JP2792445B2 - Hot rolling method for preventing steel sheet from rolling around four edges - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot rolling method capable of reducing four-period defects on a hot metal plate such as a thick steel plate.

[0002]

2. Description of the Related Art For example, in plate rolling, a forming and rolling process in which a material to be rolled is rolled several times in a longitudinal direction, and a material to be rolled is rotated by 90 °.
A tentering rolling step of rolling and rolling to a predetermined width (= product width + ear allowance); and a finish rolling for rolling a material to be rolled by 90 ° and rolling in the longitudinal direction to obtain a predetermined thickness and length. It consists of three steps.

[0003] In such a thick plate rolling, a seam flaw (edge crack) which is continuous in the longitudinal direction is generated in a product after rolling, for example, at a position 20 mm from the end face of the material to be rolled. If there is a flaw, there is a problem that an extra ear margin is required and the yield is reduced.

[0004] Such seam flaws are due to the fact that wrinkles formed on the end face of the material to be rolled in the previous step appear on the surface of the material to be rolled during reversible rolling in tentering rolling, and this is caused by the fact that it is rolled in the next step. Formed. Conventionally, the following method has been proposed as a technique for preventing the occurrence of the seam flaw.

[0005] In this method, the four side ridges of the material to be rolled are cut at an appropriate volume ratio and rolled to eliminate the curvature of the end face of the material to be rolled.

[0006] Japanese Patent Application Laid-Open No. 56-19908 discloses a method in which after rolling under light pressure, the material to be rolled is reduced to 90%.
This is a method of performing initial tentative rolling under light pressure in which only the surface layer of the material to be rolled is extended by rolling to prevent the occurrence of flaws.

[0007] This is a method of providing a forging effect by denting the center of the thickness of the slab on both side end surfaces with a convex caliber roll, thereby preventing the generation of flaws.

[0008] Japanese Patent Application Laid-Open No. 61-273202 discloses a method in which a forged layer is formed on a ridgeline of an end face of a material to be rolled to prevent generation of flaws.

[0009] Japanese Patent Application Laid-Open No. 1-210113 discloses a method in which a shape of an end face of a material to be rolled along a rolling direction is measured during rolling, and cooling devices located at upper and lower portions of the material to be rolled are measured based on the measurement result. By controlling
This is a method of providing a cooling difference between the front and back surfaces of the material to be rolled during rolling to control the difference in elongation between the front and back surfaces.

[0010]

However, the above-described method has problems that the yield is reduced by cutting and that the method cannot be applied to a slab charged into a heating furnace at a high temperature. The methods (1) and (2) are methods for preventing the occurrence of seam flaws by increasing the amount of overlap at the end of the material to be rolled. Since the amount of overlap increases, there is a problem that the yield is deteriorated. According to the method (1), it has been confirmed that seam flaws are reduced, but flaws having a greater depth than conventional seam flaws are generated due to scale residue generated during training. In the method of (1), after measuring the end face shape of the slab during hot rolling, the upper and lower cooling waters are controlled to adjust the temperature of the front and back surfaces, and after such cooling, rolling is resumed. / Hour). Further, with a specified finishing temperature material such as a controlled rolled material for improving the strength and toughness, cooling controlled rolling under predetermined conditions cannot be performed, and application to a controlled rolled material or the like is difficult.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to reduce the depth of seam flaws without increasing the amount of overlap and yield loss in products. Another object of the present invention is to provide a hot rolling method for preventing four-round defects of a steel sheet, which can be applied to a material having a specified finishing temperature such as a controlled rolling material.

[0012]

As shown in FIG. 1, the method for hot rolling of steel sheet according to the present invention is a hot rolling process for a steel sheet using a continuous cast slab or a lump slab. On the way, the shape of the end face along the rolling direction of the material S to be rolled is measured, and when this end face shape is a double bulge (see FIG. 2A), the position of the overlap a is closer to the surface than the center position of the sheet thickness. If there is, the amount of heating on the front side of the slab in the slab heating furnace 3 is over, and if the overlap a position is on the back side from the center position of the thickness, the amount of heating on the back side of the slab in the slab heating furnace 3 is over and relatively increased in accordance with the shift amount l _a from the thickness center position of the wrap a position, after heating the subsequent steel strips, rolling.

When the end face shape is a single bulge (FIG. 2)
(Refer to (B)), contrary to the case of the double bulge, if the inflection point b is on the front side from the center position of the plate thickness, the heating amount on the back side of the slab in the slab heating furnace 3 is inflected. if the point b is the back surface side of the thickness center position, the heating of the steel strip surface side in the steel slab heating furnace 3, in accordance with the shift amount l _b from the thickness center position of the inflection point b relatively After heating the subsequent billet,
To roll.

The relative amount of heating of the front and back surfaces of the slab in the slab heating furnace 3 is controlled by using an upper gas burner 4U and a lower gas burner 4L installed in the slab heating furnace 3. The flow rates F _u and F _l are controlled so that the set heating temperature is maintained and the front side or the back side is relatively strongly heated. Also, it is preferable that the end face shape measurement during hot rolling is performed on each of the materials to be rolled S ₁ , S ₂ , S _3, ... And feedback to the upper and lower gas flow ratio control in the heating furnace.

[0015]

[Action] In the above configuration, the end face shape of the rolled material S ₁ of the preceding in the middle of the hot rolling step is measured by the end surface shape measuring device 1, the measurement result is the arithmetic processing, the end surfaces bulge shape and overlap The position a or the inflection point b is recognized. In the case of the double bulge, the low temperature side where the overlap a position of the succeeding billet in the heating furnace 3 is deviated is relatively strongly heated. In the case of the single bulge, the inflection point of the succeeding billet in the heating furnace 3 is obtained. The low-temperature side opposite to the high-temperature side where the position b is displaced is relatively strongly heated.

If there is a temperature difference between the front surface and the back surface of the material to be rolled in the rolling process, the depth of the seam flaw tends to increase on the lower temperature side. When performing the above, by strengthening the heating on the low temperature side as described above, the temperature difference between the front and back surfaces is adjusted to be eliminated, and the overlap a position or the inflection point in the material to be rolled after the current rolling. The position b is located at the center of the plate thickness, and the depth of the seam flaws on the front and back surfaces of the product, which is affected by the front and back surface temperature and the end surface shape, becomes uniform.

[0017]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing a first embodiment of the present invention; This is an example applied to hot rolling of a continuously cast slab. As shown in FIG. 1, the side of the hot rolling line established the end surface shape measuring device 1 such as a laser rangefinder, the shape of the end face parallel to the rolling direction of the slab S ₁ of the middle rolling preceding laser And the like are scanned in the thickness direction of the slab and measured, and the measurement results are subjected to arithmetic processing in the arithmetic processing unit 2 to recognize the end face bulge shape and the position of the overlap a or the inflection point b. The heating of the heating furnace 3 is performed as described above, and the subsequent slabs S ₂ , S
₃ Perform optimal heating for.

The heating furnace 3 transfers the slab S in the longitudinal direction of the furnace by a moving mechanism 5 of a walking beam type or a skid pusher type, and an upper gas burner 4U and a lower gas burner arranged on both side walls of the furnace body. 4L uniformly heats to a predetermined temperature.

A coke oven gas or the like is used as the fuel gas, and the automatic combustion control device 6 controls the combustion.

The hot rolling line comprises a rough rolling step of performing a forming (shape adjustment) reduction and a tentative reduction by a rough rolling machine, and a finishing rolling step of performing a finishing reduction by a finishing rolling machine. vessel 1 is placed on the side of the rough rolling mill roller table, to be able to measure the edge shapes of the slab S ₁ after the rolling of approximately 2 to 3 paths. Further, the end face shape measuring instrument 1 may be disposed on only one side of the pass line, or may be disposed on both sides.

In the above structure, as shown in FIG. 3, the slabs S are sequentially charged into the heating furnace 3, heated, extracted, and then subjected to ordinary hot rolling. After rolling about three passes, the bulge shape is measured by the end face shape measuring instrument 1. The arithmetic processing unit 2, the measurement results from the conjunction bulge shape is determined whether a double bulge or single bulge, shift amount l _a or inflection in the case of a single bulge, from thickness center of the overlap a position in the case of a double bulge It calculates a shift amount l _b from the thickness center of the point b position,
The following control is performed by the automatic combustion control device 6.

[0022] When (A) the end surface shape of a double bulge as shown in Figure 2 (A), the deviation from the thickness center of the overlap a position in slab S ₁ of preceding if cold back side, If the rear surface of the succeeding slab S _k in the heating furnace 3 is shifted to the lower surface side, the surface of the subsequent slab S _k is heated relatively strongly. That is, the gas flow ratio R (= _Fu / _Fl ) of the upper gas burner 4U and the lower gas burner 4L.
In proportion to the shift amount l _a a performing heating and controlled. There slab thickness, relationship between shift amount l _a and the gas flow rate ratio R of the slab heating set temperature, for example, a curve as shown in FIG. 4 (A), with the current gas flow rate ratio using the shift amount l _a Control by finding the difference.

[0023] (B) if the end surface shape of the single bulge as shown in 2 (B) Figure, contrary to the double bulge, deviation from the thickness center of the inflection point b in slab S ₁ of the preceding high-temperature if the back side, the surface of the succeeding slab S _k in the heating furnace 3, shift the back surface of a subsequent slab S _k if hot surface side is heated relatively strongly. Also in this case, the gas flow ratio R of the upper gas burner 4U and the lower gas burner 4L is R.
In proportion to the shift amount l _b is carried out to heat and controlled. Relationship shift amount l _b and the gas flow rate ratio R is, for example, a curve as shown in FIG. 4 (B), is controlled as in the case of the double bulge using the shift amount l _b.

The extract subsequent slab S _k which is heated as described above from the heating furnace 3, performing hot rolling as described above. here,
Seam flaws occur-products edge after the first hot rolling of the slab S ₁ of the heating control unexecuted is by the vertical surface temperature non-uniformity of the cast strip top and bottom surfaces during rolling slab due to the temperature difference or the like in the heating furnace 3 The depth amount differs between the front and back surfaces. In the case of the double bulge of FIG. 2 (A), the lower the temperature on the shift side is, the larger the seam flaw depth is, and in the case of the single bulge of FIG. 2 (B), the lower the temperature on the side opposite to the shift is the seam flaw depth. The amount increases.

Further, the difference in the depth of the seam flaws on the front and back surfaces correlates with the vertical asymmetry of the end face shape of the material to be rolled. FIG. 5 shows the correlation, where the overlap a position and the inflection point b position are located at the center of the sheet thickness, so that the seam depth amounts on the front and back surfaces are equal, and the cutting allowance of the material to be rolled is minimized. We can see that we can do it.

In the present invention, the bulge shape of the end face, the position of the overlap a or the position of the inflection point b are recognized, and the heating of the front and back surfaces is performed in the heating furnace 3 so that these positions come to the center of the sheet thickness for the subsequent rolled material. Since the amount is adjusted, the depth of the seam flaws on the front and back surfaces, which is affected by the temperature difference between the front and back surfaces of the material to be rolled and the end face bulge shape, can be made uniform, and the yield can be improved with a minimum cutting margin.

[Specific Numerical Examples]
Heating was performed at 40 ° C. for 4 hours, and thereafter, the end surface shape of the material to be rolled was measured by a laser distance meter when two passes were rolled in the longitudinal direction of the slab with a reduction of 20 mm by a horizontal roll of a rough rolling mill. Shown in

[0028]

[Table 1]

In the case of FIG. 6, since the end face of the slab S ₁ has a single bulge shape and the inflection point b is located on the back side where the temperature is higher than the center of the plate thickness, the gas flow rate of the upper gas burner 4 U of the heating furnace 3 is reduced. The gas flow ratio was increased so as to be _lb = 0, and control was performed so that the surface side was relatively strongly heated while maintaining a predetermined heating temperature. After such heating, after the rolling of the front material was completed, the rear material was extracted from the heating furnace and rolled. Here, the heating control is carried out, for the subsequent slab S _k which is heated extraction, bulge shape during rolling is measured and fed back to the upper and lower gas flow rate control in the heating furnace, the inflection point b (overlapping a Position) to the optimal position.

When the end face shapes measured by the laser distance meter of the slab subjected to the heating flow rate control described above are arranged in time series, as shown in FIG. , And approaches l _b = 0. Also,
As a result, the depth of the seam flaw K on the front and back surfaces of the product plate is
As shown in FIG. 8, even after the upper and lower burner flow rate ratio control of the heating furnace, the uniformity occurred, the non-defective part in the plate width direction could be enlarged, and the yield could be improved. Is 6 mm [= 75-69]).

[0031]

As described above, the present invention recognizes the end face bulge shape and the overlap position or the inflection point position of the material to be rolled, and changes the upper and lower heating amount ratio of the heating furnace based on the recognized bulge shape. Since the heating control of the middle billet is performed, the temperature difference between the front and back surfaces of the material to be rolled can be eliminated in the rolling process, and the overlap position or the inflection point position is set to the center position of the thickness of the steel sheet after the control. The depth of the seam flaws on the front and back of the product can be made uniform without increasing the overlap amount and the yield loss, and the yield can be improved with a minimum cutting margin. In addition, normal water-cooling control can be performed during hot rolling, and the present invention can be applied to a finish temperature designation material such as a controlled rolled material.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a four-round flaw preventing hot rolling method according to the present invention.

FIG. 2 is a perspective view showing an end surface shape of a material to be rolled during rolling;

FIG. 3 is a flowchart of a four-round flaw preventing hot rolling method according to the present invention.

FIGS. 4A and 4B are graphs showing a relationship of a gas flow ratio with respect to a position where an overlap a occurs and a position where an inflection point b occurs.

FIGS. 5A and 5B are graphs showing seam flaw depth amounts with respect to a position where an overlap a occurs and a position where an inflection point b occurs.

FIG. 6 is a graph showing an example of an end face shape of a material to be rolled when an end face is measured during rolling.

FIG. 7 is a graph showing a change in a shift amount of an inflection point b when the heating control of the present invention is performed.

FIGS. 8 (i) and (ii) are cross-sectional views showing the depth of seam flaws of a product after the heating control according to the present invention and after the heating control is not performed.

[Explanation of symbols]

 S: slab (slab, steel plate) 1 ... end face shape measuring device 2 ... arithmetic processing unit 3 ... heating furnace 4 ... gas burner 5 ... moving mechanism 6 ... automatic combustion control device

Claims (1)

(57) [Claims] 1. During the hot rolling process of a steel sheet, the shape of the end face along the rolling direction of the material to be rolled is measured, and when the end face shape is a double bulge, the overlap position is set to be larger than the center position of the sheet thickness. If the side is the side, the heating amount on the front side of the slab in the slab heating furnace, if the overlap position is the back side from the center position of the plate thickness, the heating amount on the back side of the slab in the slab heating furnace, the overlap If the position is shifted from the center of the thickness of the sheet, it is raised relatively, the subsequent slab is heated, then rolled, and if the end face is a single bulge, the inflection point is closer to the surface than the center of the thickness. If so, the heating amount on the back side of the slab in the slab heating furnace, if the inflection point is on the back side from the center position of the thickness, the heating amount on the front side of the slab in the slab heating furnace, the inflection point Relative to the center position of the sheet thickness A hot rolling method for preventing four-round flaws in a steel sheet, wherein the steel piece is heated and then rolled.