1 and are not limited to specific dimensions.

  Range in which the level of workability and mechanical properties varies for each blank cut out from the steel plate 1 by appropriately changing the chemical composition, thickness, width, orientation, and position of the steel (welding wire) to be welded to the material to be rolled. The second area 3 can be set easily and reliably.

  In the subsequent stage of the continuous stand, the steel (welding wire) is further hot-rolled to the material to be welded, finished to a predetermined plate thickness by finish rolling, and cooled to the runout table to form the desired metal structure. Just put it in.

  The cooling rate at the run-out table is exemplified by 20 to 400 ° C./second, and the winding temperature after finish rolling is exemplified by 10 to 700 ° C. When the cooling rate at the run-out table is less than 20 ° C./second, the influence of the structure change due to the component inclination is reduced, and the effect of improving the characteristics cannot be obtained. If it exceeds 400 ° C./sec, the temperature deviation during cooling is large and it becomes difficult to create a shape. Also, if the winding temperature after finish rolling is less than 10 ° C., dew condensation occurs in the coil after winding, and if it exceeds 700 ° C., the influence of the structural change due to the component gradient becomes small, and the effect of improving the characteristics Cannot be obtained.

  Thus, the hot rolled steel sheet 1 according to the present invention is manufactured.

(2-2) Cold-rolled steel sheet After this, it is good also as the cold-rolled steel sheet 1 which concerns on this invention by passing through a normal cold rolling process and a continuous annealing process (cold-rolling / CAPL process) as needed. The conditions for cold rolling and continuous annealing may be conventional conditions for this type of cold-rolled steel sheet, and are well known to those skilled in the art, and will not be described.

  According to the present invention, the first region 2 and the second region 3 are bonded and integrated regardless of the first chemical composition of the first region 2 and the second chemical composition of the second region 3. The obtained steel plate 1 is obtained.

  If the welding can be speeded up and the shape can be predicted with high accuracy, it is possible to predict that the welded part will be in a necessary place after rolling, and to identify and weld the welded part for each part.

  Thus, according to the present invention, steel (welding wire) having a chemical composition different from that of the material to be rolled is deposited on the surface of the material to be rolled before hot finish rolling by overlay welding by arc welding, and thereafter The steel sheet 1 in which the second region 3 exists in the region 5 from the part 4 of the one surface layer 1a to the depth position in the plate thickness direction can be quickly and surely reduced in cost by performing the rolling of as usual. It is possible to manufacture with.

  In addition, according to the present invention, the chemical composition, thickness, width, orientation, and position of steel (welding wire) can be arbitrarily set. It is possible to provide characteristics and various workability.

  Thus, as required by the user of the steel plate 1, the steel plate 1 has different workability and mechanical characteristics depending on the in-plane portion. For example, processing required for an automobile underbody member, a vehicle body structural member, or the like. It is possible to provide a chemically-graded steel sheet having both properties and mechanical properties at a high level.

  Next, examples of the present invention will be described. The conditions in the examples are one example of conditions used for confirming the feasibility and effects of the present invention, and the present invention is based on this one example of conditions. It is not limited. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

  Thickness at the time of welding by hot rolling using a continuous stand having six rolling stands on slabs A to I having the chemical composition shown in Table 1 (remaining Fe and impurities) and before the first stand of the continuous stand Is the chemical composition shown in Table 2 (the balance) at the position where the adhesion bendability determined by the 180-degree adhesion bending test specified in JIS Z2248: 2006 is required on one surface of the rolled material having the values shown in Table 3. Using the welding rods a to i having Fe and impurities), vertical downward wire diameter: φ1.2 mm, torch angle: vertical downward arc overlay welding was performed, and finish rolling was performed at the finishing temperatures shown in Table 3. The welding conditions were a welding current: 200 A and a wire supply speed: 5-20 m / min.

  Then, it cooled with the cooling rate shown in Table 3, and manufactured the hot-rolled steel plates 1-33 shown in Table 3 by winding around a coil at the winding temperature shown in Table 3.

  These hot-rolled steel plates 1 to 33 were rewound to cut out samples 1 to 33, and the thickness of the samples 1 to 33, the thickness of the second region, and the area ratio were measured, and the 180-degree adhesion bending test was performed. Then, the adhesion bendability of the second region was evaluated. The results are summarized in Table 3.

  As shown in Table 3, sample No. The second regions 1 to 16, 18 to 27, and 29 to 33 are excellent in close contact bendability, whereas the comparative examples 17 and 28 are suitable for the present example in terms of the thickness of the second region. Since it was out of the range, excellent adhesion bendability could not be obtained.

DESCRIPTION OF SYMBOLS 1 Steel plate 1a Surface layer 2 1st area | region 3 2nd area | region 4 Part 5 area | region

Claims (7)

A steel plate having a first region and a second region on a steel plate surface,
In the plate thickness direction from the horizontal plane including the steel plate surface,
The first region has a first chemical composition throughout the thickness of the plate,
The second region has a second chemical composition different from the first chemical composition from the steel sheet surface to a predetermined depth, and the depth exceeding the predetermined depth includes the first chemical composition. A steel sheet having a chemical composition.   The steel plate according to claim 1, wherein the second region is present along a rolling direction of the steel plate.   3. The steel sheet according to claim 1, wherein the second region is one or two or more apart from each other.   The said 2nd area | region has a chemical composition which increased or decreased content of the at least 1 element of the chemical component of the chemical composition of the said 1st area | region. steel sheet.   The steel plate according to any one of claims 1 to 4, wherein an element constituting the first chemical composition is different from an element constituting the second chemical composition. A method of producing a hot-rolled steel sheet by performing hot rolling using a continuous stand having a plurality of rolling stands on a slab having a first chemical composition,
Finishing rolling is performed after overlay welding a steel having a second chemical composition different from the first chemical composition at a predetermined position on a part of one surface of the material to be rolled on the front stand of the continuous stand. The manufacturing method of a steel plate including a process. A method for producing a cold-rolled steel sheet by performing cold rolling after performing hot rolling using a continuous stand having a plurality of rolling stands on a slab having a first chemical composition,
A step of performing finish rolling after overlay welding a steel having a second chemical composition different from the first chemical composition at a predetermined position on a part of the surface of the material to be rolled at the front stand of the continuous stand. A method for manufacturing a steel sheet.

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