JP5014867B2 - Width reduction method for billets - Google Patents

Description

The present invention relates to a method for reducing the width of a steel slab that is reduced in the thickness direction after the steel slab (for example, slab) in a high temperature state is reduced in width.

Conventionally, when manufacturing products with different width sizes, a slab (an example of a steel slab) is cast by a continuous casting machine, and then the slab is subjected to width reduction by rolling, pressing, etc. according to the width size of the product. is doing.
As described above, when the width reduction is performed on the slab, both side corners (also referred to as corner portions) of the slab in the width direction are locally deformed, and the deformed portion is caused by the subsequent horizontal reduction in the thickness direction of the slab. May fall into the upper and lower surfaces of the slab, causing wrinkles.
For this reason, at present, there are problems such as restrictions on operating conditions and a decrease in product productivity due to dredging, an increase in manufacturing cost, a deterioration in yield, and a prolonged manufacturing period.
Therefore, in order to solve these problems, a phenomenon in which a corner portion of a slab (hereinafter also referred to as a steel material) is deformed was examined.

In general, in a steel material with C ≦ 0.765%, a temperature range that transforms into an α-γ two-phase region (hereinafter also simply referred to as a two-phase region) according to the amount of C (corresponding to the reverse region in FIG. 2). Exists. In addition, FIG. 2 has shown the relationship between the steel material temperature of (circle): extra-low carbon (SULC: C = 0.005 mass%), and the deformation resistance at that time.
Usually, the deformation resistance of steel materials increases (that is, hardens) as the temperature decreases, but in the two-phase region described above, the deformation resistance decreases (that is, softens). Then, the tendency is remarkable.

In other words, when performing the width reduction of the steel material, since the corner portion of the steel material is significantly cooled as compared with other portions, depending on the cooling conditions, only the temperature of the corner portion enters the above-described two-phase region, It may be softened compared to the material. For example, in an extremely low carbon steel material, even if the temperature of the steel material is adjusted to about 930 ° C., the temperature of the corner portion may be 870 to 880 ° C. and may be in the range of the two-phase region.
When the width of the steel material is reduced under such conditions, as shown in FIG. 3, the softened corner portion may be locally deformed, and collapse may occur due to the subsequent reduction in the thickness direction.

For example, Patent Document 1 discloses a method of forming each corner portion of a slab so that the cross section of the corner portion is substantially arcuate at least before and after the width reduction step by pressing.

JP-A 63-149001

However, in the method of Patent Document 1, when the corner portion of the slab is formed into an arc shape, when the temperature of the corner portion is in the α-γ two-phase region temperature, the above-described problem of the collapse of the collapse cannot be solved.

The present invention has been made in view of the above circumstances, and suppresses and further prevents the occurrence of falling-down flaws at the corners of a steel slab, and allows the steel slab having a desired width to be manufactured economically with high productivity. An object is to provide a method for reducing the width of a piece.

The present invention is for solving the above-mentioned problem, and the means (1) is the width of a steel slab in which a steel slab in a high temperature state is subjected to width reduction by a width reduction device and then the steel slab is reduced in the thickness direction. In the reduction method,
When the steel slab is width-reduced by the width-reducing device, the steel slab is forcibly cooled in the longitudinal direction over a range of 10 mm or more and 50 mm or less from each apex of the corner that is both side corners in the width direction, The temperature of the corner is set to be less than the α-γ two-phase region temperature.

Means (2) is Oite the means (1), after the forced cooling of the corners of the steel pieces, the time until the width reduction of the steel piece by the width reduction device to within 2 minutes.
In the means ( 3 ), in the means (1) and the means ( 2 ), the forced cooling of the corner portion of the steel slab is performed by air and water consisting of water and air.

The width reduction method of the steel slab according to the present invention forcibly cools both corners in the width direction of the steel slab, and the temperature is less than the α-γ two-phase region temperature at which the steel slab tends to soften. It can suppress that the deformation resistance of a part falls extremely compared with the deformation resistance of the peripheral part. As a result, when the steel slab is reduced in width, local deformation at the corners can be suppressed, and the occurrence of falling-down wrinkles at the corners of the steel slabs can be further suppressed, and the steel slab having the desired width can be produced. Can be manufactured economically well.
In addition, because the area of the corner is forcibly cooled, it is possible to prevent the area other than the corner from being forcibly cooled over a wide range, so that the deformation resistance of the steel slab can be reduced and the product quality is improved. It is possible to manufacture a steel sheet having a shape with a high productivity.

And when performing the width reduction of the steel piece within a predetermined time after the forced cooling of the corner portion, the width reduction can be performed before the heat of the other portion is transferred to the corner portion. As a result, the corner portion that has been forcibly cooled and adjusted to less than the α-γ two-phase region temperature can be reduced in width before entering the temperature range again, so that when the steel piece is reduced in width, local deformation at the corner portion is reduced. It can be suppressed and further prevented.
Furthermore, when forced cooling of the corners is performed with air and water consisting of water and air, forcible cooling can be performed without using excessive water, so there is no risk of other parts being forcibly cooled due to dripping water, for example. The deformation resistance at the time of width reduction of the steel piece can be reduced.

Next, embodiments of the present invention will be described with reference to the accompanying drawings for understanding of the present invention.
Here, FIG. 1 is an explanatory view of a width reduction method of a steel piece according to an embodiment of the present invention.

As shown in FIG. 1, the method for reducing the width of a steel slab according to an embodiment of the present invention is performed by pressing a pair of molds disposed opposite to each other in the width direction of a slab (an example of a steel slab) 10 in a high temperature state. This is a width reduction method in the case where the slab 10 is reduced in the sheet thickness direction by rolls disposed on the upper and lower sides of the slab 10 after the slab 10 is reduced in width by a width reduction device (not shown) that performs reduction (or reduction with a roll). When the slab 10 is width-reduced by the width-reducing device, the widthwise corners 11 to 14 of the slab 10 are forcibly cooled in the longitudinal direction. This will be described in detail below.

The slab 10 that performs width reduction has, for example, a carbon concentration of 0.05% by mass or less, a length (length in the conveyance direction, length in the longitudinal direction) of about 7 to 30 m, a thickness of about 120 to 300 mm, and a width of about 800 to 1800 mm. It is rectangular low carbon steel, for example, is in a high temperature state of about 900 to 1150 ° C.
Before the slab 10 is reduced by the width reduction device, the corners 11 to 14 at the four corners of the slab 10 are forcibly cooled so that the temperature is less than the α-γ two-phase region temperature.
Here, the α-γ two-phase region temperature is a temperature at which the slab shown in FIG. 2 is softened. For example, when the carbon concentration is 0.005% by mass or less, it is less than 865 ° C. It is preferable to do. Although the lower limit temperature is not specified, the lower the temperature at the corner of the slab, the greater the temperature drop except for the corner (width direction center and plate thickness direction center). In view of thermal energy loss, the temperature is preferably set to 700 ° C. or higher.

This forced cooling is performed by the cooling water spray nozzle 15 arranged in the transport line of the slab 10. In addition, the cooling water jet nozzle 16 of the cooling water spray nozzle 15 is respectively directed to the corner portions 11 to 14 of the four corners of the slab 10.
The cooling water spray nozzle 15 can be disposed at a plurality of locations along the conveyance line of the slab 10, but may be disposed at one location.
As a result, by continuing to blow out water and air from the cooling water spray nozzle 15, the corners 11 to 14 of the slab 10 passing in front of the cooling water spray nozzle 15 are moved in the longitudinal direction (conveyance). It can be cooled over the rear end) from the direction of the tip.

As shown in FIG. 1, the jet angle of the steam water from the cooling water jet 16 of each cooling water spray nozzle 15 (interval between the cooling water jet and the corner) is a cross section of the slab 10 (perpendicular to the conveying direction). From the vertices P1 and P2 of the corners 11 and 12 to the surface (upper surface) and side surfaces of the slab 10, and from the vertices P3 and P4 of the corner portions 13 and 14 to the back surface (lower surface) and side surfaces. The range R up to a predetermined value is set so as to be forcibly cooled. The predetermined value is in the range of 10 mm to 50 mm.
Here, when the predetermined value is less than 10 mm, the range for forced cooling becomes too narrow, and there is a possibility that the heat is reheated to the above-described two-phase temperature with heat from other portions. On the other hand, if the predetermined value exceeds 50 mm, the range for forced cooling becomes too wide, the deformation resistance of the slab itself increases, and there is a possibility that the subsequent width reduction cannot be performed with good workability.

For this reason, although it was set as the range from 10 mm to 50 mm respectively from the vertices P1 to P4, the lower limit value is preferably 20 mm, and the upper limit value is preferably 35 mm.
The range R for forced cooling is, for example, the same range from the apex P1 of the corner portion 11 to the surface and side surface of the slab 10, but may be different as long as it is within the predetermined value range. The same applies to the other corners 12 to 14.
For forced cooling of the corners, it is preferable to use air and water consisting of water and air, but cooling water can also be used. The volume of air in the air is set so that the temperature at each corner during width reduction is less than the α-γ two-phase temperature determined by the material of the slab (temperature drop due to cooling, cooling The amount of water is determined in consideration of later double heat), for example, about 20% by volume to 80% by volume.

The slab 10 in which the corners 11 to 14 are forcibly cooled by the above-described method is sent to the width reduction device. At this time, it is preferable that the time from the end of forced cooling of the corners 11 to 14 of the slab 10 to the width reduction of the slab 10 by the width reduction device is within 2 minutes.
Here, when the time until the width reduction of the slab 10 exceeds 2 minutes, the portions other than the corner portions 11 to 14 of the slab 10 are in a high temperature state, and thus each corner portion 11 to 14 forcibly cooled by this heat. (Double heat) and each corner rises to the α-γ two-phase region temperature.
For this reason, the time until the width reduction of the slab 10 is performed within 2 minutes, but preferably within 80 seconds, more preferably within 50 seconds.

And the width reduction of the slab 10 forcedly cooled is performed by the width reduction apparatus.
As this width reduction device, for example, there is a conventionally known press device. This press apparatus has a pair of metal molds arranged opposite to each other in the width direction of the slab 10, and is an apparatus for adjusting the width of the slab 10 by pressing the metal mold against the slab 10. Moreover, as another width reduction apparatus, you may use what consists of the scissors roll arrange | positioned at the width direction both sides of the slab 10, or a caliber roll.
After reducing the width of the slab 10 with this width reduction device, the slab is reduced in the plate thickness direction with a horizontal mill. This horizontal mill is composed of upper and lower cylindrical rolls arranged horizontally across the width direction of the slab 10 so as to sandwich the slab 10 in the thickness direction of the slab 10.

Next, examples carried out for confirming the effects of the present invention will be described.
The used slab (steel) had a width of 1800 mm, a thickness of 250 mm, and a length of 20 m before width reduction, and had two kinds of component elements shown in Table 1.

Table 3 shows the results obtained using these slabs under the cooling conditions shown in Table 2.

In Examples 1 , 3 to 5 and Reference Example 1 shown in Table 3, the temperature of the slab corner immediately before the width reduction rolling is less than the α-γ two-phase region temperature (steel No. 1: less than 865 ° C, Steel No. 2: less than 727 ° C., and Comparative Examples 6, 7, 9, and 10 are results in which the temperatures of the slab corners are all equal to or higher than the α-γ two-phase region temperature. In addition, the comparative example 8 is the result of having made temperature of the whole surface of a slab surface less than (alpha) -gamma two-phase region temperature.

As is clear from Examples 1 and 3 to 5 and Reference Example 1 , the slab corners were forcedly cooled, so that the temperature of the corners was less than the α-γ two-phase region temperature. No fallen wrinkles were confirmed. On the other hand, in Comparative Examples 6, 7, 9, and 10, since the temperatures at the slab corners were both α-γ two-phase region temperatures, as a result, collapsed wrinkles were confirmed by visual observation.
In Comparative Example 8, the temperature of the entire surface of the slab was set to be less than the α-γ two-phase region temperature. Could not reduce.
Reference Example 1 is a result of setting the corner cooling range wider than Examples 1 and 3 to 5 , and Example 4 is the result of Examples 1 , 3 , 5 , and Reference Example 1 . In comparison, it is the result when it takes a long time to perform the width reduction of the slab by the width reduction device, and Examples 3 and 4 are the results of using water for cooling the corners. In addition, no wrinkle was produced and width reduction was possible.
As is clear from Examples 1 and 3 to 5 and Reference Example 1 , there is no influence of the type of the width reduction device.

The present invention has been described above with reference to the embodiments. However, the present invention is not limited to the configurations described in the above-described embodiments, and the matters described in the claims are not limited. Other embodiments and modifications conceivable within the scope are also included. For example, a case where the width reduction method for a steel slab of the present invention is configured by combining some or all of the above-described embodiments and modifications is also included in the scope of the present invention.

It is explanatory drawing of the width reduction method of the steel piece which concerns on one embodiment of this invention. It is a graph which shows the relationship between the temperature of steel materials, and deformation resistance. It is explanatory drawing which shows the shape change at the time of performing thickness reduction after performing width reduction with respect to steel materials.

Explanation of symbols

10: Slab, 11-14: Corner, 15: Cooling water spray nozzle, 16: Cooling water outlet

Claims (3)

In the method of reducing the width of a steel slab, the steel slab in a high temperature state is subjected to width reduction by a width reduction device, and then the steel slab is reduced in the thickness direction.
When the steel slab is width-reduced by the width-reducing device, the steel slab is forcibly cooled in the longitudinal direction over a range of 10 mm or more and 50 mm or less from each apex of the corner that is both side corners in the width direction, A method for reducing the width of a steel slab, wherein the temperature of the corner is less than the α-γ two-phase region temperature. The width reduction method for a steel slab according to claim 1 , wherein the time until the width reduction of the steel slab by the width reduction device after forced cooling of the corner portion of the steel slab is within 2 minutes. The width reduction method of the steel piece 3. A method for reducing the width of a steel slab according to claim 1 or 2 , wherein the forced cooling of the corner portion of the steel slab is performed by water vapor comprising water and air.

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