JP2007283327A - Cooling equipment line and cooling method for thick steel plate - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a steel material having high uniformity by reducing temperature variation effect caused by scale spots when a high temperature thick steel plate is carried in a state of being restrained with restraining rolls, and is cooled using spray nozzles from the upper and lower parts. <P>SOLUTION: The cooling equipment line and a cooling method for a thick steel plate are applied when a thick steel plate is cooled after being subjected to finish rolling. The cooling equipment line comprises: a hot straightening machine, a thermometer, a plasma irradiation apparatus; and a cooling apparatus where, while the thick steel plate in a high temperature state is bitten with two or more pairs of restraining rolls each making a pair by the rolls arranged up and down, and is carried, water is injected to the upper and lower faces of the thick steel plate between the restraining rolls. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  TECHNICAL FIELD The present invention relates to a thick steel plate cooling equipment row and a cooling method, which are applied when cooling a hot-finished thick steel plate when producing a thick steel plate by hot rolling.

  Recently, in the manufacture of thick steel plates, the strength and weldability of steel plates have been improved by controlled cooling after finish rolling. In controlled cooling, in order to obtain uniform material properties and flatness, it is necessary to cool so that the temperature distribution in the plate width direction is uniform. However, it is generally known that the thickness of iron oxide (hereinafter referred to as “scale”) generated on the surface of the steel sheet varies as a condition of the steel sheet that inhibits this uniform cooling.

  In order to eliminate the influence of the scale, a method of removing the scale by descaling before cooling is disclosed in Patent Document 1. Further, although the influence on the scale is not specified, Patent Document 2 discloses a method for controlling the cooling rate by plasma irradiation before cooling.

JP 2000-271627 A JP 2003-181519 A

  In general, the following is known about the effect of scale on the cooling of steel sheets. That is, the cooling rate of the steel sheet during water cooling is improved by the adhesion of a material that does not conduct heat such as scale. As a cause of such a phenomenon, it is known that the temperature at which film boiling ends (quenching point temperature) rises as shown in FIG. 6 due to adhesion of a substance such as scale that is difficult to conduct heat. For this reason, partial peeling of the scale occurs on the surface of the thick steel plate, and if the thickness of the scale varies, the cooling rate varies within the surface of the thick steel plate, causing variations in material. When the thickness variation (scale spots) of the scale was actually examined, it was 3 to 5 μm at the thin part and 30 μm or more at the thick part.

  In the cooling method of Patent Document 1, the scale is removed by descaling and then cooled. In this method, removal of the scale lowers the temperature at which film boiling ends, resulting in a problem that the cooling capacity is reduced. When the film boiling end temperature is lowered, as shown in FIG. 6, the state of low cooling ability is maintained up to the region where the surface temperature is low, so that the cooling rate is reduced. For this reason, it is necessary to increase the cooling capacity by increasing the amount of water, or to increase the cooling time by decreasing the plate passing speed. However, this has disadvantages such as increased power necessary for cooling and reduced productivity.

  In the cooling method of Patent Document 2, it is described that the quench point temperature is increased by plasma irradiation. This is because film molecules boil because the contact angle with water on the surface of the steel sheet is reduced by removing the impurity molecules such as water and oil adhering to the surface of the steel sheet due to plasma irradiation, and the steel sheet and water are easily contacted. It is believed that the quench point temperature, which is the collapse (start of contact of steel plate and water) temperature, becomes higher. However, the method of Patent Document 2 has the following disadvantages and is difficult to apply by cooling a thick steel plate. First, as shown in FIG. 7, the thickness variation of the scale 8 on the surface of the thick steel plate 6 is large, and when there is a portion with and without the scale 8, the effect of plasma irradiation with and without the scale is unknown. . Second, in the experiment conducted by the present inventors, plasma irradiation has a characteristic that the effect is greatly reduced as the inter-surface distance (distance between the plasma ejection hole tip and the steel plate surface) increases as shown in FIG. It has been found. In the case of a thick steel plate, there is a warp at the tip or tail end of the steel plate or wave deformation in the width direction in the state after normal finish rolling, and an apparatus for keeping the plasma irradiation distance below a certain value is essential. Thirdly, the plasma irradiation time is long, so that the irradiation equipment becomes long, the productivity is remarkably lowered, or the cooling start temperature necessary for metallurgy cannot be maintained. For example, when a steel sheet of 30 mm thickness x 4 m width x 15 m length is finish-rolled and subjected to the method of Patent Document 2, that is, plasma irradiation for 60 seconds, a plasma irradiation device of the same size as the thick steel plate is installed, A method of irradiating for 60 seconds, or a method of installing a plasma irradiation apparatus having a width of 4 m and a length of 1 m and passing the steel plate at a speed of 1/60 m / second, for example, is conceivable. In any case, the temperature drop of the thick steel plate during this period is considered to be 80 ° C. or higher in consideration of the previous and subsequent transport times. For this purpose, it is necessary to take measures such as raising the heating temperature in the heating furnace in advance to 80 ° C. or higher compared to the normal temperature, resulting in a large economic loss of fuel. In addition, when the plate-type plasma irradiation device having a width of 4 m and a length of 1 m is used, it is difficult to synchronize the cooling device and the plate-feeding speed with the thick steel plate after plasma irradiation. It is necessary to cool after the steel plate has passed. In this case, since the time until cooling becomes longer, the scale grows on the surface after the plasma irradiation, and there is a disadvantage that the plasma irradiation effect is reduced. Thus, the technique of the cited document 2 cannot be simply applied to the cooling method of the cited document 1.

  The present invention advantageously solves the problem of the plasma irradiation apparatus, which is a problem of the above-described prior art, and quenches water by pouring water on the upper and lower surfaces of the thick steel plate between the restraining rolls that have bitten the thick steel plate being transferred. It is an object of the present invention to provide a steel plate cooling equipment row and cooling method capable of increasing the spot temperature, improving the flatness of the steel plate shape, and making the material uniform.

  In order to solve the above problems, the present invention has the following (1) to (5).

  (1) Equipment train that cools thick steel plates after finish rolling, and after the finish rolling mill, a set consisting of a hot straightening machine, a thermometer, a plasma irradiation device, and rolls arranged vertically A cooling apparatus for thick steel plates, comprising a cooling device for injecting water into the upper and lower surfaces of the thick steel plates between the pair of restraining rolls while biting and transporting the thick steel plates in a pair of pairs of constraining rolls Column.

  (2) A row of equipment that cools thick steel plates after finish rolling, and a plurality of sets of constraining rolls that form a pair of hot straightening machines, thermometers, and upper and lower roll pairs after the finish rolling mill And a cooling device that injects water into the upper and lower surfaces of the thick steel plate between the pair of restraining rolls while biting and transporting the thick steel plate in a high temperature state in this order, and the cooling device includes a plasma irradiation device as a first restraining roll. A thick steel plate cooling facility row characterized by having between a pair and a second constraining roll pair.

  (3) The thick steel plate cooling equipment row according to (1) or (2), wherein the distance (inter-surface distance) between the tip of the plasma ejection hole of the plasma irradiation apparatus and the steel plate surface is 100 mm or less.

  (4) In the method of cooling a thick steel plate after finish rolling, hot straightening and temperature measurement are performed after finish rolling, and then plasma irradiation is performed on the upper and lower surfaces of the steel plate, and a plurality of pairs are formed by rolls arranged vertically. A method for cooling a thick steel sheet, comprising pouring water into the upper and lower surfaces of the thick steel sheet between the pair of restraining rolls while cooling and feeding the thick steel sheet in a high temperature state with the pair of constraining rolls.

  (5) The cooling method according to (4), wherein the plasma irradiation time is 3 seconds or less.

  According to the present invention, when the steel sheet material is created by cooling after finish rolling, the quench point temperature is raised, the influence of scale spots on the steel sheet surface is suppressed, the flatness of the thick steel plate shape is good and the material is uniform. It is possible to provide a cooling equipment row and a cooling method capable of manufacturing a simple steel plate.

  As shown in FIG. 1, for example, as shown in FIG. 1, the thick steel plate cooling equipment row A of the present invention is a hot-rolled steel plate cooling device 4 arranged at the subsequent stage of the hot-rolled steel plate 1. The present invention is particularly effective when applied to a case where the high-temperature thick steel plate 6 having a surface temperature of 750 to 950 ° C. obtained by rolling is rapidly cooled to 700 ° C. to room temperature by water injection during transportation.

  Below, the cooling equipment row | line | column A of the thick rolled steel plate of this invention is demonstrated.

  As shown in FIG. 1, for example, as shown in FIG. 1, the cooling equipment row A of the thick rolled steel sheet according to the present invention includes a hot straightening machine 3 for hot straightening the shape of the thick steel sheet 6 and a temperature of the thick steel sheet 6. It comprises a thermometer 7 for measuring, a plasma irradiation device 2 for irradiating the thick steel plate 6 with plasma, and a cooling device 4 having a plurality of sets of restraining rolls in this order.

  The plasma irradiation apparatus 2 includes, for example, plasma ejection holes 2a that eject nitrogen or air plasma toward the upper and lower surfaces of the thick steel plate 6. The cooling device 4 is composed of a plurality of constraining roll pairs 53 formed by a pair of upper and lower rolls 51 and 52, and a water spray for injecting water onto the upper and lower surfaces of the thick steel plate 6 between adjacent constraining roll pairs 53 (see FIG. Not shown).

  And in the said cooling equipment row | line | column A, the high-temperature thick steel plate 6 finish-rolled in the finish rolling mill 1 is first conveyed to the hot straightening machine 3, and is pressurized and corrected by a plurality of rolls arranged up and down. . Next, the thick steel plate 6 passes under the thermometer 7 and is carried into the plasma irradiation device 2. In the plasma irradiation apparatus 2, plasma is irradiated on the upper and lower surfaces of the thick steel plate 6 under predetermined conditions. This plasma irradiation is performed from the plasma ejection hole 2a. The high-temperature thick steel plate 6 that has passed through the plasma irradiation device 2 is then carried into the cooling device 4, is bitten between the upper and lower restraining rolls 51, 52, and is transported to spray water between the restraining roll pairs 53. Thus, water is poured onto the upper and lower surfaces of the thick steel plate 6. Thus, the thick steel plate 6 is cooled.

  Here, the effect of plasma irradiation in the cooling equipment row A will be verified.

  Here, the influence of plasma irradiation on the cooling of the thick steel plate 6 in the portion with the scale (large portion) and the portion without the scale (small portion) was investigated in the case where the scale unevenness occurred in the thick steel plate 6. In this case, plasma irradiation is performed on the high-temperature thick steel plate 6 using the cooling equipment row A, and then the high-temperature thick steel plate 6 is spray-cooled, and the temperature transition during cooling of the thick steel plate 6 is measured by a thermocouple embedded in the steel plate. The quench point temperature of the thick steel plate 6 was detected by measurement.

  First, when there was a sufficient scale on the surface of the thick steel plate 6 and the scale thickness was as thick as 30 μm or more, the quench point temperature was 630 ° C. without plasma irradiation. In addition, when there was plasma irradiation, the quench point temperature was 640 ° C. and the difference was small. This is presumably because the quench point temperature has risen to a considerably high temperature due to the scale effect.

  On the other hand, the test was conducted by heating so that the surface of the thick steel plate 6 had almost no scale and the scale was about 5 μm. This scale thickness is the scale thickness when scale peeling occurs in the thick steel plate 6. In this test, FIG. 2 is a graph showing the change in quench point temperature of the thick steel plate 6 when the distance between the plasma injection hole 2a of the plasma irradiation apparatus 2 and the steel plate surface during plasma irradiation is changed, and FIG. FIG. 4 is a graph showing a change in the quench point temperature of the thick steel plate 6 when the plasma irradiation time is changed, and FIG. 4 is a graph showing a change in the quench point temperature of the thick steel plate 6 when the plasma output is changed.

  As shown in FIG. 4, it has been found that the quench point temperature can be increased by increasing the plasma output even if the irradiation time is shortened. And the raised quench point temperature was a level substantially equivalent to the quench point temperature of 640 ° C. when a scale thickness of 30 μm at the time of normal steel plate operating conditions was applied.

  As a result, the quench point temperature of 550 ° C. without plasma irradiation with a scale thickness of 5 μm can be raised to 630 ° C. by plasma irradiation, and can approach the 640 ° C. quench point temperature with plasma irradiation of a scale thickness of 30 μm. That is, by performing plasma irradiation on the surface of the thick steel plate 6 with the scale spots, the variation of the quench point temperature is changed from 80 ° C. (scale 30 μm; 630 ° C., scale 5 μm; 550 ° C.) to 10 ° C. (scale 30 μm; 640 ° C., (Scale 5 μm; 630 ° C.).

  Therefore, according to the cooling equipment row A of the above embodiment, even if there are scale spots on the surface of the thick steel plate 6, the thick steel plate 6 can be cooled uniformly, and a steel plate product having a uniform shape and material is obtained. be able to.

In addition, based on FIGS. 2, 3, and 4, when considering the appropriate plasma processing conditions in the cooling equipment row A, the plasma output from FIG. 4 is obtained as the plasma irradiation conditions that can cool the thick steel plate 6 regardless of the scale unevenness. The power density divided by the unit area is 2.5 W / mm ² or more, the irradiation time is 3 seconds or less from FIG. 3, and the distance between the surfaces of the plasma ejection hole 2a and the thick steel plate 6 at the time of irradiation is 100 mm or less from FIG. Is desirable. If the inter-surface distance is less than 15 mm, the plasma ejection hole 2a may be damaged by the vibration of the thick steel plate 6, so the inter-surface distance is preferably 15 mm or more. The plasma irradiation time is preferably 1 second or longer.

  As for the installation position of the plasma irradiation apparatus 2, it is essential that the thick steel plate 6 is flattened in consideration of the shape after the finish rolling of the thick steel plate 6. As described above, the plasma irradiation apparatus 2 was installed after the hot straightening machine 3. This is because if the flat steel plate 6 does not have sufficient flatness, the bent thick steel plate 6 may collide with the plasma irradiation device 2 and damage the plasma irradiation device 2. Furthermore, the plasma irradiation apparatus 2 was installed after the thermometer 7 for measuring the temperature before cooling the thick steel plate 6. This is because if the cooling is not started as soon as possible after the plasma irradiation, scale generation will occur on the surface of the thick steel plate, and the plasma irradiation effect will be reduced. Moreover, since the normal thermometer 7 is a radiation thermometer, it is necessary to avoid a change in the emissivity on the surface of the thick steel plate due to plasma irradiation.

  In the above embodiment, the plasma irradiation device 2 is provided in front of the cooling device 4 in the cooling equipment row A, but the plasma irradiation device 2 is connected to the first restraining roll pair of the cooling device 4 as shown in FIG. You may arrange | position between 53 and the 2nd restraint roll pair 53. FIG. By doing so, the positional relationship between the thick steel plate 6 and the plasma ejection holes 2a is stabilized, and the inter-surface distance can be made constant. This is because when the plasma irradiation device 2 is installed in front of the cooling device 4, the tip of the thick steel plate 6 vibrates slightly on the table roll before entering the cooling device 4. This is because the positional relationship with the hole 2a changes.

  The preferred embodiment of the present invention has been described above with reference to the accompanying drawings, but the present invention is not limited to such an example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the spirit described in the claims, and these are naturally within the technical scope of the present invention. It is understood that it belongs.

  Hereinafter, examples of the method for cooling thick steel plates and the cooling equipment row A for thick steel plates according to the present invention will be described in detail using Example 1, Example 2, and Comparative Example 1. These comparisons are summarized in Table 1.

Example 1
FIG. 1 shows a steel plate manufacturing equipment row from the finish rolling mill 1 to the cooling device 4 in which the steel plate cooling equipment row A of the present invention is arranged. Here, a finish rolling mill 1, a hot straightening machine 3, a thermometer 7, a plasma irradiation device 2, and a cooling device 4 including a plurality of pairs of restraining rolls are installed in this order. The hot straightening machine 3 has 15 rolls installed vertically and has a load of 2000 tons. In the plasma irradiation apparatus 2, the length in the rolling direction was set to 1 m, the plasma output was set to 12.5 MW, and the distance between the plasma ejection holes 2a and the thick steel plate 6 was set to 100 mm.

In this Example 1, the steel plate 6 having a thickness of 25 mm and a width of 4000 mm obtained by finish rolling is hot-corrected and then bitten into five pairs of constraining rolls 53 and conveyed. While transporting at 20 m / min, the upper surface was cooled by water injection at a water density of 1.0 m ³ / m ² / min. On the other hand, the lower surface side was cooled by water injection at a water density of 1.3 m ³ / m ² / min.

  When the temperature of the thick steel plate 6 after being cooled for 10 seconds by this cooling was measured, it was as high as ± 10 ° C in the width direction with respect to the steel plate temperature of 500 ° C in the center in the width direction, and warpage and residual stress A sufficiently satisfying thick steel plate 6 excellent in uniformity in both shape and material was obtained. Here, the measurement of the temperature of the thick steel plate 6 was performed by removing the edge region corresponding to twice the plate thickness from the end of the steel plate surface.

(Example 2)
In the second embodiment, as shown in FIG. 5, a finish rolling mill 1, a hot straightening device 3, a thermometer 7, a plasma irradiation device 2, and a cooling device 4 including a plurality of pairs of constraining rolls are sequentially installed. The hot straightening machine 3 has 15 rolls installed vertically and has a load of 2000 tons. The plasma irradiation apparatus 2 is installed between the first constraining roll pair 53 and the second constraining roll pair 53 from the hot straightening machine 3 side of the cooling device 4 composed of a plurality of constraining rolls, and in the rolling direction. The length of the plasma was 1 m, the plasma output was 12.5 MW, and the distance between the plasma ejection holes 2a and the thick steel plate 6 was 50 mm.

In Example 2, the steel plate 6 having a thickness of 25 mm and a width of 4000 mm obtained by finish rolling is hot-corrected and then bitten into five pairs of constraining rolls 53 and conveyed. While transporting at 20 m / min, the upper surface was cooled by water injection at a water density of 1.0 m ³ / m ² / min. On the other hand, the lower surface side was cooled by water injection at a water density of 1.3 m ³ / m ² / min.

  When the temperature of the thick steel plate 6 after being cooled for 10 seconds by this cooling was measured, it was as high as ± 10 ° C in the width direction with respect to the steel plate temperature of 500 ° C in the center in the width direction, and warpage and residual stress A sufficiently satisfying thick steel plate 6 excellent in uniformity in both shape and material was obtained.

(Comparative Example 1)
In Comparative Example 1, a finish rolling mill 1, a hot straightening machine 3, a thermometer 7, a plasma irradiation device 2, and a cooling device 4 including a plurality of pairs of restraining rolls are installed in this order. The hot straightening machine 3 has 15 rolls installed vertically and has a load of 2000 tons. The plasma irradiation apparatus 2 had a length in the rolling direction of 1 m, and no plasma was used.

In this comparative example 1, the steel plate 6 having a thickness of 25 mm and a width of 4000 mm obtained by finish rolling is hot-corrected and then bitten into five pairs of constraining rolls 53 and conveyed. While transporting at 30 m / min, the upper surface was cooled by water injection at a water density of 1.0 m ³ / m ² / min. On the other hand, the lower surface side was cooled by water injection at a water density of 1.3 m ³ / m ² / min.

  When the temperature of the thick steel plate 6 after being cooled for 10 seconds by this cooling was measured, the steel plate temperature was 500 ° C. at the center in the width direction, and the uniformity was poor at ± 40 ° C. in the width direction, and the residual stress was large. Uniformity in both shape and material was insufficient, and finishing processing (correction, heat treatment, etc.) was required in the subsequent process.

  The present invention is useful for obtaining a highly uniform steel material by reducing the temperature variation effect due to scale spots when transporting a high-temperature thick steel plate constrained by a constraining roll and cooling it from above and below using a spray nozzle. It is.

It is drawing of the typical equipment row | line | column at the time of using this invention. It is drawing which shows the relationship of the quench point temperature change at the time of cooling, and the distance between a plasma ejection hole and a thick steel plate. It is a figure which shows the relationship between the plasma irradiation time and the quench point temperature change at the time of cooling. It is a figure which shows the relationship between the plasma power density and the quench point temperature change at the time of cooling. It is a figure which shows another equipment row | line at the time of using this invention. It is a figure which shows typically the relationship between the cooling capacity at the time of the water cooling at the time of plasma irradiation, and a steel plate surface temperature. It is a figure which shows the scale dispersion | variation condition of a thick steel plate.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Finish rolling mill 2 Plasma irradiation apparatus 3 Hot straightening machine 4 Cooling apparatus 6 Thick steel plate 7 Thermometer 8 Scale 51 Upper restraint roll 52 Lower restraint roll 53 Restraint roll pair A Cooling equipment row

Claims (5)

A line of equipment that cools steel plates after finish rolling,
After the finish rolling mill, hot steel plates in a high temperature state are bitten and transported by a pair of constraining rolls, each consisting of a hot straightening machine, a thermometer, a plasma irradiation device, and a pair of upper and lower rolls. However, the cooling equipment row | line | column provided with the cooling device which injects water into a steel plate upper and lower surface between restraint roll pairs in this order. A line of equipment that cools steel plates after finish rolling,
After the finish rolling mill, a hot straightening machine, a thermometer, and a plurality of pairs of restraint rolls, each of which is a set of upper and lower rolls, bite a high-temperature thick steel plate and convey it while transporting the restraint roll pairs. A cooling device that injects water into the upper and lower surfaces of the steel plate in this order,
The said cooling device has a plasma irradiation apparatus between the 1st restraint roll pair and the 2nd restraint roll pair, The cooling equipment row | line | column of the thick steel plate characterized by the above-mentioned. The thick steel plate cooling equipment row according to claim 1 or 2, wherein the distance between the plasma ejection hole tip of the plasma irradiation apparatus and the thick steel plate surface is 100 mm or less. In the method of cooling a thick steel plate after finish rolling, hot straightening and temperature measurement are performed after finish rolling, and then plasma irradiation is performed on the upper and lower surfaces of the thick steel plate. A method of cooling a thick steel plate, wherein the steel plate is cooled by pouring water into the upper and lower surfaces of the thick steel plate between a pair of constraining rolls while biting and transporting the hot steel plate in a roll pair. 5. The cooling method according to claim 4, wherein the plasma irradiation time is 3 seconds or less.

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