JP3287257B2 - Steel sheet excellent in workability and less fluctuating in the width direction of workability and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steel sheet which is excellent in workability and hardly varies in the width direction of the workability, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Hot-rolled steel sheets and cold-rolled steel sheets are widely used in automobiles, industrial machines and the like. And since many members are formed by press working in those uses, various workability is required according to the shape of the member.

However, recent demands for rationalization from manufacturers of automobiles, industrial machines, and the like are strict, and there is a demand for further improving the yield particularly when manufacturing products by the manufacturers. From such a background, it is important to have a particularly high uniformity in the material.

[0004] From such a viewpoint, in order to make the workability of the material uniform, the heating temperature in the hot rolling is set lower than before, the rolling reduction in the finish rolling is increased, and the material is rapidly cooled after the completion of the rolling. There has been proposed a technique of winding at a relatively high temperature, followed by cold rolling and annealing (Japanese Patent Publication No. 7-56055).

[0005]

However, in this technique, although the uniformity in the longitudinal direction of the coil is improved, there is a problem in the uniformity in the lateral direction of the coil. In other words, in this technology, the heating temperature in hot rolling is set to a low temperature, and furthermore, because of the high-pressure reduction in finish rolling, the temperature at the edge of the coil and in the vicinity thereof is significantly reduced, and as a result, the structure in the width direction of the coil is reduced. The problem of variation occurs.

[0006] As described above, when the structure varies in the width direction of the coil, the uniformity of the workability in the material is reduced, and particularly in a stamped product having strict dimensional accuracy,
In the vicinity of the end portion in the width direction of the coil at the time of the press working, the workability is lower than that at the center portion of the coil. Therefore, plate picking in the coil must be performed at a low yield that does not include the vicinity of the end in the width direction of the coil.

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and has excellent workability and is uniform in the width direction of workability, and is suitable for press working with strict dimensional accuracy. The aim is to provide a method.

[0008]

Means for Solving the Problems The present inventors have intensively studied to solve the above-mentioned problems. As a result, in view of the usage conditions of manufacturers of automobiles, industrial machines, etc., in order to extract products from coils at a high yield, (1) optimizing the components in steel and removing non-metallic inclusions (2) The average crystal grain size (D) and the variation of the average crystal grain size in the width direction of the coil (Dmax / Dmin) should be within specific ranges (however, (Dmax is the maximum value of the average crystal grain size in the width direction, and Dmin is the minimum value of the average crystal grain size in the width direction).

The above-mentioned steel sheet having excellent workability and uniform workability in the width direction can be obtained by directly hot-rolling a continuous cast slab. (1) Rolling temperature of primary rolling in hot rolling And reducing the austenite grain size after primary rolling to fine grains by setting the rolling reduction to an appropriate value. (2) Subsequently, the entire material after primary rolling is heated in a specific temperature range, and (3) Next, by making the rolling reduction, temperature and winding temperature in the secondary rolling appropriate, and reducing the austenite grain size by repeated recrystallization after the secondary rolling. It has been found that this is achieved by freezing the tissue in a uniform and homogeneous manner.

Further, for example, in a manufacturing method for heating a slab obtained by continuous casting, ingot making, or slab rolling, (1) the heating temperature in hot rolling and the rolling reduction and temperature in primary rolling are adjusted appropriately. (1) Next, the whole material after the primary rolling is heated in a specific temperature range to make the austenite grain size uniform after the primary rolling. (3) Successively, the reduction ratio, temperature and winding temperature in the secondary rolling are adjusted appropriately, and the austenite grain size by recrystallization repeatedly after the secondary rolling is made fine and uniform to form the structure. It was found that this was achieved by freezing.

Further, it has been found that the cold-rolled steel sheet can be achieved by performing cold rolling and recrystallization annealing using the hot-rolled steel sheet obtained as described above as a raw material. The present invention has been made based on such findings.

That is, the present invention provides the following (1) to
(9) is provided. (1) In weight%, C: 0.2% or less, Si: 1.0%
Hereinafter, Mn: 3.0% or less, P: 0.20% or less, S:
0.10% or less, O: 0.0040% or less, sol. A
l: 0.01 to 0.10%, N: 0.02% or less, cleanliness: 0.05% or less, average crystal grain size (D) of 5 to 35 μm, in the width direction of the coil A steel sheet having excellent workability and little change in the width direction of the workability, characterized in that the average crystal grain size of (Dmax / Dmin) is 2.0 or less. Here, Dmax is the maximum value of the average crystal grain size in the width direction, and Dmin is the minimum value of the average crystal grain size in the width direction.

(2) In (1), Ti, N
One, two or more of b, V, and Zr are from 0.01 to
Excellent workability characterized by containing 0.40%,
A steel sheet with little change in workability in the width direction. (3) In (1) or (2), B: 0.0
A steel sheet having excellent workability and little change in the width direction of the workability, characterized in that the steel sheet contains 001 to 0.005%.

(4) In terms of% by weight, C: 0.2% or less, S
i: 1.0% or less, Mn: 3.0% or less, P: 0.20
%, S: 0.10% or less, O: 0.0040% or less, sol. Al: 0.01 to 0.10%, N: 0.0
After continuous casting of steel containing 2% or less and having a cleanliness of 0.05% or less, when the obtained steel slab is directly hot-rolled, a reduction ratio of 70% or more is obtained at a temperature of Ar ₃ or more. 1
A step of the next rolling is subjected to steel strip, followed by a step of reheating the entire steel band in the range of Ar ₃ point + 50 ° C. to 1150 ° C., followed by 70% at Ar ₃ point or more temperature A steel sheet having excellent workability and less variation in the width direction of the workability, characterized by comprising a step of performing secondary rolling at a reduction ratio of, and a step of successively winding at a temperature of 750 ° C or less. Manufacturing method.

(5) In terms of% by weight, C: 0.2% or less, S
i: 1.0% or less, Mn: 3.0% or less, P: 0.20
%, S: 0.10% or less, O: 0.0040% or less, sol. Al: 0.01 to 0.10%, N: 0.0
A steel containing 2% or less and having a cleanliness of 0.05% or less is continuously cast, and the resulting steel slab is directly hot-rolled at a temperature of not less than ₃ points of Ar and a reduction of 70% or more. a step of a steel strip subjected to a first rolling, then the steps of reheating the entire steel band in the range of Ar ₃ point + 50 ° C. to 1150 ° C., followed by 70% Ar ₃ point or more temperature A process of performing secondary rolling at the above reduction ratio, and a process of continuously winding at a temperature of 750 ° C. or less, thereafter, performing cold rolling, and subsequently performing recrystallization annealing. A method for producing a steel sheet that is excellent and has little variation in workability in the width direction.

(6) By weight%, C: 0.2% or less, S
i: 1.0% or less, Mn: 3.0% or less, P: 0.20
%, S: 0.10% or less, O: 0.0040% or less, sol. Al: 0.01 to 0.10%, N: 0.0
Contained 2% or less, cleanliness: 70 0.05% or less of the steel slab upon hot rolling, and heating in the range of Ar ₃ point to 1200 ° C., thereafter the Ar ₃ point or more temperature
% By rolling at a rolling reduction of at least% to form a steel strip, and thereafter, the entirety of the steel strip is Ar ₃ points + 50 ° C. to 115 ° C.
A step of reheating within a range of 0 ° C., a step of performing a secondary rolling at a temperature of not less than Ar ₃ point and a rolling reduction of not less than 70%, and a step of subsequently winding at a temperature of not more than 750 ° C. A method for producing a steel sheet having excellent workability and having less variation in the width direction of the workability.

(7) By weight%, C: 0.2% or less, S
i: 1.0% or less, Mn: 3.0% or less, P: 0.20
%, S: 0.10% or less, O: 0.0040% or less, sol. Al: 0.01 to 0.10%, N: 0.0
Contained 2% or less, cleanliness: 70 0.05% or less of the steel slab upon hot rolling, and heating in the range of Ar ₃ point to 1200 ° C., thereafter the Ar ₃ point or more temperature
% By rolling at a rolling reduction of at least% to form a steel strip, and thereafter, the entirety of the steel strip is Ar ₃ points + 50 ° C. to 115 ° C.
A step of reheating within a range of 0 ° C., a step of performing a secondary rolling at a temperature of not less than Ar ₃ point and a rolling reduction of not less than 70%, and a step of subsequently winding at a temperature of not more than 750 ° C. A method of producing a steel sheet having excellent workability and having little variation in the width direction of the workability, wherein the steel sheet is subjected to cold rolling and then recrystallization annealing.

(8) In (4) to (7), T
One or more of i, Nb, V, and Zr are 0.01
A method for producing a steel sheet having excellent workability and having little variation in the width direction of the workability, characterized by containing up to 0.40%. (9) In (4) to (8), B: 0.000
A method for producing a steel sheet having excellent workability and having little variation in the width direction of workability, characterized by containing 1 to 0.005%.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As described above, in order to obtain a product from a coil at a high yield, first, after optimizing the components in the steel, the amount of nonmetallic inclusions is adjusted and the processing is performed. It is necessary to set the average crystal grain size (D) and the variation of the average crystal grain size in the width direction of the coil (Dmax / Dmin) within specific ranges (however, Dmax Is the maximum value of the average crystal grain size in the width direction, and Dmin is the minimum value of the average crystal grain size in the width direction.

For this purpose, in the present invention, C:
0.2% or less, Si: 1.0% or less, Mn: 3.0% or less, P: 0.20% or less, S: 0.10% or less, O:
0.0040% or less, sol. Al: 0.01 to 0.1
0%, N: 0.02% or less, cleanliness: 0.05% or less, average crystal grain size (D) of 5 to 35 μm, fluctuation of average crystal grain size in the coil width direction (Dmax / Dmin) Is set to 2.0 or less. Hereinafter, the reasons for these limitations will be described.

(1) Chemical composition and cleanliness of the raw steel C: 0.2% or less C is an element that has an adverse effect on the workability of the steel sheet, so that its content is preferably small. If the C content exceeds 0.2%, the workability deteriorates significantly, so the content was made 0.2% or less. A more preferable range for improving the workability is 0.05%, and from the viewpoint of further improving the workability, the content is more preferably 0.005% or less.

Si: 1.0% or less Si has the effect of solid solution strengthening a steel sheet, but is preferably an element having a small effect because it is an element that adversely affects workability. S
If the i content exceeds 1.0%, the workability deteriorates significantly, so the content was made 1.0% or less. A more preferred range for improving workability is 0.5% or less.
0.05% from the viewpoint of further improving workability
It is more preferred that:

Mn: 3.0% or less Mn has the effect of improving the toughness of the steel sheet and strengthening the solid solution of the steel sheet, but has an adverse effect on the workability. If the Mn content exceeds 3.0%, the strength is increased and the workability is significantly deteriorated. Therefore, the content is set to 3.0% or less. A more preferred range for improving workability is 2.0%.
It is as follows. From the viewpoint of further improving the workability, the content is more preferably 0.5% or less.

P: 0.2% or less P has the effect of solid solution strengthening the steel sheet, but if its content exceeds 0.2%, grain boundary embrittlement due to grain boundary segregation tends to occur. Therefore, the content of P is set to 0.2% or less. A more preferred range for improving workability is 0.1%.
It is. From the viewpoint of further improving the processability, the content is more preferably 0.02% or less.

S: 0.1% or less If S exceeds 0.1%, the amount of sulfide precipitated increases and the workability deteriorates. Therefore, the content of S is set to 0.1% or less. A more preferable range for improving workability is 0.02% or less. From the viewpoint of further improving the workability, the content is more preferably 0.01% or less.

Sol. Al: 0.01 to 0.1% sol. Al is used as a deoxidizing material for steel, and is an additional element indispensable for increasing the addition yield of Ti, Nb, Zr, and V described later. However, if the content is less than 0.01%, the above effects cannot be obtained, while if it exceeds 0.1%, the effects are saturated and uneconomical. Therefore, so
l. The content of Al was set to 0.01 to 0.1%.

N: 0.02% or less The smaller the content of N, the smaller the amount of the carbonitride forming element described later, and the more economical. N content is 0.02%
If the N exceeds N, the workability of the steel sheet is inevitably reduced even if N is fixed by adding a carbonitride forming element. Therefore, the N content is set to 0.02% or less. A more preferable range for improving workability is 0.005% or less.

O: 0.004% or less The smaller the content of O, the better the workability. If the O content exceeds 0.004%, a reduction in workability of the steel sheet cannot be avoided. Therefore, the O content is set to 0.004% or less. The O content in such a range is determined by the sol. A
This is achieved by controlling the amount of l.

Cleanliness: 0.05% or less Cleanliness is measured by the method of JIS G0555. In the present invention, one of the important constitutional requirements to be controlled in order to impart excellent workability. One. If the cleanliness of the steel sheet exceeds 0.05%, the number of voids originating from inclusions at the time of deformation increases and the material is easily broken, so the upper limit is 0.05%. The cleanliness in such a range can be achieved by appropriately taking measures for secondary refining after smelting of steel and inclusion of inclusions during casting. A more preferable range of cleanliness for improving workability is 0.03.
% Or less.

The material steel may further contain one or more of Ti, Nb, V and Zr in addition to the above-mentioned components in an amount of 0.01 to 0.4%. These components form carbonitrides and sulfides, reduce C, N, and S in the steel and can improve workability. Therefore, they are added alone or in combination as necessary. Is preferred.

Further, in the present invention, B is added in an amount of 0.0001 to 0.005% for the purpose of improving longitudinal cracking resistance.
May be added. If the amount of B is less than 0.0001%, the effect of improving the vertical crack resistance cannot be obtained, while, on the other hand, 0.005%
%, The effect saturates. Therefore, the range of the B amount is set to 0.0001 to 0.005%.

(2) Average grain size and its variation in the coil width direction Average grain size (D): 5 to 35 μm If D is less than 5 μm, the high workability intended in the present invention cannot be obtained. On the other hand, if D exceeds 35 μm, roughening during processing becomes a problem. Therefore, D was set within a range of 5 to 35 [mu] m from the viewpoint of obtaining high workability and performing high-yield product collection from the coil without generating rough skin.
A more preferable range for improving workability is 15 to
30 μm. Further, from the viewpoint of increasing the strength while ensuring workability, the range of 5 to 15 μm is preferable.

Variation in average crystal grain size in the coil width direction (Dmax / Dmin): 2.0 or less Variation in average crystal grain size in the coil width direction (Dmax / Dmi)
When n) exceeds 2.0, as shown in FIG. 1, the in-plane uniformity of the workability in the material decreases, and near the width direction end of the coil at the time of press working, the center of the width is reduced. On the other hand, the workability is low, and the difference in the width direction of the springback exceeds 2 degrees, which causes a problem in the dimensional accuracy of the processed part after the press working. Therefore, the provisional sampling in the coil must be performed at a low yield that does not include the vicinity of the end in the width direction of the coil. To solve these problems,
In the present invention, Dmax / Dmin is set to 2.0 or less. In FIG.
4 shows the distribution of the crystal grain size in the coil width direction of the material of the present invention and the comparative material. The difference in the width of the springback in the width direction was determined by a test method as described in Examples described later, using a thin steel sheet manufactured using steel satisfying the composition of the present invention and changing the manufacturing conditions.

Next, a method for manufacturing the above steel sheet will be described. (1) A method of directly hot rolling a continuously cast slab In this case, after continuously casting a steel having the above composition,
When the obtained steel slab is directly hot-rolled, a step of performing primary rolling at a temperature of not less than Ar ₃ points and a rolling reduction of not less than 70% to form a steel sheet, and thereafter, the entire steel sheet is subjected to Ar ₃ points +
A step of reheating at a temperature in the range of 50 ° C. to 1150 ° C., a step of subsequently performing a secondary rolling at a temperature of not less than the Ar ₃ point at a rolling reduction of 70% or more, and a step of subsequently winding at a temperature of 750 ° C. or less And Hereinafter, the reasons for limiting the manufacturing conditions will be described.

Primary rolling temperature in hot rolling: Ar ₃ points or more The primary rolling temperature is first defined from the viewpoint of controlling the crystal grain size of the rough rolled material. When the Ar point is less than ₃ points, since the rolling is performed in the ferrite region, the recovery proceeds more than the progress of recrystallization. Therefore, it is impossible to reduce the size of the crystal grains, and as a result, the crystal grain size defined in the present invention is reduced. Can not get. Therefore, the primary rolling temperature was set to _three or more Ar points.

If the rolling reduction in the primary rolling in hot rolling is 70% or more, if the rolling reduction in the primary rolling is less than 70%, the austenite grain size after the primary rolling cannot be reduced to a fine grain. The grain size specified in the present invention cannot be obtained.
When the rolling reduction is 70% or more, the crystal grain size specified in the present invention can be obtained, so that the rolling reduction in the primary rolling is 70% or more.

Heating temperature of primary rolled (roughly rolled) steel strip: Ar
₃ points + 50 ° C to 1150 ° C Roughly rolled steel strip subjected to primary rolling is Ar ₃ points + 50 ° C to 11
By heating within the range of 50 ° C., the uniformity of the austenite grain size after the primary rolling can be increased, and as a result, even if the heating temperature is as low as 1200 ° C. or less,
Variations in crystal grain size can be reduced to the range specified in the present invention. If the temperature is lower than the Ar ₃ point + 50 ° C., the transformation to the ferrite phase proceeds in the surface layer and the vicinity thereof in the secondary rolling, and the surface layer becomes coarse, so that the variation in crystal grain size cannot be suppressed to the range of the present invention. . On the other hand, 115
If it exceeds 0 ° C., the average particle diameter (D) exceeds the upper limit of 35 μm specified in the present invention. Therefore, the heating temperature of the primary rolled steel strip was set to a range of ₃ points of Ar + 50 ° C. to 1150 ° C.

When the rolling reduction in the secondary rolling in hot rolling is 70% or more, if the rolling reduction in the secondary rolling is less than 70%, the austenite grain size after the secondary rolling cannot be reduced to fine grains. However, the crystal grain size specified in the present invention cannot be obtained. If the rolling reduction is 70% or more, a crystal grain size within the range specified in the present invention can be obtained, so the rolling reduction in the secondary rolling is set to 70% or more.

The secondary rolling in the hot rolling temperature: The temperature is Ar less than _three points in the Ar ₃ point or more secondary rolling, rolling portion of the ferrite phase after the primary rolling is coarsened grains of, as a result, the The grain size specified in the invention cannot be obtained. Ar ₃
Since the crystal grain size specified in the present invention can be obtained at the point or higher, the secondary rolling temperature is set to the Ar ₃ point or higher.

Winding temperature: 750 ° C. or less The winding temperature is a production condition that requires fine and uniform austenite grain size by repeated recrystallization after secondary rolling, and requires control to freeze the structure. . Winding temperature is 75
If it exceeds 0 ° C., ferrite grains grow after winding, and as a result, the crystal grain size specified in the present invention cannot be obtained. If the winding temperature is 750 ° C or less, the above structure is obtained,
The winding temperature was set to 750 ° C. or lower because the crystal grain size can be in the range specified in the present invention.

(2) A method of heating a slab obtained by continuous casting, ingot making, or slab rolling, for example. In this case, when hot rolling the steel slab having the above composition, a step of heating the steel slab within a range of Ar ₃ points to 1200 ° C.,
After that, a step of subjecting the steel strip to primary rolling at a temperature of not less than Ar ₃ points and a rolling reduction of not less than 70%, and thereafter, the entire steel strip is in the range of Ar ₃ points + 50 ° C. to 1150 ° C. A step of reheating, followed by a step of performing secondary rolling at a temperature of not less than ₃ points of Ar at a rolling reduction of not less than 70%, followed by 750 ° C.
Winding at the following temperature. According to this method, it is possible to obtain a steel sheet that is more excellent in workability and has less change in workability in the width direction than the above-described manufacturing method. Hereinafter, the reasons for limiting the manufacturing conditions will be described.

Heating temperature of primary rolling in hot rolling: Ar ₃
If the heating temperature of the primary rolling is higher than 1200 ° C., the austenite grain size during heating becomes coarse, and as a result, the crystal grain size specified in the present invention cannot be obtained. On the other hand, when the heating temperature is Ar ₃
If it is less than the point, since the rolling is in the ferrite region, the recovery proceeds more than the progress of recrystallization, it is not possible to achieve the refinement of the crystal grains, and as a result, the crystal grain size specified in the present invention is also reduced. I can't get it. Therefore, the heating temperature of the primary rolling was set to an Ar ₃ point to 1200 ° C.

When the rolling reduction of the primary rolling in hot rolling is 70% or more, if the rolling reduction in the primary rolling is less than 70%, the austenite grain size after the primary rolling cannot be reduced to a fine grain. The grain size specified in the present invention cannot be obtained.
When the rolling reduction is 70% or more, the crystal grain size specified in the present invention can be obtained, so that the rolling reduction in the primary rolling is 70% or more.

Temperature of primary rolling in hot rolling: Ar ₃ points or more If the temperature in primary rolling is less than Ar ₃ points, rolling will be partially in a two-phase region including a ferrite phase. In the ferrite phase, the rolled portion becomes coarse, and as a result, the crystal grain size specified in the present invention cannot be obtained. The crystal grain size defined in the present invention in Ar ₃ or more points is obtained, the temperature of the first rolling was Ar ₃ point or more.

Heating temperature of primary rolled (roughly rolled) steel strip: Ar
₃ points + 50 ° C to 1150 ° C Roughly rolled steel strip subjected to primary rolling is Ar ₃ points + 50 ° C to 11
By heating within the range of 50 ° C., the uniformity of the austenite grain size after the primary rolling can be increased, and as a result, even if the heating temperature is as low as 1200 ° C. or less,
Variations in crystal grain size can be reduced to the range specified in the present invention. If the temperature is lower than the Ar ₃ point + 50 ° C., the transformation to the ferrite phase proceeds in the surface layer and the vicinity thereof in the secondary rolling, and the surface layer becomes coarse, so that the variation in crystal grain size cannot be suppressed to the range of the present invention. . On the other hand, 115
If it exceeds 0 ° C., the average particle diameter (D) exceeds the upper limit of 35 μm specified in the present invention. Therefore, the heating temperature of the primary rolled steel strip was set to a range of ₃ points of Ar + 50 ° C. to 1150 ° C. FIG. 3 shows the relationship between the heating temperature in hot rolling and the heating temperature of the rough rolled steel strip as described above.

When the rolling reduction in the secondary rolling in hot rolling is 70% or more, if the rolling reduction in the secondary rolling is less than 70%, the austenite grain size after the secondary rolling cannot be reduced to a fine grain. However, the crystal grain size specified in the present invention cannot be obtained. If the rolling reduction is 70% or more, a crystal grain size within the range specified in the present invention can be obtained, so the rolling reduction in the secondary rolling is set to 70% or more.

The secondary rolling in the hot rolling temperature: The temperature is Ar less than _three points in the Ar ₃ point or more secondary rolling, rolling portion of the ferrite phase after the primary rolling is coarsened grains of, as a result, the The grain size specified in the invention cannot be obtained. Ar ₃
Since the crystal grain size specified in the present invention can be obtained at the point or higher, the secondary rolling temperature is set to the Ar ₃ point or higher.

Winding temperature: 750 ° C. or less The winding temperature is a production condition that requires a fine and uniform austenite grain size by repeated recrystallization after secondary rolling, and requires control to freeze the structure. . Winding temperature is 75
If it exceeds 0 ° C., ferrite grains grow after winding, and as a result, the crystal grain size specified in the present invention cannot be obtained. If the winding temperature is 750 ° C or less, the above structure is obtained,
The winding temperature was set to 750 ° C. or lower because the crystal grain size can be in the range specified in the present invention.

As a method for obtaining a cold-rolled steel sheet in the present invention, the hot-rolled steel sheet obtained by the above method is used as a raw material.
It is obtained by performing cold rolling and recrystallization annealing. The cold rolling is performed to make the steel sheet have a predetermined thickness, develop a rolling texture, and develop a texture that is preferable for improving workability in a subsequent recrystallization annealing step. The conditions for cold rolling are not particularly limited,
For the above purpose, it is preferable to process to a final plate thickness at a draft of 50% or more.

The recrystallization annealing may be performed under the conditions usually employed. Specifically, annealing is performed in a temperature range of 550 to 900 ° C. to recrystallize ferrite. If the temperature is lower than 550 ° C., recrystallization does not sufficiently occur even after long-time box annealing.
On the other hand, at a temperature exceeding 900 ° C., austenitization proceeds and workability deteriorates. As a method of performing recrystallization annealing, any of continuous annealing, box annealing, and continuous heat treatment preceding hot dip galvanizing may be used.

The material steel having the above-described composition is produced by, for example, a converter or an electric furnace. The production of billets may be any of ingot-bulking rolling or continuous casting, thin slab casting, and strip casting. In the present invention, in the method of heating a slab obtained by continuous casting, ingot making, or slab rolling, the slab is cooled to room temperature or higher and then charged into a hot-rolling heating furnace. In that case, it is preferable that the charging temperature to the hot-rolling heating furnace be equal to or lower than the Ar ₃ point in order to control the structure.

In the present invention, it is preferable that the shape be corrected by a straightening device such as a leveler in a step before or after the rough-rolled steel strip is heated. When straightening is performed in the pre-process of heating the rough-rolled steel strip, the uniformity of the rough-rolled steel strip during heating is improved by improving the shape of the rough-rolled steel strip, and the uniformity of the structure in the rough-rolled steel strip is improved. In addition, since the shape of the rough-rolled steel strip inserted into the finish rolling mill is good, the uniformity during plastic deformation in the finish rolling is improved, and the structure of the resulting steel sheet is also uniform. Further, when the straightening is performed in a post-process of heating the rough-rolled steel strip, at least the shape of the rough-rolled steel strip inserted into the finish rolling mill is good, so that the uniformity at the time of plastic deformation in the finish rolling is increased, and as a result, The tissue becomes uniform.

The cold-rolled steel sheet obtained by the method of the present invention comprises:
Appropriately, after being subjected to surface treatment (hot-dip galvanizing, alloyed hot-dip galvanizing, electroplating, organic coating coating, etc.) and press working, it is used, for example, for automobiles, home appliances, steel structures, etc. It has high workability and strength required for these applications.

[0054]

Next, specific examples according to the present invention will be described below in comparison with comparative examples. Steel having the chemical composition and cleanliness shown in Table 1 (material Nos. 1 to 1)
6) was hot-rolled under the conditions shown in Table 2, cooled, and taken up to obtain material No. 6). For 1 to 6, the crystal grain size of the hot rolled sheet was measured. The material No. 1 and Material No.
No. 7 was subjected to hot rolling directly after casting. The variation of the average crystal grain size (Dmax / Dmin) was determined by measuring the average grain size (D) in the width direction of the hot-rolled sheet and dividing the maximum value by the minimum value. In addition, material No. For Nos. 7 to 16, after hot-rolled sheet was pickled, cold rolling and annealing were performed under the conditions shown in Table 2 to obtain material Nos. As in the case of Nos. 1 to 6, the crystal grain size was examined.

For evaluation of the press-formed product, test pieces were taken from the center and the ends in the width direction of the hot-rolled sheet and the cold-rolled sheet, and the springback angle after bending was measured. The following cases were evaluated as “excellent press formability”, and the difference was evaluated as “good press formability” when the difference was more than 1 degree and 2 times or less, “improper press formability” when the difference was more than 2 degrees. . The results are shown in Table 2.

As is clear from Table 2, it was confirmed that the steel sheet according to the present invention did not crack during bending and was excellent in workability. Further, the difference in the pulling back angle in the width direction was 2 degrees or less, and it was confirmed that the press formability in the width direction was excellent in uniformity.

[0057]

[Table 1]

[0058]

[Table 2]

[0059]

As described above, according to the present invention,
It is possible to provide a steel sheet which is excellent in workability and has little variation in the width direction of the workability and a method for manufacturing the same, and has an industrially useful effect. The steel sheet according to the present invention is used for automobiles,
For industrial equipment, home appliances (TV frame materials, shadow mask materials and inner shield materials, various container materials, etc.),
It can be used for enamel and the like.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between Dmax / Dmin and a difference (Δθ) in a width direction of a springback angle.

FIG. 2 is a diagram showing the distribution of crystal grain size in the coil width direction of the material of the present invention and a comparative material.

FIG. 3 is a diagram showing a relationship between a heating temperature in hot rolling and a heating temperature of a rough rolled steel strip.

────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁷ Identification symbol FI C21D 9/46 C21D 9/46 T (56) References JP-A-5-271869 (JP, A) JP-A-62-185834 ( JP, A) JP-A-5-306430 (JP, A) JP-A-8-158007 (JP, A) JP-A-10-152747 (JP, A) JP-A-6-192787 (JP, A) JP Hei 6-108202 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) C22C 38/00-38/60

Claims (9)

(57) [Claims] C .: 0.2% by weight or less, Si:
1.0% or less, Mn: 3.0% or less, P: 0.2 or less,
S: 0.1% or less, O: 0.004% or less, sol. A
l: 0.01 to 0.1%, N: 0.02% or less, cleanliness: 0.05% or less, average crystal grain size (D) of 5 to 35 μm, in the width direction of the coil A steel sheet having excellent workability and little change in the width direction of the workability, characterized in that the average crystal grain size of (Dmax / Dmin) is 2.0 or less. Here, Dmax is the maximum value of the average crystal grain size in the width direction, and Dmin is the minimum value of the average crystal grain size in the width direction. 2. The composition according to claim 1, further comprising 0.01 to 0.4% of one or more of Ti, Nb, V, and Zr, A steel sheet with little change in workability in the width direction. 3. B: 0.0001 to 0.005%
3. The method according to claim 1, further comprising:
4. A steel sheet having excellent workability and having little variation in the width direction of the workability according to item 1. 4. C: 0.2% or less by weight, Si:
1.0% or less, Mn: 3.0% or less, P: 0.2% or less, S: 0.1% or less, O: 0.004% or less, so
l. When continuously casting a steel containing Al: 0.01 to 0.1%, N: 0.02% or less, and cleanliness: 0.05% or less, and then directly hot rolling the obtained steel slab. , A
r a step of subjecting the steel strip to primary rolling at a temperature of ₃ points or more at a rolling reduction of 70% or more, and thereafter, the entire steel strip is Ar
A step of reheating at ₃ points + 50 ° C. to 1150 ° C., a step of performing secondary rolling at a temperature of ₃ points or more and a rolling reduction of 70% or more, and subsequently winding at a temperature of 750 ° C. or less A method for producing a steel sheet having excellent workability and having little variation in the width direction of the workability, comprising: 5. The method according to claim 1, wherein C: 0.2% or less, Si:
1.0% or less, Mn: 3.0% or less, P: 0.2% or less, S: 0.1% or less, O: 0.004% or less, so
l. When continuously casting a steel containing Al: 0.01 to 0.1%, N: 0.02% or less, and cleanliness: 0.05% or less, and directly hot-rolling the obtained steel slab, a step of the steel strip at 70% or higher reduction rate in Ar ₃ point or more temperature subjected to primary rolling, whole Ar ₃ point subsequent to the steel band +
A step of reheating at a temperature in the range of 50 ° C. to 1150 ° C., a step of subsequently performing a secondary rolling at a temperature of not less than the Ar ₃ point at a rolling reduction of 70% or more, and a step of subsequently winding at a temperature of 750 ° C. or less A method for producing a steel sheet having excellent workability and having less variation in the width direction of the workability, comprising cold rolling and subsequently recrystallization annealing. 6. C: 0.2% or less by weight%, Si:
1.0% or less, Mn: 3.0% or less, P: 0.2% or less, S: 0.1% or less, O: 0.004% or less, so
l. When hot rolling a steel slab containing Al: 0.01 to 0.1%, N: 0.02% or less, and cleanliness: 0.05% or less, within a range of Ar ₃ points to 1200 ° C. A step of heating, followed by a primary rolling at a temperature of not less than Ar ₃ point and a rolling reduction of not less than 70% to form a steel strip, and thereafter, the whole of the steel strip is Ar ₃ point + 50 ° C. to 1150 Reheating within the range of ° C, followed by Ar at a temperature of ₃ points or more.
Excellent workability and variation in the width direction of workability, characterized by comprising a step of performing secondary rolling at a rolling reduction of 0% or more and a step of subsequently winding at a temperature of 750 ° C. or less. Method for producing steel sheets with less. 7. C: 0.2% or less by weight, Si:
1.0% or less, Mn: 3.0% or less, P: 0.2% or less, S: 0.1% or less, O: 0.0040% or less, so
l. When hot rolling a steel slab containing Al: 0.01 to 0.1%, N: 0.02% or less, and cleanliness: 0.05% or less, within a range of Ar ₃ points to 1200 ° C. A step of heating, followed by a primary rolling at a temperature of not less than Ar ₃ point and a rolling reduction of not less than 70% to form a steel strip, and thereafter, the whole of the steel strip is Ar ₃ point + 50 ° C. to 1150 Reheating within the range of ° C, followed by Ar at a temperature of ₃ points or more.
Workability characterized by comprising a step of performing secondary rolling at a rolling reduction of 0% or more and a step of subsequently winding at a temperature of 750 ° C. or less, followed by cold rolling, and subsequently recrystallization annealing. A method for producing a steel sheet that is excellent in workability and has little variation in workability in the width direction. 8. The method according to claim 4, further comprising 0.01 to 0.4% of one or more of Ti, Nb, V and Zr. 3. The method for producing a steel sheet having excellent workability and having little variation in the width direction of the workability according to the above. 9. B: 0.0001 to 0.005%
9. The composition according to claim 4, further comprising:
The method for producing a steel sheet according to any one of the above, which is excellent in workability and has little variation in the width direction of the workability.