KR101204843B1 - Method for fabricating cold rolled sheet - Google Patents

Abstract

The crown and high / low spot values of the hot rolled steel sheet were measured and compared against a reference value, and cold rolling with box annealing (BAF) was performed on the hot rolled steel sheet when the reference value was below the reference value. A method of manufacturing a cold rolled steel sheet, which is obtained by performing box annealing on the rolled product, to obtain a cold rolled steel sheet.

Description

Method for fabricating cold rolled steel sheet {Method for fabricating cold rolled sheet}

The present invention relates to a steel sheet manufacturing technology, and more particularly, to a cold rolled steel sheet manufacturing method for improving the shape quality through the shape quality control of the hot rolled steel sheet.

When manufacturing a cold rolled sheet coil by cold rolling the hot rolled steel sheet, a defect may occur in the shape quality of the cold rolled steel sheet after cold rolling due to the shape quality of the hot rolled steel sheet. Shape quality defects such as sticker defects, which are poor contact between the strips of steel sheets on the side of the cold rolled steel coil, can be caused. When cold rolled steel sheet is used as a vehicle material, surface quality control is required to a very high level, and a method of suppressing such defects in shape quality is required.

The present invention is to set the shape quality standards of hot rolled steel sheet, and to control the cold rolling process in accordance with these standards, to propose a cold rolled steel sheet manufacturing method that can improve the shape quality.

One aspect of the invention, the step of manufacturing a hot rolled steel sheet; Measuring a crown value of the hot rolled steel sheet; Comparing the measured crown value against a crown value reference value; Performing cold rolling on the hot rolled steel sheet with box annealing (BAF) when the measured crown value is less than or equal to the reference value; And it provides a cold rolled steel sheet manufacturing method comprising the step of performing the box annealing on the cold rolled product to obtain a cold rolled steel sheet.

The crown numerical reference value may be set to 60 μm.

Performing cold rolling on the hot rolled steel sheet with continuous annealing (CAL) when the measured crown value is greater than the reference value; And a step of obtaining a cold rolled steel sheet by performing the continuous annealing on the cold rolled result.

The continuous annealing (CAL) may be performed when the measured crown value is larger than the reference value and 100 μm or less.

Measuring a surface profile of the hot rolled steel sheet; Extracting a high / low spot value at the point where the profile changes abruptly in the surface profile; And comparing the extracted high-low spot values with respect to a high-low spot numerical reference value, wherein the box annealing (BAF) when the extracted high-low spot numerical value is less than the high-low spot numerical reference value. A cold rolled steel sheet manufacturing method is performed.

The high-low spot numerical reference value may be set to 10 μm.

Performing cold rolling with continuous annealing (CAL) on the hot rolled steel sheet when the extracted high-low spot value is equal to or higher than the high-low spot value reference value; And performing a continuous annealing on the cold rolled result to obtain a cold rolled steel sheet manufacturing method.

According to an embodiment of the present invention, by setting the shape quality standards of the hot rolled steel sheet, and by differently controlling the cold rolling process according to these standards, it is possible to provide a cold rolled steel sheet manufacturing method that can improve the shape quality. After the hot rolled steel sheet is manufactured, the thickness and surface profile of the hot rolled steel sheet are measured to determine crown values and high / low spot values of the manufactured hot rolled steel sheets. After setting the reference values for the crown value and the high-low spot value, for the hot rolled steel products below or below these reference values, the annealing process of the cold rolling process is performed by a Batch Annealing Furnace (BAF) method. do. In the case of hot rolled steel sheet products having the above standard value, the annealing process of the cold rolling process is performed by a continuous annealing line (CAL) method.

When the measured crown value of the hot rolled steel sheet is 60 μm and the high-low spot value is 10 μm, the reference value is set, and only the hot rolled steel sheet is selected when the crown value is 60 μm or less or the high-low spot value is less than 10 μm. The annealing process is performed by a box annealing method using a box annealing furnace. Accordingly, it is possible to effectively suppress the occurrence of side lateral defects of the cold rolled coil, such as a sticker failure, during manufacture of the cold rolled steel sheet, and to produce a cold rolled steel sheet excellent in shape and surface quality.

1 is a process flow diagram showing a cold rolled steel sheet manufacturing method according to an embodiment of the present invention.
2 to 4 are diagrams showing a method for measuring a crown value according to an embodiment of the present invention.
5-7 illustrate surface profiles for measuring high / low spot values in accordance with embodiments of the present invention.

Embodiments of the present invention are set on the basis of the surface and shape quality of the hot rolled steel sheet, based on this, the annealing process to be introduced in the subsequent cold rolled steel sheet manufacturing (BAF: Batch Annealing Furnace) process and continuous annealing (CAL: Choose from the process of Continuous Annealing Line. Among the surface and shape qualities of the hot rolled steel sheet, for the hot rolled steel sheet manufactured after hot rolled steel sheet production, the crown value and the high / low spot value of the surface profile are set based on the subsequent cold rolled steel sheet. It is used as a criterion for determining the annealing process introduced during steel sheet manufacturing.

It is proved experimentally that the crown value or the high-low spot value of the hot rolled steel sheet is associated with a defect in the shape quality of the cold rolled steel sheet to be produced subsequently. In particular, in the case of hot rolled steel sheet products having a crown value of greater than 60 μm or having a high-low spot value of 10 μm or more, as a result of performing box annealing in the subsequent cold rolled steel sheet manufacturing process, the steel sheet (strip) It can be observed that a sticker defect, which is an iron plate contact defect, is generated due to an increase in the contact surface between the pads.

On the basis of this, hot rolled steel sheet products having a crown value larger than 60 μm or a high-low spot value of 10 μm or more are controlled so as not to perform box annealing during cold rolled steel sheet manufacturing, and to perform continuous annealing. Manage. Since continuous annealing equipment performs annealing process together with temper rolling, even if cold rolling is performed on a hot rolled steel sheet having a crown value of more than 60 μm or a high-low spot value of 10 μm or more, a sticker ( It can be confirmed that surface and shape quality defects such as sticker defects are suppressed. Nevertheless, it is required to control the quality of the hot rolled steel sheet so that the crown value is not larger than 100 μm, so that the quality of the hot rolled steel sheet to which continuous annealing is applied after cold rolling is limited to the product whose crown value is larger than 60 μm and 100 μm or less. More effective.

Referring to Figure 1, the cold rolled steel sheet manufacturing method according to an embodiment of the present invention is carried out including the cold rolling and annealing process for the hot rolled steel sheet produced by the hot rolled steel sheet manufacturing 101 process. The shape quality of the hot rolled steel sheet 101 manufactured by the hot rolling process is measured, and the annealing process to be performed after cold rolling is performed by using the box annealing furnace (BAF), or continuous annealing equipment (CAL). Determine whether to perform by continuous annealing using. To this end, the crown value (C _D ) and the high-low spot value (S _D ) of the hot rolled steel sheet are measured as a criterion of determination (102).

The crown value of the hot rolled steel sheet indicates the thickness variation in the strip width direction of the hot rolled steel sheet, and as shown in FIG. 2, the thickness H _C and the two edges at the center of the strip 20 of the hot rolled steel sheet. Measure the thickness at the point spaced inward from the edge. In this case, the thickness H _O at the operator side edge and the thickness H _D at the drive side edge may be measured as thicknesses at both edges. In this case, the separation distance may be arbitrarily set to 25 mm. The measured crown value (C _D ) can be set by the formula (H _C )-((H _O ) + (H _D )) / 2, which means thickness deviation. As shown in FIG. 3, the crown shape of the hot rolled steel sheet strip 21 may be convex, and as shown in FIG. 4, the crown shape of the hot rolled steel sheet strip 23 may be concave. Since the crown value can be a positive value when convex, and a negative value when concave, it is effective to take an absolute value and apply it to a comparison with subsequent reference values.

Referring again to FIG. 1, although the measured crown value of the hot rolled steel sheet may be applied as a variable representing the shape quality of the hot rolled steel sheet, the surface profile of the hot rolled steel sheet may be measured to provide more stringent control of the shape quality. The variation value at the high / low spot, which is the point where the profile value suddenly fluctuates in the profile, is extracted as a high-low spot value S _D (102 in FIG. 1).

For example, the surface profile of a hot rolled steel sheet can be measured to represent the surface topology as shown in FIG. 5. The surface profile measured for the strip width direction of the hot rolled steel sheet may be measured with a gentle profile in which no sharp point of variation is found as shown in FIG. 5 under normal conditions. In contrast, as shown in FIG. 6, a point including a high spot, that is, a point where the surface height sharply increases at a specific point of the surface may be measured. The height difference of the profile at the high spot may be measured and extracted as the high spot value S _D1 .

On the other hand, as shown in Figure 7, at a particular point of the surface the surface height is sharply lowered, that is, a profile including a low spot (low spot) can be measured. The height difference between the periphery of the profile in the furnace spot can be measured and extracted as the furnace spot value (S _D2 ). 6 and 7 illustrate the high spot value and the low spot value, respectively, but the high spot and the low spot may exist together in one hot rolled sheet steel strip and may be extracted as the high-low spot value.

The crown value (C _D ) and the high-low spot value (S _D ) thus measured are used as a criterion for determining the subsequent cold rolling annealing method. For this purpose, the crown numerical reference value C _S and the high-low spot numerical reference value S _S are set (103 in FIG. 1). When the crown value is measured substantially within the range of 0 μm to 60 μm, it can be seen that shape quality defects, such as poor sticker, are suppressed in the result of the cold rolled steel sheet after cold rolling and box annealing. When a crown value larger than 60 μm is measured, it can be confirmed that a sticker failure occurs after cold rolling and box annealing, so that the reference value of the crown value can be set to 60 μm. In addition, in the case of a defect profile such as a high-low spot, it can be seen that shape quality defects such as stickers are suppressed when the numerical value of the spot is less than 10 μm, and shape quality defects are generated when the defect profile is higher. Thus, the high-low spot reference value can be set at 10 mu m.

Thus set crown numerical reference value (C _S) and the high-to spot numerical reference value crown value measured with the _(S S) (C _D) and the high-compares the value in (S _D), measured crown value (C _D ) Is below the reference value (C _S ) or / and if the measured high-low value (S _D ) is smaller than the reference value (S _S ), a cold rolling process including box annealing is performed (111 in FIG. 1). After cold rolling, a box annealing process (113 in FIG. 1) is performed to produce a cold rolled steel sheet 115. At this time, the hot rolled steel strip may be passed through a scale breaker and a hydrochloric acid tank before the cold rolling 111 to perform a pickling process of removing an oxide film that is a cause of surface defects in the final cold rolled product. Cold rolling is carried out at a reduction ratio of 40% to 90% to secure a thickness and material suitable for the application, and advanced controllers such as automatic thickness control and automatic shape control may be used for uniform thickness and shape control.

After cold rolling, the cold rolled steel sheet may be passed through an alkali solution prior to annealing to perform an electrolytic cleaning process to remove rolling oil and dirt through mechanical and chemical reactions, and to soften the material of the hardened steel sheet during cold rolling. The annealing process may be performed (113 in FIG. 1). Rapid heating and rapid cooling allow the production of deep steels from deep processing. After box annealing, defects such as stretcher strain, which tends to appear on the annealed steel strip, are removed by rolling with about 1% rolling on the plate, and the surface roughness is applied to perform temper rolling that produces a beautiful surface product. In addition, as a final process of production, the customer may perform a correction process using a correction line facility that determines the suitability of the product for defect inspection and use according to a desired size. As a result, the cold rolled steel sheet 115 is manufactured.

Meanwhile, when the measured crown value is larger than the reference value, cold rolling (112 in FIG. 1) with continuous annealing (CAL) may be performed on the hot rolled steel sheet. After cold rolling, continuous annealing may be performed (114 in FIG. 1), and then a correction process may be performed to obtain a cold rolled steel sheet (116 in FIG. 1). At this time, if the measured crown value is larger than 100 μm, sticker failure may be caused in spite of continuous annealing. Therefore, when the crown value is larger than 60 μm and measured to 100 μm or less, performing cold rolling with continuous annealing is performed. More effective.

Only the hot rolled steel sheet, which is strictly limited to 60 μm or less in the crown value, is subjected to box annealing after cold rolling, thereby manufacturing and managing steel sheets having excellent shape and surface quality during cold rolled steel sheet manufacturing. In the case of box annealing, since the cold rolled product rolled up after rolling is annealed in the furnace, the poor quality of the material may increase the contact surface between the steel sheet strips, thereby making it easier to generate a sticker defect, which is a poor iron sheet contact.

In the embodiment of the present invention by measuring the surface quality of the hot rolled steel sheet by the crown value and the high-low spot value, and by cold rolling only strictly limited hot rolled steel sheet products, it is possible to effectively suppress the cause of the sticker failure in advance Or can be prevented. Accordingly, a product having excellent shape and surface quality when manufacturing a cold rolled steel sheet using box annealing may be implemented. Continuous annealing equipment is accompanied by a surface modification or control process such as temper rolling during annealing, it is possible to manufacture a cold rolled steel sheet of better surface and shape quality despite the more relaxed quality of hot rolled steel sheet.

As described above, according to the embodiment of the present invention, the classification of the products to be subjected to the box annealing and continuous annealing is performed in advance by using the surface quality characteristics of the hot rolled steel sheet, for example, the crown value and the high-low spot value. By carrying out the box annealing and continuous annealing suitably for the product, it is possible to effectively suppress the occurrence of surface or shape defects in the box annealing process in which relatively weak surface quality can be caused.

Crown values and profile standards, which are quality control items for hot rolled steel sheets, are established so that shape and surface quality problems may not occur during cold rolled steel sheet manufacturing. Accordingly, quality control of raw materials may be more easily performed when manufacturing the cold rolled steel sheet. In addition, it is possible to prevent the occurrence of poor quality during the production of cold-rolled steel sheet during the production of hot-rolled steel sheet, it is possible to more effectively facilitate the yield and acceptance rate management of cold-rolled steel sheet products.

101 ... Step for manufacturing hot rolled steel sheet 102 ... Measurement step
104 ... Comparative judgment step 113 ... Box annealing step.

Claims (7)

Manufacturing a hot rolled steel sheet;
Measuring a crown value of the hot rolled steel sheet;
Comparing the measured crown value against a crown value reference value;
Performing cold rolling with a box annealing (BAF) on the hot rolled steel sheet when the measured crown value is less than or equal to the reference value, and performing the box annealing on the cold rolled result to obtain a cold rolled steel sheet; And
Performing cold rolling with continuous annealing (CAL) on the hot rolled steel sheet when the measured crown value is greater than the reference value, and performing the continuous annealing on the cold rolled result to obtain a cold rolled steel sheet. Steel plate manufacturing method.
The method of claim 1,
The crown numerical reference value is set to 60㎛ cold rolled steel sheet manufacturing method.
delete The method of claim 1,
And performing the continuous annealing (CAL) when the measured crown value is greater than the reference value and less than or equal to 100 μm.
The method of claim 1,
Measuring a surface profile of the hot rolled steel sheet;
Extracting a high / low spot value at the point where the profile changes abruptly in the surface profile; And
Comparing the extracted high-low spot values against a high-low spot value reference value,
And performing the box annealing (BAF) when the extracted high-low spot value is smaller than the high-low spot value reference value.
The method of claim 5,
And the high-low spot numerical reference value is set to 10 μm.
The method of claim 5,
Performing cold rolling with continuous annealing (CAL) on the hot rolled steel sheet when the extracted high-low spot value is equal to or higher than the high-low spot value reference value; And
Cold rolling steel sheet manufacturing method comprising the step of performing the continuous annealing on the cold-rolled product to obtain a cold rolled steel sheet.

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